Juan Yang

Chemical synthesis, characterisation and gas sensing performance of copper oxide nanoribbons

Single crystalline copper oxide nanoribbons were synthesized via a surfactant-assisted hydrothermal route. The resulting CuO nanoribbons contain substantial amounts of nanorings and nanoloops. High resolution TEM analysis identified CuO nanoribbons growing along the [010] direction. CuO nanoribbons exhibited excellent sensing performance towards formaldehyde and ethanol vapours with rapid response and high sensitivity at low operating temperatures. We found that the loading of a small amount of Au or Pt nanoparticles on the surface of CuO nanoribbons can effectively enhance and functionalize the gas sensing performance of CuO nanoribbons.

Flutelike Porous Hematite Nanorods and Branched Nanostructures: Synthesis, Characterisation and Application for Gas-Sensing

Flute-like porous alpha-Fe2O3 nanorods and branched nanostructures such as pentapods and hexapods were prepared through dehydration and recrystallisation of hydrothermally synthesised beta-FeOOH precursor. Transmission electron microscopy (TEM), high-resolution TEM and selected area electron diffraction analyses reveal that the nanorods, which grow along the [110] direction, have nearly hollow cavities and porous walls with a pore size of 20-50 nm. The hexapods have six symmetric arms with a diameter of 60-80 nm and length of 400-900 nm. The growth direction of the arms in the hexapod-like nanostructure is also along the [110] direction, and there is a dihedral angle of 69.5 degrees between adjacent arms. These unique iron oxide nanostructures offer the first opportunity to investigate their magnetic and gas sensing properties. The nanostructures exhibited unusual magnetic behaviour, with two different Morin temperatures under field-cooled and zero-field-cooled conditions, owing to their shape anisotropy and magnetocrystalline anisotropy. Furthermore, the alpha-Fe2O3 nanostructures show much better sensing performance towards ethanol than that of the previously reported polycrystalline nanotubes. In addition, the alpha-Fe2O3 nanostructure based sensor can selectively detect formaldehyde and acetic acid among other toxic, corrosive and irritant vapours at a low working temperature with rapid response, high sensitivity and good stability.

Monodisperse hematite porous nanospheres: Synthesis, characterization, and applications for gas sensors

Monodisperse α-Fe(2)O(3) porous nanospheres with uniform shape and size have been synthesized via a facile template-free route. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and Raman spectroscopy were employed to characterize the product, showing the high quality of the as-prepared α-Fe(2)O(3) porous nanospheres. Furthermore, the α-Fe(2)O(3) porous nanospheres can selectively detect ethanol, formaldehyde and acetic acid, with a rapid response and high sensitivity, from a series of flammable and toxic/corrosive gases, indicating their potential applications for high sensitivity gas sensors.

In situ growth of FeNi alloy nanoflowers on reduced graphene oxide nanosheets and their magnetic properties

FeNi alloy nanoflowers were evenly grown on reduced graphene oxide (RGO) nanosheets by the reduction of Fe2+ and Ni2+ with hydrazine in an ethylene glycol (EG) dispersion of graphene oxide (GO), and the as-synthesized products were characterized by powder X-ray diffraction (XRD), Raman spectra, energy dispersive X-ray spectroscopy (EDS), inductively coupled plasma optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). It was revealed that the morphology, size and composition of the FeNi alloy nanoparticles on the RGO nanosheets can be well controlled by adjusting synthesis parameters such as the concentration and the molar ratio of the metal ions. Through directed-flow assembly of the obtained composite materials, RGO-based magnetic papers were obtained. The RGO-FeNi alloy composites had soft magnetic characteristics and showed interesting morphology and composition dependent magnetic properties.

Facile synthesis of magnetically separable reduced graphene oxide/magnetite/silver nanocomposites with enhanced catalytic activity

In this study, the combination of magnetite (Fe3O4) with reduced graphene oxide (RGO) generates a new hybrid substrate for the dispersion of noble metal nanoparticles. Well-dispersed silver (Ag) nanoparticles loaded on the surface of Fe3O4 modified RGO are achieved by an efficient two-step approach. Through reducing Ag(+) ions, highly dispersed Ag nanoparticles are in-situ formed on the RGO/Fe3O4 substrate. It is found that the existence of Fe3O4 nanocrystals can significantly improve the dispersity and decrease the particle size of the in-situ formed Ag nanoparticles. Magnetic study reveals that the as-prepared RGO/Fe3O4/Ag ternary nanocomposites display room-temperature superparamagnetic behavior. The catalytic properties of the RGO/Fe3O4/Ag ternary nanocomposites were evaluated with the reduction of 4-nitrophenol into 4-aminophenol as a model reaction. The as-synthesized RGO/Fe3O4/Ag ternary catalysts exhibit excellent catalytic stability and much higher catalytic activity than the corresponding RGO/Ag catalyst. Moreover, the RGO/Fe3O4/Ag catalysts can be easily magnetically separated for reuse. This study further demonstrates that nanoparticles modified graphene can act as an effective hybrid substrate for the synthesis of multi-component and multifunctional graphene-based composites.

Preparation of Negative Thermal Expansion ZrW2O8 Powders and Its Application in Polyimide/ZrW2O8 Composites

Negative thermal expansion (NTE) ZrW 2 O 8 powders were prepared by step-by-step solid-state reaction with ZrO 2 and WO 3 powders. The coefficient of thermal expansion (CTE) of the as-prepared ZrW 2 O 8 was around −5.08×10 −6 K −1 at 20–700°C. Different amounts of ZrW 2 O 8 powders were added in BTDA-ODA polyamic acid to form polyimide/ZrW 2 O 8 composites (PI/ZrW 2 O 8 ). With the increment of ZrW 2 O 8 , experimental results show that ZrW 2 O 8 powders can significantly enhance the thermal stability of the composites, and reduce the thermal expansion. A 50 wt pct ZrW 2 O 8 addition can give rise to a 31% reduction of CTE. It is suggested that the PI/ZrW 2 O 8 composites have potential applications in high performance microelectronic devices.

Scalable colloidal synthesis of uniform Bi2S3 nanorods as sensitive materials for visible-light photodetectors

A facile colloidal chemistry method is reported for synthesis of uniform Bi2S3 nanorods in a mixed solution of oleylamine with other organic amines including n-dodecylamine (C12), n-octylamine (C8), and n-hexylamine (C6). The nanorod length can be tuned through the carbon-chain length of these amines and importantly multigrams of Bi2S3 nanorods can be readily synthesized in a single scaled-up batch. Current–voltage (I–V) measurements showed that the Bi2S3 nanorods, obtained from both the small and large-scale batches or ones with different chain-length amines, exhibit fast light response characteristics (at the sub-second scale) with an obviously enhanced photocurrent (or photoconductivity) under broad-spectrum white light or monochromatic visible light of different wavelengths. The as-obtained nanorods, as determined by time-dependent current (I–t) curves, also exhibit excellent photoresponsive stability and reproducibility with the on–off switch of light. The photoconductivity enhancement in the Bi2S3 nanorods is assigned to the efficient electron–hole pair separation due to a hole-trapping mechanism. These results indicate the promising potential of Bi2S3 nanorods for optoelectronic device applications including photodetection (sensing), optical switch, photocatalysis, and photovoltaics within the visible spectrum range.

Facile synthesis and enhanced catalytic performance of reduced graphene oxide decorated with hexagonal structure Ni nanoparticles

In this study, reduced graphene oxide (RGO) supported Ni nanoparticles were synthesized by a facile in-situ refluxing approach using triethylene glycol as both reductive and dispersing agent. The as-synthesized RGO/Ni nanocomposites were characterized by X-ray diffraction, Raman spectroscopy and transmission electron microscopy, which revealed that Ni nanoparticles with hexagonal close-packed structure were homogeneously dispersed on the surface of RGO sheets. The catalytic activity and electrochemical properties of the RGO/Ni nanocomposites were investigated. It is found that the RGO/Ni nanocomposites exhibit markedly enhanced catalytic activity toward the reduction of p-nitrophenol by NaBH4, which is comparable to noble metal catalyst. The RGO/Ni nanocomposites also exhibited excellent electrocatalytic response to glucose. The linear range, detection limit and sensitivity were estimated to be 0.01-3.0mM (R2=0.997), 2.8μM and 535.258μAmM-1cm-2, respectively. It is expected that this facile method presented here could be extended to synthesize other RGO/metal nanocomposites with various functions.

THERMAL EXPANSION OF ZrO2-ZrW2O8 COMPOSITES PREPARED USING CO-PRECIPITATION ROUTE

In this work, a series of ZrO2/ZrW2O8 ceramic composites with different amounts of ZrW2O8 were successfully prepared by calcining the precursors synthesized using co-precipitation route at 1150°C for 3 h. The X-ray diffraction (XRD) data confirmed that the composites only consisted of α-ZrW2O8 phase and m-ZrO2 phase. The scanning electron microscopy (SEM) analysis of the synthesized ZrO2/ZrW2O8 composites showed that the specimens had good mixed-uniformities. In addition, the thermal expansion coefficients of the composites decreased with increased amounts of negative thermal expansion ZrW2O8, specimen with 26wt% ZrW2O8 shows almost zero thermal expansion and its average thermal expansion coefficient is -0.5897×10-6K-1 in the temperature range from 30°C to 600°C.

Preparation and Negative Thermal Expansion Property of ZrWMoO8

Negative thermal expansion (NTE) material ZrWMoO8 was prepared by hydrothermal method. The phase structure and morphology of the obtained precursor and final product were examined by XRD and SEM, respectively. To study its negative thermal expansion property, two methods were utilized. One is based on the in-situ XRD results and the thermal expansion coefficient (CTE) was calculated by the cell parameters obtained at different temperatures. Another is based on the thermo-mechanical analysis (TMA) and the CTE was calculated by the length of ZrWMoO8 bar at different temperatures. The differences between these two methods were also discussed.