Préparation de matériaux à base de graphène et leur application en catalyse

[ES] Para abordar los desafíos ambientales, la química y los procesos químicos deben ser más sostenibles. Para ello, el desarrollo de nuevos catalizadores especialmente activos es de suma importancia. En catálisis heterogénea, el grafeno ha surgido recientemente como un excelente candidato desde que fue posible aislarlo a partir del grafito. Sus propiedades únicas han despertado un gran interés para aplicarlo en varios campos, desde el refuerzo de matrices poliméricas hasta el desarrollo de materiales para catálisis. En catálisis, su uso como soporte catalítico o como carbocatalizador es todavía objeto de varios estudios. Con el objetivo de preparar catalizadores extremadamente activos en varias reacciones de química fina o de producción de hidrógeno, nuestro trabajo de investigación se ha centrado en el uso de materiales a base de grafeno como soportes catalíticos. Se consideraron diferentes aspectos: La funcionalización del grafeno; al ser un material de baja dimensionalidad, las propiedades del grafeno están estrechamente relacionadas con la química de su superficie. Mediante la fosforilación del óxido de grafeno, hemos demostrado que la estabilidad térmica y la estabilización de las nanopartículas metálicas mejoran significativamente. La combinación de grafeno con otros materiales; Pequeñas nanopartículas de paladio estabilizadas sobre materiales porosos a base de óxido de grafeno y quitosano han demostrado una excelente actividad para la deshidrogenación del formiato de amonio. La estrategia de síntesis adoptada para preparar el grafeno; La pirólisis de películas de alginato de amonio y un precursor de rutenio (Ru) en diferentes atmósferas permitió la preparación de nanopartículas de Ru soportadas en grafeno cuya orientación depende de la atmósfera de pirólisis. Por lo tanto, fue posible una comparación de la actividad catalítica de diferentes facetas cristalográficas. Dopaje de grafeno; la presencia de diferentes heteroátomos en su estructura ha permitido una mejor estabilización de nanopartículas y clusters metálicos. Los materiales basados en nanopartículas de óxido de cobre y grafenos dopados han demostrado poseer una excelente actividad catalítica en la síntesis de nuevas moléculas de interés farmacéutico.[CA] Per a abordar els desafiaments ambientals, la química i els processos químics han de ser més sostenibles. Per a això, el desenvolupament de nous catalitzadors especialment actius és de summa importància. En catàlisi heterogènia, el grafé ha sorgit recentment com un excel·lent candidat des que va ser possible aïllar-lo a partir del grafit. Les seues propietats úniques han despertat un gran interés per a aplicar-lo en diversos camps,des del reforç de matrius polimèriques fins al desenvolupament de materials per a catàlisis. En catàlisi, el seu ús com a suport catalític o com carbocatalitzador és encara objecte de diversos estudis. Amb l'objectiu de preparar catalitzadors extremadament actius en diverses reaccions de química fina o de producció d'hidrogen, el nostre treball de recerca s'ha centrat en l'ús de materials a base de grafé com a suports catalítics. Es van considerar diferents aspectes: La funcionalització del grafé; a l'ésser un material de baixa dimensionalitat, les propietats del grafé estan estretament relacionades amb la química de la seua superfície. Mitjançant la fosforilació de l'òxid de grafé, hem demostrat que l'estabilitat tèrmica i l'estabilització de les nanopartícules metàl·liques milloren significativament. La combinació de grafé amb altres materials; Xicotetes nanopartícules de pal·ladi estabilitzades sobre materials porosos a base d'òxid de grafé i quitosà han demostrat una excel·lent activitat per a la deshidrogenació del formiat d'amoni. L'estratègia de síntesi adoptada per a preparar el grafé; La piròlisi de pel·lícules de alginat d'amoni i un precursor de ruteni (Ru) en diferents atmosferes va permetre la preparació de nanopartícules de Ru suportades en grafé, l'orientació del qual depén de l'atmosfera de piròlisi. Per tant, va ser possible una comparació de l'activitat catalítica de diferents facetes cristal¿logràfiques. Dopatge de grafé; la presència de diferents heteroàtoms en la seua estructura ha permés una millor estabilització de nanopartícules i clústers metàl·lics. Els materials basats en nanopartícules d'òxid de coure i grafens dopats han demostrat posseir una excel·lent activitat catalítica en la síntesi de noves molècules d'interés farmacèutic.[EN] To address environmental challenges, chemistry and chemical processes need to be more sustainable. For this, developing new particularly active catalysts is of paramount importance. In heterogeneous catalysis, graphene has emerged as an excellent candidate since it was possible to isolate it from graphite. Its properties have aroused substantial interest, earning it applications in various fields spanning from the reinforcement of polymer matrices to the development of materials for catalysis. In catalysis, its use both as a catalytic support or as a carbocatalyst is still the subject of several studies. Aiming to prepare extremely active catalysts in various fine chemical reactions or hydrogen production, our research work has focused on the use of graphene-based materials as catalytic supports. Different aspects were considered: The functionalization of graphene; being a material of low dimensionality, the properties of graphene are intimately related to the chemistry of its surface. Through phosphorylation of graphene oxide, we have shown that the thermal stability and stabilization of metal nanoparticles are significantly improved. Combination of graphene with other materials; small palladium nanoparticles stabilized on porous materials based on graphene oxide and chitosan have demonstrated excellent activity for the dehydrogenation of ammonium formate. The synthetic strategy adopted to prepare graphene; pyrolysis of films of ammonium alginate and ruthenium precursor (Ru) in different atmospheres enabled the preparation of Ru nanoparticles supported on graphene whose orientation depends on the atmosphere of pyrolysis. Thus, a comparison of the catalytic activity of different crystallographic facets was possible. Doping of graphene; the presence of different heteroatoms in its structure has allowed a better stabilization of metal nanoparticles and clusters. Materials based on copper oxide nanoparticles and tridoped graphene have demonstrated an excellent catalytic activity in the synthesis of new molecules of pharmaceutical interest.Anouar, A. (2021). Préparation de matériaux à base de graphène et leur application en catalyse [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164030TESI

Inverse filtering and principal component analysis techniques for speech dereverberation

In this work, we present a single channel approach for early and late reverberation suppression. This approach can be decomposed into two stages. The first stage employs the inverse filter to augment the signal-to-reverberant energy ratio. The second stage uses the kernel PCA algorithm to enhance the obtained dereverberant signal. It consists in extracting the main non-linear features from the speech signal after inverse filtering. Our approach appears to be efficient mainly in far field conditions and in highly reverberant environments

Quality Improvement of Few-Layers Defective Graphene from Biomass and Application for H-2 Generation

[EN] Pyrolysis of filmogenic natural polymers gives rise to the formation of films of few-layers defective, undoped, and doped graphenes with low electrical conductivity (3000 to 5000 ohm /sq). For the sake of valorization of biomass wastes, it would be of interest to decrease the density of structural defects in order to increase the conductivity of the resulting few-layers graphene samples. In the present study, analytical and spectroscopic evidence is provided showing that by performing the pyrolysis at the optimal temperature (1100 degrees C), under a low percentage of H-2, a significant decrease in the density of defects related to the presence of residual oxygen can be achieved. This improvement in the quality of the resulting few-layers defective graphene is reflected in a decrease by a factor of about 3 or 5 for alginic acid and chitosan, respectively, of the electrical resistance. Under optimal conditions, few-layers defective graphene films with a resistance of 1000 ohm /sq were achieved. The electrode made of high-quality graphene prepared at 1100 degrees C under Ar/H-2 achieved a H-2 production of 3.62 mu mol with a positive applied bias of 1.1 V under LED illumination for 16 h.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and RTI2018-098237-B-C21) and Generalitat Valencia (Prometeo 2017/083) is gratefully acknowledged. J. H. thanks the Chinese Scholarship Council (CSC) for supporting his doctoral stage at Valencia. A. P. also acknowledges the Spanish Ministry of Economy and Competitiveness for a Ramon y Cajal research associate contract.He, J.; Anouar, A.; Primo Arnau, AM.; García Gómez, H. (2019). Quality Improvement of Few-Layers Defective Graphene from Biomass and Application for H-2 Generation. Nanomaterials. 9(6):1-15. https://doi.org/10.3390/nano9060895S1159

Palladium Supported on Porous Chitosan-Graphene Oxide Aerogels as Highly Efficient Catalysts for Hydrogen Generation from Formate

[EN] Adsorption of Pd(NH3)(4)(2+) in preformed chitosan-graphene oxide (CS-GO) beads and their subsequent reduction with NaBH4 afford well-dispersed, high dispersion (similar to 21%) of uniformly sized Pd nanoparticles (similar to 1.7 nm). The resulting Pd/CS-GO exhibits interesting catalytic activity for hydrogen generation by ammonium formate decomposition. The optimal GO proportion of 7 wt% allows reaching, at 60 degrees C, a turnover frequency above 2200 h(-1)-being outstanding among the highest values reported for this process to date. Interestingly, no formation of CO or CH4 was detected. The catalyst did not leach, although it underwent gradual deactivation, probably caused by the increase in the Pd average size that became over 3 nm after three uses. Our results are relevant in the context of efficient on-board hydrogen generation from liquid organic hydrogen carriers in transportation.This research was funded by the Spanish Ministry of Science, Innovation and Universities (Grant RTI2018-098237-B-C21 and Severo Ochoa). A.P. also thanks the Spanish Ministry of Science and Education a research associate Ramon y Cajal contract. A.A. thanks UEMF for scholarship.Anouar, A.; Katir, N.; El Kadib, A.; Primo Arnau, AM.; García Gómez, H. (2019). Palladium Supported on Porous Chitosan-Graphene Oxide Aerogels as Highly Efficient Catalysts for Hydrogen Generation from Formate. Molecules. 24(18):1-13. https://doi.org/10.3390/molecules24183290S113241

Remarkable Activity of 002 Facet of Ruthenium Nanoparticles Grown on Graphene Films on the Photocatalytic CO2 Methanation

[EN] In the context of diminishing atmospheric CO2 emissions, there is an urgent need to develop processes that can be carried out at a scale commensurate with appropriate CO2 volumes. One possible reaction is the transformation of CO2 to methane (Sabatier reaction). Due to its chemical stability, catalytic CO2 hydrogenation to methane is carried out at temperatures of 450 degrees C or higher and pressures above 5 bars, thus, requiring a significant energy input. One alternative possibility to conventional thermal catalysis is the use of solar light as the primary energy, performing the photocatalytic CO2 hydrogenation. In this broad context, the present study shows the photocatalytic activity of nanometric films of oriented Ru nanoparticles (NPs) strongly grafted on defective graphene. These graphene films (thinner than 20 nm) containing Ru NPs nanoplatelets (less than 2 nanomol(Ru)/cm(2)) are among the most active photocatalysts ever prepared for CO2 hydrogenation and operate through photoinduced charge separationSupport by the Ministerio de Ciencia e Innovacion (Severo Ochoa and RTI2018-098237-B-C21) and Generalitat Valenciana (Prometeo 2017/083) was acknowledged. Thanks are due to Galicia Supercomputing Center. A.A. thanks UEMF (Euromed Unniversity Fes) and UPV for an Erasmus+ 2019-1-ES01-KA107-062073 Scholarship. A.P. thanks the Spanish Ministry for a Ramon y Cajal research associate contract.Anouar, A.; García-Aboal, R.; Atienzar Corvillo, PE.; Franconetti, A.; Katir, N.; El Kadib, A.; Primo Arnau, AM.... (2022). Remarkable Activity of 002 Facet of Ruthenium Nanoparticles Grown on Graphene Films on the Photocatalytic CO2 Methanation. Advanced Sustainable Systems. 6(5):1-10. https://doi.org/10.1002/adsu.2021004871106

Phosphorus-Rich Ruthenium Phosphide Embedded on a 3D Porous Dual-Doped Graphitic Carbon for Hydrogen Evolution Reaction

Metal phosphides have recently emerged as promising electrocatalysts for hydrogen evolution reaction (HER). Herein, we report the synthesis of ruthenium diphosphide embedded on a dual-doped graphitic carbon by pyrolyzing chitosan beads impregnated with ruthenium chloride and phosphorus pentoxide. The as-synthesized RuP2@N-P-C displays a good electrocatalytic activity in acidic, neutral and alkaline media. We show that the HER activity of the electrocatalyst can be tuned by varying the concentration of Li+ cations. Co-diffusion effects on H+ exerted by Li+ on HER in the porous carbon matrix have been observed

Beyond hydrophobisation: Deciphering the surprising reactivity of trimethylsilyl reagents towards graphene oxide

International audienceTrimethylsilylation of metal oxide surfaces (silica, titania…) is a common way to empower the handled supports with outstanding stability. This hydrophobisation prevailed in vital domains including chromatographic column, adsorption-based membranes and heterogeneous catalysis, where hydrolytic stability constituted a challenging issue. In spite of its benefits, trimethylsilylation of graphene oxide has been only sporadically investigated and this underlooked chemistry needs to be accurately addressed for further tailoring the surface properties of graphene materials. With this aim, we herein screened a set of commercially available trimethylsilyl reagents for end-cuping the surface of graphene oxide. Surprisingly, meticulous investigations show that these reagents behave primarily as nucleophiles and induce oxirane opening, with a diverging pattern depending on the functional group linked to trimethylsilyl fragments. Specifically: i) trimethylsilylchloride and trimethylsilyltriflate are not suitable because of the substantial side products formed under acidic conditions; ii) trimethylsilylimidazolium reacts rather through its imidazolium group with the simultaneous elimination of trimethylsilyl groups; iii) bis-silylated reagents like hexamethyldisilazane and N,O-bis-trimethylsilyl-trifluoroacetamide enable anchoring at least one functional arm while liberating the second trimethylsilyl moity. The introduced functionalities enhance the dispersion of the newly prepared graphenes in liquid medium, thereby broadening the library of solvents suitable for their handling and offering more possibilities for the ink processability. Regardless of the starting reagent, the resulting functionalisation do not compromise the anchoring ability of the graphene surface as illustrated by supporting InP/ZnS semiconductor nanocrystals. In the whole, these serendipitous findings challenge the conventional wisdom about the reactivity of trimethylsilyl reagents that was primarly associated to surface hydrophobisation, opening indeed new possibilities for graphene functionalisation and further use in materials science

Synthesis and multifaceted use of phosphorylated graphene oxide: growth of titanium dioxide clusters, interplay with gold nanoparticles and exfoliated sheets in bioplastics

International audienceFive different functional phosphorus motifs were trivially installed within graphene oxide (GO) sheets to provide water-dispersible and thermally-stable phosphorus graphene oxide materials (PGO). The presence of exogenous phosphorus heteroatoms on the surface of the tiny carbon sheets was harnessed for the anchoring and growth of metal oxide clusters, exemplified herein by titanium dioxide, and for the chelation and stabilization of small gold nanoparticles. Unexpectedly, both GO and PGO promoted crystallization in a low-temperature liquid-phase medium without thermal annealing treatment. However, the fingerprint of the surface chemistry is illustrated through the formation of different species; while discrete anatase nanoparticles were selectively formed on the surface of GO sheets, a biphasic mixture of anatase and rutile was grown on PGO. The latter provides a more stable material owing to the robustness of the interfacial P–O–Ti bridges. Strong coordination to gold nanoparticles was also observed for PGO due to the presence of P[double bond, length as m-dash]O(OH)2 fragments, compared to the weakly coordinating oxygenated functions in GO. Lastly, the possible delamination of PGO sheets associated with their improved thermal stability renders them promising nanosized fillers for carbohydrate-based bioplastics

Antimicrobial Effect of Chitosan Films on Food Spoilage Bacteria

Synthetic materials commonly used in the packaging industry generate a considerable amount of waste each year. Chitosan is a promising feedstock for the production of functional biomaterials. From a biological point of view, chitosan is very attractive for food packaging. The purposes of this study were to evaluate the antibacterial activity of a set of chitosan-metal oxide films and different chitosan-modified graphene (oxide) films against two foodborne pathogens: Campylobacter jejuni ATCC 33560 and Listeria monocytogenes 19115. Moreover, we wanted to check whether the incorporation of antimicrobial constituents such as TiO2, ZnO, Fe2O3, Ag, and graphene oxide (GO) into the polymer matrices can improve the antibacterial properties of these nanocomposite films. Finally, this research helps elucidate the interactions of these materials with eukaryotic cells. All chitosan-metal oxide films and chitosan-modified graphene (oxide) films displayed improved antibacterial (C. jejuni ATCC 33560 and L. monocytogenes 19115) properties compared to native chitosan films. The CS-ZnO films had excellent antibacterial activity towards L. monocytogenes (90% growth inhibition). Moreover, graphene-based chitosan films caused high inhibition of both tested strains. Chitosan films with graphene (GO, GOP, GOP-HMDS, rGO, GO-HMDS, rGOP), titanium dioxide (CS-TiO2 20:1a, CS-TiO2 20:1b, CS-TiO2 2:1, CS-TiO2 1:1a, CS-TiO2 1:1b) and zinc oxide (CS-ZnO 20:1a, CS-ZnO 20:1b) may be considered as a safe, non-cytotoxic packaging materials in the future