Nano-sized ZnO particles were synthesized by a direct precipitation, a sol-gel, and a hydrothermal method. The structures, morphology, and optical properties of these ZnO nanoparticles fabricated by the above-mentioned methods were also characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Ultraviolet-visible spectroscopy (UV-vis). In addition, the photocatalytic activities of the synthesized ZnO nanoparticles were evaluated via the degradation of methyl orange (MO) in an aqueous solution. These experimental results demonstrated that the photodegradation efficiency of MO solutions irradiated by UV for 120 minutes with ZnO nano-particles used as catalysts, which were fabricated by a direct precipitation method could reach 94.59% or so. The higher photocatalytic activity of methyl orange solutions by the ZnO nanoparticles synthesized by the direct precipitation method is probably ascribed to the spherical ZnO nanoparticles with a smaller crystalline size.

Keywords: nanoparticles, Photocatalytic degradtion, Methyl orange.