Chemical synthesis of hollow sea urchin like nanostructured polypyrrole particles through a core-shell redox mechanism using a MnO_2 powder as oxidizing agent and sacrificial nanostructured template

摘要

Hollow sea urchin shaped nanostructured polypyrrole powder was successfully synthesized chemically in an acidic medium through a core-shell redox mechanism by using a nanostructured MnO_2 powder as oxidizing agent and sacrificial template simultaneously. The morphology and the structure of MnO_2 powder based reactant and produced polypyrrole powder were characterized respectively by using FEG-SEM, TEM, EDX and XRD techniques, which led us to demonstrate clearly the formation of hollow and open microparticles of polypyrrole with the presence of nanotubes on their surface. Nanostructured polypyrrole powder was found to be rather amorphous even though the shape of the polypyrrole particles was induced by the crystalline and nanostructured sea urchin shaped MnO_2 powder on which they grew. In addition, neither MnO_2 nor any manganese based species were found within the produced polypyrrole powder, which ruled out the production of composite materials. Moreover, Raman technique showed that the synthesized PPy powder was produced in the oxidized and thus conducting state. It actually possesses a 0.31 doping level and a 0.05 S cm~(-1) conductivity, as shown by XPS and impedance spectroscopy measurements respectively. Cyclic voltammetry and UV-vis spectroscopy studies allowed us to identify the oxidation mechanism of pyrrole by our MnO_2 powder through the detection of soluble Mn~(2+) cations as reaction products isolated after filtration of the reaction medium.