Utilizing Lemon Balm extract as an effective green corrosion inhibitor for mild steel in 1M HCl solution: A detailed experimental, molecular dynamics, Monte Carlo and quantum mechanics study

This study concerns with mild steel corrosion inhibition in 1M HCl solution protected with different concentrations of Lemon Balm extract. Electrochemical and theoretical approaches are utilized for approaching this goal. The type of functional groups in the active components present in the Lemon Balm extract (LB.E) was examined through UV-visible analysis, Fourier Transform Infrared (spectroscopy) (FT-IR) and Raman spectroscopy. According to the electrochemical impedance spectroscopy (EIS) test results the maximum inhibition efficiency of about 95% was obtained in the solution containing 800 ppm LB.E. Potentiodynamic polarization test results revealed that in the presence of LB.E the rates of anodic steel dissolution and cathodic hydrogen evolution reactions significantly decreased and a mixed inhibition effect was obtained. Surface studies were done by contact angle test, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Results revealed that the steel surface damage as a result of HCl solution attack significantly decreased by addition of 800 ppm LB.E. In addition, deposition of a highly hydrophobic film composed of organic compounds of inhibitors on mild steel surface was demonstrated by contact angle test results. The excellent corrosion inhibition effect of LB.E on mild steel in HCl solution is related to the adsorption of active inhibitive compounds such as caryophyllene, germacrene, citral, luteolin, chlorogenic acid and rosmarinic acid on the anodic/cathodic places of mild steel surface. Furthermore, the theoretical results derived from Monte Carlo, molecular dynamics and quantum mechanics techniques evidenced the inhibitors adsorption onto steel substrate through donor-acceptor interactions. (C) 2018 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.