Materials for applications in photocatalysis and photoconversion

Resume : In recent years, TiO2 nanomaterial was regarded as a potential photosensitizer in the field of photodynamic therapy for cancer treatment due to its high chemical stability, biocompatibility, and photoreactivity. In this context, TiO2 can act as a very efficient photosensitizer for photo-generation of a large number of reactive oxygen species (ROS) inside the body based on its own photocatalytic properties. What needs to be avoided, however, is increased ROS photo-generation all over the body, leading to the destruction of healthy cells. Unfortunately, TiO2 is single-functional and does not have any properties useful for the types of imaging that would allow it to be tracked and monitored inside the body for selective localization and ROS photo-generation inside the cancerous cell to avoid damage to healthy cells. Recently we have been developed multifunctional Gd-doped TiO2 with similoutance optical imaging (OI) - magnetic resonance imaging (MRI) ability to track and guide TiO2 to cancer cells and selective ROS photo-generation ability inside the cancer cells. Gd-doped TiO2 showed significant cellular internalization and passive accumulation inside cancerous cells which provide a safe manner for selective ROS photo-generation inside the cancerous cells without damage to healthy cells. Here, we would like to present some of the most important and interesting results of our multidisciplinary study, for the development of targeted cancer therapy based on TiO2 photocatalysis.

Resume : Approximately 1.8 billion people do not have access to a safe source of drinking water, many of whom live in low/lower-middle income countries. Consequently, there is the need for sustainable low cost sources of disinfection. A number of pathogenic microorganisms are resistant to normal disinfection methods such as chlorine; which can produce toxic disinfection by-products (DBP’s). Photoelectrocatalytic water treatment is a novel approach to disinfection using at least one semiconducting electrode and an applied bias. This may offer an improvement over slurry based photocatalysis by removing post treatment separation, reducing recombination and electro-migration of bacteria by the presence of an electric field. In this work a novel design of a photoelectrocatalytic reactor has been designed and tested for the disinfection of real water under simulated solar irradiation. The photoanodes where produced by anodising commercial grade titanium to produce aligned self-organised TiO2 nanotubes. The reactor was testing for disinfection using untreated water from a local stream which was spiked with E. coli K12. The reactor was evaluated by examining the total count of bacterial organisms, coliforms, E. coli and total organic carbon.

Resume : Airborne bacterial microorganisms are preferentially found attached on indoor surfaces, which eventually result in development of a biofilm. Aside from conventional physico-chemical surface treatments, an alternative method for reducing frequency and level of surface contamination is based on the photocatalytic oxidation of organic compounds by TiO2, which exhibits strong bactericidal effect on a wide range of Gram-negative and Gram-positive bacteria in aqueous phase, if illuminated by ultraviolet A light. We recently developed P/F-modified TiO2 photocatalyst that revealed higher performance in terms of gas-phase photocatalytic degradation of methyl ethyl ketone compared to a commercially available TiO2 P25. We studied the photocatalytic bactericidal activity and mechanisms of the photocatalysts immobilized on glass surface, with three different bacterial species, after from short (10 min) to long (3 h) irradiation time, and immediately after UVA treatment or an overnight period of post-treatment growth. Effects of the physico-chemical surface properties and of medium-related factors were taken into account. The results showed a material nature-, illumination time- and bacterial strain-dependency, with in general higher bactericidal effect of immobilized P/F-modified TiO2 compared to P25. Typically, E. coli were affected in terms of biomass, cell membrane damages and respiratory and enzymatic activities after 10 min treatment on P/F-modified TiO2 but after 45 min on P25.

Resume : Hybrid nanoparticulate metal-oxides composite films able to generate highly oxidative radicals have been investigated during the last decade. Many of these innovative materials have been reported as effective in wastewater treatment under light irradiation. These photocatalysts are also able to carry out a) indoor disinfection, b) VOC’s reduction and c) air cleaning but only a few studies address the later processes mediated by very catalysts activated by very low light doses. The present work addresses indoor bacterial inactivation in the dark and under solar light irradiation mediated by oxides, double oxides and innovative composite robust and uniform films sputtered on 2D-surafces like polyester, cotton, polyethylene, polyurethane. A stable long-term bacterial inactivation was observed proceeding with quasi-instantaneous kinetics under low intensity solar or actinic light [1-3]. The release of surface ions from the coated surfaces during the bacterial inactivation were monitored by ICP-MS and the levels found were below the cytotoxicity levels permitted by the sanitary regulations [4]. Sputtered 3D Cu-Ag polyurethane catheters made-up amalgamated CuO/Cu2O/Ag2O lead to quasi-instantaneous bacterial inactivation. This makes these films a priority to preclude infections during their routine daily use in hospital facilities. The composite Cu-Ag- films involve the reactions Ag0/Ag+ -0.80V SHE and Cu2+/Cu+ 0.15V SHE and drive the Ag/Cu galvanic cell reaction with a potential of -0.65V SHE. The interfacial charge transfer (IFCT) mechanism and the surface properties were carried out by: TEM, XPS and fast-kinetics laser spectroscopy [5-6]. Keywords: Innovative 2D and 3D-sputtered thin films, antibacterial kinetics, film surface characterization, process thermodynamics. [1] S. Rtimi et al., ACS. Appl. Mater. & Interf. 8 (2016) 47-55. [2] S. Rtimi et al., ACS. Appl. Mater. & Interf. 8 (2016) 56-64. [3] S. Rtimi et al., Materials Today 6 (2017) 62-74. [4] S. Rtimi & J. Kiwi, Appl. Cat. B: Environ. 213 (2017) 62-73. [5] S. Rtimi, Catalysts, 2 (2017) 57. [6] S. Rtimi et al., Appl. Cat. B : Environ. 208 (2017) 135–147.

Resume : 1D nanotubular TiO2 are known to improve photocatalytic performance compared to classical 3D particles. Combination of TiO2 nanotubes (NTs) with graphene oxide (GO) was previously envisaged to limit the recombination of e--h+ pairs (Appl. Cat. B 2017, 209, 203-213). Compared to non-reduced GO, improvement in activity was noticed if partially reduced GO was used due to a decrease in charge transfer resistance after partial reduction limiting the recombination phenomenon. If GO was totally reduced, the gain in activity was lost suggesting that the driving force for the injection of electrons from TiO2 to GO comes from the consumption of oxygen groups on graphene layers. The present study proposes an alternative for avoiding the consumption of photoelectrons through the addition of Cu NPs onto GO without contact with TiO2 NTs. Such a building is facilitated by the tendency of GO to wrap up around TiO2 NTs. Comparison was herein performed between Cu/TiO2 NTs and Cu/(R)GO/NTs systems. On Cu/TiO2 NTs, results show a stabilization of Cu NPs at a +I oxidation state due to a strong interaction with TiO2 NTs leading to a 80% increase in activity for formic acid (FA) degradation under UV. TiO2 NTs are also necessary in combination with Cu to acquire an enhanced photocatalytic response in the visible region or for the production of H2. Contrary to GO/TiO2 NTs, in the presence of Cu, addition of non-reduced GO leads to a 250% increase in activity compared to TiO2 NTs alone for FA photodegradation while the use of partially reduced GO leads to a similar photocatalytic response than with Cu/TiO2 NTs alone. This effect is due to a partial dislocation of the graphene layers wrapped around TiO2 NTs leading to a preferential relocation of Cu NPs directly onto TiO2 NTs.

Resume : This paper studies the performance of a mineral-based transparent air purifying paint. The air pollutants removal efficiency of this photocatalytic paint was first determined following the ISO 22197-1 procedure under laboratory conditions. Subsequently, its air pollutants removal efficiency under realistic conditions was determined by outdoor monitoring with a duration of 20 months, applying a new monitoring protocol. The weather conditions, including temperature, wind flow, humidity, precipitation, and NOx concentration were continuously monitored. The efficiency of the photocatalytic paint was analyzed. The influence of the environmental parameters on the air pollutant removal efficiency as well as long term performance was discussed. The results show the excellent air purifying efficiency of this new paint, nevertheless the environmental parameters show dramatic effects on its long term performance. Furthermore, this study also confirmed the robustness of the proposed air purification performance monitoring protocol.

Resume : Transient changes in the IR spectra of photocatalysts may serve as an important tool for understanding the way by which photocatalytic materials operate. To large extent this technique is complementary to other transient techniques such as transient UV-vis absorption, Time Resolved Microwave Conductivity (TRMC) and EPR. Here, we present transient IR measurements performed on graphitic carbon nitride using a step-scan method, facilitating temporal resolution of 5 nanoseconds. Variations in the location and the intensity of specific peaks and emerging of new peaks were observed during the first 170 nanoseconds after excitation. A comparison was made between graphitic carbon nitride prepared at two temperatures: 510 ºC and 650 ºC. The material prepared at 650 ºC revealed very strong non-specific absorption beginning 35 nanoseconds after excitation and lasting for 20 nanoseconds. This phenomenon, termed “IR-blackening” was observed neither in g-C3N4 prepared at 510 ºC nor in g-C3N4 prepared at 650 ºC that was exposed to hole scavengers (ethanol and benzyl alcohol). In contrast, exposure of material prepared at 650 ºC to an electron scavenger (methyl viologen) hardly altered the “IR-blackening” phenomenon. The results were explained by a mechanism, predicting higher reductive activity for materials having imperfect heptazine polymerization, as indeed was found in the photocatalytic degradation of 4-nitrophenol. These results are compared with the those of nanosperes of graphitic carbon nitride, with and without decorating with platuinum nano-islands.

Resume : The study of Cu2O concave surfaces has attracted significant attention on the formation mechanisms and catalytic performances. However, the surface characteristics and photoinduced charge behaviours of the concave surface have not been thoroughly explored. Here, we demonstrate that the presence of concave surface on Cu2O {100} facet facilitates the capture of photogenerated electrons. By the PEC measurement and photocatalytic H2 evolution, the Cu2O particles with concave surfaces exhibited higher cathodic photocurrent, lower resistance, and better photocatalytic performance. Analysis from Nyquist and Mott-Schottky plots indicate that the improved photoactivity is derived from the higher carrier density and the better interfacial charge transfer. DFT calculations of charge distribution imply that the concave surfaces are catalytically active sites due to unsaturated copper atoms with increased charges. We further compare the built-in electric fields of Cu2O {100} concave surface and flat surface with KPFM technique. The surface potentials confirm that the concave surfaces have a lower surface work function to facilitate the charge separation, which is further proved via Pt photodeposition, intensively forming on {100} concave surfaces under illumination. Our study aims to understand structure-activity relationship and catalytically active sites on {100} concave surface of Cu2O, which will be helpful for the design of efficient morphology-dependent catalysts in future.

Resume : Carbon dots (CDs) are one of the most relevant novelties appeared recently in nanoscience, currently attracting a large and interdisciplinary research interest. They are small, surface-functionalized carbonaceous nanoparticles displaying interesting optical properties such as bright and tunable fluorescence and marked electron donating and accepting capabilities. Therefore, CDs are extremely promising for photocatalytic and optoelectronic applications, especially in that they present a series of key advantages when compared to other inorganic optical materials, such as non-toxicity, low cost and ease of synthesis. However, several important questions remain open on the optical response of CDs and on the nature of the electronic transitions. The LaBAM group in Palermo has been active in the study of CDs, by combining a variety of experimental approaches and involving an extensive range of collaborations. In this contribution we present a selection of our most recent results, 1-4 obtained by a synergy of optical spectroscopies conceived to address the whole photocycle of CDs, from the steady-state optical response to the sub- picosecond time scales. Our studies lead to an exhaustive understanding of the fundamental optical response of CDs, which is a crucial step towards their full optimization and control in view of future applications. 1. J. Phys. Chem. Letters 2016, 7, 3419. 2. Nanoscale 2017, 9, 11902. 3. Phys. Chem. Chem. Phys. 2017, 19, 22670. 4. Nanoscale 2018, 10, 15317.

Resume : Charge transfer (CT) state plays an important role in the performance of organic solar cells (OSCs), as the open circuit voltage is determined by the energy of CT states and the short circuit current is determined by the dynamics of CT states. However, the charge generation and recombination process in these non-fullerene acceptors (NFA)-based OSCs remains poorly understood. Specifically, the role of CT state in limiting photocurrent generation remains controversial. In this project, we use PTQ10 as the donor and IDIC as the acceptor to fabricate OSC devices, the morphology of the blend is controlled by the composition ratio of donor and acceptor. Electroluminescence (EL) and photoluminescence (PL) are used to observe the presence of different CT states. Transient absorption spectroscopy (TAS) is used to trace these different CT state dynamics within the same blend in NFA-OSC. In this work, two sorts of CT states with different energies at different interfaces have been observed in a blend. One is the tightly bound CT state, the other is the unbound or weakly bound CT state, which can dissociate easily at room temperature. The formation of the former can limit the photocurrent generation, but the formation of the latter can result in efficient photocurrent generation.

Resume : Plasmonic noble metal-facilitated photocatalysis is attracting increasing research interest thanks to increasingly mature synthetic strategies and understanding of catalytic processes at the interface. Despite immense developments achieved over the past decades in photocatalysis, crystal phase-based research in the field has been unfortunately rare, of which the advancement may spur exciting opportunities for catalysis in industry. Here, we report kinetic investigations of surface plasmon-driven hot electron-induced photocatalysis on Au nanostructures of different crystal phases using the in situ surface enhanced Raman spectroscopy (SERS) technique. Our results indicate that the Au crystallized in the unconventional 4H phase exhibits nearly seven times higher photocatalytic rates than that crystallized in the usual face centered cubic (fcc) structure, suggesting more efficient hot electron generation arising from surface plasmon decay. These findings can assist in understanding the photocatalytic nature of surface plasmons in noble metals and also prove that the rational design and synthesis of novel-phase plasmonic nanomaterials is critical to developing highly efficient nanocatalysts.

Resume : Water and oxygen reactions, which are included in artificial photosynthesis and organics decomposition, go forward and backward consuming four electrons (O2 + 4H+ + 4e– = 2H2O). However, many papers report water oxidation proceed with four holes and oxygen reduction proceed with one electron, even if they rarely showed any experimental evidences how many electrons/holes are used through the reaction, but only showing and comparing the band position of a photocatalyst and standard electrode potentials to give reasonable explanation for their result. In this study, light-intensity dependences (LIDs) of rate of photocatalytic water oxidation and oxygen reduction were studied under high-intensity 365-nm UV-LED photoirradiation to support multielectron transfer mechanism based on kinetic models. For oxygen evolution from deaerated aqueous titania suspensions with electron acceptors, small anatase (4 nm) and rutile (13 nm) particles show second-first order LID in the lower and middle intensity range, and such LID-order switching could reasonably be explained using a kinetic model in which the probability of two-electron (positive hole) accumulation in each particle governs the overall rates. Moreover, forth-first order LID was observed in some cases under further higher intensity (> ca. 280 mW), which might be attributable to the shift of reaction mechanism to four-electron transfer process. From the results including photocatalytic oxygen reduction in acetic acid decomposition, effective particle size was suggested as the size in which multiple electrons (positive holes) could be accumulated to drive multielectron transfer reactions.

Resume : Energy and environmental issues are global concerns in the present scenario. As an Advanced oxidation Process (AOP), photocatalysis is proved to be a common solution to the energy crisis and environment related pollution issues. The highly reactive oxygen species produced during heterogeneous photocatalysis allow the mineralization of wide range of organic chemicals with no selectivity thus helping in water remediation. Minimizing charge recombination loss and increasing solar energy conversion is still a key challenge in photocatalysis. Perovskite based ferroelectric materials have been able to address this issue due to permanent and controllable internal electric fields based spatial charge separation.[1] Potassium sodium niobate ((K,Na)0.5NbO3) (KNN) is one of the suitable lead free candidates with its low density, high Tc and relatively high coupling co-efficient. The phase stability of KNN is limited to 1140 degree Celsius and its piezo response is comparable to PZT.[2] These properties make KNN a suitable material for various applications such as transducers, capacitors etc. However, to date, there has been seldom report about the effect of polarization on photocatalytic dye degradation of KNN. The effect of the ferroelectric characteristics on the separation of charge carriers, which is similar to the p−n junction of a typical photovoltaic structure, reduces the recombination of holes and electrons, thus increasing the lifetime of the photo induced charge carriers. So it is important to explore the photocatalytic application of KNN. In this work, a systemic study has been carried out to observe the structure dependence photocatalytic performance of perovskite ferroelectric KNN materials. Bulk KNN is synthesized by solid state reaction method and micro structure of KNN is synthesized by molten salt reaction method.The bulk and micro perovskite structure is characterized using XRD, SEM, XPS, and RAMAN spectroscopy techniques. Photocatalytic degradation of Rhodamine 6G is observed through UV-Vis spectroscopy.Polarization plays an important role for the separation of holes and electrons. The change of polarization according to the structural change and to reveal the effect of ferroelectricity on photocatalytic activity [3] is explained in this work. The mechanism of photocatalysis is explained by ultrafast spectroscopy. All these observations combine and make KNN an intriguing material which can be applied in photocatalysis. 1. Dunn, S et al., Chemistry of Materials, 25(21), 4215-4223 (2013). 2. Setter, N et al., Journal of electro ceramics, 13, 385-392 (2004). 3. Yang, Y et al., Small, 11(2), 202-207 (2015).

Resume : Manganese(II,III,IV)oxides have been prepared by reactive magnetron sputtering on gold substrates to form active catalysts for the OER in alkaline media. They have been analyzed by XPS before and after electrochemical testing to identify their respective composition and compositional changes during the reaction. The highest activity is observed for the MnO2 showing an overpotential of 540mV @ j= 5mAcm-2 and a Tafel slope of 82mV/decade. This can be slightly improved by a special electrochemical treatment step. The other oxides show a worse performance. XPS studies after the electrochemical testing show the transformation of the Mn(II,III)oxides to mainly the Mn(IV)oxide and to a lesser extent also to Mn3O4. Hydroxides do appear for the Mn(III,IV) oxides, but they do not seem to play such an important role for the OER as has been observed for other transition metal oxides. Although, the overall activity decreases with increasing number of electrochemical cycles, there seems to be no corrosion of the material itself. The evaluation of the in-operando Raman spectra corroborates the transformation of the Mn(II,III) oxides to the Mn(IV) oxide starting already at potentials > 1.0V (vs. RHE). The active phase formed is characterized as the ∆-MnO2 (Birnessite). Furthermore, the formation of peroxo-species has been observed, which can be assigned to surface bound oxygen or intercalated water between the ∆-MnO2 layers. Manganese oxides show a strong phase dependence in their catalytic activity, which has been analyzed by XP and Raman spectroscopy. Especially the in-operando Raman mode allows the observation of these phase transitions directly as a function of applied potential in a working electrochemical environment.

Resume : Energy depletion along with global warming and environmental pollution constitute the main issues that have to be addressed in the next decades to provide sustainable growth and overall living standards to the whole population. There is therefore a strong need of “green” technologies to produce alternative fuels to conventional fossil energy resources and to achieve the efficient removal of harmful pharmaceutical or organic pollutants. In this context, heterogeneous photocatalysis involving metal oxide semiconductor nanostructures is deemed to be one of the more promising routes for environmental remediation and for hydrogen production. Nonetheless, the recombination of charge carriers constitutes one of the main limitations to achieve high photocatalytic efficiencies. Development of heterostructure photocatalysts by coupling two semiconductors with suitable band edge position can reduce recombination phenomena by vectorial transfer of charge carriers. First of all, we will report on submetallic/n-type or p-type/n-type oxide semiconductor heterojunctions such as RuO2/TiO2,(ref 1) and NiO/TiO2 (ref 2,3) heteronanostructures prepared by straightforward solution routes followed by a suitable thermal post-treatment. In a second part, a new photodeposition method using simulated solar light will be described for the selective deposition of various co-catalysts (Ag, Pt, NiOx, CoOx) onto faceted BiVO4 particles. Some of the heteronanostructures based on TiO2 showed improved photocatalytic activity in organic dye degradation and H2 production by methanol photoreforming compared to pure anatase TiO2 and commercial P25. Moreover, BiVO4-based heteronanostructures appeared to be efficient photocatalysts for the oxygen evolution reaction. These results were then rationalized on the basis of energy band alignment diagrams determined by a suitable combination of XPS/UPS and absorption spectroscopy data,(ref 4,5) and of an investigation on the role of the active species (holes, hydroxyl or superoxide radicals) in the photodecomposition processes. Favorable band bending at the metal oxide/metal oxide interface and the key role of photogenerated hole were proposed to explain the enhanced photocatalytic properties of the heterojunction photocatalysts. 1. Md. T. Uddin, O. Babot, L. Thomas, C. Olivier, M. Redaelli, M. D’Arienzo, F. Morazzoni, W. Jaegermann, N. Rockstroh, H. Junge, T. Toupance, J. Phys. Chem. C 119, 7006 (2015). 2. Md. T. Uddin, Y. Nicolas, C. Olivier, W. Jaegermann, N. Rockstroh, H. Junge, T. Toupance, Phys. Chem. Chem. Phys. 19, 19279 (2017). 3. S. Kashiwaya, C. Aymonier, J. Majimel, C. Olivier, A. Klein, W. Jaegermann, T. Toupance, New J. Chem. 42, 18649 (2018). 4. S. Kashiwaya, T. Toupance, A. Klein, W. Jaegermann, Adv. Ener. Mater., 8, 201802195 (2018). 5. Y. Hermans, A. Klein, K. Ellmer, R. von de Kroel, T. Toupance, W. Jaegermann, J. Phys. Chem. C 122, 20861 (2018).

Resume : Rare-earth (RE) ion-doped materials exhibit excellent photon upconversion (UC) properties, which could improve the efficiency of solar energy utilization. However, only a fraction of the solar spectrum is converted because of the narrow absorption bands of the RE ions. We have proposed the concept to broaden the sensitivity range of UC by introducing sensitizers of transition-metal ions, in particular six-coordinated Ni2+ for harvesting near-infrared light, and proven using Er3+ and Tm3+ emitters [1]. The next step toward high efficiency is to fabricate plate-like transparent ceramics of these UC materials to be coupled with solar cells and photoelectrodes. For this purpose, we have designed the combination of the emitters, sensitizers, and host of cubic crystal structures for transparency, considering the ionic radii and coordination numbers of the host and dopant cations [2]. Ca3Ga2Ge3O12 host with Er3+ and Ni2+ dopants promoted energy transfer from the Ni2+ to the Er3+, which efficiency was close to unity, and suppressed backward energy transfer. Additional dopants of Li+, Y3+, and Nb5+ improved the UC efficiency owing to enhanced lattice distortion, along with charge compensation. A broadband sensitivity ranging from 1.1 um to 1.6 um for the UC emission at 0.98 um was demonstrated, which just fits crystalline silicon solar cells. [1] Y. Takeda, et al., Appl. Phys. Lett. 108, 043901 (2016). [2] Y. Takeda, et al., J. Am. Ceram. Soc., https://doi.org/10.1111/jace.16193.

Resume : Graphene has recently been shown to be permeable to thermal protons, nuclei of hydrogen atoms, which sparked interest in its use as a proton-conducting membrane in relevant technologies. However, the influence of light on the proton permeation remains unknown. Here we report that proton transport through Pt-nanoparticle-decorated graphene can be enhanced strongly by illuminating it with visible light. Using electrical measurements and mass spectrometry, we find a photoresponsivity of 10^4 A W-1, which translates into a gain of 104 protons per photon, with response times below the microsecond range. These characteristics are competitive with those of state-of-the-art photodetectors based on electron transport using silicon and novel two-dimensional materials. The photo-proton effect can be important for graphene’s envisaged use in fuel cells and hydrogen isotope separation. Our observations can also be of interest for other applications such as light-induced water splitting, photo-catalysis and novel photodetectors. 1. Hu, S. et al. Proton transport through one-atom-thick crystals. Nature (2014). 2. Lozada-Hidalgo, M. et al. Sieving hydrogen isotopes through two-dimensional crystals. Science (2016). 3. Lozada-Hidalgo, M. et al. Giant photoeffect in proton transport through graphene membranes. Nature Nanotechnology (2018). 4. Lozada-Hidalgo, M. et al. Scalable and efficient separation of hydrogen isotopes using graphene-based electrochemical pumping. Nature Communications (2017).

Resume : Defect level control is one of the key factors in optimization of photocatalytic materials, since defect levels determine the photon absorption efficiency and carrier lifetime. To solve the large band gap problems of conventional photocatalytic materials, such as TiO2 and BiVO4, many dopant engineering have been tried. However, it is extremely time-consuming work to optimize the processing condition of doped photocatalytic materials. It is necessary to suggest theoretical framework to quickly optimize the processing condition and control the qualities. In this talk, I will present the recent success case of theory-based quality controls of doped photocatalytic materials of anatase TiO2 and BiVO4. Especially by controlling the gas mixtures for annealing process, we could engineered point defects to avoid deep-level defects and increase the shallow-level defects.

Resume : Conjugated polymer nanostructures (CPNs) emerge as a new class of photocatalysts for organic pollutant degradation under UV and visible light , , , . Polyprrole (PPy), as a conjugated polymer, exhibits a wide range of applications. We present here the first illustration of employing pure PPy nanostructures as a very efficient photocatalyst for water depollution5. PPy was synthesized in soft template by chemical polymerization (PPy-c), obtained by radiolysis (PPy-γ), and synthesized without template via chemical method (PPy-b) as bulk. These samples were characterized by different techniques such as SEM, TEM, NanoIR, FTIR, UV-Vis spectroscopy. PPy nanostructures exhibit higher photocatalytic performance under UV and visible light compared with PPy-bulk. We modified PPy nanostructures with co-catalysts based on Pt, Ni nanoparticles for H2 production. The modified PPy nanostructures give also promising results for hydrogen generation under ultraviolet light. The effect of the nature of the metal precursors and their concentrations were studied.

Resume : Removal of pathogenic microorganisms from water by heterogeneous photocatalysis is an area of active research. The inactivation rate of E.coli K12 as a model indicator organism in drinking water was investigated here using graphitic carbon nitride (gC3N4) and tungsten trioxide (WO3) heterostructures as photocatalytic materials under simulated solar irradiation. WO3-gC3N4 heterostructures (WCN) are potential 2D photocatalyst that could use a Z scheme mechanism. The efficiency of WCN photocatalyst was determined in suspension in a stirred tank reactor. However, no photocatalytic activity was observed towards the inactivation of E.coli. To investigate why the photocatalyst did not show activity, the generation of reactive oxygen species such as hydroxyl (●OH) radicals by photo-oxidation of RNO dye was studied. The WCN heterostructures and parent materials show limited production of ●OH probably due to fast charge carrier recombination, but with AgNO3 as an e- acceptor the ●OH production rate was increased significantly (1.5x greater than WO3). This confirmed WO3 works as an oxidation photocatalyst due to a positive VB. The reduction pathway of gC3N4 and WO3 was studied using methylviologen as an e-acceptor to determine the flat band potential of two materials. gC3N4 previously reported having a CB of -1.13 eV, was unable to reduce MV2+ to MV+ (-0.45 eV), when compared to TiO2 and WO3. Hence, this work focuses to study the electron transfer process in WO3-gC3N4 heterostructures.

Resume : Photoactive porous Metal Organic Frameworks (MOFs) are still scarce. Only a few Cu, Zn, Zr or Ti based MOFs have been shown to date to exhibit such properties but most of time suffered from either a poor activity and/or a low chemical stability. In the case of Ti based MOFs, known to be rather water stable, this is mainly due to their challenging chemistry associated with their strong chemical reactivity in water.[1] We were among the first to report open frameworks titanium phosphates or phosphonates, [2, 3] and later a hghly porous photoactive Ti polycarboxylate based MOF. [4] However these solids did not show any photoconductive behavior. We report here a unique example of porous photoconductive Ti-MOF constructed from Ti oxide nanorods.[5] This material, upon loading with a conductive polymer, exhibits an order magnitude increase of the charge separation life time under irradiation. We will finally describe its utilization for the photo-assisted production of hydrogen [6]. References. [1] H. Assi, G. Mouchaham, N. Steunou, T. Devic and C. Serre, Chem. Soc. Rev., 2017, 46(11), 3431 [2] C. Serre, F. Taulelle, G. Férey, Chem. Comm. (Feature Article), 2003, 2755 [3] C. Serre, J. A. Groves, P. Lightfoot, A. M. Z. Slawin, P. A. Wright, N. Stock, T. Bein, M. Haouas, F. Taulelle, and G. Férey: Chem. Mater. 2006 18, 1451 [4] M. Dan-Hardi, C. Serre, T. Frot, L. Rozes, G. Maurin, C. Sanchez and G. Férey , J. Am. Chem. Soc. Comm., 2009, 131, 10857 [5] S. Wang, T. Kitao, N. Guillou, M. Wahiduzzaman, C. Martineau-Corcos, F. Nouar, A. Tissot, L. Binet, N. Ramsahye, S. Devautour-Vinot, S. Kitagawa, S. Seki, Y. Tsutsui, N. Steunou, G. Maurin, T. Uemura and C. Serre, Nat. Comm., 2018, 9, 1660 [6] S. Wang, C. Serre et al., in preparation

Resume : Due to advantages such as their high synthetic flexibility, organic polymers are attracting intense research interest as photocatalysts for sunlight-driven fuel production. Such polymeric materials have been widely used as light absorbers for organic photovoltaics, however, the processes that take place upon light irradiation are not well-understood when these polymers are immersed in water. One particularly controversial aspect for their use as photocatalysts is the role of residual palladium, which is typically found in particles of conjugated polymers as a result of their synthesis via palladium-catalysed polycondensation reactions. These palladium impurities have been suggested to participate in the photocatalytic process, but clear conclusions could so far not be drawn. We use stepwise purification to investigate the impact of different residual palladium concentrations on the hydrogen evolution activity of nanoparticles of the widely used conjugated polymer F8BT.[1] We find a pronounced enhancement of the hydrogen evolution rate for palladium concentrations as low as 40 ppm and employ time-resolved spectroscopic techniques to understand the role of palladium in the sequence of photoinduced reactions. References: [1] Kosco, J.; Sachs, M.; et al. Adv. Energy Mater. 2018, 1802181, 1–7.

Resume : Come up with renewable energy sources to face the continuous growth of energy demand while minimizing the environmental impact becomes crucial. In that way, much attention has been paid to the conversion of incoming solar energy into valuable solar fuels as it is an inexhaustible and green energy source. For this, photocatalytic CO2 reduction into solar fuels is believed to be a smart and attractive option.[1] An important aspect of this reaction is the high-density storage of solar energy in the form of chemical bonds, mainly C-H enabling to produce a stable and constant energy flux as the modern society expects. At the same time this technology might contribute to reducing the CO2 emission from highly concentrated effluents (e.g. from cement plant) or at least offer a CO2 circular economy. As it is well known, in heterogeneous process, the photocatalyst is usually a multifonctional material which absorbs light, separates the photogenerated charges, transports them to the surface, and provides active sites for the catalytic reaction.[2] Each of theses steps encounters critical limitations which prevent the overall photoconversion efficiency and selectivity of CO2 reduction and industrial development. At IFPEN we develop new materials to explore these different challenges. These materials are dedicated to the production of CH4 and longer alkanes molecules and are tested on a photocatalytic unit. In this presentation, we proposed to present two late highlights of our group: addressing light diffusion within the photocatalyst by proposing a 3D photoconversion behavior wit the use of macrocellular monoliths [3,4], and fine tuning optical properties of low bandgap semiconducting materials such as MoS2 with quantum size effect.[5] Those works allowed us to propose new ways for photocatalytic CO2 reduction with water, willing to be an active contributor in the artificial photosynthesis community. References: [1] S. N. Habisreutinger, L. Schmidt-Mende, J. K. Stolarczyk, Angew. Chem. Int. Ed., 2013, 52, 7372. [2] X. Chang, T. Wang, J. Gong, Energy Environ. Sci., 2016, 9, 2177. [3] S. Bernadet, E. Tavernier, D-M.Ta, R. A. L. Vallée, S. Ravaine, A. Fécant, R. Backov, Adv. Funct. Mater., 2019, 29, 1807767. [4] S. Bernadet, A. Fécant, S. Ravaine, D. Uzio, R. Backov. FR Patents No. 3065651, 3065650, 3065649, 2017. [5] A. Fécant, A. Bonduelle. Patent filing INPI N° 17/60.718 , 2017.

Resume : The selective oxidation of high-toxic pollutants is a challenging issue in TiO2-based photocatalysis. Indeed, water effluents usually contain low concentrations of dangerous compounds (as pesticides), together with high concentrations of less-toxic substances which are preferentially degraded with conventional photocatalysis. In this work we report a fascinating approach, based on the combination of the molecular imprinting process, used to obtain the selectivity towards a specific pesticide, with the photocatalytic process, used to degrade that specific compound. The TiO2 photocatalysts were imprinted without using any organic or inorganic matrix, thus avoiding a multistep procedure and easing the materials synthesis. The chemical-physical properties of the TiO2 photocatalysts were assessed by various characterization techniques (SEM, XRD, FTIR, N2 adsorption-desorption measurements), while the photo-activity was evaluated both under UV than solar irradiation. Moreover, the non-toxicity of the investigated materials has been demonstrated through biological tests. The remarkable increase of the photocatalytic activity of the imprinted samples with the corresponding pesticides-targets compared to bare TiO2 highlighted the synergism between the molecular imprinting and the photocatalysis. The good performance of the molecularly imprinted TiO2 materials allows to consider this strategy an efficient method to obtain a selective photocatalytic process.

Resume : In this work, the polyaniline coated bacterial cellulose (PANi/BC) mat was developed for the removal of toxic Cr(VI) from the aqueous solution. The porous PANi/BC mat was prepared by in-situ chemical polymerization of aniline onto the surface of the interconnected network of bacterial cellulose fibres followed by freeze-drying and characterized by FTIR, FE-SEM, and TGA. As compared with previous reports on the removal of Cr(VI) by polyaniline based adsorbents, mainly from acidic aqueous solutions, we have examined the Cr(VI) removal from the potable drinking water. The PANi/BC mat (50 mg) showed the complete removal of Cr(VI) (200 ppm in 20 mL) from the aqueous solution at neutral pH 7. The kinetics and mechanism of Cr(VI) removal from the aqueous solution was studied by UV-Vis spectroscopy, Inductively coupled plasma-mass spectroscopy (ICP-MS) and X-ray photoelectron spectroscopy (XPS). The removal mechanism was observed to be based on three steps: 1) adsorption of Cr(VI) on the surface of PANi/BC by electrostatic interaction between Cr(VI) oxyanions (CrO42-, and HCrO4- ) and doped amine/imine (−NH+/=N+−) groups of polyaniline, 2) reduction of the adsorbed Cr(VI) oxyanions into Cr(III) and 3) desorption of Cr(III) back into the aqueous solution due to the repulsion between the doped amine/imine groups and cationic Cr(III) species. The kinetics of Cr(VI) removal by PANi/BC showed that the rate-limiting step was desorption of reduced Cr(III) from the PANi/BC mat, which is confirmed by applying the Langmuir–Hinshelwood kinetic model to the adsorption, reduction, and desorption processes.

Resume : Photocatalytic and hydrothermal catalytic conversion of glucose in aqueous solutions were studied with the objective of subsequently combining them to decrease energy expenditure and limit side products formation. The photocatalytic process (UV: 365 nm, 6.7 mW/cm², air) involved UV100, PC105, MPT-625, Rut 160, P25 and P90. It allowed the formation of formic acid, glyceraldehydes (GAL), gluconic acid (GA), erythrose (ER), arabinose, and lactic acid (LA). P25 and P90 were selective for GA and ER. MPT-625 and Rut160 were selective for GAL. The hydrothermal process (120°C) using the above catalysts allowed the formation of mainly fructose with UV100, PC105, P25 and P90; and hydroxymethylfurfural with MPT-625 and Rut160. The catalytic performances under air and argon were similar. The search for potential relationships between the acid-base properties of the catalysts and their activity was investigated using the model reaction of dihydroxyacetone conversion in water which showed that MPT-625 and Rut 160 did not promote LA formation due to absence of Lewis acid sites, P25 and P90 might have more of such sites than UV100 and PC105. The adsorption of pyridine monitored by FTIR test showed that Rut160 had the least Lewis acid sites and had BrØnsted acid sites.

Resume : Smart tiny devices that self-propel in different liquid media and perform complex tasks, have attracted worldwide attention in the last decade. Recent studies have shown that the active motion of these micro/nanomotors leads to an enhanced micromixing, favoring mass transfer and decontamination rates of different water cleaning processes. [1] Since a real-world application of these micromachines is still limited due to the need of precious metals in their structure and the high cost associated with their fabrication, we present low-cost tubular micromotors solely based on graphitic carbon nitride photocatalyst. These metal-free C3N4-based tubular micromotors are powered by visible light irradiation, which enables their remote motion control by simply turning on/off the light irradiation. [2] Moreover, taking advantage of their adsorptive capabilities and inherent fluorescence, the removal of a heavy metal from contaminated water with the concomitant optical monitoring of its adsorption by fluorescence quenching was demonstrated. Interestingly, the speed of C3N4 micromotors was enhanced in the presence of common toxic pollutants found in wastewater, showing a promising application for environmental applications. References [1] Villa et al. ACS Appl. Mater. Interfaces, 2018, 10 (24), pp 20478–20486. [2] Villa et al. ACS Nano, 2018, 12 (12), pp 12482–12491.

Resume : During the several past decades new carbon allotropes have been accounted and synthesized. Many notable breakthroughs include exciting works on synthesis, functionalization, characterization and applications of carbon nanotubes, graphene and graphene like structures, i.e. graphitic carbon nitrides. The exciting progress made since the initial use of carbons as modifiers of optical semiconductors as stimulated many researches in different fields of immediate and relevant application. Apart from the obvious applications in water treatment and remediation, there are thrilling examples in photocatalytic synthesis, assisted conversion with production of valuable chemicals or fuels, photocatalytic production of solar fuels, and photo-assisted purification of compounds of biological and health relevance. The development of such materials also prompted the development of new integrated and technological solutions, including new photoreactors and combined systems for engineering processes, including microfluidics. The duality between fundamental and applied, as well as between theory and practice will be used to present some of our latest progresses in the field of conversion of hazardous chemicals in aqueous streams with in-situ generation of added value compounds, selective photocatalytic synthesis [1-3], photo-assisted enzyme purification [4], and solar fuel production [5,6]. 1. Svoboda, L.; Praus, P.; Lima, M. J.; Sampaio, M. J.; Matysek, D.; Ritz, M.; Dvorsky, R.; Faria, J. L.; Silva, C. G., Graphitic carbon nitride nanosheets as highly efficient photocatalysts for phenol degradation under high-power visible LED irradiation. Mater Res Bull 2018, 100, 322-332. 2. Silva, C. G.; Pereira, M. F. R.; Orfao, J. J. M.; Faria, J. L.; Soares, O., Catalytic and Photocatalytic Nitrate Reduction Over Pd-Cu Loaded Over Hybrid Materials of Multi-Walled Carbon Nanotubes and TiO2. Frontiers in Chemistry 2018, 6. 3. Moreira, N. F. F.; Narciso-da-Rocha, C.; Polo-Lopez, M. I.; Pastrana-Martinez, L. M.; Faria, J. L.; Manaia, C. M.; Fernandez-Ibanez, P.; Nunes, O. C.; Silva, A. M. T., Solar treatment (H2O2, TiO2-P25 and GO-TiO2 photocatalysis, photo-Fenton) of organic micropollutants, human pathogen indicators, antibiotic resistant bacteria and related genes in urban wastewater. Water Res 2018, 135, 195-206. 4. Costa, J. B.; Lima, M. J.; Sampaio, M. J.; Neves, M. C.; Faria, J. L.; Morales-Torres, S.; Tavares, A. P. M.; Silva, C. G., Enhanced biocatalytic sustainability of laccase by immobilization on functionalized carbon nanotubes/polysulfone membranes. Chem Eng J 2019, 355, 974-985. 5. Da Silva, E. S.; Moura, N. M. M.; Coutinho, A.; Drazic, G.; Teixeira, B. M. S.; Sobolev, N. A.; Silva, C. G.; Neves, M.; Prieto, M.; Faria, J. L., beta-Cyclodextrin as a Precursor to Holey C-Doped g-C3N4 Nanosheets for Photocatalytic Hydrogen Generation. Chemsuschem 2018, 11 (16), 2681-2694. 6. Pastrana-Martinez, L. M.; Silva, A. M. T.; Fonseca, N. N. C.; Vaz, J. R.; Figueiredo, J. L.; Faria, J. L., Photocatalytic Reduction of CO2 with Water into Methanol and Ethanol Using Graphene Derivative-TiO2 Composites: Effect of pH and Copper(I) Oxide. Top Catal 2016, 59 (15-16), 1279-1291

Resume : The intermittency of solar energy limits its use at large scale. A leading approach is to store as chemical fuels the energy produced from the sun irradiation. The development of photoelectrochemical cells (PECs) that produce H2 and O2 from water photosplitting has, therefore, become very attractive. Though, this approach remains at a low technology readiness level (TRL 1-2) since the main issue is the production cost of H2. Many research groups are currently investigating different routes to fabricate cost-effective PECs. To reach this target, one has to play on the cell design and to select the appropriate electrode materials. It has also been shown that micro- or nanostructuring and/or surface functionalization of the photoelectrodes can lead to higher performances. Among the numerous approaches and techniques that have been used since nanosciences and nanotechnologies have emerged, atomic layer deposition (ALD) has recently demonstrated its high effectiveness to fabricate 3D nano-objects by combining several materials. Energy storage and production are part of the fields of applications in which ALD has shown highly promising perspectives. This presentation will show how ALD has been effectively integrated in several photoelectrode fabrication strategies. After a brief introduction on the various surface micro- and nanostructuring methods, a short description of the ALD process will be presented. Then the different types of uses (active materials, surface state passivation and corrosion protection) of ALD in the field of solar fuel production will be reported and discussed.

Resume : Solar-to-hydrogen conversion offers a clean, viable and sustainable approach for hydrogen production, replacing at long term the use of fossil fuels [1]. Semiconducting oxide photoanodes can be employed in photo-electrolysis cells to efficiently drive the water splitting reaction [2]. Under sunlight radiation, electron-hole pairs are created at the photoanode: the holes participate in the oxidation reaction, while electrons from the cathode are involved in the reduction reaction. In such systems the hydrogen production is generally quantified through the measured photocurrent generated under sunlight illumination upon applying an external voltage. Another parameter, the onset potential, which is the minimum voltage necessary to generate non-zero photocurrent, is directly related to the gain from solar energy conversion relative to standard electrolysis. This onset potential has a value of 1.6 V for simple electrolysis using two Pt electrodes, but reaches values as low as 0.6 V in the present study. Hematite photoanodes were fabricated using aqueous chemical growth [3], a simple method for generating films composed of organized nanostructures. Film thickness and morphology are tuned by adjusting the aqueous solution pH, which in turn controls the photo-electrochemical activity, the photocurrent density and the quantum efficiency. Low onset potential values characterize all our samples. We relate these low values to the Brønsted acidification of the photoanode, arising from the presence of a proton rich phase. Soft X-ray Scanning Transmission X-ray Microscopy (STXM) at the Soleil HERMES beamline was used to characterize the hematite photoanode. An additional hexahydrated iron chloride (FeCl3.6H2O) phase was identified. Fitting STXM 3D datasets (X, Y, photon energy) with reference spectra recorded from commercial hematite and the FeCl3.6H2O used as a precursor for aqueous growth, results in quantitative chemical speciation maps where spatial distribution of both phases (hematite and precursor) is clearly established. 1. S. Ardo et al., Energy Environ. Sci. 11, 2768 (2018) 2. Z. Mi, L. Wang, C. Jagadish (Eds), “Semiconductors for Photocatalysis”, Vol. 97, 1st Edition, Elsevier; A. Fujishima and K. Honda, Nature 238, 37 (1972) 3. L.Vayssieres, Appl. Phys. A 89, 1 (2007)

Resume : A photoactive amine-functionalized Ti metal-organic framework (MOF) (MIL(125)-NH2(Ti)) layer is uniformly coated on TiO2 nanorods (NRs) through a facile hydrothermal reaction, and the performance of the photoanode in photoelectrochemical (PEC) water splitting is investigated. It revealed the photocurrent density of the MIL(125)-NH2/TiO2 NRs is 1.63 mA/cm2 at 1.23 V vs. a reversible hydrogen electrode under AM 1.5 G simulated sunlight illumination, which showed ~2.7 times enhanced current density when compared with pristine TiO2 NRs. The incident photon-to-electron conversion efficiency of the MIL(125)-NH2/TiO2 NRs increased significantly at lmax = 340 nm, indicating the water oxidation is promoted by the efficient light absorption and charge separation through the coating of MIL(125)-NH2. The improvement of the PEC activity is discussed in relation to the vertically ordered configuration of the TiO2 NRs, the band gap of MIL(125)-NH2(Ti), and the type (II) band alignment. This study clearly shows the rational design and facile synthesis of semiconductor/MOF heterojunctions can be a new general approach to achieve high efficiency in photoelectrochemical water splitting.

Resume : The photo-electrochemical conversion of urea can be achieved in alkaline medium through the reaction : CO(NH2)2 + H2O + solar-hν + electrochemical-ΔV -> CO2 + N2 + 3 H2 (R1) Producing H2 from R1 requires theoretically three times less energy than from water splitting, (thermodynamic cell potential of 0.37 V vs. 1.23 V, respectively). The vast untapped resource of urea in urine (60 Mt/year from humans) makes R1 very attractive as converting pollutant into fuel with the assistance of solar energy simultaneously addresses the problematics of (1) wastewater treatment, (2) production of H2 as an energy vector and (3) energy saving by use of renewable energies. Urea electro-oxidation has been the subject of numerous studies [1] but only three works have been published so far on the photo-electro-oxidation of urea [2-4]. In this context, our goal is to design and study photoanodes for efficient conversion of solar energy (UV-Visible) to obtain high oxidation photocurrents in the presence of urea. For this purpose, we have synthesized Fe2O3 semiconductor layers, decorated with Ni-metal nanocatalysts. First, a Fe0 deposit is obtained on a Fluorine-doped Tin oxide (FTO) glass by electrodeposition from a FeII salt solution. The samples are doped with Pt or Sn by adding to the FeII salt solution either H2PtCl6 or SnCl2 at various concentrations. The deposit is then annealed at 700°C for 2 hours to obtain Fe2O3. At that point, nickel nanoparticles are electrodeposited on Fe2O3 and the resulting FTO/Fe2O3/Ni materials are characterized by X-Ray Diffraction and Scanning Electronic Microscopy to identify their structure and morphology. Then, the photoelectrochemical performances toward urea oxidation were determined by voltammetry under illumination. We will present these results and the context of hydrogen production based on the developed urea oxidation process. References [1] W. Xu, Z. Wu, S. Tao, Urea-Based Fuel Cells and Electrocatalysts for Urea Oxidation, Energy Technol. 4 (2016) 1329–1337. [2] D. Xu, Z. Fu, D. Wang, Y. Lin, Y. Sun, D. Meng, T. Feng Xie, A Ni(OH)2-modified Ti-doped α-Fe2O3 photoanode for improved photoelectrochemical oxidation of urea: the role of Ni(OH)2 as a cocatalyst, Phys. Chem. Chem. Phys. 17 (2015) 23924–23930. [3] G. Wang, Y. Ling, X. Lu, H. Wang, F. Qian, Y. Tong, Y. Li, Solar driven hydrogen releasing from urea and human urine, Energy Environ. Sci. 5 (2012) 8215–8219. [4] W.M. Omymen, J.R. Rogan, B.Z. Jugović, M.M. Gvozdenović, B.N. Grgur, Photo-assisted electrochemical oxidation of the urea onto TiO2-nanotubes modified by hematite, J. Saudi Chem. Soc. 21 (2017) 990–997.

Resume : In the thematic area of the sunlight-driven hydrogen-evolution reaction (HER), silicon has appeared as one of the most promising materials to be used as a photocathode because its abundance, nontoxicity, its ability to absorb photons from a large portion of the solar spectrum, as well as its tunable electronic properties. Nevertheless, the use of a bare semiconducting material as a photocathode does not allow to drive HER at a sufficiently low overpotential and with a sufficient rate. Therefore, the immobilization of a cocat onto the photocathode surface is required in order to increase the HER catalytic efficiency. In this presentation, the electrostatic incorporation of a polyoxothiometalate (POTM) cocat into a poly(3,4-ethylenedioxythiophene) (PEDOT) film is demonstrated to be an efficient and straightforward method to retain the cocat at the surface of a micropyramidal silicon (SimPy) photocathode, with respect to a simple physisorption at the solid-liquid interface. The so-derivatized photocathodes are stable and effective for sunlight-driven HER in acid conditions for several hours. Reflectance and incident photon-to-current efficiency measurements indicate significant losses in the photon flux reaching the Si space charge layer, due to the absorption of the PEDOT film, which results in a decreased HER photocurrent. Despite these losses, the POTM/PEDOT-modified photocathode is able to produce H2 under 1 sun illumination at a rate exceeding 400 µmol/cm2/h at 0 V vs reversible hydrogen electrode (RHE), highlighting the performance of this buried-junction-free photoelectrochemical system.

Resume : We report on properties of a metal-insulator-semiconductor photoanode for water splitting comprising a thin RuO2 film as a top catalytic layer. RuO2 offers low resistivity, high optical transparency and work function as well as high catalytic efficiency. RuO2/SiO2/n-Si photoanode exhibited a photovoltage of 0.5 V and was able to generate photocurrent with a density up to 10 mA/cm2 at a thermodynamic water oxidation potential (1.23 V) in both acid and basic solutions. Stability of the RuO2/SiO2/n-Si photoanode was examined in 1M solutions of H2SO4 (pH = 0) and Na2SO4 (pH = 6). The RuO2/SiO2/n-Si photoanode in 1M H2SO4 solution showed degradation after 1 h operation under applied voltage of 1.5 V vs. reversible hydrogen electrode (RHE) and current density of 7.5 mA/cm2. Using applied voltage of 1.25 V vs. RHE in 1M Na2SO4 resulted in current density of 0.3 mA/cm2 and stable operation up to 18 hours. Performance of the RuO2/SiO2/n-Si photoanode is examined in accordance with the corrosion stability predicted by potential-pH (Pourbaix) diagrams. It is shown, that stability of the photoanode can be further increased by alloying with IrO2. Acknowledgement This research was funded by APVV (project APVV-17-0169).

Resume : The development of DSSC has reached bottleneck in the improvement of efficiency. One reason is difficult to obtain textured TiO2 with large surface area to absorb more dye molecules. Recently ZnO nanostructures have attracted much more interest to be used as photoelectrode in DSSC application. In this report, The AZO thin film was used to replace the traditional ITO glass as the conductive film, which serves as seeds layer for homo-junction growth of ZnO nanorods.Firstly, AZO film was deposited on glass substrate by radio frequency magnetron sputtering. Secondly, the ZnO thin film was deposited on obtained AZO film. Thirdly, ZnO nanorods were fabricated by a novel multi-annealing process in which the reducing annealing and oxidization annealing were carried out in turn to achieve the re-crystallization of ZnO film on AZO film. As the result, ZnO nanorods with good alignment were fabricated vertically on the AZO film, which showed good crystallinity, large surface area as well as the high transmittance over 80%. It was found that the growth direction of the ZnO nanorods was significantly dependent on the crystallinity of AZO film. The crystallinity of ZnO nanorods was influenced significantly by the annealing processes. The growth mechanism of the ZnO nanorods was investigated in detail. The obtained ZnO nanorods using as photoanodes are expected to enhance the overall conversion efficiency of the dye sensitized solar cells.

Resume : H2 as renewable energy source can be produced by water splitting in a solar-activated photo-electrochemical cell (PEC). Our collaborative project tackles with the development of new all-solid multilayered PEC for H2 production/separation including innovative vacuum-deposited photo-anode and electrolyte membrane materials. The optimization of the TiO2-based photo-anode is central to the project. As a first approach, fully crystallized anatase thin films are synthesized by MOCVD. A continuum of morphologies are obtained from dense with a lattice-preferred orientation < 110> parallel to the growing direction to porous nanotree-like with a < 001> lattice-preferred orientation. The latter structure photo-generates (with visible light) 17 times more H2 than the densest sample despite higher bandgap and residual compressive stress. To broaden the spectral absorption range, a nanometric Co3O4 film will be deposited on top of the TiO2 one to create a p-n heterojunction. Alternatively, single-oriented pure or C and N-doped anatase films are prepared by a one-step PECVD process. Such thin films demonstrate good photo-electrochemical properties (in particular in terms of activity domain tunable from UV to visible region) that can be tailored by adjusting the plasma synthesis parameters. The all-solid multilayered PEC (including a PECVD electrolyte membrane and a Pt/C plasma-sputtered cathode in addition to the anode) is currently assembled and characterized in terms of H2 production.

Resume : Mesoporous oxide films filled with metallic nanoparticles has been widely used to enhance photocatalytic properties by reducing charge recombination, due to a controlled porosity and the presence of light absorbing metallic catalyzers. To study and distinguish these mechanisms, we chose to study nanostructured electrodes made of Ag nanoparticles inside a semi-conductor oxide (TiO2 or Fe2O3) with a control of porosity and particle dispersion as an improved photocatalytic system. We performed electrochemical experiments in a three electrode configuration under various ranges of light irradiation, from UV to visible, to determine the variations of redox potentials and photocurrent and thus getting insights on the photochemical mechanism and material structure influence. A positive shift of 0.2V is observed under visible irradiation, corresponding to a modified reactivity from silver nanoparticles within TiO2 porous matrices. Silver nanoparticles are also modified due to diffusion through the electrolyte and electrochemical Ostwald ripening during photoelectrochemical experiments and have been characterized by electron tomography.

Resume : In order to reduce CO2 emissions and utilise CO2 as a useful by-product, artificial photosynthesis is being explored for carbon capture and utilisation. Semiconductor photocatalysts excited by solar energy may be used to convert CO2 to fuels or useful chemicals, e.g. CO, CH4, CH3OH. The photocatalytic reduction of CO2 to useful products has been widely studied in order to overcome the greenhouse effect and the current energy necessities. However, this reaction has shown extremely low efficiency when compared to other processes. In order to improve these yields, photoelectrochemical reduction of CO2 has been considered, since it combines photocatalysis and electrocatalysis. To this end, a two compartment photoelectrochemical cell (PEC) has been designed and fabricated for the reduction of CO2. This custom built reactor consists of a mixed phase cathode where gas phase CO2 is feed in and an aqueous phase anode compartment utilising aligned titania nanotubes on perforated titanium foil as the photoanode. CO2 reduction products were detected with GC connected to the reactor. The products obtained with the PEC were compared to the ones produced in previous studies with a photocatalytic reactor. Keywords: CO2 reduction, PEC, photocatalysis, photoelectrocatalysis

Resume : Photocatalysis is a growing area of research with key applications in wastewater and environmental remediation. Furthermore, there has been focus on the coupling of photocatalysis with electrochemical technology for applications such as water splitting, initially introduced by Fujishima and Honda. Photoelectrochemistry (PEC) requires development of TiO2 materials capable of producing high photocurrent densities under UV illumination while maintaining high current efficiency but also the development of novel reactors. More recently photocatalytic reactors have been designed with a view towards overcoming mass transfer limitations and the same approach must be taken in the design and development of novel photoanodes in PEC reactor. This work presents the development of a titanium propeller immobilised with a thin film TiO2 catalyst designed and evaluated using modelling of fluid flow and light distribution and coupled with experimental work, with a view to overcoming mass transfer limitations and increasing reactor efficiency. The propeller has been designed to be applicable for use as a photoanode in a novel PEC reactor, with various materials such as sol-gel coatings and Titania Nanotubes (TiNTs’) with potential for application in chloride oxidation.

Resume : Increasing pollution and reduction of potable water supplies delineated today the need to develop new technologies to purify water for consumption. Nanocomposites, a new class of materials fabricated by combining polymeric materials with nanomaterials, are emerging as a promising solution to these challenges. The incorporation of nanostructured photocatalysts in polymers takes the advantages of the flexibility of the polymer and the immobilization of the photocatalyst, which avoids the recovery of the nanoparticles after the water treatment. In this context, a promising deposition technique is the atomic layer deposition (ALD), because of its unique benefits: low deposition temperature, homogeneity, conformity and scalability. This contribution summarizes the experimental work done in the last years to find original, easy and industrially-scalable methods to obtain ZnO/polymer nanocomposites with significant photocatalytic efficiency. First of all, the ALD of ZnO thin films at low deposition temperature was deeply investigated. Once the deposition conditions were optimized, the ALD process was transferred on: 1) polyethylene naphthalate (PEN) and poly methyl methacrylate (PMMA) flexible substrates, 2) PMMA powders, and 3) poly(2-hydroxyethylmethacrylate) (pHEMA) cryosponges. The photoactivity of the materials was evidenced by the degradation of methylene blue (MB) and phenol in water. All the proposed nanocomposites resulted promising candidates for novel water treatment.

Resume : Thanks to its appealing chemico-physical properties and unique morphological flexibility, ZnO has emerged as an attractive candidate for light-assisted applications, which take advantage of its photocatalytic activity, photoinduced superhydrophilicity and self-cleaning behavior. Unluckily, ZnO also suffers from some drawbacks hindering its full technological exploitation, such as a low photocorrosion resistance and a rapid charge carrier recombination. A valuable strategy to circumvent these obstacles consists in the controlled modification of ZnO surface with other suitable semiconductors, in order to benefit from additive or synergistic effects originating from the combination of the two materials. In this context, the present work is focused on the unconventional synthesis of supported WO3-decorated ZnO calyx-like nanostructures, and their use as photocatalysts for the abatement of NOX (NO+NO2), a toxic gaseous pollutant responsible for atmospheric pollution and respiratory diseases. Thanks to the remarkable ZnO porosity, the efficient dispersion of tiny WO3 nanoparticles, and the high density of ZnO-WO3 heterojunctions, appealing De-NOX characteristics in terms of degradation efficiency and selectivity were obtained. These features, along with the self-cleaning behavior and light-driven superhydrophilicity of the developed nanomaterials, candidate them as promising functional platforms for application in smart windows and building materials for environmental remediation.

Resume : We present a new kind of doped titanium dioxide (TiO2) with passivated co-dopants as a candidate material for the enhanced photocatalytic activity, which has a reduced bandgap optimized for the visible light absorption without creating recombination centers. To confirm the band edges and the relative positions of impurity levels, we perform first-principles density-functional-theory calculations within the local density approximation as well as the hybrid functional approach. From the analysis of the bandgaps of doped-TiO2 and the defect levels, we propose that the vanadium-nitrogen (V-N) pair is a suitable passivated co-dopant in TiO2. By doping TiO2 with the V-N pair, the bandgap of TiO2 is reduced; enhancing the visible light absorption. The calculated band edges after doping also match the redox potentials of hydroxyl radical and superoxide anion; improving the photocatalytic activity for the degradation of organic pollutants and acting as antibacterial agents as well.

Resume : The present work constitutes an additional example showing an increase in the photocatalytic efficiency of semiconductors by the presence of graphene materials as a consequence of an increase in the efficiency of charge separation and a decrease of charge recombination. In the present case, this effect of graphene has been applied to carry out photocatalytic hydroxylation of benzene to phenol. It has been found that the much higher reactivity of phenol results in very low phenol yields and selectivity values and the occurrence of a large degree of mineralization. However, modification of the surface polarity by attachment of long alkyl chains can serve to control the hydrophilicity/hydrophobicity of the reaction centers and favors the adsorption of the substrates versus that of the product. In this way, a phenol selectivity as high as 63.94 % at about 30 % benzene conversion could be achieved. Although the benzene hydroxylation also occurs in the dark promoted by the photocatalyst, the selectivity to phenol is about four times lower and mineralization prevails. Thus, it is the combination of light and surface modification that is responsible for the notable selectivity for phenol in the reaction of benzene.

Resume : Black brookite is the least studied material as a co-catalyst free photo-catalyst for hydrogen evolution and dye degradation. In this study pure brookite, pure anatase and mixture of them were prepared via thermal hydrolysis of commercially available aqueous solutions of titanium bis (ammonium lactate) dihydroxide in the presence of high concentrations of urea. It is possible to control the ratio between brookite and anatase by controlling the amount of the urea concentration. Then these pure and composite phases were converted to black powders by hydrogenation method in different temperatures from 700°C to 1000°C. The obtained powders were characterized by transmission and high resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, UV-Vis diffuse reflectance spectroscopy and nitrogen absorption. Then the photo-activity of pure black brookite, pure black anatase and black mixture composite were measured by hydrogen evolution and dye degradation. The results show that the mixture phase of black titanium dioxide has the best photocatalytic activity. Also there is an optimum temperature for hydrogenation in which the TiO2 powders show the best efficiency.

Resume : Perovskites based photocatalysts are mixed-metal oxides that continually increase their scientific value and application interests, owing to their chemical and thermal stability, adaptability and low price, such materials have been widely used in environmental photocatalysis applications. It has not been until the last decade that ABO3-based materials have acquired great interest as photocatalysts to carry out the photocatalytic reduction of CO2 to produce diverse solar fuels and the hydrogen generation from water. On the other hand, it is well known that nanostructured carbon presents unique properties such as; high surface area, extraordinary electrical conductivity, excellent mechanical properties but also photocatalytic properties. In this work, we report the synthesis of NaTaO3 by two different methods (solid state and solvo-combustion) to study their photocatalytic activity towards the production of solar fuels by the reduction of CO2 and the hydrogen production via photocatalysis. Furthermore, nanostructured carbon and a second perovskite were incorporated into the NaTaO3 lattice to obtain the heterogeneous photocatalysts NaTaO3-C and NaTaO3-BaBiO3, in order to study the physicochemical properties of the resulting compounds. Synthesized materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, photoluminescence (PL) and photoelectrochemical techniques, to study how that the addition of the co-catalysts caused a variation in the band positions of the base material, enhancing the photocatalytic activity to perform the reduction of CO2 when carbon was added, and the production of hydrogen by the addition of BaBiO3.

Resume : Solid state solar dye-sensitized and perovskite solar cells have been under the spotlight due to high efficiency and stability compared to their liquid state counterparts. Modeling is playing a crucial role in understanding the involved materials, namely TiO2, perovskites, dyes, hole transport materials (HTMs) and their interdependencies in defining the underlying solar cell functioning mechanism. Here I discuss the salient features of metallorganic HTMs currently used in ss-DSCs devices comparing Co(II)/Co(III) redox couples [1] with Cu(I)/Cu(II) systems [2]. A notable role of rigidification of the metal coordination sphere is highlighted both for cobalt and copper-based complexes, the latter clearly showing a role of counterions in coordinating the metal upon oxidation. The different behavior of cobalt and copper salts is notably related to the known propensity of Cu(II) complexes to undergo a Jahn-Teller distortion leading to a potential change from 4- to 5-coordination sphere. This coordination change in copper complexes translates in a higher reorganization energy, possibly related to a retarded recombination of injected electrons and oxidized HTM.[3] References: [1] M. K. Kashif et al. Adv. Energy Mater. 2016, 1600874. [2] Y. Cao et al. Nature Communications 2017, 8, 15390. [3] S. Fantacci et al., manuscript in preparation.

Resume : Efficient energy production and waste valorisation are the most challenging fields in photocatalysis. The formation of H2 from a sacrificial electron donor (SED) based photocatalytic system represents a viable and beneficial approach. Furthermore, deploying cellulose as a SED promotes an efficient and sustainable system for energy production. The use of cellulose, however, can be limited as its predominantly locked in lignocellulosic biomass, its insoluble in water and has high structural strength. In an attempt to overcome this, cellulose polymorphs, such as cellulose 2 can be produced and used as favourable starting materials. Lower crystallinity along with increased interlayer spacing can accelerate photocatalytic cellulose conversion and facilitate enhanced H2 production. Reported here is the conversion of cellulose 1 to cellulose 2 using a simple environmentally friendly solvent which accelerated H2 production. In this study, cellulose 2 was found to increase rH2 by over a 2-fold increase and improve the photonic efficiency from 3.9 to 9.4 % when suspended in water with a 0.5 % Pt-TiO2 photocatalyst. The reaction was performed in a novel propeller fluidized photo reactor (PFPR) using a bespoke low power (13.3 W) UV-LED cylindrical jacket.

Resume : Development of Photocatalytic Reactor technology for the Removal of Organic Environmental Contaminants in Water. Fast industrial development, prolonged drought periods, rigorous agriculture and global population growth have resulted in an ever-increasing demand and shortages for clean water sources. It was estimated in 2015 that 663 million people worldwide did not have access to clean drinking water resources and instead have to use unprotected springs, wells and surface water. The overuse of herbicides has become a primary concern, especially as a result of the expansion of sectors such as bioenergy, which is focused on increased crop yields. The rapid and efficient removal of pollutants from water is of vital importance. The target pollutant MCPA is an ideal target for photocatalytic removal due to its high solubility in water and its strong electrostatic attraction to TiO2. The Combination of its acidity (pKa=3.73) and the isoelectric point of TiO2 (pI=6.2), ensuring strong binding at the surface of the photocatalyst, which facilitates the breakdown. In any heterogeneous catalytic reaction, the adsorption of target molecules to the surface us crucial to ensuring a high efficiency of the desired reaction. The development of a novel photocatalytic plate reactor which utilizes a thin film immobilised catalyst to remove the need for an additional expensive filtration step. The aim of this system was to still ensure a high surface area to volume ratio of photocatalyst to water therefore minimizing any mass transfer limitations and maximising our rates of reactions. While also ensuring our system is efficient and still obtaining comparable rates of MCPA removal to our PFPR suspended system which were the fastest published.

Resume : SnO2 and TiO2 colloidal nanocrystals were prepared by coupling sol-gel and solvothermal processing. By co-processing with V chloroalkoxide and subsequent heat-treament at 400 °C, surface deposition of V2O5 layers was achieved, as resulting from several characterization techniques. The mean size of the V-modified nanocrystals was less than 5 nm. The pure oxides displayed limited Methylene Blue (MB) adsorption and fast saturation, only 30% of the dye being extracted even after 120 min. Instead, the presence of V2O5 surface layers allowed depleting the initial MB concentration to 20% of the initial 1.5 x 10-5 M concentration in aqueous solution after 15 min only. Moreover, while the pure oxides were exhausted after the first cycle, the surface modified nanocrystals displayed identical adsorption after the second cycle without any recycling. Comparison with commercial V2O5 showed that the adsorption properties were inherent to the V2O5 surface modification. The adsorption kinetics was shown to be well described by pseudo-second order law, indicating chemisorption of MB. These results support the concept that suitable combination of two oxides may result in novel materials, whose adsorption properties are the result of synergistic cooperation between the two components.

Resume : Photoelectrochemical (PEC) water splitting (into hydrogen and oxygen) is now being considered as a sustainable approach to produce clean and renewable fuel by the direct conversion of solar to chemical energy. However, sluggish water oxidation kinetics involving four-proton-coupled multi-electron processes remains as a great challenge. Consequently, strategically integrating an oxygen evolution reaction electrocatalysts with a light-absorbing semiconductor photoanode has been proposed as an efficient approach for expediting the kinetics, improving PEC performance and stablilizing photoanode. In this work, we introduce a unique ferric phosphate nanosheet as an efficient oxygen evolution catalyst on the surface of a light absorber (BiVO4) by using a facile, green and cost-efficient binderless dip-coating method. The integrated photoanode exhibits a high photocurrent density of 2.3 mAcm−2, which corresponds to a 250% increase compared to that of bare photoanode. Deposition of cocatalyst has also yielded a large cathodic shift (∼500 mV) in the onset potential and high hole utilization efficiency of about 90%. More interestingly, the composite photoanode demonstrates an impressive performance of photostability and attains a stable photocurrent density for 6h at 1.23 V without observably declining. It is found that the introduction of ferrite phosphate offers critical support to the efficient hole transfer and consumption again the unproductive and energy-waste surface recombination thus resulting in a significant reduction in surface kinetics barriers and onset potential for water oxidation. This, in turn, enhances photoelectrochemical performance and durability of photoanode. This work also provides a deeper understanding of the role of cocatalyst nanostructures decorated with semiconductors in solar water splitting.

Resume : To overcome the issues related to low photocatalytic efficiency for H2 generation due less light absorption by the semiconductor materials, cadmium sulfide (CdS) having a bandgap of ~2.4 eV is considered a suitable candidate for photocatalytic H2 generation from water. The main drawbacks of CdS are the fast recombination of electrons and holes and the self photo-oxidation of CdS into elemental sulfur due to the neutralization of holes in the conduction band. To enhance the activity of CdS, the formation of core-shell structures of CdS with TiO2 has been shown to enhance the photocatalytic activity and stability for H2 generation from water. The presence of TiO2 over CdS nanoparticles increase the charge separation efficiency due to the formation of a heterojunction which eventually leads to enhanced activity and stability. Motivated to improve the photocatalytic activity of our previous core-shell nanostructure of CdS@TiO2 [1] and to utilize the conductor role of graphene (G), we report a new core-shell structure of CdS@G@TiO2. The graphene layer present in between the CdS core and TiO2 shell acts as a conductive layer, which promotes the charge separation efficiency even more than the CdS@TiO2 nanostructure alone. We have also optimized the layer thickness of graphene and TiO2 on CdS to achieve the optimized photocatalytic H2 generation. [1] M. Zubair, I.-H. Svenum, M. Rønning, J. Yang, Catal. Today. (2018). doi:10.1016/j.cattod.2018.10.070.

Resume : ZnO structures doped with Ce and Ru have been grown by a vapor - solid method using ZnS and CeO2 or RuO2 as precursors. The influence of the dopant on the material properties has been investigated. Different morphologies have been obtained depending on the dopant used. In the case of Ce, hexagonal rods and wires, bottle-like structures or irregular rods are obtained. For the Ru doped samples, hierarchical and interconected structures are observed. The incorporation of dopants in the crystalline structure of zinc oxide and its influence on the luminescence properties have been studied by means of cathodo- and photoluminescence. Variations in the position and in the relative intensity of both band edge and deep level emission bands are detected in the spectra recorded on the different morphologies. These changes can be attributted to differences in the incorporation of dopants into the ZnO crystal faces which can also modify the defect structure, and hence the luminescent properties. Finally, the photocatalytic activities of the ZnO structures have been evaluated by removal rate of different conventional organic dyes under UV irradiation (365 nm) at room temperature. The results show high photocatalytic efficiency for all samples with degradation rates to methylene blue of 96% after 80 min of illumination for the samples doped with 5% wt. of CeO2

Resume : The utilization of solar energy to convert water into hydrogen via efficient photocatalysis is an ultimate goal of clean energy society. Engineering the electronic energy band structure of hybrid nanostructured semiconductor materials through judicious control of their atomic composition is a promising route to increase visible light photoresponse. We have calculated the electronic structure of hybrid ZnS/WS2 nanotubes of diameter of about 2 nm. Studied nanotubes found to be remarkably suitable for photocatalytic water splitting under influence of solar light. The edges of their band gaps correspond to the range of visible spectrum between the violet and red ranges of visible spectrum. The top of the valence band and the bottom of the conduction band of considered ZnS/WS2 nanotubes have been properly aligned relative to the oxidation and reduction potentials necessary for water splitting under visible light irradiation. Ab initio calculations reported here have been performed within the formalism of hybrid Density Functional Theory and Hartree-Fock method when using HSE06 Hamiltonian properly adapted and verified relatively to properties of ZnS and WS2 bulk and nanosheets. Funding from Latvian Council of Science fundamental and applied research project Nr. LZP-2018/2-0083 is greatly acknowledged.

Resume : The monomer, dimer, and trimer of 5,15-diphenyl-10,20-di(pyridin-4-yl)porphyrin are used to investigate the multianchoring effect on TiO2 for visible light-driven photocatalytic hydrogen production in a water medium. The porphyrin dimer in a 1 wt % Pt-loaded TiO2 powder photocatalyst system exhibited optimal hydrogen production performance in a stable state over a period of 80 h and at a superior rate of 1023 μmol·g–1·h–1. Further, the stability of the photocatalytic system was systematically investigated using films containing dyes on 1 wt % Pt-loaded TiO2/FTO. For a film containing the dimer, almost no change was observed in the hydrogen-bond coordination mode of the dimer and the photocurrent during the photocatalytic reaction. However, the photocurrents of the monomer and trimer were altered during visible light irradiation without altering the coordination mode, indicating that the arrangements and orientations of the porphyrins on TiO2 surfaces were altered. These results indicate that the presence of multiple anchoring groups enhance the stability of the photocatalytic system and the rate of hydrogen production.

Resume : Recently, two energy-related problems, excessive emissions of CO2 in the atmosphere and depletion of fossil fuels from the limitation of carbon energy sources, have attracted considerable attention to be solved. Using solar-driven electrical energy source, electrochemical CO2 conversion into valuable C2 fuels is considered as an ideal system. Since electrochemical conversion can be converted up to 90 % of its given energy with high desired product selectivity, separated system can be one of efficient approaches, where electrical energy comes from photovoltaic cell while electro-conversion occurs in a cathode part using this solar-driven electricity. In part of electro-conversion, Cu as a catalyst has attracted strong attention due to its unique property to produce C2 products which have high energy densities. Especially, nanostructure Cu have showed higher C2 selectivity comparing with flat surface of Cu. In this work, we developed nanostructure Cu film for highly C2 selective electrocatalyst. Resulted Cu catalyst showed high C2 products selectivity achieving 50 % of faradaic efficiency at -0.8 V vs. reversible hydrogen electrode (RHE), which is one of the largest value compared to previous reports before. In a final stage of this project, to achieve an ideal system where sunlight-driven electricity is an energy source of carbon dioxide conversion, a photovoltaic connected electrochemical cell will be operated.

Resume : The purpose of the research was to determine the effect of the size of ZnO nanoparticles on the photocatalytic degradation of phenol in a water solution under the influence of UV radiation. ZnO NPs were produced using the microwave solvothermal synthesis technology. The properties of NPs were determined using XRD, SEM, TEM, helium pycnometer, specific surface area analyser and infrared spectroscopy. The average NPs size was determined using the Scherrer’s formula, Nanopowder XRD Processor Demo web application, by converting the results of the specific surface area-density, and TEM tests using the bright field and the dark field technique. The ZnO NPs (average size between 23 nm and 71 nm) used for the photocatalytic degradation were characterised by uniform morphology and a narrow size distribution. The photocatalytic performance of ZnO NPs increased with the increase of the particle size. The highest reaction rate for phenol degradation was found for ZnO sample with the average particle size of 71 nm (total degradation of phenol after 90 min of UV radiation). Low concentrations of co-products of phenol degradation (rezorcine and hydroquinone) were finally photooxidized after 90 and 150 min, respectively.

Resume : An aircraft cabin is a unique environment due to the extremely high density of occupation and the limited available air volume. This situation leads to the dispersion of germs and viruses and the accumulation of pollutants. Among them, Volatile Organic Compounds (VOCs) include not only internal pollutants (e.g. from materials present in the cabin or related to the presence of passengers) but also outdoor pollutants which can be present on the ground and at very low altitudes. The objective of the Breeze project is to address this problematic by developing a novel air purifier to be installed after the HEPA filtration stage of the air conditioned system of the aircraft. An air filter that combine adsorption and photocatalysis process was selected. The adsorbent retains the pollutants close to the catalyst surface, enhancing their decomposition through the transfer of the adsorbed molecules onto the photoactive particles. Those combined processes should conduct to low generation of by-products and high durability of the filter (cleaned by photocatalysis). The efficiency of reactors with different geometries was assessed. Pressure drop, adsorption and photocatalytic treatment of toluene were evaluated under different experimental conditions close to aircraft environment. The results showed that air flow rate and reactor geometry have a high impact on the air purification performances.

Resume : Various technologies and materials have been recently developed to remove organic contaminants and hazardous microorganisms in water treatment. Among them, zinc oxide (ZnO) has attracted attention as a promising photocatalyst due to its excellent photochemical properties. High band-gap of ZnO minimizes electron-hole recombination, thus prolonging the duration of excitation state. ZnO thin films made by atomic layer deposition (ALD) maintain the highest quality with uniform surface structure even along complex high aspect ratio features. In addition, the ALD films have the advantage of being able to precisely control thickness at the atomic level through self-limiting reaction mechanisms. In this work, we fabricated ZnO with ALD and the photocatalytic activity of the film was evaluated. We confirmed the photocatalytic activity through the generation of reactive oxygen species (ROS), including hydroxyl radicals, superoxide anion, and singlet oxygen. The tests were carried out under irradiation of 365 nm UV-light, and the photocatalytic activity was also examined by dissolution test of methylene blue.

Resume : The organic-mediated cross-linking polymerization of polyoxometalate (POM) clusters into three-dimensional (3D) porous structures is an appealing method for targeting novel materials with functionality. Herein, we describe the synthesis of new mesoporous polymers composed of a 3D porous network of lacunary [XM₁₁O₃₉]ⁿ⁻ (XM₁₁; X=P, Si; M=W, Mo) POM units connected by ethane-bridged silsesquioxane linkers through a block copolymer-templated crosslinking polymerization method. The resulting porous materials feature an ordered mesostructured ethane–silica (MES) framework that hosts a high density of accessible [XM₁₁O₃₉]ⁿ⁻ units, which allows for efficient catalytic reactions. We evaluated the photocatalytic activity of mesoporous XM₁₁/MES for the hydrogen evolution reaction in water. The results indicated that these hybrid polymers have a relatively high activity for the hydrogen production, giving an average rate of H₂ evolution of about 6.3 μmol h⁻¹, under UV-vis light irradiation. The synergistic action of the nanoscale pore structure, large internal surface area and the framework composition of the XM₁₁/MES polymers can provide the ability to introduce important features, such as high catalytic activity and enhanced solar-light absorption, into the same material.

Resume : TiO2 and BiOCl are two well-known photocatalysts for pollutants photo-degradation. In this talk, the preparation and the photo-properties of TiO2/BiOF and BiOCl/BiOF composite photocatalysts are presented [1-2]. These materials were obtained via simple mixture method with the nano-structured compounds followed by annealing under neutral atmosphere. The as-synthesized sample was characterized by X-Ray Diffraction, Raman scattering, electron microscopies (TEM and SEM), UV–Vis. diffuse reflectance measurements and electron spin resonance. A strong visible light absorption was observed with a narrowed bandgap compared with single TiO2 and BiOCl due to presence of oxygen vacancies. The photocatalytic activities of the products were evaluated through photocatalytic degradation of Methyl Orange (MO) or Rhodamine B (RhB) under UV–Vis. light irradiation. The results show that the TiO2/BiOF and BiOCl/BiOF composite photocatalysts with optimal molar ratio (3:1) exhibit better photocatalytic activities for the degradation of pollutants than single TiO2, BiOCl or BiOF. The enhanced photocatalytic properties can be attributed to the special band structure of the composite due to a good band matching between BiOF and oxygen vacancy states in TiO2 and BiOCl leading to an effective separation of electron–hole pairs. Moreover, the specific microstructure of the composite plays an active role in the good photocatalytic performances due to the intimate interfaces between the two parts. [1] J. Cheng et al., Catal Lett (2018) 148: 1281 [2] M. Nasr et al., submitted to New Journal of Chemistry

Resume : Photocatalysts based on SrSnO3 and SrSnO3 supported on ZrO2 were prepared by the modified Pechini method and characterized by XRD, XRF, XPS, FTIR, UV-vis spectroscopy, Raman spectroscopy, SEM, TEM and electrochemical methods for evaluation of the band gap structure by the Mott Schottky method. The photocatalytic activities of the prepared materials were tested in the degradation of the Remazol Golden Yellow azo-dye under UV irradiation (254 nm). In order to investigate the role of the photogenerated active species, i.e. hydroxyl radicals, the hydroxylation of terephthalic acid was evaluated, while the role of light-induced electron-hole pairs was evaluated by the use of different scavengers. Both materials were photocatalytic active, while SrSnO3/ZrO2 showed better decolourization efficiency than the unsupported material. The higher activity of SrSnO3/ZrO2 can be attributed to the formation of nanometric particles of SrSnO3 on the ZrO2 surface, as confirmed by the TEM measurements. The participation of hydroxyl radicals in the reaction was confirmed by the formation of hydroxylated terephthalic acid, while RNL decolourization was inhibited when isopropanol was used as hydroxyl radical scavenger. No remarkable change in the potential of the conduction band edge of SrSnO3 was noticed after deposition on ZrO2, while a lower valence band edge was determined, which may be associated to the greater ability of SrSnO3/ZrO2 to produce hydroxyl radicals from photogenerated holes.

Resume : Fe2O3 is a non-toxic, low-cost and largely available semiconducting oxide, characterized by an efficient light absorption into the Vis range. Because of these characteristics, Fe2O3 candidates as an appealing technological platform for large-scale photocatalytic applications. Nevertheless, it also presents some severe limitations, of which the fast charge carrier recombination and the short hole diffusion length are particularly critical. One strategy to circumvent these issues relies on Fe2O3 functionalization with nanoparticles or ultrathin/porous layers of another suitable semiconductor, in order to synergistically exploit the favorable properties of single-phase components reducing, at the same time, their disadvantages. In this contribution, supported Fe2O3 nanomaterials are fabricated by chemical vapor deposition (CVD) and subsequently functionalized with tailored amounts of WO3 or TiO2 by radio frequency (RF)-sputtering. A careful control of the preparation conditions and of the resulting Fe2O3/WO3 and Fe2O3/TiO2 interfacial interactions yield Fe2O3-based nanoheterostructures with improved photocatalytic performaces in the liquid phase degradation of phenol and gas-phase decomposition of NOX (NO and NO2). Overall, the obtained results demonstrate the validity of the developed synthetic approach for the design of semiconductor-based functional architectures for water and air purification.

Resume : The thin layers Aluminium doped Magnésium oxide (0%, 2% , 4%, 6% and 8%) are synthesized by the chemical spray technique "SPRAY" with dissolving 0.1 M of magnesium chloride in bi-distilled water as a solvent. Structural and optical analyzes are performed by XRD and spectrophotometry. They respectively confirm the crystallization of magnesium oxide in the CFC cubic face-centered structure, The gap energy is in the order of 4 eV. Under solar irradiation, these layers have a photocatalytic activity.

Resume : Development of sustainable energy sources is an urgent issue to meet growing demand in world energy consumption. Among the various types of sustainable energy, hydrogen and ammonia are one of the most promising renewable energy sources with a high energy density. The discovery of efficient catalysts represents one of the most important and challenging issues for the implementation of photoelectrochemical (PEC) or electrochemical fuel production. A critical requirement for outstanding catalysts is not only an ability to boost the kinetics of a chemical reaction but also a durability against electrochemical and photo-induced degradation. Generally, precious metals, such as platinum, exhibit superior performance in these requirements; however, high cost of the precious metal is the biggest barrier to widespread commercial use. To address this critical and long-standing technical barrier, I have focused on an intense search for efficient, durable, and inexpensive alternative catalysts. My research have been concentrated on two subjects; (1) new possibilities of an atomic-scale catalyst as the efficient water splitting catalysts, (2) the electrochemical production of ammonia using metal nitride-based catalysts. (1) Carbon-based nanomaterials have emerged as promising candidate catalyst for HER. The design of carbon-based catalysts represent an important research direction in the search for non-precious, environmentally benign, and corrosion resistant catalysts. Especially, graphene possesses excellent transmittance and superior intrinsic carrier mobility, thus there have been several attempts to use graphene as a catalyst. It has been reported that reduced graphene oxide containing catalytic active materials exhibited improved activity in HER, oxygen evolution reactions, and oxygen reduction reactions. In most cases, the role of carbon materials is limited to an electrical conducting substrate or a supporter that enhances the performance of other decorated active catalysts. There is no report of the application of monolayer graphene to hydrogen production. For the first time, I investigated new possibilities for monolayer graphene as an electrocatalyst for efficient HER and found that atomic defect engineering such as nitrogen doping through treatment with N2 plasma improved the catalytic activity. This study has also attracted particular interest to the materials and chemical society in that it has demonstrated the role of carbon-based catalysts with comprehensive electrochemical analysis as well as the first demonstration of monolayer graphene as the HER catalyst. (2) The reduction of nitrogen to produce ammonia has been attracting much attention as a renewable energy technology. Ammonia is the basis for many fertilizers and is also considered an energy carrier that can power internal combustion engines, diesel engines, gas turbines, and fuel cells. Traditionally, ammonia has been produced through the Haber-Bosch process, in which atmospheric nitrogen combines with hydrogen at high temperature (350-550℃) and high pressure (150-300 bar). This process consumes 1-2% of current global energy production and relies on fossil fuels as an energy source. Reducing the energy input required for this process will reduce CO2 emissions and the corresponding environmental impact. For this reason, developing electrochemical ammonia-production methods under ambient temperature and pressure conditions should significantly reduce the energy input required to produce ammonia. Metal nitrides are an interesting class of materials for electrochemical ammonia synthesis because they may be able to form ammonia through Mars-van Krevelen mechanism. In the mechanism, a surface N atom is reduced to ammonia, leaving behind a vacancy in the metal nitride surface. This vacancy can then be filled by dissolved N2, which can be further hydrogenated releasing ammonia and regenerating the metal nitride surface. Thus, the suggested might also cause a dynamic Faradaic redox reaction to occur at the surface of the electrode. Here, we report on the experimental electrochemical production of ammonia using metal nitride-based catalysts. Upon applying a reducing potential in N2 purge electrolyte, ammonia was detected using a colorimetry assay test and FTIR spectroscopy. VN, ZrN, Mo2N are interesting materials going forward to study for nitrogen reduction to ammonia due to its significant Faradaic efficiency in an aqueous system under ambient conditions.

Resume : Experimental results have shown that titanium dioxide is a semiconductor with several applications in photocatalytic processes. Also, TiO2 can produce electricity from solar energy, this is very interesting because it can be used to satisfice the electrical energy requirements on the operation of electrochemical cells. Its band gap makes it very interesting in the photoelectrodes manufacturing used in photoelectrochemical cells for hydrogen production, a clean and environmentally friendly fuel. During this process pairs hole – electron are photogenerated, the efficiency can be improved if charge recombination is avoided, also if the energy absorption into the visible spectrum is increased and its specific surface area is increased. The synthesis of 1D titanium dioxide nanostructures, such as nanotubes, makes possible to produce more efficient photoelectrodes for solar energy to hydrogen conversion. In essence, this is because it increases the charge transport rate, decreasing recombination options. However, its principal constraint is to be mainly sensitive to UV range, which represents less than 8% of solar radiation that reaches earth's surface. One of the alternatives to modifying the TiO2’s band gap and improving its photoactivity under visible light irradiation is to dope the nanotubes with transition metals. This research wants to use nanotechnology in order to produce titanium dioxide nanotubes arrays (TNTs). Their morphology will be controlled during anodization of titanium foils and nickel will be deposited onto the TNTS with the purpose to increase the absorption spectrum of the visible region. This option requires fabricating efficient nanostructured photoelectrodes with controlled morphology and specific properties able to offer a suitable surface area for metallic doping. Hence, currently one of the central challenges in photoelectrochemical cells is the construction of nanomaterials with a proper band position for driving the reaction while absorbing energy over the VIS spectrum. This research focuses on the synthesis and characterization of Ni doped TiO2 nanotubes for improving its photocatalytic activity in solar energy conversion applications. Initially, titanium dioxide nanotubes (TNTs) with controlled morphology were synthesized by two-step potentiostatic anodization of titanium foil. The anodization was carried out at room temperature in an electrolyte composed of ammonium fluoride, deionized water and ethylene glycol. Consequent thermal annealing of as-prepared TNTs was conducted in the air between 450 °C - 550 °C. Afterwards, the nanotubes were superficially modified by nickel deposition. Morphology and crystalline phase of the samples were analyzed by SEM, EDS and XRD before and after nickel deposition. Determining the photoelectrochemical performance of photoelectrodes is based on typical electrochemical characterization techniques. Also, the morphological characterization associated electrochemical behavior analysis were discussed to establish the effect of nickel nanoparticles modification on the TiO2 nanotubes. The methodology proposed in this research allows using other transition metal for nanotube surface modification.

Resume : Hybrid materials have been intensively developed for optical applications (sensors, filters, imaging, photocatalysis…)..[1] Interactions between optical components and plasmonic systems have also been an intensive field of research due to the possibility to tune and optimize the optical responses (emission, absorption) using the local electromagnetic field. We have developed the synthesis of various gold nanostructures with high yield and purity and exhibiting plasmon resonance spreading from the visible to the NIR wavelengths.[2] These nanostructures can be functionalized in order to either allow their homogeneous incorporation in transparent hybrid silica matrices using the sol-gel process either as monoliths or films.[3,4] Co-dispersion of the metallic structures with dyes or semiconductors such can be achieved.[4-7] Two applications will illustrate the influence on the photoinduced processes. The prepared materials in the case of TiO2 can be used as efficient photocatalytic coating materials for depollution or bactericide. [5-7] The plasmonic nanostructure can also be combined to molecular photosensitizers to enhance the production of oxygen singlet. Demonstration of enhanced of photooxygenation reactions in microreactors will illustrate this aspect. References [1] S. Parola, B. Julian-Lopez, L. D. Carlos, C. Sanchez, Adv. Funct. Mater. 2016, 26(36), 6506. [2] D. Chateau, A. Liotta, F. Vadcard, J. R. G. Navarro, F. Chaput, J. Lermé, F. Lerouge, S. Parola, Nanoscale 2014, 7, 1934. [3] D. Chateau, A. Liotta, D. Gregori, F. Lerouge, F. Chaput, A. Desert, S. Parola, J. Sol-Gel Sci. Technol. 2017, 81, 147. [4] D. Chateau, A. Liotta, H. Lundén, F. Lerouge, F. Chaput, D. Krein, T. Cooper, C. Lopes, M. Lindgren, S. Parola, Adv. Funct. Mater., 2016, 26 (33), 6005. [5] D. Gregori, I. Benchenaa, F. Chaput, S. Therias, JL. Gardette, D. Leonard, C. Guillard, S. Parola, J. Mater. Chem. A 2014, 2(47), 20096. [6] . Levchuk, M. Kralova, J. J. Rueda-Márquez, J. Moreno-Andrés, S. Gutiérrez-Alfaro, P. Dzik, S. Parola, M. Sillanpää, R. Vahala, M. A. Manzano, App. Catal. B: Environmental, 2018, 239, 609. [7] I. Levchuk, M. Sillanpaa, C. Guillard, D. Gregori, D. Chateau, F. Chaput, F. Lerouge, S. Parola, J. Catal., 2016, 342, 117.

Resume : Metal oxide based mesoporous nanoparticle films are broadly used as electron selective layers in divergent photoconversions such as photoelectrochemical cells, dye-sensitized solar cells (DSSCs), and perovskite solar cells (PSCs). State-of-the-art mesoporous TiO2 films for these photoconversions are fabricated by annealing TiO2 paste-coated fluorine-doped tin oxide glass in a box furnace at 500 °C for ≈30 min. Here, the use of a nontraditional reactor, i.e., flame, is reported for the high throughput and ultrafast thermal treatment of TiO2 (≈60 sec). Flame has a broad tunable temperature range (from a few hundreds to a couple thousands of degree Celsius) and a typical thickness of ≈1 mm; therefore, flame has an intrinsic temperature field with a large gradient. Hence, flame treatment, when coupled with FTO glass cooling, could provide the desired temperature field for processing TiO2 films on FTO. Thus, the flame annealing of TiO2 paste can be a promising approach for fabricating PSCs with enhanced charge transport performance. In addition, a rapid sol-flame doping process to introduce Co dopant into TiO2 will be introduced. Ultrafast flame-processed Co-doping of TiO2 solves the J–V hysteresis problem and increases the open circuit potential, fill factor and power conversion efficiency of both mesoscopic and planar PSCs.

Resume : Zinc oxide (ZnO) is a well-studied wide band gap semiconductor photocatalyst. The activities of ZnO nanomaterials with different ratios of exposed crystal planes are however less understood. In this work, three different ZnO single crystals exposing different crystal planes were studied: (0001), (1-100), and (11-20). The ZnO samples were characterized with polarized Raman spectroscopy and XRD, and their photocatalytic activities were quantified by means of methylene blue degradation using in situ spectrophotometry. The ZnO (1-100) surface showed three times higher photocatalytic activity than the other two surfaces. The results are discussed in terms of crystal facet dependent reactivity due to differences in surface structure and surface potential. Since it is possible to synthesize ZnO particles and structures with different ratios of exposed crystal planes, this finding may be of importance to guide synthesis of more efficient, tailor-made ZnO photocatalysts for water cleaning.

Resume : ScF3 nanoparticles doped with trivalent ytterbium(Yb3+) and erbium(Er3+) are prepared by a modified thermal-decomposition(hot-injection) method using trifluoroacetate precursors in oleic acid (OA), oleylamine (OM) and 1-octadecene (ODE). Under the irradiation of near-infrared light, the ScF3 nanoparticles emit visible upconverted luminescence light. Taking surface defects into consideration, to minimize its quenching effects, the nanoparticles are coated with an inert shell. Especially, ScF3 is a peculiar material with negative thermal expansion (NTE) and a varying lattice parameter under different temperature conditions promising as a good candidate for thermometer which the temperature ranging from 75K to 353K. Herein, we report a novel up-conversion luminescence-based thermometer by using ScF3: Yb/Er nanoparticles with biological application potential.

Resume : Aluminum doped iron oxide thin films were successfully deposited onto glass substrate by chemical spray pyrolysis. The doping effects on the structural, morphological and optical properties of the layers were investigated. The XRD analysis proved that pure and Al: Fe2O3 possess rhomboedric structure with (104) as preferential orientation. AFM and SEM observations showed a dense surface with grains uniformly distributed over the whole surface. Optical measurements demonstrated that Al: Fe2O3 (6 and 8 at. %) were highly transparent. In addition, the band gaps values found in the range from 1.98 to 2.17 eV. Moreover, Al: Fe2O3 thin film based sensor demonstrated a good response to a small amount of ethanol vapor at low operating temparature equal to 250°C. Thus, Al: Fe2O3 thin films is a potential condidate to gas sensing application. Keywords: Iron oxide, Spray Pyrolysis, Aluminum doping, Physical properties, Gas sensing.

Resume : The production of hydrogen by electrochemical dissociation of water has been known for minimal environmental impact involved. This process consumes more electrical energy than electricity generated by the combustion of produced hydrogen, but it is still interesting in order to find sustainable future sources of clean energy. One way to address this problem is to investigate options for reducing inefficiencies on the electrochemical cell, these are voltage consuming, it is also possible to take advantage of cheaper energy sources. Photocatalysis has established as a viable option in the development of processes for the treatment of pollutants and clean energy production. This option is based on the ability of semiconductors to generate an electron flow by means of the interaction with solar radiation. Owing to its electronic structure, TiO2 is the most frequently used semiconductors in photocatalysis, although it has high recombination of photogenerated charges and low solar energy absorption. Due to TiO2 can produce electricity from solar energy, it can be used to satisfice the electrical energy requirements on the operation of electrochemical cells. During this process pairs hole-electron are photogenerated, the efficiency can be improved if charge recombination is avoided, also if the energy absorption into the visible spectrum is increased and its specific surface area is increased. An alternative to reduce these limitations is the use of nanostructured morphologies which can be produced during the synthesis of TiO2 nanotubes (TNTs). Therefore, if possible, to produce oriented nanostructures it will be possible to generate a greater contact area with electrolyte and better charge transfer. At present, however, the development of these innovative structures still presents an important challenge for the development of competitive photoelectrochemical devices. This research focuses on established correlations between synthesis variables and nanostructure morphology which has a direct effect on the photocatalytic performance. TNTs with controlled morphology were synthesized by potentiostatic anodization of titanium foil. The anodization was carried out at room temperature in an electrolyte composed of ammonium fluoride, deionized water, and ethylene glycol. Consequent thermal annealing of as-prepared TNTs was conducted in the air at 450 °C. Morphology and crystalline phase of the TNTs were analyzed by SEM, EDS, and XRD. As results, the synthesis conditions were established to produce nanostructures with specific morphological characteristics. Anatase was the predominant phase of TNTs after thermal treatment. Nanotubes longer than 7 μm and pore diameter around 50 nm with different surface-volume ratio are important in photoelectrochemical applications based on TiO2 due to their dimensional characteristics, surface-volume ratio, reduced radial dimensions, and high oxide/electrolyte interface. Finally, this knowledge can be used to improve the photocatalytic activity of TNTs by making additional surface modifications with dopants that improve their efficiency.

Resume : Photocatalytic layers can be applied on self-cleaning (SC) glass and as antifogging coating. Moreover, coating the solar glass on PV modules with simultaneous SC, IR-shielding (IR-S) and UV-Vis antireflection (AR) layers could enhance the electrical output up to 10%. TiO2 is currently used in SC or AR or IR-S applications. Adding reduced graphene oxide (r-GO) in the TiO2 matrix creates high-porosity powders and films, with tailored optical bandgap and improved charge separation. Sol-gel TiO2-rGO composite powders (TiO2 :rGO = 100:x, x=0–0.2) were obtained in water-ethanol mixtures, using TTIP, acetylacetone and sodium dodecylsulfate. The powders were aged (24 h), filtered and annealed (1 hat 100oC–550oC); the powders exhibited anatase phase, uniform morphology, high surface energy. By dispersing the powders in water-ethanol (0.5% wt.) with stabilizing agents, homogeneous dispersions were obtained. Stability (UV-Vis transmittance spectra variation in time) is directly related to the dispersion composition. The stable dispersions were sprayed on glass (at 80oC), using 8-10 layers to obtain transparent, adherent thin films. These were crystalline, continuous and mostly homogeneous, hydrophilic and have promising optical properties (T(UV-Vis)>80% and T(IR)<15%), being recommended as PV glazing. Preliminary tests performed at low irradiance (34 W/m2) on the photodegradation of methylene blue showed that the thin films were VIS-active, with rGO playing a substantial role, by increasing charge separation.

Resume : An enormous CO2 emission in nowadays world caused by an extensive usage of fossil fuels leads to colossal air pollution and consequently contributes to the global warming effect. Therefore, recycling of CO2 into fuel again by means of new functional materials is a fascinating idea that motivates the study presented herein. Ordered titania nanotubes (NTAs) can be considered as promising material for this kind of application due to their unique physicochemical properties as well as easy preparation route. However, the disadvantage of NTAs is a rather wide energy bandgap that can be overcome e.g. by decoration by transition metals. In this work, we demonstrate a robust preparation method of NTAs substrate for the further modification with Cu/CuxO nanoparticles (NPs) and discuss their morphological, optical and electrochemical properties. NTAs (diameter: 120 nm, length: 4 μm) are formed in the anodization process followed by crystallization in furnace and deposition of Cu layer by means of magnetron sputtering and electrochemical deposition. Subsequently, UV pulsed laser is used to transform thin Cu film into NPs. SEM inspection reveals the presence of a nearly spherical NPs on the NTs wall edges. Moreover, the as-prepared material exhibits significantly higher cathodic current than bare NTAs immersed in CO2 saturated electrolyte proving its usefulness for pollution reduction. This work has been financed by National Science Centre under grant no 2017/26/E/ST5/00416.

Resume : Nowadays, special attention is put into titanium dioxide nanotubes (TiO2NTs) modified with metals or metal oxides due to possibility of their usage in solar driven processes because of their improved photoactivity and photocorrosion resistance comparing to unmodified material. Currently, heat treatment realized in furnace is typically applied to ensure crystalline phase of TiO2NTs with simultaneous preservation of NTs architecture. In here, we propose robust and fast approach that allows not only conversion of NTs phase but also alteration of their morphology that strongly influences the optical and photoelectrochemical properties of prepared material. TiO2NTs decorated with Cr metal species were produced via anodization process in the presence of fluorine ions followed by magnetron sputtering of thin metal film whereas pulsed laser irradiation technique (Nd:YAG, wavelength: 266-1064 nm) was used to induce phase transition and also leads to surface modification. Raman measurements confirm successful crystallization of as-anodized NTs while the degree of surface deformation was revealed by SEM inspection. Obtained results suggest the impact of surface modification onto the photoelectrochemical performance of produced material. Further investigation of these effect may provide valuable data, that could help achieve energy-efficient production of photoactive devices based on nanomaterials. This work has been financed by National Science Centre under grant no 2017/26/E/ST5/00416.

Resume : Porous CoxNi1-xTiO3 nanorods were successfully synthesized through a solution-based method following an ethylene-glycol (EG) route at room temperature. The effect of calcination temperature (from 300oC to 900oC) of NiTiO3 and CoTiO3 nanorods were studied in order to investigate their structural and morphological properties by using X-Ray diffractometry and Scanning Electron Microscopy. The ideal calcination temperature to prepare pure trigonal/ilmenite (perovskite type) nanorods with high crystallinity, hexagonal shape, good porosity and surface area was 600oC. Co0.5Ni0.5TiO3 shown the highest photocatalytic activity for degradation of ethyl paraben under simulated solar irradiation and Visible light irradiation. Screening experiments showed that Co0.5Ni0.5TiO3 nanorods has the highest activity which was 92% , while at the same time the photocatalytic activity of CoTiO3 and NiTiO3was 42% and 67%, respectively.

Resume : We present the synthesis and characterization of thin film heterojunction, or bi-catalyst, comprising of photocatalytic coatings based on a combination of two different materials exhibiting p-type and n-type conductivity, respectively. Here we show results for the combination of CuOx together with zinc oxide (ZnO) and tungsten oxide (WO3). The purpose of such compounds is to create an intrinsic electrical field at the np-junction that helps to separate electron-hole pairs formed upon interband photon absorption. At the same time desired photochemical properties implies that the constituent catalysts have appropriate bandgap and band edge position. For this purpose, CuOx/WO3 compound films have been prepared onto glass substrates by co-sputtering of tungsten and copper targets in an argon and oxygen atmosphere. CuOx/ZnO bi-catalyst have also been prepared on glass substrates by a two-step process consisting of deposition of CuOx by reactive magnetron sputtering, followed by the application of ZnO particles by drop coating. The obtained bi-catalyst have been characterized by SEM, XRD, XPS, Raman and spectrophotometry. Finally, the photocatalytic activity of the different compound films is assessed by studying their photobleaching rate of methylene blue and orange II in water solution.

Resume : Design and subsequent application of new materials for organic photovoltaics require thorough photophysical characterization of the materials to understand structure-function correlation. In this work two similar BODIPY (Benzodithiophene) MeBDP and TfBDP with methyl and trifluoromethyl substituents at the meso positions have been synthesized and coupled with Fluorene and Benzodithiophene to form two pairs of A-D-A molecules. DFT optimized structures of these molecules suggest greater degree of planarity in Benzodithiophene-BODIPY than Fluorene-BODIPY combinations. This provides the platform to look into effect of the polarity of the meso substituent and A-D torsion angle on the photophysical properties and subsequently the photovoltaic properties of these class of molecules. Transient absorption (TA) spectroscopy has been used to characterize the evolution of the excited states of these molecules. Longer lifetimes are observed for the Fluorene-BODIPY molecules as compare to Benzodithiophene-BODIPY. The trifluoromethyl substitution shortens the radiative lifetime of the excited state (587 ps to 264 ps in Fluorene-BODIPY and 125 ps to 52 ps in Benzodithiophene-BODIPY) and hence could reduce charge separation efficiency. Steady state and time resolved fluorescence spectra of these molecules have also been studied. The HOMO and LUMO energy levels of these molecules suggest possible application as donor materials in OPV with non-fullerene acceptors such as IT-4F and IEICO.

Resume : Solar energy harvesting is undoubtedly a promising strategy to meet the demand for a renewable and clean energy system. There are two primary approaches that have been pursued in this context involving either photon-to-electricity or photon-to-chemical energy conversion. The former is achieved in the solar cell devices while the latter requires the use of photo-electro-catalysts. In both contexts, conjugated polymers and small molecules have emerged as a subclass of materials with potential applicability as photocatalysts to drive the hydrogen evolution reaction (HER). 1 By using density functional theory calculations, we investigate the effects of different electron donating moieties, viz. fluorene, thiophene derivatives, cyclopentathiophene and benzothiadiazole-based acceptor units on the electronic structure, optical properties, electrochemical potential and thermodynamics of the photocatalytic activity for HER. The combination of donor-acceptor moieties with a porphyrin core also provides interesting insight into the design highly efficient absorbing materials for energy-related application. Our results show that materials containing benzo(triazole-thiadiazole) or benzo(triazole-selenodiazole) hybrid acceptor units present a broad absorption spectrum and a suitable reduction potential for photocatalytic HER.2 In particular, PFO-DSeBTrT (poly (9,9’-dioctylfluorene)-2,7-diyl-alt-(4,7-bis(thien-2-yl)-2-dodecyl-benzo-(1,2c:4,5c’)-1,2,3-triazole-2,1,3 selenodiazole)) has maximum peak at 950 nm, while showing a hydrogen binding free energy (0.02 eV) that is lower in absolute values than Pt (-0.10 eV).2 In summary, our work combines a set of molecular properties to provide guidance for the design of novel photocatalysts for HER. References (1) Pati, P. B.; Damas, G.; Tian, L.; Fernandes, D. L. A.; Zhang, L.; Pehlivan, I. B.; Edvinsson, T.; Araujo, C. M.; Tian, H. An Experimental and Theoretical Study of an Efficient Polymer Nano-Photocatalyst for Hydrogen Evolution. Energy Environ. Sci. 2017. (2) Damas, G.; Marchiori, C. F. N.; Araujo, C. M. G. On the Design of Donor-Acceptor Conjugated Polymers for Photocatalytic Hydrogen Evolution Reaction: First-Principles Theory Based Assessment. J. Phys. Chem. C 2018.

Resume : We used density functional theory [1] to study the effect of nitrogen doping on the physical properties of anatase TiO2 nanowires. In particular, we analyzed at GGA and GGA+U level the structural and electronic properties of TiO2 nanowires with different diameters and in different nitrogen doping positions. We found that the lattice distortions induced by the presence of neutral defects are negligible and that the energy of the acceptor levels generated by nitrogen depends on the positions of the dopant within the nanowire, similar to what have been found in nitrogen doped ZnO nanowires [2]. The energetic stability of these nanostructures shows a particular dependence on the doping positions as well as on nanowire diameter. The defect formation energy decreases when going from the bulk to the surface of the wire leading to impurities accumulations on the surface of the nanostructure. Our analysis of the density of states around valence and conduction bands indicates a more pronounced states. Therefore, the presence of nitrogen in TiO2 nanostructures may improve the photocatalytic properties. [1] W. Kohn and L. J. Sham, Phys. Rev. 140, A1133 (1965). [2] S. Haffad, M. Samah, G. Cicero, Phys. Rev. B 85, 165207 (2012).

Resume : The deposition of graphene oxide layer on the surface SnS thin films had been shown to be an effective tool to improve the photoelectrochemical response. Pure phase SnS thin films were prepared using simple thermal evaporation method on ITO glass substrate followed by the deposition of graphene oxide layer with varying concentration by drop cast method. Samples were characterized using X-ray diffraction, Raman, Scanning electron microscopy, and UV–Visible absorption spectroscopy. The Results shows the formation of pure phase SnS having orthorhombic crystal structure with optical band gap of 2.1 eV and GO layer enhance absorption in the visible region. Maximum photocurrent density exhibited by SnS/GO heterojunction was 1.0 mA/cm2 as compared to pure SnS (0.3mA/cm2) at 0.95V Ag/AgCl with enhancement in photostability upto 2800 seconds, which is due to the graphene oxide layer. Graphene oxide act as protecting layer for SnS in electrolyte and play a promising role in enhancing the charge carrier’s separation at the interface. This works highlights the role of GO and SnS interface on the photoelectrochemical water splitting.

Resume : The increasing demand for a sustainable resource of energy requires a renewable and clean alternative for the fossil fuels. Storing solar energy in chemical bonds which is an artificial photosynthesis approach, has attracted a great deal of attention recently. Splitting of water into oxygen and hydrogen using photoelectrochemical (PEC) cells is a newly developed method to produce hydrogen as a clean fuel. Slow kinetics of oxygen evolution reaction (OER) in water splitting cells is a bottleneck for improving the hydrogen production efficiency. BiVO4 is one of the promising photoanodes for water oxidation. Its poor charge transport is overcome by utilizing the proper dopants and surface modification of BiVO4 using metal oxide/hydroxide oxygen evolution catalysts (OEC) is shown to improve the water oxidation kinetics effectively. However, the efficiency achieved with this material is still far away from the theoretical value. It is shown that OECs facilitates water oxidation at BiVO4 surface by either suppression of recombination centers or by kinetically accelerating the OER. One of the promising catalysts for OER is CoOx which is used as co-catalyst for improving BiVO4 photoanodes. BiVO4/CoOx photoanodes were studied intensively but most of the studies focused on BiVO4 loaded with the OECs on the surface as particles or thin layers. In the present work, we have modified the surface of nanoporous BiVO4 photoanodes by doping with CoOx for the first time using deposition of an ultrathin CoOx layer by atomic layer deposition (ALD) followed by a mild heat treatment. We observed that diffusion of CoOx into the surface of BiVO4 improves its water oxidation activity further compared to the deposition of ultrathin CoOx layer as OEC on the surface. X-ray photoelectron spectroscopy (XPS) and Raman results together with X-ray diffraction (XRD) patterns confirmed the surface doping of the BiVO4 without any structural changes in the bulk. Activity measurements were performed by photoelectrochemical tests in neutral media. We showed that surface doping of BiVO4 enhanced the water oxidation activity significantly and decreased the overpotential for running the water oxidation reaction more than 50 mV.

Resume : The dielectric constant of rutile TiO2 is influenced by pressure and temperature [1] and it depends strongly on the annealing history of the sample [2]. In this work, rectifying Schottky junctions were obtained by depositing Pd on rutile TiO2 single crystals subjected to reducing heat-treatments. The samples were implanted with 200 keV H+ to a dose of 3E13 ions/cm2. The Schottky diodes were analysed by Capacitance-Voltage (CV) measurements and Thermal Admittance Spectroscopy (TAS). Using CV, donor vs depth profiles were measured. It is found that the implantation results in a well-pronounced increase in donor concentration, corresponding to the implanted H profile. Since the depth of the H-peak is known, we can deduce the dielectric constant. Our experiments indicate that the dielectric constant increases as temperature decreases. Such a temperature dependence was previously reported for rutile [3], and can be described by a modified Curie-Weiss law [1]. This dielectric behaviour is related to the lattice dynamics of rutile and the presence of a transverse optical phonon mode with a frequency that increases with temperature [4]. Including the temperature dependence of the dielectric constant in TAS measurements enables more reliable investigations into the main donors in TiO2 using this technique. [1] Samara, Phys. Rev. B 7 (1973). [2] Li, J Alloy. Compd. 692 (2017). [3] Parker, Phys. Rev. B 124 (1961). [4] Traylor, Phys. Rev. B 3 (1971).

Resume : Inadequate disposal of industrial waste, such as textile dyes and emerging contaminants, have been caused several environmental hazards. Titanium dioxide (TiO2) photocatalysis is an efficient green method for water treatment by using solar energy. However, due to its large band gap of 3.2 eV, TiO2 absorbs mostly the UV radiation, which represents only 5-8% of the sunlight spectrum. Recent studies indicate that the surface modification of TiO2 results in an increase in the photocatalytic efficiency. In this way, the present paper aims to evaluate the effects of TiO2 surface modification by reduced graphene oxide (rGO). The 470 nm thick anatase-TiO2 films were grown by metallorganic chemical vapor deposition (MOCVD) process in a conventional horizontal homemade reactor, on borosilicate substrates at 400 °C. The TiO2 samples were dipped into an alkoxide suspension containing 0.5 and, 1.5 mg of rGO in 30 mL of isopropanol. The samples were ultrasonic-treated at room temperature for 40 min, and then heat treated in an oven at 100 and 150 °C for 24 h. The chemical, structural and morphological characteristics were evaluated by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. It was observed the presence of rGO agglomerates strongly adhered to TiO2 surface. The diffraction analysis show both anatase and graphene peaks The photocatalytic activity of rGO-TiO2 composites were evaluated by measuring the methylene blue degradation under UV and visible light. The results suggest that the rGO-TiO2 composites have a great potential to be used in water treatment under sunlight.

Resume : The aim of this work was the synthesis of photocatalytic heterostructures based on TiO2 - rutile doped with RuO2 by hydrothermal method. Doping of the TiO2 with RuO2 is as an important strategy to suppress the recombination of photoinduced electron−hole pair and decrease band gap energy. We determined band gap energy for all photocatalysts synthesized using to the Kubelka Munk theory. The crystalline phases structures of rutile TiO2 and rutile RuxTiO2 were realized by X – Ray Diffraction (DRX). The photocatalytic studies of the RuxTi1-x O2 (x= 0.05, 0.5 and 1 mol%) and TiO2 composites were evaluated via the degradation of methylene blue (MB) under sunlight with light intensity I = 50000 lx. References 1. Banerjee, S., Pillai, S.C., Falaras, P., O’Shea, K. E., Byrne, J.A., Dionysion, D. (2014) New Insights ito the Mechanism of Visible Light Photocatalysis, J. Phys. Chem. Lett., 5, 2543-2554. 2. Nguyen-Phan, T., Luo, S., Vovchok, D., Llorca, J., Sallis, S., Kattel, S., Xu, W., Piper, L. F.J., Polyansky, D. E., Senanayake, S. D., Stacchiola, D., Rodriguez, J. (2016) J. Phys. Chem. Letters.,DOI: 10.1039/C6CP00472E. 3. Uddin, M.T., Nicolas, Y., Olivier, O., Toupance, T., Müller, M.M., Kleebe, H.J., Rachut, K., Ziegler, J., Klein, A., Jaegermann, W. (2013) J. Phys. Chem., 117, 22098-22110. 4. Wang, Z., Liu, Bo., Xie, Z., Li, Y., Shen, Z.Y. (2016), Preparation and photochatalytic properties of RuO2/TiO2 composite, Ceram. Internat., 42, 13664-13669.

Resume : Among various promising photocatalysts, Titanium (IV) oxide (TiO2) is most investigated semiconductor photocatalyst because of its chemical/physical stability, non-toxicity and low-cost.[1] However, the high rate of charge recombination of photo-generated electron/hole pairs dramatically decreases the photocatalytic efficiency for its practical applications. Various methods, including the loading metal [2] and noble metal nanoparticles such as gold (Au) [3] to extend the electron/hole pairs lifetime. Various synthesis methods have been reported to prepare Au nanostructures on TiO2. In most of these synthesis methods, the controlling of the geometry, size, and distribution of such Au nanostructures is problematic by reducing agents which may cause some health problems due to their toxic nature. In this study, a photocatalytic deposition approach is demonstrated, which allows controlling the geometry, size, and distribution of such Au nanostructures on TiO2 thin film by simply altering the solution, photocatalytic activity of TiO2, UV irradiation time and intensity.

Resume : Gold nanoparticles (AuNPs) on metal oxide supports constitute plasmonic photocatalysts capable of catalyzing the photodegradation of a number of water pollutants under visible light irradiation. Their performances are linked to the Localized Surface Plasmon Resonance (LSPR) effect of AuNPs combined to the charges transfers. In order to improve both photocatalytic efficiency and AuNPs stability on their support, it is of great interest to devise nanostructured oxides. In this study, Rhodamine B degradation efficiency of Au loaded on WO3 oxide as plasmonics photocatalysts, was investigated under solar light irradiation. WO3 supports were synthesized prepared by a facile one step hydrothermal method with different morphologies, platelets and spheres, then compared to commercial WO3 and TiO2 (P25). The photocatalysts composites were prepared by impregnation of the oxide powder in aqueous gold precursor solution HAuCl4 followed by reduction by NaBH4. The physico-chemical properties of synthesized nanomaterials were systematically characterized using X-ray diffraction, Scanning and transmission electron microscopy (and HRTEM) and Raman spectroscopy. The optical properties were obtained by UV-Visible Diffuse Reflectance Spectra. The band gap energy was calculated according to Kubelka-Munk method; they vary from 2.60 eV to 3.10 eV. Whatever the morphology, the composites photocatalytic efficiency is significantly higher than the bare oxides, with faster kinetics and complete Rhodamine B photodegradation.

Resume : In this paper, we propose a new high performance ITO (Indium Tin Oxide) transparent electrode film design using plasmon resonance of metal nanoparticles that can offer the benefits of improved optical behavior and reduced resistance values. Our investigation shows that the proposed structure provides the possibility for modulating the conductivity in the ITO layer to improve the transparent electrode performances. This concept suggests achieving the dual role of an appropriate transparency behavior and enhanced resistivity values. Moreover, a new hybrid approach based on numerical simulation and metaheuristic Optimization is proposed to determinate the better compromise between the electrode transparency and resistivity of the amended transparent electrode film to achieve further optical and electrical enhancements. It is found that the optimized design exhibits superior performances. Therefore, the optimized transparent electrode film using plasmon resonance of metal nanoparticles paradigm pinpoints a new path toward recording high-performance transparent conducting electrodes for photovoltaic or flexible solar cells due to their low resistivity and high optical transmittance.

Resume : TiO2 is one of the most prominent photocatalysts for solar powered hydrogen production by water splitting; however, high band gap and high carrier recombination rate restrict its performance. To improve upon this, we investigated heterojunctions of pristine/ nitrogen (N) doped CDs with TiO2 using a density functional theory based approach. Heterostructures of pristine CDs and TiO2 displayed typical type-II band alignments that facilitate spontaneous separation of charge carriers; and thus, were well suited for sensitizer like applications. However high band gaps of the CDs still severely constricted the photocatalytic performances of these systems. Substitutional N doping drastically reduced (by ~95.2% at maximum) the band gaps of the isolated CDs, and ~64.9% band gap reduction was observed for the energetically most stable species. CD band gaps in N doped CD - TiO2 heterostructures were also found to follow a similar trend, however local interactions of the doped CDs with the top most oxygen layer manifested highly different and unequal band gaps in up and down spin channels. Subsequent investigations revealed concurrent and highly anomalous type-II band alignment in up spin channel and type-I band alignment in down spin channel in these structures. The obtained results thus possibly hint at radically new device design paradigm that could be helpful in further improving the efficiencies of water splitting photocatalysts.

Resume : Development of a new method for perovskite films with controlled morphologies can lead to more stable solar cells and with higher efficiency. The two-step method has been proved to be an effective approach to synthesize high-quality perovskite for high-performance perovskite solar cells.1 In this study, we present a new two-step process in which a thin layer of PbS is converted into PbI2 and subsequently into MAPbI3. Our group has previously reported on the control over PbS film morphology and its physical properties by optimizing the parameters of the chemical deposition (temperature, pH, growth duration etc.).2–4In this work, thin films of PbS were initially deposited over GaAs substrates. The morphology was columnar which increased the density of vertical grain boundaries which can facilitate the penetration of iodine within the films. In the first conversion step, PbS films were converted into PbI2 by treating the films in solutions of polyiodide which were dissolved in a mixture of water and isopropanol. Different mixtures of water/isopropanol resulted in a controllable process, giving rise to different PbI2 morphologies. In the second step, various PbI2 films were converted into MAPbI3 by immersion in an isopropanol solution of MAI. Different MAPbI3 grain sizes were obtained depending on the initial PbI2 morphology. The degree of conversion to perovskites was found to depend on the first step of conversion; the highest conversion to perovskite resulted from PbI2 samples prepared with solutions containing 20% water. Photoluminescence measurements were carried out to confirm the quality of the film and showed that surface passivation using pyridine was necessary in order to receive photoluminescence response from the films. Moreover, we were able to enhance the signal by growing a thicker initial PbS film while keeping the same conversion parameters. 1. Chen, H. Two-Step Sequential Deposition of Organometal Halide Perovskite for Photovoltaic Application. Adv. Funct. Mater. 27, 1–19 (2017). 2. Osherov, A., Ezersky, V. & Golan, Y. The role of solution composition in chemical bath deposition of epitaxial thin films of PbS on GaAs (100). J. Cryst. Growth 308, 334–339 (2007). 3. Osherov, A., Shandalov, M., Ezersky, V. & Golan, Y. Epitaxy and orientation control in chemical solution deposited PbS and PbSe monocrystalline films. J. Cryst. Growth 304, 169–178 (2007). 4. Osherov, A. & Golan, Y. Chemical solution deposited PbS thin films on Si(100). Phys. Status Solidi Curr. Top. Solid State Phys. 5, 3431–3436 (2008).

Resume : Today one of the most pervasive problems afflicting people is inadequate access to clean water and sanitation. The United Nations predicted that by 2030 47% of the world population will live in areas with high water stress. In particular, grey water (from bathtubs, hand basins, kitchen sinks, dishwashers and laundry machines) reuse is an attractive alternative to the sustainable management of water, especially under water scarcity situations. Indeed, grey water that is separated and treated can be safely reused for toilet flushing and/or garden irrigation. Semiconductor-based photocatalytic process has shown a great potential as a low-cost, environmentally friendly, and sustainable water treatment technology. In this work, we report on the photocatalytic activity of ZnO and TiO2 photocatalytic films deposited by atomic layer deposition on different subtracts, such as silicon, quartz, and flexible poly methyl methacrylate (PMMA). The synthesized films were also enriched with Ag nanoparticles, for their antibacterial properties, or with porphyrin, so as to create a photocatalyst sensitive to the visible light. The photocatalytic surfaces were extensively characterized by scanning electron microscopy, X-ray diffraction analyses, and X-ray photoelectron spectroscopy; the aptitude for the degradation of organic contaminants and microorganisms was, respectively, tested through the breakdown of methylene blue under UV and visible light irradiations, and through the E. coli stress.

Resume : The use of earth-abundant materials such as TiO2 as a photocatalytic agent in water splitting applications is hindered by the large bandgap, requiring optical sensitization to be cost effective in solar radiation. Light trapping via morphologically complex nanoparticles and plasmonics via noble metal decoration has progressed this problem; however, the chemical and structural complexity of these nanoscale features makes it difficult to develop a sufficiently robust model that would allow for fabrication routes to be streamlined. In this contribution, we present a methodology that can be used to spatially segregate TiO2 polymorphs such as anatase and rutile in complex hollow-shell morpholgies with nanometer spatial resolution. The approach makes us of hyperspectral datacubes acquired using Electron Energy-Loss Spectroscopy (EELS) in a Scanning Transmission Electron Microscope (STEM). We show that the spectral signatures of the differing TiO2 phases can be unmixed using multivariate statistical methods yielding quantitative abundance maps of the two phases. Simultaneously-acquired Energy Dispersive X-Ray Spectroscopy (EDX) maps allow the distribution of noble metals to be correlated to the polymorph distribution. We conclude with a discussion of how these maps can be correlated to the direct plasmonic response of individual nanoparticles using low-loss Valence EELS (VEELS), providing powerful insight into the emergence of a macroscale optical response from nanoscale constituents.

Resume : The efficient electrochemical conversion of CO2 to fuels or stock chemicals with high-energy density would be a major step forward in the introduction of a carbon neutral energy cycle, as it would allow for the direct low-temperature conversion of photo-generated electrical current to stored chemical energy, in a manner very similar to the way nature stores solar energy. The high activity and selectivity towards electrocatalytic conversion of CO2 can be achieved with careful selection of catalyst and electrolyte. Major progress in electrochemical CO2 reduction has been limited to two-electron involved products such as CO and formate. It has been known that Cu is prone to produce hydrocarbons, mainly C1 product such as methane and the formation of multi-carbon products via C-C coupling remains as one of the biggest scientific challenges to be resolved. The product selectivity of such conversion can be affected by the electrolyte composition and catalyst structure. Anion such as halides in the electrolyte nanostructures copper surface via electrochemical cycling which allows for a suppression of methane and an enhancement of ethylene and ethanol formation. On the other hands, cations have direct influence on CO2RR in which increasing the size of mono-valent cations can increase the selectivity and activity to C-C coupled products by lowering the pKa of the hydrated cations at the cathode. In addition, a new principle of catalyst design which controls an atomic-level catalyst structure to accelerate electrocatalytic activity and selectivity toward the formation of C-C bonds will be introduced. In-situ Raman and XAS analysis support the origin of the active sites for enhanced activity.

Resume : The development of powdered photocatalyst for CO2 reduction under visible light irradiation is important with respect to the development of renewable energy sources. The combination of metal oxide semiconductor photosensitizer (ex. N-Ta2O5) and a Ru-complex electrocatalyst is one promising approach to visible-light induced selective CO2 reduction [1]. Zn-based sulfides are considered to be superior because ZnS possesses a relatively negative conduction band minimum (ECBM) formed by the Zn 4s4p orbitals, which facilitates the electron transfer from the CBM of the semiconductor to the metal-complex. This work demonstrated powdered photocatalysts for CO2 reduction, employing various Zn-based metal sulfides hybridized with Ru-complex catalysts under visible light irradiation in the presence of an electron donor (acetonitrile/triethanolamine. The photocatalytic activities were largely dependent on the basic characteristics of the Ru-complex and the metal sulfide, such as polarity and the photoexited state lifetime. A neutral Ru-complex with phosphonate anchors in combination with either n-type (AgIn)0.22Zn1.56S2 or Ni-doped ZnS gives a highly enhanced turnover number for the generation of HCOOH [2]. These results suggest that Zn-based metal sulfides are potential candidates for use in powdered hybrid systems for active and selective CO2 photoreduation. Reference [1] S. Sato, et al., Angew. Chem. Int. Ed., 2010, 49, 5101, [2] T. M. Suzuki, et al., Applied Catal. B., 2018, 224, 572

Resume : Singlet fission in tetracene and its derivatives has been investigated extensively due to singlet and triplet energy levels that are favourable for down conversion of light for enhancing conventional Si-based solar cell efficiencies. Luminescent harvesting of energy from singlet fission materials provides an elegant pathway increasing the efficiency of photovoltaics. We describe the investigation of singlet fission dynamics and energy transfer dynamics in triisopropylsilyl-tetracene (TIPS-Tc) thin films and blends. In TIPS-Tc films, we study free triplet formation in amorphous TIPS-Tc films produced by thermal evaporation and spin coating. We observe a phase transition in TIPS-Tc films from amorphous phase to polycrystalline phase over long durations of time (a few weeks to a few months) allowing us to map phase change with changes in exciton and singlet fission dynamics in the films, using transient absorption and emission spectroscopy ranging from the femtosecond to the millisecond range. Our insights allow us to produce TIPS-Tc films with optimal morphologies for efficient singlet fission and triplet energy transfer. In TIPS-Tc and Yb-complex blends formed via co-evaporation, we observe triplet energy transfer from TIPS-Tc to the Yb-complex and subsequent lanthanide emission. We use magnetic field dependent steady-state emission and transient absorption spectroscopy to gain insight into their underlying photo-physics. Reference Rao, A. & Friend, R. H. Nat. Rev. Mat. (2017).

Resume : Influence of defect on reduced graphene oxide (rGO) with graphitic carbon nitrides (g-C3N4) as photocatalyst was investigated using density function theory. To verify the effect of defect on rGO, the work function of pristine rGO (PrGO) and defective rGO (DrGO) was calculated because the photocatalytic activity depends on the work function. The work function of rGO linearly increased according to O/C ratio. This phenomenon is independent of the defect on rGO. Among the various O/C ratio, the PrGO and DrGO with O/C ratio range from 4% to 13% is appropriate for the photocatalyst. The charge transfer in PrGO with 4% O/C ratio and DrGO with 8 % and 13 % O/C ratio only occur. However, in PrGO with 4% O/C ratio, heterojunction was not constructed by g-C3N4 and PrGO. H* adsorption free energy of the g-C3N4/DrGO heterojunction was investigated to further understand the mechanisms of the HER catalysis. In case of monolayer PrGO, |∆G_(H^* ) | value of monolayer PrGO with 8% O/C ratio is close to 0. All g-C3N4/DrGO with O/C ratio shows large |∆G_(H^* ) | value, demonstrating that the strong binding strength of H shows poor HER performance. From these results, the key message for materials design and optimization is that the degree of reduction should control since the optimized O/C ratio of rGO exists. Thus, g-C3N4/rGO (DrGO+PrGO) heterojunction shows good HER performance if the DrGO only transfer electron between the g-C3N4 and PrGO and the HER reaction occurs at the surface of PrGO.

Resume : Titanium dioxide is one of the most common photocatalysts used to catalyse the photochemical splitting of water. Nonetheless, it has some limitations. TiO2 possesses a comparatively large band gap of 3.2 eV, thus it can only utilise around 4 % of solar irradiation. To compensate for these restrictions, a ternary TiO2/reduced graphene oxide/Ag composite was synthesised. The addition of reduced graphene oxide, decreased the band gap from 407 nm to 427 nm and also acted as an electron acceptor for photogenerated charges, lengthening their lifetime. The optimum loading of reduced graphene oxide on TiO2 was 0.5% w/w, which improved measured photocurrent densities by 75 %. The addition of silver nanoparticles at a 2.5 % w/w loading doubled the measured photocurrent densities. This further increased efficiency by acting as a sink for electrons and improved the photocatalytic response to visible light. Finally, the ternary TiO2/reduced graphene oxide/Ag composites further doubled the photocurrent densities. For this composite, the optimum silver nanoparticles size were between 44 nm and 60 nm in diameter. These findings are currently being applied to other photocatalysts such as WO3, BiVO4 which possess similar limitations as TiO2.

Resume : Over the last two decades, cadmium sulphide CdS synthesited by chemical bath deposition (CBD) was the most used buffer layer for thin film solar cells. However, the replacement of CdS in solar cells by other possible buffer layers is of high interest for several reasons. Indeed, CdS contains the toxic metal Cd which represents a threat to the human health and the environment and has a relatively low band gap of 2.4 eV which limits the performance and the efficiency of the cells. (Zn,Sn)O material is among the most promising Cd-free materials for replacing the CdS as buffer layer in solar cells. In this work, we present experimental studies on the synthesis and characterization of non toxic and earth-abundant (Zn,Sn)O thin films. The samples were prepared by two steps method: The deposition of metalic precursors by thermal evaporation followed by an annealing in air or oxygen atmospheres. We obtained Zn2SnO4 thin film, with a stable cubic spinel structure, characterized by a high transmission rate of 80% and direct bandgap energy of 3.2 eV. Electrically, we found that the film has an n-type conductivity with activation energy “Ea” around 1.06 meV.

Resume : ZnSe nanocrystals (NCs) have attracted considerable interest for their unique electrical and optical properties. ZnSe NCs are characterized with a wide band-gap energy of 2,7 eV. These nanocrystal are very good candidates as nanofillers for polymer nanocomposites. In order to incorporate of inorganic nanoparticles into polymer matrix, the appropriate surface modification of NCs is necessary. In this work the synthesis of ZnSe nanocrystals and their surface modification are presented. ZnSe NCs were synthesized by hot-injection method using octadecylamine (ODA) as coordinating solvent. Octadecylamine is a protection agent of such ZnSe:Ag nanocrystals, however long aliphatic groups block the transition of charge between such nanocrystals. In turn, ZnSe, being on the surface ODA, cannot be used in photovoltaic and optoelectronic devices. For this purpose, the ligand exchange procedure will be performed. ODA was replaced by organic semiconductor molecules, such as derivatives of naphthalenes. Such exchange will receive a greater conductivity of nanomaterials in terms of transfer of electrical charges between one-dimensional nanocrystals. This work was financially supported by National Centre for Research and Development under Lider Program, contract no. LIDER/009/185/L-5/13/NCBR/2014 and the participation in the conference was financially supported by NAWA Programme PROM no. International scholarship exchange of PhD candidates and academic staff.

Resume : Production of renewable energy by photocatalytic degradation of organic wastes in a photoelectrochemical (PEC) cell is an attractive approach with double environmental benefit: waste materials can be consumed and solar radiation can be converted into useful forms of energy, including electricity and hydrogen [1]. Nanocrystalline titania is the most studied photocatalyst for this purpose, however its use is limited to a small part of the solar spectrum (UVA light). Thus the present work focuses on narrow energy band gap inorganic that are capable to absorb visible light. The examined photocatalysts comprise semiconducting oxides (such as Fe2O3, WO3 and BiVO4 [2]) and their doped analogues with suitable metal ions (Ti, Gd, Mo) that besides adequate light absorption, they possess proper energy levels, good electric conductivity and enhanced stability against corrosion. These materials were combined with graphitic carbon nitride (g-C3N4), which is a typical layered metal-free semiconductor having attracted intensive attention for water splitting and organic pollutants decomposition [3,4]. The novel heterostructures were characterized and were successfully incorporated as photoanodes in PEC cells. The obtained results in the degradation of biomass derived organic wastes (glycerol, ethanol and fructose) confirmed that the new materials are endowed with improved photocatalytic activity towards visible light driven energy production. Acknowledgments This project has received funding from the Hellenic Foundation for Research and Innovation (HFRI) and the General Secretariat for Research and Technology (GSRT), under grant agreement No [2490]. References [1] M. Antoniadou, P. Lianos, Catalysis Today 2009, 144, 166 [2] P. Lianos, Applied Catalysis B: Environmental, 2017,210, 235 [3] J. Xu,I. Herraiz‐Cardona, X.Yang ,S.Gimenez, M.Antonietti, Advanced Optical Materials, 2015, 3, 1052. [4] S. Tonda,S. Kumar, S. Kandula, V. Shanker, Journal of Materials Chemistry A, 2014, 2,6772.

Resume : The energy crisis and global warming concerns have increasing the demand for progress into high performance energy conversion and energy storage devices. The development of new high-performance materials is the key to new nanomaterial advances for sustainable development. In this regard researchers are looking for new material which can absorb the broad spectrum of solar light so as to bring better efficiency under solar light. First fabrication of 2D MoS2 by exfoliation of layered MoS2 with tunable band gap has been the focus of rapidly expanding research activities with other layered materials. On the other hand copper hydroxy phosphate Cu2(OH)PO4 in libethenite mineral form has shown photocatalytic activity in Vis and NIR range thus increasing the solar light absorption up to NIR. In this regard we are trying to explore the use of exfoliated 2D MoS2 and Cu2(OH)PO4 based heterojunction with TiO2 as solar photocatalyst. Materials with 10% of Cu2(OH)PO4 with TiO2 were synthesized by hydrothermal method. HRTEM conform the hetrojunction formation of diamond shaped crystalline particles with average size 20-30 nm. Light absorption extends to visible-NIR region foe the hetrojunction material having only 10% of Cu2(OH)PO4. Addition of 10% Cu2(OH)PO4 is found to decrease the overall band gap to 2.6 eV. The in-situ generated Ti3+ and oxygen vacancies in the TiO2 lattice along with the metallic copper at the interface results in extended visible light absorption with improved charge separation. Photocatalytic reduction of Cr (VI) under visible and solar light was studied to evaluate the effect of Cu2(OH)PO4 towards the photocatalytic efficiency. TiO2 heterojunction with 10% of Cu2(OH)PO4 can completely reduce 25ppm of Cr (VI) into Cr (III) within 60 minutes of visible light irradiation whereas in same duration pure TiO2 and Cu2(OH)PO4 shows negligible photoreduction capability. Exceptionally the same material can reduce Cr(VI) to Cr(III) in 50min under solar light. However TiO2-MoS2 shows complete photoreduction in 60min under both solar as well as visible light. So it can be concluded that the applicability of present TiO2-Cu2(OH)PO4 catalyst under solar light is much better than visible light. Effect of surface area and visible light absorption were discussed

Resume : Multi-junction solar cells comprising GaAsP top absorbers with Si bottom cells enable photovoltaic conversion efficiencies above 40%. However, monolithic epitaxial integration of GaAsP with As contents between 50%-75% on Si requires to overcome a significant lattice mismatch. Commonly, this is achieved with GaAsP graded buffers where the As/P ratio increases stepwise. Here, such GaAsxP1-x buffers (x ≤ 0.5) were grown on GaP(100) substrates by metalorganic chemical vapor deposition. The entire process was monitored in situ with reflection anisotropy spectroscopy (RAS), an optical surface-sensitive technique, in order to yield a better understanding of the interface preparation. Ultra-high vacuum surface-sensitive methods were used to identify the surface reconstruction and chemical composition in dependence on the GaAsP stoichiometry and post-growth process route. We show that the As content of individual GaAsP layers can be quantified in situ by RAS during the growth: With increasing As supply, a peak close to the GaP E1 critical point energy shifts towards GaAs E1 at lower energy [1]. The atomic structure of the GaAsP surfaces depends on the processing routes: While GaAsP samples annealed under H2 at 500°C exhibit a (2x4) reconstruction and are V-rich, annealing at 700°C leads to Ga-rich surfaces. Therefore, the preparation of the surfaces can be optimized in situ via their RAS fingerprints. [1] O. Supplie et al., Proceedings 45th IEEE PVSC Conf. (2018) 3923

Resume : Nanoparticle such as TiO2 nanoparticles (TiO2 NPs), have gained much attention due to their antibacterial activity, good photocatalytic performance, low cost, non-toxicity and environmentally friendliness. The antibacterial activity of TiO2 NPs mainly stems from the production of reactive oxygen species (ROS) upon illumination with UV light. However, the bandgap of TiO2 NPs (3.0-3.2 eV) is wide, which limits its visible light absorption. Herein, Au incorporated TiO2 nanocomposites with enhanced visible light absorption and transfer abilities were first synthesized through a hydrothermal method. Then, an Au-TiO2 nanocomposite incorporated sodium alginate film was prepared by a simple casting method. The film shows efficient visible light absorption ability and excellent antimicrobial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) due to large ROS produced under visible light.

Resume : Layered double hydroxides (LDHs) are promising photo/electrocatalysts for water oxidation essential to generate solar fuels such as hydrogen or C1 fuels, however, their anion layers limited accessible reaction sites resulted in low activity. Furthermore, lack of functional sites for enhancing activity such as charge transport are yet to be overcome. As a solution to solve these limitations, we report ultrathin nanosheets derived from NiAl LDHs via a nitrogen plasma dry exfoliation. Moreover, nitrogen plasma make rich O vacancies resulting in decreased Ni-O bonding length and doped nitrogen sites leading to metal-N and N-O bonds along with oxynitrides. Rich O vacancy facilitates adsorption of water oxidation intermediates by generating low-coordinated Ni and the doped N sites pull electrons from water oxidation intermediates. Therefore, ultrathin NiAl nanosheets assembled on Hematite nanorods are exhibited to surpass the water oxidation activity of Hematite by about double and to outperform the charge carrier densities of NiAl LDH nanoplates assembled on Hematite by about 4 folds, while having excellent activity retention close to 100% in a long-term stability test.

Resume : Organic semiconductors have traditionally been regarded as being delicate with respect to degradation in oxygenated/aqueous conditions, especially in the presence of light. We have recently found that, in fact, numerous examples of organic semiconductors exist where these materials support true photocatalytic redox cycles, often with good stability. One general reaction which proceeds efficiently is the photocatalytic reduction of oxygen to hydrogen peroxide. We have found that both n-type, p-type, and ambipolar semiconductors; small molecules and polymers, can generate peroxide in a wide pH range of 2-12. The p-type materials are additionally suitable for the fabrication of photocathodes, allowing the creation of peroxide-generating photoelectrochemical cells – something previously impossible with inorganic semiconductors. In our work we have made a number of free-standing photocatalytic and photoelectrochemical platforms to produce peroxide, and also have discovered the presence of catalytic peroxide production in the bioorganic semiconductors.

Resume : A hydrothermal method had been employed firstly for the preparation of La0.995Pr0.005VO4 nano-crystal phosphors, and then they were annealed from 500–800 oC for 4 h. The x-ray diffraction patterns show that the La0.995Pr0.005VO4 phosphors still keep the tetragonal structure for a lower annealing temperature (500 and 600 oC). When the annealing temperature is higher than 600 oC, the structure for La0.995Pr0.005VO4 is changed from tetragonal to monoclinic. The SEM results show that the surface morphology of phosphor particles is granular and uniform distribution. The particle size increases from 0.1 to 2.5 um as the annealing temperature increased. The excitation spectra show that an absorption band between 200 ~ 400 nm is due to the charge transfer from the oxygen ligands to the central vanadium atom inside the VO43- anionic group, and the Pr3 ion 4f-5d characteristic transition is located between in the 425 ~ 550 nm, and a red shift of host absorption is observed when the annealing temperature increases. By 315 nm excitation, the main emission band still retains the characteristics for Pr3 ion-doped LaVO4 phosphor, belonging to the host luminescent, and the 1D2→3H4, 3P0→3H6 electron transition of the Pr3 ion, respectively. As the annealing temperature increases, both the excitation and emission peaks intensities has a maximum value for the annealing temperature is 600 oC, then decreases as the annealing temperature increases further. It is due to the structure of La0.995Pr0.005VO4 phosphors transforms from tetragonal to monoclinic when the annealing temperature is higher than 600 oC. It demonstrates that the tetragonal structure is better than monoclinic structure for LaVO4 to be a host material for phosphor application. The color tones located initially in the white region (for 500 and 600 oC annealing), then to orange region (for annealing temperature higher than 600 oC).

Resume : New approaches to manufacturing the nanocrystallites (NCs) of metallic oxides are desired due to their emerging applications in a wide range of high-technology applications. Recent work showed that metal oxide NCs could be synthesized by a new pathway: submerged photosynthesis of crystallites (SPSC), which requires only light and water and generates hydrogen gas as a byproduct. Therefore, SPSC method is applied for ZnO nanorods synthesis in this work, and the photochemistry reactions and the role of light in the SPSC process are studied. In the SPSC process, Zn plate was surface plasma treated and then irradiated by UV light in ultrapure water for several hours. The size of the ZnO NCs increased with UV irradiation time and ZnO nanoflowers could be obtained by 24 h irradiation. The pH measurement and the XPS analysis show that both photoinduced reactions and hydrothermal reactions contribute to the SPSC process. Additionally, the relation between pH and temperature of the water show that light irradiation makes ZnO growth dominant and the water pH close to neutral, whereas thermal energy makes ZnO corrosion dominant and the water pH increases. The role of light in SPSC process is to enhance ZnO apical growth at relatively lower temperature by preventing the pH of water from increasing, revealing the environmentally benign characteristics of the present process.

Resume : Hydrogen energy, a clean and renewable energy source, has been one of the prominent subjects in recent decades as a result of the global energy crisis. In this work, we have demonstrated excellent photocatalytic properties for hydrogen production with ternary sulfides ZnxCd1-xS nanowires (NWs). The ZnxCd1-xS NWs photocatalyst shows much higher catalytic activity for H2-production than ZnS and CdS NWs under simulated sunlight (with AM1.5G filter). When the X ratio of Zn approaches 0.5, the Zn0.5Cd0.5S sample exhibits the highest H2-production rate of 57.07 mmol·h-1·g-1, exceeding that of the pure CdS and ZnS samples by more than 3 times and 50 times. This high photocatalytic H2-production activity is attributed predominantly to appropriate band gap width and suitable conduction band edge potential of the ZnxCd1-xS NWs. Additionally, plasmon-mediated photocatalysis may enhance photoexcitation and improved charge separation in semiconductor photocatalyst system. The ZnxCd1-xS NWs attached with Au nanoparticles (NPs) possess localized surface plasmon resonance (LSPR) at visible or near-infrared wavelengths. The ZnxCd1-xS NWs with Au NPs are shown to significantly improve the efficiency of H2-production by the LSPR effect.

Resume : Although oxygen commonly exhibits a detrimental impact on the properties of III-V nitride semiconductors, the effect of oxygen on the luminescence properties of dopants such as rare earth ions are known to be favorable up to a certain point [1-3]. Thus, it is opportune to study systematically the influence of the oxygen concentration on the emission intensity in e.g. Tb3+/Yb3+ co-doped AlOxNy thin films. This work examines the optimal oxygen to nitrogen ratio, Tb/Yb concentration and annealing treatment temperature for Yb3+ emission intensity for down-conversion process. Combinatorial thin film libraries with different elemental concentration were obtained by r.f. magnetron co-sputtering. Post-deposition annealing treatments were performed at different temperatures from 650 up to 950 °C. The sample characterization was conducted by high velocity throughput methods such as photoluminescence and energy dispersive x-ray spectroscopy. Additionally, X-ray diffraction and UV-VIS spectroscopy were complementary performed. The energy conversion of absorbed high energy photons into two emitted low energy photons is investigated by comparing the photoluminescence intensities and the lifetimes of each Tb3+ and Yb3+ in the co-doped sample. The activation energy of the rear earth ions and activation mechanisms are evaluated at each annealing step and the optimal elemental compositions in the investigated range are proposed. [1] A. Janotta, et al. 2003 Phys. Rev. B 68, 165207 [2] P. N. Favennec et al. 1990 Jpn. J. Appl. Phys. 29, L524 [3] M. A. Lourenco et al. 2016 Sci. Rep. 6, 37501

Resume : Photocatalytic hydrogen production through water splitting has recently gained significant attention for efficient solar-to-chemical energy conversion.¹ However, despite immense research efforts on semiconductor materials, key challenges of obtaining catalysts with high activity and long-term stability still remain. Herein, we present the synthesis of mesoporous networks consisting of connected β-Ni(OH)₂ and CdS nanoparticles (ca. 4–5 nm) and demonstrate their outstanding performance for visible-light photocatalytic H₂ production.² These materials combine the high reactivity of semiconductor nanoparticles with large mesoporosity (up to 207 m²/g), offering new perspectives in designing novel catalysts with improved efficiency and reliability. Photocatalytic experiments along with optical absorption, luminescence, and electrochemical impedance spectroscopy studies indicate that the p-type β-Ni(OH)₂ acts as hole collector, favoring efficient charge transfer and separation across the β-Ni(OH)₂/CdS nano-heterojunctions. As thus, the β-Ni(OH)₂/CdS catalyst containing 10 wt% Ni reached a photocatalytic H2-evolution rate of 1.4 mmol/h with an apparent QY of 72% at 420 nm, while demonstrating excellent stability in alkaline (5M NaOH) ethanol solution (10% v/v). References (1) H. Ahmad, S.K. Kamarudin, L.J. Minggu, M. Kassim, Renew. Sust. Energ. Rev. 2015, 43, 599. (2) I. Vamvasakis, I.T. Papadas, Th. Tzanoudakis, Ch. Drivas, S.A. Choulis, S. Kennou, G.S. Armatas, ACS Catal. 2018, 8, 8726.

Resume : As the promising photocatalyst for green energy, graphite-like carbon nitride attracts special attention. However, the 2.7 eV bandgap of g-C3N4 make it only utilize the solar light with wavelength below 460 nm. Thus, in order to further enhance the light harvesting ability of g-C3N4, various band-gap engineering strategies, including atom-level (especially by oxygen) doping. As a result, the oxygen-doped carbon nitride O-g-C3N4 (O – 4-7%) photoactivity boundary in the visible spectrum expands from 460 to 498 nm. A new substance with more oxygen content (O – 16%) – carbon nitride oxide (g-C3N4)O was synthesized by gas phase method under the special reactionary conditions of the pyrolysis of urea. For various kinds of photochemistry-related applications of (g-C3N4)O are decisive the optical properties, including ultraviolet–visible (UV/Vis) absorption. It is assumed that carbon nitride oxide may contain additional surface defect sites compared to g-C3N4. To test this hypothesis, electron paramagnetic resonance (EPR) spectrometry was used to detect the presence of defects. At the same time, the absorption spectrum of carbon nitride oxide (g-C3N4)O extends to the whole visible light region, possibly due to excitation into the lower energy defect states. In such case, carbon nitride oxide (g-C3N4)O would absorb more visible light than both g-C3N4 and O-g-C3N4, there by generating more charges, which contributed to the improvement in the photoactivity of the catalysts.

Resume : It is a universal quest to produce molecular hydrogen (H2) from the sustainable green routes, such as water electrolysis, to diverge the heavy dependence of fossil fuel on massive energy consumption, which brings detrimental impact to the environment upon combustion. Undoubtedly, developing earth-abundant electrocatalysts with high activity and good durability for substituting the expensive and rare platinum for Hydrogen Evolution Reaction (HER) can advance the progress of hydrogen economy. Layered transition-metal dichalcogenides, in particular, molybdenum dichalcogenides (MoS2) based materials, have been received tremendous attention because of the excellent electrocatalytic performances, high structural integrity, and ease of fabrication. However, the HER performance of MoS2 is still unsatisfactory due to intrinsic poor electrical conductivity and limited active edge sites. In this presentation, we demonstrate an effective strategy to improve the MoS2 performances by hybridizing it with other electrocatalysts. Detailed characterizations and insights will be discussed from the experimental perspective and theoretical finding.

Resume : Simultaneous ultrasonic and hydrothermal treatment, called sonohydrothermal treatment (SHT), is a promising environmentally friendly technique for the synthesis of materials with advanced properties. In this work, we report the SHT preparation of noble-metal-free Ti@TiO2 visible light photocatalyst. Stable to oxidation Ti@TiO2 nanoparticles (NPs) have been obtained by SHT treatment of air-passivated titanium metal NPs in pure water (f = 20 kHz, Pac = 10 W, T = 150 -214°C, P = 4.4 – 19.0 bar). HR TEM analysis revealed that SHT treatment leads to the formation of nanocrystalline shell composed of anatase fine particles at the surface of quasi-spherical Ti NPs having a diameter in the range of 20-80 nm. Powder XRD patterns confirmed the formation of anatase phase after the treatment. Obtained Ti@TiO2 NPs show an extended photo-response from the UV to the NIR light region due to the light absorption by a nonplasmonic Ti core via interband transitions and an absorption band at 308 nm that is due to the bandgap transition of defect-free anatase phase. It was found that Ti@TiO2 NPs exhibit strong photothermal activity in the process of photocatalytic hydrogen production from aqueous solutions of organic sacrificial reagents. More detailed results of the photocatalytic activity of Ti@TiO2 NPs will be presented in the linked oral presentation.

Resume : Abstract The present paper discusses the influence of Tin Sulphide’s grain size on the performance of ITO/PEDOT:PSS/SnS/Ag structured solar cells fabricated by thermal evaporation. The grain sizes were maintained in the range of 10-22 nm by controlling the thickness of SnS films. While the open circuit voltage (Voc) was found to be a constant for this structure, parameters such as short circuit current density (Jsc), series resistance (Rs), parallel resistance (Rp), ideality factor and the overall efficiency were found to be dependent on the SnS grain size and incident light intensity. The experimental work directly reconfirms the theoretical results and ideas raised in literature by early researchers.

Resume : SnxSy thin films with differents molar concentration (x=0.05 M, y=0; 0.03; 0.05; 0.07; 0.1 M) are deposited by spray pyrolysis technique on heated glass substrate at 350°C. The physical properties of the films are characterized by several techniques in order to study their structural, optical and electrical properties. From the study, we could understand that optimum molar concentration of the precursor solution to obtain device quality SnS thin film is x=0.05 M and y=0.05 M. It is observed from X-ray diffraction (XRD) analysis that the film is mainly composed with orthorhombic crystal structure with a preferred grain orientation along (111) plane. From optical measurements, a significant decrease in average optical transmission and the band gap value is 1.8 eV and having a very high absorption coefficient (105/cm). The Hall Effect electrical measurements show that the sample is p-type and the value of the electrical resistivity of SnS films is 2.75x10-2 (Ω.cm)

Resume : There is a growing need to develop new materials for applications in optics, electronics and photovoltaics. Organic molecules play a main role in these advances, through their structural and functional varieties. We report in this work the synthesis, the electrochemical and some spectroscopic properties of a new tetrazine-based dye, the N-(4-(6-(4-aminophenyl)-1, 2, 4, 5-tetrazin-3-yl) phenyl)-N-phenylbenzenamine (TTA), having a donor-acceptor system, designed for dye solar cells (Dye-sensitized solar cells DSCs). The s-tetrazine group was chosen as an acceptor group for its high electron affinity, while triphenylamine as a donor group for its low ionization potential. This dye was electro-grafted onto the ITO semiconductor surface, in the presence and in the absence of ZnO. The electrochemical and optical measurements allowed us to calculate the gaps of this dye. Simulations have been realized to estimate the theoretical values of the HOMO and LUMO of our product. The optimization of the geometry is carried out by the DFT method using the Gaussian program 09, with the functional B3LYP.

Resume : The main problems preventing wide spreading of solar cells as alternative energy sources are their high cost and low efficiency. Efficiency of solar cells based on semiconductors materials is limited due to high electrical and optical losses and to recombination process. Therefore and in order to surmount these problems, we propose in this work to use ZTO nanoparticles deposited on porous silicon layer as antireflection coatings. We found that the formed layer decrease the optical losses which consequently contribute to the improvement in the conversion efficiency of solar cells.

Resume : Pristine oxide photoanodes without catalyst have relatively low photocurrent densities because of the inherent limitation of insufficient visible light absorption and charge transport due to the wide band gap and high work function, respectively. Relatively narrow band gaps and lower work functions can provide advantageous situations by effectively absorbing visible light and forming large surface energy band bending, simultaneously. In this regard, chalcogenide materials are highly likely to allow high-efficient PEC operation because of their narrow band gap. Among them, binary chalcogenide Sb2Se3 with narrow band gap has low work function satisfying conditions for formation of charge-inversion state at surface if used as a photoanode, though it has shown dominantly p-type electrical conductivity and poor photocathodic performance. Ther0efore, we propose a fabrication for n-type Sb2Se3 by controling point defects affecting the conductivity type. Based on electrochemical analyses, surprisingly, synthesized n-type Sb2Se3 shows remarkable photocurrent density (5 mA/cm2 at 1.23 V vs. reversible hydrogen electrode), which is the highest performance among pristine binary photoelectrodes yet recorded. In addition, we verified that the charge inversion state with p-type conductivity at surface results in abrupt photocurrent increase at specific potential in linear sweep voltammetry from forming the conduction path of hole carriers for significant carrier injection into electrolyte.

Resume : Metal oxide nanoparticles attract considerable interest due to the potential technological application in the fields of medicine, information technology, catalysis, energy storage, and sensing, etc. In our previous study, a new pathway for the synthesis of a variety of metal oxide nanocrystallites via submerged illumination in water, called the submerged photosynthesis of crystallites (SPSC) was introduced. The SPSC process requires only light and water and does not require the incorporation of impurity precursors. Moreover, this method is applicable at low temperature and at atmospheric pressure, producing only hydrogen gas as the by-product. These characteristics give rise to the potential application of SPSC as a green technology of metal oxide nanocrystallites synthesis. In this presentation, SPSC method was used to synthesis flower-like CuO and ZnO nanocrystallites and various kinds of iron oxides nanoparticles. The morphologes of the obtained nanocrystallites were observed, and the photochemistry and the mechanism of the process are elucidated. Furthermore, the reactions involved in the SPSC process are analyzed by monitoring the pH and temperature changes of the water, based on which the role of light in the SPSC process is discussed. Finally, the possible application of the product in environment and energy fields are discussed.

Resume : Cu2O with a p-type oxide semiconductor has a high absorption coefficient and consists of eco-friendly materials, and thus it can be actively considered in various photoelectric devices. When the Cu2O films are prepared by electrochemical deposition, they exhibit lower conductivity and charge mobility than those grown by vacuum process. Consequently, the Cu2O based photoelectric or photoelectrochemical devices show lower energy conversion efficiency due to their high resistivity and non-radiative recombination. To solve these intrinsic problems, we suggest the introduction of novel dopants in the electrodeposited Cu2O films. Some metal dopants significantly control the growth behavior and induce considerable improvement in charge mobility of the film. In this study, we have synthesized the electrodeposited Cu2O films with various metal dopants and found that the resultant films have different growth behaviors depending on metal dopants. Especially, we will illustrate new electrochemical deposition models with respect to metal incorporation and compare their photoelectrochemical performances systematically.

Resume : Graphitic carbon nitride (g-C3N4) that is prepared by the condensation (heating) of nitrogen-rich organic compounds (e.g. melamine or cyanamide) at ca. 550 °C is recently getting attention as photocatalyst working under visible light. Although g-C3N4 can be prepared at the temperatures between 500 ? 650 °C, g-C3N4 prepared at ca. 550 °C was often used for the investigation, and actually showed relatively higher activity. We analysed the characteristics of polymeric- and electronic-structure of g-C3N4 prepared at different temperatures by laser desorption/ionization mass spectrometry (LDI-MS), X-ray diffractometry (XRD), UV-Vis absorption spectroscopy, and electron spin resonance (ESR) and evaluated relation with the photocatalytic activity. In the photocatalytic oxidation nitrogen monoxide (NO), the photocatalytic activity per surface area increased with increasing the preparation temperature up to 520 °C, and was decreased above 520 °C. The formation of cyano group connected with tri-s-triazine unit was observed at the higher temperatures, and the planarity of carbon nitride layer was increased. Simultaneously, the formation of mid-gap levels became noticeable and the number of unpaired electron was increased although they were not effective for the photocatalytic activity. Additionally, the photocatalytic hydrogen evolution by Mn12Bz-cluster/g-C3N4 was studied. The details will be presented in the conference.

Resume : Catalytic and photocatalytic 2-propanol dehydration to propene by using a continuous (photo)reactor at atmospheric pressure and a temperature range of 70÷120 °C were carried out in gas-solid regime. Propene and diisopropyl ether resulted the main reaction products. The (photo)catalysts were bare and supported Keggin H3PW12O40 and Wells-Dawson H6P2W18O60 heteropolyacids (HPAs). Boron nitride (BN) and carbon nitride (C3N4) were used as supports. The HPA species played the key role both in the catalytic and photocatalytic reactions. The acidity of the cluster accounts for the catalytic role, whereas both the acidity and the redox properties of the HPA species were responsible for the increase of the reaction rate in the photo-assisted catalytic reaction. The supported HPAs resulted more active than pristine heteropolyacids. The propene reaction rate increased by irradiating the catalytic system. The Wells-Dawson HPA was more active than the Keggin one both as catalyst and as photocatalyst, as previously observed [1]. The BN support resulted beneficial in comparison to C3N4. The apparent activation energy for the catalytic and photocatalytic dehydration has been determined resulting always lower for the photocatalytic process than for the catalytic one. [1] E. I. García-López et al. Applied Catalysis A:General, 528 (2016) 113-122

Resume : We present a simple copolymerization process to covalently graft pyrene-functional groups on the polymeric carbon nitride (PCN) surface. The resulted pyrene functionalized carbon nitride (Py-PCN) exhibits unique biphasic photocatalytic activities, which enables efficient CO2 photoreduction in the aqueous solution with simultaneous alkene (C=C) oxidation in the organic phase. The great biphasic activities are attributed to the increased lipophilicity from surface pyrene-functional groups that allows the hydrophobic alkene molecules to readily approach the PCN surface, and be reacted with the hydroxyl radicals created from –OH oxidaion by photogeneratd holes. By this way, the alkene compounds indirectly consume the photo-holes from excited Py-PCN, promoting the overall efficiency of the photocatalytic CO2 reduction processes. Our studies provide a new strategy of solar fuels production with simultaneous organic synthesis by the oxidization power of photo-holes on amphiphilic metal-free semiconductors.

Resume : The coupling of photocatalysis and hydrothermal process leading to the transformation of cellulose is very scarcely studied. The goal of this study is so assist the hydrothermal process with new catalytic materials possessing excellent acid-base and photocatalytic properties to decrease the reaction temperature and related energy required. For tis purpose a series of titanium dioxide and few layer graphene (FLG) composites were prepared by sol-gel method [1] and first tested towards H2 production via methanol photo-reforming. The FLG were first obtained as colloidal suspension in water through the exfoliation of expended graphite (EG) as a starting material and in the presence of large bio-surfactant [1]. Two series of TiO2/FLG nanocomposites with large FLG flakes (G1) and small FLG flakes (G2) were synthesized with different ratio of TiO2 to FLG. The photocatalytic activities of the as-obtained samples were evaluated in hydrogen evolution from the reaction of photo-reforming of methanol under UV-Vis illumination. The influence of FLG content, FLG size (G1 or G2) and also the concentration of the nanocomposites in the reaction medium were investigated. The results show that: - All the TiO2/ FLG nanocomposites have a better activity than the references samples (TiO2 sol-gel and a commercial UV100). - The concentration of the samples in the reaction medium impact the photocatalytic activity of all tested samples. - The evolution of the activity was clearly affected by TiO2 to FLG ratio and size of FLG flakes. [1] Kouamé N.A., Robert D., Keller V., Keller N., Pham C., Nguyen P., (2011). Preliminary study of the use of β-SiC foam as a photocatalytic support for water treatment. Catalysis Today, 161, 3-7 [2] Ba H., Truong-Phuoc L., Pham-Huu C., Luo W., Baaziz W., Romero T., & Janowska I. (2017). Colloid Approach to the Sustainable Top-Down Synthesis of Layered Materials. ACS Omega, 2(12), 8610–8617.

Resume : Water purification meets the needs of medical, pharmaceutical, chemical, agricultural and industrial applications for clean and potable water. Various water treatment technologies are available and direct solar distillation methods allow to produce purified water combining renewable energy (e.g. solar energy) with solid surfaces and interfaces between materials and water. The aim of this work is to increase water evaporation yield of direct solar distillation systems using graphene based-nanofluids. Stable nanofluids are needed for this purpose and the strong hydrophobic character of graphene, that avoids its long time dispersion stability in water, makes necessary the use of additives to get stable suspensions. Results show an enhancement in suspension stability of graphene nanofluids up to 50 times using additives and the evaporation rate of the stable nanofluids was 70% higher compared to pure water. This enhancement in evaporation rate is due to a light-to-heat conversion process where the solar energy absorbed by graphene is transferred to water as thermal energy, thanks to the very high thermal conductivity of graphene at room temperature. The graphene nanopowder was characterized by Raman spectroscopy and XPS. The dispersion stability of graphene nanofluids was studied in presence/absence of several additives by means spectrophotometry, while their evaporation rate was evaluated by gravimetric measurements under UV-Visible irradiation generated by a solar simulator.

Resume : The fundamental understanding of liquid-phase catalytic reactions is unavoidably complicated when the catalyst is prone to leaching since questions inevitably arise as to the true nature of the catalyst. While the catalytic reduction of 4-nitrophenol by borohydride is widely accepted as a trusted model reaction, it has faced little scrutiny concerning the potential impact of leached species or the appropriateness of assigning catalytic activity to the inserted nanostructures without rigorous experimental verification. Here, we present results from a spectroscopically monitored split test in which supported silver catalysts are physically separated from the reactants midway through the reaction. It is unambiguously demonstrated that the influence of leaching is far from benign, instead acting to extinguish the catalytic activity of the inserted nanostructures while giving rise to an unsupported species that is the true catalytic entity. With only sub-monolayer quantities of silver leached from the supported structures, the unsupported species must be exceedingly catalytic. Moreover, it is shown that leaching is inherent to aqueous media containing dissolved oxygen, without which the supported nanostructures remain catalytically active. With the same nanomaterial being able to act as either a heterogeneous catalyst or as a reservoir from which leached metal is derived, such influences have undoubtedly compromised prior studies. We, nevertheless, capitalize on the sensitivity of 4-nitrophenol reduction to leached species by using it as a reaction-based indicator able to quantitatively determine the time-dependence of the leaching process and enhancements to oxidative etching when silver, copper, palladium, platinum, and gold are exposed to chloride ions.

Resume : A meta-analysis of the device performance and transient spectroscopic results are undertaken for various electron donor:electron acceptor blends, employing three different electron donor polymers and seven different electron acceptors including nonfullerene acceptors (NFAs). From this analysis, we find that the primary determinant of device external quantum efficiency is the energy offset driving interfacial charge separation, ΔECS. In addition we focus on the impact of energy cascade between mixed and pure region that assists in free charge generation in non-fullerene acceptors (NFAs)-based organic solar cells. However, studies to date have not addressed whether successful NFAs exhibit energy offsets between mixed and pure domains analogous to the offsets observed with fullerene acceptors. As such, it is not clear whether the presence of such energy offsets is a general design requirement for both fullerene and NFAs. Our results are discussed in terms of their implications for the design of donor/NFA interfaces in organic solar cells, and strategies to achieve further advances in device performance.

Resume : Due to their large photoabsorption coefficients for visible light, porphyrin derivatives are widely used in light-harvesting applications, such as photovoltaics and photocatalysis. Numerous studies have been reported on porphyrin thin films deposited on solid substrates. They were also integrated into surface-anchored metal-organic frameworks (SURMOFs) of highly ordered structure, resulting in photovoltaic activity of MOF, their photostability and sensitizing function in photon upconversion. Here, we use quantum mechanical calculations in order to explain highly efficient excited-state transport properties of porphyrin SURMOF with Pd-coordinated organic linkers [1]. The calculated transfer rates are consistent with experimentally obtained rates, which result in micron-range exciton diffusion length in this MOF. First principle calculations are also applied to understand mechanism of charge transport in Zn-coordinated porphyrin-containing SURMOFs with embedded fullerene molecules [2]. The improved photoconductivity is shown to be derived from the spatially continuous network of donor and acceptor domains in MOF material. Owing to the fact that the porphyrin properties can be tailored by advanced organic chemistry and MOF properties can be tuned for the specific applications, ab initio calculations enable valuable predictions of new promising candidates for light harvesting. [1] M. Adams, M. Kozlowska, N. Baroni, M. Oldenburg, R. Ma, D. Busko, A. Turshatov et al., Highly efficient 1D triplet exciton transport in a Pd-porphyrin based SURMOF, submitted. [2] X. Liu, M. Kozlowska, T. Okkali, S. Bräse, W. Wenzel, C. Wöll, L. Heinke et al., Molecular photon-cunduction in thin film of metal-organic frameworks, submitted.

Resume : Wastewater remediation is a major concern due to the presence of concentrated, toxic and persistent organic pollutants. To degrade them, classical photocatalysts such as zinc oxide (ZnO) are inefficient, because they need to be activated by ultraviolet (UV) light which has a low penetration depth in turbid wastewaters. Upconverting nanoparticles (UCNP) are a recent technology that are able to generate UV light under near-infrared (NIR) illumination. As NIR light possess a better penetration depth, we developed in this project colloidal UCNP@SiO2@ZnO nanocomposites that combine (i) UCNP: a LiYF4:Yb3 ,Tm3 core (100 nm long and 60 nm large) synthesized by thermal decomposition, that enable in-situ UV light generation under NIR illumination; (ii) @SiO2: a homogeneous thin silica layer (ca. 6 nm) obtained by reverse microemulsion, to protect the core from photocatalytic corrosion; (iii) @ZnO: a loose ZnO overcoating formed by controlled heterocoagulation of UCNP@SiO2 and ZnO nanorods, whose role is to decompose the organic pollutant upon activation by the UV light emitted from the UCNP core. Properties of the obtained colloidal UCNP@SiO2@ZnO nanocomposites were evaluated by Time-resolved microwave conductivity exhibiting good charge carrier lifetime and by Upconversion luminescence showing that the ZnO shell selectively absorbs the UV emitted from the UCNP core. Moreover, promising photocatalytic activities of UCNP@SiO2@ZnO were assessed for dye degradation.

Resume : The low-cost n-type semiconductor hematite represents a promising photoanode material for solar water splitting but several severe limitations persist. The short charge carrier lifetime is for instance misaligned with the optical absorption length and represents therefore the most critical issue. Hence, nanostructured surfaces were proposed, which shall simultaneously provide an enhanced light trapping. Here, we used ambient thermal oxidation to prepare crystalline hematite nanowires and nanoflakes in a very well-controlled manner using low-cost steel foils as substrate. Light trapping can be observed for all structures but the electrochemical performance relies heavily on the synthesis parameters. We also show that the formation of a buried wustite interlayer is for instance a key factor that controls the surface nanostructure evolution. For further in-depth understanding, the surface band structure of nanowires and nanoflakes was reconstructed employing ambient-photoelectron-spectroscopy combined with a Kelvin probe. Both, nanowires and nanoflakes showed pronounced surface Fermi-level pinning, which explains the high recombination rates observed in photoelectrochemical measurements under chopped optical illumination. This method also helps to study and understand surface modifications, which will be discussed, too.

Resume : One of the most persistent problem affecting the twenty-first century is the environmental pollution and the insufficient access to clean and sanitized water. The visible-light photocatalysis (VLP) represents one of the promising environmental-friendly technology, taking advantage in the use of solar-light as clean and renewable source. In this context, the combination of organic photosensitizers with graphene can improve the photocatalytic activity by boosting the separation and transfer of photo-generated charges. We formulated a freestanding material combining polymer porphyrins by -* interaction with 3D-graphene (3DG) [1] via a time-saving etching procedure to remove Nickel substrate. The latter, could constitute a critical issue being released as Ni2+in water during the purification step. Moreover, its removal can determine higher graphene surface exposure to the light irradiation improving the photocatalytic process. The photocatalytic activity of the novel hybrid composite was evaluated by photo-degradation of Methylene Blue. Photoluminescence measurements were performed as well as free radical and hole scavenging measurements. Finally, we propose a photocatalytic mechanism, reporting for the first time the HOMO and LUMO energy levels of poly-porphyrins calculated by electrochemical study. [1] Ussia M. et al, Sci. Rep., 2018, 8:5001