Synthesis And Properties Research Of SnO₂@ZnO Hierarchical Nanostructures

With the development of the social economy,detection based on the gas sensor is of ongoing importance in the field of detection of poisonous and harmful gas.However,the application of reported resistance type gas sensor with semiconductor metal oxide is impeded by the poor gas selectivity and low response in the low concentration?at parts per billion?ppb?levels?.Thus,it is important to develop the gas sensor with high selectivity and response for detection of trace level chemical regents.In this thesis,the SnO₂@ZnO hierarchical nanostructure?HNSs?have been synthesized via traditional electric heating hydrothermal?TEHH?and microwave-assistant hydrothermal?MWAH?method for the first time.The SnO₂@ZnO HNSs shows the outstanding high selectivity of nitrogen dioxide?NO₂?gas and an extraordinary response for ppb level NO₂.The main results and discussion include:The SnO₂@ZnO HNSs have been synthesized via TEHH and MWAH method.First,ZnO nanoflowers?NFs?have been synthesized as the primary structure.Then,the secondary struc-ture of SnO₂ nanowires?NWs?have been grown on the surface of ZnO NFs forming the SnO₂@ZnO HNSs.The grown models of SnO₂@ZnO HNSs have been established based on the morphology,structure,composition and chemical bond characterization analysis.The re-sults indicated that the ZnO is almost undecomposed in the whole MWAH synthesis process and the flower morphology can be remained.Thus,the SnO₂ can be epitaxial grown on the surface of ZnO NFs to form the SnO₂@ZnO HNSs.Compared with the TEHH method,the MWAH method can maintain the morphology of added ZnO and obtain the smaller size SnO₂NWs.Meanwhile,the fast synthesis process can lead to more defects in the materials,which are beneficial for enhancement of the sensor performance.The sensor performance study indicated that the SnO₂@ZnO HNSs shows the excellent NO₂sensor performance.Based on the TEHH method,the SnO₂@ZnO HNSs shows the wide de-tection range from 5 ppb to 10 ppm NO₂,with the low detection limit of 5 ppb at 150?.The sensor response is 105.0 and the response?recovery?time is 50 s?55 s?under 10 ppm NO₂.While based on the MWAH method,the SnO₂@ZnO HNSs shows the wide detection range from 2 ppb to 10 ppm NO₂,with the low detection limit of 2 ppb at 300?.The sensor response is 52.3 and the response?recovery?time is 16 s?10 s?under 10 ppm NO₂.Compared with the TEHH method,the materials exhibited faster response recovery speed via MWAH method.The suitable synthesis parameters range for synthesis of SnO₂@ZnO HNSs by MWAH has been filtrated by single factor experiment.Then,the sensor response has been optimized by the orthogonal experiment.The optimized synthesis for SnO₂@ZnO HNSs are:Reaction time?t=45 min?,Reaction temperature?T=200??,Sn/Zn ratio?[Sn]/[Zn]=6/1?,Alkali salt ratio?[OH]/[Sn]=9/1?.Under this synthesis condition,the sensor response is 5.5,while the response?recovery?time is 100 s?92 s?at 1000 ppb NO₂.The Fe,W,Sb doping SnO₂@ZnO HNSs experiment has been carried out and the corresponding sensor performance has been tested at 100 ppb to 1000 ppb NO₂.The results indicated that Fe doping can improve the sensor response and recovery time of SnO₂@ZnO HNSs effectively,while the sensor response of SnO₂@ZnO HNSs is reduced with the increase of Fe doping concentration.The sensor response of W doping can enhance the sensor response of SnO₂@ZnO HNSs,while the response and recovery time hardly changed with the increase of W doping concentration.The Sb doping can greatly enhance the sensor response of SnO₂@ZnO HNSs.The sensor response time is reduced while the recovery time is increased with the increase of Sb doping concentration.All the results indicated that 7%Sb doping is the suitable doping concentration for the high sensor response,low response and recovery time.Finally,the SnO₂@ZnO HNSs have been used in photocatalysis and radar and infrared compatible stealth area.The results indicated that the SnO₂@ZnO HNSs shows the enhanced photocatalytic performance under visible light and enhanced radar and infrared compatible stealth properties.For the photocatalysis performance,the SnO₂@ZnO HNSs by TEHH method is excellent comparable to that of primary ZnO and SnO₂.The defects in ZnO are the main reason for the photocatalysis under visible light irradiation.The heterojunction of ZnO and SnO₂ can promote the separation of photo-generated electron and hole,which plays the key role in the enhanced photocatalytic performance of SnO₂@ZnO HNSs.In the radar and infrared compatible stealth area,the collaborative effect of the large specific surface area,interfacial polarization and complex conductive network in the space leads to enhanced radar and infrared compatible stealth properties.