Effect of the microstructure on the intercalation and exfoliation behaviour of graphite

The process of the preparation of graphitic nanoplatelets via chemical intercalation and thermal exfoliation of graphite was considered. The dependence of the properties of the final product on the microstructure of the raw material and on different process parameters was analyzed. It is shown that the microstructure of the raw material has considerable influence on the structural transformations during the different preparation steps. The observed differences can be understood assuming that intercalation is initiated at the edges of graphite crystallites by the formation of intercalate nuclei. Essential differences of the nucleation time appear for unequal types of microstructure and give rise to different intercalation states. It is also shown that the sub-process of washing and drying the samples after intercalation is most critical and has significant influence on the characteristics of the final products. The results suggest that graphite fibres with sub-micron diameter and orientation of the crystallographic c-axis along the fibre axis will be particularly favourable for the preparation of graphitic nanoplatelets.     

A cholesterol biosensor based on gold nanoparticles decorated functionalized graphene nanoplatelets

The fabrication of a cholesterol biosensor using gold nanoparticles decorated graphene nanoplatelets has been reported. Thermally exfoliated graphene nanoplatelets act as a suitable support for the deposition of Au nanoparticles. Cholesterol biosensor electrodes have been constructed with nafion solubilized functionalized graphene nanoplatelets (f-G) as well as Au nanoparticles decorated f-G, immobilized over glassy carbon electrode. f-G and Au/f-G thin film deposited glassy carbon electrodes were further functionalized with cholesterol oxidase by physical adsorption. Au nanoparticles dispersed over f-G demonstrate the ability to substantially raise the response current. The fabricated electrodes have been tested for their electrochemical performance at a potential of 0.2 V. The fabricated Au/f-G based cholesterol biosensor exhibits sensitivity of 314 nA/μM cm² for the detection of cholesterol with a linear response up to 135 μM. Furthermore, it has been observed that the biosensor exhibits a good anti-interference ability and favorable stability over a month's period.     

Lead adsorption onto exfoliated graphitic nanoplatelets in aqueous solutions

Exfoliated graphitic nanoplatelets (xGnPs) show adsorption capability and adsorption efficiency for lead removal from water, the adsorption being influenced by the solution pH value and the xGnPs surface characteristics, which are controlled by their treatment processing. The adsorption isotherms were described by both Langmuir and Freundlich models. These results suggest that xGnPs are remarkable lead adsorbents, having potential applications in environmental protection.     

Experiments and modeling for thermal conductivity of graphite nanoplatelets/carbon composites

In this work, the graphite nanoplatelets/carbon composites were fabricated from graphite nanoplatelets and pitch powders by a hot-pressing technology followed by carbonization and graphitization. The XRD and pole figure results show that the incorporation of pitch induces the decrease of size (L_a) and orientation degree of graphitic crystallites, while the in-plane thermal conductivity of graphitized sample is increased with the increasing pitch content up to 6 wt.%, achieving a maximum value of 405 W/m K. The pitch binders are filled into the voids to bridge two or more graphite nanoplatelets particles together to form extra thermal paths, which makes a great contribution to the enhancement of thermal conductivity. A thermal conductivity model for the graphitized composites is constructed based on a bridging mechanism, and the predicted results fit well with the experimental results.     

Fabrication of carbon-based nanocomposite films by spin-coating process: An experimental and modeling study of the film thickness

Spin-coating is used for the fabrication of nanocomposite thin films, consisting of carbon nanoparticles embedded in epoxy matrix, on Mylar substrate. The final thickness of the heat-cured film was measured as a function of the spinning speed and nanoparticle concentration. Multi-walled carbon nanotubes with carboxyl functionalization (MWCNT-COOH) or exfoliated graphite nanoplatelets (xGnP) were used as fillers. Experimental results were in good agreement with the predictions from a model that considered the rheology and flow behavior of the reinforced resin fluids on a rotating disk. The model was differentiated for Newtonian and non-Newtonian regime of the spinning polymer fluid. In case of non-Newtonian behavior of the epoxy resin at high particle concentrations, a semi-empirical approach was used to determine the model constants from rheology measurements. Results from this analysis also indicate how rheological and wetting properties of the nano-reinforced polymer fluids depend on the aspect ratio of the graphene nanoplatelets.     

Preparation and characterization of graphene nanoplatelets from natural graphite via intercalation and exfoliation with tetraalkylammoniumbromide

A new method for the preparation of graphene nanoplatelets (GNP) from graphite intercalation compounds (GICs) was investigated. Donor-type ternary GICs of natural graphites, lithium ions and tetrahydrofurane (NG-Li-THF) were synthesized via a solution process, with the lithium ions in the GICs then exchanged with different tetra alkyl ammonium cations to expand the interlayer distance (d-spacing) of these GICs. Microwave irradiation of these GICs resulted in the exfoliation of GICs, forming so-called 'worm-like exfoliated graphites.' Sonication of the worm-like exfoliated graphites in acetone resulted in GNPs with different aspect ratios. Powder X-ray diffractometry, scanning electron microscopy and transmission electron microscopy were employed to characterize the GICs and GNPs. It was found that the ion-exchange of NG-Li-THF increased the volume expansion ratios, and the molecular structure of the tetra alkyl ammonium cations affected the aspect ratios of the GNPs after exfoliation.     

Mechanical properties and morphological characterization of exfoliated graphite–polypropylene nanocomposites

This research explores the potential of using exfoliated graphite nanoplatelets, xGnP, (graphene sheets ∼10 nm thickness, ∼1 μm diameter), as reinforcement in polypropylene, PP. xGnP–PP nanocomposites were fabricated by melt mixing and injection molding. The feasibility of using xGnP–PP nanocomposites was investigated by evaluating the flexural strength, modulus and impact strength and studying the morphology of this system as a function of xGnP loading and aspect ratio and by comparing the xGnP–PP with composites made with commercial available reinforcements such as carbon fibers, carbon black and clays. It is concluded that the smaller aspect ratio xGnP has the strongest impact on the mechanical properties of PP, at loadings up to 5 vol.%, compared to the other reinforcements used, which reflects the compatibility between the exfoliated graphite nanoplatelets and the PP matrix and the exceptional mechanical properties of xGnP, similar to crystalline graphite.     

Reinforcing carbonized polyacrylonitrile fibers with nanoscale graphitic interface-layers

Carbon fibers going through stabilization,carbonization,and graphitization heat-treatment stages will form continuous graphitic layers that are closely packed and preferentially aligned along the fiber axis,forming high mechanical stiffness or strength and electrical or thermal conductivity.The alignment of noncontinuous,powder-like graphene layers in polymers has been challenging due to the low bend-ing modulus of a few-or even single-layered graphene,which causes aggregations or folding behav-iors.This research demonstrates the leveraging of polymer-nanoparticle interactions to align graphene nanoplatelets (GNPs) in the polyacrylonitrile (PAN) matrix.An in-house designed spinning method pro-duces a three-layered fiber that utilizes the interracial interactions between each layer for graphene align-ment between graphitic layers.This composite containing oriented GNPs significantly improves modulus(i.e.,42.3 to 74.6 GPa) and increases electrical conductivity for enhancing volatile organic compounds(VOCs) sensing behaviors.This research opens up a new scalable fabrication method for multilayered composites.     

Graphene layers from reduction of exfoliated graphite oxide

Graphene oxide (GO) of approximately 1 nm was generated from exfoliated graphitic oxide using a modified Hummers method through ultrasonic treatment in water, and the GO film was reduced under protection of Ar/H2 flow at 800 degrees C. Moreover, the obtained graphene film has a high conductivity of 383 S/cm at 10-20 nm thickness.     

Thermally stable and highly conductive free-standing hybrid films based on reduced graphene oxide

Thermally stable and highly conductive films have been prepared based on thermally reduced graphene oxide and exfoliated α-zirconium phosphate nanoplatelet (ZrP) hybrids. Exfoliated ZrP and graphene oxide (GO) were first mixed in aqueous solution to form a stable dispersion and then cast into free-standing films through flow-directed assembly. Upon annealing at 750 °C in Argon atmosphere, significant amounts of oxidized species were removed from the GO and a noticeable recovery of sp² structure of the reduced GO sheets was observed. With the incorporation of the inorganic nanoplatelets, the thermal stability and structural integrity of the hybrid films were greatly improved, while the good electrical conductivity of the reduced GO was maintained. Potential applications for graphene-based hybrid films based on the current approach are discussed.     

Edge‐Functionalized Graphene Nanoplatelets as Metal‐Free Electrocatalysts for Dye‐Sensitized Solar Cells

A scalable and low‐cost production of graphene nanoplatelets (GnPs) is one of the most important challenges for their commercialization. A simple mechanochemical reaction has been developed and applied to prepare various edge‐functionalized GnPs (EFGnPs). EFGnPs can be produced in a simple and ecofriendly manner by ball milling of graphite with target substances (X = nonmetals, halogens, semimetals, or metalloids). The unique feature of this method is its use of kinetic energy, which can generate active carbon species by unzipping of graphitic C? C bonds in dry conditions (no solvent). The active carbon species efficiently pick up X substance(s), leading to the formation of graphitic C? X bonds along the broken edges and the delamination of graphitic layers into EFGnPs. Unlike graphene oxide (GO) and reduced GO (rGO), the preparation of EFGnPs does not involve toxic chemicals, such as corrosive acids and toxic reducing agents. Furthermore, the prepared EFGnPs preserve high crystallinity in the basal area due to their edge‐selective functionalization. Considering the available edge X groups that can be selectively employed, the potential applications of EFGnPs are unlimited. In this context, the synthesis, characterizations, and applications of EFGnPs, specifically, as metal‐free carbon‐based electrocatalysts for dye‐sensitized solar cells (DSSCs) in both cobalt and iodine electrolytes are reviewed.     

Preparation and mechanical properties of exfoliated CoAl layered double hydroxide (LDH)/polyamide 6 nanocomposites by in situ polymerization

Novel exfoliated nanocomposites based on polyamide 6 (PA6)/CoAl layered double hydroxide (CoAl-LDH) have been successfully prepared via in situ polymerization. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated that the inorganic nanoplatelets of CoAl-LDH were homogeneously dispersed in the PA6 matrix. Mechanical testing (by tensile tests and nanoindentation measurements) shows that, compared with neat PA6, the tensile modulus, the yield strength, and the hardness of the nanocomposites are substantially improved by about 100%, 75%, and 25%, respectively, with incorporating only 1 wt% CoAl-LDH. In addition, tensile fracture morphologies of neat PA6 and its nanocomposites are also compared and discussed.     

Effect of exfoliated graphite nanoplatelets on the mechanical and viscoelastic properties of poly(lactic acid) biocomposites reinforced with kenaf fibers

The focus of this study is to explore synergy between nanomaterials such as exfoliated graphite nanoplatelets (xGnP) and micro-size reinforcements such as kenaf natural fibers, in poly(lactic acid) based composites. The nano-biocomposites are made by melt-mixing followed by injection molding. Prior to melt-mixing the kenaf fibers were coated with the xGnP using sonication. The reinforcement content used in the study was up to 5 wt% and up to 40 wt% for xGnP and kenaf fibers, respectively. The flexural strength and modulus and the viscoelastic properties such as storage modulus were determined. It was found that addition of 5 wt% xGnP did not increase the viscosity of the polymer melt, enhanced the flexural modulus by 25–30% at any fiber loading used but did not increase the strength, indicating insufficient load transfer at the polymer-xGnP or xGnP-kenaf interface. Finally, addition of xGnP had a positive effect on the heat distortion temperature but only at higher fiber loadings.     

Review on polymer/graphite nanoplatelet nanocomposites

Graphite nanoplatelets (GNPs) are a type of graphitic nanofillers composed of stacked 2D graphene sheets, having outstanding electrical, thermal, and mechanical properties. Furthermore, owing to the abundance of naturally existing graphite as the source material for GNPs, it is considered an ideal reinforcing component to modify the properties of polymers. The 2D confinement of GNPs to the polymer matrix and the high surface area make the GNP a distinctive nanofiller, showing superiorities in modification of most properties, compared with other carbon nanofillers. This review will summarize the development of polymer/GNP nanocomposites in recent years, including the fabrication of GNPs and its nanocomposites, processing issues, viscoelastic properties, mechanical properties, electrical and dielectric properties, thermal conductivity and thermal stability. The discussion of reinforcing effect will be based on dispersion, particle geometry, concentrations, as well as the 2D structures and exfoliation of GNPs. The synergy of GNPs with other types of carbon nanofillers used as hybrid reinforcing systems shows great potential and could significantly broaden the application of GNPs. The relevant research will also be included in this review.     

Improving electrical conductivity and mechanical properties of high density polyethylene through incorporation of paraffin wax coated exfoliated graphene nanoplatelets and multi-wall carbon nano-tubes

High Density Polyethylene (HDPE) based nanocomposites are reinforced by exfoliated graphene nanoplatelets, GNP, and multi-wall carbon nano-tubes, MWCNT, through melt extrusion and injection molding in this study. Low molecular weight paraffin wax was selected as a coating on the surface of GNP and MWCNT to improve their dispersion in HDPE. Wax coated GNP and MWCNT were fabricated by mixing wax with GNP and MWCNT in hot xylene and followed with the solvent evaporation and vacuum drying. It was found that wax coated GNP and MWCNT are much more efficient than the uncoated ones in improving the electrical conductivity and the flexural properties of HDPE nanocomposites. Morphology characterization verified that the dispersion of GNP and MWCNT in the polymer matrix was significantly enhanced by this wax coating method which was responsible for the better electrical and mechanical properties in the resulting nanocomposites.     

Preparation and characterization of in situ polymerized cyclic butylene terephthalate/graphene nanocomposites

Graphene-reinforced cyclic butylene terephthalate (CBT) matrix nanocomposites were prepared and characterized by mechanical and thermal methods. These nanocomposites containing different amounts of graphene (up to 5 wt%) were prepared by melt mixing with CBT that was polymerized in situ during a subsequent hot pressing. The nanocomposites and the neat polymerized CBT (pCBT) as reference material were subjected to differential scanning calorimetry, dynamical mechanical analysis, thermogravimetrical analysis, and heat conductivity measurements. The dispersion of the grapheme nanoplatelets was characterized by transmission electron microscopy. It was established that the partly exfoliated graphene worked as nucleating agent for crystallization, acted as very efficient reinforcing agent (the storage modulus at room temperature was increased by 39 and 89 % by incorporating 1- and 5-wt% graphene, respectively). Graphene incorporation markedly enhanced the heat conductivity but did not influence the TGA behavior, except the ash content, due to the not proper exfoliation except the ash content.     

Direct synthesis of hydrophobic graphene-based nanosheets via chemical modification of exfoliated graphene oxide

Hydrophobic graphene-based material at the nanoscale was prepared by treatment of exfoliated graphene oxide with organic isocyanates. The lipophilic modified graphene oxide (LMGO) can then be exfoliated into the functionalized graphene nanoplatelets that can form a stable dispersion in polar aprotic solvents. AFM image shows the thickness of LMGO is approximately 1 nm. Characterization of LMGO by elemental analysis suggested that the chemical treatment results in the functionalization of the carboxyl and hydroxyl groups in GO via formation of amides and carbamate esters, respectively. The degree of GO functionalization can be controlled via either the reactivity of the isocyanate or the reaction time. Then we investigated the thermal properties of the SPFGraphene by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), the TGA curve shows a greater weight loss of approximately 20% occurred indicating removal of functional groups from the LMGO sheets and an obvious exothermic peak at 176 degrees can be observed from 150 to 250 degrees. We also compared the structure of graphene oxide with the structure of chemical treated graphene oxide by FT-IR spectroscopy. The morphology and microstructure of the LMGO nanosheets were also characterized by SEM and XRD. Graphene can be used to fabricate a wide range of simple electronic devices such as field-effect transistors, resonators, quantum dots and some other extensive industrial manufacture such as super capacitor, li ion battery, solar cells and even transparent electrodes in device applications.     

Interpenetrating polymer networks (IPN) based on gelatin/poly(ethylene glycol) dimethacrylate/clay nanocomposites: Structure–properties relationship

The effects of cross-linking sequence (simultaneous or sequential) and incorporation of exfoliated sodium-montmorillonite (Na⁺-MMT) nanoclay on the structure and properties of interpenetrating polymer networks (IPNs) based on gelatin/poly(ethylene glycol)dimethacrylate were studied by means of different complementary techniques. Gelatin and PEGdmA phases were cross-linked via chemical and in-situ UV curing, respectively. 2,2-dimethoxy-2-phenylacetophenone (DMPA) (1.5% w/w) was used as photo-initiator to cross-link PEGdmA. The results showed that the incorporation of small amount of Na⁺-MMT nanoplatelets accelerates the kinetics of chemical cross-linking of gelatin by glutaraldehyde (1.0% w/w). This led to a new hypothesis concerning the tuning structural evolution of the IPNs by the Na⁺-MMT content. In the case of simultaneous IPNs, in which both phases cross-linked at the same time, the accelerated cross-linking of gelatin in the presence of exfoliated sodium-montmorillonite led to increased structural homogeneity, improved mechanical and thermal properties. Incorporation of nanoclay did not show any significant effect on the structure and properties of the IPNs synthesized via sequential method in which gelatin and PEGdma phases were cross-linked separately. For the semi-IPNs, however, Na⁺-MMT induced macroscopic phase separation and resulted in lower mechanical properties. These results might shed light on the mechanisms underlying structure–property relationship in biohybrid IPNs based on gelatin as promising candidates for tissue engineering and drug delivery applications.     

石墨烯微片/天然橡胶纳米复合材料的研究

目的 研究石墨烯微片的添量对石墨烯微片/天然橡胶纳米复合材料性能的影响,并对机械共混法和胶乳共混法进行比较。方法 探索复合材料的制备工艺,利用扫描电镜(SEM)、透射电镜(TEM)、拉曼光谱(RDS)、万能力学试验机等对石墨烯微片和石墨烯微片/天然橡胶纳米复合材料的形貌、结构以及性能进行分析和研究。结果 测试结果表明,石墨烯微片作为填料添加到复合材料中,使复合材料的性能得到了增强。相比纯橡胶而言,石墨烯微片(10 phr)/天然橡胶复合材料的拉伸强度增加了41.5%,热导率增加了153.3%。结论 石墨烯微片可以大幅度提高复合材料的性能,并且胶乳共混法制备的复合材料的性能要优于机械共混法制备的复合材料的性能。     

Microstructure and magnetic properties of Fe(x)Ni(1-x) alloy nanoplatelets

Plate-like nanoparticles (or nanoplatelets) of Fe(x)Ni(1-x) (x = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) alloy were successfully synthesized through a simple sonochemical method. The shapes of the alloy nanoplatelets with different Fe atom contents are almost same. Their average diameters are about 50 nm, and their average thicknesses are several nanometers. The obtained Fe(x)Ni(1-x) alloy nanoplatelets are single-phased and have a face-centered cubic (FCC) crystal structure. The lattice constants of the alloy nanoplatelets are larger than the corresponding bulk value and increase with increasing Fe content. The surface oxidation of the alloy nanoplatelets leads to the lattice expansion. The alloy nanoplatelet powders are all ferromagnetic, and their saturation magnetizations are slightly lower than the corresponding bulk value. The saturation magnetic field and the coercivity increase with increasing Fe content. Magnetic hysteresis loops along the directions deviating different angles from the nanoplatelets plane are obviously different, indicating that the easy-axis is in the in-plane direction and the magnetization reversal is incoherent mode. The micromagnetic simulation results for the array composed of thirty-six Fe0.6Ni0.4 alloy nanoplatelets fit well with the measured data.