Anticorrosion performance of three newly synthesized isatin derivatives on carbon steel in hydrochloric acid pickling environment: Electrochemical, surface and theoretical studies

In this work, three new isatin derivatives (5-BEI, 5-HEI and 5-FEI) were synthesized and their inhibition effect on carbon steel in hydrochloric acid medium has been evaluated. The detailed study of 5-BEI is given using gravimetric measurements and electrochemical methods (DC and AC techniques). The results showed that this new isatin is an efficient corrosion inhibitor for carbon steel in 1M HCl and an inhibition efficiency of 95.2% was exhibited by 5-BEI at 1mM concentration of 5-BEI after 6h of immersion at 303K. Polarization curves suggested that the 5-BEI acted as mixed type inhibitor. Electrochemical impedance spectroscopy showed that increase inhibitor (5-BEI, 5-HEI and 5-FEI) concentration leads to an increase in the values of the charge transfer resistance. Adsorption of 5-BEI, 5-HEI and 5-FEI molecules on the steel surface obeyed Langmuir adsorption isotherm model. X-Ray Photoelectron Spectroscopy (XPS) analyses revealed that the corrosion inhibition mechanism of 5-BEI is mainly controlled by a chemisorption process. The comparative study of inhibitive performance of the three isatin derivatives (5-BEI, 5-HEI and 5-FEI) using Density functional theory (DFT) calculations of orbital energies and reactivity indices suggested that the trend of inhibition potentials of the compounds depend on the effect of substituent atoms (Br, F, and H) on the electron donating and/or accepting ability of the molecules. The trend of reactivity of the molecules was 5-BEI>5-FEI>5-HEI. Theoretical Monte Carlo simulation studies also corroborated experimental findings. [Display omitted] •New synthesized isatin derivatives are good inhibitors for the carbon steel corrosion in 1M HCl.•5-BEI is mainly chemically adsorbed on the steel surface.•XPS analysis has provided the composition of adsorbed protective layer on the steel surface.•The DFT and Monte Carlo calculations are in good agreement with the experimental results.