Ultraselective and sensitive detection of xylene and toluene with minimum interferences of other indoor air pollutants such as benzene, ethanol, and formaldehyde is achieved using NiO hierarchical ...nanostructures doped with Cr. Pure and 1.15-2.56 at% Cr-doped NiO flower-like hierarchical nanostructures assembled from nanosheets are prepared by a simple solvothermal reaction and their gas sensing characteristics toward o-xylene and toluene gases are investigated. The 1.15 at% Cr-doped NiO hierarchical nanostructures show high responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 11.61 and 7.81, respectively) and negligible cross-responses to 5 ppm of benzene, formaldehyde, ethanol, hydrogen, and carbon monoxide. However, pure NiO nanostructures show low responses to 5 ppm of o-xylene and toluene (ratio of resistance to gas and air = 2.01 and 1.14, respectively) and no selectivity toward any specific gas is observed. Significant enhancement of the response and selectivity to o-xylene and toluene is attributed to the decrease in the hole concentration in NiO and the catalytic oxidation of methyl groups by Cr doping.
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•CdS NO2 gas sensor operated under both fluorescent lamp and natural solar light.•2D nanoflake array CdS films for enhanced light absorption and charge transport.•CdS gas sensor with ...high response to NO2, little influence by humidity.•Elucidation of visible-light-enhanced NO2 sensing mechanism.
A Highly ordered CdS nanoflake array was fabricated by CVD, and its gas sensing characteristics were investigated. The sensor exhibited high response (resistance ratio) of 89% to 5 part per million (ppm) nitrogen dioxide (NO2) under green LED illumination (wavelength 500–540nm, irradiance 21W/m2) with excellent selectivity and little interference by humidity. Moreover, the sensor showed promising potential for operating under fluorescent lamp and natural solar light, which can be used for medical diagnosis and indoor/outdoor environment monitoring. This performance is attributed to the low band gap energy (2.4eV) of CdS and the unique morphology of nanoflake array which can enhance both the light absorption and conductivity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Catalyst-loaded hollow spheres are effective at detecting ethanol with high chemical reactivity. However, this has limited the widespread use of catalyst-loaded hollow spheres in designing highly ...selective gas sensors to less-reactive gases such as aromatics (e.g., xylene). Herein, we report the preparation of xylene-selective Au–SnO2 nanoreactors by loading Au nanoclusters on the inner surface of SnO2 hollow shells using the layer-by-layer assembly technique. The results revealed that the sensor based on SnO2 hollow spheres loaded with Au nanoclusters on the inner surface exhibited unprecedentedly high xylene selectivity and an ultrahigh xylene response, high enough to be used for indoor air quality monitoring, whereas the sensor based on SnO2 hollow spheres loaded with Au nanoclusters on the outer surface exhibited the typical ethanol-sensitive sensing behaviors as frequently reported in the literature. In addition, the xylene selectivity and response were optimized when the hollow shell was sufficiently thin (∼25 nm) and semipermeable (pore size = ∼3.5 nm), while the selectivity and response decreased when the shell was thick or highly gas permeable with large mesopores (∼30 nm). Accordingly, the underlying mechanism responsible for the unprecedentedly high xylene sensing performance is discussed in relation to the configuration of the loaded Au nanoclusters and the morphological characteristics including shell thickness and pore size distribution. This novel nanoreactor concept can be widely used to design highly selective gas sensors especially to less-reactive gases such as aromatics, aldehydes, and ketones.
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IJS, KILJ, NUK, PNG, UL, UM
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 A g−1 were measured as 720 and 640 mA h g−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 A g−1 were 774, 711, 652, and 591 mA h g−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.
Fiber‐in‐tube nanostructures: A new formation mechanism for nanotubes with a fiber‐in‐tube structure based on electrospun precursors is proposed. SnO2 nanotubes have been prepared according to this new protocol. The prepared SnO2 nanotubes with a fiber‐in‐tube structure show high initial discharge capacity, as well as good cycling and rate performances when used as anode materials in lithium‐ion batteries (see graphic).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Xylene is a hazardous volatile organic compound, which should be measured precisely for monitoring of indoor air quality. The selective detection of ppm-level xylene using oxide semiconductor ...chemiresistors, however, remains a challenging issue. In this study, NiO/NiMoO4 nanocomposite hierarchical spheres assembled from nanosheets were prepared by hydrothermal reaction, and the potential of sensors composed of these nanocomposites to selectively detect xylene gas was investigated. The sensors based on the NiO/NiMoO4 nanocomposite hierarchical spheres exhibited high responses (maximum resistance ratio =101.5) to 5 ppm p-xylene with low cross-responses (resistance ratios <30) to 5 ppm toluene, benzene, C2H5OH, CH3COCH3, HCHO, CO, trimethylamine, and NH3. In contrast, a sensor based on pure NiO hierarchical spheres exhibited negligibly low responses to all 9 analyte gases. The gas-sensing mechanism underlying the high selectivity and response to xylene in the NiO/NiMoO4 nanocomposite hierarchical spheres is discussed in relation to the catalytic promotion of the xylene-sensing reaction by synergistic combination between NiO and NiMoO4, gas-accessible hierarchical morphology, and electronic sensitization by Mo addition. Highly selective detection of xylene can pave the road toward a new solution for precise monitoring of indoor air pollution.
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Au@NiO yolk-shell nanoparticles (NPs) were synthesized by simple solution route and applied for efficient gas sensor towards H₂S gas. Carbon encapsulated Au (Au@C core-shell) NPs were synthesized by ...glucose-assisted hydrothermal method, whereas Au@NiO yolk-shell NPs were synthesized by precipitation method using Au@C core-shell NPs as a template. Sub-micrometer Au@NiO yolk-shell NPs were formed having 50-70 nm Au NPs at the periphery of NiO shell (10-20 nm), which was composed of 6-12 nm primary NiO particles. Au@NiO yolk-shell NPs showed higher response for H2S compared to other interfering gases (ethanol, p-xylene, NH₃, CO and H₂). The maximum response was 108.92 for 5 ppm of H₂S gas at 300 °C, which was approximately 19 times higher than that for the interfering gases. The response of Au@NiO yolk-shell NPs to H₂S was approximately 4 times higher than that of bare NiO hollow nanospheres. Improved performance of Au@NiO yolk-shell NPs was attributed to hollow spaces that allowed the accessibility of Au NPs to gas molecules. It was suggested that adsorption of H₂S on Au NPs resulted in the formation of sulfide layer, which possibly lowered its work function, and therefore tuned the electron transfer from Au to NiO rather NiO to Au, which leaded to increase in resistance and therefore response.
Ultrahigh gas selectivity and response for ppb levels of xylene are achieved by doping Pt in CoCr2O4 hollow spheres, whereas the addition of Au or Pd is less effective or even deteriorated the ...performance.
To organize one-dimensional (1D) metal oxides into highly ordered and controllable architectures on the required regions remains challenging. Herein, we report for the first time the facile, ...versatile, and on-demand fabrication of metal oxide patterns comprising 1D nanofibers
via
near-field electrospinning (NFES), which have a wide variety of potential applications in sensors, optoelectronic circuits, and functional nanoelectronics. Grids, diamonds, and hexagrams of In
2
O
3
, Co
3
O
4
, and NiO nanofibers are first demonstrated, and the underlying mechanisms for fiber formation are systematically investigated with respect to the experimental parameters of NFES. Furthermore, we propose the nano-architectures as a novel gas sensing platform that exhibits an unprecedentedly high gas response (resistance ratio,
S
T
= 239, T: trimethylamine) and selectivity (
S
T
S
E
−1
> 7, E: ethanol) to 5 ppm trimethylamine compared with thin film counterparts (
S
T
= 24,
S
T
S
E
−1
1). The research provides a vital breakthrough to fabricate metal oxide nano-architectures of 1D nanofibers and new platforms to design next-generation functional nanodevices for a wide range of emerging applications.
On-demand, direct-write fabrication of metal oxide patterns composed of one-dimensional nanofibers using near-field electrospinning is demonstrated and their formation mechanism as well as potential applications are investigated.
The use of composite materials and polynary compounds is a promising strategy to promote conductometric sensor performances. The perovskite oxides provide various compositional combinations between ...different oxides for tuning gas-sensing reaction and endowing rich oxygen deficiencies for preferable gas adsorption. Herein, a sacrificial colloidal template approach is exploited to fabricate crystalline ternary LaFeO3 perovskite porous thin films, by transferring a La3+–Fe3+ hybrid solution-dipped template onto a substrate and sequent heat treatment. The honeycomb-like LaFeO3 film consisted of monolayer periodic pore (size: ∼ 500 nm) array can be successfully in situ synthesized in a homogeneous layout with a single phase of perovskite. This periodic porous LaFeO3 film with p-type semiconductivity exhibits a high gas response, fast response (∼4 s), trace detection capacity (50 ppb), and favorable ethanol selectivity from similar acetone. It exhibits enhanced sensing performances compared to those of a binary n-type Fe2O3 film and a nontemplated dense LaFeO3 film. In addition, a five-axe spiderweb diagram is introduced to make a feasible evaluation of the optimal practical work condition, comprehensively regarding the response/recovery rate, gas response, selectivity and operating temperature. The enhanced ethanol sensing mechanism of honeycomb-like LaFeO3 periodic porous film is also addressed. This novel and facile route to fabricate well-ordered porous LaFeO3 thin film can also be applied to many fields to obtain special performances, such as solar cells, ion conductors, gas separation, piezoelectricity, and self-powered sensing device system.
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•Rhombohedral (h-) In2O3 nanoparticles (NPs) are rapidly synthesized via a microwave-assisted hydrothermal pathway.•Gas sensing characteristics of h-In2O3 NPs are compared with those of other In2O3 ...NPs with different polymorphism.•h-In2O3 phase has better gas sensing characteristics than those of the other polymorphic phases because of its superior electrical conductivity.•h-In2O3 NPs exhibit high response and selectivity to ethanol, which can be potentially used in breathalyzers for screening drunk drivers.
Rhombohedral In2O3 exhibits high gas sensing potential. However, its rapid synthesis remains challenging, and it is yet to be revealed whether it has a higher gas sensing capability than the cubic counterpart. Herein, we report a facile and rapid synthesis of rhombohedral In2O3 nanoparticles (NPs) via a microwave-assisted hydrothermal pathway, and compare their gas sensing characteristics with those of other In2O3 polymorphs (i.e., cubic NPs and mixed rhombohedral and cubic phases). To investigate the polymorphs for optimized gas sensing, the gas sensing properties of rhombohedral In2O3 NPs are compared with those of mixed-phase In2O3 NPs prepared via a conventional hydrothermal pathway and commercial cubic In2O3 NPs. The pure cubic In2O3 NPs and the mixed-phase In2O3 NPs show similar gas responses (resistance ratios) to 100 ppm ethanol in the temperature range of 150–400 °C. In contrast, the rhombohedral In2O3 NPs exhibit much higher ethanol responses at all the sensor temperatures. In particular, their ethanol response at 300 °C (43.1) is four times higher than the values obtained for the other polymorphic NPs (9.44–11.6) at the same temperature. Furthermore, the rhombohedral In2O3 NPs possess excellent ethanol selectivity with low cross-responses to 100 ppm NH3, CH4, H2, CO, CO2, and NO2 and long-term stable ethanol sensing properties for 21 days. The excellent gas sensing characteristics of rhombohedral In2O3 NPs are strongly related to their gas adsorption, particle sizes, and electrical conductivity. The rhombohedral In2O3 NPs can be potentially used in high-performance breathalyzers for screening drunk drivers.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
