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.     

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.     

Enhanced gas sensing properties to NO2 of SnO2/rGO nanocomposites synthesized by microwave-assisted gas-liquid interfacial method

The detection of nitrogen dioxide (NO₂) is essential for the environment and human health. Tin dioxide (SnO₂) based sensors have demonstrated capabilities to detect NO₂, while their response, response/recover speed and selectivity are not good enough for their practical applications. To address these issues, the SnO₂ nanoparticles doped with reduced graphene oxides (rGO) have been synthesized by using a facile microwave-assisted gas-liquid interfacial solvothermal method in this work. The NO₂ sensing performances have been greatly enhanced after the doping of rGO due to the improved electronic conductivity and the formation of the p-n junction in the as-synthesized SnO₂/rGO nanocomposites. Moreover, our results demonstrate that the sensors based on the SnO₂/(0.3%)rGO nanocomposites (with an average diameter about 10–15 nm) exhibit the best overall performance with the high response of 247.8 to 10 ppm NO₂, fast response/recovery speed (39 s/15 s) and the excellent selectivity at the working temperature of 200 ℃. Remarkably, the SnO₂/(0.3%)rGO sensors still exhibit a good gas sensing performance to NO₂ even at room temperature.     

Highly sensitive acetone sensor based on Eu-doped SnO2 electrospun nanofibers

In this study, a series of undoped and Eu-doped SnO₂ nanofibers were synthesized via a simple electrospinning technique and subsequent calcination treatment. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were carefully used to characterize the morphologies, structures and chemical compositions of these samples. The results reveal that the as-prepared nanofibers are composed of crystallite grains with an average size of about 10 nm and Eu³⁺ ions are successfully doped into the SnO₂ lattice. Compared with pure SnO₂ nanofibers, Eu-doped SnO₂ nanofibers demonstrate significantly enhanced sensing characteristics (e.g., large response value, short response/recovery time and outstanding selectivity) toward acetone vapor, especially, the optimal sensor based on 2 mol% Eu-doped SnO₂ nanofibers shows the highest response (32.2 for 100 ppm), which is two times higher than that of the pure SnO₂ sensor at an operating temperature of 280 °C. In addition, the sensor exhibits a good sensitivity to acetone in sub-ppm concentrations and the detection limit could extend down to 0.3 ppm, making it a potential candidate for the breath diagnosis of diabetes.     

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.     

Dispersant-assisted low frequency electrophoretically deposited TiO2 nanoparticles in non-aqueous suspensions for gas sensing applications

The effect of dispersant on deposition mechanism of TiO₂ nanoparticles at 1 Hz under non-uniform AC fields was investigated. It was found that by adding Dolapix to suspension, deposition pattern is drastically changed enabling particles to enter the gap leaving the electrodes intact. Using low frequency AC electrophoretic deposition technique in the presence of dispersant, we succeeded in fabricating gas sensor in less than 2 min. Gas sensing measurements were performed in the temperature range of 450–550 °C. The results explained that the sensor has good stability in time and repeatability performance toward high response. The maximum sensitivity of about 180 for the TiO₂ nanoparticles sensor is observed with 47 ppm NO₂ gas and the response and recovery times is about 60–150 s. The optimum temperature of the gas sensor was obtained in 450 °C where sensor showed a linear trend up to 50 ppm of NO₂ gas. This sensing behavior in un-doped TiO₂ as NO₂ sensor can be mainly ascribed to the porous structure of the sensing film and its good contacts to the substrate and electrode assembly.     

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.     

Thermally evaporated copper oxide films: A view of annealing effect on physical and gas sensing properties

The present paper reports a facile approach to prepare copper oxide (CuO) films directly onto a glass substrate by thermal evaporation method and their chemiresistive properties towards hazardous nitrogen dioxide (NO₂). The influence of annealing temperature on structural, morphological, and gas sensing properties of the CuO films has been thoroughly investigated and reported. Structural and morphological analyses has confirmed the formation of polycrystalline monoclinic CuO with uniformly distributed nanoparticles over the substrate surface. Gas sensing measurements on CuO films reveal the high response, excellent selectivity, fast response-recovery time signatures, good repeatability, and stability towards lower concentration of NO₂ gas @150 °C. A maximum response of 48% towards 100 ppm NO₂ has been achieved. Gas sensing results demonstrate an influence of morphology on the NO₂ sensing performance of CuO films. In addition, the interactions between CuO sensor film and NO₂ gas molecules are studied through an impendence spectroscopy analysis.     

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.     

Stability and thermal conductivity of nanofluids of tin dioxide synthesized via microwave-induced combustion route

SnO₂ nanofluids were prepared by dispersing tin dioxide nanoparticles in deionized (DI) water as a base fluid. 4–5 nm tin dioxide crystals were synthesized via chloride solution combustion synthesis (CSCS) using SnCl₄ and sorbitol as a novel precursor and the fuel, respectively. Ammonium nitrate was also used as the combustion aid. The molar ratio of sorbitol plus ammonium nitrate to SnCl₄ was set at unity; whereas, the molar ratio of sorbitol-to-ammonium nitrate divided by that of stoichiometric value (Φ) was varied in the range of 0.5–1.4 in order to find the optimum values of specific surface area for the CSCS technique. Transition electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and Brunauer–Emmet–Teller (BET) techniques were employed for the characterization of the nanoparticles. Since SnO₂ nanoparticles form clusters within fluids, the fluids were ultrasonicated to improve the dispersion and stability of the nanoparticles. The colloidal stability of the SnO₂ nanofluids was quantitatively characterized by UV–vis spectrophotometric measurements. The results of the UV–vis experiments indicate higher dispersion together with enhanced stability for the nanofluid prepared by SnO₂ nanoparticles synthesized at Φ = 1.0. After 500 h sedimentation time, the relative concentration of the nanofluid with the highest stability is remained at around 77% of the initial concentration of the fluid.A transient hot-wire apparatus was used to measure the thermal conductivities of the nanofluids. In addition, the effects of pH and temperature on the thermal conductivity were also investigated. At 353 K, for the nanofluid prepared by SnO₂ nanoparticles synthesized at Φ = 1.0 at a weight fraction of 0.024%, thermal conductivity is enhanced up to about 8.7%, with an optimal pH = 8.     

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.     

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.     

Combustion synthesis and EIS characterization of TiO2–SnO2 system

TiO₂ is an insulator, but using specific dopants, can modify sharply its electronic structure towards semiconducting behavior. This type of response is widely applied in many electrochemical and electrocatalytical devices, namely chlorine production, hydrocarbon oxidation, CO and CO₂ hydrogenation and as electroactive substrata for biological cell growth.Combustion synthesis is a very simple, rapid and clean method for material preparation, which will be used in the preparation of the (1 − x)TiO₂–xSnO₂, x = 0.05–0.3. Tin oxalate and titanium isopropoxide are used as precursors for the synthesis. The as-prepared powders are fine and homogeneous, the average particle size is in the range of 5–10 nm, powders and ceramic compact bodies are characterized by DRX, SEM–TEM–EDX, DTA–TG and EIS. The impedance spectroscopy of the sample 10 mol% of SnO₂ indicates the presence of several phases which promote a matrix composite based in an electrical TiO₂ insulator compatible with an electronic conducting phase tin rich. This could be attributed to the spinodal decomposition effect observed in TiO₂–SnO₂ system.     

TiO2–SnO2 nanomaterials for gas sensing and photocatalysis

Nanopowders of TiO₂–SnO₂ over a full composition range extending from 100 mol% TiO₂ to 100 mol% SnO₂ are obtained by the sol–gel method from TTIP and SnCl₂·5H₂O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO₂ is 95 m²/g while that of SnO₂ amounts to 129 m²/g. The highest SSA of 156 m²/g is achieved at 20 mol% of TiO₂. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO₂–SnO₂ over the range of 0–80 mol% TiO₂ is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO₂) to 3.18 eV (100 mol% TiO₂).     

Preparation,characterization of 1D ZnO nanorods and their gas sensing properties

The 1D ZnO nanorods (NR's) were grown with Zinc (Zn) ion precursor concentration variation on seed layer glass substrate by the low temperature hydrothermal method and utilized for nitrogen dioxide (NO₂) gas sensing application. Zn ion precursor concentration varied as 0.02, 0.03, 0.04, 0.05 and 0.06 M and thin films were characterized for structural, morphological, optical, electrical, surface defect study and gas sensing properties. All the film showed dominant orientation along the (002) direction, the intensity of the peak vary with the length of the nanorods. SEM cross images confirmed that nanorods had vertical alignment perpendicular to the plane of the substrate surface. The PL intensity of oxygen vacancy related defects for prepared samples was found to be linearly proportional to gas sensing phenomena. This result in good agreement with the theoretical postulation that, oxygen vacancies plays the important role for adsorption sites to NO₂ molecule. The gas sensing performance was studied as a function of operating temperature, Zn ion precursor concentration variation, and gas concentration. The maximum gas response is 113.32–100 ppm NO₂ gas at 150 °C for 0.05 M sample out of all prepared samples. Additionally, ZnO thin film sensor has potential to detect NO₂ as low as 5 ppm.     

Carbon-coated SnO2/graphene nanosheets as highly reversible anode materials for lithium ion batteries

A simple approach is reported to prepare carbon-coated SnO₂ nanoparticle–graphene nanosheets (Gr–SnO₂–C) as an anode material for lithium ion batteries. The material exhibits excellent electrochemical performance with high capacity and good cycling stability (757 mA h g^?1 after 150 cycles at 200 mA g^?1). The likely contributing factors to the outstanding charge/discharge performance of Gr–SnO₂–C could be related to the synergism between the excellent conductivity and large area of graphene, the nanosized particles of SnO₂, and the effects of the coating layer of carbon, which could alleviate the effects of volume changes, keep the structure stable, and increase the conductivity. This work suggests a strategy to prepare carbon-coated graphene–metal oxide which could be used to improve the electrochemical performance of lithium ion batteries.     

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.     

Characterisation of SnO2–CoO–MnO–Nb2O5 ceramics

Varistors based on SnO₂ have attracted increasing interest in recent years. However, the combined effect of CoO–MnO on SnO₂ ceramics is still unclear. In this study, the non-Ohmic behaviour of the 98.95 mol%SnO₂–0.5 mol%CoO–0.5 mol%MnO–0.05 mol%Nb₂O₅ system, the microstructures and the influence of sintering temperature were investigated. The samples were prepared by the mixed oxide route, and were sintered at temperatures in the range 1250–1450 °C. SEM observation and EDS analysis revealed that the ceramics have a two-phase microstructure comprising SnO₂ primary grains and a Mn, Co rich secondary phase of small particles. The sintered density of the samples increased with the increase in sintering temperature. The maximum non-linear coefficient (α = 10) was obtained at a sintering temperature of 1350 °C.     

Electrochemical energy storage performance of heterostructured SnO2@MnO2 nanoflakes

In this work, we report synthesis of SnO₂@MnO₂ nanoflakes grown on nickel foam through a facile two-step hydrothermal route. The as-obtained products are characterized by series of techniques such as scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The as-obtained SnO₂@MnO₂ nanoflakes are directly used as supercapacitor electrode materials. The results show that the electrode possesses a high discharge areal capacitance of 1231.6 mF cm⁻² at 1 mA cm⁻² and benign cycling stability with 67.2% of initial areal capacitance retention when the current density is 10 mA cm⁻² after 6000 cycles. Moreover, the heterostructured electrode shows 41.1% retention of the initial capacitance when the current densities change from 1 to 10 mA cm⁻², which reveals good rate capability. SnO₂@MnO₂ nanoflakes products which possess excellent electrochemical properties might be used as potential electrode materials for supercapacitor applications.     

One-pot synthesis of core–shell-structured tin oxide–carbon composite powders by spray pyrolysis for use as anode materials in Li-ion batteries

Core–shell-structured tin oxide–carbon composite powders with mixed SnO₂ and SnO tetragonal crystals are prepared by one-pot spray pyrolysis from a spray solution with tin oxalate and polyvinylpyrrolidone (PVP). The aggregate, made up of SnO_x nanocrystals (several tens of nanometers), is uniformly coated with an amorphous carbon layer. The initial discharge capacities of the bare SnO₂ and SnO_x–carbon composite powders at a current density of 1 A g⁻¹ are 1473 and 1667 mA h g⁻¹, respectively; their discharge capacities after 500 cycles are 78 and 1033 mA h g⁻¹, respectively. The SnO_x–carbon composite powders maintain their spherical morphology even after 500 cycles. On the other hand, the bare SnO₂ powder breaks into several pieces after cycling. The structural stability of the SnO_x–carbon composite powders results in a low charge transfer resistance and high lithium ion diffusion rate even after 500 cycles at a high current density of 2 A g⁻¹. Therefore, the SnO_x–carbon composite powders have superior electrochemical properties compared with those of the bare SnO₂ powders with a fine size.