Studies of conducting polyaniline (PANI) wrapped-multiwalled carbon nanotubes (MWCNTs) nanocomposite and its application for optical pH sensing

Highly transparent and water soluble nanocomposite of conducting polyaniline wrapped-multiwalled carbon nanotubes (PANI-MWCNTs) was synthesized by in situ chemical polymerization method using sulphonic acid as a dopant. MWCNTs were functionalized prior to their use and then polymerized using ammonium per sulphate as an oxidizing agent. The nanocomposite was subjected for physico-chemical characterization using spectroscopic (UV–vis and FT-IR), FE-SEM and HR-TEM analysis. The UV–vis spectrum of the salt phase (dark green) of the PANI-MWCNTs nanocomposite shows a free carrier tail with increasing absorption at higher wavelength, which confirms the presence of conducting emeraldine salt phase of the polyaniline and is further supported by FT-IR analysis. However, the base form (deep blue) of the nanocomposite shows a sharp peak at 600 nm representing an insulating emeraldine base phase of the polymer. The FE-SEM images show the uniform wrapping/coating of the polyaniline over the functionalized MWCNTs and this is further supported by HR-TEM analysis. The synthesized nanocomposite was then successfully used for the determination of pH of the solution (pH 1–12) and found to be a potential candidate for optical pH sensing.