ZnO nanostructured photocatalysts for water treatment applications

Metal oxide semiconductor materials, designed to be applied in photocatalytic systems for water purification, are required to have large specific surface areas, because chemical reactions induced by suitable irradiation take place by contact between their surface and fluid. Zinc oxide is well known as a material that forms various morphologies at the micro- and nanoscale, which can easily fulfill this requirement in the case of ultraviolet irradiation. However, some nanoscaled morphologies can also provide zinc oxide catalysts that are functional in the sunlight. Photocatalytic degradation of an organic dye, as a model pollutant, was studied in aqueous solutions using structures of zinc oxide synthesized in the form of prism, spiky stick and grass blade. They were grown from a solution and their entire morphology was simply controlled by varying the growth conditions. Detailed characterization of their structure and porosity on the micro- and nanoscale was performed by scanning electron microscope and X-ray diffraction and scattering measurements. All structures exhibited notable photocatalytic activities. However, remarkable results were achieved with nanostructures in the form of grass blade, which exhibited enhanced photocatalytic activity in sunlike light. This was ascribed to their specific morphology characterized with defects and a high degree of mesoporosity.