Synthesis of Gallium Nitride Photocatalysts By Reaction of Solution Synthesized Gallium Oxide and Solid Nitrogen Sources

Abstract

Solar energy-driven water splitting is receiving considerable interest in hydrogen production as a renewable energy source. Various semiconductor materials for the photodecomposition of water have been investigated for solar energy conversion such as TiO2, TaON and BiVO4. GaN, GaN : ZnO and GaN : InN solid solution are also considered as the photoelectrochemically active material for solar energy-driven water splitting. And its band gap can be controlled by the composition of these solid solutions. We have reported a new technique to synthesize low cost GaN powder under moderate condition, Li3N or LiNH2 were used as a high reactive solid nitrogen source to improve the reaction rate and lowering the reaction temperature. A high yield and high purity GaN with wurtzite structure was synthesized [1, 2]. In this report we studied the method to synthesize GaN powders by the reaction of solution synthesized Ga2O3 powder with solid nitrogen sources. In previous reports commercially available Ga2O3 powder was used. When commercial Ga2O3 powder was used, by the inhomogeneous size, the reaction occurred partially and the yields became small. So the gallium oxide powder with homogeneous size was synthesized by the use of solution process. The photoelectrochemical properties of particulate electrode with synthesized GaN powder were also investigated. The GaCl3 was dissolved in 2-buthyl alcohol under stirring. Then the purified water was added gradually to the Ga containing solution to get the white precipitate. XRD analysis demonstrate that the synthesized powder is Ga2O3. The crucible with starting materials, Ga2O3 and Li3N were put into a sealed stainless steel reaction vessel and it was set vertically in an electric furnace. Then it was heated at 550 – 700°C, 2 hours in N2 atmosphere. After the reaction, the products were washed by alcoholic HCl solution and distilled water. Crystalline wurtzite GaN powder with several hundred nanometer size was successfully synthesized. The reaction yield for the GaN synthesis with solution processed Ga2O3 is higher than that with commercial Ga2O3 powder. Anodic photocurrent was clearly observed for the paste electrodes with GaN and this observation indicates that the GaN synthesized in this study shows n-type semiconductivity. GaN : InN solid solution was also successfully synthesized by the reaction with GaCl3, InCl3 and LiNH2. Photo-electrochemical properties of its paste electrode was also studied. References T. Zhang, A. Mabuchi, T. Sugiura, H. Minoura, Trans. Mater. Res. Soc. Jpn., 33(4), 1277-1280 (2008).T. Zhang, A. Kouyama, M. Miura and T. Sugiura, Trans. Mater. Res. Soc. Jpn., 36(3), 513-516 (2011).