Enhanced Room-Temperature catalytic oxidation of formaldehyde via A novel Na-Doped MnO2/Co3O4 Catalyst: Oxygen vacancy engineering and application in Aqueous-Gas hybrid purification system

Abstract

The degradation of indoor formaldehyde (HCHO) is crucial for safeguarding human health, yet the rational design and controlled synthesis of highly efficient non-noble metal catalysts remain challenging. In particular, strategies that enhance oxygen vacancy concentration through targeted dopant modification have emerged as promising approaches to boost catalytic oxidation activity. Herein, a novel Na-doped MnO₂/Co₃O₄ ternary composite, (MnO₂/Na_0.7MnO_2.05)/Co₃O₄, was successfully synthesized via a one-step hydrothermal treatment followed by high-temperature calcination, yielding uniform spherical architectures with high specific surface area (129.59 m²·g⁻¹) and mesoporous texture. Subsequent Na incorporation effectively increased the proportion of Mn³⁺ species and oxygen vacancies, thereby enhancing the mobility of surface-adsorbed oxygen (O_ads) and lattice oxygen (O_latt), which collectively facilitated the catalytic oxidation of HCHO. The as-prepared catalyst demonstrated excellent degradation performance: at 30 °C, a 62.42 % removal efficiency of 10 mL 100 mg L^-1 aqueous HCHO was achieved within 1 h, reaching 96.39 % after 8 h. Mechanistic insights obtained from EPR spectroscopy, reactive oxygen species (ROS) detection, and density functional theory (DFT) calculations further elucidated the adsorption and degradation pathways of HCHO in solution. Notably, beyond conventional aqueous-phase studies, the catalyst was further integrated into a hybrid aqueous-gas purification system employing a commercial air-conditioning fan. Under this practical configuration, a 56.36 % degradation efficiency was achieved for 4000 mL 10 mg·L^-1 aqueous HCHO within 5 h at room temperature. This study not only demonstrates a new material design strategy by coupling alkali-metal doping with a MnO₂/Co₃O₄ binary composite, but also pioneers a hybrid degradation concept that bridges aqueous-phase and gas-phase purification. The results highlight both the structural–electronic regulation of the catalyst and its engineering feasibility, providing new insights into catalyst development and offering a promising pathway toward the practical implementation of room-temperature VOCs removal.