Synergistic Enhancement of Photocatalytic Cr(VI) Reduction via TA-Assisted Charge Separation in MIL-88A(Fe)/BiVO₄...

The utilization of photocatalysis for reduction emerges as a highly promising approach to address the issue of toxic Cr(VI) contamination. Although the iron-based metal-organic framework MIL-88A(Fe) exhibits good visible-light response, its practical application is limited by rapid recombination of photogenerated carriers and susceptibility to photochemical corrosion. To overcome these drawbacks, an MIL-88A(Fe)/BiVO₄ heterojunction catalyst was constructed by in situ growth of BiVO₄ nanocrystals on the MIL-88A(Fe) framework, which synergistically improved both photocatalytic activity and stability. With the assistance of tartaric acid (TA), the heterojunction achieved efficient Cr(VI) reduction. Various characterizations confirmed the formation of a stable heterojunction interface via Bi-O-C bonding. Under optimized conditions, the catalyst completely reduced Cr(VI) within 9 min under visible light and retained 71.3% removal efficiency after five cycles. Mechanism studies revealed that the type-II band alignment drove electron transfer from BiVO₄ to MIL-88A(Fe), while surface oxygen vacancies and Bi-O-C bonds facilitated electron transport. Cr(VI) was directly reduced by electrons accumulated on MIL-88A(Fe), assisted by the Fe³⁺/Fe²⁺ redox cycle. Meanwhile, TA acted as an efficient hole scavenger, suppressing charge recombination and thereby ensuring a high concentration and lifetime of photogenerated electrons for efficient Cr(VI) reduction. This work proposed an effective interfacial engineering strategy to synergistically enhance the photoactivity and stability of MOF-based catalysts, offering insights for developing advanced catalysts for Cr(VI) reduction.