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. Themethyl-substitutedDAP-1 showed maximum inhibition effiency of 98.5% at 40 mgL(-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.