Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.209
Publication date: 6th July 2018
The development of semiconductors that split water photocatalytically under visible-light irradiation is a path to the efficient conversion of solar energy. 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 the first step we are producing nanoparticles by Chemical Vapor Synthesis. By adjusting process parameters such as temperature, pressure and precursor evaporation rate, we vary the characteristics of the materials, such as: surface area, crystallinity and particle size [1]. Exploiting the advantages of the synthesis from the gas phase 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 or with assistance of a microwave plasma to obtain the desired oxynitrides. It is known that photocatalytic activity of such a material strongly depends on crystallinity and its composition. Varying the nitridation time from 0.17 h to 10 h zinc and oxygen concentration in zinc-gallium oxyntrides decreases, which is associated with a change in band-gap energy.
Incorporation of nitrogen and elimination of oxygen and zinc during nitridation process should take place at the surface of β-Ga2O3 and ZnO nanoparticles, parallel with diffusion of the constituent ions to form the stoichiometric solid solution. X-Ray diffraction analyzed by Rietveld refinement reveals crystal phases, cell parameters, as well as atomic composition. These results are supported by High-Resolution Scanning-Electron Microscopy in combination with Energy Dispersive Spectroscopy. The specific surface area of the samples is analyzed by using low temperature nitrogen adsorption. The bandgap is determined by using Ultraviolet-visible Spectroscopy.
[1] S. Lukic et al., ChemSusChem, 10, (2017), 4190-4197.
[2] K. Maeda et al., J. Am. Chem. Soc. 127, (2005), 8286-8287.
[3] K. Maeda et al., J. Phys. Chem. B 109, (2005), 20504-20510.
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