Bandgap reduction of photocatalytic TiO nanotube by Cu doping.

We performed the electronic structure calculations of Cu-doped TiO nanotubes by using density functional theory aided by the Hubbard correction (DFT + U). Relative positions of the sub-bands due to the dopants in the band diagram are examined to see if they are properly located within the redox interval. The doping is found to tune the material to be a possible candidate for the photocatalyst by making the bandgap accommodated within the visible and infrared range of the solar spectrum. Among several possibilities of the dopant positions, we found that only the case with the dopant located at the center of nanotube seems preventing from electron-hole recombinations to achieve desired photocatalytic activity with n-type behavior.