| Summary: | This study successfully prepared and tested sulfur- and nitrogen-co-doped TiO<sub>2</sub>-coated α-Al<sub>2</sub>O<sub>3</sub> (S,N-doped TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub>) hollow fiber (HF) membranes for efficient photocatalytic degradation of gaseous ammonia (NH<sub>3</sub>). Thiourea was used as a sulfur- and nitrogen-doping source to produce a S,N-doped TiO<sub>2</sub> photocatalyst powder. For comparative purposes, undoped TiO<sub>2</sub> powder was also synthesized. Through the application of a phase-inversion technique combined with high-temperature sintering, hollow fibers composed of α-Al<sub>2</sub>O<sub>3</sub> were developed. Undoped TiO<sub>2</sub> and S,N-doped TiO<sub>2</sub> photocatalyst powders were coated on the α-Al<sub>2</sub>O<sub>3</sub> HF surface to obtain undoped TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> and S,N-doped TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> 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 TiO<sub>2</sub> and S,N-doped TiO<sub>2</sub> 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 NH<sub>3</sub> pollution under the limits of the lachrymatory threshold. The device, which was made up of 36 S,N-doped TiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> HF membranes, took only 15–20 min to reduce the level of NH<sub>3</sub> in a test chamber from 50 ppm to around 5 ppm, confirming the remarkable performance regarding the photocatalytic degradation of gaseous NH<sub>3</sub>.
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