S- and N-Co-Doped TiO2-Coated Al2O3 Hollow Fiber Membrane for Photocatalytic Degradation of Gaseous Ammonia

Abstract

This study successfully prepared and tested sulfur- and nitrogen-co-doped TiO₂-coated α-Al₂O₃ (S,N-doped TiO₂/Al₂O₃) hollow fiber (HF) membranes for efficient photocatalytic degradation of gaseous ammonia (NH₃). Thiourea was used as a sulfur- and nitrogen-doping source to produce a S,N-doped TiO₂ photocatalyst powder. For comparative purposes, undoped TiO₂ powder was also synthesized. Through the application of a phase-inversion technique combined with high-temperature sintering, hollow fibers composed of α-Al₂O₃ were developed. Undoped TiO₂ and S,N-doped TiO₂ photocatalyst powders were coated on the α-Al₂O₃ HF surface to obtain undoped TiO₂/Al₂O₃ and S,N-doped TiO₂/Al₂O₃ HF membranes, respectively. All prepared samples were characterized using XRD, TEM, XPS, UV-Vis, SEM, BET, FT-IR, and EDS. S and N dopants were confirmed using XPS and UV-Vis spectra. The crystal phase of the undoped TiO₂ and S,N-doped TiO₂ photocatalysts was a pure anatase phase. A portable air purifier photocatalytic filter device was developed and tested for the first time to decrease the amount of indoor NH₃ pollution under the limits of the lachrymatory threshold. The device, which was made up of 36 S,N-doped TiO₂/Al₂O₃ HF membranes, took only 15-20 min to reduce the level of NH₃ in a test chamber from 50 ppm to around 5 ppm, confirming the remarkable performance regarding the photocatalytic degradation of gaseous NH₃.

Keywords: S,N-doped TiO2; air purification; environmental protection; gaseous ammonia (NH3) degradation; indoor air pollution; photocatalytic membrane reactor; titanium dioxide.