Theoretical and experimental study on the electronic structure and optical absorption properties of nitrogen-doped nanometer TiO2

Nitrogen-doped nanosized TiO2 powders were prepared by using sol–gel technology while ammonium chloride, triethylamine and ammonia solution were taken as nitrogen precursors separately. Triethylamine with small bonding energy of N–C can introduce more nitrogen content into titania crystal than ammonium chloride and ammonia solution at the same initial molar concentration. The doping nitrogen atoms suppress the growth of titania crystal and the phase transformation, and increase the c-axis lattice parameter as well. UV–vis absorption studies confirmed that the spectral responses of nitrogen-doped TiO2 powders were shifted to the visible light region. The optimum nitrogen content in our experiments is 14.1% (mol), the absorption edge of which shift to 480 nm. The ab initio calculations support the conclusion that the doping of nitrogen can decrease the energy gap by mixing the N 2p states with O 2p states. The theoretical lattice parameters and optimum nitrogen content agree well with the experimental results.