Evaluation of inhibition performance of methylimidazolium ionic liquids on surface of mild steel in sulfuric acid

Abstract

In the present study, the microwave irradiation approach was used to synthesize two methylimidazolium-based ionic liquids (MImILs), specifically 1-Heptyl-3-methylimidazolium bromide [HMImBr] and 1-Benzyl-3-methylimidazolium bromide [BzMImBr]. Several spectroscopic methods have been used to characterize the produced compounds. Gravimetric and electrochemical techniques were employed to examine their ability to prevent corrosion of the mild steel in a 0.5 M sulfuric acid solution. Amongst all the evaluated ionic liquids, [BzMImBr] having an aromatic ring instead of hexyl ((–CH2)5–CH3) hydrocarbon of [HMImBr] manifests better inhibition efficiency of 95.49 % at 1000 ppm concentration. The experimental ionic liquids negatively impact both the anodic and cathodic Tafel reactions, exhibiting mixed-type inhibition properties, as demonstrated by the findings of the potentiodynamic polarization investigations. Through their adsorption employing their electron-rich centres, the examined ionic liquids create a corrosion-protective covering, and their adsorption follows the Langmuir isotherm model. Negative values of ΔGads indicate the spontaneous nature of [HMImBr] and [BzMImBr] adsorption, whereas values between −20 and −40 KJ mol−1 indicate the physio-chemisorption mode of adsorption. Energy dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), and field emission-scanning electron microscopy (FE-SEM) techniques were used to assess and evaluate surface morphology. The DFT-based analysis indicates that aromatic rings played a significant role in the charge sharing (donation and acceptance) in [BzMImBr].