Chemically Modified Graphene Research Articles

Stripping voltammetry at chemically modified graphenes

Several chemically modified graphene (CMG) materials were used to modify bare glassy carbon (GC) electrodes for the square wave anodic stripping voltammetry detection of cadmium ion concentration in aqueous solution, without the use of additives to amplify the detection signal. These CMGs included graphene oxide, graphite oxide, thermally reduced graphene oxide, chemically reduced graphene oxide and electrochemically reduced graphene oxide. The electrochemical performances of these modified electrodes were compared and the recently claimed advantages of using graphene materials to modify electrodes for the ASV detection of trace metal ions was thus challenged. Two CMG materials were proposed as suitable candidates for further investigations in their application towards real world sample analysis.

Impedimetric immunoglobulin G immunosensor based on chemically modified graphenes

Immunosensors which display high sensitivity and selectivity are of utmost importance to the biomedical field. Graphene is a material which has immense potential for the fabrication of immunosensors. For the first time, we evaluate the immunosensing capabilities of various graphene surfaces in this work. We propose a simple and label-free electrochemical impedimetric immunosensor for immunoglobulin G (IgG) based on chemically modified graphene (CMG) surfaces such as graphite oxide, graphene oxide, thermally reduced graphene oxide and electrochemically reduced graphene oxide. Disposable electrochemical printed electrodes were first modified with CMG materials before anti-immunoglobulin G (anti-IgG), which is specific to IgG, was immobilized. The principle of detection lies in the changes in impedance spectra of the redox probe after the attachment of IgG to the immobilized anti-IgG. It was found that thermally reduced graphene oxide has the best performance when compared to the other CMG materials. In addition, the optimal concentration of anti-IgG to be deposited onto the modified electrode surface is 10 μg ml(-1) and the linear range of detection of the immunosensor is from 0.3 μg ml(-1) to 7 μg ml(-1). Finally, the fabricated immunosensor also displays selectivity for IgG.

Nanocomposites and macroscopic materials: assembly of chemically modified graphene sheets

Self-assembly of chemically modified graphenes (CMGs), including graphene oxide (GO), reduced graphene oxide (RGO) and their derivatives, has emerged as one of the most appealing strategies to develop unprecedented graphene-based functional materials. With the assistance of various non-covalent forces such as hydrogen bonding, ionic, amphiphilic and π-π interactions, CMGs decorated with multiple functional groups are favorable for assembly with different organic and inorganic components which can result in hierarchical composites possessing unique structures and functions. In this review, we will summarize the state-of-the-art self-assembly strategies that have been established to construct CMG based nanomaterials, including nanoparticles, nanospheres, nanofibers, nanorods, nanosheets, and macroscopic thin films, fibers and porous networks. The driving forces involved in the self-assembly process will be elucidated in the context. Further, we will also highlight several representative examples of applications regarding the self-assembled CMG based materials.

Advances in Graphene-Based Sensors and Devices

-1 s -1 ), high carrier density (10 13 cm -2 ), high thermal conductivity, room temperature Hall effect, ambipolar field-effect characteristics, high signal-to-noise ratio (due to low intrinsic noises), and extremely high mechanical strength (200 times greater than steel, tensile modulus of 1 TPa). The large surface area of graphene enhances the surface loading of desired biomolecules, either through passive adsorption, or by covalent crosslinking to the reactive groups of biomolecules. On the other hand, the excellent conductivity and small band gap of graphene are beneficial for the conduction of electrons between the biomolecules and the electrode surface. Graphene has about two-fold higher effective surface area and greater cost-effectiveness than carbon nanotubes. Additionally, it has greater homogenous surface that is responsible for highly uniform and efficient functionalization. Graphene has been synthesized by several methods that include exfoliation of graphite, electric arc discharge, epitaxial growth on electrically insulating surfaces, opening of carbon nanotubes, growth from metal-carbon melts, pyrolysis of sodium ethoxide, sonication of graphite, reduction of carbon dioxide, Chemical Vapor Deposition (CVD), and reduction of graphene oxide. The mechanical exfoliation is unable to produce large graphene sheets and also has low throughput. However, CVD can produce large areas of single layer graphene for mass production. The chemical or thermal reduction of graphene oxide is another mass production method that is most commonly employed due to its higher cost-effectiveness. It has also been reported that graphene synthesized by chemical redox reaction possess many structural defects that are highly beneficial for electrochemical applications. A wide range of chemical modification and biomolecular binding strategies [3], have been developed for the induction of specific functional groups (such as carboxyl, hydroxyl, sulfonate, acid chloride and amine) on graphene and for binding the chemically-modified graphene to the biomolecules, respectively. Similarly, several methods have also been developed for preparing graphene-nanocomposites by conjugating graphene to nanomaterials, and/or polymers.

ChemInform Abstract: Two‐Dimensional Nanocomposites Based on Chemically Modified Graphene.

AbstractReview: ca. 50 refs.

Chemically-modified graphene sheets as an active layer for eco-friendly metal electroplating on plastic substrates

Eco-friendly nickel (Ni) electroplating was carried out on a plastic substrate using chemically modified graphene sheets as an active and conductive layer to initiate electroplating without using conventional pre-treatment or electroless metal-seeding processes. A graphene oxide (GO) solution was self-assembled on a polyethylene terephthalate (PET) film followed by evaporation to give GO layers (thickness around 6.5μm) on PET (GO/PET) film. Then, the GO/PET film was chemically and thermally reduced to convert the GO layers to reduced graphene oxide (RGO) layers on the PET substrate. The RGO-coated PET (RGO/PET) film showed the sheet resistance of 100Ω per square. On RGO/PET film, Ni electroplating was conducted under the constant-current condition and the entire surface of the PET film was completely metalized with Ni without any voids.

Highly dispersed Pd nanoparticles on chemically modified graphene with aminophenyl groups for formic acid oxidation

A novel electrode material based on chemically modified graphene (CMG) with aminophenyl groups is covalently functionalized by a nucleophilic ring-opening reaction between the epoxy groups of graphene oxide and the aminophenyl groups of p-phenylenediamine. Palladium nanoparticles with an average diameter of 4.2 nm are deposited on the CMG by a liquid-phase borohydride reduction. The electrocatalytic activity and stability of the Pd/CMG composite towards formic acid oxidation are found to be higher than those of reduced graphene oxide and commercial carbon materials such as Vulcan XC-72 supported Pd electrocatalysts.

Physical Vapor Deposition of Metal Nanoparticles on Chemically Modified Graphene: Observations on Metal–Graphene Interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to ∼1.5 nm for Au) and coverage (up to 5 × 10(4) μm(-2) for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metal-graphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.

Two‐Dimensional Nanocomposites Based on Chemically Modified Graphene

The multiple functional groups and unique two-dimensional (2D) morphology make chemically modified graphene (CMG) an ideal template for the construction of 2D nanocomposites with various organic/inorganic components. Additionally, the recovered electrical conductivity of CMG may provide a fast-electron-transport channel and can thus promote the application of the resultant nanocomposites in optoelectronic and electrochemical devices. This Concept article summarizes the different strategies for the bottom-up fabrication of CMG-based 2D nanocomposites with small organic molecules, polymers, and inorganic nanoparticles, which represent the new directions in the development of graphene-based materials.

Electrochemistry at Chemically Modified Graphenes

Electrochemical applications of graphene are of great interest to many researchers as they can potentially lead to crucial technological advancements in fabrication of electrochemical devices for energy production and storage, and highly sensitive sensors. There are many routes towards fabrication of bulk quantities of chemically modified graphenes (CMG) for applications such as electrode materials. Each of them yields different graphene materials with different functionalities and structural defects. Here, we compare the electrochemical properties of five different chemically modified graphenes: graphite oxide, graphene oxide, thermally reduced graphene oxide, chemically reduced graphene oxide, and electrochemically reduced graphene oxide. We characterized these materials using transmission electron microscopy, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry, which allowed us to correlate the electrochemical properties with the structural and chemical features of the CMGs. We found that thermally reduced graphene oxide offers the most favorable electrochemical performance among the different materials studied. Our findings have a profound impact for the applications of chemically modified graphenes in electrochemical devices.

Thermomechanical properties of chemically modified graphene/poly(methyl methacrylate) composites made by in situ polymerization

The morphology and thermomechanical properties of composites of poly(methyl methacrylate) (PMMA) and chemically modified graphene (CMG) fillers were investigated. For composites made by in situ polymerization, large shifts in the glass transition temperature were observed with loadings as low as 0.05 wt.% for both chemically-reduced graphene oxide (RG-O) and graphene oxide (G-O)-filled composites. The elastic modulus of the composites improved by as much as 28% at just 1 wt.% loading. Mori–Tanaka theory was used to quantify dispersion, suggesting platelet aspect ratios greater than 100 at low loadings and a lower quality of dispersion at higher loadings. Fracture strength increased for G-O/PMMA composites but decreased for RG-O/PMMA composites. Wide angle X-ray scattering suggested an exfoliated morphology of both types of CMG fillers dispersed in the PMMA matrix, while transmission electron microscopy revealed that the platelets adopt a wrinkled morphology when dispersed in the matrix. Both techniques suggested similar exfoliation and dispersion of both types of CMG filler. Structural characterization of the resulting composites using gel permeation chromatography and solid state nuclear magnetic resonance showed no change in the polymer structure with increased loading of CMG filler.

Assembly of chemically modified graphene: methods and applications

Chemically modified graphenes (CMGs) are unique building blocks for “bottom up” nanotechnology because of their single-atom thickness, two-dimensional conjugated structure, and exceptional physical and chemical properties. Various hierarchical structures and functional nanocomposites based on CMGs have been prepared by self-assembly. Here, we review the recent advances in the assembly of CMGs in solution or at interfaces, and demonstrate the wide application of the resulting materials.

Synergistic effect of Cu2+-coordinated carbon nanotube/graphene network on the electrical and mechanical properties of polymer nanocomposites

A novel hybrid nanofiller system, in which oxidized multi-walled carbon nanotubes (MWCNTs) and chemically modified graphene (CMG) are coordinated by copper ions, is fabricated. The CMG sheets are efficiently isolated and bridged by MWCNTs through copper ion coordination to form a uniform network, and the Cu2+-coordinated MWCNT/CMG network can be easily introduced to a variety of polymer matrices by solution mixing. For example, the Cu2+-coordinated MWCNT/CMG network is successfully incorporated in poly(styrene-co-butadiene-co-styrene) (SBS), one of the most widely used synthetic rubbers. The molecular-level dispersion of the nanofillers in the SBS matrix facilitates efficient electron and load transfer. The Cu2+-coordinated MWCNT/CMG network demonstrates a synergistic effect that cannot be achieved by simple physical mixing of the two nanofillers. The obtained SBS nanocomposites have much better electrical and mechanical properties than those filled with MWCNTs, CMG or a non-coordinated hybrid nanofiller system at the same loading. This fabrication method may open the door to a new class of high-performance polymer-matrix composites.

Chemically-modified graphenes for oxidation of DNA bases: analytical parameters

We studied the electroanalytical performances of chemically-modified graphenes (CMGs) containing different defect densities and amounts of oxygen-containing groups, namely graphite oxide (GPO), graphene oxide (GO), thermally reduced graphene oxide (TR-GO) and electrochemically reduced graphene oxide (ER-GO) by comparing the sensitivity, selectivity, linearity and repeatability towards the oxidation of DNA bases. We have observed that for differential pulse voltammetric (DPV) detection of adenine and cytosine, all CMGs showed enhanced sensitivity to oxidation, while for guanine and thymine, ER-GO and TR-GO exhibited much improved sensitivity over bare glassy carbon (GC) as well as over GPO and GO. There is also significant selectivity enhancement when using GPO for adenine and TR-GO for thymine. Our results have uncovered that the differences in surface functionalities, structure and defects of various CMGs largely influence their electrochemical behaviour in detecting the oxidation of DNA bases. The findings in this report will provide a useful guide for the future development of label-free electrochemical devices for DNA analysis.

High-performance supercapacitor electrodes based on graphene hydrogels modified with 2-aminoanthraquinone moieties

2-Aminoanthraquinone (AAQ) molecules were covalently grafted onto chemically modified graphene (CMG), and the AAQ functionalized CMG sheets were self-assembled into macroporous hydrogels for supercapacitor electrodes. The electrode based on the AAQ modified self-assembled graphene hydrogel (AQSGH) showed a high specific capacitance of 258 F g(-1) at a discharge current density of 0.3 A g(-1), which is much larger than that of a pure graphene hydrogel (193 F g(-1)). Furthermore, the AQSGH electrode exhibited excellent rate capability and a long cycle life. This is mainly due to the covalently bonded AAQ moieties contributing additional redox capacitance. Furthermore, the highly conductive graphene hydrogel scaffold provided a large specific surface area for forming electric double layers and convenient routes for charge transfer and electrolyte diffusion.

Chemically modified graphene sheets by functionalization of highly exfoliated graphite

Highly exfoliated graphite (HEG) containing multi-, bi- and monolayer graphenes has been prepared from an alternative class of precursors – fluorinated graphite intercalation compounds, namely, poly(dicarbon fluoride) intercalation compounds C2F·xR. Treatment of HEG by mixture of concentrated nitric and sulfuric acids results in chemically modified graphenes (CMG) dispersible in water or alcohol medium without any surfactants or stabilizers. The samples were examined by elemental analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), IR, Raman and UV-vis spectroscopies. Elemental analysis and IR data indicate that covalent functionalization with oxygen-containing groups, such as carboxyl group, occurs upon acid treatment. AFM images show thin sheets of about 1 nm, confirming the well-dispersed state of the material. Dispersions of CMG sheets from highly exfoliated graphite are very stable colloids (over a year) and can serve for further functionalization.

On the structure and topography of free-standing chemically modified graphene

The mechanical, electrical and chemical properties of chemically modified graphene (CMG) are intrinsically linked to its structure. Here, we report on our study of the topographic structure of free-standing CMG using atomic force microscopy (AFM) and electron diffraction. We find that, unlike graphene, suspended sheets of CMG are corrugated and distorted on nanometre length scales. AFM reveals not only long-range (100 nm) distortions induced by the support, as previously observed for graphene, but also short-range corrugations with length scales down to the resolution limit of 10 nm. These corrugations are static not dynamic, and are significantly diminished on CMG supported on atomically smooth substrates. Evidence for even shorter-range distortions, down to a few nanometres or less, is found by electron diffraction of suspended CMG. Comparison of the experimental data with simulations reveals that the mean atomic displacement from the nominal lattice position is of order 10% of the carbon–carbon bond length. Taken together, these results suggest a complex structure for CMG where heterogeneous functionalization creates local strain and distortion.

Development of a Glucose Biosensor Using Advanced Electrode Modified by Nanohybrid Composing Chemically Modified Graphene and Ionic Liquid

AbstractNanohybrids of chemically modified graphene (CMG) and ionic liquid (IL) were prepared by sonication to modify the electrode. The modified CMG‐IL electrodes showed a higher current and smaller peak‐to‐peak potential separation than a bare electrode due to the promoted electron transfer rate. Furthermore, the glucose oxidase (GOx) immobilized on the modified electrode displayed direct electron transfer rate and symmetrical redox potentials with a linear relationship at different scan rates. The fabricated GOx/CMG‐IL electrodes were developed selective glucose biosensor with respect to a sensitivity of 0.64 μA mM−1, detection limit of 0.376 mM, and response time of <5 s.

Monodisperse Chemically Modified Graphene Obtained by Density Gradient Ultracentrifugal Rate Separation

A simple density gradient ultracentrifuge separation method has been developed for sorting chemically modified graphene (CMG) by sheet size and surface chemistry in just a few minutes. By optimizing the parameters, including the density gradient and centrifugation time, CMG sheets with specific size ranges and optical properties can be targeted selectively. UV-vis absorbance and photoluminescence spectra revealed the properties of separated CMG samples are highly dependent on their sheet size and degree of oxidation. A possible mechanism for the separation is discussed.

Graphene-Based Single-Bacterium Resolution Biodevice and DNA Transistor: Interfacing Graphene Derivatives with Nanoscale and Microscale Biocomponents

Establishing "large-contact-area" interfaces of sensitive nanostructures with microbes and mammalian cells will lead to the development of valuable tools and devices for biodiagnostics and biomedicine. Chemically modified graphene (CMG) nanostructures with their microscale area, sensitive electrical properties, and modifiable chemical functionality are excellent candidates for such biodevices at both biocellular and biomolecular scale. Here, we report on the fabrication and functioning of a novel CMG-based (i) single-bacterium biodevice, (ii) label-free DNA sensor, and (iii) bacterial DNA/protein and polyelectrolyte chemical transistor. The bacteria biodevice was highly sensitive with a single-bacterium attachment generating approximately 1400 charge carriers in a p-type CMG. Similarly, single-stranded DNA tethered on graphene hybridizes with its complementary DNA strand to reversibly increase the hole density by 5.61 x 1012 cm(-2). We further demonstrate (a) a control on the device sensitivity by manipulating surface groups, (b) switching of polarity specificity by changing surface polarity, and (c) a preferential attachment of DNA on thicker CMG surfaces and sharp CMG wrinkles.