Unique mesoporous amorphous manganese iron oxide with excellent catalytic performance for benzene abatement under UV-vis-IR and IR irradiation

Abstract

A unique mesoporous amorphous manganese iron oxide (Mn_xFeO_y-70) was synthesized by the redox reaction between iron(II) acetate and KMnO₄ at 70 °C. By increasing the reaction temperature to 180 °C, a crystalline nanocomposite of manganite (MnOOH) nanorods and hematite (Fe₂O₃) nanoparticles (MnO_x–Fe₂O₃-180) was obtained. Interestingly, Mn_xFeO_y-70 exhibits excellent catalytic activity for the catalytic abatement of benzene (a typical refractory pollutant). Its catalytic activity is much higher than that of MnO_x–Fe₂O₃-180 and is even superior to that of 0.5 wt% Pt/Al₂O₃ and 0.5 wt% Pd/Al₂O₃ (commercial noble metal catalysts). It is found that the lattice oxygen of amorphous manganese iron oxide plays a pivotal role in the catalytic benzene abatement due to its participation in the reaction. The much higher catalytic activity of Mn_xFeO_y-70 than that of MnO_x–Fe₂O₃-180 is ascribed to its lattice oxygen activity being higher than that of the crystalline MnOOH in MnO_x–Fe₂O₃-180. Remarkably, Mn_xFeO_y-70 has excellent photothermocatalytic activity and durability with UV-vis-IR irradiation. It also has outstanding photothermocatalytic activity with λ >420 nm vis-IR and λ >830 nm IR irradiation. The excellent photothermocatalytic activity of Mn_xFeO_y-70 is attributed to its very effective light-driven thermocatalytic activity, which is markedly enhanced by a new photoactivation: the UV-vis-IR irradiation obviously enhances the lattice oxygen activity of Mn_xFeO_y-70, thus markedly facilitating the catalytic activity. Its excellent photothermocatalytic durability is attributed to its stable structure of amorphous manganese iron oxide that remains unaltered during long-term photothermocatalytic tests.