NH2-mediated indium metal–organic framework as a novel visible-light-driven photocatalyst for reduction of the aqueous Cr(VI)

• MIL-68(In)-NH2 was prepared via a simple solvothermal method.
• The product exhibited considerable photocatalytic activity.
• The addition of the ethanol could improve the Cr(VI) reduction rate.
• Cr(VI) reduction rate increased with the decreased of initial pH.

Metal–organic framework In-benzenedicarboxylate (MIL-68(In)) and its derivative (In-2-NH2-benzene-dicarboxylate, MIL-68(In)-NH2) were prepared via a simple solvothermal method. Powder X-ray diffraction (XRD) confirmed the isoreticular nature of MIL-68(In) and MIL-68(In)-NH2, while Fourier transformed infrared spectra (FTIR) proved the effective presence of amino group. Moreover, combined with UV–vis diffuse reflectance spectra (DRS) analysis, it was revealed MIL-68(In)-NH2 shown an extra absorption band in the visible light region with the absorption edge extending to around 440 nm. Importantly, MIL-68(In)-NH2 was proved to perform as an efficient visible-light-driven photocatalyst with considerable activity and stability for the reduction of Cr(VI), which could be attributed to its relatively high CB based on the result of Mott–Schottky experiment. Further experimental results revealed that the addition of hole scavenger and pH value of the reaction solution played important roles in the photocatalytic reduction of Cr(VI). Finally, a possible reaction mechanism had also been investigated in detail.

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