Bio-derived ionic liquids for iron surface protection: A multiscale investigation of cholinium lignin-based inhibitors

Cholinium lignin-based ionic liquids have emerged as attractive candidates for eco-friendly corrosion inhibition in corrosive environments, owing to their biocompatibility and rich functionality. In this work, a synergistic suite of computational techniques; ranging from density functional theory (DFT) and conductor-like screening model (COSMO-RS) to molecular dynamics (MD) and self-consistent charge density functional tight-binding (SCC-DFTB); was employed to unravel the anticorrosive behavior of Trimethyl-β-hydroxyethyl-ammonium gallate (CH-GAL), syringate (CH-SYR), and vanillate (CH-VAN) on Fe(110). DFT calculations showed that CH-SYR possessed a slightly narrower HOMO–LUMO gap (3.49 eV) and higher electron affinity than the other two, pointing to enhanced reactivity and stronger metal–inhibitor orbital overlap. COSMO-RS reveals the anion's pronounced hydrogen-bond acceptor profile, promoting robust solvation and competitive adsorption at the metal–solution interface. MD simulations confirmed stable interfacial arrangements, with the anionic moiety generally lying parallel to the iron surface to maximize contact. SCC-DFTB evaluations corroborate these observations, attributing the most exothermic adsorption energy (−3.834 eV) to CH-SYR's multi-site Fe–O coordination, followed by CH-GAL (−3.029 eV) and CH-VAN (−2.247 eV). Together, these results underscore the promise of tailoring both the lignin anion and cholinium cation to optimize electron donation, surface coverage, and solvation effects, thereby paving the way for the design of next-generation, bio-derived corrosion inhibitors with minimal environmental impact.