Experimental and Computational Investigation of New Geranyl-Based Ionic Liquids on Mild Steel as Corrosion Inhibitors in Chloride Media

In this work, geranyl-based ionic liquids (ILs) were developed as efficient dual-functional agents for corrosion protection and antibacterial applications. Geranyl piperidinium bromide (GPB) and geranyl morpholinium bromide (GMB), containing a bioderived terpene side chain, exhibited excellent surface activity and strong affinity toward mild steel in chloride-rich acidic media. Both ILs significantly enhanced corrosion resistance through the formation of a stable adsorbed protective film, achieving inhibition efficiencies of 87.61% for GPB and 81.32% for GMB. Electrochemical and adsorption analyses indicated spontaneous Langmuir-type adsorption governed mainly by physisorption with a predominantly anodic inhibition mechanism. Surface analyses confirmed the formation of a compact and uniform inhibitor film, while DFT and molecular dynamics simulations provided molecular-level validation of the experimental observations. In addition to corrosion protection, the ILs demonstrated notable antibacterial activity against both Gram-positive and Gram-negative bacteria, with GPB showing superior performance, reflected by lower minimum inhibitory concentrations (MICs). Overall, this study demonstrates that geranyl-based ILs are promising, sustainable, multifunctional alternatives to conventional corrosion inhibitors with added antimicrobial capability.