Investigation of phosphorus-based ionic liquid with long alkyl chain as high-performance corrosion inhibitor with ultralow concentration for mild steel in 1 M HCl solution

The ionic liquids (ILs) are regarded as the ideal candidate for the novel and high-efficiency corrosion inhibitors. While the cost problem caused by relatively large dosage limited the wide employments of conventional ILs. In the current study, we synthesized two novel phosphorus-based ionic liquids (PBILs) with different alkyl chain length (dodecyltriphenylphosphonium bromide (C12TPB) and cetyltriphenylphosphonium bromide (C16TPB)), and evaluated their anticorrosion efficiencies for mild steel (MS) in 1 M HCl aqueous solution by weight loss measurement, scanning electron microscope, X-ray photoelectron spectroscopy and electrochemical test. The results revealed that PBILs performed excellently (inhibition efficiencies > 93 %) at a very low concentration of 10 μM, which was much greater than those for traditional imidazole and pyridine ionic liquids at 500 μM. It was demonstrated that PBILs could adsorb on the metal surface to form the protective film, which should be mixed corrosion inhibitors with cathodic advantage. Then the adsorption study and molecular dynamics simulation confirmed that their special molecular structure highly promoted the intensity of the adsorption film mainly caused by the chemical adsorption. This study provided a novel approach for the structural design and development of high-performance IL corrosion inhibitors.