Photocatalytic degradation of dyes in water by analytical reagent grades ZnO, TiO₂ and SnO₂: a comparative study

Abstract. In this study, we evaluated the photocatalytic activities of analytical reagent (AR) grade ZnO, TiO₂, and SnO₂ to identify a low-cost photocatalyst for dye degradation. The obtained samples of ZnO, TiO₂, and SnO₂ were characterised by X-ray diffractogram (XRD), scanning electron microscope imaging, and UV-VIS diffuse reflectance spectroscopy. The decolourisation of three structurally diverse dyes, namely crystal violet, basic blue, and methyl red under solar irradiation, was used to evaluate the photocatalytic activities of three metal oxides. The photocatalytic activities of the received three metal oxides were tested with the photocatalytic degradation of dyes and compared with Degussa P-25. Dye solutions with each metal oxide at initial pH 9 were subjected to irradiation under sunlight and monitored for up to the stage of complete decolourisation. The results indicate that ZnO exhibited the highest photocatalytic activity as compared to TiO₂ and SnO₂ as well as that of Degussa P-25 (TiO₂). The photocatalytic dye decolourisation rates with ZnO were 1.14–1.35, 1.70–3.1, and 4–8.5 times higher than those of the Degussa P-25, TiO₂, and SnO₂, respectively. The percentage COD removal was studied for ZnO and partial removal was observed at the decolourisation stage. To enhance photocatalytic activity of AR grade ZnO, it was loaded with Ag metal and about 20 % enhancement in the activity was observed.