Synthesis and characterization of nanostructured SnO<Subscript>2</Subscript> film

Nanostructured tin dioxide (SnO₂) film was deposited on glass substrate by thermal evaporation of tin metal followed by thermal oxidation at 600 °C for 2 h. XRD investigation confirms that grown film is crystalline tetragonal rutile. The average optical transmittance of the film was as high as 90%. The optical band gap of the nanostructured SnO₂ was estimated from transmittance data and found to be 3.4 eV. The variation of electrical conductivity with temperature was investigated. The root mean square (RMS) roughness and topography of the film were investigated by atomic force microscopy and found to be 2 nm with grain size of 17 nm.     

Ethanol and LPG sensing characteristics of SnO<Subscript>2</Subscript> activated Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> thick film sensor

The sensing response of pure and SnO₂ activated Cr₂O₃ to ethanol vapours and liquefied petroleum gas (LPG) has been investigated. Fine particles of commercial chromium oxide powder were selected and deposited as thick film to act as a gas sensor. The sensor surface has been activated by tin dioxide, on surface oxidation of tin chloride. The concentration of tin chloride solution, used as activator, was varied from 0 to 5% and its effect on gas response, selectivity and operating temperature has been studied. It was found that response to ethanol vapours significantly improved, whereas response to LPG remained unaffected. Moreover, operating temperature remains unchanged both for LPG and ethanol vapours.     

Investigation of ethanol gas sensing properties of Dy-doped SnO<Subscript>2</Subscript> nanostructures

In this paper we report doping induced enhanced sensor response of SnO₂ based sensor towards ethanol at a working temperature of 200 °C. Undoped and dysprosium-doped (Dy-doped) SnO₂ nanoparticles were characterized by X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). XRD and Raman results verified tetragonal rutile structure of the prepared samples. It has been observed that crystallite size reduced with increase in dopant concentration. In addition, the particle size has been calculated from Raman spectroscopy using phonon confinement model and the values match very well with results obtained from TEM and X-ray diffraction investigations. Dy-doped SnO₂ sensors exhibited significantly enhanced response towards ethanol as compared to undoped sensor. The optimum operating temperature of doped sensor reduced to 200 °C as compared to 320 °C for that of undoped sensor. Moreover, sensor fabricated from Dy-doped SnO₂ nanostructures was highly selective toward ethanol which signifies its potential use for commercial applications. The gas sensing mechanism of SnO₂ and possible origin of enhanced sensor response has been discussed.     

Morphological and humidity sensing characteristics of SnO<Subscript>2</Subscript>-CuO,SnO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and SnO<Subscript>2</Subscript>-SbO<Subscript>2</Subscript> nanocooxides

This paper reports the synthesis of SnO₂-CuO, SnO₂-Fe₂O₃ and SnO₂-SbO₂ composites of nano oxides and comparative study of humidity sensing on their electrical resistances. CuO, Fe₂O₃ and SbO₂ were added within base material SnO₂ in the ratio 1: 0.25, 1: 0.50 and 1: 1. Characterizations of materials were done using SEM and XRD. SEM images show the surface morphology and X-ray diffraction reveals the nanostructure of sensing materials. The pellets were annealed at 200, 400 and 600°C respectively for 3 h and after each step of annealing, observations were carried out. It was observed that as relative humidity (%RH) increases, there was decrease in the resistance of pellet for the entire range of RH. Results were found reproducible. SnO₂-SbO₂ shows maximum sensitivity for humidity (12 MΩ/%RH) among other composites.     

Synthesis,characterization and gas sensing performance of SnO<Subscript>2</Subscript> thin films prepared by spray pyrolysis

In this work, SnO₂ thin films were deposited onto alumina substrates at 350°C by spray pyrolysis technique. The films were studied after annealing in air at temperatures 550°C, 750°C and 950°C for 30 min. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption spectroscopy technique. The grain size was observed to increase with the increase in annealing temperature. Absorbance spectra were taken to examine the optical properties and bandgap energy was observed to decrease with the increase in annealing temperature. These films were tested in various gases at different operating temperatures ranging from 50–450°C. The film showed maximum sensitivity to H ₂S gas. The H₂S sensing properties of the SnO₂ films were investigated with different annealing temperatures and H ₂S gas concentrations. It was found that the annealing temperature significantly affects the sensitivity of the SnO₂ to the H ₂S. The sensitivity was found to be maximum for the film annealed at temperature 950°C at an operating temperature of 100°C. The quick response and fast recovery are the main features of this film. The effect of annealing temperature on the optical, structural, morphological and gas sensing properties of the films were studied and discussed.     

Ethanol gas sensing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-doped ZnO thick film resistors

The characterization and ethanol gas sensing properties of pure and doped ZnO thick films were investigated. Thick films of pure zinc oxide were prepared by the screen printing technique. Pure zinc oxide was almost insensitive to ethanol. Thick films of Al₂O₃ (1 wt%) doped ZnO were observed to be highly sensitive to ethanol vapours at 300°C. Aluminium oxide grains dispersed around ZnO grains would result into the barrier height among the grains. Upon exposure of ethanol vapours, the barrier height would decrease greatly leading to drastic increase in conductance. It is reported that the surface misfits, calcination temperature and operating temperature can affect the microstructure and gas sensing performance of the sensor. The efforts are, therefore, made to create surface misfits by doping Al₂O₃ into zinc oxide and to study the sensing performance. The quick response and fast recovery are the main features of this sensor. The effects of microstructure and additive concentration on the gas response, selectivity, response time and recovery time of the sensor in the presence of ethanol vapours were studied and discussed.     

Synthesis and conductivity of Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript>-based cermet material

SHS synthesis of Zn₂SnO₄-based cermet material from Zn + NiO + SnO₂ compacted powder mixtures has been studied. The final product is obtained as a monolithic cylindrical block composed of a ZnO-based outer layer and Zn₂SnO₄-based central part, in which the metal phase is distributed. The phase composition and microstructure of combustion products have been studied by x-ray phase analysis (XPA), electron microscopy, and microprobe techniques. It is established that the structure of the obtained cermet material has a dramatic effect on their conductivity.     

Vanadium doped SnO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO₂ and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N₂ sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO₂, to 2.75 eV, for SnO₂ doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped SnO₂ nanoparticles was studied using methylene blue (MB) as model organic pollutants. The SnO₂ nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min^?1 for MB degradation that was about 2.5 times more than that of pure SnO₂ (0.014 min^?1).     

Conductance analysis of (Co,Nb, Fe)-doped SnO<Subscript>2</Subscript> thick film gas sensors

Thick films prepared with undoped nanometric SnO₂ particles and with (Co, Nb, Fe)-doped SnO₂ were studied with the purpose of developing oxygen and carbon monoxide gas sensors. The ceramic powders were obtained through the Pechini method. The morphological characteristics were studied with SEM and TEM, after which, they were subjected to sensitivity tests under different atmospheres. A correlation was established between the microstructure of the material, the effects of the additives, and the electrical behavior. The response of the sensor could be explained as the result of the characteristics of the intergranular potential barriers developed at intergrains. It was determined that the SnO₂-doped films have a greater sensitivity between 200 °C and 350 °C.     

Gas sensing properties of nano SnO<Subscript>2</Subscript> based thick films prepared by dip coating method with effect of molarity of PtCl<Subscript>2</Subscript> solution

Synthesized nanophase SnO₂ powder was used as a functional material along with optimized 15 wt% of glass, fired at 550 °C for better adhesion, to fabricate thick films using screen printing on alumina substrate. Their surface was modified by dip coating in platinum chloride solution (PtCl₂) of different molarities (0.05–0.2 M). A subsequent thermal treatment to these thick films was carried out at an optimized temperature of 750 °C in air atmosphere. The films were tested for 400 ppm concentration of H₂, CO and LPG. Sensors dip coated with 0.15 M solution of PtCl₂ show the highest sensitivity towards the test gases which is ten times higher than undoped SnO₂ sensors.XRD, EDX and SEM measurements showed that the behavior could be associated with the spatial distribution of the platinum within the tin oxide film. The sensors have fast response time of 10 s to all the three gases with a minimum detection limit of 10 ppm.     

Synthesis,microstructure, and gas-sensing properties of SnO<Subscript>2</Subscript>/MoO<Subscript>3</Subscript> nanocomposites

SnO₂/MoO₃ nanocomposites are synthesized in a broad composition range through chemical precipitation from solution, and their phase composition and microstructure are investigated by x-ray diffraction. The gas sensitivity of the nanocomposites to lower alcohols (C_nH_{2n + 1} OH, n=1–4) is studied by in situ conductance measurements. The results are interpreted in terms of the acid-base properties of the nanocomposite surface.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 442–449.Original Russian Text Copyright © 2005 by Makeeva, Rumyantseva, Gaskov.     

SnO<Subscript>2</Subscript>-based thin films with excellent photocatalytic performance

SnO₂ semiconductor is a new-typed promising photocatalyst, but wide application of SnO₂-based photocatalytic technology has been restricted by low visible light utilization efficiency and rapid recombination of photogenerated electrons–holes. To overcome these drawbacks, we prepared B/Fe codoped SnO₂–ZnO thin films on glass substrates through a simple sol–gel method. The photocatalytic activities of the films were evaluated by degradation of organic pollutants including acid naphthol red (ANR) and formaldehyde. UV–Vis absorption spectroscopy and photoluminescence (PL) spectra results revealed that the B/Fe codoped SnO₂–ZnO film not only enhanced optical absorption properties but also improved lifetime of the charge carriers. X-ray diffraction (XRD) results indicated that the nanocrystalline SnO₂ was a single crystal type of rutile. Field emission scanning electron microscopy (FE-SEM) results showed that the B/Fe codoped SnO2–ZnO film without cracks was composed of smaller nanoparticles or aggregates compared to pure SnO2 film. Brunauer–Emmett–Teller (BET) surface area results showed that the specific surface area of the B/Fe codoped SnO₂–ZnO was 85.2 m² g^?1, while that of the pure SnO₂ was 20.7 m² g^?1. Experimental results exhibited that the B/Fe codoped SnO₂–ZnO film had the best photocatalytic activity compared to a pure SnO₂ or singly-modified SnO₂ film.     

Effect of Au and NiO catalysts on the NO<Subscript>2</Subscript> sensing properties of nanocrystalline SnO<Subscript>2</Subscript>

Nanocrystalline tin dioxide has been synthesized, and its surface has been modified with Au and NiO. Their distributions in the nanocrystalline tin dioxide have been examined by X-ray diffraction and transmission electron microscopy. The NO₂ sensing properties of the materials have been studied in the range 100–1000 ppb. Both gold and nickel enhance the NO₂ response of SnO₂. Codoping with Au and NiO markedly enhances its sensing response and, in addition, lowers the peak response temperature. The observed effect of NO₂ concentration in dry air on the sensing response of the SnO₂〈Au, NiO〉 nanocomposite can be understood in terms of the sequence of processes that take place on the SnO₂ surface upon nitrogen dioxide adsorption in the presence of chemisorbed oxygen.     

Synthesis and the field emission performances of SnO<Subscript>2</Subscript> micrograsses

SnO₂ micromaterials were synthesized via hydrothermal method at a temperature of 200 °C for 24 h without employment of catalysts or surfactants. With the dosage of the precursor (SnCl₄) increasing, variable microstructures of SnO₂, ophiopogon japonicas-like micrograsses, microcones, microflowers and microcorals, were obtained. The as-prepared SnO₂ samples were characterized by X-ray diffraction (XRD), scanning electron microscope and energy dispersive spectrometer respectively. XRD results indicated the as-grown SnO₂ samples have a tetragonal rutile structure. Among those different morphologies, micrograsses SnO₂ exhibited the best field emission performance with a low turn-on field of 1.05 V/µm and a high field enhancement factor of 3880. The results are quite comparable to reported data and strongly imply the micrograsses SnO₂ is a potential material for fabricating efficient emitters of display devices and vacuum electronics.     

A facile one step synthesis of SnO<Subscript>2</Subscript>/CuO and CuO/SnO<Subscript>2</Subscript> nanocomposites: photocatalytic application

Here novel photocatalysts, SnO₂/CuO and CuO/SnO₂ nanocomposites were successfully synthesized by chemical method at room temperature. X-ray Diffraction (XRD), transmission electron microscopy (TEM), Fourier transform Infrared (FT-IR), UV–Visible (UV–Vis) and photoluminescence (PL) spectroscopy were utilized for characterization of the nanocomposites. The photocatalytic activity of the nanocomposites was investigated. The hybrid nanocomposites exhibited high photocatalytic activity as evident from the degradation of methylene blue (MB) dye. The result revealed substantial degradation of the MB dye (92 and 69.5% degradation of SnO₂/CuO and CuO/SnO₂, respectively) under visible light illumination with short period of 30 min. Their large conduction band potential difference and the inner electrostatic field formed in the p–n heterojunction provide a strong driving force for the photogenerated electrons to move from Cu₂O to SnO₂ under visible light illumination. The excellent photodegradation of methylene blue suggested that the heterostructured SnO₂/CuO nanocomposite possessed higher charge separation and photodegradation abilities than CuO/SnO₂ nanocomposite under visible light irradiation.     

Synthesis of nanocrystalline SnO<Subscript>2</Subscript> powder at 100°C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline SnO₂ at 80–100°C under refluxing conditions. Freshly prepared stannic hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4–6 h. Formation of nano crystallites of SnO₂ is confirmed by X-ray diffraction (XRD) study. Transmission electron microscopic (TEM) investigations revealed that the average particle size is 30 nm for these powders.     

Vapor growth of SnO<Subscript>2</Subscript> whiskers

Tin dioxide whiskers have been prepared by vapor growth in a tube furnace in flowing argon at a constant evaporation temperature, and the effect of carrier-gas flow rate during growth on their morphology, phase composition, and IR spectrum has been studied. The whiskers are more than 0.5 mm in length and are well crystallized. Reducing the flow rate of the carrier gas during whisker growth makes it possible to reduce the fraction of phases containing tin in lower oxidation states and favors preferential whisker growth along the c axis.     

Gas-sensing properties of antimony-doped SnO<Subscript>2</Subscript>

We report a physicochemical study of the formation of thin-film and particulate SnO₂〈Sb〉 materials from film-forming solutions of Sn(II) and Sb(III) complexes during heat treatment and describe the electrical and gas-sensing properties of the films. The particle size and antimony concentration are shown to have a significant effect on carbon monoxide adsorption by the synthesized materials.     

SO<Subscript>2</Subscript> chemisorption on SnO<Subscript>2</Subscript>〈Sb〉

We have studied SO₂ chemisorption on antimony-doped SnO₂ samples annealed at 200 and 600°C. Increasing the annealing temperature from 200 to 600°C makes the sample surface more homogeneous. In the range 100–200°C, the electrical conductivity of the samples air-annealed at 600°C increases in proportion with the amount of absorbed SO₂. Doping with 0.2 at % Sb ensures the largest increase in conductivity upon chemisorption.