Guangshuo Wang

Synthesis, characterization and magnetorheological study of 3-aminopropyltriethoxysilane-modified Fe3O4 nanoparticles

In this study, monodisperse Fe3O4 nanoparticles were synthesized successfully using a sonochemical method in the presence of 3-aminopropyltriethoxysilane (APTES). The morphology, microstructure and magnetic properties of the bare Fe3O4 and APTES-coated Fe3O4 were investigated in detail by TEM, XRD, FTIR and SQUID. It was found that APTES-coated Fe3O4 showed relatively good dispersion with a narrow size distribution of 8.4 ± 2.1 nm diameter. The functionalization of Fe3O4 was proved to be covalent linking between Fe3O4 and APTES. The field-dependent magnetization curve indicated superparamagnetic behavior of Fe3O4-APTES with a saturation magnetization (M s) of 70.5 emu g−1 at room temperature. A magnetorheological (MR) fluid was prepared using the obtained Fe3O4-APTES nanoparticles with 25 wt% particles, and its MR properties were tested using a Physica MCR301 rheometer fitted with an MRmodule. The results showed that the as-prepared APTES-coated Fe3O4 nanoparticle-based MR fluid exhibited typical MR effects, with increasing viscosity, shear stress and yield stress depending on the applied magnetic field strength.

Solvothermal synthesis, characterization, and magnetorheological study of zinc ferrite nanocrystal clusters

In this study, zinc ferrite (ZnFe2O4) nanocrystal clusters were synthesized successfully with a surfactant-assistant solvothermal method and investigated as a potential magnetorheological material. The morphology, structure, and magnetic properties of the obtained ZnFe2O4 nanocrystal clusters were investigated in detail using a scanning electron microscope, transmission electron microscope, X-ray diffraction, and superconducting quantum interference device. It was found that the ZnFe2O4 nanocrystal clusters showed well-defined shape and homogeneous dispersion with narrow size distribution of 276 nm in diameter. The field-dependent magnetization curve indicated superparamagnetic properties of as-prepared ZnFe2O4 nanocrystal clusters with saturation magnetization (Ms) of 86.6 emu/g at room temperature. The magnetorheological fluid with 25% particle mass fraction was prepared by ZnFe2O4 nanocrystal clusters, and the corresponding magnetorheological properties were also tested using a Physica MCR301 rheometer fitted with a magnetorheological module. The prepared magnetorheological fluid changed from a liquid-like to a solid-like state under an external magnetic field, suggesting typical Bingham plastic behavior. Compared with conventional carbonyl iron particles, ZnFe2O4 nanocrystal clusters–based magnetorheological fluid showed enhanced sedimentation stability. The obtained ZnFe2O4 nanocrystal clusters are considered as an ideal candidate for magnetorheological fluid with typical magnetorheological effect as well as improved sedimentation stability.

Urchin-like α-FeOOH@MnO2 core–shell hollow microspheres for high-performance supercapacitor electrode

AbstractThis work details the design and synthesis of novel urchin-like α-FeOOH@MnO2 core–shell hollow microspheres for high-performance electrode materials for supercapacitors. The core–shell heterostructures were constructed by growing strip-like MnO2 nanostructures onto the urchin-like α-FeOOH hollow microspheres that were composed of nanorods. Based on the synergetic effects and multi-functionalities of both the MnO2 shell and urchin-like α-FeOOH hollow cores, the resulting urchin-like α-FeOOH@MnO2 core–shell hollow microspheres exhibited excellent electrochemical performance with a high specific capacitance of 597xa0Fxa0g−1 at 1xa0Axa0g−1, good rate capability (capacitance retention of 74.2% at 10xa0Axa0g−1), and remarkable cycling stability (capacitance retention of 97.1% after 2000 cycles). Moreover, an asymmetric supercapacitor fabricated using α-FeOOH@MnO2 as positive electrode and activated carbon as negative electrode was found to deliver a high energy density of 34.2xa0Wxa0hxa0kg−1 and power density of 815xa0Wxa0kg−1.Graphical AbstractUrchin-like α-FeOOH@MnO2 hollow microspheres demonstrated a high specific capacitance, rate capability and cycling stability, suggesting its promising potential for high-performance supercapacitors.n

Facile preparation of MnO2@C composite nanorods for high-performance supercapacitors

Novel MnO2@C composite nanorods were successfully prepared by a facile solvothermal method. The results showed that a uniform carbon layer was formed around the MnO2 nanorods. The carbon layer provided a highly conductive pathway to boost the charge transport involved during the capacitance generation. The electrochemical properties of MnO2@C composite nanorods were investigated by cyclic voltammetry and galvanostatic charge–discharge. The composites as electrode materials of supercapacitors exhibited high specific capacitance (295xa0F/g) compared with MnO2 nanorods (149xa0F/g) with a wide operation window (0–1.0xa0V). The electrochemical impedance spectroscopic studies showed the charge-transfer resistance (Rct) of the MnO2@C composite nanorods (1.10xa0Ω) was much lower than that of pure MnO2 (2.53xa0Ω). Moreover, the MnO2@C composite nanorods exhibited excellent cycling behavior with no more than 5xa0% capacitance loss after 2000 cycles. These results indicated that the MnO2@C composite nanorods could be a promising electrode material for high-performance electrochemical capacitors.

Ag/MnO2 Nanorod as Electrode Material for High-Performance Electrochemical Supercapacitors

A one-dimensional hierarchical Ag nanoparticle (AgNP)/MnO2 nanorod (MND) nanocomposite was synthesized by combining a simple solvothermal method and a facile reduction approach in situ. Owing to its high electrical conductivity, the resulting AgNP/MND nanocomposite displayed a high specific capacitance of 314 F g-1 at a current density of 2 A g-1, which was much higher than that of pure MNDs (178 F g-1). Resistances of the electrolyte (Rs) and charge transportation (Rct) of the nanocomposite were much lower than that of pure MNDs. Moreover, the nanocomposite exhibited outstanding long-term cycling ability (9% loss of initial capacity after 1000 cycles). These results indicated that the nanocomposite could serve as a promising and useful electrode material for future energy-storage applications.

Preparation of Nano-Convex and Nano-Concave-Patterned Polyimide Surfaces and Their Nano-Tribological Behavior

In this work, nano-convex-patterned polyimide surface (notated as 1-sample) and nano-concave-patterned polyimide surface (notated as 2-sample) were prepared by self-assembly and etching. Atomic for...