Anti-corrosion performance of nanostructured poly(aniline-co-metanilic acid) on carbon steel

Abstract

In order to investigate the effect of a strongly hydrophilic substituent group on the anticorrosion properties of polyaniline (PANI) coatings, sulfonic acid groups (SO3H) were introduced into the polyaniline molecular structure by the copolymerization of aniline (ANI) and 3-aminobenzenesulfonic acid (metanilic acid, MA), using ammonium persulfate as an oxidant. The MA/ANI monomer ratio of the poly(aniline-co-metanilic acid) (PANIMA) products was systematically varied in the range 0–1. The PANIMA copolymers contained sulfur in the following forms: HSO4− from the external dopant (H2SO4 obtained from the reduction of the persulfate oxidant) or SO3H groups from the external MA dopant, and SO3H groups from the metanilic copolymerization unit. The influence of HSO4− or SO3H in the external dopant and SO3H in the copolymerization unit on the anticorrosive properties of PANIMA was observed. The morphologies of the different PANIMA products were characterized by SEM. At low MA/ANI ratios, PANIMA nanofibres formed whereas at near stoichiometric MA/ANI ratios PANIMA nanogranules were obtained. The chemical structure of the PANIMA products was determined by FTIR, UV–vis spectroscopy and XRD. The anti-corrosion behavior of PANIMA coated carbon steel electrodes was investigated in 1M H2SO4 solutions by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). Results show that the PANIMA coatings offer good anti-corrosion protection to carbon steel in 1M H2SO4 solutions, with the degree of protection depending on the sulfonic acid group and HSO4− dopant content in the coatings. Low sulfur content in the PANIMA coatings afforded the best protection, though the performance of all PANIMA coatings was inferior to PANI itself under the applied testing conditions.