GRAPHENE SEPARATION

Abstract

The present invention relates to a method of producing graphene and/or graphene oxide. The method comprises providing a copper-based sheet coated on one side with a carbonaceous material; providing a bath comprising an aqueous solution comprising a salt of at least one ion selected from Li.sup.+, Na.sup.+, K+, Mg.sup.2+ or Ca.sup.2+, in which bath a first electrode is arranged; feeding the copper-based sheet into the bath; applying a first voltage between the copper-based sheet and the first electrode; applying a second voltage, reversed as compared to the first voltage, between the copper-based sheet and the first electrode, such that graphene and/or graphene oxide is exfoliated from the carbonaceous material. The present invention also relates to a system for producing graphene and/or graphene oxide. The present invention also relates to a graphene material formed as crystalline, self-supporting hexagonal flakes. The present invention also relates to a graphene material formed as crystalline, self-supporting flakes comprising dendrites.

Claims

1. A method of producing graphene and/or graphene oxide comprising the steps of: providing a copper-based sheet coated on at least one side with a carbonaceous material; providing a bath comprising an aqueous solution comprising a salt of at least one ion selected from Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, in which bath a first electrode is arranged; feeding the copper-based sheet into the bath; applying a first voltage between the copper-based sheet and the first electrode, such that the at least one ion is intercalated into the carbonaceous material; applying a second voltage, reversed as compared to the first voltage, between the copper-based sheet and the first electrode, such that the graphene and/or graphene oxide is exfoliated from the carbonaceous material.

2. The method of producing the graphene and/or graphene oxide according to claim 1, wherein the carbonaceous material comprises a graphene film arranged on an amorphous carbon substrate.

3. The method of producing the graphene and/or graphene oxide according to claim 1, wherein the carbonaceous material comprises graphite.

4. The method of producing the graphene and/or graphene oxide according to claim 1, wherein the copper-based sheet is fed into the bath by a feeding device comprising a plurality of rollers.

5. The method of producing the graphene and/or graphene oxide according to claim 4, wherein the first electrode is arranged as a roller in the plurality of rollers.

6. The method of producing the graphene and/or graphene oxide according to claim 1, further comprising a step of: filtering the aqueous solution to collect the graphene and/or graphene oxide and to provide a filtered aqueous solution comprising copper ions.

7. The method of producing the graphene and/or graphene oxide according to claim 6, further comprising a step of: reducing the copper ions of the filtered aqueous solution on the copper-based sheet.

8. The method of producing the graphene and/or graphene oxide according to claim 1, wherein the salt comprises Na.sup.+ or Ca.sup.2+.

9. The method according to claim 1, wherein the graphene and/or graphene oxide exfoliated from the carbonaceous material comprises crystalline, self-supporting hexagonal graphene flakes having an average size of at least 1 ?m.sup.2 and/or wherein the graphene and/or graphene oxide exfoliated from the carbonaceous material comprises crystalline, self-supporting graphene flakes having an average size of at least 1 ?m.sup.2, the flakes having a plurality of dendrites.

10. A system for producing graphene and/or graphene oxide comprising: a copper-based sheet coated on one side with a carbonaceous material; a bath comprising an aqueous solution comprising a salt of at least one ion selected from Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+; a feeding device for feeding the copper-based sheet into the bath; a first electrode configured to be arranged in the bath; a voltage controlling means configured to apply a first and a second voltage between the copper-based sheet and the first electrode, wherein the second voltage is reversed as compared to the first voltage.

11. The system for producing the graphene and/or graphene oxide according to claim 10, wherein the feeding device comprises at least one powered roller configured to feed the copper-based sheet and at least one passive roller configured to guide the copper-based sheet through the bath.

12. The system for producing the graphene and/or graphene oxide according to claim 11, wherein the passive roller is configured to be arranged in the bath and wherein the passive roller comprises the first electrode.

13. A graphene material formed as crystalline, self-supporting hexagonal flakes having an average size of at least 1 ?m.sup.2.

14. The graphene material according to claim 13, wherein an area of a flake is defined by six connected line segments, wherein adjoining line segments are connected at six vertices, and wherein the internal angle at each vertex is in the range of 110?-130?.

15. A graphene material formed as crystalline, self-supporting flakes having an average size of at least 1 ?m.sup.2, the flakes having a plurality of crystal dendrites.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] The invention will be described with reference to the following figures, in which:

[0096] FIG. 1a is a schematic illustration of intercalation of ions into a carbonaceous material according to the present invention.

[0097] FIG. 1b is a schematic illustration of exfoliation of graphene and/or graphene oxide from the carbonaceous material according to the present invention.

[0098] FIG. 2 is a schematic illustration of a system according to the invention.

[0099] FIG. 3a is a scanning electron micrograph of a hexagonal carbon flake according to the invention.

[0100] FIG. 3b is a scanning electron micrograph of several hexagonal carbon flakes according to the invention.

[0101] FIG. 4 is a scanning electron micrograph of a graphene flake comprising dendrites according to the invention.

[0102] FIG. 5 is a scanning electron micrograph of carbonised bio-oil on a copper plate.

[0103] FIG. 6a-b are scanning electron micrographs of graphene flakes in different magnification.

DETAILED DESCRIPTION

[0104] FIGS. 1a and 1b show schematic illustrations useful for understanding the process for producing graphene and/or graphene oxide of the present invention. In FIG. 1, the step of applying a first voltage between the copper-based sheet and the first electrode, such that the at least one ion is intercalated into the carbonaceous material is schematically illustrated. FIG. 1a shows the carbonaceous material 101 deposited on a copper based sheet 103. The carbonaceous material is depicted herein as layers 101a-b of graphene held together by weak forces. When a voltage is provided between the copper material 103 and the first electrode 105, the ions 107 are attracted towards the copper material. Given that the ions are selected from Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, the first voltage is applied such that the copper-based sheet 103 is a negative electrode and the first electrode 105 a positive electrode. At least some of the ions may intercalate between the layers 101a-c and form intercalated ions 107a. The size of the ions will extend the distance between the graphene layers 101a-c, which weaken the bond between them.

[0105] FIG. 1b depicts the situation when the second voltage is applied. The second voltage is reversed as compared to the first voltage, making the copper based-sheet 103 a positive electrode and the first electrode 105 a negative electrode. Upon application of the second voltage, the intercalated ions 107 will be attracted by the first electrode 105. This will cause them to travel from the intercalated position. During said travel, the ions will alleviate the exfoliation of graphene and/or graphene oxide in the form of a flake 107c which is exfoliated from the carbonaceous material.

[0106] FIG. 2 shows a schematic illustration of a system 200 producing graphene and/or graphene oxide. The system 200 is provided with a copper based sheet 203 coated with a carbonaceous material 201. The copper based sheet 203 is rolled onto a first roller 211 in a feeding device 213, guided through a bath 215 by a first set of passive guide rollers 217a-d, and rolled up on a second roller 219. The first and second rollers 211, 219 are preferably motorised such that the copper-based sheet can be fed into the bath 215, conveyed through the bath 215 by the first set of guide rollers 217a-d arranged in the bath and a second set of guide rollers 218a-d arranged above the surface of the aqueous solution in the bath, and taken out of the bath 215. The bath contains an aqueous solution comprising a salt of at least one ion selected from Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.2+ or Ca.sup.2+, such as Ca.sup.2+. In the bath, at least one of the passive guide rollers 217 a-d is arranged as a first electrode 205 being a platinum electrode. In the example shown in the illustration, there is arranged a set of counter-electrodes 221a-d.

[0107] During the time a portion of the copper based sheet 203 coated with carbonaceous material 201 is in the bath 215, a first voltage between the copper-based sheet 203 and the first electrode 205 is applied, such that the at least one ion is intercalated into the carbonaceous material 203. Also during the time a portion of the copper based sheet 203 coated with carbonaceous material 201 is in the bath 215, a second voltage, reversed as compared to the first voltage, is applied between the copper-based sheet 203 and the first electrode 205, such that graphene and/or graphene oxide is exfoliated from the carbonaceous material 203.

[0108] The first and second voltages are applied by a voltage controlling means 223, such as a potentiostat. The voltage controlling means 223 is configured to apply a first voltage in the range of range of ?8 V to ?2 V, such as in the range of ?6 V to ?2 V, and a second voltage in the range +2 V to 12 V, such as in the range +2V to +8 V, such as in the range +2 V to +6 V.

[0109] The first voltage may be applied for a period of at least 0.5 seconds, such as for a period of at least 1 second such as for a period of 1 second to 5 seconds.

[0110] The second voltage may be applied for a period less than 0.15 seconds, such as of less than 0.1 seconds. Preferably, the second voltage is applied for a shorter time than the first voltage in order not to risk oxidation of the copper.

[0111] The bath 215 is further provided with a liquid outlet 225 having a valve 225a. The liquid outlet is preferably in liquid connection with a filter 227 via a pump 230, such that the aqueous solution can be filtered in a filter 229 to separate the graphene and/or graphene oxide from the aqueous solution. After the graphene has been removed, the aqueous solution may comprise carbonaceous debris and copper ions. It is contemplated that a minor part of the copper-based sheet 203 has been oxidized to copper ions now present in the aqueous solution during the application of the first and second current.

[0112] After the exfoliation, the copper based sheet 203 may be subjected to cleaning to remove carbonaceous debris from its surface. The cleaning may be performed using sonification means (not shown).

[0113] The cleaned copper based sheet 203 may be fed into a container 250 comprising an electrode 245, the aqueous solution and the copper ions. The copper based sheet is the subjected to a negative potential 240 capable of reducing the copper ions on the copper surface. This way, a method and system which provides for minimal consumption of the copper substrate is be obtained.

[0114] FIG. 3a shows an annotated scanning electron micrograph of a hexagonal graphene flake according to the invention. The graphene flake 300 has an area defined by six connected line segments 301-306, wherein adjoining line segments are connected at six vertices 307-312, and wherein the internal angle at each vertex is in the range of 110?-130?, such as of approximately 120?. It is contemplated that the hexagonal shape is indicative of a highly crystalline and pure graphene. The flake is self-supporting in the sense that it is not provided on a substrate. Instead, it can support its own weight.

[0115] FIG. 3b shows a micrograph in lower magnification, depicting several hexagonal graphene flakes.

[0116] FIG. 4 show an annotated scanning electron micrograph of graphene flakes comprising dendrites according to the invention. The flake 401 comprises a plurality of dendrites 402. It is contemplated that the dendritic state is a precursor state to the hexagonal shape shown in FIG. 3. The flake is self-supporting in the sense that it is not provided on a substrate. Instead, it can support its own weight.

EXAMPLES

Example 1

[0117] A carbon based composite material was prepared according to the following. 0.5 grams of soft wood lignin form the Lignoboost process known to a person skilled in the art was provided to a beaker along with 0.4 grams of deionized water, 0.05 g of poly(vinyl alcohol) (PVA) solution (10 mol-% PVA in water) and 1.05 g of isopropanol to form a slurry. The slurry was thereafter transferred to a ball mill (Planetary Mill Pulverisette) where the slurry was milled using grinding balls having a diameter in the range of 0.6-0.8 mm, in an amount of approximately two times the weight of the slurry. The slurry was milled in a scheme of 5?30 minutes, with a rest period of 15 minutes between each milling repetition. The milled slurry was thereafter collected from the mill using 60 ml a 1:1 solution of isopropanol and water. After milling, the milled slurry was treated in an ultrasonic bath. The milled slurry was electrocoated on a copper based sheet in the form of a copper roll in a continuous roll-to-roll system, in the same concentration as milled to obtain a layer of slurry which substantially covered both sides of the copper substrate sheet. The slurry was then allowed to dry on the copper surface for approximately 30 minutes.

[0118] The slurry deposited copper sheet was then heated in a tubular oven at a reaction temperature of approximately 805? C. in an inert atmosphere. The inert atmosphere was formed by purging the oven with argon gas. The slurry deposited copper surface was then subjected to the reaction temperature for ca 30 min. A hydrogen gas flow in the oven was 500 cc/min. After 30 minutes of heating, the oven was purged with argon gas. After this treatment, an intermediate product which comprised a carbon based composite material comprising a graphene film arranged on amorphous carbon was provided on the copper substrate sheet.

[0119] The copper roll was then provided between a first active roller and a second active roller and rolled through a bath containing an aqueous solution with a concentration of CaCl.sub.2) of about 0.004 M. In the bath, there was provided four guide rollers. The guide rollers were provided as platinum electrodes. The copper based sheet was rolled on the platinum electrodes through the bath. In the bath, there was provided 4 counter electrodes. The platinum electrodes and the counter electrodes were connected to a potentiostat running with a galvanostatic pulse sequence. A first voltage of ?4 V was applied by the potentiostat between the copper substrate sheet and the platinum electrodes. This caused Ca.sup.2+ ions from the aqueous solution to intercalate between the graphene film and the amorphous carbon. A second voltage of +4 V with reversed voltage compared to the first voltage was then applied between the copper substrate sheet and the platinum electrodes. The second voltage pulled graphene and/or graphene oxide from the carbon based composite material as the intercalated ions travels towards the platinum electrode. The first and second voltages were pulsed in an alternating manner, with each period of the first voltage being about 1.1 seconds, and each time period of the second voltage being of about 0.1 seconds. Graphene flakes were removed into the aqueous solution with minimal copper consumption.

[0120] The aqueous solution was then drained from the bath and through a filter press in which graphene and graphene oxide flakes were separated from the aqueous solution.

[0121] The copper surface sheet was then fed through a sonication bath and subsequently into a bath containing the aqueous solution and an electrode. A reduction was performed in the bath to reduce copper ions oxidized during the application of the first and second voltage back onto the copper sheet substrate.

[0122] The obtained graphene and graphene oxide were studied in a scanning electron microscope. As is shown in FIGS. 3a-b, graphene flakes formed as crystalline, self-supporting hexagonal flakes having an average size of at least 1 ?m.sup.2 was obtained. As shown in FIG. 4 crystalline, self-supporting flakes having an average size of at least 1 ?m.sup.2, the flakes having a plurality of crystal dendrites was obtained.

Example 2

[0123] A carbon based composite material was prepared according to the following. 0.5 grams of a bio-oil was electrocoated on a copper based sheet in the form of a copper roll in a continuous roll-to-roll system, to obtain a layer of bio-oil which substantially covered both sides of the copper substrate sheet.

[0124] The bio-oil deposited copper sheet was then heated in a tubular oven at a reaction temperature of approximately 820? C. in an inert atmosphere. The inert atmosphere was formed by purging the oven with argon gas. The bio-oil copper surface was then subjected to the reaction temperature for ca 30 min. A hydrogen gas flow in the oven was 350 cc/min. After 40 minutes of heating, the oven was purged with argon gas. After this treatment, an intermediate product which comprised a carbon based composite material comprising a graphene film arranged on graphite was provided on the copper substrate sheet. The results were confirmed using scanning electron microscopy. FIG. 5 is a scanning electron micrograph showing the carbon based composite material 501 on the copper substrate sheet 502.

[0125] The copper roll was then provided between a first active roller and a second active roller and rolled through a bath containing an aqueous solution with a concentration of K.sub.2SO.sub.4 of about 0.001 M. In the bath, there was provided four guide rollers. The guide rollers were provided as platinum electrodes. The copper based sheet was rolled on the platinum electrodes through the bath. In the bath, there was provided 4 counter electrodes. The platinum electrodes and the counter electrodes were connected to a potentiostat running with a galvanostatic pulse sequence. A first voltage of ?10 V was applied by the potentiostat between the copper substrate sheet and the platinum electrodes. This caused K.sup.+ ions from the aqueous solution to intercalate between the graphene film and the graphite, and/or into the graphite. A second voltage of +2 V with reversed voltage compared to the first voltage was then applied between the copper substate sheet and the platinum electrodes. The second voltage pulled graphene and/or graphene oxide from the carbon based composite material as the intercalated ions travels towards the platinum electrode. The first and second voltages were pulsed in an alternating manner, with each period of the first voltage being about 1.1 seconds, and each time period of the second voltage being of about 0.1 seconds. Graphene flakes were removed into the aqueous solution with minimal copper consumption.

[0126] The aqueous solution was then drained from the bath and through a filter press in which graphene and graphene oxide flakes were separated from the aqueous solution.

[0127] The copper surface sheet was then fed through a sonication bath and subsequently into a bath containing the aqueous solution and an electrode. A reduction was performed in the bath to reduce copper ions oxidized during the application of the first and second voltage back onto the copper sheet substrate.

[0128] The obtained graphene and graphene oxide were studied in a scanning electron microscope. Using scanning electron microscopy, it was confirmed that graphene flakes were formed, see FIGS. 6a-b. FIGS. 6a-b are scanning electron micrographs showing the formed graphene flakes positioned on a SiO.sub.2 plate.

[0129] As exemplified by examples 1 and 2, it has been realised that the inventive concept pertaining to graphene separation can be performed using any carbonaceous material.

[0130] Additionally, variations to the disclosed embodiments and examples can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.