A novel visible-light-driven TiO2 photocatalytic reduction for hexavalent chromium wastewater and mechanism

TiO2 photocatalyst was prepared with a sol-gel method and its characterizations were analyzed, then TiO2 photocatalytic reduction for Cr6+ was investigated in visible light irradiation and reduction mechanism were deduced lastly. Prepared TiO2 is anatase and bandgap is about 2.95 eV. Experimental results display that almost 100% 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 adsorbed by TiO2, forming a complex catalyst HCrO4-/TiO2 which wavelength enlarges to visible light zone, proved by UV-Vis DRS. Based on XPS data, it can be deduced that Cr6+ is adsorbed on the surface of TiO2 and then reduced to Cr(3+)in situ by photoelectrons. Self-assembly of HCrO4-/TiO2 complex catalyst and self-reduction of Cr(6+)in situ are the key steps to start visible-light-driven TiO2 photocatalytic reduction. Furthermore, TiO2 photocatalytic reduction for Cr6+ fits well with pseudo first-order kinetics and has potential application to treat chemical industrial wastewater.

Automated summary

TiO2 photocatalyst prepared by sol-gel method showed efficient reduction of Cr6+ under visible light irradiation, making it a potential application for treating chemical industrial wastewater.