Ionic liquids as green inhibitors for protection of mild steel in acidic solution: electrochemical and DFT study

A literature review of abundant publications reveals the crucial role of inhibitors as one of the most practical methods for corrosion protection of metal bodies in industrial processes such as acid pickling, acid cleaning, chemical and electrochemical etching. The use of an additive is one of the major solutions for this problem. Hence, various additives are used to protect iron and its alloy against corrosive attack. The use of organic molecules containing functional groups and p electrons in their structure, as corrosion inhibitors, is one of the most practical methods for protecting metals against corrosion and it is becoming increasingly popular. Ionic liquid compounds possessing unique properties have attracted the attention of corrosion science and engineering researchers [1-3]. In recent years, several publications have provided evidence for a revolution in ionic liquid compound chemistry, leading to a probable switchover from volatile organic solvents in the future. In the present work, different imidazolium type ionic liquid were synthesized and their inhibiting action on the corrosion of stainless steel stainless steel (SS) in HCl was investigated by means of potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results of the investigation show that the newly synthesized compounds show excellent inhibition efficiencies against the corrosion of SS in acidic solution. The adsorption of ionic liquid ions onto the SS surface followed the Langmuir adsorption model. Electronic properties such as highest occupied molecular orbital (HOMO) energy, lowest unoccupied molecular orbital (LUMO) energy and frontier molecular orbital coefficients for inhibitors have been calculated.