Synergistic effect of photo-thermal oxidation for a low concentration of HCHO over Bi-TiO/MnFeO 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 Bi-TiO/MnFeO for a low concentration of HCHO was investigated. MnFeO was synthesized by the complexation method (CM) and co-precipitation (CP), and TiO with Bi doping supported on MnFeO was prepared by using the hydrothermal method to obtain a higher oxidation performance. The results demonstrated an excellent oxidation activity of MnFeO (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 MnO and FeO. Although Bi-TiO/MnFeO showed a similar result as MnFeO 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 Bi-TiO and MnFeO with surface adsorbed oxygen, and more generated reactive oxygen species on the surface. In particular, 2 wt% Bi-TiO/MnFeO 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.