Anion additives in rapid breakdown anodization for nonmetal-doped TiO2 nanotube powders

Nonmetal-doped TiO2 powders consisting of one-dimensional nanotube bundles are prepared using electrolytes containing different kinds of anion additives via a one-step rapid breakdown anodization (RBA) process in a short time. The results show that although no nitrogen species are observed when nitrate is used as an additive, it acts as a catalyst to increase current density during the RBA process. However, substitutional P- or S-doped TiO2 nanotube powders with reduced band gap energy are obtained when electrolytes containing phosphate or sulfate are used. Compared with that of undoped-TiO2 nanotube powders, S-doped TiO2 nanotube powders exhibit significantly reduced band gap energy, from 3.36 eV to 2.93 eV as the concentration of sulfate ions increases. Keywords: TiO2 nanotube powders, Anion additive, Rapid breakdown anodization, Band gap energy, Doping