Influence of nitrogen chemical states on photocatalytic activities of nitrogen-doped TiO₂ nanoparticles under visible light

Nitrogen-doped TiO₂ (N-TiO₂) nanoparticles with a homogeneous anatase structure were synthesized using three different chemical methods. X-ray photoelectron spectra (XPS) analysis shows that nitrogen was successfully doped into TiO₂ nanoparticles and the nitrogen atoms are present in both substitutional and interstitial sites. The electron binding energy (BE) of N 1s core level is found to depend on the synthesis methods. Changes in Ti-O bond lengths of the substitutional and interstitial N doped-TiO₂ were calculated by computational geometry optimization, and confirmed by Raman shift analysis. Differences in UV-vis light absorption and visible-light-induced photocatalytic activity of three N-TiO₂ samples were attributed to their different nitrogen states within TiO ₂ lattice, which would create different defect levels. The defect levels were confirmed by photoluminescence (PL) analysis and density of states (DOSs) calculation. From one to one correspondence between XP spectrum and photocatalytic activities, it is concluded that nitrogen atoms in substitutional sites enhances the photocatalysis of TiO₂ under visible light more effectively than nitrogen atoms in interstitial sites.