Newly synthesized oxadiazole derivatives as corrosion inhibitors for mild steel in acidic medium: Experimental and theoretical approaches

Abstract

Two new 2,5-disubstituted oxadiazole derivatives, namely, 2-benzyl-5-(4nitrophenyl)-1,3,4-oxadiazole (2B54NPO) and 2-(4-methoxyphenyl)-5-(phenoxymethyl)-1,3,4-oxadiazole (24MO5POO) were synthesized and used as corrosion inhibitors against deterioration in 1 M HCl aggressive media of mild steel by electrochemical impedance spectroscopy, weight loss measurement, PDP technique, and quantum chemical calculation. A scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to perform morphological studies. The weight loss was measured at various dosages in the temperature range of 298–318 K during 12 h of immersion. As per weight loss analysis, 2B54NPO and 24MO5POO showed inhibition efficiencies of 96.54% and 92.19%, respectively at 300 ppm concentration. The EIS results reveal that increase in concentration of both 2B54NPO and 24MO5POO causes corresponding increase in the value of polarization resistance and decrease in the values of double layer capacitance. Potentiodynamic polarization studies suggest that both 2B54NPO and 24MO5POO behave as mixed-type corrosion inhibitors. In the EIS approach, the highest inhibition capability was determined to be 94.08% for 2B54NPO and 92.37 % for 24MO5POO at 300 ppm and 298 K. The adsorption mechanism of 2B54NPO and 24MO5POO on mild steel surface obeyed the Langmuir adsorption isotherm. PDP technique shows maximum inhibition efficiency values of 89.29% for 2B54NPO, and 88.85% for 24MO5POO respectively. The quantum chemical calculations provide the correlation between the inhibitor molecules and mild steel surface. SEM and EDX analyses were carried out to support the adsorption mode of corrosion inhibition.