Preparation and Sensitivity of SnO2 Grafted MCM-41 Sensor

Tin dioxide is one of the most widely used semiconductor gas sensor to detect reducing gases1-3. The sensing mechanism of SnO2 is usually based on the change of the resistance of the sensor in different gas environment. In air, the surface-adsorbed oxygen species on the surface of SnO2 act as surface acceptors of electrons, hence diminishing the conductivity of SnO2. However, when reducing gases such as H2, CO, or CH4 are introduced in the air stream, the resistance of the SnO2 sensor is …     

CeO2/SnO2纳米材料的制备与气敏性能研究

本文应用溶胶-凝胶法制备了7种不同成分和煅烧温度的CeO2/SnO2材料,应用X射线衍射方法对其中的3种进行了结构表征和粒度分析,运用自组装的气敏性能设备检测了该7种不同成分的CeO2/SnO2材料的气敏性能,简要分析了其气敏机理。结果表明:掺杂CeO2有利于SnO2晶粒的细化;掺杂CeO2和La2O3可改变或提高SnO2气敏材料对某些气体的气敏性能;煅烧温度在600℃~800℃之间,掺杂2?O2的CeO2/SnO2气敏材料,随煅烧温度上升,气敏性能下降;煅烧温度600℃、掺杂5?O2的CeO2/SnO2气敏材料,对乙醇具有较高的灵敏度和选择性,具有开发应用价值;CeO2/SnO2气敏材料的气敏机理为表面电导控制型。     

二氧化锡气体传感器快速检测挥发性有机化合物

论述了将SnO2气体传感器作为便携式气相色谱检测器,重点是挥发有机化合物(VOCs)检测方法的可行性研究。SnO2气体传感器的动态范围103;最小检测浓度(苯)8.12×10-4g/L、面积重现性<6%,取得了较满意的结果。对SnO2气体检测器的加热电压、温度特性和快速检测指标作了基本分析和考察,最后将SnO2气体传感器和FID检测器进行了初步比较。实验表明,将其作为专用便携色谱检测器,可以基本满足快速分析应用的要求。     

纳米氧化锡修饰的微催化燃烧式氢气传感器的研制

研制了一种基于多孔纳米氧化锡(SnO₂)催化剂的微催化燃烧式气体传感芯片(Pellistor). 基于微机电系统(Micro- Electro-Mechanical Systems, MEMS)工艺制备硅基封闭膜式微催化燃烧式传感器, 通过气相沉积技术在Pt微加热电极和高温绝缘层表面制备三维纳米氧化锡催化膜, 利用催化膜对氢气良好的催化特性, 采用惠斯通电桥电路进行测量, 实现对空气环境中氢气在0～4%浓度范围内的快速检测, 响应时间和恢复时间分别达到0.65 s和2.32 s, 灵敏度达75.4 mV/1% H₂, 线性度为99.4%. 考察200 天内该传感芯片对氢气的检测能力, 传感芯片表现出良好的稳定性, 精确度保持在95%以上. 在绝缘层高温性能稳定的条件下, 将三维纳米氧化锡应用于微催化燃烧式传感器的氢气检测, 对催化燃烧式传感器性能的改进具有重要的意义.     

Photocatalytic properties of SnO2–SnO nanocomposite prepared via pulse alternating current synthesis

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Selective modified SnO2-based materials for gas sensors arrays

An enhancement of selectivity of semiconductor gas sensors, based on nanocrystalline SnO2 is reported. It is shown that modification of the surface of crystallites, forming thick films of conductive sensor materials, with catalytic clusters of gold or oxides of ruthenium, nickel, copper and iron allows selective response of sensors to different gases, such as carbon monoxide, ammonia, hydrogen sulfide, nitrogen dioxide and acetone vapor. These selective sensor responses can be obtained in the ranges of gas concentrations close to or below threshold limit values while the working temperature of sensors can be kept below 300 °C. The described approach for modification of selectivity of sensor materials could be used as perspective route in developingselective gas sensors. These results allow us to propose application of obtained materials in electronic nose sensor systems.     

Molecular design of hybrid organic-inorganic materials with electronic properties

The synthesis of two classes of hybrid organic-inorganic nanocomposites with electronic properties is reported. One is made of PDMS units cross linked with vanadium oxo-species where the vanadium coordination depends on the hydrolysis pH. Tetrahedral coordination is retained at neutral pH, while acidic conditions promote the segregation of five coordinated vanadium oxo-species. The reduction process depends also on the vanadium coordination. The second system is made of siloxane T units and polypyrrole oligomers, grafted and interpenetrated at a nano size level.     

Surface chemical and physical properties of TEOS-TBOT-PDMS hybrid materials

The application of nitrogen adsorption, mercury porosimetry and inverse gas chromatography (IGC) for the examination of surface physical and chemical properties of hybrid materials is discussed. Hybrid materials were prepared from tetraethoxysilane (TEOS), tetrabutyl orthotitanate (TBOT), and hydroxyl terminated polydimethyl siloxane (PDMS) for different TBOT concentrations. It was found that TBOT affects specific surface areas, pore volumes and pore sizes, but does not affect pore morphology. Surface chemical properties were analyzed by IGC. It was found that the dispersive surface energy was a function of the material pore size. Values between 36 and 42 mJ···m^-2 were obtained for the dispersive surface energy which are consistent with those of hybrid materials. On the other hand, the acid-base (k , k ) surface constants showed good correlation with the TBOT concentration. These materials can be considered as anphoteric ones, and it was found that k increases from 1.07 to 1.47, and k increases from 0.76 to 1.73 when the TBOT concentration increases from 0 to 7%. Such increase is assigned to the formation of Si–O–Ti bonds as it was deduced from an IR band appearing at 930 cm^-1 in the FT-IR spectra.     

UV-Enhanced Room Temperature Ozone Sensor Based on Hierarchical SnO2-In2O3

SnO₂-In₂O₃ hierarchical microspheres were prepared by the hydrothermal and solvothermal method. The morphology, phase crystallinity of the obtained SnO₂-In₂O₃ were measured by X-ray diffraction(XRD), scan electron microscopy(SEM), respectively. A room temperature ozone sensor based on SnO₂-In₂O₃ hierarchical microspheres was fabricated and investigated. The gas sensing properties of the sensor using SnO₂-In₂O₃ strongly depended on the proportion of SnO₂ and In₂O₃. The sensitivity and response/recovery speed were greatly enhanced by UV illumination. A gas sensing mechanism related to oxygen defect was suggested.     

Surlyn®/[silicon oxide] hybrid materials. 2. Physical properties characterization

The influence of an in situ‐grown, sol → gel‐derived silicon oxide filler on mechanical, gas permeation and solvent affinity properties of Surlyn® materials, and melt processibility of Surlyn®/[silicon oxide] hybrid resin, was studied. Tensile modulus increases while elongation‐at‐break decreases with increasing silicon oxide uptake. He gas permeation vs. pressure profiles imply dual mode sorption. Swelling in n‐hexane, 1‐PrOH and xylene decreases as silicon oxide loading increases, the highest uptake being that of xylene. [Surlyn®Zn⁺²]/[silicon oxide] has better solvent resistance than the H‐form hybrid for each solvent. Affinity of the Zn‐form hybrid for xylene is considerably greater than that for 1‐PrOH and n‐hexane. Melt flow index of the filled H‐form is lower than that of the unfilled H‐form but higher than that of the partially Zn neutralized unfilled form. FTIR analysis of hybrids previously subjected to the melt flow index experiment shows that the silicon oxide phase remained intact but that the high temperatures drove condensation reactions between SiOH groups. After in situ sol–gel reactions and drying [Surlyn®‐H]/[silicon oxide] flakes were passed through an extruder to assess the effect on silicon oxide structure of melt‐processing conditions. All silicon oxide IR fingerprint bands for the processed hybrid persist, the spectrum closely resembling that of a nonextruded hybrid including the signature of Si–OH groups. ²⁹Si solid‐state NMR spectroscopy was used to probe degree of molecular connectivity within the silicon oxide phase. The spectrum is consistent with those of nonextruded hybrids in that Si atom coordination around SiO₄ units is predominantly Q₃ and Q₄, the bias in the distribution toward Q₃ being in harmony with the IR results. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 143–154, 1999     

Highly Sensitive to Methane Sensor Materials Based on Nano-Pd/SnO2

Theoretical and Experimental Chemistry - Catalytic activities of nanomaterials based on tin dioxide with various palladium contents in the oxidation of CH4 and sensitivities of adsorption...     

Photoelectrochemical properties of MWCNT-TiO2 hybrid materials as a counter electrode for dye-sensitized solar cells

The MWCNT-Ti02 hybrid materials were prepared by a simply mixing method and used as a counter electrode （CE） for dye-sensitized solar cells. Compared with the platinum CE, MWCNT-TiO2 CE has the similar redox voltage and current response in the cyclic voltammetry. The electrochemical catalytic activity was characterized by the electrochemical impedance spectroscopy and Tafel curve, including the equivalent circuit, the exchange current density, the limiting diffusion current density, and the diffusion coefficient of triiodide/iodide redox species. The results indicate that the reduction process from triiodide to iodide is determined by the kinetic-controlled and diffusion-limited processes. The device performance is optimal based on the MWCNT-TiO2 （mass ratio of 2：1） CE, such as the open-circuit voltage of 0.72 V, the short-circuit photocurrent density of 15.71 mA/cm2, the fill factor of 0.68, and the photon-to-electron conversion efficiency of 7.69%.     

Synthesis of mesoporous SnO2 nanomaterials with selective gas-sensing properties

Using SBA-15/KIT-5/KIT-6 as the hard templates, the mesoporous SnO₂ nanomaterials with different structures were synthesized by nanocasting. X-ray diffraction, transmission electron microscopy, and nitrogen adsorption isotherms were used to testify their structure characteristics. These mesoporous SnO₂ nanomaterials showed high specific surface areas (57–96 m² g^?1) and pore volume (0.17–0.27 cm³ g^?1). The nanopore of these templates makes the nanosize particle of the final mesoporous SnO₂ nanomaterials (4–9 nm) at last. The sensing properties of acetone, ethyl alcohol and methyl alcohol were investigated. The response of SnO₂-15, SnO₂-5, and SnO₂-6 are 17.0, 19.5, and 16.1, respectively as the concentration of ethyl alcohol on 200 ppm. The sensitivity of SnO₂-5 is 28.2 as the concentration of acetone was increased to 200 ppm. With the large surface area, high pore volume, and nanosized particles (close to 2 L = 6 nm of SnO₂), the SnO₂-5 show four fold enhancement in sensitivity compared to commercial SnO₂ powder and low detection limit (even at 200 ppb). The surface area and particle size play a significant party in the gas response. With the large surface area and smallest particle size, SnO₂-5 shows the highest sensitivity of all. These mesoporous nanomaterials show well potential application on the gas response.     

Selectivity Modification of SnO2‐Based Materials for Gas Sensor Arrays

An enhancement of selectivity of sensor materials, based on nanocrystalline SnO₂ is reported. Selectivity toward target gases such as CO, NO₂, NH₃, H₂S and acetone vapor, could be achieved by selection of catalytic cluster distributed over the surface of thick film material. Presented results allow us to propose application of obtained materials in “electronic nose” sensor systems.     

Effect of preparation conditions on structural properties of PMHS-TEOS hybrid materials

Hybrid materials based on tetraethoxysilane (TEOS) and polymethylhydrosiloxane (PMHS) have been prepared employing sol–gel synthesis pathway, and the effects of preparation parameters such as PMHS concentration, water and NaOH amount on the structural characteristics were detailed investigated based on various techniques. It is illustrated that structural characteristics especially pore size can be tuned readily by adjusting the amount of PMHS during the sol–gel reaction. Furthermore, pore size increases with water amount and contrarily is almost independent on the amount of sodium hydroxide (NaOH) added in the sol–gel process. Typical hybrid sample prepared with desirable preparation parameters presents disordered wormhole structure with uniform mesopores, developed porosity with high specific surface area and pore volume and stable framework. In virtue of facileness and tunable composition, this synthesis pathway can be favorably applied for the preparation of other fascinating materials, i.e. porous ceramics, hydrophobic coatings and aerogels as well.     

Effect of antimony dopants on the sorption properties of SnO2

The effects of antimony modifying additive (0.15—0.50 at.% Sb) on the electrophysical and sorption properties of SnO₂ powders with a well developed specific surface were studied in the temperature range of 25—250 °C. Small amounts of antimony (0.15 at.%) increase the conductivity of SnO₂ containing SO₂ and CO chemisorbed in the temperature range of 25—100 °C. This makes this composition promising as a sensitive element of gas sensors.     

Hydrothermal synthesis of Zn2SnO4 as anode materials for Li-ion battery

Spinel Zn2SnO4 particles with the cubic shape are prepared via a hydrothermal reaction under mild conditions. The hydrothermal conditions, such as alkaline concentration, reaction temperature, and duration time, have an important influence on the product structure and the performance of the electrode prepared with the product. The optimized product is cube-shaped Zn2SnO4 crystalline, which is prepared with 0.4 M of NaOH solution at 200 degrees C for 24 h. These cube-shaped Zn2SnO4 particles with the spinel structure exhibit a large electrochemical capacity of 988 mA h/g and a relatively good capacity retention as anode materials for Li-ion battery. The structures of the as-prepared product and specimens taken from the electrodes after charging-discharging cycles are analyzed by X-ray diffraction, scanning electron microscopy, and transition electron microscopy techniques. In particular, it is found for the first time that the spinel Zn2SnO4 structure exists to a great extent after the first cycle and contributes to the extremely high reversible capacity during the following cycles.     

Evaluation of physicochemical properties of a new group of SiO2/silane/POSS hybrid materials

Preparation of a new group of hybrid fillers, of SiO₂/silane/oligomeric silsesquioxane type, characterised by specific desirable physicochemical properties, was studied. Synthetic SiO₂ was precipitated by the emulsion method. At first, as a result of improved adhesion between SiO₂ and selected POSS compound, SiO₂ surface was functionalised with alkoxysilanes containing characteristics functional groups. Functionalised SiO₂ was used in the process of hybrid filler preparation according to hydrolytic condensation using methacryl POSS® mixture. To evaluate potential application of such fillers, SiO₂ systems, bifunctionalised using innovative method, were thoroughly characterised to determine their physicochemical properties as well as the effectiveness of functionalisation with silanes and POSS compound. Proposed method of SiO₂ surface modification using selected alkoxysilanes and oligosilsesquioxanes is innovative and gives very promising results. Bifunctionalisation of inorganic fillers with those compounds will substantially extended the range of their applications and probably will lead to improvement of mechanical properties of final polymer composites and reduction in the cost of their production which is the main feature of this research. Copyright © 2013 John Wiley & Sons, Ltd.