Photocatalytic oxidation of formaldehyde (HCHO) is considered as one of the promising ways to resolve indoor air HCHO pollution. TiO2 has been well known as the most extended application in photocatalysis due to its strong oxidizing ability and stability. Owing to high activity under visible light irradiation, TiO2 and Bi2O3 doping mixed with Bi2WO6 was analyzed in this study. The formation of two kinds of heterojunction caused efficient charge separation, leading to the effective reduction in the recombination of photo-generated electron and hole. The special structure and enhanced performance of these catalysts were analyzed. For the first time, the loading of alkali salts was researched for photocatalytic oxidation. In order to understand the reaction mechanism of alkali salts enhanced effects, the catalysts were investigated by using BET, XRD, UV-Vis, FT-IR, SEM, and XPS. The results found more than 2 wt% of Na2SO4 loading and the mixed methods with different solutions were key factors affecting the performance of catalysts. Nearly 92% HCHO conversion could be completed over Bi2WO6/Bi0.15Ti0.85O2 (Na2SO4), and the concentration of HCHO was only 0.07 mg/m3 for 24 h, which was below the limit of specification in China. The results also indicated that the solution mixing method was more favorable to increase the HCHO conversion due to decrease the size of Bi0.15Ti0.85O2 particles. The catalysts with Na2SO4 loading provided more surface-adsorbed oxygen that facilitated the desorption of CO2 and markedly increased the photocatalytic oxidation of HCHO. Graphical abstract Plausible mechanism over W-Bi2WO6/ Bi0.15Ti0.85O2-Na2SO4 (1:4) catalysts.
Keywords: Air pollution; Alkali-modification; Catalysts; HCHO; Photocatalytic oxidation; Visible light.