| ZnO is one of the gas sensitive materials which have high research value for its low cost, simple synthesis, stable property and rich morphology. However its practical application has been mainly restricted by poor selectivity, long recovery time and so on. This article aims at improving the gas sensitivity of ZnO, through hydrothermal process, preparing testing samples that contain different morphology, recombination of rare earth elements and mass ratio. After testing these samples, study the influences that different ZnO materials have on the sensitivity of different gases, test the microstructure by XRD and analyze the microstructure by SEM. With all these data to provide potential practical materials and the results are as followed:ZnO is made through zinc nitrate as predecessor under different hydrothermal temperature, the sensitivity of pure ZnO powder with flower structure under80℃to trimethylamine is the best. The best working temperature was340℃, trimethylamine at a lower volume fraction φ (TMA)=5×10-6, has the gas sensitivity of8.67. Preliminary finding is the larger specific surface area and good oxygen storage capacity in ZnO powder with flower structure is the main reason of high sensitivity and good selectivity. Also, good stability and fairly short response-recover of ZnO powder with flower structure has provided the basis to make trimethylamine sensor with no additives or doping (recombination).Among the samples made through different predecessors and under different hydrothermal temperature, ZnO through zinc acetate as predecessor under80℃is sheet structure, and its gas sensitivity is perfect to ethyl alcohol. Complex different rare earth oxide to modify properties and the three oxides improve the gas sensitivity of ethyl alcohol in various degrees. ZnO with compound quality of3.0%Er2O3is obviously better than the mixture of Y2O3and Sm2O3. Complex Er2O3has an effect on ZnO with sheet structure to enlarge specific surface area and contact interface. It also nearly doubles the gas sensitivity of ethyl alcohol and improves the selectivity of ethyl alcohol gas effectively. Er2O3reduces the reaction activation energy between ethyl alcohol gas and oxygen adopted on material surface, which lowers the best working temperature by70℃. As the catalyst, it provides a rich activation. It is beneficial to the adsorption and stripping of ethyl alcohol gas on ZnO surface. Response and recovery time are shortened7s and16s respectively. Composite Er2O3can improve the gas sensitivity of ZnO with sheet structure to ethyl alcohol.ZnO powder mixed with rare earth oxide and claviform ZnO powder are made through zinc nitrate as predecessor under water temperature at180℃. Sm2O3-ZnO sample has a very high sensitivity and good selectivity to formaldehyde, which shows complex Sm2O3is beneficial to improvement of formaldehyde sensor through claviform ZnO. The sensitivity of Sm2O3-ZnO sample with3.0%compound quality under the temperature of260℃by dimethylamine is obviously higher than that of trimethylamine. This sample can act as the material which differs dimethylamine gas sensor from trimethylamine one. The sensitivity of Sm2O3-ZnO sample with7.0%of propanone on gas sensitivity under400℃shows its perfect gas sensitivity, which benefits from complex Sm2O3, claviform structure, big specific surface area, rich defects, high active O2and Sm2O3with catalytic properties and oxygen storage capacity. The performance can be superb sensitivity (Sensitivity can be639.89at the volume fraction of1000×10-6), fast response-recovery time (3s and4s) and excellent selectivity, which can be ideal material to make practical propanone sensor. |
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