On the adsorption isotherms behavior of quinoaxaline as corrosion inhibitor for copper in nitric acid

The adsorption of molecules onto metal surfaces is a critical process, and understanding its mechanisms is vital for designing effective corrosion inhibitors. This study investigates the adsorption of quinoxaline (QX) as a corrosion inhibitor on copper surfaces in 1.5 M HNO₃, examining the effects of varying inhibitor concentrations and temperatures. The corrosion rate and surface coverage were assessed using the weight loss method. Various adsorption isotherm models, such as Langmuir, kinetic-thermodynamic, Freundlich, Temkin, Flory-Huggins, Frumkin, and Dubinin-Radushkevich, were applied to analyze the data. Experimental results revealed that surface coverage increases with higher inhibitor concentrations but decreases with rising temperatures. At high inhibitor concentrations and low temperatures, surface coverage values exceeded 0.9. The Langmuir isotherm indicated that QX adsorption is a spontaneous process. The average adsorption heat was calculated to be -31.38 kJ/mol, suggesting a mixed-mode adsorption mechanism. A combined mathematical model was proposed to predict surface coverage as a function of inhibitor concentration and temperature, demonstrating strong agreement between experimental and predicted results.