Study On The Green Preparetion And Performance Of ZnO

ZnO is an important semiconductor functional material. Due to its wide direct band gap, highexciton binding energy, excellent chemical/thermal stability and nontoxic, ZnO has been used as a usefulcandidate for various applications such as light emitting diode, field-effect transistors, solar cells, gassensors, photocatalysis, and so on. While recent research has reported that these applications are stronglyinfluenced by the microstructures of ZnO, such as crystal size, orientation and morphology, specific surfaceand crystalline density. Especially, the morphology greatly affects the properties of ZnO. Therefore, thedesign and tailor of ZnO nanomaterials with different morphologies and structures are very important inview of both basic fundamental research and the development of novel devices.In this paper, different morphologies of ZnO micro-nanostructures were successfully prepared bygreen hydrothermal method and dissolution-pyrolysis method. The effect of preparation conditions on theZnO structure and morphology were investigated, including reactant ratio, the pH of the solution,hydrothermal time. The photocatalytic and gas-sensing properties of the different morphologies of ZnOsamples were evaluated. At the same time, the modified methods were also investigated to improve thevisible light catalytic properties of ZnO.(1) Disk-like, hamburg-like, nanosheets composed flower-like and nanorods composedflower-like ZnO with good crystalline were successfully synthesized via a one-pot hydrothermal methodused zinc nitrate hexahydrate, trisodium citrate citric acid and sodium hydroxide as raw material.In uencing factors on the controllable morphology of ZnO architectures were discussed, including themole ratio of zinc nitrate hexahydrate/trisodium citrate citric acid, the pH of the solution and differenthydrothermal treatment time and the possible formation mechanism of different morphologies of ZnOarchitectures were proposed based on the experiment results.(2) The photocatalytic properties of the different morphologies of ZnO samples were studied.The test of photocatalytic properties of different morphologies of the pure ZnO samples under UVirradiation indicated that ZnO samples prepared on10h possessed superior photocatalytic activity to ZnOsamples prepared on8h, and the flower-like ZnO composed of nanosheets prepared on10h showed the best photocatalytic activity. After UV irradiation for20min, the degradation ratios of KGL could reach100%for this flower-like ZnO microstructures. It might be attributed to the morphologies, BET, band gap,defect concentration, surface polarity. At the same time, in order to improve the visible light photocatalyticef ciency of the ZnO, doping is employed to enhanced visible light photocatalytic activity. The test ofphotocatalytic properties of doping ZnO samples under visible light irradiation indicated that Fe-dopedenhanced visible light photocatalytic activity to a certain extent, but it could directly lead to the flower-likeZnO architectures disappear, the optimum ratio was7%. And La doping could not improve the visible lightphotocatalytic activity, and had a certain influence on the flower-like ZnO architectures with the La dopingcontents increased.(3) The gas-sensing properties of the different morphologies of ZnO samples were evaluated viathe static volumetric method. The results showed that nanorods composed flower-like ZnO gas sensorpossessed superior sensitivity (863.2) to the other ZnO microstructures to100ppm Cl2, at290℃.Moreover, the sensor shows good selectivity to other tested gas and quick response and recovery behavior,the response and recovery time was8s and4s, respectively. At the same time, the gas-sensing propertiesof nanorods composed flower-like ZnO to Cl2remained almost unchanged by45days of stability test,indicating that it had good stability.(4) The wurtzite-structure ZnO with the diameter about24nm was prepared bydissolution-pyrolysis method using oxalic acid and Zn as raw materials. The ZnO sensor has remarkablesensitivity to NO2, at290℃, the sensitivity is90.6to100ppm NO2, even to100ppm, the sensor also hascertain sensitivity to NO2. The ZnO sensor has good selectivity to NO2and has quick response and recovertimes to NO2. The response time is4s, recovery time is20s.