The Co
3O
4 nanofibers were prepared by electrospinning and their gas sensing characteristics were investigated. The Co
3O
4 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 100
ppm C
2H
5OH (
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 100
ppm CO, C
3H
8, and H
2 (
R
g/
R
a
=
1.02–2.7). In contrast, the most of one-dimensional morphology of the Co
3O
4 specimen was lost and the response to 100
ppm C
2H
5OH 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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
As an effective alternative to simple binary oxide chemiresistors, polynary oxides with excellent tunability of the composition and hetero-interfaces are considered as promising material platforms ...for designing highly selective and sensitive gas sensors. In this study, ternary spinel CoCr2O4 hollow spheres and CoCr2O4–Cr2O3 mixed oxide hollow spheres were prepared via one-pot ultrasonic spray pyrolysis using solutions with different cation compositions (i.e., Cr/Co = 2, 3, and 4), and their gas-sensing characteristics were investigated. The pure CoCr2O4 hollow spheres exhibited an unusually high response to 5 parts per million (ppm) of p-xylene (ratio of resistance to gas and air = 61.4), with negligible cross-responses to 5 ppm of ethanol, toluene, benzene, trimethylamine, ammonia, formaldehyde, and carbon monoxide. When CoCr2O4–Cr2O3 hollow spheres with discrete Cr2O3 nanoclusters were formed using a spray solution with a Cr/Co ratio of 3, the xylene response was enhanced to 144.1, which allows the sensitive and selective detection of sub-ppm level p-xylene. The unprecedentedly high xylene selectivity and response in the present study are explained by the gas-accessible hollow morphology, the unique catalytic activity of the ternary and mixed oxides, and the enhanced chemiresistivity due to the formation of a heterojunction between CoCr2O4 and Cr2O3. The novel ternary oxide-based gas sensors with excellent xylene-sensing performance can be used in indoor air-monitoring applications.
Pure and palladium‐loaded Co3O4 hollow hierarchical nanostructures consisting of nanosheets have been prepared by solvothermal self‐assembly. The nanostructures exhibited an ultrahigh response and ...selectivity towards p‐xylene and toluene. The responses (resistance ratio) of the palladium‐loaded Co3O4 hollow hierarchical nanostructures to 5 ppm of p‐xylene and toluene were as high as 361 and 305, respectively, whereas the selectivity values (response ratios) towards p‐xylene and toluene over interference from ethanol were 18.1 and 16.1, respectively. We attributed the giant response and unprecedented high selectivity towards methylbenzenes to the abundant adsorption of oxygen by Co3O4, the high chemiresistive variation in the Co3O4 nanosheets (thickness≈11 nm), and the catalytic promotion of the specific gas‐sensing reaction. The morphological design of the p‐type Co3O4 nanostructures and loading of the palladium catalyst have paved a new way to monitoring the most representative indoor air pollutants in a highly selective, sensitive, and reliable manner.
Unprecedented sensors! Giant response and unprecedented high selectivity towards methylbenzenes have been achieved by using pure and palladium‐loaded Co3O4 hollow hierarchical nanostructures assembled from nanosheets (see figure).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
p-Type Cr2O3 and Co3O4 oxide semiconductor nanofibers, with different connecting configurations, were prepared by controlling the ultrasonic disintegration of nanofibers and their C2H5OH sensing ...characteristics were investigated. The ratios between resistances in 100ppm C2H5OH, and air, of Cr2O3 (at 350°C) and Co3O4 sensors (at 300°C) consisting of long nanofibers were found to be 22.1±1.4 and 82.4±10.2, respectively. These values were significantly higher than those of Cr2O3 and Co3O4 sensors (4.9±1.1 and 5.7±1.4), which consisted of less-connective primary particles disintegrated from nanofibers. The decrease of gas response, and increase in sensor resistance, with ultrasonic disintegration of nanofibers is explained in relation to a decrease of contact area between primary particles, indicating that inter-particle connectivity is a key parameter in determining the gas response of p-type oxide semiconductors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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.
•Methyl benzene sensor using Cr-doped Co3O4 nanorods was suggested.•Responses to xylene and toluene of pure Co3O4 nanorods were high.•Doping of Cr to Co3O4 nanorods significantly enhanced selectivity ...to methyl benzenes.
Ultrasensitive and selective detection of methyl benzenes was achieved for Co3O4 nanorods through Cr-doping. Pure and 1.17–1.89at% Cr-doped Co3O4 nanorods were synthesized by a solvothermal reaction, followed by calcination at 400°C for 2h. The gas-sensing properties of the nanorods were tested to methyl benzene (toluene and xylene) and compared with interfering gases (benzene, ethanol, ammonia, CO and NO2) at various concentrations (0.25–5ppm) and temperatures (250–350°C). The results demonstrated that Cr-doping significantly enhanced the response to methyl benzenes while suppressing cross-responses to interfering gases, resulting in selectivity for methyl benzene. The ultraselectivity to methyl benzene in the Cr-doped Co3O4 nanorods was attributed to catalytic activity and the abundant adsorbed oxygen of the Cr oxides and Co3O4 for the partial oxidation of methyl benzenes to more active chemical species.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Alloy@semiconductor core-shell nanoparticles (CSNPs) offer great advantages for hydrogen sensing due to their unique properties compared to the individual components. Herein the synthesis of alloyed ...PdPt@ZnO CSNPs via a hydrothermal approach is reported. PdPt@ZnO sensor exhibits an impressive sensing response of 48 with respect to Pd@ZnO (22), Pt@ZnO (14), and free ZnO (9), along with the fast response and recovery times (0.7 and 3.0 min) to 100 ppm hydrogen at 350 °C, thus outperforming current achievements of advanced single-metal hybridized semiconductors. It further delivers high selectivity and long-term stability for hydrogen sensing. These improvements are attributed to (1) high catalytic activity of alloyed PdPt core, (2) high content of oxygen vacancies and chemisorbed oxygen in ZnO shell, (3) facile two-way transfer of electrons between the core and shell, and (4) high surface area and porosity of CSNPs. In addition, DFT calculations show that alloyed PdPt core has an excellent intrinsic hydrogen adsorption capability, superior to free-standing Pd and ZnO shell. These investigations together provide mechanistic insights into the working of the system in terms of gas adsorption, reaction, and desorption.
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•Here, PdPt@ZnO core-shell nanoparticles are hydrothermally prepared.•It delivers an unusually high hydrogen response compared to Pd@ZnO and ZnO.•PdPt@ZnO also shows high selectivity and lasting system for hydrogen detection.•Improvements are mainly contributed to the unique effects of PdPt alloy.•Such experimental results are also supported by DFT calculations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Porous CuBr films are the most promising platform for the exclusive detection of NH3 but their simple and cost-effective fabrication without employing a high-temperature process remains elusive. ...Herein, we report the facile and low-temperature preparation of porous CuBr films by a solution oxidation method, and their unprecedentedly high NH3 sensing properties. The porous CuBr films are prepared by coating Cu thin films with different thicknesses (10–100 nm) on sensor substrates by direct current sputtering, immersion of Cu thin films in a CuBr2 solution (0.001–0.1 M) for a controlled time (10–300 s), and washing of the substrate with methanol. Among the CuBr film sensors, the sensor fabricated by immersing the 30 nm-thick Cu film in 0.01 M CuBr2 solution for 120 s (30n-120s sensor) exhibits the highest NH3 response (resistance ratio = 211), which is the highest level compared with those reported in the literature. Moreover, the 30n-120s sensor exhibits ultrahigh NH3 selectivity, extremely low detection limit (∼25 ppb), excellent reversibility, and long-term stability at room temperature. The sensing film of the 30n-120s sensor has a porous structure consisting of loosely percolated CuBr particles, whereas the other films have a dense structure with tightly percolated particles or, conversely, an island configuration composed of nearly discrete particles. The superior NH3 sensing properties of the sensor are discussed in terms of the porosity and particle connectivity of the film. The high performance NH3 sensor can be used to realize flexible and even wearable NH3 detectors for emerging applications such as environmental monitoring, food freshness assessment, and breath analysis for disease diagnosis.
Volatile sulfur compounds (VSCs), such as H2S and methyl mercaptan (MM), are malodorous and harmful gases. H2S and MM share analogical origins. However, they should be discriminated because of their ...different odor thresholds and health impacts. Herein, a nanopattern chemiresistor composed of aligned CuO-loaded CuFe2O4 nanofibers was prepared via direct-write near-field electrospinning. The CuO/CuFe2O4 sensor with the atomic ratio of Cu:Fe = 3:4 exhibited extremely high responses to ppm-level H2S and MM compared with other nanopattern sensors with different compositions (Cu/Fe = 2:4, 4:4, and 0:1). This can be attributed to the gas-accessible morphology of the nanopattern sensor, the formation of a nanoscale p(CuO)-n(CuFe2O4) junction, and the intimate reaction between the discretely loaded CuO nanoparticles and the VSCs. Furthermore, the CuO/CuFe2O4 sensor exhibited high selectivities to H2S and MM at 200 ℃ and 400 ℃, respectively. The selective dual detection of H2S and MM using a single CuO/CuFe2O4 sensor via the simple modulation of the sensing temperature opens a new route for indoor air quality monitoring, ventilation control, halitosis diagnosis, and wine quality monitoring.
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Nanopattern sensor using 1D CuO/CuFe2O4 nanofibers fabricated by direct-writing near-field electrospinning exhibits high selectivity and response to volatile sulfuric compounds and the modulation of sensing temperature enables the discrimination between H2S and methyl mercaptan.
•CuO/CuFe2O4 nanopattern sensor was fabricated using near-field electrospinning.•Sensor temperature modulation enabled selective dual detection of H2S and methyl mercaptan.•PCA using the array of four Cu-Fe-O nanofiber sensors enabled the discrimination between volatile sulfuric compounds and interference gases.•Mechanism underlying gas selectivity control was elucidated by proton transfer reaction quadruple mass spectrometry.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Highly sensitive trimethylamine sensor using Au-loaded Cr2O3 yolk-shell spheres.•High response is explained by electronic and chemical sensitization of Au particles.•Gas sensing characteristics ...depend closely on size and distribution of Au particles.•P-type Cr2O3 can be used to detect sub-ppm-level trimethylamine.
An ultrasensitive and selective trimethylamine (TMA) sensor was fabricated by the urea-assisted uniform loading of Au nanoparticles (∼5nm) on Cr2O3 yolk-shell spheres prepared by ultrasonic spray pyrolysis. The response (resistance ratio) of the Cr2O3 yolk-shell spheres uniformly loaded with fine Au nanoparticles to 5ppm TMA was 200.9 at 225°C, which was significantly higher than those of pure Cr2O3 yolk-shell spheres (24.6) and Cr2O3 yolk-shell spheres loaded with heavily agglomerated Au particles (9.2). The detection limit of Cr2O3 yolk-shell spheres uniformly loaded with Au nanoparticles was as low as 4.3ppb. The unprecedentedly high TMA response is explained and discussed in relation to the gas-accessible morphology of the yolk-shell spheres, and the catalytic and electronic promotion of the gas sensing reaction by both Cr2O3 and well-dispersed Au nanoparticles.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
