A novel, synergistic, efficient inhibitor derived from onion peel extract and potassium iodide for enhanced corrosion resistance of Q235 carbon steel in sulfamic acid

Abstract

Based on the requirements of environmental sustainability, developing plant-based green corrosion inhibitors as alternatives to traditional synthetic corrosion inhibitors is a hot topic in corrosion science research. This study proposed and verified a new strategy of synergistically combining onion peel extract (OPE) and potassium iodide (KI) to enhance the corrosion resistance of Q235 carbon steel. Using electrochemical tests and the weight loss method, the corrosion inhibition performance of the compound in a 1.0 mol L⁻¹ NH₂SO₃H solution was evaluated. The weight loss method shows that the synergistic parameter S is always greater than 1, confirming that there is a synergistic effect between the two. The electrochemical polarization curve indicated that OPE, KI, and the combined system were all mixed-type corrosion inhibitors, mainly inhibiting at the cathode. Fourier transform infrared spectroscopy (FTIR) and liquid chromatography–mass spectrometry (LC-MS) were used to analyze the composition of OPE, identifying myricetin (MYR), caffeic acid (CAF), and quercetin (QUE) as the effective active components for corrosion inhibition. X-ray photoelectron spectroscopy (XPS) characterization confirmed that the active components of OPE and KI effectively adsorbed on the surface of carbon steel, forming a dense and stable protective interface film. Combined with density functional theory (DFT) calculations and molecular dynamics (MD) simulations at the molecular level, the mechanism was elucidated. DFT identified the active adsorption centers of myricetin (MYR), caffeic acid (CAF), and quercetin (QUE) in OPE. MD simulations showed that these molecules could hinder the diffusion of corrosive ions such as NH₂SO₃⁻ and H₃O⁺ to the substrate. This study breaks through the limitations of traditional synthesis and opens up a new path for plant-based green corrosion inhibitors. The elucidation of the molecular-level synergistic mechanism has significant scientific value and application prospects.