Experimental and first-principles DFT insights into the corrosion protection mechanism of carbon steel in an HCl medium by two thiazolidinedione compounds

Researchers have investigated various approaches to avoid corrosion problems in different industries in recent decades. In line with the research trend in this field, we synthesized and characterized two thiazolidinedione derivatives, namely (Z)- 5-(4-hydroxy-3-methoxybenzylidene)thiazolidine-2,4-dione (HMTZD) and (Z)- 5-(4fluorobenzylidene)thiazolidine-2,4-dione (FTZD), and then used them as potential inhibitors for protecting the corrosion of carbon steel (CS) in 1.0 mol/L. Corrosion inhibition performances were evaluated using electrochemical techniques such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), linear polarization resistance (LPR), and surface characterization using a scanning electron microscope (SEM). Besides, first principles Density Functional Theory (DFT) calculations were employed to investigate the potential bonding and charge transfer between inhibitor molecules and Fe(110) surface. Electrochemical results indicated that the addition of tested inhibitors to corrosive 1.0 mol/L HCl solution significantly reduced carbon steel corrosion by increasing the polarization resistance and blocking both anodic and cathodic corrosion reactions. Further, results indicated that HMTZD and FTZD are adsorption inhibitors following Langmuir adsorption isotherm. The HMTZD demonstrated an inhibition performance of 96% at 5 x 10-3 M. In addition, the morphological analysis revealed the formation of a protective barrier onto the CS surface, which reduced corrosion attack. The adsorption mechanism was further evaluated using first-principles DFT calculations, which showed that both inhibitors can form chemical bonds with Fe-atoms. Partial density of states (PDOSs) suggested that inhibitor molecules adsorbed through charge transfer between oxygen/sulfur of molecules and Fe-atoms. The outcomes from the present work are intended to encourage further exploration of thiazolidinediones in the corrosion protection of metals.