WO2009029984A1

WO2009029984A1 - Graphene

Info

Publication number: WO2009029984A1
Application number: PCT/AU2008/001310
Authority: WO
Inventors: John Stride; Mohammad Choucair
Original assignee: Newsouth Innovations Pty Limited
Priority date: 2007-09-03
Filing date: 2008-09-03
Publication date: 2009-03-12
Also published as: WO2009029984A8

Abstract

Graphene having a plurality of cavities therein is described. There is also described a process for producing graphene wherein a metal, for example an alkali metal, is reacted with an alcohol to produce a solvothermal product comprising a metal alkoxide. The solvothermal product is then pyrolysed to produce the graphene.

Description

Graphene Technical Field

The present invention relates to a process for making graphene and to graphene made by the process. Background of the Invention

Nanotechnology based devices and materials are developing in the market place. Novel routes to the synthesis of their components are essential in the growth of the technology. The emergence of carbon nanostructures as likely candidates for a vast range of applications in nano-molecular based technologies opens the door for research into novel synthesis techniques. Carbon is one of the most intriguing elements in the Periodic Table. It forms many allotropes, some known from ancient times (diamond and graphite) and some discovered 10-20 years ago (fullerenes and nanotubes). Interestingly, the two- dimensional form (graphene) was only obtained very recently, immediately attracting a great deal of attention. Graphene is the name given to a flat monolayer of carbon atoms tightly packed into a two dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities (Figure 1). It can be wrapped up into OD fullerenes, rolled into ID nanotubes or stacked into 3D graphite. Graphene is rapidly being realised as a contender in many promising applications, and a propitious component in bridging condensed-matter physics and quantum electronics. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into scientific research and possible industries. Fig. 1 shows, from left to right, diagrams of the structure of graphene, graphite, carbon nanotube, and fullerene. Graphene consists of a 2D hexagonal lattice of carbon atoms. Each atom is covalently bonded to three others, but since carbon has four valence electrons, one is left free allowing graphene to conduct electricity. Other well known allotropes of carbon derive from graphene: graphite is a stack of graphene layers; carbon nanotubes are rolled-up cylinders of graphene; and buckminsterfullerene (C₆₀) molecule consists of graphene balled into a sphere by introducing pentagons into the lattice. It is useful to define the transition from 2D to 3D in graphene in order to impose a boundary on the extent of two-dimensionality, and hence transition from graphene to graphite. For the case of graphene, electronically, the situation has recently become reasonably clear. It was shown that the electronic structure rapidly evolves with the number of layers, approaching the 3D limit of graphite at 10 layers. Moreover, only graphene and, to a good approximation, its bi-layer have simple electronic spectra: they are both zero-gap semiconductors (they can also be referred to as zero-overlap semimetals) with one type of electron and one type of hole. For three or more layers, the spectra become increasingly complicated: Several charge carriers appear, and the conduction and valence bands start notably overlapping. This allows single-, double- and few- (3 to 10) layer graphene to be distinguished as three different types of 2D crystals ('graphenes'). Thicker structures are considered, to all intents and purposes, as thin films of graphite. In 2004, a group of physicists from Manchester University, UK, led by Andre Geim and Kostya Novoselov, used a very different approach to obtain graphene to that of the present invention. They started with three-dimensional graphite and extracted a single sheet (a monolayer of atoms) using a technique called micromechanical cleavage [Novoselov, K. S. et al., "Electric field effect in atomically thin carbon films", Science, 306, 666-669 (2004); Novoselov, K. S. et al., "Two-dimensional atomic crystals", Proc. Natl. Acad. ScL USA, 102, 10451-10453 (2005)].

The work amongst other important issues, showed that 2D crystallites exist. Earlier attempts to isolate graphene concentrated on chemical exfoliation. To this end, bulk graphite was first intercalated so that graphene planes became separated by layers of intervening atoms or molecules [Dresselhaus, M. S. & Dresselhaus, G., "Intercalation compounds of graphite", Adv. Phys. 51, 1-186 (2002)]. This usually resulted in new 3D materials. However, in certain cases, large molecules could be inserted between atomic planes, providing greater separation such that the resulting compounds could be considered as isolated graphene layers embedded in a 3D matrix. Furthermore, one can often get rid of intercalating molecules in a chemical reaction to obtain a sludge consisting of restacked and scrolled graphene sheets. Due to its uncontrollable character, graphitic sludge has so far attracted only limited interest.

There have also been a small number of attempts to grow graphene. The same approach as generally used for the growth of carbon nanotubes so far only produced graphite films thicker than 100 layers. On the other hand, single- and few-layer graphene have been grown epitaxially by chemical vapour deposition (CVD) of hydrocarbons on metal substrates and by thermal decomposition of SiC. Such films were studied by surface science techniques, and their quality and continuity remained unknown. Only lately, few-layer graphene obtained on SiC was characterised with respect to its electronic properties, revealing high mobility charge carriers. Epitaxial growth of graphene offers, probably, the only viable route towards electronic applications and, with so much at stake, rapid progress in this direction is expected. Graphene like material has also been synthesised by the chemical reduction of graphite oxide. Again this approach was similar, if not, more complicated than the previous attempts to make graphene using a top-down approach.

In the absence of quality graphene wafers, most experimental groups are currently using samples obtained by micromechanical cleavage of bulk graphite, the same technique that allowed the isolation of graphene for the first time. Even after fine-tuning the technique, the quantity of graphene crystallites obtained are only sufficient for most research purposes, and not industrially. A similar approach was tried by other groups, but only graphite flakes 20-100 layers thick were found, demonstrating the difficulty in the reproducibility of the technique [Zhang, Y., Small, J. P., Amori, M. E. S. & Kim, P., "Electric field modulation of galvanomagnetic properties of mesoscopic graphite", Phys. Rev. Lett., 94, 176803 (2005); Ohashi, Y., Koizumi, T., Yoshikawa, T., Hironaka, T. & Shiiki, K., "Size effect in the in-plane electrical resistivity of very thin graphite crystals", TANSO, 235-238 (1997); Bunch, J. S., Yaish, Y., Brink, M., Bolotin, K. & McEuen, P. L., "Coulomb oscillations and Hall effect in quasi-2D graphite quantum dots", Nano Lett, 5, 287-290 (2005)]. The problem is that graphene crystallites left on a substrate are extremely rare and hidden in a 'haystack' of thousands of thick (graphite) flakes. So, even if one were deliberately searching for graphene by using modern techniques for studying atomically thin materials, it would be impossible to find those several micrometre-size crystallites dispersed over, typically, a 1 -cm² area.

The method to find individual graphene sheets after micro-mechanical cleavage was made using an optical microscope, by placing the sample on top of a silicon wafer with a carefully chosen thickness of SiO₂. However, even knowing the exact method of obtaining sheets, this requires special care and perseverance to find graphene. For example, only a 5% difference in SiO₂ thickness (315 nm instead of the current standard of 300 nm) can make graphene completely invisible. Careful selection of the initial graphite material (so that it has largest possible grains) and the use of freshly cleaved and cleaned surfaces of graphite and SiO₂ can also make all the difference. This needle in a hay-stack approach is unpractical, and time-consuming, with no promise of an up scalable solution. There is therefore a need for a new process for making graphene. The process should preferably be rapid, and preferably amenable to large scale production. A suitable process may also be capable of producing graphene at low cost.

Object of the Invention It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages. It is a further object to at least partially satisfy the above need.

Summary of the Invention

In a broad form of the invention there is provided graphene having a structure selected from the group consisting of porous, sponge-like, open celled foam, closed cell foam, a combination of open celled and closed celled foam and having a plurality of cavities therein.

In a first aspect of the invention there is provided graphene having a plurality of cavities therein. The following options may be used in the first aspect either individually or in any appropriate combination.

The graphene may have between about 1 and about 5 parallel layers. The graphene may at least partially surround each of said cavities. Each of the layers may comprise a hexagonal lattice of carbon atoms. The graphene may be a foam. The foam may be an open celled foam. It may be a closed cell foam. It may comprise both open cells and closed cells.

The cavities may have a mean diameter of about lOOnm to about 500nm.

The cavities may have a diameter in the range of about lOOnm to about 500nm. In an embodiment there is provided graphene in the form of a foam, said graphene having a plurality of cavities of mean diameter of about 100 to about 500nm therein.

In another embodiment there is provided graphene in the form of an open celled foam, said graphene having a plurality of cavities of mean diameter in the range of about 100 to about 500nm therein.

The invention includes a mass of graphene comprising a plurality of cavities therein.

In another embodiment there is provided graphene having a plurality of cavities therein, said graphene having between about 1 and about 5 parallel layers, each layer comprising a hexagonal lattice of carbon atoms, and said graphene at least partially surrounding each of said cavities.

In a second aspect of the invention there is provided a process for producing graphene comprising: (i) reacting a metal with an alcohol to produce a solvothermal product comprising a metal alkoxide, said metal alkoxide being a reaction product of the metal with the alcohol; and (ii) pyrolysing the solvothermal product to produce the graphene.

The following options may be used in the second aspect either individually or in any appropriate combination.

The metal may be an alkali metal. The alkali metal may be sodium.

The alcohol may be volatile. It may be a primary alcohol. It may comprise ethanol.

The molar ratio of the metal to the alcohol may be between about 1.5: 1 and about 1 : 1.5. It may be about 1 : 1.

Step (i) may be conducted at between about 0 and about 25O⁰C.

Step (ii) may be conducted under conditions under which the graphene does not oxidise substantially to carbon dioxide. It may be conducted at a temperature at which the graphene does not oxidise substantially to form carbon dioxide. It may for example be conducted at a temperature of between about 250 and about 2000⁰C, or between about 250 and about 500⁰C. Step (ii) may be initiated by a flame. It may comprise applying a flame to the solvothermal product. The alcohol may be such that, when ignited, it does not generate a temperature sufficient for the graphene to oxidise substantially to form carbon dioxide. The process may additionally comprise washing the graphene. It may comprising drying the graphene after said washing.

The process may additionally comprise comminuting the graphene.

In an embodiment there is provided a process for producing graphene comprising: (i) reacting sodium with ethanol to produce a solvothermal product comprising sodium ethoxide; and (ii) pyrolysing the solvothermal product to produce the graphene.

In another embodiment there is provided a process for producing graphene comprising: (i) reacting sodium with ethanol to produce a solvothermal product comprising sodium ethoxide;

(ii) applying a flame the solvothermal product so as to initiate pyrolysis thereof to produce the graphene; and (iii) washing and drying the graphene.

The invention also provides graphene made by the process of the second aspect. The graphene made by the process of the second aspect may be as described in the first aspect (or the broad form of the invention) and/or as described herein in the detailed description of the preferred embodiments. It may have a structure selected from the group consisting of porous, sponge-like, open celled foam, closed cell foam, a combination of open celled and closed celled foam and having a plurality of cavities therein.

In a third aspect of the invention there is provided a composite material comprising graphene according to the present invention, said graphene being dispersed in a matrix.

The following options may be used in the third aspect either individually or in any appropriate combination.

The graphene may be present in the composite material at a concentration of between about 0.05 and about 5% by weight. The composite material may have an electrical conductivity of at least about

0.1 Sm^'1. The graphene may be present in the composite material at a concentration sufficient that the composite material has an electrical conductivity of at least about 0.1Sm^"1.

The matrix may have an electrical conductivity of less than about 0.1 Sm^"1. The matrix may comprise a polymer or a ceramic or a metal.

In an embodiment there is provided a composite material comprising graphene according to the present invention, said graphene being dispersed in a matrix having an electrical conductivity of less than about 0.1 Sm^"1, wherein the graphene is present in the composite material at a concentration of between about 0.05 and about 5% by weight.

In a fourth aspect of the invention there is provided a process for making a composite material comprising: (i) providing graphene according to the invention; (ii) combining the graphene with a matrix or with a precursor to a matrix, said matrix or precursor being in liquid form; and

(iii) if step (ii) comprises combining the graphene with a precursor to a matrix, converting the precursor to the matrix. Step (i) may comprise producing the graphene according to the process of the present invention. The ratio of the graphene to the matrix or precursor may be such that the resulting composite material has an electrical conductivity of at least about

0.1 Sm^"1. The ratio may be between about 1 :2000 and about 1 :20 by weight.

In an embodiment there is provided a process for making a composite material comprising:

(i) reacting a metal with an alcohol to produce a solvothermal product comprising a metal alkoxide, said metal alkoxide being a reaction product of the metal with the alcohol; and

(ii) pyrolysing the solvothermal product to produce graphene; (iii) combining the graphene with a matrix or with a precursor to a matrix, said matrix or precursor being in liquid form; and

(iv) if step (ii) comprises combining the graphene with a precursor to a matrix, converting the precursor to the matrix.

In another embodiment there is provided a process for making a composite material comprising:

(i) reacting sodium with ethanol to produce a solvothermal product comprising sodium ethoxide;

(ii) applying a flame to the solvothermal product so as to initiate pyrolysis thereof to produce graphene; (iii) washing and drying the graphene, and optionally comminuting the graphene;

(iv) combining the graphene with a matrix or with a precursor to a matrix, said matrix or precursor being in liquid form; and

(v) if step (ii) comprises combining the graphene with a precursor to a matrix, converting the precursor to the matrix. In a fifth aspect of the invention there is provided the use of graphene according to the invention for reinforcing a composite or for manufacturing an electronic device or for manufacturing a sensor or for manufacturing a battery or for manufacturing a device for storage of hydrogen or as a catalyst. In a sixth aspect there is provided graphene produced by pyrolysis of a clathrate-like structure comprising a metal alkoxide.

In a seventh aspect there is provided graphene produced by pyrolysis of a metal alkoxide. In a eighth aspect there is provided graphene produced by pyrolysis of a porous mass of a metal alkoxide.

In a ninth aspect there is provided graphene produced by pyrolysis of a porous mass of a metal alkoxide containing alcohol within said pores.

In a tenth aspect there is provided graphene produced by a solvothermal process.

The solvothermal process may comprise the steps of producing a clathrate-like structure comprising a metal alkoxide and pyrolysis of the clathrate-like structure to produce graphene.

The graphene of the sixth to tenth aspects may have cavities therein in the range of from lOOnm to 500nm in diameter.

The graphene of the sixth to tenth aspects may have cavities therein having a mean diameter in the range of from lOOnm to 500nm.

The graphene of the sixth to tenth aspects may be a foam comprising cavities therein having a mean diameter in the range of from lOOnm to 500nm. The graphene of the sixth to tenth aspects may be a foam comprising cavities therein having a diameter in the range of from lOOnm to 500nm. The foam may be a closed cell foam. It may be an open celled foam. It may be a foam having some open cells and some closed cells.

The graphene of the sixth to tenth aspects may be a mass comprising cavities therein having a mean diameter in the range of from lOOnm to 500nm.

The graphene of the sixth to tenth aspects may be a mass comprising cavities therein having a diameter in the range of from lOOnm to 500nm.

Brief Description of the Drawings

A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein:

Figure 1 shows structures of different materials containing hexagonal carbon lattices; Figure 2 illustrates a proposed mechanism for formation of graphene in the present invention; Figure 3 shows a scanning electron microscope (SEM) image of a piece of porous graphene;

Figure 4 shows atomic force microscopy (AFM) images of graphene sheets;

Figure 5 shows transmission electron microscope (TEM) images of graphene; Figure 6 shows scanning electron microscope (SEM) images of graphene;

Figure 7 shows SEM images of the solvothermal product;

Figure 8 shows a scanning electron microscope (SEM) image of porous graphene;

Figure 9 shows an XPS spectrum of a graphene sample;

Figure 10 shows an FTIR spectrum of a graphene sample showing weak -OH stretching and C-O peaks;

Figure 11 shows TGA of a pre-dried graphene sample heated under a flow of air to an isothermal temperature of 800°C (dashed line shows temperature profile);

Figure 12 shows TGA of a pre-dried graphene sample heated under a flow of nitrogen to an isothermal temperature of 800⁰C (dashed line shows temperature profile); Figure 13 shows TGA of a graphene sample heated under a flow of nitrogen to an isothermal temperature of 60°C (dashed line shows temperature profile);

Figure 14 shows TGA of graphene heated under the flow of air and nitrogen to an isothermal temperature of 800⁰C (inset: first derivative of TGA curve);

Figure 15 shows by electron ionization mass spectroscopy (EIMS) traces of: a) background (air); b) a graphene sample washed with copious amounts of ethanol during purification; and c) a subtracted spectra of the background and graphene sample, showing ethanol present;

Figure 16 shows: a) top: AFM topography image (levelled by a 2^nd order plane subtraction) of a dried ethanol suspension of graphene on mica; bottom: height profile obtained by taking a horizontal cross-section as indicated by the white arrows on the top image; and b) a close-up (zoom) topography image of the area indicated by a rectangle on the left-hand image; and

Figure 17 shows two different areas showing graphene double layers: top - AFM topography images (levelled by a 3^r order plane subtraction) of a dried ethanol suspension of graphene on mica; bottom - height profile obtained by taking a horizontal cross-section as indicated by the white arrows on the top images.

Detailed Description of the Preferred Embodiments

A novel route to the synthesis of graphene has been developed, involving the pyrolysis of the solvothermal product of an alcohol, e.g. ethanol, and a metal, e.g. sodium, to yield graphene, optionally single-layer graphene, and/or under certain controllable conditions, carbon nanotubes.

In the first step of the process for producing graphene a metal is reacted with an alcohol to produce a solvothermal product. This step is referred to herein as the "solvothermal process". The solvothermal product comprises the alkoxide of the metal, thus for example if the metal is sodium and the alcohol is ethanol, the solvothermal product comprises sodium ethoxide. The solvothermal product is commonly a solid, for example a powdery or granular solid. The reaction of the alcohol with the metal may be incomplete. It may for example be about 50% complete, or about 60, 70, 80, 90, 95 or 99% complete, or about 50 to 95, 60 to 95, 75 to 95, 90 to 95, 50 to 90, 50 to 80, 50 to 70 or 95 to 99% complete on a mole basis relative to either the alkali metal or to the alcohol. The solvothermal product may comprise unreacted alcohol. It may comprise intercalated alcohol. It may comprise between about 1 and about 50% of the alcohol on a weight or a mole basis, or about 1 to 30, 1 to 20, 1 to 10, 1 to 5, 5 to 50, 10 to 50, 20 to 50, 10 to 30, 10 to 20, 10 to 15 or 15 to 20%, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45 or 50% alcohol on a weight or mole basis. It may comprise unreacted metal. In the case where both unreacted metal and unreacted alcohol are present, they may be prevented from reacting with each other due to spatial separation within a matrix of the metal alkoxide. In some cases they may be prevented from reacting with each other by returning the solvothermal product to a temperature at which the metal and the alcohol do not react, or react only very slowly. In the event that the solvothermal product comprises unreacted metal, this may if desired be removed, for example by filtration or by other mechanical means (e.g. removal by use of forceps, or by suspension in an inert solvent followed by filtration etc.) prior to the pyrolysis step. Thus the process may also comprise the step of removing unreacted metal from the solvothermal product.

The metal may be any suitable metal capable of reacting with the alcohol. The range of suitable metals will therefore depend in part on the nature, in particular the reactivity, of the alcohol. The metal may be an alkali metal. It may be an alkaline earth metal. It may be for example lithium, sodium, potassium, rubidium, caesium, beryllium, magnesium, strontium or barium. Commonly it is sodium, as sodium has sufficient reactivity for rapid formation of the solvothermal product under relatively mild reaction conditions. When using alcohols of reduced reactivity (e.g. secondary or tertiary alcohols), use of a more reactive alkali metal such as potassium may be preferable. The metal may be added in particulate form. The particles of the metal may have a mean diameter of between about 0.5 and about 5mm. In this context the diameter of a non-spherical particle may be taken to be either its maximum diameter s or its mean diameter or its hydrodynamic diameter. The mean diameter of the particulate alkali metal may be about 0.5 to 2, 0.5 to 1, 1 to 5, 2 to 5 or 1 to 3mm, e.g. about 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5mm, or may be larger, e.g. about 6, 7, 8, 9 or 10mm.

The alcohol may be a volatile alcohol. It may be a combustible alcohol. It may io be a primary alcohol, or may be a secondary alcohol or may be a tertiary alcohol. It may be a Cl to C 12 alcohol. It may be straight chain or it may be branched chain or it may be cyclic or it may be a combination thereof (e.g. cyclohexylmethanol). It may be Cl to C6, Cl to C3, C2 to C12, C6 to C12 or C2 to C6. It may be for example methanol, ethanol, 1- or 2-propanol, 1-butanol, 2-butanol, isobutanol, tert- i₅ butanol, cyclopentanol, cyclohexanol or some other alcohol. In some cases a mixture of two or more alcohols selected from those described above may be used.

The ratio of metal to alcohol on a molar basis may be between about 1.5: 1 and about 1:1.5, or about 1.5:1 to 1:1.2, 1.5:1 to 1:1, 1.5:1 to 1.1:1, 1.5:1 to 1.2:1, 1.2:1 to 1:1.5, 1.1:1 to 1:1.5, 1:1 to 1:1.5, 1:1.1 to 1:1.5, 1:1.2 to 1:1.5, 1.4:1 to 1:1.4,0 1.3:1 to 1:1.3, 1.2:1 to 1:1.2 or 1.1:1 to 1:1.1, e.g. about 1:5:1, 1.4:1, 1.3:1, 1.2:1, 1.1:1, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4 or 1:1.5. The weight ratio may depend on the formula weight of the metal and of the alcohol.

An additive may be also used in the reaction of the metal with the alcohol. For example the alcohol may have a diluent. The additive, or diluent, may be inert to the₅ alkali metal, or may be less reactive towards the alkali metal than is the alcohol. The diluent may be volatile or non- volatile under the conditions of the solvothermal process. It may be more volatile than the alcohol, or it may be less volatile than the alcohol. It may be of comparable, optionally about the same, volatility as the alcohol. It may be miscible with the alcohol. It may for example be a hydrocarbon,0 or a ketone or an ester or an ether. It may be present as a proportion of the alcohol of between about 5 and about 500%, or about 5 to 200, 5 to 100, 5 to 50, 5 to 20, 5 to 10, 10 to 500, 50 to 500, 100 to 500, 200 to 500, 10 to 200, 50 to 200, 50 to 100 or 100 to 200% by weight, mole or volume, e.g. about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 200, 250, 300, 350, 400, 450 or 500%. The solvothermal process, i.e. the reaction of the alcohol with the metal, may be conducted in a vessel e.g. a sealed vessel. Thus step (i) of the process may comprise loading the metal and the alcohol into a sealable vessel and sealing the vessel. The vessel may be capable of withstanding the pressure evolved in the reaction vessel during step (i). The vessel may be capable of withstanding an internal pressure of between about 10 and about 200 atmospheres, or about 10 to 180, 10 to 150, 10 to 100, 10 to 50, 50 to 200, 100 to 200, 150 to 200, 180 to 200, 50 to 150 or 100 to 180 atmospheres, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200 atmospheres. The internal volume of the sealed vessel may be about equal to the combined volume of the alkali metal and the alcohol, or about 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 times or more than 100 times the combined volume of the alkali metal and the alcohol or about 1 to 100, 5 to 100, 10 to 100, 20 to 100, 50 to 100, 1 to 50, 1 to 20, 20 to 50, 1 to 10, 2 to 10, 5 to 10, 1 to 5, 1 to 2, 2 to 8 or 3 to 7 times the combined volume of the alkali metal and the alcohol. The vessel may have a pressure relief valve in order to prevent the internal pressure building up beyond a desired value. As noted above, the pressure increases during the reaction of step (i). Thus step (i) may be conducted at above ambient pressure. The pressure may start at about 1 atmosphere, or at ambient pressure. Alternatively, once the vessel in which step (i) is conducted is sealed with the reagents therein, the pressure may be raised. It may be raised to between about 1.1 and about 10 atmospheres, or about 1.5 to 10. 2 to 10, 5 to 10, 1.1 to 5, 1.1 to 2, 1.1 to 1, 1.1 to 1.5, 2 to 5 or 1.5 to 3 atmospheres, e.g. about 1.1, 1.2, 1.3, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10 atmospheres. The maximum pressure of step (i) may be between about 10 and about 200 atmospheres, or about 10 to 180, 10 to 150, 10 to 100, 10 to 50, 50 to 200, 100 to 200, 150 to 200, 180 to 200, 50 to 150 or 100 to 180 atmospheres, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190 or 200 atmospheres.

Step (i) of the process may be conducted at a temperature of between about 0 and about 25O⁰C, or about 0 to 200, 0 to 150, 0 to 100, 0 to 50, 0 to 20, 0 to 10, 20 to 250, 20 to 220, 50 to 250, 100 to 250, 150 to 250, 200 to 250, 50 to 200, 50 to 100 or 100 to 200⁰C, e.g. about 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240 or 25O⁰C. The temperature may vary through the progress of step (i) e.g. due to evolution of heat of reaction. It should be conducted below the temperature at which the metal alkoxide decomposes. Any heating may be accomplished for example in an oven, an autoclave, a heating bath, a muffle furnace, or using an electrical heater. The reaction may take from about 6 to about 120 hours, or about 12 to 120, 24 to 120, 48 to 120, 72 to 120, 96 to 120, 6 to 96, 6 to 72, 6 to 48, 6 to 24, 6 to 12, 24 to 96, 48 to 96 or 72 to 96 hours, e.g. about 6, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72, 78, 84, 90, 96, 104, 1 12 or 120 hours. Commonly, higher temperatures require shorter reaction times, although this is not necessarily the case. Suitable temperature-time combinations include 220°C-72 hours, 200⁰C- 12 hours and 22⁰C- 60 hours.

Step (i) of the process may be conducted in an air atmosphere, or may be conducted in a different atmosphere, e.g. an inert atmosphere. It may be conducted, for example, under nitrogen, argon, neon, helium, carbon dioxide or a mixture of any two or more of these. Step (i) may therefore comprise flushing the vessel with the atmosphere, as described above, and this may be done before, during or after loading either or both of the alkali metal or the alcohol in the vessel. Thus in one example, the alcohol is loaded into the vessel which is then flushed with nitrogen, the metal is then added and the vessel sealed and maintained at the desired temperature for the desired time. In one embodiment the process of step (i) may be conducted in an autoclave. It will be clear that other orders of these steps will also be suitable, and these are also encompassed by the present invention.

With a 1 :1 molar ratio of metal to alcohol, it may be expected that the metal and alcohol would react completely. However, as the reaction is conducted in a enclosed vessel, the solution of alcohol becomes more and more saturated with the metal alkoxide as it forms, resulting in the metal alkoxide absorbing some of the alcohol (for example about 20% by mass) under pressure. It should be noted that the vessel builds up pressure due to heat of reaction, the temperature at which the reaction is run and the evolution of gas during the reaction. Some metal hydroxide may also be formed if water is present, due to reaction of the metal with the water or of the metal alkoxide with the water. In many cases, some of the metal is dispersed in the solid metal alkoxide during the reaction. This is commonly rapidly hydrolysed to metal hydroxide when exposed to water vapour in the air and the solid metal may in such cases be observed to change from a light grey/white to a yellow/white. When the solvothermal process is performed at lower temperature, there may be insufficent energy in the form of heat to take the reaction of metal and alcohol to high conversion, depending on the temperature and on the nature of the metal and the alcohol. It is thought that this is due to formation of alkoxide on the surface of the metal (i.e. a 5 form of passivation). Thus larger pieces of metal remain in the solvothermal product. By contrast, at higher reaction temperatures, the metal is more dispersed, i.e. the particle size of the residual sodium is smaller. The larger pieces of metal are then commonly encrusted with the solvothermal product, and possibly also with metal hydroxide, which makes them relatively inert to the atmosphere. The metal pieces may then be removed usingG tweezers or by using a plastic sieve. The metal pieces may then be discarded, for example by washing with 2-propanol, then ethanol, then water, or may be placed in paraffin oil or other inert liquid to be recycled as needed. When higher temperatures (above about 100⁰C) are used in the solvothermal process, may be no need to remove the metal as it may be dispersed throughout the solvothermal product and quickly hydrolyse to forms metal hydroxide when exposed to air.

When the reaction is conducted for a longer period of time at lower temperature, smaller pieces of the metal (which disperse) may react preferentially to larger pieces, leaving behind larger pieces. These larger pieces are easily identified and removed. At lower reaction temperature and shorter reaction time, the smaller pieces of metal remain,G and are difficult to remove. At higher temperatures near complete reaction may be achieved, and removal of the metal may not be necessary.

Following the solvothermal process of step (i) of the process, the resulting solvothermal product may optionally be cooled. It may be cooled for example to about room temperature. In some circumstances, particularly if the metal is a low melting metal,₅ it may be advantageous to cool to below room temperature, e.g. to about 15, 10, 5 or O⁰C. This may facilitate solidification of the metal and hence facilitate its removal from the solvothermal product.

Following the solvothermal process of step (i) of the process, the solvothermal product is pyrolysed to generate the graphene (step ii). The pyrolysis may beG conducted under conditions that are not conducive to oxidation of the graphene formed in the pyrolysis. Since the pyrolysis is conducted under conditions where the solvothermal product is combusted, it is possible that some oxidation of graphene does occur. However the conditions should be such that the degree of oxidation to carbon dioxide is sufficiently low as to afford the desired yield of graphene, i.e. that the graphene does not substantially oxidise to carbon dioxide. The yield of graphene based on initial alcohol may be at least about 30%, or at least about 40, 50, 60, 70 or 80%, or may be about 30 to about 95%, or about 30 to 90, 30 to 80, 30 to 70, 30 to 60, 30 to 50, 40 to 95, 50 to 95, 60 to 95, 70 to 95, 50 to 75 or 40 to 60%, e.g. about 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90 or 95%. The pyrolysis may be conducted at a temperature of between about 250 and about 2000⁰C, or about 250 to 1000, 250 to 500, 500 to 2000, 1000 to 2000, 500 to 1500, 500 to 1000 or 1000 to 1500⁰C, e.g. about 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1 100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000⁰C. It may be conducted in air, or in some other gas containing oxygen. The content of oxygen in the gas may be between about 5 and about 100% by volume, or about 5 to 50, 5 to 20, 5 to 10, 10 to 100, 20 to 100, 50 to 100, 10 to 50, 10 to 20, 20 to 15 or 15 to 30%, e.g. about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100%. Thus it may be conducted in pure oxygen or in an oxygen containing mixture. It may be conducted in air depleted in oxygen relative to ambient concentrations, or in air enriched in oxygen relative to ambient concentrations, or in air with a normal or approximately normal oxygen concentration (i.e. about 20%). It may be conducted in a mixture of oxygen with some other gas, e.g. with nitrogen, helium, neon, argon or carbon dioxide or a mixture of any two or more of these. During the pyrolysis, it is possible that some degree of oxidation of the graphene occurs. This may form graphene oxide. Thus the graphene of the present invention may comprise graphene oxide. The oxidation content (or oxygen content) of the graphene may therefore be between about 0 and about 20%, or about 0 to 10, 0 to 5, 5 to 20, 10 to 20, 5 to 10, 10 to 15 or 5 to 15%, e.g. about 0, 1, 2, 3, 4, 5, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19 or 20% on a weight basis. In some cases it may be greater than 20%. The oxygen may be in the form of carbonyl groups (ketones, carboxylic acids etc.) or in some other form, or may be in a combination of several of such forms. The oxygen may be randomly distributed through the graphene. The pyrolysis should be conducted for sufficient time for conversion

(optionally substantially complete conversion) of the solvothermal product to graphene. The time for pyrolysis may depend on the amount and nature of solvothermal product used. For a quantity of about lOOmg solvothermal product produced from sodium and ethanol, the time may be about 10 to about 15 seconds. Once the pyrolysis has been initiated, it may be self-sustaining. Thus the heat evolved by combustion of the alcohol in the solvothermal product may be sufficient to sustain the pyrolysis. The time for pyrolysis may therefore be the time taken for the alcohol to combust. The time for pyrolysis may be about 5 to 60 seconds, or about 5 to 30, 5 to 20, 5 to 10, 10 to 60, 20 to 60, 30 to 60, 10 to 30 or 10 to 20 seconds, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 or 60 seconds, although in some cases it may be longer than that, depending in part on the mass of solvothermal product used. It is observed that the pyrolysis does not appear to proceed smoothly, but rather in a series of bursts or pops. It is thought that these are the result of bursting of clathrate-like structure(s) of graphene or of some precursor thereto as material inside combusts and/or expands and as the clathrate-like structure is pyrolysed. The reason for using the term 'clathrate-like' structure(s) is that at this stage the inventors have no direct measurement of clathrated alcohol (i.e. alcohol inside a clathrate structure). However, it makes sense that clathrated alcohol is present as the amount of residual alcohol present determined from TGA was about 20% by weight and the microstructure of the final graphene product shows an open framework with pores suited to alcohol inclusion prior to bursting. It is worth noting that the metal alkoxide precursor commonly is prepared under pressure above 1 atmosphere. It is noted that clathrates may form under conditions of elevated pressure. As described elsewhere herein, the conditions of pyrolysis may affect the structure of the product obtained. It appears that higher temperature and longer pyrolysis time may favour at least partial formation of carbon nanotubes. Thus the pyrolysis may be conducted under conditions of relatively low temperature and short time so as to encourage production of graphene rather than carbon nanotubes. This may for example be encouraged by spreading the solvothermal product into a thin layer prior to initiating pyrolysis. The layer may be less than about 5mm thick, or less than about 4, 3, 2 or lmm thick, or about 1 to about 5mm thick, or about 1 to 4, 1 to 3, 2 to 5, 3 to 4 or 2 to 4mm thick, e.g. about 1, 2, 3, 4 or 5mm thick. The solvothermal product immediately prior to initiation may have between about 0.01 and 0.5g/cm², or about 0.01 to 0.2, 0.01 to 0.1, 0.01 to 0.05, 0.05 to 0.5, 0.1 to 0.5, 0.2 to 0.5, 0.05 to 0.2, 0.05 to 0.1, 0.1 to 0.3 or 0.1 to 0.2g/cm², e.g. about 0.01 , 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5g/cm . This may be regarded as a surface density of the solvothermal product. In this context the term "surface density" refers to the amount of material present per unit area of surface. Thus for example a surface density of O.lg.cm^"2 refers to a situation in which each square centimetre of area has O. lg material thereon. This may have variable thickness, depending in part on the actual surface density.

The pyrolysis may be conducted in the same vessel as the solvothermal process, or may be conducted in a different vessel. The pyrolysis may be conducted open to the atmosphere, or it may be conducted in a closed vessel. The solvothermal product may be isolated, or removed from the vessel, before the pyrolysis step, or may be left in the vessel between the two steps.

The pyrolysis may be initiated by exposure of the solvothermal product to a flame or to an electrical spark or to some other form of ignition, or may be initiated by heating the solvothermal product to a temperature at which ignition occurs. It may be initiated by heating the solvothermal product to a temperature of at least that of the spontaneous ignition temperature of the alcohol. This temperature will depend on the nature of the alcohol. It may be about 250 to about 500⁰C, or about 250 to 400, 250 to 300, 300 to 500, 400 to 500 or 300 to 400⁰C, e.g. about 250, 300, 350, 400, 450 or 500⁰C. Heating for the pyrolysis may be by means of a muffle furnace or other furnace, or by an electrical heating element, or by microwave heating, or by induction heating, or by some other suitable heating method.

Following formation of the graphene in the pyrolysis step, it may be removed from the pyrolysis vessel and cooled. It may be washed to remove residual metal and/or salts thereof (e.g. an oxide and/or a hydroxide of the metal). The washing may use a suitable solvent. This may be an aqueous solvent, and may be water. It may be mildly acidic so as to facilitate the dissolution of alkaline salts, or it may be neutral. It may have a pH of between about 2 and about 7, or about 2 to 5, 2 to 3, 3 to 7, 5 to 7 or 3 to 6, e.g. about 2, 3, 4, 5, 6 or 7. The washing may comprise suspending the graphene in the solvent, optionally agitating it therein, and filtering to isolate the graphene. It may comprise passing the solvent through the graphene, optionally by use of a partial vacuum, in a filtration device. The graphene may be washed once, or more than once e.g. twice, or 3, 4 or 5 times. Different washings may use the same solvent or may use different solvents.

Following the washing, the graphene may be dried to remove residual solvent, residual alcohol if present etc. Drying may be accomplished by heating, e.g. in an oven, passing a gas, optionally a heated gas, through or past the graphene, applying a vacuum or partial vacuum to the graphene, or by some combination of these. For example the graphene may be dried by heating under vacuum. The temperature of the heating (or of the heated gas if used) may be between about 50 and about 500⁰C, or about 50 to 200, 50 to 100, 100 to 500, 200 to 500, 100 to 300 or 70 to 130⁰C, e.g. about 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 200, 250, 300, 350, 400, 450 or 500⁰C. The vacuum or partial vacuum may have an absolute pressure of about 0.01 and about lOmBar, or about 0.1 to 10, 1 to 10, 0.01 to 1, 0.01 to 0.1 or 0.1 to lmBar, e.g. about 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or lOmBar. The time for the drying will depend on the conditions used. It may be between about 5 minutes and about 2 days, or about 30 minutes to 2 days, 1 hour to 2 days, 12 hours to 2 days, 1 to 2 days, 5 minutes to 1 day, 5 minutes to 12 hours, 5 minutes to 1 hour, 5 to 30 minutes, 5 to 10 minutes, 30 minutes to 1 day, 12 hours to 1 day, 1 hour to 1 day or 1 to 12 hours, e.g. about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or 55 minutes, 1, 2, 3, 4, 5, 6, 12 or 18 hours, or about 1, 1.5 or 2 days. The resulting graphene may have a purity of at least about 95% by weight, or at least about 96, 97, 98, 99, 99.5 or 99.9% by weight.

Depending on the intended use of the graphene, it may be comminuted, i.e. its particle size reduced. This may be by mechanical means, e.g. crushing, grinding, pulverising, milling (e.g. with a ball mill) etc, or may be by some other means for example using sonication, e.g. high intensity sonic comminution. The final particle size of the graphene may be less than about lmm, or less than about 0.5, 0.2, 0.1 or 0.05mm, or may be between about 0.01 and about lmm, or about 0.01 to 0.5, 0.01 to 0.1, 0.01 to 0.05, 0.05 to 1, 0.1 to 1, 0.5 to 1, 0.05 to 0.5 or 0.1 to 0.5mm, e.g. about 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9 or lmm. The particle size may be a maximum particle size or a mean (number average or weight average) particle size. It may be a particle diameter. Prior to said comminution (i.e. the crude product following pyrolysis of the solvothermal product), the mean particle size of the graphene may be between about 0.1 and about 2mm, or about 0.1 to 1, 0.1 to 0.5, 0.5 to 2, 1 to 2 or 0.5 to 1.5mm, e.g. about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 , 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2mm

The graphene of the present invention may be in the form of a 3 dimensional open framework or form. Fragmentation of this, e.g. under the influence of mechanical agitation, may provide free sheets of graphene. The free sheets, or some of the free sheets, may be flat. The free sheets, or some of the free sheets, may be curved. The sheets may comprise defect sites. They may comprise defect-laden long range ordering. They may be amorphous. They may be partially amorphous. The graphene of the present invention has a plurality of cavities therein. The cavities may be three-dimensional cavities. They may be holes, or pores, or apertures, or cells. They may have a mean diameter of about 100 to about 500nm, or about 100 to 400, 100 to 300, 100 to 200, 200 to 500, 300 to 500 or 200 to 400nm, e.g. about 100, 150, 200, 250, 300, 350, 400, 450 or 500nm. The cavities may be spherical, or approximately spherical. They may be irregular shaped. They may be cubic. They may be polyhedral (either regular or irregular), optionally with between 4 and 20 sides (e.g. 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 sides) or may have more than 20 sides. They may be elongated cavities. There may be cavities of different shapes and/or of different sizes.

The graphene may at least partially surround each of said cavities. The graphene may constitute the walls of the cavities. Thus the graphene may have a number of cavities therein, either open or closed or a combination of open and closed cavities, whereby the walls of the cavities comprise the graphene. The graphene may therefore define the cavities. The cavities may be interconnected. They may be isolated. Some may be isolated while others may be interconnectied. Thus the invention provides a porous mass of graphene comprising cavities (either interconnected or isolated or a mixture of the two) wherein the walls of the cavities comprise graphene having between about 1 and about 5 layers, each layer comprising a hexagonal lattice of carbon atoms.

The graphene may have between about 1 and about 5 parallel layers, or about 1 to 3, 3 to 5 or 2 to 4 layers, e.g. 1, 2, 3, 4 or 5 layers. In some cases the graphene may have up to 10 layers, e.g. 6, 7, 8, 9 or 10 layers. The above numbers may represent average numbers of layers. The graphene may have different numbers of layers in different regions, or may have the same number of layers throughout. Each of the layers may comprise a hexagonal lattice of carbon atoms. Thus each layer may form an extended lattice of carbon atoms similar to the layers within graphite. The layers may be in the form of an extended fused aromatic system. The network is illustrated in the left-hand image of Figure 1. The graphene may be a foam. The foam may be an open celled foam. It may be a closed cell foam. It may comprise both open cells and closed cells. It may be sponge-like. It may have a sponge structure.

The graphene may be porous. It may be a porous mass. It may have a porous microstructure. The graphene may be in the form of a plurality of burst bubbles, wherein said bubbles have walls comprising said graphene. The graphene may be in the form of a sponge.

The graphene of the present invention may have a morphology comprising a plurality of bubble-like structures wherein the walls of the bubbles are incomplete or open. Thus the bubble-like structures may appear as burst bubbles. It is thought that this morphology is a consequence of the mechanism of formation of the graphene, as described elsewhere herein. The diameter of the bubble-like structures may be between about 100 to about 500nm in mean diameter, as described above. By varying the conditions used form making the material, products of different structures may be obtained. For example, if pyrolysis conditions (e.g. heat density of pyrolysis) are varied, materials ranging from graphene to carbon nanotubes may be obtained. Heat density of the pyrolysis may be varied by reacting larger quantities of the solvothermal product under the same conditions, and/or by using a prolonged pyrolysis reaction time. A variation of 5 fold or more (e.g. 6, 7, 8, 9 or 10 fold) may lead to such changes. In one example, pyrolysis of a solvothermal product at a surface density of O. lg.cm^"2 provided graphene, as described herein, whereas if a surface density of 0.5g.cm^" was used with the same solvothermal product and otherwise similar pyrolysis conditions, carbon nanotubes were obtained.

The graphene (for example in the walls of the burst bubbles described above) may be single layer graphene, or may be bilayer graphene, or may have more graphene layers. Thus the graphene may be in the form of sheets, each sheet comprising one or more layers. Each of the layers may comprise a graphite plane, said plane comprising a hexagonal 2 dimensional lattice of carbon atoms. In this context it will be understood that "2-dimensional" does not suggest that the lattice has no thickness (the thickness being orthogonal to said plane). Indeed, the thickness of a single layer may be the thickness of a carbon atom in an aromatic system such as benzene. However the lattice extends only in 2-dimensions. Also "2- dimensional" does not suggest that the lattice (or layer) is flat. As noted above, the layer (and consequently the lattice or lattices thereof) may be curved, and may appear as bubble-like structures. It may also be in the form of a 3 -dimensional network of such layers.

The thickness of the graphene layers (e.g. the thickness of the walls of the apertures) will depend on the number of parallel sheets therein. The thickness may be less than about 20 angstroms, or less than about 10 or 5 angstroms, or may be 2 to 20, 5 to 20, 10 to 20, 2 to 10, 2 to 5 or 5 to 10 angstroms, e.g. about 2, 3, 4, 5, 6,

7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18, 19 or 20 angstroms.

The graphene may be in the form of particles, each being as described above. The mean particle size may be between about 10 to about 1000 microns. In this context, the size of an individual particle may be its mean diameter, maximum diameter or hydrodynamic diameter. The mean particle size may be abut 10 to 500, 10 to 200, 10 to 100, 10 to 50, 10 to 20, 20 to 1000, 50 to 1000, 100 to 1000, 500 to 1000, 50 to 500, 50 to 200 or 200 to 500 microns, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900 or 1000 microns. It may have a broad particle size distribution or a narrow particle size distribution. It may have a polydispersity (defined here as weight average particle size divided by number average particle size) of between about 1 and about 20, or about 1.5 to 20, 2 to 20, 5 to 20, 10 to 20, 1 to 10, 1 to 5, 1 to 2, 2 to 10, 1 to 5 or 5 to 10, e.g. about 1, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 1 1, 12, 13, 14, 15, 16, 17, 18 19 or 20.

The graphene of the present invention may have a purity of at least about 95% by weight, or at least about 96, 97, 98, 99, 99.5 or 99.9% by weight. It may have less than about lOOppm trace element, e.g. sodium or chlorine, on a weight basis, or less than about 50, 20, 10, 5, 2 or lppm of trace element. It may have a level of trace element below the detection limit of XPS. The graphene may show no decomposition, in air or in nitrogen, below about 300⁰C, or below about 310, 320, 330 or 34O⁰C. It may show less than about 10% decomposition by weight at the above temperatures, or less than about 5, 2 or 1%, when heated at 10°C/minute in a TGA apparatus. It may have less than about 10% moisture by weight, or less than about 9, 8, 7, 6, 5, 4, 3, 2 or 1% moisture by weight, or about 0 to 5, 5 to 10, 1 to 10, 1 to 5 or 2 to 8% moisture. It may have an electrical resistivity of about 1 to about 100 Ω.m, or about 1 to 50, 50 to 100, 1 to 20, 1 to 10, 10 to 100, 20 to 100, 20 to 80 or 30 to 70 Ω.m, e.g. about 1, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100 Ω.m. It may have a specific surface area of about 1 to about 2000m²g^"', or about 1 to 1700, 1 to 1500, 1 to 1000, 1 to 500, 1 to 100, 1 to 50, 1 to 20, 1 to 10, 10 to 2000, 100 to 2000, 200 to 2000, 500 to 2000, 1000 to 2000, 100 to 1000, 100 to 500 or 500 to 1000 mV, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500,1600, 1700, 1800, 1900 or 2000 mV-

₅ The graphene of the present invention may be used in a composite material, wherein the composite material comprises the graphene dispersed within a matrix. The composite material may have greater resilience, strength, elongation, electrical conductivity or some other property than the same matrix without the graphene. The matrix may be a polymeric matrix or it may be a ceramic matrix or it may be a io metallic or metal alloy matrix. Suitable polymeric matrices include polyolefins (polyethylene, polypropylene, polymethylpentene), polystyrenes, polyurethanes, epoxy resins, polyamides, polyacrylates (e.g. polymethylmethacrylate, polybutyl methacrylate, polymethyl acrylate), vinyl polymers (e.g. polyvinylchloride, polyvinylacetate) etc. Suitable ceramic matrices include hydroxyapatite, glass etc. A i₅ suitable metal alloy is Al:Mo:Ni alloy. The matrix may have an electrical conductivity of less than about 0.1Sm^"1, or less than about 0.05, 0.02 or 0.01 Sm^"1 or less than about 10^"3, 10^"4, 10^"5, 10^"6, 10^"7, 10^"8, 10^"9 or 10^"10Sm-'.

The concentration of graphene in the matrix may be sufficient to achieve the desired properties for the composite. For example it may be sufficient to achieve an0 electrical conductivity of at least about 0.1Sm^"1, or at least about 0.2, 0.5 or I Sm^'1, or about 0.1 to about 2 Sm^"1, or about 0.1 to 1, 0.1 to 0.5, 0.5 to 2, 1 to 2 or 0.5 to I Sm^"1, e.g. about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2Sm^"1. The concentration of the graphene may be between about 0.05 and about 5% by weight, or about 0.05 to 1 , 0.05 to 0.5, 0.05 to 0.1, 0.1 to 5,5 0.5 to 5, 1 to 5, 2 to 5, 0.1 to 2, 0.1 to 1 , 0.1 to 0.5, 0.5 to 2, 0.5 to 1 or 1 to 2%, e.g. about 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5%. In some cases the graphene concentration may be higher than this, e.g. about 6, 7, 8, 9, 10, 15 or 20%.

The composite described above may be made by combining the graphene with0 the matrix or with a precursor to a matrix. During said combining the matrix or precursor is preferably in liquid form so as to facilitate the combining. Thus the matrix may be melted, the graphene added and the resulting composite allowed to cool and solidify. Alternatively, if the matrix is a reaction product of two components (as for example an epoxy resin or two part polyurethane resin), a first part of the resin, commonly in liquid form, may be combined with the graphene, a second part of the resin then added (commonly mixed in), and the first and second parts allowed to react to form the matrix having the graphene therein. In this case, the first part of the resin may be considered to be a precursor to the resin, and the process of reacting the first and second parts of the resin may be considered to convert the precursor to the matrix. Alternatively, if the matrix is a solid, it may be mixed in solid, preferably particulate, granular or powder form, with the graphene and the resulting mixture heated to melt the matrix. It will be apparent that various mixing steps may be advantageous or necessary in the above process. Thus, for example, following combination of the graphene with a molten matrix, the resulting mixture may be mixed, stirred, agitated, or otherwise homogenised, so that the resulting composite has the graphene substantially homogeneously distributed therethrough.

Graphene according to the present invention may be used in a wide variety of applications, for example for reinforcing a composite (as described above), manufacturing electronic devices, manufacturing sensors, manufacturing devices for storage of hydrogen or as a catalyst. These take advantage of various properties of graphene, including electrical properties, physical morphology (e.g. high surface area, porosity), surface chemistry etc. In order to gain an understanding of the mechanisms taking place in the process for making graphene described herein, a series of experiments was conducted exploring different combinations of the parameters involved in the synthesis of the carbon nanostructures. Thus control experiments were run involving pyrolysis (thermal decomposition) of naphthalene, using sodium ethoxide without included ethanol, pyrolysis of the solvothermal product under an inert atmosphere, and reduction of the solvothermal product with sodium in an inter atmosphere. None of these control experiments provided the desired graphene. With this understanding, a deterministic approach could be adopted to selectively synthesise a required carbon nanostructure. The carbon nanostructures synthesised include carbon nanotubes, single-layer graphene and bi-layer graphene. The chemical pathway of the present invention provides a novel route to carbon nanostructures which have many emerging and industrial applications. In particular, and of main interest, single-layer graphene. The route developed provides a simple, feasible and low cost path to the synthesis of carbon nanostructures (graphene), in large quantities, with the ability for large scale production. A preferred form of the invention uses sodium as the metal, and ethanol as the alcohol, in the solvothermal process. The solvothermal parameters (i.e. the parameters of the solvothermal process) may be varied in accordance to whether it is required that the up-scaled process be cost effective, to retrieve and recycle the sodium, or whether it is required to consume all the sodium (and start with a fresh sample). By varying the time- temperature parameters it is possible to either retrieve the sodium (low-temperatures, longer time), or allow the sodium to disperse (high-temperatures, shorter time). The latter may be advantageous in that a greater amount of product is formed (i.e. 200°C, 12h) compared to a product requiring recycling (22°C, 6Oh). Furthermore, when the sodium is dispersed, it readily forms sodium hydroxide, and may be easily washed away, allowing a safer alternative in the handling of sodium metal. The compromise in time and temperatures may promote safe operation. If, however, it is not feasible to conduct experiments at 200⁰C, a different compromise may be drawn at lower temperatures with an emphasis on safety. The novel route to graphene described herein addresses key issues which have to date impeded the growth of the technology previously: the ability to develop an up- scalable process to mass produce pure graphene, through a low cost, feasible pathway. Through the route described, large quantities of graphene may be produced in very limited time, and the process can be up-scaled having a 'production-line' methodology. The graphene product may be simply washed with water, to remove impurities left behind after the solvothermal step, and dried. This allows pure graphene to be obtained without costly purification procedures, or unwanted impurities remaining. There is no need for 'finding' the graphene in amongst other materials, as the product consists essentially of entirely graphene. The graphene produced may be further be treated to obtain a desired size. Thus large sheets of graphene may be cut to produce sheets of a desired size.

The inventors consider, without wishing to be limited to any particular mechanism, that the adsorption and dispersion of the alcohol, e.g. ethanol, throughout the solvothermal product is necessary in underlying the mechanism involved in the formation of graphene. The process appears not to be simply combustion of the sodium ethoxide, but rather it is thought that the ignition sparks the ethanol present, and hence decomposes the surrounding ethoxide. Thus, as the ethanol is volatile, it can ignite during pyrolysis, and then vaporise due to the local heat density. This heat density is insufficient to cause complete oxidation of the carbon to carbon dioxide, but is sufficient to cause decomposition of the alkoxide to generate carbon in the form of graphene. Due to the small individual ignitions of ethanol (non-excessive), a 'popcorn' effect occurs, and nucleation of thin sheets occurs throughout the regions where ethanol is present. The degree of carbon material formed is dependent on the material's ability to conduct heat. The ethanol then evaporates out of the porous structure, and can be observed with the naked eye as ripples on the surface of the solvothermal product. This may also be accomplished by placing the solvothermal product in paraffin oil and heating, upon which small bubbles become evident. Without the ethanol present, graphene is not observed. The proposed mechanism of the process of formation of graphene in the solvothermal step is outlined in Figure 2. Fig. 2 shows sodium ethoxide surrounding ethanol (left) in the form of a clathrate-like structure. Sodium ethoxide is the bulk porous material, which is able to absorb ethanol into valleys and cavities. Only a single bubble is shown in Fig. 2, whereas in reality a large number of such bubbles would be present. The solvothermal product may therefore be considered contain many droplets of ethanol surrounded by ethoxide, analogous to a sponge absorbing water. The solvothermal product is formed by reaction of ethanol with sodium metal, more generally by an alcohol with a metal. The reaction is:

EtOH(I) + Na(s) → EtO^"Na⁺(s) + l/2H₂(g) or, more generally, nROH(l) + M(s) → (RO^")_nMⁿ⁺(s) + n/2H₂(g) (where R is an alkyl group, M is a metal and n is the charge on the Mⁿ⁺ ion).

The sequence shown in Fig. 2 describes the proposed mechanism occurring in the formation of bi-layer graphene by pyrolysis of the solvothermal process. The mechanism is described in relation to the example which uses ethanol and sodium, however it is thought that an analogous mechanism would also operate with other alcohols and metals. As described above, the solvothermal product, in a preferred embodiment, contains ethanol in sodium ethoxide. Either in the solvothermal product, or at the start of the pyrolysis process, this is in the form of ethanol regions (possibly liquid droplets) surrounded by sodium ethoxide (left hand image of Fig. 2). As the pyrolysis progresses, thermolysis of the ethoxide, and possibly of the ethanol, causes it to decompose and give rise to a thin sheet of graphene around the inner region (centre image). As the ethanol evaporates, a carbon shell (right hand image) remains. The evaporation of ethanol may cause the shell (bubble) of graphene to burst. Short bursts of heat are sufficient to form bi- layer graphene and not graphite. Applications The ability to now produce large, pure quantities of graphene, provided by the present invention, allows the realisation of large scale applications to no longer be that of dreams, or a centre for scepticism but accessible through this novel route to graphene. The most immediate application of graphene is most likely its use in composite materials. The challenge hitherto has been to find a process that yielded a uniform distribution of graphene in a polymer matrix. A series of surface modifications has in the past been carried out to yield a composite material retaining the properties of the graphene and enhancing that of the plastic. However, with the novel route to graphene provided herein, a uniform distribution of graphene may be produced, commonly with a porous structure. This may allow re-enforcement without the need to disperse into the medium (as the plastic or other material can fill the vacancies or cavities, analogous to concrete setting with steel grids inside the concrete). This allows the graphene to retain its original properties. Hitherto, the clear advantage carbon nanotubes had over graphene was in re- enforcement (mechanical strength), due to the entanglements of the carbon nanotubes. The graphene produced by the present process may produce a network with the potential to provide rigidity and sturdiness when used as a filler in a composite system.

Earlier work has shown that use of graphene in composites can produce materials with intriguing properties. Only 0.1% by volume of graphene in the composite is required for electrical conduction - this is the lowest threshold observed for conductive polymer composite materials, except for those using carbon nanotubes. The conductivity rapidly increases by incorporating more graphene, reaching 1 Siemen per metre (Sm^"1) at a loading of 2.5% by volume. Conductivities in the range of 0.1 Snϊl are sufficient for many applications. Graphene composites may be very useful, for example, in the manufacture of fuselages for aircraft, which must combine low weight, high strength and electrical conductivity.

One promising application for nanotubes is field emitters, and although there have been no reports to date about such use of graphene, thin graphite flakes have been used in plasma displays (commercial prototypes) long before graphene was isolated, and many patents were filed on this subject. It is therefore thought that graphene powder can offer even more superior emitting properties. Figure 3 shows a piece of bi-layer graphene isolated on the surface of carbon tape. This micrograph shows that the graphene produced by the present process may possess sharp tips necessary for field emission (and other microscopy techniques). Furthermore, these points can act as natural binding sites to silicon (due to dangling bonds on the surface), and may therefore be used in nano- electrical components and interconnects.

Carbon nanotubes have been reported to be an excellent material for solid-state gas sensors but graphene also offers clear advantages in this particular direction. Spin-valve and superconducting field effect transistors may also be applications for the graphene of the present invention. Recent reports describing a hysteretic magnetoresistance and substantial bipolar supercurrents prove graphene' s major potential for these applications. Furthermore the graphene of the invention may find application in low-temperature experiments on fundamental and relativistic physics. An extremely weak spin-orbit coupling and the absence of hyperfine interaction in ¹²C-graphene make it an excellent if not ideal material for making spin qubits. This guarantees graphene-based quantum computation to become an active research area.

Graphene exhibits a high mobility of its charge carriers thereby making it suitable for use in electronics applications. However, the truly exceptional feature of graphene is that the mobility remains high even at highest electric-fϊeld-induced concentrations, and seems to be little affected by chemical doping. This translates into ballistic transport on a sub-micrometre scale at 300K. A room-temperature ballistic transistor has long been a tantalizing but elusive aim of electronic engineers, and it appears that graphene is suitable for this application. The large value of Fermi velocity (vp) and low-resistance contacts without a

Schottky barrier may help further reduce the switching time. Relatively low on-off ratios (reaching only about 100 because of graphene's minimum conductivity) do not seem to present a fundamental problem for high-frequency applications, graphene based electronics may therefore employ transistors operational at THz frequencies. For many mainstream logic applications, the fact that graphene remains metallic even at the neutrality point may present problems. However, significant semiconductor gaps can still be engineered in graphene, and ΔE of up to 0.3 eV can be induced in bi-layer graphene externally by applying a gate voltage (for example if SiO₂ is used as a dielectric). This may be useful in making tuneable infrared lasers and detectors. Graphene may be viewed as a conductive sheet, in which various nanometre-size structures can be carved to make a single-electron-transistor (SET) circuitry. Unlike other materials, graphene nanostructures are stable down to true nanometre sizes. This allows the exploration of a region somewhere in between SET and molecular electronics (but by using the top-down approach). The advantage of this is that everything including conducting channels, quantum dots, barriers and interconnects may be cut out from a graphene sheet.

With fullerenes and carbon nanotubes, surface plasmon resonance (SPR) can be used for real-time protein-binding measurements. Attachment of one of the interacting partners to an SPR gold sensor surface allows for consistent and repeatable binding experiments. This technique may be extended to the graphene synthesised by the present process, to proteins with possible graphene surface affinity, where a protein or anti-body could be flowed across the surface, and binding data obtained. Due to the porous nature of the graphene synthesised by the present process, it may be used as a template or molecular trapping device (i.e. membrane or filter), as the pore size is in the range of microns.

Graphene powder may also be used in electric batteries, which are already one of the large markets for graphite. An extremely large surface-to-volume ratio and high conductivity provided by graphene powder provides improvements in the efficiency of batteries, taking over from the carbon nano-fibres used in modern batteries. The high surface area the graphene possesses, may also give rise to catalytic behaviour in industrial, large scale chemical reactions.

When charcoal is heated and then cooled without exposure to air, it takes up several times its own volume of air upon subsequent exposure. Pores in the charcoal account for much of the gas uptake by condensation therein and many solids exhibit adsorption phenomena to different degrees. The graphene synthesised by the present process has an extensive porous structure, with an extremely high surface area and is suitable for alternative energy applications in the form of hydrogen storage. Calculations have been made on graphene sheets for hydrogen storage and show that graphene is a likely candidate for future developments in hydrogen storage.

The novel route to graphene described herein allows a chemical pathway to now produce large, pure quantities of graphene, and the realisation of large scale applications incorporating graphene components. Graphene applications may be realised with the confidence of deterministic control of the nanomolecular world, from our macro-world we live in. Example

A novel route to the synthesis of graphene has been developed, involving the pyrolysis of the solvothermal product of ethanol and sodium, to yield single-layer graphene, and under certain controllable conditions, carbon nanotubes. Sodium and ethanol are added in a 1 :1 molar ratio to a reaction vessel (Parr 4749 General Purpose Acid Digestion Bomb), the reaction vessel is closed (sealed), and placed into a muffle furnace (Heraeus MI lO Muffle Furnace) at 220°C for 72 hours to yield the solid solvothermal product. The solvothermal product is then pyrolysed in ambient conditions using a small quantity of the solvothermal product (about O.lg) spread over an area of about lcm². The pyrolysis was initiated using a flame. The product was washed with de- ionised water, vacuum filtered using a Hirsch funnel, and dried in a vacuum oven (100°C for 24 hours).

In a typical reaction: 2g of sodium was added to 5mL of ethanol in a reaction vessel (Parr 4749), and heated to 220°C for 72hours (Ml 10 Muffle Furnace). Once the reaction vessel cooled, the solvothermal product was collected. A small amount of the solvothermal product (about O.lg) was then pyrolysed, and the remaining product washed thoroughly with de-ionised water (about 10OmL), vacuum filtered using a Hirsch funnel, and dried in a vacuum oven (100°C for 24 hours). The resulting material was identified as graphene, with 98% purity or greater. X-Ray Photoemission Spectroscopy (XPS) showed that the crude carbon product contained sodium oxide (Na₂O, 16.569% by weight), however after washing with distilled water, this was reduced to a much smaller value (1.787% by weight), leaving pure graphene (98+ % by weight).

From X-ray diffraction data obtained, it was determined that the value corresponding to the size of crystallites along the c-axis (L_c) was 3.9A. This indicated that the carbon material synthesised had a thickness of two atomic layers (i.e. bi-layer graphene). However, later characterisation done by Atomic Force Microscopy (AFM) (Figure 4) showed that this was due to multiple single sheets stacking on one another, and that the thickness of the sheets was 4A ± lA, further implying a single sheet was present, and correlating with the XRD value. Thus Fig. 4 shows AFM images of a graphene sheet. The topology image (left) shows that the step height on either side of the sheet is 4A ± lA. The phase contrast image (right) shows that the material is inherently different to the substrate, indicating the presence of graphene. The centre image of Fig. 4 shows the amplitued mode of the AFM. The topology image did not appear to show the graphene sheet, whereas it was visible in the phase contrast image; indicating that the graphene sheet was extremely flat. Transmission electron microscope images (Figure 5) and scanning electron microscope images (Figure 6) show the inherent sheet like structure and an intricate array of folding patterns. SEM images also show the porous nature of the graphene synthesised. Thus the TEM images show the extensive array of the bi-layer graphene sheets synthesised using the present process. The SEM images show bi-layer graphene, and illustrate the porous structure (left) and the extensive formation of bi-layer graphene (right).

Further investigation of the solvothermal product provided support for the proposed s mechanism for the formation of graphene. Thermo-gravimetric analysis (TGA) was conducted on the solvothermal product, and showed that it contained of 19.14% ± 0.73% water and ethanol. X-ray diffraction performed on the solvothermal product showed that it contained sodium ethoxide and sodium hydroxide. Infra-red spectroscopy suggested that ethanol, sodium hydroxide, and water were present in the solvothermal product.

I₀ Carbon nuclear magnetic resonance and hydrogen nuclear magnetic resonance indicated that ethoxide was present.

The solvothermal product synthesised was a mixture of sodium ethoxide (the carbon source), sodium hydroxide, sodium metal (which later forms sodium hydroxide), and ethanol. The solvothermal step is critical in the formation of graphene, as the is solvothermal product produced was porous, in which ethanol was dispersed through the material. The dispersed ethanol is adsorbed into cavities and in the valleys in the solvothermal product. Evidence of this is shown in SEM images of the microstructure of the solvothermal product obtained (Figure 7), as a porous structure is apparent which provides suitable regions in which the ethanol can be adsorbed. The porous nature of the0 solvothermal product is shown, with valleys (left) and cavities (right) evident.

The proposed mechanism described earlier is be supported by SEM images taken of the graphene material produced (Figure 8). The SEM image shows the voids left behind by evaporated ethanol, and the porous nature of the bi-layer graphene synthesised using the process of the present invention. The liquid-solid nucleation process is fundamentally5 different than the vapour-liquid nucleation in that the solid phase has broken continuous symmetry. Associated with any broken continuous symmetry is the presence of elastic forces to prevent thermal fluctuations from destroying the new phase, resulting in stable graphene (as ethanol evaporates). The solvothermal product appears to be amorphous, and have no long-range ordering. It is thought that the graphene is produced at the interface0 between ethanol and ethoxide. Heat transfer within the forming graphene phase is thought to dictate the nucleation process: defects and dislocations that stabilise the sheets are frozen into the structure, thereby destabilising a 3 -dimensional structure. Analytical data Various analytical data were obtained for graphene produced by the process of the present invention. These are set out below, and are illustrated in Figs. 9 to 17. Elemental Anal sis

X-Ra Photoemission S ectroscopy (XPS)

X-Ra Photoemission S ectrosco XPS

Elemental Analysis Method was conducted at The University of Otago, School of Chemistry, Campbell Microanalytical Laboratory, Dunedin, New Zealand. Acid washed decolorizing charcoal (BDH Chemicals), 98-99% natural graphite (Hopkins and Williams), and synthetic graphite (Aldrich) were used for comparison. The analytical method is based on the complete and instantaneous oxidation of the sample by "flash combustion" which converts all organic and inorganic substances into combustion products. The sample is held in a tin capsule and dropped into a vertical quartz tube, containing catalyst (tungstic oxide) and copper, which is maintained at a temperature of 1020°C. The helium carrier gas is temporarily enriched with pure oxygen as the sample is dropped into the tube. The sample and its container melt and the tin promotes a violent reaction. Under these favourable conditions, even thermally resistant substances are completely oxidized. Quantitative combustion is then achieved by passing the mixture of gases over a catalyst layer, then through copper to remove excess oxygen and reduce nitrogen oxides to nitrogen. The resulting mixture is directed to the chromatographic column where the components (carbon dioxide, water, sulfur dioxide and nitrogen) are separated and detected by a thermal conductivity detector which gives an output signal proportional to the concentration of the individual components of the mixture. The information is fed into a work station and the percentages calculated using the weight of sample.

XPS (X-ray Photoelectron Spectroscopy — Fig. 9)

The defective nature of the graphene synthesised gives rise to regions of the material where carbon is bound to oxygen, which is also apparent in natural graphite (Raman spectra showing it is defective to a certain degree). However, there is no evidence of a periodicity in this chemical bonding, as SAED (selected area electron diffraction) patterns observed indicate bond lengths of a hexagonal arrangement of carbon atoms bound only to carbon atoms, agreeing with theoretical calculations. XPS spectroscopy also shows that the graphene synthesised contains no trace elements after purification. Trace elements that might have been present include for example those that may have been added during sample handling, e.g. from spatulas, filters etc. Fourier Transform Infra-red Spectroscopy (FTIR - Fig. 10)

Infra-red measurements were performed on Nicolet Avatar 320 FT-IR and Thermonicolet Avatar 370 FT-IR spectrometers. The graphene sample was ground with KBr, and pressed into a thin disc. The IR spectra taken show that there is a small amount of water being absorbed after drying and preparation, with evidence of C-O bonding arising from either tightly bound water molecules or defective sites in the graphene. Thermogravimetric Analysis (TGA - Figs. 11 to 14)

Samples were run in "heat and hold" mode at 10°C/min when purged with air, and 20°C/min when purged with nitrogen, to isothermal temperatures of 800°C and 60°C. In Figs. 11 to 13 the dashed trace relates to the temperature (right hand scale) whereas the solid trace relates to the weight of the sample (left hand scale). The TGA of the pre-dried graphene sample conducted to 800°C under air purge (Fig. 11) shows some surface moisture being lost, followed by a thorough decomposition (pyrolysis) of the graphene material. The TGA of the graphene sample conducted to 800°C under nitrogen purge (Fig. 12) shows some surface moisture being lost (ca. 7.5%), followed by some decomposition of the graphene material. The TGA of the graphene sample conducted at 60⁰C under nitrogen purge (Fig. 13) shows some surface moisture being lost (ca. 2.5%). The TGA responses of samples heated under both air and nitrogen follow a common path to around 400⁰C - this is clearly shown in the differential plot - beyond which the air- heated sample rapidly decomposes via combustion, whilst under nitrogen, only a partial decomposition is observed (possibly as a result of residual oxygen). The % weight loss at the point that the two curves diverge is about 13%, suggesting a residual value for bound water that includes strongly-bound molecules. Mass spectrometry (MS - Figs. 15a-c)

Samples (approximately 1 mg) were analyzed by direct insertion probe electron impact ionization (EI⁺) mass spectrometry, using a Thermo DSQ II mass spectrometer (Thermo Fisher Scientific Inc., Waltham, MA). The mass spectrometer scanned from m/z 10 to m/z 50 in 0.33 seconds. The direct insertion probe was maintained at 50⁰C for 1 minute, then heated ballistically to 200⁰C and held at that temperature for 90 seconds. The ion source was maintained at a temperature of 150⁰C and all sample cups were pre-heated to 200⁰C in vacuo prior to sample loading, or acquisition of background spectra. Control analyses were performed using empty sample cups, and the data obtained were used to provide background subtraction for carbon sample spectra. Background subtracted spectra were searched against the Wiley 7 and NIST 98 mass spectral libraries to provide identification of the desorbed analytes.

From the data obtained after subtracting the background, water and molecular oxygen do not appear to be present. Rather, fragments of ethanol are apparent, remaining after washing (i.e. the sample was wet with ethanol). However, the absence of water and molecular oxygen fragments in the subtracted spectra can also suggest that the amounts of water and molecular oxygen in the sample are comparable to those in the atmosphere.

The high abundance of water and molecular oxygen in air make it difficult to distinguish their presence in the graphene sample, as the primary indication of their presence would be by observation of an increase in their fragment signals. The presence of water and molecular oxygen in the graphene sample could also result in a blank spectrum upon subtraction of the background (air) spectrum, as comparable amounts could be present in both air and the sample in air. AFM (Figs. 16, 17)

Figure 4 is not unique. Figs. 16 and 17 show two more examples showing the topography images of various graphite sheets on top of each other. Height profiles are indicated by white arrows. These images have been levelled by 2^nd or 3 ^rd order plane subtraction and no other data manipulation was done on these images. It should be noted that plane subtraction is applied to correct for the non-linearity of the piezo-AFM scanner but a sloping baseline may still remain. A residual slope in the baseline may still be detected and combined with tip-convolution effects may make some of the steps in the above images appear to be at little less or more than 4-5 A (single sheets in Figure 16) or 7-9 A (double sheets in Figure 17). Bulk Electrical Conductivity

The conductivity of a bulk sample of graphene was taken by pressing the graphene powder into a disc using a 15 mm diameter dye under a hydraulic press and measuring the resistance between two points on the sample. The conductivity was calculated using the equation:

R = pL/A ... 1 where R is resistance, p is resistivity, A is the cross-sectional area of the sample in contact with the electrodes, and L is the distance between the electrodes, with the conductivity being the inverse of resistivity: σ = l/p ... 2

The conductivity of natural graphite was taken for comparison. The conductivity was measured both across the surface of the pressed discs, and between the two sides of the discs. The results are summarised below.

[a] A. R. Coutinho, J.D. Rocha, CA. Luengo. "Preparing and characterizing biocarbon electrodes", Fuel Processing Technology, 67 93-102 (2000).

The graphene conductivity lies approximately half way between graphite and charcoal on logarithmic scale. The authors have found that use of different carbon sources in the process of the invention can lead to different graphene forms - from sheets through to ribbons and rods. When using lithium metal in step (i) of the process, spheres of about 350 nm diameter were obtained. There is also the potential to chemically dope the graphene of the invention. These options are not available to workers starting with graphite precursors rather than using the process of the present invention to generate the graphene. The oxygen content using the process of the invention is commonly about 10-15% (by weight) following purification and drying. Bulk conductivity measurements of the graphene products of the invention reflect high intrinsic conductivity with many interfaces, resulting in the observed intermediate conductivity. By varying the synthesis time of the 'clathrate' precursor (the solvothermal product) from about 6 to about 72 hours and the synthesis temperature from about room temperature to about 22O⁰C the inventors obtained surface areas of the graphene product from several m²g^"1 through to about 1700m²g^~' in solid and solution. In general, the smaller the sheets of graphene, the higher the solution surface area and the lower the solid surface area. This reflects a tendency of the small sheets to stack in the solid state whereas they may be easily dispersed in solution.

Claims

Claims:

1. Graphene having a plurality of cavities therein.

2. The graphene of claim 1 wherein the graphene comprises between about 1 and about 5 parallel layers and at least partially surrounds each of said cavities, and wherein each of said layers comprises a hexagonal lattice of carbon atoms.

3. The graphene of claim 1 or claim 2, said graphene being a foam.

4. The graphene of claim 3 wherein the foam is an open celled foam.

5. The graphene of any one of claims 1 to 4 wherein the cavities have a mean diameter of about 100 to about 500nm.

6. A process for producing graphene comprising:

(ii) pyrolysing the solvothermal product to produce the graphene.

7. The process of claim 6 wherein the metal is an alkali metal.

8. The process of claim 7 wherein the alkali metal is sodium.

9. The process of any one of claims 6 to 8 wherein the alcohol is volatile.

10. The process of any one of claims 6 to 9 wherein the alcohol is a primary alcohol.

1 1. The process of claim 10 wherein the alcohol comprises ethanol.

12. The process of any one of claims 6 to 1 1 wherein the molar ratio of the metal to the alcohol is between about 1.5: 1 and about 1 : 1.5.

13. The process of claim 12 wherein the molar ratio is about 1 : 1.

14. The process of any one of claims 6 to 13 wherein step (i) is conducted at between about 0 and about 250°C.

15. The process of any one of claims 6 to 14 wherein step (ii) is initiated using a flame.

16. The process of any one of claims 6 to 15 wherein step (ii) is conducted at a temperature of between about 250 and about 500⁰C.

17. The process of any one of claims 6 to 16 additionally comprising washing the graphene.

18. The process of claim 17 comprising drying the graphene after said washing.

19. The process of any one of claims 6 to 18 additionally comprising comminuting the graphene.

20. Graphene made by the process of any one of claims 6 to 19.

21. A composite material comprising graphene according to any one of claims 1 to 5 or 20 dispersed in a matrix.

22. The composite material of claim 21 wherein the graphene is present in the composite material at a concentration of between about 0.05 and about 5% by weight.

23. The composite material of claim 21 or claim 22 having an electrical conductivity of at least about 0.1 Sm^"1.

24. The composite material of any one of claims 21 to 23 wherein the matrix has an electrical conductivity of less than about 0.1 Sm^"1.

25. The composite material of any one of claims 21 to 24 wherein the matrix comprises a polymer or a ceramic or a metal or a metal alloy.

26. A process for making a composite material comprising:

(i) providing graphene according to any one of claims 1 to 5 or 20;

(ii) combining the graphene with a matrix or with a precursor to a matrix, said matrix or precursor being in liquid form; and

(iii) if step (ii) comprises combining the graphene with a precursor to a matrix, converting the precursor to the matrix.

27. Use of graphene according to any one of claims 1 to 5 or 20 for reinforcing a composite or for manufacturing an electronic device or for manufacturing a sensor or for manufacturing a battery or for manufacturing a device for storage of hydrogen or as a catalyst.