Formation Mechanism for Particulate Y₂Ti₂O₅S₂ Photocatalyst by the Solid-State Reaction

Y₂Ti₂O₅S₂ (YTOS) is a stable oxysulfide photocatalyst applicable to water splitting under visible light with wavelengths of up to 650 nm. However, the activity of YTOS in the overall water-splitting reaction is still low, possibly because YTOS particles prepared by a solid-state reaction (SSR) method have large sizes and high defect density. Therefore, understanding the formation mechanism is indispensable for synthesizing YTOS with the desired physical properties to improve its performance. In this study, we investigated the formation mechanism for YTOS produced by an SSR method. The results indicated that Y₂Ti₂O₇, Y₂O₂S, and TiS₂ are key intermediate phases in the formation of YTOS. Detailed formation steps are proposed for YTOS particles as they pass through these intermediate phases. By controlling the formation process for these intermediates, it was possible to prepare YTOS with a reduced particle size and enhanced activity for photocatalytic H₂ evolution.