Effects of solvent and doping acid on the morphology of polyaniline prepared with the ice-templating method

Various morphologies of polyaniline (PANI), such as microflakes stacked by 1D nanofiberes, porous microwebs, hemispheres, and nests piled by nanoparticles, were prepared through an ice-templating method, using different doping acids assisted by secondary solvent. The structure and morphology of these PANI were characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) patterns, and scanning electron microscope images (SEM). Although the ice-templating method has been used for preparing conducting polymer materials with unique structures in recent years, to the best our knowledge, this is the first report on synthesizing PANI doped with polyoxometalates (POMs) using the ice-templating method assisted by secondary solvent to direct the polymerization of aniline. In this paper, the effects of doping acid and the secondary solvent on the morphology of PANI were investigated in detail. All the results showed that just the doping acids, POMs with unique nucleophilic oxygen-enriched surfaces, multi-hydrogen proton, and the binding capacity with the secondary solvent play a major role in determining the formation of various morphologies of PANI. A possible mechanism for the formation of the different morphologies of PANI was proposed. The gas-responses to ammonia were examined at room temperature. Compared with PANI porous microwebs, hemispheres, or nests piled by nanoparticles, the PANI microflakes stacked by nanofibers showed the best performance in both sensitivity and time response due to their small nanofiber diameter, high surface area, and porous nature, which will have potential application in the area of chemical sensors.