Precise Tuning of Surface Composition and Electron‐Transfer Properties of Graphene Oxide Films through Electroreduction

Graphene materials are generally prepared from the exfoliation of graphite oxide (GO) to graphene oxide, followed by subsequent chemical or thermal reduction. These methods, although efficient in removing most of the oxygen functionalities from the GO material, lack control over the extent of the reduction process. We demonstrate here an electrochemical reduction procedure that not only allows for precise control of the reduction process to obtain a graphene material with a well‐defined C/O ratio in the range of 3 to 10, but also one that is able to tune the electrocatalytic properties of the reduced material. A method that is able to precisely control the amount and density of the oxygen functionalities on the graphene material as well as its electrochemical behaviour is very important for several applications such as electronics, bio‐composites and electrochemical devices.     

Single‐Step Functionalization and Exfoliation of Graphene with Polymers under Mild Conditions

The simultaneous polymer functionalization and exfoliation of graphene sheets by using mild bath sonication and heat treatment at low temperature is described. In particular, free‐radical polymerization of three different vinyl monomers takes place in the presence of graphite flakes. The polymerization procedure leads to the exfoliation of graphene sheets and at the same time the growing polymer chains are attached onto the graphene lattice, which gives solubility and stability to the final graphene‐based hybrid material. The polymer‐functionalized graphene sheets possess fewer defects as compared with previously reported polymer‐functionalized graphene. The success of the covalent functionalization and exfoliation of graphene was confirmed by using a variety of complementary spectroscopic, thermal, and microscopy techniques, including Raman, IR and UV/Vis spectroscopy, thermogravimetric analysis, and transmission electron microscopy.     

Halogenation of Graphene with Chlorine,Bromine, or Iodine by Exfoliation in a Halogen Atmosphere

Nanoarchitectonics on graphene implicates a specific and exact anchoring of molecules or nanoparticles onto the surface of graphene. One such example of an effective anchoring group that is highly reactive is the halogen moiety. Herein we describe a simple and scalable method for the introduction of halogen (chlorine, bromine, and iodine) moieties onto the surface of graphene by thermal exfoliation/reduction of graphite oxide in the corresponding gaseous halogen atmosphere. We characterized the halogenated graphene by using various techniques, including scanning and transmission electron microscopy, Raman spectroscopy, high‐resolution X‐ray photoelectron spectroscopy, and electrochemistry. The halogen atoms that have successfully been attached to the graphene surfaces will serve as basic building blocks for further graphene nanoarchitectonics.     

Influence of parent graphite particle size on the electrochemistry of thermally reduced graphene oxide

Electrochemical applications of graphene are of very high importance. For electrochemistry, bulk quantities of materials are needed. The most common preparation of bulk quantities of graphene materials is based on oxidation of graphite to graphite oxide and subsequent thermal exfoliation of graphite oxide to thermally reduced graphene oxide (TR-GO). It is important to investigate to which extent a reaction condition, that is, composition of the oxidation mixture and size of graphite materials, influences the properties of the resulting materials. We characterised six graphite materials with a range of particle sizes (0.05, 11, 20, 32, 35 and 41 μm) and the TR-GO products prepared from them by use of scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Cyclic voltammetric performance of the TR-GO samples was compared using ferro/ferricyanide and ascorbic acid. We observed no correlation between size of initial graphite and properties of the resultant TR-GO such as density of surface defects, amount of oxygen-containing groups, or rate of heterogeneous electron transfer (HET). A positive correspondence between HET rate and high defect density as well as low amounts of oxygen functionalities was noted. Our findings will have profound influence upon practical fabrication of graphene for applications in sensing and energy storage devices.     

Graphene oxide dispersions in organic solvents

The dispersion behavior of graphene oxide in different organic solvents has been investigated. As-prepared graphite oxide could be dispersed in N, N-dimethylformamide, N-methyl-2-pyrrolidone, tetrahydrofuran, and ethylene glycol. In all of these solvents, full exfoliation of the graphite oxide material into individual, single-layer graphene oxide sheets was achieved by sonication. The graphene oxide dispersions exhibited long-term stability and were made of sheets between a few hundred nanometers and a few micrometers large, similar to the case of graphene oxide dispersions in water. These results should facilitate the manipulation and processing of graphene-based materials for different applications.     

The Influence of Dimensional Effects on the Composition and Properties of Polydicarbonfluoride

The influence of dimensional effects on the compositions and properties of polydicarbonfluoride (C₂F)_n prepared from multilayered graphenes was investigated. Multilayered graphenes were produced by destructive thermal decomposition of intercalation compounds of “idealized” (C₂F)_n that were obtained by reaction of gaseous ClF₃ with natural graphite at a room temperature. The precursors of multilayered graphenes have a common formula (C₂F?xR)_n where R is an organic or inorganic component. It was shown that polydicarbonfluoride prepared from multilayered graphene does not form stable intercalation compound with ClF₃, in contrast to polydicarbonfluoride prepared from graphite, that forms its intercalation compound with ClF₃ during fluorination of initial graphite in the ClF₃ excess. Investigations of polydicarbonfluoride prepared from multilayered graphene showed that it cannot form intercalation compounds with different classes of organic and inorganic compounds as polydicarbonfluoride prepared from graphite can do. The absence of such intercalation activity for polydicarbonfluoride prepared from multilayered graphene can be explained by high exfoliation degree of multilayered graphene (3–4 nm) along the c‐axis that results in the presence of two‐dimensional (2D) structure properties in multilayered graphene. Dimensional effects transformed the chemical properties of polydicarbonfluoride prepared from multilayered graphene and lowered its decomposition temperature by 150 K in comparison with polydicarbonfluoride prepared from graphite.     

The Formation of Large‐Area Conducting Graphene‐Like Platelets

The treatment of a suspension of graphite oxide (GO) with sodium azide leads to a material that, after reduction, features amino groups at the top and bottom of the sheets. These groups react through microcontact printing with an isothiocyanate monolayer on a silicon oxide substrate to form covalent bonds that strongly attach to the particles on the surface. With ultrasonication it is possible to obtain exfoliation of the sheets that are not covalently bound to the surface leaving single‐layer platelets attached to the substrate. The azido derivative can be also used to functionalize the graphene oxide with long alkylic chains through a click chemistry approach. This functionalization results in the exfoliation of this material in dimethylformamide. The novel materials were fully characterized by different techniques including IR spectroscopy, thermogravimetric analysis (TGA), scanning and transmission electron microscopy (SEM and TEM), X‐Ray photoelectron spectroscopy (XPS), and solid state NMR spectroscopy. The material with amino groups, after the reduction step, is conductive with a resistivity only approximately seven times larger than that of unprocessed graphite. This implies that after reduction of the GO, the conjugated sp² network is largely restored. We consider this to be an important step towards a chemical approach for forming conducting large‐area platelet films of single‐layer graphene.     

Exfoliating and Dispersing Few‐Layered Graphene in Low‐Boiling‐Point Organic Solvents towards Solution‐Processed Optoelectronic Device Applications

With normal organic surfactants, graphene can only be dispersed in water and cannot be dispersed in low‐boiling‐point organic solvents, which hampers its application in solution‐processed organic optoelectronic devices. Herein, we report the exfoliation of graphite into graphene in low‐boiling‐point organic solvents, for example, methanol and acetone, by using edge‐carboxylated graphene quantum dots (ECGQD) as the surfactant. The great capability of ECGQD for graphene dispersion is due to its ultralarge π‐conjugated unit that allows tight adhesion on the graphene surface through strong π–π interactions, its edge‐carboxylated structure that diminishes the steric effects of the oxygen‐containing functional groups on the basal plane of ECGQD, and its abundance of carboxylic acid groups for solubility. The graphene dispersion in methanol enables the application of graphene:ECGQD as a cathode interlayer in polymer solar cells (PSCs). Moreover, the PSC device performance of graphene:ECGQD is better than that of Ca, the state‐of‐the‐art cathode interlayer material.     

Electrochemically Exfoliated Graphene and Graphene Oxide for Energy Storage and Electrochemistry Applications

Top‐down methods are of key importance for large‐scale graphene and graphene oxide preparation. Electrochemical exfoliation of graphite has lately gained much interest because of the simplicity of execution, the short process time, and the good quality of graphene that can be obtained. Here, we test three different electrolytes, that is, H₂SO₄, Na₂SO₄, and LiClO₄, with a common exfoliation procedure to evaluate the difference in structural and chemical properties that result for the graphene. The properties are analyzed by means of scanning transmission electron microscopy (STEM), Raman spectroscopy, and X‐ray photoelectron spectroscopy. We then tested the graphene materials for electrochemical applications, measuring the heterogeneous electron transfer (HET) rates with a Fe(CN)₆^3?/4? redox probe, and their capacitive behavior in alkaline solutions. We correlate the electrochemical features with the presence of structural defects and oxygen functionalities on the graphene materials. In particular, the use of LiClO₄ during the electrochemical exfoliation of graphite allowed the formation of highly oxidized graphene with a C/O ratio close to 4.0 and represents a possible avenue for the mass production of graphene oxide as valid alternative to the current laborious and dangerous chemical procedures, which also have limited scalability.     

Preparing graphene oxide–copper composite material from spent lithium ion batteries and catalytic performance analysis

The wide use of lithium ion batteries (LIBs) has created much waste, which has become a global issue. It is vital to recycle waste LIBs considering their environmental risks and resource characteristics. Anode graphite from spent LIBs still possess a complete layer structure and contain some oxygen-containing groups between layers, which can be reused to prepare high value-added products. Given the intrinsic defect structure of anode graphite, copper foils in LIB anode electrodes, and excellent properties of graphene, graphene oxide–copper composite material was prepared in this work. Anode graphite was firstly purified to remove organic impurities by calcination and remove lithium. Purified graphite was used to prepare graphene oxide–copper composite material after oxidation to graphite oxide, ultrasonic exfoliation to graphene oxide (GO), and Cu²⁺ adsorption. Compared with natural graphite, preparing graphite oxide using anode graphite consumed 40% less concentrated H₂SO₄ and 28.6% less KMnO₄. Cu²⁺ was well adsorbed by 1.0 mg L^?1 stable GO suspension at pH 5.3 for 120 min. Graphene oxide–copper composite material could be successfully obtained after 6 h absorption, 3 h bonding between GO and Cu²⁺ with 3/100 of GO/CuSO₄ mass ratio. Compared to CuO, graphene oxide–copper composite material had better catalytic photodegradation performance on methylene blue, and the electric field further improved the photodegradation efficiency of the composite material.     

Dispersion of graphene oxide and its flame retardancy effect on epoxy nanocomposites

Graphene oxide was prepared by ultrasonication of completely oxidized graphite and used to improve the flame retardancy of epoxy.The epoxy/graphene oxide nanocomposite was studied in terms of exfoliation/dispersion,thermal stability and flame retardancy.X-ray diffraction and transmission electron microscopy confirmed the exfoliation of the graphene oxide nanosheets in epoxy matrix.Cone calorimeter measurements showed that the time to ignition of the epoxy/graphene oxide nanocomposite was longer than that of neat epoxy.The heat release rate curve of the nanocomposite was broadened compared to that of neat epoxy and the peak heat release rate decreased as well.     

功能型单层石墨烯的热剥离法制备及其超电容性能

以氧化石墨(GO)作为前驱体,在两种不同热剥离温度下制备了两类功能型单层石墨烯.其中第一类功能型单层石墨烯通过在较低温度及空气气氛下热剥离GO制备;第二类功能型单层石墨烯通过在氮气保护下高温热剥离GO得到;利用氮气吸附-脱附方法测定了两类样品的比表面积,利用电化学测试方法分析了其超电容性能.结果表明,通过低温热剥离的方式即可以有效剥离GO;两类样品均具有较高的BET比表面积.低温热剥离GO所制备的功能型单层石墨烯在2 mol/L KOH体系中的最大比电容值约为220 F/g;而通过高温热剥离GO所制备的功能型单层石墨烯虽然同样具有较高的BET比表面积,但其最大比电容值下降至约150 F/g.这表明通过低温热剥离GO所制备的功能型单层石墨烯具有更优异的超电容性能.     

Concurrent Phosphorus Doping and Reduction of Graphene Oxide

Doped graphene materials are of huge importance because doping with electron‐donating or electron‐withdrawing groups can significantly change the electronic structure and impact the electronic and electrochemical properties of these materials. It is highly important to be able to produce these materials in large quantities for practical applications. The only method capable of large‐scale production is the oxidative treatment of graphite to graphene oxide, followed by its consequent reduction. We describe a scalable method for a one‐step doping of graphene with phosphorus, with a simultaneous reduction of graphene oxide. Such a method is able to introduce significant amount of dopant (3.65 at. %). Phosphorus‐doped graphene is characterized in detail and shows important electronic and electrochemical properties. The electrical conductivity of phosphorus‐doped graphene is much higher than that of undoped graphene, owing to a large concentration of free carriers. Such a graphene material is expected to find useful applications in electronic, energy storage, and sensing devices.     

Functionalized single graphene sheets derived from splitting graphite oxide

A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting.     

An efficient way to functionalize graphene sheets with presynthesized polymer via ATNRC chemistry

Graphene nanosheets offer intriguing electronic, thermal and mechanical properties and are expected to find a variety of applications in high‐performance nanocomposite materials. The great challenge of exfoliating and dispersing pristine graphite or graphene sheets in various solvents or matrices can be achieved by facilely and properly chemical functionalization of the carbon nanosheets. Here we reported an efficient way to functionalize graphene sheets with presynthesized polymer via a combination of atom transfer nitroxide radical coupling chemistry with the grafting‐onto strategy, which enable us to functionalize graphene sheets with well‐defined polymer synthesized via living radical polymerization. A radical scavenger species, 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), was firstly anchored onto ? COOH groups on graphene oxide (GO) to afford TEMPO‐functionalized graphene sheets (GS‐TEMPO), meanwhile, the GO sheets were thermally reduced. Next, GS‐TEMPO reacted with Br‐terminated well‐defined poly(N‐isopropylacrylamide) (PNIPAM) homopolymer, which was presynthesized by SET‐LRP, in the presence of CuBr/N,N,N′,N′,N″‐pentamethyldiethylenetriamine to form PNIPAM‐graphene sheets (GS‐PNIPAM) nanocomposite in which the polymers were covalently linked onto the graphene via the alkoxyamine conjunction points. The PNIPAM‐modified graphene sheets are easily dispersible in organic solvents and water, and a temperature‐induced phase transition was founded in the water suspension of GS‐PNIPAM. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Capillary zone electrophoresis of graphene oxide and chemically converted graphene

The preparation of processable graphene oxide colloids called chemically converted graphene (CCG) involves the following steps: oxidation of graphite to form graphite oxide; exfoliation of graphite oxide to form graphene oxide (GO); and reduction of GO to form CCG. In this work, the exfoliation and reduction steps were monitored by capillary zone electrophoresis (CZE). CZE was performed in fused silica capillaries with UV absorbance at 230 nm (GO) and 270 nm (CCG) using 250 μM tetrapropylammonium hydroxide (pH 10.4). The results indicate that almost complete exfoliation of graphite oxide (0.05 wt%) and higher recovery of CCG were obtained by sonication at 50% power for more than 15 h. CZE is considered a valuable tool for the fractionation and analysis of GO nanoparticles and, hence, for the control of different steps in preparation of CCG.     

Polyethylene glycol/graphene oxide coated solid‐phase microextraction fiber for analysis of phenols and phthalate esters coupled with gas chromatography

A new polyethylene glycol/graphene oxide composite material bonded on the surface of a stainless‐steel wire was used for solid‐phase microextraction. The layer‐by‐layer structure increased the adsorption sites of the novel fiber, which could facilitate the extraction of trace compounds. The polyethylene glycol/graphene oxide was characterized by Fourier transform infrared spectroscopy and elemental analysis, which verified that polyethylene glycol was successfully grafted onto the surface of graphene oxide. The performance of the polyethylene glycol/graphene oxide coated fiber was investigated for phenols and phthalate esters coupled with gas chromatography with flame ionization detection under the optimal extraction and desorption conditions, and the proposed method exhibited an excellent extraction capacity and high thermal stability. Wide linear ranges were obtained for the analytes with good correlation coefficients in the range of 0.9966–0.9994, and the detection limits of model compounds ranged from 0.003 to 0.025 μg/L. Furthermore, the as‐prepared fiber was used to determine the model compounds in the water and soil samples and satisfactory results were obtained.     

The Role of Oxidative Debris on Graphene Oxide Films

We study the effect of oxidative impurities on the properties of graphene oxide and on the graphene oxide Langmuir–Blodgett films (LB). The starting material was grupo Antolín nanofibers (GANF) and the oxidation process was a modified Hummers method to obtain highly oxidized graphene oxide. The purification procedure reported in this work eliminated oxidative impurities decreasing the thickness of the nanoplatelets. The purified material thus obtained presents an oxidation degree similar to that achieved by chemical reduction of the graphite oxide. The purified and non‐purified graphene oxides were deposited onto silicon by means of a Langmuir–Blodgett (LB) methodology. The morphology of the LB films was analyzed by field emission scanning microscopy (FE‐SEM) and micro‐Raman spectroscopy. Our results show that the LB films built by transferring Langmuir monolayers at the liquid‐expanded state of the purified material are constituted by close‐packed and non‐overlapped nanoplatelets. The isotherms of the Langmuir monolayer precursor of the LB films were interpreted according to the Volmer’s model.     

Graphene preparation and graphite exfoliation

The synthesis of Graphene is critical to achieving its functions in practical applications. Different methods have been used to synthesis graphene, but graphite exfoliation is considered the simplest way to produce graphene and graphene oxide. In general, controlling the synthesis conditions to achieving the optimum yield, keeping the pristine structure to realize on-demand properties, minimum layers with the smallest lateral size, and minimum oxygen content are the most obstacles experienced by researchers. Each application requires a specific graphene model, graphene oxides GO, or even graphene intercalated compounds (GIC) depending on synthesis conditions and approach. This paper reviewed and summarized the most researches in this field and focusing on exfoliation methods.     

Photocatalytic patterning and modification of graphene

TiO(2)-based photocatalysis has been widely used to decompose various organic pollutants for the purpose of environmental protection. Such a "green" photochemical process can ultimately degrade organic compounds into CO(2) and H(2)O under ambient conditions. We demonstrate here its extended application on the engineering of single- or few-layer graphene. Using a patterned TiO(2) photomask, we have achieved various photochemical tailorings of graphene, including ribbon cutting, arbitrary patterning on any substrate, layer-by-layer thinning, and localized graphene to graphene oxide conversion. UV-visible spectroscopic studies indicate that the photogenerated, highly reactive ·OH radicals work as sharp chemical scissors. Being a solution-free, cost-effective, scalable, and easy handling technique, the presented photocatalytic patterning and modification approach allows for the versatile design and fabrication of graphene-based devices and circuits, compatible with current microelectronic technology, as demonstrated by this fabricated all-carbon field effect transistor (FET) array.