Synthesis of N and S Co-doped TiO₂ Nanotubes for Advanced Photocatalytic Degradation of Volatile Organic Compounds (VOCs) in Gas Phase

In this study, sol–gel combining with hydrothermal methods were successfully used to synthesize N and S co-doped TiO₂ nanotubes (N@S-TiO₂ NTT) for efficient photocatalytic degradation of volatile organic compounds (VOCs). The obtained characterization results indicated that the synthesized N@S co-doped TiO₂ existed as nanotubes. Specific surface areas of these synthesized nanotubes was greatly that of these nanoparticles. The largest surface area recorded at N@S-TiO₂ nanotubes was 105.3 m³/g. FTIR spectrum results showed that the presence of N–H and S–O bond, which confirmed that nitrogen and sulfur were successfully doped into TiO₂ lattice. We also investigated that N@S dopants significantly improved the photocatalytic activity of TiO₂ nanotubes for efficient degradation of gaseous VOCs. Therefore, photocatalytic activity for VOCs degradation by the N@S-TiO₂ nanotubes was greater than that by the undoped TiO₂ nanotube. Optimized humidity for degradation of VOCs was medium condition (55–70%). Under dry conditions, lack of water for hydroxyl radical production led to decrease in photocatalytic activity. Under humidity conditions, the excess water molecules competed with VOCs for adsorbing on material surface leading to decrease in photocatalytic degradation efficiency. Under the optimized humidity, the highest photocatalytic efficiency of the synthesized N@S-TiO₂ nanotubes for degradation of gaseous VOCs for 3 h was approximately 94%. The VOCs degradation capacity by the synthesized N@S-TiO₂ nanotubes was approximately 90 (ppm/g h).