Materials for applications in water treatment and water splitting

Resume : During recent years, the interest in ZnO has grown dramatically because of its promising technological applications, ranging from efficient light emitting devices operating in the blue/UV range and as a transparent conductive and active layer in transparent electronics and PV, to the use in photocatalytic degradation processes for water treatment. The wide range of useful properties displayed by ZnO has been recognized for a long time, including i) a direct wide-bandgap (ii) high solubility of n-type dopants; and (iii) large exciton binding energy and excellent luminescence properties, and (iv) availability of large area substrates promoting epitaxial layer growth. However, the technological advances of ZnO have been hindered by the lack of control over its electrical conductivity. In particular, the formation of stable p-type material remains as a major issue. In this work we review the status of ZnO for device applications, and report on some of the major challenges related to controlling the electrical conductivity during growth and processing. In particular, the self-compensation effect will be addressed, where unintentional impurities like hydrogen and intrinsic defects limits the conductivity of n-type layers and renders p-type challenging to form. For highly n-type layers, a compensating complex between the dopant and a zinc vacancy is shown be incorporated during growth and in processing like ion implantation or in-diffusion. Hydrogen, on the other hand, limits the p-type conductivity, and electrically active defect complexes involving hydrogen will be discussed.

Resume : High power impulse magnetron sputtering (HiPIMS) of a pure Zn target in Ar/N2/O2, gas mixture with low content of oxygen was used to synthesize crystalline ZnOxNy thin films with the nitrogen content ranged from 0 to 6.2 at.%. The optical band-gap decreased with the increase of the nitrogen content of the deposited films from 3.34 to 1.67 eV. Investigation of the water splitting efficiency in visible light (sun light simulated by a xenon lamp) using ZnOxNy films deposited on copper as photo-anode indicated the best activity for the film with a content of 1.5 at.% nitrogen and optical bandgap of 2.95 eV. Interdigital electrodes were deposited on film surfaces in order to investigate the excitation efficiency and life time of photogenerated charge carriers by photocurrent measurements during light irradiation on/off cycles.

Resume : Among the several features of nanostructures, one of the most interesting is the large surface-to-volume ratio, key element for enhancing the material-environment interactions. Still, a good control of nanostructures fabrication is typically obtained with expensive techniques, while low-cost synthesis is often requested for disposable and massive production. ZnO NS are extremely active in gas-, bio-sensing, and in photocatalysis and can be synthesized with a good control via low-cost methods (such as, chemical bath deposition, CBD, involving abundant and non-toxic materials) [1]. Here we report on a novel ZnO nanostructures, named nanowalls (NWs), composed of intertwined nanoplatelets grown vertically on Al covered substrates. NWs have a very large surface-to-volume ratio and can be grown by CBD at 70-90 °C, with hexamethylenetetramine (HMTA) and/or ammonium hydroxide, as pH modifier agents. We investigated the effects of the pH and of a prior Al oxidation on the thickness and quality of ZnO NW film. The growth kinetics was investigated and modeled assuming the formation of an Al hydroxide complex. We demonstrated that a good quality ZnO NWs film can be obtained at low temperatures by using anodized Al. The photocatalytic activity of this low-cost ZnO NWs film was tested in a methyl-orange solution, by UV irradiation, evidencing a remarkable degradation reaction constant of about 2×10-4 min-1. [1] V. Strano et al., J. Phys. Chem. C, Vol. 118, pp. 28189, 2014.

Resume : Semiconductor photocatalysts have recently attracted considerable attention for advanced oxidation processes used in water and wastewater purification. In this field ZnO represents a promising material, due to its remarkable photocatalytic performance, low cost and environmental friendliness. In particular, the photocatalytic efficiency of ZnO nanostructures and metal-ZnO combined systems is improved with respect to that of thin films or bulk material as result of the higher surface area-to-volume ratio of the former and the reduced electron-hole recombination rate of the latter. In this study we originally investigate the photocatalytic performance of ZnO nanofibers (about 100 nm in mean diameter) decorated with Pt nanoparticles (about 30 nm in mean diameter), fabricated by a facile electrospinning method coupled with subsequent thermal treatments. The material was morphologically and structurally characterized by scanning electron microscopy, energy-dispersive X-ray analyses and X-ray diffraction. The methylene blue was employed as a representative dye pollutant to evaluate the ultraviolet photocatalytic activity of the nanofibers. It was found that the Pt-ZnO fibers exhibits a photo-degradation reaction rate that is 55% higher than the one obtained for reference ZnO fibers. These encouraging results demonstrate that Pt-ZnO nanofibers can be fruitfully applied for environmental applications.

Resume : Our group has been involved in the organic functionalization of various types of nanocarbons, including carbon nanotubes, fullerenes and, more recently, graphene. The chemical functionalization represents an important and versatile tool for tuning the chemical and physical properties of the carbon nanostructures (CNS). For example, chemical functionalization can render CNS dispersible in different solvents. During this talk, we will summarize our most recent results in the chemistry and applications of functionalized CNS for the splitting of water.

Resume : Nanomaterials represent a possible solution to solve many of the current issues involving water quality but several limitations exist for efficient applications, primarily concerning the dispersion in water and the resulting impact on human health and ecosystems. In this work, we present polymeric nanocomposites as valid systems to overcome these problems. This new class of materials has attracted extensive attention in the recent years in several fields of science and technology, because they join structural flexibility and relatively simple processing of the polymers with the properties of the nanomaterials, such as the photocatalytic activity of TiO2. We hence embedded active nanostructures in PMMA, with the advantage of no need of recovery of the nanomaterial after water treatment. We combined titanium dioxide with carbon nanotubes, as acceptor systems of electrons, and obtained a significantly higher photocatalytic efficiency under UV irradiation, compared to the systems with TiO2 only. Furthermore, we synthesized operative materials even under visible light thanks to the functionalization of TiO2 surface with Porphyrin as dye sensitizer. We realized these polymeric nanocomposites by sonication and solution casting method, and we evaluated their photocatalytic activity with the current ISO10678:2010 test by degradation of methylene blue in an aqueous medium. We tested the antibacterial activity through CFU count using Escherichia coli as a model organism.

Resume : Carbon nanotubes (CNTs) have extraordinary properties, such as high thermal conductivity and electric-current carrying capacity. Besides, their large specific surface area and excellent mechanical and chemical properties make CNTs extremely interesting for the use in filtration. The main difficulties of using CNTs in filtration are however handling and retrieving of the CNTs. We suggest a novel route by modifying commercially available porous membranes by directly growing CNTs inside the pores. In this work, well-aligned CNT bundles were grown by means of the catalytic chemical vapor deposition (CVD) technique using a porous anodized aluminium oxide (AAO) membrane as substrate. We elaborated a novel process to have the porous channels parallel with the gas flow so that CNTs grow inside the pores and align with the channels. We systematically investigated the growth parameters and identified the catalyst deposition as well as the AAO surface morphology as the major obstacles to tackle. Also the high density of CNTs can lead to gas obstruction and terminate the growth. By reducing the concentration of the catalyst solution the CNTs density and length can be tuned. The as-grown CNTs were characterized by Raman spectroscopy and transmission electron microscopy. Especially 3D electron tomography combined with energy dispersive X-ray chemical analysis gave detailed information about the CNTs growth on the nanoscale. This newly developed process to fabricate CNTs/AAO hybrid membranes has high potential for water filtering applications.

Resume : Disruptive technologies are usually characterised by universal, versatile applications, which change many aspects of our life simultaneously, penetrating every corner of our existence. In order to become disruptive, a new technology needs to offer not incremental, but dramatic, orders of magnitude improvements. Moreover, the more universal the technology, the better chances it has for broad base success. Does graphene have a chance to become the next disruptive technology? Can graphene be the material of the 21th century? Are the properties of graphene so unique to overshadow the unavoidable inconveniences of switching to a new technology, a process usually accompanied by large R&D and capital investments? In spite of the inherent novelty associated with graphene and the lack of maturity of graphene technology, a roadmap can be envisaged, including short-term milestones, and some medium- to long-term targets, intrinsically less detailed, but potentially even more disruptive. This should guide the transition towards a technological platform underpinned by graphene, with opportunities in many fields and benefits to society.

Resume : Heterogeneous photocatalysis has been shown to be effective for the inactivation of a wide range of microbiological species. Titanium dioxide is a good photocatalyst but requires UV which is only 4% of the solar spectrum. One approach to improving the solar efficiency of TiO2 is modification with graphene. In this work, titania- reduce graphene oxide composites (TiO2-rGO) were prepared by the photocatalytic reduction of exfoliated graphene oxide (GO) using P25 (Evonik-Aeroxide) as the photocatalyst. The composites were tested for the inactivation of E.coli as the model microorganism in a stirred tank reactor under UV-vis and visible only irradiation. The results showed a 5 log inactivation of E. coli after 120 min with P25 and 90 min with TiO2-rGO under UV-vis irradiation. Under visible light only irradiation, the TiO2-rGO gave a 5.3 log-reduction following 180 min of treatment but only a 1 log reduction with P25. The reactive oxygen species produced by the composites were investigated using different probes. The results indicate that the main ROS involved in the photocatalytic disinfection with TiO2-rGO composites were hydroxyl radical and singlet oxygen under UV-Vis irradiation, but only singlet oxygen under visible irradiation.

Resume : The photocatalytic properties of graphene oxide flakes functionalized with 3-amino-1-propanesulfonic acid (denoted as GOSULF) as powder or incorporated into a polymeric membrane such as Nafion (DuPont) were studied for water purification applications. Nanocomposite Nafion-GOSULF membranes were prepared by the solvent casting method. Scanning electron microscopy was used to verify the homogeneous dispersion of the nanomaterials into the polymeric membranes. The photocatalytic activity of such nanocomposite membranes and GOSULF powder was investigated by measuring the degradation of methylene blue (MB) and methyl orange (MO) under UV/visible or visible light illumination. The degradation of the azo dyes depends on the mutual interaction between GOSULF flakes and the polymeric matrix: Nafion-GOSULF strongly reduces MB both in dark and illumination condition in the same way than GOSULF powder, while Nafion-GOSULF is more efficient than GOSULF for MO degradation. Therefore, the advantage of embedding nanomaterials in a membrane is the possibility to reuse the same the photocatalytic materials several times. As a comparison for MO degradation efficiency, TiO2 nanoparticles dispersed in solution or embedded in a Nafion membrane were studied. During the photocatalytic degradation, TiO2 induces the formation of toxic by-products that are not observed by using GOSULF, that can be an advantage for the use of GOSULF in the safe removal of pollutants from water.

Resume : Carbon nanostructures have been already used as high-capacity and selective sorbents for organic solutes in aqueous solutions. In particular, graphene oxide (GO) and reduced graphene oxide (RGO) have been used as scaffold materials for photocatalytic nanoparticles showing higher binding capacity for different water contaminants than free nanoparticles. Furthermore, GO has shown photocatalytic properties and the ability of enhancing the activity of known photocatalyst as TiO2. This work reports the preparation of RGO by pulsed laser irradiation starting from commercial GO solutions or GO prepared by the modified Hummers method, in order to investigate any modifications of the photocatalytic properties after the reduction. Pulsed laser with visible wavelength (532 nm) is suitable to finely tune the degree of reduction and tailor both the hydrophilicity and the spectroscopic features of the final GO suspension. In addition, in this work pulsed laser irradiation is also used for producing mixed solution of GO and RGO with P25 titania. The produced materials are characterized by scanning electron microscopy (SEM), infrared and Raman spectroscopy. The photocatalytic activity is investigated by studying the decolorization of methylene blue and methyl orange solutions under UVA-visible and visible irradiation.

Resume : In the frame of photocatalysts for water purification, TiO2 has gained great attention due to its abundancy, high activity, stability and safety. Different structures and morphologies have been produced and studied, such as powders, nanotubes, nanoparticles, films and many efforts have been spent to reach good efficiency even under visible illumination. Indeed, it has been demonstrated that the presence of metal nanoparticles (NPs) improve the visible conversion efficiency of TiO2 due to their Localized Surface Plasmon Resonance properties. In this sense, Au and Ag are of particular interest since exhibit excellent plasmonic properties, with resonances in the visible range. In this work, metal NPs loaded on TiO2 films are obtained via sputtering, ion implantation, thermal and laser treatment. Optical and structural analyses of nanocomposite films having different designs allow us to evaluate the impact of the embedding matrix, crystal phase (anatase or rutile), surface coverage, size and plasmonic response of the metal NPs on the photocatalytic activity of the nanocomposite films under UV and visible illumination.

Resume : Anatase nanostructured TiO2 film (a-nTiO2), rutile TiO2 nanorods (r-TNR) and hybrid r-TNR/a-nTiO2 were prepared, respectively. All of the films were prepared using hydrothermal method and spray pyrolysis deposition method. These nanostructured semiconducting oxide films were used for its photocatalytic activity for the treatment of textile factory waste water treatment. From the results, hybrid r-TNR/a-nTiO2 has exhibited the highest photocatalytic activity for the degradation of textile factory waste water as supported by the results of surface area, band gap and porosity of the TiO2 films.

Resume : Nowadays, photocatalytic nanoparticles are used in application including air and wastewater treatment, self-cleaning, chemical weapon decontamination, etc. Ink-formulations based on these particles are a more recent approach that has the advantage of easy deposition technology. In this study, aqueous and aqueous-alcoholic/alcoholic dispersions of TiO2 Degussa/TiO2 obtained by sol-gel method are prepared in a two-step procedure: stirring under magnetically stirring to insure the nanoparticles wetting followed by ultrasonication. To minimize the nanoparticle‘s agglomeration driven by van der Waals attractions, surface modifications are targeted by adding different surfactants (cationic-DTAB, anionic-SDS, neionic-PEG/Tween or their mixtures) and/or polymers (polyvinylpyrrolidone/polyvinylalcohol) as stabilizers. The influence of the nanoparticles concentration, the ionic strength, pH, the solvent and the surfactant (STA)/polymer on the dispersion stability was studied using UV-Vis transmittance spectra as quantitative criteria. Stabilization mechanisms are proposed and discussed considering the interactions of the stabilizers at the particle/liquid interface and the double layer formation/modification and charge in the presence of solvent. These allow recommendation on the preparation and use of the photocatalytic inks TiO2-based.

Resume : TiO2 is one of the promising materials for photocatalytic applications under intense research. Theoretically, maximum solar energy conversion degree for a catalyst with 3.2 eV wide band gap is approximately 1% and could be increased up to 15% for a catalyst with a 2.2 eV band gap. Various doped TiO2 nanostructures have already shown improved efficiencies because inclusion of dopants leads to reduction of band gap from ~3.2 eV (pristine material) to ~2.0 eV. To shed more light on changes of the electronic structure induced by inclusion of dopants, we have performed ab initio simulations of TiO2 nanotubes. Earlier we studied 9-layered (001) TiO2 anatase nanotubes possessing the negative strain energy. S-doped nanotube yields the most promising results. In this study, we simulate anatase nanotubes with (101) morphology, choice of which is motivated by the highest stability of this surface amongst TiO2 slabs. Simulations of S and N co-doped 6-layered (101) TiO2 anatase nanotubes have been performed using DFT method combined with the hybrid exchange-correlation B3LYP functional. We also discuss a strategy in order to reduce the size of our model. For smaller nanostructures, more precise calculations can be performed in a shorter time, as well as more complicated methods can be applied for their simulations, such as molecular dynamics and calculation of excited states. Both will provide comprehensive information on phenomena underlying the material’s photocatalytic properties.

Resume : Metal oxide semiconductors hold great promise for applications in energy conversion and storage, environmental remediation, and other areas. However, critical factors such as the high rate of charge-carrier recombinations and limited light absorption have restricted more practical and viable applications (Saji et al, 2013). Plasmonic nanostructures of noble metals have been attracting significant attention for their ability to interact with light from visible to near IR range through the creation of resonant surface plasmon (Stewart et al, 2008). Plasmonic nanostructures of noble metals in combination with semiconductors offer a promising future for the next generation of energy needs. Various methods have been described for the synthesis of TiO2 and metal nanoparticles hybrid. In this study, GNPs were fabricated in a thin film of nanocrystalline TiO2 by sol-gel spin coating method. The thickness can be adjusted by repeating the cycle from adding the Titanium alkoxide precursor on the substrate after calcination at 450˚C. The morphology of the nanocomposite and the phases of the films were determined by SEM and Raman. The interaction with noble metal and semiconductor nanostructures under visible light is investigated. Particularly, we study the photocatalytic degradation of Methylene Blue (BM) and Bisphenol A (BPA) under visible light using Au-TiO2 and Au-ZnO as photocatalysts. Green laser emitting at 532 nm was used to excite the resonance band of the GNPs. The influence of various parameters such as irradiation time, laser power, and catalyst type and amount has been studied. References Saji Thomas Kochuveedu, Yoon Hee Jang and Dong Ha Kim (2013) A Study for the interaction of ligh with noble –metal oxide semiconductor nanostruc-tures for various photophysical applications, RSC publishing, Chem soc Rev. Stewart M.E , . Anderton C.R, Thompson L.B, Maria J, Gray S.K, Rogers J.A and Nuzzo R.G (2008) Nanostructured plasmonic sensors, Chem. Rev,108,494.

Resume : Household- and industrial waste left at landfill sites contains a great variety of organic pollutants, which ends up in leachates and enters the hydrosphere through percolation. For the above-mentioned problems heterogeneous photocatalysis is a promising alternative. Different semiconductor photocatalysts were obtained, such as TiO2-Au/Pt composites and Bi2WO6. Their characterization was performed using different techniques, such as XRD, DRS, SEM and TEM. Several photocatalytic tests were carried out, such as the removal of different model pollutants (phenol, oxalic acid). These results were used to adjust the materials’ properties to be able to degrade real garbage dump leek waters, while degradation intermediates (HPLC-MS) and TOC values were systematically monitored. The best photocatalyst was tested under real conditions in Pata Rât, Cluj county, Romania (15 km east from Cluj-Napoca). In this neighborhood a toxic waste landfill is present, while circa 1500 Roma people live here. Their living conditions are inhuman, acquiring heat through waste-burning, without cold water, and few of homes are in lack of electricity. Due to the toxic environment, the pollution of their surface waters is high, while the access to potable water is limited. This work was supported: by a grant of the Romanian National Authority for Scientific Research, CNCS—UEFISCDI, project number PN-II-ID-PCE-2011-3-0442; and by the College of Student Excellence of Babeș-Bolyai University, project CHEAP-A.

Resume : TiO2 is a well-known photocatalytic material. Its combination with plasmonic nanoparticles (NPs) has been demonstrated in the literature in various ways. A vast majority of the publications have focused on reactions involving photocatalytic decomposition of organic compounds and water splitting. However, there is little evidence on the efficiency of such composite materials in the intermediate photo-oxidation step required to achieve the removal of heavy metals during water purification (e.g. As, Mn). In the present study we investigate the enhanced photocatalytic activity of TiO2 (Eg=3.2 eV) and TiOxNy (N content set to provide samples with Eg either 2.8 eV or 2.4 eV) with optically active Ag and Au NPs towards oxidation of As and Mn aqueous species. The photocatalytic templates were immersed on aqueous solutions of As(III) and Mn(II) oxy-anions. For the illumination of the samples we used a white LED lamp. XPS has been used to identify the retention of the metal ions and their oxidation state during photocatalysis. We demonstrate that the performance of the photocatalysts is a strong function of the Eg of the semiconductor and the properties of the NPs. This can be explained by the specific optical activity of the Ag or Au NPs on top of the different photoactive materials. We show that by tailoring the Eg and the size of the NPs it is possible to maximize the photochemical activity of a semiconductor and create more efficient devices for heavy metal purification of water.

Resume : Metal foams exhibit unusual properties compared to bulk materials, which are attractive for several applications such as sound dampeners and impact-energy absorbers. Furthermore, biocompatible metal foams can be applied as bone prosthetics. A new application, not yet extensively exploited, is as drinking water Cr purifier in filters. During this process, water is conducted through the porous network of the foam where by an electron exchange mechanism, hexavalent Cr is reduced to trivalent species forming an insoluble hydroxide. High porosity and nanostructured morphology are the main features that a foam component must have in order to ensure high density of reducing sites in the final product. In this work, Cu-Zn foams were fabricated by a sequence of electrochemical and cold pressing methods. Two different approaches were followed; in the first one, foams consisting of a homogeneous Cu-Zn alloy were obtained from metallic powders produced by a high voltage electrodeposition. Mixtures of metallic powders, at various compositions, were synthesized directly by the two-step electrodeposition in CuSO4 and ZnSO4 solutions or by the separate production of Cu and Zn powders by the same method and manually mixing. The corresponding foams were prepared by a space-holder technique and proper thermal treatment. The second approach involved the fabrication of Zn-coated Cu foams by using a Cu foam as the substrate/electrode for the electrodeposition of Zn in a ZnSO4 solution. The obtained foam materials were structurally and chemically characterized while Cr(VI) adsorption tests were carried out for their technological evaluation. Financial support by Research Committee of Aristotle University of Thessaloniki is gratefully acknowledged.

Resume : Currently, semiconductor photocatalysts have attracted increasing interest by owing to their potential in solving environmental problems. ZnO nanoparticles are widely investigated for efficient disinfection and microbial control of the wastewater by advanced oxidation processes (AOP) used as treatment technologies. This paper reports on the synthesis of iron-doped zinc oxide (Fe:ZnO) nanoparticles through precipitation method at low temperature followed by thermal treatment. Fe:ZnO nanoparticles were characterized by X-ray diffraction (XRD), scaning electron microscopy (SEM) and ultraviolet-visible (UV–Vis) spectroscopy. The effect of iron content on structural and morphological properties of obtained doped ZnO nanoparticles has been reported. The photocatalytic activity of the nanoparticles was tested by degradation of methylene blue (MB) solution under UV light for 60 min irradiation. The antimicrobial activity of the Fe:ZnO nanoparticles, determined by using the paper disc method on Mueller-Hinton agar against the Gram-negative bacteria, Escherichia coli (E. coli) and the Gram-positive bacteria, Staphylococcus aureus (S. aureus), was compared to that of undoped ZnO. Consistent improvement on the photocatalytic and antimicrobial activity of Fe-doped ZnO nanoparticles was noticed.

Resume : Nano zinc oxide (ZnO) and Gallium doped zinc oxide (GZO) nanopowders were synthesized by sol–gel method from pyrogallol and formaldehyde (PF) mixtures in water using picric acid as catalyst. Gallium doped zinc oxide (GZO) were prepared at different Ga concentrations from 1 wt% to 3 wt%. The obtained nanopowders were characterized by transmission electron microscopy, X-ray diffraction and nitrogen porosimetry. The objective of this work is to find a new and highly efficient nanomaterial for the adsorption of heavy metals. For this reason, the nanopowders were used to uptake heavy metals from aqueous solution. The obtained results show that the incorporation of Ga in nanoparticles zinc oxide (ZnO) increases the capacity adsorption of nanopowders. In this work we studied also the equilibrium isotherms, adsorption reaction kinetic and mechanisms as well as, effect of initial concentration, pH values and temperature on the removal of heavy metal ions from aqueous solution by GZO

Resume : Superhydrophobic surfaces are often found on the plants leaves and insects wings in nature. Till now, inspired from nature, researchers have tried to prepare artificial superhydrophobic surfaces and to employ them for various practical applications such as protective coating for electronic circuit devices, self-cleaning and anti-contamination coatings for solar panels/smart windows. ZnO nanowires (NWs) were synthesized by chemical vapor deposition method. These ZnO nanowires were dispersed on different transparent substrates like PDMS, glass and quartz. The contact angle was found to be greater than 150° with more than 70 % transparency on these substrates after ZnO nanowires coating. The CA show transition from superhydrophobic (CA~155°) to superhydrophilic (CA~0°) under UV light exposure. The defects responsible for water repellent nature of ZnO NWs are investigated by using Photoluminescence, Raman and FTIR measurements. Also, the transition in CA from superhydrophobic to superhydrophilic on ZnO NWs is investigated in the presence of UV-light and in three different atmospheres; air, O2 and H2 gases. The rate of transition of CA with UV exposure is highest in O2 atmosphere. The observed results indeed show that oxygen rich surface of ZnO NWs is more favorable for water wetting. Here we provided a clear idea about the defects responsible for wetting of ZnO nanowires and a facile route to prepare transparent superhydrophobic surfaces which can be used in future nanodevices.

Resume : GaSe (Eg = 2 eV at T = 300 K) is a promising material for usage in THz electronics, as the basis of various optoelectronic devices, a matrix for hydrogen storage, substrates in planar nanotechnologies, etc. GaSe crystals are insoluble in water. It is generally accepted that a cleaved surface (0001) of GaSe is perfect not only from the viewpoint of geometrical structure but also is nonwettable and inactive to sorption processes of the foreign impurities. In this communication for the first time we demonstrate that the exposure of GaSe single crystals in distilled water under daylight illumination at room temperature leads to decreasing the electrical conductivity of the water by more than order of magnitude. As follow from the investigations (AFM images and XRD measurements) the deionization of distilled water is connected to a partial transition of GaSe into an ionic condition (the formation of Se vacancies and of selenium acids (H2SeO3, H2Se, H2SeO4), an etching of dislocations on cleaved surface (0001) of GaSe, the formation of reaction products between selenium acids and semiconductor substrate including amorphous gallium hydroxide). It is found that the dissolution of GaSe in distilled water is initiated on the cleaved surface (0001) of the crystals and does not occur when single crystals with a damaged (0001) surface or powdered samples of GaSe were used.

Resume : New hybrid clay adsorbent based on kaolinite clay and Carica papaya seeds with improved cation exchange capacity (CEC), rate of heavy metal ion uptake, and adsorption capacity for heavy metal ions were prepared. The CEC of the new material is ca. 75 meq/100g in spite of the unexpectedly low surface area (≈ 9 m2/g). Accordingly, the average particle size of the hybrid clay adsorbent decreased from over 200 m to 100 m. The hybrid clay adsorbent is a highly efficient adsorbent for heavy metals. With an initial metal concentration of 1 mg/L, the Hybrid Clay adsorbent reduces the Cd2+, Ni2+, and Pb2+ concentration in aqueous solution to ≤ 4, 7, and 20 g/L, respectively, from the first minute to over 300 minutes using a fixed bed containing 2 g of adsorbent and a flow rate of ≈ 7 mL/min. These values are (with the exception of Pb2+) in line with the WHO permissible limits for heavy metal ions. In a cocktail solution of Cd2+, and Ni2+, the hybrid clay shows a reduced rate of uptake but an increased adsorption capacity. The CEC data suggest that the adsorption of Pb2+, Cd2+ and Ni2+ on the Hybrid Clay adsorbent is essentially due to ion exchange. This hybrid clay adsorbent is prepared from materials that are abundant and by a simple means that is sustainable, easily recovered from aqueous solution, non-biodegradable (unlike numerous biosorbent) and easily regenerated but a highly efficient alternative to activated carbon for water treatment.

Resume : Urea is a non-toxic, non-flammable hydrogen carrier which can be easily transported, stored and recovered from wastewater. Electro-oxidation of urea in the presence of a Ni catalyst is considered an effective approach for hydrogen production via urea decomposition. In this work, three different catalysts based on Ni metallic particles (Ni/C, Ni/SWNTs, Ni(OH)2,) were synthesized, characterized and used as catalyst incorporated in an ionic membrane electrode assembly (MEA) for urea electro-decomposition in dedicated fuel cells. The physico-chemical properties of catalysts were investigated by Scanning Electron Microscopy, RamanSpectroscopy,Chrono-amperommetry and Cyclic Voltammetry. Electrochemical measurements showed that Ni is promising alternative catalyst material for applications in wastewater treatment, hydrogen production and fuel cells.

Resume : Hexavalent chromium Cr(VI) is regarded as hazardous due to its mutagenicity and carcinogenicity to living organisms, and its facile solubility in neutral water provides both mobility and bio-accessibility. Because the maximum allowed limit of Cr(VI) is strictly regulated for many water sources around the world, simple and fast detection methods are necessary to monitor and maintain Cr(VI) concentrations in environmental waters at lower than limited levels. Recently, layered rare earth hydroxides (LRHs), composed of alternately stacked rare earth hydroxocation layers and anion layers, have been attracted as a promising material for the detection and removal of heavy metal-oxoanions due to their adsorption ability and selectivity. Here, we have demonstrated a Tb-doped layered yttrium hydroxychloride (LYH:Tb) sensor as a representative example of LRH adsorbents for the detection of Cr(VI) (both HCrO4− and CrO42− forms) based on the inner filter effect (IFE). The effective shielding of excitation light for LYH:Tb by adsorbed Cr(VI) could achieve a feasible IFE-based detection sensitivity. The striking contrast in the brightness of green emission before and after adsorption of Cr(VI), which is distinguishable even with the naked eye, would enable LYH:Tb powder to be exploited as a simple and sensitive portable kit for field detection of Cr(VI) for monitoring chromium contamination at low concentration levels in natural surface water bodies or wastewater treatment plants.

Resume : In 21th century, rapid industrialization increases different toxic the heavy metals like As (V), Hg (II), Cd (II) and Cr (VI) in the ground water. Among these, Cr (VI) has been identified as one of the most hazardous metals to living organism due to its carcinogenic and strong oxidizing property. According to WHO, allowed limiting concentration of Cr(VI) is < 100 μ g/L in drinking water. Mainly in tannery based area, Cr(VI) conc. is quite high in ground water. Different physical techniques like ion-exchange, cyanide treatment, reverse-osmosis, electro-chemical precipitation are used so far to remove those toxic metals but the results are not so promising. Recently, adsorption technique has become very popular because of its several advantages like easy process, high efficiency and good recycling ability. Although, different nano materials have already been applied for this purpose, results are not upto the mark. After revolutionary discovery of graphene, it has taken a great interest in modern research fields. Possessing a monolayer of carbon atoms with honey comb structure, graphene is considered as the most suitable material for this adsorption purpose as it possesses very high specific surface area and excellent stability in aqueous medium. Recently, functionalization of graphene oxide has been carried out to remove different toxic metals including Cr(VI) from water, but they are mainly effective for low concentration. To make more effective in high concentration as well as time consumption limit for modern filtration units, we have designed a new polymer compound on graphene surface. In the present work, we have polymerized 2, 6-diamino pyridine for the first time insitu on graphene oxide surface by mutual oxidation reduction mechanism to prepare poly 2, 6-diaminopyridine/graphene (PDAP/RGO) composite. We have doped sulphate ions on polymer chains during polymer synthesis. We have characterized the material by FTIR, RAMAN, XPS, TGA, UV and SEM analysis. This material shows large specific surface area of 328 m2/g. With highly porous surface, we can use this composite as an efficient adsorbent to enhance Cr(VI) removal efficiency. Now, we can easily remove high concentration of Cr(VI) (500 mg/L) within 4 h and 50 mg/L Cr(VI) in quick 30 min using 1 g/L adsorbent dose at pH 1. With increasing adsorbent dose, we can decrease the removal time. With 1.5 g/L adsorbent dose, it takes only 100 min to remove 500 mg/L Cr(VI). High surface area and presence of nitrogen groups help this material to give such high adsorption capacity of 610 mg/g. Using nitrogen containing graphene adsorbent, there is some problem to remove Cr(VI) at basic condition as their removal efficiency decreases drastically with increase in pH of the solution. While, we have achieved to overcome this problem with our prepared sulphate ion doped polymer composite. It shows ~71, 59 and 46% removal efficiency at pH 5, 7 and 9 respectively. At basic condition, facile anions exchange between mobile sulphate dopant and chromate ions helps to increase Cr(VI) removal efficiency. We have successfully demonstrate from XPS and AAS measurements that our prepared material mainly follows reduction mechanism at higher acidic condition while anions exchange mechanism at lower acidic condition during this removal experiments. Our prepared material shows good recycling ability with ~92 % removal efficiency after fifth cycle. Our material is also pretty selective towards Cr(VI) as it shows quite high removal efficiency in presence of other coexisting ions in water. Finally, we believe this study will provide a good impact for waste water purification particularly in industrial areas where Cr(VI) concentration is relatively high in ground water.

Resume : In photocatalytic applications such as solar disinfection or water splitting, efficiencies can be increased by reducing electron-hole charge recombination, thereby increasing lifetimes of excitons. One approach to achieve this is to couple two or more appropriate photoactive materials into a heterojunction device, where the materials work in tandem to enhance charge separation. In this work, we will discuss how robust, bilayer heterojunction photodiodes (Figure 1a) were prepared by a simple, low-cost powder pressing technique followed by heat-treatment. The monoliths comprised of single layers of TiO2 and WO3, and showed efficient vectorial charge separation. Consequently, the photodiodes displayed enhanced photocatalytic degradation towards stearic acid, compared to the respective individual materials as a monolith. The heterojunctions were also evaluated for the photocatalytic disinfection of water, where favourable kinetics were observed compared to a single TiO2 monolith, for the inactivation of gram-negative bacteria. We will also discuss the degradation of organic dyes and the structure-property-composition relationships in doped nano-zinc oxides, which are of interest in solar UV protection (Figure 1b), and were prepared by a novel high-throughput continuous hydrothermal flow synthesis (CHFS) process.

Resume : The quest for Vis-active photocatalytic materials and working systems led to various solutions, supporting the process efficiency, towards mineralization. This involves the pH-adjustment (supporting the pollutant adsorption on the photocatalyst) and the addition of electron trappers, as H2O2. While these may be effective on the process efficiency, they also can have photo-corrosion as side effect, thus reducing the chances for the final goal: up-scaled photocatalytic processes. The paper presents a three-layered tandem system of SnO2/CuxS/TiO2, and proved its Vis-activity in the photocatalytic mineralisation of methylene blue (MB) and phenol. In optimised conditions, after 6 hours, MB mineralisation reaches 77% for total carbon removal and 66% for total nitrogen removal. The effect of pH (3?.9) is comparatively analysed considering the electrostatic interactions substrate ? pollutant (based on pzc and pKa), the speciation of the mineralisation species (particularly the pH-dependent equilibria) and the photocatalyst stability (evaluated based on changes in surface morphology and optical transmittance). Two parallel experimental sets are further discussed, with and without H2O2 addition. The results show the need to optimise the photocatalytic process design with a compromise between the electrostatic attraction and the photo-corrosion conditions.

Resume : Iron(III) oxide has emerged as a platform material the properties of which can be improved by doping and surface functionalization towards the photoelectrochemical oxidation of water. In this paper, we systematically study the geometric effects of nanostructuring a pure Fe2O3 surface on its electrochemical water oxidation performance at neutral pH. Atomic layer deposition (ALD) is used to coat the inner walls of cylindrical 'anodic' nanopores ordered in parallel arrays with a homogeneous layer of iron(III) oxide. Annealings and electrochemical treatments generate a roughened surface, as demonstrated by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS), which increases its geometric area and concomitantly the current densities. Combining these treatments with the 'anodic' pore geometry delivers a stabilized current density of up to 60 µA cm–2 at η = 0.48 V overpotential. This represents an effective turnover increase by three orders of magnitude with respect to the smooth, planar iron(III) oxide surface delivered by ALD. The current density depends on the pore length in a non-monotonic manner. A certain optimal length is found which maximizes steady-state electrochemical current density by equating the rates of charge transport towards the interface and of charge transfer across the interface, as demonstrated by EIS.

Resume : Perovskite bismuth ferrite (BiFeO3) has garnered significant attention over the past few years due to its outstanding ferroelectric and antiferromagnetic properties. Recently, it has been reported that BiFeO3 could be promising photocatalyst due to its visible light response, high chemical stability and internal electric field produced by local ferroelectric polarization. Here we report, for the first time, the synthesis of high-surface-area mesoporous BiFeO3 semiconductor via nano-replication technique, using mesoporous carbon as hard template. Characterization by X-ray diffraction, transmission electron microscopy (TEM) and N2 physisorption measurements showed that the template-free material has a hexagonal honeycomb structure with large internal surface area (141 m2g-1) and uniform pores (ca. 4 nm). Also, the pore walls comprise single-phase BiFeO3 nanocrystals according to the high-resolution TEM, electron diffraction and magnetic studies. This material shows high activity for the photocatalytic oxygen evolution reaction (OER) under UV-visible light (λ>380 nm), affording an average O2 evolution rate of 66 µmol·h-1g-1. We also show that the propensity of photogenerated holes for OER can be significantly enhanced when 1% Au NPs are deposited on the pore surface of BiFeO3. The mesoporous Au/BiFeO3 heterostructure reach excellent OER activity (586 µmol·h-1g-1) and long-term cycling stability, raising the possibility for the design of effective and robust OER photocatalysts.

Resume : Physical vapor deposition techniques are proposed as highly performing and easily tunable ways to synthesize mixed-metal oxides thin films as catalysts for the water oxidation reaction. The search of efficient catalysts for the oxygen evolution reaction is a key point to develop economically viable hydrogen production technologies. Water oxidation catalysts based on abundant first-row transition metals are currently studied in the scientific community since they are cheap and environmentally friendly materials. Recent systematic studies on iron, cobalt and nickel oxides thin films obtained by chemical deposition techniques have experimentally shown the good potentiality of mixed-metal oxides. Binary and ternary metal oxides thin films based on iron, cobalt and nickel are currently under study in our laboratory, using different physical vapor deposition techniques. These strategy allow us to have a good control on the films surface morphology and crystallinity, with good adhesion of the catalysts on the electrodes. The prepared samples are systematically studied through SEM microscopy, Raman spectroscopy, XPS analysis and the electrochemical characterization of the catalysts has been carried out to explain the relevance of synergic effects of mixed oxides in water oxidation reaction.

Resume : We propose novel composite systems that comprise secondary building units of two different compounds. These systems are designed with the aim of electron–hole separation, which is a process of fundamental interest in electrochemistry, photocatalysis, and optoelectronic devices. The main building block in this class of material is a “bubble”, or a cage, which may be inserted into another bubble forming a double bubble. A zeolite-like framework of such double bubbles possesses excellent electronic properties, which we demonstrate for the zinc oxide and gallium nitride secondary building units using ab-initio approaches. Enthalpies of formation for all systems are comparable with fullerenes.

Resume : Hierarchical or quasi-1D TiO2 nanostructures obtained by pulsed laser deposition (PLD) were tested as photoanodes for hydrogen production by photoelectrochemical water splitting. Their morphology could be controlled by performing the deposition at different O2 background pressures, obtaining vertically oriented nanoparticle assemblies with amorphous structure and varying density, whereas the effect of thermal treatments at different temperatures on the crystallization process has been investigated, obtaining mainly a nanostructured anatase phase. BET, SEM and Raman spectroscopy were employed as characterization techniques, while the photoelectrochemical water splitting performances were investigated by monitoring the photocurrent produced under illumination in a three-electrode cell. A direct connection between structural-morphological properties and photoelectrochemical response was evidenced, allowing the identification of an optimum procedure for both the deposition and thermal treatment, leading to quasi-1D TiO2 nanostructures characterized by nanoscale porosity, large surface area and preferential charge transport. We also discuss further strategies, currently under investigation, to extend the photoresponse towards the visible range, by means of a hydrogenation or reducing treatment, aiming to the formation of the so-called black titania with an optimized morphology.

Resume : The technological vision of solar energy conversion to generate solar fuel relies on semiconductor material combinations with high photon-to-current conversion efficiency that can operate under visible light illumination, where the Sun emits its maximum energy (λmax = 600nm). In this regards, surface disor¬dering at nano-level by hydrogen treatment is a promising tool for altering the optical absorption and carrier transport in metal oxide nanocatalyst which can be used an efficient photoelectrode in photoelectrochemical cell for solar energy harvesting. Here, we demonstrate that by treating white TiO2 nanocrystals with mild hydrogen under vacuum condition creates the disordered surface with colour change to black for the solar-driven photoelectrochemical water splitting. In the present work, we have prepared TiO2 nanocrystals by hydrothermal method using titanium tetra isopropoxide as the starting precursors and treated with mild hydrogen under vacuum at 300oC. The photocatalytic feasibility of the material was evaluated by UV-Visible spectroscopy which displayed long wavelength absorption. High optical absorption, high carrier density and low recombination in vacuum hydrogen treated TiO2 nanocrystals exhibits the excellent photocatalytic performance in photoelectrochemical water splitting for hydrogen production. Further, the effect of surface disordering by vacuum hydrogen treatment in TiO2 nanocrystals on optical, electrical and photoelectrochemical will be discussed.

Resume : The synthesis and the activity of composite photocatalysts are intensively studied research fields in material science. The reason behind the great interest is that these represent a promising solution for the wastewater treatment and H2 generation as well. One of the best performing photocatalysts are the composites based on semiconductors and noble metals. In the present work, Au and Pt nanoparticles were deposited on three different commercial titanias: Evonik Aeroxide P25, Aldrich anatase and Aldrich rutile. The deposition order (TiO2→Au→Pt, TiO2→Pt→Au and TiO2→Pt and Au) and the ratio of Au and Pt were varied, while the impregnation and in situ methods were used. For these composites the photocatalytic activity (oxalic acid degradation) and photocatalytic hydrogen production capacity was evaluated under UV irradiation. The morpho-structural and optical properties were investigated by using SEM, DRS, TEM, HR-TEM and XRD methods. The correlation between the different synthesis approaches, structural/morphological peculiarities and photocatalytic activity was successfully examined. Acknowledgments: This work was supported for the Romanian authors by a grant of the Romanian National Authority for Scientific Research, CNCS—UEFISCDI, project number PN-II-ID-PCE-2011-3-0442. The Hungarian authors express their gratitude to the grant from Swiss Contribution (SH/7/2/20)

Resume : ZnO-TiO2 oxide thin films were prepared in electro-deposition baths with three electrodes. The electro-deposition baths solutions contain ZnNO3 with different concentrations (0, 1, 2, 3 and 4 mM) and NaOH (0.1M) as host composition. The TiO2 work electrode is kept at – 1 Voltage v.s Saturated Calomel Electrode. The morphology, structure and electrochemical properties are investigated using atomic force microscopy, X-ray diffraction, photoluminescence spectroscopy, and photo electrochemical measurements. Compared with the pure TiO2 electrodes, these TiO2-ZnO hybrid films demonstrated a higher photo-electrochemical and phocatalytic activity and the optimum was registered for a concentration of Zn equal to 2 mM.

Resume : Photochemistry of organic dyes adsorbed or chemisorbed at the surface of wide bandgap semiconductors is determined by several possible pathways of excited states deactivation. A possible fate of the excited molecule involves the electron transfer from the dye to the conduction band. This process, considered as a key step of semiconductor photosensitization, opens a possibility to use such hybrid systems as photocatalysts, photovoltaic or optoelectronic materials. The goal of this research was to search for hybrid photomaterials based on organic dyes and TiO2 which could offer a visible light induced catalytic activity and/or visible light induced generation of current for optoelectronic or photovoltaic applications (photoelectrochemical logic devices and sensors, dye sensitized solar cells). For our studies we have selected three organic dyes. Their adsorption was optimized by controlling the hydrophilicity of titania surface. Photoactivity was monitored through photocurrent measurements as a function of the electrode potential and incident light wavelength. All tested dyes sensitized TiO2 towards visible light. The highest values of photocurrent were measured for samples based on hydrophobic TiO2 T-805. The mechanism of photosensitization was studied basing on photoelectrochemical and spectroscopic measurements. Fluorescence spectra and determined lifetimes of excited states revealed the mechanism of the photoinduced electron transfer within the studied systems.

Resume : Semiconductor photocatalysis is a promising strategy to produce hydrogen by water splitting by using solar light irradiation. In addition to its environmental compatibility, its ease of production and its low cost, iron oxide has a proper band gap of about 2.1 eV which lies in the visible region of the solar spectrum and allows utilization of 45% of the solar radiation. For the purpose of exploiting iron oxide as effective photocatalyst, various shapes of iron oxide (Fe2O3) nanostructures were prepared from a thin film of iron deposited on fused silica. The nanostructures were synthesized by using a micro-afterglow produced downstream an argon-oxygen microwave plasma at atmospheric pressure. We also tried to control the morphologies by adjusting the treatment parameters (iron film thickness, treatment duration and oxygen percentage in the plasma). In a second step, we elaborated nanostructures from iron-copper alloys. We aim to better control the growth of the nanostructures and their shapes. Copper oxide CuO formed by the same process is known to grow as walls or wires depending on the synthesis conditions. Then, the question is whether the iron oxide, depending on the concentration of copper, can adopt morphological changes similar to those adopted by CuO. It turns out that, in appropriate conditions, the introduction of copper drives the development of instabilities during the growth of Fe2O3 nanowires, leading to small branches that develops perpendicularly on the nanowire.

Resume : Many efforts were conducted in the last decades towards the development of efficient materials for water splitting in artificial photosynthesis applications. In this frame, tungsten trioxide (WO3) emerged as an attracting material due to its optical properties, transport properties and stability in aqueous solutions. In this work, WO3 films with different thickness (ranging from 100 to 500 nm) were deposited on different substrates by magnetron sputtering. SEM analyses revealed a columnar structure, with column diameter increasing with film thickness. WO3 films on FTO electrodes were annealed and used as photoanodes in PEC (photoelectrochemical cell) measurements. Morphological, structural (x-ray diffraction) and optical characterizations were conducted to evaluate the film modifications induced by the thermal treatment. Linear sweep voltammetry, chrono-amperometry and IPCE (incident photon-to-current efficiency) tests under AM 1.5G simulated solar light showed the best photocatalytic response for the 200 nm-thick film. Further enhancements in water splitting efficiency are in progress through the addition of dopants (i.e. C), the improvement of nanostructuration by means of chemical etching and glancing angle deposition techniques, and the coupling of WO3 with other materials (such as BiVO4), in order to combine the optimum transport properties of the prepared WO3 films with an enhanced visible-light absorption.

Resume : In recent years, BiVO4 has attracted great attention as promising photoanode in water splitting applications. The experimental photocurrent densities found in literature are far from the theoretical value expected from its band gap (2.4 eV) because of some intrinsic drawbacks (poor carrier mobility and slow kinetics for O2 evolution). Thus, different alternatives for improving the quantum efficiency have been widely studied (doping, heterojunctions and OEC addition), using a varied number of deposition techniques. Recent efforts on the synthesis by reactive sputtering, as a scalable thin film deposition technique, led to very complicated deposition procedures employing separate targets. In this work, we report an alternative deposition technique based on pulsed laser deposition (PLD) that allows the synthesis of stoichiometric BiVO4 using one single target. Undoped BiVO4, SnO2/BiVO4, W-doped BiVO4 and BiVO4/SnO2/WO3 films have been easily obtained in a controlled way by changing the deposition parameters with a facile control of the film thickness. Additionally, different heterostructures can be design by alternating targets of different materials. Moreover, good current densities and IPCE values have been obtained even for undoped BiVO4 films, which can be improved by a simple post-annealing treatment. The optimal parameters for obtaining a good starting material are proposed, before carrying out several modifications in order to enhance their performance.

Resume : Photoelectrochemical water splitting is an advanced chemical process for the generation of hydrogen (H2) using solar energy. Since the discovery of photoelectrochemical water splitting using TiO2 semiconductor, many metal oxide semiconductors have been extensively used as photoelectrodes for water splitting. However, due to the larger band gap of most of the oxide semiconductors, they use only UV light which is only 5 % of the solar spectrum incident on the earth’s surface. Therefore, for the generation of hydrogen on a larger scale, there is a need to develop visible light active photoanode materials for water splitting. Among visible light active semiconductor materials, CdS has attracted much attention due its optical band gap of 2.4 eV and has an optimal position of band edges for splitting of water into hydrogen. However, the phototelectrochemical activity of CdS is limited by various factors such as (i) CdS is unstable in aqueous solution and readily become deactivated through photocorrosion and (ii) high rate of charge carrier recombination. In order to address these limitations and improving the solar energy conversion efficiency of CdS, we have synthesized CdS/CoFe2O4 (CdS/CFO) core/shell nano heterostructure having a type-II band-edge alignment. CFO has a band gap of 1.8 eV and is very much chemically and thermally stable. The key strategy in the designing of CdS/CFO core/shell nanostructure is to achieve the efficient transfer of electrons within the coupled components for enhancing the activity for phototelectrochemical water splitting and also protects CdS from photocorrosion in aqueous solution using CFO as an outer layer of CdS. CdS/CFO core/shell nanostructures are synthesized by self assembly using a soft chemical method. First, CdS nanorods are synthesized by hydrothermal method using cadmium nitrate and thiourea in 50 ml ethylenediamine. Before growing CFO, the surface of the CdS nanorods is functionalized using a suitable functionalizing agent which leaves the surface of the nanorods with negatively charged ions. The core/shell nanostructures of CdS/CFO are obtained by using hydrothermal technique by keeping functionalized CdS nanostructures in cobalt nitrate and iron nitrate solution. The hydrothermal reaction is carried out in Teflon lined stainless steel autoclave at 120 °C for 10 hours. The synthesized core/shell nanostructures are characterized by X-ray diffraction, UV-visible spectroscopy and Transmission electron microscopy. Photoelectrochemical measurements are performed using a three electrode electrochemical cell assembly. The thin films of CdS and CdS/CFO core/shell nanostructures are deposited by spray coating technique and are used as working electrodes. The CdS/CFO core/shell nanostructure films show significant improvement in the photocurrent density and the incident photon to current efficiency as compared to CdS nanostructure films. The enhancement in the photoelectrochemical activity in CdS/CFO core/shell nanostructure is due to the formation of heterojunction between CdS and CFO. The efficient transfer of the charge carriers at the interface between CdS and CFO reduces the recombination rate of the photogenerated charge carriers and thus improves the overall photocurrent conversion efficiency.

Resume : In this presentation, we report the fabrication of p-type silicon (Si) photocathodes consisting of well-ordered Si microwire (Si-MW) arrays decorated with non-precious and earth-abundant amorphous molybdenum oxysulfide (MoOxSy) as both a catalyst and a passivation layer. The MoOxSy is conformally grown on the Si-MW surface through photoelectrochemical cyclic voltammetric (CV) deposition. By varying cycle numbers of the CV deposition, Si-MW array electrodes with various MoOxSy catalyst loadings (Si-MWs@MoOxSy) have been obtained and comprehensively characterized by SEM, TEM and XPS. The photoelectrochemical (PEC) performance of the Si-MWs@MoOxSy electrodes toward water reduction is investigated and compared with that of the platinum nanoparticle decorated Si-MW array electrodes (Si-MWs@PtNPs). The optimized Si-MWs@MoOxSy photocathode exhibits activity comparable to that of the Si-MWs@PtNPs, but having better stability in an acidic medium. In the practically important neutral electrolyte, the Si-MWs@MoOxSy electrode outperforms the Si-MWs@PtNPs in terms of both activity and stability. The excellent catalytic activity originates from the predominance of reduced Mo oxidation states in MoOxSy layer that, presumably, give rise to high electrical conductivity, which helps to accelerate charge transfer kinetics; while the extended stability of the photocathodes arises from effective passivation of Si-MWs by the continuous and conformal MoOxSy layers.

Resume : One of the key processes for hydrogen production is electrochemical water splitting. Recent experimental works suggest Co3O4 as anode material for this application. Co3O4 exhibits high catalytic activity in the oxygen evolution reaction (OER) [1]. Understanding the process of water adsorption on the Co3O4 surface at the atomistic level is essential for designing an effective anode material for electrochemical water splitting. Our study is focused on one of the most abundantly presented in Co3O4 nanoparticles surfaces - (111)[2]. We performed modeling of the water adsorption process on the Fluorine-doped Co3O4 surfaces and compared obtained results with those for undoped material. Applying DFT+U method in combination with thermodynamics we calculated free energy changes along the reaction pathway. Using the standard hydrogen electrode (SHE), we replaced in our calculations proton and electron with a half of hydrogen molecule at U = 0. Free energies were calculated for the standard conditions (pH = 0, T = 298.15 K) and U = 0. From the computed free-energy changes along the OER, we found that the fluorine-doped (111) surface is catalytically more active than the perfect one. [1] I. C. Man, H.-Y. Su, F. Calle-Vallejo, H. A. Hansen, J. I. Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. K. Nørskov, and J. Rossmeisl, ChemCatChem (2011) 3, 1159 – 1165. [2] F. Zasada, W. Piskorz, S. Cristol, J.-F. Paul, A. Kotarba, and Z. Sojka, J. Phys. Chem. C (2010), 114, 22245–22253

Resume : Microbial fuel cells (MFCs) have been hailed as a promising technology for electricity production through microbial degradation of organic substrates. Applications have mainly targeted wastewater treatment and processing, thus a great part of research efforts have focused on the scalability of MFCs and their incorporation into the existing water treatment infrastructure. However, the main problems associated with this technology ?namely: low energy yields and efficiencies - pose as threats to the financial sustainability of MFC-powered water treatment projects, as energy production alone cannot account for the increased cost of such applications. Changing perspective by not allocating MFCs as primary energy sources, we examine more versatile uses of this technology while still focusing on water treatment applications. To this end, we investigated the potential of monochamber MFCs to reduce high nitrate concentrations from wastewaters, with simultaneous energy production. MFC anolytes consisted of synthetic wastewater with a concentration of 2.5% NaNO3 and a COD value of 3,500mg/L; two MFC systems were inoculated with microbial cultures isolated: i) from the active sludge of a wastewater treatment facility and ii) from the silt from a river basin that regularly accepts heavy loads of nitrates from the local agriculture. The systems where characterized according to their capacity for simultaneous organic matter and nitrate removal, as well as current and power density production. The MFC system inoculated with the microflora from the active sludge showed a lower response in current generation, nitrate and organics removal than the system with the silt-born species. Apart from demonstrating that MFC technology is applicable in nitrate reduction, which by itself is most promising for cleaning water applications, our research also highlights the higher efficiency and versatility of naturally grown microbial communities over ones coming from a highly specialized environment (i.e. active sludge).

Resume : Hydrogen, being a safe, sustainable, and storable energy source, has gained great importance in recent decades as an alternative energy source. Photoelectrochemical splitting offers an efficient way of forming hydrogen from source compounds. Polyoxotungstates are potentially useful for photocatalytic hydrogen evolution reactions.Graphene, consisting of a monolayer of sp2 carbon atoms, is an attractive material in many research fields including electrocatalytic applications owing to its unique properties such as high surface area, outstanding electrical properties and high mechanical and thermal properties. Graphene is a unique candidate for a POM support material to overcome problems of both low surface area and high solubility of POMs. Here we report the synthesis of a polyoxotungstates (POTs) / Oxidized Graphene multilayers for photocatalytichydrogene evolution reaction. A significant property of this compound is its photocatalytic activity for H2 evolution in visible-light. Keggin type α‐(nBu4N)3[PW9O34(tBuSiOH)3](PW9) heteropolytungstates clusters (POTs) and oxdizedgraphenesheets (OG) were used to prepare POTs/OG multilayers.The growth process of (PW9/OG) multilayer films was monitored by UV-visible spectroscopy, Cyclic Voltammetry,Atomic Force Microscopy(AFM) and Scanning Electron Microscopy(SEM). The multilayers clearly exhibited HER signal because of the presence of OG in multilayer nanocomposite. The CV results revealed alteration of the electronic structure of deposited PW9 as a result of strong interaction with the oxidized graphene surface. [1]Z. Zhang,Q.Lin, S. Zheng, X.Bu and P. Feng, A novel sandwich-type polyoxometalate compound with visible-light photocatalytic H2 evolution activity,Chem. Commun., 2011, 47, 3918–3920,California,USA.

Resume : For over forty years the photocatalytic degradation of organic contaminants in water, air, and on surfaces is dominated by the use of titanium dioxide as the photocatalyst of choice. Nevertheless, the last years have shown an increase in the scientific efforts towards the utilization of new photocatalysts. This presentation surveys the various non-TiO2 photocatalysts used for decontamination, under both UV and visible light. It reviews the background that led to the growing interest in such materials and tries to relate this growing interest to the evolution in closely- related areas such as photovoltaics and water splitting. Particular attention is given to various pitfalls associated with the use of new classes of photocatalysts. In this context one of the most common pitfalls is the use of the decontamination of dyes as a predictor for the photocatalytic properties of new photocatalysts. At the end we will try to set a list of attributes for materials and applications that are likely to be more suitable for non-TiO2 photocatalysts than for TiO2.

Resume : Polyoxometalates (POMs), as a group of well-defined early transition metal-oxygen macroanion cluster species with unrivaled structural diversity, can possess fascinating properties in extensive fields such as catalysis, materials science, medicine and biology. Nonetheless, the construction of POMs-based nanoarchitectures for functional materials design is always a challenge because of the high crystalline energy and hydrophilic nature of POM clusters. Herein, a novel surfactant encapsulated polyoxometalate (SEP) with nanospherical morphology has been synthesized with a simple ion-exchange method. It can be further incorporated into polymeric membranes for practical environmental applications. Polyvinylidene fluoride (PVDF) was selected as the polymer matrix to fabricate SEP incorporated composite membrane (SEP-M). Both the SEP and SEP-M exhibited excellent dye removal activities and detailed mechanism studies were carried out to elucidate the nature of dye decolorization. Various methods to regenerate SEP-M were also proposed and evaluated. The used SEP-M can be easily recycled without loss of dye removal efficiency. The current research not only provides a new example for the simple and direct construction of POMs-based nanoarchitecture, but more importantly renders an efficient dye removal methodology, which may inspire rational design of POMs-based functional materials.

Resume : Orthorhombic pseudobrookite-type ceramics have relatively low bulk thermal expansion coefficients among oxides. Aluminum titanate (Al2TiO5, AT), has been most eagerly studied as a thermal-shock resistant material among pseudobrookite-type oxides. Undoped Al2TiO5, however, tends to decompose into Al2O3 and TiO2 at elevated temperatures, because Al2TiO5 phase is metastable below 1200?C due to its large distortion of MeO6-octahedra. Furthermore, microcracks induced by the strong thermal-expansion anisotropy gradually degrade mechanical properties. Since the thermal-expansion anisotropy of MgTi2O5 is not so prominent as Al2TiO5, MgTi2O5 is thermally more stable than Al2TiO5. Thinking about its low thermal expansion, low-cost, non-toxicity, and refractory composition, MgTi2O5 is a potential thermal-shock resistant material. In particular, porous MgTi2O5 can be used as a light-weight high-temperature structural material and a recyclable water-purifying filter material. In this presentation, our recent studies on pseudobrookite-type ceramics will be reported: - Uniformly porous MgTi2O5 with narrow pore-size distribution - XAFS Study, and new in-situ surface coating for porous MgTi2O5 - Porous MgTi2O5 ceramics for water purification filters

Resume : For an effective photocatalysis in water treatment a number of elementary processes as well as their coupling to each other must be optimized without severe losses in the number and the chemical potential of the originally generated electron-hole pairs. Light absorption coupled to efficient charge carrier generation and separation may be realized by Janus type photocatalysts which favour vectorial electron-hole pair transport into opposite directions. In addition, recombination reactions of electron hole pairs must be minimized, which will be achieved when the above given separation of electron-hole pairs is favoured by gradients of the electrochemical potentials provided in our case by nanoscopic heterojunctions. Subsequently, electrocatalytic redox reactions reactions must be possible by electron and hole transfer reactions with minimized loss of chemical potential. This will only be possible if the involved charge transfer steps are coupled to selective multi-electron transfer catalysts allowing electron transfer reactions with isoenergetic coupling of their electronic states We have prepared nano-sized semiconductor heterostructures combining oxides with different electron electrochemical potentials (Fermi levels) as e. g. ZnO/SnO2, TiO2/RuO2 or ZnO/RuO2 combinations using a wet sol-gel chemistry approach. The nano catalysts are formed after subsequent annealing steps. The particulates are characterized by TEM, XRD, BET, optical and Raman spectroscopy. In addition, the device structure is analyzed by applying photoelectron spectroscopy to the particles as well as to UHV prepared model interfaces. In all cases the formation of heterostructures with the formation of space charge layers could be proven, which is made responsible for improved charge carrier separation. In all cases we have found a clear correlation of increased photocatalytic activity also with respect to H2 evolution with the particulate heterostructures clearly exceeding the values of Degussa TiO2 25 as well as to the isolated parent photocatalysts. Evidently, electron-hole separation is strongly increased due to the built-in electronic asymmetry of the heterojunction particles. Thus we conclude that the design of advanced photocatalyic nanoparticles needs engineering principles following the same specific design rules controlling charge carrier dynamics as also valid for macroscopic semiconductor heterostructures.