Guoxing Zhu

Reduced graphene oxide/nickel nanocomposites: facile synthesis, magnetic and catalytic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered a low cost alternative to carbon nanotubes in nanocomposites. In this paper, we demonstrate a facile in situreduction approach for the synthesis of reduced graphene oxide/Ni (RGO/Ni) nanocomposites with different morphologies. The concentration of nickel ions has a great influence on the morphology of the RGO/Ni nanocomposites and an interesting RGO-wrapped nanostructure was obtained. Magnetic studies reveal a room-temperature ferromagnetic behavior of the RGO/Ni nanocomposites. The catalytic activities of the RGO/Ni nanocomposites were investigated for the reduction of p-nitrophenol by NaBH4. It was found that the nanocomposites show higher catalytic activity compared with the unsupported Ni nanoparticles. The catalytic performance of the RGO/Ni nanocomposites was even better than the RANEY® Ni catalyst. Moreover, after completion of the reaction the nanocomposite catalyst can be easily re-collected from the reaction system by a magnet. Thus, the RGO/Ni nanocomposites obtained in this work may find applications in catalysis, data storage, targeted drug transportation and magnetic resonance imaging technologies.

Facile Fabrication and Enhanced Sensing Properties of Hierarchically Porous CuO Architectures

Hierarchically porous CuO architectures were successfully fabricated via copper basic carbonate precursor obtained with a facile hydrothermal route. The shape of the precursor is preserved after its conversion to porous CuO architectures by calcination. The obtained CuO are systemically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N(2) adsorption-desorption analysis. The results reveal that hierarchical CuO microspheres are monoclinic structure and are assembled by porous single-crystal sub-microplatelets. The Brunauer-Emmett-Teller N(2) adsorption-desorption analysis indicates that the obtained CuO has a surface area of 12.0 m(2)/g with pore size of around 30 nm. The gas sensing performance of the as-prepared hierarchical CuO microspheres were investigated towards a series of typical organic solvents and fuels. They exhibit higher sensing response than that of commercial CuO powder. Their sensing properties can be further improved by loading of Ag nanoparticles on them, suggesting their potential applications in gas sensors.

Synthesis of reduced graphene oxide/CeO2 nanocomposites and their photocatalytic properties

With a unique structure and extraordinary properties, graphene has attracted tremendous attention in the preparation of graphene-based composites for various applications. In this study, two different strategies, including in situ growth and a self-assembly approach, have been developed to load CeO2 nanoparticles onto reduced graphene oxide (RGO) nanosheets. The microstructure and morphology of the as-synthesized RGO/CeO2 nanocomposites were investigated by x-ray diffraction, Raman spectroscopy and transmission electron microscopy. The results reveal that CeO2 nanoparticles with well-controlled size and a uniform distribution on RGO sheets with tunable density can be achieved through the self-assembly approach. The significantly enhanced photocatalytic activity of the RGO/CeO2 nanocomposites in comparison with bare CeO2 nanoparticles was revealed by the degradation of methylene blue under simulated sunlight irradiation, which can be attributed to the improved separation of electron-hole pairs and enhanced adsorption performance due to the presence of RGO. A suitable loading content of CeO2 on RGO was found to be crucial for optimizing the photocatalytic activity of the nanocomposites. It is expected that this convenient assembly approach with high controllability can be extended to the attachment of other functional nanoparticles to RGO sheets, and the resultant RGO-supported highly dispersed nanoparticles are attractive for catalysis, sensing and power source applications.

In situ Growth of NixCo100–x Nanoparticles on Reduced Graphene Oxide Nanosheets and Their Magnetic and Catalytic Properties

Ni(x)Co(100-x) (x = 0, 25, 50, 75, and 100) nanoparticles were uniformly in situ grown on reduced graphene oxide (RGO) nanosheets by a coreduction process for the first time. The as-synthesized products were characterized by X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometry (ICP-OES), and transmission electron microscopy (TEM). It was found that RGO nanosheets can effectively prevent the aggregation of Ni(x)Co(100-x) nanoparticles. The size and morphology of the Ni(x)Co(100-x) nanoparticles on RGO nanosheets can be slightly adjusted by changing the Ni:Co atomic ratio. The magnetic properties of the RGO-Ni(x)Co(100-x) composites were investigated at 300 and 1.8 K, respectively. The results reveal that the composites have ferromagnetic characteristics and show composition dependent magnetic properties. In addition, these RGO-Ni(x)Co(100-x) nanocomposites also exhibit enhanced catalytic activities toward the reduction of 4-nitrophenol (4-NP) by NaBH(4) as compared with bare Ni(x)Co(100-x) alloy, and the RGO-Ni(25)Co(75) shows the highest catalytic activity among the obtained nanocomposites. This general and facile coreduction route can be extended to synthesize other alloy nanostructures on RGO nanosheets with various morphologies and functions, and provides a new opportunity for the application of graphene-based materials.

Hierarchical NiO hollow microspheres assembled from nanosheet-stacked nanoparticles and their application in a gas sensor

A facile and robust route for the mass preparation of hollow NiO microspheres assembled from nanosheet-stacked nanoparticles is developed. The Ni(HCO3)2 precursor with a hollow spherical structure was firstly prepared by a hydrothermal reaction without any surfactants or organic additives. The reaction generated gas bubble may act as a template for the formation of Ni(HCO3)2 hollow microspheres. These are converted into hierarchical NiO hollow microspheres assembled from nanoparticles (with diameter of ∼25 nm) upon calcination, which are further assembled by the stacking of ultrathin nanosheets. The hierarchical NiO hollow structures are attractive for catalyst, sensor and environmental applications, benefiting from their large surfaces. The sensing properties of the hierarchical NiO hollow microspheres were evaluated. They show high sensitivity, short response and recovery times, and good response and recovery characteristics to n-butanol. As compared with NiO nanoparticles with similar dimensions (∼20–35 nm), the nanoparticle assembled NiO hollow microspheres exhibit enhanced gas sensing properties. The effective integration of several nanostructures in one microunit would provide a novel way to design new materials for nanodevices.

Ultrathin ZnS Single Crystal Nanowires: Controlled Synthesis and Room-Temperature Ferromagnetism Properties

Highly uniform single crystal ultrathin ZnS nanowires (NWs) with 2 nm diameter and up to 10 μm length were fabricated using a catalyst-free colloidal chemistry strategy. The nanowires crystallized in hexagonal phase structure with preferential growth along the direction of the (001) basal plane. The strong polarity of the (001) plane composed of Zn cations or S anions drives the oriented attachment of ZnS nanocrystals (NCs) along this direction via electrostatic (or dipole) interaction. The ultrathin ZnS nanowires show intrinsic ferromagnetism at room temperature and other unusual properties related to its unique nature, such as large anisotropic lattice expansion, large blue-shift of UV-vis absorption band of the excition, and photoluminescence spectrum of the exciton band edge. First-principles DFT computation results show that Zn vacancies can induce intrinsic ferromagnetism in these undoped ZnS NWs. The main source of the magnetic moment arises from the unpaired 3p electrons at S sites surrounding the Zn vacancies carrying the magnetic moment ranging from 0.26 to 0.66 μ(B). Calculated results indicate that the magnetic moment of the ultrathin ZnS NWs can be increased by increasing the Zn vacancy concentration without significant energy cost. The calculated magnetization value (1.96 or 0.40 emu/g for Zn vacancies on the surface of NWs or inside, respectively) by Zn(53)S(54) supercell model is larger than our experimental value (0.12 emu/g at 1.8 K and 0.05 emu/g at 300 K), but the ferromagnetic result is qualitatively in agreement.

Reduced graphene oxide supported FePt alloy nanoparticles with high electrocatalytic performance for methanol oxidation

Pt-based materials have been widely used as electrocatalysts in direct methanol fuel cells (DMFCs) due to their significant activity for methanol oxidation as well as their superior poison tolerance. In this study, a reduced graphene oxide (RGO) supported FePt alloy electrocatalyst is successfully synthesized by a facile in situ co-reduction route. The microstructure, composition and morphology of the synthesized materials are systematically investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It is shown that the as-formed FePt nanoparticles with a size of 4 nm are well spread out on the RGO sheets and as a result, re-stacking of the RGO sheets is effectively inhibited. Their catalytic performance for electrocatalytic oxidation of methanol is investigated by cyclic voltammetry and amperometric method, which indicate that the RGO/FePt catalyst exhibits much higher catalytic activity and stability than the RGO/Pt nanocomposites. It is proposed that the addition of Fe, which increases the number of Pt active sites, is responsible for the improved catalytic performance. This result implies that the prepared RGO/FePt nanocomposites have great potential applications in DMFC.

CoP nanoparticles deposited on reduced graphene oxide sheets as an active electrocatalyst for the hydrogen evolution reaction

A novel composite with CoP nanoparticles uniformly deposited on reduced graphene oxide (RGO) sheets is prepared through a facile two-step approach. The as-prepared CoP/RGO composite is investigated as an electrocatalyst for the hydrogen evolution reaction (HER). It is found that the CoP/RGO composite shows an enhanced catalytic activity with a smaller Tafel slope (104.8 mV per decade), a much larger exchange current density (4.0 × 10−5 A cm−2) and lower estimated HER activation energy (41.4 kJ mol−1) than pure CoP. Besides, the CoP/RGO composite exhibits good stability in acidic solution, the HER catalytic activity of which shows no obvious degradation after 500 cycles. Such enhanced catalytic activity stems from the abundance of active catalytic sites, the increased electrochemically accessible surface area and significantly improved electrochemical conductivity of the CoP/RGO composite. The good catalytic activity demonstrates that the CoP/RGO composite could be a promising electrocatalyst in hydrogen production.

Photochemical deposition of Ag nanocrystals on hierarchical ZnO microspheres and their enhanced gas-sensing properties

We present a facile photochemical route to load Ag nanoparticles on hierarchical ZnO microspheres forming Ag–ZnO nanocomposites, which were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. The results reveal that Ag nanoparticles with average diameters of 5–6 nm are uniformly deposited on the surface of ZnO, and there are not any voids or organic linkers or surfactants at the interfaces between Ag and ZnO. The distribution density of Ag nanoparticles on ZnO can be tuned by the concentration of the silver precursor. In addition, the hierarchical ZnO microspheres and Ag–ZnO nanocomposites were configured as high performance sensors to detect ethanol and formaldehyde. Importantly, in comparison with the pure ZnO microspheres, the Ag-loaded ZnO nanocomposite sensors show 8.9-fold and 2.1-fold enhancement in gas responses to 100 ppm of ethanol and formaldehyde at 350 °C, respectively. This enhancement may originate from the effective chemisorption of molecular oxygen or atomic oxygen on Ag in the Ag–ZnO nanocomposites.

A solution phase fabrication of magnetic nanoparticles encapsulated in carbon

To avoid high energy consumption, intensive use of hardware and high cost in the manufacture of nanoparticles encapsulated in carbon, a simple, efficient and economical solution-phase method for the fabrication of FeNi@C nanostructures has been explored. The reaction to the magnetic metal@C structures here is conducted at a relatively low temperature (160??C) and this strategy can be transferred to prepare other transition metal@C core?shell nanostructures. The saturation magnetization of metal in metal@C nanostructures is similar to those of the corresponding buck metals. Magnetic metal@C nanostructures with magnetic metal nanoparticles inside and a functionalized carbon surface outside may not only provide the opportunity to tailor the magnetic properties for magnetic storage devices and therapeutics but also make possible the loading of other functional molecules (e.g. enzymes, antigens) for clinic diagnostics, molecular biology, bioengineering, and catalysis.