A combined electrochemical and theoretical study of pyridine-based Schiff bases as novel corrosion inhibitors for mild steel in hydrochloric acid medium

Three pyridine-based Schiff bases namely N ²,N ⁶-bis(4-methylbenzylidene)pyridine-2,6-diamine (DAP-1), N ²,N ⁶-dibenzylidenepyridine-2,6-diamine (DAP-2) and N ²,N ⁶-bis(4-nitrobenzylidene)pyridine-2,6-diamine (DAP-3) were synthesized, characterized, and their corrosion inhibition performance was studied on mild steel (MS) in 1 M hydrochloric acid solution using electrochemical experiments and theoretical study. The results showed that all the three DAPs act as mixed type corrosion inhibitors, and are adsorbed on MS surface by following Langmuir adsorption isotherm. The methyl-substituted DAP-1 showed maximum inhibition effiency of 98.5% at 40mgL-1. The formation of inhibitor film on MS surface was confirmed by SEM and AFM. Quantum chemical calculations and Monte Carlo simulations were used to understand metal-inhibitor interaction and orientation of adsorption of DAP molecules. A good correlation was observed between theoretical and experimental results. Graphical Abstract: Synopsis Three pyridine-based Schiff bases were synthesized, characterized, and their corrosion inhibition performance was studied on mild steel in 1 M HCl solution. Results of gravimetric measurements, potentiodynamic polarization, EIS, and SEM, AFM image analyses are reported. The inhibitor molecules follow Langmuir isotherm and showed mixed-type behavior. Experimental results were supported by DFT calculations and Monte Carlo simulations. [Figure not available: see fulltext.].