Photocatalytic activity of kaolin–titania composites to degrade methylene blue under UV light irradiation; kinetics, mechanism and thermodynamics

In the present study, the photocatalytic activity of kaolin-anatase titania nanoparticles (KT) composites in the degradation of methylene blue (MB) under UV light irradiation was investigated. The composites were synthesized by the incipient wetness impregnation method, and the incorporation of titania nanoparticles (TiO₂ NPs) is expected to enhance the photocatalytic activity of kaolin, a cost-effective and abundant clay mineral in nature. The formations of KT composites were confirmed by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The photodegradation of MB in the presence of KT composites was systematically evaluated at different irradiation times, catalyst dosages, dye concentrations, and temperatures. The photodegradation of the synthetic dye was found to be pseudo-first order according to the Langmuir–Hinshelwood kinetics model. The photocatalytic activity of KT composites was indicated by the higher degradation efficiency of MB compared to its photolysis and adsorptive removal. It was further revealed that the photocatalysis degradation efficiency was increased with TiO₂ NPs loading content. It is conceivable that the incorporation of TiO₂ NPs in KT composites reduced the potential barrier of the photocatalytic degradation of MB due to the accelerated generation of OH^⋅ radical on the KT composite surface. The photocatalytic activity can be optimized by adjusting the ratio of the KT composites dosage and the initial MB concentration. Overall, the results indicated that although the kaolin showed very low photocatalytic activity, it can be enhanced when it turned into KT composites while the catalysts are still economically cost-effective.