Functional Group Effects on the Interfacial Adsorption of Arylquinoline-3-Carbonitriles on Iron: A DFT-D3 Investigation of Surface Interaction Mechanisms

Reliable corrosion inhibition systems are crucial for extending the lifespan of industrial metal structures. Quinolines, with their high adsorption capacity and protective efficiency, are promising next-generation inhibitors. However, the impact of substitutions on their coordination with iron surfaces requires deeper understanding. Herein, we investigate the influence of various functional groups on the adsorption behavior of three 2-amino-4-arylquinoline-3-carbonitriles (AACs) on iron surfaces using first-principles density functional theory calculations. Results reveal that nitrophenyl and hydroxyphenyl significantly enhance the adsorption strength of AACs on the Fe(110) surface, facilitated by donor-acceptor interactions. Neutral molecules were more stable than their protonated counterparts. Key results show strong adsorption energies, with values ranging from -2.005 to -1.809 eV for the AACs, along with significant electron gains across carbon atoms as indicated by Bader charge analysis. These strong interactions result in notable charge redistribution and bond formation, as shown by projected density of states and electron density difference iso-surfaces. Furthermore, electron localization function analysis indicates that van der Waals interactions, influenced by multiple nitrogen atoms, play a crucial role in stabilizing the adsorbed molecules. Stronger adsorption through electron donation and retro-donation mechanisms suggests enhanced corrosion protection efficiency of these substituted quinolines. The conductor-like screening model for real solvents analysis provides complementary insights into the solvation characteristics. Overall, the findings demonstrate the specific role functional groups play in the coordination of arylquinoline-3-carbonitriles with iron surfaces.