Spatially decoupled Janus membrane with Z-scheme Ag/BiOBr@MIL-53(Fe) heterojunction for enhanced solar-driven interfacial photocatalysis and Cr(VI) remediation: A proof-of-concept laboratory study for model dye degradation and Cr(VI) reduction under simulated solar irradiation

The remediation of persistent organic dyes and hexavalent chromium (Cr(VI)) in industrial wastewater remains challenging because these pollutants require different redox processes and efficient charge separation. Herein, we introduce a rationally designed, self-floating Janus membrane, Ag/BiOBr@MIL-53(Fe)@CF/SS, as a proof-of-concept platform for solar-driven interfacial photocatalysis. The membrane integrates a superhydrophilic stainless-steel (SS) layer, which promotes rapid capillary-driven pollutant transport, with a hydrophobic and conductive carbon-fiber (CF) support that facilitates directional electron migration. Discontinuous Ag nanoparticles were introduced into the BiOBr@MIL-53(FE) framework by 2s magnetron sputtering, providing plasmonic active sites without forming a continuous metallic layer. The observed band-alignment and charge-transfer behavior are consistent with a Z-scheme-type charge-transfer pathway, although alternative pathways (e.g., type-II with Schottky trapping) cannot be excluded based on the present data. In separate single-component model pollutants under simulated solar irradiation, the membrane achieved 99% Rhodamine B removal within 60 min, with a rate constant of k = 4.5 × 10 −2 min −1 , and complete Cr(VI) reduction within 165 min, with a rate constant of k = 1.6 × 10 −2 min −1 . Dark adsorption removed 49% of Rhodamine B and 31% of Cr(VI), demonstrating a pre-concentration effect that accelerated subsequent photocatalytic reactions. Mechanistic studies indicated electron-dominated Cr(VI) reduction and synergistic adsorption-oxidation of Rhodamine B. Further studies under continuous floating operation and real wastewater conditions are required.