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 Fe-3-mu(3)-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 Fe-3-mu(3)-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 Fe-3-mu(3)-oxo clusters, the amine functionality in NH2-MIL-88B (Fe) can also be excited and then transferred an electron to Fe-3-mu(3) -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)).