Improved ethanediol sensing with single Yb ions doped SnO2 nanobelt

Yb-doped SnO₂ nanobelts (Yb–SnO₂ NBs) and pure SnO₂ nanobelts (SnO₂ NBs) are successfully synthesized by thermal evaporation method and their composition and morphology are characterized. The single nanobelt device is fabricated by dual-ion beam deposition system, and the gas sensing performance to ethanediol, methanal, ethanol and acetone is investigated. The results show that the best working temperature of single Yb–SnO₂ NB sensor to ethanediol is 190 °C, which is lower than that of pure counterpart and the highest sensitivity is 10.5 to 100 ppm of ethanediol. In addition, it is found that the response/recovery time is short and the sensor exhibits excellent selectivity and stability. The sensing performance of SnO₂ NB is actually improved by Yb.     

Synthesis,characterization and enhanced acetone sensing performance of Pd loaded Sm doped SnO2 nanoparticles

In the present communication, we have presented a high performance acetone sensor based on Pd loaded Sm doped SnO₂ nanomaterial. The (0.5, 1, 2 and 3) wt% Pd loaded 6 mol% Sm doped SnO₂ nanoparticles were prepared using a co-precipitation method. The characterization of samples was done by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Analysis by X-rays (EDAX), High Resolution-Transmission Electron Microscopy (HR-TEM) and Selective Area Electron Diffraction (SAED) techniques. The gas response studies such as sensitivity, selectivity and stability towards liquid petroleum gas, ammonia, ethanol and acetone were measured at 100 ppm concentrations. The results show that optimum Pd loading (2 wt%) results in smaller crystallite size (~3.1 nm), lower operating temperature (200 °C), higher gas response (94%),better selectivity, faster response (~3 s) and quicker recovery (~12 s) towards acetone.     

Influence of Pd-loading on gas sensing characteristics of SnO2 thick films

Nanocrystalline pristine and 0.5, 1.5 and 3.0 wt% Pd loaded SnO₂ were synthesized by a facile co-precipitation route. These powders were screen-printed on alumina substrates to form thick films to investigate their gas sensing properties. The crystal structure and morphology of different samples were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The 3.0 wt% Pd:SnO₂ showed response of 85% toward 100 ppm of LPG at operating temperature of 250 °C with fast response (8 s) and quick recovery time (24 s). The high response toward LPG on Pd loading can be attributed to lowering of crystallite size (9 nm) as well as the role of Pd particles in exhibiting spill-over mechanism on the SnO₂ surface. Also selectivity of 3.0 wt% Pd:SnO₂ toward LPG was confirmed by measuring its response to other reducing gases like acetone (CH₃COCH₃), ethanol (C₂H₅OH) and ammonia (NH₃) at optimum operating temperature.     

Nanostructured SnO2 thin films for NO2 gas sensing applications

We report the synthesis of nanostructured SnO₂ by a simple inexpensive sol–gel spin coating method using m-cresol as a solvent. This method facilitates rapid synthesis at comparatively lower temperature enabling formation of nanostructures suitable for gas-sensing applications. Various physicochemical techniques have been used for the characterization of SnO₂ thin films. X-ray diffraction analysis confirmed the single-phase formation of tetragonal SnO₂ having crystallite size 5–10 nm. SnO₂ showed highest response (19%) with 77.90% stability toward 100 ppm nitrogen dioxide (NO₂) at 200 °C. The response time of 7 s and recovery time of 20 min were also observed with the same operating parameters. The probable mechanism is proposed to explain the selective response toward nitrogen dioxide. Impedance spectroscopy studies showed that the response to nitrogen dioxide is mainly contributed by grain boundaries. The reproducibility and stability study of SnO₂ sensor confirmed its candidature for detection of NO₂ gas at low concentration (10–100 ppm) and lower operating temperature.     

Trimethylamine sensing properties of nano-SnO2 prepared using microwave heating method

The precursor was obtained through the reaction between SnCl₄·5H₂O and NaOH in the presence of PEG400 (polyethylene glycol, M = 400). Tin oxide (SnO₂) nano-powders were prepared by heating the precursor with microwave method. SnO₂ thick film sensors were fabricated using SnO₂ nano-materials as sensing materials. The phase composition and morphology of the material particles were characterized through X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The average particle sizes of the samples obtained with 616 W microwave heating and 800 W microwave heating (20 min) are about 5 and 15 nm, respectively. The influence of the heating duration and heating power on the gas-sensing properties of sensors based on SnO₂ nano-materials were investigated. The sensitivities of the sensors based on SnO₂ nano-materials heated with 616 and 800 W for 20 min were higher than those of the sensors based on SnO₂ nano-materials heated with 136, 264 and 440 W for 20 min. When operating at 200–310 °C, the sensor based on SnO₂ heated with 616 W for 20 min exhibits highest sensitivities in all sensors based on SnO₂ heated with 616 W for different duration. The sensitivity to a few kinds of organic gases, such as (CH₃)₃N and (CH₃)₂CO were studied. It was found that the sensor based on SnO₂ nano-materials (with 616 W microwave heating for 20 min) exhibited good performance characterized by high sensitivity and short response time to dilute trimethylamine when operated at 255 °C. The sensitivity to 0.001 ppm (CH₃)₃N at 255 °C was 3. The response time and recovery time were about 30 and 100 s, respectively.     

Tin–Zinc oxide composite ceramics for selective CO sensing

Composite metal oxide gas sensors were intensely studied over the past years having superior performance over their individual oxide components in detecting hazardous gases. A series of pellets with variable amounts of SnO₂ (0–50 mol%) was prepared using wet homogenization of the component oxides leading to the composite tin-zinc ceramic system formation. The annealing temperature was set to 1100 °C. The samples containing 2.5 mol% SnO₂ and 50 mol% SnO₂ were annealed also at 1300 °C, in order to observe/to investigate the influence of the sintering behaviour on CO detection. The sensor materials were morphologically characterized by scanning electron microscopy (SEM). The increase in the SnO₂ amount in the composite ceramic system leads to higher sample porosity and an improved sensitivity to CO. It was found that SnO₂ (50 mol%) - ZnO (50 mol%) sample exhibits excellent sensing response, at a working temperature of 500 °C, for 5 ppm of CO, with a fast response time of approximately 60 s and an average recovery time of 15 min. Sensor selectivity was tested using cross-response to CO, methane and propane. The results indicated that the SnO₂ (50 mol%)-ZnO (50 mol%) ceramic compound may be used for selective CO sensing applications.     

Bias dependent NO2 sensitivity of SnO2 thin films at room temperature

Amorphous granular SnO₂ thin films were investigated from a standpoint of an NO₂ gas sensor working at room temperature. The films were deposited using pulsed laser deposition method with substrate at room temperature and ～90 nm thick SnO₂ films with amorphous structure were obtained as a result. SnO₂ films deposited on Pt electrode substrates formed a sensor structure that showed response I_air/I_gas to 4 ppm NO₂ up to ～8000. I–V characteristics of the sensor structure were described by the power law dependence, whereas the power indexes were different for measurements in pure air and in the presence of NO₂. As a result, the sensor response was highly dependent on bias voltage between the sensor electrodes. It was demonstrated that the nonlinear electrical characteristics and bias dependent gas sensitivity were the inherent properties of thin films and the contacts were ohmic.     

Synthesis,characterization and alcohol sensing property of Zn-doped SnO2 nanoparticles

The Zn-doped SnO₂ nanoparticles synthesized by the chemical co-precipitation route and having dopant concentration varying from 0 to 4 at%, were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) for structural and morphological studies. XRD analyses reveal that all the samples are polycrystalline SnO₂ having tetragonal rutile structure with nanocrystallites in the range 10–25 nm. The TEM images show agglomeration of grains (cluster of primary crystallites). A corresponding selected area electron diffraction pattern reveals the different Debye rings of SnO₂, as analyzed in XRD. Alcohol sensing properties of all the Zn-doped samples were investigated for various concentrations of methanol, ethanol and propan-2-ol in air at different operating temperatures. Among all the samples examined, the 4 at% Zn-doped sample exhibits the best response to different alcohol vapors at the operating temperature of 250 °C. For a concentration of 50 ppm, the 4 at% Zn-doped sample shows the maximum response 85.6% to methanol, 87.5% to ethanol and 94.5% to propan-2-ol respectively at the operating temperature of 250 °C. A possible reaction mechanism of alcohol sensing has been proposed.     

Ultrafine SnO2 nanoparticles as a high performance anode material for lithium ion battery

In this paper, the ultrafine tin oxides (SnO₂) nanoparticles are fabricated by a facile microwave hydrothermal method with the mean size of only 14 nm. Phase compositions and microstructures of the as-prepared nanoparticles have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the ultrafine SnO₂ nanoparticles are obtained to be the pure rutile-structural phase with the good dispersibility. Galvanostatic cycling and cyclic voltammetry results indicate that the first discharge capacity of the ultrafine SnO₂ electrode is 1196.63  mAh g⁻¹, and the reversible capacity could retain 272.63 mAh g⁻¹ at 100 mA g⁻¹ after 50 cycles for lithium ion batteries (LIBs). The excellent electrochemical performance of the SnO₂ anode for LIBs is attributed to its ultrafine nanostructure for providing active sites during lithium insertion/extraction processes. Pulverization and agglomeration of the active materials are effectively reduced by the microwave hydrothermal method.     

Enhanced performance of γ-Fe2O3:WO3 nanocomposite towards selective acetone vapor detection

Metal oxide nanocomposite sensors based on γ-Fe₂O₃ and WO₃ were investigated in acetone vapor of various concentrations (1–100 ppm) at operating temperatures between 250 and 350 °C. The composites were prepared by simple solid state mixing and porous thick-film gas sensors were fabricated on alumina substrates. The γ-Fe₂O₃:WO₃ (50:50) nanocomposite showed a marked enhancement in sensing response down to 1 ppm acetone vapor detection at 300 °C. The response was ~2-fold better compared to pure WO₃ or pure γ-Fe₂O₃ with a very fast response (1 s) and very short recovery time (3 s). No appreciable sensitivity was observed towards alcohol vapor (an interfacing agent for diabetics) and in moisture (present in breath). The enhanced performance was due to n–n heterojunction effect.     

Synthesis of porous CeO2-SnO2 nanosheets gas sensors with enhanced sensitivity

Two-dimension (2D) CeO₂-SnO₂ nanosheets with uniform size and small rhombus nanopores were synthesized by the hydrothermal method. The structure of CeO₂-SnO₂ nanosheets was confirmed by X-ray diffraction (XRD), energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The gas sensing behaviors of the fabricated sensors were systematically investigated. Under optimum operating temperature (340 °C), the response to 100 ppm ethanol of the CeO₂-SnO₂ sensor was 44, which was 2 times larger than that of the SnO₂ sensor (about 19). The response and recovery time of the CeO₂-SnO₂ sensor were 25 s and 6 s, while that of the SnO₂ sensor were 29 s and 7 s, respectively. The results revealed that porous CeO₂-SnO₂ nanosheets enhanced the gas sensing properties and shortened the response/recovery time, which were attributed to the porous structure and the effect of the CeO₂-doping. In addition, the ethanol sensing mechanism was carefully discussed.     

Electrospun ZnO–SnO2 composite nanofibers with enhanced electrochemical performance as lithium-ion anodes

ZnO–SnO₂ composite nanofibers with different structures were synthesized by a simple electrospinning approach with subsequent calcination at three different temperatures using polyacrylonitrile as the polymer precursor. The electrochemical performance of the composites for use as anode materials in lithium-ion batteries were investigated. It was found that the ZnO–SnO₂ composite nanofibers calcined at 700 °C showed excellent lithium storage properties in terms of cycling stability and rate capability, compared to those calcined at 800 and 900 °C, respectively. ZnO–SnO₂ composite nanofibers calcined at 700 °C not only delivered high initial discharge and charge capacities of 1450 and 1101 mAh g⁻¹, respectively, with a 75.9% coulombic efficiency, but also maintained a high reversible capacity of 560 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles. Additionally, a high reversible capacity of 591 mAh g⁻¹ was obtained when the current density returned to 0.1 A g⁻¹ after 50 cycling at a high current density of 2 A g⁻¹. The superior electrochemical performance of ZnO–SnO₂ composite nanofibers can be attributed to the unique nanofibrous structure, the smaller particle size and smaller fiber diameter as well as the porous structure and synergistic effect between ZnO and SnO₂.     

Enhanced NO2 sensing properties of Zn2SnO4-core/ZnO-shell nanorod sensors

Zn₂SnO₄-core/ZnO-shell nanorods were synthesized using a two-step process: synthesis of Zn₂SnO₄ nanorods the thermal evaporation of a mixture of ZnO, SnO₂, and graphite powders, followed by atomic layer deposition (ALD) of ZnO. The nanorods were 50–250 nm in diameter and a few to a few tens of micrometers in length. The cores and shells of the nanorods were face-centered cubic-structured single crystal Zn₂SnO₄ and wurtzite-structured single crystal ZnO, respectively. The multiple networked Zn₂SnO₄-core/ZnO-shell nanorod sensors showed a response of 173–498% to NO₂ concentrations of 1–5 ppm at 300 °C. These response values are 2–5 times higher than those of the Zn₂SnO₄ nanorod sensor over the same NO₂ concentration range. The NO₂ sensing mechanism of the Zn₂SnO₄core/ZnO-shell nanorods is discussed.     

Solvothermal preparation and gas sensing properties of hierarchical pore structure SnO2 produced using grapefruit peel as a bio-template

Hierarchical pore structure nano-sized SnO₂ was synthesized using a solvothermal method with SnCl₄ as the raw material and grapefruit peel as the bio-template. The products were characterized by powder X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption measurements. The results show that the SnO₂ prepared from the grapefruit peel bio-template consists of many large size (5–20 µm) interconnected pores with a honeycomb structure and nanosized pores (9.46 nm) on the walls of the large pores. The as-prepared SnO₂ presented a high specific surface area of 42.98 m²/g and the average crystallite size was about 10±0.5 nm. The gas sensing performance of the prepared material toward several volatile organic compounds was investigated. The results show that the hierarchical pore structure nano-sized SnO₂ was highly sensitive and selective to n-butanol, indicating that this material may be a promising candidate for future development as a n-butanol gas sensor.     

Enhanced gas sensing properties of hierarchical SnO2 nanoflower assembled from nanorods via a one-pot template-free hydrothermal method

Well-defined three-dimensional (3D) hierarchical tin dioxide (SnO₂) nanoflowers with the size of about 200 nm were successfully synthesized by a simple template-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂ adsorption-desorption analyses were used to characterize the structure and morphology of the products. The as-synthesized full crystalline and large specific surface area SnO₂ nanoflowers were assembled by one-dimensional (1D) SnO₂ nanorods with sharp tips. A possible self-assembly mechanism for the formation the SnO₂ nanoflowers was speculated. Moreover, gas sensing investigation showed the sensor based on SnO₂ nanoflowers to exhibit high response and fast response-recovery ability to detect acetone and ethanol at an operating temperature lower than 200 °C. The enhancement of gas sensing properties was attributed to their 3D hierarchical nanostructure, large specific surface area, and small size of the secondary SnO₂ nanorods.     

Synthesis and ethanol sensing properties of CuO nanorods coated with In2O3

CuO/In₂O₃ core–shell nanorods were fabricated using thermal evaporation and radio frequency magnetron sputtering. X-ray diffraction and transmission electron microscopy showed that both the cores and shells were crystalline. The multiple networked CuO/In₂O₃ core–shell nanorod sensors showed responses of 382–804%, response times of 36–54 s and recovery times of 144–154 s at ethanol (C₂H₅OH) concentrations ranging from 50 to 250 ppm at 300 °C. These responses were 2.3–2.8 times higher than those of the pristine CuO nanorod sensor over the same C₂H₅OH concentration range. The origin of the enhanced ethanol sensing properties of the core–shell nanorod sensor is discussed.     

Annealing impact on the structural and optical properties of electrospun SnO2 nanofibers for TCOs

Tin oxide (SnO₂) nanofibers were fabricated by electrospinning technique and subsequent annealed at different temperatures. The structure, morphology and optical properties of the annealed samples were characterized by X-ray diffraction (XRD), Raman, scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), transmission electron microscopy (TEM), Fourier transformed infrared (FTIR),and optical absorption techniques. The phase of SnO₂ of all samples is rutile (tetragonal), and at higher annealing temperatures, good crystallinity and lower absorption were obtained. Annealing of the samples at 600 °C caused the lower absorption and higher optical band gap, and the decrease of the absorption was probably because the fiber structure changed from solid to hollow structure. From PL spectra, it was observed that the SnO₂ hollow nanofibers annealed at 600 °C revealed green emission at 530 nm.     

Raman spectra,photoluminescence and ferromagnetism of pure,Co and Fe doped SnO2 nanoparticles

The pure and transition metal (Co and Fe = 3 and 5 mol%) doped SnO₂ nanoparticles have been synthesized by a chemical route using polyvinyl alcohol as surfactant. These nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR) spectroscopy, photoluminescence (PL) and magnetic measurements. The XRD patterns show that all the samples have tetragonal rutile structure without any extra phase and the value of average particle size using FWHM lies within 12–29 nm is also confirmed by TEM. FTIR spectrum has been used to confirm the formation of SnO bond. Raman spectroscopy shows the intensity loss of classical cassiterite SnO₂ vibration lines which is an indication of significant structural modifications. From PL, an intense blue luminescence centered at a wavelength ～530 nm is observed in the prepared SnO₂ nanoparticles, which is different from the yellow-red light emission observed in SnO₂ nanostructures prepared by other methods. The strong blue luminescence from the as-grown SnO₂ nanoparticles is attributed to oxygen-related defects that have been introduced during the growth process. These Co and Fe-doped SnO₂ nanoparticles exhibit room temperature ferromagnetism and the value of their magnetic moment and phase transition temperature are sensitive to their size and stoichiometric ratio.     

Cr-doped WO3 nanosheets: Structural,optical and formaldehyde sensing properties

Co-precipitated undoped and Cr-doped WO₃ nanosheets have been investigated by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) in order to study the influence of Cr doping on their structural and morphological properties. XRD analyses confirm the monoclinic structure of nanocrystalline WO₃, whereas the FESEM and TEM images exhibit nanosheet-like morphology of the as-synthesized WO₃ materials. Among all the samples examined, the 1.5 at% Cr-doped WO₃ nanosheets exhibit the selective maximum response (~82%) to formaldehyde over methanol, ethanol, propan-2-ol and acetone at the operating temperature of 200 °C for 50 ppm concentration in air. The sensing mechanism has been explained based on chemisorption of oxygen on the WO₃ surface and the subsequent reaction between the adsorbed oxygen species and the formaldehyde molecules.     

Excellent humidity sensing properties of cadmium titanate nanofibers

We report humidity sensing characteristics of CdTiO₃ nanofibers prepared by electrospinning. The nanofibers were porous having an average diameter and length of ～50–200 nm and ～100 μm, respectively. The nanofiber humidity sensor was fabricated by defining aluminum electrodes using photolithography on top of the nanofibers deposited on glass substrate. The performance of the CdTiO₃ nanofiber humidity sensor was evaluated by AC electrical characterization from 40% to 90% relative humidity at 25 °C. The frequency of the AC signal was varied from 10^?1 to 10⁶ Hz. Fast response time and recovery time of 4 s and 6 s were observed, respectively. The sensor was highly sensitive and exhibited a reversible response with small hysteresis of less than 7%. Long term stability of the sensor was confirmed during 30 day test. The excellent sensing characteristics prove that the CdTiO₃ nanofibers are potential candidate for use in high performance humidity sensors.