Treating NO_x gas Pollution by Visible Light Photocatalytic Reaction of S-doped TiO₂ Nanotubes

The TiO₂ nanomaterial is a traditional photocatalyst that was applied externally in environmental and energy fields. However, a large band gap of TiO₂ is a limitation of this material in applications in visible-light regions. Sulfur (S) doped TiO₂ nanotubes were synthesized with different weight ratios of the S precursor and TiO₂ nanotubes by a thermal diffusion process. Techniques including Fourier transform infrared (FTIR), UV-vis diffuse reflection spectroscopy (DRS), photoluminescence spectroscopy (PL), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) were used to confirm the successful doping of the S-TiO₂ nanotubes. The treatment of nitrogen oxide (NO_x) gas through photocatalysis using S-doped TiO₂ nanotubes represents an innovative and environmentally friendly approach. Sulfur doping narrows the band gap of TiO₂ nanotubes (from 3.22 to 3.14 eV), allowing for better absorption of visible light. Furthermore, the photocatalytic NO_x removal performance of S-TiO₂ nanotubes was significantly enhanced with more than 40% NO at 500 ppb, and the efficiency of NO emission decreased significantly after five cycling tests.