Photocatalytic degradation of Rhodamine B using nanocrystalline TiO2–zeolite surface composite catalysts: effects of photocatalytic condition on degradation efficiency

Abstract

Nanocrystalline TiO₂–zeolite surface (TZS) composites were prepared by a novel technique, i.e., sol–gel method with the assistance of supercritical pretreatment. The samples were characterized by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscopy (SEM) and BET surface area analysis. The behavior of TZS in the catalytic degradation of Rhodamine B (RhB) dye under UV-light was examined as a function of the pH values in solution, light intensity, irradiation time, TiO₂ coating ratio of TZS and its concentration in solution, and initial RhB concentration. The kinetics of photocatalytic RhB degradation was found to follow a pseudo-first-order rate law. It was observed that the presence of the zeolites enhanced the photoefficiency of the titanium dioxide due to synergistic effects of the improved adsorption of RhB with efficient delocalisation of photogenerated electrons and TiO₂ photocatalysis. Furthermore, the photocatalytic activity of TiO₂ was further enhanced by a zeolite support pretreated in supercritical CO₂. It is mainly attributed to the fact that TZS has high surface area in comparison with TiO₂–zeolite (TZ) composites prepared by the sol–gel method only. The optimal conditions were a concentration of 2 mg L⁻¹ at pH 10 with 32 mW cm⁻² of illumination and a catalyst content of 6 g L⁻¹ for the fastest rate of RhB photocatalytic degradation.