Synthesis and Characterization of Polypyrrole– Magnetite–Silica Particles

Abstract

The synthesis of colloidal polypyrrole–magnetite-silica nanocomposites is described. First, silica-coated magnetite particles were prepared by the aqueous deposition of silica onto ultrafine (5–20 nm) magnetite particles via controlled hydrolysis of sodium silicate. Then pyrrole was chemically polymerized using (NH4)2S2O8, H2O2/Fe3+/HCl, or FeCl3oxidants in the presence of these silica-coated magnetite particles to yield colloidal dispersions of polypyrrole–magnetite–silica particles. The magnetite contents of these materials were as high as 17.5% by mass. Vibrating sample magnetometry measurements confirmed that these nanocomposites were superparamagnetic, with bulk saturation magnetization values of up to 10.9 emu g−1. Disc centrifuge photosedimentometry was used to assess particle size and degree of dispersion, yielding weight-average particle diameters in the range 100–520 nm. Electron microscopy studies indicated a rather ill-defined particle morphology but provided some evidence for the magnetite component within the nanocomposites. Stable colloidal dispersions were obtained using the H2O2/Fe3+/HCl and (NH4)2S2O8, oxidants, whereas FeCl3-based syntheses yielded only flocculated particles or macroscopic precipitates under similar conditions. Solid-state electrical conductivities of nanocomposites synthesized using (NH4)2S2O8, H2O2/Fe3+/HCl, and FeCl3were about 10−3, 10−2, and 10−1S cm−1, respectively.