Adsorption of water molecules on the surface of photo-catalyst: a first principles theoretical comparison between InVO 4
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Adsorption of water molecules on the surface of photo-catalyst: a first principles theoretical comparison between InVO4 and rutile TiO2 M. Oshikiri1, M. Boero2 and J. Ye3 1 Nanomaterials Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan 2 Institute of Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8571, Japan 3 Materials Engineering Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan ABSTRACT The adsorption process of water molecules on the surface of InVO4 has been investigated via first principles molecular dynamics simulations and compared with that of the well-known rutile TiO2. We have found that the surface of InVO4 shows a remarked chemical reactivity whenever comes in contact with water and H2O molecules are often adsorbed dissociatively on its surface. The reaction proceeds spontaneously in a way similar to the case of TiO2 and does not require the overcoming of an activation energy barrier. The peculiar atomic connectivity of the InVO4 bulk crystal structure and the changes at the catalyst surface induced by the water adsorption are discussed and compared with the TiO2 system.
INTRODUCTION In recent years, some interesting photo-catalysts such as InMO4 (M = V [1], Nb [2,3], Ta [2,3]) and BiVO4 [4], which are active in the visible light wavelength range, have been discovered. Among them, as reported in previous works [1,5], InVO4 has been shown to be particularly active and able to decompose water molecules, with associated hydrogen evolution, when irradiated with visible light, up to a wavelength of about 600 nm. Alongside with experiments on the photo-catalytic properties of InVO4, our group focused also on the theoretical aspects of this system and its peculiar electronic structures by performing first principles calculations, in an attempt to figure out analogies and differences with the wellknown rutile TiO2 system [5,6]. Our aim is to address the problem of the wavelength dependency of the photo catalytic activity of the TiO2, InMO4 (M = V, Nb, Ta) and BiVO4 systems and how this is related to the crystal structure. After assessing the electronic structure of the pristine system, the next step is, of course, the adsorption of water molecules on the surface of InVO4. This is the target of the present work: we simulated the H2O adsorption process and made a comparison with that of the rutile TiO2 in order to figure out analogies and differences with respect to the TiO2 system and to understand which are the atoms exposed at the surface that act as a catalyst and how relaxations and/or reconstructions affect the surface itself. Some results relevant to the adsorption of a Li atom onto a two-dimensional surface of TiO2 have already been reported by us [7], however the problem of the interaction with water was not considered there. Similarly, preliminary investigations on the surface relaxation phenomena induced by the interaction of a single H2O molecule with the InVO4 surface
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