聚苯胺及其掺杂材料的制备及气敏特性的研究

采用质子酸化学聚合法,以苯胺（An）为单体,过硫酸铵（APS）为氧化剂,在盐酸（HCl）溶液中,合成了聚苯胺（PANI）及In2O3、TiO2和SnO2掺杂的聚苯胺。分别通过X射线衍射仪（XRD）,红外光谱仪（FT-IR）,场发射扫描电镜（FE-SEM）对其结构和形貌进行了表征,制成了基于聚苯胺及其掺杂材料的氨气传感器。室温下,对1.0×10-5～1.50×10-4浓度范围的氨气进行了气敏测试,测试结果表明,基于聚苯胺及其掺杂材料的气敏元件对氨气响应灵敏度基本呈线性关系。掺杂In2O3的聚苯胺气敏元件对氨气的响应灵敏度最大,在1.50×10-4时响应灵敏度达到50;而掺杂TiO2的聚苯胺气敏元件对1.00×10-4氨气的响应时间最短,为60s。分析了聚苯胺及其掺杂材料的气敏机理,结果表明,金属氧化物的掺杂对聚苯胺材料的灵敏度、响应及恢复时间等气敏特性有很大的影响。     

稀土杂质对纳米BaTiO3湿敏性能的影响

分别研究了钠盐和稀土杂质对BaTiO3纳米晶材料湿敏元件电学性能的影响,结果表明钠盐和稀土金属氧化物都能降低湿敏元件的电阻和湿滞.掺钠盐的湿敏元件电阻较低,但长期稳定性不如掺稀土金属氧化物的湿敏元件.初步分析了掺杂影响湿敏材料特性的机理.     

超支化聚季胺盐的湿敏响应特性

以超支化结构聚酯为核,制备了超支化聚季胺盐湿敏材料。采用浸涂法制备薄膜电阻型湿敏元件,研究了其湿敏响应特性。发现其在较宽湿度范围(5%～96%RH)具有较高响应灵敏度,且响应快,湿滞小(1%RH)。     

无机杂质对改善纳米BaTiO_3湿敏特性的作用

用硬酯酸盐法合成了纳米ＢａＴｉＯ３材料，它对湿度有良好的敏感性能。在纳米ＢａＴｉＯ３中掺入少量杂质，会影响其感湿性能。本文研究了掺杂方法、掺杂种类及掺杂浓度对纳米ＢａＴｉＯ３湿敏元件的电阻和湿滞的影响。混合掺入Ｎａ２ＣＯ３和ＮａＨ２ＰＯ４可以使纳米ＢａＴｉＯ３湿敏元件的电阻为１０６～１０３Ω，湿滞＜３％。     

基于c‒MWCNTs/GO体系的湿敏型智能包装研究

目的 优选羧基化多壁碳纳米管(c–MWCNTs)与氧化石墨烯(GO)作为敏感材料制备湿度传感器,对其湿敏特性进行研究,探索一种能够快速精确监测包装内湿度变化的传感器。方法 通过丝网印刷工艺印制传感器电极基底,在电极表面涂布c–MWCNTs/GO湿敏溶液,混合湿敏溶液中c–MWCNTs的质量分数分别为20%和67%,烘干后得到电阻型湿度传感器,测定其灵敏度、动态响应、响应恢复时间、吸湿滞后性、重复性等湿敏特性。结果 选用长度为0.5~2 μm的c–MWCNTs制备的湿度传感器灵敏度、线性度优于10~30 μm的。质量分数分别为20%和67%的c–MWCNTs的湿敏溶液制备而得的传感器均对不同湿度敏感,而当c–MWCNTs质量分数为67%时灵敏度更高,线性度更好,在低湿(相对湿度为33%)时响应和恢复时间分别为7 s和3.9 s,高湿(相对湿度为85%)时分别为20 s和15 s,最大吸湿滞后值为17%。结论 将c–MWCNTs与GO掺杂用于制备湿度传感器,可以检测的相对湿度范围为11%~98%,且c–MWCNTs质量分数为67%时传感器具有较高的灵敏度、良好的线性度、良好的重复性、快速的响应恢复能力和较小的吸湿滞后,在未来包装湿度监控应用方面具有广阔前景。     

磺基水杨酸掺杂聚苯胺的气敏性能

采用化学氧化聚合法分别在磺基水杨酸和盐酸中合成了聚苯胺,并用FT-IR和TG-DTA技术对聚苯胺掺杂前后的结构变化和热稳定性进行了分析。研究了不同质子酸掺杂对聚苯胺气敏性能的影响,结果表明,磺基水杨酸掺杂的聚苯胺不仅比普通盐酸掺杂的聚苯胺具有更好的环境稳定性,而且对目标气体具有更好的灵敏性,在室温下对10-3L/L NH3的灵敏度达到了15.47。     

SnO2-K2O-LiZnVO4系材料湿敏性能及导电机理的研究

采用共沉淀法制备出SnO2-K2O-LiZnVO4系湿敏粉体,考察了液相掺杂K 对材料湿敏特性的影响,并用直流特性法对材料的导电机理进行了分析.实验结果表明,适当的K 液相掺杂可使材料具有低湿电阻小,灵敏度适中的特性.直流特性法分析表明,材料属电子-离子混合导电机制,且离子电导成分越多材料的湿敏特性越好.     

碱金属掺杂的铁系陶瓷湿敏材料特性研究

本文报导了碱金属掺杂对以 Fe_2O_3为基的陶瓷材料湿敏特性影响的研究结果。碱金属掺杂对改善材料敏感性与微组织结构有显著作用。研究发现,K~+,La~(3+)等离子的掺杂能明显降低材料固有阻值,提高低湿区敏感特性,改善阻—湿特性的线性关系。文中对水法处理与多元掺杂对减小材料湿滞,提高感湿灵敏度的作用机制给予了讨论。     

MnWO_4-Li_2WO_4系厚膜湿敏元件的性能

本文采用溶胶凝胶法制备WO3纳米粉体,再与MnCO3固相反应合成MnWO4,掺杂得到不同配比的MnWO4一Li2WO4湿敏材料,通过丝网印刷工艺制备厚膜湿敏元件.实验研究表明在适当的工艺条件下,MnWO4中掺杂30m01%Li2WO4的材料,所制备的元件具有低湿电阻小、灵敏度高、响应速度快、湿滞小的特点,这些特点为产品的实用化提供了有利条件.SEM照片和复阻抗分析.表明,该方法制备的材料具有纳米晶粒和优良的晶界微结构,是改善元件性能的重要原因.     

MgO改性PbCrO4基湿敏电阻机理研究

对MgO改性的PbCrO4，基湿敏电阻进行了研究。随着MgO含量的增加使得该系列湿敏电阻在低、中湿范围内感湿灵敏度增大，当MgO含量超过0．5mol时，在全湿度范围内，湿阻特性曲线接近直线。结合X－ray衍射分析及扫描电镜分析，探讨了MgO改性的PbCrO4基湿敏电阻的感湿特性机理在于水蒸气将通过气孔在OH^－根上形成多分子层的水分子吸附层。     

Electrical and optical properties of ZnO–WO<Subscript>3</Subscript> nanocomposite and its application as a solid-state humidity sensor

This study reports the humidity sensing characteristics of ZnO–WO₃ nanocomposite. Pellet samples of 0–5 weight% ZnO in WO₃ were sintered from 300 to 600 ^° C. When exposed to humidity, the resistance of the sensing samples was found to decrease with increase in relative humidity (RH). Five percent ZnO-doped WO₃ showed maximum sensitivity of 20.95 M Ω/%RH in 15–95% RH range. Sensor parameters like reproducibility, aging, hysteresis, response and recovery times were also studied. Sensing mechanism is discussed in terms of sintering temperature, composition and crystallite size of the sensing element. It was observed that sensing mechanism is strongly based on annealing temperature and percentage of doping. The sensing samples have also been investigated by X-ray diffraction, scanning electron microscope (SEM) and Raman spectroscopy. The crystalline size of the sample was identified by powder X-Ray Diffraction data. The SEM analysis was used to study the surface morphology. The structure, phase and the degree of crystallinity of the materials were examined by Raman spectroscopy.     

Effect of crystallization on humidity sensing properties of sol-gel derived nanocrystalline TiO2 thin films

In the present work, we describe the effect of crystallization on humidity sensing properties of nanocrystalline TiO₂ thin films prepared by sol-gel techniques. Here, we report an enhancement in the relative humidity (RH) sensitivity just after the crystallization at 375 °C, which is attributed to increased surface activity near crystallization and lower crystallite size. After crystallization, the RH sensitivity was found to decrease with increasing grain size. The complex impedance of the sensor, measured using impedance spectroscopy, fits well with an equivalent circuit consisting of inter-granular resistance and capacitance in parallel. It was found that with the change in RH, only resistance changes significantly, when compared with the capacitance.     

The sol-gel template synthesis of porous TiO2 for a high performance humidity sensor

This research develops a simple template assisted sol-gel process for preparing porous TiO2 for a high performance humidity sensor. Tetraethyl orthosilicate (TEOS) as a template was directly introduced into TiO2 sol formed by the hydrolysis and condensation of titanium alkoxide; the following calcination led to the formation of TiO2-SiO2 composite, and the selective removal of SiO2 by dilute HF solution led to the formation of porous structure in TiO2. The resulting porous TiO2-based sensor exhibits high sensitivity and linear response in the wide relative humidity (RH) range of 11%-95%, with an impedance variation of four orders of magnitude to humidity change. Moreover, it exhibits a rapid and highly reversible response characterized by a very small hysteresis of <1% RH and a short response-recovery time (5 s for adsorption and 8 s for desorption), and a 30-day stability test also confirms its long-term stability. Compared with pure TiO2 prepared by the conventional sol-gel method, our product shows remarkably improved performance and good prospect for a high performance humidity sensor. The complex impedance spectra were used to elucidate its humidity sensing mechanism in detail.     

Nitrogen‐Doped Single Graphene Fiber with Platinum Water Dissociation Catalyst for Wearable Humidity Sensor

Humidity sensors are essential components in wearable electronics for monitoring of environmental condition and physical state. In this work, a unique humidity sensing layer composed of nitrogen‐doped reduced graphene oxide (nRGO) fiber on colorless polyimide film is proposed. Ultralong graphene oxide (GO) fibers are synthesized by solution assembly of large GO sheets assisted by lyotropic liquid crystal behavior. Chemical modification by nitrogen‐doping is carried out under thermal annealing in H₂(4%)/N₂(96%) ambient to obtain highly conductive nRGO fiber. Very small (≈2 nm) Pt nanoparticles are tightly anchored on the surface of the nRGO fiber as water dissociation catalysts by an optical sintering process. As a result, nRGO fiber can effectively detect wide humidity levels in the range of 6.1–66.4% relative humidity (RH). Furthermore, a 1.36‐fold higher sensitivity (4.51%) at 66.4% RH is achieved using a Pt functionalized nRGO fiber (i.e., Pt‐nRGO fiber) compared with the sensitivity (3.53% at 66.4% RH) of pure nRGO fiber. Real‐time and portable humidity sensing characteristics are successfully demonstrated toward exhaled breath using Pt‐nRGO fiber integrated on a portable sensing module. The Pt‐nRGO fiber with high sensitivity and wide range of humidity detection levels offers a new sensing platform for wearable humidity sensors.     

The effect of carbon nanotube dispersion on CO gas sensing characteristics of polyaniline gas sensor

Polyaniline is one of the most promising conducting polymers for gas sensing applications due to its relatively high stability and n or p type doping capability. However, the conventionally doped polyaniline still exhibits relatively high resistivity, which causes difficulty in gas sensing measurement. In this work, the effect of carbon nanotube (CNT) dispersion on CO gas sensing characteristics of polyaniline gas sensor is studied. The carbon nanotube was synthesized by Chemical Vapor Deposition (CVD) using acetylene and argon gases at 600 degrees C. The Maleic acid doped Emeradine based polyaniline was synthesized by chemical polymerization of aniline. CNT was then added and dispersed in the solution by ultrasonication and deposited on to interdigitated AI electrode by solvent casting. The sensors were tested for CO sensing at room temperature with CO concentrations in the range of 100-1000 ppm. It was found that the gas sensing characteristics of polyaniline based gas sensor were considerably improved with the inclusion of CNT in polyaniline. The sensitivity was increased and response/recovery times were reduced by more than the factor of 2. The results, therefore, suggest that the inclusion of CNT in MA-doped polyaniline is a promising method for achieving a conductive polymer gas sensor with good sensitivity, fast response, low-concentration detection and room-operating-temperature capability.     

Zinc oxide nanoparticle based optical fiber humidity sensor having linear response throughout a large dynamic range

The main objective of the present work is to develop an optical fiber relative humidity (RH) sensor having a linear response throughout over the widest possible dynamic range. We report an optical fiber RH sensor based on the evanescent wave absorption spectroscopy that fulfills this objective. The fiber sensor employs a specific nanoparticle (zinc oxide) doped sol-gel nanostructured sensing film of optimum thickness, synthesized over a short length of a centrally decladded straight and uniform optical fiber. A detailed experimental investigation is carried out to analyze the sensor response/characteristics. Fiber sensor response is observed to be linear throughout the dynamic range as wide as 4% to 96% RH. The observed linear sensitivity for the fiber sensor is 0.0012?RH(-1). The average response time of the reported sensor is observed to be as short as 0.06?s during the humidification. In addition, the sensor exhibited a very good degree of reversibility and extremely high reliability as well as repeatability.     

Construction of Dual-Channel Water Transport in Mesoporous Silica Low Humidity Sensors to Achieve High Sensitivity

In this paper, strong hydrophilic poly(ionic liquid)s (PILs) are selectively grafted on different positions (mesoporous channels and outer surface) of mesoporous silica via thiol-ene click chemical reaction. The purposes of selective grafting are on the one hand, to explore the differences of adsorption and transportation of water molecules in mesoporous channels and on the outer surface, and on the other hand, to combine the two approaches (intra-pore grafting and external surface grafting) to reasonably design SiO₂@PILs low humidity sensing film with synergetic function to achieve high sensitivity. The results of low relativehumidity （RH） sensing test show that the sensing performance of humidity sensor based on mesoporous silica grafted with PILs in the channels is better than that of humidity sensor based on mesoporous silica grafted with PILs on the outer surface. Compared with water molecules transport single channel, the construction of dual-channel water transport significantly improves the sensitivity of the low humidity sensor, and the response of the sensor is up to 4112% in the range of 7–33% RH. Moreover, the existence of micropores and the formation of dual-channel water transport affect the adsorption/desorption behaviors of the sensor under different humidity ranges, especially below 11% RH.     

Thin plasma-polymerized layers of hexamethyldisiloxane for humidity sensor development

The response of resistive-type sensors based on thin hexamethyldisiloxane layers to relative humidity (RH) was evaluated. Humidity sensitive layers were plasma polymerized at low frequency glow discharge using a capacitively coupled parallel plate reactor. The sensor design comprises the absorbing layer deposited on clean glass substrate with comb-shape aluminum electrodes (interdigitated structure). The change in electrical impedance of the sensing film was monitored as the device was exposed to humidity. The variation of the plasma-polymerization parameters resulted in different humidity sensing properties which could be correlated to the results of Fourier transform infrared spectroscopy (FTIR). The deposited films exhibited a detectable response to RH ranging from 30 to 95% with low hysteresis, good reproducibility and stability in long-term use. Films with a greater thickness showed a significant decrease in the humidity sensing capability. FTIR analysis revealed the presence of SiH bonding groups, which are frequently linked to the film density. The increase in the plasma discharge power induced also a significant decrease in the diffusion process of water vapor inside the sensitive layer bulk.     

Relative humidity sensors based on an environment-sensitive fluorophore in hydrogel films

A fluorescence-based sensing scheme exploiting an environment-sensitive fluorophore embedded in a hydrogel has been developed for measurement of relative humidity (RH). The fluorophore, dapoxyl sulfonic acid (DSA), is incorporated into two different hydrogel films, agarose and a copolymer of acrylamide and 2-(dimethylamino)ethyl methacrylate (DMAEM) cross-linked with N,N'-methylenebisacrylamide. The swelling and contracting of the hydrogels in response to relative humidity alters the polarity of the environment of DSA, stimulating a shift in the emission wavelength. From 0 to 100% RH, acrylamide-DMAEM sensors exhibited a 40 and 15 nm wavelength shift in still air and flowing gas, respectively. Agarose sensors showed a 40 nm wavelength shift from 0 to 100% RH in still air and a 30 nm shift from 0 to 70% RH in flowing gas. Response times for both sensors were 15 min in still air and less than 5 min in flowing gas. The sensing approach is straightforward and cost-effective, yields sensors with characteristics suitable for commercial measurement of RH (i.e., sensitivity, response times, reproducibility), and allows ease of adaptability to specific RH measurement requirements. The results support the potential extension of the method to a wide variety of analytes in the vapor phase and aqueous solution by incorporation of functionalized "smart" hydrogels.