Electrochemical and computational investigation of Tinospora cordifolia fractions as a novel corrosion inhibitor for carbon steel in seawater medium.

This study employed electrochemical techniques and computational analyses to evaluate the efficacy of Tinospora cordifolia fraction (TCF) as an anticorrosion agent for carbon steel in a seawater medium. Electrochemical methods were employed to investigate the corrosion performance of carbon steel with and without TCF at different concentrations (25 to 150 mg.L-1) and temperatures (300 K to 320 K). The findings revealed that TCF significantly decreased the corrosion current density, exhibiting its efficacy as a corrosion inhibitor. The inhibition efficiency increases with the concentration of TCF and decreases with rising temperature. The most excellent value of efficiency inhibition corrosion based on concentration is around 90.89% (PDP) and 92.25% (EIS) with the addition of 150 mg.L-1 of TCF. The temperature dependence of the inhibitor efficiency shows that its performance decreases slightly (from 90.89% to 83.74%) with increasing temperature (from 300 to 320 K), but remains effective even at high temperatures. The inhibitor exhibited a mixed-type inhibitory mechanism, although it tends to reduce the cathode oxygen reaction (cathodic-type). Adsorption studies revealed that bioactive compounds from TCF adhered to the steel surface, following the Langmuir isotherm, with a negative free energy value (ΔGads = - 26.73 kJ/mol at 300 K), indicating spontaneous adsorption. Computational analyses with density functional theory (DFT) confirmed the molecular interactions between moupinamide (the dominant active substance in TCF) and the steel surface in corrosion inhibition. This study highlights the effectiveness of TCF as a corrosion inhibitor and elucidates its inhibition mechanism, sorption behaviour, and fundamental molecular interactions.