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

Hierarchical nanoporous epsilon-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 epsilon-MnO2 could be selectively generated. After preparation of epsilon-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 epsilon-MnO2 structure but also increased the specific surface area, the catalytic performance of the formed epsilon-MnO2 in the oxidation of formaldehyde (HCHO) was enhanced. The specific surface area of nanoparticle aggregated microspheres was 168.3 m(2) 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.