New imidazolium ionic liquids as ecofriendly corrosion inhibitors for mild steel in hydrochloric acid (1 M): Experimental and theoretical approach

Highlights

• Imidazolium ionic liquids [Imid-3PE] Br and [Imid-4PE] br were showing a good performance as corrosion inhibitors for mild steel.

• A stable passive layer was formed on the mild steel surface.

• [Imid-3PE] Br and [Imid-4PE] Br showed a good inhibition performance during the immersing time.

• Molecular dynamics simulations were performed involving the experimental conditions.

• The theoretical part was confirmed by the experimental findings.

Abstract

The present paper was designed to investigate an original synthesized ionic liquid (ILs) named 1-phenethyl-3-(3-phenoxypropyl)-1H-imidazol-3-ium bromide [Imid-3PE] Br, and 1-phenethyl-3-(4-phenoxybutyl)-1H-imidazol-3-ium bromide [Imid-4PE] Br as corrosion inhibitors. These inhibitors were evaluated against mild steel corrosion in 1 M hydrochloric acid medium using electrochemical techniques. PDP experiments revealed that the [Imid-3PE] Br and [Imid-4PE] Br behaved as mixte type inhibitors. Electrochemical impedance spectroscopy (EIS) results indicated that the both compounds showed a good inhibition of the steel surface with an inhibition efficiency of 95.8% for [Imid-3PE] Br and 96.7% for [Imid-4PE] Br at the optimum concentration. According to Langmuir isotherm model and the activation parameters, these ILs can be adsorbed onto the mild steel surface through physical and chemical bonds. The theoretical approach confirms the adsorption behavior of the studied ILs based on DFT calculation and molecular dynamic simulation.

Introduction

Generally, the ionic liquids (ILs) defined as organic salts which contain ligation of an inorganic anion such as bromide, iodide, chloride and organic cations such as N-alkylimidazolium, alkylphosphonium, alkylpyridinium or alkylammonium [1]. These ILs salts are a new interested topic of many researchers because of its unique properties such as the high polarity, the low toxicity, the lower vapor pressure, the non-flammability, and their excellent solubility and thermal stability [2,3]. Therefore, some class of these salts were applicated as catalysts and biocatalysts [4], as alternative solvents of volatile organic compounds [5], as media for the metal electrodeposition [6], antimicrobial activity [7], in food science [4], and as corrosion inhibitors [2].

Many industrial fields using construction materials composed of the mild steel because of its high availability and physicochemical characteristics and low cost [8]. On the other side, this steel can be easily deteriorated and provokes an economic and human damages when it's contacting an aggressive acidic medium. Therefore, the best preventing in this case is the application of inhibitors compounds which is function as a barrier film between the steel surface and the aggressive solution [9,10]. Furthermore, this film formed can be explained by the adsorption of these molecules on the metal surface by several heteroatoms’ centers such as N, S and O heteroatoms, and π-electrons. Also, this adsorption can be formed through either physical adsorption, chemisorption or sometimes by the both (Physical & Chemical) [9].

Recently, many researches focused on the application of ecofriendly corrosion inhibitors such as the natural extracts [11], biological polymers [12], pharmaceutical products [13] and ionic liquids etc. Among these, the ionic liquids considered the most interested one that can be applied as ecological inhibitors to reduce the corrosion of a variety of metals in aggressive media [14,15]. Furthermore, the association of cationic and anionic ligand can result a phenomenon of intermolecular synergism and the large organic cation of these ILs can coverage a large surface area of the metallic specimens and showing a great adsorption. Several previous works were focused on the application of these salts as corrosion inhibitors [16].

As many researchers reported, these salts can base on ammonium [17], pyridazinium [18], pyridinium [14] and imidazolium showing therefore a good inhibition performance against the corrosion process in aggressive solution. For example, Murulana et al., the corrosion inhibition of mild steel in 1 M HCl solution by some selected imidazolium-based ionic liquids using various experimental techniques and theoretical methods. The obtained results showed the high inhibition performance of this base [19]. In addition, Li Meng and their collaborators were studied how the anions affect the inhibition performance of imidazolium derivatives in acidic media using various techniques to approach the anions effect on the adsorption of the investigated molecules. However, the substitution of the imidazole ring is a new topic that can increase the inhibition performance of imidazolium -based ionic liquid against corrosion of several materials [20].

The present work focused on the investigation of three newly synthesized ionic liquids derived from pyridine namely: 1-phenethyl-3-(3-phenoxypropyl)−1H-imidazol-3-ium bromide [Imid-3PE] Br, and 1-phenethyl-3-(4-phenoxybutyl)−1H-imidazol-3-ium bromide [Imid-4PE] Br as corrosion inhibitors. This investigation was performed on mild steel specimens using various electrochemical techniques, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). This study was confirmed with theoretical approach based on DFT calculation and Molecular dynamic simulation.