A sustainable and scalable method for graphene production

Abstract

The present disclosure relates to an environmentally sustainable and scalable process for graphene production from recycled carbon under mild conditions. The proposed method comprises subjecting one or more carbon sources (CS) to a pyrolysis (a) at a pyrolysis temperature of up to 400°C under nitrogen atmosphere, thereby obtaining a recycled carbon black as a precursor with an oily portion. The method further comprises subjecting the recycled carbon black to a potassium hydroxide solution treatment (b), thereby obtaining an output of step-b. The method further comprises subjecting the output of step-b to an iron chloride solution treatment (c), thereby obtaining an output of step-c. The method further comprises subjecting the output of step-c to a carbonization (d) at an argon atmosphere, thereby obtaining one or more graphene nanoplatelets, at a temperature within a range between 900 °C and 1800 °C.

Description

[0001] A SUSTAINABLE AND SCALABLE METHOD FOR GRAPHENE PRODUCTION

[0002] Technical Field

[0003] The present disclosure relates to a method for obtaining graphene. In particular, the present disclosure relates to a sustainable and scalable graphene production method.

[0004] Background

[0005] Graphene is regarded as one of the most remarkable achievements in the field of science and technology. This hexagonal crystalline single layer of graphite has garnered significant attention in diverse industries such as electronics, energy, defense automotive, and aerospace, playing a pivotal role in sensors, biomedicals, composite materials, and microelectronics. Widespread application of graphene forthese purposes has been hindered by challenges in its production, which, fortunately, has seen recent improvements, addressing a historical bottleneck. These methods can be categorized into four main groups: micromechanical cleavage, chemical exfoliation, epitaxial growth on substrates, and chemical vapor deposition technique.

[0006] Among these methods, chemical vapor deposition (abbreviation: CVD), which is based on the bottom-up method provide to produce high-quality graphene sheets with perfect structure and large lateral area size. However, higher production cost, lower production efficiency and complex preparation procedures greatly limit its large-scale application. On the other hand, the top-down method, which is mainly dependent upon the exfoliation of graphite, exhibits its unique advantages in terms of low-cost, high efficiency and large-scale. This method, aimed at the straightforward separation of graphene layers from bulk graphite through multiple steps, relies on overcoming the weak van der Waals forces between adjacent layers of graphene necessitating mechanical or chemical energy. The process of exfoliation, achieved through both mechanical and chemical means, stands as a significant pathway in production. Utilizing the scotch tape method to obtain graphene layers exemplifies a common example of mechanical exfoliation.

[0007] Moreover, graphene-intercalated compounds are employed as another method to transform graphite into graphene. During the exfoliation process, alkali metals such as potassium and sodium are introduced to graphite flakes to improve interlayer spacing and reduce van der Waals interactions, followed by sonication to yield monolayer graphene. For this process, in prior art, a chemical exfoliation process is carried out by means of potassium alkali metal to produce graphene nanoplatelets (GNP).

[0008] Synthesis of graphene from natural or waste materials has gained attention due to its potential to promote sustainability and resource reusability. In addition to graphite, low- cost graphitic carbon derived from various organic wastes, including animal, agricultural, and plastic residues offer a versatile resource for graphene production. Traditionally, graphene has been synthesized from graphite, a crystalline form of carbon. However, this method may not be the most sustainable and cost-effective. Various organic wastes such as agricultural residues (e.g., rice husks, sugarcane bagasse), animal residues, and plastic residues serve as alternative sources of carbon for graphene synthesis. In addition, some researchers have investigated the synthesis of graphene nanoplatelet from different recycled carbon black derivatives such as waste plastics, pyrolyzed tires, waste rubber and biomass as the choice of starting material depends on desired properties of the final product. Furthermore, the use of these carbon-rich materials for the graphene synthetic processes is not only economically beneficial but also provides a profitable way for their disposal. The core principle of biomass or waste-derived graphene involves pyrolysis under an inert atmosphere, utilizing diverse feedstocks as carbon sources. In a study by Ramesh et al. have reported the utilization of black carbon to synthesize graphene nanosheet via catalytic chemical vapor deposition (C-CVD) technique with the help of bi-metallic catalyst (Fe-Ni) for multifunctional biological studies. In one of the recent studies, it is shown that porous graphene-like nanosheets with a large surface area were synthesized by a simultaneous activation-graphitization route from renewable biomass waste coconut shell by using the graphitic catalyst precursor (FeCH) and activating agent (ZnCIz). In another work, it is found that a hybrid of graphene flakes and tubular shape nano carbon was produced from the pyrolysis of a salt milled solid carbon source under non-oxidizing environment using a specific Fe relative catalyst.

[0009] The quality of pyrolysis products is largely determined by the operating temperatures. Research suggests that higher pyrolysis temperatures yield higher-quality graphene materials. It is commonly advised to begin pyrolysis at lower temperatures to fully carbonize the feedstock, followed by high-temperature heating for graphitization. The process of washing the char with either acid and distilled water serves to remove impurities and enhance the surface area. A prior art study shows that when lignin- derived graphitic char is washed with KOH, its surface area increases from 117 to 983 m2 / g. Similarly, washing with H3PO4 results in an increase in surface area to 737 m2 / g. For instance, a prior art disclosure showcases a low-temperature Fe-assisted catalytic process, transforming waste-expanded polystyrene into a graphene derivative by impregnating EPS with FeCH particles and subsequently carbonizing at different temperature ranges (600 °C, 700 °C, and 800 °C), resulting in the catalytic formation of crystalline few-layered graphene sheets with electrical conductivity. For instance, a prior art disclosure explores a method using KOH as a catalyst, the intercalation of metallic potassium into the carbon network and microwave heating to rapidly convert waste tires into porous graphene with the catalytic reaction catalyzed by potassium ions at temperatures exceeding 750°C, demonstrating reduced preparation time and improved graphene quality.

[0010] Process of obtaining graphene from recycled carbon black involves several key steps, each crucial for the successful synthesis of graphene nanoplatelets (GNP). These steps typically include oxidation and exfoliation, exfoliation and reduction. Recycled carbon black undergoes chemical oxidation using strong oxidizing agents such as concentrated acids and a mixture of acids (e.g., sulfuric acid and nitric acid). In a rather recent prior art study, it is investigated a cost-efficient method for producing graphene-based materials by modified Hummers' method. Also, exfoliation methods consist of sonication, mechanical and chemical shearing with suitable solvents. Moreover, Sharief et al. demonstrated the successful synthesis of few-layer graphene-like (FLG) sheets from carbon black by electrochemical exfoliation and also proposed binding the carbon black particles together using a pH-independent intrinsically electrically conducting polymer to form a porous working electrode.

[0011] Accordingly, the present disclosure is directed to provide an improved method for production of graphene.

[0012] Summary

[0013] Widespread adoption of graphene is currently hindered by several technical challenges associated with its synthesis. These challenges can be broadly categorized into two main areas, namely carbon source availability and cost, and environmental and safety-related concerns.

[0014] Regarding carbon source availability and cost; graphite as a primary known carbon source for graphene, faces limitations in terms of its availability, mesh size and cost. Large-scale production of high-quality graphene necessitates readily available and affordable graphite sources.

[0015] Regarding environmental and safety-related concerns; conventional synthesis methods rely on hazardous and harsh chemicals such as hydrazine, sulfuric acid, and nitric acid. These chemicals pose significant environmental and safety risks. These risks include:

[0016] - toxicity and carcinogenicity to humans and the environment;

[0017] - pollution from waste generation and disposal;

[0018] - high energy consumption during processing, leading to increased cost and contributing to carbon footprint;

[0019] - scalability limitations due to the fact that the amount and type of chemicals required vary significantly with production scale, presenting a barrier for upscaling production. Addressing these technical problems will pave the way for a more sustainable, cost- effective, and commercially viable route to graphene production, ultimately unlocking its full potential for diverse applications. Therefore, the present disclosure addresses an urgent need that exists to develop novel and efficient graphene synthesis method.

[0020] The primary object of the present application is to overcome the above-mentioned shortcomings of the prior art. The present disclosure achieves this object with the features that constitute the appended independent claim.

[0021] The proposed method solves several problems in upscaling of graphene synthesis. The method provides optimized reaction conditions, allow flexibility in design of equipment that can be employed in performing the method. The method also enables the employment of optimal process parameters. Thus, the method allows a high extent of scalability and repeatability. The method reduces costs related to raw materials (that is, carbon sources), energy consumption and possible process equipment, thereby further enhancing the ability to upscale. Since the carbon sources for the proposed method are available with low-cost and readily available in large amounts, the cost-effectiveness and scalability of the method is to be considered as one of prominent advantages thereof.

[0022] Accordingly, the proposed method for obtaining graphene comprises the following sequential steps: a) subjecting one or more carbon sources to a pyrolysis at a nitrogen atmosphere at a pyrolysis temperature of up to 400°C, preferably within the range between 350 °C and 400°C, thereby obtaining a recycled carbon black as a precursor, that can be considered to include an oily portion; b) subjecting the recycled carbon black to a potassium hydroxide solution treatment, thereby obtaining an output of step-b; c) subjecting the output of step-b to an (anhydrous-) iron chloride solution treatment, thereby obtaining an output of step-c; d) subjecting the output of step-c to a carbonization at an argon atmosphere, thereby obtaining one or more graphene nanoplatelets, at a temperature within a range between 900 °C and 1800 °C.

[0023] The method successfully enables the use of one or more low-cost and abundant carbon sources from one or more waste sources. The one or more waste sources can be selected from waste tires, waste rubber, carbonized biomass disposal and thermosets. For instance, the carbon source can include waste tires.

[0024] The step-a can further comprise an acid treatment of the recycled carbon black. The acid treatment can be followed by one or more filtration and drying. Similarly, the step-b and / or step-c can further comprise one or more filtration and drying.

[0025] The potassium hydroxide solution treatment in step-b can comprise one or more of the following:

[0026] - arranging that a potassium hydroxide concentration in the solution is within a range between 0.5 and 1.0 moles per liter;

[0027] - arranging that the potassium hydroxide solution treatment is performed along a treatment duration within a range between 4 hours and 24 hours;

[0028] - arranging that a treatment temperature is applied within the range between 80 °C and 120 °C,

[0029] - arranging that a gradual heating is applied;

[0030] - arranging that the potassium hydroxide solution further includes one or more surfactants selected from sodium dodecyl sulphate and sodium dodecylbenzene sulfonate; wherein an amount of surfactants in a respective treatment medium is at a carbo surfactant weight ratio within a range between 50:1 and 100:1.

[0031] The iron chloride solution treatment in step-c can comprise one or more of the following:

[0032] - arranging that an (anhydrous-) iron chloride concentration in the solution is within a range between 0.5 and 1.0 moles per liter; - arranging that the iron chloride solution treatment is performed along a treatment duration within a range between 4 hours and 24 hours;

[0033] - arranging that a treatment temperature is applied within the range between 80 °C and 120 °C;

[0034] - arranging that a gradual heating is applied;

[0035] - arranging that the iron chloride solution further includes one or more surfactants selected from sodium dodecyl sulphate and sodium dodecylbenzene sulfonate; wherein an amount of surfactants in a respective treatment medium is at a carbo surfactant weight ratio within a range between 50:1 and 100:1.

[0036] The carbonization in step-d can be considered as performed at a duration within a range between 5 minutes and 30 minutes at a carbonization temperature higher than 900°C up to 1800°C, by starting from an ambient temperature such as 20°C or room temperature to the carbonization temperature by gradual heating under argon atmosphere.

[0037] Brief Description of the Figure

[0038] Fig.l shows a schematical flow diagram of an exemplary implementation of the method according to the present disclosure.

[0039] Detailed Description

[0040] With reference to Fig.l, the present disclosure proposes a method for obtaining graphene. Combination of features in the method enable the production of graphene from low-cost carbon black sources, that are readily available in large amounts. The carbon source (CS) can be selected from, e.g., waste tire, waste rubber, carbonized biomass disposal, thermosets, and thermoplastics that are already subjected to a pyrolysis. Thus, it can be considered that obtainment of the carbon source (CS) corresponds to a preparatory or initial step of the proposed method. In order to provide a facilitated graphitization, it is preferable that the one or more carbon sources is selected in accordance with one or more of the following criteria: - based on total weight of the carbon source (CS), the carbon content of the carbon source (CS) can be higher than 65 wt.% on the basis of the total weight of the carbon source (CS);

[0041] - the carbon source (CS) can have a particle size distribution higher than 100 mesh;

[0042] - the carbon source (CS) can have a high adsorption-specific surface area;

[0043] - the carbon source (CS) can have a high oil absorption value;

[0044] - the carbon source (CS) can have a low heating loss;

[0045] - the carbon source (CS) can have a low impurity level.

[0046] As a step-a, the method comprises pyrolysis (a) of the carbon source (CS) at a pyrolysis temperature within the range between 350°C and 400°C under a nitrogen atmosphere, thereby obtaining a recycled carbon black as a precursor. The pyrolysis (a) can be also referred to as a carbonization. Said pyrolysis temperature range is considered mild and minimizes the formation of char from the carbon source (CS), maximizing the formation of polycyclic aromatic hydrocarbons in the recycled carbon black. Thus, the recycled carbon will include an oily portion that corresponds to said polycyclic aromatic hydrocarbons and can further contain other possible organic components that emerge during the pyrolysis (a). Because of such oily portion, the recycled carbon obtained at the end of pyrolysis (a) is preferably not to be subjected to any milling prior to the KOH treatment step (b). Further, since a milling would decrease particle size of the recycled carbon black; it is preferred to avoid milling and thereby refrain from decreasing particle size and thus increase the yield of resulting graphene as a final product. The pyrolysis (a) can be performed for a duration of, e.g., 6 hours or longer.

[0047] It should be noted that the recycled carbon black with an oily portion as the product of the step-a shall be considered non-equivalent to a carbon black obtained through a way that is different from the step-a, and then mixing it with polycyclic aromatic hydrocarbons that were obtained separately. This is because the recycled carbon black and the oily portion as in the product of step-a are inherently chemically bonded to each other. This enables or provides the resulting graphene nanoplatelets as product of the method. Following the step-a, the method can include an acid treatment (al) of the recycled carbon black, which can be concluded by one or more filtration and drying (a 2). The acid treatment (al) can involve contacting the recycled carbon black with sulphuric acid (H2SO4) or mixtures thereof.

[0048] As a step-b that follows the step-a or step-al, the method comprises with a potassium hydroxide solution treatment (b) of the recycled carbon black, thereby obtaining an output of step-b. The step-b can be considered to further involve one or more filtration and drying (bl). The step-b provides elimination of any impurities from pyrolysis (a) (such as, excess iron, oily portion, etc.), increasing surface area of the recycled carbon black, introduction of functional groups to the recycled carbon black (that can be referred to as surface activation of the recycled carbon black), thereby enhancing the quality of the recycled carbon black. So, the step-b provides an output that has an enhanced quality when compared to the recycled carbon black (as the output of step- a), by having an activated surface and being comparatively or entirely free of impurities.

[0049] In step-b, the solution of potassium hydroxide can be an aqueous solution. The potassium hydroxide solution treatment (b) can be performed in accordance with one, more or all of the following measures:

[0050] - it can be arranged that a potassium hydroxide concentration in the potassium hydroxide solution can be within a range between 0.5 and 1.0 moles per liter;

[0051] - it can be arranged that a treatment temperature can be within the range between 80 °C and 120 °C, that can be exerted with a gradual heating throughout a treatment duration;

[0052] - it can be arranged that the treatment duration can be within a range between 4 hours and 24 hours;

[0053] - it can be arranged that the potassium hydroxide solution can further include one or more surfactants that can be selected from, e.g., sodium dodecyl sulphate and sodium dodecylbenzene sulfonate. Here, the amount of surfactant(s) in a respective treatment medium can be at a carbo surfactant weight ratio within a range between 50:1 and 100:1. As a step-c that follows the step-b, the method comprises an iron chloride (FeCH) solution treatment (c) of the output of step-b, thereby obtaining an output of step-c. The step-c can be considered to further involve one or more filtration and drying (cl). The step-c provides a catalytic impregnation and an enhanced interaction of carbon atoms in the output of step-b with iron atoms. The catalytic impregnation can be also referred to as deposition of iron species on carbon structure in the output of step-b.

[0054] In step-c, the solution of iron chloride can be an aqueous solution. The iron chloride solution treatment (c) can be performed in accordance with one, more or all of the following measures:

[0055] - it can be arranged that an iron chloride concentration in the iron chloride solution can be within a range between 0.5 and 1.0 moles per liter; the iron chloride concentration can be determined on the basis of anhydrous iron chloride to be solved in water, or any crystal water that can be present in iron chloride can be taken into consideration when calculating the amount of water as solvent;

[0056] - it can be arranged that a treatment temperature can be within the range between 80 °C and 120 °C, that can be exerted with a gradual heating throughout a treatment duration;

[0057] - it can be arranged that the treatment duration can be within a range between 4 hours and 24 hours;

[0058] - it can be arranged that the iron chloride solution can further include one or more surfactants that can be selected from, e.g., sodium dodecyl sulphate and sodium dodecylbenzene sulfonate. Here, the amount of surfactant(s) in a respective treatment medium can be at a carbo surfactant weight ratio within a range between 50:1 and 100:1.

[0059] As a step-d, that follows the step-c, the method comprises carbonization (d) of the output of step-c at an argon atmosphere, thereby obtaining one or more graphene nanoplatelets (abbreviation: GNP). The carbonization (d) can be also referred to as catalytic carbonization. The catalytic carbonization (d) can be also referred to as graphitization. The catalytic carbonization (d) in step-d can be performed at a temperature within a range between 900 °C and 1800 °C. The catalytic carbonization (d) in step-d can be performed at a duration within a range between 5 minutes and 30 minutes. The term "catalytic" here refers to the role of iron present in the output of step step (c) because of the FeCIs treatment.

[0060] The proposed method provides the following upsides when compared to prior art graphene production technologies:

[0061] - high reaction yields are available, that are greater than 75% by weight (that is, even more than 75 grams of GNP can be obtained on the basis of 100 grams of carbon source (CS);

[0062] - GNP as a valuable product can be obtained at low costs and in high amounts, starting from low-cost carbon sources (CS) that are readily available in large amounts, thereby allowing a high extent of scalability;

[0063] - thermal process conditions are rather moderate, thereby reducing the production costs and safety;

[0064] - the process can be completed without necessitating hazardous chemicals, thereby providing a mild, safe and environmentally benign process;

[0065] - the process provides GNP with a high quality, that are in the form of planar platelets, that can have a particle size (length or width that is orthogonal to thickness, whichever is greater) of around 50 nanometers.

[0066] The present disclosure proposes the use of sustainable carbon sources (CS). That is, the method utilizes readily available and cost-effective recycled carbon black derived from biomass or waste materials (e.g., waste rubbers, tires). This not only addresses the cost and scalability limitations of graphite but also contributes to waste management and a circular economy.

[0067] The present disclosure is convenient with green chemistry. That is, the method employs moderate chemical processes and heat treatments, significantly reducing dependence on hazardous chemicals and minimizing energy consumption. The method utilizes basic solutions instead of harsh acidic chemicals such as sulphuric acid and nitric acid and mixing the precursor in aqueous solutions thereof.

[0068] The present disclosure provides a high extent of scalability and reliability in GNP production. That is, the method can be considered to implement a meticulous control of process parameters and product quality checks at various stages (e.g., oily portion after pyrolysis) to ensure reliability and effectiveness. Oily carbon is useful to initiate graphitization (d) that can be operated at a temperature of 350 °C or greater, under nitrogen atmosphere required for pyrolysis process. Carbon materials obtained by a pyrolysis under vacuum, would not be suitable for graphene manufacturing.

[0069] The present disclosure provides a high-quality product. That is, the method delivers a final graphene product (that is, GNP; in other words, few-layers graphene, that can be considered to have functionalized surfaces) with quality matching or exceeding conventional methods, ensuring compliance with industry standards. Graphene product in platelet form can be obtained with the average particle size of about 50 nm or even greater.

[0070] The integrated and sustainable approach of the proposed method offers a promising route to overcome the limitations of prior art graphene synthesis methods, paving the way for its broader adoption and impactful applications across various fields.

[0071] Thus, the proposed method provides:

[0072] - industrial-scale, reliable, economical, and sustainable production of graphene and utilization of recycled carbon black;

[0073] - elimination of risks related to originally unknown waste carbon sources (CS) and a reliable synthesis process starting therefrom;

[0074] - development of an enhanced upscaling process;

[0075] - improvement of recycling routes to diminish risks on environment and human health. Expected impact of the present disclosure can be considered to involve the following: As an exemplary carbon source (CS) within the context of the present disclosure, waste tires are a significant environmental concern globally, with millions of tons generated each year. Also, the industrial scale up of few-layer graphene (that is, GNP) as the product of the proposed method, and its low cost when compared to prior art methods relieve current restrictions against the widespread use of GNP. The proposed method opens up new market opportunities for GNP, as it offers a cost-effective and sustainable alternative to traditional production methods. This can stimulate innovation and growth in the GNP industry and create reliable, cost-effective and fast processes capable of fulfilling all requirements for large volume production of functional graphene. Moreover, Life Cycle Assessment (abbreviation: LCA) methodology provide valuable insights into the environmental impacts and benefits of the synthesis of GNP from recycled carbon black LCA evaluate the resource efficiency of the GNP synthesis process, including the use of recycled carbon black as a starting material. This can help identify opportunities to optimize resource use and minimize waste generation. With the concept proposed with the present disclosure; simulation of use, recycling or end-of-life processes of graphene-based products can be conducted to minimize environmental and toxicological risks for cradle-to-grave monitoring regarding to Environmental Protection Agency (abbreviation: EPA) regulations.

[0076] EXAMPLE 1:

[0077] The following discussion refers to an exemplary implementation of the proposed method, several aspects of any feature thereof can be attributed to the general context of the present disclosure without prejudice. None of the content in the following discussion intends to delimit the intended scope of protection with regard to the present application:

[0078] - The exemplary method highlights an enhanced synthesis procedure for the production of graphene nanoplatelets (GNP) derivable from different recycled carbon black sources, obtained specifically from biomass, waste tire and other thermoset wastes. - Recycled carbon black is a byproduct as a result of the combustion of hydrocarbons and it is widely used as a filler material in rubber and thermosets in the industry. The exemplary method promotes the utilization of recycled carbon black, thereby addressing sustainability concerns associated with waste tire and rubbery products or carbonized biomass disposal while simultaneously advancing the production of high-quality graphene nanomaterials.

[0079] - Selection of recycled carbon as carbon source (CS) is one of the aspects of the present exemplary method. In this context, an oily portion (that is constituted from hydrocarbons and other possible organic compounds) of carbon derived from the pyrolysis (a) process conducted under Nz / vacuum is useful in initiation of graphitization (d) process. Moreover, in order to facilitate the initiation of the graphitization (d) process; the selected recycled carbon can possess one, preferably more, or more preferably all of the following qualities: a high carbon content (>90 wt%), high particle size distribution (> +100 mesh), high adsorption-specific surface area, high oil absorption value, low heating loss and low impurity levels. In addition, the dispersion of recycled carbon black can be suitably arranged for mixing in respective aqueous solutions of KOH in step-b and FeCH in step-c with a gradual heating process according to the proposed methodology. If the mixing does not disperse, the dispersion of carbon materials in said aqueous solutions can be improved in order to break down the surface tension between water and carbon particles (that is, recycled carbon black as the output of step-a and in the output of step b), by adding surfactants such as SDS (sodium dodecyl sulfate) or SDBS (sodium dodecylbenzenesulfonate) at an appropriate carbon / surfactant ratio (e.g., from 50:1 to 100:1).

[0080] - In this methodology, the synthesis procedure of graphene nanoplatelets (GNP) from recycled carbon black involves steps aimed at exfoliating and transforming the recycled carbon black into graphene nanoplatelets (GNP). This process can provide it economically feasible to convert into high-quality graphene nanoparticles (GNP).

[0081] - For this purpose, the step-a corresponds to a preparation of recycled carbon black obtained from waste tire sources through the pyrolysis (a) process. Subsequently, as step-b, potassium hydroxide (KOH) solution treatment (b) activates the surface of recycled carbon black, increasing its surface area and introducing functional groups; and eliminates impurities coming from pyrolysis (a) process. Step-b enhances the material's reactivity and compatibility with other substances, such as polymer based composite materials. In addition, potassium hydroxide solution treatment (b) provides removal of impurities, thereby improving purity and quality of the carbon black. The potassium hydroxide solution treatment (b) can be performed with a KOH concentration between 0.5 M and 1 M, at a temperature that can be between 80°C and 120°C (here: approximately 80°C), for 4 hours to 24 hours.

[0082] - Then, as step-c, catalytic impregnation of recycled carbon black with iron chloride (FeCIs) can be carried out, in order to enhance the interaction between the iron atoms and the carbon atoms and the deposition of iron species on carbon structure. This iron chloride solution treatment (c) can be performed with an iron chloride concentration between 0.5 M and IM, at a temperature that can be between 80°C and 120°C (here: approximately 80°C), for 4 h to 24 h.

[0083] - This is followed by a carbonization (d), conducted at around 900°C-1800°C under an inert atmosphere (especially argon gas not nitrogen atmosphere) by keeping the material from 5 min to 30 min to provide the graphitization. Thus, a valuable material is obtained from a waste product, reducing the cost of graphene production thanks to the proposed process by converting recycled carbon black into high-quality graphene nanoplatelets with high reaction yields (such as, higher than 75 wt.%).

[0084] - The present disclosure not only provides remarkable recycling and upcycling benefits and technological advancements, but also enables scaling up the synthesis process to an industrial level.

[0085] - In addition, the use of the output of pyrolysis (a) (that is, recycled carbon black as a precursor material), makes the synthesis procedure more economically feasible when compared to using pristine carbon sources. Moreover, by having enhanced properties including a high surface area, reactivity, and conductivity; graphene nanoplatelets (GNP) as output of the proposed method are suitable for use in a wide range of applications across various industries, such as composites and polymer materials, polymeric and non-polymeric composites. By starting from recycled carbon black and undergoing controlled processing steps, GNP exhibit improved performance when compared to conventional carbon black materials. These enhancements also lead to superior mechanical strength, electrical conductivity, thermal stability, and chemical reactivity in end-use applications.

[0086] - The proposed method for producing graphene nanoplatelets (GNP) from recycled carbon black that can be derived from the pyrolysis of wastes such as waste tires, utilizes recycling and upcycling technologies. A key advantage of the proposed method is that it offers a more cost-effective way of producing GNP compared to other options that start from virgin graphite, thanks to the fact that carbon source (CS) in this method is readily available and relatively inexpensive. By utilizing these waste materials, the proposed method not only reduces the environmental impact of wastes such as waste tires, but also provides a more sustainable and economically viable way for producing graphene. This approach aligns with principles of circular economy by extracting value from waste materials and integrating them back into the production cycle. To sum up, synthesis of GNP from recycled carbon black represents a significant innovation with far-reaching benefits, including sustainability, cost-effectiveness, versatility, and enhanced material performance, opening up new opportunities for diverse industrial applications.

[0087] Reference Signs: a pyrolysis al acid treatment a2 filtration and drying b potassium hydroxide treatment bl filtration and drying c iron chloride treatment cl filtration and drying d carbonization CS carbon source

[0088] GNP graphene nanoparticles

Claims

Claims1. A method for obtaining graphene, comprising the following sequential steps: a) subjecting one or more carbon sources (CS) to a pyrolysis (a) at a temperature of up to 400°C under a nitrogen atmosphere, thereby obtaining a recycled carbon black as a precursor with an oily portion; b) subjecting the recycled carbon black to a potassium hydroxide solution treatment (b), thereby obtaining an output of step-b; c) subjecting the output of step-b to an iron chloride solution treatment (c), thereby obtaining an output of step-c; d) subjecting the output of step-c to a carbonization (d) at an argon atmosphere, thereby obtaining one or more graphene nanoplatelets, at a temperature within a range between 900 °C and 1800 °C.

2. Method according to claim 1; wherein the one or more carbon sources (CS) comprise one or more waste sources.

3. Method according to claim 2; wherein the one or more waste sources are selected from waste tires, waste rubber, carbonized biomass disposal, thermosets, and thermoplastics that are already subjected to a pyrolysis.

4. Method according to claim 2; wherein the one or more carbon sources (CS) comprise waste tires.

5. Method according to any of claims 1 to 4; wherein the step-a further comprises an acid treatment (al) of the recycled carbon black.

6. Method according to claim 5; wherein the acid treatment (al) is followed by one or more filtration and drying (a2).

7. Method according to any of claims 1 to 6; wherein the step-b further comprises one or more filtration and drying (bl).

8. Method according to any of claims 1 to 7; wherein the step-c further comprises one or more filtration and drying (cl).

9. Method according to any of claims 1 to 8; wherein the potassium hydroxide solution treatment (b) comprises one or more of the following: arranging that a potassium hydroxide concentration in the solution is within a range between 0.5 and 1.0 moles per liter; arranging that the potassium hydroxide solution treatment (b) is performed along a treatment duration within a range between 4 hours and 24 hours; arranging that potassium hydroxide solution treatment (b) is performed at a treatment temperature within the range between 80 °C and 120 °C; arranging that a gradual heating is applied; arranging that the potassium hydroxide solution further includes one or more surfactants selected from sodium dodecyl sulphate and sodium dodecyl benzene sulfonate; wherein an amount of surfactants in a respective treatment medium is at a carbo surfactant weight ratio within a range between 50:1 and 100:1.

10. Method according to any of claims 1 to 9; wherein the iron chloride solution treatment (c) comprises one or more of the following: arranging that an iron chloride concentration in the solution is within a range between 0.5 and 1.0 moles per liter; arranging that the iron chloride solution treatment (c) is performed along a treatment duration within a range between 4 hours and 24 hours; arranging that the iron chloride solution treatment (c) is performed at a treatment temperature within the range between 80 °C and 120 °C; arranging that a gradual heating is applied; arranging that the iron chloride solution further includes one or more surfactants selected from sodium dodecyl sulphate and sodium dodecylbenzene sulfonate; wherein an amount of surfactants in a respective treatment medium is at a carbomsurfactant weight ratio within a range between 50:1 and 100:1.

11. Method according to any of claims 1 to 10, wherein the carbonization (d) is performed at a duration within a range between 5 minutes and 30 minutes.

12. Method according to any of claims 1 to 11, wherein the pyrolysis (a) is performed at a temperature of 350 °C or higher.

13. Method according to any of claims 1 to 12, wherein the carbon source (CS) has a carbon content higher than 65 wt.% on the basis of the total weight of the carbon source (CS).

14. Method according to any of claims 1 to 13, wherein the pyrolysis (a) is performed for a duration of 6 hours or longer.

15. Method according to any of claims 1 to 14, wherein the recycled carbon black from pyrolysis (a) is not subjected to milling prior to the step (b).

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