Monte Carlo simulations of corrosion inhibition of mild steel in 0.5 M sulphuric acid by some green corrosion inhibitors

Atomistic modelling and simulations are becoming increasingly important in the field of corrosion inhibition. New research and development efforts and new possibilities for using computational chemistry in studying the behaviour of corrosion inhibitors on the metal surfaces are introduced. In this study, Monte Carlo simulations technique incorporating molecular mechanics and molecular dynamics were used to simulate the adsorption of methionine derivatives, namely l-methionine, l-methionine sulphoxide and l-methionine sulphone, on iron (110) surface in 0.5 M sulphuric acid. Adsorption energy as well as hydrogen bond length has been calculated. Results show that methionine derivatives have a very good inhibitive effect for corrosion of mild steel in 0.5 M sulphuric acid solution. Tafel polarisation studies have shown that methionine derivatives act as mixed-type inhibitors, and their inhibition mechanism is adsorption assisted by hydrogen bond formation. Impedance results indicate that the values of the constant phase element tend to decrease with increasing methionine derivatives concentrations due to the increase in the thickness of the electrical double layer. In addition, both polarisation resistance and inhibition efficiency Ei(%) tend to increase with increasing inhibitors concentrations due to the increase of the surface coverage, i.e., the decrease of the electrochemical active surface area. The quantum mechanical approach may well be able to foretell molecular structures that are better for corrosion inhibition.