Evanescent-wave optical Cr VI sensor with a flexible fused-silica capillary as a transducer

A light-guiding, flexible fused-silica (FFS) capillary has been used in designing an optical fiber Cr VI sensor for monitoring Cr VI ions in water samples. The FFS capillary is similar to a conventional silica optical fiber in that it can guide light in the wavelength region from the UV to the near IR but different from a conventional optical fiber in that it is a tubular waveguide. The inner surface of the FFS capillary is fused silica, which one can modify to design an optical fiber chemical sensor. The FFS capillary has a cladding layer plus a protective polymer coating on its outside surface. The cladding layer ensures the ability of the FFS capillary to guide light. The protective coating increases the FFS capillary's mechanical strength and makes it robust for practical applications. Compared with conventional silica optical fibers, it is much easier and more feasible to use this FFS capillary to fabricate long-path (tens of meters to thousands of meters) evanescent-wave based chemical sensors. We describe a Cr VI sensor based on the intrinsic evanescent-wave absorption by Cr VI ions in a water sample filled inside the capillary as an example of use of a FFS capillary in chemical sensor design. This simple sensor, using a 30 m light-guiding FFS capillary as a transducer, has the capability of detecting as little as 31 parts in 10(9) of Cr VI in a water sample, which is close to the detection limit of some sophisticated, expensive analytical instruments.     

Density profile of water confined in cylindrical pores in MCM-41 silica

Recently, water absorbed in the porous silica material MCM-41-S15 has been used to demonstrate an apparent fragile to strong dynamical crossover on cooling below ～220 K, and also to claim that the density of confined water reaches a minimum at a temperature around 200 K. Both of these behaviours are purported to arise from the crossing of a Widom line above a conjectured liquid-liquid critical point in bulk water. Here it is shown that traditional estimates of the pore diameter in this porous silica material (of order 15 ?) are too small to allow the amount of water that is observed to be absorbed by these materials (around 0.5 g H(2)O/g substrate) to be absorbed only inside the pore. Either the additional water is absorbed on the surface of the silica particles and outside the pores, or else the pores are larger than the traditional estimates. In addition the low Q Bragg intensities from a sample of MCM-41-S15 porous silica under different dry and wet conditions and with different hydrogen isotopes are simulated using a simple model of the water and silica density profile across the pore. It is found the best agreement of these intensities with experimental data is shown by assuming the much larger pore diameter of 25 ? (radius 12.5 ?). Qualitative agreement is found between these simulated density profiles and those found in recent empirical potential structure refinement simulations of the same data, even though the latter data did not specifically include the Bragg peaks in the structure refinement. It is shown that the change in the (100) peak intensity on cooling from 300 to 210 K, which previously has been ascribed to a change in density of the confined water on cooling, can equally be ascribed to a change in density profile at constant average density. It is further pointed out that, independent of whether the pore diameter really is as large as 25 ? or whether a significant amount of water is absorbed outside the pore, the earlier reports of a dynamic crossover in supercooled confined water could in fact be a crystallization transition in the larger pore or surface water.     

光纤SPR湿敏传感器及其共振光谱特性研究

提出并研制了基于光纤SPR传感探针的新型湿敏传感器。首先研究了光纤SPR传感探针对环境湿度变化的敏感特性,在此基础上提出在光纤SPR传感探针表面增覆不同厚度且具有水分子吸附功能的PVA薄膜来实现环境相对湿度的监测。研究结果表明,增覆双层PVA薄膜的光纤SPR传感探针在高湿区具有较好监测效果,其共振强度对应的相对湿度测量灵敏度达到1.59%/%RH,较光纤SPR探针呈现显著提高。而增覆单层PVA薄膜的光纤SPR传感探针在高湿区共振波长对应的相对湿度监测灵敏度达到2.411nm/%RH。此外所提出的新型光纤SPR湿敏探针在PVA薄膜失效后经过特殊工艺处理仍可重复镀膜使用。     

常压百级洁净度环境中SiO2薄膜稳定性

在常压百级洁净度环境下,采用三种不同折射率的SiO₂溶胶在熔石英基底上涂制四种不同薄膜,利用光学理论计算模拟了三种胶体涂制的膜层稳定性,通过实验考查了膜层光学指标随时间的变化规律。SiO₂薄膜能够显著提升光学元件透射率,但由于膜层表面的大量羟基及其多孔结构,SiO₂薄膜易吸附周围环境中的有机污染物及水分填充膜层孔隙,从而导致膜层折射率发生变化,影响膜层透射率、反射率等光学性能。实验结果发现,三种溶胶凝胶化学膜在常压百级环境中的有效期为80 d(绝对变化率小于0.1%),且三种胶体涂制的膜层稳定性由高到低依次为折射率1.19, 1.15, 1.25的膜层。     

Subfemtomole detection of small molecules with microsphere sensors

We investigated the feasibility of using a silica microsphere sensor for detection of small molecules. Using the silica molecules (60 Da) at the sphere's surface as a model system, we measured the spectral shifts in the whispering-gallery modes (WGMs) when the sphere size was decreased by a hydrofluoric acid (HF) solution. The results demonstrate that our sensor is capable of detecting a 4 pm (or 0.01 layer of silica) decrease in sphere radius, corresponding to a change of 0.4 fmol silica molecule. These results suggest that small molecules can be detected in trace quantities at the surface of an optical microsphere sensor.     

基于傅里叶红外光谱的生物质环境协调功能材料制备机理及性能研究

以废弃核桃壳为载体材料、癸酸为相变材料,采用微波加热法制备癸酸/多孔活性炭功能材料。采用傅里叶红外光谱仪对癸酸/多孔活性炭功能材料制备过程各阶段的合成物质进行测试,即活性炭前驱体制备阶段、多孔活性炭制备阶段和癸酸/多孔活性炭功能材料制备阶段。研究癸酸/多孔活性炭功能材料制备过程中多孔活性炭复杂网络结构形成机理、癸酸嵌入方式、癸酸与多孔活性炭的嵌合机理,阐明微波加热法制备癸酸/多孔活性炭功能材料的相关机理。同时采用动态水分吸附分析仪、差示扫描量热仪和环境测试舱对癸酸/多孔活性炭功能材料的湿性能、热性能和吸附性能进行测试。结果表明：癸酸/多孔活性炭功能材料具有发达的孔结构和复杂的网络结构,其中部分孔隙吸附癸酸,部分孔隙吸附甲醛分子,孔隙表面具有亲水性的官能团吸附水分子。癸酸/多孔活性炭功能材料具有较好的湿性能、热性能和吸附性能,其在相对湿度40%~60%,平衡含湿量为0.063 1~0.257 0 g·g-1;相变温度为27.42~33.96 ℃,相变焓为52.14~52.67 J·g-1;经过4 h对甲醛气体的吸附效率为50.57%。     

Realisation of a humidity sensor based on perfect metamaterial absorber

In this paper, we have proposed and investigated a humidity sensor based on perfect metamaterial absorber. The sensor is composed of three layers, which are metallic particle array on the top, porous silicon in the middle layer and metallic film at the bottom. According to the effective medium approximation, the effective permittivity of porous silicon is mainly determined by the filling fraction of water condensation. It is shown that the resonant wavelength displays significant red-shift with the increasing effective permittivity of porous silicon. Furthermore, the simulation results indicate that the refractive index sensitivity of absorber is high to 249 nm/RIU, which makes our structure be an ideal candidate for evaluating the humidity of environment.     

多孔颗粒内气体传递反应双阶段描述

本文采用双阶段模型描述多孔颗粒与气体的传递反应。反应分为两个阶段:气体反应物在扩散进入颗粒内部同时与颗粒发生反应的第一阶段;形成产物层后,扩散和反应用双区域模型来描述的第二阶段。分析发现,蒂勒数是描述过程特性的重要参数,同时反映反应和扩散速度的影响,且与总阻力存在一定关系。利用TGA进行了脱硫反应实验,分析了反应温度、颗粒大小等对反应的影响,实验结果很好地证实了理论分析结论。     

Water vapour sorption on hydrophilic and hydrophobic nanoporous materials

The aim of this study is to compare water vapour sorption isotherms on various mesoporous materials in their pristine state and after silanisation. Commonly the pristine state is regarded as hydrophilic and the silanised one as hydrophobic. Water vapour sorption experiments are discussed for a highly ordered nanoporous aluminium oxide with straight cylindrical channels of ca. 25 nm diameter and for various controlled porous glasses (CPGs) with disordered pores in the range of 13 nm diameter. The water sorption isotherms exhibit in both cases a hysteresis over the entire humidity range. At higher humidities the pristine materials show capillary condensation whereas for the silanised samples this phase transition does not occur or even a loss of water is recorded as for the silanised Al₂O₃. Surprisingly, for the silanised Al₂O higher water uptake is observed in the low humidity region. Application of the excess surface work (ESW) method delivers a reduced structural component in the long range interaction of the water molecules with a hydrophobic surface. Inverse gas chromatography studies of the silanised CPGs result in an increased short range dispersive part of the surface energy with the increasing degree of silanisation.     

A novel humidity sensor using yb-doped SrCeO3 ionic conductor with a au-pd filter

A novel humidity sensor operating at T<580K using Yb-doped SrCeO₃ ionic conductor with a Au-Pd chemical filter has been developed. In this unique design, both the electrodes are exposed to the same test gas and therefore do not require separation of working and reference compartments. A thin layer of impervious Au-Pd alloy on one surface of the perovskite electrolyte allows selective access to oxygen gas, while the other surface coated with porous Pt is exposed to both H₂O and oxygen. Sensor emfs are found to be directly proportional to log pH₂O and independent of pO₂. The design aspects of the sensor, the experimental set-up, some typical results and a postulated mechanism of sensor operation are described in this paper. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

Study on the design of ZnO/PANI composites and the mechanism of enhanced humidity sensing properties

ZnO/PANI composite humidity sensor was prepared by hydrothermal method. The first principles of density functional theory study the sensing mechanism. The calculation shows that the oxygen vacancy on ZnO surface is beneficial to the adsorption of water molecules. The {0 0 0‾1} crystal plane with the largest lattice oxygen number in ZnO has a strong adsorption capacity for water molecules, which is also conducive to improving the humidity sensitivity. PANI is easy to be combined on {0 1‾1 0} plane of ZnO, and it indirectly promotes the growth of {0 0 0‾1} plane, increasing the adsorption of water molecules and the proportion of H⁺ and H₃O⁺ ions. In addition, the N–H group in ZnO/PANI enhances the H⁺ conduction, which further improves the performance of the sensor. The results concluded that the proportion of lattice oxygen in humidity sensor is an important factor of humidity sensor sensitive detection.     

The improvement of gas-sensing properties of SnO<Subscript>2</Subscript>/zeolite-assembled composite

SnO₂-impregnated zeolite composites were used as gas-sensing materials to improve the sensitivity and selectivity of the metal oxide-based resistive-type gas sensors. Nanocrystalline MFI type zeolite (ZSM-5) was prepared by hydrothermal synthesis. Highly dispersive SnO₂ nanoparticles were then successfully assembled on the surface of the ZSM-5 nanoparticles by using the impregnation methods. The SnO₂ nanoparticles are nearly spherical with the particle size of ~?10 nm. An enhanced formaldehyde sensing of as-synthesized SnO₂-ZSM-5-based sensor was observed whereas a suppression on the sensor response to other volatile organic vapors (VOCs) such as acetone, ethanol, and methanol was noticed. The possible reasons for this contrary observation were proposed to be related to the amount of the produced water vapor during the sensing reactions assisted by the ZSM-5 nanoparticles. This provides a possible new strategy to improve the selectivity of the gas sensors. The effect of the humidity on the sensor response to formaldehyde was investigated and it was found the higher humidity would decrease the sensor response. A coating layer of the ZSM-5 nanoparticles on top of the SnO₂-ZSM-5-sensing film was thus applied to further improve the sensitivity and selectivity of the sensor through the strong adsorption ability to polar gases and the “filtering effect” by the pores of ZSM-5.     

Sliding behavior of water drops on sol-gel derived hydrophobic silica films

Control on the wettability of solid state materials is a classical and key issue in surface engineering. Optically transparent methyltriethoxysilane (MTES)-based silica films with water sliding angle as low as 9° were successfully prepared by two-step sol-gel co-precursor method. The emphasis is given to the effect of trimethylethoxysilane (TMES) as a co-precursor on water sliding behavior of silica films. The coating sol was prepared with molar ratio of methyltriethoxysilane (MTES), methanol (MeOH), acidic water (0.01 M, oxalic acid) and basic water (12 M, NH₄OH) kept constant at 1:12.73:3.58:3.58 respectively, and the molar ratio of TMES/MTES (M) was varied from 0 to 0.22. The static water contact angle as high as 120° and the water sliding angle as low as 9° was obtained by keeping the molar ratio (M) of TMES/MTES at 0.22. When the modified films were cured at temperature higher than 280 °C, the films became superhydrophilic. Further, the humidity study was carried out at a relative humidity of 90% at 30 °C over 60 days. We characterized the water repellent silica films by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), % of optical transmission, humidity tests and static and dynamic water contact angle (CA) measurements.     

FTIR和XRD研究甲酰胺在高岭石插层复合体系中的形态及其复合物的微观结构

插层复合体系中,有机插层剂在插层的同时也可能吸附在复合物的表面或以自由态存在,对插层分子的表征将会产生较大的影响。以丙酮作淋洗剂,用FTIR及XRD技术对淋洗前后的插层复合体系监控,插层剂分子在复合体系中的可能存在形式,探讨水的作用及复合物微观结构的变化。结果显示：甲酰胺有插层、游离和吸附在复合物表面三种存在形态。3 355和3 462 cm-1处的红外振动峰归属于表面吸附的插层剂分子,3 626 cm-1的峰归属于插层的H₂O分子,在干燥后均消失。H₂O作为填充空间的分子参预了插层过程,且插入到层间,并在干燥后脱嵌。3 534 cm-1处的振动峰在淋洗前后一直存在,是由于插层的甲酰胺分子与高岭石层间形成氢键作用的结果。以丙酮作为淋洗剂,可以选择性的消除表面吸附的甲酰胺而不影响复合物的结构。插层的甲酰胺分子以C—N键垂直于层片呈单分子层排列,并通过氨基与高岭石铝氧八面体层的内表面羟基和硅氧四面体层的氧形成了两种氢键作用。     

提高多孔硅传感特性的一种新方法(英文)

研究了多孔硅(PS)吸附有机溶剂分子后对多孔硅荧光谱的淬灭效应。结果表明:淬灭多孔硅发光的有机溶剂分子是极性分子,有机溶剂分子的极性不同对多孔硅发光的淬灭程度也不同,且有些有机溶剂分子吸附氧化多孔硅比吸附多孔硅引起的发光淬灭具有更好的可逆性和选择性;用含有胺基的正丁胺(CH3CH2CH2CH2-NH2)作碳源,用射频辉光放电等离子系统在多孔硅表面沉积c n膜对多孔硅进行钝化处理后发现:其电致发光强度明显增强,发光峰位兰移,且在大气中存放60天后,其电致发光谱强度基本不衰减,峰位不再移动。经钝化处理的器件较未经处理的器件具有小的串联电阻Rs和低的驱动电压。这为提高多孔硅的传感特性提供了一种新方法。     

Surface diffusion and entrapment of simple molecules on porous silica

Interactions of simple molecules with the surface of porous silica have been investigated using time-of-flight secondary ion mass spectrometry and temperature programmed desorption. A monolayer of water diffuses into pores at temperatures higher than 110 K. Multilayers of water are also incorporated in pores via sequential surface diffusion. In contrast, a methanol monolayer tends to stay on the surface up to 150 K, and carbon dioxide diffuses into pores rather gradually. Results can be explained as the contribution of hydrogen bonds between the adsorbate–substrate and adsorbate–adsorbate interactions. The predominance of the former (latter) might be responsible for single-molecule migration of methanol and carbon-dioxide (collective diffusion of water molecules) on the surface. These molecules are entrapped at higher coordination sites in pores, as revealed from thermal desorption peaks appearing at higher temperatures than those from non-porous silica. However, no significant difference is observed in desorption kinetics of CF₂Cl₂, Kr, CH₄, and N₂ molecules between the porous and non-porous silica substrates.     

水蒸气对二氧化硅膜的影响：吸附性能与渗流效应

研究了在50和90 oC时水蒸气对孔径约为4 ?的二氧化硅膜的吸附性能和渗流效应影响,采用椭圆偏振光谱分析水蒸气的吸附性能,以及测定氦气-H₂O二元混合气体的透过性能. 研究表明水蒸气在二氧化硅膜上的吸附行为符合一阶Langmuir等温线,同时,在H₂O分子存在的条件下,氦气的透过率会急剧下降. 通常,在极小孔内气体分子的传输被认为是不连续的,而是在势能下从一个占有位置跳跃到另外一个空位上. 当在二氧化硅表面的H₂O分子覆盖率上升时,氦气的透过率急剧下降可能与渗流效应有关,其中吸附在二氧化硅表面的H₂O分子阻碍了氦气分子的跳跃.     

石墨烯表面的特征水分子排布及其湿润透明特性的分子动力学模拟

石墨烯因其独特的分子构型、卓越的物理化学性能而受到广泛关注.本文首先利用分子动力学模拟比较了单层石墨烯、铜、二氧化硅三者表面的浸润性,除了接触角的比较,还分析了基底表面的水分子排布,得到石墨烯表面的特征水分子排布为:表面有两层密集的水分子层,其中靠近基底的密集水分子层中O—H键与垂直基底方向夹角集中在90°附近,并且基底表面的氢键几乎都垂直于基底.另一方面,本文研究了石墨烯浸润透明特性,发现在铜和二氧化硅上添加一层石墨烯,对铜的浸润性影响较小,对二氧化硅的浸润性影响很大,不仅使其上接触角显著增大,还使得基底表面的水分子排布呈现出类似单层石墨烯上的规律.本文使用分子动力学模拟方法从微观尺度验证了文献的实验结果,从基底表面水分子排布角度分析了石墨烯独特的浸润透明特性,为进一步开发石墨烯在微结构设计上的应用提供了理论指导.     

Porous silicon with β-cyclodextrin modified surface for photoluminescence sensing of organic molecules in gas and liquid phase

Porous silicon surface was modified by photochemically activated hydrosilylation reaction with permethyl-6^I-alkenoylamino-6^I-deoxy-β-cyclodextrins terminated with linear alkenoyl spacers of various lengths. As compared to unmodified surface, derivatized surfaces revealed modified photoluminescence response in the presence of controlled amounts of various organic molecules in gas and liquid phase. For the selected set of analytes we observed most significant modification of photoluminescence response for aromatic compounds what corresponds to optimum molecular size for strong host–guest interaction with β-cyclodextrin cavity. Aliphatic compounds quenched photoluminescence from both unmodified and surface modified porous silicon. For low gas phase concentrations of aromatic analytes β-cyclodextrin modified porous silicon revealed photoluminescence enhancement, at higher concentrations common photoluminescence quenching was observed. The size-dependent host–guest interaction between β-cyclodextrin cavity and detected molecule was observed in photoluminescence quenching in the presence of aliphatic molecules in liquid phase. The role of the strength of host–guest interactions between detected analytes and β-cyclodextrin cavity on photoluminescence sensor response is discussed.