Facile synthesis of Ti3+ self-doped and sulfur-doped TiO2 nanotube arrays with enhanced visible-light photoelectrochemical performance

Titanium dioxide nanotube arrays (TiO2 NTAs) has shown its promising properties for use as a photoelectrode material. However, the efficiency in this regard is restricted by the wide band gap of TiO2. In this study, a facile method was employed to prepare Ti3+ self-doped and sulfur-doped (S-doped) TiO2 NTAs (H-S-TiO2 NTAs). The Ti3+ and S co-doping greatly improved the photoelectrochemical performances of TiO2 NTAs. The optimized H-S-TiO2 NTAs showed obviously red-shifted compared with the optimized TiO2 NTAs. The saturation photocurrent density and the photoelectric conversion efficiency of the optimized H-S-TiO2 NTAs reached 1.97 mA/cm2 and 1.18%, which were 3.72 and 4.92 times higher than that of the optimized TiO2 NTAs, respectively. Furthermore, the optimized H-S-TiO2 NTAs exhibited the highest transient photocurrent density (1.08 mA/cm2) with excellent photoelectric response characteristics, indicating that the transfer efficiently of photogenerated carriers was increased in the optimized H-S-TiO2 NTAs. On the basis of research results, such enhanced performances could prove that the Ti3+ self-doping and S-doping had synergistic effects. The established S-doping as well as introduced Ti3+ self-doping of TiO2 NTAs resulted in enhanced visible-light absorption and rapid electron transfer rate.