Synergistic effect of photo-thermal oxidation for a low concentration of HCHO over Bi3+-TiO2/MnFeOx catalysts at ambient temperature.

Formaldehyde (HCHO) has been one of the important air pollutants, and the effective removal of HCHO at ambient temperature has been a big challenge. In this work, the synergistic effect of photo-thermal oxidation with Bi3+-TiO2/MnFeOx for a low concentration of HCHO was investigated. MnFeOx was synthesized by the complexation method (CM) and co-precipitation (CP), and TiO2 with Bi3+ doping supported on MnFeOx was prepared by using the hydrothermal method to obtain a higher oxidation performance. The results demonstrated an excellent oxidation activity of MnFeOx (CM) for HCHO at ambient temperature, attributed to the morphology effect (large surface areas and small crystal sizes), the large absorption of oxygen, and the interaction and oxygen vacancy formed between MnO2 and FeOx. Although Bi3+-TiO2/MnFeOx showed a similar result as MnFeOx at 48 h, the oxidation activities for HCHO were improved prominently under photo-thermal oxidation at 12 h. The improvement was ascribed to the synergistic effect of Bi3+-TiO2 and MnFeOx with surface adsorbed oxygen, and more generated reactive oxygen species on the surface. In particular, 2 wt% Bi3+-TiO2/MnFeOx displayed the highest activity (90.2%) and good stability (5 cycles), and the HCHO average conversion was increased from 46.2 to 58.2% at 12 h. The feasible oxidation mechanism and reaction pathway were also interpreted. This work provides a new insight for the development of photocatalysts supported on transition metal oxides to oxidize HCHO at ambient temperature.