Experimental Investigation and DFT-Based Modeling of a Novel Schiff Base Derivative as a Corrosion Inhibitor for Mild Steel in Acidic Medium

Corrosion of mild steel in acidic environments remains a practical concern, motivating the evaluation of organic compounds that may reduce metal dissolution. This study investigated the corrosion-inhibition behaviour of a halogenated Schiff base derivative, (E)-N-(2,4-dichlorobenzylidene)-4-(2,2,2-trifluoroethoxy)aniline (PSB), synthesised through bovine serum albumin-catalysed condensation in an aqueous medium. The synthesised compound was characterised by proton and carbon-13 nuclear magnetic resonance spectroscopy. Its performance as an inhibitor for mild steel in 1 M hydrochloric acid was assessed at 303 K by Tafel polarisation and electrochemical impedance spectroscopy (EIS). The polarisation results showed a decrease in corrosion current density with increasing inhibitor concentration. EIS measurements indicated an increase in polarisation resistance from 9 Ω cm² in the uninhibited solution to 65 Ω cm² at 20 ppm PSB, accompanied by a decrease in double-layer capacitance from 23.5 to 9.5 μF cm⁻². The maximum EIS inhibition efficiency reported was 86.2% at 20 ppm. Density functional theory calculations were also used to examine the electronic descriptors of PSB. The reported HOMO and LUMO energies were −6.183 and −2.327 eV, respectively, with a reported energy gap of 3.856 eV. The electrochemical trends and calculated molecular descriptors are consistent with adsorption-associated inhibition at the mild steel–acid interface. These findings indicate corrosion-inhibition potential for PSB under the specific laboratory conditions investigated.