Polyaniline nanotubes: Facile synthesis, electrochemical, quantum chemical characteristics and corrosion inhibition efficiency

• Nano-tubular structure of polyaniline, with inner diameter of 20–30 nm and outer diameter of 80–Q1 100 nm, were prepared.
• The quantum chemical calculations suggesting higher adsorption on the metal surface and thus higher inhibition efficiency.
• The potentiodynamic polarization curves indicated that PANI and self-doped PANI behaved as mixed type inhibitors.
• The decrease in charge transfer resistance, increase in double layer capacitance were significant in self-doped PANI.
• The inhibition efficiency results were in a high agreement with the calculated chemical quantum parameters.

This work represents the preparation of polyaniline in its free and self-doped forms. The polymers were formed as nanotubes using template free self-curling preparation. Chemical oxidation polymerization of aniline and 4-aminobenzene sulphonic acid individually as monomers was carried out without adding acids or templates. The electron microscope image of the polymer reveals the nano-tubular structure with inner diameter of 20–30 nm and outer diameter of 80–100 nm. Quantum chemical calculations of the repeating units were calculated to correlate the chemical structure to the mechanism of inhibition. The corrosion inhibition behavior of the polymers in 1 M HCl has been evaluated using Tafel’s extrapolation method and electrochemical impedance spectroscopy (EIS). Self-doped polyaniline showed the greater inhibition efficiency compared with un-doped polyaniline. Results of electrochemical impedance and Tafel’s polarization measurements consistently showed that both compounds can be effectively used as corrosion inhibitors.

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