AgGaS2-type photocatalysts for hydrogen production under visible light: Effects of post-synthetic H2S treatment

Bulky AgGaS2 was synthesized as a p-type semiconductor photocatalyst by a conventional solid state reaction under N2 flow for hydrogen production under visible light. To remove impurity phases involved in the synthesized material and improve crystallinity, the material was treated at various temperatures of 873–1123 K under H2S flow. Impurity phases were identified as β-Ga2O3 and Ag9GaS6 with the cell refinements of XRD and the local coordination structure around gallium atom in AgGaS2 was investigated by EXAFS. As the H2S-treatment temperature increased, the contribution from impurity phases was diminished. When the temperature reached 1123 K, the impurity phases were completely removed and the material showed the highest photocatalytic activity. Thus, the post-synthetic H2S treatment could be applied for the synthesis of sulfide-type photocatalysts with high activity.