Decoding the corrosion inhibition mechanism of a new cinnamaldehyde derivative for mild steel in HCl medium by ToF-SIMS and AIMD

A green corrosion inhibitor, (2 E , 4 E )-2-cyano-5-phenyl-2,4-pentadienoic acid (CPPA), was synthesized via one-step modification of cinnamaldehyde. CPPA exhibits outstanding inhibition effect for mild steel (MS) in HCl medium with an inhibition efficiency of 98.83 % at a concentration of 0.6 mM with good inhibition stability. The inhibition mechanism of CPPA was elucidated by combining surface characterization techniques with ab initio molecular dynamics (AIMD) simulations. XPS and ToF-SIMS analyses indicate that CPPA molecules could adsorb on MS surface by covalent bonding through N, C, and O atoms. AIMD simulations reveal that CPPA approaches to steel surface motivated by van der Waals force, i.e., physisorption occurs. Subsequently, the physisorption of CPPA is transformed into a strong and stable chemisorption, which was demonstrated by IGMH, CPPA-Fe bond length, electron density difference and PDOS characteristics. The adsorbed CPPA film significantly improves the hydrophobicity of MS surface, and acts as a shield to effectively hinder the diffusion and access of corrosive particles to steel surface, thus exhibiting outstanding and stable corrosion inhibition performance.