Experimental and computational exploration of synergistic effect of Laurus nobilis extract:Zinc cation on mild steel corrosion inhibition in saline solution

Abstract

According to the literature, the effectiveness of green corrosion inhibitors in chloride-containing solutions is not acceptable. To improve the anti-corrosion efficiency, a mixture of metal cations and green corrosion inhibitors can be used. In the current study, the synergistic corrosion mitigation effect of Laurus nobilis (LN) extract: Zn mixture on the mild steel (MS) in 3.5% NaCl solution was comprehensively studied by aiding various electrochemical and morphological techniques, as well as molecular-electronic scale modeling approaches (Molecular Dynamics coupled with Monte Carlo, and DFT). The observations from the EIS and polarization methods confirmed 90% inhibition degree using 200–600 ppm LN:Zn mixture along with mixed protection mechanism. Also, EIS results displayed maximum corrosion resistance achievement in the presence of 200–600 ppm LN:Zn mixture (about 10,000 Ω cm2 at 24 h of immersion). The MS surface characterizations via FE-SEM (equipped with EDS) technique disclosed the production of a smooth protective film composed of the LN molecules, Zn oxide/hydroxide species as well as LN/Zn chelation. Additionally, the outcome of the contact angle (CA) analysis clarified the hydrophilic nature of the sample surface protected by LN:Zn mixtures. FT-IR and UV–Visible analyses illustrated the successful LN molecules and Zn cations adsorption over the metal surface. The detailed findings proposed by computational studies (Molecular Dynamics (MD), Monte Carlo (MC), and Density Functional Theory (DFT)) revealed that the LN:Zn+2 complexes interfacially adsorbed onto the metal-based adsorbents through local/global atomic regions, further affirming their strong anti-corrosion propensity.