A Facile and Controllable Vapor-Phase Hydrothermal Approach to Anionic S^2--doped TiO₂ Nanorod Arrays with Enhanced Photoelectrochemical and Photocatalytic Activity

Anionic S^2--doped TiO₂ nanorod arrays (S^2--TiO₂) were synthesized by a facile and controllable vapor-phase hydrothermal (VPH) approach based on the sulfur source of H₂S gas. After the VPH treatment of TiO₂ nanorod arrays (TNA), the isolated O^2- species replaces the S^2- ion in TiO₂ (TiO_2-xS_x). The structural, morphological, optical, compositional, photocatalytic and photoelectrochemical (PEC) properties of the obtained samples were investigated in detail. It was found that S^2--TiO₂ can enhance the separation rate of electron-hole pairs, improve the absorption of visible light, and augment the photocatalytic and photoelectrochemical properties. Anionic S^2- doping can significantly adjust the absorption cut-off wavelength (409.5-542.5 nm) and shorten the bandgap (3.05-2.29 eV) of TNA. For the degradation of methylene orange (MO) under mercury lamp light, the 0.24 At%S^2--TiO₂ (0.24S^2--TiO₂) sample exhibited the best photogradation efficiency of 73% in 180 min compared to bare TiO₂ (46%). The 0.24S^2--TiO₂ showed the highest photocurrent of 10.6 μA/cm², which was 1.73 times higher than that of bare TiO₂ (6.1μA/cm²). The results confirmed that the visible light absorption, photocurrent and photocatalytic activity optimization of TNA are closely related not only to anionic S^2--doped but also different ratios of anionic S^2--doped. It is noteworthy that the VPH approach is very promising for applications in low cost and highly efficient ion doping into nanomaterials for energy devices.