Enhanced dielectric properties of polyvinylidene fluoride with addition of SnO2 nanoparticles

In this letter, SnO₂/polyvinylidene fluoride (PVDF) nanocomposites with outstanding dielectric properties were fabricated. The SEM and TEM images showed that SnO₂ nanoparticles with size of 5–7 nm dispersed homogeneously in polymer matrix. The significantly improved dielectric constant was well explained by percolation theory. The nanocompo‐ sites can retain a certain value of breakdown field. The maximum energy density of SnO₂/PVDF nanocomposites was 5.4 J/cm³, two times that of the pure polyvinylidene fluoride. These findings suggest that SnO₂/PVDF nanocomposites are suitable candidates for energy storage applications. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Analysis of fiber optic SPR sensor utilizing platinum based nanocomposites

SPR based fiber optic sensor using nanocomposite is presented. Nanocomposites comprising of Pt nanoparticles with various volume fractions embedded in dielectric matrices of TiO₂ and SnO₂ are considered. Sensitivity enhances with increase in thickness of nanocomposite and volume fraction of nanoparticles for both nanocomposites. Optimized thicknesses are obtained to be 40 and 50 nm for Pt–TiO₂ and Pt–SnO₂ nanocomposites respectively while optimized volume fraction is found to be 0.85 for both nanocomposites. 40 nm thick Pt–TiO₂ nanocomposite based sensor with 0.85 volume fraction possesses utmost sensitivity.     

Sensing low concentrations of CO using flame-spray-made Pt/SnO2 nanoparticles

Tin dioxide nanoparticles of different sizes and platinum doping contents were synthesized in one step using the flame spray pyrolysis (FSP) technique. The particles were used to fabricate semiconducting gas sensors for low level CO detection, i.e. with a CO gas concentration as low as 5 ppm in the absence and presence of water. Post treatment of the SnO₂ nanoparticles was not needed enabling the investigation of the metal oxide particle size effect. Gas sensors based on tin dioxide with a primary particle size of 10 nm showed signals one order of magnitude higher than the ones corresponding to the primary particle size of 330 nm. In situ platinum functionalization of the SnO₂ during FSP synthesis resulted in higher sensor responses for the 0.2 wt% Pt-content than for the 2.0 wt% Pt. The effect is mainly attributed to catalytic consumption of CO and to the associated reduced sensor response. Pure and functionalized tin dioxide nanoparticles have been characterized by Brunauer, Emmett and Teller (BET) surface area determination, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) while the platinum oxidation state and dispersion have been investigated by X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). The sensors showed high stability (up to 20 days) and are suitable for low level CO detection: <10 ppm according to European and 50 ppm according to US legislation, respectively.     

Room temperature response of SnO2-electrode modified solid state electrochemical CO2 sensors

A thin film solid state electrochemical gas sensor has been investigated for CO₂ detection based on the cell reaction: Na⁺+OH+CO₂=NaHCO₃. The galvanic cell arrangement is Au | Na_xCoO_2−δ (ref.) | NASICON | Au, SnO₂ where the right hand electrode is in contact with CO₂ and O₂ in a humid atmosphere. The response has been compared to results obtained with a conventional pellet type sensor. Furthermore, both devices have been exposed to CO and humidity. Strong cross-sensitivities were observed leading to large changes in the emf in both cases. The response to moisture is reversible and fast with a response time of about 1 min according to a fast surface reaction of H₂O with SnO₂. The presence of CO leads to a signal change with a high response time and a very slow reverse reaction. However, the response to CO₂ is not influenced by the presence of CO or H₂O with regard to the signal height and response time. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

使用金属掺杂SnO2(110)作为表面催化剂的电催化CO2还原反应：通过调控Sn:O原子比例来控制产物

电催化CO₂还原反应可以产生HCOOH和CO,目前该反应是将可再生电力转化为化学能存储在燃料中的最有前景的方法之一. SnO₂作为将CO₂转换为HCOOH和CO的良好催化剂,其反应发生的晶面可以是不同的. 其中(110)面的SnO₂非常稳定,易于合成. 通过改变SnO₂(110)的Sn:O原子比例,得到了两种典型的SnO₂薄膜：完全氧化型(符合化学计量)和部分还原型. 本文研究了不同金属(Fe、Co、Ni、Cu、Ru、Rh、Pd、Ag、Os、Ir、Pt和Au)掺杂的SnO₂(110),发现在CO₂还原反应中这些材料的催化活性和选择性是不同的. 所有这些变化都可以通过调控(110)表面中Sn:O原子的比例来控制. 结果表明,化学计量型和部分还原型Cu/Ag掺杂的SnO₂(110)对CO₂还原反应具有不同的选择性. 具体而言,化学计量型的Cu/Ag掺杂的SnO₂(110)倾向于产生CO(g),而部分还原型的表面倾向于产生HCOOH(g). 此外,本文还考虑了CO₂还原的竞争析氢反应. 其中Ru、Rh、Pd、Os、Ir和Pt掺杂的SnO₂(110)催化剂对析氢反应具有较高的活性,其他催化剂对CO₂还原反应具有良好的催化作用.     

Spectroscopic ellipsometry study of porous silicon-tin oxide nanocomposite layers

The layer-by-layer distribution of components in a porous silicon-tin oxide nanocomposite produced by the following three methods is studied by spectroscopic ellipsometry: chemical vapor deposition, atomic layer deposition, and magnetron sputtering. It is shown that, in the nanocomposites fabricated by these methods, SnO _x penetrates to a depth more than 400 nm and is nonuniformly distributed over the porous layer thickness. The nanocomposite prepared by magnetron sputtering followed by heat treatment has the maximum penetration depth and the maximum uniformity of layer-by-layer SnO _x distribution.     

Pd nanoparticle-mediated acetone sensing performance improvement of SnO2 substrate: A combined DFT and experimental study

The article presents a combined theoretical and experimental study attempting to show how Pd nanoparticles (NPs) loading onto SnO₂ substrate improves the acetone gas sensing performance. Pristine nanostructured SnO₂ and Pd nanoparticles (Pd NPs) loaded SnO₂ substrates have been prepared, characterized, and their acetone sensing performances have been measured. Experimental measurements have shown that Pd NP loading onto SnO₂ suppresses the interfering effects of ethanol, water vapors, etc., and enhances the acetone sensor response, reversibility, response/recovery speeds, and signal-to-noise ratio. Various parameters like the adsorption energy, HOMO–LUMO energy gap, charge distribution, polarizability change, electrophilicity index, global hardness, etc., of several model systems, have been computed by using DFT. The computed parameters have been correlated with the conductivity, local reactivity, sensor response and selectivity, response/recovery times, etc., of the systems to understand the molecular-level effects of the Pd NP loading onto the SnO₂ on the gas sensing process.     

Low-temperature CO gas sensors based on Au/SnO2 thick film

A study on the low-temperature CO gas sensors based on Au/SnO₂ thick film was reported. Au/SnO₂ powders were prepared by a deposition-precipitation method. Thick films were fabricated from Au/SnO₂ powders. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses were carried out for investigation of morphology and crystalline structure. Au/SnO₂ thick film sensors exhibited high sensitivity to CO gas at relatively low operating temperature (83-210 °C). We also reported the effect of the calcination temperature of Au/SnO₂ on the CO gas sensing behavior. The optimal calcination temperature of Au/SnO₂ was 300 °C.     

A novel method to synthesize ordered porous SnO2 nanostructures and their optical properties

Three-dimensional porous ordered SnO₂ nanostructures have been fabricated by templating a sol–gel precursor solution against the polystyrene nanospheres for the first time. Field emission scanning electron micrography (FESEM) indicates that the surface of the nanostructures is highly regular and the porous structures are perfectly ordered. Besides a broad emission band at 600 nm, the porous SnO₂ nanostructures show an additional emission band at 430 nm, which is seldom seen in the bulk SnO₂ materials. Spectral examinations and analyses reveal that the 430 nm band is induced by the interfacial effects between the porous frameworks.     

Nanocrystalline ZnO Film Grown on Porous SnO2/Si(111) Substrate

Porous tin oxide was prepared on silicon(111) substrate by the sol–gel route. Then, the samples were dried in air at 600°C for 30 min in an electric furnace. Scanning electron microscope (SEM) images indicated the high density of the pores. Circular microvoids formed by the rigid shaped microarray network of 200–300 nm sizes are clearly seen in the plan view SEM image. The high homogeneity and uniformity of the porous region could also be visualized by this easy method. Nanocrystalline zinc oxide (ZnO) thin films have been deposited onto porous SnO₂substrates at high growth rates by radio frequency (RF) sputtering using a ZnO target. The surface morphology of the nanocrystalline ZnO films was characterized by scanning electron microscope (SEM). Photoluminescence (PL) spectroscopy is a powerful, contactless and excellent nondestructive optical tool to study the acceptor binding energy of ZnO nanostructures. The PL measurements were also operated at room temperature. The peak luminescence energy in nanocrystalline ZnO on porous SnO₂ is blue-shifted with regard to that in bulk ZnO (381 nm). PL spectra peaks are distinctly apparent at 375 nm for ZnO film grown on porous SnO₂/Si(111) substrates.     

Can electron paramagnetic resonance measurements predict the electrical sensitivity of SnO<Subscript>2</Subscript>-based film?

Paramagnetic singly ionized oxygen vacancies V_o and chemisorbed Sn⁴⁺-O₂⁻ species were detected by electron paramagnetic resonance measurements on SnO₂ and transition metal (Pt, Ru)-doped SnO₂ thin film that had been reduced with CO at different temperatures and then brought into contact with oxygen. The amounts of the two paramagnetic species were evaluated and are discussed as a function of the film annealing temperature in air, the reduction temperature under CO, and the type and concentration of the doping transition element. Also the structural properties of the film were identified through glancing incidence X-ray diffraction analysis. Measurements of the electrical sensitivityS(S=R _air/R _CO, whereR _air andR _CO are the resistance under air and under CO(800 ppm)/air respectively) show that the trend of the sensitivity values vs. the reduction temperature with CO could be predicted by the parallel trend of the number of Sn⁴⁺−O₂⁻ centers.     

Gas sensors made of multiwall carbon nanotubes modified by tin dioxide

Thin film gas sensors made of nanocomposite MWCNT·SnO₂(1:66), semiconductor compound WO₃·SnO₂(1:9), and also multicomponent structure MWCNT·SnO₂(1:66)/WO₃·SnO₂(1:9) have been fabricated by high-frequency magnetron sputtering and electron-beam deposition methods. Sensitivity of the prepared sensors to influence of gases, such as hydrogen, methane, butane, and also ethanol vapors, was investigated. Sensors made of MWCNT·SnO₂(1:66) and WO₃·SnO₂(1:9) show appreciable sensitivity to hydrogen and alcohol vapors already at working body temperature 100–150°C. Sensors made of MWCNT·SnO₂(1:66)·WO₃·SnO₂(1:9) can be used for detection of low concentrations of hydrogen and ethanol vapors; besides, monotonous increase in the structure sensitivity with increase in content of the alcohol vapors allows one to apply these sensors also for fast detection of concentration of these vapors in air.     

Grain Size Effects in Sensor Response of Nanostructured SnO2- and In2O3-Based Conductometric Thin Film Gas Sensor

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO₂ and In₂O₃ films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO₂- and In₂O₃-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or worsen of operating characteristics of gas sensors. Therefore, the choice of optimal grain size should be based on the detailed consideration of all possible consequences of their influence on the parameters of sensors designed.     

Novel synthesis of highly ordered mesoporous Fe2O3/SiO2 nanocomposites for a room temperature VOC sensor

The controlled synthesis of mesoporous silica and metal oxide nanocomposites with a highly ordered porous structure and large specific surface area for specific applications has been an attractive topic in the field of porous materials. Herein, we introduce a novel method for the fabrication of highly ordered mesoporous structured and large specific surface area Fe₂O₃/SiO₂ nanocomposites, and consider their application in room temperature gas sensors. The mesoporous Fe₂O₃/SiO₂ nanocomposites were synthesised by a two-step method, which combines the hydrothermal growth of Fe₂O₃ nanoparticles and the microemulsion phase of Brij 56 (C₁₆EO₁₀) surfactant as templates in instantly direct-templating synthesis. This synthesis method enables the fabrication of mesoporous Fe₂O₃/SiO₂ nanocomposites without distortion of the ordered porous structure after calcination at high temperature. The synthesised materials were found to be efficient in a room temperature VOC sensor application, with good recovery.     

SnO2-decorated multiwalled carbon nanotubes and Vulcan carbon through a sonochemical approach for supercapacitor applications

Multiwalled carbon nanotubes (MWCNTs) and Vulcan carbon (VC) decorated with SnO₂ nanoparticles were synthesized using a facile and versatile sonochemical procedure. The as-prepared nanocomposites were characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra red spectroscopy. It was evidenced that SnO₂ nanoparticles were uniformly distributed on both carbon surfaces, tightly decorating the MWCNTs and VC. The electrochemical performance of the nanocomposites was evaluated by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO₂/MWCNTs nanocomposites show a higher capacity than the SnO₂/VC nanocomposites. Concretely, the SnO₂/MWCNTs electrodes exhibit a specific capacitance of 133.33 F g⁻¹, whereas SnO₂/VC electrodes exhibit a specific capacitance of 112.14 F g⁻¹ measured at 0.5 mA cm⁻² in 1 M Na₂SO₄.     

Influence of CuO catalyst in the nanoscale range on SnO2 surface for H2S gas sensing applications

The dispersal of CuO catalyst on the surface of the semiconducting SnO₂ film is found to be of vital importance for improving the sensitivity and the response speed of a SnO₂ gas sensor for H₂S gas detection. Ultra-thin CuO islands (8 nm thin and 0.6 mm diameter) prepared by evaporating Cu through a mesh and subsequent oxidation yield a fast response speed and recovery. Ultimately nanoparticles of Cu (average size = 15 nm) prepared by a chemical technique using a reverse micelle method involving the reduction of Cu(NO₃)₂ by NaBH₄ exhibited significant improvement in the gas sensing characteristics of SnO₂ films. A fast response speed of ∼14 s and a recovery time of ∼60 s for trace level ∼20 ppm H₂S gas detection have been recorded. The sensor operating temperature (130° C) is low and the sensitivity (S = 2.06 × 10³) is high. It is found that the spreading over of CuO catalyst in the nanoscale range on the surface of SnO₂ allows effective removal of excess adsorbed oxygen from the uncovered SnO₂ surface due to spill over of hydrogen dissociated from the H₂S-CuO interaction.     

Highly active Ce1−xCuxO2 nanocomposite catalysts for the low temperature oxidation of CO

A series of Ce_1−xCu_xO₂ nanocomposite catalysts with various copper contents were synthesized by a simple hydrothermal method at low temperature without any surfactants, using mixed solutions of Cu(II) and Ce(III) nitrates as metal sources. These bimetal oxide nanocomposites were characterized by means of XRD, TEM, HRTEM, EDS, N₂ adsorption, H₂-TPR and XPS. The influence of Cu loading (5-25 mol%) and calcination temperature on the surface area, particle size and catalytic behavior of the nanocomposites have been discussed. The catalytic activity of Ce_1−xCu_xO₂ nanocomposites was investigated using the test of CO oxidation reaction. The optimized performance was achieved for the Ce_0.80Cu_0.20O₂ nanocomposite catalyst, which exhibited superior reaction rate of 11.2 × 10⁻⁴ mmol g⁻¹ s⁻¹ and high turnover frequency of 7.53 × 10⁻² s⁻¹ (1% CO balanced with air at a rate of 40 mL min⁻¹, at 90 °C). No obvious deactivation was observed after six times of catalytic reactions for Ce_0.80Cu_0.20O₂ nanocomposite catalyst.     

Synthesis of Au-functionalized SnO2 nanotubes using TeO2 nanowires as templates and their enhanced gas sensing properties

Au-functionalized SnO₂ nanotubes were prepared for use as gas sensors using TeO₂ nanowires as templates. Transmission electron microscopy revealed tube diameters, tube lengths and tube wall thicknesses ranging from 50 to 200 nm, 5 to 50 μm, and 13 to 18 nm, respectively. The Au-functionalized SnO₂ nanotube sensors showed responses of 179–473 % to 1–5 ppm NO₂ at 300 ^°C. These values are much higher than those obtained using bare SnO₂ nanotubes synthesized in this study and most other SnO₂ one-dimensional nanostructure-based sensors reported in the literature. The NO₂ gas sensing mechanism of the Au-functionalized SnO₂ nanotube sensors is also discussed.     

Dependence of the selectivity of SnO2 nanorod gas sensors on functionalization materials

Effects of functionalization materials on the selectivity of SnO₂ nanorod gas sensors were examined by comparing the responses of SnO₂ one-dimensional nanostructures functionalized with CuO and Pd to ethanol and H₂S gases. The response of pristine SnO₂ nanorods to 500 ppm ethanol was similar to 100 ppm H₂S. CuO-functionalized SnO₂ nanorods showed a slightly stronger response to 100 ppm H₂S than to 500 ppm ethanol. In contrast, Pd-functionalized SnO₂ nanorods showed a considerably stronger response to 500 ppm ethanol than to 100 ppm H₂S. In other words, the H₂S selectivity of SnO₂ nanorods over ethanol is enhanced by functionalization with CuO, whereas the ethanol selectivity of SnO₂ nanorods over H₂S is enhanced by functionalization with Pd. This result shows that the selectivity of SnO₂ nanorods depends strongly on the functionalization material. The ethanol and H₂S gas sensing mechanisms of CuO- and Pd-functionalized SnO₂ nanorods are also discussed.