Interfacial Synthesis: Amphiphilic Monomers Assisted Ultrarefining of Mesoporous Manganese Oxide Nanoparticles and the Electrochemical Implications

Amphiphilic monomers, namely pyrrole and aniline, were used to reduce permanganate ion (MnO4-) at the dichloromethane/water interface for the preparation of ultrafine manganese oxide (MnOx, x <= 2) nanoparticles (NPs). These monomers did not undergo polymerization upon oxidation by MnO4-, but exerted an interesting effect of ultrarefining the produced MnOx NPs from reducing MnO4- at the organoaqueous interface. This was attributed to the ability of the monomer to access the interfacial reaction sites from both organic and aqueous phases, and hence retard the as-produced MnOx nuclei from aggregation at the interface. Such obtained products were mesoporous matrixes of three-dimensionally interconnected and uniform pseudospherical MnOx NPs (<20 nm). On the contrary, using a more hydrophobic monomer, i.e., o-aminophenol, to reduce MnO4- produced a composite of nanobelts of poly(o-aminophenol) embedded in micrometer-sized MnOx blocks. The ultrafine MnOx NPs prepared from using aniline or pyrrole exhibited highly capacitive behavior in aqueous Na2SO4, promising their use in supercapacitors. It was also found that the MnOx NPs prepared from pyrrole-assisted synthesis possessed higher specific capacitance than that from aniline-assisted synthesis, despite the latter having a higher specific surface area. This difference is discussed in terms of crystallographic properties and water contents of these two samples.