Density functional theory calculations for the investigation of (Ag, N) codoping effect on the electronic and optical properties of anatase TiO2

Efficient absorption of light in visible range and enhance separation of photoexcited electron-hole pairs (EHPs) are crucial for improving the photoactivity of metal nonmetal codoped TiO2. By using density functional theory (DFT) calculations, an effective metal (Ag) and nonmetal (N) codoping approach is described to modify the photoelectrochemical properties of titanium dioxide (TiO2). Nitrogen (N) doping introduces isolated N-2p states above the valence band maximum (VBM) which acts as an electron trap to promote EHP recombination. For Ag-doped TiO2, Ag-4d states are introduced above the VBM which leads to the band gap narrowing. Silver (Ag) and nitrogen codoped TiO2 possess stable configuration, narrowed band gap and best visible light absorption. Defect pair binding energy calculation shows that individual dopants, located at a distance of 8.951 angstrom bind each other, which indicates that the defect pair is stable compared to the isolated impurities in the host lattice. Ag and N codoped TiO2 shows better visible light absorption as compared to other doped models due to the reduced band gap. N doping reduces the band gap of TiO2 while Ag doping enhances the EHPs separation, so their combined presence in a sample would improve the photocatalytic activity due to their synergistic codoping effect. Our calculations provide reasonable explanation for the experimental findings.