(E)-2-styryl-1H-benzo[d]imidazole as novel green corrosion inhibitor for carbon steel: Experimental and computational approach

A new green corrosion inhibitor (E)-2-styryl-1H-benzo[d]imidazole (STBim) was synthesized in a facile single step reaction from cinnamaldehyde and o-phenylenediamine. The STBim molecule showed a high LD₅₀ value of 2000 mg/kg and satisfactorily fulfilled several green chemistry metrics indicating its environmentally benign nature. STBim was, for the first time, evaluated as an inhibitor for corrosion of carbon steel in 15% HCl. The STBim produced a remarkable efficiency of 98% at optimum dosage of 200 mgL⁻¹. The adsorption of STBim followed the Langmuir isotherm, with the efficiency increasing with a rise in the inhibitor dose. Impedance measurements supported a betterment in the capacitive behavior with the corrosion inhibitor. The inhibitor exhibited a mixed type behavior as visualized from the potentiodynamic polarization (PDP) studies, with a cathodic predominance. A detailed computational study via density functional theory (DFT) simulations revealed that the inhibitor adsorbed on the carbon steel mainly in the protonated form. Calculations of the work function indicate that the protonated form resulted in a shift of 3.46 eV of the workfunction of steel. This shift in the work function presumably is due to the stabilization of the valence band of the metal surface.