Study of Photocatalytic Degradation of Methyl Orange on Different Morphologies of ZnO Catalysts

In this study, several ZnO catalysts were prepared using different zinc sources as precursors. The different catalyst morphologies obtained were used to degrade photocatalytically a methyl orange (MO) dye solution, which was used to model wastewater pollution. The precursors, Zn(CH3COO)2, ZnCl2 and Zn(NO3)2, were individually added to a solution containing cetyltrimethylammonium bromide (CTAB) and sodium hydroxide (NaOH) for the hydrothermal synthesis of ZnO. After the hydrothermal reaction, the samples of ZnO were filtered, washed, dried at 110 ̊C and calcined at 550 ̊C, resulting in the formation of the rod-like (designated ZnO(I)), the rice-like (designated ZnO(II)) and the granular-like (designated ZnO(III)) catalysts. The catalysts were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM) and their UV-visible diffuse reflectance spectra (UV-Vis DRS). The results indicate that the photocatalytic degradation of the MO solution, after 60 min of UV irradiation, can reach percentages of 40%, 96% and 99% using the catalysts ZnO(I), ZnO(II) and ZnO(III), respectively. The morphology of the ZnO catalyst had an apparent effect on the rate of the photocatalytic degradation of MO. The ZnO(II) and ZnO(III) catalysts have higher S/V ratios and a greater content of oxygen vacancies, resulting in different absorbances of ultraviolet light, which leads to different rates of photocatalytic degradation of MO.