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

Abstract

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 1 M HCl and an inhibition efficiency of 95.2% was exhibited by 5-BEI at 1 mM concentration of 5-BEI after 6 h of immersion at 303 K. 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.