ABSTRACT The structural parameters, band structures and density of states of anatase TiO2 co-doped with Cu and S were calculated by first-principles based on the density functional theory. The results indicate that the volumes of the co-doped TiO2 increase due to the lattice distortion. The calculated X-ray diffraction pattern shows that the crystal phase of TiO2 is still kept as anatase after Cu and S co-doping. The band gap of TiO2 broadened when S substitutes for Ti or O along with Cu substitutes for Ti. The calculated partial density of states shows that the impurity energy levels mainly come from the Cu 3d and S 3p orbital. The calculated results may provide some theoretical foundations for the photocatalytic activity enhancement of TiO2 co-doped with Cu and S.

ABSTRACT Band structures, density of states, and absorption spectra of pure, Nd doped, C doped, and Nd-C codoped TiO2 are calculated using first-principles based on density functional theory. Calculation results show that Nd 4f state forms empty impurity energy levels below conduction band, and C 2p state together with Nd 2f state forms occupied impurity energy levels with higher density than that of single doped TiO2 above valence band. Consequently, more electrons in occupied energy levels can be excited by visible light to empty Nd 4f states rather than Ti 3d states, resulting in further enhancement of visible light absorption and absorption edge red shift. In addition, the impurity energy levels act as carriers trap centers, thus decreasing the recombination rate of carriers.