Adsorption and inhibition mechanisms of chitosan derivatives on carbon steel surface: a combined DFT and MD study

Density functional theory (DFT) was employed in conjunction with molecular dynamics (MD) simulation to investigate the adsorption and inhibition mechanisms of two chitosan derivatives (i.e., vanillin-chitosan and 3NiSA-chitosan) on carbon steel (Fe) surface. Quantum chemical descriptors and MD simulation parameters were calculated and discussed. Our study shows that 3NiSA-chitosan has higher adsorption efficiency on carbon steel surface than vanillin-chitosan. Next, MD simulation was adopted again to evaluate the inhibition performance of 3NiSA-chitosan at multiple inhibitor concentrations. The adsorption configuration and inhibition performance were studied. The inhibitor molecules can form different adsorption configurations on Fe surface by physical and chemical adsorption: near-flat, partial chemisorption, and physisorption. Concentration plays a key role in the formation of adsorption film. Further analyses demonstrated that the inhibition mechanism can be explained to a certain extent by the following two parameters: change in solvent concentration near Fe surface, and diffusion property of the constrained water molecules in the inhibitor film.