Impact of selected ionic liquids on corrosion protection of mild steel in acidic medium: Experimental and computational studies

The corrosion potential of three newly studied ionic liquids (ILs) namely, 5-(Trifluoromethyl) dibenzothiopheniumtetrafluoroborate (TDTB), 5-(Trifluoromethyl)dibenzothiopheniumtrifluoromethanesulfonate (TDTM) and 1-Ethyl-3-methylimidazolium ethyl sulfate (EMIM)(ESO₄) were investigated for mild steel (MS) in 1 M hydrochloric acid using electrochemical, Fourier trans­form in­frared (FTIR) spec­troscopy and gravimetric tech­niques. The potentiodynamic polarization data shows that the three inhibitor molecules studied possess characteristics that correspond to mixed-type inhibitors but TDTM exhibits more anodic characteristics. Scan­ning electron microscopy (SEM) was used for the surface studies. Remarkable corrosion inhibition of mild steel was also predicted using energy dispersive spectroscopy (EDS). FTIR spectroscopy established the functional group interrelationship showing disappearance of characteristic absorption bands in the adsorption film FTIR spectra. Quantum chemical calculations and Monte Carlo mod­els were utilized to gain more in­sight into the electronic properties of the compounds in rela­tion to the corrosion inhibition effect and the binding and/or adsorption of ionic liquids on the surfaces of MS. The adsorption en­ergy adopts the order: TDTB ≈ TDTM >(EMIM)(ESO4). The numerical val­ues of adsorption energy is −3.72 kcal mol−1, −3.77 kcal mol−1 and −3.04 kcal mol−1 for TDTB, TDTM and (EMIM)(ESO4), respectively.