Enhanced Photocatalytic Hydrogen Production of ZnIn₂S₄ by Using Surface-Engineered Ti₃C₂T_x MXene as a Cocatalyst

Developing efficient and stable photocatalysts is crucial for photocatalytic hydrogen production. Cocatalyst loading is one of the effective strategies for improving photocatalytic efficiency. Here, Ti₃C₂T_x (T_x = F, OH, O) nanosheets have been adopted as promising cocatalysts for photocatalytic hydrogen production due to their metallic conductivity and unique 2D characterization. In particular, surface functionalized Ti₃C₂(OH)_x and Ti₃C₂O_x cocatalysts were synthesized through the alkalization treatment with NaOH and a mild oxidation treatment of Ti₃C₂F_x, respectively. ZnIn₂S₄/Ti₃C₂T_x composites, which were fabricated by the in-situ growth of ZnIn₂S₄ nanosheets on the Ti₃C₂T_x surface, exhibited the promoted photocatalytic performance, compared with the parent ZnIn₂S₄. The enhanced photocatalytic performance can be further optimized through the surface functionalization of Ti₃C₂F_x. As a result, the optimized ZnIn₂S₄/Ti₃C₂O_x composite with oxygen functionalized Ti₃C₂O_x cocatalyst demonstrated excellent photocatalytic hydrogen evolution activity. The characterizations and density functional theory calculation suggested that O-terminated Ti₃C₂O_x could effectively facilitate the transfer and separation of photogenerated electrons and holes due to the formation of a Schottky junction, with the largest difference in work function between ZnIn₂S₄ and Ti₃C₂O_x. This work paves the way for photocatalytic applications of MXene-based photocatalysts by tuning their surface termination groups.