Synthesis And Characterization Of Nanometer ZnO

Nanometer Zinc oxide (ZnO) is currently a functional inorganic material withan extensive applied foreground. Nanometer ZnO have many special mechanical,optical, electrical, magnetic, calorifics and chemical properties which differ from thecorresponding bulk material due to their size effect, surface effect and quantum effect,thereby making them attractive for many new applications in industry as well ashigh-tech fields. Preparation of the nanometer ZnO plays a key role in nanometer ZnOresearch. Various methods have been used for the preparation of nanometer ZnO.However, many intriguing questions require answer even now. It is important toexplore novel methods for synthesis of nanometer ZnO with controllable size andshape and to understand the mechanism and rule of the growth process of nanometerZnO for further applications.This thesis is based on the domestic and the foreign references about thepreparation of nanometer ZnO. The object is to focus on the industrial production. Anew process of direct precipitation approach was established to synthesize ZnOnanopowders and ZnO nanorods.On the basis of the systemic research on the mechanism of the preparation ofnanometer particle by direct precipitation, a new process which can be easilyindustrialized was provided. The evenness and relative over-saturated solution of theconcentration of reaction solution was sustained by a droping way which can controlthe flow rate of the reaction. The pH value of reaction solution was maintained byproperly using amortize solution system;proper dispersant and protection reagent wasappended and proper washing way was selected to eliminate or inhibit theagglomerate particles so as to make the product prepared by direct precipitation asgood as that prepared by homogeneous precipitation method.The effect of various factors has been investigated. It is can be conclude that theappropriate process is: the droping way which can control the flow rate of the reaction,the concentration of Zn2+ is 1.70mol/L, the ratio of OH-/ Zn2+ is 1.75, reaction time in30min, the pH value of reaction solution is maintained in 8~10, mulriple surfactant,product is washed by lye and anhydrous ethanol, the temperature of baking is300~400℃ and the time of baking in 60min.The product was characterized by XRD, BET, TEM and TG-DTA. The resultsshow that the product with single crystal type can be prepared by direct precipitationapproach in this research. The purity of product is high. Most of the particle are inball-shape, only is in club-shape. The distribution of particles are even, thedispersibility is excellent, the average particle size is less than 25nm and the specificsurface area of ZnO is more than 70.4781m2/g.The synthesis of 1D ZnO nanomaterials has been a research focus now. Variousof reports had brought forward all kinds of methods to synthesize 1D ZnOnanomaterials. However, these methods are unfavorable to produce large numbers ofZnO nanorods rapidly and at low cost. The reasons are that the catalytic methodbrings impurities into the desired products, which probably influence the purity ofZnO nanoparticles and hence their electrical and light emission properties. The othermethods involve the use of the high temperature, vacuum, inert atmosphere andautoclave, which will increase high-energy consumption and the cost. To overcomethese problems, we report a novel and simple approach to synthesis of ZnO nanorodsusing a direct precipitation method in this paper. This method is simple, convenient,with low cost and can make perfect ZnO nanorods.In the studies, we found that ultrasonic was an important qualification. At onetime, with the increase of the mole ratio of OH-/ Zn2+, the ZnO phase is easy to form,and the crystal modality becomes gradually integrity. The crystal growth direction isc-axis. The surfactant PEG-400 has important stimulative effect in the growth of ZnOnanorods.The products were characterized by XRD, FT-IR, TEM, HRTEM and SAED, theresults show that the products belong to a kind as the hexagonal structure of bulk ZnOand no impurity was found. ZnO nanorods were straight and their surfaces wererelatively smooth with diameters ranging from 20 to 40nm, and lengths ranging from300 to 800nm. The sizes of ZnO nanorods are consistent with the result of XRD.Perfect ZnO nanopowders and ZnO nanorods were synthesized by directprecipitation method. The results show that direct precipitation method is an effectiveway to synthesize nanometer ZnO. Especially, the preparation of ZnO nanorods canreduce the manufacture cost and the demand for equipment, because the products canbe obtained without high temperature. In this paper, we only discussed simply thegrowth mechanism of ZnO crystal and the form mechanism of ZnO nanorods. So thedeeper research is needed in the future.