Green approach to bulk and template-free synthesis of thermally stable reduced polyaniline nanofibers for capacitor applications

Abstract

An extremely simple green approach is described that generates bulk quantities of nanofibers of the electronic polymer polyaniline in fully reduced state (leucoemeraldine form) in one step without using any reducing agent, surfactants, and/or large amounts of insoluble templates. Chemical oxidative polymerization of aniline with acetic acid instead of HCl (conventional synthesis) dramatically changes the morphology of the resulting doped polyaniline powder from nonfibrillar (particulate) to almost exclusively nanofibers of the reduced leucoemeraldine state in the diameter range 20 nm to 50 nm depending on the acetic acid concentration. These reduced leucoemeraldine polyaniline nanofibers undergo a spontaneous redox reaction with noble metal ions under mild aqueous conditions, resulting in deposition of various shapes, such as leaf, particulate, nanowires and cauliflower for Ag, Pd, Au, and Pt, respectively, on the surface of polyaniline nanofibers, affording a facile entry into this technologically important class of metal–polymer nanocomposites. These nanofibers also can act as seed templates to synthesize polyaniline nanofibers by conventional HCl doped synthesis where particulate morphology normally dominates. The ensuing polyaniline nanofibers have a broad final decomposition temperature which is at least 120 °C higher and have a very high dielectric constant ≈3500 at higher frequency when compared to reported reduced polyaniline and HCl based polyaniline.