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

Titanium dioxide (TiO) photocatalyst was prepared with a sol-gel method and its characterizations were analyzed TiO photocatalytic reduction of Cr was investigated in visible light irradiation and reduction mechanisms were calculated. Prepared TiO is anatase with a bandgap of about 2.95 eV. Experimental results display that almost 100% of Cr is removed by visible light-driven TiO photocatalytic reduction after 120 min when CrO initial concentration is 1.0 mg·L, TiO dosage is 1.0 g·L, and pH value is 3. In acidic aqueous solution, HCrO is the dominant existing form of Cr and is adsorbed by TiO, forming a complex catalyst HCrO/TiO 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 Cr is adsorbed on the surface of TiO and then reduced to Cr in situ by photoelectrons. Self-assembly of HCrO/TiO complex catalyst and self-reduction of Cr in situ are the key steps to start the visible light-driven TiO photocatalytic reduction. Furthermore, TiO photocatalytic reduction of Cr fits well with pseudo-first-order kinetics and has the potential application to treat chemical industrial wastewater.