Journal of Applied Chemical Science International

This study aims to examine the photodegradation kinetics of Methyl Orange (MO) dye in an aqueous medium using CuO–clay composite as a heterogeneous photocatalyst. The composite was synthesized through two stages, namely intercalation of natural clay with 0.1 M CMC surfactant and impregnation of Cu²⁺ ions from CuSO₄·5H₂O followed by calcination at 400 °C. Characterization using SEM–EDX showed that the aluminosilicate clay framework was maintained and CuO was loaded in significant amounts on the composite surface. Photodegradation tests were conducted on a 25 mg/L MO solution with the addition of 0.5 g of composite in 50 mL of solution and UV irradiation for 60, 90, 120, 150, and 180 minutes. The results showed that the degradation efficiency increased sharply up to 120 minutes of irradiation, with a degradation percentage of around 85–86%, and then tended to plateau, so that 120 minutes could be considered the optimum time. The data on MO concentration decrease over time were analyzed using first-order and second-order pseudo-kinetic models, where the second-order pseudo-kinetic model showed the best R²value of 0.804, indicating the important role of surface processes and chemical adsorption on the active sites of the CuO–clay composite in controlling the photodegradation rate.