Abstract
M.Sc. (Chemistry)
Improper treatment of wastewater from industries before disposal poses severe environmental and health hazards to the surrounding communities. Several treatment techniques have been developed and applied in making sure that these wastewaters are properly treated before being discharged into the environment. Photocatalysis is the most promising of all the techniques that have been employed. This is because its operation is simple and involves the use of readily available semiconductors and sunlight. However, the disadvantage of using these semiconductors as photocatalysts for photocatalytic degradation of organic pollutants are among others their wide band gap and the rate at which photogenerated electrons and holes recombine. These demerits make it difficult for the photocatalytic activities of these semiconductors to be extended into the more abundant visible light region of the solar spectrum.
This research work focused on the synthesis of visible light active ZnO photocatalyst through its modification with nitrogen and graphene oxide followed by its application towards the degradation of Brilliant green (BG) dye. The GO and ZnO were synthesized using Hummers and co-precipitation methods respectively while N-ZnO and NZnO-GO composites were synthesized using solvent free method. The characterization of the synthesized photocatalysts was done using optical approaches such as X-Ray Diffraction (XRD), Fourier Transform Infra-red (FTIR), Transmission Electron Microscopy (TEM) and UV–Vis Absorption and Diffuse Reflectance Spectra (UV-Vis DRS). ZnO modified with nitrogen and graphene oxide (N-ZnO-GO) having different weight percentages of GO (0.1% wt-GO, 0.5% wt-GO, and 1% wt-GO) showed a higher photocatalytic activity in degrading BG dye in water compared to the bare ZnO and nitrogen-doped ZnO (N-ZnO) nanoparticles. The composite with 0.1% wt GO achieved 100% degradation and 80% mineralization of BG within 90 mins of irradiation. The results also showed that the degradation of BG using 0.1% wt-GO occurred faster in basic medium (pH 9) compared to acidic medium. Photostability test of 0.1% wt-GO analyzed after three cycles of exposure gave 94% degradation of BG which implied that the composite is also highly stable and can be recovered and reused. The results obtained highlighted that the modifications made on ZnO increased its light absorption capability into the visible region and thus drastically improved its photocatalytic activity under visible light...