A novel visible light-driven TiO2 photocatalytic reduction for hexavalent chromium wastewater and mechanism
Baoxiu Zhao, Kaixin Zhang, Yue Huang, Qi Wang, Hao Xu, Yilin Wang, Jincheng Li, Tianwen Song, Wenxiang Xia, Jie Liu
Abstract
Abstract Titanium dioxide (TiO2) photocatalyst was prepared with a sol-gel method and its characterizations were analyzed TiO2 photocatalytic reduction of Cr6+ was investigated in visible light irradiation and reduction mechanisms were calculated. Prepared TiO2 is anatase with a bandgap of about 2.95 eV. Experimental results display that almost 100% of Cr6+ is removed by visible light-driven TiO2 photocatalytic reduction after 120 min when Cr2O72− initial concentration is 1.0 mg·L−1, TiO2 dosage is 1.0 g·L−1, and pH value is 3. In acidic aqueous solution, HCrO4− is the dominant existing form of Cr6+ and is adsorbed by TiO2, forming a complex catalyst HCrO4−/TiO2 with an increase in wavelength to the visible light zone, demonstrated by UV–Vis diffuse reflection spectroscopy. Based on X-ray photoelectron spectroscopy data, it can be deduced that Cr6+ is adsorbed on the surface of TiO2 and then reduced to Cr3+ in situ by photoelectrons. Self-assembly of HCrO4−/TiO2 complex catalyst and self-reduction of Cr6+ in situ are the key steps to start the visible light-driven TiO2 photocatalytic reduction. Furthermore, TiO2 photocatalytic reduction of Cr6+ fits well with pseudo-first-order kinetics and has the potential application to treat chemical industrial wastewater.