Charge-Tunable Bismuth-Hydroxamate Metal–Organic Frameworks for Photocatalytic Cr(VI) Mitigation

This study presents three bismuth-hydroxamate metal–organic frameworks (MOFs), namely, SUM-90A/B/C (SUM = Sichuan University Materials), prepared from Bi³⁺ and the same bridging ligand (1,4-benzenedihydroxamic acid). By varying the synthetic conditions, the charge states of the framework backbones and the coordination environments of the Bi³⁺ centers were finetuned, resulting in distinct structures and properties. The performances of MOFs as heterogeneous photocatalysts for Cr(VI) mitigation were comparatively studied, using both theoretical and experimental methods, and they exhibited remarkable kinetic stability in aqueous media and varied electronic structures. Specifically, SUM-90C, with an experimental band gap of 1.92 eV, was identified as a promising photocatalyst that could effectively convert Cr(VI) within 4 h and retain 96% of its capability over 3 cycles.