Integrated experimental and theoretical analysis of Millettia pinnata (Karanja) Leaf extract as an eco-friendly inhibitor for zinc in hydrochloric acid

The newly developed, environmentally benign Karanja leaf ethanolic extract (KLE) was thoroughly evaluated as a green inhibitor for zinc corrosion in 0.05–0.1 M HCl at various temperatures. “Potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and complementing mass-loss measurements confirmed that KLE functions “as a mixed-type inhibitor, mostly through adsorption onto the zinc surface. At an ideal concentration of 2.0 g/L,” KLE achieved an inhibitory effectiveness of 98.64 %. The Freundlich and Langmuir isotherm models describe how KLE molecules interact with the zinc surface, as evidenced by adsorption studies. Gas chromatography mass spectroscopy (GC-MS) and Fourier transform infrared spectroscopy (FTIR) measurements were used to characterise the extract. When KLE was added to the corrosive solution, surface deterioration was significantly reduced, according to surface characterisation by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM). Gas chromatography mass spectroscopy (GC-MS) and Fourier transform infrared spectroscopy (FTIR) measurements were used to characterise the extract. A thorough theoretical perspective was provided by the use of density functional theory (DFT) and molecular dynamics (MD) simulations to further comprehend the inhibitory mechanism. According to comparative electronic structure studies, the molecular architecture of principal components, specifically their ability to donate and accept electrons, significantly influences their inhibitory potential. This study introduces Karanja leaf extract as a sustainable, plant-based corrosion inhibitor for zinc, achieving high efficiency through combined experimental and theoretical validation. The novelty lies in correlating electronic-structure descriptors with adsorption behaviour, thereby offering a predictive framework for eco-friendly corrosion protection.