TWO-DIMENSIONAL MATERIALS

Abstract

A method of preparing a 2D material (e.g. graphene or of boron nitride), the method comprising: (i) selecting a fluid comprising the 2D material dispersed in a solvent; (ii) using a filtration device to remove solvent from the fluid and increase the concentration of 2D material in the fluid, wherein the fluid suitably includes a surfactant, which may be sodium cholate or sodium dodecylbenezenesulphonate and wherein the filtration device is suitably a cross-flow filtration device.

Claims

1. A method of preparing a 2D material, the method comprising: (i) selecting a fluid comprising a 2D material dispersed in a solvent; (ii) using a filtration device to remove solvent from the fluid and increase the concentration of 2D material in the fluid; wherein said filtration device comprises an inlet for passage of fluid into the filtration device and an outlet for passage of unfiltered fluid away from the filtration device, wherein a filtration surface is positioned between the inlet and outlet and the filtration device is arranged to direct fluid tangentially or parallel to the filtration surface.

2. A method according to claim 1, wherein said 2D material has, on average, fewer than 10 layers; and said fluid selected in step (i) includes graphene or boron nitride.

3-36. (canceled)

37. A method according to claim 1 wherein said device includes a conduit for passage of filtrate away from the filtration surface and said filtration surface is arranged so that at least 80 wt % of said 2D material included in said fluid selected in step (i) does not pass through said filtration surface.

38. A method according to claim 1, wherein said filtration surface has a pore size of less than 1000 kDa; and preferably at least 200 kDa.

39. A method according to claim 38, wherein said filtration device includes an elongate conduit having an inlet and outlet, wherein a wall of the conduit defines said filtration surface; and a lumen defined by said wall has a diameter of at least 0.1 mm; and the diameter is less than 2 mm.

40. A method according to claim 1, wherein the pressure of fluid at the inlet of the filtration device is in the range 200,000 to 300,000 Pa and the pressure across the filtration surface of the device is in the range 50,000 to 200,000 Pa.

41. A method according to claim 1, wherein the rate of flow of fluid comprising said 2D material dispersed in said solvent into the filtration device is greater than 300 litres/hour.

42. A method according to claim 1, wherein said fluid selected in step (i) includes a surfactant, wherein said surfactant has a solubility of at least 10 g/L; and/or a molecular weight of less than 800 g/mol.

43. A method according to claim 1, wherein said solvent is water.

44. A method according to claim 1, wherein said fluid selected in step (i) includes at least 0.02 g/L of said 2D material and it includes less than 2 g/L of said surfactant.

45. A method according to claim 44, wherein said fluid selected in step (i) has a bulk conductivity at 20° C. of at least 50 μS/cm; and/or the conductivity is less than 350 μS/cm.

46. A method according to claim 1, wherein, in said fluid selected in step (i), the ratio of the concentration of 2D material divided by the concentration of surfactant is in the range 0.025 to 2.

47. A method according to claim 1, wherein, during the method, the ratio of the concentration of 2D material in the unfiltered fluid at said outlet divided by the concentration of 2D material selected in step (i) is at least 10.

48. A method according to claim 1, wherein the method includes a wash step wherein unfiltered fluid from said outlet is diluted with additional solvent and the diluted unfiltered fluid is reintroduced into the filtration device via its inlet.

49. A method according to claim 1, wherein the ratio of the concentration of surfactant at the beginning of the method divided by the concentration of surfactant in the unfiltered fluid in said outlet, is at least 15.

50. A method according to claim 1, wherein, prior to step (i), the method includes a step (A) which comprises selecting a 3D material and treating the 3D material to exfoliate it and produce said 2D material, wherein step (A) comprises selecting a liquid formulation (A) comprising said 3D material, a surfactant and said solvent; wherein a liquid formulation (B) produced after exfoliation in step (A) is treated in a step (B) to remove the 3D material from liquid formulation (B) and increase the concentration of 2D material relative to 3D material, wherein treatment of liquid formulation (B) in step (B) comprises use of a hydrocyclone.

51. A method according to claim 50, wherein liquid formulation (A) includes 2000 to 4000 parts by weight (pbw) 3D material, 20000 to 40000 pbw of solvent which is water and 10 to 100 pbw of said surfactant.

52. A method according to claim 1, wherein said 2D material has, on average, fewer than 10 layers and is selected from the group comprising graphene and boron nitride; wherein said device includes a conduit for passage of filtrate away from the filtration surface and said filtration surface is arranged so that at least 80 wt % of said 2D material included in said fluid selected in step (i) does not pass through said filtration surface; wherein said filtration surface has a pore size of less than 1000 kDa; and at least 200 kDa; wherein said filtration device includes an elongate conduit having an inlet and outlet wherein a wall of the conduit defines said filtration surface; and a lumen defined by said wall has a diameter of at least 0.1 mm; wherein the pressure of fluid at the inlet of the filtration device is in the range 200,000 to 300,000 Pa and the pressure across the filtration surface of the device is in the range 50,000 to 200,000 Pa.

53. A method according to claim 1, wherein said fluid selected in step (i) includes graphene or boron nitride; wherein said fluid selected in step (i) includes a surfactant; wherein said solvent is water; wherein said fluid selected in step (i) includes at least 0.02 g/L of said 2D material; wherein said fluid selected in step (i) includes at least 0.2 g/L of said surfactant; wherein said fluid selected in step (i) has a bulk conductivity at 20° C. of at least 50 μS/cm and less than 350 μS/cm; wherein, in said fluid selected in step (i), the ratio of the concentration of 2D material divided by the concentration of surfactant is in the range 0.025 to 2; wherein, after step (ii), the concentration of surfactant in said solvent is less than 0.5 g/L.

54. A method of increasing the concentration of 2D material in a fluid, said 2D material being selected from the group comprising graphene and boron nitride, the method comprising: (i) selecting a fluid comprising a 2D material dispersed in a solvent; (ii) using a filtration device to remove solvent from the fluid and increase the concentration of 2D material in the fluid; wherein said filtration device comprises an inlet for passage of fluid into the filtration device and an outlet for passage of unfiltered fluid away from the filtration device, wherein a filtration surface is positioned between the inlet and outlet and the filtration device is arranged to direct fluid tangentially or parallel to the filtration surface.

Description

[0082] Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0083] FIG. 1 is a schematic of a graphene production process;

[0084] FIG. 2 is a schematic representation of Procedure A of FIG. 1;

[0085] FIG. 3 is a representation of an in-line filter used in Procedure B;

[0086] FIG. 4 is a representation of a hydrocyclone;

[0087] FIG. 5 is a representation of a cross-flow filtration assembly;

[0088] FIG. 6 is a schematic representation of a cross-flow filtration unit;

[0089] FIG. 7 is a graph illustrating particle sizes, on a particle volume basis, within the graphene dispersion before and after Procedure D;

[0090] FIG. 8 is a graph illustrating particle sizes, on a particle number basis, within the graphene dispersion before and after Procedure D;

[0091] FIG. 9 includes Raman traces of the graphene dispersion before and after Procedure D;

[0092] FIG. 10 is a graph of graphene concentration v. exfoliation time for different starting graphite concentrations; and

[0093] FIG. 11 is a graph of graphene concentration v. exfoliation time for different graphite:surfactant ratios.

[0094] The following are referred to hereinafter:

[0095] Graphite (A)—a commercially available graphite having a D.sub.50 by volume, as measured by Malvern Mastersizer, of 18 μm.

[0096] Graphite (B)—a flake graphite with a mean size greater than 100 μm, as measured by sieve analysis.

[0097] A process for producing graphene from graphite is illustrated generally in FIG. 1. Referring to the figure, the following procedures are undertaken.

[0098] Procedure A—Graphite is selected and exfoliated in an aqueous medium in the presence of surfactant to produce a liquid mixture comprising graphene, graphite, water, surfactant and other contaminants which is fed into Procedure B.

[0099] Procedure B—the liquid mixture of Procedure A is treated to remove bulk graphite which is recycled and re-treated in Procedure A. Liquid from Procedure B is then fed into Procedure C.

[0100] Procedure C—the liquid mixture of Procedure B is treated to reduce the level of surfactant and produce a liquid which has a higher concentration of graphene. This is then fed into Procedure D.

[0101] Procedure D—the liquid containing graphene is subjected to a “polishing” step to remove graphite from the liquid which is recycled back into Procedure A.

[0102] Procedure E—the product of Procedure D is tested to assess its characteristics, properties and purity.

[0103] Features of the process are described in more detail below.

[0104] Referring to FIG. 2, in Procedure A, a 50 litres tank 10 is charged with graphite (3.5 kg, 100 g/l), surfactant (sodium cholate) (35 g, 1 g/l) and water (35 litres). Slurry from tank 10 is pumped into an inline rotor/stator shear mixer 12 which is arranged to impart a shear stress to the slurry. Provided the local shear rate imparted on the slurry exceeds 10000 s.sup.−1, the graphite can be efficiently exfoliated to form graphene sheets. The mixture may suitably have a flow rate of 6000 l/hr, a rotation rate of 3000 rpm and a shear rate over 45000 s.sup.−1. Batches of slurry may be processed as described over a four hour period. The mixer has several effects—mixing of surfactant with graphite, exfoliating the graphene from the graphite, facilitating recirculation back to tank 10 and pumping material into Procedure B.

[0105] The typical yield at the end of the procedure is 2.5-3.5 g of graphene per batch per 3.5 kg of initially charged graphite. This equates to a yield of 0.07-0.10 wt %. The product of Procedure A (comprising 2.5-3-5 g graphene, approx. 3497 g graphite, surfactant and water) is fed into Procedure B.

[0106] The aim of procedure B is to separate out the majority of the graphite (or boron nitride) flakes from the dispersion produced in Procedure A so the graphite (or boron nitride) flakes can be recycled back into Procedure A and exfoliated and a dispersion comprising graphene and residual graphite (or boron nitride flakes and powder) can move on to downstream washing and concentration steps.

[0107] Procedure B comprises a two stage separation process which includes inline filtration 20 (FIG. 1) and use of hydrocyclone technology 22.

[0108] An inline-filtration device 22 is shown diagrammatically in FIG. 3. It may suitably be a Russel Finex Filtration Unit. The device includes a body 24 which houses a removable cylindrical filtration cartridge 26. An auger (not shown) is positioned within the cartridge 26 and is arranged to rotate above axis 28, driven by a motor 30. During rotation, the helical blade-like periphery of the auger contacts the internal cylindrical surface of the cartridge 26 thereby to dislodge solids from it. The solids are then directed by the rotating auger to outlet 30 wherein they are removed from the device. In use, the dispersion from Procedure A is introduced into device 22 via inlet 32; it passes within cartridge 26; solids which are too large to pass through the filtration mesh of the cartridge are retained within the cartridge for subsequent removal by the rotating auger; and filtrate passes through the filtration mesh, as represented by arrows 34, and then passes through outlet 36. In one embodiment the mesh may be a 100 μm mesh.

[0109] From outlet 36, the filtrate is introduced into a hydrocyclone 36 represented in FIG. 4. The hydrocyclone 36 includes an inlet 38 for the filtrate from the device 22. The filtrate is fed in under pressure and, by virtue of the high centrifugal forces, solids of sizes generally higher than a predetermined size are directed towards outlet 40 and solids of smaller sizes are directed towards outlet 42. Solids from outlet 40 may be recirculated back to Procedure A. Solids (and associated fluid) from outlet 42 are directed into Procedure C. The hydrocyclone used may suitably have a D.sub.50 cut size selected in the range 3 to 10 μm.

[0110] The fluid which is directed into Procedure C may contain graphene, graphite, surfactant and water. Objectives of Procedure C are to remove water and thereby increase the concentration of graphene in the water which remains, and also to minimize the concentration of surfactant. No removal of graphite takes place at this stage.

[0111] It is believed the surfactant is either: [0112] (i) physisorbed onto the graphene flakes, held on by weak Van der Waal's forces and imparting a charge to the graphene. As a result there is a repulsive force between individual flakes which keeps them in dispersion; or [0113] (ii) the surfactant forms micelles with individual graphene flakes at the centre, again keeping them in dispersion.

[0114] Zeta potential of a graphene nanoplatelets has been measured and the results are as follows: [0115] The Zeta Potential of Graphene Nanoplatelets in a 1 g/litre sodium cholate solution is −38.47 mV [0116] The Zeta Potential of Graphene Nanoplatelets diluted in de-ionized water is −17.55 mV.

[0117] This points to mechanism (i) dominating—ie the surfactant is weakly physisorbed on the surface and dilution in water allows the sodium cholate to desorb into the bulk.

[0118] If left unwashed, the presence of surfactant will cause an unacceptably high sheet resistance in subsequently produced graphene films. This is believed to be caused by the interaction between the surfactant and the electron layer within the graphene sheets. This is illustrated in the table below:

TABLE-US-00001 Estimated Measured Graphene surfactant resistance Surfactant Concen- concentration Viscosity [kOhm/ Level tration (g/L) [g/L] [cP] 5 mm spot] Low surfactant 1.1 2.2-2.3 2 20 High surfactant 1.7   17-25.5 2 >>1000

[0119] It is extremely difficult to maximize the concentration of graphene and minimize the level of surfactant. For example, typical approaches which involve evaporating off the water to concentrate the graphene will leave an even higher concentration of surfactant associated with the graphene. In addition, it should be appreciated that graphene is present as platelets (i.e. particles which are very thin but have a surface area, length and width many times greater than the thickness). For example, graphene flakes may have lengths up to 1000 μm and thicknesses as small as sub-nanometer to a few nanometers.

[0120] In Procedure C, a cross-flow filtration assembly 40 is used as illustrated in FIG. 5. The assembly 40 comprises a feed vessel 42 which initially receives the relatively dilute, surfactant-containing, graphene fluid from Procedure B.

[0121] The vessel 42 is connected to a cross-flow filtration device 44 via pipe 46 with which a peristaltic pump 48, having a flow rate rating of 120 litres/hour, is associated. An inlet pressure indicator 50 measures the pressure of fluid in the pipe 46. This is typically 2-3 barg. The system can be protected from overpressure by the use of a pressure switch or other relief device. The functioning of the device 44 is illustrated in FIG. 6. The unit comprises a body 52 in which many porous conduits 54 (only one of which is shown in FIG. 6 in the interests of clarity) are arranged. The conduits have a porous cylindrical wall with a 500 kDa pore size. In use, fluid from feed vessel 42 is introduced into the device 44 via inlet 56, at a pressure in the range 2-3 barg. By selection of a suitable pump with a variable speed drive, the same feed tank and pipework can be used to service multiple filter units, therefore increasing processing rates. The pressure on the permeate side of the porous cylindrical wall is ambient pressure although, in some cases, it could be pressurized. Thus, the pressure across the porous cylindrical wall, which serves to drive permeate through the wall, is 2-3 barg. From inlet 56, the fluid passes into the interior of conduits 54. As the fluid is forced, under pressure, through conduits 54, water containing associated surfactant passes through the pores as illustrated by arrows 56. Thus filtrate is led way from the unit 52 via a pipe 58 (FIG. 5) into a collection tank 60. Fluid containing graphene, which is too large to pass through the pores, passes down the conduit 54, as illustrated by arrows 62, and subsequently passes from unit 52 via outlet 64. By virtue of preferential removal of surfactant from the fluid, the concentration of surfactant relative to the concentration of graphene in the fluid which passes from unit 52 via outlet 64, is less than the concentration of surfactant in the fluid introduced into the device 44 via inlet 56. Fluid from outlet 64 can be recirculated, via pipe 66, as often as desired. Typically, it is recirculated twice per batch. Demineralised water may be added to vessel 42 to facilitate further removal of surfactant by device 44. Typically, the process uses 20 to 25 litres of demineralised water to wash 20 to 25 litres of graphene dispersion.

[0122] Thus, the device 44 is essentially operated in two modes: [0123] (i) a concentration step, whereby the graphene fluid from Procedure B is concentrated up by removal of permeates, aiming for a concentration of 1 g/L of graphene. [0124] (ii) a wash step in which the concentrated aqueous graphene dispersion is then mixed with fresh demineralised water and re-introduced into unit 52 and filtered. The procedure may be repeated until the conductivity of the permeate (i.e. the aqueous graphene dispersion passing through outlet 64) is below 5 micro S/cm measured using a standard conductivity meter at 20° C.

[0125] The performance of the unit 52 is monitored periodically by measuring the permeate flux. This gives an indication of the filtration rate per unit are of filtration membranes of the porous conduits 54. In general terms, it is found that permeate flux (i.e. filtration rate) starts off high, but decays with time to a reasonably steady state value of about 20 l/m.sup.2 hr. To offset this, the unit 52 may be operated for four days prior to regeneration of the conduits 54. Regeneration may involve flushing the conduits with a dilute caustic solution. The performance can be further improved by restricting the permeate flow from the permeate line by the use of a suitable restrictor valve, (thereby maintaining a steady flux.

[0126] Advantageously, device 44 can be used to increase the graphene concentration by ten times or more compared to the concentration of graphene in fluid at the end of Procedure B. Furthermore, the concentration of surfactant in the fluid at the end of Procedure C may be up to thirty times less than in fluid at the end of Procedure B.

[0127] Important parameters of device 44 are the circulation rate of fluid introduced and the pressure across the filtration membrane (i.e. the porous cylindrical wall). The circulation rate is set by the pump speed and must be high enough to prevent settling out in the conduits 54 but not too low so as to avoid fouling of the conduits due to settling of solids on surfaces of the conduits. It is desirable for the pressure across the membrane to be high, (within the limits of the filter and pipework design conditions); thereby to maximize the driving force to permeate removal. A variable speed drive can be used to set the pump speed and a pressure switch can be used to avoid over-pressurising the lines.

[0128] The concentrated aqueous graphene dispersion of Procedure C (e.g. having a conductivity in the range 3-5 micro S/cm) is next introduced into Procedure D which has the objective of removing as much residual graphite from the graphene dispersion as possible.

[0129] It is found that Procedures A to C can be used to produce a graphene dispersion in which about 99.9 wt % of the graphite has been removed. Typically, the dispersion includes 2 pbw graphene and 2 pbw graphite.

[0130] In Procedure D, a polishing step is undertaken which comprises centrifuging the graphene dispersion. The centrifugation step has a significant impact on the particle size distribution of the graphene dispersion as illustrated in FIGS. 7 and 8. As seen from FIG. 7, the volume distribution before centrifuging (represented by line 60) is significantly greater than after centrifugation (represented by line 62). Similarly, referring to FIG. 8, the particle size distribution on a number basis 64 is significantly greater before centrifugation than after (represented by line 66). In general terms, it is found that centrifuging for longer at high velocity results in production of smaller graphene nanoplatelets with fewer layers as larger nanoplatelets are lost in the centrifugal sludge At lower centrifuge velocities, there are reduced losses of platelets but there is greater potential for graphite to break through into the final product.

[0131] FIG. 9 is a comparison of the Raman traces of the graphene dispersion before Procedure D and the product after Procedure D. The most important features of the Raman spectra are the D band at about 1300 cm.sup.−1 and the G band at about 1600 cm.sup.−1. The bands are associated with defects and graphitic carbon respectively. The ratio of D to G band intensities is a measure of defect content. Referring to FIG. 9, the 2D peak before Procedure D, referenced 100, shows a “jagged” shape indicating multi-layered material (i.e. graphite) is present. The 2D peak after centrifugation, referenced 102, is more rounded which is consistent with graphene nanoplatelets of about 5-7 layers.

[0132] In a preferred embodiment, after procedure D the D/G ratio is 0.05 or below and graphite is not detected by Raman Spectroscopy.

[0133] The table below summarises characteristics of the process and products at various stages referred to in FIG. 1.

TABLE-US-00002 Stage Details Procedure A Reagents introduced into tank 10: graphite (3.5 kg) water (35 L) sodium cholate (35 g) this equates to: 100 g/L graphite 1 g/L sodium cholate the graphite contains less than 0.1 wt % inorganic residues in bulk phase. After Procedure A Fluid includes: and before   99 g/L graphite Procedure B 0.07 g/L graphene   1 g/L sodium cholate Bulk conductivity of fluid is 150-200 μS/cm After Procedure B Fluid includes: 0.1-0.2 g/L graphite 0.07 g/L graphene   1 g/L sodium cholate Bulk conductivity of fluid is 150-200 μS/cm About 25 L of fluid is fed into Procedure C. During Procedure C Uses 25 L of water to “wash” the material concentrate fluid in the process by factor of about 25 - i.e. 25 L from Procedure B is concentrated up to about 1 L. After Procedure C Fluid includes: 2.5-5 g/L graphite 1.75 g/L graphene 0.04 g/L sodium cholate Bulk conductivity of fluid is 3-5 μS/cm Approximately 1 L of fluid obtained at this stage. After Procedure D D/G ratio determined by Raman Spectroscopy. It was deemed to be a “pass” on the basis that its D/G was 0.5 or below. Fluid includes: 1.75 g/L graphene 0.04 g/L sodium cholate 2-5 wt % inorganic residues Bulk conductivity of fluid is 3-5 μS/cm

[0134] Features of the process described were further assessed and/or modified as described in the following examples.

EXAMPLE 1—ESTABLISHING BASE-LINE EXFOLIATING CONDITIONS

[0135] Procedure A was undertaken using the following features (i.e. reagents/conditions):

TABLE-US-00003 General Feature Specifics Graphite type Graphite (A) Mass of graphite 3.5 kg (100g/L graphite) Mass of sodium cholate  35 g (1g/L surfactant) Volume of water added  35 L Total exfoliation time 8 hours

[0136] The product was sampled every 30 minutes, centrifuged (speed 1500 rpm, 75 minutes. RCF: 500 g) to remove graphite flakes and graphene concentration analysed by UV spectrometry at 600 nm. Results are provided in the table below.

TABLE-US-00004 Exfoliation time (mins) Graphene concentration (g/L) 60 0.0066 120 0.012 180 0.017 240 0.017 300 0.021 360 0.022 420 0.027 480 0.029

EXAMPLE 2—ADJUSTING STARTING GRAPHITE CONCENTRATION

[0137] Compared to Example 1, the concentration of graphite in the fluid subjected to exfoliation was doubled, whilst maintaining the same concentration of sodium cholate surfactant. As a result, the ratio of wt % of graphite to surfactant is double compared to that in Example 1. The process undertaken had the following features:

TABLE-US-00005 General Feature Specifics Graphite type Graphite (A) Mass of graphite 7.0 Kg (200 g/L graphite) Mass of sodium cholate  35 g (1g/L surfactant) Volume of water added  35 L Total exfoliation time 6 hours

[0138] The product was sampled and assessed as described in Example 1 and results are provided in the table below.

TABLE-US-00006 Exfoliation time (mins) Graphene concentration (g/L) 60 0.03 120 0.04 180 0.06 240 0.09 300 0.12 360 0.13

[0139] FIG. 10 summarizes the results of Examples 1 and 2 from which the increased graphene concentration produced is clearly illustrated. This is particularly advantageous since increased graphene concentration is achieved using a higher graphite:surfactant ratio which is desirable since purification of the final produce may be facilitated and/or surfactant concentration in the final graphene product may be reduced.

EXAMPLE 3—ADJUSTING SURFACTANT LEVEL USED IN EXFOLIATION TO 400:1 (GRAPHITE:SURFACTANT)

[0140] The mass of surfactant used in the Example 1 process was varied so the ratio of the wt % of graphite to the wt % of surfactant was 400:1. The yield after 4 hours was only 0.005 g/L graphene which is significantly inferior to that achieved using a ratio of 100:1 (Example 1) or 200:1 (Example 2).

EXAMPLE 4—COMPARISON OF EFFECTIVENESS OF EXFOLIATION AT DIFFERENT RATIOS OF GRAPHITE TO SURFACTANT

[0141] The mass of surfactant used in Example 1 was varied so the ratio of the wt % of graphite to the wt % of surfactant was 300:1. Results are produced in FIG. 11 which also includes a comparison with ratios of 100:1 and 200:1. Thus, there appears to be a “sweet spot”. It will be appreciated that increasing the amount of surfactant does not necessarily increase the amount of graphene exfoliated from graphite; and reducing the amount of surfactant eventually leads to a very significant fall off in the amount of graphene produced.

EXAMPLE 5—EXFOLIATION AT 1000 L SCALE—BASE LINE CONDITIONS

[0142] Procedure A was undertaken using the following features (i.e. reagents/conditions):

TABLE-US-00007 General Feature Specifics Graphite type Graphite (A) Mass of graphite  75 kg (100 g/L graphite) Mass of sodium cholate 750 g (1 g/L surfactant) Volume of water added 750 L Total exfoliation time 6 hours

[0143] The product was sampled every 60 minutes, centrifuged (speed 1500 rpm, 75 minutes. RCF: 500 g) to remove graphite flakes and graphene concentration analysed by UV spectrometry at 600 nm. Results are provided in the table below.

TABLE-US-00008 Exfoliation time (mins) Graphene concentration (g/L) 60 0.015 120 0.029 180 0.04 240 0.056 300 0.074 360 0.083

[0144] The table above shows how the graphene exfoliation process can be scaled up from 50 L to 1000 L.

EXAMPLE 6—EXFOLIATION AT 1000 L SCALE—ADJUSTING STARTING GRAPHITE CONCENTRATION

[0145] Procedure A was undertaken using the following features (i.e. reagents/conditions):

TABLE-US-00009 General Feature Specifics Graphite type Graphite (A) Mass of graphite 150 Kg (200 g/L graphite) Mass of sodium cholate 750 g (1 g/L surfactant) Volume of water added 750 L Total exfoliation time 6 hours

[0146] The product was sampled every 60 minutes, centrifuged (speed 1500 rpm, 75 minutes. RCF: 500 g) to remove graphite flakes and graphene concentration analysed by UV spectrometry at 600 nm. Results are provided in the table below.

TABLE-US-00010 Exfoliation time (mins) Graphene concentration (g/L) 60 0.03 120 0.05 180 0.06 240 0.09 300 0.1 360 0.12

[0147] The product was sampled every 60 minutes, centrifuged (speed 1500 rpm, 75 minutes. RCF: 500 g) to remove graphite flakes and graphene concentration analysed by UV spectrometry at 600 nm. Results are provided in the table below.

[0148] The above table shows how increasing the graphite yield gives an increase in graphene yield.

EXAMPLE 7—EXFOLIATION AT 1000 L SCALE—USE OF SODIUM DODECYLBENZENESULPHONATE (SDBS) AS A SURFACTANT

[0149] Procedure A was undertaken using the following features (i.e. reagents/conditions):

TABLE-US-00011 General Feature Specifics Graphite type Graphite (A) Mass of graphite 225 Kg (300 g/L graphite) Mass of sodium 750 g (1 g/L surfactant) dodecylbenzenesulphonate Volume of water added 750 L Total exfoliation time 12 hours

[0150] The product was sampled every 60 minutes, centrifuged (speed 1500 rpm, 75 minutes. RCF: 500 g) to remove graphite flakes and graphene concentration analysed by UV spectrometry at 600 nm. Results are provided in the table below.

TABLE-US-00012 Exfoliation time (mins) Graphene concentration (g/L) 60 0.102 120 0.149 180 0.194 240 0.229 300 0.252 360 0.285 420 0.308 480 0.357 540 0.378 600 0.386 660 0.409 720 0.417
The table shows that:
1. SDBS is a viable surfactant. The material formed in Procedure A was successfully processed through Procedures B, C and E;
2. Increasing the starting graphite concentration gives an improvement in yield for a given time;
3. Increasing the production time gives an improvement in yield.

EXAMPLE 8—ABILITY TO DESTABILISE USING SULPHURIC ACID

[0151] A batch of concentrated dispersion produced according to Example 5, was “destabilised” by the addition of 0.225 g of concentrated sulphuric acid per litre of dispersion. This yielded 132 g of graphene nanoplatelet powder that was filtered in demineralised water and washed in acetone, subsequent to drying to yield a dryer graphene powder.

EXAMPLE 9—BORON NITRIDE EXFOLIATION AND SEPARATION IN THE 50 L REACTOR

[0152]

TABLE-US-00013 General Feature Specifics Boron Nitride Type Hexagonal Boron Nitride -particle = 100 micron Mass of graphite  1 kg (28.6 g/L Boron Nitride) Mass of sodium cholate 35 g (1 g/L surfactant) Volume of water added 35 L Total exfoliation time 6 hours

[0153] After exfoliation, the mixture was allowed to settle in the 50 L reactor. Approx 20 L of supernatant was extracted and allowed to settle for approximately 4 weeks. The samples were analysed using a Malvern Mastersizer and it was found that by both centrifugation and settling, the amount of larger flakes was reduced, leading to a dispersion that mainly consists of nanoplatelets.

[0154] Upon drying down the 20 L of supernatant, approximately 20 g of solid boron nitride nanoplatelets was obtained. This was a surprising result as the yield was almost 10 times higher than for graphene exfoliated from graphite, especially at a lower feed material loading. This suggests that BN exfoliates more readily than graphite, possibly due to weaker forces in between layers. Thus, the graphene production route described in FIG. 1 can also be used for BN production.