MIL-68(Fe) as an efficient visible-light-driven photocatalyst for the treatment of a simulated waste-water contain Cr(VI) and Malachite Green

A highly effective Iron Metal-Framework photocatalyst (MIL-68(Fe)) has been successfully prepared via a facile solvothermal method under acidic condition. The UV–vis diffuse reflectance spectrum reveals that the absorption edge of MIL-68(Fe) is 440   nm. The flat-band potential of MIL-68(Fe) is −0.6   V vs. NHE at pH   =   6.8, which is more negative than the redox potential of Cr(VI)/Cr(III) (+0.51   V, pH   =   6.8). Consequently, it is thermodynamically permissible for the transformation of photogenerated electrons to the Cr(VI) to produce Cr(III). Moreover, MIL-68(Fe) could perform as an efficient photocatalyst towards the reduction of Cr(VI) aqueous with a wide pH range. After 5   min of visible light illumination (λ   >   420   nm), almost 100% Cr(VI) can convert to Cr(III) with (NH 4 ) 2 C 2 O 4 as a scavenger (pH   =   3), which is also higher than that of N-doped TiO 2 (50%) and ZnO (7.6%) under identical conditions. Furthermore, MIL-68(Fe) is proved to perform as a highly efficient photocatalyst for remove of different aqueous contaminant with malachite green (MG) as a scavenger. Finally, a possible reaction mechanism has also been investigated in detail.