Showing papers on "Nanocomposite published in 2012"

Graphene–Multilayer Graphene Nanocomposites as Highly Efficient Thermal Interface Materials

Abstract: We found that the optimized mixture of graphene and multilayer graphene, produced by the high-yield inexpensive liquid-phase-exfoliation technique, can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The “laser flash” measurements revealed a record-high enhancement of K by 2300% in the graphene-based polymer at the filler loading fraction f = 10 vol %. It was determined that the relatively high concentration of the single-layer and bilayer graphene flakes (∼10–15%) present simultaneously with the thicker multilayers of large lateral size (∼1 μm) were essential for the observed unusual K enhancement. The thermal conductivity of the commercial thermal grease was increased from an initial value of ∼5.8 W/mK to K = 14 W/mK at the small loading f = 2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene–multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotub...

Graphene -- Based Nanocomposites as Highly Efficient Thermal Interface Materials

Abstract: We found that an optimized mixture of graphene and multilayer graphene - produced by the high-yield inexpensive liquid-phase-exfoliation technique - can lead to an extremely strong enhancement of the cross-plane thermal conductivity K of the composite. The "laser flash" measurements revealed a record-high enhancement of K by 2300 % in the graphene-based polymer at the filler loading fraction f =10 vol. %. It was determined that a relatively high concentration of single-layer and bilayer graphene flakes (~10-15%) present simultaneously with thicker multilayers of large lateral size (~ 1 micrometer) were essential for the observed unusual K enhancement. The thermal conductivity of a commercial thermal grease was increased from an initial value of ~5.8 W/mK to K=14 W/mK at the small loading f=2%, which preserved all mechanical properties of the hybrid. Our modeling results suggest that graphene - multilayer graphene nanocomposite used as the thermal interface material outperforms those with carbon nanotubes or metal nanoparticles owing to graphene's aspect ratio and lower Kapitza resistance at the graphene - matrix interface.

Crumpled Nitrogen‐Doped Graphene Nanosheets with Ultrahigh Pore Volume for High‐Performance Supercapacitor

Abstract: Continuous scientifi c endeavors have been directed toward the optimization of graphene by manipulating its electronic, mechanical, chemical, and structural properties, such as surface area, pore geometry, and functional sites, in order to advance various potential applications, including nanoelectronics, energy storage/conversion, and catalysis. [ 1 ] The structural reformation of graphene, from pore generation to morphology transformation, is receiving growing attention, because the reconstruction of graphene could potentially result in localized highly reactive regions and thus unexpected properties for specifi c applications. [ 2 ] For instance, it was reported that crumpled graphene allows for the fabrication of polymer-graphene nanocomposite fi lms with low O 2 permeability and effective reduction of transparency. [ 3 ] Chemical functionalization of graphene (e.g., graphene oxide or GO) is another effective method for manipulating physical and chemical properties of graphene, because enriched reactive oxygen functional groups in GO can provide ample covalent bonding sites for the chemical functionalization. The functionalized GO can be easily converted to graphene-like materials through chemical or thermal reduction of GO. [ 4 ] For instance, nitrogen-doped graphene (NG) can be synthesized through thermal annealing of GO in ammonia, and the resulting NG showed some unique properties including improved conductivity and excellent catalytic activity. Actually, NG has been intensively investigated as electrode materials for lithium-ion batteries, catalysts for oxygen reduction reac-

Synthesis of silica nanoparticles by sol-gel: size-dependent properties, surface modification, and applications in silica-polymer nanocomposites — a review

Abstract: Application of silica nanoparticles as fillers in the preparation of nanocomposite of polymers has drawnmuch attention, due to the increased demand for new materials with improved thermal, mechanical, physical, and chemical properties. Recent developments in the synthesis of monodispersed, narrow-size distribution of nanoparticles by sol-gel method provide significant boost to development of silica-polymer nanocomposites. This paper is written by emphasizing on the synthesis of silica nanoparticles, characterization on size-dependent properties, and surface modification for the preparation of homogeneous nanocomposites, generally by sol-gel technique. The effect of nanosilica on the properties of various types of silica-polymer composites is also summarized.

Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption

Abstract: Light-weight nanocomposites filled with carbon nanotubes (CNTs) are developed for their significant potentials in electromagnetic shielding and attenuation for wide applications in electronics, communication devices, and specific parts in aircrafts and vehicles. Specifically, the introduction of a second phase into/onto CNTs for achieving CNT-based heterostructures has been widely pursued due to the enhancement in either dielectric loss or magnetic loss. In this work, ferroferric oxide (Fe(3)O(4)) was selected as the phase in multiwalled carbon nanotube (MWCNT)-based composites for enhancing magnetic properties to obtain improved electromagnetic attenuation. A direct comparison between the two-phase heterostructures (Fe(3)O(4)/MWCNTs) and polyaniline (PANI) coated Fe(3)O(4)/MWCNTs, namely, three-phase heterostructures (PANI/Fe(3)O(4)/MWCNTs), was made to investigate the interface influences of Fe(3)O(4) and PANI on the complex permittivity and permeability separately. Compared to PANI/Fe(3)O(4)/MWCNTs, Fe(3)O(4)/MWCNTs exhibited enhanced magnetic properties coupled with increased dielectric properties. Interfaces between MWCNTs and heterostructures were found to play a role in the corresponding properties. The evaluation of microwave absorption of their wax composites was carried out, and the comparison between Fe(3)O(4)/MWCNTs and PANI/Fe(3)O(4)/MWCNTs with respect to highly efficient microwave absorption and effective absorption bandwidth was discussed.

A nanocomposite ultraviolet photodetector based on interfacial trap-controlled charge injection.

Abstract: A solution-processed ultraviolet photodetector with a nanocomposite active layer composed of ZnO nanoparticles blended with semiconducting polymers can significantly outperform inorganic photodetectors

Porous Electrode Materials for Lithium‐Ion Batteries – How to Prepare Them and What Makes Them Special

Abstract: Numerous benefits of porous electrode materials for lithium ion batteries (LIBs) have been demonstrated, including examples of higher rate capabilities, better cycle lives, and sometimes greater gravimetric capacities at a given rate compared to nonporous bulk materials. These properties promise advantages of porous electrode materials for LIBs in electric and hybrid electric vehicles, portable electronic devices, and stationary electrical energy storage. This review highlights methods of synthesizing porous electrode materials by templating and template-free methods and discusses how the structural features of porous electrodes influence their electrochemical properties. A section on electrochemical properties of porous electrodes provides examples that illustrate the influence of pore and wall architecture and interconnectivity, surface area, particle morphology, and nanocomposite formation on the utilization of the electrode materials, specific capacities, rate capabilities, and structural stability during lithiation and delithiation processes. Recent applications of porous solids as components for three-dimensionally interpenetrating battery architectures are also described.

The Fabrication, Properties, and Uses of Graphene/Polymer Composites

Abstract: Graphene is a potential nanofiller that can dramatically improve the properties of polymer-based composites at a very low loading. This article reviews the state-of-the-art progress in the fabrication, properties, and uses of polymer composites with different kinds of graphene fillers. The results so far reported in the literature indicate that graphene/polymer composites are promising multifunctional materials with significantly improved tensile strength and elastic modulus, electrical and thermal conductivity, etc. Despite some challenges and the fact that carbon naotube/polymer composites are sometimes better in some particular performance, graphene/polymer composites may have wide potential applications due to their outstanding properties and the availability of graphene in a large quantity at low cost.

Hard nanocomposite coatings: Thermal stability, oxidation resistance and toughness

Abstract: The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000 °C, X-ray amorphous coatings thermally stable above 1000 °C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E ⁎ satisfying the condition H/E ⁎ > 0.1, (ii) high elastic recovery W e ≥ 60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E ⁎ = E(1−ν 2 ), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined.

Column with CNT/magnesium oxide composite for lead(II) removal from water.

Abstract: In this study, manganese dioxide-coated multiwall carbon nanotube (MnO2/CNT) nanocomposite has been successfully synthesized. The as-produced nanocomposite was characterized by different characteristic tools, such as X-ray diffraction, SEM, and FTIR. The MnO2/CNT nanocomposite was utilized as a fixed bed in a column system for removal of lead(II) from water. The experimental conditions were investigated and optimized. The pH range between 3 and 7 was studied; the optimum removal was found when the pH was equal to 6 and 7. The thickness of MnO2/CNT nanocomposite compact layer was also changed to find the optimum parameter for higher removal. It was observed that the slower the flow rates of the feed solution the higher the removal because of larger contact time.

Hierarchical Nanocomposites Derived from Nanocarbons and Layered Double Hydroxides - Properties, Synthesis, and Applications

Abstract: The combination of one-dimensional and two-dimensional building blocks leads to the formation of hierarchical composites that can take full advantages of each kind of material, which is an effective way for the preparation of multifunctional materials with extraordinary properties. Among various building blocks, nanocarbons (e.g., carbon nanotubes and graphene) and layered double hydroxides (LDHs) are two of the most powerful materials that have been widely used in human life. This Feature Article presents a state-of-the-art review of hierarchical nanocomposites derived from nanocarbons and LDHs. The properties of nanocarbons, LDHs, as well as the combined nanocomposites, are described first. Then, efficient and effective fabrication methods for the hierarchical nanocomposites, including the reassembly of nanocarbons and LDHs, formation of LDHs on nanocarbons, and formation of nanocarbons on LDHs, are presented. The as-obtained nanocomposites derived form nanocarbons and LDHs exhibited excellent performance as multifunctional materials for their promising applications in energy storage, nanocomposites, catalysis, environmental protection, and drug delivery. The fabrication of LDH/carbon nanocomposites provides a novel method for the development of novel multifunctional nanocomposites based on the existing nanomaterials. However, knowledge of their assembly mechanism, robust and precise route for LDH/nanocarbon hybrid with well designed structure, and the relationship between structure, properties, and applications are still inadequate. A multidisciplinary approach from the scope of materials, physics, chemistry, engineering, and other application areas, is highly required for the development of this advanced functional composite materials.

Graphitic carbon nitride (g-C3N4)–Pt-TiO2 nanocomposite as an efficient photocatalyst for hydrogen production under visible light irradiation

Abstract: Porous graphitic carbon nitride (g-C3N4) was prepared by a simple pyrolysis of urea, and then a g-C3N4–Pt-TiO2 nanocomposite was fabricated via a facile chemical adsorption followed by a calcination process. The obtained products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance absorption spectra, and electron microscopy. It is found that the visible-light-induced photocatalytic hydrogen evolution rate can be remarkably enhanced by coupling TiO2 with the above g-C3N4, and the g-C3N4–Pt-TiO2 composite with a mass ratio of 70 : 30 has the maximum photoactivity and excellent photostability for hydrogen production under visible-light irradiation, and the stable photocurrent of g-C3N4–TiO2 is about 1.5 times higher than that of the bare g-C3N4. The above experimental results show that the photogenerated electrons of g-C3N4 can directionally migrate to Pt-TiO2 due to the close interfacial connections and the synergistic effect existing between Pt-TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently separated in space, which is beneficial for retarding the charge recombination and improving the photoactivity.

Polyacrylonitrile/graphene composite as a precursor to a sulfur-based cathode material for high-rate rechargeable Li–S batteries

Abstract: Polyacrylonitrile/graphene (PAN/GNS) composites have been synthesized via an in situ polymerization method for the first time, which serve as a precursor to prepare a cathode material for high-rate rechargeable Li–S batteries. It is observed from scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the PAN nanoparticles, less than 100 nm in size, are anchored on the surface of the GNS and this unique structure is maintained in the sulfur composite cathode material. The electrochemical properties of the pyrolyzed PAN-S/GNS (pPAN-S/GNS) composite cathode have been evaluated by cyclic voltammograms, galvanostatic discharge–charge cycling and electrochemical impedance spectroscopy. The results show that the pPAN-S/GNS nanocomposite, with a GNS content of ca. 4 wt.%, exhibits a reversible capacity of ca. 1500 mA hg−1sulfur or 700 mA hg−1composite in the first cycle, corresponding to a sulfur utilization of ca. 90%. The capacity retention is relatively stable at 0.1 C. Even up to 6 C, a competitive capacity of ca. 800 mA hg−1sulfur is obtained. The superior performance of pPAN-S/GNS is attributed to the introduction of the GNS and the even composite structure. The GNS in the composite materials works as a three-dimensional (3-D) nano current collector, which could act not only as an electronically conductive matrix, but also as a framework to improve the electrochemical performance.

Improving the Electrode Performance of Ge through Ge@C Core–Shell Nanoparticles and Graphene Networks

Abstract: Germanium is a promising high-capacity anode material for lithium ion batteries, but it usually exhibits poor cycling stability because of its huge volume variation during the lithium uptake and release process. A double protection strategy to improve the electrode performance of Ge through the use of Ge@C core–shell nanostructures and reduced graphene oxide (RGO) networks has been developed. The as-synthesized Ge@C/RGO nanocomposite showed excellent cycling performance and rate capability in comparison with Ge@C nanoparticles when used as an anode material for Li ion batteries, which can be attributed to the electronically conductive and elastic RGO networks in addition to the carbon shells and small particle sizes of Ge. The strategy is simple yet very effective, and because of its versatility, it may be extended to other high-capacity electrode materials with large volume variations and low electrical conductivities.

Mechanical Milling: a Top Down Approach for the Synthesis of Nanomaterials and Nanocomposites

Abstract: Synthesis of nanomaterials by a simple, low cost and in high yield has been a great challenge since the very early development of nanoscience. Various bottom and top down approaches have been developed so far, for the commercial production of nanomaterials. Among all top down approaches, high energy ball milling, has been widely exploited for the synthesis of various nanomaterials, nanograins, nanoalloy, nanocomposites and nano -quasicrystalline materials. Mechanical alloying techniques have been utilized to produce amorphous and nanocrystalline alloys as well as metal/non-metal nano- composite materials by milling and post annealing, of elemental or compound powders in an inert atmosphere. Mechanical alloying is a non-equilibrium processing technique in which different elemental powders are milled in an inert atmosphere to create one mixed powder with the same composition as the constituents. In high-energy ball milling, plastic deformation, cold-welding and fracture are predominant factors, in which the deformation leads to a change in particle shape, cold-welding leads to an increase in particle size and fracture leads to decrease in particle size resulting in the formation of fine dispersed alloying particles in the grain-refined soft matrix. By utilizing mechanical milling various kind of aluminium/ nickel/ mag- nesium/ copper based nanoalloys, wear resistant spray coatings, oxide and carbide strengthened aluminium alloys, and many other nanocomposites have been synthesized in very high yield. The mechanical milling has been utilized for the synthesis of nanomaterials either by milling and post annealing or by mechanical activation and then applying some other process on these activated materials. This review is a systematic view of the basic concept of mechanical milling, historical view and appli- cations of mechanical milling in the synthesis of various nanomaterials, nanosomposites, nnaocarbons and nano quasicrys- talline materials.

Hydrothermal synthesis of MnO2/CNT nanocomposite with a CNT core/porous MnO2 sheath hierarchy architecture for supercapacitors

Abstract: MnO2/carbon nanotube [CNT] nanocomposites with a CNT core/porous MnO2 sheath hierarchy architecture are synthesized by a simple hydrothermal treatment. X-ray diffraction and Raman spectroscopy analyses reveal that birnessite-type MnO2 is produced through the hydrothermal synthesis. Morphological characterization reveals that three-dimensional hierarchy architecture is built with a highly porous layer consisting of interconnected MnO2 nanoflakes uniformly coated on the CNT surface. The nanocomposite with a composition of 72 wt.% (K0.2MnO2·0.33 H2O)/28 wt.% CNT has a large specific surface area of 237.8 m2/g. Electrochemical properties of the CNT, the pure MnO2, and the MnO2/CNT nanocomposite electrodes are investigated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The MnO2/CNT nanocomposite electrode exhibits much larger specific capacitance compared with both the CNT electrode and the pure MnO2 electrode and significantly improves rate capability compared to the pure MnO2 electrode. The superior supercapacitive performance of the MnO2/CNT nancomposite electrode is due to its high specific surface area and unique hierarchy architecture which facilitate fast electron and ion transport.

Noble Metal Coated Single-Walled Carbon Nanotubes for Applications in Surface Enhanced Raman Scattering Imaging and Photothermal Therapy

Abstract: Single-walled carbon nanotubes (SWNTs) with various unique optical properties are interesting nanoprobes widely explored in biomedical imaging and phototherapies. Herein, DNA-functionalized SWNTs are modified with noble metal (Ag or Au) nanoparticles via an in situ solution phase synthesis method comprised of seed attachment, seeded growth, and surface modification with polyethylene glycol (PEG), yielding SWNT-Ag-PEG and SWNT-Au-PEG nanocomposites stable in physiological environments. With gold or silver nanoparticles decorated on the surface, the SWNT-metal nanocomposites gain an excellent concentration and excitation-source dependent surface-enhanced Raman scattering (SERS) effect. Using a near-infrared (NIR) laser as the excitation source, targeted Raman imaging of cancer cells labeled with folic acid (FA) conjugated SWNT-Au nanocomposite (SWNT-Au-PEG-FA) is realized, with images acquired in significantly shortened periods of time as compared to that of using nonenhanced SWNT Raman probes. Owing to the strong surface plasmon resonance absorption contributed by the gold shell, the SWNTs-Au-PEG-FA nanocomposite also offers remarkably improved photothermal cancer cell killing efficacy. This work presents a facile approach to synthesize water-soluble noble metal coated SWNTs with a strong SERS effect suitable for labeling and fast Raman spectroscopic imaging of biological samples, which has been rarely realized before. The SWNT-Au-PEG nanocomposite developed here may thus be an interesting optical theranostic probe for cancer imaging and therapy.

Tuning the mechanical properties of graphene oxide paper and its associated polymer nanocomposites by controlling cooperative intersheet hydrogen bonding.

Abstract: The mechanical properties of pristine graphene oxide paper and paper-like films of polyvinyl alcohol (PVA)-graphene oxide nanocomposite are investigated in a joint experimental–theoretical and computational study. In combination, these studies reveal a delicate relationship between the stiffness of these papers and the water content in their lamellar structures. ReaxFF-based molecular dynamics (MD) simulations elucidate the role of water molecules in modifying the mechanical properties of both pristine and nanocomposite graphene oxide papers, as bridge-forming water molecules between adjacent layers in the paper structure enhance stress transfer by means of a cooperative hydrogen-bonding network. For graphene oxide paper at an optimal concentration of ∼5 wt % water, the degree of cooperative hydrogen bonding within the network comprising adjacent nanosheets and water molecules was found to optimally enhance the modulus of the paper without saturating the gallery space. Introducing PVA chains into the gall...

ZnO/graphene-oxide nanocomposite with remarkably enhanced visible-light-driven photocatalytic performance

Abstract: In this work, a high-performance photocatalyst of ZnO/graphene-oxide (ZnO/GO) nanocomposite was synthesized via a facile chemical deposition route and used for the photodegradation of organic dye from water under visible light. The nanocomposite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller N2 adsorption–desorption analysis, and UV–Vis diffusion reflectance spectroscopy. The ZnO/GO nanocomposite consisting of flower-like ZnO nanoparticles anchored on graphene-oxide sheets has a high surface area and hierarchical porosity, which is benefit to the adsorption and mass transfer of dye and oxygen species. For the photodegradation of organic dyes under visible light, ZnO/GO nanocomposite exhibited remarkably enhanced photocatalytic efficiency than graphene-oxide sheets and flower-like ZnO particles. Moreover, the photocatalytic efficiency of ZnO/GO nanocomposite could be further improved by annealing the product in N2 atmosphere. The outstanding photocatalytic performance was ascribed to the efficient photosensitized electron injection and repressed charge carriers recombination in the composite with GO as electron collector and transporter, thus leading to continuous generation of reactive oxygen species for the degradation of methylene blue.

Metal‐Organic Framework Templated Synthesis of Fe2O3/TiO2 Nanocomposite for Hydrogen Production

Abstract: A new metal-organic framework (MOF)-templated method has been developed for the synthesis of a metal oxide nanocomposite with interesting photophysical properties. Fe-containing nanoscale MOFs are coated with amorphous titania, then calcined to produce crystalline Fe(2)O(3)/TiO(2) composite nanoparticles. This material enables photocatalytic hydrogen production from water using visible light, which cannot be achieved by either Fe(2)O(3) or TiO(2) alone or a mixture of the two.