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In this work, the synthesized Co 3 O 4 /NiCo 2 O 4 /CC is a layered structure, which was prepared by a feasible method of hydrothermal reaction, thermal annealing of ZIF-67 template and other thermal treatment. This novel structure is based on carbon cloth, and Co 3 O 4 hollow nanocubes as semiconductor material grow in situ on nanowire arrays. Under the condition of different temperatures and different concentrations of ethanol, the response of the gas sensor based on Co 3 O 4 /NiCo 2 O 4 was studied. The result shows high sensitivity, good linear relationship and excellent response-recovery properties. And its high sensitivity is demonstrated with a maximum response up to 35 at 180 °C and 200 ppm. The sensor performs well in gas sensitivity thanks to the structure of the material. Large specific surface area, high porosity and fast electronic transport channel between Co 3 O 4 and CC are all important reasons. Accordingly, this method of preparing the novel hierarchical structure can improve the gas sensitive performance. This work would provide a reference for further research on the application of Co 3 O 4 MOF-derived structure in gas sensitive. [ABSTRACT FROM AUTHOR]

Abstract An intricate sea-urchin-like hexagonal WO 3 nanostructure was synthesized by a facile hydrothermal approach. Sensing properties of the as-fabricated sensor exhibited surpassing response and selectivity for NO 2 in comparison of H 2 after corroborating the composition, phase-purity and surface morphology using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Formation of the urchin-like structure was ascribed to the capping effects of potassium sulfate that prompts the anisotropic growth of WO 3 , leading to hierarchical complex with a large surface-volume ratio. In particular, first-principle calculation had provided a new perspective for us to delve into the sensing process of H 2 and NO 2 from an atomic level. It was found that the sensing properties mainly arose from the tuning of electronic structure and electrons transfer between the adsorbed gas and the sensitized surface along with the charge relocation between them. Finally, a plausible mechanism was proposed as theoretical guidance for achieving high-performance sensors experimentally and supposedly. [ABSTRACT FROM AUTHOR]

Abstract In this work, we report a simple synthesis of hierarchical flower-like NiO/ZnO heterostructure consisting of numerous nanosheets via a facile one-step hydrothermal method. The gas-sensing results reveal that the NiO/ZnO composite based sensor presents excellent properties towards ethanol such as high gas response and good repeatability. The excellent performances are predominantly ascribed to the p-n heterojunction strengthening at the interface between p-type NiO and n-type ZnO, which causes the change of depletion layer and potential barrier height. Moreover, the unique hierarchical architectures may play an evenly important role in the surface sensing reaction. [ABSTRACT FROM AUTHOR]

The pristine and Cr-doped ZnO nanorods were successfully synthesized via a facile hydrothermal route. We found that the ethanol gas response of ZnO was improved significantly by Cr doping. In particular, the enhanced gas-sensing mechanism was investigated by first-principles calculations upon proposed surface adsorption models. The calculated results revealed that the Cr-doped ZnO (0 0 0 1) surface enabled transfer larger electrons and adsorb more oxygen molecules than that of undoped one, thus holding the potential for further enhancement in gas response of ZnO-based sensors. [ABSTRACT FROM AUTHOR]

The manner how nano building blocks assemble into hierarchical architectures exerts a tremendous influence on gas-sensing performance of the metal oxides. Herein, we focus on tuning the 1D nanorods into 3D hierarchical urchins with various assembly densities, aiming at investigating the effect between gas diffusion and charge transfer. Via modulating the additive amount of NaOH, loose-, moderate- and close-assembled SnO 2 nanourchins aggregated with nanorods were successfully prepared, respectively. The relationships of nanorond assembly behavior to specific surface and average pore size of the urchin-like nanostructures were discussed in detail. A comparison study reveals that an enhanced gas sensing performance for the sensor made of the moderate-assembled SnO 2 nanourchins towards ethanol occurs over the other two, implying that perhaps there exists an optimizing assembly density range which provides not only enough space for gas diffusion but also sufficient contact network for charge transfer, in terms of good contacts among nanorods in an urchin-like sphere and among nanorods from adjacent spheres. [ABSTRACT FROM AUTHOR]

We report on the synthesis of pristine and Cu-doped SnO 2 spheres using a facile hydrothermal method and investigate their microstructures and gas-sensing response. We focus on how Cu doping can have an impact on gas-sensing behavior of SnO 2 -based sensors toward H 2 S. We find that Cu doping can enhance significantly the gas response of SnO 2 toward H 2 S, the origin of which can be clarified with a proposed adsorption model. First-principles calculations reveal that adsorption energy of H 2 S on Cu-doped surface is lower than that on undoped one and the interaction between adsorbed H 2 S and Cu-doped surface is stronger than that between adsorbed H 2 S and pure surface, which consequently improves gas-sensing performances of SnO 2 toward H 2 S. Such a combined experimental and calculational study offers an explanation on how Cu doping affects gas-sensing performances of SnO 2 . [ABSTRACT FROM AUTHOR]

We report a successful synthesis of three hierarchical NiO nanoflowers via a surfactant-assisted hydrothermal method. We find that the NiO hierarchical architectures are self-assembled by uniform nanosheets with different petal thicknesses. Moreover, we develop gas sensors based upon the nanomaterials and demonstrate that the nanoflower with the thinnest petal exhibits the best gas-sensing functionalities. By conducting a comprehensive characterization of microstructures and morphologies of the nanomaterials, we propose a possible nucleation-growth mechanism and explain how the petal thickness affects the gas-sensing properties of the nanoflowers. [ABSTRACT FROM AUTHOR]

Sulfur dioxide (SO 2) is one of the main harmful gas in agricultural greenhouse. Its concentration can effectively reflect the health status of plants in agricultural greenhouse. In this paper, the adsorption characteristics of SO 2 on modified graphene-based were studied in comparison. The adsorption models of epoxy grouped graphene (G-O), palladium doped graphene (Pd-G) and epoxy and palladium co-doped graphene (Pd-G-O) to SO 2 were established based on the first-principles, analyzing in terms of adsorption energy, density of states, orbitals, charge density and desorption time of the adsorption models. The results showed that Pd-G-O exhibited strong chemisorption with adsorption energy of -1.237 eV. Furthermore, three modified graphene-based sensing materials were prepared via the redox method in this paper, and their crystal morphology and chemical elemental composition were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), respectively. The response performance of the graphene-based sensor to SO 2 was tested by a gas-sensitive testbed. The test results confirmed that the response of the Pd-G-O sample to 50 ppm SO 2 at room temperature was 10.5 (1.567 and 1.235 times than that of G-O, Pd-G). Pd-G-O provides theoretical basis and experimental support for the development of a highly sensitive and fast response sensor for the detection of harmful gases in agricultural greenhouse. [ABSTRACT FROM AUTHOR]

The selection of electrode materials and the optimization of electrode configurations are two effective approaches to achieve high-performance energy storage. As a representative ternary metal oxide, CoMoO 4 has been directly grown on the carbon cloth via a facile hydrothermal method and subsequent calcination, forming a binder-free electrode. Further measurements reveal that this electrode is composed of CoMoO 4 nanosheets assembled 3D-framworks (NAFs) and thereby shows a superb electrochemical property in KOH solution. It is worth mentioning that the specific capacitance reaches as high as 1234 F/g at the current density of 1 A/g, which exceeds most of CoMoO 4 and CoMoO 4 -based composites reported so far. Meanwhile, when the current density increases to 10 A/g, a considerable specific capacitance of 446 F/g is still obtained and can maintain nearly unchanged after 5000 cycles. [ABSTRACT FROM AUTHOR]

Four MoO 3 samples with the Zn element doped mole ratio of 0%, 3%, 6% and 9% were prepared by applying a convenient one-step hydrothermal synthesis method, and the samples presented three-dimensional microflower-like structures assembled by nanosheets. The systematic analysis results indicate that the 6 mol% Zn-doped sample had the most amazing detection characteristics for 50 ppm CO, with a response of 31.23 (4 times of the pure MoO 3) at a lower temperature (240 °C). The large specific surface area, big pore size and tiny particle size were proved to be beneficial to the gas sensitivity, which promotes gases transfer and provides more gases landing points during the gas-sensitive reaction. Besides, based on the density functional theory (DFT), the facilitation effect of doped Zn on the adsorption ability of MoO 3 to CO molecule was verified from the perspective of electronic properties. The excellent gas-sensing performances indicate that the 6 mol% Zn-doped MoO 3 has potential to be applied as a reliable CO sensor. [ABSTRACT FROM AUTHOR]

In this study, ZnO–SnO 2 heterojunction nanofibers were fabricated using electrospinning and treated by Ar plasma. The post treatment demonstrated the ability to regulate adsorbed oxygen of nanofibers and thus affecting the gas sensing performance. The results revealed that the gas sensing performances increased with the increase of plasma treatment time at first, then showed a downward trend. The setting for the best H 2 gas performance was 20 min of plasma treatment, under which the response of the sample was 80% higher and the response time was two thirds shorter than those of the untreated sample. The explanation can be that appropriate plasma treatment can increase the oxygen vacancy on the surface of heterojunction nanofibers as well as the resistance modulation range in the air; however, excessive plasma treatment can result in the reduction of the resistance modulation range in the air by reducing the metal oxide to metal. [ABSTRACT FROM AUTHOR]

It is of great significance to monitor internal faults of transformer and ensure its normal and safe operation. Usually, acetylene (C 2 H 2) is considered as the characteristic gas caused by discharge failure in transformer. Using gas sensor technology to analyze dissolved gases in transformer oil is an important strategy. Recently, metal oxide semiconductor (MOS) heterojunctions with tailored microstructures have been developed to fabricate high quality gas sensors for gas detection. In this paper, hierarchical flower-like NiO/ZnO heterostructures assembled with 2D nanosheets have been synthesized by a facile hydrothermal method and calcination process. Noticeably, the introduction of different contents of NiO (3.0 at%, 5.0 at% and 10.0 at%) leads to different assembly manners of the building nanosheets into hierarchical flower-like structures, thus affecting the gas performances. Given this, a variety of microscopic characterization methods were used to observe and compare the differences in the structures and morphologies of the composites. Through the gas sensing test, it was found that the 5.0 at% NiO-modified ZnO based sensor exhibited superior sensing performances to C 2 H 2 compared with that of others. The enhanced properties may be attributed to the formation of p-n heterojunctions as well as high porosity of the nanosheets. This promising approach is versatile for the applications of high-quality gas sensors. [ABSTRACT FROM AUTHOR]

Pd-doped SnO 2 nanofibres were prepared by electrospinning and magnetron sputtering. It was found that the efficiency of gas sensing properties in these fibres depends primarily on the density of oxygen vacancies, which can be regulated by plasma treatment. We demonstrated that moderate plasma treatment can increase the oxygen vacancy as well as improve the gas sensing performance of SnO 2. However, excessive plasma treatment led to the production of other substances that deteriorated the gas sensing performance. Furthermore, the best results for hydrogen gas sensing were obtained when the nanofibres were subjected to plasma treatment for 1 min. The fabricated material demonstrated a response of more than 53 for 500 ppm hydrogen at the optimum temperature (130 °C), which is a significant improvement as compared to sensors without plasma treatment. Evidently, plasma treatment is an effective method to further enhance the sensing properties of the fabricated nanofibres. [ABSTRACT FROM AUTHOR]

In this paper, we present the synthesis of novel three-dimensional SnO 2 /MoS 2 nanocomposites via electrospinning combined with a hydrothermal method and their application to CH 4 gas detection. Morphological characterization proved that the flower-like MoS 2 structures were successfully connected to the surface of porous SnO 2 nanofibers. The CH 4 gas-sensing test results indicated that the gas-sensing properties of SnO 2 /MoS 2 nanocomposites were better than those of pure MoS 2 ; the SnO 2 /MoS 2 nanocomposites exhibited lower optimal operation temperature and higher gas response. Such excellent performance is mainly attributable to the special hierarchical structure and the existence of n–n junctions between SnO 2 and MoS 2. [ABSTRACT FROM AUTHOR]

Acetylene (C 2 H 2) gas concentration is a key parameter in transformer monitoring. In current work, the selective acetylene sensors which based on flower-like ZnO structures with NiO nanoparticles were successfully fabricated. The NiO–ZnO composites were synthesized by two-step hydrothermal method. And various of characterization analyses had been applied to the exploration of crystal structure and the p-n heterojunction. According to the systematic gas sensitivity tests, the response of NiO–ZnO (5%) to 50 ppm C 2 H 2 was 15.23 at 200 °C whereas the response of pure ZnO was 4.1 in the same condition. In addition, the response value of NiO–ZnO (5%) to 50 ppm C 2 H 2 was 3.6 times to 50 ppm H 2. Such a good gas-sensing property of NiO–ZnO composites is due to p-n heterojunction and high catalytic activity of NiO. [ABSTRACT FROM AUTHOR]

Abstract A novel MnO 2 nanosheet-coated CeO 2 nanosphere (CeO 2 @MnO 2) core-shell composite was successfully prepared by a simple two-step hydrothermal process as efficient catalyst for oxygen reduction reaction (ORR). XRD, XPS, SEM and TEM analysis techniques were sequentially employed to evidence this CeO 2 core-MnO 2 shell structure. When utilized for ORR catalyst, such hierarchical core-shell structured CeO 2 @MnO 2 composite delivers a superior electrocatalytic activity than that of MnO 2 nanoflowers and CeO 2 nanospheres, which is in close proximity to that of commercial 20 wt% Pt/C in alkaline solution, and also exhibits an excellent durability. These properties make the composite potential as cathode catalyst for metal-air battery application. In addition, the enhanced mechanism arising from the synergetic effect of the MnO 2 and CeO 2 was preliminarily discussed. [ABSTRACT FROM AUTHOR]

Ternary metal oxides have great potential for chemical storage devices because of their outstanding synergistic effects as well as rich redox reactions. However, there are limited reports of 3D structure BiCoO 3 materials and relevant electrochemical properties. Meanwhile, the study of BiCoO 3 is reasonably important for underlying metal oxides researches. In this work, we have successfully developed a 3D urchin-like BiCoO 3 material without using any template and surfactant. For the supercapacitor application, the BiCoO 3 material showed a specific capacitance of 152 F g −1 at the current density of 1 A g −1 , and this value exhibited a rate capability of 82.3% at a high current density of 10 A g −1 . Furthermore, the sample showed the ideal cycling stability (92.7% retention after 5000 times cycles at the current density of 1 A g −1 and nearly invariable specific capacitance during different current density cycles). These results suggest that the obtained urchin-like BiCoO 3 sample has superb electrochemical performances which suggest its promising applications as renewable and clean energy storage devices electrode materials in the future. [ABSTRACT FROM AUTHOR]

Low-cost dynamic materials for Faradaic redox reactions are needed for high-energy storage supercapacitors. A simple and cost-effective hydrothermal process was employed to synthesize amaryllis-like NiCo 2 S 4 nanoflowers. The sample was characterized by X-ray powder diffraction, Brunauer–Emmett–Teller method, scanning electron microscopy, and transmission electron microscopy. NiCo 2 S 4 nanoflowers were coated onto carbon fiber fabric and used as a binder-free electrode to fabricate a solid-state supercapacitor compact device. The solid-state supercapacitor exhibited excellent electrochemical performance, including high specific capacitance of 360 F g −1 at scan rate of 5 mV s −1 and high energy density of 25 W h kg −1 at power density of 168 W kg −1 . In addition, the supercapacitor possessed high flexibility and good stability by retaining 90% capacitance after 5000 cycles. The high conductivity and Faradic-redox activity of NiCo 2 S 4 nanoflowers resulted in high specific energy and power. Thus, NiCo 2 S 4 nanoflowers are promising pseudocapacitive materials for low-cost and lightweight solid-state supercapacitors. [ABSTRACT FROM AUTHOR]

Noble metals decorated two-dimensional nanostructures with a large surface-to-volume ratio raise substantial promise for many technological applications particularly for high-performance chemical sensing. Here, we design and synthesize a hierarchical heterojunction comprising ultrathin two-dimensional polycrystalline ZnO nanosheets on a large scale, which serve as reaction positions for reduced gases, and uniformly dispersed Ag nanoparticles to enhance reaction activity. We find that the Ag nanoparticles in the heterostructural system act as strong electron acceptors, inducing remarkable surface space charge layers. As a result, the heterostructural system shows significantly improved gas-sensing performance to ethanol as compared to pure ZnO. Such metal nanoparticles decorated two-dimensional polycrystalline ZnO nanosheets can be applied in not only as gas-sensing but also catalytic and photocatalytic fields. [ABSTRACT FROM AUTHOR]

We report a successful synthesis of hexagonal boron nitride ( h -BN) nanosheets with a few atomic layers by a facile yet efficient solvothermal method at the relatively low temperature. After identifying the pure h -BN phase by the X-ray diffraction, the ultrathin BN nanosheets were systematically characterized by field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) element mapping and high-resolution transmission electron microscopy (HRTEM). We find that the h -BN nanosheet has a nearly transparent morphology with a thickness of ~1.36 nm (four atomic layers) and shows dozens of square microns in area. We test the gas-sensing properties of the ultrathin h -BN nanosheets towards ethanol and NH 3 , and find that the fabricated gas sensors show a fast response and excellent repeatability to ethanol at optimal operating temperature of 300 o C. [ABSTRACT FROM AUTHOR]

In the work, four types of typical morphologies of differently dimensional pure V 2 O 5 nanostructures including nanoflowers, nanoballs, nanowires and nanorods were synthesized through a simple hydrothermal method. The morphology of the product depends on the types of solvent and acid. Hierarchical nanoflowers and zero-dimensional (0D) nanoballs of V 2 O 5 nanocrystals were obtained when using C 2 H 5 OH as solvent. One dimensional (1D) nanowires and nanorods were obtained if H 2 O was used to participate in the reaction. The morphology and structure of the samples were characterized by XRD and SEM, respectively. The electrochemical behaviors of nanoflowers, nanoballs, nanowires and nanorods as electrodes in a supercapacitor device were tested using cyclic voltammetry (CV) curves and galvanostatic charge–discharge (GCD) curves. The electrochemical test results indicate that the rod-like structure leads to a significant improvement of storage capacity, electrochemical kinetics and rate capability. And 1D V 2 O 5 nanorods show the largest specific capacitance of 235 F g −1 at the current density of 1 A g −1 when used as supercapacitor electrode in 1 mol/L Na 2 SO 4 electrolyte. It turns out that 1D V 2 O 5 nanorod is an ideal material compared with other morphologies for supercapacitor electrode. [ABSTRACT FROM AUTHOR]

Regular hexagonal embedded ZnO nanorods were successfully prepared by a simple hydrothermal method. The addition of urea as a homogeneous precursor was found to play a vital role in the embedding of secondary nanorods. The nanostructures were characterized by XRD, SEM, and EDS. The gas-sensing properties of secondary grown embedded nanorods were reported for formaldehyde, ethanol, methanol, acetone, and ammonia at different concentrations and temperatures. A higher response and greater selectivity toward formaldehyde than other gases was observed. A sharp response with the best recovery time was achieved at an optimum temperature of 200 °C. [ABSTRACT FROM AUTHOR]

Abstract: Different morphologies including bulk, layer by layer structure and nanosheets-like spheres of vanadium pentoxide (V2O5) precursor have been synthesized via a simple and direct hydrothermal method. Field emission scanning electron microscopy, X-ray powder diffraction and UV–vis diffuse reflectance were used to characterize the fabricated materials. The results showed that the reaction time had a great influence on the morphology evolution processes of the as-synthesized precursors. The photocatalysis measurements showed that the nanosheet-like spheres exhibited the highest activity for degrading rhodamine B under UV light. The possible morphology transformation mechanism and the schematic representation of the precursor are also discussed. [Copyright &y& Elsevier]

Abstract: Different morphologies of vanadium pentoxide (V2O5) from 1D to 3D, including nanospheres, nanowires, urchin-like and flower-like nanostructures, have been synthetized by a simple hydrothermal method. Some parameters, such as the reaction temperature, the volume of polyvinyl pyrrolidone (PVP) and possible formation mechanisms of different V2O5 nanostructures were discussed. The results demonstrate that PVP and the reaction temperature play a critical role on the morphology of vanadium pentoxide. [Copyright &y& Elsevier]