One-Step Preparation of Large Area Films of Oriented MoS2 Nanoparticles on Multilayer Graphene and Its Electrocatalytic Activity for Hydrogen Evolution

[EN] MoS2 is a promising material to replace Pt-based catalysts for the hydrogen evolution reaction (HER), due to its excellent stability and high activity. In this work, MoS2 nanoparticles supported on graphitic carbon (about 20 nm) with a preferential 002 facet orientation have been prepared by pyrolysis of alginic acid films on quartz containing adsorbed (NH4)(2)MoS4 at 900 degrees C under Ar atmosphere. Although some variation of the electrocatalytic activity has been observed from batch to batch, the MoS2 sample exhibited activity for HER (a potential onset between 0.2 and 0.3 V vs. SCE), depending on the concentrations of (NH4)(2)MoS4 precursor used in the preparation process. The loading and particle size of MoS2, which correlate with the amount of exposed active sites in the sample, are the main factors influencing the electrocatalytic activity.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2015-69513-CO2-R1) and Generalidad Valenciana (Prometeo 2013/014) is gratefully acknowledged. Jinbao He thanks the Chinese Scholarship Council for supporting his PhD studies.He, J.; Fernández-Blanco, AC.; Primo Arnau, AM.; García Gómez, H. (2018). One-Step Preparation of Large Area Films of Oriented MoS2 Nanoparticles on Multilayer Graphene and Its Electrocatalytic Activity for Hydrogen Evolution. Materials. 11(1):1-11. https://doi.org/10.3390/ma11010168S111111Chhowalla, M., Shin, H. S., Eda, G., Li, L.-J., Loh, K. P., & Zhang, H. (2013). The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nature Chemistry, 5(4), 263-275. doi:10.1038/nchem.1589Lukowski, M. A., Daniel, A. S., Meng, F., Forticaux, A., Li, L., & Jin, S. (2013). Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets. Journal of the American Chemical Society, 135(28), 10274-10277. doi:10.1021/ja404523sVoiry, D., Yamaguchi, H., Li, J., Silva, R., Alves, D. C. B., Fujita, T., … Chhowalla, M. (2013). Enhanced catalytic activity in strained chemically exfoliated WS2 nanosheets for hydrogen evolution. Nature Materials, 12(9), 850-855. doi:10.1038/nmat3700Li, Y., Wang, H., Xie, L., Liang, Y., Hong, G., & Dai, H. (2011). MoS2Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction. Journal of the American Chemical Society, 133(19), 7296-7299. doi:10.1021/ja201269bLatorre-Sánchez, M., Esteve-Adell, I., Primo, A., & García, H. (2015). Innovative preparation of MoS2–graphene heterostructures based on alginate containing (NH4)2MoS4 and their photocatalytic activity for H2 generation. Carbon, 81, 587-596. doi:10.1016/j.carbon.2014.09.093Primo, A., Sánchez, E., Delgado, J. M., & García, H. (2014). High-yield production of N-doped graphitic platelets by aqueous exfoliation of pyrolyzed chitosan. Carbon, 68, 777-783. doi:10.1016/j.carbon.2013.11.068Mateo, D., Esteve-Adell, I., Albero, J., Royo, J. F. S., Primo, A., & Garcia, H. (2016). 111 oriented gold nanoplatelets on multilayer graphene as visible light photocatalyst for overall water splitting. Nature Communications, 7(1). doi:10.1038/ncomms11819Primo, A., Esteve-Adell, I., Blandez, J. F., Dhakshinamoorthy, A., Álvaro, M., Candu, N., … García, H. (2015). High catalytic activity of oriented 2.0.0 copper(I) oxide grown on graphene film. Nature Communications, 6(1). doi:10.1038/ncomms9561Primo, A., Esteve-Adell, I., Coman, S. N., Candu, N., Parvulescu, V. I., & Garcia, H. (2015). One-Step Pyrolysis Preparation of 1.1.1 Oriented Gold Nanoplatelets Supported on Graphene and Six Orders of Magnitude Enhancement of the Resulting Catalytic Activity. Angewandte Chemie International Edition, 55(2), 607-612. doi:10.1002/anie.201508908Primo, A., Atienzar, P., Sanchez, E., Delgado, J. M., & García, H. (2012). From biomass wastes to large-area, high-quality, N-doped graphene: catalyst-free carbonization of chitosan coatings on arbitrary substrates. Chemical Communications, 48(74), 9254. doi:10.1039/c2cc34978gPedraza, F., Cruz-Reyes, J., Acosta, D., Yanez, M. J., Avalos-Borja, M., & Fuentes, S. (1993). Journal of Physics: Condensed Matter, 5(33A), A219-A220. doi:10.1088/0953-8984/5/33a/069Li, H., Zhang, Q., Yap, C. C. R., Tay, B. K., Edwin, T. H. T., Olivier, A., & Baillargeat, D. (2012). From Bulk to Monolayer MoS2: Evolution of Raman Scattering. Advanced Functional Materials, 22(7), 1385-1390. doi:10.1002/adfm.201102111Yan, Y., Ge, X., Liu, Z., Wang, J.-Y., Lee, J.-M., & Wang, X. (2013). Facile synthesis of low crystalline MoS2 nanosheet-coated CNTs for enhanced hydrogen evolution reaction. Nanoscale, 5(17), 7768. doi:10.1039/c3nr02994hLi, H., Tsai, C., Koh, A. L., Cai, L., Contryman, A. W., Fragapane, A. H., … Zheng, X. (2015). Activating and optimizing MoS2 basal planes for hydrogen evolution through the formation of strained sulphur vacancies. Nature Materials, 15(1), 48-53. doi:10.1038/nmat4465Tsai, C., Chan, K., Nørskov, J. K., & Abild-Pedersen, F. (2015). Theoretical insights into the hydrogen evolution activity of layered transition metal dichalcogenides. Surface Science, 640, 133-140. doi:10.1016/j.susc.2015.01.01

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

Porous Graphitic Carbons Containing Nitrogen by Structuration of Chitosan with Pluronic P123

[EN] Using Pluronic P123 as a structure-directing agent and chitosan as a carbon precursor, different porous carbons with remarkable morphologies such as orthohedra or spheres with diametrically opposite holes are obtained. These particles of micrometric size are constituted by the stacking of thin sheets (60 nm) that become increasingly bent in the opposite sense, concave in the upper and convex in the bottom hemispheres, as the chitosan proportion increases. TEM images, after dispersion of the particles by sonication, show that besides micrometric graphene sheets, the material is constituted by nanometric onion-like carbons. The morphology and structure of these porous carbons can be explained based on the ability of Pluronic P123 to undergo self-assembly in aqueous solution due to its amphoteric nature and the filmogenic properties of chitosan to coat Pluronic P123 nanoobjects undergoing structuration and becoming transformed into nitrogen-doped graphitic carbons. XPS analysis reveals the presence of nitrogen in their composition. These porous carbons exhibit a significant CO2 adsorption capacity of above 3 mmol g(-1) under 100 kPa at 273 K attributable to their large specific surface area, ultraporosity, and the presence of basic N sites. In addition, the presence of dopant elements in the graphitic carbons opening the gap is responsible for the photocatalytic activity for H-2 generation in the presence of sacrificial electron donors, reaching a H-2 production of 63 mu mol g(-1) in 24 h.The Spanish Ministry of Science, Innovation and Universities (Severo Ochoa and RTI2018-89237-CO2-R1) and Generalitat Valenciana (Prometeo 2017/083).Peng, L.; Peng, Y.; Primo Arnau, AM.; García Gómez, H. (2021). Porous Graphitic Carbons Containing Nitrogen by Structuration of Chitosan with Pluronic P123. ACS Applied Materials & Interfaces. 13(11):13499-13507. https://doi.org/10.1021/acsami.0c19463S1349913507131

A reliable procedure for the preparation of graphene-boron nitride superlattices as large area (cm x cm) films on arbitrary substrates or powders (gram scale) and unexpected electrocatalytic properties

[EN] Herein, a reliable procedure for the preparation of graphene-boron nitride superlattices, either as films or powders, consisting of the pyrolysis at 900 degrees C of polystyrene embedded pre-formed boron nitride single sheets is reported. The procedure can serve to prepare large area films (cm x cm) of this superlattice on quartz, copper foil and ceramics. Selected area electron diffraction patterns at every location on the films show the occurrence of the graphene-boron nitride superlattice all over the film. The procedure can also be applied to the preparation of powdered samples on a gram scale. Comparison with other materials indicates that the superlattice appears spontaneously as the growing graphene sheets develop, due to the templating effect of pre-existing boron nitride single sheets. Since the characteristic boron nitride emission in the visible region is completely quenched in the superlattice configuration, it is proposed that fluorescence microscopy can be used as a routine technique to determine the occurrence of superlattice in large area films. Electrodes of this material show an unforeseen catalytic activity for oxygen reduction reaction and exhibit a decrease of the heterojunction-electrolyte interphase electrical resistance.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ-2015-69653-CO2-R1) is gratefully acknowledged. AR and AP thank the Spanish Ministry of Economy and Competitiveness for a postgraduate scholarship and a Ramon y Cajal research associate contract, respectively.Rendon-Patiño, A.; Doménech, A.; García Gómez, H.; Primo Arnau, AM. (2019). A reliable procedure for the preparation of graphene-boron nitride superlattices as large area (cm x cm) films on arbitrary substrates or powders (gram scale) and unexpected electrocatalytic properties. Nanoscale. 11(6):2981-2990. https://doi.org/10.1039/c8nr08377kS2981299011

Superior Electrocatalytic Activity of MoS2-Graphene as Superlattice

[EN] Evidence by selected area diffraction patterns shows the successful preparation of large area (cm x cm) MoS2/graphene heterojunctions in coincidence of the MoS2 and graphene hexagons (superlattice). The electrodes of MoS2/graphene in superlattice configuration show improved catalytic activity for H-2 and O-2 evolution with smaller overpotential of +0.34 V for the overall water splitting when compared with analogous MoS2/graphene heterojunction with random stacking.This research was funded by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2015-68653-CO2-R1) and Generalitat Valenciana (Prometeo 2017-083).Rendon-Patiño, A.; Domenech-Carbó, A.; Primo Arnau, AM.; García Gómez, H. (2020). Superior Electrocatalytic Activity of MoS2-Graphene as Superlattice. Nanomaterials. 10(5):1-9. https://doi.org/10.3390/nano10050839S1910

Band gap alignment of structured microporous graphitic carbons by N doping and its influence on photocatalytic overall water splitting

[EN] Hydrogen generation from water using solar light could be a process of paramount importance in the forthcoming decarbonized society. This reaction requires efficient photocatalysts based on earthabundant elements. Metal-free carbon semiconducting materials are very appealing in this regard. This manuscript shows that N-doping is a convenient strategy to increase the photocatalytic activity of microporous graphitic carbons obtained from the pyrolysis of a-, b- and g-cyclodextrins. These (N)C carbons exhibit enhanced photocatalytic activity for H2 generation in the presence of methanol with respect to their undoped analogs. The optimal (N)C material (pore size, 0.65 nm) was the one derived from a-cyclodextrin at a N content of 3.1%, achieving a H2 productivity of 1.8 mmol g1 at 4 h in the presence of methanol. These materials also exhibit photocatalytic activity for overall water splitting, although with lower efficiency than for H2 generation in the presence of sacrificial electron donors. The present results illustrate the tuning of band alignment by N-doping in the graphitic matrixFinancial support by the Spanish Ministry of Science and Innovation (Severo Ochoa and CTQ2018-98237-CO2-1) and Generalitat Valenciana (Prometeo 2017-083) is gratefully acknowledged. AR and AP thanks the Spanish Ministry of Economy and Competitiveness for a postgraduate scholarship and a Ramon y Cajal research associate contract, respectively.Rendon-Patiño, A.; Torres-Martí, F.; Primo Arnau, AM.; García Gómez, H. (2022). Band gap alignment of structured microporous graphitic carbons by N doping and its influence on photocatalytic overall water splitting. Sustainable Energy & Fuels. 6(9):2170-2178. https://doi.org/10.1039/D2SE00078D217021786

All-carbon microporous graphitic photocatalyst-promoted reduction of CO2 to CO in the absence of metals or dopant elements

[EN] Microporous graphitic carbon (mp-C) derived from the pyrolysis of alpha-, beta-, and gamma-cyclodextrins exhibited photocatalytic activity in CO2-saturated acetonitrile-water upon irradiation with UV-Vis light and in the presence of triethanolamine, forming H-2 (19 mu mol h(-1)) and CO (23 mu mol h(-1)) accompanied by a lesser proportion of CH4 (4 mu mol h(-1)). The most efficient was the mp-C material derived from alpha-cyclodextrin (mp-C-alpha) and having a pore dimension of 0.68 nm. The process also occured, although to a much lesser extent, under simulated sunlight or with UV-Vis irradiation in the absence of a sacrificial agent, with H2O being the electron donor. The origin of the CO was proved by isotopic C-13 labelling experiments. Photocurrent measurements proved the occurrence of charge separation and the increase in photocurrent intensity in the presence of CO2. Transient absorption spectroscopy was used to detect the charge separate state decay in the microsecond time scale and proved that a fraction of the photogenerated electrons were able to react with CO2.Financial support by the Spanish Ministry of Science and Innovation (Severo Ochoa, PID-2021-12607OB-C21 and RTI2018-89237-CO2-1) and Generalitat Valenciana (Prometeo 2021/083) are gratefully acknowledged. A. G.-M. thanks the Spanish Ministry of Science and Innovation for a postgraduate scholarship.Garcia-Mulero, A.; Asiri, AM.; Albero-Sancho, J.; Primo Arnau, AM.; García Gómez, H. (2022). All-carbon microporous graphitic photocatalyst-promoted reduction of CO2 to CO in the absence of metals or dopant elements. Nanoscale. 14(32):11575-11582. https://doi.org/10.1039/d2nr02655d1157511582143

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

Tridimensional N, P-Codoped Carbon Sponges as Highly Selective Catalysts for Aerobic Oxidative Coupling of Benzylamine

[EN] Two tridimensional N-doped porous carbon sponges (3DC-X) have been prepared by using cetyltrimethylammonium chloride ( CTAC) and cetyltrimethylammonium bromide (CTAB) as soft templates and alginate to replicate the liquid crystals formed by CTA+ in water. Alginate is a filmogenic polysaccharide of natural origin having the ability to form nanometric defectless films around objects. Subsequent pyrolysis at 900 degrees C under an Ar flow of the resulting CTA(+)-polysaccharide assemblies result in 3DC-1 and 3DC-2, with the N percentages of 0.48 and 0.36 wt % for the materials resulting from CTAC and CTAB, respectively. Another four 3DC materials were obtained via pyrolysis of the adduct of phytic acid and chitosan, rendering an amorphous, N and P-codoped carbon sample (3DC-3 to 3DC-6). The six 3DC samples exhibit a large area (>650 m(2) x g(-1)) and porosity, as determined by Ar adsorption. The catalytic activity of these materials in promoting the aerobic oxidation of benzylamine increases with the specific surface area and doping, being the largest for 3DC-4, which is able to achieve 73% benzylamine conversion to N-benzylidene benzylamine in solventless conditions at 70 degrees C in 5 h. Quenching studies and hot filtration tests indicate that 3DC-4 acts as a heterogeneous catalyst rather than an initiator, triggering the formation of hydroperoxyl and hydroxyl radicals as the main reactive oxygen species involved in the aerobic oxidation.Financial support by the Spanish Ministry of Science and Innovation (Severo Ochoa 2016 and RTI2018-890237-CO2-R1) and Generalitat Valenciana is gratefully acknowledged. A.P. thanks the Spanish Ministry for a Ramon y Cajal Research associate contract. A.D. is thankful to the University Grants Commission, New Dekhi, for awarding Assistant Professorship through the Faculty Recharge Programme.Peng, L.; Garcia-Baldovi, H.; Dhakshinamoorthy, A.; Primo Arnau, AM.; García Gómez, H. (2022). Tridimensional N, P-Codoped Carbon Sponges as Highly Selective Catalysts for Aerobic Oxidative Coupling of Benzylamine. ACS Omega. 7(13):11092-11100. https://doi.org/10.1021/acsomega.1c07179110921110071

Co-Fe Clusters Supported on N-Doped Graphitic Carbon as Highly Selective Catalysts for Reverse Water Gas Shift Reaction

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry & Engineering, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acssuschemeng.1c01401[EN] Graphitic carbons are suitable supports of metal nanoparticles with catalytic activity. In the present study, the preparation of N-doped graphitic carbon supporting clusters of Fe-Co alloys starting from biomass waste is reported. These sub-nanometric Co-Fe clusters supported on N-doped graphitic carbon at a metal loading below 0.2 wt % exhibit high activity for the selective hydrogenation of CO2 to CO. Operating at 500 degrees C and 10 bar with an H-2/CO2 molar ratio of 7 and a space velocity of 600 h(-1), a conversion of 56% with a selectivity of over 98% to CO, and remarkable stability over 30 h operation was obtained. Interestingly, analogous catalysts based on N-doped graphitic carbon with much higher Co-Fe loadings and an average particle size range of 1-5 nm exhibit only half of this activity, with similar CO selectivity. This contrasting behavior reveals the dramatic effect of the particle size on the catalytic activity. In comparison, SiO2 as support under similar conditions affords CH4 as the main product.Financial support by the Spanish Ministry of Science, Innovation, and University (Severo Ochoa and RTI2018.98237-B-CO1) and Generalitat Valenciana (Prometeo 2017/083) is gratefully acknowledged. L.P. thanks the Generalitat Valenciana for a Santiago Grisolia scholarship. BASF is thanked for financial support.Peng, L.; Jurca, B.; Primo Arnau, AM.; Gordillo, A.; Parvulescu, VI.; García Gómez, H. (2021). Co-Fe Clusters Supported on N-Doped Graphitic Carbon as Highly Selective Catalysts for Reverse Water Gas Shift Reaction. ACS Sustainable Chemistry & Engineering. 9(28):9264-9272. https://doi.org/10.1021/acssuschemeng.1c014019264927292