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The sensing layer composited from the inorganic particles, organic materials, polymers could be regarded as an important and functional component used in electronic devices, such as chemical sensor. Furthermore, it is very important for these materials to own hierarchical and porous structures leading to a large effective specific surface area. Among these, hybrid materials with yolk double-shelled architecture can further realize the required surface chemical reactions. However, it is rarely reported in gas sensors. Herein, a novel SnO 2 -TiO 2 hollow nanostructure consisting of double shells was successfully designed and synthesized. Due to the special multi-shelled structure and abundant hetero-interface, the sensing layer based on SnO 2 -TiO 2 realizes a rapid response rate within 1.7 s to ethanol gas and alluring reproducibility (15 days), which are superior over those for compact structure with similar sensors. The results indicated that the SnO 2 -TiO 2 yolk double-shelled microsphere have the huge potential for designing high performance practical ethanol devices in environmental monitoring and drunk driving. [ABSTRACT FROM AUTHOR]

Uniform Co 3 O 4 nanocubes have been prepared via an effective one-pot hydrothermal method. Sphere-shape Co 3 O 4 nanomaterials can be synthesized by varying the concentration of Co(NO 3 ) 2 ·6H 2 O and NaOH without the utilization of surfactants. Co 3 O 4 nanocubes and Co 3 O 4 nanospheres show regular geometry structure with diameters of 250 nm and 300 nm, respectively. Gas sensors based on different Co 3 O 4 nanostructured are fabricated and used for investigating acetone sensing performances. The response of Co 3 O 4 nanocubes based sensor to 500 ppm acetone is 4.88 at 240 °C, which is higher than that of Co 3 O 4 nanospheres. In addition, sensors based on Co 3 O 4 nanocubes not only exhibit a high response but also have a rapid response time (2 s) and recovery process (5 s) to acetone. The enhanced sensing performances to acetone can be attributed to the effective catalytic activity of Co 2+ at special low-index crystal facets. This finding demonstrates the shape-related synthesis of nanomaterials can be an effective way of designing high performance gas sensor, and also provides a new insight into gas-sensing mechanism. [ABSTRACT FROM AUTHOR]

Cube-shaped ZnSnO 3 with hollow structure were prepared by a co-precipitation method followed by subsequent alkali etching and annealing in inert condition (nitrogen gas environment). As-synthesized ZnSnO 3 hollow cubes (ZHC) have an average width of about 700 nm and wall thickness of about 110 nm. The sensor based on ZHC exhibited high response to 100 ppm ethanol at the optimal operating temperature of 260 °C, which was approximately 1.77-times higher than that of ZnSnO 3 solid cubes (ZSC). Additionally, ZHC based sensor also displayed great selectivity, reproducibility and long-term stability. The excellent gas sensing performance of ZHC could be attributed to the porous surface and the hollow interior structure, which provided large surface area and good permeation. The results indicate that ZHC are highly promising materials for potential application in the field of gas sensing. [ABSTRACT FROM AUTHOR]

Air pollution poses a serious threat to public health, and gas sensors for detection of the pollution has gained great attention over the past decades. In this work, a novel idea based on the substrate material integrated by structure and function was built to prepare NH 3 sensor with an improving sensing properties. Hybrid organic–inorganic sol gel with methacryloxy and epoxy groups was first synthesized. A hybrid organic–inorganic substrate was then prepared based on continuous condensation, radical polymerization and anionic polymerization. The thermal stability and microstructural of the hybrid substrate were studied and the results indicated that the hybrid has excellent thermal and structural stability. Then, polyaniline (PANI) was directly loaded on the hybrid substrate due to hydrogen bonding though a facile in-situ polymerization method to fabricate a PANI/hybrid nanocomposite for NH 3 sensing. The hydroxyl groups generated from the epoxide ring-open reaction and silane hydrolysis condensation contribute to improve the sensing properties. This sensor showed superior selectivity and reproducibility to 50 ppm NH 3 at room temperature. The low detection limit towards NH 3 at room temperature can reach 1 ppm. This strategy may provide a promising and straightforward method in gas sensing electronics at room temperature. [Display omitted] • A hybrid substrate was prepared based on continuous condensation, radical and anionic polymerization. • Polyaniline could directly load on the hybrid substrate without further surface treatment to fabricate a NH 3 sensor. • The hydroxyl groups on the substrate contribute to improving sensing properties. [ABSTRACT FROM AUTHOR]

Abstract: N-type Fe2O3 nanobelts and P-type LaFeO3 nanobelts were prepared by electrospinning. The structure and micro-morphology of the materials were characterized by X-ray diffraction (XRD) and scanning of electron microscopy (SEM). The gas sensing properties of the materials were investigated. The results show that the optimum operating temperature of the gas sensors fabricated from Fe2O3 nanobelts is 285°C, whereas that from LaFeO3 nanobelts is 170°C. Under optimum operating temperatures at 500ppm ethanol, the response of the gas sensors based on these two materials is 4.9 and 8.9, respectively. The response of LaFeO3-based gas sensors behaves linearly with the ethanol concentration at 10–200ppm. Sensitivities to different gases were examined, and the results show that LaFeO3 nanobelts exhibit good selectivity to ethanol, making them promising candidates as practical detectors of ethanol. [Copyright &y& Elsevier]

Abstract: Hollow ZnSnO3 nanocubes with peculiar cage- and skeleton-like architectures are successfully synthesized by a simple hydrothermal process at 180°C for 12h. These ZnSnO3 nanostructures exhibit almost uniform cubic structures with side length of 200–400nm. The gas sensor based on these ZnSnO3 nanostructures exhibits high response and quick response-recovery to ethanol and HCHO, which also shows superior sensitive performance compared with the results of sensor based on solid ZnSnO3 nanocubes. [Copyright &y& Elsevier]

Abstract: High preferential c-axis oriented ZnO nanorods aligned on SiO2/Si substrates with interdigital electrodes have been successfully fabricated through aqueous solution methods. The transparent ZnO buffer layer covered on both the conducting electrodes and the insulating SiO2 spacer regions acts as lattice-matched template for the assembly of c-axis oriented ZnO nanorod arrays, and the subsequent growth of ZnO nanorods has been completed via a low temperature hydrothermal process. Detailed structural characterizations reveal that the as-synthesized nanorods are single crystalline, with a hexagonal phase, and with growth along the [001] direction. The gas-sensing properties of ZnO nanorod thin films are studied. It is found that the ZnO nanorod thin film sensor exhibits excellent sensing properties towards acetone at 300°C with the response time shorter than 5s. [Copyright &y& Elsevier]

Abstract: The large-scale flowerlike ZnO nanostructures, consisting of many aggregative nanorods with the diameter of about 60nm, were prepared by a simple and facile hydrothermal route. The toluene sensing properties of the pure ZnO and TiO2-doped ZnO nanostructures were tested at different operating temperatures from 160 to 390°C and toluene concentrations ranging from 1 to 3000ppm. The results indicate that the response of the ZnO nanostructures towards toluene was enhanced significantly by TiO2 doping, which was deposited onto the ZnO products by evaporation. It is found that the TiO2-doped ZnO sensor exhibits remarkably enhanced response of 17.1 at the optimal operating temperature of 290°C to 100ppm toluene, which has been improved up from 7.4 at 390°C from pure ZnO nanostructures. [Copyright &y& Elsevier]

Abstract: In/Pd-doped SnO2 is synthesized via a sol–gel method and coated on a silicon substrate with Pt electrodes to fabricate a microstructure sensor. The sensor shows high response to CO with very low cross response to common interference gases at an operating temperature of 140°C. Especially, the sensor can detect CO down to 1ppm (the response value is about 3), and the response time and recovery time are about 15 and 20s, respectively. These results make our sensor a good candidate in practical CO sensors. [Copyright &y& Elsevier]

Abstract: Cu–Zn/ZnO nanocomposites with a novel core-shell structure have been prepared by a surface precipitation process in aqueous solution. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy are employed to analyze the structure and morphology of the present products. The influence of the annealing temperature on the core-shell structure of the nanocomposites is investigated, and a possible growth model is proposed. Furthermore, the gas sensors based on the Cu–Zn/ZnO nanocomposites are fabricated and tested, which exhibits high sensitivity and fast response to CO. The best results are obtained for the sensor based on the film annealed at 350°C, which shows that the sensitivity is about 6.3 when the sensor is exposed to 100ppm CO at the operating temperature of 240°C. The possible sensing mechanism of the Cu–Zn/ZnO sensing film has also been discussed. [Copyright &y& Elsevier]

Abstract: Dumbbell-like ZnO microcrystals have been obtained through a facile solution method. The structure, morphology and optical properties of the as-prepared ZnO microcrystals have been characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and photoluminescence. The as-prepared ZnO microcrystals exhibit excellent sensing properties against acetone at an operating temperature of 300°C. The response and recovery times are found to be 1.5 and 3s, respectively. Moreover, the sensor holds the successful discrimination between acetone and ethanol, which makes our product a good candidate in fabricating highly selective sensors in practice. [Copyright &y& Elsevier]

Abstract: A micro-structure ethanol gas sensor on a silicon substrate based on the nano complex oxide La0.7Sr0.3FeO3 was successfully designed and fabricated. The heater electrode and signal electrode were designed on the same plane in order to reduce the cross-talk and make the fabrication easier. The results of the simulations are used to improve the temperature distribution on the sensor. Compared to classical sintered gas sensors, the optimized design leads to a low power consumption. The experimental results show that the power consumption is approximately two thirds of the sintered gas sensors with the same active material. The sensitivity of this novel sensor is 8.0 when the concentration of ethanol is 500ppm, and the response time is about 1.5s and the recovery is about 2.5s. [Copyright &y& Elsevier]

Gas sensors for the detection of toxic gases have attracted extensive attention due to the growing environment issue. Polysiloxane is an ideal substrate material for the flexible electronic devices. In this work, dual-activity siloxane monomer with double bonds and epoxy groups (MAGETDS) was synthesized via hydrosilylation reaction. A series of flexible polysiloxane substrate were then prepared based on the dual-activity siloxane via UV-thermal induced polymerization reaction. Besides, the regulating of reactive monomers endows the flexible polysiloxane with tunable properties. Then, polyaniline (PANI) was synthesized via a facile in-situ chemical oxidation polymerization technique and directly loaded on the polysiloxane substrate to fabricate a polyaniline/polysiloxane flexible nanocomposite film as a novel room temperature NH 3 sensor. This novel NH 3 sensors exhibited good selectivity, reproducibility and a low detection limit of 5 ppm towards NH 3 at room temperature. The strategy we developed may provide a promising approach in flexible electronics for room temperature gas sensing application. Image 1 [ABSTRACT FROM AUTHOR]

CO 2 is one of the main components of air, accounting for 0.03–0.04% (300–400 ppm) of the total volume of the atmosphere. CO 2 gas is chemically stable and is an inert gas, which makes the means of detecting it extremely limited. To overcome these challenges, in this paper, nanoscale M-MOF-74 (M=Mg, Ni, Zn, Co) was synthesized by a facile method in a two-hour reaction at room temperature, which combined with a quartz crystal microbalance (QCM) sensor-enabled the detection of CO 2 gas at room temperature. The CO 2 sensing performance of M-MOF-74 coated QCM sensors at room temperature was systematically investigated. The experimental results showed that the Mg-MOF-74 sensor responded to 2000 ppm CO 2 at room temperature with 66, and at the same time, had good linearity, high response/recovery (75 s/50 s), and good selectivity to CO 2. The electrical parameters and quality factor of the QCM were further verified by impedance analysis. In addition, the potential CO 2 adsorption mechanism may be mainly related to the open metal sites in the Mg-MOF-74 material and the synergistic effect of Mg-O bonds. This work confirms that the M-MOF-74 material provides a new avenue for QCM CO 2 sensing, and the sensor is expected to be a potential candidate for CO 2 detection. [Display omitted] • The nano-sized MOF-74 were successfully synthesized by a facile method. • The effect of open metal sites on the gas-sensitive properties was investigated. • The Mg-MOF-74 gas sensor has good sensing performance for CO 2 at room temperature. • The exceptional uptake of CO 2 by Mg-O bonds enhances the sensing performance. [ABSTRACT FROM AUTHOR]

Xylene is a flammable, toxic and harmful inert gas. Achieving highly selective detection of xylene gas is essential for protecting the environment and health, but is full of challenges. Herein, NiCo 2 O 4 with multilayer hexagonal structure has been synthesized through a combination strategy of hydrothermal and annealing, and is applied to detect xylene gas. The effect of composition, surface area, crystallinity and porous degree on gas sensing performance has also been investigated. NiCo 2 O 4 multilayer hexagonal structures annealed at 400 °C (NCO MHs-400) exhibit a better gas sensing selectivity toward xylene gas compared to NiCo 2 O 4 multilayer hexagonal structures annealed at 500 °C and at 600 °C (NCO MHs-500 and NCO MHs-600), which predominantly originates from the catalytic oxidation of cobalt component to xylene in the as-prepared pure phase NiCo 2 O 4. Furthermore, NCO MHs-400 presents a superior stability and reliability, well moisture resistance, and a detection limit of 1 ppm toward xylene at a working temperature of 170 °C. [Display omitted] • NiCo 2 O 4 multilayer hexagonal structures (NCO MHs) have been synthesized. • NiCo 2 O 4 MHs annealed at 400 °C (NCO MHs-400) exhibits a high xylene selectivity. • The superior stability, reliability and humidity-tolerance of NCO MHs-400. • Co component in NCO MHs-400 facilitates the catalytic oxidation of xylene gas. [ABSTRACT FROM AUTHOR]

As the typical toxic and hazardous gases, volatile organic compounds (VOCs) and hydrogen sulfide (H 2 S) pose a threat to the environment and human health. The demand for real-time detection of VOCs and H 2 S gases is growing in many application to protect human health and air quality. Therefore, it is essential to develop advance sensing materials for the construction of effective and reliable gas sensors. Herein, bimetallic spinel ferrites with different metal ions (MFe 2 O 4 , M = Co, Ni, Cu and Zn) were designed by using metal-organic frameworks as templates. The evaluation of cation substitution on crystal structures (inverse/normal spinel structure) and electrical properties (n/p type and band gap) is systematically discussed. The results indicate that p-type NiFe 2 O 4 and n-type CuFe 2 O 4 nanocubes with inverse spinel structure exhibit high response and great selectivity towards acetone (C 3 H 6 O) and H 2 S, respectively. Moreover, the two sensors also display the detection limits as low as 1 ppm (C 3 H 6 O) and 0.5 ppm (H 2 S), which are far below the threshold values of 750 ppm to acetone and 10 ppm to H 2 S for 8 h exposure set by American Conference of Governmental Industrial Hygienists (ACGIH). The finding provides new possibilities for the design of high-performance chemical sensors, which display tremendous potential for practical applications. [Display omitted] • The cation substitution effect was studied for MOF-derived spinel ferrites. • The NiFe 2 O 4 based sensor showed high response to C 3 H 6 O. • The CuFe 2 O 4 based sensor showed the best H 2 S sensing properties. • The sensors were applied in exhaled breath analysis and food quality monitoring. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MOF–derived 1D α–Fe 2 O 3 /NiFe 2 O 4 nanomaterials provide the high specific surface area and a mass of active sites. • The α–Fe 2 O 3 /NiFe 2 O 4 -based sensors exhibit the enhanced acetone sensing performances compared to α–Fe 2 O 3 and NiFe 2 O 4. • The α–Fe 2 O 3 /NiFe 2 O 4 sensing layer achieves a high acetone response and fast response process. Abstract The key challenge to develop gas sensors with high performances lies in the novel design of superior functional materials for effective reactions between target gases and sensing layers. Metal–organic frameworks (MOFs) have emerged as versatile candidates for preparation of ideal nanostructured materials with controllable composition, various structures and tunable pore size. Herein, a series of Fe–based and Fe/Ni–based one–dimensional (1D) nanostructures using MOFs as templates were prepared systematically. As a result of the hollow structure and nanohybrid features, the optimized α–Fe 2 O 3 /NiFe 2 O 4 nanotubes can exhibit high specific surface area (118.03 m2 g−1) and provide a mass of active sites compared to individual components (α–Fe 2 O 3 nanowires and NiFe 2 O 4 nanowires), which is beneficial to improve the response (R a /R g = 23) to acetone vapors. In addition, the smart design also endows the sensor based on α–Fe 2 O 3 /NiFe 2 O 4 nanotubes with good selectivity, fast response time (4 s) and long–term stability (30 days). In this work, the advantages of 1D hollow heterogeneous materials will provide a new perspective of MOF–derived nanostructures for the particular application in acetone gas sensors. [ABSTRACT FROM AUTHOR]

The porous flake-like Co 3 O 4 and Co 3 O 4 /graphene hybrids with different graphene contents were prepared through a facile two-step method. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) characterizations proved the tight adherence of graphene sheets to the surface of porous Co 3 O 4 slices. Gas sensors based on the as-synthesized products were then fabricated to explore their potential applications. The results indicated that the optimal hybrid exhibited a response of 26.8% to 5 ppm of NO 2 at room temperature (RT), which was 2.27 times higher than that of undoped Co 3 O 4 (100 °C). The hybrid sensor also showed fast response, excellent selectivity, long-term stability and extremely low detection limit toward NO 2 at RT. The significantly enhanced sensing properties to NO 2 could be attributed to larger specific surface area, more chemisorbed oxygen species and the coupling effect between Co 3 O 4 and graphene in the hybrid. As we all know, as a typical p-type semiconductor, the gas-sensing properties of Co 3 O 4 toward oxidizing gases including NO 2 was rarely reported. We believe that our work could pave the way for the future design of Co 3 O 4 -based gas sensors for oxidizing gases detection at low or even room temperature. [ABSTRACT FROM AUTHOR]

SnO 2 /Au-doped In 2 O 3 core-shell (CS) nanofibers (NFs) were designed and synthesized through a facile coaxial electrospinning method. To investigate its potential application, commercial gas sensor was fabricated and its gas sensing properties were tested. The SnO 2 /Au-doped In 2 O 3 CS NFs sensor showed enhanced acetone gas sensing properties compared to the Au-doped In 2 O 3 single NFs sensor counterpart. The SnO 2 /Au-doped In 2 O 3 CS NFs sensor exhibited a high response to acetone at 300 °C, whereas Au-doped In 2 O 3 NFs sensor showed a relative low response to acetone at 300 °C. Furthermore, the former sensors also showed a fast response speed and a good selectivity to acetone. In addition, the underlying mechanism for the enhanced acetone sensing properties of SnO 2 /Au-doped In 2 O 3 CS NFs sensor could be attributed to the catalytic activity of Au and the CS structure. The approach and results proposed in this study may contribute to the realization of more sensitive CS structure NFs sensors. [ABSTRACT FROM AUTHOR]

A core-shell heterostructure nanofibers (NFs) have been synthesized via a coaxial electrospinning approach. Two semiconducting metal oxides (SMOX) with different work function were selected to form the core-shell heterostructure NFs. In this work, SnO 2 and TiO 2 were chosen as the selected SMOXs for the synthesis of the core-shell heterostructure NFs. The electrons in TiO 2 will flow to SnO 2 , because the work function of TiO 2 is smaller than SnO 2 . This phenomenon could result in an increase of the electrons concentration in the SnO 2 shell layers and the amount of adsorbed oxygen species increased. Therefore, the gas sensing properties of the TiO 2 -SnO 2 core-shell heterostructure NFs were enhanced including a high response to the target gas, good selectivity to the target gas and the rapid response/recovery processes. The approach and results proposed in this study may contribute to the realization of more sensitive core-shell heterostructure NFs sensors. [ABSTRACT FROM AUTHOR]

The crucial challenge to exploit effective ozone (O 3) gas sensors lies in developing novel functional sensing materials to meet the requirement of trace-level detection threshold (50 ppb). Metal oxide semiconductors (MOSs) with controllable heterogenous composites as high-performance sensing layers are expected to break through this bottleneck. This work proposes the hybridization of MIL-68 (In) and ZIF-8, which are employed as dual metal organic frameworks (MOFs) sacrificial templates to design n-n heterostructures. The derived In 2 O 3 backbone showed a hexagonal prismatic structure with a large aspect ratio. The robust architecture enabled the uniform decoration of mass of ZnO nanoparticles (NPs) on the surfaces without the damage of high porosity for the gas diffusion. Consequently, the optimal sensor with appropriate ZnO NPs loading amount exhibited trace O 3 detection ability as low as 15 ppb, which was attributed to the smart design of n-n heterostructure, rich active sites and improved oxygen-adsorbing capacity. Thus, this work inspires a new way to utilize the versatile dual MOFs template for constructing heterogenous composites as O 3 sensing materials. • Dual metal organic frameworks derived ZnO functionalized In 2 O 3 were designed to fabricate efficient O 3 gas sensors. • By ZnO decoration, the optimal sensor showed enhanced response to 160 ppb O 3 , nearly 2.5-folds higher than pristine In 2 O 3. • The In 2 O 3 /ZnO based sensor showed the remarkable O 3 detection limit as low as 15 ppb. • The design of heterostructure, rich active sites and improved oxygen-adsorbing ability contributed to O 3 sensing processes. [ABSTRACT FROM AUTHOR]

Ordered mesoporous Zr-doped In 2 O 3 and undoped In 2 O 3 nanostructures were synthesized via nanocasting method which is an easy, repeatable and friendly route. Zr incorporation might lead to In 2 O 3 lattice deformation without destroying the original crystal structure and increased chemical adsorbed oxygen species. Gas sensors based on undoped and Zr-doped In 2 O 3 were fabricated and their NO 2 gas sensing properties were tested. The sensor performance was improved by Zr-doped strategy. The Zr-doped In 2 O 3 based sensor showed good response (169) toward 1 ppm NO 2 at the operating temperature of 75 °C with low resistance of 23 kΩ and the detection limit was 20 ppb. Such favorable sensing performances endowed mesoporous Zr-doped In 2 O 3 with a potential application in the field of gas sensor. The enhanced sensing properties were mainly attributed to its mesoporous microstructures, increased chemical adsorbed oxygen and limited grain size by Zr-doping. [ABSTRACT FROM AUTHOR]

Mesoporous ZnFe 2 O 4 with ordered tunnel and large specific surface area has been successfully prepared through hard template (mesoporous silica KIT-6). The necessary characterizations such as X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) have been carried out to investigate the obtained material. ZnFe 2 O 4 with mesoporous structure presents excellent crystallinity and periodic mesostructure. The sensing properties of gas sensor based on ZnFe 2 O 4 mesoporous material towards acetone has been investigated. The sensor presents outstanding sensitivity, selectivity and longtime stability. This indicates that the obtained mesostructured ZnFe 2 O 4 through hard template method is a potential acetone gas sensor material. [ABSTRACT FROM AUTHOR]

A facile and effective strategy has been successfully developed to synthesize reduced graphene oxide-multiwalled carbon nanotubes-tin oxide nanoparticles (rGO-CNT-SnO 2 ) hybrids by hydrothermal method. The combined characterizations of X-ray diffraction, Raman spectrum and Transmission electron microscopy were used to characterize the samples thus obtained, indicating the successful preparation of rGO-CNT-SnO 2 hybrids. A room temperature NO 2 sensor was fabricated by dropping the dispersion of rGO-CNT-SnO 2 hybrids on the surface of ceramic substrate previously printed Au electrodes. Most importantly, the sensor based on rGO-CNT-SnO 2 hybrids shows high response, fast response and recovery rate, high selectivity and good stability, which are much better than NO 2 sensors based on pure rGO and rGO-SnO 2 hybrids. [ABSTRACT FROM AUTHOR]

Hierarchical Co 3 O 4 nanorods are prepared by effective hydrothermal strategy. The morphology and structure of the hierarchical nanostructures are characterized by means of field emission scanning electron microscope, high-resolution transmission electron microscopy and X-ray diffraction. The as-prepared Co 3 O 4 nanorods with the diameters about 200 nm are composed of small nanorods with average sizes of 20 nm. The gas-sensing properties of synthesized nanorods are tested to ammonia. Results reveal that hierarchical Co 3 O 4 nanorods have excellent sensing performance. Moreover, the sensor consisting of hierarchical Co 3 O 4 nanorods exhibits high response and fast response/recovery speed to ammonia gas, while the sensor made of normal Co 3 O 4 nanorods do not exhibit notable response to ammonia gas. Significant enhancement of the sensing performance is attributed to the unique hierarchical nanostructure and good catalytic activity of Co 3 O 4 nanomaterials. [ABSTRACT FROM AUTHOR]

Abstract: The flower-like pristine (ZnO) and PdO-decorated ZnO (PdO-ZnO) materials with hierarchical structure were synthesized by a surfactant-free hydrothermal route and subsequent heat treatment. This method requires high concentrations of a zinc precursor (0.1M) and introduction of an amount of PdO nanoparticles into the reaction system. The flower-like ZnO nanostructures comprises many aggregative rods with the diameter of about 200nm. Having fabricated gas sensors based on the pristine and PdO-decorated flower-like ZnO, we find that the PdO-ZnO sensor exhibits a response of 100ppm C7H8 and C2H5OH, which is about 4–5 times higher than that of pristine ZnO at the optimal operating temperature of 240 and 320°C. The enhanced sensing performance demonstrates that the distinct increases in response are attributed to the sensitisation effect of PdO. The effects of PdO decorating on the sensing properties of flower-like ZnO structures have been investigated. [Copyright &y& Elsevier]

Abstract: La x Sr1− x FeO3 nanofibers were synthesized via electrospinning and characterized by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The diameters of the La x Sr1− x FeO3 nanofibers produced were in the range of 30–80nm. When the La/Sr ratio was 0.7:0.3, La0.7Sr0.3FeO3 nanofibers showed high and rapid response and good repeatability to 500ppm ethanol. At 185°C, the response and recovery time of La0.7Sr0.3FeO3 nanofiber were 11s and 21s, respectively. The La0.7Sr0.3FeO3 nanofibers are promising sensitive materials for ethanol detecting. [Copyright &y& Elsevier]

• Polypyrrole decorated-reduced graphene oxide (PPy-rGO) hybrids were successfully synthesized by a self-redox strategy. • The PPy-rGO-3-based sensor exhibits a higher response and fast response and recovery behavior to DMMP than pristine rGO. • The enhanced DMMP sensing properties were attributed to formation of hydrogen bonds between DMMP and PPy. The development of fast-response, high sensitivity and selectivity gas sensors for monitoring of organophosphorus is essential, where two dimensional graphene-based materials possessing exceptionsal carrier mobility are considered as promising candidates for room-temperature organophosphorus detection. However, it is challenging to fabrication of graphene-based gas sensors for detection of organophosphorus with excellent sensing performances. Herein, we develope a self-redox strategy to synthesize polypyrrole decorated-reduced graphene oxide hybrids (PPy-rGO) by redox reactions between pyrrole and GO during hydrothermal treatment process. This self-redox strategy results in the formation of perfact interfical strucutre between PPy and rGO through the π-π interactions without the impurity from the conventional oxidation/reducing agents. Most importantly, such PPy-rGO hybrids can be used as novel sensing materials for detection of dimethyl methylphosphonate (DMMP) at room temperature. Specially, the response of PPy-rGO-based sensor towards 100 ppm DMMP can reach 12.9 %, which is 3-fold higher than that pristine rGO-based sensor. Meanwhile, PPy-rGO-based sensor exhibits short response time/recovery time (43 s/75 s), low detection limit (5 ppm), excellent repeatability, and high selectivity. By combination of FT-IR and N 2 sorption isotherms, the enhanced DMMP sensing performances of PPy-rGO hybrids are concluded as following two aspects. Firstly, the formation of hydrogen bonds between PPy-rGO hybrids and DMMP molecules regulates the adsorption/desorption of DMMP. Secondly, increasing BET surface area by introduction of PPy into rGO matrix is beneficial to DMMP diffusion among the sensing materials. Our work would offer a new strategy for rational development of graphene-based materials for detection of organophosphorus at room temperature. [ABSTRACT FROM AUTHOR]

• The Cr 2 O 3 -TiO 2 core-shell fibers with different shell thicknesses were fabricated by a coaxial electrospinning method. • The effect of shell thickness on acetone gas sensing properties of core-shell nanofibers was investigated. • The Cr 2 O 3 -TiO 2 core-shell fibers with optimized shell thickness showed better sensing performance than pure fibers. • A possible gas sensitivity mechanism of Cr 2 O 3 -TiO 2 core-shell fibers was proposed. Cr 2 O 3 -TiO 2 core-shell fibers (Cr-Ti CS-Fs) with different shell thicknesses were synthesized by a facile coaxial electrospinning technique. The gas-sensitive performance of Cr-Ti CS-Fs to acetone was enhanced by optimizing the TiO 2 shell thickness. With the increase of the thickness of the TiO 2 shell, the response of Cr-Ti CS-Fs to acetone showed a transition from p-type to n-type. Besides, the formation of Cr 2 O 3 -TiO 2 heterojunction enabled the gas sensors to possess short response and recovery time to target gas. A possible mechanism of the enhancement of gas-sensitive performance of core-shell Fs was also illustrated. [ABSTRACT FROM AUTHOR]

• Stannate spinel oxide Co 2 SnO 4 was firstly adopted for gas sensing showed excellent properties. • The TEA sensing properties was highly improved by the stannate spinel structure and Co2+ ion. • The modification of the morphology of Co 2 SnO 4 can result in the improvement of selectivity. The spinel oxides are identified as the highly promising materials for gas sensing application due to their good thermal stability, low cost and nice sensitivity. The spinel oxide nanocomposites of Co 3 O 4 /SnO 2 and Co 2 SnO 4 /SnO 2 were prepared by the co-precipitation method, and their gas sensing characteristics were investigated in this work. Compared with the Co 3 O 4 /SnO 2 nanocomposites, the sensor based on Co 2 SnO 4 /SnO 2 nanocomposites exhibited significantly enhanced response and selectivity performance toward triethylamine (TEA). The response of the Co 2 SnO 4 /SnO 2 composites is about 45.9 to 100 ppm TEA at 270 °C, which was almost 4 times higher than that of Co 3 O 4 /SnO 2 nanocomposites. The excellent performance of the Co 2 SnO 4 /SnO 2 composites can be attributed to the catalytic ability of divalent Co2+ cation located in octahedral sites in spinel structure, which results in enhanced gas absorption and catalytic performance. [ABSTRACT FROM AUTHOR]

One-dimensional hybrid In 2 O 3 -Co 3 O 4 ribbon-based sensing platform exhibits an excellent response/recovery acetone and formaldehyde behavior at the working temperature of 280 °C and 260 °C, respectively. • The heteroassembly of p-type Co 3 O 4 nanoparticles into an n-type In 2 O 3 matrix as a novel 1D hierarchical nanostructure is reported. • The hetero-interfacial structure with different loaded content can be successfully tailored by electrospinning. • The In 2 O 3 -Co 3 O 4 hetero-materials sensing layer achieves a high response to formaldehyde and acetone gas. The development of gas sensor with innovative designs is highly desirable for widespread deployments of sensors in applications of monitoring indoor air quality and industrial safety. Herein, an approach is put forward to substantially improve gas sensing performance via electrospinning of metal ion and cross-linked polymer to porous and hetero indium trioxide (In 2 O 3) ribbon combined with cobaltosic oxide (Co 3 O 4) particles. The structural evaluation was systematically discussed and the content of the Co 3 O 4 was subtly regulated. The gas sensing results indicated that the obtained vacancy oxygen and adsorbed oxygen-abundant In 2 O 3 -Co 3 O 4 ribbons exhibited significantly high response towards volatile organic compounds (VOCs) encompassing acetone (52, 280 °C) and formaldehyde (39, 260 °C), which can be ascribed to hierarchical porous hetero-structures, ion mismatch and catalytic property of p-type Co 3 O 4. This facile way sheds light on the rational design of gas sensitive materials via structure and composition engineering, resulting in facilitating the gas molecules adsorption and diffusion. [ABSTRACT FROM AUTHOR]

A porous nanosheet-assembled hierarchical Co 3 O 4 -based sensing platform exhibits a selective response/recovery toluene behavior at a working temperature of 180 °C. • The construction of Co 3 O 4 nanoparticles into a pore-rich nanostructure is reported. • The surface structure can be tailored by initial concentration of reactant. • The nanosheets-assembly sensing layer achieves a highest sensitivity. • Gas sensors are able to retain 88% of this sensitivity after 30 days. Rational structure design of sensing materials plays a crucial part in fabricating high performance gas sensors. In this work, three Co 3 O 4 samples with different morphologies, including Co 3 O 4 -C (Cube-shaped Co 3 O 4), Co 3 O 4 -R (Rod-shaped Co 3 O 4) and Co 3 O 4 -S (Sheet-shaped Co 3 O 4), were synthesized through a hydrothermal route. Hierarchical structures-dependent gas-sensing properties were further investigated. The toluene sensing performance of Co 3 O 4 -S hierarchical structure-based sensor outperforms the other two ones. It exhibited higher sensitivity, faster response-recovery speed and better selectivity to toluene at the working temperature of 180 °C. In addition, the Co 3 O 4 -S-based gas sensor can maintain its sensitivity to toluene after one month, suggesting it good reliability. Preliminary functional tests for the detection of toxic analytes indicated it can be considered as a promising candidate for applications in detecting toluene. [ABSTRACT FROM AUTHOR]