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We successfully synthesized three kinds of NiO microspheres with solid, porous and hollow nanostructure via one-step hydrothermal method. The results indicated that the gas sensing performances of the porous sphere and hollow sphere are better than that of the solid sphere, which was attributed to the high specific surface area and the small size of Debye length. We find that the ethanol molecules can enter the interior of the NiO hollow sphere to have completed gas-sensing reactions because of enough response time, which lead to abundant effective gas diffusion and sufficient contact between with NiO, and it means more atoms can directly react with the gas to increase sensitivity. In this way, this article provides some suggestions and ideas for the development of gas sensor in the future. [ABSTRACT FROM AUTHOR]

We report a preparation of titanium dioxide regular nano-polyhedron with reactive (001) facets by simple yet efficient hydrothermal synthesis process. It has been found that the (001) surfaces are terminated with F atoms, and the F-terminated surfaces, which reduce the surface energy of anatase titanium dioxide, provide a stable condition for the existence of (001) facets. Ni doping, additionally, restrict the growth of particle, making the morphology of anatase titanium dioxide regular plus uniform. Besides, the as prepared titanium dioxide with high reactive (001) facets exhibit far better gas sensing performance over ethanol than those mainly having exposed (101) facets. Such a facile method and interpretation mechanisms could be applicable to many other nanomaterials for a wide range of study. [ABSTRACT FROM AUTHOR]

The assembly design of nanostructures has taken a dominated position in improving gas sensing properties. In our work, multi-hierarchical (nanoneedles assembled and nanosheets assembled) SnO nanostructures with size-controllable blocking units were synthesized via facile hydrothermal method. As is recorded, the addition of PVP led to the transformation from nanoneedles assembled nanostructures into nanosheets assembled nanostructures, which can be ascribed to linear molecule structures. While the sizes of the blocking units can be controlled by the temperature due to the Ostwald ripening. And seeing from the gas sensing measurement, the thinner ones had higher gas response and quicker gas response and recovery judging from the sizes of blocking units, at the same time, nanoneedles assembled hierarchical structures possessed higher gas response while nanosheets assembled hierarchical structures had shorter gas response and recovery time. [ABSTRACT FROM AUTHOR]

Monodisperse NiO with hierarchical nanostructures has been successfully synthesized via a surfactant-assisted hydrothermal process followed by subsequent calcination treatment. It is notable that the NiO nanoflowers are self-assembled by abundant ultrathin nanosheets, and polyvinylpyrrolidone (PVP) plays a key role on the constructions of flower-like architectures. In addition, gas sensors based on NiO nanoflowers were developed and demonstrated outstanding functionalities, owing to the open and well-defined structure as well as abundant micro reaction rooms built by nanosheets. Moreover, a feasible formation mechanism was put forward in detail to illuminate the morphology evolution and the interactions between PVP and Ni ions. [ABSTRACT FROM AUTHOR]

ZnO nanostructures with four different morphologies (nanoparticles, nanorods, mixtures of nanoparticles and nanorods as well as nanoflowers aggregated by nanoparticles and nanorods) were synthesized successfully via simple hydrothermal method. The crystalline structures of ZnO samples were characterized by the X-ray diffraction and the microscopic morphologies of ZnO samples were observed by the scanning electron microscopy. Besides, the probable growth mechanisms of ZnO nanostructures with four different morphologies were proposed. We found that Hexamethylenetetramine (HMT), the halogen ion F and the concentration of OH played a significant role in the morphology of ZnO nanocrystalline. In addition, further gas sensitivity measurements revealed that all the as-synthesized ZnO performed gas-sensing properties towards the ethanol gas with very low concentration. Furthermore, the gas-sensing properties of nanoflowers were much more excellent than the other three low-dimension nanostructures, which indicated that the splendid gas-sensing properties of ZnO nanoflowers were contributed to their large specific area. [ABSTRACT FROM AUTHOR]

We report the microstructures and gas-sensing properties of various low dimensional nano-TiO prepared by hydrothermal method. In particular, we make a comparison of the ethanol sensing properties among TiO nanospheres, nanorods, nanobelts. The obtained nanobelts TiO is found to show best sensing performances owing to the largest surface area and porous structure providing many quick passages to absorb and desorb gas, suggesting that the gas sensing properties of nanocrystals can be significantly improved by tailoring the shapes and morphologies of nanocrystals. [ABSTRACT FROM AUTHOR]

Morphologies frequently play a critical role in determining the properties of nanomaterials. In current researches, we successfully synthesized varieties of SnO nanostructures from 1D to 3D via a facile hydrothermal method. The as-obtained samples were characterized by X-ray diffraction and scanning electron microscopy. Then the plausible growth mechanism are proposed in detail. Furthermore, PEG and CO(NH) may have an effect on the formation of 1D and 2D nanostructures of SnO as aggregation and template, respectively. The gas sensing properties of SnO nanostructures from 1D to 3D toward ethanol were investigated. Surprisingly, we noticed that SnO nanosheets show the highest gas sensing response while the nanospheres is opposite, which provided a substantial promising candidate of gas sensors and further indicated that gas sensing properties can be enhanced by tailoring the morphologies of nanomaterials in practical application. [ABSTRACT FROM AUTHOR]

Flower-like ZnO microstrucutures (ZMFs) self-assembled by nanosheets were fabricated by a simple template-free hydrothermal method, and the nanosheets were observed with a great many of mesopores. Without adding NaOH, sphere-like ZnO microstrucutures (ZMSs) which were covered by nanosheets were obtained. Subsequently, according to the characterization of SEM and TEM for ZMFs nanosheets, the possible formation mechanisms and simulation of ZMFs were discussed. The novel ZMFs presented numerous mesopores of size around 6 nm and high BET specific area (about 36.886 m/g) which contributed to its high gas-sensing performance. In comparison with the ZMSs-based sensor, the ZMFs-based sensor displayed excellent gas-sensing performance to the ethanol gas with high sensitivity of nearly 35 at the concentration of 250 ppm. [ABSTRACT FROM AUTHOR]

ZnO nanodisks exhibiting regular hexagonal structures were successfully synthesized using two surfactants via a hydrothermal method. The surfactants, namely, cetyltrimethylammonium bromide and sodium dodecyl sulfate, had vital functions in the formation of nanodisk structures. The fabricated ZnO nanodisk-based sensor was exposed to reductive gases. The performance of the developed gas sensor to formaldehyde was superior than that to ethanol. The highest sensitivity values for formaldehyde and ethanol (150 ppm) were 81.6 and 43.2, respectively, at an optimal temperature of 300 °C. [ABSTRACT FROM AUTHOR]

We report the microstructures and gas sensing properties of two novel SnO nanorods prepared by hydrothermal method with the utilizing of cetyltrimethylammonium bromide and polyethylene glycol. The structures and morphologies of the dense and porous nanorods were characterized by means of powder X-ray diffraction and scanning electron microscopy. The gas sensing performances towards ethanol of the two samples were investigated. The results show that the porous SnO nanorods display excellent gas response to ethanol, indicating SnO as a potential gas sensing material for broad applications. [ABSTRACT FROM AUTHOR]

Materials with porous and hierarchical structures are of great interest for potential use in energy and environmental applications. Here, we fabricate the WO microspheres which consist of the nanosheets by using a simple hydrothermal process. The likely formation mechanism of the porous microspheres is proposed based on the time-dependent experiments. As a consequence of the unique hierarchical and porous architecture, the microspheres show excellent gas sensing properties due to their large amount of petals and pores, which benefited for the gas diffusion. [ABSTRACT FROM AUTHOR]

We have successfully reported a new diamond-like morphology of zinc oxide (ZnO) structures via a simple hydrothermal method and discussed its probable growth mechanism. Compared with other morphologies of ZnO structures (microrods and nanosheets), nanodiamonds have excellent gas-sensing property owning to its large specific surface area, holding the perfect promise for ZnO powders as underlying gas-sensing materials. Furthermore, the as-prepared nanosheets assisted with the sodium citrate as an additive were found to show better gas-sensing property due to the smaller size than microrods. We found the positive role of the sodium citrate and reaction time in the growth of nanosheets and nanodiamonds respectively and the corresponding influences on growth mechanism were discussed. [ABSTRACT FROM AUTHOR]

Porous architectures consisting of three-dimensional nanostructures are of great interest for potential applied in gas-sensing. Herein, novel net-like MoO porous architectures were successfully synthesized via a facile hydrothermal method. The as-prepared MoO porous architectures were in fact assembled by numerous nanorods to form a net. The results found that the existence of chromic chloride hexahydrate played a significant role in governing morphologies of MoO during hydrothermal process. Based on comparative studies, a possible formation mechanism was also proposed in detail. Further, gas-sensing measurement showed that the well-defined net like MoO porous architectures exhibited the excellent gas sensing properties. [ABSTRACT FROM AUTHOR]

In this work, 2D SnO nanosheets were synthesized via a polyvinylpyrrolidone (PVP)-assisted hydrothermal method. X-ray diffraction and scanning electron microscopy were used to examine the chemical composition and nanostructures. It was found that the concentration of PVP played a critical role in governing the assembly process of nanostructures. Further, their gas-sensing performances were investigated comprehensively. The nanosheet-III structures were found to show the most superior gas-sensing properties due to their largest specific surface and fashionable assembly. [ABSTRACT FROM AUTHOR]

Different morphologies of 3D SnO nanostructures, including sphere-like, net-like, and flower-like, have been successfully synthesised via a facile hydrothermal method. The products were characterized by X-ray diffraction and scanning electron microscopy. The possible growth mechanism of different SnO nanostructures was discussed in detail. We found that the citric acid and PEG play significant roles in synthesizing the flower-like and net-like nanostructures. Furthermore, the gas-sensing properties of the samples were investigated towards the reducing ethanol gas. The results indicate that the flower-like and net-like SnO show larger gas sensing properties than sphere-like SnO. [ABSTRACT FROM AUTHOR]

Gas-sensing performances can often be enhanced significantly once the size of sensing nanomaterials approaches a critical value of 15 nm. Here, we synthesize, by a simple hydrothermal method accompanied by the calcination process, ultrathin ZnO nanosheets with a thickness as thin as 10-13 nm. We find that the prepared zinc hydroxide carbonate precursor is largely agglomerated, yet transformed to the ultrathin ZnO nanosheets in a dispersive fashion after the calcination process. The as-prepared ultrathin nanosheets exhibit excellent gas-sensing functions to ethanol gas at the optimal temperature as low as 300 °C under the concentration of 50 ppm, rendering them a promising sensing material for the on-site detection of ethanol. [ABSTRACT FROM AUTHOR]