Controllable synthesis of hierarchical nanoporous ε-MnO2 crystals for the highly effective oxidation removal of formaldehyde

Abstract

Hierarchical nanoporous ε-MnO₂ crystals were prepared through thermal decomposition of hydrothermally-synthesized MnCO₃ precursors without any external templates or surfactants. Through reactant altering, cubes, nano-block aggregated microspheres and nanoparticle aggregated microspheres of ε-MnO₂ could be selectively generated. After preparation of ε-MnO₂, the filtrate containing triethylene glycol (TEG) and ethylene diamine (EDA) could be reused to synthesize the MnCO₃ precursor. Since the thermal decomposition of the MnCO₃ precursor not only led to formation of a hierarchical ε-MnO₂ structure but also increased the specific surface area, the catalytic performance of the formed ε-MnO₂ in the oxidation of formaldehyde (HCHO) was enhanced. The specific surface area of nanoparticle aggregated microspheres was 168.3 m² g⁻¹ in which HCHO conversion could remain above 96% over 72 h with 160 ppm HCHO and 84 000 mL g⁻¹ h⁻¹ of gas hourly space velocity.