Photocatalytic removal of chromium(VI) and sulfite using transition metal (Cu, Fe, Zn) doped TiO2 driven by visible light: Feasibility, mechanism and kinetics

To cooperatively oxidize sulfite and reduce Cr(VI), this paper proposed a visible-light driven photocatalytic method, with using the photocatalysts of transition metals (Cu, Fe and Zn) doped TiO2. The photocatalysts were characterized by means of XRD, BET, SEM and UV-vis. 0.5Cu-TiO2 exhibited the best performance, and the existing forms of Ti and Cu were Ti4+/Cu+ and/or Cu-O-Ti. Cu-doping introduced an energy level of Cu 3d which was useful in decreasing the band gap and increasing the visible light utilization. Cu-doping also made the TiO2 grains well dispersed, increased the amount of hydroxyl group, decreased the grain size and increased the specific surface area, which facilitated the adsorption process. Hydrothermal method (8 h and 180 degrees C) favored the formation of anatase crystal. FT-IR results revealed that most of produced Cr(III) and sulfate were adsorbed onto the catalyst. Kinetics results suggested that the rate constant for Cr(VI) removal was 5.05 x 10(-3) min(-1). The photo-produced electrons (e(-)) and holes (h(+)) contributed to the reduction of Cr(VI) and oxidation of sulfite, respectively: the continual consumption of e(-) and h(+) enhanced the separation of the h(+)-e(-) pairs. (C) 2019 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.