Bioinspired synergistic formulation from dihydropyrimdinones and iodide ions for corrosion inhibition of carbon steel in sulphuric acid

The adsorption and corrosion inhibition behavior of three dihydropyrimidinone (DHPM) derivatives on carbon steel in 0.5 M sulphuric acid solution is investigated in the present work. It was observed that among the three studied DHPMs; the inhibition efficiency trends were governed by substituent effects where the –OCH₃ substituted DHPM provided the best performance (96.05% efficiency) at a concentration of 3.27 × 10⁻⁴ M. The influence of iodide ions is also studied using electrochemical methods, gravimetric studies, and surface analysis. It was observed that the addition of iodide ions further improved the inhibition efficiency to >99% at 3.01 × 10⁻⁴ M concentration of KI. This significant increase in corrosion protection was explained by the synergistic action of DHPM derivatives and iodide ions. The adsorption of the inhibitor obeyed the Langmuir isotherm and exhibited a mixed physical/chemical adsorption. Potentiodynamic polarization studies showed a decrease in both anodic and cathodic reactions at carbon steel/0.5 M H₂SO₄ interface. The adsorption was supported by scanning electron microscopy study, and the reactivity parameters of the inhibitors were computationally evaluated using DFT analysis and Monte Carlo simulations.