Experimental and computational investigation of Paronychia argentea extract as a novel eco-friendly corrosion inhibitor for carbon steel in 1 M HCl

Eco-friendly corrosion inhibitors derived from plant extracts have attracted considerable attention as sustainable alternatives to conventional toxic chemicals. Paronychia argentea, a perennial plant rich in bioactive phytochemicals, represents a promising natural source for corrosion inhibition. In the present work, the corrosion-inhibition performance of Paronychia argentea extract (PAE) was investigated as a novel green inhibitor for carbon steel in 1 M HCl, using combined experimental and computational approaches. The inhibition efficiency was evaluated using weight-loss measurements, potentiodynamic polarisation (PDP), electrochemical impedance spectroscopy (EIS), and surface characterisation techniques. The results showed that inhibition efficiency increased with inhibitor concentration, reaching a maximum of 84% at 560 mg.L−1 at 298 K. PAE acted as a mixed-type inhibitor and followed the Langmuir adsorption isotherm. Kinetic and thermodynamic parameters revealed a dual adsorption mechanism, involving physisorption and chemisorption, with a ΔG°ads value of −25.4 kJ.mol−1. After 100 h of immersion, PAE exhibited good stability in acidic media. Surface morphology analysis using SEM/EDS, FTIR, and AFM confirmed the formation of a protective organic film on the steel surface. Density functional theory (DFT) and Fukui function analyses supported the experimental findings by identifying the active adsorption sites and donor–acceptor interaction capability.