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- Synthesis of graphene
- Hydrazine-reduction of graphite- and graphene oxide
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Graphene, a two-dimensional material of sp 2 hybridization carbon atoms, has fascinated much attention in recent years owing to its extraordinary electronic, optical, magnetic, thermal, and mechanical properties as well as large specific surface area. For the tremendous application of graphene in nano-electronics, it is essential to fabricate high-quality graphene in large production.
There are different methods of generating graphene. This review summarizes the exfoliation of graphene by mechanical, chemical and thermal reduction and chemical vapor deposition and mentions their advantages and disadvantages. This article also indicates recent advances in controllable synthesis of graphene, illuminates the problems, and prospects the future development in this field.
Carbon is a ubiquitous material that has been ever found whereas the epoch making material graphene is also an allotropy of carbon. Actually graphene is a two-dimensional, single-layer sheet of sp 2 hybridized carbon atoms and has arrested enormous attention and research motives for its versatile properties.
However, its applicability cannot be effectively realized unless superficial techniques to synthesize high-quality, large-area graphene are developed in a cost effective way. Besides, a great deal of effort is required to develop techniques for modifying and opening its band structure so as to make it a potential replacement for silicon in future electronics.
The basic building blocks of all the carbon nanostructures are a single graphitic layer that is covalently functionalized sp 2 bonded carbon atoms in a hexagonal honeycomb lattice which forms 3D bulk graphite, when the layers of single honeycomb graphitic lattices are stacked and bound by a weak van der Waals force. When the single graphite layer forms a sphere, it is well known as zero-dimensional fullerene; when it is rolled up with respect to its axis, it forms a one-dimensional cylindrical structure called a carbon nanotube; and when it exhibits the planar 2D structure from one to a few layers stacked, it is called graphene.
One graphitic layer is well known as monoatomic or single-layer graphene and two and three graphitic layers are known as bilayer and tri-layer graphene, respectively. Synthesis of graphene refers to any process for fabricating or extracting graphene, depending on the desired size, purity and efflorescence of the specific product.
In the earlier stage various techniques had been found for producing thin graphitic films. In , few-layer graphite was synthesized on a single crystal platinum surface via chemical decomposition methods, but was not designated as graphene due to a lack of characterization techniques or perhaps due to its limited possible applications [ 26 ]. In those periods, their electronic properties never were investigated because of the difficulty in isolating and transferring them onto insulating substrates.
However there was no report on their electrical property characterization. Using a similar method this was later achieved in by Kim and co-workers and the electrical properties were reported [ 27 ]. But the real prompt advancement in graphene research began after Geim and co-workers first published their work of isolating graphene on to SiO 2 substrate and measuring its electrical properties.
After discovery of graphene in various techniques were developed to produce thin graphitic films and few layer graphene. The experimental evidence of 2D crystals came in [ 15 ] and [ 28 ] when thin flakes of graphene and other materials molybdenum disulphide, niobium diselenide and hexagonal boron nitride were first exfoliated from their bulk counterparts Fig.
But graphene was first obtained in the form of small flakes of the order of several microns through mechanical exfoliation of graphite using scotch tape [ 4 , 9 ].
Although this method gives the highest quality graphene but for mass production, fabrication method is needed that can synthesize wafer scale graphene.
Mother of all graphene forms. Graphene is a 2D building material for carbon material of all other dimensionalities. It can be wrapped up into 0D buckyballs, rolled into 1D nanotubes or stacked into 3D graphite [ 23 ].
In recent years, various techniques have been established for graphene synthesis. However, mechanical cleaving exfoliation [ 15 ], chemical exfoliation [ 29 , 30 ], chemical synthesis [ 21 ], and thermal chemical vapor deposition CVD [ 31 ] synthesis are the most commonly used methods today. Some other techniques are also reported such as unzipping nanotube [ 32 — 34 ] and microwave synthesis [ 35 ]. In chemical exfoliation method, solution dispersed graphite is exfoliated by inserting large alkali ions between the graphite layers.
Chemical synthesis is the similar process which consists of the synthesis of graphite oxide, dispersion in a solution, followed by reduction with hydrazine. Similarly for carbon nanotube synthesis, catalytic thermal CVD has proved most significant process for large-scale graphene fabrication.
In this world as nothing is unmixed blessing, all synthesis methods have some drawbacks too depending upon the final application of graphene. For instance, the mechanical exfoliation method is capable of fabricating monolayer to few-layers of graphene, but the reliability of obtaining a similar structure using this technique is quite insignificant.
Furthermore, chemical synthesis processes are low temperature processes that make it more comfortable to fabricate graphene on multi-types of substrates at ambient temperature, particularly on polymeric substrate. But, large-area synthesized graphene produced in this process are non-uniform and dispersed. Again, graphene synthesized from reduced graphene oxides RGOs usually causes incomplete reduction of graphite oxide that results in the successive debasement of electrical properties depending on its degree of reduction.
In contrast, thermal CVD methods are more advantageous for large-area device fabrication and favorable for future complementary metal-oxide semiconductor CMOS technology by replacing Si [ 36 ]. Epitaxial graphene means thermal graphitization of a SiC surface which is another method of graphene synthesis, but the limitation of this method are high process temperature and inability to transfer on any other substrates.
So, the thermal CVD method is unique because of producing uniform layer of thermally chemically catalyzed carbon atoms and that can be deposited onto metal surfaces and also can be transferred over a wide range of substrates. An overview of graphene synthesis techniques is shown in the flow chart in Fig. Mechanical exfoliation is may be the rarest and eminent process for extracting single layer graphene flakes on preferred substrates. It is the first recognized method of graphene synthesis.
This is a top-down technique in nanotechnology, by which a longitudinal or transverse stress is created on the surface of the layered structure materials. Graphite is formed when mono-atomic graphene layers are stacked together by weak van der Waals forces. The interlayer distance and interlayer bond energy is 3.
Exfoliation is the reverse of stacking; owing to the weak bonding and large lattice spacing in the perpendicular direction compared to the small lattice spacing and stronger bonding in the hexagonal lattice plane [ 58 ]. Graphene sheets of different thickness can indeed be obtained through mechanical exfoliation or by peeling off layers from graphitic materials such as highly ordered pyrolytic graphite HOPG , single-crystal graphite, or natural graphite [ 59 — 63 ].
In certain studies the HOPG has also been bonded to the substrate either by regular adhesives like epoxy resin [ 64 , 68 ] or even by SAMs [ 69 ] to improve the yield of single and few layer graphene flakes. A recent study also demonstrates transfer printing of macroscopic graphene patterns from patterned HOPG using gold films [ 70 ].
It is by far the cheapest method to produce high-quality graphene. Graphene flakes obtained by mechanical exfoliation methods are usually characterized by optical microscopy, Raman spectroscopy and AFM.
AFM analysis is carried out on exfoliated graphene to assess its thickness and number of layers. Finding a single layer flake is a fact of chance plus the yield of single and few layer graphene obtained by this method is more weaker and the flakes are randomly diffused on the substrate. Optical microscopy is another popular method of identifying single layer graphene. Raman spectroscopy is also carried out on graphene acquiring by mechanical exfoliation.
It is the quickest and most precise method of identifying the thickness of graphene flakes and estimating its crystalline quality. This is because graphene exhibits characteristic Raman spectra based on number of layers present [ 72 — 74 ]. In this micromechanical exfoliation method, graphene is separated from a graphite crystal using adhesive tape. After peeling it off the graphite, multiple-layer graphene remains on the tape. By repeated peeling the multiple-layer graphene is cleaved into several flakes of few-layer graphene.
Subsequently the tape is attached to the acetone substrate for detaching the tape. Finally one last peeling with an unused tape is performed. The obtained flakes vary substantially in size and thickness, where the sizes range from nanometers to several tens of micrometers for single-layer graphene, based on wafer. Actually it is not easy to obtain larger amounts of graphene by this exfoliation method, not even taking into account the lack of sustainable flakes.
The difficulty of this method is really low, nevertheless the graphene flakes require to be found on the substrate surface, which is labor exhaustive. The quality of the prepared graphene is very high with almost no defects.
The graphene formed by these mechanical exfoliation methods was used for production of FET devices Fig. Still, the mechanical exfoliation method needs to be enhanced further for large-scale, defect-free, high-purity graphene for mass production in the field of nanotechnology.
Graphene films. Colors: dark brown , SiO 2 surface; brown—red central area , 0. Chemical method is one of the best appropriate method for synthesis of graphene. In chemical method producing colloidal suspension which modify graphene from graphite and graphite intercalation compound. Different types of paper like material [ 20 ], [ 76 — 80 ] polymer composites [ 18 ], energy storage materials [ 81 ] and transparent conductive electrodes [ 82 ] have already used chemical method for production of graphene.
In graphene oxide was first manufactured Brodie [ 83 ], Hummers [ 84 ] and Staudenmaier [ 85 ] methods. Chemical exfoliation is a two-step process. At first reduces the interlayer van der Waals forces to increase the interlayer spacing. Thus it forms graphene-intercalated compounds GICs [ 86 ].
Then it exfoliates graphene with single to few layers by rapid heating or sonication. For single-layer graphene oxide SGO uses ultrasonication [ 84 , 87 — 91 ] and various layer thickness using Density Gradient Ultracentrifugation [ 92 , 93 ].
For this reason interlayer spacing increases from 3. For oxidization high density of functional groups, and reduction needs to be carried out to obtain graphene-like properties.
Single layer graphene sheets are dispersed by chemical reduction with hydrazine monohydrate [ 88 , 90 ]. Polycyclic aromatic hydrocarbons PAHs [ 94 — 96 ], has used for synthesis of graphene. Using a dendrict precursor transformed by cyclodehydrogenation and planarization [ 97 ]. Poly-dispersed hyper branched polyphenylene, precursor give larger flakes [ 97 ].
The first were synthesized through oxidative cyclodehydrogenation with FeCl 3 [ 97 ]. Variety of solvents are used to disperse graphene in perfluorinated aromatic solvents [ 54 ], orthodichloro benzene [ 98 ], and even in low-boiling solvents such as chloroform and isopropanol [ 99 , ].
Thermal exfoliation and reduction of graphite oxide also produce good-quality graphene, generally referred to as reduced graphene oxide RGO. Chemical reduction of graphite oxide is one of the conventional procedures to prepare graphene in large quantities [ 84 ]. Graphite oxide GO is usually synthesized through the oxidation of graphite using oxidants including concentrated sulfuric acid, nitric acid and potassium permanganate based on Brodie method [ 83 ], Staudenmaier method [ 85 ], Hummers method [ 84 ].
Another approach to the production of graphene is sonication and reduction of graphene oxide GO. Addition of H 2 occurs across the alkenes, coupled with the extrusion of nitrogen gas, large excess of NaBH 4 have been used as a reducing agent [ ]. Other reducing agents used include phenyl hydrazine [ ], hydroxylamine [ ], glucose, [ ] ascorbic acid [ ], hydroquinone [ ], alkaline solutions [ ], and pyrrole [ ].
GO was formed by the chemical reaction between organic isocyanates and the hydroxyl is shown in Fig. With permission of [ ]. Electrochemical reduction is another means to synthesize graphene in large scale [ — ]. In , first established monolayer flakes of reduced graphene oxide. The graphite oxide solution can then be sonicated in order to form GO nanoplatelets.
Synthesis of graphene
Skip to search form Skip to main content You are currently offline. Some features of the site may not work correctly. DOI: An and J. Potts and Aruna Velamakanni and S.
Hydrazine-reduction of graphite- and graphene oxide
ACS Nano, In this study, the aggregation kinetics and stability of GO were investigated using time-resolved dynamic light scattering over a wide range of aquatic chemistries pH, salt types NaCl, MgCl 2, CaCl 2 , ionic strength relevant to natural and engineered systems. Create a free account to download. The mechanical strength of graphene-cement nanocomposites containing 0. The degree of reduction, measured by the change in carbonto-oxygen - ratio, is quantified with respect to the power density and the surface temperature of the graphene oxide film.
IntroductionGraphene is an exciting material. Properties Abstract This review selectively describes the recent progress in the interactions of proteins enzymes and short-chain peptides with graphene and graphene oxide GO. A short summary of this paper.
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In very basic terms graphene could be described as a single, one atom thick layer of the commonly found mineral graphite ; graphite is essentially made up of hundreds of thousands of layers of graphene. In actuality, the structural make-up of graphite and graphene, and the method of how to create one from the other, is slightly different. In fact, rather than referring to the chemical element and heavy metal, lead, this central core is most commonly made from graphite mixed with clay.
Graphene, a two-dimensional material of sp 2 hybridization carbon atoms, has fascinated much attention in recent years owing to its extraordinary electronic, optical, magnetic, thermal, and mechanical properties as well as large specific surface area. For the tremendous application of graphene in nano-electronics, it is essential to fabricate high-quality graphene in large production. There are different methods of generating graphene. This review summarizes the exfoliation of graphene by mechanical, chemical and thermal reduction and chemical vapor deposition and mentions their advantages and disadvantages. This article also indicates recent advances in controllable synthesis of graphene, illuminates the problems, and prospects the future development in this field.
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