Comparative experimental and quantum chemical investigation of para anisidine and para chloroaniline formaldehyde copolymers as corrosion inhibitors

This study investigates the application of para-anisidine formaldehyde (pAF) and para-chloroaniline formaldehyde (pCF) copolymers as effective corrosion inhibitors with potential environmental advantages for mild steel in 0.5 N HCl solution. These copolymers exhibited high inhibition performance at low concentrations and showed low volatility, indicating potential environmental compatibility. Gravimetric analysis revealed high inhibition efficiencies of 97.1% for pAF and 95.2% for pCF at an optimal concentration of 12 ppm. Electrochemical impedance spectroscopy (EIS) results showed a significant increase in charge transfer resistance (R ct ) values from 54.3 Ω cm 2 for the blank solution to 173.8 Ω cm 2 for pAF and 149.5 Ω cm 2 for pCF, indicating effective surface protection. Potentiodynamic polarization studies confirmed that both inhibitors act as mixed-type, reducing both anodic and cathodic reactions, with corrosion current density (i corr ) values decreasing from 154 µA cm −2 for the blank to 4.5 µA cm −2 for pAF and 7.3 µA cm −2 for pCF. Adsorption behavior was consistent with the Langmuir adsorption isotherm, indicating the formation of a protective adsorbed layer on the mild steel surface. Density Functional Theory (DFT) calculations were performed to investigate the electronic properties and adsorption mechanism of the copolymers. The results suggested that the higher electron density around the oxygen atoms in pAF and pCF facilitated stronger interactions with the mild steel surface. Surface characterization and DFT calculations supported the proposed corrosion inhibition mechanism. Overall, both copolymers demonstrated effective corrosion inhibition in acidic media, with pAF exhibiting a higher inhibition efficiency (97.1%) than pCF (95.2%) under the investigated conditions.