Template free large scale synthesis of multi-shaped ZnO nanostructures for optical, photocatalytical and antibacterial properties

In this article, ZnO nanostructures with diverse morphologies have been synthesized via a simple, rapid and cost effective solid state thermal decomposition method. The as-synthesized ZnO nanostructures were characterized by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy, scanning electron microscope (SEM), high-resolution transmission electron microscope (HR-TEM), UV–Vis. diffuse reflectance spectra (UV–Vis-DRS) and photoluminescence (PL). The XRD patterns and HR-TEM image indicated a hexagonal wurtzite structure of ZnO. The SEM images of ZnO samples show the different morphologies such as nanowire, nanorods, spherical and irregular microsphere at different calcination temperatures. Room temperature PL spectra of the samples exhibited characteristics blue and green emission bands in accordance with calcination temperature. Moreover, photocatalytic as well as antimicrobial activities were evaluated using ZnO synthesized at different calcination temperatures. The effects of calcination temperature, catalyst loading and pH on the photodegradation efficiency were systematically studied. A highest (99 %) photocatalytic activity of ZnO nanorods towards the Acid Green 25 (AG-25) was achieved within 35 min at optimal conditions under UV light. As-synthesized ZnO nanorods are found to be more efficient than TiO 2 (P25) towards the degradation of AG-25. It was found that the antimicrobial activity of ZnO nanorods (13 mm) obtained at 300 °C showed significantly higher inhibition efficiencies than the other samples. The mineralization of AG-25 was confirmed from a reduction of 85 % the chemical oxygen demand within 35 min. In addition, ZnO nanorods could be easily reusable up to four runs without changing its photocatalytic activity.