【作者】 杨颖；

【导师】 付宏刚；

【作者基本信息】 黑龙江大学 ， 无机化学， 2014， 博士

【摘要】 在全球的环境污染问题中，气体污染属于环境污染中一项十分重要的研究课题。目前，已知的大气污染物约有100多种，SO2、CO以及NO2作为三大气体污染物，尤其是NOx，对它的检测和控制在气敏传感等领域具有重要的实用价值和商业前景。在各种新型气敏传感材料中，晶态碳材料由于其优异的导电性、高效电子传输效率已被用作气敏传感领域，将晶态碳与对NOx有气敏响应的半导体金属氧化物形成复合材料可以实现在室温下对NOx气体的快速响应。本论文基于对气敏传感器中结构与性能关系的理解，设计合成出一系列金属氧化物/晶态碳基气敏传感材料，这些材料都是具有独特结构的高性能，高稳定性的非常有潜力的室温NOx气敏材料。本论文主要研究内容如下：(1)通过两步法合成了四氧化三铁/还原氧化石墨烯复合体(Fe/rGO-400)。首先在水热的条件下合成FeOOH/GO复合物，然后进一步在N2气氛下400℃焙烧得到Fe/rGO-400复合体。TEM分析表明在Fe/rGO2-400中Fe3O4纳米粒子均匀分散在还原氧化石墨表面，粒径在20~50nm左右；随着椭圆形Fe3O4在rGO上负载量的增大，纳米椭圆形Fe3O4的粒径尺寸逐步增大。XPS分析表明：在Fe3O4纳米粒子与rGO基底之间存在较强的相互作用。本实验所合成的Fe/rGO2-400材料在室温下对NOx有很好的气敏响应，对97.0ppm的NOx的气敏响应为35.6%，响应时间为29.3s。Fe/rGO-400具有特殊的层状结构，有利于待检测气体的扩散、吸附和脱附。此外，采用rGO作为碳基底，除了增加复合体的导电性以外，对纳米粒子的生长起到限域的作用，是制备该小尺寸、高分散Fe3O4粒子的必要条件。(2)采用液相回流法制备了三氧化二铟/还原氧化石墨复合体(In2O3/rGO)。在合成中，采用氧化石墨为碳源，硝酸铟为金属盐、SDBS为表面活性剂与尿素作为沉淀剂。同时，在没有氧化石墨时，合成了不同形貌的三氧化二铟气敏材料。采用所合成的气敏材料组装成气敏元件，对其进行室温下的NOx气敏测试。研究表明，三氧化二铟/还原氧化石墨复合体具有N型半导体特性，在室温下对97.0ppmNOx的响应为1.45，响应时间为25.0s。组装的纯三氧化二铟气敏传感器在室温下对NOx具有较好的气敏响应，对97.0ppm NOx的响应为17.0，响应时间为17.3s。材料在室温下NOx气敏性能增强的原因为特殊形貌和多孔结构。(3)以廉价的膨胀石墨为碳源，硝酸铈为金属盐，采用水热法合成了大约3nm的CeO2纳米粒子高度分散的二氧化铈/类石墨烯复合体(CeGNCs)。在合成中，在真空诱导下硝酸铈的溶液进入到膨胀石墨的层中，经过水热后CeO2纳米粒子在层中逐渐的长大，并剥离了膨胀石墨片层，最终形成二氧化铈/类石墨烯复合体。结果表明，大约3nm的CeO2的纳米粒子高度分散在大约10层的类石墨烯纳米片上。其中，CeO2含量为46.7wt%的CeGNC2在室温下对NOx展现了非常好的气敏性能，最低检测限可达5.0ppm，对100ppm NOx的响应为10.39%，响应时间为7.33s。该复合体在室温下NOx气敏响应增强主要是由于这种小尺寸的CeO2纳米粒子以及复合物导电性增强。CeO2纳米粒子与类石墨烯纳米片形成了肖特基接触，电子能够快速从导带上的获得并且迁移。(4)本文组装了基于三维纳米花状CuxO/多层石墨烯纳米片复合物(CuMGCs)的一种新型的室温NOx气敏器。在合成中，首先，对膨胀石墨采用KOH进行活化，在表面形成一些适中的活性基团，然后，醋酸铜以及表面活性剂(CTAB)在真空诱导下被压入活化的膨胀石墨层间，在回流过程中，同步地剥离活化的膨胀石墨形成多层石墨。最后，由5~9nm CuxO组装的三维纳米花均匀地生长在多层石墨烯的表面。KOH活化步骤在形成均匀的复合物中起到了非常重要的作用。将所合成的复合材料组装成气敏传感元件在室温下用于检测NOx，研究发现所合成的复合材料对NOx气体的气敏响应均比CuxO气敏性能显著提高。其中，CuMGC2气敏传感器在室温下对NOx的检测限可达ppb级，对97.0ppm NOx的灵敏度为95.1%，响应时间仅为9.6s。气敏响应增强主要归因于CuMGCs的导电性提高。一系列Mott-Schottky和EIS测量表明，CuMGCs的载流子密度远高于CuxO，很容易从导带上捕捉电子，并且快速的迁移。更多还原

【Abstract】 During the global environmental pollution, air pollution is regarded as one of themost important research subjects. At present, there are more than100hundred kinds ofair pollutants, as we known. SO2, CO and NO2are known as three great environmentalpollutions, especially for NO2, their detection and control has the important practicalvalue and business prospects in gas sensors. Among various kinds of new gas sensormaterials, crystalline carbon materials could be applied as room temperature gas sensors,which was due to the superior electrical conductivity, exceeding electronic transmissionefficiency, and the combining crystalline carbon with the traditional metal oxidesemiconductor to form composite materials can be achieved the fast response to the gasat room temperature. In this thesis, based on the understanding of relation betweenmaterial structure and performance of gas sensors, a series of metal oxide/crystallinecarbon gas sensing composites were designed and already prepared. All the preparedgas sensing materials possess unique structure with high performance, high stability andgreat potential of room temperature NOxgas sensing materials. The main researchcontents are as following.(1) Ferroferric oxide/reduced graphite oxide composite (Fe/rGO-400) has beensynthesized with a two-step synthetic method. Firstly, FeOOH/graphite oxide composite(FeOOH/GO) precursors have been prepared by hydrothermal method, and thenFe/rGO-400were obtained after calcinated at400℃under N2atmosphere. The TEManalysis indicate that Fe3O4nanoparticles with a diameter of20~50nm uniformlydispersed on the surface of the rGO. With the increment of Fe3O4load, the size of Fe3O4nanoparticles in composite gradually became bigger. XPS analysis shows that there is astrong interaction between the metal oxide and rGO substrate. The synthesis ofFe/rGO2-400materials has good gas response to NOxgases at room temperature, in which the gas sensitivity to97.0ppm NOxis35.6%and the response time is29.3s.Fe/rGO-400have special layered structures, which is favor for the diffusion, adsorptionand desorption of the target gas. In addition, the introduction of rGO as carbon substrateincrease the conductivity of composite, restrict the growth of FeOOH nanoparticles, it isnecessary for the preparation of the small size, high dispersion of Fe3O4particles.In2O3/reduced graphite oxide composites (In2O3/rGO) have been successfullysynthesized. In the synthesis, GO was used as carbon resource, Indium nitrate as themetal salts, SDBS as surfactant and urea as precipitant. In addition, differentmorphological In2O3have been prepared in absence of GO. When being as the gassensing materials to fabricate into gas sensors, the room temperature NOxgas test havebeen carried out. Studies have shown that the In2O3/rGO have the N type semiconductorcharacteristic, which shows NOxgas sensing performance with high gas response of1.45and the response time of25.0s to97.0ppm NOxat room temperature. In addition,the sensor based on pure In2O3have better response to NOxthan that of In2O3/rGO, thesensor has higher gas response of17.0and the response time of17.3s to97.0ppm NOxat room temperature. The improvement of room temperature NOxgas sensingperformance for the synthesized products is due to the special morphology and porousstructure.(3) The CeO2/graphene-like nanosheet composites (CeGNCs) have beensynthesized via a facile solvothermal reaction by using expanded graphite as carbonsource and cerium nitrate as metal salts. In the synthesis, Ce(NO3)3precursor waspromoted full infusion into the interlayers of expanded graphite (EG) undervacuum-assisted conditions, and then CeO2nanoparticles grow in situ in the interlayersof inexpensive EG under solvothermal condition to form CeGNCs. The results showthat the CeO2particles (about3nm) are highly dispersed on graphene-like nanosheet(>10layers). Especially, the CeGNCs with46.7wt%of CeO2shows higher NOxgassensing performance with low detection limit of5.0ppm, high sensitivity (10.39%), short response time (7.33s) towards100ppm NOx. The enhancement of roomtemperature gas response to NOxfor the composites is due mainly to tiny CeO2nanoparticles and improved conductivity of the composites. CeO2nanoparticles andgraphene like nanosheet can formed a schottky contact, electronics can be quicklyobtained from conduction band and migrated.(4)3D nanoflower-like CuxO/multilayer graphene composites (CuMGCs) havebeen successfully synthesized as a new type of room temperature NOxgas sensor.Firstly, the expanded graphite was used as carbon resource and activated by KOH andmany moderate functional groups were generated; and secondly, the Cu(CH3COO)2andCTAB were promoted full infusion into the interlayers of activated EG (aEG) by meanof a vacuum-assisted technique and then react with functional groups of aEGaccompanied by the exfoliation of aEG via a reflux treatment. Eventually, the3Dnanoflower consisting of5~9nm CuxO nanoparticles homogeneously in situ grow onaEG. The KOH activation EG plays a crucial role in uniformly formation for CuMGCs.When being used as gas sensors for detection of NOx, the CuMGCs achieved a higherresponse at room temperature than that of the corresponding CuxO. In detail, theCuMGCs shows higher NOxgas sensing performance with low detection limit of97ppb, high gas response of95.1%and short response time of9.6s to97.0ppm NOxatroom temperature. Meantime, the CuMGCs sensor presents a favorable linearity, goodselectivity and stability. The enhancement of the sensing response is mainly attributed tothe improved conductivity of the CuMGCs. A series of Mott-Schottky and EISmeasurements demonstrated that the CuMGCs have much higher donor densities thanthe CuxO and can easily capture and migrate electrons from the conduction band,resulting in the enhancement of electrical conductivity.更多还原