Green Corrosion Inhibitors from Plant Extracts: Computational and Electrochemical Studies on Mild Steel Protection in Acidic Media

Abstract

Corrosion of mild steel in acidic solutions is a persistent industrial challenge in petrochemical and construction sectors. This research evaluates the corrosion inhibition efficiency of Azadirachta indica (Neem) leaf extract, a locally available and eco-friendly resource, for protecting mild steel surfaces. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were performed to determine inhibition efficiency, complemented by quantum chemical calculations. Experimental results showed that inhibition efficiency increased with extract concentration, reaching 87% at 600 ppm. Adsorption followed the Langmuir isotherm, confirming monolayer formation on the steel surface. DFT-based simulations revealed strong interactions between phytochemical functional groups (–OH, –NH₂, –C=O) and Fe atoms, with calculated adsorption energies of approximately −178 kJ/mol. Frontier molecular orbital analysis showed favorable electron donation from plant molecules to steel, enhancing protective film formation. The study concludes that Neem extract is an efficient, cost-effective, and environmentally benign corrosion inhibitor suitable for Nigerian industries.