An Amine‐Functionalized Iron(III) Metal–Organic Framework as Efficient Visible‐Light Photocatalyst for Cr(VI) Reduction

The photocatalytic reduction of Cr(VI) is investigated over iron(III)-based metal-organic frameworks (MOFs) structured as MIL-88B. It is found that MIL-88B (Fe) MOFs, containing Fe₃-μ₃-oxo clusters, can be used as photocatalyst for the reduction of Cr(VI) under visible light irradiation, which is due to the direct excitation of Fe₃-μ₃-oxo clusters. The amine-functionalized MIL-88B (Fe) MOFs (denoted as NH₂-MIL-88B (Fe)) shows much higher efficiency for the photocatalytic Cr(VI) reduction under visible-light irradiation compared with MIL-88B (Fe). It is revealed that in addition to the direct excitation of Fe₃-μ₃-oxo clusters, the amine functionality in NH₂-MIL-88B (Fe) can also be excited and then transferred an electron to Fe₃-μ₃-oxo clusters, which is responsible for the enhanced photocatalytic activity for Cr(VI) reduction. The enhanced photocatalytic activity for Cr(VI) reduction is also achieved for other two amine-functionalized iron(III)-based MOFs (NH₂-MIL-53 (Fe) and NH₂-MIL-101 (Fe)).