Ultrathin MnO2-Coated FeOOH Catalyst for Indoor Formaldehyde Oxidation at Ambient Temperature: New Insight into Surface Reactive Oxygen Species and In-Field Testing in an Air Cleaner

Herein, we tailored a series of ultrathin MnO2 nanolayers coated on the surface of commercial goethite (alpha-FeOOH) by a facile in situ chemical precipitation method. alpha-FeOOH inhibited the MnO2 crystal growth via the incorporation of K+ ions between MnO2 and alpha FeOOH interfaces during the synthesis process. The hybrid design of MnO2 with an ultrathin nanolayer structure could reduce the electron transfer resistance and bring abundant oxygen vacancies, accelerating the activation of molecular O2 to generate more oxygen-free radical species and favoring the thermodynamic HCHO oxidation. The ROS quenching in gas/aqueous systems and DRIFTS results demonstrated that center dot O2- was responsible for HCHO oxidization, which assisted the preliminary intermediate dioxymethylene dehydrogenation into formate species. The 25%MnO2@FeOOH(25wt% of MnO2) catalyst was subsequently loaded into the filter substrates of a commercial air cleaner and tested in an indoor room with actual application conditions. As a result, the composite filter could eliminate different initial concentrations of HCHO (150-450 ppb) to the WHO guideline value (approximate to 81 ppb) within 60 min. Furthermore, the 25%MnO2@FeOOH sample was also effective against the representative bacteria and mold in indoor air. This study provides new insight into the role of the chemisorbed ROS for HCHO oxidation at ambient temperature.

Automated summary

In this study, ultrathin MnO2 nanolayers were coated on the surface of commercial goethite using a simple chemical precipitation method. This hybrid design enhanced the HCHO oxidation reaction and effectively removed HCHO and bacteria from indoor air.