Search

Approximately one in 10 people worldwide suffer from irritable bowel syndrome (IBS). Thus, early diagnosis and simple monitoring of chronic diseases will help to improve the patient's quality of life. Herein, we report a chemiresistive-type gas sensor for exhaled hydrogen detection that was fabricated by combining hierarchically porous SnO2 nano-architectures and PdO. The unique structured PdO-functionalized SnO2 hydrogen sensor exhibited excellent selectivity (response ratio > 5.2), high response (resistance ratio = 6.3), extremely fast sensing kinetics (response speed: 4.0 s and recovery period: 36.2 s), and low detection limit (0.096 ppm) under high humidity (relative humidity 80%). These exceptional sensing properties toward hydrogen were investigated from multiple perspectives, including effective gas diffusion through multimodal pores, changes in charge-carrier concentration in p–n heterojunctions, and the catalytic effect of PdO. The proposed sensor has a high potential for practical high-performance hydrogen sensor applications and will offer new possibilities for a simple disease diagnosis based on breath analysis. [ABSTRACT FROM AUTHOR]

The precise detection of trace concentrations of ethylene, a plant hormone gas, is essential for controlling plant health and status. However, owing to the simple chemical structure and low reactivity of ethylene, the highly sensitive and exclusive detection of ethylene has been a significant challenge, despite the strong demand from the agricultural industry. Herein, we report a novel bilayer ethylene gas sensor consisting of a Pd-doped V2O5–TiO2 yolk–shell catalytic overlayer and an In2O3 sensing layer. The coating of 2 wt% Pd-doped V2O5–TiO2 on the In2O3 sensing film remarkably enhances the ethylene response and selectivity over a wide range of operating temperatures (300–400 °C). This is attributed to the reforming of ethylene into more reactive acetaldehyde and the filtering of interference gas into non-reactive forms using the unique Pd–V2O5–TiO2 catalytic overlayer for heterogeneous Wacker oxidation promoted by the yolk–shell sphere structure. To the best of our knowledge, this paper presents the first report on the design of a catalytic overlayer that converts less-reactive ethylene into more-reactive species. The outstanding capability of the unique bilayer sensor proposed in this study enables the monitoring of the ripeness of fruits and correlates well with the results of proton transfer reaction-quadrupole mass spectrometry (PTR-QMS). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Water poisoning has been a long-standing problem in oxide semiconductor gas sensors. Herein, for the first time, we report that pure and Pr-doped Ce4W9O33 provide humidity-independent gas sensing characteristics. Ce4W9O33 and Pr-doped Ce4W9O33 powders with a porous structure have been successfully prepared by ultrasonic spray pyrolysis and subsequent annealing at low temperature (600 °C). Interestingly, these p-type oxide semiconductors exhibited nearly the same gas sensing characteristics at 300 °C regardless of humidity variation, whereas pure WO3 showed a significant decrease of sensor resistance and gas response when the atmosphere is changed from dry to relative humidity 80%. Furthermore, Ce4W9O33-based sensors showed highly selective and sensitive detection of ppm-level trimethylamine (TMA). Moisture-endurant gas sensing characteristics were discussed in relation to surface regeneration through the hydroxyl scavenging reaction assisted by abundant Ln3+ (Ln = Ce, Pr) in (Ce1−xPrx)4W9O33 (x = 0–0.3) and TMA selectivity was explained by the acid–base interaction between the analyte gas and sensing material. Phase-pure ternary or quaternary oxides with a decreased oxidation state of lanthanide components provide a new and general strategy to design humidity-independent gas sensors with new functionality. [ABSTRACT FROM AUTHOR]

Multishell structured metal oxide microspheres with considerable structural stabilities during repeated cycling and higher volumetric capacities than those of hollow structured microspheres are popular as anode materials for lithium-ion batteries. However, the long-term cycling and rate performances of multishell metal oxide microspheres for lithium-ion storage require further improvement. Herein, novel and unique structured microspheres (Fe3O4–GC) with multishells comprising graphitic carbon (GC)-coated Fe3O4 hollow nanopowders are successfully synthesized. The reduction of pitch-infiltrated Fe2O3 yolk–shell microspheres yields metallic Fe yolk–shell microspheres filled with pitch-derived carbon. Oxidation yields yolk–shell Fe3O4–GC microspheres with multishells comprising hollow nanopowders coated with GC via the selective decomposition of amorphous carbon and oxidation of metallic Fe. Metallic Fe nanocrystals transform into hollow Fe3O4 nanopowders due to nanoscale Kirkendall diffusion. The primary hollow Fe3O4 nanopowders comprising yolk–shell microspheres and GC layer formed by pitch-derived carbon decrease the distance for lithium-ion diffusion and improve the electrical conductivity resulting in outstanding cycling and rate performances of Fe3O4–GC, respectively. The discharge capacity of Fe3O4–GC microspheres for the 1000th cycle at a current density of 2.0 A g−1 is 1018 mA h g−1, and the microspheres exhibit a high reversible capacity of 649 mA h g−1 even at 20 A g−1. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) and MoS2, the most representative two-dimensional (2D) materials, are receiving significant attention for the fabrication of sensing devices owing to their high surface area, many abundant sites, and excellent mechanical flexibility. Herein, we demonstrated chemoresistive humidity sensors with fast response, excellent selectivity, and ultrahigh sensitivity based on 2D rGO and 2D MoS2 hybrid composites (RGMSs). The RGMSs were fabricated by simple ultrasonication without the addition of additives and additional heating. Compared to pristine rGO, the RGMS exhibited a 200 times higher response to humidity at room temperature. The significant enhancement in the sensing performance of the composite was attributed to electronic sensitization due to p–n heterojunction formation and porous structures between rGO and MoS2. The synergistic combination of rGO and MoS2 could be applied to construct a flexible humidity sensor. The sensing performance of an RGMS flexible device remains the same before and after bending; this indicates that the use of rGO and MoS2 is a viable new and simple strategy to realize a humidity sensor for use in wearable electronics. [ABSTRACT FROM AUTHOR]

Ultra-selective and sensitive detection of carcinogenic benzene vapor with negligible interferences from other major indoor pollutants is not only critical but also challenging because the BTX gases (benzene, toluene, and xylene) are generally less reactive to a majority of n-type oxide semiconductor gas sensors and the similar chemical structures of BTX gases hamper their discrimination by chemiresistive variation. Through this paper, we propose a new strategy to detect sub-ppm-level benzene vapor in a highly selective manner using oxide semiconductor chemiresistors. A Pd-loaded SnO2 yolk–shell sensing film coated with a thin catalytic Co3O4 overlayer showed an ultrahigh response (resistance ratio = 88) to 5 ppm benzene with negligibly low cross-responses to the other representative and ubiquitous indoor pollutants such as toluene, xylene, HCHO, CO, and ethanol. The response to benzene vapor was significantly enhanced by reforming of highly stable benzene into more active and smaller species. The reforming was synergistically assisted by the Co3O4 catalytic overlayer and sensing layer consisting of Pd-loaded SnO2 micro-reactors, while the cross-responses to the other indoor pollutants became low because of the catalytic oxidation of the gases into less- or non-reactive species. This method will pave a new way to the precise monitoring of critically harmful benzene in both indoor and outdoor atmospheres. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) molybdenum disulfide (MoS2) has been attracting rapidly increasing interest for application in chemoresistive gas sensors owing to its moderate band gap energy and high specific surface area. However, the mechanism of chemoresistive sensing via the adsorption and desorption of gas molecules and the influence of the shape of 2D materials are not well understood yet. Herein we investigate the oxygen sensing behavior of MoS2 microflakes and nanoparticles prepared by mechanical and liquid exfoliation, respectively. Liquid-exfoliated MoS2 nanoparticles with an increased number of edge sites present high and linear responses to a broad range of oxygen concentrations (1–100%). The energetically favorable oxygen adsorption sites, which are responsible for reversible oxygen sensing, are identified by first-principles calculations based on density functional theory. This study serves as a proof-of-concept for the gas sensing mechanism depending on the surface configuration of 2D materials and broadens the potential of 2D MoS2 in gas sensing applications. [ABSTRACT FROM AUTHOR]

Pd@In2O3 yolk–shell nanoparticles (NPs) were synthesized by a simple solution route using Pd@C core–shell NPs as template and applied for gas sensing. A glucose-assisted hydrothermal method was used for the synthesis of Pd@C core–shell NPs. Pd@In2O3 yolk–shell NPs were formed after calcination (450 °C for 3h) of Pd@C core–shell NPs containing indium precursor. In the Pd@In2O3 yolk–shell geometry, about 50–70 nm Pd NPs were present at the periphery of an In2O3 shell (10–20 nm thickness). The In2O3 shell was composed of ∼10 nm primary particles. The role of Pd NPs in gas sensing behavior of In2O3 has been investigated. The loading of In2O3 with Pd NPs improved the response for reducing gases, but reduced the response for oxidizing gases. The response of Pd@In2O3 yolk–shell NPs to ethanol was approximately 14 times higher than that of pure In2O3 hollow nanospheres at 350 °C. However, no response was recorded for NO2 for Pd@In2O3 as compared to In2O3 (resistance ratio Rs = 2.50) at 350 °C. The maximum response of Pd@In2O3 yolk–shell NPs to 5 ppm ethanol was 159.02 at 350 °C, which was approximately 2.5 times higher than those for other interfering gases (NO2, p-xylene, trimethylamine, HCHO, CO and H2). The effect of humidity on the gas sensing characteristics of Pd@In2O3 yolk–shell NPs suggested that the present sensor can be used to detect ppm-level ethanol even in highly humid atmosphere (80% RH). The improved gas sensing performance of Pd@In2O3 yolk–shell NPs was attributed to catalytic activity of Pd NPs as well as hollow spaces that allowed the accessibility of Pd NPs to gas molecules. [ABSTRACT FROM AUTHOR]

The detection of nitrogen dioxide, NO2, is currently the subject of extensive scientific and technological research, motivated by its deleterious impact on the environment and on human health and safety. However, detecting trace levels of NO2 gas in a timely, sensitive, and selective manner remains challenging, while the mechanisms governing selective NO2 sensing are still unclear. In this work, a monolayer α-Fe2O3 inverse opal (IO) film with single-crystalline 3-fold rotocenters is firstly synthesized in situ on a substrate using a sacrificial template and evaluated as a sensitive NO2 chemiresistor. Interestingly, the Fe2O3 macroporous film manifests abnormal sensing behavior with reversible transitions from p- to n-type sensing as a function of the NO2 concentration (C) and working temperature (T). Based on more familiar phase diagrams, a binary (T–C) transition diagram has been created in terms of the gas sensing response, which can be directly used to design and control the p–n transitions. Further investigations also show that such abnormal p–n transitions do not occur if a different sensing material (e.g. SnO2 IO) is used, or on exposure to gases other than NO2. The porous Fe2O3 sensor is capable of detecting trace levels of NO2, as low as 10 ppb, and shows good stability. Finally, the mechanisms underlying the unusual NO2 sensing transitions are described based on the nature of the materials and the well-known Lennard-Jones model. Reversible switching from p- to n-type sensing and the associated transition diagram carry great potential for the recognition and sensitive detection of trace levels of NO2. [ABSTRACT FROM AUTHOR]

Thermoelectric transport properties of Te-substituted In4Se3 compounds are presented in terms of the condenson state. Regardless of anionic substitution, the condenson-related charge and thermal transport properties were clearly observed in the anionic substituted In4(Se0.95Te0.05)3−δ compound, and the enhanced thermoelectric performances were achieved due to the reduced lattice thermal conductivities by the Te alloying effect. Moreover, almost Te-free nanoinclusions, coherently embedded in the matrix, were discovered in the Te-substituted compounds. Detailed structural and compositional characterizations on the nanoinclusions strongly suggest that there is a certain relationship between the formation of the nanoinclusion and the condenson state, which governs the thermoelectric transport properties in the In4Se3 material system. [ABSTRACT FROM AUTHOR]