【作者】 黄伟；

【导师】 丁彬；

【作者基本信息】 东华大学 ， 纺织材料与纺织品设计， 2014， 硕士

【摘要】 甲醛是一种常见的易挥发、有害的环境污染物,对人体有较大的危害,容易引起人体中枢神经损害、免疫系统失调以及癌变等。常见检测甲醛的方法有很多,主要有分光光度法、色谱分析法、电化学法等,但这些方法通常需要复杂的设备、繁琐的样品处理以及专业的操作人员,难以实现在室温下原位、快速、低成本地检测微量甲醛的目标。气体传感器检测甲醛成为近年来甲醛检测研究的热点,在众多类型的传感器中,振频式传感器以其检测快速、可现场连续检测等优点引起了国内外学者的普遍关注。作为振频式传感器检测平台的石英晶体微天平(QCM)能够精确检测出纳克数量级的微小质量变化,但QCM电极本身对甲醛没有选择性,需要在电极上修饰一层能选择性吸附甲醛的敏感材料,且传感器的灵敏性和选择性等随着敏感材料比表面积的增大而提高。虽然目前有采用振频式QCM传感器检测甲醛的报道,但大多是在QCM电极上修饰平滑膜作为敏感材料,这限制了传感器灵敏性的进一步提升。采用静电纺丝技术制备的纳米纤维具有三维立体结构、比表面积大、孔隙率高等特点,可以作为一种理想的敏感材料。近年来,有学者将静电纺丝技术与QCM检测平台结合,制备高性能的QCM甲醛气体传感器,但尚存在一些不足之处：共混纺丝制备的复合纳米纤维中有效组分的包埋问题以及模板材料的疏松性和疏水性问题等。针对目前存在的问题,本论文将静电纺丝技术与自主研发的QCM检测平台结合,采用亲水性的模板材料和纳米材料表面修饰技术制备了灵敏度高、选择性好、响应时间短且可重复的QCM甲醛气体传感器。本论文首先采用静电纺丝法制备了具有高比表面积(13.89m2/g)和孔隙率(0.031cm3/g)的聚丙烯腈(PAN)纳米纤维膜。实验所采用的纺丝参数为：PAN溶液浓度为6wt%,高压电源为25kV,接收距离为15cm,纺丝推进速度为1.5mL/h,纺丝环境温湿度分别为25℃和40%。随后对制得的PAN纳米纤维膜进行场发射扫描电镜(FE-SEM)和比表面积分析(BET)测试。然后,对纺制的PAN纳米纤维膜进行表面改性。本论文采用滴铸法分别将聚乙烯亚胺(PEI)溶液和聚乙烯胺(PVAm)溶液直接滴加到PAN纳米纤维膜上,进行功能化表面改性,以实现敏感物质PEI和PVAm的纳米结构化。接着对改性后的PAN纳米纤维膜进行FE-SEM表征,发现敏感物质成功地修饰到PAN纳米纤维膜的表面,且改性前后纳米纤维膜的形貌结构没有发生明显变化。最后,利用设计的QCM甲醛气体传感器进行甲醛的实时检测。本论文以自主研发的QCM-1000型石英晶体微天平系统为检测平台,研究了平滑膜与纳米纤维膜的结构差异、敏感物质加载量、纳米纤维膜加载量等对设计的传感器性能的影响。结果表明,纳米纤维膜修饰的传感器比平滑膜修饰的传感器灵敏度至少高2倍,检测下限可达到ppb数量级。利用Fick扩散定律对传感器的响应曲线进行模拟得到两种敏感膜的气体扩散系数,理论分析结果与实测数据相符。在低加载量范围内,随着敏感物质加载量的增加,传感器的灵敏性增大,这主要是由于单位面积上甲醛的吸附位点数随之增多。传感器的灵敏性随着纳米纤维膜加载量增加先增大后减小,这可能是因为纳米纤维膜是一种软性物质,其加载量过大时,膜的结构开始变得疏松,刚性变小,不利于振动的传递。此外,本论文还对传感器的选择性、重现性进行了测试。研究发现,该传感器对其他常见有机挥发性气体的响应远远小于对甲醛的响应,且经氮气解吸附后可以多次重复使用。更多还原

【Abstract】 Formaldehyde is a common harmful, volatile organic compound, which could cause great hazard to human body. It probably brings damage to human central nervous system and immune system, and it is even easy to induce cancer and other disorders. There are many methods for formaldehyde detection, such as spectrophotometry, chromatography, electrochemical method and so on. However, all the mentioned methods require sophisticated instruments, complex sample handling, and professional operators, which makes it difficult to detect formaldehyde gas in situ, quickly and at low cost under room temperature. Utilizing gas sensor to detect formaldehyde has become a hot spot in recent years, and in many types of sensors, the vibration frequency sensor caused widespread concern of researchers both at home and abroad for the advantages of detecting fast and continuously in situ. Quartz crystal microbalance (QCM), as one of the detecting platforms of vibration frequency sensor, is able to measure tiny mass changes (even nanogram). Whereas, the QCM electrode is not selective for formaldehyde, it’s needed to modify the electrode with a sensitive layer which can selectively absorb formaldehyde gas. It has been proved that the sensitivity and selectivity of sensor will be enhanced with increase of the specific surface area of sensitive materials. Although there were researches on formaldehyde detection by means of vibration frequency QCM sensor, most of them modified flat films on QCM electrode as sensitive materials, which limited the further enhancement of the sensitivity of sensors. Electrospun nanofibrous membrane is characterized by three-dimensional structure, large specific surface area and high porosity. So it can act as an ideal sensitive material. In recent years, the electrospinning technology and QCM platform were combined to produce formaldehyde sensors with high performance. However, there are still some shortcomings:on one hand, the active part of composite nanofibers is embedded easily; on the other hand, the template material is hydrophobic and fluffy. In our work, the QCM platform independently developed by ourselves was combined with the electrospinning technology to fabricate a formaldehyde gas sensor based on QCM with high sensitivity, good selectivity, quick response and good reproducibility by utilizing hydrophilic template material and surface modification technology for nanomaterials.In our research, we first prepared polyacrylonitrile (PAN) nanofibrous membranes (NFM) with high specific surface area (13.89m2/g) and porosity (0.031cm3/g) by method of electrospinning. We set the electrospinning parameters as follows:the concentration of PAN polymer solution was6wt%, the voltage was25kV, the tip to QCM electrode distance was15cm, the flow rate was1.5mL/h, the temperature and relative humidity of the surroundings were25℃and40%respectively. Then we conducted the test of field emission scanning electron microscope (FE-SEM) and specific surface area analysis (BET) for the result PAN NFM.Subsequently, the surface modification of the PAN NFM was realized by drop casting of sensitive materials:polyethyleneimine (PEI) and polyvinylamine (PVAm). After trial electrospin-ning, we found it’s nearly impossible to collect electrospun PEI and PVAm nanofibers. So we decided to use drop-casting method, which could be a good solution to realize the sensitive materials nanostructured. Afterwards, the modified PAN NFM were characterized through FE-SEM method, the result of the observation indicated the sensitive materials (PEI and PVAm) had been successfully modified on the surface of PAN NFM. Moreover, the morphology and structure of the surface modified PAN NFM did not change significantly.At last, the fabricated formaldehyde gas sensor based on QCM was utilized to detect the formaldehyde gas in real time. A self-developed quartz crystal microbalance system named QCM-1000was put into use, and we comparatively studied the influence of the structural differences between flat film and NFM, the sensitive materials loading, and the NFM loading on the performances of the result formaldehyde gas sensor. As a result, the sensitivity of the NFM modified formaldehyde gas sensor based on QCM shows at least two times higher than that of the flat film modified one, and the detecting limit reaches ppb level. We got the gas diffusion coefficient of two kinds of sensitive membrane by simulating the response curve based on the Fick’s law of diffusion, and it shows the theoretical analysis results are in conformity with the experimental data. Within the low loading range, the increasing of the PVAm loading can bring more formaldehyde molecule adsorption sites, thus the sensor has higher sensitivity. However, the influence of the PAN NFM loading is quite different. The PAN NFM loading has a critical value. This is mainly for the reason when the PAN NFM loading is too large, the structure of the membrane is loose, which means less rigidity. As far as we know, the rigidity of sensitive materials is very important for the vibration transmission. Moreover, the selectivity and reproducibility of the result sensor had also been tested, it displays that the response of the fabricated sensor to other VOCs is far less than the response to formaldehyde gas. After one circle test, the sensor can be recovered by exposure to N2.更多还原