Effect of naturally occurring doping acids towards polyaniline properties and contaminant removal

The tuneable properties of polyaniline (PAni) make it a versatile candidate to be applied as contaminant adsorbent for wastewater treatment. In this research, naturally occurring doping acids namely acetic acid, benzoic acid, citric acid, formic acid, and tartaric acid are used to replace conventional use of hydrochloric acid (HCl) to eradicate usage of toxic and corrosive mineral doping acid in PAni synthesis. The chemical structures of all doped PAni samples were confirmed by Fourier-Transform Infrared spectroscopy (FTIR). In addition, all the PAni samples were confirmed to be in the oxidation state of emeraldine salt through Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) analysis and through conductivity measurement using four-point probe resistivity meter. It was shown that naturally occurring acids doped-PAni samples showed conductivity of 0.0199–0.1553 S/cm while PAni doped with HCl measured a conductivity of 0.1915 S/cm. Also, naturally occurring acids-doped PAni samples recorded BET surface area of 15.55–24.95 m 2 /g while that of HCl recorded BET surface area of 16.37 m 2 /g. Among all the PAni samples doped with different naturally occurring acids, PAni-Benzoic exhibited the highest nickel (Ni) removal efficiency of 19.44 % compared to 12.67 % of PAni doped with HCl due to enhanced surface area from π–π interaction between benzoic acid and PAni chain.