Highly efficient visible light photocatalytic activity of Cr-La codoped SrTiO3 with surface alkalinization: An insight from DFT calculation

Keeping Cr in +3 charge state is crucial to Cr-doped SrTiO3 as a visible-light response photocatalyst. Codoping with Cr and other elements has achieved this goal. In this study, density functional theory calculation was used to investigate CrTi + LaSr codoped SrTiO3, in which Cr and La substituted for Ti and Sr, respectively. The results showed that Cr can be effectively compensated by La, and that CrTi + LaSr codoped SrTiO3 exhibited visible light absorption. By comparison between CrTi + LaSr codoped and CrTi + MTi (M = V, Nb, Ta, Sb, Bi) codoped SrTiO3, it was found that equimolar Cr and La can be easily codoped into SrTiO3. Efficient charge compensation between Cr and La maintained Cr in +3 charge state and reduced harmful defects such as Cr6+ and VO, giving one proper explanation to the experimental highest apparent quantum efficiency of CrTi + LaSr codoped SrTiO3 under visible light. We also studied effects of surface alkalinization on electronic structures of CrTi + LaSr codoped SrTiO3 (1 1 0) surface, and the results illustrated that surface alkalinization induced negative band shift of CrTi + LaSr codoped SrTiO3, which was in agreement with the experimental results. Our calculations will not only elucidate the highly efficient visible light photocatalytic activity of CrTi + LaSr codoped SrTiO3 with surface alkalinization, but also enlighten the codoping strategy for developing photocatalytic materials.