Azadeh Madadi - Department of Marine Science and Technology, Islamic Azad University, North Tehran Branch
Shahram Moradi - Faculty of Chemistry, Islamic Azad University, North Tehran Branch.

ZnO nanostructures are very premising because of the wide band gap(3.37 e.V) and large free excition binding energy(60 meV) which exhibit a wide range of applications including field emission displays, nano-photonic devices, piezoelectric transducer, varistors, phosphors, and transparent conducting films[1-3]. Different synthesis methods have been devised, including sol-gel technique[4,5] microemulsion synthesis[6], mechanochemicals processing [7], spray pyrolysis and drying[8,9], thermal decomposition of organic precursor[10], RF plasma synthesis[11], supercritical-water processing[12], self-assembling[13], hydrothermal processing[14,15], vapor transport process[16], sonochemical or microwave–assisted synthesis[17,18], direct precipitation[19] and homogeneous precipitation[20,21].In the nanometric domain, it has been demonstrated that physical and chemical properties are usually closely related to the shape and size of the nonomaterial. Up to now, intense interests have been devoted to synthesizing ZnO with various morphologies such as nanorods [22], nanotetrapods [23] nanofloweres [24] nanorings [25] nanobelts [26] and so on. In recent years, intensive research has been focused on fabricating anisotropic nanocrystals owing to their unique properties [27]. Although many kind of anisotropic ZnO nanocrystals have been synthesized, most of them are limited to nanorod [22, 28] or nanowire [29] shapes. The Hyeon group [30] has reported synthesis so anisotropic hexagonal pyramid-shaped ZnO nanocrystals by the thermolysis of Zn-Oleate complex. Tang et al reported a method for synthesis of hexagonal cone-shaped ZnO nanoparticles [31]. Wang and co-workers obtained [32] starlike nanocrystals in mixed solvent of ethanol and ethylene glycol, but in the same reaction by other homologous alcohol (EGC and 2-propanol) it is surprising that we obtained the hexagonal shaped ZnO nanocrystals.