Synchronous Photocatalytic Redox Conversion of Chromium(VI) and Arsenic(III) by Bimetallic Fe/Ti Metal-Organic...

In this work, bimetallic organic frameworks NH₂-MOFs(Fe, Ti) with different Fe³⁺/Ti⁴⁺ molar ratios were prepared by a hydrothermal method for the synchronous redox transformation of Cr(VI) and As(III). These results showed that NH₂-MIL-125(Ti) was less effective in the photocatalytic removal of Cr(VI), whereas NH₂-MIL-88B(Fe) was less effective in the photocatalytic oxidative removal of As(III). Due to the introduction of Fe³⁺, the photocatalytic reduction removal of Cr(VI) (23.04 → 42.56%) and the photocatalytic oxidation removal of As(III) (5.58 → 26.09%) by NH₂-MOFs(Fe, Ti) were significantly enhanced. Among them, NH₂-MIL-88B(Fe_0.6Ti_0.4) exhibited the best performance in the photoreduction of Cr(VI) and photo-oxidation of As(III), which balanced the insufficiency of monometallic MOFs(Fe/Ti). In this case, the total removal of Cr(VI) and As(III) by NH₂-MIL-88B(Fe_0.6Ti_0.4) was found to be 94.19 and 83.54%, respectively. The excellent photocatalytic property could account for the ligand-to-metal charge transfer (LMCT), where photogenerated e^- generated by -NH₂ group excitation was transferred to the active site Fe-O clusters, as well as e^- transported along Ti → O → Fe (metal-to-metal charge transfer, MMCT). Therefore, the synergetic effect of LMCT and MMCT could efficiently inhibit the recombination of e^--h pairs, improving the photocatalytic performance of NH₂-MOFs(Fe, Ti).