Functionalized MIL-68(In) for the photocatalytic treatment of Cr(VI)-containing simulation wastewater: Electronic effects of ligand substitution

A family of functionalized MIL-68(In) have been successfully synthesized and applied to photoreduction of Cr(VI) aqueous under simulated sunlight (280 nm < λ < 980 nm) irradiation. Meanwhile, we have studied the effect of modification with electron-donating or electron-withdrawing groups (H₂BDC, H₂BDC-NH₂, H₂BDC-NO₂ and H₂BDC-Br) on photocatalytic performance of MIL-68(In)-X (X = H, NH₂, NO₂, Br). Further experimental results demonstrated that the photoactivities of the obtained MIL-68(In)-X have been greatly affected by the electronic effect of ligand substituent. That is, the reaction rates obtained by functionalized MIL-68(In) have been linearly associated with the Hammett coefficients of different substituents. More significantly, MIL-68(In)-NH₂ has also exhibited outstanding performance in a co-existed model system (Cr(VI)/dyes), which represents a first example to use the In-based MOFs as bifunctional photocatalysts. It is hope that this work not only represents the structure-property relationships on photocatalysis in MOFs, but also promotes further interest in design and construction of more efficient MOFs-based photocatalysts for environmental remediation.