111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting

[EN] Development of renewable fuels from solar light appears as one of the main current challenges in energy science. A plethora of photocatalysts have been investigated to obtain hydrogen and oxygen from water and solar light in the last decades. However, the photon-to-hydrogen molecule conversion is still far from allowing real implementation of solar fuels. Here we show that 111 facet-oriented gold nanoplatelets on multilayer graphene films deposited on quartz is a highly active photocatalyst for simulated sunlight overall water splitting into hydrogen and oxygen in the absence of sacrificial electron donors, achieving hydrogen production rate of 1.2 molH2 per gcomposite per h. This photocatalytic activity arises from the gold preferential orientation and the strong gold–graphene interaction occurring in the composite system.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2012-32315) and Generalitat Valenciana (Prometeo 2013-019) is gratefully acknowledged. D.M. and I.E.-A. thank to Spanish Ministry of Science for PhD scholarships.Mateo Mateo, D.; Esteve Adell, I.; Albero Sancho, J.; Sánchez Royo, JF.; Primo Arnau, AM.; García Gómez, H. (2016). 111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting. Nature Communications. 2016(7):1-8. https://doi.org/10.1038/ncomms11819S1820167Lv, X. J., Zhou, S., Huang, X., Wang, C. & Fu, W. F. Photocatalytic overall water splitting promoted by SnOx-NiGa2O4 photocatalysts. Appl. Cat. B: Environ. 182, 220–228 (2016).Xu, J., Wang, L. & Cao, X. 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Palladium supported on porous chitosan-graphene oxide aerogels as highly effcient catalysts for hydrogen generation from formate

Adsorption of Pd(NH) in preformed chitosan-graphene oxide (CS-GO) beads and their subsequent reduction with NaBH afford well-dispersed, high dispersion (∼21%) of uniformly sized Pd nanoparticles (∼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 °C, a turnover frequency above 2200 h-being outstanding among the highest values reported for this process to date. Interestingly, no formation of CO or CH 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 Ramón y Cajal contract. A.A. thanks UEMF for scholarship

Shaping MOF oxime oxidation catalysts as three-dimensional porous aerogels through structure-directing growth inside chitosan microspheres

Metal-organic frameworks stand as unique building blocks, bridging the gap between coordination chemistry and materials science. While significant advances have been made in their design, current efforts focus on expanding their pore size above the microporous regime and on their shaping into well suitable end use devices. For such a purpose, we herein explored the use of chitosan hydrogel microspheres as a mold to grow an extended network of MOFs, followed by CO-supercritical drying to generate three-dimensional polysaccharide nanofibrils embedding entangled MOF nanoclusters. This strategy was found to be highly versatile, and allows for shaping HKUST-1, ZIF-8, ZIF-67 and Fe-BTC inside chitosan microspheres. The resulting lightweight aerogels display excellent activity for oxime oxidation, with HKUST-1 loaded on chitosan beads standing as the most promising. The virtues of supercritical drying were substantiated by comparing the catalytic activity of these aerogels with their xerogel analogues as well as pristine HKUST-1. Interestingly, moreover, the configuration of MOFs in chitosan beads precludes the metal from leaching and allows easy recovery of the catalyst from the medium and its possible recycling.NH thanks UEMF and UPV for an Erasmus+ 2019-1-ES01-KA107-062073 Scholarship. AEK thanks UEMF for funding. Partenariat Hubert Curien – Toubkal (project no. 18/70) is acknowledged for supporting and partially funding this work. Chevreul Institute (FR 2638), Ministère de l'Enseignement Supérieur et de la Recherche, Région Hauts-de-France and FEDER are acknowledged for funding. The authors are also thankful for the technical support from Lille University: Martine Trentesaux and Pardis Simon for the XPS analysis, Olivier Gardoll for the TGA analysis, Laurence Burylo for the XRD experiments, and Jeremy Dhainaut for the mechanical tests, and Ridvan Yildiz from LMCPA, Hauts de France Polytechnic University for mercury intrusion

Orthogonal synthesis of covalent polydendrimer frameworks by fusing classical and onion-peel phosphorus-based dendritic units

International audienceWe report novel and new giant three-dimensional polymers having dendrimers as repeating units. The approach is illustrated here for macromolecular synthesis by polymeric condensation of well-defined single phosphorus dendrimers units. Specifically, classical and onion-peel phosphorus dendrimers, constructed by a divergent method from a cyclotriphosphazene core, were fused within the same tectonic nanostructure by several polymeric condensation approaches including hydrazine-to-aldehyde Schiff-base formation and amine-to carboxylic acid peptide-like coupling. These reticular, easy to run metal free routes afford a new library of hyperbranched macromolecular materials, featuring various phosphorus layers (both alternated and dissymmetrical), well-defined textured nanospheres, and controllable nanometric ordered substructures. The scope of the concept is successfully expanded to the integration of electro-redox viologen units resulting in the synthesis of new photoactive macromolecular materials

Synthesis of onion-peel nanodendritic structures with sequential functional phosphorus diversity

International audienceThe preparation of novel families of phosphorusbased macromolecular architectures called “onion peel” phosphorus nanodendritic systems is reported. This construct is based on the versatility of methods of synthesis using several building blocks and on the capability of these systems to undergo regioselective reactions within the cascade structure. Sustainable metal-free routes such as the Staudinger reaction or Schiff-base condensation, involving only water and nitrogen as byproducts, allow access to several dendritic macromolecules bearing up to seven different phosphorus units in their backbone, each of them featuring specific reactivity. The presence of the highly aurophilic P= N_P=S fragment enables selective ligation of AuI within the dendritic framework

Nanosized copper stabilized on ternary P, N, S-doped graphene from chitosan shellfish waste: preparation and catalysis of single and double A3-type amine coupling

Heteroatom-doping carbons are conventionally accessed through multistep procedures, often necessitating tedious postgrafting and the use of harsh conditions, while providing less-defined heterogeneous catalysts. We herein disclose a time-saving approach based on straightforward modification of chitosan, an abundant marine waste, followed by its graphitization to access texturally tunable, ternary-doped nitrogen, phosphorus, and sulfur-containing porous carbon material. The presence of functional groups in the edges ensures total exfoliation and dispersion of the sheets, whereas the presence of different coordinating sites inside accounts for efficient stabilization of the embedded metal nanoclusters. Preliminarily, good catalytic activity was noticed for the synthesis of propargylamines and dipropargylamines. The following approach combining active metals and discarded biowaste constitutes a highly versatile entry to heterogeneous carbon-based catalysts.UEMF is acknowledged for financial support. AA thanks UEMF and UPV for an Erasmus+ 2019-1-ES01-KA107-062073 Scholarship

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

In the context of diminishing atmospheric CO emissions, there is an urgent need to develop processes that can be carried out at a scale commensurate with appropriate CO volumes. One possible reaction is the transformation of CO to methane (Sabatier reaction). Due to its chemical stability, catalytic CO hydrogenation to methane is carried out at temperatures of 450 °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 CO 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/cm) are among the most active photocatalysts ever prepared for CO hydrogenation and operate through photoinduced charge separation.Support by the Ministerio de Ciencia e Innovación (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 Ramón y Caja

Nanometer-thick defective graphene films decorated with oriented ruthenium nanoparticles. Higher activity of 101 vs 002 plane for silane-alcohol coupling and hydrogen transfer reduction

Pyrolysis of ammonium alginate films containing Ru(NH)Cl leads to the formation of Ru nanoparticles (NPs) supported on defective graphene films. The procedure allows controlling the preferential facet orientation of small Ru NPs (5–20 nm), either 002 when the pyrolysis is carried out under Ar atmosphere or the 002 and 101 planes for pyrolysis in the presence of H. Ru is a metal difficult to prepare in preferential facet orientation compared to noble metals due to its higher reactivity and smaller particle size. Theoretical calculations substantiated the inhibition of Ru(0 0 2) growth by H adsorption, with restructuration to Ru(002–101) NPs. The defective graphene films of about 15 nm thickness containing one of the two types of Ru NPs (150 ng/cm) exhibit distinctive catalytic activity for the dehydrogenative coupling of silanes and alcohols and hydrogen transfer reduction of cyclohexanone. Comparison of turnover frequencies indicates that the 101 facet is more efficient than the 002 plane. Overall, this study illustrates that pyrolysis conditions can control the preferential crystallographic orientation of the growing Ru NPs and the relative catalytic activity of their specific crystallographic planes.Support by the Ministerio de Ciencia e Innovación (Severo Ochoa and RTI2018-098237-B-C21) and Generalitat Valenciana (Prometeo 2017/083) is acknowledged. Thanks are due to Galicia Supercomputing Center. AA thanks UEMF and UPV for an Erasmus + 2019-1-ES01-KA107-062073 Scholarship