Improved ethanol sensing properties of Cu-doped SnO2 nanofibers

Pure and Cu-doped SnO₂ nanofibers are synthesized via a simple electrospinning method, and characterized by transmission electron microscopy and X-ray diffraction. The sensor fabricated from Cu-doped SnO₂ nanofibers exhibits improved sensing properties to ethanol at 300 °C. The sensitivity is up to 3 when this sensor is exposed to 5 ppm ethanol. The response and recovery times are about 1 and 10 s, respectively. The linear dependence of the sensitivity on the ethanol concentration is observed in the range of 5-500 ppm. Good selectivity is also observed in our studies. The results make Cu-doped SnO₂ nanofibers good candidates for fabricating high performance ethanol sensors.     

Preparation, characterization, and gas-sensing properties of Pd-doped In2O3 nanofibers

Pure and Pd-doped In₂O₃ nanofibers are synthesized via a simple electrospinning method and characterized by scanning electron microscopy and X-ray diffraction. Comparing with pure In₂O₃ nanofibers, Pd-doped In₂O₃ nanofibers exhibit much higher sensitivity to ethanol at 200 °C. The sensor fabricated from Pd-doped In₂O₃ nanofibers can detect ethanol down to 1 ppm (the corresponding sensitivity is 4) with good selectivity, and the response and recovery times are 1 and 10 s, respectively. The sensing mechanism and the effect of Pd doping are discussed. The results indicate that the Pd-doped In₂O₃ nanofibers can be used to fabricate high performance ethanol sensors.     

Fast response detection of H2S by CuO-doped SnO2 films prepared by electrodeposition and oxidization at low temperature

Fast response detection of H₂S by CuO-doped SnO₂ films prepared was prepared by a simple two-step process: electrodeposition from aqueous solutions of SnCl₂ and CuCl₂, and oxidization at 600 °C. The phase constitution and morphology of the CuO-doped SnO₂ films were characterized by X-ray diffraction and scanning electron microscopy. In all cases, a polycrystalline porous film of SnO₂ was the product, with the CuO deposited on the individual SnO₂ particles. Two types of CuO-doped SnO₂ films with different microstructures were obtained via control of oxidation time: nanosized CuO dotted island doped SnO₂ and ultra-uniform, porous, and thin CuO film coated SnO₂. The sensor response of the CuO doped SnO₂ films to H₂S gas at 50–300 ppm was investigated within the temperature range of 25–125 °C. Both of the CuO-doped SnO₂ films show fast response and recovery properties. The response time of the ultra-uniform, porous, and thin CuO coated SnO₂ to H₂S gas at 50 ppm was 34 s at 100 °C, and its corresponding recovery time was about 1/3 of the response time.     

Electrospinning route for α-Fe2O3 ceramic nanofibers and their gas sensing properties

In this paper, α-Fe₂O₃ ceramic nanofibers were prepared by electrospinning poly(vinyl alcohol)/Fe (NO₃)₃·9H₂O composite nanofibers and followed by calcination. The morphologies and structures of the as-prepared samples were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The gas sensing properties of the sensor based on the as-prepared α-Fe₂O₃ nanofibers were investigated in detail. The experimental results exhibited that our product held rapid response-recovery and high sensitivity characteristics to ethanol vapor. The response and recovery time of the sensor to C₂H₅OH vapor (from 100 to 5000 ppm) are about 3 and 5 s, respectively.     

High-performance ammonia gas sensor based on bimetallic oxide Zn2SnO4 decorated with reduced graphene oxide

The coupling effect and synergistic effect between the two metal elements of the bimetallic oxide make it has unique electrical characteristics and gas-sensitive properties, but it has the limitation of low conductivity. In this paper, the bimetallic oxide Zn₂SnO₄ was decorated with reduced graphene oxide (rGO) to increase its electrical conductivity and promote charge transfer during gas adsorption, which enhances the response and shortens the response time of the bimetallic oxide gas sensor. The high-performance ammonia sensor based on Zn₂SnO₄/rGO nanocomposite material was prepared by environmentally friendly hydrothermal method and spin coating technology. The structure and properties of composite materials were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The ammonia sensing performance of Zn₂SnO₄/rGO nanocomposite sensor was tested at room temperature, including the dynamic response, response/recovery time, selectivity, repeatability, long-term stability. It showed a good sensing response to ammonia (22.94 for 100 ppm), and a fast response/recovery time (20 s/27 s). Finally, the response mechanism of Zn₂SnO₄/rGO nanocomposite sensor is explained. The enhanced ammonia sensing properties of Zn₂SnO₄/rGO nanocomposite sensor were ascribed to the synergistic effect and p–n heterojunction between Zn₂SnO₄ and rGO.

     

Gas-sensing properties of nanostructured SnO2-based sensor synthesized with different methods

Herein we report the preparation of SnO₂ nanomatierials by chemical precipitation, sol-gel and dissolution-pyrolysis. Furthermore, we studied their sensing properties. The composition, crystal structure and ceramic microstructure of the powders obtained are characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The results show SnO₂ fabricated through the three methods has rutile structure and the sizes of spherical particles are below 30 nm. From the result, we can also know that the thick films deposited onto alumina substrates show different morphology, and which are fabricated by dissolution-pyrolysis has fibrous structure. We investigate the sensitivities, response and recovery times of the three sensors. The results of gas sensing measurement show that SnO₂-based sensor prepared by dissolution-pyrolysis method has high sensitivity, quick response and recovery behavior to the gases we studied. It also has wider range of working temperature that is from 25 to 400 °C compared with SnO₂-based sensor fabricated by the other two methods.     

TiO2-SnO2 system for gas sensing—Photodegradation of organic contaminants

Catalytic photodegradation of organic contaminants by means of UV light has been demonstrated for gas sensors based on composites of TiO₂-SnO₂. Thin film resistive-type gas sensors of TiO₂-SnO₂ have been deposited at 350 °C by RF sputtering from a Ti-SnO₂ target with varying surface ratio of SnO₂/Ti. Photodegradation experiments of bromothymol blue by UV light have been performed by means of the optical spectrophotometry over the wavelength range extending from 300 nm to 600 nm. The influence of the UV illumination on the sensor response to 100-20,000 ppm of H₂ has been investigated in situ on motor oil contaminated sensors. It has been found that sequential exposures to UV light lead to a partial recovery of the sensor signal to hydrogen.     

Self-construction of SnO2 cubes based on aggration of nanorods

The SnO₂ cubes with the rutile structure have been successfully synthesized without using any catalyst. Their morphology and microstructure were studied by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and elected area electron diffraction (SAED). It is revealed that the SnO₂ nanocubes exhibit high crystalline quality. The size of the nanocubes ranges from 100 nm to 300 nm. The side surfaces of nanocubes are {110} planes, while their cube axes are [001] direction. The growth mechanism of SnO₂ nanocubes was discussed and we suggested vapor-solid process should dominate the growth. These SnO₂ nanostructures represent an important example of spontaneous organization.     

HCHO sensing properties of Ag-doped In2O3 nanofibers synthesized by electrospinning

Ag-doped In₂O₃ nanofibers with diameters ranging from 60 to 130 nm and lengths of several tens of micrometers were synthesized by an electrospinning method. The XRD results indicated that the dopant in the nanofibers was metal Ag. The sensor fabricated from these fibers exhibited excellent HCHO sensing properties at 115 °C. The sensitivity was up to 3 when the sensor was exposed to 5 ppm HCHO, and the response and recovery time were about 5 and 10 s, respectively. Good selectivity was also observed in our investigations. These results indicated that the Ag-doped In₂O₃ nanofibers could be used to fabricate high performance HCHO sensors in practice.     

Synthesis of novel hexagon SnO2 nanosheets in ethanol/water solution by hydrothermal process

The novel hexagon SnO₂ nanosheets are successfully synthesized in ethanol/water solution by hydrothermal process. The samples are characterized by X-ray diffraction (XRD), infrared ray (IR) and transmission electron microscopy (TEM). By changing the reaction conditions, the size and the morphology can be controlled. Comparison experiments show that when the temperature increased from 140 °C to 180 °C, the edge length of the hexagon nanoparticles increases from 300-450 nm to 700-900 nm. On the other hand, by adjusting the ratios of water to ethanol from 2 to 0.5, SnO₂ nanoparticles with different morphologies of triangle and sphere are obtained. When the concentration of NaOH is increased from 0.15 M to 0.30 M, a hollow ring structure can be obtained.     

Mesoporous tin dioxide nanopowders based sensors to selectively detect ethanol vapor

In the paper, mesoporous SnO₂ nanopowders were synthesized via a simple and mild SnCl₄ hydrolysis process using cationic surfactant (cetyltrime thylammonium bromide, CTAB: CH₃(CH₂)₁₅N⁺(CH₃)₃Br^?) as structure directing agent and ammonia as an alkali source at room temperature, combined with a subsequent calcination process. The products were characterized by X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and nitrogen adsorption–desorption experiment. A gas sensor was fabricated from the as-prepared mesoporous SnO₂ nanopowders and used to test the response to different concentrations of ethanol, methanol, hexane, NH₃, H₂ and CO at different operating temperatures. The results showed that the mesoporous SnO₂ sensor exhibited high sensitivity, good selectivity and quick response–recovery characteristics to ethanol, implying the potential application of the sensor for detecting ethanol.     

Synthesis of SnO2 hollow microspheres from ultrasonic atomization and their role in hydrogen sensing

Nanostructured SnO₂ hollow microspheres were synthesized using ultrasonic atomization technique. It is interesting that hollow microspheres could be prepared from ultrasonic atomization technique without any aid of template and surfactant. X-ray powder diffraction (XRD) confirmed the material to be SnO₂ having tetragonal structure. Average crystallite size calculated from X-ray diffractogram using Scherer's equation was found to be 8.45 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the microscopic study of fine powder particles. Powder consists of hollow microspheres of average diameter of 0.58 μm as well as nanoparticles of average diameter of 6 nm. The sensors fabricated from such powder show high hydrogen (1000 ppm) response (S = 2379) under the optimized experimental conditions. Sensor performance merits, such as, high hydrogen response, high hydrogen selectivity, short response time (2 s) and quick recovery time (15 s) may be due to both nanocrystallites and hollow microspheres associated in SnO₂ sensing material. The dramatic change in gas response was explained by the rapid diffusion of the target gas through the nano-porous structure of SnO₂ hollow microspheres.     

Alcohol sensing of tin oxide thin film prepared by sol-gel process

The present paper describes the alcohol sensing characteristics of spin coated SnO₂ thin film deposited by using sol-gel process. The sensitivity of the film was measured at different temperatures and different concentrations of alcohol at ppm level. Alcohol detection result shows peak sensitivity at 623 K. The variation of sensitivity and ethanol concentration has shown a linear relationship up to 1150 ppm and after that it saturates. The response time measurement of the sensor was also observed and it was found that the response time is 30 sec. The results obtained favour the sol-gel process as a low cost method for the preparation of thin films with a high sensing characteristic.     

Interaction of reducing gases with tin oxide films prepared by reactive evaporation techniques

SnO_2−x films were prepared by reactive thermal and e-beam evaporation of Sn on alumina substrates and by post deposition thermal treatment. X-ray diffraction measurements found that films are tin dioxide (SnO₂) phase with small amounts of SnO phase. The surface conductivity of films was measured in air and in presence of H₂S, H₂ and C₂H₅OH vapors at four sensor operating temperatures of 433-493 K. The resistance of SnO_2−x films decreases on exposure to H₂S but shows no change with hydrogen and ethanol. H₂S response decreases with rise in sensor temperature while both response and recovery times improve. H₂S signal enhances with increase in resistivity of SnO_2−x coatings. Our experiments conclude that increase in film conductance is due to chemical reaction between H₂S and SnO_2−x surface and there is little or no role of interaction of gas molecules with surface adsorbed charged oxygen species.     

Influence of effective surface area on gas sensing properties of WO3 sputtered thin films

WO₃ thin films having different effective surface areas were deposited under various discharge gas pressures at room temperature by using reactive magnetron sputtering. The microstructure of WO₃ thin films was investigated by X-ray diffraction, scanning electron microscopy, and by the measurement of physical adsorption isotherms. The effective surface area and pore volume of WO₃ thin films increase with increasing discharge gas pressure from 0.4 to 12 Pa. Gas sensors based on WO₃ thin films show reversible response to NO₂ gas and H₂ gas at an operating temperature of 50-300 °C. The peak sensitivity is found at 200 °C for NO₂ gas and the peak sensitivity appears at 300 °C for H₂ gas. For both kinds of detected gases, the sensor sensitivity increases linearly with an increase of effective surface area of WO₃ thin films. The results demonstrate the importance of achieving high effective surface area on improving the gas sensing performance.     

Impact of Pd nanoparticle loading method on SnO2 surface for natural gas detection in humid atmosphere

To improve the sensor response to low concentrations of methane (CH₄) at low operating temperatures in humid atmospheres, we prepared Pd-loaded SnO₂ (Pd-SnO₂) nanoparticles via two different Pd-loading processes: (i) a general impregnation method and (ii) a new loading method using poly(N-vinyl-2-pyrrolidone) (PVP) as a protective agent for Pd receptor particles. According to the measured electric resistances, the Pd particles limited the hydroxyl-poisoning of the SnO₂ particle surface. Because Pd is oxidized to PdO, a p–n junction is formed at the interface between PdO and SnO₂, and such interface gives the enlargement of the electron depletion layer. Therefore, Pd further improved the resistance against hydroxyl poisoning of the SnO₂ surface in humid air. In addition, although the sensor based on neat SnO₂ did not respond to low-concentration CH₄ at 200–400 °C, both the sensors based on the Pd-loaded SnO₂ samples exhibited high sensor response to 200 ppm CH₄ in a humid atmosphere. The Pd-SnO₂ obtained by the new loading method exhibited a higher response to CH₄ at lower concentrations in the lower operating temperature range (200–250 °C). This improvement in the sensor response is probably due to the catalytic activity of the larger Pd nanoparticles. According to high-resolution transmission electron microscopy–energy-dispersive X-ray spectroscopy images, the new loading method successfully provided Pd-loaded SnO₂ nanoparticles with Pd nanoparticles dispersed uniformly on the SnO₂ particle surface. The average particle size of Pd nanoparticles loaded on the surface of SnO₂ by the new loading method was slightly larger than that of the Pd nanoparticles loaded by the impregnation method. As the Pd particle size increases, it is thought that crystalline PdO particles are formed more easily, thereby improving the combustion activity of CH₄ under humid conditions. These results are of great significance for further decreasing the energy consumption of the CH₄ sensor and increasing its sensor response in humid atmospheres.

     

Synthesis and gas sensing characteristics of SnO2 “dandelions”

SnO₂ dandelions-like architectures that composed of numerous one-dimensional tetragonal prism nanorods were synthesized by a simple hydrothermal method with the help of the surfactant poly(vinyl pyrrolidone) (PVP). The structure and morphology of resulting samples were characterized by means of X-ray powder diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The results show that diameter of as-synthesized nanorods are less than 50 nm. The sensors fabricated from the SnO₂ nanorods exhibited good sensitivity, high selectivity and rapid response and recovery times to ethanol vapors at 280 °C.     

Synthesis and enhanced ethanol sensing performance of nanostructured Sr doped SnO<Subscript>2</Subscript> thick film sensor

In the present paper we have synthesized pristine and Sr doped SnO₂ in order to prepare a selective ethanol sensor with rapid response–recovery time and good repeatability. Pristine as well as Sr (2, 4 and 6 mol%) doped SnO₂ nanostructured powder was synthesized by using a facile co-precipitation method. The samples were characterized by TG–DTA, XRD, HR-TEM, SAED, FEG-SEM, SEM–EDAX, XPS, UV–Vis and FTIR spectroscopy techniques. The gas response performance of sensor towards ethanol, acetone, liquid petroleum gas and ammonia has been carried out. The results demonstrate that Sr doping in SnO₂ systematically decreases crystallite size, increases the porosity and hence enhances the gas response properties of pristine SnO₂ viz. lower operating temperature, higher ethanol response and better selectivity towards ethanol. The response and recovery time for 4 mol% Sr doped SnO₂ thick film sensor at the operating temperature of 300 °C were 2 and 7 s, respectively.     

静电纺丝法制备CuO/SnO2复合材料及其气敏特性研究

为研究p型材料和n型材料复合时气敏特性的变化,采用静电纺丝法分别制备了CuO、SnO_2以及3种比例混合的CuO/SnO_2复合纳米纤维材料,并通过XRD及SEM对其形貌、微观结构等进行表征.测试了该5种材料对丙酮、甲醛、甲醇、乙醇、甲苯等VOC气体的敏感特性.研究表明,CuO/SnO_2=2∶1的复合材料对丙酮、甲苯和乙醇的的响应值有一定提高;CuO/SnO_2=1∶1的复合材料对丙酮具有很高响应的同时,对乙醇和甲苯的响应产生了一定的抑制作用,从而大大提高了材料的选择性.其机理是:半导体材料复合后,在复合材料的表面会有更多的氧吸附,导致更多的VOC气体在半导体材料表面发生反应,使材料的电阻值变化更加明显,提高了材料的响应值.     

Sensing behaviour of nanosized zinc-tin composite oxide towards liquefied petroleum gas and ethanol

A chemical route has been used to synthesize composite oxides of zinc and tin. An ammonia solution was added to equal amounts of zinc and tin chloride solutions of same molarities to obtain precipitates. Three portions of these precipitates were annealed at 400, 600 and 800 °C, respectively. Results of X-ray diffraction and transmission electron microscopy clearly depicted coexistence of phases of nano-sized SnO₂, ZnO, Zn₂SnO₄ and ZnSnO₃. The effect of annealing on structure, morphology and sensing has been observed as well. It has been observed that annealing promoted growth of Zn₂SnO₄ and ZnSnO₃ at the expense of zinc. The sensing response of fabricated sensors from these materials to 250 ppm LPG and ethanol has been investigated. The sensor fabricated from powder annealed at 400 °C responded better to LPG than ethanol.