【作者】 王佳；

【导师】 贺竞辉；

【作者基本信息】 苏州大学 ， 化学工程与技术， 2024， 博士

【摘要】 二氧化氮(NO2)作为空气污染的主要成分之一,会导致光化学烟雾、酸雨、臭氧层的破坏。人体长期暴露于低浓度NO2的环境中,呼吸系统会受到严重损害,引发气管炎、支气管狭窄、肺水肿等呼吸系统疾病。因此,开发性能优异的NO2传感器对空气中低浓度NO2的准确检测十分重要。电阻式NO2气体传感器具有结构简单、性能稳定、成本低等优点得到广泛研究和应用,但存在能耗高、灵敏度低、选择性差等缺点,亟待气敏材料的进一步革新以提升传感性能。离子共轭材料将化学计量的离子态物种/基团引入有机共轭骨架中,利用氢键、双氢键以及离子-偶极相互作用等适中强度的相互作用力,能高选择性、高灵敏度地检测NO2。但空气中水蒸气浓度,即湿度远高于通常需要检测的NO2浓度范围(ppb、ppm),对NO2气体传感造成严重干扰。本论文以离子共轭材料为NO2气体传感材料研究对象,研究了不同种类离子共轭材料通过合适的抗湿策略,包括加热、疏水层覆盖、材料设计实现抗湿高选择性NO2传感,探究了离子共轭材料抗湿的机理。本文主要从以下几个方面展开:(1)将两种离子共轭小分子,即罗丹明B和6G染料制备成垂直电阻器件测试其阻变性能,高电场(>～107 V/m)下发生导电击穿。而在低电场(<107 V/m)下电压-电流变化符合欧姆定律,可以应用于NO2传感。制备的叉指电极气体传感器在低电场时可检测最低浓度为100 ppb的NO2。密度泛函理论(DFT)计算表明,与其他干扰气体相比,罗丹明B和6G与NO2分子间具有最大的结合能(罗丹明B:0.856 eV,罗丹明6G:0.751 eV)和电子转移量(罗丹明B:0.536 e-,罗丹明6G:0.553 e-),因此对NO2检测具有高选择性。但是空气中的水分子会严重影响对NO2的定性和定量检测,相对湿度RH>54%时,已经无法评价NO2浓度的响应和敏感性。传感器工作温度为100℃时可减弱54%RH的影响,恢复对NO2传感性能,但连续加热时小分子受腐蚀严重,性能快速衰减,无法应用于实际NO2的检测。因此需要探索更稳定的材料,以实现在实际环境中对NO2的有效检测。(2)设计并合成了一种具有离子共轭结构的共价有机框架(COF)材料,命名为SA-TAPB。该材料展现出了高结晶性和优异的热稳定性。基于SA-TAPB所制备的传感器件能够检测低至30 ppb的NO2。即使在不同曲率半径的弯曲状态下,SA-TAPB柔性传感器也能保持其对NO2的传感性能。SA-TAPB传感器对NO2的高选择性主要归功于其与NO2分子结合后具有最大的结合能(0.045 eV)和电子转移量(0.574 e-)。通过谐振微悬臂梁传感器的测试进一步证实了 SA-TAPB在多种气体中对NO2具有最大的吸附量。然而,当RH达到75%时,传感器对NO2的传感能力受到显著影响。通过将传感器的工作温度提升至80℃,成功减弱了 75%RH的湿度影响,实现了对NO2的抗湿检测。这一现象的原因在于,提高工作温度导致SA-TAPB对NO2和水分子的吸附均有所减弱,但与NO2相比,对水分子的吸附降低更为显著,从而相对提高了对NO2的选择性。(3)通过醋酸铜与二苯并[G,P]屈-2,3,6,7,10,11,14,15-辛醇的水热反应成功合成了一种导电离子共轭金属有机框架材料Cu-DBC。所制备的电阻式传感器件对NO2的最低检测限达到50 ppb。Cu-DBC电阻式传感器展现出对NO2的优异选择性,这主要归因于其吸附NO2后具有最大的电子转移量(0.237e)。然而,当暴露于33%RH湿空气中时,传感器无法有效检测NO2浓度。为了解决这一问题,我们通过静电纺织聚四氟乙烯纤维(PTFE)覆盖于Cu-DBC传感器表面,实现了在室温下对50 ppb NO2的抗湿检测,无需额外加热。研究发现,PTFE薄膜能有效阻碍水蒸气进入气敏活性层,从而在0-75%RH的范围内实现了对NO2的抗湿检测。该策略简化了传感器的操作条件,而且提高了其在实际应用中的稳定性和可靠性。(4)通过方酸与含有不同数量甲基的芳香胺(对苯二胺、2,5-二氨基甲苯和2,5-二甲基-1,4-苯二胺)的缩合反应,成功合成了三种离子共轭聚合物:p-PPS、p-PTS和p-PDPS。这些聚合物所制备的传感器能够实现低至200 ppb NO2的有效检测。与吸附其它干扰气体相比,这些聚合物在吸附NO2后展现出最大的电子转移量(p-PPS:0.317 e-,p-PTS:0.337 e-,p-PDPS:0.344 e-),从而赋予了传感器对NO2的高选择性。值得注意的是,即使在0-75%的相对湿度范围内,这三种聚合物传感器均能稳定检测NO2。特别是p-PTS传感器,在室温下无需加热或疏水层覆盖,对NO2的响应最大下降仅为10.3%。理论计算揭示了甲基的引入增强了聚合物骨架的平面性,有效促进了 NO2吸附后的电荷转移。同时,甲基的存在还阻碍了水分子进入吸附位点,从而实现了无需外部加热或引入疏水层的本征抗湿性能。这些发现为开发具有本征抗湿性能的高性能NO2传感器提供了新的策略,并为未来在更复杂环境条件下的应用奠定了基础。本论文发现相比于水分子,离子共轭材料对NO2吸附和电荷转移具有优势,可通过合适的方法,如提高传感器工作温度、疏水层覆盖和疏水基团引入策略提高传感器的抗湿性能。更多还原

【Abstract】 Nitrogen dioxide(NO2)is one of the main components of air pollution,which can lead to photochemical smog,acid rain,and depletion of the ozone layer.When the human body is exposed to low concentrations of NO2 for a long period of time,the respiratory system can be severely damaged,leading to respiratory diseases such as tracheitis,bronchial narrowing,and pulmonary edema.Therefore,the development of high-performance NO2 sensors for accurate monitoring of low concentrations of NO2 in the environment is crucial.Resistive NO2 gas sensors,with advantages such as simple structure,stable performance,and low cost,have been widely studied and applied.However,they have drawbacks such as high energy consumption,low sensitivity,and poor selectivity,requiring further innovation in gas-sensitive materials to enhance their sensing performances.Ion-in-conjugation materials introduce stoichiometric ionic species/groups into organic conjugated skeletons,utilizing moderate interactions including hydrogen bonds,dihydrogen bonds,and ion-dipole interactions to detect NO2 with high selectivity and sensitivity.However,the concentration of water vapor in the ambient air,i.e.,humidity,is much higher than the typical NO2 concentrations that need to be detected(ppb,ppm),causing serious interference with NO2 gas sensing.This thesis focuses on ion-in-conjugation materials as the research object for NO2 gas sensing materials,studying different types of ion-inconjugation materials through appropriate anti-moisture strategies,including heating,hydrophobic layer covering,and material design to achieve anti-moisture,highselectivity NO2 sensing,and exploring the mechanism of anti-moisture of ion-inconjugation materials therebehind.This thesis mainly includes the following aspects:(1)Two types of ion-in-conjugation small molecules,namely Rhodamine B and 6G dyes,were casted onto vertical resistor devices to test their resistive performance.A conductive breakdown occurs at higher electric fields(>～107 V/m).At low electric fields(<107 V/m),the voltage-current relationship is consistent with Ohm’s law and could be applied to NO2 sensing.The prepared gas sensor can detect a minimum concentration of 100 ppb of NO2 under a low electric field.Density functional theory(DFT)calculations show that compared to other interfering gases,Rhodamine B and 6G have the highest binding energy(Rhodamine B:0.856 eV,Rhodamine 6G:0.751 eV)and electron transfer amount(Rhodamine B:0.536 e-,Rhodamine 6G:0.553 e-)with NO2 molecules,making them highly selective for NO2 detection.However,water molecules in the air can significantly impact the qualitative and quantitative detection of NO2.When the relative humidity RH>54%,the response and sensitivity of NO2 concentration can no longer be evaluated.The sensor’s operating temperature of 100℃can mitigate the impact of 54%RH humidity,restoring the sensor’s performance for NO2 detection.However,continuous heating causes severe corrosion of small molecules,leading to rapid performance degradation,rendering it unsuitable for practical NO2 detection.Therefore,it is necessary to explore more stable materials to achieve effective detection of NO2 in real environments.(2)A covalent organic framework(COF)material,SA-TAPB,with an ion-inconjugation structure has been designed,which exhibits high crystallinity and excellent thermal stability.SA-TAPB sensors can detect NO2 levels as low as 30 ppb.Even in a bent state with different curvature radii,the SA-TAPB flexible sensor can maintain its sensing performance for NO2.The SA-TAPB sensor shows excellent selectivity towards NO2 due to its highest binding energy(0.045 eV)and electron transfer amount(0.574 e-)after NO2 adsorption.Testing the adsorption performance of SA-TAPB using resonant microcantilever sensors revealed that SA-TAPB has the highest adsorption capacity for NO2 among various gases.However,when the humidity level increased to 75%RH,it impairs the sensor’s ability to detect NO2,but this effect can be mitigated at a working temperature of 80℃,achieving anti-moisture NO2 detection.The reason for achieving anti-moisture detection through heating is that raising the sensor’s working temperature weakens the adsorption of both NO2 and water molecules by SA-TAPB,but compared to NO2,the sensor’s adsorption of water decreases more,thus relatively enhancing the selectivity towards NO2.(3)The conductive ion-in-conjugation metal-organic-framework Cu-DBC was obtained through the hydrothermal reaction of copper acetate with dibenzo[G,P]chrysene-2,3,6,7,10,11,14,15-octol.The fabricated resistive sensor component has a minimum detection limit of 50 ppb for NO2.Cu-DBC resistive gas sensor exhibits excellent selectivity towards NO2,mainly due to its maximum electron transfer amount(0.237 e-)after adsorbing NO2.However,when exposed to 33%RH humid air,the material is ineffective to detect NO2 concentrations.In order to solve this problem,we covered the surface of the Cu-DBC sensor with electrospun polytetrafluoroethylene(PTFE)fibers,achieving anti-humidity detection of 50 ppb NO2 at room temperature without the need for additional heating.Research has found that PTFE film can effectively block water vapor from entering the gas-sensitive active layer,thereby achieving anti-humidity detection of NO2 within the range of 0-75%RH.This strategy simplifies the operating conditions of the sensor,and improves its stability and reliability in practical applications.(4)By condensing quadric acid with aromatic amines containing different numbers of methyl groups:p-phenylenediamine,2,5-diaminotoluene,and 2,5-dimethyl-1,4phenylenediamine,three ion-in-conjugation polymers,namely p-PPS,p-PTS,and pPDPS,are obtained.The prepared sensor enables effective detection of NO2 as low as 200 ppb.Compared to adsorbing other interfering gases,these polymers exhibit the highest electron transfer amounts after adsorbing NO2(p-PPS:0.317 e-,p-PTS:0.337 e-,p-PDPS:0.344 e-),making the three polymer sensors highly selective towards NO2.All three polymers can sense NO2 as humidity varies from 0-75%.The p-PTS sensor does not require heating or a hydrophobic layer,with a maximum response decrease of only 10.3%at room temperature.DFT calculations show that the introduction of methyl groups into the ion-in-conjugation aromatic framework enhances planarity for p-PTS and p-PDPS after adsorbing water molecules,effectively promoting charge transfer after NO2 adsorption while hindering water molecules from entering the adsorption sites,achieving intrinsic anti-moisture without the need for external heating or introduction of a hydrophobic layer.These findings provide new strategies for developing high-performance NO2 sensors with intrinsic anti-humidity,and lay the foundation for future applications in more complex environmental conditions.This paper found that compared to water molecules,ion-in-conjugation materials have advantages in NO2 adsorption and charge transfer.The sensor’s moisture resistance can be improved through appropriate methods such as increasing the sensor’s operating temperature,hydrophobic layer coverage,and hydrophobic group introduction strategy.更多还原