Mn-Modified MIL-100(Fe)-Derived FeOx to Boost Toluene Photothermal Catalytic Degradation

Abstract

The development of highly efficient catalysts is important for the photothermal catalytic oxidation of volatile organic compounds (VOCs). Herein, MIL-100(Fe) was used as the sacrificial template to prepare MnFeOx catalysts with different Mn contents through the impregnation–calcination method, and their performance in photothermal catalytic oxidation of toluene was investigated. The results show that the content of Mn significantly affects the crystal phase structure, pore properties, surface chemical state, and optical response of the catalyst. Among them, 30%MnFeOx exhibits the best photothermal catalytic activity, with T50 and T90 being 211 and 237 °C, respectively, which are significantly lower than those of FeOx (232 and 260 °C). Characterization results suggested that the introduction of Mn caused the bandgap of FeOx to decrease from 1.96 to 1.67 eV. Meanwhile, the surface Fe2+, adsorbed oxygen (Oads) species, and oxygen vacancies were increased, enhancing visible light absorption and gaseous oxygen species adsorption and activation, which promoted the photothermal catalytic oxidation of toluene. Additionally, the 30%MnFeOx catalyst presented good thermal stability and water resistance. Furthermore, during the reaction process, the in situ activation of the catalyst’s surface induced the increase in surface Fe2+, Mn3+, and Oads species, which enhances the photothermal catalytic activity of the catalyst. Importantly, the in situ DRIFTS results further indicate that toluene is mainly oxidized along the path of toluene → benzyl alcohol → benzoate → maleic anhydride → CO2 and H2O. This work provides a theoretical basis for the construction of low-cost, non-precious-metal Mn–Fe-based photothermal catalysts.