First-Principles Calculation of Synergistic (N, P)-Codoping Effects on the Visible-Light Photocatalytic Activity of Anatase TiO2

The energetic and electronic properties of N- and/or P-doped bulk and anatase TiO2 (101) surfaces have been calculated based on first-principles density functional theory. For the bulk system, (N, P)-codoping of anatase TiO2 does not narrow the band gap much more than that of single N-doped anatase TiO2 at low concentration. An increasing P/N concentration ratio leads to more significant band-gap narrowing. For (N, P)-codoped surface systems, the band gap is narrowed slightly when both N and P act as substitutional dopants. However, upon N and P adsorption on the surface, the band gap narrows significantly even at low dopant concentrations. The calculated energy results support the viewpoint that incorporation of P into N-doped bulk TiO2 cannot promote further N introduction, whereas N and P can be doped on the pristine anatase (101) surface more easily vis-a-vis single N- or P-monodoping. These results provide a reasonable explanation for recent experimental observations of different photocatalytic efficiencies in (N, P)-codoped and N- or P-monodoped anatase TiO2.