Synthesis and Structural properties of Zinc Oxide Nano Particles (ZnO NPs): A Review

ZnO (Zinc Oxide) is generally recognized as safe (GRAS) material by FDA (Food and Drug Administration, USA) that is why it is used as food additive and in various medicine. The FESEM (Field Emission Scanning Electron Microscopy) of hydrothermally synthesize ZnO NPs showed that ZnO NPs are spherical in shape with a diameter of 20-30 nanometer. The XRD (X-rays Diffractometery) and TEM (Tunneling Electron Microscopy) studies of ZnO nanopowder synthesized by ultrasonic Spray pyrolysis (USP) technique showed that the crystalline size increased with an increase in the pyrolysis temperature and also exhibit direct band gap in the range 3.37 ? 3.40 eV. Also the band energy gap of bulk ZnO crystals was approximately 3.3 eV. The SEM (Scanning Electron Microscopy) micrographs of ZnO NPS prepared by chemical method using PVP (Polyvinyl Pyrolidine) as capping agent showed spherical shape of nanoparticles, having band gap energy of 3.4 ev and these nanoparticles also showed lattice contraction due to high electrostatic interaction between Zn2+ and O2- ions. ZnO is an important member of semiconducting material of II-VI group. Due to unique properties, ZnO is the richest family of nano structures among all semiconducting materials and thus used in the number of application like gas sensor, varistors and low voltage phosphor. ZnO is only semiconductor material extensively investigated after Si/Ge. Also nano cluster of ZnO, which exists as nanoparticles, nanobelts, nanorods, nanotubes, nanowires, nanoflowers as well as colloid and bulk nanoparticles also have shown potential/excellent luminescence properties.