Graphene-based electrodes have recently gained popularity due to their superior electrochemical properties. However, the exact mechanisms of electrochemical activity are not yet understood. Here, we present data from NADH oxidation and ferri/ferrocyanide redox probe experiments to demonstrate that both (i) the porosity of the graphene electrodes, as effected by the packing morphology, and (ii) the functional group and the lattice defect concentration play a significant role on their electrochemical performance.
A polymer compn., contg. a polymer matrix which contains an elastomer; and a functional graphene which displays no signature of graphite and/or graphite oxide, as detd. by x-ray diffraction, exhibits excellent strength, toughness, modulus, thermal stability and elec. cond. [on SciFinder(R)]
When applied on the counter electrode of a dye-sensitized solar cell, functionalized graphene sheets with oxygen-containing sites perform comparably to platinum (conversion efficiencies of 5.0 and 5.5%, respectively, at 100 mW cm(-2) AM1.56 simulated light). To interpret the catalytic activity of functionalized graphene sheets toward the reduction of triiodide, we propose a new electrochemical impedance spectroscopy equivalent circuit that matches the observed spectra features to the appropriate phenomena. Using cyclic voltammetry, we also show that tuning our material by increasing the amount of oxygen-containing functional groups can improve its apparent catalytic activity. Furthermore, we demonstrate that a functionalized graphene sheet based ink can serve as a catalytic, flexible, electrically conductive counter electrode material.
Graphene, emerging as a true 2-dimensional material, has received increasing attention due to its unique physicochemical properties (high surface area, excellent conductivity, high mechanical strength, and ease of functionalization and mass production). This article selectively reviews recent advances in graphene-based electrochemical sensors and biosensors. In particular, graphene for direct electrochemistry of enzyme, its electrocatalytic activity toward small biomolecules (hydrogen peroxide, NADH, dopamine, etc.), and graphene-based enzyme biosensors have been summarized in more detail; Graphene-based DNA sensing and environmental analysis have been discussed. Future perspectives in this rapidly developing field are also discussed.
An electrochemical sensor based on the electrocatalytic activity of functionalized graphene for sensitive detection of paracetamol is presented. The electrochemical behaviors of paracetamol on graphene-modified glassy carbon electrodes (GCEs) were investigated by cyclic voltammetry and square-wave voltammetry. The results showed that the graphene-modified electrode exhibited excellent electrocatalytic activity to paracetamol. A quasi-reversible redox process of paracetamol at the modified electrode was obtained, and the over-potential of paracetamol decreased significantly compared with that at the bare GCE. Such electrocatalytic behavior of graphene is attributed to its unique physical and chemical properties, e.g., subtle electronic characteristics, attractive pi-pi interaction, and strong adsorptive capability. This electrochemical sensor shows an excellent performance for detecting paracetamol with a detection limit of 3.2 x 10(-8) M, a reproducibility of 5.2% relative standard deviation, and a satisfied recovery from 96.4% to 103.3%. The sensor shows great promise for simple, sensitive, and quantitative detection and screening of paracetamol. (C) 2010 Elsevier B.V. All rights reserved.
Nanocomposite materials consist of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]
Nanocomposite materials consists of a metal oxide bonded to at least one graphene material. The graphene layer has a carbon to oxygen ratio of (20-500):1 and a surface area of 600-2630 m2/g. The metal oxide can be an oxide of Ti, Sn, Ni, Mn, V, Si, or Co, preferably titania in the form of rutile or anatase, or tin oxide. The nanocomposite materials exhibit a specific capacity of at least twice that of the metal oxide material without the graphene at a charge/discharge rate of ⪆10 C. The nanocomposite material is prepd. by providing graphene in a first suspension; dispersing the graphene with a surfactant, esp. sodium dodecyl sulfate; adding a metal oxide precursor to the dispersed graphene to form a second suspension; and pptg. the metal oxide from the second suspension onto at least one surface of the dispersed graphene to form the nanocomposite material. The nanocomposite material can be used in an energy storage device, esp. in a lithium ion battery as electrode material. [on SciFinder(R)]
Nitrogen-doped graphene (N-graphene) is obtained by exposing graphene to nitrogen plasma. N-graphene exhibits much higher electrocatalytic activity toward oxygen reduction and H(2)O(2) reduction than graphene, and much higher durability and selectivity than the widely-used expensive Pt for oxygen reduction. The excellent electrochemical performance of N-graphene is attributed to nitrogen functional groups and the specific properties of graphene. This indicates that N-graphene is promising for applications in electrochemical energy devices (fuel cells, metal-air batteries) and biosensors.
Fibers comprise a compn. including a polymer and graphene sheets. The fibers can be further formed into yarns, cords, and fabrics. The fibers can be polyamide, polyester, acrylic, acetate, modacrylic, spandex, lyocell fibers, and the like. Such fibers can take on a variety of forms, including, staple fibers, spun fibers, monofilaments, multifilaments, and the like. [on SciFinder(R)]
A novel electrochemical immunosensor for sensitive detection of cancer biomarker alpha-fetoprotein (AFP) is described that uses a graphene sheet sensor platform and functionalized carbon nanospheres (CNSs) labeled with horseradish peroxidase-secondary antibodies (HRP-Ab2). Greatly enhanced sensitivity for the cancer biomarker is based on a dual signal amplification strategy: first, the synthesized CNSs yielded a homogeneous and narrow size distribution, which allowed several binding events of HRP-Ab2 on each nanosphere. Enhanced sensitivity was achieved by introducing the multibioconjugates of HRP-Ab2-CNSs onto the electrode surface through "sandwich" immunoreactions. Second, functionalized graphene sheets used for the biosensor platform increased the surface area to capture a large amount of primary antibodies (Ab1), thus amplifying the detection response. On the basis of the dual signal amplification strategy of graphene sheets and the multienzyme labeling, the developed immunosensor showed a 7-fold increase in detection signal compared to the immunosensor without graphene modification and CNSs labeling. The proposed method could respond to 0.02 ng mL(-1) AFP with a linear calibration range from 0.05 to 6 ng mL(-1). This amplification strategy is a promising platform for clinical screening of cancer biomarkers and point-of-care diagnostics.
Surfactant or polymer directed self-assembly has been widely investigated to prepare nanostructured metal oxides, semiconductors, and polymers, but this approach is mostly limited to two-phase materials, organic/inorganic hybrids, and nanoparticle or polymer-based nanocomposites. Self-assembled nanostructures from more complex, multiscale, and multiphase building blocks have been investigated with limited success. Here, we demonstrate a ternary self-assembly approach using graphene as fundamental building blocks to construct ordered metal oxide-graphene nanocomposites. A new class of layered nanocomposites is formed containing stable, ordered alternating layers of nanocrystalline metal oxides with graphene or graphene stacks. Alternatively, the graphene or graphene stacks can be incorporated into liquid-crystal-templated nanoporous structures to form high surface area, conductive networks. The self-assembly method can also be used to fabricate free-standing, flexible metal oxide-graphene nanocomposite films and electrodes. We have investigated the Li-ion insertion properties of the self-assembled electrodes for energy storage and show that the SnO2-graphene nanocomposite films can achieve near theoretical specific energy density without significant charge/discharge degradation.
A modified graphite oxide material contains a thermally exfoliated graphite oxide with a surface area of from ∼300-2600 m2/g, wherein the thermally exfoliated graphite oxide displays no signature of the original graphite and/or graphite oxide, as detd. by x-ray diffraction. [on SciFinder(R)]
Tire cords comprising fibers including at least one polymer and graphene sheets. Graphene sheets are added to poly(ethylene terephthalate) (PET) by melt compounding in an extruder to yield a PET compn. comprising about 0.25 wt.% graphene sheets. The PET compn. is then solid phase polymd. at 215° to an IV of about 1 dL/g. The compn. is spun into monofilaments that are then post drawn to a draw ratio of about 4 to 5. After drawing, the filaments have a diam. of about 120 μ. The storage modulus of the monofilaments is then measured as a function of temp. using a dynamic mech. analyzer (DMA). [on SciFinder(R)]
We have developed electrically conducting silicone elastomer nanocomposites that serve both as compliant electrodes in an electrostatic actuator and, at the same time, as optically active elements creating structural color. We demonstrate the capabilities of our setup by actuating an elastomeric diffraction grating and colloidal-crystal-based photonic structures. (C) 2010 Optical Society of America