Evaluation of imidazolium ionic liquids as green corrosion inhibitors for carbon steel in HCl solution

Two newly environmentally friendly ionic liquids with imidazolium functionality, PPIPF6 (1-phenethyl-3-(3-phenylpropyl)imidazolium hexafluorophosphate) and DPIPF6 (1,3-diphenethylimidazolium hexafluorophosphate), were evaluated for their anti-corrosion performance on carbon steel in 1 M HCl. The evaluation employs a combination of electrochemical tests, spectroscopic techniques, surface analysis , and theoretical approaches (DFT, DFTB plus, molecular dynamics (MD) simulations). The results show that the imidazolium-functionalized ionic liquids act as highly effective corrosion inhibitors within the tested concentration and temperature range. At 10 –3 M, the performance reached 94.8 % for PPIPF6 and 94.4 % for DPIPF6. Potentiodynamic polarization (PP) revealed that these cationic imidazolium liquids function as mixed-type corrosion inhibitors . The composition of the carbon steel surface was examined using spectral techniques (FT-IR, UV–vis, contact angles, XRD), while surface characterization was conducted using SEM/EDS and AFM . These analyses confirmed the formation of a protective film on the metal surface through chemical adsorption , with PF6 - playing a crucial role in enhancing the film's stability and hydrophobicity . Quantum chemical analyses indicate that PPIPF6 exhibits a greater capacity to donate electrons and possesses superior adsorption stability compared to DPIPF6, which accounts for its improved inhibitory effectiveness. This research underscores the potential of PPIPF6 and DPIPF6 as efficient corrosion inhibitors in acidic conditions, with PPIPF6 showing robust performance, especially at ambient temperatures.