Cysteamine modified polyaspartic acid as a new class of green corrosion inhibitor for mild steel in sulfuric acid medium: Synthesis, electrochemical, surface study and theoretical calculation

In the present work, an attempt has been made for the development of green and high efficiency acid pickling inhibitor based on the eco-friendly polyaspartic acid (PASP). In this view, cysteamine modified PASP (PASP-S) containing S atom was prepared by ring-opening reaction of polysuccinimide with cysteamine. The corrosion inhibition performance of PASP and PASP-S for mild steel in 0.5 M H2SO4 medium were evaluated using weight loss, electrochemical impedance and potentiodynamic polarization methods. The inhibition performance of PASP-S is greatly improved with a high efficiency of 93.9% (weight loss method) at a very low concentration of 100 mg L-1 at 298 K in comparison with unmodified PASP. The obtained results also indicate that PASP-S is a mixed inhibitor and the adsorption of PASP-S on the mild steel surface follows Langmuir adsorption isotherm. Theoretical chemical parameters are calculated using the Density Functional Theory method (DFT). The excellent inhibition performance of PASP-S is due to the presence of pendent functional sulfhydryl group, which can be confirmed by X-ray photoelectron spectroscopy (XPS) analysis of the mild steel samples. The present work provides a simple and effective pathway for synthesizing high efficiency acid pickling inhibitor by introducing a functional group into the PASP chains. Such chemical modification method may also be an effective strategy to improve the efficiency of other polymer acid pickling inhibitors.