Structural and gas sensing behavior of nanocrystalline BaTiO3 based liquid petroleum gas sensors

In this paper nanosized BaTiO₃ thick films based gas sensor has been fabricated for liquid petroleum gas (LPG). Doping with different concentrations of metal oxides influenced the sensitivity of BaTiO₃ thick films for LPG sensor. We present the characterization of both their structural properties by means of X-ray powder diffraction (XRD) and the electrical characteristics by using gas-sensing properties. X-ray powder diffraction analyses revealed the persistence of cubic phase with grain growth 65 nm. The LPG-sensing properties of BaTiO₃ thick films doped with CuO and CdO are investigated. It was found that 10 wt.% CuO: 10 wt.% CdO doped BaTiO₃ based LPG sensor shows better sensitivity and selectivity at an operating temperature 250 °C which is an important commercial range for LPG alarm development. Incorporation of 0.3 wt.% Pd doped CuO:CdO:BaTiO₃ element shows maximum sensitivity with high cross selectivity to the other gases including CO, H₂ and H₂S at an operating temperature 225 °C for low concentrations of LPG sensor.     

Enhanced catalytic activity of nanoscale platinum islands loaded onto SnO<Subscript>2</Subscript> thin film for sensitive LPG gas sensors

In the present study, different catalysts (∼ 10 nm thick) including metals, noble metals and metal oxides, were loaded in dotted island form over SnO₂ thin film for LPG gas detection. A comparison of various catalysts indicated that the presence of platinum dotted islands over SnO₂ thin film deposited by r.f. sputtering exhibited enhanced response characteristics with a high sensitivity, ∼ 742, at an operating temperature of ∼ 280°C. Different characterization techniques have been employed such as atomic force microscopy, X-ray diffraction and UV-vis spectroscopy, to study the surface morphology, grain size and optical properties of the deposited thin films. The results suggest the possibility of utilizing the sensor element with the present novel method of catalyst dispersal for the efficient detection of LPG.     

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.     

Development of sensors based on CuO-doped SnO2 hollow spheres for ppb level H2S gas sensing

An effort has been made to develop a new kind of SnO₂–CuO gas sensor which could detect an extremely small amount of H₂S gas at relatively low working temperature. The sensor nanomaterials were prepared from SnO₂ hollow spheres (synthesized by employing carbon microspheres as temples) and Cu precursor by dipping method. The composition and structural characteristics of the as-prepared CuO-doped SnO₂ hollow spheres were studied by X-ray photoelectron spectroscopy, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Gas-sensing properties of CuO-doped SnO₂ hollow sphere were also investigated. It was found that the sensor showed good selectivity and high sensitivity to H₂S gas. A ppb level detection limit was obtained with the sensor at the relatively low temperature of 35 °C. Such good performances are probably attributed to the hollow sphere nanostructures. Our results imply that materials with hollow sphere nanostructures are promising candidates for high-performance gas sensors.     

Selective detection of hydrogen sulfide using copper oxide-doped tin oxide based thick film sensor array

In this work, copper oxide-doped (1, 3 and 5 wt%) tin oxide powders have been synthesised by sol–gel method and thick film sensor array has been developed by screen printing technique for the detection of H₂S gas. Powder X-ray diffraction pattern shows that the tin oxide (SnO₂) doped with 3 wt% copper oxide (CuO) has smaller crystallite size in comparison to 0, 1 and 5 wt% CuO-doped SnO₂. Furthermore, field emission scanning electron microscopy manifests the formation of porous film consisting of loosely interconnected small crystallites. The effect of various amounts of CuO dopant has been studied on the sensing properties of sensor array with respect to hydrogen sulfide (H₂S) gas. It is found that the SnO₂ doped with 3 wt% CuO is extremely sensitive (82%) to H₂S gas at 150 °C, while it is almost insensitive to many other gases, i.e., hydrogen (H₂), carbon monoxide (CO), sulphur dioxide (SO₂) and liquefied petroleum gas (LPG). Moreover, at low concentration of gas, it shows fast recovery as compared to response time. Such high performance of 3 wt% CuO-doped SnO₂ thick film sensor is probably due to the diminishing of the p–n junction and the smallest crystallite size (11 nm) along with porous structure.     

Solid-state reaction synthesized Pd-doped tin oxide thick film sensor for detection of H2, CO, LPG and CH4

This paper deals with the synthesis of tin oxide (SnO₂) nano-powders by a solid-state reaction technique. The synthesized powders have been characterized by simultaneous thermo gravimetric and differential thermal analysis (TG–DTA) and X-ray diffraction (XRD) techniques. Suitable calcination temperature is established by XRD and TG–DTA analysis. Thick film sensors have been developed from as-prepared undoped and palladium (Pd) doped (0.5 and 1 wt%) SnO₂ powders using screen printing technology for the detection of various pollutant gases such as, hydrogen (H₂), carbon monoxide (CO), liquefied petroleum gas (LPG) and methane (CH₄). The surface of the thick film sensor has been characterized by field emission scanning electron microscopy (FESEM). The sensing characteristics of thick films have been studied from the aspect of crystallite size of sensing material and microstructure of the thick film surface. It is found that SnO₂ doped with 1 % Pd exhibits the maximum sensitivity (79 %) towards CO gas along with fast response/recovery time (80 s, 197 s) and almost insensitive for H₂, LPG and CH₄.     

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.     

Effect of processing and palladium doping on the properties of tin oxide based thick film gas sensors

In the present work, solid-state reaction and sol–gel route derived pure tin oxide (SnO₂) powders have been used to develop the palladium (Pd)-doped SnO₂ thick film sensors for detection of liquefied petroleum gas (LPG). Efforts have been made to study the gas sensing characteristics i.e., sensor response, response/recovery time and repeatability of the thick film sensors. The response of the sensors has been investigated at different operating temperatures from 200 to 350 °C in order to optimise the operating temperature which yields the maximum response upon exposure to fixed concentration of LPG. The optimum temperature is kept constant to facilitate the gas sensing characteristics as a function of the various concentration (0.25–5 vol%) of LPG. The structural and microstructural properties of Pd-doped SnO₂ powder and developed sensors have been studied by performing X-ray diffraction and field emission electron microscopy measurements. The improvement in the response along with better response and recovery time have been correlated to the reduction in crystallite size of SnO₂ powder and morphology of printed sensor in thick film form. It is found that the thick film sensor developed by using sol–gel route derived SnO₂ powder with an optimum doping of 1 wt% Pd is extremely sensitive (86 %) to LPG at 350 °C.     

Water-assisted growth and characterization of SnO2 nanobelts

SnO₂ nanobelts have been synthesized by water-assisted growth at 850 °C using high pure Sn powders as the source materials. The as-synthesized products were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy(TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersed X-ray spectroscopy (EDX), infrared spectrum (IR) and room-temperature photoluminescence (PL) spectrum. XRD pattern of the sample is quite in accord with the standard pattern of the tetragonal rutile SnO₂; SEM and TEM images show that the uniform single-crystalline SnO₂ nanobelts are about tens of micrometers in length, 70-100 nm in width and 5-8 nm in thickness, and is smooth in surface. The special IR and PL properties were also detected by IR and PL testing. The growth mechanisms and special properties relative to the SnO₂ nanostructures are discussed.     

Hydrogen sensing properties of Pd-doped SnO2 sputtered films with columnar nanostructures

Pd-doped SnO₂ sputtered films with columnar nanostructures were deposited using reactive magnetron sputtering at the substrate temperature of 300 °C and the discharge gas pressures of 1.5, 12, and 24 Pa. Structural characterization by means of X-ray diffraction and scanning electron microscopy shows that the films composed of columnar nanograins have a tetragonal SnO₂ structure. The films become porous as the discharge gas pressure increases. Gas sensing measurements demonstrate that the films show reversible response to H₂ gas. The sensitivity increases as the discharge gas pressure increases, and the operating temperature at which the sensitivity shows a maximum is lowered. The highest sensitivity defined by (R_a − R_g) / R_g, where R_a and R_g are the resistances before and after exposure to H₂, 84.3 is obtained for the Pd-doped film deposited at 24 Pa and 300 °C upon exposure to 1000 ppm H₂ gas at the operating temperature of 200 °C. The improved gas sensing properties were attributed to the porosity of columnar nanostructures and catalytic activities of Pd doping.     

FeSbO4 semiconductor ceramics: a new material for sensing liquid-petroleum gas

FeSbO₄-based semiconducting ceramics used as a promising candidate for sensing liquid-petroleum gas (LPG) are presented here for the first time. Precursor powders of FeSbO₄ were prepared by two different methods (i.e., ball-milling and chemical coprecipitation). The solid-state reaction in the Fe₂O₃-Sb₂O₃ system was investigated by means of thermal gravimetric-differential thermal analysis (TG-DTA) and X-ray diffraction (XRD). Based on our experimental results and previous work, the diffusion of antimony oxide onto -Fe₂O₃ is assumed to be a controlling step of the solid-state reaction. Scanning electron microscopy (SEM) and the BET method were used to characterize the samples calcined at 550 to 1000 °C. It was found that a sudden change in specific surface area, crystallite size and particle size takes place between 550 °C calcining and 600 °C calcining, which has an obvious influence on gas-sensing properties. FeSbO₄-based sensors operating at 370 °C show a high sensitivity and selectivity to liquid-petroleum gas (LPG) over H₂ CO or i-C₄H₁₀. Addition of Pd shows a fair increase in sensitivity to LPG, but a remarkable improvement in response and recovery times which is advantageous for its practical application.     

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.

     

Low temperature synthesis of SnO2 nanocrystals from tin, sulfur and ammonium chloride powders

Tetragonal phase SnO₂ nanocrystals were synthesized directly by heating the mixture of tin (Sn), sulfur (S) and ammonium chloride (NH₄Cl) powders in air at 400 °C for 2-5 h. The phase, size and purity of the resultant products were characterized by means of powder X-ray diffraction (XRD), filed emission scanning electronic microscope (FESEM), and energy dispersive X-ray (EDX) spectra. Besides, the effects of heating temperature, duration, and composition of the reactants on the phases of the resultant products were investigated. It was found that both of the S and NH₄Cl additives played important roles in the current low temperature (400 °C) synthesis of pure SnO₂.     

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.     

Preparation and ethanol sensing properties of the superstructure SnO2/ZnO composite via alcohol-assisted hydrothermal route

Self-assembled superstructure of SnO₂/ZnO composite was synthesized by using alcohol-assisted hydrothermal method gas sensing properties of the material were investigated by using a static test system. The structure and morphology of the products were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM). The diameter of the SnO₂ nanorods was about 40 nm with a length of about 300 nm, SnO₂ nanorods and ZnO nanosheets interconnect each other to form a superstructure. The gas sensing properties of superstructure SnO₂/ZnO composite with different content of ZnO were investigated. Furthermore, the superstructure SnO₂/ZnO composite sensor is characterized at different operating temperatures and its long-term stability in response to ethanol vapor is tested over a period of 3 months.     

Synthesis and characterization of CdO-doped nanocrystalline ZnO:TiO2-based H2S gas sensor

This paper reports the preparation and gas-sensing characteristic of ZnO:TiO₂-based hydrogen sulfide (H₂S) gas sensor with different mol% of CdO by polymerized complex method. The structural and gas-sensing properties of ZnO:TiO₂ materials have been characterized using X-ray diffraction and gas-sensing measurement. The electrical resistance response of the sensor based on the materials was investigated at different operating temperatures and different gas concentrations. The sensor with 10 mol% CdO-doped ZnO:TiO₂ shows excellent electrical resistance response toward H₂S gas. The cross sensitivity was also checked for reducing gases like CH₄, CO and H₂ gas. The selectivity and sensitivity of ZnO:TiO₂-based H₂S gas sensor were improved by the addition of 10 mol% of CdO at an operating temperature of 250 °C.     

Structure and field emission properties of SnO2 nanowires

SnO₂ nanowires were fabricated using a simple and economical method of rapid heating SnO₂ and graphite powders at 850 °C in a flow of high-purity N₂ as carrier gas. Research by using X-ray diffraction (XRD) indicates that SnO₂ nanowires are primitive tetragonal in structure with the lattice constant a = b = 0.443 nm and c = 0.372 nm. Observations by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that SnO₂ is of nanowire structure. The selected area electron diffraction (SAED) shows that the nanowires are perfect single crystal structure. The Fourier transform infrared (FT-IR) exhibits the difference of nanostructure materials and general materials. The field emission (FE) properties had also been studied.     

Structural,morphological, optical and gas sensing properties of pure and Ce doped SnO<Subscript>2</Subscript> thin films prepared by jet nebulizer spray pyrolysis (JNSP) technique

Pure and cerium (Ce) doped tin oxide (SnO₂) thin films are prepared on glass substrates by jet nebulizer spray pyrolysis technique at 450 °C. The synthesized films are characterized by X-ray diffraction (XRD), scanning electron microscopy, energy dispersive analysis X-ray, ultra violet visible spectrometer (UV–Vis) and stylus profilometer. Crystalline structure, crystallite size, lattice parameters, texture coefficient and stacking fault of the SnO₂ thin films have been determined using X-ray diffractometer. The XRD results indicate that the films are grown with (110) plane preferred orientation. The surface morphology, elemental analysis and film thickness of the SnO₂ films are analyzed and discussed. Optical band gap energy are calculated with transmittance data obtained from UV–Visible spectra. Optical characterization reveals that the band gap energy is found decreased from 3.49 to 2.68 eV. Pure and Ce doped SnO₂ thin film gas sensors are fabricated and their gas sensing properties are tested for various gases maintained at different temperature between 150 and 250 °C. The 10 wt% Ce doped SnO₂ sensor shows good selectivity towards ethanol (at operating temperature 250 °C). The influence of Ce concentration and operating temperature on the sensor performance is discussed. The better sensing ability for ethanol is observed compared with methanol, acetone, ammonia, and 2-methoxy ethanol gases.     

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.     

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.