Gas And Humidity Sensing Properties Of Sensors Based On ZnO

Since the year of1962, when the conductance of ZnO was found to change withthe appearance of ethanol, study on ZnO gas and humidity sensor has come to be thehot topic. With the development of nanotechnology and production, preparation ofZnO sensing materials has become perfect, and most of the attentions have beenfocused on how to improve the sensing properties. In this paper, we studied the gasand humidity sensing properties of sensors based on ZnO. The effect of morphologyand structure, dopping, materials composite, and modifying on the sensing propertieswas investigated. The main conclueds were as follows:1. Studies on preparation and gas sensing properties of porous flake ZnO spheresWe prepared ZnO spheres composed of porous flake by hydrothermal methodcombined with heat treatment, and their morphology and structure were characterized.Resistance-type gas sensor based on porous flake ZnO spheres was prepared and itsethanol gas sensing property was studied. It is found the sensor desmontrated obviousresponse to2ppm ethanol with the corresponding response of2.8at the optimumoperation temperature of280oC, and the response and recovery time of10and15s.The sensor showed good linearity with the concentration of ethanol in the range of2~500ppm. The sensos based on porous ZnO spheres showed improved ethanolresponse on working temperature and sensitivity compared to that based oncomemerical ZnO powders.2. Studies on preparation and gas sensing properties of Zn-doped SnO2poroushollow microspheres.Zn-doped SnO2porous hollow microspheres have been prepared by a directprecipitation methoed combined with heat treatment, using colloidal carbon sphere astemplate, and their morphology and structure were characterized. Resistance-type gassensor based on Zn-doped SnO2porous hollow microspheres was prepared and itsethanol gas sensing property was studied. It is found the sensor has a good selectivityto ethanol at the optimum working temperature of240oC. The response of the sensor to ethanol with the concentration of2,5,10,50,100,200,300and500ppm was2.8,4.6,16,27.4,48.8,71.9and100, respectively. The response and recovery time was29and16s, respectively. Compared to the single ZnO and SnO2with the samenanostructure, Zn-doped SnO2porous hollow microspheres sensor exhibitedimproved ethanol gas sensing properties on sensitivity and stability.3. Studies on preparation and gas sensing properties of Zn2SnO4nanostructure.Ternary material Zn2SnO4were prepared by hydrothermal method combinedwith heat treat, and their morphology and structure were characterized. It is found wecan regulate the morphology and preferential orientation of Zn2SnO4by the pH value.The morphology of Zn2SnO4nanostructure changed from single nanoparticles to bothnanoparticles and nanorods, the preferential orientation varied from (311) to (311),and the special surface area increased when the pH value of the solution changedfrom9to13. Zn2SnO4sensor prepared at the pH of13exhibited the best gas sensingproperties. At the working temperature of300oC, the sensor response to100ppmethanol was30.7, the response and recovery time was10and9s, respectively, andthe stability was good after aging for15weeks.4. Studies on preparation and humidity sensing properties of ZnO/Si-NPA.ZnO/Si-NPA was prepared by sol-gel method combined with dipping, usingSi-NPA as the template and substrate, and their morphology and structure werecharacterized. It is found the morphology of ZnO nnaoparticles on Si-NPA wasapproximately sphere-like, with the size of5.87nm, and the ZnO/Si-NPA keep thepillar arrays. Studies on humidity sensing properties of ZnO/Si-NPA sensor found thatwhen the ZnO/Si-NPA humidity sensor was exposed in33%,54%,75%,95%RH, thesensitivity was124.5%,536.2%,2035.4%and5522%, respectively. The response andrecovery time was65and48s, respectively. After aging for15weeks, the variation ofcapacitance was relatively large, and we should improve it in further studies.5. Studies on preparation and humidity sensing properties of PVP modifiedZnO/Si-NPA.PVP modified ZnO nanoparticles was prepared by sol-gel method. Theabsorption edge of ZnO exhibited blue shift with the increment of PVP. And that exhibited red shift with the increment of PVP when the mole ratio of Zn2+/PVP wassmaller than5:3. When the mole ratio of Zn2+/PVP was5:3, PVP modified ZnO wassphere-like, with good dispersion and uniform size of5.87nm. Studies on humiditysensing properties of PVP modified ZnO found that the sensitivity and hysteresis ofPVP modified ZnO/Si-NPA sensor increased with the increment of PVP. Humiditysensor with the mole ratio of Zn2+/PVP of5:3, exhibited the best sensing properties.When the sensor was exposed in33%,54%,75%,95%RH, the sensitivity was80.9%,571%,10334%and1127198%, respectively. The response and recovery time was16and8s, respectively. After aging for15weeks, the variation of capacitance was slight,and the sensor exhibited good stability.