Experimental and theoretical analysis of expired doxycycline and Klacid as aluminum corrosion inhibitors in HCl

The inhibitory potency of expired doxycycline and klacid on the corrosion of aluminum (Al) in 1.0 M HCl solution was examined employing chemical, electrochemical and computational measurements. All the protection efficacy obtained from various measurements confirm that these drugs work as excellent inhibitors of aluminum corrosion. The potentiodynamic polarisation measurement suggests that the expired drugs function as mixed inhibitors. The inhibition impacts of doxycycline and klacid owing to their spontaneous adsorption on the Al surface which complies with the Langmuir isotherm. Based on the predicted adsorption free energy values, the adsorption procedure mixes of chemical and physical adsorption. The protection efficacy values of klacid are greater than those of doxycycline reaching 99.66% at a concentration 900 ppm while in the existence of doxycycline they reach 98.63% utilising potentiodynamic polarisation measurements. The activation thermodynamic functions are defined and interpreted. Theoretical calculations were performed in an aqueous environment using density functional theory. Quantum chemical parameters align with experimental observations. Monte Carlo simulations confirm strong and stable adsorption of klacid and doxycycline on the Al(111) surface. Klacid's strong adsorption is evidenced by its high negative adsorption energy, underscoring its effectiveness as a corrosion inhibitor.