Advanced carbon materials

Resume : Glassy carbon (GC) is a well-known carbon material consisting of sp2 hybrid carbon and having fullerene-like nanostructures.[1] GC is recognized to have several advantages such as good electroconductivity, low density, gas- and liquid- impermeability, high resistance to graphitization, unusual hardness, and good chemical inertness. However, in our recent investigation, we found for the first time that micro-sized glassy carbon microspheres (GCMs) could be completely transformed into nanostructures by concentrated nitric acid (HNO3) treatment, showing that GC did not have good chemical inertness upon exposure to oxidizing acid such as HNO3. The resultant products contain large amounts of carbon quantum dots, fullerene-like quantum dots, fullerene-like nanosheets, and some non-degradable graphite-like nanoparticles. The work not only provides a new insight into chemical properties and structures of GC, but also suggests a new, easy and efficient way to obtain fluorescent and electrochemiluminescent carbon dots. [1] Harris P J F. Fullerene-related structure of commercial glassy carbons[J]. Philosophical Magazine, 2004, 84(29): 3159-3167.

Resume : Carbon dots (CDs) are a family of fluorescent nanoparticles displaying a wide range of interesting properties which make them attractive for several potential applications. In fact, these zero-dimensional fluorescent nanoparticles have shown great potentialities in fields like bioimaging, photocatalysis, optical sensing and many others. However, despite many years of dedicated studies, wide variations exist in literature concerning the reported photostability of CDs, and even the photoluminescence mechanism is still unclear. CD fluorescence has been indeed attributed to many different origins, for example to the quantum confinement effect or to molecular fluorophores, either attached or not to the CDs surface, to mention only two. Furthermore, an increasing number of recent studies have highlighted the photobleaching (PB) of CDs under intense UV or visible light beams. For these reasons, PB is currently a hot topic which has not received enough attention and whose dynamics can constitute a useful route to get precious information on CD photophysics. Another huge gap is the substantial lack of systematic studies comparing several types of CDs displaying different fluorescence properties. In this study, we explored the optical properties of a full palette of CDs displaying a range from blue- to red-emissions, synthesized by using different routes and varying precursors. We investigated the photostability of the different CDs and observed their fluorescence degradation under equivalent experimental conditions and laser irradiation. In our experiments we used a time-resolved spectroscopic setup, which allowed us to investigate in situ and in real time the PB phenomenon. In this way, we could precisely monitor the kinetics of the undergoing PB processes and discriminate different contributions to the PB phenomenon. The results clearly indicate that even CDs showing comparable emission properties may exhibit radically different resistances to PB, and suggest systematic connections between the resistance to PB, the characteristic spectral range of emission, and CD quantum yields. To exploit the PB dynamics as a powerful method to investigate on CD photophysics, we also carried out dedicated experiments in a partial illumination geometry: in this way, we were able to analyze the recovery of the fluorescence due to diffusion and we could strictly exclude that the nature of the CD fluorescence is solely ascribable to small optically-active molecules free diffusing in solution. In fact, with our study we get both an estimation of the size of the units contributing to CDs’ emission and the information that the ones freely diffusing constitute only a restricted part the total, then contributing to the whole sample emission only to a relatively small extent. Our findings reveal important details on the fundamental mechanisms of CD fluorescence, and represent a first step to achieve non-fading CDs towards their industrialization in real applications.

Resume : Light-emitting nanoparticles based on carbon, named carbon dots (CDs), have recently gained much traction in the research community thanks to the interest surrounding their usage in various application fields. Helped by their low toxicity and bio-compatibility, these nanoparticles have been studied for their significant light-absorption capabilities which result in intense emission bands often displaying high quantum yields. Depending on the used precursors and followed synthetic procedures, CDs are able to express fluorescence covering all regions of the visible-light spectrum; nevertheless, we are still far from achieving a precise control in the optical properties of the resulting particles. In particular, the syntheses leading to red-emitting CDs are still based on trial-and-error approaches, resulting in low emission intensity, and the mechanisms at the origin of this red fluorescence are yet lacking a complete understanding. Carbon dots are nonetheless regarded as viable safe substitutes for the nanoparticles currently used in biological applications, nanomedicine, and for the fabrication of optoelectronic devices: as the latter are nanomaterials commonly based on rare elements or heavy metals, it is of utter importance to find a reliable alternative to these toxic and polluting particles. It is in this context that we have been exploring a wide variety of solvothermal synthetic approaches for red-emitting CDs: our research is based on investigating the role of both employed solvents and precursors, as well as of other reaction parameters such as temperature and pressure which the reaction is carried out at. With the goal of obtaining CDs with intense emission bands peaking at wavelengths longer than 600nm, we have developed straightforward purification strategies based on the nanoparticles’ surface charge distribution. In addition, by analyzing the optical properties of the obtained CDs and their dependency on the properties of the surrounding environment, we have gained insight into the mechanisms allowing for the resulting absorption and emission bands. Our results focus on isolating and controlling the fluorophores responsible for the red emission, to achieve high quantum yields while studying their involvement in the CDs’ structure, with the final aim to realize active materials for light emission devices based on carbon dots. The Italian MIUR PRIN 2017 Candl2 Project Prot. n. 2017W75RAE is gratefully acknowledged.

Resume : Carbon dots (CDs) are one of the most significant classes of carbon-based nanoflurophores, that have attracted extensive attention in recent years. Such nanoparticles are composed of carbon structures with sp2- or sp3-based architectures and display intense emission in the visible range, often comparable to that of fluorescent organic molecules or semiconductor quantum dots, combined with low environmental and cost impact. Many recent studies have aimed at developing new synthetic routes for CDs with enhanced photoluminescence (PL) properties. In particular, bottom-up syntheses of CDs generally involve thermal carbonization of opportunely selected organic molecules (e.g. citric acid, urea, carbohydrates, small aromatic molecules, …) and are performed mainly by solvothermal or microwave approaches. Here, CDs are synthesized trough the thermal treatment of resorcinol (1,3-hydroxybenzene), in ethylene glycol at high temperature (180°C) at atmospheric pressure in an open reactor vessel. The advantage of such synthetic strategy is twofold as it allows i) to increase the carbonization by promoting water evaporation, that form as secondary product and ii) to monitor the evolution of CDs formation and their optical properties during the synthesis. By spectroscopically monitoring the reaction, we infer the formation of two emission bands: one in the green, originated by highly fluorescent polycyclic aromatic hydrocarbons (PAHs) arising from resorcinol polycondensations and the other in the blue, by radiative recombination at their surface energy states in the carbogenic nanoparticles. We were able to sensibly increase the rate of the carbonization process by introducing acid or basic catalysts in the reaction solution, namely NaOH and H2SO4. Then, we investigate variations of the spectroscopic properties of the CDs under exposure to prolonged UV irradiation, proving that the two emission bands of CDs exhibit a different resistance to photobleaching, further supporting their attribution. Finally, we demonstrate a marked and interesting quenching/enhancing effect of the CDs emission in the presence of acidic or basic compounds in the surrounding environment of CDs, which suggests a profitable use of such CDs in on/off sensors or stimulus-responding devices.

Resume : There are many kinds of carbon materials such as activated carbons, nanoporous carbons, carbon blacks, graphite, carbon nanotubes, carbon nanofibers, and graphene-like materials, and they have been used in a variety of batteries as active materials, conductive additives, and gas diffusion layers. Depending on the purpose of use, carbon materials are required to have appropriate porosity, electric conductivity, mechanical stability, and electrochemical stability. While the above mentioned carbon materials have individual advantages and disadvantages, it has been a challenging target to develop next-generation carbon materials to satisfy all the necessary requirements at the same time. In this talk, a new class of carbon material, “graphene mesosponge (GMS)”, is introduced as a feasible candidate [1]. GMS is synthesized by a hard-templating method using Al2O3 [1] or MgO [2] nanoparticles via precisely controlled chemical-vapor deposition in which the average stacking number of graphene sheets is adjusted to 1. After template removal, the resulting mesoporous carbon is annealed at 1800 °C to form GMS. By such a high-temperature treatment, most of carbon edge sites which cause corrosion of batteries can be removed, and GMS exhibits ultra-high stability against chemical oxidation as well as electrochemical oxidation. Despite such durability, GMS possess a high surface area (ca. 2000 m2/g) and a large pore volume (> 3 cm3/g). Moreover, GMS has a high electric conductivity which is superior to carbon blacks. Furthermore, GMS is mechanically flexible and tough. GMS shows reversible deformation and recovery upon applying mechanical force and its removal [3]. Such unique properties of GMS enable its use as next-generation durable and high-performance carbon material to battery applications. As an electrode material for electric double-layer capacitors, GMS exhibits ultra-high voltage stability up to 4.4 V even in a conventional organic electrolyte (Et3MeN/BF4), which surpass single-walled carbon nanotubes [4]. Also, GMS is useful to a Pt support of polymer-electrolyte fuel cells [5] and to a cathode of Li-air batteries. Reference [1] H. Nishihara, T. Simura, S. Kobayashi, K. Nomura, R. Berenguer, M. Ito, M. Uchimura, H. Iden, K. Arihara, A. Ohma, Y. Hayasaka, T. Kyotani, Adv. Funct. Mater. 2016, 26, 6418-6427. [2] S. Sunahiro, K. Nomura, S. Goto, K. Kanamaru, R. Tang, M. Yamamoto, T. Yoshii, J. N. Kondo, Q. Zhao, A. Ghulam Nabi, R. Crespo-Otero, D. Di Tommaso, T. Kyotani, H. Nishihara, J. Mater. Chem. A 2021, 9, 14296-14308. [3] K. Nomura, H. Nishihara, M. Yamamoto, A. Gabe, M. Ito, M. Uchimura, Y. Nishina, H. Tanaka, M. T. Miyahara, T. Kyotani, Nat. Commun. 2019, 10, 2559. [4] K. Nomura, H. Nishihara*, N. Kobayashi, T. Asada, T. Kyotani, Energy Environ. Sci. 2019, 12, 1542-1549. [5] A. Ohma, Y. Furuya, T. Mashio, M. Ito, K. Nomura, T. Nagao, H. Nishihara, H. Jinnai, T. Kyotani, Electrochim. Acta 2021, 370, 137705.

Resume : Hybrids comprising cellulose nanocrystals (CNCs) and percolated networks of single-walled carbon nanotubes (SWNTs) may serve for casting of hybrid materials with improved optical, mechanical, electrical, and thermal properties. However, CNCs-dispersed SWNTs are depleted from the chiral nematic (N*) phase and enrich the isotropic phase. Herein, we report that SWNTs dispersed by non-ionic surfactant or triblock copolymers are incorporated within the surfactant-mediated CNCs mesophases. Small Angle X-ray measurements indicate that the nanostructure of the hybrid phases is only slightly modified by the presence of the surfactants, and the chiral nature of the N* phase is preserved. Cryo-TEM and Raman spectroscopy show that SWNTs networks with typical mesh size from hundreds of nanometers to microns distribute equally between the two phases. We suggest that the adsorption of the surfactants or polymers mediates the interfacial interaction between the CNCs and SWNTs, enhancing the formation of co-existing meso-structures in the hybrids phases.

Resume : It is foreseen that many future electronic devices will require electrical conductors with electrical and thermal properties largely exceeding the performance of traditional copper. In that regard, the design of an enhanced composite material with a copper matrix is an interesting approach to improve the electrical characteristic of copper conductor[1]. Carbon Nanotubes (CNTs) have been recognized as ?the perfect filler? thanks to their good electrical, mechanical and thermal properties. Unfortunately, the proper integration of CNTs in a copper matrix remains challenging as these two materials do not mix or interact[2]. In this research copper-CNT composites were prepared using an electrochemical co-deposition method. Double-Walled Carbon Nanotubes (DWCNTs) were used for the first time to prepare novel conducting materials with tubes incorporated within the copper matrix by co-electrodeposition means. Suspensions of DWCNTs in copper salt solution were stabilized by surfactant Pluronic P123, a symmetric triblock copolymer PEG-PPG-PEG. A wide discussion about the dispersion mechanism is provided in this work. At first the DWCNTs were submitted to a one-pot gas phase purification treatment developed by our group[3]. The impurity removal efficiency was confirmed by Thermogravimetric Analysis (TGA). Secondly, different kinds of surfactants, including ionic and nonionic, were tested by varying the DWCNT/surfactant ratio until an optimal concentration was established by both direct visual observations and optical microscopy (OM). Afterwards, a constant current was applied to simultaneously electrodeposit the DWCNTs and copper on a copper rod electrode. The obtained Cu-DWCNT composite powders were characterized by Transmission and Scanning electron microscopy, (TEM) and (SEM), respectively, as well as by micro Raman spectroscopy. With the latter technique, the presence of the characteristic DWCNT Radial Breathing Mode (RBM) bands was used to confirm their proper integration within the composite. Finally, a comparative TGA analysis between electrodeposited copper and the obtained composite material aimed to determine the amount of DWCNTs incorporated within the copper matrix. [1] W. a. D. M. Jayathilaka, A. Chinnappan and S. Ramakrishna, J. Mater. Chem. C, 2017, 5, 9209?9237. [2] E. Kazimierska, E. Andreoli and A. R. Barron, J Appl Electrochem, 2019, 49, 731?741. [3] A. Desforges, A. V. Bridi, J. Kadok, E. Flahaut, F. Le Normand, J. Gleize, C. Bellouard, J. Ghanbaja and B. Vigolo, Carbon, 2016, 110, 292?303.

Resume : 5-Chloro-2-(2,4-dichlorophenoxy) phenol, known as triclosan (TCS), is antibacterial and antifungal widely used in cosmetics. Moreover, it is a common additive in many antimicrobial household products, including oral sanitary products, medical disinfectants, and liquid detergents [1]. Using these commodities on a large scale resulted in contaminating water sources, such as rivers, lakes, wastewater, sediments [1]. TCS and dioxin-type TCS degradation products are bioaccumulative in a number of aquatic species. TCS has been detected in breast milk, urine and plasma [2-3]. Thus the analytics of TCS and safe degradation is an important factor in environmental safety. We present here novel, chronoamperometric detection of TCS and its derivative compounds at boron-doped diamond electrodes. The cyclic voltammetry and differential pulse voltammetry techniques were utilized to determine TCS concentrations in environmental samples. The obtained electrochemical data were compared with concentrations estimated by High Performance Liquid Chromatography Mass Spectroscopy (HPLC-MS). A proposed approach was also applied to gain and control the parameters of electrolysis processes of TCS conducted at nanocarbon or diamond-based electrodes. TCS decomposition products identified by standard mass techniques have been assigned to the electrochemically observed oxidation processes, which will allow for faster environmental analysis and the detection of undesirable decomposition pathways. [1] C. Solá-Gutiérrez, M.F. San Román, I. Ortiz, Sci. Total Environ. 626 (2018) 126–133. [2] A.P. Iyer, J. Xue, M. Honda, M. Robinson, T.A. Kumosani, K. Abulnaja, K. Kannan, Environ. Res. 160(2018) 91–96. [3] M. Allmyr, M. Adolfsson-Erici, M.S. McLachlan, G., Sci. Total Environ. 372 (2006) 87–93. Acknowledgements This work was supported by The National Centre for Research and Development under project i-CLARE number NOR/POLNOR/i-CLARE/0038/2019-00

Resume : 2D red phosphorus nanosheets (RPNSs) were generated in situ between the interlaced spaces of 1D single-walled carbon nanotubes (SWNTs) through phosphorus-amine method, forming a unique network architecture (RPNSs/SWNTs). Using hydrophilic polyvinylidene fluoride (PVDF) membrane as the substrate, three-electrode arrays consisted of RPNSs/SWNTs were easily fabricated through scalable filtration. More importantly, the obtained sensors are qualified for the direct measurements of liquid samples without further pretreatment. The liquid samples are dropped onto the reverse-side of sensors (i.e. the other side without the coverage of RPNSs/SWNTs), and the contained targets rapidly reach the surface of RPNSs/SWNTs through hydrophilic apertures. The RPNSs/SWNTs membrane sensors can be prepared in mass with very low cost, and have good repeatability and stability, exhibiting great potential in point-of-care testing (POCT).

Resume : Graphene nanosheets (GS) were prepared by ultrasonic exfoliation of bulk graphite in N-methyl-2-pyrrolidone (NMP) solvent with the assistance of sodium pyrophosphate. The obtained GS was modified on the surface of glassy carbon electrode, and then functionalized through constant-potential oxidation in pH 7.0 phosphate buffer. It is found that the electrochemical activity and sensing performance of GS obviously enhance after oxidation functionalization, probably due to the introduction of oxygen-containing functional groups and the improvement of detect level. The influences of oxidation potential and time were examined. The oxidation signal of nitrofurazone (NFZ), a prohibited medicine in aquaculture, increased obviously on the surface of GS, and further enhanced greatly on the surface of electrochemically functionalized graphene (EGS). The signal enhancement mechanism of EGS was discussed, and a novel electrochemical method was developed for NFZ detection. The linear range was 0.01-0.8 μmol L-1, and the detection limit was 2 nmol L-1. Finally, it was successfully applied in fish samples, and the accuracy was satisfactory.

Resume : Bulk Ti3AlC2 powder was etched to Ti3C2Tx through hydrothermal reaction in NaF/HCl mixed solution, and Al element was totally removed from bulk phase after hydrothermal etching (160 oC, 9h). The obtained Ti3C2Tx powder was then exfoliated into aqueous solution of different quaternary ammonium hydroxide, including tetramethylammonium hydroxide (TMAOH), tetraethylammonium hydroxide (TEAOH), tetrapropylammonium hydroxide (TPAOH) and tetrabutylammonium hydroxide (TBAOH). The influences of quaternary ammonium hydroxide on the exfoliation efficiency, morphology and layer number of Ti3C2Tx MXenes were examined. After that, the exfoliated Ti3C2Tx MXenes were ultrasonically dispersed into N-methyl pyrrolidone (NMP), and then used for constructing a series of electrochemical sensing platforms. The electrochemical active area, electron transfer ability and catalytic activity of Ti3C2Tx MXenes were investigated. Additionally, their sensing performances for environmental pollutants and small biomolecules were discussed.

Resume : As the world experiences a data explosion and ever increased demand for computation which is met with serious bottlenecks in conventional computing paradigms, memristors have attracted great attention recently as candidates that can bring about the next computing revolution. Amongst the numerous memristive devices, electrochemical metallization memories (ECMs) have shown promise owing to their incredible versatility which includes digital/analog operation, volatile/nonvolatile behaviour, and operability with various materials enabling soft or flexible electronics. Such properties, featuring quantized conductance, make ECMs apt as adaptive electronics for applications in neuromorphic computing. However, ECMs still face significant obstacles, manifest as cycle-to-cycle and device-to-device variability and poor endurance, that stem from a lack of understanding of the complex microscopic processes underpinning their function. Notably, the electrochemical (EC) environment, including moisture levels and the nature of the electrolyte, has been shown to play an important role recently with observed effects on conductance quantization, ion transport, memristive behaviour and stability. With recent advancements in computational electrochemistry, it is now possible to better explore the effects of the EC environment on device operation and gain atomistic insights into the microscopic processes at play, which cannot be resolved experimentally. As such, DFT is used in this study to discern the effects of moisture and later, a water electrolyte, on conductance quantization in ECMs. A model consisting of a simple gold nanojunction, with two slabs connected by an atomically thin wire subjected to a defined bias, is studied under transforming EC environments for wires of increasing realism. DFT as implemented on CP2K is used for all simulations. Implementation includes applying the GTH pseudopotential, periodic boundary conditions and the supercell approximation. The exchange correlation functional is approximated using the robust GGA-PBE functional and electron transport properties of all structures are determined using the nonequilibrium Green’s function approach in combination with DFT (NEGF + DFT). Finally, the Nørskov method is used for bias dependency. In this presentation the formalism of first principles electrochemistry will be outlined and its application to the molecular engineering of memristors discussed.

Resume : Radiofrequency magnetron sputtering has been used for the synthesis of graphene by carbon target[1]. This method allows the use of substrates without the need for a surface predeposition of catalytic particles. In this study, we coat different substrates such as silicon, indium thin oxide, germanium and polyethylene with graphene thin films generated in radio frequency magnetron discharges. By applying a supplementary polarization voltage to the substrate, the physicochemical and morphological properties of layers can be changed. The RAMAN and XRD spectral analysis[1] highlighted that the physicochemical properties of the layers depend on the supplementary applied voltages to the substrate. During the experiments, we try to improve the adhesion of our material on the substrate[2]. Also, the adherence of the layers to substrates increased with the applied voltage. The graphene layers improved the conductivity and the electrical properties in the heterojunction structure as the electrical measurements are shown. The material based on carbon functionalization is very important in the view of new thin layers generation for application in solar energy. Reference: [1] Fabrication of carbon nanowalls by radio frequency magnetron sputtering of graphite target in argon plasma, Journal of Physics: Conference Series, 1697 (2020) 012108 [2] Synthesis of large-area carbon nanosheets for energy storage applications, Daire J. Cott et all., July 2013, Carbon 58:59–65 Acknowledgments: This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS - UEFISCDI, project number PN-III-P1-1.1-PD-2019-0540, within PNCDI III

Resume : Nowadays, with fresh water scarcity being one of the most challenging global issues, several desalination technologies have been proposed for sustainable water recovery. Capacitive deionization has emerged as an efficient, energy-saving approach for brackish water desalination. Currently, activated carbon (AC) has gained a lot of attention as electrode material candidate due to the ease of fabrication, as well as its tunable surface properties. However, the utilization of AC in practical applications is limited by its low conductivity, broad pore size distribution and irregular particle shapes, all leading to poor electrical contact between AC particles. This work provides a simple, low cost and scalable approach to produce nanocomposite electrodes combining activated carbon with an extremely low content of carbon nanotubes (CNTs). In brief, activated carbon yielded from carbonization of sucrose and subsequent activation under carbon dioxide (CO2) gas flow at high temperature. Nanocomposite electrodes were manufactured by mixing the as-prepared activated carbon with carbon nanotubes and the slurry was then deposited on graphite substrates in the form of coating. The electrochemical performance of the nanocomposite electrodes was evaluated in 1M sodium chloride (NaCl) aqueous solution using a three-electrode configuration with porous carbon, platinum (Pt) sheet and silver/silver chloride (Ag/AgCl) as working, counter and reference electrode, respectively. The specific capacitance of the nanocomposite electrodes was determined by Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS) measurements. Afterwards, batch-mode electrosorption experiments were carried out in a lab-scale CDI cell with synthetic sodium chloride (NaCl) solution to evaluate the desalination performance of the composite electrodes. Impressively, a low content of carbon nanotubes (only 1%) has resulted in significant increase of salt adsorption capacity leading to enhanced desalination performance of the composite electrodes. The outcome was ascribed to the synergistic effect of both carbons with its upgraded electrical conductivity inherited by CNTs combined with the high specific surface area (1495m2/g) of activated carbon making them attractive for application as electrode materials for capacitive deionization. The fabricated composite electrodes showed an excellent performance with capacitance of 463 mF/cm2 (at 5 mV/s), salt adsorption capacity of 4.8 mg/g and current efficiency of 93% at 1.2 V in 300 ppm NaCl solution.

Resume : Transition metal dichalcogenides (TMDs) have attracted much attention recently due to their versatility of their electronic and photonic properties, which stems out of their compositional tuneability. Single/few layers of TMDs can be isolated from bulk crystals by mechanical exfoliation techniques or synthesised by decomposition of suitable chemical precursors. It has been recently demonstrated that MoS2 and WS2 films can be synthesised in ambient conditions using local laser irradiation which induces local thermal decomposition of a precursor-containing compound which has been deposited on the surface of various substrates. In this implementation a solution containing (NH4)2MoS4 or (NH4)2WS4 was prepared using organic solvents, which have suitable viscosity to facilitate deposition of the solution onto various substrates by spin coating. Local heating by laser radiation, which is absorbed by the precursor film and/or the substrate decomposes the precursor, thus producing the target material (MoS2 or WS2 depending on the precursor composition). Scanning of a laser beam can therefore produce tracks of TMD films with widths that are of the order of the size of the irradiating laser spot. The unexposed precursor can be readily removed by ?development? of the processed sample using organic solvents, which dissolve the precursor film but not the synthesised TMD that remains attached to the surface. Here we show that, under certain conditions, laser synthesised MoS2 film tracks feature periodically modulated thickness with a period that is of order of the wavelength of the laser. The thickness variation can be severe enough to produce regularly arranged, isolated ribbons with sub-micron width. The occurrence of these periodic features have been observed to depend upon various parameters of the synthesis, which include the speed of scanning of the laser beam across the substrate, the concentration of the precursor in the solution that was spin-coated onto the substrate and laser beam polarization. 1D and 2D laser-induced periodic surface structures (LIPSS) occur in the central region of the laser-irradiated track for certain combination of precursor concentration, laser intensity, scanning speed. The linear (1D) periodic features, are aligned along the direction of the polarisation of the laser beam. In the experiments that are reported here, a visible laser (lamda=532 nm) was used, therefore the period of the features were also of that order. Interestingly the linear periodic features consist of isolated film sections forming free ribbons. At higher speed/lower laser intensity combinations 2D features emerge. The threshold for the occurrence of 1D and 2D LIPSS shifts to higher scanning speeds for lower laser power. Furthermore, preliminary results indicate that higher concentrations of precursor shift the threshold to lower laser powers. The reported study was financially supported by the Russian Science Foundation (RSF) grant No. 21-79-20208.

Resume : Graphene-ferroelectric heterostructures can be successfully used in improving the functionalities of graphene-based transistors/devices. The properties of the ferroelectric surface layer and the growth/transfer process of graphene on it are of paramount importance for obtaining nanoelectronic devices with enhanced properties and functionalities. HfO2 was recently found to exhibit, in certain structures and combinations, attractive ferroelectric properties, compatible with graphene-based transistors/devices. A parametric study regarding the deposition of very thin (pure or embedded in different heterostructures) HfO2 layers (thicknesses in the nm-tens of nm range) directly on Silicon substrate, with very low roughness and appropriate ferroelectric properties was carried out. A comparison between properties of layers grown by Pulsed Laser Deposition and those obtained by magnetron sputtering (as it results from AFM, PFM, SEM, HRTEM, XRD spectroellipsometric investigations) has been also done.

Resume : A simple, fast, and efficient synthesis of paper-like carbon nanohybrids decorated with silver nanoparticles is demonstrated, where direct nondestructive gas-phase covalent functionalization was applied to prefabricated graphene oxide paper (GOP) and buckypaper (BP) with two aliphatic amines: 1-octadecylamine (ODA) and 1,8-diaminooctane (DAO). The functionalization was performed in a temperature range of 160 - 180°C under 10-2 Torr constant vacuum which requires about 2 h only. Ag nanoparticles were generated in situ by using silver nitrate as a precursor and citric acid as a non-toxic and eco-friendly reducing agent. Comparative characterization of pristine and amine-functionalized GOP and BP mats, along with their respective hybrids was carried out by means of Fourier-transform infrared, and energy-dispersive X-ray spectroscopy, scanning and transmission electron microscopy, as well as thermogravimetric analysis. The infrared spectra indicate that BP was covalently functionalized with amines mainly through an amidation mechanism, whereas GOP functionalization occurred through both amidation and epoxy ring opening reactions. The micrographs show that the size of the Ag nanoparticles on non-functionalized surfaces fluctuates between 10–35 nm, with a clear tendency to agglomeration. We explain this behavior by the coordination of silver species to the O donor atoms of oxygenated groups present, which serve as efficient sites for nanoparticle nucleation and growth. Ag nanoparticles on the amine-derivatized GOP and BP were found to measure from 3 to 15 nm, with significantly lower agglomeration; particularly, on DAO-functionalized materials the nanoparticle size was limited to ~ 5 nm. We suggest that in these cases, the formation of Ag nanoparticles occurs via reduction of metal ions coordinated to N donor atoms of the covalently attached amine molecules, resulting in a more homogeneous size distribution, and preventing the agglomeration observed in pristine materials. Thermogravimetric analysis shows that the silver content of DAO-functionalized samples is almost twice that of ODA-derived materials, because additional amino groups serve as coordination centers for anchoring and stabilization of the nanoparticles. Moreover, the amino-functionalized and silver decorated papers show a significant increase of thermal stability with respect to the pristine ones. These results expand the possible uses of eco-friendly solvent-free functionalization techniques to the fabrication of silver-decorated carbon nanomaterials, where the size and uniform distribution of NPs is an important prerequisite for successful electrochemical, catalytic, and biomedical applications. Acknowledgments: Financial support from the National Autonomous University of Mexico (UNAM, grant DGAPA-IN100821 is greatly appreciated. D.I.R.O. is indebted to the Doctorate Degree Program in Chemical Sciences at UNAM and CONACyT for the Ph.D. scholarship.

Resume : Metal decoration carbon nanomaterials have been proposed for applications in catalysis, sensorics and energy storage. Among the most interesting metals are rare earth metals, especially lanthanides with their peculiar 4f-electron configuration because the combination of the unique characteristics of carbon nanomaterials with the properties of lanthanide oxides opens the way to novel materials with unusual magnetic, luminescent, and catalytic properties useful for a broad spectrum of applications in different areas of science and technology. Synthetic routes for such hybrid nanomaterials commonly involve large amounts of organic solvent compared to the quantity of nanomaterial processed (litters per gram), which can produce harmful effects on the environment and human health. For this reason, the development of new alternative synthetic routes is highly desirable. Here we propose a solvothermal approach as an alternative route to the synthesis of hybrid nanomaterials combining graphene oxide powder and lanthanum, europium, gadolinium, and terbium oxides. Scanning electron microscopy characterization of the materials obtained through a solvothermal treatment of GO with lanthanide salts under variable experimental conditions showed the formation of micro and nanoparticles of lanthanide oxides of different sizes. Infrared and Raman spectra revealed the presence of characteristics bands due to lanthanide species. Thermogravimetric analysis showed that the composite material is considerably less thermally stable than the starting graphene oxide powder. The results obtained demonstrate that solvothermal synthesis can be considered as a simple, efficient, and eco-friendly pathway to new nanohybrid materials based on graphene oxide and lanthanide elements.

Resume : Electrochemical hydrogen production is regarded as an effective method to alleviate resource crisis and environmental problems, but its large-scale application is limited by the slow oxygen evolution reaction (OER) thermodynamics. It is of great significance to explore a thermodynamically more favorable oxidation reaction to replace the oxygen evolution reaction for hydrogen production and value-added chemical products simultaneously. In this work, the selective oxidation of Tetrahydroisoquinoline (THIQs) to Dihydroisoquinolines (DHIQs) is integrated with hydrogen production in two-chamber electrolytic cell, which acquire 95.92% yield of DHIQs and hydrogen production of 113.9 mol cm-2 h-1 at a potential of 1.45 V vs RHE on Cu(OH)2 nanorod electrode. Compared with the KOH solution, the addition of THIQs effectively reduces the anodic oxidation overpotential and increases the hydrogen production by 5 times, indicating that the controllable selective oxidation of THIQs to DHIQs can completely replace OER and synergistically promote hydrogen production. The transformation between cuprous oxide and copper oxide is monitored by Operando Raman and is responsible for high selective oxidation of THIQs. This integrated overall reaction promote the simultaneous production of high value-added chemicals and hydrogen energy, which can further alleviate the energy crisis and environmental problems.

Resume : Electrocatalysis for the conversion of NO3 to N2 is an environmentally friendly strategy aimed at ending the man-made nitrogen cycle. This work reported a MOF-derived electrocatalyst (Fe3Ni-NC) with Fe-Ni-N6 coordination centers that realizes efficient nitrate conversion (~97.9%) and exhibits high N2 selectivity (~99.3%). The coordination structure of Fe and Ni metals with N not only makes the metals highly dispersed, increasing the catalytic active site, but avoids metal leaching and improves the stability of the material. The extremely short distance between Fe and Ni species facilitates the transfer of nitrite from Fe to Ni surface for efficient relay catalysis, thereby improving N2 selectivity. In situ characterization and DFT calculations show that the thermodynamics of the NRR process on Fe3Ni-NCs is favorable compared to other catalysts. The Fe site lowers the reaction potential for NO3 conversion and the Ni center promotes the adsorption and activation of reaction intermediates (NO2-, NO* and N2O*). This work will provide new insights to open up MOF-derived multi-metal catalytic sites for NO3- reduction electrocatalysts.

Resume : The cathode microporous layer (MPL), as one of the key components of the proton exchange membrane fuel cell (PEM-FC), requires specialized carbon materials to produce the two-phase flow and interfacial effects. In this respect, we designed a novel MPL based on super-hydrophobic nitrogen doped carbon nanowalls (N-CNW). Employing radio-frequency plasma deposition techniques directly on carbon paper we produced high quality microporous layers at competitive yield-to cost ratio with distinctive MPL properties: high porosity, good stability, considerably durability, super-hydrophobicity and substantial conductivity. Platinum-ink, serving as fuel cell (FC) catalyst, was directly sprayed on the MPLs and incorporated in the FC assembly by hot-pressing against a polymeric membrane. The integrated PEM-FCs were tested in a single cell PEM-FC on a BT-112 Single Cell Test System, showing power performance comparable to industrial quality membrane assemblies (0.35 W/cm2), with elevated working potential (0.99 V) and impeccable fuel crossover for a low-cost system resulting from a highly scalable, inexpensive, and rapid manufacturing method. Acknowledgements: This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI – UEFISCDI, project numbers: PD 106/2020 and TE 205/2021

Resume : With the advances of electronic device technologies, the continuing trend of miniaturization and integration impose challenges of heat dissipation in microelectronics and stimulate increasing interests on thermal management materials and methods. Great efforts have been made in search for materials with high thermal conductivity for high power electronic device packaging as well as to understand nanoscale heat transfer. In addition to traditional graphite materials, two-dimensional (2D) materials, especially graphene and hexagonal boron nitride, have emerged as potential candidates for thermal management solutions due to their high intrinsic thermal conductivity and good mechanical flexibility, aiming to address the challenges for next-generation electronic and opto-electronic devices. Besides, thermal insulation is important for many applications, which also needs to be well addressed.

Resume : We investigate the charge transport physics of a previously unidentified class of electron-deficient conjugated polymers that do not contain any single bonds linking monomer units along the backbone but only double-bond linkages. Such polymers would be expected to behave as rigid rods, but little is known about their actual chain conformations and electronic structure. Here, we have shown evidence that the persistence length of these polymers matches/exceeds their contour length. We present a detailed study of the structural and charge transport properties of a family of four such polymers. By adopting a copolymer design, we achieve high electron mobilities up to 0.5 cm2 V−1 s−1. Field-induced electron spin resonance measurements of charge dynamics provide evidence for relatively slow hopping over, however, record-long distances. We have also uncovered some of the transport-limiting factors that prevent achieving even higher carrier mobilities: In the systems investigated to date, the polymer backbone is not expected to be planar due to steric hindrance between a carbonyl carbon and an adjacent C─H group, and the torsion potentials are sufficiently flat around the equilibrium configurations that they allow significant variations in torsion angles. Besides, the torsional fluctuations are facilitated in the ionized state where the double-bond linkages largely stretch out compared to the neutral ground state. These polaronic effects combined with the increased torsional energetic disorder act against the large electronic dispersion and slow down electron transport. In the future, molecular designs should be sought within this class of polymers that allow planar backbone conformations without steric hindrance and exhibit a narrower distribution of torsion angles. Such systems could potentially retain the unique rigid-rod nature of these polymers but achieve lower energetic disorder and reorganization energies and allow reaching even higher charge carrier mobilities, potentially exceeding those of state-of-the-art systems. In sum, our work provides important insights into the factors that limit charge transport in this unique class of polymers and allows us to identify molecular design strategies for achieving even higher levels of performance.

Resume : We report a simple, scalable two-step method for direct-write laser fabrication of 3D, porous graphene-like carbon (LIG) electrodes from polyimide films with integrated contact plugs to underlying metal layers (Au or Ni). A “keyhole” contact plug is written at high average CO2 laser power (30 W) and low scan speed (~18mm/s) leading to local ablation of polyimide (initial thickness 17 um) and graphitization of the plug perimeter. A top-surface LIG electrode is then superimposed on the contact plug by raster patterning at lower laser power (3.7 W) and higher scan speed (200 mm/s). Raman data yielded sharp first- and second-order peaks which indicates the formation of high-quality LIG, consistent with the sheet resistance data (71±15 Ohm/sq.). We have also demonstrated that high-quality LIG requires a minimum initial polyimide thickness. Capacitance data measured between surface LIG electrodes and the buried metal film indicate a polyimide layer of thickness ~7um remaining following laser processing. By contrast, laser graphitization of polyimide of initial thickness ~8 um yielded devices with large sheet resistance (> 1 k Ohm/sq.). Raman data also indicated significant disorder. Plug contact resistance values were calculated from analysis of Transfer Line Measurement data for single- and multi-plug test structures. Contacts to buried nickel layers yielded lower plug resistances (1-plug: 158 ± 7 Ohm, 4-plug: 31± 14 Ohm) compared to contacts to buried gold (1-plug: 346 ± 37 Ohm, 4-plug: 52 ± 3 Ohm). Further reductions are expected for multi-plug structures with increased areal density. Proof-of-concept mm-scale LIG electrochemical devices with local contact plugs yielded rapid electron transfer kinetics (rate constant k0 ~ 0.017 cm/s), comparable to values measured for exposed Au films (k0 ~ 0.023 cm/s). Our results highlight the potential for scalable integration of LIG-based sensor electrodes with semiconductor or roll-to-roll manufacturing.

Resume : I will describe our recent efforts in developing a nanoscale MRI approach at high magnetic field using hyperpolarized 13C nuclear spins in diamond as quantum sensors. The high field regime is naturally advantageous because the chemical shift dispersion is larger, and analyte nuclei carry higher polarization. I will elucidate a method for continuously tracked AC magnetometry allowing for sub-nT sensitivity and sub-ppm frequency resolution sensing at high fields (>7T).

Resume : Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors for a variety of applications ranging from material science to bio-medicine. The dependence of the zero field splitting of NV on temperature makes it a feasible temperature sensor. A few features of NV based thermal sensing, including the high spatial resolution, high sensitivity, wide working temperature range, and compatibility with various working environment, make it a most promising candidate for nanothermometry applications. In the present talk, we first show that spatially resolved temperature evolution can be monitored using NV-based thermal sensing in a working electrochemical device using nanodiamond (ND) sensors. We will then discuss a major limitation of the current thermal sensing using ND, that is, the temperature sensitivity, and further extends the discussion to strategies that can largely improve its sensitivity. We show by using a hybrid sensor approach, the temperature sensitivity of NV based thermometry can be improved to 76 μK Hz−1/2. This work has been carried out in collaboration with Renbao Liu, Kangwei Xia, Wenghang Leong, Ning Wang, Gangqin Liu, Ting Zhang, Manhin Kwok, Chufeng Liu, and Ruqiang Dou. We acknowledge funding from ANR/RGC (project No. A-CUHK404/18).

Resume : Understanding the temperature-regulated thermodynamic behavior in living cells is an effective way to decipher the structure and the motions in the intracellular environment. In this work, we investigate the thermodynamic behavior in HeLa cells by tracking the intracellular motions of nanodiamond (ND) complexes subject to light-absorption-induced local temperature gradients. Two kinds of nanodiamond-based intracellular thermometers and heaters are prepared, and their nanoscale temperature-sensing and light-modulated temperature changes are tested in living cells. The 3D coordinates of the ND complexes under different local or environmental temperatures are recorded in real-time. The mean square displacements (MSDs) of the 3D trajectories are calculated and analyzed by using a power-law relation to elucidate the diffusion behaviors of the tracked ND complexes. As temperature increases, the diffusion behavior tends to change from subdiffusion to superdiffusion. However, controlling the local, nanoscale temperature has a similar effect on the diffusion behavior of the tracked ND complexes as controlling the environmental temperature. Since the former approach has a much weaker influence on cell viability than the latter, this work demonstrates the benefits of quantitatively understanding the nanoscale intracellular thermodynamic behavior in living cells, which could stimulate the emerging field of thermal biology.

Resume : With the rapid growth of population, industrialization and climate emergency, access to safe drinking water is one of the major challenges to governments worldwide. It is estimated that 2.2 billion people lack access to safe drinking water. Harmful nanoscale contaminants like viruses, dyes, pharmaceutical by-products form the biggest challenge for water purification processes. While current technologies like nanofiltration or reverse osmosis can achieve high retention levels of such harmful contaminants, these systems are expensive and complicated, limiting their usage in centralized water treatment plants. This has led to development of filters like Brightstar (Invitrogen), ZetaPlus (3M), Nanoceram (Argonide), Posidyne (Pall), Zeta-pak (ErtelAlsop) etc. These filters use adsorptive depth filtration (ADF) technique to remove contaminants. The key benefit of this technique is the retention of contaminants is not due to size exclusion, allowing for higher flow and smaller pressure differentials. In this work [1], nanodiamond particles were attached to the quartz filter to switch the zeta potential of the filter from negative to positive over a wide range of pH. These filters were then tested for retention of acid black 2 (a dye used in leather and textile industry). The diamond coated filters showed 25 times retention of the dye when compared with uncoated filter. Retention performance of these filters were then tested against MS2 bacteriophage, which has an approximate size of around 26nm. The retention was measured in log10 reduction value (LRV), which is the log of the ratio of number of viruses in feed water to filtered water. More details can be found here[1]. While the untreated filters showed a LRV of 0.5, the coated filters had a LRV of 6.2 (>99.9999%), showing a far more efficient removal of the test virus. Finally, we have compared the diamond filter with various positive filters available in the market where it demonstrated higher positive zeta potential against most filters. To test the efficacy of the diamond filter against commercially available positive filters, a concentrated dye solution was used. An equal volume of filter was dipped in a specified volume of dye solution. The absorbance of the dye solution before and after the dipping process was measured. It was found that the diamond modified filters were most effective in removing the dye from the solution. Thus, filters modified with diamond offer a higher positive zeta potential over a wider pH range along with higher dye removal rate, and thus has the potential for higher virus retention over the current ADF technologies. References [1] H. A. Bland et al., ACS Appl. Nano Mater. 4, 3252 (2021).

Resume : In the cancer-targeting nanomedicine, requisite functions have to be programmed for nanoparticles such as 1) dispersibility in a physiological medium, 2) stealth effect on the immune system, 3) targeting specificity, and 4) therapeutic and diagnostic efficacy. In 2011, we imparted very high aqueous dispersibility to nanodiamond (ND) by polyglycerol (PG) functionalization through ring-opening polymerization of glycidol.[1] Further functional programming has been developed through multi-step organic transformations on the surface of ND-PG.[2] In addition, the quantitative characterization methodology has been established for the functionalities by elemental analysis, solution-phase NMR spectroscopy and thermogravimetric analysis. [1-4] The quantitative characterization have made clear the various linear relationships between the amounts of the surface functionalities and the physical or biological properties of the nanoparticles. [3-6] In particular, high density of the PG on the ND surface is found to shield the protein corona formation, giving ND-PG an efficient stealth effect to prolong the circulation in the blood.[5] This greatly improved the targeting specificity of the ND-PG in the tumor through enhanced permeation and retention (EPR) effect, which was confirmed by the fluorescence imaging.[7] When boron-containing carbonaceous nanoparticles with PG were administered to cancered mice, the tumor growth was found to be suppressed under neutron irradiation.[8] The boron neutron capture therapy (BNCT) worked very efficiently through functional programming by 10B and PG at the core and periphery, respectively. Reference [1] L. Zhao, T. Takimoto, M. Ito, N. Kitagawa, T. Kimura, N. Komatsu, Angew. Chem. Int. Ed. 2011, 50, 1388. [2] L. Zhao, Y.-H. Xu, H. Qin, S. Abe, T. Akasaka, T. Chano, F. Watari, T. Kimura, N. Komatsu, X. Chen, Adv. Funct. Mater. 2014, 24, 5348. [3] Y. Zou, N. Komatsu, Carbon 2020, 163, 395. [4] Y. Zou, M. Nishikawa, H. G. Kang, G. Cheng, W. Wang, Y. Wang, N. Komatsu, Mol. Pharmaceutics 2021, 18, 2823. [5] Y. Zou, S. Ito, F. Yoshino, Y. Suzuki, L. Zhao, N. Komatsu, ACS Nano 2020, 14, 7216. [6] Y. Zou, S. Ito, M. Fujiwara, N. Komatsu, Adv. Func. Mater., 2022, 32, 2111077. [7] F. Yoshino, T. Amano, Y. Zou, J. Xu, F. Kimura, Y. Furusho, T. Chano, T. Murakami, L. Zhao, N. Komatsu, Small 2019, 15, 1901512. [8] M. Nishikawa, H. G. Kang, Y. Zou, H. Takeuchi, N. Matsuno, M. Suzuki, N. Komatsu, Bull. Chem. Soc. Jpn. 2021, 94, 2302.

Resume : Fluorescent carbon dots (C-dots) are a relatively new class of carbon nanomaterials that show great promise for applications such as imaging, biosensing and detection. Furthermore, very recent studies revealed that fluorescent C-dots can improve the growth of crops by harvesting ultraviolet light and elevating the photosynthetic efficiency of the crops. In this study, we integrated C-dots into a core-shell mesh network to devise a controlled delivery system of the C-dots to a complex media. For this reason, we synthesised the fluorescent C-dots using a facile one-step hydrothermal treatment. These C-dots then were formulated in ink forms and manufactured using a coaxial 3D printing method using Axolotl A1 bioprinter from Axolotl Biosystems at room temperature. Our main aim in this study is to demonstrate the controlled release of the C-dots in complex chemical environments and the ability to monitor the particle interactions using a confocal fluorescence microscopy system. Our results revealed significant changes in the fluorescent signal of the C-dots due to their surface functionalization and interactions with their carrier polymer shell system. In this talk we will discuss our findings received from the confocal fluorescence microscopy on a theoretical point of view. We will also discuss the potential of this core-shell design of delivery system and applications of the fluorescent C-dots in the sunlight conversion-related sustainable agriculture.

Resume : Quantum dots are well-known fluorophores used in many applications due to their high photostability and brightness. Among them, carbon quantum dots (CQDs) are a relatively new class of carbon nanomaterials which have been extensively studied in the last years to improve their properties towards the final application. Nowadays, most common approaches for CQDs production span from laser ablation, microwave-mediated synthesis, hydro-/solvo-thermal methods and pyrolysis. Here we propose an innovative one-pot synthesis to obtain pH-sensitive CQDs with tunable fluorescence properties. In particular, the procedure is based on the pyrolysis of citric acid (CA) in the presence of different amino acids (i.e., phenylalanine, Phe, or tryptophan, Try). The synthesis has been optimised in terms of decomposition time and dopant concentration to tune the response to pH. Obtained CQDs result sensitive to very small changes in the pH of the aqueous environment thanks to remarkable variations of their fluorescence. Our results evidence that in the CA/Phe case the fluorescence decreases as the pH decreases with an inflection point at pH 6.6, while the system prepared with Try shows an opposite behaviour with an inflection point shifting at higher pH (i.e. 8.3). These different optical response can be addressed to the different functional groups localised at the surface of the CQDs. These carbon-based nanostructures have been tested, in vitro, for the evaluation of the susceptibility of E. coli ATCC 25922 to ampicillin and eventually to estimate the Minimal Inhibitory Concentration (M.I.C.).

Resume : Carbon nanomaterials have seen wide use in supported metal electrocatalyst systems, in biosensors and as the electrode materials in microbial fuel cells (MFCs). Heteroatom-doped nanocarbons may even be applied as catalysts themselves for important processes including the Oxygen Reduction Reaction (1). These applications exploit the intrinsic qualities of carbon materials such as their good conductivity, chemical stability and ease of functionalisation with surface moieities. The modification with specific heteroatoms or covalent grafting of biomimetic layers are both common strategies for tailoring the carbon electrode surface properties for optimal activity in particular applications. In bioelectrochemical applications the carbon material must often be engineered for performance in a complex biological milieu, which adds additional challenges to researchers. In this work we present strategies for the covalent modification of carbon electrode materials with glycan layers for nonspecific fouling-resistant biosensing in complex milieu (2). By contrast, electrografting of mannoside glycans on graphite electrodes is presented as a route for enhancing the selective adhesion of bacteria and biofilm formation on carbon electrodes, thereby accelerating MFC start up times and improving device performance reproducibility (3). We also demonstrate through a combination of microscopy, voltammetric studies, X-ray photoelectron and Raman spectroscopy the effects of altering nanocarbon surface structure and surface chemistry through heteroatom incorporation on fundamental electrode performance in both ex situ biomolecule detection and electrocatalysis (4, 5). References 1. J. A. Behan, E. Mates-Torres, S. N. Stamatin, C. Domínguez, A. Iannaci, K. Fleischer, M. K. Hoque, T. S. Perova, M. García-Melchor and P. E. Colavita, Small, 2019, 15, 1902081. 2. J. A. Behan, A. Myles, A. Iannaci, É. Whelan, E. M. Scanlan and P. E. Colavita, Carbon, 2020, 158, 519-526. 3. A. Iannaci, A. Myles, T. Flinois, J. A. Behan, F. Barrière, E. M. Scanlan and P. E. Colavita, Bioelectrochemistry, 2020, 136, 107621. 4. J. A. Behan, M. K. Hoque, S. N. Stamatin, T. S. Perova, L. Vilella-Arribas, M. García-Melchor and P. E. Colavita, The Journal of Physical Chemistry C, 2018, 122, 20763-20773. 5. J. A. Behan, A. Iannaci, C. Domínguez, S. N. Stamatin, M. K. Hoque, J. M. Vasconcelos, T. S. Perova and P. E. Colavita, Carbon, 2019, 148, 224-230.

Resume : Free radicals are generated as host-derived factors, which mediate various signaling processes in host cells during interactions between viruses and hosts. Although this information is of utmost importance to thoroughly understand the virus pathogenesis and design better anti-viral drugs or vaccines, obtaining it with the conventional free radical/ROS detection techniques is impossible. Here, we elucidate the utility of diamond magnetometry for studying the transient free radical response of baby hamster kidney-21 (BHK-21) cells upon Semliki Forest virus (SFV) infection, without influence on the intracellular redox reactions or enzymatic activity. Nitrogen-Vacancy (NV) defect centers in diamond crystals can detect magnetic noise nearby (< 10 nm), which is produced by the spin of unpaired electron of free radicals. Although diamond magnetometry can only reflect the paramagnetic ROS, free radicals are, however, either the source of the oxidative stress response (i.e. nitric oxide and superoxide anion radicals) or the most reactive ROS (i.e. hydroxyl radical). In this study, we report the formation and characterization of nanodiamond-virus conjugates, SFV-FND. By using this conjugates, we optically probe the alterations in free radical composition near infectious virus via measuring the spin-lattice relaxation (T1) of NV defect ensembles embedded in intracellular nanodiamond. In our conclusion, the alterations of T1, which represents the intracellular free radicals’ concentration, is related to the viral replication process. Moreover, diamond magnetometry is also used to monitor real-time free radical levels during the early infectious process (which is also called the latent period). Diamond magnetometry appears to be a powerful technique for unraveling viral-infected pathways and pathogenesis that involve free radicals.

Resume : Carbon-based quantum particles (CQDs) are an emerging class of quantum dots with unique properties owing to their quantum confinement effect. Many reviews appeared recently in the literature, highlightening their optical properties, structures, and applications. The potentials of CQDs functionalized with boronic acid and/or amine functions to interfere with the entry of herpes simplex virus type 1 (HSV-1) and as therapeutic options for highly pathogenic human coronavirus (HCoV) infections have been investigated lately by us and some of the materials related aspects will be presented here. We will demonstrate in addition that fibrillation of collagen I is prevented most strongly by positively charged CQDs with pulsed-laser illumination allowing the destruction of type I collagen aggregates and vitreous opacities (as obtained from patients after vitrectomy). Vitreous opacities degrade contrast sensitivity function and can cause significant impairment in vision-related quality-of-life, representing an unmet and underestimated medical need. Thanks to the dual effect of cationic CQDs as protein aggregation inhibitors as well as disaggregation capacity, CQDs might become attractive therapeutic tools for the treatment of vitreous opacities by avoiding or postponing their reformation after laser treatment. References [1] K. Nekoueian, M. Amiri, M. Sillanpää, F. Marken, Boukherroub, S. Szunerits, Chemical Society Reviews 2019, 48, 4281-4316. Carbon-based quantum particles: an electroanalytical and biomedical perspective [2]A. Łoczechin, K. Séron, A. Barras, S. Belouzard, Y.-T. Chen, N. Metzler-Nolte, R. Boukherroub, J. Dubuisson, S. Szunerits. ACS Applied Materials and Interfacs 2019, 11, 46, 42964-42974. Functional Carbon quantum dot as medical countermeasures to humancorona virus (HCoV). [3] A. Barras, Q. Pagneux, F. Sané, R. Boukherroub, D. Hober, S. Szunerits . ACS Applied Materials & Interfaces 2016, 13, 9004-9013. Inhibition of Herpes simplex virus type 1 entry by functional carbon nanodots [4] A. Barras, F. Sauvage, I. de Hoon, K. Braeckmans, D. Hua, G. Buvat, J. C. Fraie, C ; Lethien, J. Sebag, M. Harrington, A. Abderrahamni, R. Boukherroub, St. De Smedt, S. Szunerits. Carbon quantum dots as a dual platform for the inhibition and light-based destruction of collagen fibers: implications for the treatment of eye floaters. Nanoscale Horizons, 2021, 6, 449-461 (Cover art)

Resume : A promising battery electrode architecture is the hybridization of two nanomaterials – a current collector and an active material – into a single structure to maximize stress/charge transfer between the building blocks [1, 2]. Hybrids based on a nanocarbon and an inorganic are particularly suited to this purpose as they eliminate the need for polymeric binders, additives, or metallic current collectors while enhancing battery performance [1]. CNT fibres are ideal as current collectors due to their unique combination of high electrical conductivity, porosity, toughness, and electrochemical stability [2, 3]. In addition, they provide a scaffold for the growth of the active material. It has been recently shown that integrating MoS2 into a nanocarbon network of CNT fibres gives a flexible hybrid electrode that outperforms most high-capacity structural electrodes and provides high out-of-plane electrical conductivity [1]. In this work, we applied novel processing methods for the controlled fabrication of CNT fibre/inorganic hybrids to study their structure and mechanical properties in detail. Gas-phase functionalization and electrodeposition were used to synthesize the hybrids, and then targeted Joule heating was done to crystallize the inorganic phase. Compared to traditional heating using a furnace, Joule heating is more efficient in terms of time, cost, and energy. The structure-processing-property relationships for several hybrid structures composed of CNT fibres and ceramic matrices were characterized using advanced electron microscopy, Raman, XRD, and mechanical testing.

Resume : Carbon cloth (CC) is a widely employed flexible electrode material for supercapacitor (SC) applictions. However, the commercially available CCs usually suffer from hydrophobic and relatively inert surface chemistry, and low specific surface area. Although the activation of CC with concentrated acids, or KOH solution leads to increased capacitance of the electrodes by introducing oxygen-containing functionalities and increasing the porosity and surface area, the values measured (e.g., 21.3 mF cm-2 at 20 mA cm-2 for concentrated acids activated CC electrode in 1.0 M Na2SO4) are still not high enough to meet specific application requirements. In this talk, two approaches have been proposed to improve the performance of CC based capacitor electrodes. One is the addition of redox species on the electrode surface and/or in the electrolyte solution to form pseudocapacitors (PCs) or redox-electrolyte enhanced SCs. The other is the fabrication of hybrid carbon materials through the growth of three-dimensional and porous cabron nanofibers (CNFs) on CC. In this context, the coating of MnO2 on CC and the performance of fabricated MnO2/CC PCs will be first disclosed. The MnO2/CC PC shows a high capacitance of 758.8 mF cm-2 at 20 mA cm-2 in 1.0 M Na2SO4 aqueous solution. With the additional introduction of a water-soluble redox specie of 0.1 M KI in the electrolyte, a higher capacitance of 1867.1 mF cm-2 (20 mA cm-2) has been achieved. On the other hand, CNFs have been grown on CC using copper catalyst and C2H2 reaction gas with a thermo-chemical vapour deposition technique. The CNF/CC electrical double layer capacitor (EDLC) exhibits a capacitance of 699.6 mF cm-2 at 10 mV s-1 in 1.0 M H2SO4 aqueous solution. These values are 30 to 90 times higher than that of activated CC based EDLCs. Comparison of our results with those shown in the literature enables us to conclude that these approaches are useful and promising for future power devices.

Resume : CuS has shown promising properties for its use as electrode material for lithium- and sodium-ion batteries because of its low cost, resource abundance, superior theoretical capacity (560 mAh g−1), and high electronic conductivity (10000 S cm−1). Moreover, CuS nanoparticles have shown good results when employed as cathodes in rechargeable magnesium batteries. In order to increase conductivity and active surface area of this material, several copper sulphide-reduced graphene oxide aerogels (CuS-rGO) with different CuS:rGO ratios have been prepared. In this presentation the preparation method, their physico-chemical properties, and their promise as electrodes in rechargeable batteries will be discussed.

Resume : Molecular oxygen is considered as a green, cheap and ideal oxidant for environmental water treatment. However, most organic compounds are difficult to be directly oxidized by molecular oxygen due to their spin restriction. Molecular oxygen can be activated to produce a variety of reactive oxygen species (ROS). Among these ROS, the hydroxyl radical (HO∙) has the highest oxidation potential (2.8 V) and can degrade and even mineralize organic pollutants without selectivity. However, the steady-state concentration of HO∙ is only 7.5× 10-12-3 ×10-11 M, resulting in a slow apparent rate constant for degradation of pollutants by conventional advanced oxidation processes (AOPs). To solve this problem, we designed Pd-SA/F-TiO2 catalyst to achieve rapid HO∙ generation by molecular oxygen activation by constructing chemical channels to regulate the electron transfer path in the photoelectrocatalytic process. The main conclusions of this study are as follows: (1) A chemical channel for electron transfer was constructed for the first time to rapidly produce HO∙ (9.18 μ mol L-1 min-1), which is 2.6 ~ 52.5 times higher than AOPs. We demonstrate fast electron transfer and high HO∙ yield through experimental and theoretical calculations. (2) HO∙ generation is accelerated by designing single atom catalyst to construct a chemical channel that regulates the electron transfer path. The O2-Pd-F4 structure on the catalyst surface improves the selectivity of 2-electron oxygen reduction (~ 99%), and the constructed Pd-F-TiO2 chemical bond facilitates electron transfer from conduction band to single atom Pd to reduce Pd∙∙∙O-OH to HO∙. (3) Photoelectrochemical activation of molecular oxygen overcomes the pH limitation of AOPs and exhibits high HO∙ production over a wide pH range (pH = 3 to 11). The degradation of pollutants showed high TOC removal (93.2 %) and toxicity removal (99.3 %), and the degradation of pollutants was less affected by the actual water, which provided guidance for the treatment of actual wastewater.

Resume : Abstract Carbon-based nanostructures have received much attention due to their unique physicochemical properties and diverse applications. Compared to other carbon nanostructures, carbon dots (C-Dots) exhibit abundant photoluminescence (PL) and photoelectrochemical properties. C-Dots can be defined as spherical-like carbon particles (graphitic fragments) with sizes less than 10 nm. In 2010, we developed a facile electrochemical approach for the large-scale fabrication of high-quality C-Dots with high purity, using graphite rods and pure water as the starting materials. These well crystalline C-Dots show size-dependent photoluminescence and rich photoelectrocatalytic properties. Further, C-Dots with definite chemical structures and controlled morphology are being pursued, such as chiral C-Dots and crystalline C3N C-Dots. We demonstrated C-Dots have many unique properties, such as tunable PL, dispersibility, low toxicity, biocompatibility, bio-degradation, abundant raw materials and low cost. Those features thus bode well for the wide applications of C-Dots in bioimaging, optoelectronic devices, catalysis and functional materials. The relationships between the structure, surface composition and photoelectrochemical properties of C-Dots were clarified. Especially, we have proposed a simple semi-empirical equation for determining the conduction bands and valence bands of the C-Dots calculated from their band gaps. In such semi-empirical model, a linear relationship between CB (VB) and band gap is observed. A series of carbon-based, highly efficient photocatalytic, electrocatalytic and photoelectrocatalytic systems for energy and environmental applications were designed and prepared. C-Dots show high catalytic activities for many reactions, C-Dots also act as functional components for the high-performance photocatalyst and electrocatalyst design. We proposed a new design concept of a cheap composite EC catalyst for a tunable, stable, selective and efficient production of syngas, made of three components: a HER catalyst, a CO2 reduction catalyst towards CO and a catalyst which stabilizes the active hydrogen (H•) necessary to trigger both HER and the CO2 reduction reactions. In which, CDots are the generation site of H• needed to trigger both the reduction of CO2 to CO and the HER. A new method to analyze the electron transfer number of photocatalysis by forced kinetic process under steady-state photoexcitation was proposed for the first time, and then demonstrated a new mechanism of "two-step two-electron pathway" for efficient overall water photo-splitting. We also proposed a new in-situ and transient photoelectrochemical analysis system, by which we found a new photoelectrochemical property of C-Dots, namely, salt-enhanced electron sink effects. The ions in seawater ionize the functional groups of CDs, which enhances the electron sink effect of CDs, making the photocatalytic activity in seawater better than that in the pure water. C-Dots promise highly efficient new photoelectrocatalysts towards clean and new energy catalysis and the conversion from solar energy to chemical energy. Keywords: Carbon Dots; Photocatalysis; Electrocatalysis; Photoelectrochemical property. Reference. 1. Q. Y. Wu, J. J. Cao, X. Wang, Y. Liu, Y. J. Zhao, H. Wang, Y. Liu, H. Huang, F. Liao, M. W. Shao, Z. H. Kang, Nature Communications, 2021, 12, 483. 2. S. J. Guo, S. Q. Zhao, X. Q. Wu, H. Li, Y. J. Zhou, C. Zhu, N. J. Yang, X. Jiang, J. Gao, L. Bai, Y. Liu, Y. Lifshitz, S. T. Lee, Z. H. Kang, Nature Communications, 2017, 8, 1828. 3. C. Zhu, Y. J. Fu, C. A. Liu, Y. Liu, L. L. Hu, J. Liu, I. Bello, H. Li, N. Y. Liu, S. J. Guo, H. Huang, Y. Lifshitz, S. T. Lee, Z. H. Kang, Advanced Materials, 2017, 29, 1701399. 4. J. Liu, Y. Liu, N. Y. Liu, Y. Z. Han, X. Zhang, H. Huang, Y. Lifshitz, S. T. Lee, J. Zhong, Z. H. Kang, Science, 2015, 347, 970. 5. H. T. Li, X. D. He, Z. H. Kang, H. Huang, Y. Liu, J. L. Liu, S. Y. Lian, C. C. A. Tsang, X. B.Yang, S. T. Lee, Angew. Chem. Int. Ed. 2010, 49, 4430.

Resume : The research of easy and inexpensive assembly strategies of well-defined nanostructures represents nowadays a huge challenge for nanoscience. In particular, a great attention is being devoted to the design of new hybrid nanostructures that exploit the synergetic combination of different nanomaterials to obtain specific functional features, generally absent in the individual components, as for example photocatalytic or photovoltaic properties. In this perspective, Carbon Dots (CDs), a novel family of small (<10 nm) luminescent carbon nanoparticles, possess particularly beneficial characteristics to be incorporated in more complex structures by coupling them to other species. Here we investigated the photo-physical and -chemical response of binary nanohybrids obtained through the spontaneous coupling of specific CDs to metallic nanoparticles (MNPs) with controlled surface charge. Specifically, we aimed to investigate whether the strong propensity of CDs to engage in photoinduced charge-transfer can complementarily cooperate with the carrier mobility within MNPs, to achieve a photocatalytic response in the newly constituted nanohybrids. By means of a simple bottom-up approach involving a thermally-induced decomposition route, we synthetized heavily nitrogen-doped CDs characterized by strong optical absorption-emission bands. Such CDs were coupled via a quick self-assembly method to noble-metal plasmonic nanoparticles, obtained by the Turkevich method and engineered in order to have both a negative and a positive surface charge version of each type of MNP. Evidence of the successful CDs-MNPs couplings and interactions is provided by steady-state and time-resolved optical measurements and further confirmed by direct imaging. The optical data show a CDs photoluminescence quenching on a sub-nanosecond time scale, due to a very efficient photoinduced charge transfer between the interacting nanosystems. We also found that the driving force leading to CD-MNP self-assembly is not purely electrostatic, although surface charge appears to play a role in the charge-transfer processes. Finally, as anticipated, we assessed the photocatalytic responses of the nanohybrids by evaluating the photodegradation of methylene blue under UV-VIS light. Some of the CD-MNP nanohybrids displayed an emergent photocatalytic activity due to the interface charge separation triggered by light absorption. The results are very promising and encourage further studies to develop a new generation of eco-friendly photocatalytic carbon-based devices for light-driven applications.

Resume : Black carbon with high surface area, conductivity and stability is widely applied as the support for metal nanoparticle catalysts in various electrochemical reactions. However, there is a challenge to modulate the metallic nucleation growth on black carbon due to the deficiency of nucleation sites derived from its high graphitization nature. Herein, Rhodium (Rh) nanoparticles, as one of classic noble metals, were realized to uniformly on-site deposit on the surface of black carbon with controllable sizes via the CoP nanoparticles served as a bridge. As a result, it is found the obtained Rh/black carbon exhibits the obvious size effect in the hydrogen evolution reaction (HER), and Rh with the size of ~3.23 nm shows excellent HER reaction activity with the overpotential of only 3 mV at 10 mA cm-2, far surpassing other reported Rh-based catalysts. Moreover for the practical applications, the Rh/black carbon catalyst also displays lower cell voltage of 1.81 V at 1 A cm-2 and smaller charge transfer resistance of 0.299 Ω at 60°C than those of commercial 20 wt% Pt/C-JM (1.84 V and 0.337 Ω) in the anion exchange membrane water electrolysis system. This work provides a facile strategy to control the size of metallic nanoparticles with high dispersion on the intrinsic surface of black carbon for the design of advanced electrocatalysts.

Resume : Apart from the noticeable photoluminescent properties, graphene quantum dots (GQDs) have exhibited as powerful coreactants for the anodic electrochemiluminescence (ECL) of Ru(bpy)32+ in recent studies. Herein, a universal approach to integrate the luminophor (Ru(bpy)32+) and coreantants (oxygen-rich GQDs) in a single molecule was developed to enhance the luminous efficiency. Due to the more efficient electron transfer in the intramolecular, the covalently-linked Ru(bpy)32+-GQDs (Ru-GQDs) hybrid exhibited more efficient ECL than the uncoupled Ru(bpy)32+/GQDs system. This self-enhanced ECL approach shows great potential in the trace analysis.

Resume : Electrochemical water splitting driven by renewable energy sources is considered to be a promising carbon-free pathway for the production of the “green” fuel hydrogen. Such electrochemical water splitting can be realized by water electrolysis powered by renewable electricity [e.g., photovoltaic (PV) cells or wind turbines] or alternatively by direct light utilization [e.g., using a photoelectrochemical (PEC) cell or photocatalysis]. Despite the promises of such an approach, the process economics are not yet favorable. For this reason, novel electrochemical approaches have been proposed such as integration of electrochemical processes. In this context, the use of membrane divided electrochemical reactors is a well-known technology in hydrogen production (at the cathodic compartment). Nevertheless, the anodic reactions have not received great attention. Then, on the one hand, an alternative is that the electricity supply for promoting anodic reactions can be considered the main vector to parallel hydrogen production, reducing the energy consumption and costs. Being an eco-friendly sustainable process, if the electricity is produced by PV cells. On the other hand, the use of boron doped diamond technologies, in the anodic electrolytic-compartment, can be considered a promising alternative because the wastewater treatment, disinfection of water or electrosynthesis of oxidants can be attained. Thus, here we have proposed the production of sulfate-based oxidizing species as anodic reactions using boron doped diamond (BDD) with simultaneous production of green hydrogen. Results clearly have demonstrated that higher production efficiencies, from 0.5 to 2.0 mM, of sulfate-based oxidizing species can be obtained depending on applied current densities with BDD, producing in parallel, from 0.2 to 0.8 L of pure hydrogen in 120 min, at cathodic reservoir. Solutions of sulfate-based oxidizing species can be used as an off-grid technology for degrading organic pollutants, increasing the high-added value of the technology. Meanwhile, lower consumption requirements were estimated by green hydrogen production with PV panels.

Resume : Graphene quantum dots (GQDs) and oxidized GQDs (GOQDs) were successfully prepared via ultrasonic stripping and oxidation of graphite nanoparticles in solution, respectively. The size, structure, fluorescent properties, and electron transfer rate of both GQDs and GOQDs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), fluorescence spectrophotometer, and electrochemical impedance spectroscopy (EIS), respectively. Both GQDs and GOQDs exhibited catalytic activity to H2O2, which was similar to that of nano-enzyme. Compared to GOQDs, GQDs showed faster electron transfer rate, but GOQDs had better catalytic activity. It indicated that the oxygen content on the surface has an important effect on the catalytic activity of GQDs as nano-enzyme.

Resume : Photocatalytical systems are used as a promising way to produce sustainable hydrogen, seen for the next years as an efficient alternative to fossil fuels. These systems are generally composed by a semi-conducting metal oxide. In fact, as photocatalysts, semi-conducting metal oxides are particularly recognized for their photocatalytical and photo-electrocatalytical applications. Nevertheless, they suffer from drawbacks such as a low photoactivity in the visible domain, a low conductivity and a high rate of electron hole pair recombinations. In order to overcome this issue, several works have already demonstrated the possibility to couple few semi-conducting materials to metallic nanoparticles or quantum dots (QDs). However, this type of nanoparticles are usually expensive, toxic and non-environmentally friendly particles. In this study, we decided to work with a new promising family of carbon nanoparticles, with very exciting optical properties, named carbon dots (Cdots). These carbon nanoparticles which have already shown auspicious catalytic benefits, have QDs like interesting fluorescence properties. Normally smaller than 10 nm, they present a tunable fluorescence, UV and visible absorption and low photobleaching. Thanks to their graphitic structure, they can also improve the electronic conductivity and promote the separation of charge carriers of various semi-conducting materials. Moreover, they present a low cytotoxicity and excellent biocompatibility – because mainly made of carbon – compared to the other quantum dots with heavy metal cores. The aim of this work is to use the Cdots as co-catalysts for the photocatalytical production of dihydrogen. The strategy is to photosensitize our semi-conducting materials, zinc oxide (ZnO) and tungsten oxide (WO3), by the formation of hybrids. Discovered 15 years ago, the Cdots are the subjects of many articles of these last ten years, speaking about easy ways to produce them. In this context, an investigation on the N-doped Cdots synthesis from small organic molecules by a hydrothermal method using microwaves, commonly used in the literature, is performed. We evidenced the presence of large amount of organic fluorophores, responsible for the commonly describe Cdots typical fluorescence. These results are in agreement with several very recent studies published. Such observation has stimulated a real debate about the products of the synthesis and has questioned even more the role of Cdots in photocatalysis, despite the many works in the literature extolling the astounding properties of Cdots. To clarify the situation, our approach tackles this issue by performing additional purification processes which should allow to produce pure Cdots without fluorophores, in order to investigate the role of each compounds in the photocatalytical activity. In parallel, we analyzed other Cdots synthesis processes in order to obtain clear Cdots and study their influence on the photocatalytical dihydrogen production.

Resume : For the realization of sustainable development goals, it is important that regional ecosystems develop and use universal sustainable technologies. It is considered that the widespread use of renewable energy is essential for this purpose. Thus, there is an urgent need to develop renewable energy production and storage devices. A wood-derived carbon is a promising electrode as an energy device because of its high porosity improving the surface area of the carbon. Recently, we have reported highly active wood-derived electrochemical catalyst for oxygen reduction reaction which occurs on the cathode of metal-air batteries and fuel cells (1). The pyrolyzed wood performed high porosity and high catalytic activity. The pyrolysis is required to control the atmosphere at high temperatures and under inert gas, resulting in being expensive and cumbersome. Herein, we report the direct laser-pyrolysis with a commercial blue laser and apply the carbon to the electrocatalyst for the oxygen reduction reaction. Paulownia was used as a wood carbon source. Wood chips were pyrolyzed with the blue laser under the ambient atmosphere. The irradiated area became black and metallic. The obtained carbon had macro-scale pores confirmed by an optical microscope and showed the graphitic peaks confirmed by Raman spectra. The electric resistance was improved by increasing the intensity of the blue laser, and the obtained carbon performed highly active electrocatalytic activity by adding metal sources as catalysts. Next, the obtained wood-derived carbon was used as the electrocatalyst for the oxygen reduction reaction. The laser-induced carbon has catalytically active, but the metal sources added before and after laser carbonization are also catalytic active sites. In particular, molecular catalysts are promising materials since they show superior oxygen reduction activity without any pyrolysis processes2. In this study, the Fe(NO3)3 was used as a metal source and added to the wood before the pyrolysis (wood-Fe). In addition, iron phthalocyanine was modified on the obtained carbon material using the organic solvent (wood-FePc) (2). The oxygen reduction properties were evaluated in 0.1 M KOH, and the catalytic activity was found to increase in the order of wood, wood-Fe, and wood-FePc. From these results, the wood-derived laser-induced graphene for the electrocatalysts of the oxygen reduction reaction was successfully obtained from wood using the blue laser under the ambient atmosphere. References: 1) Y. Goto, Y. Nakayasu, H Abe, Yuto Katsuyama, T. Itoh and M. Watanabe, Phil. Trans. R. Soc. A (2021) 379: 20200348. 2) H. Abe et al., NPG Asia Materials 11, Article number: 57 (2019)

Resume : The sp2-hybridized carbon network can make the transformation of nanomolecular structures such as fullerene, carbon nanotubes and graphene. Their constructed molecular structures are the key to introduce their unique physical properties caused by their localized density of states. Indeed, those features are also reflected to their electrochemical performance for energy applications. For the investigation of those performance with nanomolecular structures, it is required to apply an electrochemical analytical technique. As a quantitative nanoscale electrochemical analysis, we have applied a self-developed scanning electrochemical cell microscopy (SECCM) which uses a droplet-based electrochemical cell created by their pipette-probe. In this study, we have applied SECCM to various carbon structures such as folded edge, armchair/zigzag edges, wrinkle, bilayer structures etc. in graphene, graphite and carbon nanotubes for visualization of their electrochemical activities as nanoscale electrochemical imaging. Those imaging results showed the importance of their structures to enhance or weaken their local electrochemical behavior, leading to the effective structural design of high-performance electrochemical systems.

Resume : The production of cheap energy from renewable sources, like solar or wind energy, provides the opportunity to use electrochemistry for the synthesis of chemical products in a cost-effective manner. The development of photoelectrochemical systems and electrolyzers to produce H2 from water has been the most studied as a means to store renewable energy and thus solve the inherent problem of the source intermittency. Lately, the reduction of CO2 to energy-rich chemicals (CO, formic acid, methane, etc.) is gaining increasing attention. However, none of these routes have become competitive with conventional, but less environmentally friendly, production methods yet. To overcome this gap, there are other alternative chemical routes, such as the synthesis of products with added value for the chemical industry which may combine both environmental and economical interests, despite being much less developed. One chemical transformation of interest is the oxidation of 5-hydroxymethyl-furfural (HMF), obtained from biomass, to produce 2,5-furandicarboxylic acid (FDCA), a precursor of poly-ethylene 2,5-furandicarboxylate (PEF) a polymer called to substitute polyethylene terephthalate (PET) thanks to its renewable origin. Among reduction reactions, the production of aniline from nitrobenzene has a great interest as this species is widely employed as a building block for the production of aniline-based dyes, explosives, pesticides and drugs. This is a 3-steps mechanism that involves the insertion of 2e- and 2H+ species in each of the hydrogenation steps of the NO2 group of the molecule. Electrodes made of Cu and Cu-based compounds have efficiently been used for the electro-reduction of nitrobenzene in aqueous media due to their high energy of activation for the competing hydrogen evolution reaction (HER). Compared with copper, palladium shows high activity for the hydrogenation of organic compounds, mainly due to its affinity for the adsorption and storage of H* species. In this work, decoration of Cu foil surface with Pd by galvanic replacement technique was used to improve the catalytic properties of the reduction electrode. An enhancement of the performance and selectivity of this electrode was obtained with respect to pure Cu, achieving a complete reduction nitrobenzene solution and obtaining aniline with 70% yield for aniline. Finally, a detailed analysis using Impedance Spectroscopy has revealed the improvement in the catalytic performance of Cu with Pd electrodes by increasing the adsorption of hydrogen in the electrode surface, which favours the selectivity in the reduction of nitrobenzene to aniline in a simple three-electrode system like batch reactor type, using inexpensive Cu subtract and an easy modification technique. In conclusion, developing materials capable of producing and stabilize H* in the electrode surface is key to reach an effective reduction and hydrogenation of organic species.

Resume : The lithium-ion (de)intercalation process of graphite has been widely studied as a typical anodic process of lithium-ion battery systems for few decades. This process simply expected to be caused by the insertion of lithium-ions into the graphene-graphene layers of the graphite via their edges and some structural defects on the basal plane. However, it is still not observed with the direct evidence by electrochemical analysis. In general, the electrochemical analysis for the insertion process performs in bulk sample, which is difficult to distinguish the process at the edge and basal plane. Furthermore, the potential range of the insertion process in graphite is known to be introduced at about +0.21 V (vs Li/Li+). The range is also sufficiently low to introduce some decomposition of organic electrolyte on whole the graphite surface as solid electrolyte interphase (SEI), and some compounds of the SEI would support the lithium-ion insertion. The presence of the SEI also hinders the insertion process between graphene-graphene layers. In this study, we have prepared two samples; few layered graphene on SiC substrate and thin film graphite cleaved from HOPG. For the spatially resolved electrochemical analysis of lithium-ion insertion on those samples, the scanning electrochemical cell microscopy (SECCM) was applied with a probe filled with organic electrolyte and a lithium metal reference electrode. The probe of SECCM creates a droplet which behaves as an electrochemical cell on the samples. The confined local area by the probe showed clear difference of lithium insertion process at the edge and basal plane, showing a direct evidence of the lithium-ion insertion process.

Resume : Abstract: Diamond electrochemistry is known to be mainly affected by the amounts of sp3-carbon and carbon impurities, surface terminations, and diamond crystallinity. In this presentation, we will introduce the effect of the used substrate during diamond growth on diamond electrochemistry. In this regard, boron and nitrogen bi-element incorporated nanocrystalline diamond (B-N-NCD) films with a thickness of about 180 nm were grown on a Si, Ti and Ta substrates. They are named B-N-NCD/Si, B-N-NCD/Ti/Si/, and B-N-NCD/Ta/Ti/Si/, respectively. These samples were characterized using different microscopies, spectroscopies, and electrochemical techniques. The electrochemical results showed that the B-N-NCD/Ta/Ti/Si/ features superior electrochemical activities to B-N-NCD/Si and B-N-NCD/Ti/Si. The diamond films grown on the Ta substrate exhibit faster electron transfer processes and smaller electron transfer resistance of redox probes ([Fe(CN)6]3-/4- and [Ru(NH3)6]3+/2+) than those grown on other substrates. Moreover, these films have larger effective response areas and lower potentials toward oxygen and hydrogen evolution. In summary, the intrinsic activity, reaction kinetics and electrochemical applications of diamond films are highly dependent on the substrate that is employed for the diamond growth.

Resume : Graphene is promising a sensor material, thanks to its excellent electron transport properties. Advantageously, graphene is highly versatile and can be altered in composition (through doping, defects and chemical functionalisation) as well as structurally (from planar to 3D via laser ablation). Changes in the composition and structure can alter the sensing properties of these graphene materials. In this study, we are investigating the behaviour of graphene and graphene-based materials for application as electrochemical sensors, through combination of experimental characterisation and theoretical modelling. As the first key step, electrochemical performance of graphene and graphene-based materials in sensing a standard redox probe, the hexaaminoruthenium complex, was investigated. Cyclic voltammetry experiments showed that composites of graphene with carbon nanotubes and graphene aerogels showed a stronger response than pure graphene towards the redox probe. To interpret these results, the interaction of hexaaminoruthenium with graphene, with a single-wall nanotube and with curved graphene was modelled using dispersion corrected density functional theory. Few-layers graphene and defects such as a monovacancy and a divacancy in graphene were also considered. Graphene curved in the armchair and zigzag direction was considered as a model for graphene aerogel. The hexaaminoruthenium molecule adsorbed via physisorption on all of these materials. The rates of charge transfer from hexaaminoruthenium to the carbon materials were evaluated using Marcus theory of electron transfer. Our calculations showed faster rates of charge transfer to nanotubes and curved graphene compared to pure graphene, and significantly faster charge transfer rates to vacancy-containing graphene compared to the defect-free material. These results indicate that nanotubes, defects in graphene and changes in morphology (curvature) result in a stronger electrochemical sensor response than pristine graphene and would produce a better sensor material.

Resume : Fluorescent nanodiamonds (FNDs) have emerged as promising quantum materials for bio-medical applications and precision sensing due to their unique magneto-optical properties. They are obtained by implementing elemental defects into the carbon lattice, such as the nitrogen vacancy (N-V) or silicon vacancy (Si-V) centers, which results in unconditionally stable fluorescence without bleaching or blinking even after several months of continuous excitation. The emission wavelength of FNDs is not size-dependent and is tunable from the visible to the near infrared region according to the elemental defects. In addition, the N-V center in FNDs serves as single-spin sensor that locally detects various physical properties with nanoscale precision offering great potential for elucidating crucial parameters in complex biological environments. There is currently no other nanomaterial that would offer such unique features. There is an urgent need to prepare high quality FNDs in a controlled fashion to customize diamond sizes and lattice defects. We present the synthesis of FNDs from molecular seeds at low temperature and pressure that paves the way to tailored quantum materials with precisely defined lattice defects. In addition, functionalization of FNDs is crucial for imaging and nanoscale sensing applications in biology and medicine. FND surface coatings based on biopolymers, proteins and nanogels will be presented that enable cellular uptake and intracellular sensing of local temperature changes. Temperature is an essential parameter in all biological systems but information about the actual temperature in living cells is limited. We report FND nanothermometers that serve as a heat generators and sensors at the same time. This approach allows recording local temperature changes in different cellular environments inside cells and correlate these with i.e. phototoxic features.

Resume : Sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials. Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects [1]. Depending on the material studied, some specific spectroscopic parameters (e.g., band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects. We review the way Raman spectroscopy is used for studying sp2 based carbon samples containing defects, with a special focus on a-C:H layers, with post heat treatment up to 800°C [2-5]. Counterintuitively, because of the electronic structure of aromatic building blocks, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism. This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials. We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of a-C:H and defective carbons Raman spectra. Related references [1] A. Merlen, J. G. Buijnsters and C. Pardanaud A Guide to and Review of the Use of Multiwavelength Raman Spectroscopy for Characterizing Defective Aromatic Carbon Solids: from Graphene to Amorphous Carbons Coatings 7 (2017), 153 [2] L. Lajaunie, C. Pardanaud, C. Martin, P. Puech, C. Hu, M.J. Biggs, R. Arenal Advanced spectroscopic analyses on a:C-H materials: Revisiting the EELS characterization and its coupling with multi-wavelength Raman spectroscopy Carbon 112 (2017) 149 [3] C. Pardanaud, G. Cartry, L. Lajaunie, R. Arenal, J. G. Buijnsters Investigating the Possible Origin of Raman Bands in Defective sp2/sp3 Carbons below 900 cm−1: Phonon Density of States or Double Resonance Mechanism at Play? C-journal of carbon research 5 (2019) 79 [4] C. Pardanaud , C. Martin, G. Giacometti, N. Mellet, B. Pégourié, P. Roubin Thermal stability and long term hydrogen/deuterium release from soft to hard amorphous carbon layers analyzed using in-situ Raman spectroscopy. Comparison with Tore Supra deposits Thin solid films 581 (2015), 92 [5] C. Pardanaud, C. Martin, P. Roubin, G. Giacometti, C. Hopf, T. Schwarz-Selinger, W. Jacob. Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers Diamond and Related Materials 34 (2013), 100-104

Resume : Fully Hydrogenated graphene, also known as graphane (GA), offers a safe and high hydrogen storage capacity, but its production requires a high energy consumption. Graphene oxide (GO) can be an alternative to bound hydrogen to carbon atoms using an electrochemical procedure. Then, this hydrogen may be released from the resulting hydrogenated reduced GO (rGO-H) and fed into alkaline fuel cells to produce electricity. However, there are several limitations that hamper the development of this technology, especially at industrial level, and some of them can be solved through the development of reliable, fast and non-destructive methodologies for monitoring the GO hydrogenation degree and its concentration in water dispersions that are compatible with industrial process monitoring. In the present study, Raman scattering spectroscopy is proposed as a very suitable technique for development of such methodologies. GO, GA, and rGO-H samples with different hydrogenation and oxidation degree in powder, flake and dispersion samples were measured by Raman spectroscopy varying the experimental conditions and identifying the key features in the spectra that can be applied for the monitoring purposes. Additionally, a methodology to monitor the GO concentration in water dispersions based solely on Raman spectroscopy is also proposed. As result, adequate measurement conditions and spectra processing procedures were developed allowing to propose methodologies compatible with real-time and in-line process monitoring that enable to discriminate hydrogenated and non-hydrogenated GO, to estimate the C/O ratio, the C-H amount, and to determine the GO weight concentration in a water dispersion. Hydrogen loading in rGO-H of 20-30% with faradic efficiencies up to 50% were achieved in the samples subjected to the analysis, thus assuring the viability of employing GO for hydrogen storage and the applicability of the proposed methodologies for the high performance material. The testing process methodologies in conditions close to an industrial environment will be also presented together with a monitoring system design compatible with in-line process monitoring (acquisition time < 1 min).

Resume : One of the most important challenge that will face optoelectronic devices in the future is to find a suitable and viable substitution material to Transparent Conductive Oxide (TCO) and more especially to Indium based oxides like Indium Tin Oxide (ITO). We recently demonstrated that a full laser process allows the synthesis of a pure carbon transparent conductive electrode showing performances in the same range that ITO. This process only made of two steps consists in a synthesis (typically 20 nm) of Diamond-Like Carbon (DLC) by Pulsed Laser Deposition (PLD) from a high purity graphite target, followed by a laser surface annealing. By sharing many properties with diamond, DLC offers for example, a very transparency in the visible range, chemical inertness, high wear resistance and a very high electrical insulation. Despite all these common points, DLC present a relative high opacity in the UV range. Thanks to this particularity, an UV-laser surface treatment permits to bring energy to the DLC surface, leading to the formation of a Thin Graphitic Layer (TGL). Being highly opaque in the UV-range, the laser energy absorption is restricted to the very first atomic layers of the DLC thin film and leads to the formation of a pure graphitic layer (typically 2 nm as confirmed by X-ray Photoemission Spectroscopy). This promising technology owns very interesting perspectives as being obtained at low temperature and via a full laser process and therefore compatible with all standard microelectronic technological steps. We also investigate the direct integration of this technology in an Organic Light Emitting Diode (OLED) showing the potential of this original process. We also highlight the biocompatibility of the layers, offering very large application fields.

Resume : Gapped bilayer graphene can support the presence of intragap states due to top and bottom gate potentials applied to the graphene layers. Electrons in these states display valley-momentum locking, which makes them attractive for topological valleytronics. We show that kink-antikink local potentials enable modulated scattering of topological currents. We find that the kink-antikink coupling leads to anomalous steps in the junction conductance. Further, when the constriction detaches from the propagating modes, forming a loop, the conductance reveals the system energy spectrum. Remarkably, these kink-antikink devices can also work as valley filters with tiny magnetic fields by tuning a central gate. We also investigate the electronic confinement in bilayer graphene by closed topological loops of different shapes. References: 1. Nassima Benchtaber, David Sánchez, and Llorenç Serra, “Scattering of topological kink-antikink states in bilayer graphene structures,” Phys. Rev. B 104, 155303 (2021). 2. Nassima Benchtaber, David Sánchez, and Llorenç Serra, “Geometry effects in topologically confined bilayer graphene loops,” New Journal of Physics 24, 013001 (2021).

Resume : Fullerenes, and in particular C60, are promising nanomaterials, due to their biological, physical, photochemical, and electrical properties. However, their low solubility in water (less than 0.04 ng/mL for C60) represents a limit to their extensive use. The physicochemical properties of water dispersions (namely, nano-C60) were widely described in literature. Wet chemistry methods and mechanical ones (extensive stirring/sonication) have already been developed to ease the dispersion of C60 in water by introducing polar functional groups on the fullerene cage. Still, these methods are time consuming and scarcely adhere to green chemistry principles due to the use of organic solvents. In this work, we will introduce a timesaving, dry chemistry approach based on O2 Low-Pressure (LP) Plasma treatment to enhance the dispersion of C60 in water. A similar surface modification was already performed on multi-walled carbon nanotubes to increase their hydrophilicity. [1] To the best of our knowledge, it is the first time that such treatment is used to modify C60 powder surface with polar oxygenated moieties. Different conditions of power and treatment time were tested; subsequently, treated powders were dispersed in distilled deionized water. The non-destructivity of plasma treatment was proved via MALDI-TOF analysis on both powders and suspensions. The enhancement in C60 concentration in water was supported by UV-Vis spectroscopy and TOC measurements. Particles’ size (~200-250nm), polydispersity index (~0.15) and ζ potential (~ -40mV) of the suspensions were assessed via DLS and ELS. Furthermore, XPS analysis both on powders and aqueous dispersions, drop-casted on Si wafers, highlighted the massive presence of carboxylic groups especially on the surface of the fraction of powder dispersed in water after treatment. [1] M. Garzia Trulli, E. Sardella, F. Palumbo, G. Palazzo, L. C. Giannossa, A. Mangone, R. Comparelli, S. Musso, P. Favia, J. Colloid Interface Sci. Apr. 1 (2017) 255-264.

Resume : Printing is widely regarded as a promising manufacturing pathway for large area electronics on flexible substrates. Flexographic printing, in particular, is ideally suited due to its very high print speed with roll-to-roll (R2R) capabilities. To date, there have been attempts in using graphene as an active pigment in functional inks, most notably for relatively slower, laboratory-scale printing techniques such as inkjet and screen printing. However, formulation of graphene-enhanced inks for high-speed, industrial-scale printing and its effect on key metrics such as conductivity, print quality, statistical performance variation and durability have never been investigated. Herein, we demonstrate a method for the incorporation of graphene nanoplatelets (GPs) into a commercially available conductive flexographic ink without compromising the rheological properties, maintaining good printability. The pristine and our GP- enhanced inks are printed on paper and polyethylene terephthalate (PET) substrates using a commercial flexographic press on an industrial scale at 100 m.min-1. Statistical performance variations are investigated by measuring 625 data points across four individual print runs. We show that GP-incorporation enhances sheet-resistance (Rs) and uniformity, with improvements of up to 54% in average Rs and 45% in the standard-deviation on PET. The adhesion on both the substrates improves with GP-incorporation, as verified by tape and crosshatch adhesion tests. The durability of GP-enhanced samples is probed with a 1000 cyclic bend-test, with 0.31% average variation in resistance in the flat state on PET between the first and last 100 bends, exhibiting a robust print. Our statistically scalable results show that GP-incorporation offers a cost-performance advantage for flexographic printing of large-area conductive patterns using a traditional high-speed graphics printing press without any modifications to the press.