Solvothermal syntheses of Bi and Zn co-doped TiO with enhanced electron-hole separation and efficient photodegradation of gaseous toluene under visible-light.

This study investigated the effects of Bi doped and Bi-Zn co-doped TiO on photodegradation of gaseous toluene. The doped TiO with various concentration of metal was prepared using the solvothermal route and characterized by SEM, XRD, Raman, BET, DRS, XPS, PL and EPR. Their photocatalytic activities under visible-light irradiation were drastically influenced by the dopant content. The results showed that moderate metal doping levels were obviously beneficial for the toluene degradation, while high doping levels suppressed the photocatalytic activity. The photocatalytic degradation of toluene over TiBiO and TiBiZnO can reach to 51% and 93%, respectively, which are much higher than 25% of TiO. Bi doping into TiO lattice generates new intermediate energy level of Bi below the CB edge of TiO. The electron excitation from the VB to Bi orbitals results in the decreased band gap, extended absorption of visible-light and thus enhances its photocatalytic efficiency. Zn doping not only further enhances the absorption in this visible-light region, but also Zn dopant exists as the form of ZnO crystallites located on the interfaces of TiO agglomerates and acts as a mediator of interfacial charge transfer to suppress the electron-hole recombination. These synergistic effects are responsible for the enhanced photocatalytic performance.