Electrochemical, surface, and quantum chemical investigations of 5-carboxypentyl triphenylphosphonium bromide as an effective corrosion inhibitor for mild steel

Abstract

The corrosion inhibition performance of 5-Carboxypentyl Triphenylphosphonium Bromide (5-CPTPPB) for mild steel (MS) in 0.5 M H₂SO₄ solution was investigated using electrochemical, surface and computational methods. Galvanostatic polarisation and EIS show that at an optimal concentration of 10⁻² M, 5-CPTPPB exhibited an inhibition efficiency above 97%, functioning as a mixed-type inhibitor that effectively suppressed both anodic and cathodic reactions. Thermodynamic studies show that the adsorption of inhibitor on the metal surface follows the Langmuir adsorption isotherm. Surface characterization techniques, including atomic force microscopy (AFM), and scanning electron microscopy (SEM) confirmed the development of 5-CPTPPB barrier layer on the metal surface. Fukui function analysis showed that protonation enhanced the electrophilic character of key atomic sites, supporting dual donor–acceptor reactivity. Molecular dynamics (MD) simulations further validated these findings showing highly negative interaction and binding energies, confirming spontaneous and stable adsorption. Additionally, Non-Covalent Interaction (NCI) analysis highlighted mixed physisorption–chemisorption mechanism. Collectively, the integrated experimental and theoretical results establish 5-CPTPPB as a highly effective, stable, and environmentally sustainable corrosion inhibitor for MS under aggressive acidic conditions. • 5-CPTPPB controls the corrosion process of mild steel acidic solution. • Maximum inhibition efficiency above 97% was recorded at 10⁻² M, 5-CPTPPB dose. • The 5-CPTPPB acted as a mixed-type corrosion inhibitor as proven via EIS studies. • Computational insights aligned with the experimental studies.