Dyes are the main textile pollutant present in natural water bodies that pose a severe threat to human beings and other living organisms. To overcome dye wastewater pollution, Advanced Oxidation Process (AOP) especially UV photodegradation has been explored as a better alternative method over conventional treatment methods. However, UV photodegradation poses some shortcomings which impede its practical application. Among the photocatalysts, TiO2 is widely used due to its better photocatalytic properties. However, TiO2 requires some surface modifications and developments to improve its photocatalytic activity. To deal with it, the effectiveness of 85%TiO2-ZnO/BAC1 (51:9:40) composite was investigated and evaluated as a novel photocatalyst for colour removal and Chemical Oxygen Demand (COD) reduction from aqueous solution under UV irradiation. The dyes used as a model pollutant in this study are methylene blue (MB), malachite green (MG), and rhodamine (R6G). To enhance the photocatalytic activity, the TiO2 surface was modified with ZnO and subsequently supported on banana peel activated carbon (BAC1), forming a composite referred to as 85%TiO2-ZnO/BAC1. TiO2 physicochemical properties before and after surface modification were characterized by X-ray diffractometer (XRD), Fourier transform infrared (FTIR), Scanning electron microscopy (SEM), Photoluminescence (PL), Thermal gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) and Laser diffraction technique. The catalysts performance and optimization of the operation conditions on colour removal and COD reduction of the dyes were determined in Lab-scale stirred tank reactor (STR) system under UV irradiation. From the study, 85%TiO2-ZnO/BAC1 has demonstrated its potential as a promising photocatalyst for dye removal. It showed a higher colour removal of 95.7% compared to TiO2, ZnO and 85%TiO2-ZnO having 46.3%, 30.9%, and 55.5%, respectively under 50 mg/L initial dye concentration, 1.3 g/L photocatalyst loading, and 160 min UV irradiation conditions. The study revealed that UV photodegradation is more effective for colour removal of the dyes (MB, MG, and R6G) as compared to COD reduction, with about 95% and 70% reductions, respectively. The colour removal of R6G was still as high as 90% after four recycling runs, confirming the good stability and reusability of 85%TiO2-ZnO/BAC1 composite. The photocatalytic mechanism of 85%TiO2-ZnO/BAC1 has been proposed, as a hole (h+) and superoxide (O2●) radicals as primarily the main active species responsible for the degradation of R6G UV irradiation. Therefore, oxygen in the air used as a fluidizing medium is essential since it can trap electrons and consequently enhance O2●- formation and generation of h+. The goal of this work was also to examine the applicability of 85%TiO2-ZnO/BAC1 composite on the degradation of R6G dye in a fluidized bed reactor (FBR) system under UV irradiation. A preliminary hydrodynamic experiment was first conducted before the photodegradation experiment in the FBR system. From hydrodynamic experiments, the 90° inclination angle (reactor vertical position) resulted in a good gas holdup (𝜀𝑔), but poor particle distribution compared to 80°, 70°, 60°, and 50° inclination angles. Although the 70° inclination angle at superficial gas velocity (Ug) of 0.02405 ms-1 showed a lower 𝜀𝑔 of 0.1597 compared to 90° and 80° with 0.2132 and 0.1791 respectively, it had good particle distribution and average 𝜀𝑔. At 70° inclination angle and Ug of 0.02405 ms-1 were found to be the optimum hydrodynamic conditions. However, photodegradation experiments, revealed that the optimum hydrodynamic conditions are at 0.01923 ms-1 superficial gas velocity and 70° inclination angle of the reactor. From the study, it can be concluded that 85%TiO2-ZnO/BAC1 composite shows great potential as a solution to textile dye wastewater treatment and environmental remediation. Moreover, this work may provide a reference for hydrodynamic conditions governing the photodegradation process for environmental mediation and economic concern.

Thesis (MEng of Engineering in Chemical Engineering--Botswana International University of Science and Technology, 2022