【作者】 陶传义；

【导师】 黎学明；

【作者基本信息】 重庆大学 ， 光学工程， 2011， 博士

【摘要】 气体传感器是通过物理、化学效应将气体的种类、浓度等按一定规律转化为可测电量或非电量信息的气体测量传感器件。光纤气体传感器作为一类重要的气体传感器,已在工业气体监测、环境空气质量检测、有害气体分析、爆炸气体实时监测、火山喷发气体分析等领域获得广泛应用。甲烷及其氯化物之一的三氯甲烷是一类对安全生产、环境和人体健康有重要影响的气体,其中甲烷气体极易发生爆炸,是煤矿事故的“头号杀手”,也是天然气储运、加工、使用过程中的重要危险源,而挥发性三氯甲烷则可作用于中枢神经系统,具有麻醉作用,对心、肝、肾有损害,吸入后引起急性中毒,因此监测甲烷及其挥发性三氯甲烷的浓度对于煤矿安全生产、天然气安全使用、人体健康具有十分重要的作用。为了进一步提高传感器监测甲烷及其挥发性三氯甲烷气体浓度的性能,论文提出两种基于cryptophane包合作用的荧光猝灭型传感器,分别用于甲烷和挥发性三氯甲烷的检测,即基于cryptophane修饰SiO_x纳米线（NWs）的荧光猝灭型甲烷传感器和基于cryptophane-E-（OEt）₆修饰SiO_xNWs的荧光猝灭型三氯甲烷气体传感器。具体研究内容包括:①分析荧光猝灭型气体传感器的光学系统、敏感元件及其工作原理,提出将基于激发/猝灭特性非均匀分布的荧光猝灭型传感器的数学模型应用到连续激发方式的荧光测量中。②分别以香兰素、乙基香兰素为起始原料,采用略为改进的直接法合成主体化合物cryptophane-A和cryptophane-E-（OEt）₆。采用量子化学方法研究了cryptophane-A与甲烷（CH₄）的相互作用。荧光光谱研究表明,CHCl₃能够被cryptophane-E-（OEt）₆选择性包合。cryptophane主体对客体的包合不仅取决于客体尺寸相对于内腔的大小,还取决于客体可进入和离开腔入口的大小,这种包合作用主要是通过范德华力来稳定的。该研究结果为基于cryptophane的甲烷（或三氯甲烷）传感器设计与制作奠定了理论基础。③基于SiO高温热蒸发法,提出一种可规模合成超长无定形氧化硅纳米线的方法。该方法采用抛光p型单晶硅片为基板,分别在有或无铝热剂条件下进行。由于SiO_x纳米线比表面积大且易于连接各种功能基团,能够为气体传感器提供平台。④设计并制作一种基于cryptophane-A修饰SiO_x纳米线荧光猝灭型光纤传感元件,用于3.5% （v/v）以下的低浓度甲烷动态监测。结果表明,该甲烷传感元件的检出限低于0.1%,具有响应快速、恢复时间短（仅几秒钟）、重复性好、选择性强、长期稳定性良好。实验还开展了基于cryptophane-E-（OEt）₆修饰SiO_x纳米线的甲烷敏感性能研究,发现在甲烷浓度小于0.5%的低浓度区域,I0/I^[CH₄]曲线满足Stern-Volmer方程线性特征,而较高浓度甲烷时转为非线性。同时,实验证明该传感器在矿井环境下对甲烷同样具有良好的选择性。⑤基于V.I. Ogurtsov等建立的通用数学模型和强度调制型传感器研究对象,在连续激励条件下,研究了激活介质内的主要参数（即猝灭常数、甲烷气体和cryptophane分子浓度和激发强度）在非均匀分布情况下荧光猝灭型甲烷传感器的积分荧光信号（强度）变化规律。具体分析了离散单指数模型和正定义的瑞利（Rayleigh）和麦克斯韦（Maxwell）分布,表明瑞利分布和麦克斯韦分布的逼近误差显著小于离散单指数模型;瑞利分布模型使实验和计算的荧光强度数据最一致（对于cryptophane-A和cryptophane-E-（OEt）₆,δin分别为0.34%和1.66%）;分布式猝灭常数的平均值大于单指数模型;同时,还采用双指数模型（属于三参数模型） fδ（k-k₁） + （1-f）δ（k-k₂）对数据进行逼近,对于基于cryptophane-E-（OEt）₆的传感器,δin减小为1.14%,逼近效果明显优于单参数模型。⑥设计和制作一种荧光猝灭型三氯甲烷传感器,其敏感元件为crptophane-E-（OEt）₆分子固定于SiO_x纳米线,分析反射荧光信号强度变化即可实现对三氯甲烷的检测。研究表明,随着三氯甲烷浓度增加,荧光强度逐渐减低,即被三氯甲烷有效猝灭,且传感器输出信号满足Stern-Volmer线性关系。传感器对三氯甲烷检出限为52.4 ppm,响应时间80 s,恢复时间150 s,且四氯化碳和二氯甲烷几乎不干扰三氯甲烷的响应。此传感器对三氯甲烷的检测时间比现有的气相色谱法具有明显效率优势,有望应用于工作环境中三氯甲烷监测。更多还原

【Abstract】 Gas sensors detect different gas types and transform current gas concentration in an electrical signal （or non-electrical signal） which can be read by indicators, regulators, alarm systems and other another analysis systems. Recently, optical fiber gas sensors have been attracting attention owing to several advantages over conventional electricity-based gas sensors. Methane （CH₄） is extremely flammable and may form explosive mixtures with air. As one of chlorinated derivatives of methane, chloroform （CHCl₃） is harmful to both human health and the environment. Inhaling its vapors depresses the central nervous system and can cause dizziness, fatigue, and headache. Chronic exposure may damage the liver and kidneys, and some people have an allergic reaction to it. Thus, developing sensors for the detection of methane and volatile chloroform is gaining interest in fields related to coal mine production and industrial and environmental applications.Therefore, this paper presents two novel quenched-luminescence gas sensors based on the binding properties of cryptophanes for detection of methane and volatile chloroform, respectively. They are optical methane sensor based on luminescence quenching of silica nanowires （SiO_xNWs） modified with cryptophane-A and volatile chloroform sensor based on cryptophane-E-（OEt）₆@SiO_xNWs. The detailed contents are as follow:①The operation principle of luminescence-based fibre-optical sensor with methane-sensing element comprising cryptophane-functionalized SiO_x nanowires immobilized on the silicon substrate was analysed. A general mathematical model, which describes the integral luminescent intensity signal of the quenched-luminescence methane sensor, was applied in the continuous excitation condition.②Cryptophane-A and cryptophane-E-（OEt）₆ were synthesized from the starting materials vanillin and ethyl vanillin, respectively, according to the well-known“direct method”with modified procedures. A quantum chemical study was devoted to the complexation of methane by cryptophane-A. The spectral studies indicate that cryptophane-E-（OEt）₆ is able to selectively encapsulate chloroform. The complexation of a nonpolar substrate by a cryptophane host depends mainly on the size of the guest with respect to the size of the cavity, and on the size of the portals through which the guest can enter and leave the cavity. The association is stabilized mainly through van der Waals forces. This knowledge has been gained from recent endeavors, which allow sensitive investigation of cryptophane-based sensor and other devices using cryptophanes, likely to develop in the field of environmental chemistry.③Based on the thermal evaporation of silicon monoxide at high temperature, an improved method has been developed for large-scale synthesis of ultralong amorphous silica sub-micron wires using polished p-Si wafers as substrates. The synthesis was done with and without thermite. Silica nanowires as excellent candidate materials for chemical sensors and biosensors, have attracted wide attention due to their intrinsic vast surface-to-bulk ratio, good reversibility, quick response, and oxide-coated or H-terminated surface, which allows easy attachment to various functional groups.④An optical sensor based on luminescence quenching of cryptophane-A@silica nanowires was successfully constructed and used to dynamically monitor methane gas at low concentration below 3.5% （v/v）. The sensing element shows an intensive and stable blue luminescence when excited by UV light source at wavelength of 380 nm, and it is efficiently quenched by molecular methane. The response of the sensing element demonstrates excellent linear Stern-Volmer behavior at the fixed wavelength 439 nm within the methane concentration range between 0.1% and 3.5% （v/v）. A detection limit of below 0.1% （v/v） is estimated for the methane sensing element. This newly developed methane sensing element has significant advantages over the currently available methane sensors such as fast response and recovery （within seconds）, good repeatability, selectivity, and long-term stability. On the other hand, experimental investigations of the methane sensing performance of the fabricated cryptophane-E-（OEt）₆@SiO_xNWs material show that there was a downward curvature of the Stern-Volmer plots （i.e. turning nonlinear） especially at higher methane concentrations （above 0.5% v/v）. This methane sensor will also have good selectivity in the mine environment.⑤According a general mathematical model suggested by V.I. Ogurtsov et al., just considering the continuous excitation, the integral luminescent intensity signal of the quenched-luminescence methane sensor was described in the case of non-uniform distribution of the main parameters inside active medium, namely the quenching constant, methane concentration and cryptophane distribution and intensity of excitation. Firstly, discrete single-exponential model and Rayleigh and Maxwell distributions （positively defined） were analyzed. For both Rayleigh and Maxwell distributions approximation errors were smaller than for the discrete single-exponential model. The model with Rayleigh distribution provided the best agreement between experimental and calculated intensity data （δin = 0.34 for the sensor based on cryptophane-A; andδin = 1.66 for the sensor based on cryptophane-E-（OEt）₆）. Average of distributed quenching constant was larger than for the single-exponential model. On the other hand, double-exponential model fδ（k-k₁） + （1-f）δ（k-k₂）, which belongs to three-parametric model, was analyzed. This model provided better approximation than above one-parametric models. Approximation errorδin reduces to 1.14 for the sensor based on cryptophane-E-（OEt）₆.⑥A quenched-luminescence sensor for chloroform vapor detection was designed and implemented successfully through the employment of silica nanowires as a substrate for the immobilization of the cryptophane-E-（OEt）₆ transducer, coupled with a fiber optical device, which was designed to operate via luminescence reflection. The sensing material shows a stable blue luminescence, and it is efficiently quenched by chloroform vapor. The prepared optical sensor was highly sensitive to 52.4 ppm of chloroform vapor and the response time was very fast within 80 s. There is almost no interference from CCl4 and CH2Cl2 on the detection. This novel efficient chloroform vapor sensor has significant advantages over gas chromatography and might have application potential.更多还原