The Preparation Of Zno-Based Nanomaterials And Its Gas-Sensing Properties

ZnO is one of the most inportant semiconduct meterials. At room temperature, the band gap of ZnO is 3.37 eV, which makes it very suitable for a wide applications especially in gas sensors. In previous studies, gas sensors based on ZnO nanomaterials have obtained good results in the aspect of poisonous and harmful gas analysis. The gas-sensing properties have significant difference when the structures of ZnO nanomaterials are different. Besides the affect of ZnO structures, the addition of noble metals can also increase the gas sensing properties of ZnO nanomaterials. The improvement of gas sensing property attribute not noly the catalysis of noble metals but also the synergistic reaction of guest-host. This thesis synthesis two class of ZnO nanometerials though hydrothemal method. One is ZnO nanosheets, and the other is Au@ZnO yolk-shell nanopaticals. This thesis was focused on the improvement of gas-sensing properties of ZnO nanomaterials and investigated the influences of structures, morphology and noble metals catalyst on gas sensors.1. The layered basic zinc chloride (Zn5(OH)gCl2·H2O) precursor has been prepared by the reaction of ZnCl2 and ammonia through a simple hydrothermal method. Two kinds of ZnO materials with different morphologies were obtained by calcining the precursor at high temperature (400? and 500?) in the air. The products were characterized by XRD, SEM, TEM, FTIR and XPS. The thickness of ZnO nanosheets calcined at 400? is about 25 nm, marked as Zn04oo. ZnO nanodisk formed at 500?, resulting from the destruction of layered structure and reunion of nanoparticles, marked as ZnO500.It is found that Zn04oo with high chemical adsorbed oxygen content, exposed high polar facets and narrow band gap, showed higher gas sensing performance. Compared with the response(-37) of ZnO500, ZnO400 exhibited higher response(-37). What's more, Zn04oo showed high selectivity to ethanol and short response/recovery time (17 s/6 s). The test results indicated that ZnO nanosheet (ZnO400) is a promising sensor material.2. Au@MOF-5 core-shell nanoparticles were successfully synthesized. Three samples can be obtained by controlling the calcination conditions of Au@MOF-5 precursor. At the same time, ZnO hollow nanoparticles also were prepared by using the MOF-5 template. The morphological and structural properties of the samples were characterized by XRD, SEM, TEM, TGA, XPS and UV-vis DRS. The sample obtained at 350? has perfect yolk-shell structure with the ZnO shell of ?70 nm in thickness and the Au core of ?47 nm in size, marked as S350. And S350 sensor exhibits the most optimal gas-sensing property to acetone gas-sensing test. The S350 sensor showed high response (43 to 10 ppm acetone), low detection concentration of 50 ppb, excellent selectivity to 10 ppm acetone), low detection concentration of 50 ppb, excellent selectivity and short response/recovery time (15 s/12 s).