Production of aqueous graphene oxide for use as a concrete admixture

Abstract

Aqueous dispersions of graphene oxide are produced in an additive process by subjecting graphitic carbon, such as biochar, in water or an aqueous solution to a high shear environment in the presence of a dispersing agent to exfoliate the graphene oxide. An intercalating agent may be added to facilitate exfoliation and may optionally be neutralized. The graphitic carbon can be pretreated by wet-milling prior to exfoliation. Aqueous dispersions of graphene oxide can be used as a concrete admixture in concrete compositions.

Description

[Technical Field]

[0001] The present disclosure relates to auxiliary materials for strengthening concrete, and in particular to the preparation of graphene oxide-based admixtures for concrete mixtures. [Background technology]

[0002] Modern high-strength concrete is expensive to produce and often suffers from cracking and spalling, primarily due to its porous nature. Supplementary cementitious materials (SCMs) such as fly ash, slag, or silica fume have helped to mitigate this to some extent, as have advanced water-reducing agents such as polycarboxylic ethers (PCEs), but these materials are expensive and can face supply uncertainty (e.g., fly ash as coal-fired power plants decline).

[0003] Nanocarbon and micronized biochar additives have been proposed for use in the design of high-strength concrete mixtures; however, there are challenges facing the commercialization of nanocarbon concrete additives; costs can potentially be high even when used at low mix ratios; strong van der Waals forces between nanocarbon particles create a tendency for nanocarbon additives to agglomerate, preventing effective dispersion in the concrete matrix; smaller biochar particle sizes have been shown to produce better results, but particle size reduction using typical comminution equipment (e.g., ball mills, attritors, sonicators) is limited and cost-prohibitive. [Brief explanation of the drawings]

[0004] [Figure 1] FIG. 1 is a flow chart illustrating the high-level manufacturing process of aqueous oxidized biographene. [Figure 2] FIG. 2 is a schematic diagram of a first exemplary system for the production of aqueous oxidized biographene. [Figure 3] FIG. 3 is a schematic diagram of a second exemplary system for the production of aqueous oxidized biographene. DETAILED DESCRIPTION OF THE INVENTION

[0005] The following embodiments and examples provide a method for producing a graphene oxide-based additive using a low-cost, highly scalable, high-shear, liquid-phase exfoliation technique with a dispersant. When added to concrete, this additive, hydrous bio-graphene oxide (hBGO), provides enhanced hydration and micro-reinforcement, enabling it to meet or exceed the performance of SCMs and superplasticizers commonly used in the production of high-strength concrete, but at a lower cost and from renewable biomass feedstocks.

[0006] Briefly, as shown in Figure 1, a graphitic carbon source is provided in a solvent and subjected to liquid-phase exfoliation in a high-shear environment using a dispersing agent, preferably an aqueous surfactant or water-miscible solvent, to produce a stable aqueous graphene dispersion (graphene oxide, or GO) that can be more easily dispersed into a concrete matrix. Preferably, biochar provides (three-dimensional) graphitic carbon for the production of sustainable (two-dimensional) graphene carbon (biographene oxide, or BGO). Biochar is a heat-generating carbonaceous material produced by thermochemical conversion (e.g., by pyrolysis, carbonization, and / or activation) of renewable carbonaceous biomass feedstocks. In contrast, activated carbon can be produced from any carbon source, including fossil sources, waste materials, or renewable resources. Methods for carbonizing feedstocks will be known to those skilled in the art.

[0007] The method can include one or more preparatory or intermediate steps, such as wet milling, the use of an intercalating agent (which may subsequently be fully or partially neutralized), and at least partial exfoliation. These additional steps can facilitate the exfoliation and dispersion of the oxidized biographene when subjected to high shear liquid phase mixing.

[0008] Graphene oxide generally has an affinity for both polar and non-polar solvents, so either type of solvent can be used, although in the case of concrete admixtures it may be desirable to use water or another polar water-soluble solvent in the dispersion to ensure compatibility with the concrete mixture.

[0009] The surfactant in the dispersion reduces the surface tension of water and adsorbs to the two-dimensional graphene. This helps induce dispersion and reduce aggregation of the exfoliated BGO crystals and few-layer biographene oxide (FLBGO) particles, which have strong van der Waals attractive forces. This provides a more stable colloidal dispersion of BGO that does not need to be redispersed (or can be easily redispersed) prior to application at the ready-mix plant or job site. Furthermore, the better the colloidal stability of BGO, the greater the probability that it will be uniformly dispersed in the alkaline mortar or concrete matrix, resulting in optimal performance from BGO and / or FLBGO.

[0010] Surfactants and solvents for use in the present method include lignosulfonates, polycarboxylic acid ethers (PCE), dihydrolevoglucosenone (DLGO, e.g., Cyrene®), sodium dodecyl sulfate (SDS), sodium cholate, supercritical carbon dioxide (scCO2), poloxamers (Pluronics®), saponins, and combinations thereof. The appropriate selection of surfactants and / or solvents can be made by one skilled in the art based on the desired effect on concrete. For example, lignosulfonates are recognized as important admixtures for concrete as plasticizers and set retarders and have been shown to be effective dispersants for graphene. PCE is also recognized as an important admixture for concrete as a superplasticizer and an effective dispersant for graphene in cement paste. DLGO has similar solubility properties to graphene and is a good solvent for rapid exfoliation and stable dispersion. While low concentrations of aqueous-phase anionic and nonionic surfactants are known to provide good results for dispersing graphene oxide via liquid-phase exfoliation, anionic polymeric surfactants such as lignosulfonates and PCEs may be selected when polydispersed, i.e., water-reducing polymers, are desired in the preparation of composite matrices. The inclusion of lignosulfonates or PCEs in the dispersant can, in fact, provide a dual benefit to concrete mixes, as they are both useful water reducers and plasticizers for concrete.

[0011] Intercalation chemicals can be used to facilitate the process of high-shear liquid-phase exfoliation. Intercalation reversibly inserts molecules or ions into materials with layered structures, such as graphitic carbon, increasing the interplanar spacing and subsequently reducing interlayer van der Waals forces, aiding in the mechanical exfoliation of the graphitic carbon. An appropriate intercalating agent can be selected by one skilled in the art to provide a source of ions small enough to enter the interplanar spaces in the graphitic carbon. Examples of agents suitable for use in concrete admixtures include potassium hydroxide (KOH), sodium hydroxide (NaOH), and lithium hydroxide (LiOH). Strong caustic intercalating agents can induce functionalization and etching (the formation of oxygen functional groups and defects on the flat surfaces and edges of the carbon sheets), both of which are potentially beneficial when hBGO is used as a concrete additive because they can provide nucleation sites that promote the hydration of cement particles.

[0012] Strong caustic intercalants can significantly increase the pH of hBGO (up to 14), which can cause challenges in handling and use as an admixture and can also lead to aggregation or clumping of aqueous BGO particles (small particles tend to clump under high pH conditions). To mitigate the issues of high pH mixing and aggregation or clumping, the pH of hBGO may be lowered to a more neutral range (e.g., 7 or 8). Selection of an appropriate neutralizing agent is known to those skilled in the art. For example, an acid such as acetic acid can be added to the dispersion directly or in solution. As another example, the hBGO dispersion may be sparged with carbon dioxide (CO), which is optionally collected as waste CO. When combined with water, the CO produces carbonic acid, which is available for reaction. In the case of KOH, NaOH, or LiOH used as intercalants, they react with carbonic acid to form potassium carbonate (K2CO3), sodium carbonate (Na2CO3), or lithium carbonate (Li2CO3), which are water-soluble salts and are compatible with concrete when included as admixtures, if not advantageously. Furthermore, such neutralization with CO2 will act as a method of sequestration of carbon in concrete without adversely affecting mechanical performance.

[0013] The inclusion of approximately 0.1% hBGO by weight in concrete can achieve early strength development, resulting in increased compressive strength, flexural strength / ductility, and reduced permeability without adversely affecting workability. Without wishing to be bound by theory, it is believed that these performance improvements can be attributed to enhanced hydration, i.e., increased formation of calcium silicate hydrate (CSH) crystals. This is due to the diverse oxygen functional groups of BGO, which provide strong nucleation sites for hydrated crystals. This increased hydration can result in increased consumption of mixing water for the formation of CSH crystals, meaning that higher water ratios can be used for concrete, improving concrete workability without compromising strength or increasing porosity. Furthermore, because BGO particles are hygroscopic, they can help retain water within the concrete matrix and provide nanohardening for enhanced hydration at the capillary and gel pore level (<10 nm). Furthermore, graphene oxide is known to provide nanoreinforcement in the concrete matrix, contributing to fractured fractal planes. Finally, graphene oxide particles have been shown to act as a type of antifreeze, limiting ice crystal growth, which can impart additional resistance to the harmful effects of freeze-thaw cycles to concrete.

[0014] It should be noted that the amount of hBGO required in a concrete mix to produce a beneficial effect is relatively small compared to the amounts of other commonly used ingredients, such as SCMs. This means that the inclusion of hBGO is unlikely to affect the proportions of other components of the mixture (water, cement, admixtures), allowing for the continued use of previously developed concrete formulations. Furthermore, when hBGO is produced using lignosulfonate or PCE, which are already commonly used admixtures, hBGO can provide a source of admixture in the concrete mix, reducing the amount of additional lignosulfonate or PCE that needs to be added.

[0015] FIG. 1 is a flowchart illustrating a process for producing an hBGO dispersion for use in concrete mixes. In a first example, a graphitic carbon source, such as biochar, is provided at S1 and dispersed (doped) in a solvent (e.g., water) at S2. A dispersant is added at S7, and the mixture is exfoliated under high shear at S8. In a further exemplary embodiment, one or more additional steps are optionally performed before the addition of the dispersant. The initial dispersion in the solvent at S2 can result in an initial reduction in graphitic carbon particle size (e.g., <300 microns). The carbon is then optionally wet-milled at S3 to further reduce particle size. As a further optional step, an intercalating agent may be added at step S4 to facilitate the exfoliation step S5. After this exfoliation step, a neutralizing agent is optionally introduced at S6, and a dispersing agent (such as lignosulfonate, PCE, or other suitable agent) is added at S7 to improve stability and reduce agglomeration in the hBGO dispersion. The mixture is then subjected to a high shear mixing environment in a stripping step, S8, which may be continued until the concentration and particle size distribution of BGO in the dispersion reaches the desired target range.

[0016] Those skilled in the art will appreciate that these steps can be modified, reordered, or combined. For example, in a first implementation, the initial step of dispersion in a solvent S2 and the addition of a dispersant S7 can be effectively combined by providing an aqueous solution of the dispersant and then combining it with graphitic carbon for exfoliation in step S8. The wet-milling step, if performed, can be combined with the introduction of an intercalating agent (which can be added to the solvent used during wet-milling), or alternatively, the addition of the intercalating agent can occur in the exfoliation step S5. The order of addition of the dispersant and neutralizing agent can be reversed, or the two components can be added together to the hBGO; or the dispersant can be added before or during exfoliation. The final concentration and particle size distribution of BGO in the aqueous dispersion can be adjusted by adding one or more components during the final exfoliation in S8, although such adjustments can also be made earlier in the process if desired.

[0017] Figure 2 is a schematic diagram of an exemplary system 100 for the production of hBGO. Briefly, biochar and an aqueous dispersant (in this example, aqueous lignosulfonate) are fed into a high-shear mixer by a dosing system under operator control to produce dispersed hBGO at a specific concentration according to the desired application. The resulting hBGO can be fed into a concrete batch mixer.

[0018] In the exemplary system 100, a biochar source 15, in this example a primary hopper, feeds biochar to a secondary hopper 25 via a rotating feeder 20. A load cell 30 measures the weight of biochar fed into the secondary hopper until a predetermined amount is contained within the secondary hopper. The output of the load cell 30 is directed to a digital controller 10 (e.g., a programmable logic controller, desktop computer, or other suitable microprocessor-based computing system), which monitors the sensor output and, based on operator input 5, controls the operation of various components of the system, such as valves and a high-shear pump. Once the digital controller 10 determines that the target amount of biochar has been obtained from the primary hopper 15, the biochar in the secondary hopper 25 is released via a slide gate valve 35 to a high-shear pump 40.

[0019] Aqueous dispersant is stored in tank 45 and fed to high shear pump 40 through flow control valve 50. A flow meter 60 in communication with digital controller 10 monitors the flow from tank 45 to determine the (approximate) amount of dispersant entering pump 40. The flow of dispersant into pump 40 draws biochar into the inlet stream and into the volute of high shear pump 40. When a certain amount of dispersant is detected entering pump 40, digital controller 10 closes valve 50.

[0020] A variable frequency drive 42 (e.g., a Silverson variable frequency drive) of high shear pump 40 (e.g., a variable frequency drive) capable of rotating a rotor or impeller to provide high shear mixing. TMThe High Shear Inline Mixer (Silverson Machines, Inc., Massachusetts, USA) is controlled by a digital controller. When pump 40 is activated, its rotor generates mechanical and hydraulic forces to drive suspended biochar particles (typically larger than 50 microns) toward the stator, crushing, exfoliating, and dispersing the BGO in an aqueous dispersion to produce hBGO. The resulting hBGO is directed through an outlet and open valve 55 (valve 75 may be closed at this stage) to an hBGO holding vessel or tank 60, where the concentration of BGO in the dispersion is measured using an inline ultraviolet-visible (UV-vis) spectrophotometer 65, which can be used to estimate the concentration from UV-vis light absorbance measurements. When the hBGO dispersion is within a specified UV-vis absorbance range, valve 75 can be opened and the hBGO can be dispensed into a concrete drum mixer. Alternatively, the hBGO can be repeatedly recycled through valve 70 to high shear pump 40, where additional dispersant, biochar, or both can be added to the pump for further shear until the concentration of BGO meets a specified range.

[0021] The concentration and, optionally, quality of hBGO can be determined by other means. As another example, the particle size distribution of BGO in the dispersion may be measured using an in-line laser diffraction sensor (not shown in FIG. 1 ) based on particle size estimates derived from diffraction of laser radiation photons by hBGO. If the determined particle size distribution is within a target range (e.g., the quality target may be set at 90% below 50 microns, consistent with the typical particle size of Portland cement), valve 75 can be opened and the hBGO can be dispensed into a concrete drum mixer. Otherwise, as described above, the hBGO can be repeatedly recycled through valve 70 to high-shear pump 40, where additional dispersant and / or biochar can optionally be added to the pump for further shearing until the particle size of the BGO meets a specified range. Those skilled in the art will understand that other known sensors and techniques may be used to determine the concentration of BGO or the quality of hBGO.

[0022] Because the input biochar and dispersant are under computer control, the specific composition of the resulting hBGO can be specified by the operator to suit a particular application. For example, it may be desirable to have a specific target concentration of lignosulfonate or PCE (if used as a dispersant) in the concrete mix. Different compositions can be provided based on the target composition of biochar (e.g., by weight) and the target ratio of biochar to dispersant in the final concrete mix. These inputs, along with any constraints (e.g., maximum dispersant dosage in concrete), can be used to determine the dispersant and biochar input rates or amounts for the high shear pump 40 and the target concentration or concentration range of BGO in the hBGO produced by the high shear pump 40. Furthermore, because the system allows for customization of the BGO concentration in the hBGO for a desired concrete mix, the system can be provided on a skid that can be transported to a job site, so that hBGO dispersions can be produced on-demand on-site ready to be mixed with concrete. Alternatively, hBGO can be manufactured off-site, dispensed into plastic or metal containers for storage, and transported to the concrete manufacturing or mixing facility in either colloidal or dry form.

[0023] The aforementioned exemplary process can be performed on pre-calculated amounts of graphitic carbon source and aqueous dispersant to produce a predetermined concentration of hBGO for use as a concrete admixture. In another exemplary process, the components of the final admixture may be calculated and dosed during dispersion or exfoliation. FIG. 3 is a schematic diagram of a further exemplary system 200 for the production of hBGO. As previously described, a similar dosing system controlled by operator input 5 to digital controller 110 can be used to receive sensor inputs from various points within system 200 and control valves, pumps, and mixers to appropriately cycle the flow of components, as would be understood by one of ordinary skill in the art. Thus, in this exemplary system, graphitic carbon source (e.g., biochar) in primary hopper 115 is fed into secondary hopper 120 via rotary feeder 118 until digital controller 110 determines from load cell 122 feedback that the target amount has been received in the secondary hopper. The biochar is then dispensed (e.g., by opening a slide valve) into high-shear dispersion unit 130, where it is initially dispersed in water. The amount of water may also be controlled by the digital controller 110, which monitors the output from a flow meter 132. The water and graphitic carbon are subjected to a high shear environment, such as a high shear dispersing unit 130, such as the high shear pump described above. Another example of a suitable unit is the Quadro® Ytron ZC pump manufactured by Quadro Engineering Corp. of Waterloo, Ontario, Canada. TM If additional wet-grinding and / or intercalation steps are to be performed, the initial dispersion is pumped using pump 140 to another high shear environment, such as a high shear wet-grinding unit 150, where the particle size of the biochar can be further reduced and exfoliation can occur. A suitable unit 150 is the Quadro® HV Disperser, available from Quadro Engineering Corp. TM Includes Emulsifier & Wet Mill.

[0024] The dispersion is circulated through unit 150 and tank reactor 160 using pump 140. While in tank reactor 160, the dispersion may be continuously mixed by mixer 170 to produce a substantially uniform dispersion. One or more sensors (e.g., pH meter 162, temperature sensor 164, spectrophotometer 166, and / or laser diffraction sensor 168) are also provided to detect the concentration and / or particle size distribution and / or quality of the hBGO, and, optionally, to effect dosing of intercalating agents, neutralizing agents, and dispersing agents. The intercalating agents are dispensed into tank reactor 160, for example, using a dosing pump, where they are mixed by mixer 170. The dispersion is circulated by pump 140 through high shear wet-milling unit 150, where the BGO is exfoliated (or further exfoliated), and then circulated back to tank reactor 160, where one or more sensors measure properties of the dispersion until a target value or range (e.g., BGO concentration and / or particle size distribution) is achieved. Once the target is achieved, the intercalant is optionally neutralized by the addition of a neutralizing agent. For example, the dispersion can be sparged with CO from a local flue gas source until a pH sensor 162 indicates that the target pH range has been reached, or an appropriate dosage of neutralizing agent based on the amount of intercalant is calculated and introduced into the tank reactor 160. A dispersing agent, such as an aqueous surfactant, can then be added and mixed into the hBGO dispersion in the tank reactor 160. The dispersion can then be circulated through unit 150 for stripping until the final BGO concentration and target particle size distribution are achieved. The final dispersion can then be dispensed.

[0025] As will be appreciated by those skilled in the art, the exemplary processes and variations described above provide a "one-pot" synthesis of stable hBGO dispersions ready for use as concrete admixtures, in that the process generates virtually no waste because no further separation or purification steps are required to remove intermediate chemicals or by-products. The chemicals selected for use in the example methods serve a dual purpose by both facilitating the production of graphene oxide from graphitic carbon and enhancing the effectiveness of graphene oxide as a concrete additive. Due to the high atomic economy of the process, costs and productivity can be kept low, and waste can be minimized.

[0026] Accordingly, there is provided a concrete additive comprising an aqueous dispersion of aqueous graphene oxide, wherein the graphene oxide may be biographene oxide.

[0027] Further provided is a method for making an aqueous dispersion of graphene oxide, the method comprising subjecting graphitic carbon in water or an aqueous solution in the presence of a dispersing agent to a high shear environment to exfoliate the graphene oxide.

[0028] In one embodiment, the method further comprises adding a dispersing agent to the graphitic carbon in the water or aqueous solution prior to subjecting the graphitic carbon in the water or aqueous solution to a high shear environment.

[0029] In another embodiment, the method further comprises the step of wet-milling said graphitic carbon in said water or aqueous solution prior to the step of adding said dispersing agent.

[0030] In a further aspect, the method further comprises adding an intercalating agent to said graphitic carbon in said water or aqueous solution prior to or simultaneously with subjecting said graphitic carbon in said water or aqueous solution to a high shear environment.

[0031] In another aspect, the intercalating agent comprises a caustic intercalating agent. The intercalating agent comprises at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide. In some embodiments, the intercalating agent comprises potassium hydroxide.

[0032] In yet another aspect, the method further comprises neutralizing the exfoliated graphene oxide in the water or aqueous solution prior to adding the dispersing agent. Neutralization can include adding an acid or sparging the exfoliated graphene oxide in the water or aqueous solution with carbon dioxide.

[0033] In a further aspect, the step of subjecting the graphitic carbon in the water or aqueous solution to a high shear environment comprises circulating the graphitic carbon in the water or aqueous solution in a high shear wet milling process.

[0034] In some embodiments, the graphitic carbon is provided in an aqueous solvent solution that is water.

[0035] In one embodiment, the dispersant comprises at least a lignosulfonate and / or a polycarboxylic acid ether.

[0036] In yet another aspect, the method further comprises determining the amount of graphitic carbon and the amount of dispersing agent required for the concrete composition by receiving the graphitic carbon and the dispersing agent in the aqueous solution in a predetermined ratio, measuring the concentration or particle size distribution of graphene oxide in the aqueous dispersion after exfoliation, and recirculating the graphene oxide in the aqueous dispersion in a high shear environment according to the measured concentration or particle size distribution.

[0037] In a further aspect, the graphitic carbon is biochar and the exfoliated graphene oxide is exfoliated biographene oxide.

[0038] Also provided is a concrete admixture comprising an aqueous dispersion of graphene oxide.

[0039] In one embodiment, the graphene oxide is biochar-derived graphene oxide.

[0040] In another embodiment, the aqueous dispersion comprises a dispersant, the dispersant comprising at least a lignosulfonate and / or a polycarboxylic acid ether.

[0041] In a further aspect, the concrete admixture comprises potassium carbonate and / or sodium carbonate.

[0042] In another aspect, the concrete admixture comprises at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide. In one embodiment, the admixture comprises potassium hydroxide.

[0043] In yet another aspect, the concrete admixture further comprises a water reducer or plasticizer.

[0044] The concrete admixture may be included in a concrete composition.

[0045] Also provided is an apparatus for producing aqueous graphene oxide, the apparatus comprising: a graphitic carbon source; a dispersant source; a high shear device having an inlet in fluid communication with the graphitic carbon source and the dispersant source, the high shear device comprising: a vessel in fluid communication with an outlet of the high shear device and configured to contain the aqueous graphene oxide; and at least one measurement means for determining at least one property of the graphene oxide contained in the contained aqueous graphene oxide. In one embodiment, the high shear device comprises a wet-grinding unit.

[0046] In one embodiment, the device further comprises an intercalant source having an outlet in fluid communication with the container.

[0047] In another aspect, the apparatus further includes a neutralizing agent source having an outlet in fluid communication with the container.

[0048] In a further aspect, the at least one characteristic comprises pH, graphene oxide concentration, and / or particle size distribution.

[0049] In yet another embodiment, the at least one measuring means includes a pH meter, a spectrophotometer, and / or a laser diffraction sensor.

[0050] Those skilled in the art will appreciate that the systems shown in Figures 2 and 3 can be modified so long as the production of hBGO dispersions is achieved. Various elements can be omitted or combined. For example, the preliminary wet-milling step in unit 150 of system 200 of Figure 3 prior to exfoliation in aqueous dispersion can be omitted or combined with the addition of an intercalating agent. In some embodiments, wet-milling can be performed without the addition of an intercalating agent and / or a neutralizing agent. A dispersing agent can be added to the dispersion prior to circulation through the high-shear wet-milling unit. Different types of sensors can be employed to measure the properties or quality of the produced hBGO. Such modifications are well within the capabilities of those skilled in the art.

Claims

1. 1. A method for producing an aqueous dispersion of graphene oxide, comprising: The method comprises: receiving biochar and a dispersant in a predetermined ratio; subjecting the biochar in a solvent comprising an aqueous solution of the dispersant to a high shear rotor-stator mixing environment to exfoliate graphene oxide; measuring the concentration or particle size distribution of graphene oxide in the solvent after exfoliation using at least one in-line sensor in the high shear rotor-stator mixing environment; adding one or more of biochar, dispersing agents, intercalating agents, or neutralizing agents to the biochar in the solvent in accordance with the measured concentration or particle size distribution; and further subjecting the biochar in the solvent to the high shear rotor-stator mixing environment to exfoliate graphene oxide and further measure the concentration or particle size distribution until the measured concentration or particle size distribution reaches a target range; Includes.

2. adding the dispersant to the biochar in water before subjecting the biochar to the high shear rotor-stator mixing environment to exfoliate; The method of claim 1, thereby comprising providing the biochar in the solvent.

3. 3. The method of claim 1 or 2, further comprising wet-milling the biochar in the solvent prior to subjecting the biochar in the solvent to the high shear rotor-stator mixing environment to exfoliate.

4. 4. The method of any one of claims 1 to 3, further comprising adding an intercalating agent to the biochar in the solvent prior to or simultaneously with subjecting the biochar in the solvent to the high shear rotor-stator mixing environment for exfoliation.

5. the intercalating agent comprises a caustic intercalating agent; the intercalating agent is added to the biochar in the solvent prior to subjecting the biochar to the high shear rotor-stator mixing environment for exfoliation; The method comprises: performing an initial exfoliation of the biochar in the solvent in the presence of the intercalating agent to provide exfoliated graphene oxide in the solvent; 5. The method of claim 4, further comprising the step of adding a neutralizing agent prior to subjecting the exfoliated graphene oxide to the high shear rotor-stator mixing environment in a further exfoliation step.

6. 6. The method of claim 5, wherein adding the neutralizing agent comprises sparging the exfoliated graphene oxide in the solvent with carbon dioxide.

7. The method of any one of claims 1 to 6, wherein the high shear rotor-stator mixing environment comprises high shear wet milling.

8. The method of any one of claims 1 to 7, wherein the dispersant comprises a lignosulfonate, a polycarboxylic ether, or a composition of at least a polycarboxylic ether and a lignosulfonate.

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