Showing papers on "Nanocomposite published in 2014"

Highly aligned graphene/polymer nanocomposites with excellent dielectric properties for high-performance electromagnetic interference shielding.

Abstract: Nanocomposites that contain reinforcements with preferred orientation have attracted significant attention because of their promising applications in a wide range of multifunctional fields. Many efforts have recently been focused on developing facile methods for preparing aligned graphene sheets in solvents and polymers because of their fascinating properties including liquid crystallinity and highly anisotropic characteristics. Self-aligned in situ reduced graphene oxide (rGO)/polymer nanocomposites are prepared using an all aqueous casting method. A remarkably low percolation threshold of 0.12 vol% is achieved in the rGO/epoxy system owing to the uniformly dispersed, monolayer graphene sheets with extremely high aspect ratios (>30000). The self-alignment into a layered structure at above a critical filler content induces a unique anisotropy in electrical and mechanical properties due to the preferential formation of conductive and reinforcing networks along the alignment direction. Accompanied by the anisotropic electrical conductivities are exceptionally high dielectric constants of over 14000 with 3 wt% of rGO at 1 kHz due to the charge accumulation at the highly-aligned conductive filler/insulating polymer interface according to the Maxwell-Wagner-Sillars polarization principle. The highly dielectric rGO/epoxy nanocomposites with the engineered structure and properties present high performance electromagnetic interference shielding with a remarkable shilding efficiency of 38 dB.

Nanocomposite hydrogels for biomedical applications.

Abstract: Hydrogels mimic native tissue microenvironment due to their porous and hydrated molecular structure. An emerging approach to reinforce polymeric hydrogels and to include multiple functionalities focuses on incorporating nanoparticles within the hydrogel network. A wide range of nanoparticles, such as carbon-based, polymeric, ceramic, and metallic nanomaterials can be integrated within the hydrogel networks to obtain nanocomposites with superior properties and tailored functionality. Nanocomposite hydrogels can be engineered to possess superior physical, chemical, electrical, and biological properties. This review focuses on the most recent developments in the field of nanocomposite hydrogels with emphasis on biomedical and pharmaceutical applications. In particular, we discuss synthesis and fabrication of nanocomposite hydrogels, examine their current limitations and conclude with future directions in designing more advanced nanocomposite hydrogels for biomedical and biotechnological applications.

Metal Matrix Composites Reinforced by Nano-Particles—A Review

Abstract: Metal matrix composites reinforced by nano-particles are very promising materials, suitable for a large number of applications. These composites consist of a metal matrix filled with nano-particles featuring physical and mechanical properties very different from those of the matrix. The nano-particles can improve the base material in terms of wear resistance, damping properties and mechanical strength. Different kinds of metals, predominantly Al, Mg and Cu, have been employed for the production of composites reinforced by nano-ceramic particles such as carbides, nitrides, oxides as well as carbon nanotubes. The main issue of concern for the synthesis of these materials consists in the low wettability of the reinforcement phase by the molten metal, which does not allow the synthesis by conventional casting methods. Several alternative routes have been presented in literature for the production of nano-composites. This work is aimed at reviewing the most important manufacturing techniques used for the synthesis of bulk metal matrix nanocomposites. Moreover, the strengthening mechanisms responsible for the improvement of mechanical properties of nano-reinforced metal matrix composites have been reviewed and the main potential applications of this new class of materials are envisaged.

Cellulose nanocrystals and related nanocomposites: Review of some properties and challenges

Abstract: Cellulosic nanoparticles with high Young's modu- lus, crystallinity, specific surface area, and aspect ratio can be found in the natural structure of plant fibers. Indeed, lignocel- lulosic fibers consist of semicrystalline cellulose nanofibrils embedded in an amorphous matrix mainly composed of lignin and hemicelluloses. These nanostructures give the mechanical strength to higher plant cells, and are biodegradable, renew- able, resistant, and widely available to produce nanocompo- sites with low density, and improved and controlled mechanical, optical, and barrier properties. Nanoparticles can be extracted from cellulose using a top-down mechanically or chemically assisted deconstructing strategy, and owing to their highly reactive surface ensuing nanomaterials can be chemi- cally modified to tailor their properties for a wide range of applications. This review is limited to cellulose chemically extracted nanocrystals and aims to provide an overview about several aspects that involve this material, including sources, properties, challenges, and perspectives. V C 2014 Wiley Periodi- cals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 00, 000-000

Near Infrared Laser-Induced Targeted Cancer Therapy Using Thermoresponsive Polymer Encapsulated Gold Nanorods

Abstract: External stimuli, such as ultrasound, magnetic field, and light, can be applied to activate in vivo tumor targeting. Herein, we fabricated polymer encapsulated gold nanorods to couple the photothermal properties of gold nanorods and the thermo- and pH-responsive properties of polymers in a single nanocomposite. The activation mechamism was thus transformed from heat to near-infrared (NIR) laser, which can be more easily controlled. Doxorubicin, a clinical anticancer drug, can be loaded into the nanocomposite through electrostatic interactions with high loading content up to 24%. The nanocomposite’s accumulation in tumor post systematic administration can be significantly enhanced by NIR laser irradiation, providing a prerequisite for their therapeutic application which almost completely inhibited tumor growth and lung metastasis. Since laser can be manipulated very precisely and flexibly, the nanocomposite provides an ideally versatile platform to simultaneously deliver heat and anticancer drugs in a lase...

Enhanced removal of methylene blue and methyl violet dyes from aqueous solution using a nanocomposite of hydrolyzed polyacrylamide grafted xanthan gum and incorporated nanosilica.

Abstract: The synthesis and characterization of a novel nanocomposite is reported that was developed as an efficient adsorbent for the removal of toxic methylene blue (MB) and methyl violet (MV) from aqueous solution. The nanocomposite comprises hydrolyzed polyacrylamide grafted onto xanthan gum as well as incorporated nanosilica. The synthesis exploits the saponification of the grafted polyacrylamide and the in situ formation of nanoscale SiO2 by a sol–gel reaction, in which the biopolymer matrix promotes the silica polymerization and therefore acts as a novel template for nanosilica formation. The detailed investigation of the kinetics and the adsorption isotherms of MB and MV from aqueous solution showed that the dyes adsorb rapidly, in accordance with a pseudo-second-order kinetics and a Langmuir adsorption isotherm. The entropy driven process was furthermore found to strongly depend on the point of zero charge (pzc) of the adsorbent. The remarkably high adsorption capacity of dyes on the nanocomposites (effici...

Cobalt sulfide nanosheet/graphene/carbon nanotube nanocomposites as flexible electrodes for hydrogen evolution.

Abstract: Flexible three-dimensional (3D) nanoarchitectures have received tremendous interest recently because of their potential applications in wearable electronics, roll-up displays, and other devices. The design and fabrication of a flexible and robust electrode based on cobalt sulfide/reduced graphene oxide/carbon nanotube (CoS2 /RGO-CNT) nanocomposites are reported. An efficient hydrothermal process combined with vacuum filtration was used to synthesize such composite architecture, which was then embedded in a porous CNT network. This conductive and robust film is evaluated as electrocatalyst for the hydrogen evolution reaction. The synergistic effect of CoS2 , graphene, and CNTs leads to unique CoS2 /RGO-CNT nanoarchitectures, the HER activity of which is among the highest for non-noble metal electrocatalysts, showing 10 mA cm(-2) current density at about 142 mV overpotentials and a high electrochemical stability.

Humidity-sensing properties of chemically reduced graphene oxide/polymer nanocomposite film sensor based on layer-by-layer nano self-assembly

Abstract: Chemically reduced graphene oxide (RGO)/poly(diallylimethyammonium chloride) (PDDA) nanocomposite film sensor with high-performance humidity properties was reported in this paper. The film sensor was fabricated on flexible polyimide substrate with interdigital microelectrodes structure. By the layer-by-layer nano self-assembly approach, graphene oxide and PDDA were exploited to form hierarchical nanostructure, and then was partially reduced via solution-based chemically reduction for obtaining both conductivity and chemically active defect sites. The effect of hydrobromic acid treatment on the conductivity properties of PDDA/GO film was examined, further verifying the advantage of hydrobromic acid reduction. The humidity sensing properties of the presented nanocomposite film sensor, such as repeatability, hysteresis, stability, response–recovery characteristics, were investigated by exposing to the wide relative humidity range of 11–97% at room temperature. As a result, the sensor exhibited not only excellent sensing behavior to humidity, but also fast response–recovery time and good repeatability, highlighting the unique advantages of layer-by-layer nano self-assembly for film sensors fabrication. As last, the possible humidity sensing mechanism of the proposed sensor was discussed in detail.

Highly Thermally Conductive Papers with Percolative Layered Boron Nitride Nanosheets

Abstract: In this work, we report a dielectric nanocomposite paper with layered boron nitride (BN) nanosheets wired by one-dimensional (1D) nanofibrillated cellulose (NFC) that has superior thermal and mechanical properties. These nanocomposite papers are fabricated from a filtration of BN and NFC suspensions, in which NFC is used as a stabilizer to stabilize BN nanosheets. In these nanocomposite papers, two-dimensional (2D) nanosheets form a thermally conductive network, while 1D NFC provides mechanical strength. A high thermal conductivity has been achieved along the BN paper surface (up to 145.7 W/m K for 50 wt % of BN), which is an order of magnitude higher than that in randomly distributed BN nanosheet composites and is even comparable to the thermal conductivity of aluminum alloys. Such a high thermal conductivity is mainly attributed to the structural alignment within the BN nanosheet papers; the effects of the interfacial thermal contact resistance are minimized by the fact that the heat transfer is in the ...

Yolk–Satellite–Shell Structured Ni–Yolk@Ni@SiO2 Nanocomposite: Superb Catalyst toward Methane CO2 Reforming Reaction

Abstract: The CO2 (dry) reforming of methane (DRM) reaction is an environmentally benign process to convert two major greenhouse gases into synthesis gas for chemical and fuel production. A great challenge for this process involves developing catalysts with high carbon resistance abilities. Herein we synthesize, for the first time, a yolk–satellite–shell structured Ni–yolk@Ni@SiO2 nanocomposite for the DRM reaction by varying the shell thickness of Ni@SiO2 core shell nanoparticles. The formation of Ni–yolk@Ni@SiO2 is proved to be shell thickness dependent. Compared with Ni@SiO2, Ni–yolk@Ni@SiO2 with 11.2 nm silica shell thickness shows stable and near equilibrium conversion for CH4 and CO2 for 90 h at 800 °C with negligible carbon deposition. The dual effects of formation of small satellite Ni particles due to strong Ni–SiO2 interactions and yolk shell structures contribute to its high activity and stability. These findings shed light on the design of other metal yolk silica shell nanocomposites to be utilized in r...

Facile Synthesis of Au/g‐C3N4 Nanocomposites: An Inorganic/Organic Hybrid Plasmonic Photocatalyst with Enhanced Hydrogen Gas Evolution Under Visible‐Light Irradiation

Abstract: Noble-metal Au nanoparticles deposited on graphitic carbon nitride polymer (g-C3N4) photocatalyst by a facile deposition–precipitation method exhibited high photocatalytic activity for hydrogen gas production under visible-light irradiation. The Au/g-C3N4 nanocomposite plasmonic photocatalysts were characterized by X-ray diffraction spectroscopy, diffuse reflectance UV/Vis spectroscopy, FTIR spectroscopy, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical measurements. We studied the effect of Au deposition on the photocatalytic activity of g-C3N4 by investigation of optical, electronic, and electrical properties. Enhanced photocatalytic activity of Au/g-C3N4 naocomposite for hydrogen production was attributed to the synergic mechanism operating between the conduction band minimum of g-C3N4 and the plasmonic band of Au nanoparticles including high optical absorption, uniform distribution, and nanoscale particle size of gold. The mechanism of te photocatalytic activity of the nanocomposite photocatalyst is discussed in detail. Deposition of Au nanoparticles on g-C3N4 was optimized and it was found that 1 wt % Au-loaded g-C3N4 composite plasmonic photocatalyst generated a photocurrent density of 49 mA cm−2 and produced a hydrogen gas amount of 532 μmol under visible light, which were more than 3000 times higher and 23 times higher, respectively, than the values of neat g-C3N4.

Turn-On Fluorescence Sensor for Intracellular Imaging of Glutathione Using g-C3N4 Nanosheet–MnO2 Sandwich Nanocomposite

Abstract: Herein, a novel fluorescence sensor based on g-C3N4 nanosheet–MnO2 sandwich nanocomposite has been developed for rapid and selective sensing of glutathione (GSH) in aqueous solutions, as well as living cells. The graphitic-phase C3N4 (g-C3N4) nanosheet used here is a new type of carbon-based nanomaterial with high fluorescence quantum yield and high specific surface area. We demonstrate a facile one-step approach for the synthesis of a g-C3N4 nanosheet–MnO2 sandwich nanocomposite for the first time. The fluorescence of g-C3N4 nanosheet in this nanocomposite is quenched, which attributing to fluorescence resonance energy transfer (FRET) from a g-C3N4 nanosheet to the deposited MnO2. Upon the addition of GSH, MnO2 is reduced to Mn2+, which leads to the elimination of FRET. As a result, the fluorescence of g-C3N4 nanosheet is restored. Importantly, the chemical response of the g-C3N4–MnO2 nanocomposite exhibits great selectivity toward GSH relative to other electrolytes and biomolecules. Under the optimal co...

Topological‐Structure Modulated Polymer Nanocomposites Exhibiting Highly Enhanced Dielectric Strength and Energy Density

Abstract: Dielectric materials with high electric energy densities and low dielectric losses are of critical importance in a number of applications in modern electronic and electrical power systems. An organic–inorganic 0–3 nanocomposite, in which nanoparticles (0-dimensional) are embedded in a 3-dimensionally connected polymer matrix, has the potential to combine the high breakdown strength and low dielectric loss of the polymer with the high dielectric constant of the ceramic fillers, representing a promising approach to realize high energy densities. However, one significant drawback of the composites explored up to now is that the increased dielectric constant of the composites is at the expense of the breakdown strength, limiting the energy density and dielectric reliability. In this study, by expanding the traditional 0–3 nanocomposite approach to a multilayered structure which combines the complementary properties of the constituent layers, one can realize both greater dielectric displacement and a higher breakdown field than that of the polymer matrix. In a typical 3-layer structure, for example, a central nanocomposite layer of higher breakdown strength is introduced to substantially improve the overall breakdown strength of the multilayer-structured composite film, and the outer composite layers filled with large amount of high dielectric constant nanofillers can then be polarized up to higher electric fields, hence enhancing the electric displacement. As a result, the topological-structure modulated nanocomposites, with an optimally tailored nanomorphology and composite structure, yield a discharged energy density of 10 J/cm3 with a dielectric breakdown strength of 450 kV mm–1, much higher than those reported from all earlier studies of nanocomposites.

Self sensing carbon nanotube (CNT) and nanofiber (CNF) cementitious composites for real time damage assessment in smart structures

Abstract: The self sensing properties of cementitious composites reinforced with well dispersed carbon nanotubes and carbon nanofibers were investigated. The electrical resistance of cementitious nanocomposites with w/c = 0.3 reinforced with well dispersed carbon nanotubes (CNTs) and nanofibers (CNFs) at an amount of 0.1 wt% and 0.3 wt% of cement was experimentally determined and compared with resistivity results of nanocomposites fabricated with “as received” nanoscale fibers at the same loading. Results indicate that conductivity measurements, besides being a valuable tool in evaluating the smart properties of the nanocomposites, may provide a good correlation between the resistivity values measured and the degree of dispersion of the material in the matrix. The addition of CNTs and CNFs at different loadings was proven to induce a decrease in electrical resistance, with the nanocomposites containing 0.1 wt% CNTs yielding better electrical properties. Furthermore, conductivity measurements under cyclic compressive loading provided an insight in the piezoresistive properties of selected nanocomposites. Results confirm that nanocomposites, reinforced with 0.1 wt% CNTs and CNFs, exhibited an increased change in resistivity, which is indicative of the amplified sensitivity of the material in strain sensing.

Electrically controlled drug delivery from graphene oxide nanocomposite films.

Abstract: On-demand, local delivery of drug molecules to target tissues provides a means for effective drug dosing while reducing the adverse effects of systemic drug delivery. This work explores an electrically controlled drug delivery nanocomposite composed of graphene oxide (GO) deposited inside a conducting polymer scaffold. The nanocomposite is loaded with an anti-inflammatory molecule, dexamethasone, and exhibits favorable electrical properties. In response to voltage stimulation, the nanocomposite releases drug with a linear release profile and a dosage that can be adjusted by altering the magnitude of stimulation. No drug passively diffuses from the composite in the absence of stimulation. In vitro cell culture experiments demonstrate that the released drug retains its bioactivity and that no toxic byproducts leach from the film during electrical stimulation. Decreasing the size and thickness of the GO nanosheets, by means of ultrasonication treatment prior to deposition into the nanocomposite, alters the film morphology, drug load, and release profile, creating an opportunity to fine-tune the properties of the drug delivery system to meet a variety of therapeutic needs. The high level of temporal control and dosage flexibility provided by the electrically controlled GO nanocomposite drug delivery platform make it an exciting candidate for on-demand drug delivery.

Photoinduced Superwetting Single-Walled Carbon Nanotube/TiO2 Ultrathin Network Films for Ultrafast Separation of Oil-in-Water Emulsions

Abstract: A SWCNT/TiO2 nanocomposite ultrathin film that has superhydrophilic and underwater superoleophobic properties after UV-light irradiation is successfully prepared by coating TiO2 via the sol–gel process onto an SWCNT ultrathin network film. The robust and flexible SWCNT/TiO2 nanocomposite films with a thickness and pore size of tens of nanometers can separate both surfactant-free and surfactant-stabilized oil-in-water emulsions in an ultrafast manner with fluxes up to 30 000 L m–2 h–1 bar–1, which is 2 orders of magnitude higher than commercial filtration membranes with similar separation performance, and with high separation efficiency. Most importantly, the films exhibit excellent antifouling and self-cleaning performance during multiple cycles with the aid of the photocatalytic property of TiO2 nanoparticles. This work provides a route for designing ultrathin and superwetting films for effective separation of oil-in-water emulsions. The SWCNT/TiO2 ultrathin film is potentially useful in treating emulsif...

Na3V2(PO4)3@C core–shell nanocomposites for rechargeable sodium-ion batteries

Abstract: Na3V2(PO4)3 (NVP) is an attractive cathode material for sodium ion batteries due to its high theoretical energy density and stable three-dimensional (3D) NASICON structure. In this paper, a NVP@C core–shell nanocomposite has been synthesized through a hydrothermal assisted sol–gel method. Ascorbic acid and polyethylene glycol 400 (PEG-400) were synergistically used to control the particle growth and provide the surface coating of conductive carbon. The as-prepared nanocomposite was composed of a nanosized Na3V2(PO4)3 core with a typical size of ∼40 nm and a uniformly amorphous carbon shell with the thickness of a few nanometers. The electrode performance of the NVP@C core–shell nanocomposite as cathode for sodium ion batteries is investigated and compared with that of bare NVP and NVP/C. Among the samples examined, the NVP@C nanocomposite showed the best cycle life and rate capability. It rendered an initial capacity of 104.3 mA h g−1 at 0.5 C and 94.9 mA h g−1 at 5 C with a remarkable capacity retention of 96.1% after 700 cycles. Moreover, a full cell using the as-prepared nanocomposite as both the cathode and the anode active material has been successfully built, showing a reversible capacity of 90.9 mA h g−1 at 2 C with an output voltage of about 1.7 V and a specific energy density of about 154.5 W h kg−1. The enhanced electrode performance is attributed to the combination of particle downsizing and carbon coating, which can favor the migration of both electrons and ions.

Carbon functionalized TiO2 nanofibers for high efficiency photocatalysis

Abstract: TiO2 nanofibers (30–50 nm diameter), fabricated by the electro-spinning process, were modified with organo-silane agents via a coupling reaction and were grafted with carbohydrate molecules. The mixture was carbonized to produce a uniform coating of amorphous carbon on the surface of the TiO2 nanofibers. The TiO2@C nanofibers were characterized by high resolution electron microscopy (HRTEM), x-ray diffraction (XRD), x-ray photoelectron (XPS), Fourier transform infrared (FTIR) and UV-vis spectroscopy. The photocatalytic property of the functional TiO2 and carbon nanocomposite was tested via the decomposition of an organic pollutant. The catalytic activity of the covalently functionalized nanocomposite was found to be significantly enhanced in comparison to unfunctionalized composite and pristine TiO2 due to the synergistic effect of nanostructured TiO2 and amorphous carbon bound via covalent bonds. The improvement in performance is due to bandgap modification in the 1D co-axial nanostructure where the anatase phase is bound by nano-carbon, providing a large surface to volume ratio within a confined space. The superior photocatalytic performance and recyclability of 1D TiO2@C nanofiber composites for water purification were established through dye degradation experiments.

Highly conducting, strong nanocomposites based on nanocellulose-assisted aqueous dispersions of single-wall carbon nanotubes.

Abstract: It is challenging to obtain high-quality dispersions of single-wall nanotubes (SWNTs) in composite matrix materials, in order to reach the full potential of mechanical and electronic properties. The most widely used matrix materials are polymers, and the route to achieving high quality dispersions of SWNT is mainly chemical functionalization of the SWNT. This leads to increased cost, a loss of strength and lower conductivity. In addition full potential of colloidal self-assembly cannot be fully exploited in a polymer matrix. This may limit the possibilities for assembly of highly ordered structural nanocomposites. Here we show that nanofibrillated cellulose (NFC) can act as an excellent aqueous dispersion agent for as-prepared SWNTs, making possible low-cost exfoliation and purification of SWNTs with dispersion limits exceeding 40 wt %. The NFC:SWNT dispersion may also offer a cheap and sustainable alternative for molecular self-assembly of advanced composites. We demonstrate semitransparent conductive fi...