Triphase photocatalytic hydrogel for molecule oxygen activation with enhanced interfacial electric field by Ti-O-Fe...

Solar-driven heterogeneous photocatalysis offers a green and sustainable approach for converting abundant O₂ and H₂O into reactive oxygen species (ROS), addressing key pollution control and energy storage challenges. However, traditional diphase photocatalytic systems face significant problems, including sluggish interfacial reaction kinetics, limited O₂ diffusion, poor long-term stability, and recovery of catalyst. In this study, we constructed a composite MOF-on-MOF (NH₂-MIL125(Ti)/NH₂-MIL88B(Fe)) S-scheme heterojunction photocatalyst embedded in a cross-linked dual-network hydrogel (HG) composed of the carboxymethylcellulose (CMC) and polyvinyl alcohol (PVA), as a self-suspending triphase interfacial superwetting photocatalytic platform. Comprehensive experimental characterizations and theoretical calculations reveal that the atomic-level Ti-O-Fe bonding at the heterojunction interface facilitates efficient directional migration of photogenerated carriers. Moreover, the porous hydrogel structure significantly enhances O₂ diffusion, mass transfer processes, and the conversion of O₂ into highly oxidative ROS (H₂O₂, ¹O₂, •O₂^-, and •OH). Compared with the conventional diphase system, our triphasic platform achieves superior mass transfer efficiency and interfacial reaction kinetics, ensuring long-term stability in purifying diverse pollutants in natural water systems. These findings provide valuable insights into the rational design of efficient, stable, and scalable triphase photocatalytic systems.