Interface-driven electronic synergy in delta-phase and alpha-phase manganese dioxide heterostructures for sustainable room-temperature formaldehyde oxidation.

Indoor formaldehyde (HCHO) pollution poses a serious threat to human health, driving the urgent need for highly efficient catalysts capable of oxidizing HCHO at room temperature. Manganese oxide (MnO2), owing to its earth-abundant nature, rich redox flexibility, and polymorphic structures, represent promising green catalysts. However, the intrinsic limitations of single-phase manganese dioxide hinder efficient low-temperature oxidation. Herein, delta-phase and alpha-phase manganese dioxide heterostructures (δ-MnO2/α-MnO2) are constructed through a facile and scalable one-pot redox route involving potassium permanganate and manganese (II) precursors under mild conditions. By tuning the anionic identity of the manganese (II) precursor (chloride, sulfate, or nitrate), the phase composition, surface chemistry, and catalytic behavior can be effectively modulated. Among them, the manganese chloride-derived heterostructure delivers the highest activity, achieving 93% removal and complete conversion of 200 ppm HCHO within 60 min at room temperature. Mechanistic investigations reveal that the interface-driven electronic synergy between delta-phase and alpha-phase manganese dioxide significantly enhances the generation of reactive oxygen species and facilitates the adsorption and activation of molecular oxygen, formaldehyde, and water. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) identifies key intermediates and confirms the cooperative involvement of molecular oxygen and water in the catalytic cycle. This study not only offers a green synthesis platform for efficient indoor formaldehyde abatement but also provides fundamental mechanistic insights into designing transition-metal oxide heterostructures for sustainable low-temperature oxidation reactions.