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/MnFeO_x for a low concentration of HCHO was investigated. MnFeO_x was synthesized by the complexation method (CM) and co-precipitation (CP), and TiO₂ with Bi³⁺ doping supported on MnFeO_x was prepared by using the hydrothermal method to obtain a higher oxidation performance. The results demonstrated an excellent oxidation activity of MnFeO_x (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 FeO_x. Although Bi³⁺-TiO₂/MnFeO_x showed a similar result as MnFeO_x 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 MnFeO_x with surface adsorbed oxygen, and more generated reactive oxygen species on the surface. In particular, 2 wt% Bi³⁺-TiO₂/MnFeO_x 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. [ABSTRACT FROM AUTHOR]