# Synthesis and assessment of ionic liquid derived from benzalkonium chloride as corrosion inhibitor for carbon steel

## TL;DR

This study creates and tests ionic liquids that effectively prevent carbon steel corrosion in acidic environments.

## Contribution

The synthesis and evaluation of novel ionic liquids as highly efficient corrosion inhibitors for carbon steel in 1 M HCl.

## Key findings

- The ionic liquids achieved up to 97% corrosion inhibition at 100 ppm in 1 M HCl.
- The compounds act as mixed-type inhibitors by adsorbing onto the steel surface.
- Quantum chemical analysis showed ILII–ILIV had better inhibition due to their aromatic ring structure.

## Abstract

Corrosion poses a significant challenge in the materials industry, especially when carbon steel (C-steel) is subjected to highly corrosive environments such as 1 M HCl. In this study, four ionic liquids (ILs)-1-benzyl-1-methylpiperidin-1-ium chloride (ILI), 1-benzyl-2-methylpyridin-1-ium chloride (ILII), 1-benzyl-3-methylpyridin-1-ium chloride (ILIII), and 1-benzyl-4-methylpyridin-1-ium chloride (ILIV) were synthesized and characterized using spectroscopic techniques, including FT-IR and 1HNMR. Electrochemical analyses such as potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) demonstrated excellent protective performance for C-steel in 1 M HCl, reaching a maximum inhibition of 97% at an optimum concentration of 100 ppm. Insights from polarization and impedance analyses confirmed that these compounds act as mixed-type inhibitors by adhering to the steel surface. The adsorption behavior followed the Langmuir isotherm model, with ΔG0 ads values suggesting a combination of physisorption and chemisorption. Quantum chemical assessments validated the experimental results, indicating that ILII–ILIV, due to their two aromatic rings, exhibited superior surface interaction and inhibition efficiency because of their reduced HOMO-LUMO energy gaps. These findings affirm the strong inhibitory potential of the tested ILs in acidic media.

The online version contains supplementary material available at 10.1038/s41598-025-14549-0.