Synergistic effect of xSi-TiO2 ceramic membrane on photocatalytic oxidation and water vapor recovery of high humidity NO

Photocatalytic membranes were prepared by hydrothermal method using in situ growth of silica-doped titanium dioxide nanorods with different molar ratios on the surface of hollow ceramic membranes. The removal of nitrogen oxides from high humidity flue gas at ppm level and the recovery of flue gas water vapor were investigated for the first time. The optimized 0.2Si-TiO2 photocatalytic membrane achieved complete conversion of 50 ppm NO carrying saturated water vapor in only 11 min under UV light source irradiation, and the generation of toxic intermediate product NO2 was significantly reduced to 4.2 ppm. Further studies have shown that the presence of water vapor can facilitate the conversion of the toxic intermediate NO2 to nitrate. Moreover, the water vapor recovery flux was 4.18 kg·m−2·h−1, and the water vapor recovery efficiency reached 7.04%. The main water vapor recovery method was membrane condensation. Mechanistic analysis showed that hydroxyl radicals and superoxide radicals are the main components of photocatalytic oxidation, and this work provides a reference for enhancing the photocatalytic conversion of NO and suppressing the emission of toxic intermediates NO2 in the process.