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.     

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.     

Controllable synthesis of Ho-doped In<Subscript>2</Subscript>O<Subscript>3</Subscript> porous nanotubes by electrospinning and their application as an ethanol gas sensor

Pure and Ho-doped In₂O₃ nanotubes (NTs) and porous nanotubes (PNTs) were successfully synthesized by conventional electrospinning process and the following calcination at different temperatures. X-ray diffractometry (XRD), thermogravimetric analysis (TGA), Raman spectrometer, energy-dispersive spectroscopy, scanning and transmission electron microscopy were carefully used to investigate the morphologies, structures and chemical compositions of these samples. Their sensing properties toward ethanol gas were studied. Compared with pure In₂O₃ NTs (response value is 17), pure In₂O₃ PNTs (response value is 20) demonstrated enhanced sensing characteristics. What’s more, the response of Ho-doped In₂O₃ PNTs sensors to 100 ppm ethanol was up to 60 at 240 °C, which increased three times more than that of the pure In₂O₃ PNTs. Additionally, the minimum concentration for ethanol was 200 ppb (response value is 2). The increased gas-sensing ability was attributed not only to the hollow and porous structure, but to the Ho dopant. Furthermore, Ho-doped In₂O₃ PNTs enable sensor to discriminate between ethanol and the other gas distinctly, particularly acetone that is usually indistinguishable from ethanol. Also, by analyzing XRD, TGA and Raman spectrometer, a possible formation mechanism of porous nanotubes and sensing mechanism were put forward.     

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.     

Preparation and gas-sensing properties of SnO<Subscript>2</Subscript>/graphene quantum dots composites via solvothermal method

SnO₂/graphene quantum dots (GQDs) nano-composites were prepared via solvothermal method (160 °C, 10 h), in which graphene quantum dots were synthesized from graphene oxide by one-step solvothermal method. The nano-composites were characterized by means of HRTEM, XRD, SEM, FTIR, XPS and N₂ adsorption–desorption, respectively. The sensor devices were fabricated using SnO₂/GQDs nano-composites as sensing materials. The effect of the GQDs content on the gas-sensing responses and the gas-sensing selectivity was investigated. The experimental results showed that the sensor based on SnO₂/GQDs nano-composite (S-2) exhibited good response and good selectivity to acetone vapor. When operating at 275 °C, the responses of the sensor based on SnO₂/GQDs nano-composite (S-2) to 1000 and 0.1 ppm acetone reached 120.6 and 1.3, respectively; the response time and the recovery time for 1000 ppm acetone were 17 and 13 s, respectively.     

Band gap narrowing and photocatalytic studies of Nd<Superscript>3+</Superscript> ion-doped SnO<Subscript>2</Subscript> nanoparticles using solar energy

Pure and Nd³⁺-doped tin oxide (SnO₂) nanoparticles have been prepared by the sol–gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM, energy-dispersive spectroscopy and UV–visible spectroscopy. The XRD patterns of all the samples are identified as tetragonal rutile-type SnO₂ phase which is further confirmed by TEM analysis. Neodymium doping introduces band gap narrowing in the prepared samples and enhances their absorption towards the visible-light region. The photocatalytic activity of all the samples was evaluated by monitoring the degradation of methylene blue solution under day light illumination and it was found that the photocatalytic activity significantly increases for the samples calcined at 600 than 400°C, which is due to the effective charge separation of photogenerated electron–hole pairs. The efficiency of photocatalysts was found to be related to neodymium doping percentage and calcination temperature.     

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.     

UV-enhanced ethanol-sensing properties of TiO<Subscript>2</Subscript>-decorated ZnSnO<Subscript>3</Subscript> hollow microcubes at low temperature

This work demonstrates the combined effect of nano-TiO₂ decoration and UV radiation on the ethanol sensing of ZnSnO₃ hollow microcubes. TiO₂-decorated ZnSnO₃ samples were synthesized by a facile co-precipitation method, followed by the calcination treatment of precursor–dehydration. The morphology and structure of the as-prepared samples were further characterized by XRD, EDS, SEM and TG analysis. Obtained samples were fabricated to thick film gas sensors for ethanol detection. Sensing tests showed a strong influence of TiO₂ decoration on the sensing properties. Light excitation by means of a low-powered UV source (365 nm) has been used to reinforce the sensor performance especially at lower operating temperature. The optimal sensor based on TiO₂-decorated ZnSnO₃ showed promising performance towards ethanol, ensuring high response and fast dynamics at operating temperature as low as 80?°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.     

Microstructure and H<Subscript>2</Subscript>S gas sensing properties of nanocrystalline perovskite-type La<Subscript>0.6</Subscript>Co<Subscript>0.4</Subscript>Mn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>

Nanocrystalline La_1−x Co _x Mn_1−y Ni _y O₃ (x = 0.2 and 0.4; y = 0.1, 0.3, and 0.5) thick films sensors prepared by sol–gel method were studied for their H₂S gas sensitivity. The structural and morphological properties have been carried out by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Average particle size estimated from XRD and TEM analyses was observed to be 30–35 nm. The gas response characteristics were found to depend on the dopants concentration and operating temperature. The maximum H₂S gas response of pure LaMnO₃ was found to be at 300 °C. In order to improve the gas response, material doped with transition metals Co and Ni on A- and B-site, respectively. The La_0.6Co_0.4Mn_0.5Ni_0.5O₃ shows high response towards H₂S gas at an operating temperature 250 °C. The Pd-doped La_0.6Co_0.4Mn_0.5Ni_0.5O₃ sensor was found to be highly sensitive to H₂S at an operating temperature 200 °C. The gas response, selectivity, response time and recovery time were studied and discussed.     

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).     

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.     

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.     

Magnetic and antibacterial properties of Zr-doped SnO<Subscript>2</Subscript> nanopowders

Zirconium doped tin oxide (SnO₂:Zr) nanopowders were synthesized by a simple soft chemical route adding various concentrations of zirconyl chloride (0, 5, 10 and 15 wt%). The samples were characterized by techniques like XRD, SEM, TEM, EDX, FTIR spectroscopy, UV–Vis-NIR spectroscopy and photoluminescence spectroscopy. XRD studies confirm that all the samples exhibit rutile tetragonal crystal structure with a strong (1 0 1) preferential growth texture. Hexagonal shaped grains were evinced from the SEM images. Nanosized grains are evinced from the TEM images and EDX spectra confirm the presence of Zr in the doped samples. The bands at 523 and 583 cm^?1 observed in the FTIR spectra which are attributed as the characteristics of γ (Sn–OH) terminal bond of the SnO₂ crystalline phase confirm the presence of Sn–O in the synthesized samples. The doped samples exhibit ferromagnetic behavior. Enhanced antibacterial activity was observed for the doped samples. The obtained results show that zirconium strongly influenced the structural, morphological, optical, magnetic and antibacterial properties of pure SnO₂ nanopowders.     

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.     

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.     

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.     

Controllable synthesis of SnO2 photocatalyst with superior photocatalytic activity for the degradation of methylene blue dye solution

SnO₂ photocatalyst was successfully synthesised by novel chemical route in hydrothermal environment and annealed at two different temperatures viz 550 and 600 °C, respectively. The crystal structure, optical properties, surface and bulk morphology have been characterised using various tools like X-ray diffraction (XRD), UV visible spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscope (TEM) and scanning electron microscope (SEM). Cubic, spheres and porous like morphology of SnO₂ photocatalyst was successfully confirmed using SEM micrographs and TEM. In addition to this the photocatalytic activity was evaluated towards the degradation of methylene blue dye solution. SnO₂ photocatalyst annealed at 600 °C exhibits excellent photocatalytic efficiency which may be attributed to the unique morphology, high crystalline nature and charge separation. The photocatalyst efficiency was further tested towards the concentration of dye, catalyst dosage and pH of the dye. The involvement of ?OH in the photocatalytic reaction was evidenced using trapping experiment by employing different scavengers. The photocatalyst was moderately active, stable upto its fifth usage and stability of the photocatalyst before and after the photocatalytic reaction was also been studied using XRD and SEM.     

Microwave assisted hydrothermal synthesis of mesoporous SnO2 nanoparticles for ethanol sensing and degradation

We report the synthesis of mesoporous SnO₂ nanoparticles by a microwave assisted hydrothermal process and their application as a gas sensor. The synthesized materials were characterized by transmission electron microscopy, X-ray diffraction technique, X-ray photoelectron spectroscopy, and Photoluminescence spectroscopy. As the results, we found that as-synthesized SnO₂ was synthetic Cassiterite with tetragonal structure and spherical in shape with the primary crystallite size of 6–8 nm, and the SnO₂ embedded material was mesoporous with average pore sizes of ≈15 nm. Moreover, this material showed excellent thermal stability from 80 to 800 °C and its crystal structure after heat treatment was preserved even at ultrahigh temperature of 800 °C. We demonstrated that this material could be used for detection of the ethanol gas because of its stability and nanoscale size at high temperature. Additionally our investigations also suggest that the processed materials can be used for the photocatalytic oxidation of ethanol. These results propose the potential application of the material for a sense and shoot kind of approach for indoor air purification in pharmaceutical and fermentation monitoring and vehicular control through breath analyzer.     

Hydrothermally synthesized cubic magnesium stannate (Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>) nanoparticles and its electrochemical performances

Cubic crystalline Mg₂SnO₄ nano particles (NPs) were prepared by the facile hydrothermal method and NaOH used as a mineralizer. The synthesized product was calcinated at different temperatures and sample calcinated at 900?°C was optimized by using XRD and TG/DT analysis. XRD result confirms that the Mg₂SnO₄ NPs has cubic phase with lattice space group of Fd3m with mean crystalline size of 26 nm. The sample calcinated at 900?°C was further characterized by FE-SEM with EDS, HR-TEM with SAED pattern, DLS and Cyclic Voltammetry. The effect of calcination temperature on the formation of Mg₂SnO₄ NPs as well as the particle size and crystalline structure were observed. The surface morphology of the sample indicates that the NPs were in irregular cubic shape and EDS analysis revealed the presence of the Mg, Sn, and O. Zeta potential depicts good stability of the sample and a specific capacitance value of 328 Fg^?1 was observed which suggests that Mg₂SnO₄ NPs could be a potential candidate for super capacitor applications.