ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Green synergistic corrosion inhibition of carbon steel in 1 m HCl using Euphorbia milii and Euphorbia officinarum: electrochemical and computational insights

Wissal Kotmani, Youssef El-Gheryby, Issam Forsal, Abdelali Grich, Anas Elharami, Sara Lahmady, Sofia Kerouad, and Mohammed Ellaite

Laboratory of Engineering and Applied Technologies, School of Technology, Beni Mellal, Morocco

E-mail: wissal.kotmani@usms.ac.ma

Received: 5 December 2025  Accepted: 11 March 2026

Abstract:

This work reports a novel synergistic approach using two plant extracts, Euphorbia milii (EM) and Euphorbia officinarum (EO), as sustainable corrosion inhibitors for carbon steel in 1 M HCl. Their abundance, low cost, and biodegradability make them promising ecological alternatives to toxic inhibitors. Unlike conventional single-extract systems, their combination exhibits enhanced inhibition efficiency at a remarkably lower concentration. Electrochemical techniques (OCP, EIS and PDP), supported by FTIR and SEM/EDX analyses, were used to evaluate the inhibition performance. Both extracts act as mixed-type inhibitors, suppressing anodic and cathodic reactions. While EM and EO individually achieved inhibition efficiencies of 94% and 93% at 2 g L⁻¹, their mixture reached 95% efficiency at only 0.5 g L⁻¹, demonstrating superior performance with reduced dosage. EIS and SEM confirmed the formation of a compact, stable protective film, whereas FTIR identified hydroxyl, carbonyl, and aromatic functional groups responsible for adsorption on the steel surface. Thermodynamic analysis revealed spontaneous and endothermic adsorption following the Langmuir isotherm. Theoretical findings (DFT) revealed that flavonoids (quercitrin, luteolin and kaempferol-3-glucuronide) provide localized electron-rich adsorption sites, while lupeol exhibits high softness and delocalized electron density, enabling broad surface coverage, this electronic complementarity explains the enhanced adsorption strength and stability of the EM-EO mixture and its superior inhibition efficiency, where aromatic fragments stabilize the metal surface and polar groups block active sites, enhancing coating stability and protection. These outcomes declare that combining natural extracts offers a highly efficient, low-dose, and environmentally friendly strategy for corrosion protection, providing a promising pathway for green industrial applications.

Graphical abstract

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04806-5

Chemical Papers 80 (6) 6909–6932 (2026)