Isotopic H/D exchange on graphenes. A combined experimental and theoretical study

[EN] Adsorption of H-2/D-2 on graphene (G), graphene oxide (GO), single walled carbon nanotube (SWCNT), N-doped graphene [(N)G], and a sample of active carbon (C) has led to the detection of HD, indicating dissociative chemisorption of hydrogen on the surface of the material. The amount of HD detected follows the order G > SWCNT > GO similar to (N)G similar to C, G giving about five-fold higher H-2/D-2 adsorption and HD exchange level than SWCNT and about ten-fold larger values than that of the other samples. Quantum-chemistry calculations modeling a carbon atom vacancy on a G cluster estimates an activation barrier for H-2 dissociation of ca. 84 kJ/mol for a mechanism involving under coordinated carbon atoms at the defect site.Financial support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa SEV-2016-0267 and CTQ2015-69153-C2-R1) and Generalitat Valenciana (Prometeo 2013/014) is gratefully acknowledged. G. S. thanks the Scientific Division of SGAI CSIC for computing facilities.Sastre Navarro, GI.; Forneli Rubio, MA.; Almasan, V.; Parvulescu, VI.; García Gómez, H. (2017). Isotopic H/D exchange on graphenes. A combined experimental and theoretical study. Applied Catalysis A General. 547:52-59. https://doi.org/10.1016/j.apcata.2017.08.018S525954

A Quasi-Metal-Organic Framework Based on Cobalt for Improved Catalytic Conversion of Aquatic Pollutant 4-Nitrophenol

[EN] To generate purposely defects that can increase the catalytic activity, cobalt-based metal-organic framework (MOF) TMU-10 has been subjected to thermal treatment under an air atmosphere at temperatures between 100 and 700 degrees C. This process causes partial ligand removal, generating structural defects and additional hierarchical porosity in a convenient way. The resulting materials, denoted as quasi-MOFs, were subsequently employed as catalysts for the room-temperature borohydride reduction of 4-nitrophenol (4-NP). The quasi TMU-10 framework obtained at 300 degrees C (QT-300) exhibits excellent catalytic performance with an apparent rate constant, activity factor, and half-life time of 2.8 X 10(-2) s(-1), 282 g(-1), and 24.8 s, respectively, much better values than those of parent TMU-10. Coexistence of micro and mesopores, coordinatively unsaturated cobalt nodes, tetrahedral Co(II) ions, and Co(III) in QT-300 are responsible for this enhanced activity. Kinetic studies in the range of 25-40 degrees C varying the 4-NP and BH4- concentrations agree with the Langmuir-Hinshelwood model in which both reactants are adsorbed on the catalyst surface. Reduction of 4-NP by the surface-hydrogen species is the rate-determining step.This work was supported by Iran Science Elites Federation and Arak University.Bagheri, M.; Masoomi, MY.; Forneli Rubio, MA.; García Gómez, H. (2022). A Quasi-Metal-Organic Framework Based on Cobalt for Improved Catalytic Conversion of Aquatic Pollutant 4-Nitrophenol. The Journal of Physical Chemistry C. 126(1):683-692. https://doi.org/10.1021/acs.jpcc.1c08658683692126

Production of H2 by Ethanol Photoreforming on Au/TiO2

A deposition-precipitation method is used to prepare Au/TiO 2 solids (0.45–1.7 wt% Au). These materials, consisting of gold nanoparticles (diameter range = 1.5–6.5 nm) supported on the surface of TiO 2 , are used as photocatalysts for the ethanol photoreforming reaction under either UV-rich or simulated solar light. The main products of such reactions are H 2 in the gas phase and acetaldehyde in the liquid phase according to the reaction CH 3 CH 2 OH → CH 3 CHO + H 2 . Among the gaseous products, H 2 amounts to around or above 99% in all cases; other minor products found in the gas phase are, in decreasing order of molar production: CH 4 > CO > C 2 H 4 > CO 2 > C 2 H 6 > C 3 H 8 . The photoactivity is lower under CO 2 atmosphere, as compared to analogous reactions performed under Ar. The H 2 production yields are very high (up to a maximum 30 mmol g cat−1 h −1 ) under UV irradiation, and increase with increasing gold loading. The reactions under simulated solar light also yield signifi cant amounts of H 2 (5–6 mmol g cat−1 h −1 ) as the main gaseous product.This work has been supported by the JAE-Doc program, co-funded by the Consejo Superior de Investigaciones Cientificas (CSIC) and the European Social Fund (ESF). A.V.P. is grateful to CSIC for a JAE-Doc post-doctoral grant. Financial support by the Generalitat Valenciana (Prometeo 20/2/014) is gratefully acknowledged.Vaca Puga, A.; Forneli Rubio, MA.; García Gómez, H.; Corma Canós, A. (2014). Production of H2 by Ethanol Photoreforming on Au/TiO2. Advanced Functional Materials. 24(2):241-248. doi:10.1002/adfm.201301907S24124824

p-n Heterojunction of Doped Graphene Films Obtained by Pyrolysis of Biomass Precursors

Nitrogen-doped graphene [(N)G] obtained by pyrolysis at 900 degrees C of nanometric chitosan films exhibits a Hall effect characteristic of n-type semiconductors. In contrast, boron-doped graphene [(B)G] obtained by pyrolysis of borate ester of alginate behaves as a p-type semiconductor based also on the Hall effect. A p-n heterojunction of (B) G-(N) G films is built by stepwise coating of a quartz plate using a mask. The heterojunction is created by the partial overlapping of the (B) G-(N) G films. Upon irradiation with a xenon lamp of aqueous solutions of H2PtCl6 and MnCl2 in contact with the heterojunction, preferential electron migration from (B) G to (N) G with preferential location of positive holes on (B) G is established by observation in scanning electron microscopy of the formation of Pt nanoparticles (NP) on (N) G and MnO2 NP on (B) G. The benefits of the heterojunction with respect to the devices having one individual component as a consequence of the electron migration through the p-n heterojunction are illustrated by measuring the photocurrent in the (B) G-(N) G heterojunction (180% current enhancement with respect to the dark current) and compared it to the photocurrent of the individual (B) G (15% enhancement) and (N) G (55% enhancement) components.Financial Support by the Spanish Ministry of Economy and Competitiveness (Severo Ochoa and CTQ2012-32315) is gratefully acknowledged. MLS and PA thank also to the Spanish Ministry and the National Research Council for a postgraduate scholarship and a research associate contract, respectively.Latorre Sánchez, M.; Primo Arnau, AM.; Atienzar Corvillo, PE.; Forneli Rubio, MA.; García Gómez, H. (2015). p-n Heterojunction of Doped Graphene Films Obtained by Pyrolysis of Biomass Precursors. Small. 11(8):970-975. https://doi.org/10.1002/smll.201402278S970975118Dreyer, D. R., & Bielawski, C. W. (2011). Carbocatalysis: Heterogeneous carbons finding utility in synthetic chemistry. Chemical Science, 2(7), 1233. doi:10.1039/c1sc00035gGeim, A. K., & Novoselov, K. S. (2007). The rise of graphene. Nature Materials, 6(3), 183-191. doi:10.1038/nmat1849Huang, C., Li, C., & Shi, G. (2012). Graphene based catalysts. Energy & Environmental Science, 5(10), 8848. doi:10.1039/c2ee22238hLatorre-Sánchez, M., Lavorato, C., Puche, M., Fornés, V., Molinari, R., & Garcia, H. (2012). Visible-Light Photocatalytic Hydrogen Generation by Using Dye-Sensitized Graphene Oxide as a Photocatalyst. Chemistry - A European Journal, 18(52), 16774-16783. doi:10.1002/chem.201202372Lavorato, C., Primo, A., Molinari, R., & Garcia, H. (2013). N-Doped Graphene Derived from Biomass as a Visible-Light Photocatalyst for Hydrogen Generation from Water/Methanol Mixtures. Chemistry - A European Journal, 20(1), 187-194. doi:10.1002/chem.201303689Xiang, Q., Yu, J., & Jaroniec, M. (2012). Graphene-based semiconductor photocatalysts. Chem. Soc. Rev., 41(2), 782-796. doi:10.1039/c1cs15172jYeh, T.-F., Syu, J.-M., Cheng, C., Chang, T.-H., & Teng, H. (2010). Graphite Oxide as a Photocatalyst for Hydrogen Production from Water. Advanced Functional Materials, 20(14), 2255-2262. doi:10.1002/adfm.201000274Zhang, N., Zhang, Y., & Xu, Y.-J. (2012). Recent progress on graphene-based photocatalysts: current status and future perspectives. Nanoscale, 4(19), 5792. doi:10.1039/c2nr31480kPrimo, 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/c2cc34978gPrimo, 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.2013.11.068Latorre-Sánchez, M., Primo, A., & García, H. (2013). P-Doped Graphene Obtained by Pyrolysis of Modified Alginate as a Photocatalyst for Hydrogen Generation from Water-Methanol Mixtures. Angewandte Chemie International Edition, 52(45), 11813-11816. doi:10.1002/anie.201304505Dhakshinamoorthy, A., Primo, A., Concepcion, P., Alvaro, M., & Garcia, H. (2013). Doped Graphene as a Metal-Free Carbocatalyst for the Selective Aerobic Oxidation of Benzylic Hydrocarbons, Cyclooctane and Styrene. Chemistry - A European Journal, 19(23), 7547-7554. doi:10.1002/chem.201300653Caughey, D. M., & Thomas, R. E. (1967). Carrier mobilities in silicon empirically related to doping and field. Proceedings of the IEEE, 55(12), 2192-2193. doi:10.1109/proc.1967.6123Spear, W. E., & Le Comber, P. G. (1975). Substitutional doping of amorphous silicon. Solid State Communications, 17(9), 1193-1196. doi:10.1016/0038-1098(75)90284-7Cui, Y., Duan, X., Hu, J., & Lieber, C. M. (2000). Doping and Electrical Transport in Silicon Nanowires. The Journal of Physical Chemistry B, 104(22), 5213-5216. doi:10.1021/jp000930