Evaluation of the Senecio scandens leaf extract as an eco-conscious corrosion inhibitor for X70 steel in HCl medium

Abstract

To address the urgent demand for eco-friendly and high-efficiency corrosion inhibitors, this study investigates the Senecio scandens leaf extract (SSE) as a green inhibitor for X70 steel in 1 M HCl. The SSE was prepared via a room-temperature ball-milling water extraction method and characterized by spectroscopic analysis, revealing the presence of bioactive constituents (e.g., polyphenols and flavonoids) with heteroatoms (O and N) and π-electrons. Electrochemical tests revealed that the SSE acts as a hybrid-type inhibitor, achieving a maximum inhibition efficiency of 93.62% at 0.8 g L⁻¹ by increasing charge transfer resistance (R_ct) and reducing double-layer capacitance (C_dl). Surface analysis manifested the generation of a protective SSE film on the metal substrate, markedly decreasing surface roughness. Isothermal adsorption studies showed that the adsorption followed the Langmuir model, with a negative Gibbs free energy (−26.65 kJ mol⁻¹), indicating a spontaneous process involving both physical and chemical adsorption. Additionally, analysis of the isotherm data indicated lateral repulsive interactions among adsorbed molecules, with each SSE molecule occupying an average of over two active sites. Theoretical calculation and simulation moreover validated the electron-donating ability of SSE's active components, confirming their strong affinity for the steel surface. This work highlights the SSE as a superior green inhibitor with advantages in environmental protection and efficiency over reported corrosion inhibitors.