Effects of preparation condition on the photocatalytic activity of porphyrin-modified GaN:ZnO for water splitting

Effects of nitridation condition on gallium-zinc oxynitride solid solution (GaN:ZnO) was investigated to optimize the composition of GaN:ZnO for dye-modified photocatalysts. Gallium nitride (GaN) formed from Ga₂O₃ at 973 K, and GaN:ZnO was obtained over 1073 K under NH₃ gas flow. Nitrogen content in GaN:ZnO increased with increasing nitridation temperature and time, while zinc content decreased because of evaporation. Although UV–vis absorption spectra of GaN:ZnO powders were not significantly changed in different compositions, the water splitting activities of the dye-modified GaN:ZnO photocatalysts depended on the composition of GaN:ZnO. The highest formation rates of H₂ and O₂ were achieved by the GaN:ZnO containing 15% of zinc and 73% of nitrogen. Finally, the nitridation condition was optimized at 1123 K 15 h under NH₃ gas flow (200 ml/min) for preparation of the dye-modified GaN:ZnO powder as water splitting photocatalyst.