Constructing bimetallization and hydroxylation in metal-organic framework for efficient Cr(VI) photoreduction

Metal-organic frameworks (MOFs), as promising photocatalysts, have been widely used in Cr(VI) removal due to their high porosity and structural tunability, whereas the simple hybridization of MOFs was not beneficial for the separation of photogenerated carriers. In this study, a novel Al-doped and hydroxyl-functionalized Zr-based MOF (named as Al/Zr-UiO-66-(OH)2) was synthesized via dual strategies of bimetallization and hydroxylation. Characterization results confirmed that the incorporation of Al and hydroxyl groups effectively reduced the bandgap and enhanced separation efficiency of photogenerated charge. Al/Zr-UiO-66-(OH)2 (1:5) exhibited outstanding photocatalytic reduction performance towards Cr(VI) (99.3% within 2 h) under visible light. The photocatalytic rate of Al/Zr-UiO-66-(OH)2 (K = 0.0148 min-1) was 74 times higher than that of UiO-66 (K = 0.0002 min-1). Trapping experiments, EPR and XPS analysis revealed that highly efficient photoreduction of Cr(VI) into Cr(III) was attributed to electrons and ·O2- radicals. These findings provide a feasible strategy for designing MOF-based photocatalysts for practical environmental remediation.