Chen-Chi M. Ma

Design and tailoring of a hierarchical graphene-carbon nanotube architecture for supercapacitors

Stacking of individual graphene sheets (GS) is effectively inhibited by introducing one-dimensional carbon nanotubes (CNTs) to form a 3-D hierarchical structure which significantly enhances the electrochemical capacitive performances of GS-based composites. From SEM images, inserting proper quantity of CNTs as nanospacers can effectively impede the stacking of GS and enlarge the space between GS sheets, leading to obtain a highly porous nanostructure. The specific capacitance of GS-CNTs-9-1 (∼326.5 F g−1 at 20 mV s−1) is much higher than that of GS material (∼83 F g−1). Furthermore, the energy and power densities of GS-CNTs-9-1 are respectively as high as 21.74 Wh kg−1 and 78.29 kW kg−1, revealing that the hierarchical graphene-CNT architecture provides remarkable effects on enhancing the capacitive performance of GS-based composites. Therefore, the GS-CNT composites are promising carbon materials for supercapacitors.

Preparation of Covalently Functionalized Graphene Using Residual Oxygen-Containing Functional Groups

When fabricated by thermal exfoliation, graphene can be covalently functionalized more easily by applying a direct ring-opening reaction between the residual epoxide functional groups on the graphene and the amine-bearing molecules. Investigation by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM) all confirm that these molecules were covalently grafted to the surface of graphene. The resulting dispersion in an organic solvent demonstrated a long-term homogeneous stability of the products. Furthermore, comparison with traditional free radical functionalization shows the extent of the defects characterized by TEM and Raman spectroscopy and reveals that direct functionalization enables graphene to be covalently functionalized on the surface without causing any further damage to the surface structure. Thermogravmetric analysis (TGA) shows that the nondestroyed graphene structure provides greater thermal stability not only for the grafted molecules but also, more importantly, for the graphene itself, compared to the free-radical grafting method.

Platinum nanoparticles/graphene composite catalyst as a novel composite counter electrode for high performance dye-sensitized solar cells

We herein describe our use of a water–ethylene method to prepare a composite material consisting of platinum nanoparticles and graphene. Results obtained using XPS and XRD show that the degree of reduction of graphene was increased by the incorporation of Pt, and in addition, the increased concentration of defects was confirmed by the D/G ratio of the Raman spectra obtained. In comparison with Pt films, results obtained using CV and EIS showed that the electrocatalytic ability of the composite material was greater, and afforded a higher charge transfer rate, an improved exchange current density, and a decreased internal resistance. SEM images showed that the morphology of PtNP/GR counter electrodes is characterized by a smooth surface, however, resulting in a lower resistance to diffusion, thereby improving the total redox reaction rate that occurs at the counter electrode. PtNP/GR electrodes have a number of advantages over other electrodes that consist solely of graphene or Pt films, including a high rate of charge transfer, a low internal resistance, and a low resistance to diffusion. In our study, we showed that DSSCs that incorporate platinum-grafted graphene had a conversion efficiency of 6.35%, which is 20% higher than that of devices with platinized FTO.

Synthesis, characterization and thermal properties of novel epoxy containing silicon and phosphorus nanocomposites by sol-gel method

Abstract Organic–inorganic hybrids were prepared using diglycidyl ether of bisphenol A (DGEBA) type epoxy and tetraethoxysilane via the sol–gel process. The DGEBA type epoxy was modified by a coupling agent to improve the compatibility of the organic and inorganic phases. The sol–gel technique was used successfully to incorporate silicon and phosphorus into the network of hybrids increasing flame retardance. Fourier transform infrared spectroscopy and 29Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids. In condensed siloxane species for TEOS, silicon atoms through mono-, di-, tri-, and tetra-substituted siloxane bonds are designated as Q1, Q2, Q3, Q4, respectively. For 3-isocyanatopropyltriethoxysilane and diethylphosphatoethyltriethoxysilane, mono-, di-, tri-, tetra-substituted siloxane bonds are designated as T1, T2, T3. Results revealed that Q4, Q3, T3 are the major environments forming a network structure. The morphology of the ceramer was examined by scanning electron microscopy and Si mapping. Particle sizes were below 100 nm. The hybrids were nanocomposites. The char yield of pure epoxy resin was 14.8 wt.% and that of modified epoxy nanocomposite was 31 wt.% at 800 °C. A higher char yield enhances the flame retardance. Values of limiting oxygen index of pure epoxy and modified epoxy nanocomposites are 24 and 32, respectively, indicating that modified epoxy nanocomposites possess better flame retardance than the pure epoxy resin.

Preparation and properties of graphene oxide/polyimide composite films with low dielectric constant and ultrahigh strength via in situpolymerization

This study proposes an effective approach using in situpolymerization, to fabricate large-area graphene oxide (GO)/polyimide (PI) composite films with outstanding mechanical properties. The GO/PI composite films provide ultrahigh tensile strength (up to 844 MPa) and Youngs modulus (20.5 GPa). The NH2-functionalized GO (ODA-GO) is a versatile starting platform for polymer grafting, promoting excellent dispersion of GO within the polymer matrix, and forming strong links with the polymer to facilitate load transfer. The Youngs modulus of the integrated GO–PI composite films with 3.0 wt% ODA-GO loading is 15 times greater, and the tensile strength is 9 times greater than comparable properties of pure PI film. The dielectric constant decreases with increasing GO content and a dielectric constant (Dk) of 2.0 was achieved. This approach provides a strategy for developing ultrahigh performance GO–polymer composite materials.

Dual targeted delivery of doxorubicin to cancer cells using folate-conjugated magnetic multi-walled carbon nanotubes.

By combining the advantage of multi-walled carbon nanotubes (MWCNTs) and iron oxide magnetic nanoparticles (MNs), we develop a magnetic dual-targeted nanocarrier for drug delivery. MWCNTs were functionalized with poly(acrylic acid) through free radical polymerization, decorated with MNs, conjugated with a targeting ligand folic acid (FA), for loading of an anti-cancer drug doxorubicin (DOX). The proposed methodology provides dual targeted delivery of the anti-cancer drug to cancer cells under the guidance of a magnetic field and through ligand-receptor interactions. The chemico-physical properties of the nanocarrier were characterized, in addition to its drug loading efficiency and drug releasing characteristics. Doxorubicin could be loaded to MWCNTs with high efficiency via π-π stacking and hydrogen bonding and showed enhanced cytotoxicity toward U87 human glioblastoma cells compared with free DOX. From transmission electron microscopy and confocal laser scanning microscopy, we confirmed that DOX-FA-MN-MWCNT could be efficiently taken up by U87 cells with subsequent intracellular release of DOX, followed by transport of DOX into the nucleus with the nanocarrier left in the cytoplasm. These properties make the magnetic nanocarrier a potential candidate for targeted delivery of DOX for cancer treatment.

Synthesis, characterization, thermal properties and flame retardance of novel phenolic resin/silica nanocomposites

Novel phenolic/silica hybrid ceramers were synthesized by the sol-gel process. FTIRand 29 Si NMRwere used to characterize the structure of the hybrids. The results revealed that Q 4 ,Q 3 andT 3 are the major microstructures. That is, network structures were formed. SEM, TEM and Si mapping revealed that the hybrids were nanocomposites. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the hybrids increased with TEOS content. Td5 (the degradation temperature at 5% weight loss) of the hybrid that contained 20 wt.% TEOS was 290 � C. The Td5 of the hybrid rose to 312 � C as the TEOS content was increased to 80 wt.%. TEOS inorganic components enhance the thermal stability of the hybrids. The limiting oxygen index (L.O.I.) and the UL-94 test revealed that the hybrid ceramer possesses excellent flame retardance. # 2003 Elsevier Ltd. All rights reserved.

Mechanical, thermal and morphological properties of glass fiber and carbon fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites

Carbon fiber and glass fiber reinforced polyamide-6 and polyamide-6/clay nanocomposites were prepared. Results show that the mechanical and thermal properties of the polyamide-6/clay nanocomposites are superior to those of polyamide-6 composite in terms of the heat distortion temperature, tensile and flexural strength and modulus without sacrificing their impact strength. This may be due to the nanoscale effects, and the strong interaction force existed between the polyamide-6 matrix and the clay interface. The mechanical properties of neat polyamide-6/clay nanocomposites are better than those of 10 wt.% glass fiber or carbon fiber reinforced polyamide-6. The effect of nanoscale clay on toughness is more significant than that of the fiber.

Lightweight and flexible reduced graphene oxide/water-borne polyurethane composites with high electrical conductivity and excellent electromagnetic interference shielding performance.

In this study, we developed a simple and powerful method to fabricate flexible and lightweight graphene-based composites that provide high electromagnetic interference (EMI) shielding performance. Electrospun waterborne polyurethane (WPU) that featured sulfonate functional groups was used as the polymer matrix, which was light and flexible. First, graphene oxide (GO)/WPU composites were prepared through layer-by-layer (L-b-L) assembly of two oppositely charged suspensions of GO, the cationic surfactant (didodecyldimethylammonium bromide, DDAB)-adsorbed GO and intrinsic negatively charged GO, depositing on the negatively charged WPU fibers. After the L-b-L assembly cycles, the GO bilayers wrapped the WPU fiber matrix completely and revealed fine connections guided by the electrospun WPU fibers. Then, we used hydroiodic acid (HI) to obtain highly reduced GO (r-GO)/WPU composites, which exhibited substantially enhanced electrical conductivity (approximately 16.8 S/m) and, moreover, showed a high EMI-shielding effectiveness (approximately 34 dB) over the frequency range from 8.2 to 12.4 GHz.

Magnetic gold-nanorod/ PNIPAAmMA nanoparticles for dual magnetic resonance and photoacoustic imaging and targeted photothermal therapy

Nanomedicine can provide a multi-functional platform for image-guided diagnosis and treatment of cancer. Although gold nanorods (GNRs) have been developed for photoacoustic (PA) imaging and near infra-red (NIR) photothermal applications, their efficiency has remained limited by low thermal stability. Here we present the synthesis, characterization, and functional evaluation of non-cytotoxic magnetic polymer-modified gold nanorods (MPGNRs), designed to act as dual magnetic resonance imaging (MRI) and PA imaging contrast agents. In addition, their high magnetization allowed MPGNRs to be actively localized and concentrated by targeting with an external magnet. Finally, MPGNRs significantly enhanced the NIR-laser-induced photothermal effect due to their increased thermal stability. MPGNRs thus provide a promising new theranostic platform for cancer diagnosis and treatment by combining dual MR/PA imaging with highly effective targeted photothermal therapy.