Millimeter-long multilayer graphene nanoribbons prepared by wet chemical processing

Millimeter long multilayer graphene nanoribbons were prepared by a chemical treatment of graphite oxide (GO). To our knowledge, this is the very first report to harvest ultralong graphene ribbons with length dimension >1 mm using a wet chemical process. Scanning electron microscope (SEM) images reveal the nanoribbon length larger than 1 mm and width ∼10 μm. X-ray photoelectron spectroscopy (XPS) analysis shows that oxygen-containing functional groups decreased as the extent of the chemical treatment increased. X-ray diffraction (XRD) and Raman spectroscopy studies confirmed the XPS result and unveil more graphitic sheet like structure formed as GO was reduced by more concentrated NaOH. It is found that by adjusting NaOH/GO mass ratio during the chemical treatment, we can produce >1 mm long multilayer graphene nanoribbons and achieve controllable degree of reduction to the GO material. It is expected that this technique will make ultralong graphene nanoribbons readily available for research and applications.     

Characterization and performance of dodecyl amine functionalized graphene oxide and dodecyl amine functionalized graphene/high‐density polyethylene nanocomposites: A comparative study

Dodecyl amine (DA) functionalized graphene oxide(DA‐GO) and dodecyl amine functionalized reduced graphene oxide (DA‐RGO) were produced by using amidation reaction and chemical reduction, then two kinds of well dispersed DA‐GO/high‐density polyethylene (HDPE) and DA‐RGO/HDPE nanocomposites were prepared by solution mixing method and hot‐pressing process. Thermogravimetric, X‐ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, X‐ray diffractions, and Raman spectroscopy analyses showed that DA was successfully grafted onto the graphene oxide surface by uncleophilic substitution and the amidation reaction, which increased the intragallery spacing of graphite oxide, resulting in the uniform dispersion of DA‐GO and DA‐RGO in the nonpolar xylene solvent. Morphological analysis of nanocomposites showed that both DA‐GO and DA‐RGO were homogeneously dispersed in HDPE matrix and formed strong interfacial interaction. Although the crystallinity, dynamic mechanical, gas barrier, and thermal stability properties of HDPE were significantly improved by addition of small amount of DA‐GO or DA‐RGO, the performance comparison of DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites indicated that the reduction of DA‐GO was not necessary because the interfacial adhesion and aspect ratio of graphene sheets had hardly changed after reduction, which resulting in almost the same properties between DA‐GO/HDPE and DA‐RGO/HDPE nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39803.     

Synthesis and exfoliation of isocyanate-treated graphene oxide nanoplatelets

A number of functionalized graphite oxides were prepared by treatment of graphite oxide (GO) with organic isocyanates. These isocyanate-treated GOs (iGOs) can then be exfoliated into functionalized graphene oxide nanoplatelets that can form a stable dispersion in polar aprotic solvents. Characterization of iGOs by FT-IR spectroscopy and elemental analysis suggested that the isocyanate 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. When used with functionalized isocyanates, the described methodology allows for the elaboration of graphene oxide nanoplatelets with different surface functional groups.     

Influences of graphene oxide support on the electrochemical performances of graphene oxide-MnO2 nanocomposites

MnO₂ supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of MnO₂-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO₂, which lead to the fact that the loading amount of MnO₂ on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO₂ loading on GO(1). As the electrode of supercapacitor, MnO₂-GO(1) nanocomposites show larger capacitance (307.7 F g^-1) and better electrochemical activity than MnO₂-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO₂ on GO(1) support.     

Facile and safe graphene preparation on solution based platform

Graphene has attracted increasing attention because of its interesting properties. In this study, graphene was prepared from graphite by a very simple and easy process. The two-step protocol involves conversion of graphite to graphene oxide (GO) by oxidation, and subsequent reduction of GO to graphene. The structures and properties of the obtained GO and graphene were characterized via X-ray diffraction, and Raman, NMR, UV–vis absorption, and X-ray photoelectron spectroscopic techniques. The morphologies of these products were observed via field emission scanning electron microscopy. The preparation protocol is simple, easy, environmental friendly, i.e., nontoxic, and the yield of graphene is high.     

In-situ synthesis and characterization of electrically conductive polypyrrole/graphene nanocomposites

Polypyrrole (PPy)/graphene (GR) nanocomposites were successfully prepared via in-situ polymerization of graphite oxide (GO) and pyrrole monomer followed by chemical reduction using hydrazine monohydrate. The large surface area and high aspect ratio of the in-situ generated graphene played an important role in justifying the noticeable improvements in electrical conductivity of the prepared composites via chemical reduction. X-ray photoelectron spectroscopy (XPS) analysis revealed the removal of oxygen functionality from the GO surface after reduction and the bonding structure of the reduced composites were further determined from FTIR and Raman spectroscopic analysis. For PPy/GR composite, intensity ratio between D band and G band was high (∼1.17), indicating an increased number of c-sp² domains that were formed during the reduction process. A reasonable improvement in thermal stability of the reduced composite was also observed. Transmission electron microscopy (TEM) observations indicated the dispersion of the graphene nanosheets within the PPy matrix.     

Graphene oxide covalently functionalized with zinc phthalocyanine for broadband optical limiting

A soluble graphene oxide (GO) covalently functionalized with zinc phthalocyanine (PcZn), GO–PcZn, was synthesized by an amidation reaction. The formation of an amido bond between PcZn and GO has been confirmed by X-ray photoelectron and Fourier transform infrared spectroscopy. At the same level of linear extinction coefficient, GO–PcZn exhibited much larger nonlinear optical extinction coefficients and broadband optical limiting performance than GO at both 532 and 1064 nm, indicating a remarkable accumulation effect as a result of the covalent link between GO and PcZn.     

Easy and green synthesis of reduced graphite oxide-based hydrogels

We report an environmentally-friendly and easy to scale-up route to synthesize reduced graphite oxide (RGO) hydrogel by simple reduction of exfoliated graphite oxide (GO) with excess vitamin C (VC). Mono-layer graphene sheets self-assembling into a well-defined and interconnected 3D porous network through π–π interaction during gelation can be seen by scanning electron microscopy and atomic force microscopy images. The RGO hydrogels were further functionalized and the corresponding RGO/carbon nanotube or RGO/noble metal hybrid hydrogels were obtained after similar reduction or co-reduction when carbon nanotubes were added to and stabilized with GO sheets or when noble metal precursors were added and incorporated with GO sheets. Rheological performance and electrical conductivities of these RGO-based hydrogels were also investigated in this study. The residual VC retained in these hydrogels as a biofunctional component can be gradually released in a diffusion-controlled manner, which may endow these RGO-based hydrogels with a biofunctionality. Because encapsulated bioactive VC simultaneously occurs with the formation of these assemblies, the resulting RGO-based hydrogels may have great potential in use as transdermal systems for controlled delivery of VC, tissue engineering, biosensors, etc.     

An improved strategy to synthesize graphite oxide with controllable interlayer spacing as coatings for anticorrosion application

A facile method to synthesize nanoscale graphene oxide (GO) with controllable interlayer spacing was carried out using two-step oxidation process and much less acid to improve the efficiency of the oxidation. The X-ray diffraction results demonstrated that GO had been successfully prepared from graphite because of disappearance of characteristic peaks of pristine graphite at about 2θ = 26.5° along with appearance of a sharp major peak of GO at about 2θ = 9.4°. The increased basal spacing d₀₀₁ of as-prepared GO could reach as high as 9.39 Å, suggesting higher degree of oxidation than that prepared by the classical Hummers' synthesis, and characterization results from Fourier transform infrared spectrometer, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy further confirmed this conclusion. The influence of GO on anti-corrosion performance of nanocomposite coatings composited with the 2,5-dimethoxyaniline (DMA) conductive polymer was examined via potentiodynamic polarization curve tests in 3.5 wt% NaCl aqueous solution. The results demonstrated that the incorporation of GO significantly decreased the corrosion current density (i_corr = 2.62 μA/cm²) in the case of GO-PDMA coating, reflecting excellent physical isolation of GO and its synergistic effect with PDMA against the infiltration of water and corrosive electrolyte.     

Janus graphene oxide nanosheets prepared via Pickering emulsion template

Janus graphene oxide (GO) nanosheets functionalized by amino-containing chemicals were prepared via Pickering emulsion template. A wax-in-water Pickering emulsion was used to mask one side of GO nanosheets in order to achieve asymmetric chemical functionalization. Janus particles were obtained by removing the oil phase. The successful reaction of epoxy groups on the surface of GO with amino-containing chemicals was confirmed by Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The asymmetric surface structure of Janus GO nanosheets was detected by atomic force microscope (AFM) and X-ray diffraction (XRD). The efficient stabilization of an oil-in-water Pickering emulsion by Janus GO was proved. Polymer microspheres fabricated by using Janus GO as Pickering stabilizer had a more hydrophilic surface compared with those stabilized by symmetrically modified GO.     

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.     

化学氧化法合成氧化石墨及其陶瓷复合材料

基于Hummer化学氧化法,以不同纯度的石墨为原料,在氧化阶段改变氧化剂(KMnO4)的添加速率,研究了氧化石墨的制备及其结构形成。结果表明:石墨原料纯度及氧化剂添加速率对氧化石墨结构有重要影响。以高纯度石墨为原料,在合适的添加速率下制备出的氧化石墨具有高的结晶性和纯度。扫描电镜观察制得的氧化石墨呈片层结构,厚约50nm。X射线分析显示对称氧化石墨(002)强衍射峰,无残留石墨峰和其它杂质峰。红外光谱分析氧化石墨含—OH,C=O,C—O等含氧基团。Ar气氛下对氧化石墨进行热解,产物为石墨烯。将制得的氧化石墨引入聚硅氧烷中,经交联和热解制出具有层状复合结构呈一定取向分布的石墨烯和硅氧碳陶瓷复合材料。     

Electrospinning of poly(ε‐caprolactone) solutions containing graphene oxide: Effects of graphene oxide content and oxidation level

The morphological appearance, fiber diameter, and structure of poly(ε‐caprolactone) (PCL) nanofibers produced by the electrospinning process were studied in the presence of different amounts of graphene oxide (GO) with different oxidation levels. Scanning electron microscope micrographs of electrospun fibers showed that the average fiber diameter decreases in the presence of GO with different loading and oxidation levels. The loading level of GO especially higher than 0.3 wt% was influential in decreasing the diameter of PCL electrospun fibers rather than oxidation level. Contact angle, infrared spectroscopy, and conductivity measurements on graphite oxide (GtO) samples, as well as rheological, conductivity, and surface tension experiments on PCLGO solutions were performed to describe the role of GO in the significant reduction of fiber diameter. It was found that three factors are involved in generating a driving force for more stretching of the electrospinning jet. One is the viscosity reduction of PCLGO solution, which intensifies by more GO content and less GO oxidation level. The second is solution conductivity which enhances by GO loading and the third is the charge relaxation time of the spinning solution, which grows with increasing the oxidation level of GO as well as the GO content. POLYM. COMPOS., 131–140, 2016. © 2014 Society of Plastics Engineers     

Solid-phase electrochemical reduction of graphene oxide films in alkaline solution

Graphene oxide (GO) film was evaporated onto graphite and used as an electrode to produce electrochemically reduced graphene oxide (ERGO) films by electrochemical reduction in 6 M KOH solution through voltammetric cycling. Fourier transformed infrared and Raman spectroscopy confirmed the presence of ERGO. Electrochemical impedance spectroscopy characterization of ERGO and GO films in ferrocyanide/ferricyanide redox couple with 0.1 M KCl supporting electrolyte gave results that are in accordance with previous reports. Based on the EIS results, ERGO shows higher capacitance and lower charge transfer resistance compared to GO.     

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.     

Graphite–graphite oxide composite electrode for vanadium redox flow battery

A graphite/graphite oxide (GO) composite electrode for vanadium redox battery (VRB) was prepared successfully in this paper. The materials were characterized with X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The specific surface area was measured by the Brunauer–Emmett–Teller method. The redox reactions of [VO₂]⁺/[VO]²⁺ and V³⁺/V²⁺ were studied with cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the electrochemical performances of the electrode were improved greatly when 3 wt% GO was added into graphite electrode. The redox peak currents of [VO₂]⁺/[VO]²⁺ and V³⁺/V²⁺ couples on the composite electrode were increased nearly twice as large as that on the graphite electrode, and the charge transfer resistances of the redox pairs on the composite electrode are also reduced. The enhanced electrochemical activity could be ascribed to the presence of plentiful oxygen functional groups on the basal planes and sheet edges of the GO and large specific surface areas introduced by the GO.     

Synthesis of click‐coupled graphene sheets with hyperbranched polyurethane: Effective exfoliation and enhancement of nanocomposite properties

Graphene oxide (GO) was functionalized with hyperbranched polyurethane (HBPU) via click coupling between azide‐functionalized HBPU and alkynyl‐decorated GO. HBPU‐functionalized GO composites of various compositions were prepared. The azide‐containing HBPU was characterized using Fourier‐transform infrared (FT‐IR) spectroscopy and ¹H‐nuclear magnetic resonance spectroscopy. The HBPU‐functionalized GO composites were characterized using transmission electron microscopy and FT‐IR spectroscopy. The functionalized GO showed excellent dispersion in the HBPU matrix, giving composites with enhanced mechanical and thermal properties. The material properties were effectively regulated by click‐coupled exfoliation of GO with HBPU, enabling the production of high‐performance materials. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44631.     

In‐plane functionalizing graphene nanolayers with polystyrene by atom transfer radical polymerization: Grafting from hydroxyl groups

Graphene oxide (GO) was prepared from the oxidation of graphite and then it was functionalized with (3‐aminopropyl)triethoxysilane (APTES) from hydroxyl groups by a coupling reaction. Subsequently, alpha‐bromoisobutyryl bromide (BiBB) was attached to the APTES groups to yield initiator anchored graphene nanolayers (GOHBr). Then, GOHBr was used in different amounts as the precursor for atom transfer radical polymerization of styrene to evaluate the effect of graphene loading along with the graft density on the properties of final product. Successful in‐plain attachment of APTES, BiBB, and polystyrene to GO was evaluated by Fourier transform infrared spectroscopy. Graphene interlayers expansion by oxidation and functionalization processes was evaluated using X‐ray diffraction. The ordered and disordered crystal structures of carbon were evaluated by Raman spectroscopy. Morphology of graphene nanolayers was studied by scanning electron microscopy and also transmission electron microscopy. POLYM. COMPOS., 35:386–395, 2014. © 2013 Society of Plastics Engineers     

氧化石墨烯的可控还原及表征

采用Hummers修正法制备氧化石墨烯(GO),用壳聚糖(CS)作为“绿色”无毒还原剂,以反应温度和反应时间来控制氧化石墨烯的还原程度。用红外光谱、紫外可见吸收光谱、拉曼光谱和X射线衍射等多种表征手段研究不同还原程度的还原氧化石墨烯的结构与性能。结果表明,改变温度不能有效地控制氧化石墨烯的还原程度;在50℃低温环境下,控制反应时间可以得到不同还原程度的还原氧化石墨烯,为进一步研究不同还原程度还原氧化石墨烯的非线性光学性质奠定了基础。     

Utilization of green reductant Thuja Orientalis for reduction of GO to RGO

It is well known that graphene (G), graphene oxide (GO) and reduced graphene oxides (RGO) are materials of today with immense application potentials. However, to realize the same large scale, reproducible, sustainable synthesis techniques such as greener methods which avoid utilization of toxic chemicals for synthesis, must be adopted. It is in this context, that here we report the reduction of GO to RGO by the extract of Thuja Orientalis (TO) seeds. As such, TO is a well-known bio-resource for medicinal and various other biotechnological applications as it contains Alpha Tocopherol, the major constituent of vitamin E. To the best of our knowledge, despite the wealth of literature, the current work makes a pioneering effort in applying TO seeds extract for reduction of GO to RGO. Thus, the reduction of GO, synthesized by the well-known modified Hummer's method to RGO by TO extract, is confirmed from the results obtained by ultra-violet visible (UV–Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) analysis, selected area electron diffraction (SAED), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM) and especially, gas chromatograph mass spectrometry (GCMS) techniques. Furthermore, the GCMS study is used to identify the compound Alpha Tocopherol responsible for reduction of GO to RGO. Based on current experimental evidences and literature views, the possible mechanism of reduction is suggested. Finally, the implications of present studies in the perspective of large scale, sustainable synthesis of RGO for various technological applications are discussed.