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Tin oxide (SnO2) nanotubes with a fiber-in-tube structure have been prepared by electrospinning and the mechanism of their formation has been investigated. Tin oxide-carbon composite nanofibers with a filled structure were formed as an intermediate product, which were then transformed into SnO2 nanotubes with a fiber-in-tube structure during heat treatment at 500°C. Nanofibers with a diameter of 85 nm were found to be located inside hollow nanotubes with an outer diameter of 260 nm. The prepared SnO2 nanotubes had well-developed mesopores. The discharge capacities of the SnO2 nanotubes at the 2nd and 300th cycles at a current density of 1 Ag-1 were measured as 720 and 640 mAhg-1, respectively, and the corresponding capacity retention measured from the 2nd cycle was 88%. The discharge capacities of the SnO2 nanotubes at incrementally increased current densities of 0.5, 1.5, 3, and 5 Ag-1 were 774, 711, 652, and 591 mAhg-1, respectively. The SnO2 nanotubes with a fiber-in-tube structure showed superior cycling and rate performances compared to those of SnO2 nanopowder. The unique structure of the SnO2 nanotubes with a fiber@void@tube configuration improves their electrochemical properties by reducing the diffusion length of the lithium ions, and also imparts greater stability during electrochemical cycling. [ABSTRACT FROM AUTHOR]

Hierarchical SnO2 fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin-walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO2 layers. Highly porous SnO2 fibers synthesized at a high flow rate show five-fold higher acetone responses than densely packed SnO2 fibers synthesized at a low flow rate. Interestingly, thin-wall assembled SnO2 fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un-doped SnO2 fibers, even at low acetone concentrations. Moreover, Pt-decorated SnO2 fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin-wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer. [ABSTRACT FROM AUTHOR]

Pure and 0.18–13.2 at.% Fe-doped NiO nanofibers were prepared by electrospinning and their gas sensing characteristics and microstructural evolution were investigated. The responses ((Rg − Ra)/Ra, where Rg is the resistance in gas and Ra is the resistance in air) to 5 ppm C2H5OH, toluene, benzene, p-xylene, HCHO, CO, H2, and NH3 at 350–500 ° C were significantly enhanced by Fe doping of the NiO nanofibers, while the responses of pure NiO nanofibers to all the analyte gases were very low ((Rg − Ra)/Ra = 0.07–0.78). In particular, the response to 100 ppm C2H5OH was enhanced up to 217.86 times by doping of NiO nanofibers with 3.04 at.% Fe. The variation in the gas response was closely dependent upon changes in the base resistance of the sensors in air. The enhanced gas response of Fe-doped NiO nanofibers was explained in relation to electronic sensitization, that is, the increase in the chemoresistive variation due to the decrease in the hole concentration induced by Fe doping. [ABSTRACT FROM AUTHOR]

Hollow thin walled NiO tubes functionalized by catalytic Pt were synthesized viananofiber templating and multilayered sputter-coating of Pt and NiO thin overlayers followed by heat-treatment at 600 °C. Sandwich Pt–NiO–Pt tube networks exhibited superior C2H5OH sensing response and remarkable selectivity against CO and H2gases. [ABSTRACT FROM AUTHOR]

Microstructural evolution of spinel Zn2SnO4nanofibers was manipulated viaan in situphase separation process of inorganic precursors and a matrix polymer during electrospinning and calcination. Chemiresistive gas sensors using porous Zn2SnO4fibers exhibited superior C2H5OH sensing response. [ABSTRACT FROM AUTHOR]

Abstract: Three different compositions of ZnO–In2O3 composite nanofibers were prepared by electrospinning, and their gas sensing characteristics were compared to those of pure ZnO and In2O3 nanofibers. All ZnO–In2O3 composite nanofibers showed high response to trimethylamine (TMA), relatively low cross-response to C2H5OH, and negligible cross-responses to CO and H2; pure ZnO or In2O3 nanofibers did not show selective detection of TMA. The maximum responses to 5ppm TMA of the ZnO–In2O3 composite nanofibers with the compositions of [Zn]:[In]=67:33, 50:50, and 33:67 by at% were 133.9 at 300°C, 82.9 at 350°C, and 119.4 at 375°C, respectively. Considering all the sensing characteristics such as gas response, selectivity, and sensing/recovering kinetics together, the operation of the ZnO–In2O3 nanofiber sensor with the composition of [Zn]:[In]=33:67 by at% at 375°C was determined to be in optimal condition to detect TMA. The significant enhancement of gas response and selectivity by the formation of composite nanofibers is discussed in relation to the variation of particle size, the formation of hetero-interfaces between ZnO and In2O3, and the combination of two sensing materials with different catalytic properties, gas adsorption behaviors, and acid–base properties. [Copyright &y& Elsevier]

Abstract: The Co3O4 nanofibers were prepared by electrospinning and their gas sensing characteristics were investigated. The Co3O4 sensors prepared by heat treatment of as-spun precursor fibers at 500 and 600°C showed well-developed one-dimensional morphologies and exhibited high responses to 100ppm C2H5OH (R g/R a =51.2 and 45.3; R g, resistance in gas; R a, resistance in air) at 301°C with negligible cross-responses to 100ppm CO, C3H8, and H2 (R g/R a =1.02–2.7). In contrast, the most of one-dimensional morphology of the Co3O4 specimen was lost and the response to 100ppm C2H5OH became significantly lower when the heat treatment temperature was increased to 700°C or when the nanofibers were ultrasonically disintegrated into primary particles. The significant decrease of the gas response was explained and discussed in relation to the gas sensing mechanism of a p-type semiconductor, the morphology of specimens, and the connecting configuration between nanoparticles and nanofibers. [Copyright &y& Elsevier]

Highlights • Fabrication of a sensor array using pure and Fe-doped In 2 O 3 nanofibers. • Discriminative detection of benzene, xylene, toluene, ethanol, and formaldehyde. • Distinction between aromatic and non-aromatic indoor pollutants using sensor array. • Gas sensing mechanism underlying Fe-induced change in response and selectivity. Abstract Representative indoor volatile organic compounds (VOCs) such as benzene, xylene, toluene, formaldehyde, and ethanol need to be detected in a highly sensitive and discriminative manner because of their different impact on human health. In this study, pure and 0.05, 0.1, 0.3, and 0.5 at% Fe-doped In 2 O 3 nanofibers were prepared by electrospinning and their gas sensing characteristics toward the aforementioned VOCs were investigated. The doping of In 2 O 3 nanofiber sensor with 0.05 and 0.1 at% Fe shifted the temperature to show the maximum responses to benzene, xylene, and toluene, and reduced responses to ethanol and formaldehyde, thus demonstrating changed gas selectivity. The gas sensing characteristics of 0.5 at% Fe-doped In 2 O 3 nanofiber sensor were substantially different from those of the other sensors. Significantly different gas sensing patterns of pure and Fe-doped In 2 O 3 sensors could be used to discriminate between the five different VOCs at 375 °C and to distinguish between the aromatic and non-aromatic gases at all sensing temperatures. The mechanism underlying the Fe-induced change in gas sensing characteristics has been discussed in relation to the variation of catalytic activity, morphology, oxygen adsorption, and charge carrier concentration. [ABSTRACT FROM AUTHOR]

Pure and CuO-loaded In 2 O 3 nanofibers were prepared by electrospinning and their H 2 S sensing characteristics were investigated. The loading of CuO on In 2 O 3 nanofibers significantly enhanced the gas response (ratio of the resistance in air to that in gas) toward 5 ppm H 2 S from 515 to 1.16 × 10 5 at 150 °C. The CuO-loaded In 2 O 3 nanofibers also exhibited high gas response (9.17 × 10 3 toward 5 ppm H 2 S) at room temperature. The CuO-loaded In 2 O 3 nanofibers showed ultrahigh selectivity to H 2 S concerning interferences with NO 2 , H 2 , CO, NH 3 , C 2 H 5 OH, C 3 H 6 O, TMA, C 7 H 8 , and C 8 H 10 at room temperature and 150 °C. The operation of the sensor using pulse heating was suggested reliable H 2 S sensing with complete recovery. The ultrasensitivie and ultraselective H 2 S sensing characteristics are explained in terms of the creation and disruption of p–n junctions in the presence and absence of H 2 S, respectively, the high specific surface area provided by the networks of one-dimensional polycrystalline nanofibers, and the abundance of p–n junctions due to the uniform mixing between p-CuO and n-In 2 O 3 nanograins within the nanofibers. [ABSTRACT FROM AUTHOR]

Abstract: Gas sensors were designed and fabricated using oxide nanofibers as the sensing materials on micro platforms using micromachining technology. Pure and Pt doped SnO2 nanofibers were prepared by electrospinning and their H2S gas sensing characteristics were subsequently investigated. The sensing temperatures of 300 and 500°C could be attained at the heater powers of 36 and 94mW, respectively, and the sensors showed high and fast responses to H2S. The responses of 0.08wt% Pt doped SnO2 nanofibers to 4–20ppm H2S, were 25.9–40.6 times higher than those of pure SnO2 nanofibers. The gas sensing characteristics were discussed in relation to the catalytic promotion effect of Pt, nano-scale morphology of electrospun nanofibers, and sensor platform using micro heater. [Copyright &y& Elsevier]

Abstract: Undoped and Pd-doped SnO2 hollow nanofibers were prepared by single capillary electrospinning and their gas sensing characteristics for 100ppm H2, 100ppm CO, 500ppm CH4, and 100ppm C2H5OH were investigated. The gas responses and responding kinetics were closely dependent upon the sensor temperature and Pd doping concentration. The undoped and 0.08wt% Pd-doped SnO2 nanofibers showed selective detection to C2H5OH at 385 and 440°C. In the 0.4wt% Pd-doped SnO2 nanofiber sensor, the selective detection to CH4 and H2 was optimized at 440°C with the minimum cross-sensitivity to C2H5OH. The tuning of gas selectivity via the combinatorial control of Pd doping concentration and sensor temperature in the electrospun hollow nanofibers was discussed in relation to the gas sensing mechanism. [Copyright &y& Elsevier]