Surface Modification Of Graphene Research Articles

Low Temperature Plasma Process Effectively Modifies Surface of Graphene

Abstract Harnessing graphene's potential for commercial use requires attaining homogeneous dispersion and strong chemical bonding with the matrix of a target material. This can be achieved by effective surface modification. This article discusses approaches to graphene surface modification and includes a case study for using graphene as a filler to improve the mechanical properties of polymer composites.

Fabrication of graphene quantum dot-decorated graphene sheets via chemical surface modification.

A novel approach to link graphene quantum dots (GQDs) with graphene was explored via chemical surface modification of graphene using 1,5-diaminonapthalene (DAN).

Graphene/thermoplastic polyurethane nanocomposites: Surface modification of graphene through oxidation, polyvinyl pyrrolidone coating and reduction

Herein, oxidation, polyvinyl pyrrolidone (PVP) coating and reduction are used to modify the surface of graphene in thermoplastic polyurethane (TPU)/graphene nanocomposites. It is demonstrated that graphene could be easily dispersed in TPU with PVP absorbed on reduced graphene oxide (RGO) as stabilizer during reduction. In the stress–strain curves for these composites containing GO, PVP coated GO (GO/PVP) and reduced GO/PVP (RGO/PVP) as filler, PVP coating and reduction can largely enhance the stress in low modulus region. It is thought to largely related with enhanced interfacial interaction between filler and matrix and healing of graphene structure during reduction. Consequently, the modulus of TPU/GO/PVP and TPU/RGO/PVP is significantly increased. Meanwhile, an electrical percolation threshold of 0.35wt.% is obtained for TPU/RGO/PVP. Comparing with the results in literature, the filler surface modification used in this study has created nanocomposites with a good balance between electrical conductivity and mechanical properties.

Synthesis of graphene@branching-like polypyrrole@CoFe2O4 composites and their excellent electromagnetic wave absorption properties

In order to expand the scope of electromagnetic wave absorbers, the ternary composites composed of graphene, branching-like polypyrrole and CoFe2O4 nanoparticles were synthesized. TEM results indicated that polypyrrole on the surface of graphene had a branching-like geometrical morphology and the diameter of CoFe2O4 nanoparticles ranged from 5 to 15nm. The electromagnetic wave absorbability revealed that the ternary composites exhibited excellent electromagnetic wave absorption properties. The maximum reflection loss was up to −50.8dB at 14.5GHz and the absorption bandwidths with the reflection loss exceeding −10dB were 4.2GHz with a thickness of only 1.5mm. Furthermore, our development strategies confirmed that the surface modification of graphene with branching-like polypyrrole and CoFe2O4 nanoparticles could make the ternary composites have a promising future in electromagnetic wave absorption materials.

Polyamidoamine dendrimer and oleic acid-functionalized graphene as biocompatible and efficient gene delivery vectors.

Functionalized graphene has good potential in biomedical applications. To address a better and multiplex design of graphene-based gene vectors, the graphene-oleate-polyamidoamine (PAMAM) dendrimer hybrids were synthesized by the oleic acid adsorption and covalent linkage of PAMAM dendrimers. The micromorphology, electrical charge property, and amount of free amine groups of the graphene-oleate-PAMAM hybrids were characterized, and the peripheral functional groups were identified. The PAMAM dendrimers could be tethered onto graphene surface in high density. The graphene-oleate-PAMAM hybrids exhibit relatively good dispersity and stability in aqueous solutions. To evaluate the potential application of the hybrids in gene delivery vectors, cytotoxicity to HeLa and MG-63 cells and gene (plasmid DNA of enhanced green fluorescent protein) transfection capacity of the hybrids were investigated in detail. The graphene-oleate-PAMAM hybrids show mammalian cell type- and dose-dependent in vitro cytotoxicity. Under the optimal condition, the hybrids possess good biocompatibility and gene transfection capacity. The surface modification of graphene with oleic acid and PAMAM improves the gene transfection efficiency 13 times in contrast to the ultrasonicated graphene. Moreover, the hybrids show better transfection efficiency than the graphene oxide-PAMAM without the oleic acid modification.

A powerful tool for graphene functionalization: Benzophenone mediated UV-grafting

The surface modification of graphene is of fundamental importance when working on the fabrication of high performing polymeric nanocomposite exploiting the exciting properties of this carbon-based material. Using low cost graphene oxide as starting material, trading on its richness of –OH groups and its ability to be reduced under UV light, a facile two-step UV-based process for the reduction to graphene and the simultaneous covalent grafting of initiating moieties at its surface is here proposed. This procedure enables the subsequent photo-grafting of a great variety of monomers for graphene surface functionalization.Chemical, structural and electrical analysis of the functionalized graphene sheets demonstrated the reduction of the starting oxide and the grafting of the initiator and of the acrylic monomers used in this study. This procedure opens the route for a low cost production of grafted graphene that can be easily dispersed in organic matrices, in order to produce highly performing functional materials.

Functionalized graphene foam as electrode for improved electrochemical storage

We report on a non-covalent functionalization of graphene foam (GF) synthesized via chemical vapour deposition (CVD). The GF was treated with pyrene carboxylic acid (PCA) which acted as a source of oxygen and/or hydroxyl groups attached to the surface of the graphene foam for its electrochemical performance improvement. The modified graphene surface enabled a high pseudocapacitive effect on the GF. A specific capacitance of 133.3 F g−1, power density ∼ 145.3 kW kg−1 and energy density ∼ 4.7 W h kg−1 were achieved based on the functionalized foam in 6 M KOH aqueous electrolyte. The results suggest that non-covalent functionalization might be an effective approach to overcome the restacking problem associated with graphene electrodes and also signify the importance of surface functionalities in graphene-based electrode materials.

Tuning TiO2nanoparticle morphology in graphene–TiO2hybrids by graphene surface modification

We report the hydrothermal synthesis of graphene (GNP)-TiO2 nanoparticle (NP) hybrids using COOH and NH2 functionalized GNP as a shape controller. Anatase was the only TiO2 crystalline phase nucleated on the functionalized GNP, whereas traces of rutile were detected on unfunctionalized GNP. X-Ray Photoelectron spectroscopy (XPS) showed C-Ti bonds on all hybrids, thus confirming heterogeneous nucleation. GNP functionalization induced the nucleation of TiO2 NPs with specific shapes and crystalline facets exposed. COOH functionalization directed the synthesis of anatase truncated bipyramids, bonded to graphene sheets via the {101} facets, while NH2 functionalization induced the formation of belted truncated bipyramids, bonded to graphene via the {100} facets. Belted truncated bipyramids formed on unfunctionalized GNP too, however the NPs were more irregular and rounded. These effects were ascribed to pH variations in the proximity of the functionalized GNP sheets, due to the high density of COOH or NH2 groups. Because of the different reactivity of anatase {100} and {101} crystalline facets, we hypothesize that the hybrid materials will behave differently as photocatalysts, and that the COOH-GNP-TiO2 hybrids will be better photocatalysts for water splitting and H2 production.

Surface Modification of Graphene with Layered Molybdenum Disulfide and Their Synergistic Reinforcement on Reducing Fire Hazards of Epoxy Resins

In this work, molybdenum disulfide (MoS2)–modified graphene (MoS2/GNS) hybrids were prepared by the hydrothermal method and characterized by X-ray diffraction (XRD), Laser Raman spectroscopy (LRS) ...

Significant Efficiency Enhancement of Bulk Heterojunction Organic Photovoltaics Using Solution-Processable Interfacial Bilayers

A solution-processable interfacial bilayer is found to be able to significantly increase a short-circuit current and thus the overall performance of bulk heterojunction organic photovoltaic cells. The interfacial bilayer is comprised of surface-modified single-layer graphene oxide and a donor polymer. The use of the interfacial bilayer can minimize exciton quenching and inverse current and does not alter the energy level of photovoltaic devices, which is also applicable to other organic optoelectronic diode devices.

Stable colloidal dispersion of functionalized reduced graphene oxide in aqueous medium for transparent conductive film

We prepared stable colloidal suspension graphene in aqueous medium by surface modification of graphene with 4-benzenediazonium sulfonate. The sulfonate group on graphene surface interacts with water, exhibits well dispersibility and which prevents the aggregation even at neutral pH. This dispersion shows stability for three months and facile to produce films. Using such a modified graphene dispersion, transparent conductive film (TCF) has been fabricated on glass substrate by spin coating method. At appropriate concentration, the film exhibits an excellent optoelectrical property with resistivity of 1.1kΩ with the transparency of 89% at the wavelength of 550nm. Further, we also demonstrated the mechanical, thermal, and optoelectrical properties of prepared films.

Modified Graphene/Polyimide Nanocomposites: Reinforcing and Tribological Effects

By taking advantage of design and construction of strong graphene-matrix interfaces, we have prepared modified graphene/polyimide (MG/PI) nanocomposites via a two-stage process consisting of (a) surface modification of graphene and (b) in situ polymerization. The 2 wt % MG/PI nanocomposites exhibited a 20-fold increase in wear resistance and a 12% reduction in friction coefficient, constituting a potential breakthrough for future tribological application. Simultaneously, MG also enhanced thermal stability, electrical conductivity, and mechanical properties, including tensile strength, Young's modulus, storage modulus, and microhardness. Excellent thermal stability and compatibility of interface, strong covalent adhesion interaction and mechanical interlocking at the interface, as well as homogeneous and oriented dispersion of MG were achieved here, contributing to the enhanced properties observed here. The superior wear resistance is ascribed to (a) tribological effect of MG, including suppression effect of MG in the generation of wear debris and protective effect of MG against the friction force, and (b) the increase in mechanical properties. In light of the relatively low cost and the unique properties of graphene, the results of this study highlight a pathway to expand the engineering applications of graphene and solve wear-related mechanical failures of polymer parts.

Synthesis and Characterization of Ionic Graphene Oxides (GO) for the Generation of New Multilayered Structures and Hybrid GO/Polymer Nanocomposites

AbstractThe chemical surface modification of graphene and graphene oxide materials is a burgeoning area of investigation. We report the preparation of new ionic forms of graphene oxide by wet chemical modification and metathesis reactions. Graphene oxide (GO) was prepared by a modified Hummers method and functionalized to form cationic and anionic species. The former were prepared via nucleophilic substitution of alkyl amines at the epoxy and hydroxyl groups on the GO while the latter, consisting of sulfonated GO, was prepared via an aryl diazonium salt. The functionalized graphene oxide sheets consist of quaternary ammonium ion substituted GO, GO+, with Cl‐ or I‐ as counter ion and sulfonated GO, GO‐, with H+, Ba2+ or tetraphenylphosphonium (TPP+) ion as counter ions. The addition reaction between GO+ and GO‐ in aqueous solution by metathesis to form a black [GO+][GO‐] precipitate was also investigated. Materials were characterized by XRD, FTIR, Raman, STEM and TEM/HRTEM. Chemically modified graphene and graphene oxides are expected to facilitate further understanding of the chemistry and physics of graphene materials in general and contribute to the formation and further understanding of advanced hybrid graphene and graphene oxide polymer nanocomposites.1,2

Facile synthesis of triangular shaped palladium nanoparticles decorated nitrogen doped graphene and their catalytic study for renewable energy applications

We report a novel method for the synthesis of triangular shaped palladium nanoparticles (Pd NPs) decorated nitrogen doped graphene. Nitrogen doped graphene (N-G) is synthesized by uniform coating of polyelectrolyte modified graphene surface with a nitrogen containing polymer followed by their pyrolysis. The triangular shaped Pd NPs are decorated over nitrogen doped graphene (Pd/N-G) by kinetically controlling the polyol reduction process. The kinetic control of the growth of the nanoparticles and nitrogen doping of the supporting material leads to the formation of highly dispersed anisotropic nanoparticles over the graphene support. Hydrogen storage study of N-G and Pd/N-G give a storage capacity of 1.1 wt% and 1.9 wt%, respectively at 25 °C and 2 MPa hydrogen equilibrium pressure. Electrocatalytic study of Pd/N-G shows that it is a very good electrocatalyst for oxygen reduction reaction and highly stable in acidic media due to the strong binding between Pd NPs and graphene support as a result of nitrogen doping besides has high methanol tolerance in acidic media. The present synthesis procedure highlights a new pathway for the highly dispersed and different morphological metal nanoparticles decorated graphene composites for energy related applications.

Effects of covalent surface modifications on the electrical and electrochemical properties of graphene using sodium 4-aminoazobenzene-4′-sulfonate

The broad application of graphene is impeded by its intrinsically insoluble property. Therefore, two types of water dispersible graphene were synthesized by the reaction of graphene oxide (GO) with sodium 4-aminoazobenzene-4′-sulfonate (SAS) and its aryl diazonium salt (ADS). The maximum dispersibilities of SAS- and ADS-functionalized graphene (SAS-G and ADS-G) in water were 1.4 and 2.9mgmL−1, respectively. Fourier transform infrared, Raman and X-ray photoelectron spectroscopy (XPS) revealed successful surface modification of graphene using SAS and ADS. The electrical conductivity of ADS-G (1120Sm−1) was much greater than SAS-G (149Sm−1), which is attributed to two-step reduction of GO to graphene. Thermogravimetric analysis revealed that excess surface modifier was attached to the surface of the ADS-G compared to SAS-G, which corroborates the Raman and XPS analysis. The electrochemical properties of the formed SAS-G and ADS-G were investigated, and the results demonstrated that ADS-G showed better specific capacitance (210Fg−1) than SAS-G (170Fg−1). All these observations confirmed that the surface modified graphene can be used as energy storage electrode materials because of their high specific capacitance values.

Facile Method for the Preparation of Water Dispersible Graphene using Sulfonated Poly(ether–ether–ketone) and Its Application as Energy Storage Materials

A simple and effective method for the preparation of water dispersible graphene using sulfonated poly(ether-ether-ketone) (SPEEK) has been described. The SPEEK macromolecules are noncovalently adsorbed on the surface of graphene through π-π interactions. The SPEEK-modified graphene (SPG) forms an aqueous dispersion that is stable for more than six months. An analysis of the ultraviolet-visible spectra shows that the aqueous dispersion of SPG obeys Beer's law and the molar extinction coefficient has been found to be 149.03 mL mg(-1) cm(-1). Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy analyses confirm successful reduction and surface modification of graphene. An atomic force microscopy (AFM) analysis reveals the formation of a single layer of functionalized graphene. Transmission electron microscopy results are also in good agreement with the AFM analysis and support the formation of single-layer graphene. SPG shows good electrochemical cyclic stability during cyclic voltammetry and charge/discharge process when used as a supercapacitor electrode. A specific capacitance of 476 F g(-1) at a current density of 6.6 A g(-1) is observed for SPG materials.

Modified graphene/polyaniline nanocomposites for supercapacitor application

This work explored the effect of graphene surface modification on the electrochemical performance of polyaniline-based nanocomposite. The surface modification of graphene was confirmed by Fourier transform infrared spectroscopy. Field emission scanning electron microscopy and high-resolution transmission electron microscopy showed uniform polyaniline coating of the modified graphene. The specific capacitance of the graphene/polyaniline composite was 242 F/g, but it decreased to 193 F/g after graphene modification. However, the capacitance retention increased from 86% to 89% after 500 cycles due to the graphene modification. The thermal stability of the composite also increased after the graphene modification. Open image in new window

Detection of Biomolecules via Benign Surface Modification of Graphene

A functionalized biotin compound is synthesized and assembled on a graphene surface where the electrical and optical properties of graphene are retained. Surface plasmon resonance spectroscopy (amo...

Controllable synthesis, magnetism and solubility enhancement of graphene nanosheets/magnetite hybrid material by covalent bonding

Hybrids of Fe 3O 4 nanoparticles and surface-modified graphene nanosheets (GNs) were synthesized by a two-step process. First, graphene nanosheets were modified by SOCl 2 and 4-aminophenoxyphthalonitrile to introduce nitrile groups on their surface. Second, the nitrile groups of surface-modified graphene nanosheets were reacted with ferric ions on the surface of Fe 3O 4 with the help of relatively high boiling point solvent ethylene glycol to form a GNs/Fe 3O 4 hybrid. The covalent attachment of Fe 3O 4 nanoparticles on the graphene nanosheet surface was confirmed by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectrometer (EDS) and scanning electron microscopy (SEM). TEM and HRTEM observations indicated that the sizes of the nanoparticles and their coverage density on GNs could be easily controlled by changing the concentration of the precursor and the weight ratio to GNs. Magnetic measurements showed that magnetization of the hybrid materials is strongly influenced by the reaction conditions. Chemically bonded by phthalocyanine, the solubility of as-synthesized GNs/Fe 3O 4 hybrid materials was greatly enhanced, which was believed to have potential for applications in the fields of composites, wastewater treatment and biomaterials.

Epoxy/graphene platelets nanocomposites with two levels of interface strength

Graphene platelets (GP) are a novel class of nanofillers due to its good compatibility with most polymers, high aspect ratio, high absolute strength and cost-effectiveness. We in this study synthesised two types of epoxy/GP nanocomposites with different interface strength using the combination of sonication and chemical modification. Although the surface-modified graphene platelets (m-GP) formed clusters, a higher degree of dispersion and exfoliation of graphene was observed in each cluster owning to the improved interface by modification. The scrolling of graphene was found predominantly in the interface-modified nanocomposite. At 4 wt%, the modified nanocomposite shows fracture energy release rate G1c 613.4 J m−2, while the unmodified nanocomposite indicates 417.3 J m−2, in comparison with neat epoxy G1c 204.2 J m−2. The interface modification enhanced the glass transition temperature of neat epoxy from 94.7 to 108.6 °C, 14.7% increment. Toughening mechanisms are attributed to the voiding, microcracking and breakage of GP, while matrix may not consume as much fracture energy as m-GP do.