Efficient and Scalable Synthesis of Pure Polypyrrole Nanoparticles Applicable for Advanced Nanocomposites and Carbon Nanoparticles

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Abstract

Pure polypyrrole (PPy) nanoparticles that are well-applicable for nanocomposite and nanocarbon precursor were productively synthesized by necessarily unstirred oxidative polymerization of pyrrole in acidic aqueous media at 0 °C without any template. The species and concentration of acid and oxidant have been carefully investigated to optimize the polymerization yield, conjugated structure, size, and conductivity of the PPy particles. Laser particle-size analysis, field-emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy all revealed that the PPy particles produced in still acid media have narrow size distribution and uniform spheroid morphology. Homogeneous nucleation and static repulsion are proposed as the formation and self-stabilization mechanisms of the PPy nanoparticles. Combination of HNO3 medium and (NH4)2S2O8 oxidant is optimal for the synthesis of PPy nanoparticles possessing maximal yield of 87.2%, small diameter, and high conductivity which has been confirmed by a strong UV−vis band due to a large π-conjugated chain structure. This quiescent polymerization could be simply scaled up or down to synthesize a larger or smaller amount of PPy nanoparticles without compromising their yield, structure, and properties. Furthermore, the conductivity of the nano-PPy could reach 2.8 S/cm upon doping in 2.0 M HClO4. Simultaneous thermogravimetry−differential thermal analysis technique demonstrates that the PPy nanoparticles at 1000 °C can be efficiently carbonized into carbon nanoparticles with narrower size distribution, smaller diameter of 62 nm, and much higher conductivity of about 21 S/cm. In particular, the conductivity will dramatically be enhanced to 219 S/cm and even 370 S/cm at the carbonization and graphitization temperatures of 1300 and 2300 °C in nitrogen and argon, respectively. A conductive nano-PPy/cellulose diacetate nanocomposite film with low percolation threshold down to 0.2 wt %, good conductivity stability for at least 8 weeks, and potential bioapplicability was simply fabricated. The present synthesis requires no external templates and provides a facile and direct route to scalable synthesis of PPy exclusive nanoparticles with high yield, controllable size, strong re-dispersibility, high purity, adjustable conductivity, and high nanocarbon yield.

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