ELECTROCHEMICAL REACTOR FOR THE PRODUCTION OF GRAPHENE OXIDE NANOSHEETS

Abstract

The present description discloses an electrochemical reactor for the production of graphene oxide, as well as a method for the preparation of graphene oxide using the electrochemical reactor. The graphene oxide herein obtained exhibits a homogeneous degree of oxidation.

Claims

1. A dissolution cell comprising: a cylindrical container; an anode and a cathode immersed in an electrolyte, said anode, cathode and electrolyte contained within the cylindrical container; and an upper insulating disk and a lower insulating disk, wherein each of said insulating disks comprises a plurality of openings.

2. The dissolution cell according to claim 1, wherein the anode and the cathode are placed between the upper insulating disk and the lower insulating disk.

3. The dissolution cell according to claim 1, wherein the anode is a graphite rod comprising a threaded hole at the top thereof and a concentric hole at the bottom thereof.

4. The dissolution cell according to claim 1, wherein the cathode comprises a cylindrical body and three rods attached to said body, wherein said rods are used for electrical power supply and mechanical fastening, and wherein said rods are insulated with heat-shrinkable insulation so that they do not contribute any reaction area to the cathode.

5. The dissolution cell according to claim 1, wherein the electrolyte consists of a solution comprising sulphate ion.

6. The dissolution cell according to claim 5, wherein the electrolyte is a solution of ammonium sulfate.

7. The dissolution cell according to claim 6, wherein the electrolyte is a 0.1 mol/L solution of ammonium sulfate.

8. The dissolution cell according to claim 1, wherein the openings of the disks allow an upper face and a lower face thereof to be in fluid communication.

9. The dissolution cell according to claim 8, wherein the openings are in the form of portions of annular sections concentric to the disk.

10. The dissolution cell according to claim 8, wherein the upper disk further comprises a hole at the center thereof and the lower disk further comprises a cavity having a protrusion in the center thereof.

11. The dissolution cell according to claim 1, wherein the insulating disks maintain the distance between the anode and the cathode.

12. An electrochemical reactor comprising a dissolution cell according to claim 1, wherein the electrochemical reactor further comprises: a heat exchanger coupled to the dissolution cell; an extraction hood in the upper part of the dissolution cell; and a conical decanter in the lower part of the dissolution cell.

13. The electrochemical reactor according to claim 12, wherein the dissolution cell comprises side connectors located on an external surface thereof, wherein said side connectors allow coupling the dissolution cell to an external tube comprising the heat exchanger, and wherein said external tube and heat exchanger allow the recirculation of the contents inside the dissolution cell.

14. The electrochemical reactor according to claim 12, further comprising temperature sensors and a water flow meter.

15. The electrochemical reactor according to claim 12, wherein the dissolution cell further comprises a discharge valve in a lower part thereof, wherein below said discharge valve a sampling device is located.

16. A method for preparing graphene oxide comprising the following steps: electrochemically exfoliating a graphite electrode using an electrochemical reactor; emptying the cell and collecting the raw graphene oxide; removing graphite particles by sieving the raw graphene oxide; removing the residual electrolyte by filtration; resuspending the cake with distilled water; and 1 obtaining the graphene slurry.

17. The method according to claim 16, wherein the electrochemical exfoliation is carried out under the following conditions: current in a range of 290 A to 300 A, voltage in a range of 7 V to 24 V, and an electrolyte temperature in the range of 24 C. to 52 C., for a period of 180 h to 240 h.

18. The method according to claim 16, wherein the raw graphene oxide collected from the cell is sieved on a 100 m mesh stainless steel screen.

19. The method according to claim 16, wherein the filtration to remove residual electrolyte is performed using a double filter paper on a perforated support for 36 h to 38 h.

20. The method according to claim 16, wherein the resuspension of the cake is performed with a sonicator at a 3:1 weight ratio with distilled water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIGS. 1A and 1B show a schematic view of a first embodiment of the electrochemical reactor of the present invention.

[0051] FIGS. 2A and 2B show a side view and a top view of the lower insulating disk of the dissolution cell of the present invention.

[0052] FIGS. 3A and 3B show the current density distribution over an anode with an insulating disc.

[0053] FIGS. 4A and 4B show the current density distribution over an anode without an insulating disk.

[0054] FIG. 5 shows a schematic view and detailed views of the anode used in the dissolution cell of the present invention.

[0055] FIG. 6 shows an image of the cathode used in the dissolution cell of the present invention.

[0056] FIGS. 7A and 7B show a schematic view and an isometric view of a preferred embodiment of the electrochemical reactor of the FIG. 1.

[0057] FIGS. 8A and 8B show a perspective view and a lateral view of a second embodiment of the electrochemical reactor provided by the present invention.

[0058] FIG. 9 illustrates a schematic view of the installation for the operation of the electrochemical reactor of FIGS. 8A and 8B.

[0059] FIGS. 10A and 10B show a schematic view and an isometric view of a preferred embodiment of the electrochemical reactor of FIGS. 8A and 8B.

[0060] FIG. 11 shows a use of the electrochemical reactor of FIGS. 10A and 10B.

[0061] FIG. 12 shows TEM, FTIR and Raman characterization of the product obtained by the electrochemical reactor of FIGS. 7A and 7B.

DETAILED DESCRIPTION OF THE INVENTION

[0062] The present invention will be described in greater detail below, with reference to the accompanying Figures illustrating exemplary embodiments of the invention, which are not to be construed as limiting the invention.

[0063] In each of the Figures the same or similar reference numbers are used for each element of the device of the invention.

[0064] The present application discloses an electrochemical reactor, wherein the electrochemical reactor comprises a dissolution cell, which allows the production of graphene oxide (GO).

[0065] As understood according to the present description, the terms graphene oxide or GO refer to the compound typically obtained by oxidation of graphite, either by the application of oxidizing compounds, or by applying an oxidizing current to a graphite electrode, which consists of discrete layers of graphene with different degrees of oxidized groups dispersed within each layer.

[0066] FIGS. 1A and 1B show a schematic view of a first embodiment of the electrochemical reactor provided by the present invention, wherein said electrochemical reactor comprises a dissolution cell 100, comprising an upper section, a lower section, an external surface and an inner volume, wherein the dissolution cell further comprises a cylindrical container 101.

[0067] As can be seen in FIGS. 1A and 1B, the electrochemical reactor comprises a conical decanter 102 in the lower section that allows product separation. In addition, below the conical decanter 102, there is a valve 103 which allows the total emptying of the dissolution cell 100.

[0068] The cylindrical container 101 comprises two side connectors located on the external surface of the cylindrical container (that is, on the external surface of the dissolution cell), a side connector 104a at the top of the container 101 and a side connector 104b at the bottom of the container 101, wherein said connectors allow to recirculate the contents of the dissolution cell 100 within the dissolution cell when necessary.

[0069] The dissolution cell 100 of the electrochemical reactor provided by the present invention comprises an anode 105 and a cathode 106, as electrodes, an electrolyte in which said electrodes are immersed and two insulating disks, an upper insulating disk 107a and a lower insulating disk 107b, wherein the anode 105, the cathode 106 and the insulating disks 107a, 107b are located in the inner volume of the dissolution cell 100 (as shown in FIG. 1A). Particularly, the anode 105 and the cathode 106 are located between the upper insulating disk 107a and the lower insulating disk 107b.

[0070] A solution containing sulphate ion, in particular ammonium sulfate, is used as an electrolyte to intercalate and promote exfoliation. The solution comprises a concentration of ammonium sulfate (NH.sub.4).sub.2SO.sub.4 of 0.1 mol/L and a density of .sub.20 C.=1.0060 g/cm.sup.3. The preferred solution volume to be used is 10 L.

[0071] It should be noted that the electrochemical reactor of the present invention consists of a dissolution cell with parallel electrodes arranged in columns, i.e. arranged vertically, wherein the electrochemical reactor is controlled at constant current. The working current densities are in the range of 50i.sub.c200 mA/cm.sup.2 at a temperature of 25 C. The preferred initial current density is i.sub.c=100 mA/cm.sup.2. The reactor operates at constant current to improve electrochemical exfoliation control, i.e. to avoid a significant ohmic drop.

[0072] The cylindrical container 101 is a plastic tube, preferably a PVC tube, arranged vertically.

[0073] The internal diameter of cylindrical container 101 is about 153 mm and its height is about 600 mm. It should be understood that these dimensions can be modified as necessary, thus, said dimensions should not be construed as limiting the cylindrical container.

[0074] Referring to FIGS. 2A and 2B, these show a side view and a top view, respectively, of the lower insulating disk 107b of the dissolution cell of the present invention.

[0075] The insulating disks 107a, 107b located in the inner volume of the dissolution cell 100 are used to generate a homogeneous current density distribution and an even dissolution of the anode, and to maintain the distance between the electrodes.

[0076] Each insulating disk comprises a plurality of openings arranged therein, wherein said openings allow an upper face and a lower face of the disk to be in fluid communication.

[0077] In an exemplary embodiment, the openings (that is, their cross sections) are in the form of portions of annular sections concentric to the disk. In a preferred exemplary embodiment, the plurality of openings consists of a first group of openings and a second group of openings, wherein the openings of the first group of openings define portions of an annular section having a larger diameter than the annular section that is defined by the portions of the openings of the second group of openings, that is, the openings of the first group of openings are farther apart than the openings of the second group of openings with respect to the central longitudinal axis of the disk. In a more preferred exemplary embodiment, the openings of each of the first group and second group of openings are angularly spaced apart from each other in relation to the central longitudinal axis of the disk, as it can be seen in FIGS. 2A and 2B.

[0078] Particularly, in said FIGS. 2A and 2B, the first group of openings comprises four openings, wherein each opening is spaced both from the opening that follows it and from the opening that precedes it by 90 with respect to the central longitudinal axis; whereas the second group of openings comprises three openings, wherein each opening is spaced both from the opening that follows it and from the opening that precedes it by 120 with respect to the central longitudinal axis.

[0079] The differences between the upper disk 107a and the lower disk 107b are that the upper disk 107a comprises a hole at the center thereof, whereas the lower disk 107b comprises a cavity having a protrusion in the center thereof (as it can be seen in FIG. 2B).

[0080] The insulating disks 107a, 107b are made of plastic material, such as PVC.

[0081] In addition, the insulating disks 107a, 107b are used to maintain the distance between the electrodes. The openings of the insulating disks allow the recirculation of the contents inside the dissolution cell 100.

[0082] Furthermore, as can be seen in FIGS. 3A and 3B, the insulating disks 107a, 107b, allow to generate a homogeneous current density distribution and achieve an even dissolution of the electrode. It is also observed that the current density, in the areas close to the insulating disk, reaches i.sub.c135 mA/cm.sup.2 and an average of i.sub.c=100 mA/cm.sup.2, which is an acceptable value for the operation of an electrochemical reactor.

[0083] On the contrary, as can be seen in FIGS. 4A and 4B, when no insulating disk is used, the current density distribution is not homogeneous over the whole electrode surface, generating an uneven dissolution of the electrode. Therefore, the use of non-conductive insulating accessories, such as insulating disks, is necessary to mitigate the edge effects on the dissolution of the working electrode as it will be described in detail below.

[0084] FIGS. 5 and 6 show embodiments of the electrodes used in the dissolution cell of the present invention.

[0085] Particularly, FIG. 5 shows a schematic view and detailed views of the anode 105 which consists of a graphite rod comprising a threaded hole 108 at the top thereof and a concentric hole 109 at the bottom thereof, wherein said threaded hole 108 and concentric hole 109 are shown in more detail, respectively, in the detailed views of FIG. 5.

[0086] The threaded hole 108, located at the top of the rod, allows to hold a bolt as a mechanical fastener and current feeder, wherein said bolt is made of an inert material, such as titanium. It should be noted that said bolt, in order to be fastened with the threaded hole, passes through the hole of the upper disk.

[0087] The concentric hole 109 at the bottom of the graphite rod 105 is used for centering the anode. This centering is achieved by coupling the concentric hole 109 with the protrusion of the lower disk.

[0088] The graphite anode 105 has, preferably, 23 mm in diameter and, preferably, a height of 200 mm, and the hole 109 has, preferably 5 mm in diameter and is, preferably, 5 mm deep. It should be understood that these dimensions can be modified as necessary, thus, said dimensions should not be construed as limiting the anode 105.

[0089] Referring now to FIG. 6, this shows a perspective view of an exemplary embodiment the cathode 106, wherein said cathode 106 comprises a cylindrical body and three rods 110a, 110b, 110c, attached to said body, and wherein said rods are used for electrical power supply and mechanical fastening. Additionally, the rods 110a, 110b, 110c are insulated with heat-shrinkable insulation so that they do not contribute any reaction area to the cathode.

[0090] The cylindrical body of the cathode 106 is a tube made of stainless steel, preferably, AISI 304 stainless steel, that is placed inside the dissolution cell, between the upper and lower disks, as mentioned above.

[0091] In addition, said tube has a thickness of, preferably, 2 mm and an internal diameter of, preferably, 148 mm. It should be understood that these dimensions can be modified as necessary, thus, said dimensions should not be construed as limiting the cathode 106.

[0092] Referring to FIGS. 7A and 7B, these figures show a preferred embodiment of the electrochemical reactor provided by the present invention, wherein said electrochemical reactor further comprises a heat exchanger 211, temperature sensors 212a, 212b, 212c, 212d, a water flow meter 213, a sampling device 214 and an extraction hood 215.

[0093] In this preferred embodiment, the cylindrical container 201 is such that a section of the plastic tube is replaced by a glass tube, to allow the direct observation of the electrodes.

[0094] The heat exchanger 211 is coupled to an external tube that is coupled to the side connectors 204a, 204b (shown in FIG. 7B), wherein said external tube allows to connect said connectors 204a, 204b in fluid communication on the outside of the dissolution cell 200, thereby allowing the recirculation of the contents inside the dissolution cell 200. More precisely, the recirculation of the contents inside the dissolution cell 200 is achieved by means of temperature differences and, consequently, density differences, between the content that is located in the external tube and the content that is located within the dissolution cell 200, since the content in the external tube will be at a lower temperature, as it is being cooled by the cooling water of the heat exchanger 211, and the content within the dissolution cell will be at a higher temperature as the electrodes are subjected to current.

[0095] An extraction hood 215 is located on the upper part of the dissolution cell 200, in order to extract the produced gases.

[0096] As shown in FIGS. 7A and 7B, a sampling device 214 is provided in the lower discharge valve 203 to collect the decanting product. In addition, the temperature sensors 212a, 212b are placed close to the side connectors 204a, 204b in order to measure, respectively, the temperature of the contents exiting the dissolution cell 200 and entering the dissolution cell 200, thereby allowing to have an adequate temperature control of the contents stream X. In other words, said temperature sensors 212a, 212b allow measuring the temperature before the contents enter the heat exchanger zone and the temperature after the contents leaves the heat exchanger zone.

[0097] Regarding the temperature sensors 212c, 212d, these are placed, respectively, before the cooling water enters the heat exchanger zone and after the cooling water leaves the heat exchanger zone, to monitor the cooling water stream Y.

[0098] Additionally, the tubes that allows the cooling water to pass through the heat exchanger can comprise a water flow meter 213, as shown in FIG. 7A.

[0099] In this preferred embodiment, the cathode 206 is a stainless steel tube, preferably constructed with expanded metal; and the anode 205 is a graphite rod, preferably a graphite LK9001 rod with a density of 1.696 g/cm.sup.3. Both electrodes are located between the insulating disks 207a and 207b, as described for the embodiment of the electrochemical reactor of FIGS. 1A and 1B.

[0100] The use of a cathode constructed with expanded metal generates a shutter effect evacuating the generated bubbles (H.sub.2 gas) towards the back of the cathode, avoiding the increase of the cell voltage.

[0101] This preferred embodiment allows a continuous operation for about 23 hours, until the collapse of the anode. Table 1 shows the morphological change of the anode after the electrochemical exfoliation.

TABLE-US-00001 TABLE 1 Anode changes after 22 h 48 m of electrochemical exfoliation. Parameter Initial Final Variation Diametre (mm) 23.0 10.6 12.4 Mass (g) 131.9 24.0 107.9 Length (mm) 200.0 200.0 0 Area (cm.sup.2) 144.5 66.6 77.9

[0102] The electrochemical reactor of FIGS. 1A, 1B, 7A, 7B achieves a maximum current of 15 A, a maximum voltage of 10 V, while having a minimum production rate of 4.35 g/h of graphene oxide using a maximum power of 150 W.

[0103] FIGS. 8A and 8B illustrate another embodiment of the electrochemical reactor provided by the present invention, wherein said electrochemical reactor comprises a dissolution cell 300 and an overflow 316.

[0104] The overflow 316 located on the upper part of the dissolution cell 300 allows the exit of the solution and the collection of the product suspended in the solution.

[0105] FIG. 9 illustrates a schematic view of the installation for the operation of the electrochemical reactor of FIGS. 8A and 8B, wherein said installation comprises a dissolution cell 300, a tank 317, a heat exchange system 311 and a separation unit 302.

[0106] In this embodiment, the tank 317 is a recirculating tank that allows to increase the capacity, i.e., to introduce a larger volume of electrolyte into the dissolution cell.

[0107] In addition, the heat exchange system 311 is located within the electrolyte solution tank 317 to control the temperature of the solution supplying the system 311 with 5 KW of power, and to avoid wasting water. Preferably, the heat exchange system 311 is either a chiller, a coil, or a cooling tower; and more preferably the heat exchange system is a water cooler in series with an exchange coil.

[0108] The flow of the electrolyte solution is carried out by forced circulation using a centrifugal pump 318, so that an upward flow is generated inside the vertical cylindrical dissolution cell 300 allowing the renewal of electrolyte solution inside the cell and the exit of the product from the top of the dissolution cell.

[0109] At the outlet of dissolution cell 300, a separation operation is carried out. Preferably, the separation operation 302 consists of a separation or decanting step.

[0110] The dissolution cell 300 of the electrochemical reactor of FIGS. 8A and 8B comprises an anode (not shown), a cathode (not shown) and an electrolyte solution in which they are immersed. Preferably, the anode is a cylindrical graphite rod, more preferably a cylindrical graphite rod of 75 mm diameter and 1500 mm length. It should be understood that these dimensions can be modified as necessary, thus, said dimensions should not be construed as limiting the anode. The preferred cathode is made of stainless steel, and more preferably of AISI 304 stainless steel.

[0111] In this embodiment, the electrolyte comprises a solution of ammonium sulfate at 0.1 mol/L.

[0112] Referring to FIGS. 10A and 10B, these figures show a schematic view and an isometric view of a preferred embodiment of the electrochemical reactor. In this preferred embodiment, the exfoliation, separation and heat exchange stages are carried out in a single unit.

[0113] By using the electrochemical reactor of FIGS. 10A and 10B, the separation of the product by means of decanting operations is possible, when the exfoliated graphene agglomerates are broken by shear stresses (agitation, pumping, transfer, etc.).

[0114] As can be seen in FIGS. 10A and 10B, the electrochemical reactor of this preferred embodiment comprises a dissolution cell 400 comprising an upper portion, a lower portion, an external surface and an inner volume, wherein said electrochemical reactor further comprises a conical decanter 402, a heat exchange system 411 and two side connections 404a, 404b.

[0115] The conical decanter 402 in the lower portion allows product separation. The conical decanter volume is, preferably, about 5 L. In addition, underneath the conical decanter, a clamp discharge valve 403 is provided to allow the total emptying of dissolution cell 400.

[0116] A sampling device 414 is incorporated into the lower discharge valve 403 to collect the decanting product.

[0117] The temperature control is carried out by a heat exchanger 411 through constant recirculation of cooling water in the dissolution cell 400, wherein a fraction of the cooling water circulates through a cooling tower.

[0118] An electrolyte reservoir (not shown) is connected to the dissolution cell 400 through the side connectors 404a, 404b.

[0119] In this preferred embodiment, the cathode (not shown) consists of a stainless steel tube, preferably an AISI 304 stainless steel tube; and the anode (not shown) consists of a graphite rod, preferably a graphite LK1802, and more preferably a graphite LK1802 graphite rod having 75 mm in diameter and 1500 mm in length. It should be understood that these dimensions can be modified as necessary, thus, said dimensions should not be construed as limiting the cathode. Both electrodes are immersed in a 0.1 mol/L ammonium sulfate electrolyte solution, as in the above embodiments.

[0120] Within the dissolution cell electrolyte homogenization is generated due to the production of gases (hydrogen, carbon dioxide and oxygen) from water electrolysis and the electrolyte exfoliation. The total electrolyte solution volume used is about 31 L.

[0121] This preferred embodiment allows a continuous operation for about 74 continuous hours, until the collapse of the anode. Table 2 shows the morphological change of the anode after electrochemical exfoliation.

TABLE-US-00002 TABLE 2 Anode changes after 74 h 31 min of electrochemical exfoliation. Parameter Initial Final Variation voltage (60 C.) (V) 10.1 12.3 2.2 Current (A) 300 300 0 dissolved mass (g) 601.54 4307 3705.46 Diametre (mm) 73 59 14 Current density (mA/cm.sup.2) 88.21 109.34 21.13

[0122] An extraction hood 415 is located on the upper section of the dissolution cell 400, in order to extract the gases produced.

[0123] The electrochemical reactors of FIGS. 10A, 10B can operate at a maximum current of 250 A, a maximum voltage of 20 V, a maximum power of 5000 W and a minimum production of 41 g/h of graphene oxide.

[0124] If needed, two or more electrochemical reactors corresponding to the electrochemical reactor shown in FIGS. 10A, 10B may be arranged in parallel to form an industrial installation as shown in FIG. 11.

[0125] FIG. 11 shows an application of the electrochemical reactor of FIGS. 10A, 10B and an industrial installation. The installation comprises an electric panel 519, an electrolyte solution tank 517, a secondary decanter 520, one or more dissolution cells 500, a cooling tower 511 and one or more extraction hoods 515.

[0126] The electrolyte solution enters the tank 517 and then circulates to the dissolution cells 500. As previously mentioned, said dissolution cell 500 may comprise one or more dissolution cells as depicted in FIGS. 10a, 10b, arranged in parallel.

[0127] The electrolyte is recirculated through a cooling tower 511, a pump is used to generate an upward flow inside the cooling tower.

[0128] The electrolyte is a solution containing sulphate ion, in particular ammonium sulfate. The solution comprises ammonium sulfate at a concentration of (NH.sub.4).sub.2SO.sub.4 of 0.1 mol/L and has a density of .sub.20 C.=1.0060 g/cm.sup.3.

[0129] The product obtained by the one or more dissolution cells 500 present in the installation can be conveyed to a secondary decanter 520 for further separation.

[0130] One or more extractions hoods 515 are provided above the dissolution cells 500, in order to extract the gases produced.

[0131] A cathode of stainless steel and an anode of graphite are used. Preferably, anodes which have already been partially exfoliated in the electrochemical reactor described in FIGS. 10A, 10B are used, to optimize resources such as electrical power and cooling capacity.

[0132] Preferably, the operating conditions of the industrial installation described in FIG. 11, comprise a maximum current of 900 A, a maximum voltage of 24 V, a maximum power of 216000 W and a minimum production of 150 g/h of graphene oxide.

[0133] Considering the equipment of the installation presented in FIG. 11, another aspect provided by the present invention is to provide a method for preparing graphene oxide by using the electrochemical reactor provided by the present invention.

[0134] The method is carried out according to the following steps, electrochemically exfoliating a graphite electrode using the electrochemical reactor provided by the present invention; emptying the cell and collecting the raw graphene oxide; removing graphite particles by sieving the raw graphene oxide; removing the residual electrolyte by filtration; resuspending the cake with distilled water; and obtaining the graphene slurry.

[0135] In a preferred embodiment, the electrochemical exfoliation using the electrochemical reactor provided by the present invention is carried out under the following conditions: current in a range of 290 A to 300 A, voltage in a range of 7 V to 24 V, and an electrolyte temperature in the range of 24 C. to 52 C., for a period of 180 h to 240 h.

[0136] In a preferred embodiment, the raw graphene collected from the cell is sieved on a 100 m mesh stainless steel screen.

[0137] In a preferred embodiment, the filtration to remove residual electrolyte is performed using a double filter paper on a perforated support for 36 h to 38 h.

[0138] In a preferred embodiment, the resuspension of the cake is performed with a sonicator at a 3:1 weight ratio with distilled water.

[0139] The graphene slurry obtained can be diluted to the required concentration.

EXAMPLES

Product Characterization

[0140] The degree of oxidation of GO is strongly dependent on the process by which it is obtained and is typically characterized by the carbon/oxygen (C/O) ratio of the compound. Such C/O ratio may be determined by spectroscopic techniques, such as, for example, X-ray photoelectron spectroscopy (XPS). Preferably, the C/O ratio of the GO obtained by the electrochemical reactor provided by the invention is 8.7 and the oxidization degree is between 5-20%, more preferably between 5-10%.

[0141] Several samples of graphene nanosheets produced by means of the embodiments of the electrochemical reactors provided by the present invention were collected. These samples were characterized by Transmission Electron Microscope (TEM), Raman, FTIR and XPS spectroscopies, where all the characterizations showed that all the analyzed samples present homogeneity among them.

[0142] Table 3 and FIG. 12 show the results obtained when oxidizing graphite with the electrochemical reactor described in FIGS. 7A, 7B, i.e., under the following conditions: maximum current of 15 A, a maximum voltage of 10 V, a maximum power of 150 W and a minimum production of 4.35 g/h of graphene oxide, a temperature of 60 C.

TABLE-US-00003 TABLE 3 Product quality obtained by the electrochemical reactor of FIGS. 6a, 6b. Characterization Result Raman ID/IG = 1.1 0.2 XPS (%) C: 90.9% S: 0.4% O: 0.4% N: 0.5% Z potential 30 mV

[0143] In addition, the samples obtained by the electrochemical reactor described in FIGS. 8A, 8B also showed homogeneity between them. Table 4 and 5 show the results obtained by Raman and XPS spectroscopies and the technical characteristics of the product, under the following conditions: maximum current of 900 A, a maximum voltage of 24 V, a maximum power of 21.6 KW and a minimum production of 150 g/h of graphene oxide, a temperature of 60 C.

TABLE-US-00004 TABLE 4 Product quality obtained by the electrochemical reactor of FIGS. 8A, 8B. Characterization Result Raman ID/IG = 1.1 0.2 XPS (%) C: 88.1%, 90.7%, 93.7% S: 0.6%, 0.4%, 0.2% O: 10.1%, 8.2%, 5.6% N: 1.1%. 0.8%, 0.6%

TABLE-US-00005 TABLE 5 Technical characteristics of the product obtained by the electrochemical reactor of FIGS. 8A, 8B. Form Powder Lateral size (SEM) <50 m Colour Black Odour Odourless Dispersibility Polar solvents pH 6 Raman intensity ratio (I.sub.D/I.sub.G) 1.0 0.1 C/O atomic ratio (XPS) 8.7 Thickness Few layer graphene (FLG) Zeta potential 32.8 1.9 (mV)

[0144] Finally, samples of the product obtained by the electrochemical reactor shown in FIGS. 10A, 10B using partially exfoliated anodes, were studied. The results are similar to those obtained in the previous embodiments.

TABLE-US-00006 TABLE 6 Product quality obtained by the electrochemical reactor of FIGS. 10A, 10B using partially exfoliated anodes. Characterization Result Raman ID/IG = 1.1 0.2 XPS (%) C: 88.1% S: 0.6% O: 10.1% N: 1.1%

[0145] These results show that by using the electrochemical reactor of the present invention at a current of 50 A, GO nanoparticles have an oxidation degree of 5-10% with a lateral size of less than 50 m, 1-3 atomic layers.

[0146] Finally, after one year of operation, Table 7 summarizes the Raman and XPS spectroscopy results of the graphene oxide nanoparticles produced, corroborating a continuous production of similar characteristics.

TABLE-US-00007 TABLE 7 Raman and XPS spectroscopy results of the graphene oxide nanoparticles produced. Operating time Raman XPS (%) (months) (ID/IG) C S N O 1 1.1 +/ 0.2 88.63 1.09 1.54 8.75 3 1.1 +/ 0.2 90.48 0.12 0.68 8.7 6 1.1 +/ 0.2 88.49 0.3 0.41 10.8 9 1.1 +/ 0.2 91.35 0.45 0.33 7.87 12 1.1 +/ 0.2 89.06 0.78 0.72 9.45