Thiosemicarbazide and thiocarbohydrazide functionalized chitosan as ecofriendly corrosion inhibitors for carbon steel in hydrochloric acid solution

Organically functionalized chitosan macromolecules namely Chitosan-Thiosemicarbazide (CS-TS) and Chitosan-Thiocarbohydrazide (CS-TCH) were synthesized and evaluated as new corrosion inhibitors for mild steel corrosion in 1 M HCl. The FTIR and ¹H NMR studies confirmed the formation of the derivatives. The corrosion tests were performed using weight loss method, electrochemical measurements, surface morphology (AFM), quantum chemical investigation and molecular dynamics simulation methods. The maximum efficiency of 92% was obtained at a concentration as low as 200 mg L⁻¹. The inhibitors were found to obey Langmuir adsorption isotherm and exhibited both physical and chemical adsorption. Electrochemical impedance spectroscopy (EIS) results showed an increase in polarization resistance which supported the adsorption of inhibitors on the mild steel surface. Tafel data showed a mixed type behavior with cathodic predominance. The data of quantum chemical calculations and molecular dynamics simulation supported the experimental findings.