Proceedings of nanoGe Fall Meeting 2018 (NFM18)
Publication date: 6th July 2018
The overall water splitting reaction on a semiconductor photocatalyst occurs in three steps: I) absorption of the photon energy greater than the band-gap of the semiconductor and generation of electron-hole pairs, II) separation and migration of electrons and holes to the surface with minimum recombination, III) redox reactions at different reaction sites for generation of H2 and O2. Various oxides with d0 and d10 electron configuration possess such photocatalytic activity, but suffer from poor oxygen and hydrogen evolution or work only in the ultraviolet regime [1]. Domen et. al. developed gallium-oxynitride (Ga1-xZnx)(N1-xOx) as such a material by nitriding mixture of Ga2O3 and ZnO in a solid solution. It is capable of absorbing visible light efficiently with a bandgap of 2,6 eV [2,3].
In order to have active photocatalytic systems for overall water splitting reaction it is necessary first to obtain semiconductor nanoparticles with desired characteristics. We are producing nanoparticles by Chemical Vapor Synthesis. Exploiting the advantages of different synthesis routes we are able to obtain pure phase or mixture of ZnO and β-Ga2O3, as well as the complex spinel phase ZnGa2O4. In second step these powders are nitrided thermally to obtain the desired oxynitrides, which also leads to elimination of highly volatile Zn from the system, since Zn-O bond is easier to break than Ga-O bond. Increasing the nitridation time the Zn content decreases and defect density increases, which has negative impact on photocatalytic activity. In this work we present the overview of different material mixtures and their photocatalytic activities. For better understanding of nitridation kinetics we have investigated samples before and after the nitridation process with High-Resolution Transmission Electron Spectroscopy in combination with Energy Dispersive Spectroscopy. X-Ray diffraction analyzed by Rietveld refinement reveals crystal phases, cell parameters, as well as atomic composition.
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