Abstract

In this study, the inhibition efficiency (IE) of symmetrical bis(imino)pyridines (BIPs) used in corrosion protection for zinc and iron was investigated in 0.5 M NaCl (pH 3 and pH 7) and an acidic (1 M HCl) medium using linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). Three derivatives, BIP-9, BIP-14 and BIP-16, exhibited the most relevant inhibition performance and acted as mixed-type corrosion inhibitors. In a neutral medium, BIP-16 exhibited the highest IE calculated from EIS, reaching 74.8% on iron and 61.2% on zinc. In 1 M HCl, the highest IE inhibition efficiency was obtained for BIP-9 on iron (93.7%), while BIP-16 and BIP-14 reached 78.8% and 75.1%, respectively. The IE increased with concentration up to an optimum value, while time- and temperature-dependent studies indicated partial loss of protection for individual inhibitor systems and improved long-term protection for the Ce(III) acetate + BIP-16 system, particularly on iron. The highest IE was observed at 25 °C, likely due to inhibitor desorption at higher temperatures. Ce(III) acetate also showed the highest IE for iron in 0.5 M NaCl at pH 3. Adsorption of inhibitors followed the Langmuir model, and calculated parameters indicated spontaneous adsorption with dominant physisorption. DFT calculations supported a medium-dependent inhibition mechanism. Environmental hazard assessment identified BIP-16 as the least hazardous compound with promising eco-friendly potential.

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