Preparation and corrosion inhibition mechanism of a chitosan ionic liquid Schiff base for the protection of N80 in HCl solution

Abstract

Three chitosan ionic liquid type Schiff bases (CS-IL-SBs) were synthesized by grafting three aldehydes (vanillin, cinnamaldehyde, and pyridine-4-carboxaldehyde) on CS-IL (chitosan grafted with p-toluene sulfonic acid) through a Schiff base reaction. Thermogravimetric analysis indicated that the thermal stability of CS was enhanced by the modification of IL and Schiff base groups. All CS-IL-SBs present a non-crystalline structure as analyzed using X-ray diffraction technique and have a positively charged surface in solution for improved dispersion stability as analyzed using zeta potential testing. A corrosion inhibition performance investigation using electrochemical and mass loss methods was undertaken, which were supported with surface analysis and computational studies. All the CS-IL-SBs act as effective corrosion inhibitors obeying Langmuir adsorption isotherm containing both chemisorption and physisorption for N80 steel in 15% HCl solution. Among them, CS-IL-Vin (grafted by vanillin) exhibits a maximum inhibition efficiency of 83.66% at 400 mg L⁻¹. The analysis of the corroded metal surface via scanning electron microscopy depicts a considerably smooth morphology in the presence of adsorbed CS-IL-SBs. Contact angle tests indicated that the water-repellent ability of the metal surface was increased by the addition of CS-IL-SBs. Density functional theory calculations indicated that the active regions of CS-IL-SBs are mainly distributed in –SO₃⁻, benzene rings, and Schiff base groups. Molecular dynamics simulations show that CS-IL-SBs are parallelly adsorbed on the metal surface to form a stable protective film. CS-IL-Vin shows the best performance among the three CS-IL-SBs, which was selected to be compounded with aided inhibitors with different electrical properties. When CS-IL-Vin was compounded with negatively charged 3-carboxybenzene sulfonate in a ratio of 1 : 3, corrosion inhibition efficiency was the highest, reaching 93.45%.