Synthesis and study of Bi2Ti2O7/TiO2 composites as efficient visible-light-active photocatalysts in the reduction of aqueous Cr（VI）

In this work, Bi2Ti2O7/TiO2 composites were synthesized and studied as potential visible-light-activated photocatalysts in the reduction of aqueous Cr（VI）. Bi2Ti2O7/TiO2 composites with tunable compositions were synthesized via a solvothermal-calcination two-step method, simply by changing the molar ratios of Bi（NO3）3·5H2O to tetrabutyl titanate in the reactants. The compositions, structures and optical properties of the as-synthesized Bi2Ti2O7/TiO2 composites were characterized by X-ray diffraction, field emission scanning electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized Bi2Ti2O7/TiO2 composites was tested in the reduction of aqueous Cr（VI）under visible-light（λ420 nm） irradiation, and compared with that of TiO2 nanoparticles. It was observed that the as-synthesized Bi2Ti2O7/TiO2 composites exhibited much higher photocatalytic activity than TiO2 nanoparticles, and the most efficient composite（300 mg） can achieve the complete reduction of Cr（VI） in 300 mL of 50 mg/L K2Cr2O7 aqueous solution under visible-light（λ420 nm）irradiation in 90 min.