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

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.