Preparation And Environmental Application Of Hierarchically Porous MnO₂Nano-materials

As the fast growing of the global economy and increasing living standard ofpeople, environmental pollution has become one of the important issues confrontedwith the world nowadays. Generally speaking, environmental pollution consists ofwater pollution, air pollution and soil pollution. As an important part of waterpollution, dye manufacturing waste water has great harm to human body. At the sametime, the formaldehyde in indoor air pollutant is the most worst among air pollution.The efficient application of the functional oxides to treat the dyes in the wastewaterand noble metal loaded functional oxide material for formaldehyde oxidation at roomtemperature in order to imporove air quality have become a hot research coveringmaterials science, chemistry and environmental science. At the same time, it also hasthe extremely important research significance. In this paper, valuable explorationshave been carried out on the synthesis, characterization, and adsorption capability ofmanganese dioxide nano-materials. The main points could be summarized as follows:(1) Hierarchically porous manganese dioxide (MnO2) microspheres werefabricated by a facile hydrothermal method using potassium permanganate as theprecursor at different hydrothermal temperatures. The as-prepared samples werecharacterized by X-ray diffraction (XRD), field-emission scanning electronmicroscopy (FE-SEM), transmission electron microscopy (TEM), nitrogenadsorption–desorption isotherms and Fourier transform infrared (FTIR) spectroscopy.Adsorption of methyl blue (MB) onto the as-prepared samples from aqueous solutionswas investigated and discussed. In addition, adsorption data were fitted using thepseudo-second-order kinetics equation. The as-prepared hierarchically porous MnO2microspheres turned out to be an effective adsorbent for the removal of MB fromeffluent because of their unique hierarchical porous microstructure and high specificsurface areas. Our results shall form a solid basis for developing cost-affordable,environmentally friendly, easily available and high-performance adsorbents for watertreatment.(2) Hierarchical MnO2nanotubes and nanosheets were prepared by ahydrothermal method using potassium permanganate as the the source of manganeseelement. Pt nanoparticles were then deposited on the as-prepared MnO2microsphereswith different morphologies as backbones via a combined NaOH-assistedimpregnation of MnO2with Pt precursor and NaBH4-reduction process, in order to study noble metal loaded catalysts for formaldehyde oxidation at room temperature.Our results indicate MnO2nanotubes for formaldehyde oxidation was superior toMnO2nanosheets under the same platinum load and experimental conditions. As forMnO2nanotubes, the best mass fraction content of Pt was identified as1%. Moreover,the formaldehyde removal efficiency can reach98%even after5recyclingexperiments.