Intensified redox co-conversion of As(III) and Cr(VI) with MIL-125(Ti)-derived COOH functionalized TiO2: Performance and mechanism

MIL-125(Ti)-derived titanium oxides, a functionalized cake-like 3D material, is becoming increasingly attractive to researchers. In this work, COOH functionalized anatase TiO2 (TiO2@C) was prepared by one-step calcination method. And the TiO2@C, as a novel catalyst, was used to accelerate electron transfer from As(III) to Cr(VI) for simultaneous Cr(VI) reduction and As(III) oxidization in aqueous solution. The results showed that the addition of TiO2@C greatly accelerates the coupled As(III)/Cr(VI) reaction. This reaction is further enhanced at acidic pH and higher concentrations of material. Furthermore, the mutual conversion is equally sensitive to ion initial concentration. Accordingly, a new microscopic redox reaction process of As(III) and Cr(VI) was proposed, which was first made clear of the mutual redox via XPS and FTIR analysis. To be specific, the carboxyl on anatase not only offers As(III) and Cr(VI) ions binding sites, but also initiates the electron transfer from As(III) to Cr(VI) on the solid surface. While the cake-like geometry with high surface area serves for the electron transfer pathways. This unparalleled reaction mechanism enlighten us on a new field of COOH functionalized catalyst used for the coupled removal of As(III)/Cr(VI).