Fabrication of Core–Shell MIL-88A(Fe)/In ₂ S ₃ Heterojunction for Efficient Photocatalytic Cr(VI) Reduction with Improved Charge Separation and Stability

Iron-based metal–organic frameworks (MOFs) have attracted considerable attention as promising photocatalysts for the reduction of Cr(VI) in industrial wastewater. Nevertheless, the practical application of single-component MOFs is limited by the rapid recombination of photoexcited electron–hole pairs. To circumvent this limitation, a core–shell MIL-88A(Fe)/In 2 S 3 heterojunction photocatalyst with enhanced visible-light-driven activity was constructed by in situ growing photoactive In 2 S 3 nanoparticles on the surface of structurally stable MIL-88A(Fe). Structural and spectroscopic characterizations confirmed the successful integration of In 2 S 3 with MIL-88A(Fe), forming an intimate heterointerface that effectively broadened the light absorption range and promoted charge separation and transfer. As a result, the optimized composite exhibited outstanding photocatalytic performance, achieving 97.34% Cr(VI) reduction within 30 min under visible-light irradiation. In addition, the photocatalyst showed remarkable stability and anti-interference capability, retaining a reduction efficiency of 93.50% after four consecutive cycles. Mechanistic insights indicated that the construction of a Type-II staggered heterojunction between MIL-88A(Fe) and In 2 S 3 was responsible for the boosted catalytic efficiency. The internal potential established at the contact interface promoted the rapid charge separation and drove the directional transfer of electrons from In 2 S 3 to MIL-88A(Fe), where accumulated electrons reduce Cr(VI) to Cr(III). Meanwhile, part of the photogenerated electrons converted dissolved oxygen into •O 2 –, which served as an auxiliary reactive species to further promote Cr(VI) reduction. This work demonstrated a feasible strategy for constructing high-efficiency and stable MOF-based heterojunction photocatalysts, and provided new insights into the rational design of advanced photocatalytic systems for heavy-metal wastewater remediation.