Synthesis Of High-quality Graphene Research Articles

Thermal Exfoliation of Natural Cellulosic Material for Graphene Synthesis

Hibiscus flower petals have been used as a cheap natural resource precursor for cost-effective synthesis of high quality graphene by thermal exfoliation process. In order to compare the quality of graphene obtained from the flower petals directly with the flower petals pretreated with nickel(II) chloride, Raman spectroscopic technique has been used as the structural probe. The role of temperature and the effect of nickel on thermal exfoliation process have been examined. It has been observed that graphene obtained via nickel incorporation is of better quality because NI2+ ions that get dispersed in the layered-structured cellulose at elevated temperatures get reduced to the metallic state, which in turn push the graphitic layers during thermal exfoliation to produce good quality graphene. In contrast, no such driving force is present in cellulose and hemi-cellulose of flower petals that contain lignin.

Preparation of colloidal graphene in quantity by electrochemical exfoliation

We reported the preparation of colloidal graphene in quantity via the anodic exfoliation of graphite in (NH4)2SO4 aqueous solution. In the currently designed electrochemical exfoliation route, mass high-quality graphene was produced within short reaction time, around 1h. The proposed electrochemical exfoliation mechanism showed that SO42− and H2O can be intercalated into those graphite sheets, monolayer and few-layer graphene were obtained by the formation of gaseous SO2 and O2 within graphite sheets. Stability evaluation showed that our exfoliated colloidal graphene can be perfectly stabilized in DMF solvent more than 1week. The colloidal graphene can be used to construct various simple and complex patterns by writing it on A4 paper, which can be applied to flexible printed electronic devices. Furthermore, colloidal graphene can show promising applications in the fabrication of binder- and additive-free electrodes for supercapacitors and lithium-ion batteries. Our present method shows huge potential for industrial-scale synthesis of high-quality graphene and further commercialization of graphene colloid for numerous advanced applications in flexible printed electronics and energy storage devices.

Templated Growth of Multilayer Graphene from Cellulose for the Fabrication of Photovoltaic Devices

Graphene is one of the fast emerging materials in the field of material chemistry. Graphene possesses exceptionally great flexibility, extremely high electrical and thermal conductivity which makes it stand out for numerous applications in materials chemistry. The growing demand to produce high quality graphene inexpensively in larger scale remains a challenge for researchers. Our work emphasizes a straightforward and simple method of high-quality graphene synthesis on substrates with area of many cm2. The multilayer graphene was grown utilizing renewable material (cellulose) as a source of carbon. In our first venture cellulose paper was used as a carbon source soaked in iron catalyst. We achieved high-quality multilayered graphene sheets of ~6.8 cm2 area. In the present talk, I will demonstrate graphene based photovoltaic device (figure 1) with photo-to-electron conversion efficiency ranging from 0.5-2 %. SEM images of nanotubes gave average diameter of the nanotubes to be 200 nm and average nanotubes thickness of 3-10 nm. Graphene films and nanotubes (figure 1 a and b) were characterized using infrared (IR), Raman, X-ray diffraction (XRD), energy-dispersive X-ray (EDS)) spectroscopy; scanning electron (SEM), and transmission electron (TEM) microscopy. The devices are characterized using AFM, Solar-simulator (AM 1.5), and I-V curves.

Effects of substrate defects on the carbon cluster formation in graphene growth on Ni(111) surface

Abstract The growth of graphene by chemical vapor deposition on transition metal has shown promise in this regard. The main hurdle for further improvement is the lack of complete understanding of the atomistic processes involved in the early growth stages, which is conceivable because there are too many factors affecting the growth process. Using first-principles calculations, we investigate the effect of substrate defects on the graphene nucleation on the Ni(111) surface. Our calculations reveal that the defects on substrates can induce the carbon aggregation, and the corresponding structures are completely different from that on the perfect Ni surface. We also compare the critical cluster sizes for the transition from one-dimensional carbon chains to two-dimensional graphene flakes in the growth sequence. Our investigations on the effects of substrate defects would be extremely useful for the future experimental synthesis of high-quality graphene.

An efficient way to reduce graphene oxide by water elimination using phosphoric acid

This study concerns the synthesis of high-quality graphene by the water elimination reaction in the presence of phosphoric and sulfuric acid (H3PO4–G and H2SO4–G). Graphene was synthesized via a single-step efficient reduction method which is not yet found in the literature. This new method is called the acidic method and offers significant advantages, such as absence of toxic products, ease of purification and a high-quality graphene yield. Graphene formation from graphene oxide (GO) was verified by the use of Fourier transform infrared spectroscopy (FT-IR), raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Thermal properties and the surface morphology of the graphene obtained were elucidated by the use of thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). H3PO4–G prepared by this method was observed to have a very high conductivity value of 3860 S m−1 and a low capacitance value of 114 F g−1 cm2. The capacitance and conductivity values of graphene samples obtained with the conventional method by the use of sodium borohydride (NaBH4–G) as a reducing agent were compared with those obtained with the acidic reduction method. It was seen that the acidic reduction method showed promising features for the production of high-quality graphene and its applications.

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 (2.6at.% 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.

Exfoliation of Graphite into Graphene in Aqueous Solutions of Inorganic Salts

Mass production of high-quality graphene sheets is essential for their practical application in electronics, optoelectronics, composite materials, and energy-storage devices. Here we report a prompt electrochemical exfoliation of graphene sheets into aqueous solutions of different inorganic salts ((NH4)2SO4, Na2SO4, K2SO4, etc.). Exfoliation in these electrolytes leads to graphene with a high yield (>85%, ≤3 layers), large lateral size (up to 44 μm), low oxidation degree (a C/O ratio of 17.2), and a remarkable hole mobility of 310 cm(2) V(-1) s(-1). Further, highly conductive graphene films (11 Ω sq(-1)) are readily fabricated on an A4-size paper by applying brush painting of a concentrated graphene ink (10 mg mL(-1), in N,N'-dimethylformamide). All-solid-state flexible supercapacitors manufactured on the basis of such graphene films deliver a high area capacitance of 11.3 mF cm(-2) and an excellent rate capability of 5000 mV s(-1). The described electrochemical exfoliation shows great promise for the industrial-scale synthesis of high-quality graphene for numerous advanced applications.

Synthesis of High Quality Few Layer Graphene from the Exfoliation of Graphite

The emergence of graphene in the scientific community has been the cause of much excitement among material scientists and physicists due to its potential applications in many aspects. Despite its unusual physical and chemical properties, the much sought after monolayer graphene has proven to be difficult to produce in sufficient quantities, with most processes outputting high layer or even defect ridden graphene instead. This experiment aims to correct this problem, concerning itself with the synthesis of high quality graphene through continuous sonication with surfactant added throughout, as well as the issue of graphene quality as a function of sonication time. This was accomplished through the creation and addition of a Triton X-100 surfactant solution to a graphite suspension during sonication lasting for 50 minutes, 80 minutes, 110 minutes, 140 minutes, 170 minutes, and 200 minutes respectively. The resulting suspension was then filtrated to separate out the graphene, before being tested for quality through Raman spectroscopy, scanning electron microscopy, and X-ray diffraction. It was revealed that graphite had been exfoliated into few layer graphene after a short sonication time (less than 50 minutes). And the quality of graphene was improved with the sonication time increased, indicated by the reduced number of graphene layers. This completely physical method of graphene synthesis provides a simple way to achieve the highly desired few layer graphene, and will hopefully allow for greater use of graphene in industry and its implementation into new technology.

Review of CVD Synthesis of Graphene

AbstractThis article presents an overview of the research highlights in graphene synthesis by CVD. The growth mechanisms over transition metals and alloys (with emphasis on Cu and Cu alloys) are discussed, including new developments and experiments in transfer‐free graphene growth on dielectric materials. The focus is on the role of the various synthesis parameters, including the thermodynamic aspects of the chemical process, and the physical, chemical, and morphological properties of the substrate catalyst. The relationships between these parameters, and the properties of the as‐grown graphene are discussed. Some important relationships are reviewed and used to influence the fundamental parameters of, and methods for, the synthesis of high quality graphene.

Graphene at the Atomic‐Scale: Synthesis, Characterization, and Modification

AbstractGraphene is nature's ideal two‐dimensional conductor and is comprised of a single sheet of hexagonally packed carbon atoms. Since the first electrical measurements made on graphene, researchers have been trying to exploit the unique properties of this material for a variety of applications that span numerous scientific and engineering disciplines. In order to fully realize the potential of graphene, large scale synthesis of high quality graphene and the ability to control the electronic properties of this material on a nanometer length‐scale are necessary and remain key challenges. This article will review the efforts at the Center for Nanoscale Materials that focus on the atomic‐scale characterization and modification of graphene via scanning tunneling microscopy and its synthesis on various materials (SiC, Cu(111), Cu foil, etc.). These fundamental studies explore growth dynamics, film quality, and the role of defects. The chemical modification of graphene following exposure to atomic hydrogen will also be covered, while additional emphasis will be made on graphene's unique structural properties.

Formation and Healing of Vacancies in Graphene Chemical Vapor Deposition (CVD) Growth

The formation and kinetics of single and double vacancies in graphene chemical vapor deposition (CVD) growth on Cu(111), Ni(111), and Co(0001) surfaces are investigated by the first-principles calculation. It is found that the vacancies in graphene on the metal surfaces are dramatically different from those in free-standing graphene. The interaction between the vacancies and the metal surface and the involvement of a metal atom in the vacancy structure greatly reduce their formation energies and significantly change their diffusion barriers. Furthermore, the kinetic process of forming vacancies and the potential route of their healing during graphene CVD growth on Cu(111) and Ni(111) surfaces are explored. The results indicate that Cu is a better catalyst than Ni for the synthesis of high-quality graphene because the defects in graphene on Cu are formed in a lower concentration and can be more efficiently healed at the typical experimental temperature. This study leads to a deep insight into the atomic process of graphene growth, and the mechanism revealed in this study can be used for the experimental design of high-quality graphene synthesis.

Production of a 100-m-long high-quality graphene transparent conductive film by roll-to-roll chemical vapor deposition and transfer process

A high-quality graphene transparent conductive film was fabricated by roll-to-roll chemical vapor deposition (CVD) synthesis on a suspended copper foil and subsequent transfer. While the high temperature required for the CVD synthesis of high-quality graphene has prevented efficient roll-to-roll production thus far, we used selective Joule heating of the copper foil to achieve this. Low pressure thermal CVD synthesis and a direct roll-to-roll transfer process using photocurable epoxy resin allowed us to fabricate a 100-m-long graphene transparent conductive film with a sheet resistance as low as 150 Ω/sq, which is comparable to that of state-of-the-art CVD-grown graphene films.

A bifunctional approach for the preparation of graphene and ionic liquid-based hybrid gels

The synthesis of high quality graphene in large quantities from graphene oxide (GO) and its dispersion in a chemical environment is essential for the real-life applications. Although GO can be converted to reduced graphene oxide (RGO) by using reducing agents, in the absence of suitable stabilizing agents, RGO undergoes an irreversible aggregation in solution. Herein, we propose and illustrate the concept of using bifunctional molecules which (1) can enable the solubilization of GO sheets in ionic liquids (ILs) and (2) can facilitate the highly efficient thermal reduction of GO to RGO on account of the high thermal stability of ILs. We have demonstrated this concept by incorporating an imidazolium cation onto pyrene which can interact with RGO via cation–π and π–π interactions to form highly stable, porous hybrid gel materials.

Methane as an effective hydrogen source for single-layer graphene synthesis on Cu foil by plasma enhanced chemical vapor deposition

A single-layer graphene is synthesized on Cu foil in the absence of H(2) flow by plasma enhanced chemical vapor deposition (PECVD). In lieu of an explicit H(2) flow, hydrogen species are produced during the methane decomposition process into their active species (CH(x<4)), assisted with the plasma. Notably, the early stage of growth depends strongly on the plasma power. The resulting grain size (the nucleation density) has a maximum (minimum) at 50 W and saturates when the plasma power is higher than 120 W because hydrogen partial pressures are effectively tuned by a simple control of the plasma power. Raman spectroscopy and transport measurements show that decomposed methane alone can provide a sufficient amount of hydrogen species for high-quality graphene synthesis by PECVD.

High quality graphene grown on single-crystal Mo(110) thin films

In this paper, the synthesis of high quality graphene on single-crystal Mo(110) films by chemical vapor deposition (CVD) of methane was reported for the first time. X-ray diffraction proves that carbon species had dissolved into the metal. The micro-Raman spectroscopy indicates that the thickness of Mo films, cooling rate and growing time play significant roles in the quality of as-grown graphene films. By optimizing the growth time (15min) and cooling rate (10°C/s), we achieved high quality graphene films with the small ratio IG/I2D≈0.26 and the FWHM(2D)≈30.4cm−1 on 200nm-thick Mo films. Our experiments also suggest that graphene growth on Mo is a dissolution and segregation process as Ni.

Graphene from Molecules

Step by step: According to the molecular approach to the production of graphene, precursor molecules are cross-linked to form two-dimensional intermediates, and pyrolysis transforms the intermediates into graphene. This type of highly efficient synthesis of high-quality graphene is crucial to the development of innovative applications.

Microbial reduction of graphene oxide by Escherichia coli: A green chemistry approach

Graphene and graphene related materials are an important area of research in recent years due to their unique properties. The extensive industrial application of graphene and related compounds has led researchers to devise novel and simple methods for the synthesis of high quality graphene. In this paper, we developed an environment friendly, cost effective, simple method and green approaches for the reduction of graphene oxide (GO) using Escherichia coli biomass. In biological method, we can avoid use of toxic and environmentally harmful reducing agents commonly used in the chemical reduction of GO to obtain graphene. The biomass of E. coli reduces exfoliated GO to graphene at 37°C in an aqueous medium. The E. coli reduced graphene oxide (ERGO) was characterized with UV–visible absorption spectroscopy, particle analyzer, high resolution X-ray diffractometer, scanning electron microscopy and Raman spectroscopy. Besides the reduction potential, the biomass could also play an important role as stabilizing agent, in which synthesized graphene exhibited good stability in water. This method can open up the new avenue for preparing graphene in cost effective and large scale production. Our findings suggest that GO can be reduced by simple eco-friendly method by using E. coli biomass to produce water dispersible graphene.

Controllable Synthesis of High-Quality Graphene Using Inductively-Coupled Plasma Chemical Vapor Deposition

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LiAlH4 and PBr3 assisted high quality synthesis of graphene with excellent performances for lithium ion batteries

An easy novel approach which offers a fast pathway of macroscopic quantity preparation of graphene nanosheets (GS) at room temperature has been firstly proposed via lithium aluminum tetrahydride (LiAlH4) and phosphorus tribromide (PBr3) as the deoxidizer based on graphite oxide (GO). The structure of the graphene was investigated by high-resolution transmission electron microscopy (HR-TEM) indicating the GS with few layers (~3 layers). It is found that the GS as anode material used for lithium ion battery (LIB) has high initial coulombic efficiency (83.1%). The first discharge and charge capacity of the prepared GS were 1029.4mAh·g−1 and 855.1mAh·g−1 at a current density of 100mA·g−1, respectively. After 21cycles, the reversible capacity is still kept at 760.7mAh·g−1. The as-prepared GS with few layers and defects could be optimized for excellent electrochemical performance as lithium ion battery anode material.

Microorganism mediated synthesis of reduced graphene oxide films

The wide-ranging industrial application of graphene and related compounds has led researchers to devise methods for the synthesis of high quality graphene. We recently reported on the chemical synthesis, patterning, and doping of graphene films by the chemical exfoliation of graphite into graphene oxide (GO) with subsequent chemical reduction into graphene films [1, 2]. Here, we describe a hybrid approach for the synthesis of reduced graphene sheets, where chemically derived GO was reduced by microorganisms extracted from a riverside near the University. Our procedure enabled the production of ∼100 μm sized reduced graphene sheets, which showed excellent Raman spectra associated with high quality reduced graphene. We give a detailed account of the relationship between the type of microorganisms and the properties of the resulting reduced graphene.