Water-dispersible Graphene Research Articles

Supramolecular Surface Modification and Dispersion of Graphene in Water and Organic Solvents

Graphene sheets have been dispersed in water and organic solvents by noncovalent surface modification with the assistance of bifunctional molecule pyrene-adamantane (Py-Ad) carrying a pyrene moiety. Lipophilic graphene sheets have been obtained in the form of graphene-Py-Ad in a wide variety of organic solvents, such as dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N'-dimethylformamide, and tetrahydrofuran, in which the adamantane moieties served as the three-dimensional steric groups keeping the graphene sheets from stacking. Supramolecular complexes were employed as the dispersing agent for graphene formed through in situ reduction by hydrazine or hydroquinone. Water-dispersible graphene sheets have been obtained in the form of graphene-Py-Ad-bMCD (methylated beta-cyclodextrin, bMCD), in which the pyrene moiety attached to graphene by pi-pi stacking interaction and hydrophobic effect, and the adamantane group formed complex with bMCD, yielding a supramolecular system that made graphene sheets dissolved in water through the formed hydrophilic cyclodextrin shell. The resulting supramolecular complexes were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermal gravimetric analysis, transmission electron microscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, and Raman spectroscopy.

Effects of sodium hydroxide on the yield and electrochemical performance of sulfonated poly(ether-ether-ketone) functionalized graphene

An environmentally friendly method for the one-step electrochemical synthesis of water dispersible graphene directly from graphite is reported. Sulfonated poly(ether-ether-ketone) (SPEEK) dissolved in deionised water was used as an electrolyte and a surface modifying agent for graphene. The effects of sodium hydroxide (NaOH) on the production yield and electrochemical performance of graphene were investigated in detail. The production yield of few-layer graphene increased to above 40%, as compared to the 6% in the absence of NaOH. Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) analyses suggested that the oxygen functionalities (hydroxyl and carboxyl) generated during the electrochemical exfoliation of graphite in the absence of NaOH were decreased significantly during the electrolysis experiment in an alkaline solution of SPEEK. This is attributed to the NaOH induced reduction of oxygen functionalities present on the surface of graphene sheets. XPS elemental analysis also confirmed the removal of oxygen functionalities in an alkaline medium during the graphite exfoliation experiment. Transmission electron microscopy and atomic force microscopy analyses confirmed the formation of single layer functionalized graphene. A charge–discharge experiment showed that the specific capacitance of the as-prepared graphene in the absence of NaOH was 18 F g−1 at a current density of 2.2 A g−1. In contrast, the specific capacitance was increased to 244 F g−1 for graphene prepared under alkaline condition indicating its suitability as an energy storage electrode material. The high electrochemical performance may be due to the large surface area of graphene (433 m2 g−1) prepared under alkaline condition as observed by the Brunauer–Emmett–Teller surface area analysis.

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.

Microbial reduction of graphene oxide by Escherichia coli: A green chemistry approach

Graphene and graphene related materials are an important area of research in recent years due to their unique properties. The extensive industrial application of graphene and related compounds has led researchers to devise novel and simple methods for the synthesis of high quality graphene. In this paper, we developed an environment friendly, cost effective, simple method and green approaches for the reduction of graphene oxide (GO) using Escherichia coli biomass. In biological method, we can avoid use of toxic and environmentally harmful reducing agents commonly used in the chemical reduction of GO to obtain graphene. The biomass of E. coli reduces exfoliated GO to graphene at 37°C in an aqueous medium. The E. coli reduced graphene oxide (ERGO) was characterized with UV–visible absorption spectroscopy, particle analyzer, high resolution X-ray diffractometer, scanning electron microscopy and Raman spectroscopy. Besides the reduction potential, the biomass could also play an important role as stabilizing agent, in which synthesized graphene exhibited good stability in water. This method can open up the new avenue for preparing graphene in cost effective and large scale production. Our findings suggest that GO can be reduced by simple eco-friendly method by using E. coli biomass to produce water dispersible graphene.

Noninvasive Cell-Based Impedance Spectroscopy for Real-Time Probing Inhibitory Effects of Graphene Derivatives

Three water-dispersible graphene derivatives, graphene oxide (GO), sulfonated graphene oxide (SGO), and sulfonated graphene (SG), were prepared and probed for their plausible cytotoxicity by non-invasive electric cell-substrate impedance sensing (ECIS). With Spodoptera frugiperda Sf9 insect cells adhered on gold microelectrodes as an active interface, it is feasible to monitor changes in impedance upon exposure to different graphene derivatives. Sf9 insect cells were then exposed to different concentrations of graphene derivatives and their spreading and viability were monitored and quantified by ECIS in real-time. On the basis of the 50% inhibition concentration (ECIS50), none of the graphene derivatives were judged to have any significant cytotoxicity with respect to the chosen cell line as the ECIS50 values were all above 100 μg/mL. However, all graphene derivatives exhibited inhibitory effects on the Sf9 response at the cell spreading level with the following order: SG (ECIS50 = 121 ± 8 μg/mL), SGO (ECIS50 = 151 ± 9 μg/mL), and GO (ECIS50 = 232 ± 27 μg/mL), reflecting differences observed in their ζ-potential and surface area. The presence of phenyl sulfonyl groups in SGO and SG improves their aqueous dispersity which enables these materials to have a greater inhibitory effect on Sf9 insect cells in comparison to GO. Such results were corroborated well with the cell count and viability by the Trypan Blue exclusion assay.

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.

Functionalization of graphene and grafting of temperature-responsive surfaces from graphene by ATRP “on water”

Water-dispersible graphene with temperature-responsive surfaces has successfully been synthesized by grafting poly(N-isopropylacrylamide) (PNIPAM) from graphene via surface-initiated atom transfer radical polymerization (ATRP). First, graphene surfaces are functionalized with aminophenol groups by diazonium reaction on water. Subsequently, bromoisobutyrate groups are covalently attached to the phenol-functionalized graphene (G-OH) surface by esterification of 2-bromoisobutyrate with the hydroxyl groups, forming bromoisobutyrate-functionalized graphene (G-Br). Finally, PNIPAM is then grafted from G-Br via ATRP. Data from Raman spectroscopy, 1H NMR, and transmission electron microscopy (TEM) confirm that PNIPAM chains grow from graphene by ATRP. Thermogravimetric analysis shows that the amount of PNIPAM grown from the graphene increases with the increase of monomer ratios. TEM images also show that functionalized polymer structures (PNIPAM cluster or agglutination) on graphene sheets can be well tuned by controlled polymerization. The obtained graphene-PNIPAM (G-PNIPAM) composite has PNIPAM surface which is highly sensitive to the temperature change. This temperature-responsive and water-dispersible G-PNIPAM composite may find potential applications in environmental devices as well as controlled release drug delivery.

Gelatin-assisted fabrication of water-dispersible graphene and its inorganic analogues

Two dimensional nanomaterials are of great significance in a wide range of applications due to their high surface area and novel properties. Here we offer a simple and large-scale method to prepare graphene and its inorganic analogues (MoS2, WS2 and boron nitride) by the sonication of their bulk materials in an aqueous solution of gelatin. The concentrations of the obtained stable dispersions were up to 0.6, 0.8, 0.9 and 1.4 mg mL−1 for graphene, MoS2, WS2 and boron nitride, respectively. Transmission electron microscopy strongly suggests that the materials have been exfoliated into few- or mono-layer thin sheets. Specifically, graphene and MoS2 dispersion have been directly employed to fabricate gelatin–graphene composites. Scanning electron microscope images show that graphene flakes were homogeneously dispersed in the composites. The tensile test results show that the mechanical properties of gelatin films have been remarkably improved by graphene rather than MoS2.

Facile preparation of water-dispersible graphene sheets stabilized by acid-treated multi-walled carbon nanotubes and their poly(vinyl alcohol) composites

Graphene has attracted tremendous interest in reinforcing fillers due to its unique structure and excellent physical properties. However, efficient reinforcement has been largely limited because graphene tends to agglomerate within a polymer matrix. In this study, direct reduction of graphene oxide (GO) in water in the presence of acid-treated multi-walled carbon nanotubes (t-CNTs) results in a homogeneous dispersion of reduced graphene oxide (r-GO) and t-CNT hybrids. The three-dimensional r-GO/t-CNTs hybrids (abbreviated as G-CNT hybrids) possess unique properties, making them ideal reinforcing fillers for polymer nanocomposites. Poly(vinyl alcohol) (PVA) composite containing G-CNT hybrids is then prepared by a simple water casting method. Due to the synergistic interaction of the two kinds of nanofillers, the tensile strength and Young's modulus of the resulting PVA nanocomposite filled with only 0.6 wt% G-CNT hybrids are significantly improved by about 77% and 65%, respectively. The results indicate that the nanohybrids are well dispersed throughout the PVA matrix and form strong interfacial interactions with the matrix. Besides, the presence of G-CNT hybrids slightly increases the thermal stability at 5% weight loss and remarkably improves the amount of residues of PVA nanocomposites. For comparison, we also prepare a PVA composite with the addition of only t-CNTs and find that its mechanical properties show limited enhancement owing to the decreased length-to-diameter ratio and structural defects of CNTs by acid treatment. Our work therefore provides a new way for the preparation of hybrid carbon nanomaterials with unique structure and excellent properties for fabricating high-performance polymer nanocomposites.

A novel approach for transferring water-dispersible graphene nanosheets into organic media

Graphene, which is in the form of chemically reduced graphene oxide (r-GO), has been homogeneously dispersed in organic media without the addition of complicated dispersing agents or the need for functionalization of the starting graphene oxides. The aqueous colloids of r-GO sheets are synthesized in an alkaline solution. By using NaCl salts as flocculants, the resultant r-GO aggregates can be easily redispersed in appropriate organic media as individual nanosheets with the aid of sonication, which is a facile and economical approach for the large-scale production of graphene dispersions in organic solvents with high concentrations. The homogeneous graphene organic dispersion facilitates solution-processing procedures for incorporating graphene materials into novel composites and other applications.

Simultaneous bio-functionalization and reduction of graphene oxide by baker's yeast

An environmentally friendly, cost effective, and simple methodology for the preparation of surface modified graphene has been described in this paper. Baker's yeast containing nicotinamide adenine dinucleotide phosphate (NADPH) has been used as a reducing and functionalizing agent. The amine functional groups of NADPH can easily couple with the epoxy functionalities of graphene oxide (GO) and forms stable water dispersion of yeast-reduced graphene oxide (YR-GO). Ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) analysis confirm the successful reduction of GO to graphene. FT-IR and XPS analysis also indicate the doping of amine (NH2) functionalities of NADPH molecules on the surface of graphene. The formation of defects further supports the bio-functionalization of graphene as indicated in the Raman spectrum of YR-GO. All these findings clearly indicate that GO can be reduced and functionalized by simple eco-friendly method by using Baker's yeast to produce water dispersible graphene.

Facile Preparation of Water-Dispersible Adenosine-Functionalized Graphene Nanosheets

Water-dispersible graphene nanosheets were achieved by a simple three-step process. First, pristine graphite was oxidized and exfoliated to obtain graphene oxide, which was further acylated with thionyl chloride to introduce acyl chloride groups on the surfaces. Second, graphene oxide was covalently functionalized with an environment-friendly reagent, namely, adenosine. Subsequently, adenosine-functionalized graphene oxide was reduced to obtain graphene nanosheets by using NaBH4 as a reducing agent. This approach facilitates graphene nanosheets that have a combination of stable aqueous dispersions and an electrical conductivity that are much better in comparison to graphene oxide, offering a great flexibility for further applications.

Preparation of water-dispersible graphene by facile surface modification of graphite oxide

Water-dispersible graphene was prepared by reacting graphite oxide and6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS). X-ray diffraction study showed thatthe basal reflection (002) peak of graphite oxide was absent in the ANS-functionalizedgraphene (ANS-G), indicating crystal layer delamination. Ultraviolet–visible spectral datawere recorded to assess the solubility of the ANS-G in water. Fourier transform infraredspectral analysis suggested the attachment of ANS molecules to the surface ofgraphene. Raman and x-ray photoelectron spectroscopy revealed that oxygenfunctionality in the graphite oxide had been removed during reduction. Atomicforce microscopy found that the thickness of ANS-G in water was about 1.8 nm,much higher than that of single layer graphene. Thermal stability measurementsalso indicated successful removal of oxygen functionality from the graphite oxideand the attachment of thermally unstable ANS to the graphene surfaces. Theelectrical conductivity of ANS-G, determined by a four-point probe, was 145 S m − 1 at room temperature.

Water dispersible graphene noncovalently functionalized with tryptophan and its poly(vinyl alcohol) nanocomposite

Graphene sheets functionalized noncovalently with aromatic amino acid, tryptophan (Tryp), were prepared by reducing graphene oxide through hydrazine hydrate. Tryp-functionalized graphene is water dispersible and can be stabilized for several months. Atomic force microscopy (AFM), X-ray diffraction (XRD), UV–vis absorption and Raman spectroscopy were used to investigate the nanostructures and the properties of graphene. Application of the graphene dispersion to poly(vinyl alcohol) (PVA) with the help of tryptophan to prepare nanocomposite was also carried out. And the PVA/graphene nanocomposite was characterized by thermogravimetric analysis (TGA) and tensile testing. A 23% improvement in tensile strength and moderate increases in Young’s modulus and thermal stability for PVA were achieved by adding only 0.2 wt% graphene sheets.

Graphene-Based Antibacterial Paper

Graphene is a monolayer of tightly packed carbon atoms that possesses many interesting properties and has numerous exciting applications. In this work, we report the antibacterial activity of two water-dispersible graphene derivatives, graphene oxide (GO) and reduced graphene oxide (rGO) nanosheets. Such graphene-based nanomaterials can effectively inhibit the growth of E. coli bacteria while showing minimal cytotoxicity. We have also demonstrated that macroscopic freestanding GO and rGO paper can be conveniently fabricated from their suspension via simple vacuum filtration. Given the superior antibacterial effect of GO and the fact that GO can be mass-produced and easily processed to make freestanding and flexible paper with low cost, we expect this new carbon nanomaterial may find important environmental and clinical applications.

Polyoxometalate assisted photoreduction of graphene oxide and its nanocomposite formation

We have developed a green method to reduce graphene oxide via a UV-irradiated photoreduction process in which H(3)PW(12)O(40) was used as photocatalyst. Moreover, H(3)PW(12)O(40) can adsorb on the reduced graphene oxide as anionic stabilizer and lead to water dispersible graphene sheets.

DNA mediated water-dispersible graphene fabrication and gold nanoparticle-graphene hybrid

Water dispersible single- and bilayered graphene sheets are produced by a direct exfoliation from graphite flakes in the presence of pyrene-labeled single stranded DNAs, and the immobilized DNA on the graphene surface is further hybridized with a gold nanoparticle labeled complementary DNA to generate gold nanoparticle-graphene nanocomposites.

5543564 Process for releasing acidic organic compounds from salts thereof by carbon dioxide : Kulpe Juml urgen; Strutz Hein; Ruml uffer Hans-Martin; Rittner Siegber Frankfurt, Germany assigned to Hoechst Aktiengesellschaft

Water-dispersible 8-hydroxy-1,3,6-pyrene trisulfonic acid trisodium salt (PyS)-functionalized graphene (PyS-graphene) sheets were prepared by a π–π interaction method, in which the aromatic organic molecules of PyS were reacted with graphene. The PyS-graphene sheets were used as Pt nanoparticle support to prepare a Pt/PyS-graphene catalyst for direct methanol fuel cells. The prepared materials were characterized by ultraviolet spectrometry (UV–vis), Fourier transform infrared spectrometry (FT-IR), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy (SERS), and transmission electron microscopy (TEM). The electrocatalytic properties of the catalysts for methanol oxidation were evaluated by cyclic voltammetry (CV). The Pt/PyS-graphene catalysts were found to have higher electrocatalytic activity for methanol oxidation than Pt/graphene catalyst. This finding can be attributed to the introduction of negative sulfonic (SO3−) groups to the graphene sheet surface, which makes the graphene sheets dispersible in water. Consequently, the Pt nanoparticles were uniformly and securely deposited onto the graphene sheet surface. These results suggested that the sulfonic group-modified water-dispersible graphene sheets can be used to improve the electrocatalytic activity of catalysts for fuel cells.