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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]

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]

Monodisperse hexagonal tungsten oxide (h-WO 3 ) nanowires were novelly prepared on a large scale by the hydrothermal method with the assistance of K 2 SO 4 and Na 2 SO 4 . The morphologies and structures of the nanowires were characterized by X-ray diffraction (XRD), focused ion beam scanning electron microscopy (FIB-SEM) and high-resolution transmission electron microscopy (TEM). These nanowires with a diameter of 80 nm and high crystallinity are especially bundles-like structure, which are growth from primary particles with same growth direction of [001] and the exposure to 〈200〉 facets. These primary nanoparticles are believed to have a crystal structure of hexagonal prism morphology. Based on the TEM characterizations and crystal structure analyses, the morphology evolvement and is given and the growth mechanism is discussed. This research is potentially applied to controlled synthesis 1D semiconductor oxides through hydrothermal route. [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]

Abstract: Materials with hierarchical architectures often exhibit novel functional properties. In this paper, the hierarchical SnO2 flower-like architecture, consisting of numerous aggregative nanosheets was successfully synthesized via a facile hydrothermal method and subsequent calcination. The structures and morphologies of this hierarchical architecture were characterized in detail by means of powder X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). Further comparative experiments show that the sodium citrate was benefit to promote the growth of SnO2 nanosheets and accelerate the assembling of nanosheets into flower-like architecture, the PEG provided nucleation sites and made the nanoflowers grow uniformly and separated. Moreover, a possible growth mechanism of the flower-like architectures was proposed. The non-trivial behavior of flower-like SnO2 may be driven by the properties of grain boundaries. [Copyright &y& Elsevier]

Monodisperse WO3·H2O square nanoplates were obtained under hydrothermal conditions with the assistance of malic acid. The morphologies and structures of the plates are characterized by the analyses of XRD, SEM and TEM. In addition, the growth mechanism of the plate-like tungsten oxides has been primarily discussed and the schematic model and crystal structure have been given out. These WO3·H2O nanoplates are revealed as orthorhombic crystal structure with exposure (010) facet. It is proved that malic acid will preferable absorb on the (010) facets during the crystal growth, leading to the growth along the crystal direction [100] and [001], and further determining the formation of plate-like WO3·H2O. This research is of great significance in the preparations, characterizations and applications of various 2D semiconductor metal oxides. [ABSTRACT FROM AUTHOR]

Multi-layered ZnO circular nanodisks were efficiently fabricated using sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) polymer by a controlled hydrothermal method. As-prepared ZnO nanostructures were characterized by X-ray powder diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy. The effect of SDS and PVP polymer on the formation of ZnO multi-layer nanostructures was described in detail. Based on experimental results, a possible mechanism of circular disk formation was proposed. The gas-sensing properties of multi-layered nanodisks were reported for formaldehyde under different concentrations from 5 to 1200 ppm at 300 °C. A higher response toward formaldehyde was observed, rendering the multi-layered nanostructures a promising gas-sensing material for the on-site detection of formaldehyde. [ABSTRACT FROM AUTHOR]

In this article, a sealed nanotube of ZnO was successfully obtained by a simple hydrothermal technique, which employed Hexamethylene tetramine (HMT) and Fluorinion (F−) as the active agents. The rod-like nanotubes structures were observed through field-emission scanning electron microscopy. The high-resolution transmission electron microscope exhibited a shell-enclosed nanotube structures. On the basis of experimental observations, including temperature, pH of the solution and acting agents, a growth mechanism was proposed. The as-prepared nanostructures showed excellent gas sensitivities to different gases (ethanol, ammonia gas, formaldehyde gas) with a quite low concentration respectively. [ABSTRACT FROM AUTHOR]

Abstract: Hexagonal ZnO nanocones were successfully prepared using a controlled hydrothermal method with the assistance of double anionic surfactants. The products were characterized using X-ray powder diffraction. The morphologies of ZnO nanostructures were characterized using field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The effects of the addition of one anionic to another anionic reagent in the crystal structure formation were discussed in detail. The gas sensing properties were measured for formaldehyde. [Copyright &y& Elsevier]