Corrosion Inhibition of Mild Steel in 1.0 M HCl from Thiadiazole Derivative Schiff Bases and Their Complexes with Co(II) and Ni(II): Synthesis, Characterization, DFT Study, and Monte Carlo Simulation

Schiff base ligand of 2-(((1,3,4-thiadiazol-2-yl)imino)methyl)phenol (HL) and its complexes with Co(II) (Co-L) and Ni(II) (Ni-L) have been successfully synthesized and characterized (UV–Vis, FTIR, NMR, XRD, magnetic susceptibility balance, and elemental analysis). This study aimed to determine the corrosion inhibition efficiency of the synthesized ligands and complexes. The corrosion inhibition activity of the inhibitor molecules in mild steel was evaluated in 1.0 M HCl solution using the weight-loss and potentiodynamic polarization (PDP) method at 298 K. The PDP test shows that the inhibitor molecules HL, Co-L, and Ni-L acted as mixed-type inhibitors with the highest inhibition efficiency were 83.78%, 91.49%, and 89.03% at a concentration of 1 × 10⁻⁴ M, respectively. The adsorption of HL, Co-L, and Ni-L followed the Langmuir isotherm model through a chemisorption mechanism. DFT studies show that the electron donor ability of the Co-L > Ni-L > HL molecule is correlated with the inhibitory ability. The Monte Carlo (MC) simulation displays that the inhibitor molecule is adsorbed on the metal surface, and the adsorption energy of the inhibitor molecule is Co-L > Ni-L > HL.