Electronic structure of graphite oxide and thermally reduced graphite oxide

We present the electronic structure evolution from graphite oxide to thermally reduced graphite oxide. Most functional groups were removed by thermal reduction as indicated by high resolution X-ray photoelectron spectroscopy, and the electrical conductivity increased 6 orders compare with the precursor graphite oxide. X-ray absorption spectroscopy reveals that the thermally reduced graphite oxide shows several absorption peaks similar to those of pristine graphite, which were not observed in graphite oxide or chemically reduced graphite oxide. This indicates the better restoration of graphitic electronic conjugation by thermal reduction. Furthermore, the significant increased intensity of Raman 2D band of thermally reduced graphite oxide compared with graphite oxide also suggests the restoration of graphitic electronic structure (π orbital). These results provide useful information for fundamental understanding of the electronic structure of graphite oxide and thermally reduced graphite oxide.     

Microwave assisted exfoliation and reduction of graphite oxide for ultracapacitors

We report a simple yet versatile method to simultaneously achieve the exfoliation and reduction of graphite oxide. By treating graphite oxide powders in a commercial microwave oven, reduced graphite oxide materials could be readily obtained within 1 min. Extensive characterizations showed that the as-prepared materials consisted of crumpled, few-layer thick and electronically conductive graphitic sheets. Using the microwave exfoliated graphite oxide as electrode material in an ultracapacitor cell, specific capacitance values as high as 191 F/g have been demonstrated with KOH electrolyte.     

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.     

Crystallization,rheological behavior and mechanical properties of poly(vinylidene fluoride) composites containing graphitic fillers: a comparative study

The effect of three kinds of graphitic fillers with distinct morphologies, natural graphite sheets (NGs), chemically reduced graphite oxide sheets (CRGs) and thermally reduced graphite oxide sheets (TRGs), on the crystallization, rheological behavior and mechanical properties of poly(vinylidene fluoride) (PVDF)‐based composites has been investigated comparatively. NGs exhibit smooth surface and multilayer‐stacked structure; most CRGs are in the form of aggregates that are restacked during reduction; while TRGs show a wrinkled topography of relatively thin graphene sheets. The introduction of these graphitic fillers into the PVDF matrix contributes differently to the crystallization, rheological behavior and mechanical properties of the composites. Among them, TRGs show the greatest strengthening effect, as revealed by rheological and dynamic mechanical responses. Compared with chemical reduction technology, thermal reduction is a more economical, environmentally friendly and scalable approach to prepare functionalized graphene sheets. Copyright © 2012 Society of Chemical Industry     

Utilization of multiple graphene layers in fuel cells. 1. An improved technique for the exfoliation of graphene-based nanosheets from graphite

An improved, safer and mild method was proposed for the exfoliation of graphene like sheets from graphite to be used in fuel cells. The major aim in the proposed method is to reduce the number of layers in the graphite material and to produce large quantities of graphene bundles to be used as catalyst support in polymer electrolyte membrane fuel cells. Graphite oxide was prepared using potassium dichromate/sulfuric acid as oxidant and acetic anhydride as intercalating agent. The oxidation process seemed to create expanded and leafy structures of graphite oxide layers. Heat treatment of samples led to the thermal decomposition of acetic anhydride into carbondioxide and water vapor which further swelled the layered graphitic structure. Sonication of graphite oxide samples created more separated structures. Morphology of the sonicated graphite oxide samples exhibited expanded the layer structures and formed some tulle-like translucent and crumpled graphite oxide sheets. The mild procedure applied was capable of reducing the average number of graphene sheets from 86 in the raw graphite to nine in graphene-based nanosheets. Raman spectroscopy analysis showed the significant reduction in size of the in-plane sp² domains of graphene nanosheets obtained after the reduction of graphite oxide.     

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.     

Aerospace Application of Polymer Nanocomposite with Carbon Nanotube,Graphite, Graphene Oxide,and Nanoclay

In this review, potential and properties of carbon nanotube, graphite, graphene oxide, and clay nanofiller have been deliberated with reference to aerospace application. The polymers discussed as matrices are polypropylene, polyaniline, polyurethane, polystyrene, and polyamide. Main focus of the review is to converse space competency of polymer/carbon nanotube, polymer/graphite, polymer/graphene oxide, and polymer/clay nanocomposite. The effect of nanofiller addition on the desired aerospace properties of polymeric nanocomposite has been conversed. Attractive features are high glass transition temperature, thermal stability, high modulus, chemical resistance, and nonflammability. Toward the end, challenges in the enhancement of materials’ properties for aerospace relevance have been considered.     

Simple and cost-effective reduction of graphite oxide by sulfuric acid

We report a simple, cost-effective, and environmentally benign process for reducing graphite oxide by treating solely with sulfuric acid. The suggested process consists of a two-step reduction of graphite oxide, first in aqueous sulfuric acid at room temperature and then in concentrated sulfuric acid with refluxing. X-ray diffractometry, X-ray photoelectron spectroscopy, Raman spectroscopy and thermogravimetric analysis demonstrated that the graphite oxide was reduced effectively and was comparable in composition to reduced graphite oxide prepared using previously described methods that rely on toxic and hazardous reducing agents, such as hydrazine, sodium borohydride, or hydrohalic acids.     

The effects of boron additives on the oxidation behavior of carbons

Impregnation of graphite with aqueous solutions of boric oxide or with organo-borates has been found to result in marked reduction in the rate of oxidation of the graphite in dry or moist air between 600 and 1000°C. At these temperatures, the additives probably form a glassy oxide residue which blocks active sites on the graphite surface.     

Composite graphitic nanolayers prepared by self-assembly between finely dispersed graphite oxide and a cationic polymer

Chemical flaking of graphite has been performed by reacting natural graphite with a strong oxidizing agent, NaClO₃/HNO₃. The formed hydrophilic, negatively charged graphite oxide (GO) colloids can be dispersed in water which allows the deposition of thin GO/cationic polymer (poly(diallyldimethylammoniumchloride, PDDA) multilayer films on a glass substrate by wet-chemical self-assembly. The feasibility of the charge-regulated layer-by-layer deposition is demonstrated by mutual charge titrations of the film-forming species. Visible-light spectroscopy revealed progressive growth of the film thickness with the number of deposition of steps, while XRD and AFM showed that partially exfoliated, highly anisometric (aspect ratio >50) graphite oxide platelet aggregates were deposited with an average thickness of the stacked graphite oxide platelets of 10 carbon layers (7.4 nm). Reduction of multilayer assemblies of GO and PDDA on glass yielded a non-conductive turbostratic carbon nanofilm. The original, conductive graphite-like structure was restored by reduction with N₂H₄ and annealing at 400 °C which, by gradual ordering of the carbon crystallites, caused a significant decrease in the resistivity.     

Preparation of pillared carbon thin films from the reduction of silylated graphite oxide by UV light irradiation and their size selective electrical response to various molecules

Silylated graphite oxide thin films were reduced by UV light irradiation using a super high pressure Hg lamp at 95 °C. The reduction of silylated graphite oxide was completed within 24 h and a new pillared carbon with an interlayer spacing of 0.81 nm was obtained. Pillared carbons with larger interlayer spacings of about 1.13 nm were also obtained from graphite oxide silylated with octyltrichlorosilane and then with 3-aminopropyltriethoxysilane for 1.5–6 h, when they were reduced by UV light irradiation and heating at 200 °C under vacuum. Selective electrical response during exposure to gaseous vinylene carbonate, acetonitrile, ozone and hydrogen molecules has been achieved by changing the pillar density in the resulting pillared carbon films.     

磺化聚醚醚酮／氧化石墨复合膜的制备与表征

采用液相氧化法制备了氧化石墨（GO）,以浓硫酸为磺化剂与聚醚醚酮反应制备了磺化聚醚醚酮（SPEEK）。采用溶液共混法制备了不同组成的SPEEK／GO复合膜,并运用FTIR、XRD、DSC、TG对复合膜进行了表征。研究表明,当氧化石墨和磺化聚醚醚酮复合后,氧化石墨的层间距由0．8nm增大至1．1nm,这说明磺化聚醚醚酮极性基团或者高分子链段已经插入到氧化石墨片层之间。DSC结果显示,氧化石墨的加入,在一定程度上降低了SPEEK的结晶性能。TG分析表明,在温度低于300℃,复合膜的热稳定性比磺化聚醚醚酮的略有降低,但当温度高于450℃后,复合膜的热稳定性反而得到提高。     

In situ thermal reduction of graphene oxide forming epoxy nanocomposites and their dielectric properties

The electrical properties of epoxy based composites modified by low amounts of graphite oxide, below the conduction threshold, have been investigated. The composites have been prepared without the use of solvents by direct sonication of graphite oxide (GO) powders and of chemically modified and partially reduced GO powders in the based epoxy monomer. Through a mild thermal treatment, in situ reduction of the previously dispersed GO has been obtained directly inside the epoxy resins. The changes in the electrical response of the materials thus obtained have been compared to that of pristine unmodified epoxy resin. Data so far collected underline the possibility to tune the electrical conductivity of the composites within two orders of magnitude and to increase the values of permittivity without significantly worsening dielectric losses. POLYM. COMPOS., 36:294–301, 2015. © 2014 Society of Plastics Engineers     

Use of exfoliated graphite filler to enhance polymer physical properties

Three sets of exfoliated graphite filled polymers, having three different particle sizes, were prepared with load levels from 0.1-20% by weight. After sieving, the particles were reduced to nanometer size through exfoliation, shear mixing, and ultrasonication, which further breaks and delaminates them. The electrical, thermal and mechanical properties of the nanoparticle filled polymers were measured. In addition, light, scanning electron, and atomic force microscope characterization were performed. The exfoliated graphite filled polymer material could be tailored to be high modulus and vary from insulating to highly conducting. Compared with the pure polymer, the polymers filled with 20% wt. exfoliated graphite has seen an significant reduction in electrical resistivity from 1.5⁸ to 0.5 Ω cm. The thermal conductivity for the polymers containing 20% wt exfoliated graphite has also been drastically improved, increasing from 0.2 to 5 W/m K. The flexural modulus achieved a maximum increase of 3.8 GPa which is a 60% above the value for the pure polymer (2.4 GPa).     

Material characterization of graphite nanosheet composites

Three sets of expanded graphite‐filled polymers, having three different particle sizes, were reinforced with 1–5% by weight. The structural, mechanical, electrical, and thermal properties of these composites were studied and compared. After dispersion, the particles were reduced to nanometer size through exfoliation, sonication, and high‐shear strain rate mixing, which further breaks and delaminates them. In addition, scanning electron microscope characterizations were performed. The expanded graphite‐filled polymer material could be tailored to be high conducting. Compared with the pure polymer, the polymers filled with 5 wt% expanded graphite have seen a significant reduction in electrical resistivity by orders. The thermal expansion coefficient and water absorption for the weight containing 5 wt% expanded graphite has also been drastically improved, decreasing with the weight percentage of graphite content. Compression and impact tests were conducted. The influence of dispersion on the material behavior was studied. Some fracture modes associated with the layered microstructures of the graphite nanosheets were observed. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Fabrication of polymer/microwave‐reduced graphite oxide nanocomposites by ball‐milling assisted wet compounding

Microwave‐induced reduction of graphite oxide (GO) is a promising method for rapid and scalable production of graphene. However, homogeneous incorporation of thus prepared graphene into polymer matrix is still a hard task. In this article, we present a ball‐milling assisted wet compounding method for the fabrications of microwave‐reduced GO (MRGO)/polymer composites. MRGO powders were added into a solution of polystyrene (PS) and then mechanically exfoliated in a stirring mill. Scanning electron microscopy and transmission electron microscopy investigations show that the graphene sheets have been homogeneously dispersed in the PS matrix. The composites show pronouncedly improved properties. The thermal degradation temperature of composites increased by 34°C with the addition of 5wt% MRGO in PS. Up to 76% improvement of storage modulus (at 30°C) is achieved by compounding with 10wt% MRGO.POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

KH-560改性氧化石墨/环氧树脂复合材料的制备与性能研究

以廉价石墨(GR)为起始原料制备氧化石墨(GO),用KH-560(γ-(2,3-环氧丙氧)丙基三甲氧基硅烷)对GO表面进行改性,改性氧化石墨(m-GO)与环氧树脂E51发生交联固化。扫描电镜(SEM)及电阻率测试表明:采用该方法制备的无机/有机聚合物复合材料,石墨颗粒均匀分散于环氧树脂中,导电阈值低。掺杂量为1.0%~2.0%的m-GO/E51复合材料的表面电阻率在1010~1011Ω之间,达到空间聚合物抗介质带电的需求。该方法简单实用,具有很好的工程化应用前景。     

Polymer and Graphite-Derived Nanofiller Composite: An Overview of Functional Applications

In this article, applications of polymer and graphite-derived nanofiller composite have been presented with special emphasis on epoxy composite. Various types of graphitic nanofillers such as graphite, graphene oxide, graphene, and graphene nanoplatelets are reviewed. Recently, polymer/graphite, polymer/graphene oxide, polymer/graphene, and polymer/graphene nanoplatelet-based materials have gained interest due to high performance. Property enhancement is due to high aspect ratio; high surface area; excellent electrical, thermal, and mechanical properties of nanofillers. The filler dispersion depends upon selection of suitable fabrication technique. We also reported on applications of epoxy/graphite-based filler composites in technical fields such as Li-ion batteries, sensors, and solar cells.     

Polyurethane Composite Foams in High-Performance Applications: A Review

Polyurethane foam is a polymeric material having cellular structure. Multifunctional polyurethane foams reinforced with nanofiller have combined enhanced specific properties with density reduction. This article primarily considers important aspects of various foam processing techniques. Numerous nanofillers such as graphite, graphene, graphene oxide, carbon black, carbon nanotube, nanoclay, and inorganic nanoparticle have been reinforced in polyurethane foam. Particular attention is given to various categories of polymer/carbon nanofiller and polymer/inorganic nanofiller composite foams. Applications of polyurethane composite foams have been focused with relevance to aerospace and automotive industry, radar absorbing and electromagnetic interference shielding, oil absorbants, sensors, fire proof, shape memory, and biomedical materials.     

聚合物/氧化石墨纳米复合材料的研究进展

氧化石墨因具有层状结构,能够以插层复合的方式与聚合物形成聚合物纳米复合材料。本文介绍了氧化石墨的结构、性能特点以及聚合物/氧化石墨纳米复合材料的研究进展情况,包括聚合物/氧化石墨纳米复合材料的制备方法、种类、结构与性能特点、应用前景与研究展望。