Oxygen vacancies play a crucial role in modulating the chemical and catalytic properties of metal oxide catalysts. Herein, quercetin was used as a green reducing agent to prepare Cu-doped MnO2 (Cu-MnO2) composite catalysts with varying Cu doping levels via an ultrasonically assisted strategy. The structure-activity relationships were systematically investigated using XRD, Raman, XPS, H2-TPR, and O2-TPD. Benefiting from optimized surface lattice defects induced by an appropriate Cu doping level, the Cu-MnO2-2 sample, which exhibited the highest oxygen vacancy concentration, achieved a HCHO removal efficiency of 99.2% for 1 ppm HCHO at room temperature (25 °C) and 50% relative humidity within 30 min. The enrichment of Mn3+, Cu+, and surface-adsorbed oxygen species (Oads) further corroborated the increased oxygen vacancy density, indicating that moderate Cu doping effectively promotes electron transfer and oxygen activation. After five consecutive cycles, the HCHO conversion remained above 96%. Post-cycling characterizations (XRD, FTIR, EDS, and XPS) confirmed the excellent structural and chemical stability of the catalyst, with the Mn3+ proportion and Cu+/Cu2+ ratio well preserved. In situ DRIFTS analysis revealed that surface-adsorbed oxygen and oxygen-vacancy-activated reactive oxygen species (ROS) are key factors in the efficient HCHO oxidation over the green Cu-MnO2-2 catalyst, promoting rapid conversion of intermediates and ultimately generating CO2 and H2O. This study provides a facile, low-cost, and green synthesis strategy for Cu-MnO2 composite catalysts for indoor, room-temperature HCHO abatement, offering new insights into the design of other composite catalyst materials.
Tao et al. (Wed,) studied this question.