Tianxi Liu

Graphene-Wrapped Polyaniline Hollow Spheres As Novel Hybrid Electrode Materials for Supercapacitor Applications

Polyaniline hollow spheres (PANI-HS)@electrochemical reduced graphene oxide (ERGO) hybrids with core-shell structures have been fabricated via a solution-based coassembly process. The hollow nanostructured designing for the PANI-HS greatly enlarges the specific surface area, providing high electroactive regions and short diffusion lengths for both charge and ion transport. The wrapping of ERGO sheets on the PANI-HS can offer highly conductive pathways by bridging individual PANI-HS together, thus facilitating the rate and cycling performance of supercapacitors. The specific capacitance of PANI-HS36@ERGO hybrids can reach 614 F g(-1) at a current density of 1 A g(-1). Furthermore, the capacitance of the PANI-HS36@ERGO hybrids maintains 90% after 500 charging/discharging cycles at a current density of 1 A g(-1), indicating a good cycling stability. The greatly enhanced electrochemical performance can be ascribed to the synergic effects of the two components of PANI-HS and ERGO, suggesting that the PANI-HS@ERGO hybrids as novel electrode materials may have potential applications in high-performance energy storage devices.

Preparation and characterization of nylon 11/organoclay nanocomposites

Nylon 11/organoclay nanocomposites have been successfully prepared by melt-compounding. X-ray diffraction and transmission electron microscopy indicate the formation of the exfoliated nanocomposites at low clay concentrations (less than 4 wt%) and a mixture of exfoliated and intercalated nanocomposites at higher clay contents. Thermogravimetric and dynamic mechanical analyses as well as tensile tests show that the degree of dispersion of nanoclay within polymer matrix plays a vital role in property improvement. The thermal stability and mechanical properties of the exfoliated nylon 11/clay nanocomposites (containing lower clay concentrations) are superior to those of the intercalated ones (with higher clay contents), due to the finer dispersion of organoclay among the matrix.

In Situ Thermal Preparation of Polyimide Nanocomposite Films Containing Functionalized Graphene Sheets

Graphene oxides (GO) were exfoliated in N,N-dimethylformamide by simple sonication treatment of the as-prepared high quality graphite oxides. By high-speed mixing of the pristine poly(amic acid) (PAA) solution with graphene oxide suspension, PAA solutions containing uniformly dispersed GO can be obtained. Polyimide (PI) nanocomposite films with different loadings of functionalized graphene sheets (FGS) can be prepared by in situ partial reduction and imidization of the as-prepared GO/PAA composites. Transmission electron microscopy observations showed that the FGS were well exfoliated and uniformly dispersed in the PI matrix. It is interesting to find that the FGS were highly aligned along the surface direction for the nanocomposite film with 2 wt % FGS. Tensile tests indicated that the mechanical properties of polyimide were significantly enhanced by the incorporation of FGS, due to the fine dispersion of high specific surface area of functionalized graphene nanosheets and the good adhesion and interlocking between the FGS and the matrix.

Hybridization of graphene sheets and carbon-coated Fe3O4 nanoparticles as a synergistic adsorbent of organic dyes

Magnetic graphene–Fe3O4@carbon (GFC) hybrids with hierarchical nanostructures have been synthesized and their application as an adsorbent for the removal of organic dyes has been investigated. Graphene–Fe3O4 hybrids were first prepared via a facile one-pot solvothermal process, then carbonaceous coatings on Fe3O4 nanoparticles of nanometer thickness were synthesized by a hydrothermal carbonization process using eco-friendly glucose as a carbon source. Graphene sheets acting as two-dimensional (2D) substrates can effectively prevent the Fe3O4 nanoparticles from aggregating and enable a good dispersion of these magnetic nanoparticles. The carbonaceous layer protects the Fe3O4 nanoparticles in acidic environments and greatly enhances the specific surface area of the hybrids which is beneficial for the removal of organic dyes, such as methylene blue (MB). The resultant GFC hybrids exhibit great adsorption properties not only in water but also in acidic environments, and about 86% and 77% of the dye removal efficiency can be retained after five adsorption–desorption cycles in water and 1 M HCl, respectively. The rapid and efficient adsorption of organic dyes from water as well as acid suggests that the GFC hybrids have potential environmental applications as alternatives to commercial materials in wastewater treatment for the removal of organic dyes.

Immobilization of Co–Al Layered Double Hydroxides on Graphene Oxide Nanosheets: Growth Mechanism and Supercapacitor Studies

Layered double hydroxides (LDHs) are generally expressed as [M(2+)(1-x)M(3+)(x) (OH)(2)] [A(n-)(x/n)·mH(2)O], where M(2+) and M(3+) are divalent and trivalent metal cations respectively, and A is n-valent interlayer guest anion. Co-Al layered double hydroxides (LDHs) with different sizes have been grown on graphene oxide (GO) via in situ hydrothermal crystallization. In the synthesis procedure, the GO is partially reduced in company with the formation of Co-Al LDHs. The morphology and structure of LDHs/GO hybrids are characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The growth mechanism of LDHs on GO nanosheets is discussed. Moreover, both LDHs and LDHs/graphene nanosheets (GNS) hybrids are further used as electrochemical supercapacitor materials and their performance is evaluated by cyclic voltammetry (CV) and galvanostatic charge/discharge measurements. It is shown that the specific capacitances of LDHs are significantly enhanced by the hybridization with GNS.

Synthesis of Fe nanoparticles@graphene composites for environmental applications

Fe nanoparticles@graphene composites (FGC) are successfully synthesized by using graphene oxide (GO) as a supporting matrix. GO is first treated with Fe(3+) to form Fe(3+)@GO complexes. Then, by adding NaBH(4) solution, Fe(3+) and GO are simultaneously reduced in situ to Fe and graphene respectively, forming FGC hybrid composites. The structures, properties and applications of the hybrids thus obtained are investigated by X-ray diffraction, Raman spectroscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis and magnetization measurements. The hybrids are also evaluated for decolorization of methyl blue solution, a model dye in wastewater of dyeing industry. Compared with bare Fe particles, the high removal capacities of FGC are due to the increased adsorption sites in the hybrids, which are achieved by inhibiting the particle aggregation and reducing the size of Fe nanoparticles.

Facile Fabrication of Functionalized Graphene Sheets (FGS)/ZnO Nanocomposites with Photocatalytic Property

Functionalized graphene sheets (FGS)/ZnO nanocomposites were fabricated via thermal treatment method, using graphene oxide as a precursor of graphene, Zn(NH(3))(4)CO(3) as a precursor of zinc oxide, and poly(vinyl pyrrolidone) as an intermediate to combine zinc with carbon materials. Thermogravimetric analysis, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize crystal structure and morphology of FGS/ZnO nanocomposites. It was shown that the well-dispersed ZnO nanoparticles were deposited on FGS homogeneously. The composites exhibited photocatalytic activity to decompose rhodamine 6G efficiently under low-power ultraviolet (UV) light. This facile and low-cost method makes the composite a perfect candidate in applications of catalysis and other areas.

High-performance supercapacitors based on hollow polyaniline nanofibers by electrospinning.

Hollow polyaniline (PANI) nanofibers with controllable wall thickness are fabricated by in situ polymerization of aniline using the electrospun poly(amic acid) fiber membrane as a template. A maximum specific capacitance of 601 F g(-1) has been achieved at 1 A g(-1), suggesting the potential application of hollow PANI nanofibers for supercapacitors. The superior electrochemical performance of the hollow nanofibers is attributed to their hollow structure, thin wall thickness, and orderly pore passages, which can drastically facilitate the ion diffusion and improve the utilization of the electroactive PANI during the charge-discharge processes. Furthermore, the high flexibility of the self-standing fiber membrane template provides possibilities for the facile construction and fabrication of conducting polymers with hollow nanostructures, which may find potential applications in various high-performance electrochemical devices.

Carbon Nanotubes Bridged with Graphene Nanoribbons and Their Use in High‐Efficiency Dye‐Sensitized Solar Cells

To improve the practical application of functional nanomaterials, it is critically important, but often challenging, to extend their excellent properties from the nanoscale to the macroscopic scale. For example, carbon nanotubes (CNTs) have been widely studied as a new family of electrode materials for various optoelectronic and electronic devices, owing to their unique structure and remarkable electronic and catalytic properties. However, CNTs were typically aggregated to form networks with many boundaries, which significantly inhibited rapid charge transport. The resulting CNT-based electrodedevices showed much lower efficiency than expected. To solve the above problem and achieve high performance at the macroscopic scale, a general strategy is to design novel structures to realize effective interactions among CNTs at the molecular scale. To this end, nature provides excellent models for efficiently performing complex functions through the creation of elaborate structures. Well-known examples are blood vessels, which are constructed with trunks interconnected by a lot of branches, a paradigmatic structure to rapidly deliver nutrients throughout our bodies. Inspired by nature, herein we discuss the development of a new structure in which CNTs are bridged by graphene nanoribbons. Briefly, multiwalled CNTs are partially unzipped to form nanoribbons with one end on the mother CNT and the other on a neighboring CNT. Due to the strong p–p interaction between nanotube and nanoribbon, and the high charge mobility in nanoribbons, produced electrons can be rapidly transported among CNTs to macroscopically achieve high performance. As a demonstration, dye-sensitized solar cells (DSCs) with graphene-nanoribbon-bridged CNTs as counter electrodes (Figure 1) showed an energy conversion efficiency of up to 8.23%, compared with 7.61% for a conventional platinum counter electrode under similar conditions. Multiwalled CNTs with a diameter of 20–40 nm and a wall number of 20–30 were primarily studied (Supporting Information, SFigure S1). The CNTs were chemically unzipped to produce graphene oxide nanoribbons (GONRs; Figure S2). The degree of unzipping could mainly be increased by increasing the amount of potassium permanganate. X-ray diffraction (XRD) analysis was undertaken to quantitatively determine the degree of unzipping. Figure S3 shows typical XRD patterns for the mixtures of GONR and CNT with different GONR weight percentages. As the amount of GONR in the mixture increased, the characteristic GONR peak (2q= 11.28) gradually increased while the CNT peak (2q= 26.18) gradually decreased. Based on the intensity of their characteristic peaks, a relationship curve between GONR weight percentage and intensity ratio was obtained. This curve could be then used to calculate the weight percentage of GONRs in the resulting hybrid (Figure S4). Figure 2 compares the XRD patterns of pristine CNTs, GONR/CNT hybrids with different GONR weight percentages, and pure GONR. The GONR weight percentages in three hybrid samples were calculated as approximately 16%, 55%, and 85%. For simplicity, they were defined as GONR16%/CNT, GONR55%/CNT and GONR85%/CNT. CNTs could be also completely unzipped to form pure nanoribbons. Raman spectroscopy was used to monitor structural changes during the unzipping process of CNTs (Figure S5). The D band at ca. 1350 cm 1 gradually broadened and increased in intensity as the reaction progressed, a result which corresponds to increasing GONR weight percentage. As a result, the ratio between the intensities of the D and G bands (ID/IG) was enhanced, which indicates a decrease in Figure 1. a) the structure of dye-sensitized solar cells based on R-GONR-bridged CNTs as counter electrode. b) the mechanism of rapid electron transport in the counter electrode.

Biomass-Derived Nitrogen-Doped Carbon Nanofiber Network: A Facile Template for Decoration of Ultrathin Nickel-Cobalt Layered Double Hydroxide Nanosheets as High-Performance Asymmetric Supercapacitor Electrode.

The development of biomass-based energy storage devices is an emerging trend to reduce the ever-increasing consumption of non-renewable resources. Here, nitrogen-doped carbonized bacterial cellulose (CBC-N) nanofibers are obtained by one-step carbonization of polyaniline coated bacterial cellulose (BC) nanofibers, which not only display excellent capacitive performance as the supercapacitor electrode, but also act as 3D bio-template for further deposition of ultrathin nickel-cobalt layered double hydroxide (Ni-Co LDH) nanosheets. The as-obtained CBC-N@LDH composite electrodes exhibit significantly enhanced specific capacitance (1949.5 F g(-1) at a discharge current density of 1 A g(-1) , based on active materials), high capacitance retention of 54.7% even at a high discharge current density of 10 A g(-1) and excellent cycling stability of 74.4% retention after 5000 cycles. Furthermore, asymmetric supercapacitors (ASCs) are constructed using CBC-N@LDH composites as positive electrode materials and CBC-N nanofibers as negative electrode materials. By virtue of the intrinsic pseudocapacitive characteristics of CBC-N@LDH composites and 3D nitrogen-doped carbon nanofiber networks, the developed ASC exhibits high energy density of 36.3 Wh kg(-1) at the power density of 800.2 W kg(-1) . Therefore, this work presents a novel protocol for the large-scale production of biomass-derived high-performance electrode materials in practical supercapacitor applications.