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In this study, a novel high length-diameter ratio NiO nanorods decorated with uniformly ZnO nanoparticles was synthesized via a facile one-step hydrothermal process. • A novel NiO nanorods decorated with uniformly ZnO nanoparticles was synthesized. • The NiO/ZnO composites based sensor show excellent ethanol gas response. • The p-n heterojunction and astonishing synergistic played an essential role in tgas-sensing performance. In this study, a novel high length-diameter ratio NiO nanorods decorated with uniform ZnO nanoparticles was synthesized via a facile one-step hydrothermal process. It was a surprise to find that the NiO/ZnO nanorods heterostructure based sensor demonstrated much more excellent ethanol gas sensing properties than that of undoped NiO nanorods. This enhancement of sensing properties may be attributed to their synergetic effect as well as the heterojunction at interface between the NiO nanorods and ZnO nanoparticles. [ABSTRACT FROM AUTHOR]

In this work, WO 3 ·H 2 O nanorods and spherical network were successfully synthesized via a simple hydrothermal process and the gas sensing performance of the samples was investigated. The spherical network shows superior performance due to its porous structure and efficient electronic transmission on the network. • A novel spherical WO 3 ·H 2 O network was successfully prepared. • The spherical WO 3 ·H 2 O network exhibits an enhanced gas sensing performance compared to uniformly dispersed nanorods. • The porous structure as well as efficient electronic transmission play an important role in gas sensing process. A novel 3D spherical WO 3 ·H 2 O network assembled by numerous partially connected nanorods was successfully synthesized by a facile hydrothermal method. The ethanol sensing characteristics of two samples were investigated systematically and the results indicated that the spherical WO 3 ·H 2 O network exhibited an enhanced gas sensing performance due to its large specific surface area. In addition, the porous structure provides abundant channels for gas diffusion and the connected nanorods facilitate the transfer of electrons along the network, resulting in the improvement of gas sensing properties. [ABSTRACT FROM AUTHOR]

Unique nanosheet-assembled Ce-doped NiO hierarchical microflowers, whose nanosheet is comprised of a large amount of nanowires, was successfully synthesized via a hydrothermal route. The sensor based on the Ce-doped NiO microflowers exhibited a superior gas response towards ethanol than that of the pure sample. The novel hierarchical nature as well as the incorporation of Ce into NiO played an essential role in the sensing reaction. • Novel hierarchical Ce-doped NiO microflowers were synthesized hydrothermally. • The Ce-doped NiO based sensor exhibited enhanced ethanol gas response. • The unique hierarchical nature and incorporation of Ce into NiO played a vital role in sensing reaction. In this work, novel flower-like Ce-doped NiO hierarchical architectures were successfully prepared through a facile one-step hydrothermal route. Morphological and structural observations demonstrate that such microflower is assembled by a large amount of nanosheets, and the nanosheets is comprised of numerous nanowires which are randomly interwoven to each other. In comparison to the pure sample, the Ce-doped NiO microflowers exhibit superior ethanol sensing properties. The higher sensor response is primarily responsible for the unique hierarchical nanostructure and the change in effective hole concentration due to the incorporation of Ce into NiO. [ABSTRACT FROM AUTHOR]

Novel loosely and tightly arranged nanosheet-assembled flower-like WO 3 nanostructures were controllably synthesized under hydrothermal conditions. Through gas-sensing experiments towards NH 3 , it was found that the loosely-arranged WO 3 nanostructures exhibited a higher NH 3 response. This difference was due to the sparse cross-arrangement of the nanosheets on the surface of the sample and the larger specific surface area of the loosely-arranged structure. • Novel loosely and tightly arranged nanosheet-assembled flower-like WO 3 were synthesized. • The loosely-arranged WO 3 nanostructures exhibited the superior NH 3 sensing performance. • The factors affecting NH 3 -sensing properties are discussed in detail. Novel loosely and tightly arranged nanosheet-assembled flower-like WO 3 nanostructures were controllably synthesized via a facile hydrothermal approach. Additionally, NH 3 -sensing measurements were performed based on both samples. Remarkably, the loosely-arranged WO 3 nanostructures, which possess an abundance of semi-closed spaces and a larger specific surface area, exhibited improved NH 3 -sensing properties compared to that of the tightly-arranged WO 3 nanostructures. This discovery can provide guidance for improving the gas-sensing properties of nanosheet-assembled hierarchical MO x flower-like nanostructures. [ABSTRACT FROM AUTHOR]

A nest-like TiO 2 structure with remarkable gas sensitivity toward ethanol. • A Multilayer nest-like TiO 2 nanostructure has been synthesized by simple hydrothermal method. • The gas sensor based on the nest-like TiO 2 shows excellent response to ethanol. • The plausible mechanism involved in enhancing the gas sensing performances was discussed. A multilayer nest-like TiO 2 nanostructure assembled from one-dimensional nanowires has been synthesized by a simple hydrothermal method. This special structure not only has the characteristics of a network structure with many nanojunctions but also has high efficiency of gas transmission. We have revealed its remarkable gas sensitive property toward ethanol through a comparative study with unmodified nanowires. It is believed that its excellent gas sensing is due to its special nest-like structure providing a large number of chemical reaction chambers and sufficient gas transmission channels. [ABSTRACT FROM AUTHOR]

Graphical abstract In the study, a facile, inexpensive solution approach was utilized to prepare novel 3D porous Cu 2 O-MoS 2 microspheres, which were employed for NH 3 gas detection. The results indicated the sensor fabricated by the porous Cu 2 O-MoS 2 microspheres exhibited fascinating gas-sensing properties to NH 3 with high gas response and short response time. Remarkably, the unique architecture and p-n heterojunction design and build play a vital role in the gas sensing properties improvement. Highlights • Novel 3D porous Cu 2 O-MoS 2 microspheres were synthesized via a facile solution route. • The Cu 2 O-MoS 2 microspheres based sensor exhibited excellent gas sensing performances. • The mechanism enhanced sensing properties was discussed in detail. Abstract A facile, inexpensive solution approach was utilized to prepare novel 3D porous Cu 2 O-MoS 2 microspheres, which were employed for NH 3 gas detection. Morphological characterizations indicated porous MoS 2 microspheres were decorated with numerous Cu 2 O nanoparticles. The fabricated gas sensor based on the Cu 2 O-MoS 2 microspheres possessed high gas response of 43 with fast response and recovery speed towards NH 3 , good reproducibility as well as satisfactory stability, which were mainly ascribed to the distinctive 3D porous microsphere architecture and the formation of p-n heterojunction at the interface between the n-type MoS 2 and p-type Cu 2 O. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Nanorods assembled and nanosheets assembled WO 3 ·H 2 O hierarchical structures were synthesized. • Growth mechanisms for the morphologies evolution of the WO 3 ·H 2 O hierarchical structures were proposed. • Nanorods assembled hierarchical structures exhibited quicker gas response. • Nanosheets assembled microspheres showed higher gas response. Abstract WO 3 ·H 2 O hierarchical structures assembled by nanorods or nanosheets were successfully synthesized via a facile hydrothermal method. Gas sensing behaviors were investigated for these two different nanostructures towards ethanol gas. The results indicated that the nanorods assembled flower-like structure exhibits faster response and recovery time as compared with the nanosheets assembled microspheres, which may be attributed to fast gas diffusion speed in the nanorods assembled nanostructures, while the nanosheets assembled hierarchical flower-like WO 3 ·H 2 O structures exhibited higher response (54) than that of the WO 3 ·H 2 O microspheres (25) because of the larger specific surface area and the abundant micro reaction rooms. [ABSTRACT FROM AUTHOR]

In this work, a novel two-dimensional seawave-like hierarchical WO 3 nanocomposite was synthesized by a one-step hydrothermal route. • Novel seawave-like hierarchical WO 3 nanocomposite was synthesized. • The sensor fabricated by seawave-like h-WO 3 nanostructure exhibited ultra-sensitivity to NH 3. • The mechanism enhanced gas sensing properties was discussed in detail. In this work, a novel two-dimensional seawave-like hierarchical WO 3 nanocomposite was synthesized by a one-step hydrothermal route. It was amazing that this novel two-dimensional WO 3 nanostructure was composed of one-dimensional worm-like WO 3 nanowires. Furthermore, a ultra-sensitivity towards ammonia was shown primarily attributed to abundant gas diffusion channels and large gas-sensitive reaction surface area furnished by one-dimensional worm-like WO 3 nanowires. Meanwhile, as the building units, the worm-like nanowires promote the directional transmission of electrons, resulting in an improvement of WO 3 gas sensing characteristics. [ABSTRACT FROM AUTHOR]

Owing to the slenderness of the single spider silk and the fluffy arrangement of numerous monomers, the cobweb has the sufficient contact with the water vapor in air and can form dewdrops on it. Enlightened by this, WO 3 nanowires with a great length-diameter ratio and a non-compact assembly are inferred to possess an excellent gas-sensing property. As a proof-of-concept, the cobweb-like WO 3 was firstly synthesized through a facile solvothermal method using the water-ethanol mixed solution. The subsequent gas-sensing measurements testified this kind of cobweb-like WO 3 indeed displays an enhanced sensitivity towards the ethanol at a relatively low temperature. [ABSTRACT FROM AUTHOR]

In this work, hierarchical WO 3 ·H 2 O porous microspheres and conventional smooth WO 3 ·H 2 O microspheres were successfully fabricated via a simple hydrothermal process. The products were characterized by X-ray diffraction and scanning electron microscope. Meanwhile, the possible evolution processes of the two products were discussed based on time-dependent experiments. Remarkably, hierarchical porous spherical architectures which possess abundant micro reaction rooms, exhibited improved gas-sensing performance compared to smooth sphere-like structures. It is believed that this unique nanostructure has great potential to enhance the gas-sensing properties of tungsten oxides and other semiconductor materials. [ABSTRACT FROM AUTHOR]

A facile hydrothermal route was developed for the preparation of well-aligned hierarchical flower-like NiO nanostructure with the assistance of SDS that served as a structure-directing agent as well as a capping agent in the process of aggregation and assembly. Notably, the NiO sensors exhibit enhanced gas-sensing performance towards ethanol, which could be explained in association with the ultrathin nanosheets that are close to Debye length (L D ) scale and thus get the majority carriers fully depleted due to the ionization of adsorbed oxygen, abundant effective gas diffusion paths as well as high surface-to-volume ratio to promote sufficient contact and reaction between the NiO sample and ethanol molecules, and numerous miniature reaction rooms assembled with nanosheets to make the test gas molecules stay long enough for completed gas-sensing reactions. Besides, a novel growth mechanism with the passage of reaction time was also proposed in detail. [ABSTRACT FROM AUTHOR]

A novel WO 3 ·H 2 O nanostructure assembled by numerous one-dimensional nanorods as building units were synthesized successfully through a facile hydrothermal process. As a comparison, we also prepared the monodispersed WO 3 ·H 2 O nanorods. The crystal structures and morphologies of two products were characterized by X-ray diffraction and scanning electron microscope. Furthermore, gas sensing experiments indicated that a superior gas-sensing property of aligned WO 3 ·H 2 O nanorods occurs over that of the monodispersed WO 3 ·H 2 O nanorods, which is likely attributed to large effective surface areas and abundant accessible diffusion channels provided by this special structure for sufficient gas reactions. [ABSTRACT FROM AUTHOR]

Herein, a novel hierarchical cactus-like WO 3 -SnO 2 nanocomposite was synthesized by a one-step hydrothermal route. It was a surprise to find that such nanostructure consisting of diminutive SnO 2 nanospheres decorated bulky WO 3 nanosphere exhibited a high gas response and fast response-recovery speed towards acetone, mainly attributed to their synergetic effect as well as the heterojunction at the interface between the bulky WO 3 nanosphere and diminutive SnO 2 nanosphere, resulting in adequate surface adsorption and efficient electron transport. [ABSTRACT FROM AUTHOR]

The designed nanosheet-assembled hollow NiO/ZnO microspheres have been successfully synthesized by a facile one-step hydrothermal process. Such constructions are developed and employed in ethanol gas detection. The measured results reveal that the hollow NiO/ZnO hierarchical heterostructure based sensor exhibits outstanding ethanol gas sensing performances with superior gas response and excellent repeatability, which are predominantly ascribed to the hierarchical hollow architectures as well as the formation of p-n heterojunction at the interface between the p-type NiO and n-type ZnO structures. [ABSTRACT FROM AUTHOR]

In this study, the hollow MoO 3 microcages were successfully synthesized using a one-step hydrothermal route, and their gas-sensing properties towards ethanol were further investigated. It was found that such MoO 3 microcages possessed excellent ethanol gas response, which benefited from their unique hollow structure with a less stacking aggregation, offering sufficient pathways for gas diffusion as well as abundant adsorption sites for surface chemical reaction. [ABSTRACT FROM AUTHOR]

ZnO nanorods and nanosheets were synthesized via a facile hydrothermal route, and their gas sensing properties were tested to figure out the effect of surface morphologies on gas sensing performance. It was surprisely found that the ZnO nanorods exhibit quicker response and recovery speed towards ethanol, which may be ascribed to the better conductivity and lower potential barrier, whereas the nanosheets display larger ethanol gas response owing to its higher specific surface area. [ABSTRACT FROM AUTHOR]

Sparsely and closely flower-like WO 3 ·H 2 O hierarchical architectures were successfully synthesized via a one-step hydrothermal process. The obtained samples are both WO 3 ·H 2 O nanoflowers assembled by ultrathin nanosheets with the thickness less than electron deletion layer. And the possible formation processed was proposed based on the comparative studies. Furthermore, gas sensing experiments demonstrated that the closely WO 3 ·H 2 O nanoflowers which possess numerous semi-closed spaces have a superior gas-sensing performance compared with the sparsely one. We believe this unique structure will critically enhance the gas sensing properties of WO 3 ·H 2 O nanomaterials. [ABSTRACT FROM AUTHOR]

Nanomaterials with hierarchical architectures consisting of two-dimensional nanostructures have attracted considerable attention for their potential applications in recent years. In current work, flake-flower NiO architectures self-assembled by aggregative nanosheets have been successfully synthesized via the hydrothermal route. It is notable that the NiO sensors exhibit excellent gas sensing performances owing to the open and well-defined structure as well as abundant micro reaction rooms built by two-dimensional ultrathin nanosheets, which are thinner than the thickness of electron depletion layer. Moreover, a possible growth mechanism for the interactions between PVP and Ni 2+ ions in the synthesis of the precursors Ni(OH) 2 and the novel morphology evolution of the NiO nanoflowers are proposed in detail. [ABSTRACT FROM AUTHOR]

Hollow spheres are usually fabricated by hard template methods or soft template methods with soft surfactants, which is quiet tedious and time-consuming. In this paper, NiO hollow spheres with fluffy surface were successfully synthesized by a facile hydrothermal method and subsequent calcination, where bubbles acted as the template. NiO hollow spheres exhibited excellent gas sensing performances, which results from its hollow structure and high specific surface area. In addition, a possible evolution mechanism of NiO hollow spheres was proposed based on experimental results. [ABSTRACT FROM AUTHOR]

Nanorod arrays possess a large surface area due to the orderly arrangement of monomers, and thus are considered as an ideal microstructure to be utilized in the interface-related process such as the gas-sensing reaction. But their adoption is plagued by the complicated synthesis route in which the substrate is usually necessary. Here we propose a substrate-free fabrication of WO 3 nanorod arrays through the facile hydrothermal method. Subsequent measurements testify the superior NH 3 -sensing property of WO 3 nanorod arrays. The corresponding response is as high as 8.3 at a concentration of 50 ppm and a temperature of 200 °C, surpassing other WO 3 -based NH 3 sensors reported. [ABSTRACT FROM AUTHOR]

In present work, a novel coral rock-like ZnO with porous structure was successfully synthesized via a solvothermal method and subsequent calcination. We were surprise to find that such ZnO nanostructure exhibited super high gas response to ethanol, which was attributed to the novel coral rock-like structure with porous nature, leading to effective gas diffusion and sufficient surface chemical reaction during sensing measurement. [ABSTRACT FROM AUTHOR]

Novel urchinlike hexagonal WO 3 microspheres have been fabricated by a facile hydrothermal method in the presence of K 2 SO 4 . Morphology analysis reveals that the as-synthesized WO 3 microstructures are assembled by numerous one-dimensional nanorods. Based on comparative studies, a possible formation mechanism is proposed in detail. What’s more, gas-sensing measurement indicates that the well-defined urchinelike WO 3 microspheres exhibit excellent gas sensing properties. [ABSTRACT FROM AUTHOR]

Nanoneedle-assembled hierarchical and nanosheet-assembled hierarchical NiO nanoflowers were successfully synthesized via a facile hydrothermal method and subsequent calcination. And we proposed their growth mechanisms and the influences on gas-sensing properties. The results indicated that the gas sensing properties of NiO nanocrystals can be dramatically enhanced by tailoring the nanoscale building blocks. In addition, it was surprisingly noticed that the nanoneedle-assembled hierarchical NiO structures exhibited quicker gas response and recovery than the nanosheet-assembled ones. While nanosheet-assembled hierarchical NiO nanoflowers demonstrated higher gas response towards ethanol. [ABSTRACT FROM AUTHOR]

Novel sparse-type and close-type NiO nanoflowers have been controllably synthesized via hydrothermal process assisted with CTAB and SDS, respectively. The sensing performance of the close-type NiO was superior to the other, which benefits from the following factors: In the close-type nanoflower, (1) the architecture is more porous and closer; (2) more nanojunctions between adjacent nanosheets are formed; (3) abundant micro reaction rooms are assembled by nanosheets; (4) the thickness of nanosheets are much smaller than twice Debye length. [ABSTRACT FROM AUTHOR]

Monodisperse NiO hierarchical nanoflowers fabricated by nanobundles have been successfully synthesized under hydrothermal conditions followed by a calcination treatment. It is amazingly observed that the bundle-like nanoflowers possessed the emanative needle-like ends on the nanoscale, which was different from the previous 3D hierarchical architectures only fabricated by nanosheets, entire solid rod-like and emanative needle-like structures. Furthermore, based on the further experiments, the amount of ethylene glycol (EG, 99.5 wt%) play a key role on the formation of emanative needle-like ends and constructions of the 3D hierarchical flower-like architectures, and the relative formation mechanism was primarily discussed. Such an unexpected morphology may provide a non-trivial behavior driven by the properties of emanative needle-like ends and electron transformation continuity. [ABSTRACT FROM AUTHOR]

A unique nanoflower assembled from porous nanosheets was synthesized successfully via a novel one-step hydrothermal method for the first time. Namely, there was no calcination conducted on the whole preparation process, which was different from what the previous researches did. The unique architecture was characterized in detail using X-ray diffractometer, field-emission electron microscope. A possible growth mechanism was further proposed. We find that the obtained material shows a very excellent gas-sensing performance due to unique architecture with lots of pores on the petals. [ABSTRACT FROM AUTHOR]

Nanomaterials with low-dimensional architectures frequently exhibit novel functional properties. In current work, NiO nanobelts with well-defined morphologies and uniform size have been successfully synthesized via a facile hydrothermal method. Furthermore, a novel growth mechanism of NiO nanobelts has been proposed in detail. Surprisingly, it is worth mentioning that the sodium oxalate is of great benefit to the formation of NiO one-dimensional nanostructures and plays a vital role on tailoring morphologies of nanobelts on the basis of further comparative experiments. Such a synthetic way may open up an avenue to prepare some other oxides. [ABSTRACT FROM AUTHOR]

Molybdenum trioxides (MoO 3 ) with flower-like hierarchical structure and distinct nanobelts have been synthesized via a hydrothermal method. A series of comparative experiments show that cetyltrimethyl ammonium bromide (CTAB) and HNO 3 have evident impact on forming the morphologies of MoO 3 . Interestingly, the add order of CTAB and HNO 3 can be also a determinant factor in the assemble process. This research is of great significance in the preparations, characterizations and applications of various 1D and 3D semiconductor metal oxides. The possible growth mechanism is also proposed. [ABSTRACT FROM AUTHOR]

Abstract: Self-assembly of one-dimensional nanoscale building blocks into functional 2D or 3D complex superstructures has stimulated a great deal of interest. In current work, using the hydrothermal method and reagent of hexamethylenetetramine (HMT), we synthesize the SnO2 3D hierarchical nanostructures with an average diameter of 200–400nm, which exhibit flower-like architectures assembled by numerous one-dimensional tetragonal prism nanorods. Further comparative studies demonstrate that the HMT provides nucleation sites for the assembling of the nanorods, which plays a crucial role in producing such unique flower-like architectures. Meantime, a novel growth mechanism is proposed in detail. In property, the prepared SnO2 nanoflowers show excellent gas-sensing performances to ethanol of 50ppm at an optimal temperature as low as 250°C. Such unique architectures may open up an avenue to further enhance the gas-sensing performances of SnO2 nanostructures for future sensor application. [Copyright &y& Elsevier]

In this work, ZnCo 2 O 4 microrods with nanosheets on the surface were successfully synthesized on nickel foam by a simple hydrothermal process and its catalytic properties towards glucose were investigated. The results show that the as-prepared sample exhibits superior performance, which is attributed to the direct growth of active material on the substrate and the synergetic effect of zinc and cobalt. • ZnCo 2 O 4 microrods with nanosheets on the surface were successfully synthesized. • The ZnCo 2 O 4 microrods/Ni foam electrode was used to fabricate non-enzyme glucose sensor. • The as-prepared electrode exhibits excellent catalytic performance towards glucose. In this paper, ZnCo 2 O 4 microrods with nanosheets on the surface were successfully synthesized on nickel foam (NF) via a two-step process including hydrothermal reaction and subsequent calcination. The as-prepared sample was used to fabricate non-enzymatic glucose sensor which was proven to have excellent catalytic performance toward glucose in alkaline medium, such as high sensitivity (16.60 mA mM−1 cm−2), low detection limit (0.15 μM, S/N = 3) and excellent selectivity. These results suggest that ZnCo 2 O 4 microrods wrapped on nickel foam are promising electrode material for non-enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]

The unique flower-like NiO/ZnO composite with porous nanosheets was triumphantly manufactured via the one-step hydrothermal method initially. It was considered that the construction of P-N junctions at the interface as well as the sheet-like porous microflowers architecture greatly contribute to the fantastic gas sensing properties of the prepared materials. Furthermore, a possible formation mechanism was proposed. • Nanosheet-assembled porous NiO/ZnO microflowers were fabricated hydrothermally. • The NiO/ZnO composites based sensor presented superior ethanol gas response. • The sheet-like porous microflowers architecture and P-N junctions greatly contributed to gas sensing. The unique flower-like NiO/ZnO composite with porous nanosheets has been triumphantly manufactured via the one-step hydrothermal method initially. On the basis of morphology observations and ethanol gas measurements, it is considered that the construction of P-N junctions at the interface as well as the sheet-like porous microflowers architecture greatly contribute to the fantastic gas sensing properties of the prepared materials, which exhibit superb gas response value and outstanding repeatability. Furthermore, a possible formation mechanism is proposed, elucidating the process of the oriented-attachment, the self-assembly in addition to the pores-development. [ABSTRACT FROM AUTHOR]

In this work, we have triumphantly synthesized porous NiCo 2 O 4 nanowires array on nickel foam (NiCo 2 O 4 NWs/NF) via a facile hydrothermal method. The sensitivity could reach up to 5916 μA mM−1 cm−2, meanwhile, the linear range was 1 μM–3.987 mM with a low detection limit of 0.94 μM (S/N = 3). Furthermore, it displayed good selectivity. • The porous NiCo 2 O 4 nanowires were constructed on nickel foam. • The sensor showed the highest sensitivity of 5916 μA mM−1 cm−2 in a wide linear range of 0.001–3.987 mM. • The structure offers abundant transport pathways and active sites to boost the electrochemical activity. In this work, we have triumphantly synthesized porous NiCo 2 O 4 nanowires array on nickel foam (NiCo 2 O 4 NWs/NF) via a facile hydrothermal method. Benefiting from its great one-dimensional porous nanowires architecture along with synergistic interactions between NiCo 2 O 4 arrays and Ni foam, the NiCo 2 O 4 NWs/NF-based sensor exhibited enhanced glucose sensing performance. The sensitivity could reach up to 5916 μA mM−1 cm−2, meanwhile, the linear range was 1 μM–3.987 mM with a low detection limit (LOD) of 0.94 μM (S/N = 3). Furthermore, it displayed good selectivity. These results inspire that the porous NiCo 2 O 4 nanowires will be a promising candidate for non-enzymatic glucose sensors. [ABSTRACT FROM AUTHOR]

We successfully synthesized MoO 3 hierarchical structures assembled with nanofibers and nanosheets via a hydrothermal method assisted with hexadecyl trimethyl ammonium bromide (CTAB) and polyvinyl pyrrolidone (PVP), respectively. Then, we characterized the structure and morphology of the as-synthesized samples by X-ray diffraction and scanning electron microscopy. We analyzed the formation process of the two structures and verified the effects of different dimensionality assembly units on their gas-sensing properties through gas sensing experiments. Remarkably, nanosheet-assembled hierarchical MoO 3 structures, which possess abundant semi-closed microreaction spaces, exhibited an enhanced gas response. The gas response (the ratio of test voltage in the air to test voltage in the target gas) of a nanosheet-assembled MoO 3 based-sensor to 400 ppm ethanol reached 32 at an operating temperature of 300 °C. While nanofiber-assembled hierarchical structures showed a shorter response (3.2s) and recovery time (2.4s), which was due to the faster gas and electronic diffusion rate of the nanofibers. MoO 3 hierarchical structures assembled by nanofibers and nanosheets have been synthesized under hydrothermal conditions assisted with CTAB and PVP, respectively. Nanofiber-assembled hierarchical MoO 3 structures demonstrate less response and recovery time than the other. However, sensors based on nanosheet-assembled structures exhibit a higher gas response. The differences in the above properties can be attributed to their different dimensionality assembly units. Image 1 [ABSTRACT FROM AUTHOR]

Multiply networked NiO nanostructures were synthesized via a simple hydrothermal process, also, discontinuous net-like NiO structures were prepared as a comparison. The morphologies of two samples were analyzed by SEM and TEM observation. Moreover, the gas sensing results indicated that the multiple networked NiO architectures assembled by nanowires which possess continuous structure exhibit an enhanced gas-sensing performance compared to the other one, which is likely attributed to efficient transmission of carrier and abundant open diffusion channels provided by this novel structure. [ABSTRACT FROM AUTHOR]

Nanomaterials with three-dimensional architectures, frequently exhibiting novel functional properties, have attracted considerable attention of the researchers. In current work, we have successfully synthesized the NiO flower-like microspheres with abundant nanoparticles adhering to the petals via a facile hydrothermal method. Interestingly, it is found that the excellent gas sensing properties of the samples towards ethanol are likely attributed to the well-aligned porous architectures as well as great amounts of nanoparticles adhering to the petals, considered as active sites. Meanwhile, we also elaborated a distinctive growth mechanism of such a unique architecture and a plausible gas sensing mechanism, respectively. [ABSTRACT FROM AUTHOR]

We report the successful synthesis of novel Sn 2 O 3 with hierarchical 3D nanostructures via a facile hydrothermal method for the first time. The as-prepared Sn 2 O 3 products transform into SnO 2 after calcinations (800 °C) and a simultaneous TGA and DSC analysis of the as-prepared Sn 2 O 3 sample determines that the main increment of mass takes place in the temperature range 534–800 °C. The well-defined nanostructures are composed of thin nanosheets. The growth mechanisms are also discussed by observing the morphology revolution at various reaction times. Furthermore, the oxidation states of the Sn 2 O 3 hierarchical nanostructures are confirmed by the shape analysis of corresponding XPS O 1 s and Sn 3 d peaks using the decomposition procedure. [ABSTRACT FROM AUTHOR]

Abstract: New morphologies often play a critical role in governing properties of nano-materials. Here, using hydrothermal method and reagents of sodium citrate and polyethylene glycol (PEG), we synthesize the ZnO nano-crystals and find that they exhibit hierarchical flower-like architectures assembled by nanosheets. Further comparative studies demonstrate that the sodium citrate assists a uniform growth of the nanosheets, and the PEG provides nucleation sites for the assembling of the nanosheets, both of which play a critical role in producing such unique flower-like architectures. Consequently, this sample is found to show excellent sensing performances to the target ethanol owing to its largest amount of petals, intervals, and pores. Such an unexpected morphology holds substantial promise for rendering ZnO as a potential gas-sensing material for a broad range of future sensor applications. [Copyright &y& Elsevier]

Cu 2 O microspheres with hollow and solid features were successfully prepared via a convenient liquid phase reducing method. Interestingly, we found that the discrepancy in morphology arose from a simply changing on the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 with other conditions unchanged. Based on experimental results, the feasible formation mechanisms of both morphologies were deduced, where the relative concentration of SDS and CuCl 2 was a crucial factor that effect the resultant morphologies. In comparison with the solid microspheres, the hollow Cu 2 O exhibited superior gas sensing performance. The significant performance might ascribe to its unique hollow structure, contributing to plenty of active sites existed on both the inner and outer surface and unrestricted gas diffusion in the hollow microspheres. In this work, hollow and solid cuprous oxide microspheres were successfully synthesized by liquid phase reducing method and the gas sensing performance of the samples was investigated. In addition, we also explore the effect of the adding sequence of aqueous sodium dodecyl sulfate (SDS) and CuCl 2 on the resultant morphologies of Cu 2 O and propose the growth formation mechanism. Image 1 • Cu 2 O microspheres with hollow and solid features were successfully prepared. • The hollow structure exhibited superior gas sensing performance than the solid microspheres. • The adding sequence played a vital role on the morphology of materials. [ABSTRACT FROM AUTHOR]

Graphical abstract A novel porous NiO nanosheet was synthesized by a one-step hydrothermal route and the gas sensor based on the porous nanosheet exhibits excellent gas response to hydrogen. We proposed a plausible mechanism of the sensing process and found that the porous structure improved the gas sensing performance with abundant gas channels and larger surface areas. Highlights • A novel porous NiO nanosheet was synthesized by a one-step hydrothermal route. • The gas sensor based on the porous nanosheet shows excellent response to hydrogen. • The plausible mechanism involved in enhancing the gas sensing performances was discussed. Abstract In this work, we reported the successful synthesis of a novel two-dimensional porous NiO nanosheet via a one-step hydrothermal route and subsequent calcination. It was surprise found that such NiO nanosheet exhibits a superior gas response towards H 2. The enhanced sensing ability may be benefited from the porous nanostructure, resulting in more sufficient pathways for gas diffusion and larger surface for chemical reaction. We hoped our findings could be in favor of further investigations on the fabrication of perfect two dimensional architectures. [ABSTRACT FROM AUTHOR]

Graphical abstract The flower-like hollow CeO 2 spheres decorated MnO 2 composite was successfully prepared by a simple two-step hydrothermal process. When utilized for oxygen reduction reaction (ORR), such electrocatalyst exhibit the highly efficient catalytic activity for ORR than that of flower-like MnO 2 and hollow CeO 2 spheres monomers, which may be attributed to the enhanced mechanism arising from the hierarchical architecture as well as the synergetic effect of the MnO 2 and CeO 2. Highlights • A flower-like hollow CeO 2 spheres decorated MnO 2 composite was synthesized hydrothermally. • The CeO 2 /MnO 2 composite possessed excellent electrocatalytic activities. • The synergistic effect between CeO 2 and MnO 2 plays a vital role in the ORR. Abstract Herein, novel multiple hollow CeO 2 spheres decorated nanosheet-assembled MnO 2 microflower as an electrocatalyst towards oxygen reduction reaction (ORR) was successfully synthesized through a two-step hydrothermal approach. It is surprising to find that this composite with unique architecture exhibits a superior ORR catalytic activity than that of flower-like MnO 2 and hollow CeO 2 spheres monomers. The ORR catalytic activity is also comparable to that of 20 wt% Pt/C. The excellent electrocatalytic performance for ORR attributes to the synergistic effect between the hollow CeO 2 spheres and hierarchical nanosheet-assembled MnO 2. [ABSTRACT FROM AUTHOR]

Novel urchin-like SnO 2 nanostructures were prepared by a facile hydrothermal process. The well-defined nanostructures were composed of numerous one-dimensional nanowires with a diameter of ∼8–10 nm. Based on comparative studies, a possible formation mechanism was proposed in detail. It was believed that the nucleation was initiated by formation of ZnSn(OH) 6 . Furthermore, gas-sensing measurement indicated that the urchin-like SnO 2 nanoflowers showed excellent gas-sensing properties. [ABSTRACT FROM AUTHOR]

Abstract: Uniform hexagonal NiO nanosheets were perfectly prepared by a controlled hydrothermal method followed by calcination. The as-prepared products were characterized by X-ray powder diffraction (XRD), which illustrated the precursor Ni(OH)2 and the final product NiO. The morphologies of NiO were characterized in detail by field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HRTEM). The SAED pattern is detected from a sampling area covering a collection of constituent nanoparticles. Based on the experimental results and the crystal structure theory, the chemical reaction processes and the growth mechanism for hexagonal structure were proposed. In addition, the gas-sensing performances of uniform hexagonal NiO were investigated toward 50ppm of several reductive gases including ethanol, CO, H2S, CH4 and NH3 at different working temperatures. [Copyright &y& Elsevier]

• The hierarchical WO 3 /NiO porous microsphere and rough microsphere were synthesized via hydrothermal process. • The gas sensor based on the porous microsphere shows more excellent performances to ethanol. • The possible mechanism involved in enhancing the gas sensing performances was discussed in detail. Two novel hierarchical WO 3 /NiO microspheres with porous and rough surface have been prepared through a simple one-stop hydrothermal method. Interestingly, it is a surprise that the introduction of different amounts of WO 3 plays a critical role in the growth and self-assembly of nanosheets and then the morphology of microsphere. Further gas sensing experiment demonstrates that the sensor based on porous microsphere possesses prominent performance towards 100 ppm ethanol at the optimal working temperature of 300 °C compared with that of rough microsphere. It is believed that the enhanced gas sensing properties benefit from the porous structure on the surface with abundant active sites and gas passages for sufficient gas adsorption and diffusion. [ABSTRACT FROM AUTHOR]

The two-dimensional (2D) honeycomb-like nanoplates assembled by nanosheet arrays were synthesized using one-step hydrothermal method and the growth mechanism of this nanostructure was proposed. The sensor based on as-prepared NiO exhibits superior gas-sensing properties to CO. The results verified that the hollow structure of 2D nanoplates could enhance the gas sensing performance by providing sufficient gas diffusion pathways and reaction sites in the gas-sensitive process. • The novel 2D honeycomb-like NiO nanoplates assembled by nanosheet arrays were synthesize. • The possible growth mechanism of the honeycomb-like NiO nanoplates was discussed in detail. • The effect of hollow 2D honeycomb-like nanostructure on gas-sensing properties of NiO nanoplates was discussed. Herein, we successfully prepared the Nickel oxide (NiO) nanomaterials with the structure of two-dimensional (2D) honeycomb-like nanoplates assembled by nanosheet arrays through the hydrothermal synthesis. In addition, the growth mechanism of this unusual nanostructure was proposed. Surprisingly, such NiO nanoplates exhibits superior gas-sensing properties to CO, which is mainly attributed to the hollow structure produced by the arrangement of nanosheets, contributing not only enough gases diffusion pathways but sufficient reaction sites during the gas sensing processes. [ABSTRACT FROM AUTHOR]