Electrochemical explorations, SEM/EDX analysis, and quantum mechanics/molecular simulations studies of sustainable corrosion inhibitors on the Cu-Zn alloy in 3% NaCl solution

Abstract

Essential oils (EOs) have recently gained attention as sustainable corrosion inhibitors due to their biodegradability, environmental friendliness, low cost, and easy availability. This paper aimed to investigate the synergistic impact of the active green molecules from two essential oils (EO16/EO18) derived from A. visnaga (L.) Lam on the corrosion of Cu-Zn alloy (brass) in a 3% NaCl environment using open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS), surface morphology analysis and computer modelling methods, including density functional theory (DFT) and Monte Carlo (MC) simulations. The electrochemical results demonstrated show that EO18 and EO16 at an ideal concentration of 2 (g/L) and after 6 h of immersion at 298 K, exhibited high inhibition efficiencies (ƞPDP(%), reaching a maximum of 93.04% and 84.57%, respectively. Moreover, the PDP experiments revealed that EO16 and EO18 acted as mixed inhibitors, with a predominant cathodic inhibitory behavior. Additionally, EO16 and EO18 have strong inhibitory efficacy throughout a wide temperature range (298–338 K), especially EO18. Also, the thermodynamic parameters showed a good relationship with the inhibition efficiency of the EO16/EO18. The examination of surface morphology (SEM/EDX) indicated less degradation of the metallic surface in the presence of both EOs in a corrosive environment, with the formation of resistant protective films, particularly notable for EO18. These findings confirmed the adsorption of EOs molecules onto the active sites of the brass surface, facilitated by the synergistic action of various phytochemical elements, including oxygenated monoterpenes/sesquiterpenes (minor compounds) and major compounds (Croweacin/Linalool). Furthermore, computational investigations utilizing DFT and MC simulations revealed a significant adsorption of EO18/EO16 compounds (both major and minor components) onto Cu (111) and Zn (110) surfaces. The MC simulation results further demonstrate that the synergistic effect of EO18 compounds on Cu/Zn surfaces results in the formation of stronger and more protective layers compared to the synergistic effect of EO16 compounds. These computational findings align well with the results obtained from experimental inhibition efficiencies. The combination of experimental and computational approaches enhanced our understanding of the corrosion inhibition mechanism and underscored the potential of EOs as sustainable and effective corrosion inhibitors. These findings can serve as a useful guideline for future research aimed at investigating the synergistic inhibitory impact of the components present in the green extracts.