Jiangtao Chen

Fabrication of Free-Standing, Electrochemically Active, and Biocompatible Graphene Oxide−Polyaniline and Graphene−Polyaniline Hybrid Papers

In this work, we report a low-cost technique via simple rapid-mixture polymerization of aniline using graphene oxide (GO) and graphene papers as substrates, respectively, to fabricate free-standing, flexible GO-polyaniline (PANI) and graphene-PANI hybrid papers. The morphology and microstructure of the obtained papers were characterized by FESEM, FTIR, Raman, and XRD. As results, nanostructural PANI can be deposited on the surfaces of GO and graphene papers, forming thin, lightweight, and flexible paperlike hybrid papers. The hybrid papers display a remarkable combination of excellent electrochemical performances and biocompatibility, making the paperlike materials attractive for new kinds of applications in biosciences.

Novel and high-performance asymmetric micro-supercapacitors based on graphene quantum dots and polyaniline nanofibers

In comparison with graphene sheets, graphene quantum dots (GQDs) exhibit novel chemical/physical properties including nanometer-size, abundant edge defects, good electrical conductivity, high mobility, chemical inertia, stable photoluminescence and better surface grafting, making them promising for fabricating various novel devices. In the present work, an asymmetric micro-supercapacitor, using GQDs as negative active material and polyaniline (PANI) nanofibers as positive active material, is built for the first time by a simple and controllable two-step electro-deposition on interdigital finger gold electrodes. Electrochemical measurements reveal that the as-made GQDs//PANI asymmetric micro-supercapacitor has a more excellent rate capability (up to 1000 V s(-1)) than previously reported electrode materials, as well as faster power response capability (with a very short relaxation time constant of 115.9 μs) and better cycling stability after 1500 cycles in aqueous electrolyte. On this basis, an all-solid-state GQDs//PANI asymmetric micro-supercapacitor is fabricated using H3PO4-polyvinyl alcohol gel as electrolyte, which also exhibits desirable electrochemical capacitive performances. These encouraging results presented here may open up new insight into GQDs with highly promising applications in high-performance energy-storage devices, and further expand the potential applications of GQDs beyond the energy-oriented application of GQDs discussed above.

Enhancement of Field Emission and Photoluminescence Properties of Graphene-SnO2 Composite Nanostructures

In this study, the SnO(2) nanostructures and graphene-SnO(2) (G-SnO(2)) composite nanostructures were prepared on n-Si (100) substrates by electrophoretic deposition and magnetron sputtering techniques. The field emission of SnO(2) nanostructures is improved largely by depositing graphene buffer layer, and the field emission of G-SnO(2) composite nanostructures can also further be improved by decreasing sputtering time of Sn nanoparticles to 5 min. The photoluminescence (PL) spectra of the SnO(2) nanostructures revealed multipeaks, which are consistent with previous reports except for a new peak at 422 nm. Intensity of six emission peaks increased after depositing graphene buffer layer. Our results indicated that graphene can also be used as buffer layer acting as interface modification to simultaneity improve the field emission and PL properties of SnO(2) nanostructures effectively.

Synthesis of fluorine-doped multi-layered graphene sheets by arc-discharge

Fluorine-doped graphene sheets (F-doped GSs) were synthesized by arc discharge. The products were characterized by scanning and transmission electron microcopies, X-ray diffraction, Raman and X-ray photoelectron spectroscopies. The F-doped GSs contain about 10 wt% F. They are mainly multi-layered, with a much larger size than pure GSs, and are super-hydrophobic.

Temperature dependence of the field emission from the few-layer graphene film

Temperature dependence of field-emission (FE) characteristics was investigated for the spray-coated few-layer graphene (FLG) film. The results show that the turn-on field and work function both decrease with increasing temperature from room temperature to 623 K. The possible physical mechanism was proposed based on that the FLG sheets with different stacking orders are nonzero or zero band gapsemiconductors.

Preparation of porous BiVO4 fibers by electrospinning and their photocatalytic performance under visible light

In this study, porous BiVO4 fibers were fabricated by a simple electrospinning technique followed by a controllable annealing of electrospun precursor fibers at different temperatures. The crystal structure, morphology, pore structure and photocatalytic properties of as-made porous BiVO4 fibers were systematically investigated. The results show that the final products have fibrous morphology and the phase structure of porous fibers belongs to monoclinic scheelite structure. The crystallinity and crystalline size increases, but the specific surface area decrease with increasing calcination temperature. These porous fibers all exhibit good optical absorption in visible light. As the sample calcined at 500 °C has larger specific surface area and better crystallinity, it exhibits the best photodegrading properties for rhodamine B solution.

Carbon encapsulated RuO2 nano-dots anchoring on graphene as an electrode for asymmetric supercapacitors with ultralong cycle life in an ionic liquid electrolyte

Assembling asymmetric supercapacitors (SCs) combined with ionic liquid (IL) electrolytes is a very efficient strategy to enhance the energy density of SCs. However, the poor cycle stability of pseudocapacitive metal oxides in ILs seriously affects the performance of this class of asymmetric SCs. Improving the structural stability of metal oxides during the charge/discharge process is one of the greatest challenges at present. Herein, RuO2 nano-dots/reduced graphene oxide (RGO) composites are firstly prepared, and an IL-based asymmetric SC is built using the component-optimized composite (20 wt% RuO2/RGO) as the cathode and activated polyaniline-derived carbon nanorods (denoted as APDC) as the anode. It exhibits a high energy density of 108 W h kg−1, but shows poor cycling stability. In order to solve this problem, an ultrathin carbon layer originating from glucose is employed to encapsulate RuO2 nano-dots anchoring on RGO, forming a core/shell structure of RuO2@C. With the protection of the carbon shell, the as-made RuO2@C/RGO//APDC asymmetric SC exhibits superior long-term stability with 98.5% capacitance retention after 100 000 cycles in the IL electrolyte, as well as a high energy density of 103 W h kg−1 with a potential window of 3.8 V. Furthermore, this protection mechanism of the carbon layer is analyzed by electrochemical quartz crystal microbalance experiments.

Morphology and crystallinity-controlled synthesis of MnO2 hierarchical nanostructures and their application in lithium ion batteries

We demonstrate a novel strategy for the well-controlled preparation of MnO2 hierarchical nanostructures, i.e. MnO2 submicron fibers composed of nanosheets or nanorods with different crystalline phases (δ- and α-MnO2), by integrating electrospinning, hydrothermal synthesis and subsequent heat-treatment. Specifically, δ-MnO2 submicron fibers with different surface morphologies are synthesized via a template-assisted hydrothermal process and by using electrospun nanofibers (Polyacrylonitrile (PAN), oxidized PAN and carbonized PAN nanofibers); after that, α-MnO2 nanostructures composed of different nanorod-like nanostructures are prepared by the heat-treatment of the corresponding δ-MnO2 nanostructures at 700 °C in air. The effects of the reaction parameters (i.e. different templates and growth conditions) on the morphology and crystal phase are investigated in detail. The results demonstrate that the microstructures and structural conversion of the MnO2 nanostructures are closely correlated with the initial templates. Furthermore, the potential application of the α-MnO2 hierarchical nanostructures as the anode for a lithium ion battery is studied, and the results show that the pine-like α-MnO2 exhibits a stable capacity up to 380 mA h g−1 after 150 cycles.

Enhanced field emission properties from aligned graphenes fabricated on micro-hole patterned stainless steel

The graphene emitters on micro-hole patterned stainless steel (SUS304) were prepared using electrophoresis method. The field emission property of three-dimensional graphene emitters was enhanced remarkably compared to that of graphene on flat substrates. The turn-on and threshold fields of the patterned emitter were, respectively, 4.8 and 5.6 V μm−1 lower than those of graphene on flat SUS304 (turn on field is 5.6 V μm−1). The micro-hole patterned cathode provides 10 times higher current density due to vertical aligned sharp edges of graphene in micro holes, and this design may open a potential way to layered-nanomertial-based cold cathodes.

Comparison between metal ion and polyelectrolyte functionalization for electrophoretic deposition of graphene nanosheet films

Graphene nanosheets (GNSs) were modified either by metal magnesium (Mg) ions or a polyelectrolyte, polydiallyldimethylammonium chloride (PDDA), to produce positive charges on them. The two materials were used to produce GNS films with different surface morphologies. They were deposited on single-crystal silicon substrates using simple direct current electrophoretic deposition method. The Mg ion-modified GNS film has a relatively rough surface with some GNSs almost perpendicular to the surface, whereas the PDDA-modified GNS film has a relatively smooth surface with most GNSs parallel to the substrate. This difference is attributed to the different interactions of Mg ions and PDDA molecules with GNSs. Because of the favorable surface morphology, the Mg ion-modified GNS film displays better field emission compared with the PDDA-modified GNS film. Biocompatibility tests indicate that the rougher Mg ion-modified GNS film is more beneficial to cell adhesion and growth.