A novel coumarin-azo Schiff base for dual corrosion inhibition for steel in acidic environments and anti-SRB protection: Experimental and computational insights
Mahmoud A. Bedair
Abstract
This study presents a newly synthesized coumarin-azo Schiff base (4,4' - (((([1,1' - bi phenyl] −4,4' - diyl bis (azaneylylidene)) bis (ethan – 1 – yl – 1 - ylidene)) bis (2 – oxo - 2H – chromene - 3,6 - diyl)) bis (di azene - 2,1 - diyl)) di benzene sulfonic acid ( PEOB )) as a dual-function inhibitor for steel protection in acidic environments, combining corrosion resistance with anti-microbial activity against sulfate-reducing bacteria (SRB). The corrosion inhibition performance of PEOB was evaluated using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM), demonstrating an outstanding inhibition efficiency of 96.43 % at 7.5 × 10 −4 M in 1M HCl. The adsorption mechanism followed the Langmuir isotherm, indicating strong monolayer adsorption, further supported by thermodynamic studies confirming a chemisorption-dominated process. Surface analysis via SEM/EDS revealed the formation of a protective inhibitor film, preventing acid attack. Additionally, PEOB exhibited moderate resistance against SRB-induced microbiologically influenced corrosion (MIC), as confirmed by microbial growth inhibition assays and molecular docking simulations, which showed strong interactions with bacterial functional proteins. Computational investigations, including density functional theory (DFT), natural bond orbital (NBO) analysis, and molecular dynamics (MD) simulations, confirmed the inhibitor's strong adsorption on the steel surface through Fe–N and Fe–O interactions. Monte Carlo simulations further demonstrated the superior adsorption energy of PEOB compared to water and aggressive ions in the corrosive medium. This study introduces PEOB as a novel, high-performance corrosion and microbial inhibitor, offering dual protection for steel in aggressive environments. The combined experimental and theoretical approach provides deep mechanistic insights, paving the way for advanced, multifunctional inhibitors in industrial applications.