Qiuyun Ouyang

Graphene–Fe3O4 nanohybrids: Synthesis and excellent electromagnetic absorption properties

Graphene (G)–Fe3O4 nanohybrids were fabricated by first depositing β-FeOOH crystals with diameter of 3–5 nm on the surface of the graphene sheets. After annealing under Ar flow, β-FeOOH nanocrystals were reduced to Fe3O4 nanoparticles by the graphene sheets, and thus G–Fe3O4 nanohybrids were obtained. The Fe3O4 nanoparticles with a diameter of about 25 nm were uniformly dispersed over the surface of the graphene sheets. Moreover, compared with other magnetic materials and the graphene, the nanohybrids exhibited significantly increased electromagnetic absorption properties owing to high surface areas, interfacial polarizations, and good separation of magnetic nanoparticles. The maximum reflection loss was up to −40.36 dB for G–Fe3O4 nanohybrids with a thickness of 5.0 mm. The nanohybrids are very promising for lightweight and strong electromagnetic attenuation materials.

Three‐Dimensional Hierarchical Architectures Constructed by Graphene/MoS2 Nanoflake Arrays and Their Rapid Charging/Discharging Properties as Lithium‐Ion Battery Anodes

Charged up: Three-dimensional architectures constructed from graphene/MoS2 nanoflake arrays have been successfully fabricated by a one-step hydrothermal method. MoS2 nanoflakes with thicknesses less than 13 nm grow vertically on both sides of graphene sheets (see figure), which allows the architectures to be more stable during charging and discharging. Even at a high current density of 8000 mA g(-1), their discharge capacity is still up to 516 mA h g(-1).

Three-dimensional hierarchical MoS2 nanoflake array/carbon cloth as high-performance flexible lithium-ion battery anodes

Flexible lithium-ion batteries are the key to powering a new generation of flexible electronics such as roll-up displays, smart electronics, and wearable devices. Here we report, for the first time, one-step hydrothermal synthesis of a three-dimensional (3D) hierarchical MoS2 nanoflake array/carbon cloth which shows potential for improving the performance of flexible lithium-ion batteries. Structural characterizations show that the 3D hierarchical MoS2 nanoflake array/carbon cloth has a similar ordered woven structure to the bare carbon cloth. Each carbon microfiber is covered with many highly ordered 3D MoS2 nanoflake arrays, and a typical MoS2 nanoflake, with expanded spacing of the (002) crystal plane, has a uniform width of about 400 nm and a thickness of less than 15 nm. The flexible 3D MoS2 nanoflake array/carbon cloth as a flexible lithium-ion battery anode has a high reversible capacity of 3.0–3.5 mA h cm−2 at a current density of 0.15 mA cm−2 and outstanding discharging/charging rate stability. Moreover, a fabricated full battery, with commercial LiCoO2 powder and the hierarchical architectures as electrodes, exhibits high flexibility and good electrochemical performance, and can light a commercial red LED even after 50 cycles of bending the full battery.

Fe2O3/TiO2 tube-like nanostructures: synthesis, structural transformation and the enhanced sensing properties.

The paper describes for the first time the successful synthesis of Fe(2)O(3)/TiO(2) tube-like nanostructures, in which TiO(2) shell is of quasi-single crystalline characteristic and its thickness can be controlled through adjusting the added amount of aqueous Ti(SO(4))(2) solution. The characterization of samples obtained at different stages using transmission electron microscope indicates that the outer TiO(2) shell is changed gradually from amorphous and polycrystalline phase into quasi-single crystal under thermal actions through the Ostwald ripening process, accompanying the corrosion of the central parts of Fe(2)O(3) nanorods, and the formation of small particles separating each other, leading to the special core/shell nanorods. Furthermore, Fe(2)O(3)/TiO(2) tube-like nanostructures can be transformed into Fe(2)TiO(5) nanostructures after they are thermally treated at higher temperatures. Those nanostructures exhibit enhanced ethanol sensing properties with respect to the monocomponent. Our results imply that not only hollow nanostructures, but also a novel type of nanostructures can be fabricated by the present method for nanodevices.

Porous iron molybdate nanorods: in situ diffusion synthesis and low-temperature H2S gas sensing.

In the paper, we developed an in situ diffusion growth method to fabricate porous Fe2(MoO4)3 nanorods. The average diameter and the length of the porous nanorods were 200 nm and 1.2-4 μm, respectively. Moreover, many micropores existed along axial direction of the Fe2(MoO4)3 nanorods. In terms of nitrogen adsorption-desorption isotherms, calculated pore size was in the range of 4-115 nm, agreeing well with the transmission electron microscope observations. Because of the uniquely porous characteristics and catalytic ability at low temperatures, the porous Fe2(MoO4)3 nanorods exhibited very good H2S sensing properties, including high sensitivity at a low working temperature (80 °C), relatively fast response and recovery times, good selectivity, and long-term stability. Thus, the porous Fe2(MoO4)3 nanorods are very promising for the fabrication of high-performance H2S gas sensors. Furthermore, the strategy presented here could be expended as a general method to synthesize other hollow/porous-type transition metal molybdate nanostructures by rational designation in nanoscale.

Saturable absorption and the changeover from saturable absorption to reverse saturable absorption of MoS2 nanoflake array films

MoS2 nanoflake array films on different glass substrates were fabricated by an in situ growth method. The nonlinear absorption (NLA) properties of the MoS2 nanoflake array films were investigated by an open-aperture Z-scan technique. The MoS2 nanoflake array films exhibited different NLA properties dependent on the input energy. In the case of lower input energy, the films exhibited saturable absorption (SA); however, if the input energy was increased, a changeover from SA to reverse saturable absorption (RSA) was observed. The interesting NLA properties of the films could be attributed to the competition between the ground-state absorption and the excited-state absorption in terms of the energy-level model of MoS2.

In situ diffusion growth of Fe2(MoO4)3 nanocrystals on the surface of α-MoO3 nanorods with significantly enhanced ethanol sensing properties

In situ diffusion growth of Fe2(MoO4)3 nanocrystals on the surface of α-MoO3 nanorods was achieved through a facile method. The obtained Fe2(MoO4)3@α-MoO3 nanorods exhibit significantly enhanced ethanol sensing properties compared with those of the pristine α-MoO3 nanorods and the Fe2(MoO4)3 nanoparticles, which are attributed to the improved catalytic properties of Fe2(MoO4)3 at low temperature.

Branched polyaniline/molybdenum oxide organic/inorganic heteronanostructures: synthesis and electromagnetic absorption properties

In this work, we developed an efficient and facile method to fabricate branched polyaniline (PANI)/α-MoO3 organic/inorganic heteronanostructures. Scanning electron and transmission electron microscope measurements showed that PANI nanorods with an average diameter and length of about 55 and 110 nm respectively were grown perpendicularly on the surfaces of α-MoO3 nanorods and the density of the PANI nanorods could be readily controlled by simply changing the addition amount of aniline in the reaction system. The minimal reflection loss for the electromagnetic wave absorbent material was up to −33.7 dB at 16.88 GHz for the branched heteronanostructures/paraffin composites with a thickness of 2.0 mm, and all of the minimal reflection losses were less than those of the pure PANI nanorods in the frequency range of 2–18 GHz. More importantly, the content of the branched nanostructures in the paraffin matrix was only 10 wt%. Thus, the method presented here is a very efficient strategy to fabricate lightweight materials for strong electromagnetic wave absorbents.

Graphene-MoO2 hierarchical nanoarchitectures: in situ reduction synthesis and high rate cycling performance as lithium-ion battery anodes

Hierarchical nanoarchitectures constructed by MoO2 nanocrystal-functionalized graphene were fabricated through an in situ reduction process. As an anode, even at a 10C (0.1 h per half cycle) charging–discharging rate, the reversible capacity is much higher than the theoretical capacity of graphite. Thus, rapid charging–discharging of the anodes is achieved by the nanoarchitectures.

Synthesis and enhanced nonlinear optical properties of graphene/CdS organic glass

Graphene/CdS (G/CdS) nanocomposite was first fabricated by a hydrothermal method. G/CdS nanocomposite was then dispersed in polymethyl methacrylate (PMMA) for preparation of organic glass by a casting method. The G/CdS/PMMA organic glass exhibits enhanced nonlinear optical (NLO) properties compared to G/PMMA and CdS/PMMA organic glass. Moreover, NLO properties of the G/CdS/PMMA organic glass can be controlled by adjusting the addition amount of G/CdS nanocomposite in PMMA. Our results demonstrate that the G/CdS/PMMA organic glass is very promising for optical devices, such as optical limiters and optical switch.