Osteo mineralization of fibrin-decorated graphene oxide

Surface functionalized graphene oxide (GO) was synthesized by coating fibrin on its surface. The fibrin coated graphene oxide (FGO) was characterized for its physiochemical properties and its potential as an osteoinductive material was evaluated using osteoblast like cell line MG-63 and normal cell line NIH 3T3. The scanning electron microscopy (SEM) has confirmed the coating of fibrin on GO and the transmission electron microscopy (TEM) revealed both spherical and cubical nature of GO nanoparticles and FGO. In in vitro studies, FGO exhibited higher levels of alkaline phosphatase and calcium ion release which confirmed the osteoinductive nature of FGO. The 3-(4,5-dimethylthiazol-2-Y)-2,5-diphenyltetrazolium bromide (MTT) assay proved FGO as a biocompatible material. The results have suggested that FGO might be a promising scaffold for bone tissue engineering applications.     

Incorporation of silica network and modified graphene oxide into epoxy resin for improving thermal and anticorrosion properties

In this study, the silica network and functionalized graphene oxide (GO) were incorporated into the epoxy coating systems, which was aimed to improve the thermal property and corrosion resistance of epoxy coatings. First, tetraethyl orthosilicate (TEOS) oligomers and epoxy hybrid was fabricated through sol–gel method. Then the (3-aminopropyl) triethoxysilane (APTES) modified graphene oxide (FGO) was added into the epoxy hybrid composite to obtain anticorrosion coatings. Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA), Raman spectrum, and X-ray photoelectron spectrum were conducted to evaluate the structural information of GO and APTES modified GO nanosheets. The results indicated that the APTES successfully grafted onto the surface of GO sheets. Besides, TGA curves, electrochemical measurements and salt spray test were also carried out to characterize the thermal performance and corrosion resistance of GO based epoxy coatings. The TGA results revealed that the thermal performance of epoxy coating containing silica network and FGO nanofiller (ES/FGO) was significantly strengthened compared to pure epoxy. The initial degradation temperature of epoxy coating was increased from 300 to 343.7°C after incorporation of silica component and FGO. The EIS measurements demonstrated that the impedance modulus of ES/FGO was significantly higher than neat epoxy, which indicated that the corrosion resistance of epoxy was substantially strengthened after introduction of silica component and FGO. The corrosion rate and inhibition efficiency of epoxy composite coatings were also shifted from 1.237 × 10⁻⁷ mm/year and 76.6% (for neat epoxy) to 1.870 × 10⁻⁹ mm/year and 99.6% (for ES/FGO), respectively. The salt spray test also revealed that the silica and FGO can improve the corrosion resistance of epoxy coating. Additionally, the dispersion of GO sheets was also enhanced after the modification of APTES siloxane.     

Application of functionalized graphene oxide in flame‐retardant polypropylene

A surface functionalized graphene oxide (FGO) was prepared by a simple and efficient method of treating graphene oxide (GO) with pentaerythritol (PER) in water using an ultrasound process. After the PER was grafted onto the surface of the GO, the GO became hydrophobic instead of hydrophilic and precipitated as a dark brown material. The results of Fourier‐transform infrared analysis, X‐ray photoelectron spectroscopy, X‐ray diffraction, and transmission electron microscopy demonstrated that the PER had been successfully attached to the GO. Subsequently, the FGO was incorporated into the intumescent flame‐retardant‐polypropylene system. The presence of FGO improved the flame‐retardant efficiency as evidenced by the limiting oxygen index (LOI) and vertical burning test (UL‐94) test. Analysis by scanning electronic microscopy indicated that the FGO promoted the formation of a continuous, intact residual char layer on the surface of the polymer, which acts as an insulating barrier to protect the base material. As a result, it delayed the peak of heat release rate and increased the residual mass obtained on combustion of the polymer. J. VINYL ADDIT. TECHNOL., 21:278–284, 2015. © 2014 Society of Plastics Engineers     

Effect of synthesis method on solvation and exfoliation of graphite oxide

Graphite oxides (GOs) synthesized by Brodie’s and Hummers’ methods are significantly different with respect to hydration, solvation and exfoliation properties. Hummers GO is more easily intercalated by liquid water and alcohols, exhibiting osmotic type of swelling. In contrast, Brodie GO shows crystalline swelling in alcohol solvents with step-like insertion of methanol or ethanol monolayers. However, the stronger hydration and easier dispersion in water observed for Hummers GO do not correlate with better dispersion of graphene powder obtained by thermal exfoliation. Higher surface area graphene powder was obtained by exfoliation of Brodie GO, while the temperature of its exfoliation is about 75 °C higher than that for the studied sample of Hummers GO. It is suggested that higher exfoliation temperature and better crystallinity of GO are important factors for preparation of graphene powder using thermal exfoliation.     

Chemically modified graphene oxide/polybenzimidazobenzophenanthroline nanocomposites with improved electrical conductivity

Graphene/polybenzimidazobenzophenanthroline nanocomposites were prepared through the liquid-phase exfoliation of graphene oxide (GO) and reduced graphene oxide (rGO) in methanesulfonic acid with subsequent solution mixing. Various chemical and combined chemical-thermal methods were examined to be effective for producing rGO with highly graphitic structure and excellent electrical conductivity. Raman and X-ray photoelectron spectroscopy showed higher degree of reduction of the GO with the combined chemical-thermal method compared to other chemical reduction processes. Structural characterization of the nanocomposites by X-ray diffraction, scanning electron microscopy and transmission electron microscopy showed good exfoliation and dispersion of both GO and rGO fillers in the polymer matrix. The thermogravimetric analysis found that the nanocomposites with rGO have higher onset and maximum weight loss temperatures than those with GO. Compared with the pure polymer, the electrical conductivity of the nanocomposites containing 10 wt% GO and GO reduced by the combined chemical-thermal treatment showed a remarkable increase by four and seven orders of magnitude, respectively. Long-term in-situ thermal reduction was performed to further improve the conductivities of the nanocomposites.     

Synthesis of modified graphene oxide and its improvement on flame retardancy of epoxy resin

In this work, the small molecule with double-phosphaphenanthrene structure was successfully grafted on the surface of graphene oxide (GO), which is called functionalized graphene oxide (FGO). The introduction of FGO improved the poor interfacial compatibility between graphene and epoxy matrix. And FGO could be used as the highly effective flame retardant. The thermogravimetric analysis results showed a significant improvement in the char yield of cured FGO/EP. When the content of FGO was 3 wt %, the limiting oxygen index value reached 30.4%. At the same time, the three-point bending and thermomechanical tests confirmed that the mechanical properties of the epoxy resin composites were improved. Based on the char analyses of SEM images and Raman spectroscopy, the flame retardant could promote the formation of a stable carbon layer. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47710.     

Vacuum-assisted microwave reduction/exfoliation of graphite oxide and the influence of precursor graphite oxide

One-step synthesis of high quality graphene at gram-scale quantities is important for industrial applications, e.g. in electrochemistry for sensing and energy storage. Currently, thermal reduction/exfoliation of graphite oxide (GO) is a typical method of choice. However, it has the drawback of requiring specialized equipment for rapid thermal shock. A recent alternative method, microwave-assisted exfoliation, usually suffers from poor reduction of graphite oxide and thus low C/O ratios. Herein we show that vacuum-assisted microwave reduction/exfoliation of graphite oxide in a closed system leads to high C/O ratios and partial hydrogenation of graphene (2.6 at.% of H). Microwave irradiation of graphite oxide in vacuum leads to outgassing from GO and the creation of plasma which aids temperature distribution and hydrogenation. This plasma is quickly extinguished by further dramatic evolution of gases from GO and consequent pressure increase. We assess the influence of precursor graphite oxide, prepared by Hummers, Staudenmaier, and Hofmann methods, upon the materials properties of microwave exfoliated graphene. We show that microwave-exfoliated graphenes prepared from different graphite oxides show very fast heterogeneous electron transfer rates, with similar electrochemical behaviour to thermally reduced graphene oxide.     

Towards low temperature thermal exfoliation of graphite oxide for graphene production

Realizing mass production of graphene materials at low cost and high quality is urgently required for their real applications. Thermal exfoliation of graphite oxide (GO) is considered as a promising strategy though it normally requires a high exfoliation temperature together with a fast heating rate, making the produced graphenes suffer from high cost and concentrated topological defects. A mild exfoliation of GO at a far lower temperature than the predicted minimum temperature, has been demonstrated by introducing a high vacuum to exert an outward drawing force which helps effective exfoliation of the stacked graphene layers. In this contribution, together with a discussion on the foundation of thermal exfoliation and the general principle for low-temperature exfoliation, we review current strategies and indicate possible novel approaches. Low cost and easy operability are highlighted for the low-temperature exfoliation and the resulting graphene materials are characterized by low defect concentration, and unique and tunable surface chemistry to promote potential mass applications in energy-related areas.     

An efficient interface model to develop scalable methodology of melt processing of polypropylene with graphene oxide produced by an improved and eco-friendly electrochemical exfoliation

This study developed a scalable and straightforward adaptation methodology for melt processing of polypropylene (PP) to provide a high degree of exfoliation of multilayer graphene oxide (GO) by using a high-shear mixer. GO was first produced by an improved and eco-friendly electrochemical exfoliation by using an environmentally friendly aqueous methanesulfonic acid (MSA) and a sodium sulfate salt system to minimize the environmental impact. The produced GOs then were melt blended with PP and their mechanical, thermal, and morphological properties were investigated under different GO loadings to attain ideal configuration and increase interfacial interactions between polymer matrix and reinforcer. Comparisons were made by producing different PP composites using two different GO types produced in salt and acid environments. Additionally, by applying different voltages to salt system, the effect of applied voltage on the properties of both GO material and the composites were discussed. The characterization results indicated that GO obtained in MSA solution caused a 71% increase in flexural modulus and 46% in flexural strength with the addition of 1 wt% GO. The rheological characterization also showed that dispersion and viscosity improved with lower GO loadings compared to neat polymer by providing cost-effective and scalable graphene manufacturing.     

Size-controlled synthesis of graphene oxide sheets on a large scale using chemical exfoliation

The synthesis of graphene oxide (GO) sheets with controlled size on a large scale was developed using chemical exfoliation by simply controlling the oxidation and exfoliation procedure. The GO samples prepared under different conditions, which all have excellent water dispersion, are characterized by thermal gravimetric analysis, Ultraviolet-visible spectroscopy, X-ray diffraction and atomic force microscopy. It is found that as longer oxidation times and more oxidants are used, the mean size of the GO sheets, which has a Gaussian distribution, decreases from ∼59,000 to ∼550 nm².     

Supramolecular Poly(cyclotriphosphazene) Functionalized Graphene Oxide/Polypropylene Composites with Simultaneously Improved Thermal Stability,Flame Retardancy,and Viscoelastic Properties

A novel crosslinkable supramolecular poly(cyclotriphosphazene) functionalized graphene oxide (FGO) is synthesized and melt‐processed with polypropylene (PP), which results in a PP composite with simultaneously improved flame retardancy, smoke‐suppression, and thermal and viscoelastic properties. The cone‐calorimetry test results reveal that the peak heat‐release rate and total heat release of the composite (2 wt% FGO) are reduced by 39.7% and 29.9%, respectively, compared to those of the neat PP. Meanwhile, the total smoke released and total smoke production of PP are significantly (42.7% and 34.9%, respectively) reduced after composite formation with 2 wt% FGO. Similarly, the PP/FGO composite shows an improved maximum weight loss temperature of 392.4 °C, compared to that of neat PP (361.4 °C). Thermogravimetric Fourier‐transform infrared spectroscopy (TG‐FTIR) analysis further confirms that the composite reduces the evolution of the flammable components and toxic gases, especially CO gas, indicating that the FGO significantly decreases the fire hazards of the PP. The thermomechanical and melt‐rheological analyses reveal that the composite has higher mechanical stiffness and viscoelastic properties than the neat polymer. In summary, FGO is shown to have potential as an advanced additive to obtain PP composites with multifunctional properties; however, higher FGO loading would be needed to improve UL‐94 rating from V‐2 to V‐0.     

Actuation triggered exfoliation of graphene oxide at low temperature for electrochemical capacitor applications

An actuation triggered thermal exfoliation process was realized at a low temperature of 200 °C and atmospheric pressure. Densely packed graphene oxide (GO) paper was transformed into airy-like expanded architectures. The underlying mechanism was found to be similar to corn popping and attributed to the thermally-stimulated-actuation and molecules escape. Scanning electron microscopy, X-ray photoelectron spectra and electrochemical characterization showed that after the exfoliation process, the resultant popped graphene oxide (P-GO) exhibited highly expanded structures; the oxygen-containing groups were effectively removed; and the P-GO demonstrated good electrochemical capacitance performance with excellent stability.     

The reduction of graphene oxide

Graphene has attracted great interest for its excellent mechanical, electrical, thermal and optical properties. It can be produced by micro-mechanical exfoliation of highly ordered pyrolytic graphite, epitaxial growth, chemical vapor deposition, and the reduction of graphene oxide (GO). The first three methods can produce graphene with a relatively perfect structure and excellent properties, while in comparison, GO has two important characteristics: (1) it can be produced using inexpensive graphite as raw material by cost-effective chemical methods with a high yield, and (2) it is highly hydrophilic and can form stable aqueous colloids to facilitate the assembly of macroscopic structures by simple and cheap solution processes, both of which are important to the large-scale uses of graphene. A key topic in the research and applications of GO is the reduction, which partly restores the structure and properties of graphene. Different reduction processes result in different properties of reduced GO (rGO), which in turn affect the final performance of materials or devices composed of rGO. In this contribution, we review the state-of-art status of the reduction of GO on both techniques and mechanisms. The development in this field will speed the applications of graphene.     

Effects of humic acid on copper adsorption onto few-layer reduced graphene oxide and few-layer graphene oxide

The effects of humic acid (HA) on copper (Cu(II)) adsorption onto few-layer reduced graphene oxide (FRGO) and few-layer graphene oxide (FGO) were investigated using a batch equilibration method, micro-Fourier transform infrared spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The results showed that HA was adsorbed on FRGO through π–π interaction. The adsorbed HA introduced O-containing functional groups and negative charges to FRGO surfaces, increasing Cu(II) adsorption through chemical complexation and electrostatic attraction. In contrast, HA was adsorbed onto FGO mainly through polar interactions, due to its rich O-containing functional groups. The adsorbed HA had little effect on Cu(II) adsorption onto FGO because the shielding effect of HA on Cu(II) adsorption was offset by newly introduced adsorption sites of HA on FGO. EXAFS results suggested that Cu(II) was adsorbed on FRGO and FGO mainly through the coordination with their O-containing functional groups. When HA was added at pH 4.0 and 6.0, more Cu(II) was adsorbed on HA-coated FRGO. At pH 8.0, a portion of Cu(II) in solution precipitated on FRGO surface, while the presence of HA led to the formation of FRGO-HA-Cu ternary surface complexes instead of Cu(II) precipitation.     

Preparation and properties of acrylonitrile–butadiene rubber–graphene nanocomposites

The graphene oxide (GO) was prepared by sonication‐induced exfoliation from graphite oxide, which was produced by oxidation from graphite flakes with a modified Hummer's method. The GO was then treated by hydrazine to obtain reduced graphene oxide (rGO). On the basis of the characterization results, the GO was successfully reduced to rGO. Acrylonitrile–butadiene rubber (NBR)–GO and NBR–rGO composites were prepared via a solution‐mixing method, and their various physical properties were investigated. The NBR–rGO nanocomposite demonstrated a higher curing efficiency and a change in torque compared to the gum and NBR–GO compounds. This agreed well with the crosslinking density measured by swelling. The results manifested in the high hardness (Shore A) and high tensile modulus of the NBR–rGO compounds. For instance, the tensile modulus at a 0.1‐phr rGO loading greatly increased above 83, 114, and 116% at strain levels of 50, 100, and 200%, respectively, compared to the 0.1‐phr GO loaded sample. The observed enhancement was highly attributed to a homogeneous dispersion of rGO within the NBR matrix; this was confirmed by scanning electron microscopy and transmission electron microscopy analysis. However, in view of the high ultimate tensile strength, the NBR–GO compounds exhibited an advantage; this was presumably due to strong hydrogen bonding or polar–polar interactions between the NBR and GO sheets. This interfacial interaction between GO and NBR was supported by the marginal increase in the glass‐transition temperatures of the NBR compounds containing fillers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42457.     

Investigation of thermal behaviour and mechanical property of the functionalised graphene oxide/epoxy resin nanocomposites

ABSTRACT

Graphite oxide (GO) and functionalised graphite oxide (FGO) were successfully prepared with -NH₂-terminated GO in the paper, and their chemical structures were characterised with Fourier transform infrared (FTIR), Energy-Dispersive X-ray Spectroscopy (EDS), UV spectrum analysis and XRD, their microstructures were researched by a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and their thermal properties were characterised by TG. The result showed the carbon residue of FGO was 82.1% and the residual char of GO was 48%, the composite materials were prepared with curing for epoxy resin. The thermal stability, mechanical properties, and morphology after impacting tests of composite materials were investigated using thermogravimetric analysis, tensile and charpy impact tests and SEM. The result showed when the 0.2% FGO was filled into the epoxy, the tensile strength was 55.4?MPa, the impact strength was 17.3?KJ/m², the flexural strength was 82?MPa, and the flexural modulus was 2760?MPa. The mechanical properties of composite materials were higher than those of pure epoxy and improved the strength and toughness of epoxy nanocomposites.     

Hydrazine-reduction of graphite- and graphene oxide

We prepared hydrazine-reduced materials from both graphite oxide (GO) particles, which were not exfoliated, and completely exfoliated individual graphene oxide platelets, and then analyzed their chemical and structural properties by elemental analysis, XPS, TGA, XRD, and SEM. Both reduced materials showed distinctly different chemical and structural properties from one another. While hydrazine reduction of graphene oxide platelets produced agglomerates of exfoliated platelets, the reduction of GO particles produced particles that were not exfoliated. The degree of chemical reduction of reduced GO particles was lower than that of reduced graphene oxide and the BET surface area of reduced GO was much lower than that of reduced graphene oxide.     

Tunable uptake of poly(ethylene oxide) by graphite-oxide-based materials

We investigate the role of structure and chemical composition on the uptake of poly(ethylene oxide) by a series of graphite oxides (GOs) and thermally reduced GOs, leading to the formation of polymer-intercalated GO and polymer-adsorbed graphene nanostructures. To this end, a series of poly(ethylene oxide) (PEO) - GO hybrid materials exhibiting a variable degree of GO oxidation and exfoliation has been investigated in detail using a combination of techniques including X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry, scanning-electron microscopy, and nitrogen adsorption. Intercalation of the polymer phase into well-defined GO galleries is found to correlate well with both the degree of GO oxidation and with the presence of hydroxyl groups. The latter feature is an essential prerequisite to optimize polymer uptake owing to the predominance of hydrogen-bonding interactions between intercalant and host. Unlike the bulk polymer, these intercalation compounds show neither crystallisation nor glass-transition associated with the polymer phase. Exfoliation and reduction of GO result in high-surface-area graphene layers exhibiting the highest polymer uptake in these GO-based materials. In this case, PEO undergoes surface adsorption, where we observe the recovery of glass and melting transitions associated with the polymer phase albeit at significantly lower temperatures than the bulk.     

Effect of centrifugal cleaning on the electro-optic response in the preparation of aqueous graphene-oxide dispersions

The quality of aqueous graphene oxide (GO) dispersions relies partially on the centrifugal cleaning process in the Hummers method. As the number of centrifugal cleaning cycle increases, the concentration of the residual salts of oxidizing reagents decreases, and the exfoliation of graphite oxide into GO sheets is enhanced. We found that the electrical sensitivity of a GO dispersion in its electro-optic dynamics increases sharply with an increasing number of cleaning cycles. We discovered that the removal of the residual salts decreases the solvent conductivity, and the exfoliation increases the aspect ratio of GO particles, which are closely related to the anisotropic polarizability of GO particles and the electrical sensitivity.     

High-Performance and Biobased Polyamide/Functionalized Graphene Oxide Nanocomposites through In Situ Polymerization for Engineering Applications

In this study, biobased polyamide/functionalized graphene oxide (PA-FGO) nanocomposite is developed using sustainable resources. Renewable PA is synthesized via polycondensation of hexamethylenediamine (HMDA) and biobased tetradecanedioic acid. Furthermore, GO is functionalized with HMDA to improve its compatibility with biobased PA and in situ polymerization is employed to obtain homogeneous PA-FGO nanocomposites. Compatibility improvement provides simultaneous increases in the tensile strength, storage modulus, and conductivity of PA by adding only 2 wt% FGO (PA-FGO2). The tensile strength and storage modulus of PA-FGO2 nanocomposite are enhanced dramatically by ≈50% and 30%, respectively, and the electrical conductivity reached 3.80 × 10^–3 S m⁻¹. In addition, rheology testing confirms a shear-thinning trend for all samples as well as a significant enhancement in the storage modulus upon increasing the FGO content due to a rigid network formation and strong polymer-filler interactions. All these improvements strongly support the excellent compatibility and enhanced interfacial interactions between organic–inorganic phases resulting from GO surface functionalization. It is expected that the biobased PA-FGO nanocomposites with remarkable thermomechanical properties developed here can be used to design high-performance structures for demanded engineering applications.