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In search of a photocatalyst to get hydrogen from water with visible light

The COMPHOCAT project has worked on the computational model of titanium dioxide nanoparticles (TiO₂) to search for a catalyst which, with visible light, favours the division of water to generate hydrogen.

The COMPHOCAT project has worked on the computational model of titanium dioxide nanoparticles (TiO₂) to search for a catalyst which, with visible light, favours the division of water to generate hydrogen.

13/03/2018

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Hydrogen is the cleanest potential fuel we have; the challenge is to get a clean process to stop using fossil fuels. The COMPHOCAT project, led by Professor Francesc Illas, director of the Institute of Theoretical and Computational Chemistry of the University of Barcelona (IQTCUB), has worked on the computational model of titanium dioxide nanoparticles (TiO₂) to search for a catalyst which, with visible light, favours the division of water to generate hydrogen.

TiO₂ is a material with unique photocatalysis properties and is now being applied to many areas of technology. One of the main properties it has is the ability to photocatalyse the breaking of the water molecule to obtain a hydrogen molecule and molecular oxygen. The main objective in COMPHOCAT was to study TiO₂ properties at the nanoscale and build computational models to simulate the behaviour of the nanoparticles to be used.

“So far, it has not been possible to identify photocatalysts with activity in the area of visible light, which restricts our practical applications”, says Francesc Illas. “To get a photocatalyst to be practical –he continues- we need to get light in the ultraviolet range, where the TiO₂ works better, or we should change the compound so that it has the same properties as visible light”. Illas believes the first option is ruled out “because we cannot get enough ultraviolet light from solar light, since the atmosphere absorbs this range’s light”. The second option –changing TiO₂’s nanoparticles- is being studied at the IQTCUB.

The research team led by Illas is formed by the IQTCUB researchers Stefan Bromley (ICREA), Francesc Viñes, Kyoung Chul Co, Ángel Morales, Rosendo Valero, and the researchers in training Antoni Macià and Oriol Lamiel. These researchers created realists models of TiO₂ nanoparticles in which they could study the electronic properties using models based on the density functional theory, and conducted precise calculations considering all electrons and adding relativist effects. “Each particle’s geometry has been determined by the minimization of energy, a technique which is used to get the most stable atom distribution for a molecule”, says Illas. Electronic properties were studied as the function of the shape and size of the nanoparticle. “These TiO₂ structure models allowed researchers build a database with nanoparticles which, if suitably modified, can lead to candidates with an absorption spectrum that works well with the window of visible light”, says the UB researcher.

The COMPHOCAT project was carried out thanks to the 52 million hours of calculation with the MareNostrum supercomputer from the Barcelona Supercomputingn Center (BSCN-CNS) given by the Partnership for Advanced Computing in Europe (PRACE). In order to continue with this study, PRACE platform gave the team led by Illas 40 million additional calculation hours for the new project EXCIPHOCAT, which will enable researcher characterize the compounds that were designed in this first stage.

Reference articles for the COMPHOCAT project:

A. Morales-García, O. Lamiel-Garcia, R. Valero and F. Illas. “Properties of single oxygen vacancies on a realistic (TiO2)84 nanoparticle: a challenge for density functionals”. The Journal of Physical Chemistry C, January 2018. DOI: 10.1021/acs.jpcc.7b11269

F. Viñes, O. Lamiel-Garcia, F. Illas and S. T. Bromley. “Size dependent structural and polymorphic transitions in ZnO: from nanocluster to bulk”. Nanoscale, 2017. Doi: 10.1039/C7NR02818K

O. Lamiel-Garcia, K. C. Ko, J. Y. Lee, S. T. Bromley and F. Illas. “When anatase nanoparticles become bulk-like: properties of realistic TiO2 nanoparticles in the 1-6 nm size range from all electron relativistic density functional theory based calculations”. Journal of Chemical  Theory and Computation, 2017. Doi: 10.1021/acs.jctc.7b0008

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