【作者】 闫里；

【导师】 黄开金；

【作者基本信息】 华中科技大学 ， 材料学， 2011， 硕士

【摘要】 本文首先在Al₂O₃基底上以Zn（NO₃）₂·6H₂O为锌源,六次甲基四胺为沉淀剂,分别选取十二烷基苯磺酸钠、十六烷基三甲基溴化铵、柠檬酸、三聚磷酸钠、聚乙烯醇和聚乙二醇2000六种表面活性剂,采用水热法成功地制备出各种形貌的纳米ZnO如纳米片、纳米微球、纳米棒、纳米墙和花状结构等。采用XRD和FSEM技术对所获得的纳米ZnO进行了表征。研究结果表明:不同表面活性剂组合会通过吸附作用或者电荷作用来影响纳米ZnO生长基元的生长方式;表面活性剂的量则会影响纳米ZnO生长基元的自组装方式;水热前驱液浓度会对纳米ZnO颗粒大小和密集程度产生影响。其次,结合水热法调控纳米ZnO的结果,通过丝网印刷和水热处理相结合的工艺将体控制型气敏材料γ-Fe₂O₃和表面控制型气敏材料ZnO复合,制备出气敏性能更好的γ-Fe₂O₃/ZnO纳米复合双层膜。通过改变水热过程中表面活性剂种类和前驱液浓度,研究了不同形貌复合膜对乙醇、甲醛、氨气和甲苯四种还原性气体的敏感性能,并探讨了其气敏机理。研究结果表明:γ-Fe₂O₃/ZnO纳米复合双层膜对四种气体的灵敏度相对于单层γ-Fe₂O₃气敏膜和单层ZnO气敏膜都得到了不同程度的提高。单层丝网印刷的γ-Fe₂O₃气敏膜F0在最佳工作温度点对100ppm乙醇、甲醛、氨气和甲苯的灵敏度分别为15.1、3.9、2.2和4.0,单层水热制备的ZnO气敏膜Z2在最佳工作温度点对100ppm四种气体的灵敏度分别只有5.7、1.4、1.3和1.2;而在0.01g表面活性剂CA作用下得到的γ-Fe₂O₃/ZnO复合膜F2对100ppm乙醇的灵敏度在320℃时达到65.4,对100ppm甲醛的灵敏度在300℃时达到7.6;在0.005 g CA和₀.033g SDS共同作用下得到的γ-Fe₂O₃/ZnO复合膜F5对100ppm氨气的灵敏度在320℃时达到5.9,对100ppm甲苯的灵敏度在300℃时达到8.8;复合膜的最佳工作温度为300℃左右;不同形貌复合膜对于气体的敏感度有很大不同,这与复合膜的表面积、纳米ZnO在γ-Fe₂O₃上的生长位置以及复合膜表面能的大小有关。最后,本文探讨了γ-Fe₂O₃/ZnO纳米复合双层膜的气敏机理。我们认为有两个方面的原因使得γ-Fe₂O₃/ZnO纳米复合双层膜的气敏性能相对于单层的高。其一,γ-Fe₂O₃与ZnO复合后由于各自气敏机理不同,能通过不同的形式与所测气体发生反应,使得复合膜整体的电阻相较于单层膜的电阻有了更大的变化,因此响应也更高。其二,ZnO和γ-Fe₂O₃都是纳米级的,气敏材料本身的纳米效应也使得其性能有所提高。此外,复合膜对于不同气体有不同程度的响应主要与待测气体本身的分子结构有关。更多还原

【Abstract】 In the experiment,firstly, using zinc nitrate and HMTA as zinc source and precipitator, respectively , in addition to different surfactants of dodecyl sulfate, hexadecyl trimethyl ammonium bromide,citric acid,sodium tripolyphosphate,polyvinyl alcohol and polyethylene glycol 2000, we successfully synthesized nano-ZnO with different morphologies on the Al₂O₃ substrates via a hydrothermal method, including ZnO nanorods,ZnO nano-wall,ZnO fine microspheres and flower-like ZnO etc. The obtained nano-ZnO was studied by X-ray diffraction（XRD） and field-emission scanning electron microscopy（FESEM）.The results show that the different surfactants influenced the morphologies of nano-ZnO by means of electrostatic interactions or absorption interactions. The amount of surfactants would influence the assemble way of the growth unit of ZnO crystal. And the precursor concentration would influence the size and intensive degree of ZnO crystal.Then,using the results of controlling the mophologies of nano-ZnO via hydrothermal method,a new kind of high gas sensing property nano structure composite films composed ofγ-Fe₂O₃ and ZnO was prepared by screen printing process combined with hydrothermal treatment. By changing different kinds of surfactants and precursor concentration in hydrothermal treatment, composite sensitive films with different microstructures were fabricated and the films’sensitivities to ethanol, formaldehyde, ammonia and methylbenzene were tested .The results indicate that the sensitivities to all four gases ofγ-Fe₂O₃/ZnO composite films were higher compared with single-layerγ-Fe₂O₃ gas sensing film and single-layer ZnO gas sensing film .The sensitivities at the best working temperature of screen printing single-layerγ-Fe₂O₃ film F0 to ethanol, formaldehyde, ammonia and methylbenzene are 15.1、3.9、2.2 and 4.0, respectively; The sensitivities at the best working temperature of hydrothermal single-layer ZnO film Z2 to the four gases are only 5.7、1.4、1.3 and 1.2, respectively; The sensitivity of samble F2 synthesized with 0.01g surfanctant CA to ethanol is 65.4 at 320℃,the sensitivity of samble F2 to formaldehyde is 7.6 at 300℃,the sensitivity of samble F5 synthesized with 0.005 g surfanctant CA and 0.033g SDS to ammonia is 5.9 at 320℃,the sensitivity of samble F5 to methylbenzene is 8.8 at 300℃. The perfect working temperature ofγ-Fe₂O₃/ZnO composite films was about 300℃which was lower than that of single-layer ZnO gas sensing film. Theγ-Fe₂O₃/ZnO composite films with different morphologies displayed very different gas sensing properties. The surface area ,the growth position and the surface energy are the three factors.The gas sensing mechanism ofγ-Fe₂O₃/ZnO composite films was also discussed. We consider that two reasons lead to the improvement of the sensitivities ofγ-Fe₂O₃/ZnO composite films to ethanol, formaldehyde, ammonia and methylbenzene. First,because of different gas sensing mechanism ,ZnO andγ-Fe₂O₃ would react with the testing gases in different ways which lead to greater change of the bulk resistant of composite materials.Thus ,the sensing property of composite film is better than that of single film .Second, both ZnO andγ-Fe₂O₃ are nano scale,the nano effect of sensing materials would also make the composite films display better sensing property. In addition, the different structures of different gases lead to the different sensitivities .更多还原