Electrochemical performance of a novel 1-(benzo[d]thiazol-2-yl)-3-methylguanidine as effective corrosion inhibitor for carbon steel in 1 M hydrochloric acid.

Guanidine benzothiazole (G) and 1-(benzo[d]thiazol-2-yl)-3-methylguanidine (AG) were successfully synthesized and characterized by infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. Both compounds act as novel corrosion inhibitors for carbon steel in 1.0 M hydrochloric acid solution. Their inhibition efficiency was evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). Surface analysis via scanning electron microscope (SEM) and energy dispersive X-ray (EDX) confirmed the formation of a protective film on the steel surface. PDP results indicate that G and AG function as mixed-type inhibitors, with inhibition efficiency increasing with concentrations, reaching a maximum of 80% for G and 91.4% AG. The AG compound was seen to retard the rate of corrosion of carbon steel more effective than PP compound. Adsorption followed the Langmuir isotherm, suggesting monolayer adsorption on the metal surface. The high inhibition efficiencies were attributed to strong adsorption and the formation of a dense, protective barrier film. The corrosion inhibition performance of the synthesized molecule was evaluated using density functional theory (DFT). Quantum chemical parameters, including highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO), energy gap, hardness, and dipole moment, and other quantum descriptors were analyzed. Density functional theory (DTF) calculation supported the experimental finding, showing that the high efficiency correlates with a low energy gap and high dipole moment, which promote electron transfer and adsorption strength. Theoretical and experimental results showed strong agreement, confirming the potential of G and AG as effective inhibitors for carbon steel.