Evaluation of the Temperature-Dependent Adsorption and Corrosion Inhibition Performance of Rhizophora racemosa and Rhizophora harrisonii Leaf Extract on Mild Steel in Nitric Acid Medium

Abstract

The search for environmentally sustainable corrosion inhibitors has intensified due to the environmental and health concerns associated with conventional synthetic inhibitors. This study evaluated the influence of temperature on the adsorption characteristics and corrosion inhibition performance of Rhizophora racemosa and Rhizophora harrisonii leaf extracts on mild steel in a 1 M nitric acid solution using the weight loss technique. The effects of inhibitor concentration (0.4, 0.6, 0.8, and 1.0 g/L), temperature (303.15–343.15 K), and immersion time (2–10 hours) were investigated. The corrosion inhibition efficiency of both extracts improved with increasing inhibitor concentration, demonstrating enhanced adsorption of phytochemical constituents onto the mild steel surface. Temperature-dependent adsorption behaviour was evaluated using Langmuir and Freundlich adsorption isotherms. The adsorption pattern of Rhizophora harrisonii conformed predominantly to the Langmuir model at elevated temperatures, whereas Freundlich behaviour was more evident at lower temperatures, indicating changes in the adsorption mechanism with temperature. Activation energies of 17.6 kJ mol⁻¹ for Rhizophora racemosa and 21.8 kJ mol⁻¹ for Rhizophora harrisonii confirmed a physisorption mechanism. From the findings, both mangrove leaf extracts provide effective, eco-friendly corrosion protection for mild steel in a nitric acid medium and possess considerable potential as sustainable green corrosion inhibitors.