Corrosion Inhibition of Mild Steel in Hydrochloric Acid Solution by Benzimidazole: Experimental and Theoretical Studies

This study examined the effectiveness of two newly synthesized benzimidazole derivatives as corrosion inhibitors for mild steel in 1 M HCl solution. The newly synthesized benzimidazole derivatives are 1-(Cyclohex-1-enyl)-3-((3-(4-nitrophenyl)isoxazol-5-yl)methyl)-1H-benzimidazol-2(3H)-one (as P1) and 1-(Cyclopent-1-en-1-yl)-benzimidazol-2(3H)-one (as P2). Potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied, complemented by density functional theory and Monte Carlo simulations. Results showed that both compounds act as mixed-type inhibitors, simultaneously reducing anodic and cathodic reactions. At an optimal concentration, they achieved inhibition efficiencies of more than 97%. Quantum chemical analysis revealed a change in energy gap and stronger adsorption energy, displayed greater reactivity and stability. SEM-EDX confirmed the formation of a protective layer through spontaneous adsorption, consistent with the Langmuir isotherm model. These findings highlight the potential of benzimidazole derivatives as efficient and sustainable corrosion inhibitors because they enhance material protection, improve thermodynamic stability, and reduce environmental and economic losses in industrial uses.