Electrochemical graphene oxide nanosheet production

Abstract

The present disclosure relates to graphene oxide nanosheet comprising nitrogen incorporated into its structure and to an electrochemical process for producing graphene oxide nanosheets comprising nitrogen incorporated into its structure from carbon fibres. In one embodiment of the process, carbon fibres are immersed in an acidic electrolyte solution and subjected to an electric potential to induce electrochemical exfoliation, yielding nitrogen-incorporated graphene oxide nanosheets. The method enables controlled oxidation and tuneable material properties, including nanosheet thickness, lateral dimensions, and functionalization. Compared to conventional graphite-based methods, this process offers enhanced scalability, reproducibility, and environmental sustainability. The disclosure further includes a production system, and the use of the produced nanosheets in energy storage, composite materials, coatings, flexible electronics, and tribological applications.

Description

[0001] Graphene Oxide Nanosheet Production

[0002] Technical field

[0003] The present disclosure relates to the production of graphene oxide nanosheets and to processes for producing such nanosheets.

[0004] Background

[0005] Graphene oxide has attracted considerable interest in applications such as energy storage, composite materials, electronics, and advanced coatings due to its unique two-dimensional structure and high surface area. Conventionally, graphene oxide is synthesized by chemically oxidizing natural graphite using well-established methods. These processes typically involve the use of strong acids and oxidizing agents to disrupt the van der Waals forces between graphene layers, facilitating exfoliation into nanosheets.

[0006] While these chemical oxidation techniques have enabled large-scale graphene oxide production, they often come with inherent drawbacks. High concentrations of strong acids and oxidants contribute to substantial chemical consumption and environmental concerns. Additionally, these methods require prolonged reaction times and energy intensive conditions to achieve sufficient exfoliation, leading to increased processing costs. Another challenge lies in product consistency, as variations in oxidation levels and nanosheet morphology across production batches can impact material performance in downstream applications.

[0007] To address these limitations, alternative feedstocks and processing strategies have been investigated. Some efforts focus on improving scalability, while others aim to reduce environmental impact or enhance material uniformity. However, many existing techniques struggle to balance oxidation efficiency with process control, minimize degradation while ensuring effective exfoliation, and maintain adaptability for different carbon sources. Furthermore, the reliance on natural graphite, a nonrenewable resource, raises concerns about long-term supply sustainability. Accordingly, there remains a need for an improved method of producing graphene oxide nanosheets that offers enhanced scalability, reduced environmental footprint, and improved process control. Ideally, such a method would mitigate the challenges associated with conventional techniques while maintaining compatibility with large- scale production and diverse material applications.

[0008] Summary

[0009] The present disclosure relates to an electrochemical process for producing graphene oxide nanosheets, addressing key limitations in conventional methods that rely on natural graphite and chemically aggressive oxidation techniques. Traditional approaches, such as the Hummers and Brodie methods, employ highly concentrated acids and strong oxidizing agents, leading to excessive chemical consumption, energy- intensive processing, and significant environmental impact. Moreover, these processes often result in inconsistent oxidation levels, uncontrolled defect formation, and batch-to- batch variability, limiting scalability and reproducibility.

[0010] In contrast, the disclosed method provides a controlled, tuneable, and scalable alternative by utilizing carbon fibres as a feedstock and an acidic electrolyte solution to facilitate electrochemical exfoliation under moderate reaction conditions. This novel approach eliminates the reliance on mined graphite, offers greater precision in oxidation control, and enables the direct incorporation of nitrogen functional groups, which is not achievable in conventional chemical oxidation techniques. By maintaining adjustable process parameters, including acid concentration, applied potential, and reaction time, the method allows for customization of nanosheet properties while improving yield, reproducibility, and environmental sustainability.

[0011] Thus, in one aspect, the present disclosure relates to A method for producing graphene oxide nanosheets, comprising:

[0012] (a) immersing carbon fibres in an acidic electrolyte solution;

[0013] (b) applying an electric potential to the immersed carbon fibres to electrochemically exfoliate the fibres; and

[0014] (c) separating and collecting the exfoliated material. In a further aspect, the present disclosure relates to a system for producing graphene oxide nanosheets, comprising:

[0015] (a) a reaction chamber configured to contain an acidic electrolyte solution;

[0016] (b) a fibre feed mechanism configured to introduce carbon fibres into the reaction chamber, such as wherein the carbon fibres are selected from the group consisting of PAN-based carbon fibres, pitch-based carbon fibres, rayon-based carbon fibres, and lignin-based carbon fibres;

[0017] (c) an electrode assembly configured to apply an electric potential to the carbon fibres for electrochemical exfoliation; and

[0018] (d) a collection unit configured to separate and collect the graphene oxide nanosheets.

[0019] In another aspect, the present disclosure relates to a computer- readable medium storing instructions which, when executed by a processor, cause the processor to control a production unit to perform the method for producing graphene oxide nanosheets as disclosed herein.

[0020] In another aspect, the present disclosure relates to use of graphene oxide nanosheets produced by the method for producing graphene oxide nanosheets as disclosed herein, in applications selected from the group consisting of energy storage devices, composite materials, coatings, flexible electronics, and tribological applications.

[0021] In another aspect, the present disclosure relates to a graphene oxide nanosheet comprising nitrogen incorporated into its structure.

[0022] The disclosed process provides a controlled and efficient method for producing graphene oxide nanosheets, offering advantages over conventional approaches that rely on high voltages, excessive oxidizing agents, and extreme reaction conditions. By operating under moderate acid concentrations and carefully regulated electric potentials, the method achieves effective exfoliation while minimizing structural degradation and excessive oxidation, leading to improved consistency in nanosheet morphology, fewer defects, and enhanced reproducibility. A key distinguishing feature of this process is the ability to incorporate nitrogen into the graphene oxide structure during exfoliation, unlike traditional oxidation techniques that primarily introduce oxygen functionalities. This unexpected effect enables further tunability in surface chemistry, making the resulting graphene oxide suitable for energy storage, catalysis, and advanced coatings. Additionally, the scalability of the process — whether implemented in batch or continuous configurations — enhances its industrial viability, offering a flexible and efficient route for graphene oxide production with optimized material properties.

[0023] Detailed description

[0024] In a first aspect, the present disclosure relates to a graphene oxide nanosheet comprising nitrogen incorporated into its structure. Unlike conventionally produced graphene oxide, which is primarily functionalized with oxygen-containing groups, the disclosed nanosheets exhibit nitrogen doping as a direct result of an electrochemical exfoliation process. This incorporation occurs during oxidation in a nitric acid-based electrolyte, wherein nitrogen species interact with the carbon lattice, forming stable nitrogen functional groups. The presence of nitrogen within the nanosheets can enhance material properties such as surface reactivity, dispersibility, and catalytic performance.

[0025] In one embodiment, the nitrogen content in the graphene oxide nanosheets may be at least 0.1 atomic%, such as at least 0.5 atomic%, at least 1 atomic%, at least 2 atomic%, or at least 3 atomic%. The nitrogen incorporation may also be less than 10 atomic%, such as less than 8 atomic%, less than 6 atomic%, or less than 5 atomic%. In some implementations, the nitrogen content may be within a range of 0.1 atomic% to 5 atomic%, 0.5 atomic% to 4 atomic%, 1 atomic% to 3 atomic%, or 1 atomic% to 2 atomic%, depending on the electrochemical conditions used. X-ray photoelectron spectroscopy (XPS) analysis, as shown in FIG. 4f, has confirmed nitrogen incorporation, distinguishing the disclosed nanosheets from conventional chemically exfoliated graphene oxide, which typically lacks nitrogen functionalization.

[0026] In one embodiment, the amount of impurities in the graphene oxide nanosheets is less than 10 atomic%, preferably less than 5 atomic%, more preferably at least 1 atomic%. By these features, the graphene oxide nanosheets achieve a high degree of purity. The nitrogen present in the graphene oxide nanosheets may exist in the form of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, or combinations thereof. These nitrogen species contribute different functionalities to the material. Pyridinic and pyrrolic nitrogen typically enhance surface reactivity and catalytic properties, while graphitic nitrogen can modify the electronic structure, improving electrical conductivity. The ability to control the distribution and type of nitrogen functionality provides tunability for applications such as energy storage, electrocatalysis, and water purification. In one embodiment, the nitrogen present in the graphene oxide nanosheets may exist in the form of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, pyridinic nitrogenoxide, nitro groups, nitrosyl groups, imine groups, amino groups, or any combination thereof.

[0027] In one embodiment, the disclosed graphene oxide nanosheets may have a thickness of at most 2 nm, such as at most 1.5 nm, at most 1.2 nm, or at most 1 nm. Conversely, the nanosheets may have a thickness of at least 0.5 nm, such as at least 0.7 nm, at least 0.8 nm, or at least 0.9 nm. The thickness may also be within a range of 0.5 nm to 2 nm, 0.7 nm to 1.5 nm, or 0.8 nm to 1.2 nm, ensuring a balance between surface area and structural integrity. The thinness of the nanosheets ensures high surface area while maintaining structural stability, making them suitable for applications requiring large interfacial interactions, such as in composite materials, coatings, and filtration membranes. FIG. 4e provides TEM images of the exfoliated nanosheets, confirming their thin-layer structure, while FIG. 4c shows an AFM measurement validating their monolayer thickness.

[0028] The lateral dimension of the graphene oxide nanosheets may be at most 10 pm, such as at most 5 pm, at most 2 pm, or at most 1 pm. Conversely, the lateral dimension may be at least 100 nm, such as at least 200 nm, at least 300 nm, or at least 400 nm. The lateral dimension may also be within a range of 100 nm to 1 pm, 200 nm to 900 nm, or 300 nm to 800 nm, depending on exfoliation parameters. Larger lateral dimensions may be advantageous for applications requiring extensive sheet-to-sheet interactions, such as in conductive films, composite reinforcements, or electrode materials. FIG. 4d presents SEM images of the exfoliated nanosheets, illustrating their size distribution and confirming the variation in lateral dimensions compared to commercial GO (FIG. 4a).

[0029] In some embodiments, the oxygen-to-carbon atomic ratio may be at most 1 :1 , such as at most 0.8:1 , at most 0.6:1, or at most 0.5:1. Conversely, the ratio may be at least 0.1 :1, such as at least 0.2:1, at least 0.3:1, or at least 0.4:1. The ratio may also be within a range of 0.1 :1 to 1:1 , 0.2:1 to 0.8:1 , or 0.3:1 to 0.6:1, providing an indication of the oxidation level of the material. The oxygen functionalization contributes to hydrophilicity and dispersibility in aqueous and organic media, facilitating integration into various material formulations. FIG. 4f provides Raman spectra comparing the exfoliated graphene oxide with commercial GO, highlighting the differences in oxidation patterns and structural characteristics.

[0030] The disclosed nitrogen-functionalized graphene oxide nanosheets offer potential advantages over conventional graphene oxide, particularly in fields such as catalysis, energy storage, and environmental remediation. Their nitrogen doping enhances catalytic activity in electrochemical reactions, while the controlled oxidation state supports improved mechanical and electrical properties. The ability to tune nitrogen content, oxidation level, and nanosheet dimensions makes the disclosed material highly adaptable for diverse applications.

[0031] In a further aspect, the present disclosure relates to a method for producing graphene oxide nanosheets of the first aspect. In one embodiment, carbon fibres can be immersed in an acidic electrolyte solution comprising nitric acid at a concentration of from 0.5 % to 20 % by weight. This immersion may allow for close contact between the fibres and the solution, thereby facilitating subsequent electrochemical reactions. An electric potential may be applied to the immersed carbon fibres, and the applied potential can be arranged so as to induce an electrochemical reaction at the interface between the fibres and the electrolyte. For example, the electrochemical reaction can be arranged to exfoliate the fibres into graphene oxide nanosheets comprising nitrogen incorporated into its structure.

[0032] One unexpected effect observed in this process is that efficient exfoliation and nitrogen incorporation can still occur at relatively low acid concentrations and moderate voltages. This contrasts with conventional techniques, such as the Hummers method, which does not typically result in nitrogen incorporation and requires more aggressive oxidation conditions to achieve exfoliation. The use of nitric acid in the electrolyte solution can lead to the incorporation of nitrogen-containing functional groups into the exfoliated graphene oxide nanosheets. Unlike conventional methods that primarily result in oxygen-functionalized graphene oxide, the present method enables controlled nitrogen doping as an inherent outcome of the electrochemical exfoliation. This effect is observed when nitric acid is present in the electrolyte at concentrations of at least 1 wt.%, with significant nitrogen incorporation typically occurring when the nitric acid concentration ranges from 3 wt.% to 10 wt.%. At these concentrations, nitrogen species from the electrolyte interact with the carbon fibre surface during oxidation, leading to the formation of nitrogen functional groups such as pyridinic, pyrrolic, and graphitic nitrogen. X-ray photoelectron spectroscopy (XPS) analysis of the exfoliated graphene oxide has confirmed nitrogen incorporation, with concentrations typically ranging from 1 to 5 atomic%, depending on process conditions.

[0033] In one embodiment, the acidic electrolyte solution used in the method may comprise nitric acid at a concentration of from 1 % to 20 % by weight. In another embodiment, the acidic electrolyte concentration comprises a mixture of nitric acid and at least one additional acid. The additional acid may be selected from hydrochloric acid, sulfuric acid, phosphoric acid, and lactic acid. The ratio of nitric acid to the additional acid may be up to 50:50, allowing for flexibility in adjusting the electrolyte composition based on processing requirements. The total acid concentration may range between 1 % and 20% by weight, with a preference for concentrations below 10%. This controlled concentration range may facilitate the exfoliation process while minimizing excessive oxidation and material degradation.

[0034] The use of nitric acid, alone or in combination with other acids, can influence the efficiency of the electrochemical exfoliation. Nitric acid is known to enhance oxidation reactions, while the presence of additional acids may modify reaction kinetics, improve electrolyte conductivity, or alter the interaction with the carbon fibres. For example, sulfuric acid may contribute to the formation of sulfonic functional groups on the graphene oxide surface, while phosphoric acid may influence defect density and dispersibility. By allowing variations in acid composition, the method can be adapted to optimize the exfoliation process for different carbon fibre types and application requirements.

[0035] Unexpectedly, maintaining a lower total acid concentration may still result in efficient exfoliation while reducing material degradation and minimizing harsh reaction conditions. This is in contrast to conventional methods that rely on highly concentrated acid solutions, which can introduce excessive oxidative defects or compromise nanosheet integrity. The ability to achieve controlled oxidation under milder conditions contributes to improved product consistency and reproducibility, making the process more industrially viable while also reducing safety and environmental concerns associated with high-acid-content electrolytes.

[0036] The acidic electrolyte solution used in the method may comprise nitric acid alone or in combination with one or more auxiliary acids. These auxiliary acids may include, but are not limited to, sulfuric acid, phosphoric acid, hydrochloric acid, lactic acid, acetic acid, and other mineral or organic acids capable of influencing the electrochemical environment. The ratio of nitric acid to the auxiliary acid may be up to 50:50, allowing for flexible adjustment of the electrolyte composition to suit different processing requirements. In some implementations, the ratio may be within the range of 90:10 to 50:50, with variations such as 90:10, 80:20, 70:30, 60:40, and 50:50 being possible depending on the desired oxidation kinetics and exfoliation efficiency. However, the auxiliary acids may also be present in amounts outside these ranges depending on the specific characteristics of the carbon fibre feedstock and the intended product properties.

[0037] The total acid concentration may range between 1 wt.% and 50 wt.%, with a preferred range of 3 wt.% to 10 wt.%, ensuring effective exfoliation while minimizing excessive oxidation and fibre degradation. The specific choice and concentration of the auxiliary acids may affect exfoliation efficiency, surface functionalization, and material dispersibility. For example, sulfuric acid may contribute to the introduction of sulfonic functional groups, which can enhance hydrophilicity, while phosphoric acid may affect the degree of structural defects, influencing electrical and mechanical properties. Organic acids such as lactic acid or acetic acid may alter oxidation selectivity, potentially leading to a more uniform nanosheet structure.

[0038] In one example, following the electrochemical exfoliation, the resulting material can be processed by separating it from the reaction medium — such as by filtration or centrifugation — and then collecting the exfoliated material. The collected material may comprise or consist of graphene oxide nanosheets that exhibit a controlled thickness and lateral size distribution. In some implementations, the nanosheets may have an average layer thickness of about 1 nm (±0.2 nm) and average lateral dimensions ranging from about 500 nm to about 1200 nm, as determined by atomic force microscopy (AFM) and transmission electron microscopy (TEM). These dimensions are consistent with high-quality exfoliated graphene oxide and can influence material properties such as dispersion stability, mechanical performance, and surface reactivity.

[0039] The carbon fibres can, for example, be selected from the group consisting of polyacrylonitrile (PAN)-based carbon fibres, pitch-based carbon fibres, rayon-based carbon fibres, and lignin-based carbon fibres, and may be either newly manufactured or recycled. This broad selection allows for the use of diverse feedstocks, enabling the process to accommodate different material sources and manufacturing conditions. The ability to work with various fibre types provides flexibility in tailoring the process to meet specific production requirements, where fibre properties such as uniformity, purity, and degree of graphitization can influence the efficiency and quality of the electrochemical exfoliation.

[0040] The selection of carbon fibre types may impact exfoliation performance in different ways. PAN-based fibres, known for their high consistency and well-defined structure, can serve as a reliable precursor for producing uniform graphene oxide nanosheets. In particular, some embodiments of PAN-based fibres are carbonized at high temperatures, such as at least 2000 °C, ensuring that no metallic or inorganic impurities are introduced into the graphene oxide nanosheets during the electrochemical exfoliation process. Pitch-based fibres, with their higher degree of graphitization, may enhance exfoliation efficiency by offering greater conductivity and structural integrity. Rayon-based and ligninbased fibres, being derived from renewable resources, provide a more sustainable alternative, while still offering performance characteristics suitable for electrochemical exfoliation. The option to employ both newly manufactured and recycled fibres further expands material sourcing possibilities, potentially reducing production costs and enhancing resource efficiency.

[0041] This adaptability in fibre selection presents several technical advantages, enabling the process to be optimized based on available materials and specific production goals. For instance, one implementation may use recycled PAN-based fibres to strike a balance between cost-effectiveness and performance, while another may prioritize lignin-based fibres to enhance environmental sustainability. By accommodating a variety of fibre inputs, the disclosed method provides a flexible and scalable approach that maintains reproducibility and consistent graphene oxide quality across different operational settings.

[0042] In one embodiment, the process parameters — including acid concentration, electric potential, and reaction duration — may be dynamically adjusted to control the degree of exfoliation, oxidation efficiency, and nitrogen incorporation into the graphene oxide nanosheets. These tuneable parameters allow for optimization based on the desired properties of the final material while maintaining flexibility for different feedstocks and industrial applications.

[0043] The electric potential applied to the carbon fibres may range from 1V to 12V, with a preferred range of 2V to 6V, depending on the desired exfoliation rate and the structural characteristics of the resulting graphene oxide nanosheets. In a two- electrode system, the applied voltage may correspond to the potential difference between the working electrode (carbon fibre) and the counter electrode. The actual potential experienced at the fibre surface may be influenced by factors such as electrolyte composition, electrode geometry, and system configuration, and thus may be further refined by adjusting current density, electrode spacing, or electrolyte flow dynamics.

[0044] The reaction duration may be adjusted between 30 minutes and 6 hours, allowing for precise control over nanosheet thickness, oxidation state, and exfoliation yield. The method may be implemented in both batch and continuous processes, with fibre feeding rates and reaction chamber configurations modifiable to maintain consistent exposure to electrolyte conditions.

[0045] The presence of nitrogen functional groups in graphene oxide can influence its electronic properties, chemical reactivity, and dispersibility, making it advantageous for various applications. For example, nitrogen- doped graphene oxide may enhance electrocatalytic performance in energy storage devices, improve hydrophilicity for coatings and composites, and modify adsorption properties for water purification applications. Additionally, the ability to introduce nitrogen into the nanosheets through an electrochemical route rather than post-synthetic functionalization simplifies processing and provides a more uniform distribution of nitrogen sites within the material. This effect is directly related to the controlled oxidation process facilitated by nitric acid within the specified concentration range and represents a key distinction from conventional chemical exfoliation methods that do not inherently introduce nitrogen into the graphene oxide structure.

[0046] The presence of auxiliary acids in the electrolyte solution may further modify the oxidation kinetics and alter the surface chemistry of the nanosheets. For example, sulfuric acid may promote sulfonation, introducing functional groups that improve dispersibility, while phosphoric acid may influence structural defect density and material morphology, optimizing performance for specific applications. Lactic acid and other organic acids may facilitate milder oxidation, reducing defect formation while maintaining effective exfoliation. The ability to modify exfoliation conditions based on fibre composition, electrolyte composition, and applied potential allows for broad process adaptability.

[0047] The ranges provided for acid concentration, voltage, and reaction time serve as examples and should not be construed as limiting the invention to any specific set of parameters. The method may be configured to achieve different levels of oxidation and exfoliation efficiency, reinforcing its applicability across various industrial-scale processes.

[0048] In one embodiment, the electric potential applied to the carbon fibres during electrochemical exfoliation may range from 1V to 12V, with a preferred range of 2V to 6V. The applied voltage influences the oxidation rate, exfoliation efficiency, and final properties of the graphene oxide nanosheets. By maintaining the voltage within this range, the method can promote controlled oxidation while avoiding excessive degradation of the carbon fibres, which may otherwise lead to undesired byproducts or structural defects in the resulting nanosheets.

[0049] The selection of an appropriate voltage range may be tailored based on the electrolyte composition, carbon fibre type, and desired material properties. A lower voltage may enable milder exfoliation conditions, reducing over-oxidation and preserving structural integrity, while a higher voltage within the specified range may enhance reaction kinetics and exfoliation speed. Additionally, the applied voltage interacts with other process variables, including acid concentration and reaction duration, further influencing the efficiency and uniformity of exfoliation.

[0050] Unexpectedly, efficient exfoliation can still be achieved at these moderate voltage levels, despite conventional electrochemical exfoliation techniques often relying on significantly higher voltages. Such conventional approaches can lead to excessive oxidation and rapid degradation of carbon fibres, reducing the yield of high-quality graphene oxide. In contrast, the present method demonstrates that by operating at a lower voltage range, an effective balance between exfoliation efficiency and material preservation can be maintained. This controlled approach improves reproducibility, scalability, and energy efficiency while reducing undesired oxidative defects, making it well-suited for industrial-scale applications.

[0051] In one embodiment, the reaction duration for electrochemical exfoliation may range from 30 minutes to 6 hours, depending on the desired properties of the resulting graphene oxide nanosheets. The reaction time influences the degree of exfoliation, oxidation level, and yield of the graphene oxide product. A shorter reaction time may promote partial exfoliation while preserving more of the original fibre structure, whereas a longer reaction time may result in increased oxidation and higher exfoliation efficiency. The appropriate reaction duration may be selected based on the electrolyte composition, applied voltage, and carbon fibre characteristics. When operating within a preferred reaction time range of 45 minutes to 3 hours, efficient exfoliation can be achieved while maintaining control over oxidation and minimizing degradation. In some implementations, a reaction time of approximately 60 minutes may be optimal for achieving monolayer graphene oxide nanosheets with controlled oxygen and nitrogen functionalization.

[0052] Unlike conventional chemical oxidation methods, which may require prolonged reaction times and multiple processing steps to achieve comparable exfoliation, the present method demonstrates that effective exfoliation can occur under controlled electrochemical conditions within a shorter timeframe. Furthermore, by dynamically adjusting the reaction duration in combination with acid concentration and applied voltage, the process can be optimized for different feedstocks and scalability requirements.

[0053] When implemented in a continuous process, the reaction time may be indirectly controlled by adjusting the fibre feeding rate through the electrolyte solution. In such configurations, exposure time within the reaction chamber may be tuned by modifying the flow rate of the electrolyte or the residence time of fibres within the electrochemical setup. This flexibility allows for precise adaptation of exfoliation conditions to suit industrial-scale production while ensuring consistent graphene oxide quality.

[0054] In one embodiment of the present disclosure, the acidic electrolyte solution may comprise a surface-active agent configured to promote intercalation of the electrolyte solution into the carbon fibres and facilitate exfoliation during the application of the electric potential. The presence of such an agent can enhance the penetration of the electrolyte into the fibre structure, allowing for improved ion diffusion and promoting more uniform electrochemical exfoliation. This can result in a more controlled oxidation process, leading to improved yield and consistency in the graphene oxide nanosheets produced.

[0055] As used herein, a 'surface-active agent' refers to a compound that modifies the surface properties of a material, promoting interfacial interactions, wetting, dispersion, or intercalation. Such agents may include surfactants, dispersants, polyelectrolytes, amphiphilic molecules, or other substances that facilitate electrolyte penetration into the fibre structure and assist in exfoliation. The surface-active agent can function by reducing the surface tension between the electrolyte and carbon fibre surface, thereby enhancing wetting and diffusion. Additionally, it may introduce electrostatic or steric stabilization effects that prevent premature aggregation of exfoliated nanosheets.

[0056] The surface-active agent may be selected from a range of compounds known to modify surface interactions and enhance intercalation. Examples of suitable surface-active agents include surfactants, dispersants, and intercalation-promoting compounds such as sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), polyelectrolytes such as poly(styrene sulfonate) (PSS), non-ionic surfactants, anionic / cationic surfactants, zwitterionic surfactants, and block copolymers, such as amphiphilic block copolymers, or other compounds capable of facilitating the penetration of the electrolyte into the fibre structure. The concentration of the surface- active agent in the electrolyte solution may be optimized depending on the desired exfoliation rate and fibre composition, and may typically range from 0.01% to 5% by weight.

[0057] By incorporating a surface-active agent, the method may improve exfoliation efficiency while reducing the need for excessive voltage or highly corrosive conditions. This can be advantageous compared to conventional electrochemical exfoliation techniques, which often rely on high voltages and aggressive electrolytes to drive the process. The controlled exfoliation promoted by the surface-active agent may also reduce fibre degradation, preserving the structural integrity of the resulting graphene oxide nanosheets and leading to improved performance characteristics in downstream applications.

[0058] In some implementations, the surface-active agent may also help stabilize the exfoliated nanosheets in suspension, reducing aggregation and facilitating downstream processing steps such as separation and drying. This stabilization effect may be particularly beneficial when producing high-quality graphene oxide nanosheets with uniform thickness and lateral dimensions.

[0059] The inclusion of a surface-active agent provides an additional degree of process control, enabling greater flexibility in tuning exfoliation conditions while maintaining or even enhancing product quality. This modification may be particularly useful in applications where precise control over nanosheet morphology, oxidation state, and dispersibility is desired.

[0060] In one embodiment of the present disclosure, the method may be performed as a batch process. A batch process can provide a controlled environment for the electrochemical exfoliation of carbon fibres, allowing for precise regulation of reaction parameters such as acid concentration, applied electric potential, and reaction time. By processing discrete quantities of carbon fibres in separate reaction cycles, a batch approach can facilitate reproducibility and ensure consistency in the properties of the produced graphene oxide nanosheets.

[0061] The batch process may involve immersing a predetermined amount of carbon fibres in an acidic electrolyte solution within a reaction vessel, where the exfoliation process is initiated by applying an electric potential. Once exfoliation has been completed, the reaction may be halted, and the exfoliated material can be separated from the electrolyte for further processing. The electrolyte solution may then be refreshed or treated before initiating a new batch cycle, helping to maintain optimal reaction conditions.

[0062] In one embodiment of the present disclosure, the method may be performed as a continuous process. In such an implementation, carbon fibres can be continuously fed into an acidic electrolyte solution while an electric potential is applied. This setup allows for ongoing exfoliation of graphene oxide nanosheets without requiring intermittent batch processing steps.

[0063] Continuous processing may be facilitated by maintaining controlled reaction conditions, including the concentration of the acidic electrolyte and the applied electric potential.

[0064] By optimizing these parameters, the process can sustain uniform exfoliation rates while minimizing degradation of the carbon fibres. In contrast to conventional approaches that may require aggressive reaction conditions unsuitable for continuous operation, the disclosed method enables exfoliation under conditions that provide process stability and scalability.

[0065] The fibre feed mechanism can be configured to transport the carbon fibres at a controlled speed through the reaction chamber, allowing sufficient interaction with the electrolyte while ensuring that exfoliation occurs efficiently. The electrode assembly may also be adapted to accommodate continuous material flow, preventing clogging or inconsistent exfoliation, which may be challenges in conventional setups.

[0066] The ability to implement the process continuously offers significant advantages in scalability and efficiency. Unlike batch processes, where material handling and process interruptions can limit throughput, continuous operation enables a steady production rate, reducing processing time and energy consumption. Additionally, continuous exfoliation may improve the consistency of the graphene oxide nanosheets produced, leading to a more uniform product quality.

[0067] This capability may be particularly advantageous for industrial-scale graphene oxide production, where maintaining high throughput and reproducibility is essential. By addressing limitations associated with batch processing, the disclosed method provides a practical route for large-scale manufacturing of graphene oxide nanosheets.

[0068] The continuous process may be implemented with controlled feeding of carbon fibres at a speed ranging from about 0.1 cm / min to about 5 cm / min. This controlled feeding speed may allow for optimized exfoliation efficiency, ensuring that the carbon fibres remain within the acidic electrolyte solution for a sufficient duration to facilitate electrochemical exfoliation while minimizing over-oxidation or degradation.

[0069] The fibre feed mechanism can be configured to regulate the speed at which the carbon fibres pass through the reaction chamber. By adjusting the feed rate within the specified range, the process can maintain a balance between reaction efficiency and product quality. A slower feed rate may provide extended exposure to the electrolyte and electric field, potentially enhancing exfoliation, while a higher feed rate may improve throughput and scalability without compromising the integrity of the nanosheets.

[0070] In one embodiment of the present disclosure, the process may be conducted under ambient temperature conditions. Performing the electrochemical exfoliation at ambient temperature can simplify the operational setup, reduce energy consumption, and eliminate the need for additional heating or cooling systems. This can be particularly advantageous for large-scale or industrial implementations, where maintaining temperature control can add complexity and cost.

[0071] The ability to perform the process at ambient temperature may also contribute to process stability, as excessive heating could lead to uncontrolled oxidation or degradation of the carbon fibres, potentially impacting the structural integrity and quality of the produced graphene oxide nanosheets. Additionally, maintaining ambient conditions may reduce side reactions that could occur at elevated temperatures, leading to a purer product.

[0072] In one embodiment of the present disclosure, the process may be conducted under controlled temperature conditions to optimize the electrochemical exfoliation. Implementing temperature control may allow fine-tuning of reaction kinetics, potentially influencing the rate and uniformity of exfoliation. For example, slightly elevated temperatures may enhance the intercalation of the acidic electrolyte into the carbon fibres, improving exfoliation efficiency, while lower temperatures may slow down oxidation, providing more controlled processing.

[0073] Temperature regulation may be achieved through various means, such as external heating elements, immersion cooling, or active thermal management of the reaction chamber. The ability to adjust temperature conditions can help mitigate excessive oxidation, ensuring that the produced graphene oxide nanosheets exhibit the desired structural and chemical characteristics.

[0074] In one embodiment of the present disclosure, the method may further comprise a pretreatment step performed prior to immersing the carbon fibres in the acidic electrolyte solution to remove any polymeric coating on the carbon fibres. Many commercially available carbon fibres are coated with polymeric materials, such as polyurethane or epoxy, which can act as barriers to electrolyte penetration and interfere with the electrochemical exfoliation process. Removing these coatings can improve the accessibility of the electrolyte to the fibre surface, enhancing the efficiency and uniformity of exfoliation.

[0075] The pretreatment step can be performed using various techniques, including chemical, thermal, or mechanical treatments, alone or in combination. The choice of pretreatment method may depend on factors such as the type of polymer coating, the fibre substrate, and processing conditions. Ensuring adequate removal of surface coatings may contribute to higher exfoliation efficiency, improved process consistency, and more uniform graphene oxide nanosheets.

[0076] The pretreatment step can comprise a chemical treatment using a solvent selected from the group consisting of acetone, methanol, and mixtures thereof to dissolve polymeric coatings such as polyurethane or epoxy. Chemical pretreatment can provide a controlled and selective means of removing polymeric coatings while minimizing structural damage to the underlying carbon fibres. The use of organic solvents can facilitate efficient dissolution of polymer layers, allowing for effective removal prior to electrochemical exfoliation.

[0077] The effectiveness of chemical pretreatment may depend on factors such as solvent concentration, immersion duration, and agitation. In some cases, mild heating of the solvent may enhance polymer dissolution. Additionally, chemical pretreatment may be followed by rinsing or drying steps to ensure complete removal of residual solvent before proceeding with the electrochemical exfoliation process.

[0078] Alternatively, of additionally, the pretreatment step can further comprise a thermal treatment by heating the carbon fibres to a temperature above 400 °C to remove the polymeric coating. Thermal decomposition of polymeric coatings may be advantageous in cases where chemical solvents are ineffective or undesirable. Heating the fibres to sufficiently high temperatures can cause decomposition or volatilization of surface coatings, exposing the carbon fibre surface for subsequent electrolyte interaction.

[0079] The thermal treatment may be conducted in an inert atmosphere, such as nitrogen or argon, to prevent unwanted oxidation of the carbon fibres during heating. Alternatively, controlled oxidative conditions may be employed if partial oxidation is beneficial for promoting fibre reactivity. The temperature and duration of heating may be adjusted to optimize polymer removal while minimizing structural degradation of the fibres.

[0080] Alternatively, of additionally, the pretreatment step can comprise a combination of chemical and thermal treatments. Combining chemical and thermal approaches may provide a more comprehensive means of removing polymeric coatings. For example, an initial chemical treatment may weaken or dissolve the polymer layer, followed by a thermal treatment to remove any remaining residues.

[0081] This dual-step process may be particularly useful for polymer coatings that are resistant to a single method of removal. The sequence and parameters of chemical and thermal treatments may be optimized based on the specific coating composition and the properties of the carbon fibres. The combination of these methods can enhance the overall efficiency of pretreatment, ensuring complete removal of coatings and improving exfoliation consistency.

[0082] Alternatively, of additionally, the pretreatment step can be performed for a duration sufficient to remove at least 90% of the polymeric coating as determined by surface analysis. Ensuring a high level of polymer removal can contribute to improved electrochemical exfoliation efficiency and higher graphene oxide yield. The degree of removal may be assessed using surface characterization techniques such as spectroscopy, microscopy, or weight-loss analysis.

[0083] The duration of the pretreatment step may vary depending on the method used, the type and thickness of the polymer coating, and processing conditions. In some cases, optimizing the pretreatment time may involve balancing polymer removal efficiency with maintaining the integrity of the carbon fibres. By ensuring at least 90% removal of the polymeric coating, the process can achieve a high degree of fibre accessibility for electrolyte penetration, leading to improved exfoliation performance and consistent graphene oxide quality.

[0084] In one embodiment of the present disclosure, the acid concentration and electric potential can be optimized to achieve controlled oxidation of the carbon fibres, thereby reducing degradation relative to conventional natural graphite-based production methods. The electrochemical exfoliation process can be tuned to balance oxidation and exfoliation efficiency while minimizing unwanted structural damage to the carbon fibres.

[0085] As used herein, controlled oxidation refers to a process in which the degree of oxidation is precisely regulated to achieve effective exfoliation while avoiding excessive oxidative damage to the fibre structure. This control can be achieved by adjusting parameters such as acid concentration, electric potential, reaction time, and electrolyte composition to establish conditions that promote exfoliation without inducing unwanted deterioration.

[0086] Conventional electrochemical exfoliation techniques frequently employ high acid concentrations and elevated voltages to accelerate exfoliation. However, these aggressive conditions can lead to over-oxidation, resulting in significant structural degradation and inconsistencies in product quality. In contrast, the disclosed method demonstrates that by carefully modulating the acid concentration and electric potential, efficient exfoliation can be achieved while reducing excessive oxidation, leading to improved material integrity and product consistency. This counterintuitive advantage enables the production of graphene oxide nanosheets with fewer defects, improved mechanical properties, and enhanced performance in downstream applications.

[0087] By preventing over-oxidation, the disclosed process yields graphene oxide nanosheets with a uniform oxidation state, fewer basal-plane defects, and improved dispersion characteristics. These attributes are particularly beneficial for applications requiring high electrical conductivity, mechanical strength, and compatibility with functionalization strategies.

[0088] In some implementations, real-time monitoring techniques such as electrochemical impedance spectroscopy, in-situ Raman spectroscopy, or pH tracking may be employed to dynamically adjust process parameters and maintain an optimal oxidation state throughout the exfoliation process. These adaptive control strategies can further refine oxidation levels, ensuring consistent exfoliation efficiency across different fibre sources and processing conditions. The selection of acid concentration plays a critical role in determining the extent of oxidation, intercalation, and exfoliation. A lower acid concentration can reduce excessive oxidation while still enabling effective exfoliation, thereby preserving the nanosheet structure. Similarly, the applied electric potential influences the oxidation rate and exfoliation efficiency. A carefully controlled voltage can facilitate exfoliation without introducing excessive structural defects or fragmentation in the graphene oxide nanosheets.

[0089] By optimizing these parameters, the disclosed process achieves higher exfoliation efficiency while mitigating degradation compared to conventional methods that rely on natural graphite as a precursor. As a result, this method enhances graphene oxide quality, improves yield, and increases reproducibility, making it more viable for scalable industrial production.

[0090] The method can further comprise a post-treatment step for the acidic electrolyte solution, wherein the post-treatment step can involve the use of an ion exchange resin to remove residual acid and ionic contaminants. Following the exfoliation process, the electrolyte solution may contain unreacted acid, oxidation byproducts, and dissolved impurities that could affect the stability of the process and the purity of the final graphene oxide product.

[0091] The use of an ion exchange resin can selectively remove ionic contaminants while maintaining the efficiency of the electrolyte solution for potential reuse. This approach can contribute to waste reduction and sustainability by minimizing acid consumption and the need for frequent electrolyte replacement. Alternative purification techniques may also be employed, such as neutralization, filtration, or membrane separation, depending on process requirements and environmental considerations.

[0092] By implementing post-treatment, the method can enhance process sustainability while ensuring the purity and consistency of the exfoliated graphene oxide nanosheets.

[0093] In some implementations, the process can yield at least 10 mg of graphene oxide per gram of carbon fibre. Higher yields can also be achieved, such as at least 25 mg, at least 50 mg, at least 75 mg, at least 100 mg, at least 125 mg, at least 150 mg, or at least 200 mg per gram of carbon fibre. In certain examples, the process can yield approximately 20% of the initial carbon fibre mass as graphene oxide, though this value may vary depending on process conditions.

[0094] Alternatively, or additionally, the process can provide yields within various ranges, depending on parameters such as acid concentration, applied potential, and exfoliation time. For example, the yield can range from 5% to 15%, 10% to 25%, or 15% to 30% of the initial carbon fibre mass. In some implementations, optimized process conditions may result in a yield between 10 mg to 200 mg per gram of carbon fibre. The ability to finetune the exfoliation process to achieve these yield levels can provide significant advantages in terms of material efficiency and scalability.

[0095] In some implementations, the process can yield at least 50 mg of graphene oxide per gram of carbon fibre. Higher yields can also be achieved, such as at least 100 mg, at least 150 mg, at least 200 mg, at least 250 mg, at least 300 mg, at least 350 mg, at least 400 mg, at least 450 mg, or at least 500 mg per gram of carbon fibre. In some examples, the process can yield at least 300 mg of graphene oxide per gram of carbon fibre.

[0096] Alternatively, or additionally, the process can provide yields within various ranges, depending on process parameters and material selection. For example, the yield can range from 50 mg to 200 mg, 100 mg to 300 mg, 150 mg to 400 mg, or 200 mg to 500 mg per gram of carbon fibre. The ability to control the exfoliation process to achieve these yield levels can provide significant advantages in terms of material efficiency and scalability.

[0097] The exfoliation efficiency of the method can be influenced by various factors, including the nature of the carbon fibre precursor, the electrolyte composition, and the applied electric potential. By optimizing these parameters, the method can achieve high yields of graphene oxide while maintaining desirable structural and chemical properties.

[0098] The yield can be determined based on the weight of the collected graphene oxide relative to the initial carbon fibre mass. A high conversion efficiency can indicate effective exfoliation and oxidation, demonstrating the viability of carbon fibres as an alternative feedstock to natural graphite.

[0099] This level of yield can offer advantages in terms of material efficiency and production scalability. Compared to conventional approaches, the disclosed method can provide a cost-effective and sustainable route for graphene oxide production while maintaining high product quality.

[0100] The method can further comprise a drying step performed on the collected graphene oxide nanosheets, wherein the drying can be conducted under ambient or controlled temperature conditions to produce a dry powder. Once the exfoliation process is complete, the collected graphene oxide nanosheets may exist in a dispersed form within the electrolyte solution. To facilitate handling, storage, and further processing, the nanosheets can be subjected to a drying process.

[0101] The drying step can be carried out at ambient temperature, allowing for solvent evaporation under natural conditions. Alternatively, controlled drying conditions, such as vacuum drying, freeze-drying, or mild thermal drying, can be used to accelerate solvent removal while preserving the structural integrity of the graphene oxide nanosheets. The choice of drying method may depend on factors such as desired final moisture content, process efficiency, and product stability.

[0102] By producing a dry graphene oxide powder, the method can enhance the material’s versatility for subsequent applications, such as dispersions, coatings, or composite fabrication. The ability to control the drying conditions can help maintain the nanosheet morphology and prevent aggregation, ensuring high-quality material for various end uses.

[0103] The process can be conducted under conditions that avoid the use of additional oxidizing chemicals beyond those present in the acidic electrolyte solution. In some conventional methods, strong oxidizing agents such as potassium permanganate or concentrated sulfuric acid are introduced to promote oxidation and exfoliation.

[0104] However, these reagents can lead to excessive oxidation, undesirable structural damage, and environmental concerns related to waste disposal.

[0105] By relying solely on the acidic electrolyte solution and the applied electric potential to induce exfoliation, the disclosed process can achieve controlled oxidation while reducing chemical waste and operational hazards. The absence of additional oxidizing agents can help maintain a balance between effective exfoliation and the preservation of graphene oxide structural integrity, resulting in a more controlled and reproducible process.

[0106] This approach can also contribute to sustainability by minimizing chemical consumption and reducing the need for complex post-processing steps to remove residual oxidants. Additionally, the avoidance of harsh oxidizing conditions may enhance the compatibility of the process with various feedstock materials, broadening its applicability across different carbon fibre sources.

[0107] In a further aspect, the present disclosure relates to a system for producing graphene oxide nanosheets comprising nitrogen incorporated into its structure. In one embodiment, a reaction chamber can be configured to contain an acidic electrolyte solution comprising nitric acid at a concentration of from 0.5 % to 20 % by weight, thereby establishing the environment for the electrochemical process. A fibre feed mechanism may be arranged to introduce carbon fibres into the reaction chamber. The fibre feed mechanism may be arranged to introduce carbon fibres suitable for electrochemical exfoliation, such as PAN-based, pitch-based, rayon-based, or lignin-based fibres. An electrode assembly may be configured to apply an electric potential to the carbon fibres to facilitate their electrochemical exfoliation, and a collection unit may be arranged to separate and collect the produced graphene oxide nanosheets. The collected nanosheets can have an average layer thickness of about 1 nm and average lateral dimensions of about

[0108] 500 nm to about 1200 nm. This system may be implemented in a manner that supports scalable and reproducible production. In one embodiment of the present disclosure, the electrode assembly of the system for producing graphene oxide nanosheets can comprise a two- electrode configuration. The carbon fibres can serve as an anode, while a counter electrode can be positioned to facilitate the application of an electric potential. The counter electrode may be formed from an inert conductive material, such as platinum. Other conductive materials may also be used, including but not limited to titanium, gold, iridium, graphite, or conductive metal oxides, depending on the electrochemical stability requirements of the process.

[0109] The two-electrode configuration can be arranged to optimize the exfoliation efficiency by ensuring uniform charge distribution and minimizing unwanted side reactions. The spacing between the electrodes, the electrolyte composition, and the applied voltage can all be adjusted to achieve controlled exfoliation while reducing degradation of the fibres. Additionally, alternative electrode configurations, such as a three-electrode system with a reference electrode, may also be implemented in some embodiments to further refine process control.

[0110] By utilizing a counter electrode composed of an inert conductive material, the system can facilitate stable and reproducible electrochemical exfoliation, reducing contamination risks and ensuring consistent graphene oxide quality. The electrode materials and arrangement can be tailored to suit different electrolyte compositions and process conditions, allowing for broad applicability across different production environments.

[0111] The fibre feed mechanism can be configured to introduce carbon fibres into the reaction chamber at a controlled rate. In some embodiments, the fibre feed speed can range from about 0.1 cm / min to about 5 cm / min, allowing for controlled processing conditions that balance exfoliation efficiency with production throughput. The specific feed rate can be adjusted based on factors such as fibre type, electrolyte composition, and applied potential to optimize the exfoliation process.

[0112] The fibre feed mechanism can include components such as motorized rollers, tension control systems, or guiding structures that ensure the fibres are properly positioned within the reaction chamber. In some implementations, the fibre feed mechanism can operate in a continuous manner, allowing for seamless processing of fibre spools without interruption. Alternatively, batch feeding configurations can be used, where predefined fibre segments are sequentially introduced into the reaction chamber.

[0113] By providing a controlled and adjustable feed rate, the system can achieve consistent exfoliation conditions, enabling a scalable and industrially viable approach to graphene oxide production. The ability to finely tune the fibre feed speed can further allow for customization of graphene oxide properties, such as sheet size and oxidation level, depending on the intended application.

[0114] The system for producing graphene oxide nanosheets can be arranged to perform the method as described herein. The system can integrate the steps of immersing carbon fibres in an acidic electrolyte solution, applying an electric potential to induce electrochemical exfoliation, and separating and collecting the resulting graphene oxide nanosheets. By configuring the system to execute these steps in a controlled manner, process parameters such as electrolyte composition, applied voltage, and fibre feed rate can be systematically managed to optimize exfoliation efficiency and graphene oxide yield.

[0115] The reaction chamber can be designed to accommodate continuous or batch processing, thereby aligning with the method’s flexibility regarding process modes. The fibre feed mechanism, electrode assembly, and collection unit can be precisely calibrated to ensure that the exfoliation conditions are maintained within optimal ranges, minimizing variations in graphene oxide quality. In some implementations, automated control systems can be employed to monitor key parameters and dynamically adjust process conditions based on real-time measurements.

[0116] In some implementations, the system may be configured to operate with an acidic electrolyte solution comprising a surface-active agent. The presence of such an agent can influence system design, particularly in maintaining homogeneity within the electrolyte solution and optimizing exfoliation efficiency.

[0117] To accommodate the use of surface-active agents, the reaction chamber may be equipped with agitation mechanisms, such as mechanical stirring, ultrasonication, or recirculating pumps, to ensure uniform dispersion of the agent within the electrolyte. Additionally, the electrode assembly may be designed to minimize unwanted deposition of surface-active compounds, for example, by using inert or coated electrode materials to prevent interference with the exfoliation process.

[0118] Furthermore, a post-exfoliation separation system can be integrated into the collection unit to facilitate the removal of any residual surface-active agents. This can include filtration systems, dialysis membranes, or chemical neutralization techniques to ensure the final graphene oxide product meets purity requirements.

[0119] In another aspect, the present disclosure relates to a computer-readable medium storing instructions which, when executed by a processor, cause the processor to control a production unit to perform the method for producing graphene oxide nanosheets as disclosed herein. In one embodiment, the instructions may be arranged to direct the production unit to immerse carbon fibres in an acidic electrolyte solution, apply an electric potential to the immersed fibres to induce electrochemical exfoliation, and subsequently separate and collect the resulting graphene oxide nanosheets. This embodiment may enable automated process control, facilitating consistent production and allowing for real-time adjustments of operating parameters.

[0120] In some implementations, real-time process monitoring and control may be employed to optimize the exfoliation process. The system may incorporate sensors to track key parameters such as pH, conductivity, oxidation potential, and exfoliation progress. A feedback control system may be configured to dynamically adjust process parameters based on real-time data acquisition.

[0121] For instance, a closed-loop control system can be implemented, wherein an electrochemical sensor array continuously measures the oxidation state of the exfoliating carbon fibres. This data can be processed by a microcontroller or industrial automation unit, which may adjust applied voltage, reaction duration, or electrolyte composition to maintain optimal exfoliation efficiency while preventing over-oxidation.

[0122] In one example, a PID (Proportional-lntegral-Derivative) control algorithm may be employed to regulate the applied electric potential. The controller may compare real- time voltage readings against a predefined setpoint and apply incremental adjustments to maintain stable conditions.

[0123] Alternatively, a machine learning-based optimization model may be used to predict ideal process conditions based on historical exfoliation data, thereby improving reproducibility across different material batches.

[0124] This automation and control approach enhances process stability, scalability, and efficiency, reducing variability and ensuring consistent graphene oxide nanosheet quality. The system may be integrated into existing industrial process control frameworks, such as SCADA (Supervisory Control and Data Acquisition) systems, for seamless large- scale production.

[0125] In yet another aspect, the present disclosure relates to the use of graphene oxide nanosheets produced by the disclosed method in various applications. In one embodiment, the graphene oxide nanosheets can be employed in energy storage devices, composite materials, coatings, flexible electronics, and tribological applications. The unique properties of the produced nanosheets — including their controlled layer thickness and defined lateral dimensions — may contribute to enhanced performance and improved material properties in these applications.

[0126] While the embodiments described herein illustrate specific implementations of the disclosed method and system, it will be understood that various modifications, substitutions, and improvements may be made without departing from the scope of the disclosure. The features described in connection with a particular embodiment may be combined with those of other embodiments unless explicitly stated otherwise. The invention is not limited to the precise configurations disclosed but encompasses variations that fall within the spirit and scope of the claims.

[0127] Unless explicitly stated otherwise, singular forms of terms used in this disclosure (e.g., ‘a,’ ‘an,’ ‘the’) should be interpreted as including the plural forms. Similarly, ‘comprising’ should be interpreted in an open-ended sense, meaning ‘including but not limited to,’ unless explicitly stated otherwise. All numerical ranges disclosed herein are intended to encompass endpoints as well as values between them, unless clearly stated otherwise.

[0128] Drawings

[0129] The invention will now be described in more detail with reference to the appended drawings, wherein:

[0130] FIG.1 presents a schematic representation of an electrochemical exfoliation apparatus according to the invention;

[0131] FIG.2 illustrates an embodiment of a pretreatment setup configured for removing polymeric coatings from carbon fibres before electrochemical exfoliation;

[0132] FIG. 3 provides a comparative visualization of two embodiments of the disclosed electrochemical exfoliation method;

[0133] FIG.4 presents a detailed comparison between commercially available graphene oxide (GO) nanosheets and those exfoliated from carbon fibres using the disclosed electrochemical method.

[0134] FIG.5 illustrates a flowchart representing an embodiment of the disclosed method for producing graphene oxide nanosheets.

[0135] FIG.6 presents a schematic representation of a system configured for carrying out the disclosed method for producing graphene oxide nanosheets.

[0136] Examples

[0137] The following examples illustrate various implementations of the present disclosure. These examples are intended to provide representative embodiments and should not be construed as limiting the scope of the invention. Unless stated otherwise, features described in one example may be combined with those of another example where technically feasible.

[0138] Example 1 : Electrochemical Exfoliation of Graphene Oxide from PAN- Based Carbon Fibres with Epoxy Coating

[0139] Materials & Methods PAN-based carbon fibres, initially coated with an epoxy layer, were used as the precursor material. The fibres underwent a chemical pretreatment step using a solvent to remove the epoxy coating before exfoliation. The pretreated fibres were then immersed in an acidic electrolyte solution consisting of a 5% nitric acid solution. An electric potential of 3±1 volts was applied across the fibres for 40 minutes to induce electrochemical exfoliation.

[0140] Results

[0141] The exfoliated material was collected and analysed using Atomic Force Microscopy (AFM), which revealed nanosheet thickness of 0.9 nm and lateral dimensions ranging from 500 nm to 900 nm. Additional characterization using Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) confirmed the structural integrity and morphology of the exfoliated graphene oxide (GO). Surface composition analysis indicated an oxygen-to-carbon (O / C) ratio between 2 and 10, suggesting successful oxidation and exfoliation.

[0142] Conclusion

[0143] Graphene oxide nanosheets were successfully exfoliated from PAN- based carbon fibres using an electrochemical process with controlled voltage and acid concentration. The method enabled efficient exfoliation while maintaining the structural quality of the GO.

[0144] Example 2: Electrochemical Exfoliation of Graphene Oxide from PAN- Based Carbon Fibres with Polyurethane Coating

[0145] Materials & Methods

[0146] PAN-based carbon fibres coated with polyurethane were pretreated using a thermal process at 600°C for 30 minutes to remove the polymer coating. The pretreated fibres were then immersed in an 8% nitric acid solution, and an electric potential of 3±1 volts was applied for 40 minutes to exfoliate the fibres into graphene oxide nanosheets.

[0147] Results

[0148] The exfoliated graphene oxide was collected and characterized, revealing a layer thickness of 1.1 nm and lateral dimensions ranging from 400 nm to 600 nm. Surface composition analysis confirmed a C / O ratio of 3 to 9, indicating a high degree of oxidation and exfoliation.

[0149] Conclusion

[0150] The electrochemical exfoliation of polyurethane-coated PAN-based carbon fibres resulted in high-purity graphene oxide nanosheets with well-defined structural properties. The thermal pretreatment effectively removed the polymeric coating, allowing for improved exfoliation efficiency.

[0151] Example 3: Effect of Acid Concentration and Exfoliation Time on Graphene Oxide Production

[0152] Materials & Methods

[0153] The impact of acid concentration and exfoliation time on graphene oxide (GO) production was evaluated by immersing PAN-based carbon fibres in nitric acid solutions of varying concentrations (1 wt.%, 5 wt.%, 10 wt.%, and 50 wt.%). The fibres were subjected to a chemical pretreatment step using a solvent to remove polyurethane coatings before exfoliation. Electrochemical exfoliation was carried out in a two-electrode system, where the carbon fibre acted as the working electrode, and a platinum counter electrode was used. The applied electric potential was maintained at 2.5±0.5V, and exfoliation times were varied between 30 and 120 minutes to assess their effect on yield and nanosheet characteristics. The exfoliated material was filtered, washed, and purified using an ion exchange resin to remove residual electrolyte species.

[0154] Results

[0155] Exfoliation efficiency and graphene oxide yield exhibited strong dependence on both acid concentration and exfoliation time.

[0156] At 1 wt.% nitric acid, exfoliation was incomplete, yielding a mixture of partially oxidized carbonaceous material and fragmented nanosheets. The yield was below 5% of the fibre weight, and the resulting material exhibited limited oxidation, making it unsuitable for applications requiring well-dispersed graphene oxide.

[0157] At 5 wt.% nitric acid, the exfoliation process was significantly improved, producing graphene oxide nanosheets with thicknesses of 0.8-1.1 nm and lateral dimensions of 200-800 nm. The process yield increased to approximately 20% of the fibre weight after 45 minutes, with an optimal balance of oxidation and structural integrity. These nanosheets exhibited a more rounded or oblong shape, as seen in FIG. 4d, in contrast to the polygonal morphology of commercial GO in FIG. 4a.

[0158] At 10 wt.% nitric acid, the exfoliation rate increased further, leading to slightly thinner nanosheets (0.7-1.0 nm), but also introduced a higher defect density. The yield reached 25% after 60 minutes but plateaued thereafter. Structural analysis using Raman spectroscopy (FIG. 4f) confirmed an increase in defect-related features, which could influence the electronic and mechanical properties of the material.

[0159] At 50 wt.% nitric acid, excessive oxidation caused degradation of the carbon fibres, producing highly defective graphene oxide sheets with irregular lateral dimensions. The exfoliation efficiency was lower, and the resulting material exhibited a high concentration of oxygen-containing functional groups, as confirmed by X-ray photoelectron spectroscopy (XPS). However, the structural integrity was compromised, making it less suitable for applications requiring robust nanosheets.

[0160] When varying the exfoliation time at a fixed acid concentration (5 wt.%), prolonging the reaction time from 30 to 60 minutes increased the yield by 10-20% without significantly affecting nanosheet thickness or oxidation level. However, beyond 90 minutes, the degree of oxidation increased, leading to more basal-plane defects and reduced lateral dimensions of the nanosheets.

[0161] XPS confirmed the presence of nitrogen incorporation into the graphene oxide structure, with nitrogen content ranging from 1 to 4 atomic%, depending on both acid concentration and reaction time. The highest nitrogen incorporation was observed at 5- 10 wt.% nitric acid, while extreme conditions (either low acid concentration or prolonged exfoliation times) resulted in lower nitrogen retention. The nitrogen incorporation effect is further illustrated in FIG. 4d-e, where the exfoliated nanosheets demonstrate distinct morphological differences from commercial GO. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) further characterized the exfoliated nanosheets, confirming their morphology, thickness, and lateral dimensions (FIG. 4c- e).

[0162] Conclusion

[0163] The study demonstrated that moderate nitric acid concentrations (5-10 wt.%) and reaction times between 45-60 minutes provide an optimal balance between exfoliation efficiency and material quality. Lower acid concentrations led to incomplete exfoliation, while higher concentrations induced excessive oxidation. The ability to achieve controlled exfoliation under moderate conditions, while also enabling nitrogen incorporation, highlights the advantages of the present method over conventional chemical oxidation approaches. The process allows for tunability, offering a scalable approach for the production of high-quality graphene oxide nanosheets.

[0164] Example 4: Continuous Electrochemical Exfoliation of Graphene Oxide from Carbon Fibres

[0165] Materials & Methods

[0166] A continuous electrochemical exfoliation process was implemented, where PAN-based carbon fibres were fed into an exfoliation system containing a 5% nitric acid solution.

[0167] An electric potential of 4±1 volts was applied to induce exfoliation as the fibre moved through the electrolyte bath. The system was configured to ensure controlled exposure and exfoliation.

[0168] The fibre was fed into the exfoliation system at a controlled rate of 1 cm / min, ensuring uniform exposure to the acidic electrolyte and electric field. Each fibre section remained in the exfoliation chamber for approximately 25 minutes, allowing for complete exfoliation into graphene oxide nanosheets.

[0169] Results

[0170] Graphene oxide nanosheets with lateral dimensions of 800 to 1200 nm and thickness of approximately 1.0 nm were obtained. The exfoliated material was characterized using TEM and AFM, confirming nanosheet uniformity and high exfoliation efficiency.

[0171] Conclusion

[0172] The continuous electrochemical exfoliation process enabled scalable graphene oxide production, achieving high-quality nanosheets under controlled conditions. The results demonstrated that continuous processing is a viable alternative to batch exfoliation.

[0173] Description of the drawings

[0174] The accompanying drawings and examples provided herein are intended to illustrate aspects of the present disclosure but should not be construed as limiting. Features shown in one figure may be combined with those in another unless stated otherwise. The described examples are merely illustrative and do not restrict the scope of the claims.

[0175] The present disclosure provides a graphene oxide nanosheet comprising nitrogen incorporated into its nanosheet structure. By incorporation herein, it is meant that the graphene oxide nanosheet is doped with nitrogen. Nitrogen doping modifies the electronic structure of the graphene oxide nanosheets, whereby electron transfer though the graphene oxide nanosheets are facilitated. Unlike conventional graphene oxide, which is typically functionalized only with oxygen-containing groups, the nanosheets according to the invention contain nitrogen that are integrated into the carbon lattice or attached as functional groups. The nitrogen content in these nanosheets is at least 0.1 atomic percent, as determined by X-ray photoelectron spectroscopy (XPS) a surface analysis technique. The nitrogen content is controlled by the conditions used during the electrochemical exfoliation, such as the voltage applied, the reaction duration and characteristics of the carbon fiber feedstock. An optimal nitric acid concentration for incorporating nitrogen into the graphene oxide nanosheets ranges from about 1 wt.% to 50 wt.%, with a preferred range of 3 wt.% to 10 wt.%. Excessively high concentrations may lead to overoxidation and reduced nitrogen retention.

[0176] In certain embodiments, the nitrogen incorporated into the graphene oxide nanosheets is present in specific chemical forms, including pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, pyridinic nitrogen-oxide, nitro groups, nitrosyl groups, imine groups, amino groups, or any combination thereof. In certain embodiments, the nanosheets has a thickness of 2 nanometers or less, with preferred embodiments exhibiting a thickness of 1.5 nanometers or less, and more preferably about 1 nanometer or less. Conversely, the nanosheets may have a thickness of at least 0.5 nm, such as at least 0.7 nm, at least 0.8 nm, or at least 0.9 nm. The thickness may also be within a range of 0.5 nm to 2 nm, 0.7 nm to 1.5 nm, or 0.8 nm to 1.2 nm, ensuring a balance between surface area and structural integrity. In addition, the lateral dimension of the nanosheets is at least 100 nm and may extend to 1200 nm or more. The thickness and lateral dimensions are determined by atomic force microscopy (AFM) or transmission electron microscopy (TEM). The oxygen-to-carbon atomic ratio of the nanosheets is maintained within the range of 0.1:1 to 1 :1, and preferably between 0.1:1 and 0.6:1 , as measured by X-ray photoelectron spectroscopy (XPS). This combination of thin, large-area nanosheets with a controlled degree of oxidation results in materials with excellent dispersibility, tunable surface chemistry, and enhanced suitability for applications in composites, coatings, membranes, and electronic devices.

[0177] FIG.1 presents a schematic representation of an electrochemical exfoliation apparatus that can be used in the method disclosed herein. The apparatus comprises a reaction chamber (101) that contains an acidic electrolyte solution (105), in which carbon fibres

[0178] (103) are immersed. A voltage source (102) is connected to a carbon fibre electrode (103) and a counter electrode (104), applying an electric potential to induce electrochemical exfoliation of the fibres. As the voltage is applied, oxidation and intercalation processes take place at the interface of the fibre and electrolyte, resulting in the controlled exfoliation of graphene oxide nanosheets.

[0179] FIG.2 illustrates an embodiment of a pretreatment setup configured for removing polymeric coatings from carbon fibres before electrochemical exfoliation. Coated carbon fibres (201) may be subjected to one or more pretreatment processes, such as high-voltage treatment (202), chemical treatment (203), or mechanical treatment (204), depending on the nature of the polymeric layer. In the case of high-voltage treatment (202), an electrical discharge or plasma-assisted process may be employed to break down or weaken the coating, making it more susceptible to removal. Alternatively, a chemical treatment process (203) may involve the use of solvents or reactive chemicals to dissolve polymer layers such as polyurethane or epoxy, facilitating their elimination before exfoliation. Mechanical treatment (204), including abrasive cleaning, ultrasonic agitation, or other physical means, may also be used to ensure the effective removal of coatings that could otherwise interfere with the electrochemical process.

[0180] FIG. 3 provides a comparative visualization of two embodiments of the disclosed electrochemical exfoliation method: a continuous process system (300) and a batch process system (310). Both configurations implement the inventive method, with the selection of a particular approach depending on process requirements, scalability, and operational preferences.

[0181] In the continuous process system (300), a carbon fibre bobbin (303) feeds fresh carbon fibre through a holder (304) into an acidic electrolyte solution (306), where electrochemical exfoliation occurs at the graphene exfoliation site (307) under the influence of a potential / voltage source (302). A counter electrode (314) facilitates the electrochemical reaction, and the fibre moves in the pull direction (305), ensuring a steady and uninterrupted process. A condenser or multiple condensers (301) may be incorporated to manage vapor or temperature fluctuations. During exfoliation, graphene oxide nanosheets are released from the carbon fibre into the electrolyte, while the remaining fibre structure, which may be partially degraded, exits the system as waste material (309).

[0182] In the batch process system (310), a stationary carbon fibre (312) is immersed in an acidic electrolyte solution, where an applied potential from a voltage source (311) drives exfoliation at the fibre surface in conjunction with the counter electrode (314). A heating device (313) may be employed to regulate reaction temperature, thereby influencing exfoliation efficiency. Unlike the continuous process, the batch process operates in discrete cycles, which may offer advantages for laboratoryscale production or when specific process conditions require controlled exposure times.

[0183] Both configurations provide effective exfoliation of carbon fibres into graphene oxide nanosheets. The continuous process enables increased throughput, uniform exfoliation, and reduced handling, making it well- suited for industrial-scale applications. However, the batch process may offer advantages in settings where controlled, smaller-scale production is required or where particular process conditions favour discrete rather than continuous operation. The choice between these implementations depends on the specific requirements of the production environment and the desired characteristics of the resulting graphene oxide nanosheets. FIG.4 presents a detailed comparison between commercially available graphene oxide (GO) nanosheets and those exfoliated from carbon fibres using the disclosed electrochemical method. FIG. 4a shows a scanning electron microscopy (SEM) image of commercial GO nanosheets, which exhibit a polygonal morphology with well-defined edges and relatively uniform lateral dimensions, characteristic of graphite-derived materials. FIG. 4b displays a transmission electron microscopy (TEM) image of the same commercial GO, further highlighting its structured edges and layered nature. FIG. 4c provides an atomic force microscopy (AFM) height measurement, confirming a monolayer thickness of approximately 0.9 nm.

[0184] In contrast, FIG. 4d illustrates the morphology of GO nanosheets exfoliated from carbon fibres using a single-step electrochemical process without chemical pre- treatment. These exfoliated sheets display a more rounded or oblong shape, lacking sharp edges, which suggests a difference in oxidation patterns between carbon fibre- derived GO and conventional graphite-based GO. FIG. 4e presents a TEM image of an exfoliated nanosheet, showing its layered structure and an inset of the selected area electron diffraction (SAED) pattern, which further characterizes its crystallinity. FIG. 4f depicts the Raman spectra of the exfoliated GO nanosheets in comparison to commercial GO, confirming the structural differences in oxidation patterns and defect distributions.

[0185] The exfoliation process was conducted using a 5 wt.% nitric acid electrolyte (105) and an applied potential of 3V, following thermal treatment of the carbon fibres at 600°C. The resulting nanosheets exhibited monolayer characteristics, with an average thickness of 0.9 (± 0.2) nm, as determined by AFM and TEM. This thickness is consistent with reported literature values for monolayer GO, ranging between 0.4 and 1.13 nm. The lateral size distribution of the exfoliated GO nanosheets, shown as insets in FIG. 4d, reveals a broader range of 0.1 to 1 m, compared to the commercial GO in FIG. 4a, which exhibited a narrower distribution of 0.2 to 0.8 pm. Despite this variation, the average lateral sizes of the two types of GO nanosheets remain comparable.

[0186] Structural differences between the commercial and exfoliated GO nanosheets suggest that the absence of a strict crystalline lattice in carbon fibres influences the oxidation and exfoliation pattern. The commercial GO sheets in FIG. 4a, derived from natural graphite, retain a crystalline structure with straight edges, while the fibre-derived GO nanosheets in FIG. 4d exhibit a more irregular morphology, potentially reflecting a less uniform oxidation pattern. This structural variation, along with the control over oxidation conditions provided by the electrochemical exfoliation method, allows for a tuneable approach to graphene oxide production, enabling the generation of nanosheets with specific structural and chemical characteristics tailored for various applications.

[0187] FIG.5 illustrates a flowchart representing an embodiment of the disclosed method for producing graphene oxide nanosheets. The process begins with immersing carbon fibres (501) in an acidic electrolyte solution comprising nitric acid at a concentration of from 0.5 % to 20 % by weight, ensuring sufficient contact between the fibres and the electrolyte to facilitate subsequent electrochemical exfoliation. An electric potential is then applied (502) to the immersed carbon fibres, inducing electrochemical reactions that promote exfoliation of the fibres into graphene oxide nanosheets. Finally, the exfoliated material undergoes separation and collection (503), wherein the graphene oxide nanosheets are isolated from the reaction medium. Arrows between the steps indicate the sequential nature of the process, demonstrating the transformation from raw carbon fibre material to exfoliated nanosheets through controlled electrochemical processing.

[0188] FIG.6 presents a schematic representation of a system (601) configured for carrying out the disclosed method for producing graphene oxide nanosheets. The system includes a reaction chamber (602) designed to hold the acidic electrolyte solution and facilitate controlled electrochemical exfoliation. A fibre feed mechanism (603) is provided to introduce carbon fibres into the reaction chamber in a manner that ensures consistent exposure to the electrolyte. An electrode assembly (604) is configured to apply an electric potential across the fibres, promoting exfoliation while minimizing unwanted oxidation. Finally, a collection unit (605) is incorporated to separate and collect the exfoliated graphene oxide nanosheets. This schematic representation highlights the functional components of the system and their interactions, demonstrating how the disclosed method may be implemented in a controlled and scalable manner.

[0189] These drawings are provided solely as examples to illustrate certain aspects of the disclosure and do not limit the invention to the specific embodiments shown.

[0190] Items

[0191] 1. A method for producing graphene oxide nanosheets, comprising:

[0192] (a) immersing carbon fibres in an acidic electrolyte solution;

[0193] (b) applying an electric potential to the immersed carbon fibres to electrochemically exfoliate the fibres; and

[0194] (c) separating and collecting the exfoliated material.

[0195] 2. The method according to item 1, wherein the process yields at least 200 mg of graphene oxide per gram of carbon fibre.

[0196] 3. The method according to any one of the preceding items , wherein the collected material comprises graphene oxide nanosheets having an average layer thickness of about 1 nm and average lateral dimensions of about 500 nm to about 1200 nm.

[0197] 4. The method according to any one of the preceding items, wherein the carbon fibres are selected from the group consisting of polyacrylonitrile (PAN)-based carbon fibres, pitch-based carbon fibres, rayon-based carbon fibres, and lignin- based carbon fibres, and wherein the carbon fibres may be either newly manufactured or recycled.

[0198] 5. The method according to any one of the preceding items, wherein the acidic electrolyte solution comprises nitric acid or a mixture of nitric acid and at least one additional acid selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and lactic acid, the ratio of nitric acid to the additional acid being up to 50:50, and wherein the total acid concentration is between 1% and 20% by weight, with a preference for concentrations below 10%. The method according to any one of the preceding items, wherein the electric potential applied to the carbon fibres ranges from 1 to 12 volts, with a preferred range of above 2 volts and below 6 volts. The method according to any one of the preceding items, wherein the acidic electrolyte solution comprises a surface-active agent configured to promote intercalation of the acidic electrolyte solution into the carbon fibres and facilitate exfoliation during the application of the electric potential. The method according to any one of the preceding items, wherein the method is performed as a batch process. The method according to any one of item 1-6, wherein the method is performed as a continuous process, wherein the carbon fibres are continuously fed through the acidic electrolyte solution while the electric potential is applied. The method according to item 8, wherein the continuous feeding of carbon fibres is performed at a speed of from about 0.1 cm / min to about 5 cm / min. The method according to any one of the preceding items, wherein the process is conducted under ambient temperature conditions. The method according to any one of the preceding items, wherein the process is conducted under controlled temperature conditions to optimize the electrochemical exfoliation. The method according to any one of the preceding items, further comprising a pretreatment step performed prior to immersing the carbon fibres in the acidic electrolyte solution, for removing any polymeric coating on the carbon fibres.

[0199] 14. The method according to item 12, wherein the pretreatment step comprises a chemical treatment using a solvent selected from the group consisting of acetone, methanol, and mixtures thereof to dissolve polymeric coatings such as polyurethane or epoxy.

[0200] 15. The method according to item 12 or 13, wherein the pretreatment step further comprises a thermal treatment by heating the carbon fibres to a temperature above 400 °C to remove the polymeric coating.

[0201] 16. The method according to any one of items 12-14, wherein the pretreatment step comprises a combination of chemical and thermal treatments.

[0202] 17. The method according to any one of items 12-15, wherein the pretreatment step is performed for a duration sufficient to remove at least 90% of the polymeric coating as determined by surface analysis.

[0203] 18. The method according to any one of the preceding items, wherein the acid concentration and electric potential are optimized to achieve controlled oxidation of the carbon fibres, thereby reducing degradation relative to natural graphite-based production methods.

[0204] 19. The method according to any one of the preceding items, further comprising a post-treatment step for the acidic electrolyte solution, the post-treatment step comprising the use of an ion exchange resin to remove residual acid and ionic contaminants.

[0205] 20. The method according to any one of the preceding items, further comprising a drying step performed on the collected graphene oxide nanosheets, wherein the drying is conducted under ambient or controlled temperature conditions to produce a dry powder.

[0206] 21 . The method according to any one of the preceding items, wherein the process is conducted under conditions that avoid the use of additional oxidizing chemicals beyond those present in the acidic electrolyte solution.

[0207] 22. A system for producing graphene oxide nanosheets, comprising:

[0208] (a) a reaction chamber configured to contain an acidic electrolyte solution;

[0209] (b) a fibre feed mechanism configured to introduce carbon fibres into the reaction chamber, such as wherein the carbon fibres are selected from the group consisting of PAN-based carbon fibres, pitch-based carbon fibres, rayon- based carbon fibres, and lignin-based carbon fibres;

[0210] (c) an electrode assembly configured to apply an electric potential to the carbon fibres for electrochemical exfoliation; and

[0211] (d) a collection unit configured to separate and collect the graphene oxide nanosheets.

[0212] 23. The system according to item 22, wherein the electrode assembly comprises a two-electrode configuration with the carbon fibres serving as an anode and a counter electrode selected from the group consisting of platinum and other inert conductive materials serving as a cathode.

[0213] 24. The system according to any one of items 22-23, wherein the fibre feed mechanism is configured to feed the carbon fibres at a speed of from about 0.1 cm / min to about 5 cm / min.

[0214] 25. The system according to any one of items 22-24, wherein the system is configured to carry out the method according to any one of items 1-21 .

[0215] 26. The system according to any one of items 22-25, wherein the system is configured to operate under the conditions set forth in any one of items 1-21.

[0216] 27. A computer-readable medium storing instructions which, when executed by a processor, cause the processor to control a production unit to perform the method according to any one of items 1-21. 28. Use of graphene oxide nanosheets produced by the method according to any one of item 1-21 in applications selected from the group consisting of energy storage devices, composite materials, coatings, flexible electronics, tribological applications, catalysis, water purification, and high-voltage insulation materials.

[0217] 29. A graphene oxide nanosheet comprising nitrogen incorporated into its structure.

[0218] 30. The graphene oxide nanosheet according to item 29, wherein the nitrogen content is at least 0.1 atomic%.

[0219] 31 . The graphene oxide nanosheet according to any one of items 29-30, wherein the nitrogen is present in the form of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, or combinations thereof.

[0220] 32. The graphene oxide nanosheet according to any one of items 29- 31 , wherein the nanosheet has a thickness of 2 nm or less, such as 1.5 nm or less, such as 1 nm or less.

[0221] 33. The graphene oxide nanosheet according to any one of items 29-32, wherein the lateral dimension is at least 100 nm.

[0222] 34. The graphene oxide nanosheet according to any one of items 29- 33, wherein the oxygen-to-carbon atomic ratio is between 0.1 :1 and 1 :1 , such as between 0.1 :1 and 0.6:1.

Claims

Claims1 . A graphene oxide nanosheet comprising nitrogen incorporated into its structure.

2. The graphene oxide nanosheet according to claim 1 , wherein the nitrogen content is at least 0.1 atomic%.

3. The graphene oxide nanosheet according to any one of the preceding claims, wherein the nitrogen content is at most 10 atomic%.

4. The graphene oxide nanosheet according to any one of the preceding claims, wherein the nitrogen content ranges from about 1 atomic% to 5 atomic%.

5. The graphene oxide nanosheet according to any one of the preceding claims, wherein the nitrogen is present in the form of pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, pyridinic nitrogen-oxide, nitro groups, nitrosyl groups, imine groups, amino groups, or combinations thereof.

6. The graphene oxide nanosheet according to any one of the preceding claims, wherein the nanosheet has a thickness of 2 nm or less, such as 1.5 nm or less, such as 1 nm or less.

7. The graphene oxide nanosheet according to any one of the preceding claims, wherein the lateral dimension of the graphene oxide nanosheets is at least 100 nm.

8. The graphene oxide nanosheet according to any one of the preceding claims, wherein the oxygen-to-carbon atomic ratio is between 0.1 :1 and 1 :1 , such as between 0.1 :1 and 0.6:1.

9. A method for producing a graphene oxide nanosheets according to any of claims 1 to 8, comprising:(a) immersing carbon fibres in an acidic electrolyte solution comprising nitric acid at a concentration of from 0.5 % to 20 % by weight;(b) applying an electric potential to the immersed carbon fibres toelectrochemically exfoliate the fibres; and(c) separating and collecting the exfoliated material.

10. The method according to claim 9, wherein the process yields at least 100 mg of graphene oxide per gram of carbon fibre.

11. The method according to any of claims 9 to 10, wherein the acidic electrolyte solution comprises nitric acid at a concentration of from 1 % to 20 % by weight.

12. The method according to any of claims 9 to 10, wherein the acidic electrolyte solution comprises nitric acid and at least one additional acid selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, and lactic acid; wherein the ratio of nitric acid to the additional acid is up to 50:50; and wherein the total acid concentration is between 1 % and 20% by weight.

13. The method according to any of claims 9 to 12, wherein the electric potential applied to the carbon fibres ranges from 1 to 12 volts.

14. The method according to any of claims 9 to 13, wherein the acidic electrolyte solution comprises a surface-active agent configured to promote intercalation of the acidic electrolyte solution into the carbon fibres and facilitate exfoliation during the application of the electric potential.

15. The method according to any of claims 9 to 14, wherein the method is performed as a continuous process, wherein the carbon fibres are continuously fed through the acidic electrolyte solution while the electric potential is applied.

16. The method according to any of claims 9 to 15, further comprising, following step (c), a post-treatment step for the acidic electrolyte solution resin to remove residual acid and ionic contaminants.

17. A system for producing graphene oxide nanosheets according to any of claims 1 to 8, comprising:(a) a reaction chamber configured to contain an acidic electrolyte solution comprising nitric acid at a concentration of from 0.5 % to 20 % by weight;(b) a fibre feed mechanism configured to introduce carbon fibres into the reaction chamber, wherein the carbon fibres are selected from the group consisting of PAN-based carbon fibres, pitch-based carbon fibres, rayonbased carbon fibres, and lignin-based carbon fibres;(c) an electrode assembly configured to apply an electric potential to the carbon fibres for electrochemical exfoliation;(d) a collection unit configured to separate and collect the graphene oxide nanosheets; and(e) a processor configured to control the system to perform the method according to any one of claims 8 to 16.

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