Exploring the Corrosion Potential of Three Bio-Based Furan Derivatives on Mild Steel in Aqueous HCl Solution: An Experimental Inquiry Enhanced by Theoretical Analysis

This research deals with the corrosion inhibition of mild steel in a highly corrosive aqueous HCl medium with a concentration of 0.5 M, using three different corrosion inhibitors: furan-2-carboxylic acid (1), furan-2,5-dicarboxylic acid (2), and furan-2,5-diyldimethanol (3). Various electrochemical tests, such as potentiodynamic polarization (PP or Tafel curve) and electrochemical impedance spectroscopy, were systematically performed. The experimental results underscore the remarkable corrosion mitigating properties of inhibitors 1–3 on mild steel, showing inhibition efficiencies of 97.6, 99.5, and 95.8%, respectively, at a concentration of 5 × 10–3 M and temperature T = 298 K. Notably, the inhibition efficiency of each inhibitor 1–3 shows a positive correlation with its concentration. In addition, consistent results from all electrochemical methods confirm that 1–3 act as mixed inhibitors. These findings remain robust across different experimental techniques, ensuring the reliability and comprehensiveness of the results. Theoretically, the inhibitors were optimized using the Density Functional Theory/B3LYP/6-311++G­(d,p) method in gas and aqueous phase to evaluate their reactivity and stability. Among them, compound 2 stands out for its enhanced reactivity and stability, highlighted by optimal EHOMO and ELUMO values. Negative electrostatic potential mapping suggests potential reaction centers, while Fukui functions reveal localized sites of reactivity, supported by a favorable electronic distribution and specific interactions with metal surfaces. Reduced density gradient analysis also confirms the suitability of this compound for noncovalent interactions, in agreement with experimental data.These theoretical results are in good agreement with experimental data, confirming the excellent performance of compound 2 as a corrosion inhibitor.