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In the current investigation, a triazole, namely 1-Amino-2-mercapto-5-(4-(pyrrol-1-yl)phenyl)-1,3,4-triazole (AMPPT), was synthesized and characterized using ¹H and ¹³C nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies in addition to CHN micro elemental analysis. A preliminary study of the title compound as corrosion inhibitor for mild steel in 1 M hydrochloric acid solution was evaluated by performing gravimetrical, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements in addition to scanning electronic microscope (SEM). The obtained experimental results indicated that AMPPT works perfectly as a corrosion inhibitor for mild steel in 1 M HCl solution and its effectiveness is up to 96.3% at 500 ppm and corrosion inhibition efficiency increase with increasing the concentration of tested inhibitor, suggests that the adsorption of AMPPT molecules on the mild steel surface obeyed the Langmuir adsorption model. Polarization measurements show that the studied inhibitor is a mixed type. EIS measurements revealed that the charge transfer resistance increases with increasing concentration of AMPPT. The free energy (ΔGoads) value showed that the adsorption of AMPPT molecules suggesting a mixed-mode of physisorption and chemisorption. Density functional theory (DFT) calculations were performed on AMPPT molecules to determine the quantum parameters and the relationship between the inhibitor structure and inhibiting efficiency. The molecular parameters, such as energy gap and frontier molecular orbitals (HOMO and LUMO), the absolute electronegativity (χ) value, and the fraction transfer of electrons (∆N) were also calculated and correlated with inhibition activity. The theoretical outcomes showed that the inhibition efficiency of AMPPT increased with the increase the energy of HOMO, and the nitrogen and sulphur atoms are the most likely sites for bonding by giving electrons to the unoccupied 3d-orbitals of Fe atoms on the mild steel surface.

The corrosion inhibition efficiency of the novel pyridine namely, 4-(Benzoimidazole-2-yl)pyridine has been studied for mild steel in a 1 M hydrochloric acid environment by utilizing gravimetrical techniques. The synthesized inhibitor exhibits a significant inhibitive efficiency of 93.8% at 0.005 M. The adsorption isotherm of the investigated inhibitor on mild steel surface obeys the Langmuir isotherm. Surface morphology investigated by utilizing scanning electron microscopy (SEM) demonstrates a smooth metal surface with the addition of 4-(Benzoimidazole-2-yl)pyridine in a hydrochloric acid environment. Quantum chemical calculations using density functional theory (DFT) have been used to investigate the molecular structure and behavior of 4-(Benzoimidazole-2-yl) pyridine as a corrosion inhibitor. Different parameters have been calculated using DFT, such as energies of highest occupied molecular orbital and lowest occupied molecular orbital (EHOMO and ELUMO), energy gap (∆E), and dipole moment (μ). These parameters were important to elucidate the behavior of the investigated molecule as a corrosion inhibitor in acidic solution and also suggest the mechanism of inhibition.