ZnO基纳米纤维的制备及其紫外光激发的低温气敏性能研究

【作者】 张敏；

【导师】 卢红兵；

【作者基本信息】 陕西师范大学 ， 凝聚态物理， 2020， 硕士

【摘要】 宽带隙和大激子束缚能的半导体纳米材料ZnO已广泛应用于气敏传感器中,其形貌可控,响应值高,稳定性佳,可检测的气体种类繁多（如H₂S、CO、NO₂、C₂H₅OH等）。然而ZnO气敏传感器的工作温度大多高于200℃,功耗大,不利于其商业应用;已有的报道中低温下ZnO气敏传感器的灵敏度也偏低。复合不同材料的金属氧化物、贵金属修饰等方法来提高ZnO气敏传感器的灵敏度已有大量的研究,但缺陷的调控对气敏性能的研究尚少,特别是低温下缺陷对ZnO气敏传感器性能的影响还少见报道,还需进一步深入研究。因此,研究ZnO在低温条件下缺陷对其气敏性能的影响有重要的意义。经报道,紫外光照可以有效降低金属氧化物半导体气敏传感器的工作温度。所以,我们拟通过紫外光照来降低ZnO纳米材料的工作温度,并研究缺陷对ZnO传感器气敏性能的影响,期望通过缺陷的调控提高传感器的灵敏度;在此基础上,进一步复合还原氧化石墨烯来进一步降低ZnO气敏传感器的工作温度。具体研究内容如下:1通过静电纺丝法制备了形貌可控的ZnO纳米纤维,并将ZnO纳米纤维在N₂气氛不同温度（300℃、400℃、500℃）退火,探究紫外光照下N₂气氛退火对酒精的气敏性能的影响。拉曼结果表明N₂气氛400℃退火的ZnO样品中含有更多的氧空位缺陷,PL结果也表明N₂气氛退火后的ZnO样品中VO+强度比直接制备的样品的VO+强度高一个数量级,这些都表明N₂退火的ZnO样品中含有更多的氧空位缺陷。气敏响应结果显示,N₂气氛400℃退火的ZnO纳米纤维具有更高的气敏响应性能。在最佳温度160℃时,N₂气氛400℃退火的ZnO纳米纤维对500 ppm的酒精响应值为42.0,是直接制备的ZnO纳米纤维的3.6倍。传感器响应的增敏机制为N₂气氛退火后氧空位缺陷的增加,产生更多的吸附氧,更多的吸附氧与酒精分子发生反应,释放更多的电子到ZnO的导带,增强对电阻的调制能力,从而提高传感器的响应。2将氧化石墨烯（GO）在管式炉中Ar气氛下高温加热还原成还原氧化石墨烯（rGO）,使用静电纺丝法制备出不同浓度（0 mol%、0.5 mol%、1 mol%和2 mol%）的rGO-ZnO复合纳米纤维,并在N₂气氛400℃退火。气敏性能的测试显示:与纯的ZnO纳米纤维相比,复合的rGO-ZnO纳米纤维的最佳工作温度降低了 40℃,且显示出更好的气敏性能,包括更高的响应值和更低的检测极限。在紫外光照下,温度120℃,C₂H₅OH的气体浓度为500 ppm时,1 mol%的复合纳米纤维的响应值为77.0,是纯的ZnO纳米纤维的4.4倍。此样品对酒精也显示出较好的选择性和稳定性。增强的气敏性能可归因于p-n异质结的形成和比表面积的增大。异质结的形成同时也降低了材料表面的反应活化能,从而降低了传感器的工作温度。更多还原

【Abstract】 ZnO,a semiconductor nanomaterial with wide band gap and large exciton binding energy,has been widely used in gas sensors.It has controllable morphology,high response value and good stability.It can detect many gases（such as H₂S,CO,NO₂,C₂H₅OH,etc.）.However,the operating temperature of ZnO gas sensors is mostly higher than 200℃,which is not conducive to commercial applications.It has been reported that the responses of ZnO gas sensor at low temperatures are low.A lot of researches have been done to improve the responses of ZnO gas sensors by construction of composite metal oxides and noble metal decoration.However,there are few studies on the effects of defects on the gas sensing performance of ZnO,especially at low temperatures.Therefore,it is of significance to study the effects of defects on the gas sensing performance of ZnO at low temperatures.It has been reported that UV irradiation can effectively reduce the working temperature of metal oxide semiconductor gas sensor.Therefore,we planned to reduce the working temperature of ZnO nanomaterials by UV irradiation,and study the effect of defects on the gas sensing performance of ZnO sensors,with the aim to improve the responses of the sensors by defect regulation.In addition,the working temperature of ZnO gas sensor were further reduced by introducing reduced graphene oxide.The main points were summarized as follows:Firstly,ZnO nanofibers with controllable morphology were prepared by electrospinning,and then annealed at different temperatures（300℃,400℃,500℃）in N₂.The effect of N₂ annealing on the gas sensing performance of ZnO nanofibers to ethanol underultraviolet light irradiation was investigated.The Raman results showed that there were more oxygen vacancy defects in the ZnO samples annealed in N₂.PL results also showed that the intensity of VO+ in the ZnO sample annealed in N₂ atmosphere was one order of magnitude higher than that of as-prepared sample.Both of these results indicated that there were more oxygen vacancy defects in the samples annealed in N₂.The sensing results showed that the ZnO nanofibers annealed in N₂ at 400℃ had high response.Particularly,under UV irradiation,the ZnO nanofibers annealed in N₂ at 400℃ displayed the highest response of 42.0-500 ppm ethanol at 160℃,which is 3.6 times higher than that of as-prepared ZnO nanofibers.The gas sensing enhancement mechanism was ascribed to the increase of oxygen vacancy defects by annealing in N₂ atmosphere,resulting in more adsorbed oxygen.More adsorbed oxygen ions reacted with ethanol molecules to releasing more electrons back to the conduction band of ZnO,which increases the modulation ability of resistance and the response of sensor.Then,rGO was prepared by thermal treatment of GO under Ar.Different concentrations（0 mol%,0.5 mol%,1 mol%and 2 mol%）of rGO-ZnO composite nanofibers were prepared by electrospinning and annealed at 400℃ in N₂.Compared with the pure ZnO nanofibers,the working temperature of the composite rGO-ZnO nanofibers decreased by 40℃.The composite nanofibers showed better gas sensing performance,including higher response value and lower detection limit.Under UV irradiation,the response of 1 mol%composite nanofiber was 77.0,which was 4.4 times of that of pure ZnO nanofiber at 120℃ to 500 ppm C₂H₅OH.The rGO-ZnO sample also showed good selectivity and stability to ethanol.The enhancement sensing performance can be attributed to the formation of p-n heterojunctions and increased surface area of 1 mol%rGO-ZnO nanofibers.The formation of heterojunctions also reduced the reaction activation energy,thus reducing the working temperature of the rGO-ZnO sensor.更多还原