Structural and electronic impacts on corrosion inhibition activity of novel heterocyclic carboxamides derivatives on mild steel in 1 M HCl environment: Experimental and theoretical approaches

Abstract

To study the corrosion mitigation on mild steel (MS) in 1 M HCl, the carboxamide derivatives namely: N–(1–benzyl piperidin–4–yl)pyridine–4–carboxamide (N–BPPC), N–(4–(pyridin–4–ylmethyl) phenyl)pyridine–4–carboxamide (N–PMPPC), (4–methylpiperazin–1–yl)pyrazin–2–yl) methanone (4–MPPM) were synthesized and characterized by spectroscopy techniques like FT-IR, LC-MS, and 1H &13C NMR. Experimental techniques like the weight-loss method, potentiodynamic, electrochemical impedance studies, and surface analysis were performed at 303 K. Their anti-corrosion efficiency was proportional to their concentration. Electrochemical techniques revealed that they acted as mixed-type inhibitors and proceeded via single charge transfer at the metal–electrolyte interface. Strong adsorption of carboxamide derivatives on mild steel (MS) was supported by surface morphology studies and obeyed the Langmuir model of the isotherm. The thermodynamic and activation parameters were measured to study the temperature effect, revealing that physicochemical adsorption took place. Anti-corrosion efficiencies were decreased with temperature rise. DFT and molecular dynamics studies have been utilized in their neutral and protonated form of inhibitors in the aqueous phase to study inhibitors’ structural and electronic impacts on the corrosion process. The optimized structure and spatial configuration exposed the influence of the molecule's alignment with the metal plane on corrosion mitigation. The molecules' bulk and local reactivity parameters show that the electron density of atoms of molecules coordinates with the metal surface. Finally, the order of corrosion retardation effect was found to be 4–MPPM > N–BPPC > N–PMPPC from experimental and theoretical studies.