A green graphene preparation process based on arc discharge method

Abstract

The application discloses a kind of green preparation process of graphene based on arc discharge method, belong to the technical field of graphene preparation, for solving the technical problems that the conductivity and specific surface area of graphene material in prior art need to be further improved;A kind of green preparation process of graphene based on arc discharge method, comprising the following steps: after heat treatment to graphene, obtain purified graphene;The scheme is by constructing Schiff base coating anode, introducing deep eutectic reaction liquid and combining mild reduction repair process, realize energy uniform dispersion, interface stable doping and defect effective repair in arc stripping process, three form continuous control chain, make graphene sheet layer stripping fully, stacking reduction, π conjugated structure is complete, and the material obtained has low defect concentration, high conductivity and large specific surface area, balanced and stable performance.

Description

Technical Field

[0001] This invention relates to the field of graphene preparation technology, specifically to a green graphene preparation process based on arc discharge. Background Technology

[0002] Arc discharge, a commonly used method for preparing carbon nanomaterials, was first applied to the preparation of carbon nanotubes and fullerenes, and was subsequently extended to the preparation of graphene. This method relies on the instantaneous release of energy by a high-energy arc to vaporize or peel off graphite electrodes, thereby generating sheet structures during condensation and deposition. With the advancement of research, people have made continuous progress in terms of electrical conductivity: by adjusting the arc current, atmosphere and electrode spacing, defects can be reduced to a certain extent and the continuity of graphene sheets can be improved, making its electrical conductivity gradually approach the level of tens to hundreds.

[0003] In terms of specific surface area, graphene prepared by arc discharge method is usually more prone to sheet aggregation and local stacking. Therefore, researchers have tried to introduce different atmospheres, cooling rates or auxiliaries to improve sheet dispersion and increase specific surface area. Overall, this method has become one of the important ways to obtain graphene with better conductivity and specific surface area due to its high energy density and controllable product layer number.

[0004] Existing arc discharge processes still face several common problems in graphene preparation. First, the highly concentrated release of arc energy can easily lead to edge cracking and point defect accumulation due to local overheating, resulting in insufficient lattice continuity of graphene and limited electrical conductivity. Second, the uneven distribution of ions and gases in the discharge environment often leads to differences in sheet thickness and uneven agglomeration during the exfoliation process, causing a decrease in specific surface area. Third, the defects generated by the arc lack effective subsequent repair, leaving some oxygen-containing groups and structural vacancies in the sheets, which further form carrier scattering centers.

[0005] In addition, the existing system has limited means to control the interface reaction and doping, making it difficult to improve charge transport efficiency while ensuring the integrity of the layer structure. These shortcomings make it difficult for the existing process to achieve ideal levels in terms of defect concentration, conductivity and specific surface area at the same time, thus limiting the overall performance of the material.

[0006] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a green graphene preparation process based on arc discharge method, which solves the technical problem that the conductivity and specific surface area of ​​graphene materials in the prior art need to be further improved.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] A green graphene preparation process based on arc discharge includes the following steps:

[0010] S1. Add the regulator dropwise to the deep eutectic reaction solution until the conductivity reaches 4-6 mS·cm. -1 A conductive dielectric liquid is obtained;

[0011] S2. Insert the Schiff base-coated anode and graphite cathode into a conductive dielectric liquid, discharge by DC arc with a current of 40-45A, a voltage of 30-36V, an electrode spacing of 1.2-1.5mm, a system temperature of 36-45℃, and react for 16-20min. Then, after post-treatment, graphene is obtained.

[0012] S3. After heat treatment, graphene is purified.

[0013] The reaction principle for preparing purified graphene is as follows:

[0014] Graphene is obtained by rapidly exfoliating graphite through electric arc discharge. After washing to remove residual impurities, the surface defects of graphene are repaired by the mild reducing environment generated by the decomposition of urea and hypophosphoric acid, thereby obtaining purified graphene material with complete structure and enhanced conductivity.

[0015] First, an appropriate amount of regulator is introduced into the deep eutectic reaction solution to bring the ionic strength and conductivity of the system into a suitable range, thereby ensuring a stable discharge environment for the DC arc. The arc discharge generates high-temperature, high-energy plasma on the surface of the anode graphite, which promotes the rapid stripping of the interlayer bonds of graphite to form dispersed graphene sheets. Since the Schiff base-coated anode can provide nitrogen, phosphorus and other heteroatom sources during the arc process, and stabilize the electrode surface interface, its role is not limited to mechanical stripping, but also promotes the uniform formation and functional doping of graphene sheets.

[0016] Subsequently, after washing and neutralization, the deep eutectic medium and its byproducts are removed, and the residual acidic or phosphorus-containing components are converted into easily soluble salts through ammonium bicarbonate solution and discharged, thus obtaining a relatively pure graphene solid.

[0017] Finally, under mild heat treatment conditions, graphene forms a reducing atmosphere with decomposed urea and hypophosphite. The thermal decomposition of urea releases amino free radicals, and the decomposition of hypophosphite generates phosphorus-containing reducing species. These active gases work together on the graphene surface, which can partially repair defects generated during the arc stripping process, reduce the D / G ratio, and improve the conductivity and structural integrity of the graphene sheets.

[0018] Furthermore, in step S1, the regulator is obtained by mixing anhydrous ethanol and deionized water in a volume ratio of 1 mL: 4 mL.

[0019] Furthermore, in step S2, the post-processing includes: after the reaction is completed, wait for the temperature of the reaction solution to drop to room temperature, filter the reaction solution to collect the filter cake, and wash the filter cake 1-2 times each with 0.2 mol / L ammonium bicarbonate solution and anhydrous ethanol to obtain graphene;

[0020] Further, in step S3, the heat treatment includes: spreading graphene flat inside an alumina boat, placing it in the central temperature zone of a single-temperature zone quartz tube furnace (Φ40-60mm), placing another alumina boat 5-8cm upstream, adding urea and a 50wt% hypophosphite aqueous solution, purging with high-purity nitrogen at 300-500mL / min for 10-15min to replace the air, maintaining nitrogen flow, and raising the temperature to 260-280℃ at 10℃ / min. The sample was kept at a constant temperature for 20-30 minutes. After the treatment, nitrogen gas was continuously introduced to cool it to 60°C. The sample was then removed and added to anhydrous ethanol and sonicated for 3-5 minutes. After filtration, the filter cake was collected and rinsed with deionized water 2-3 times. Finally, it was vacuum dried in an 80°C drying oven to constant weight to obtain purified graphene. The ratio of graphene, urea and 50wt% hypophosphite aqueous solution was 0.8-1.0g:0.50g:0.4-0.6mL.

[0021] Furthermore, the method for preparing the Schiff base coated anode includes the following steps:

[0022] A1. Immerse the graphite anode in a 10wt% phosphoric acid solution and let it stand for 8-10 minutes. Then, perform post-treatment to obtain an etched graphite anode.

[0023] A2. Dip the etched graphite anode into Schiff base coating and form a uniform film at a pull-out speed of 2-5 mm / s. Then, perform post-treatment on the Schiff base coated anode.

[0024] The reaction principle for preparing Schiff base coated anodes is as follows:

[0025] By introducing surface active sites through phosphoric acid etching and utilizing the multifunctional structure of Schiff base coating to interact with the graphite interface, a stable conjugated coating is finally cured, thereby obtaining an anode material with adhesion, stability and functionality.

[0026] First, after the graphite anode is treated with phosphoric acid solution, the graphite layer on its surface is partially etched, generating a certain number of defect sites and oxygen-containing functional groups. These structures not only increase the surface roughness and specific surface area, but also introduce chemically active sites that can undergo hydrogen bonding or esterification reactions with coating molecules, thereby significantly improving the affinity of the graphite anode surface for organic molecules.

[0027] Subsequently, the etched graphite surface comes into contact with the Schiff base coating. The polyhydroxy, amino, and -C=N- conjugated structures in the Schiff base coating can interact with the defect sites, oxygen-containing groups, and phosphate residues on the graphite surface in multiple ways, including hydrogen bonding, π–π stacking, and partial chemical bonding. These interactions promote the uniform spread and firm adhesion of the coating molecules on the graphite surface.

[0028] During the drying and curing process of the coating, the cross-linking structure inside the Schiff base network is further improved, forming a dense and continuous organic-inorganic hybrid film. This film not only endows the graphite anode with excellent mechanical stability and chemical resistance, but also provides a uniform reaction interface for the subsequent arc stripping process, and can serve as a potential doping source for heteroatoms such as nitrogen and phosphorus.

[0029] Furthermore, in step A1, the ratio of graphite anode to 10wt% phosphoric acid solution is 2g:20mL. The post-treatment includes: after standing, taking out the graphite electrode, washing it with deionized water 3-5 times, and then transferring it to a drying oven at a temperature of 80-100℃ for vacuum drying to constant weight to obtain etched graphite anode.

[0030] Furthermore, in step A2, the ratio of etched graphite anode to Schiff base coating is 1g:5-8mL. The post-treatment includes drying in a drying oven at 80-100℃ for 30min, repeating the operation until a Schiff base coating anode with a thickness of 3-5μm is formed after curing.

[0031] Furthermore, the preparation method of Schiff base coating includes the following steps:

[0032] B1. Add phytic acid and dopamine to a mixed solvent and stir. After purging with nitrogen, add glacial acetic acid to adjust the pH to 4-5. Then add succinic acid and sorbitol and stir at 70-85℃ for 2-3 hours. The post-treatment yields phosphate phenol prepolymer.

[0033] B2. Disperse the phosphate phenol prepolymer in a 50wt% ethanol aqueous solution, add a 40wt% glyoxal aqueous solution under nitrogen protection, and stir at 60-70℃ for 2-3 hours to obtain a Schiff base coating.

[0034] The reaction principle for preparing Schiff base coatings is as follows:

[0035] Phytic acid, dopamine, and small molecule polycarboxylic / hydroxyl components form a prepolymer network through phosphorylation, hydrogen bonding, and phenol-amine interaction. Subsequently, the network is cured into a stable conjugated structure by glyoxal-induced Schiff base condensation reaction, thereby obtaining a coating precursor liquid with adhesiveness, chemical stability, and functionality.

[0036] First, phytic acid molecules, as a polyphosphate structure, can interact with the catechol / amine groups of dopamine through multiple sites via phosphate groups, generating a prepolymer network containing phosphate phenol bonds in an acidic environment. In this process, succinic acid and sorbitol act as auxiliary crosslinking agents, providing carboxyl and polyhydroxy functional groups respectively, further enhancing the intermolecular hydrogen bonding and esterification, and gradually transforming the system into a stable organic-inorganic hybrid prepolymer.

[0037] Based on this, after the prepolymer is dispersed in an ethanol / water system, it is contacted with glyoxal. Its active aldehyde group undergoes a typical condensation reaction (Schiff base reaction) with the primary amine group of dopamine residue to generate a -C=N- structure. This process not only endows the material with a unique Schiff base conjugated network, but also significantly improves the film-forming properties and stability of the coating through multi-point crosslinking.

[0038] Further, in step B1, the ratio of phytic acid, dopamine, mixed solution, succinic acid, and sorbitol is 1g:2.5-3.0g:100mL:0.08-0.10g:0.2-0.4g. The mixed solvent is obtained by mixing deionized water and anhydrous ethanol in a ratio of 1mL:1mL. The post-treatment includes: cooling to room temperature after the reaction, pouring the reaction solution into 2 times the volume of anhydrous ethanol to precipitate solids, collecting the filter cake by vacuum filtration after precipitation, washing the filter cake 3-5 times with anhydrous ethanol and deionized water, and vacuum drying it in a drying oven at 80-100℃ to a constant temperature to obtain phosphate phenol prepolymer.

[0039] Furthermore, in step B2, the ratio of the phosphate phenol prepolymer, 50wt% ethanol aqueous solution, and 40wt% glyoxal aqueous solution is 1g:80-100mL:0.3-0.5g.

[0040] Furthermore, the preparation method of the reactive eutectic melt includes the following steps:

[0041] C1. After mixing boric acid and glycerol, the mixture is reacted under reduced pressure at 90-110℃ for 2-3 hours under nitrogen protection to obtain boric ester mother liquor.

[0042] C2. After mixing the borate ester mother liquor, betaine and ammonium formate, react them at 60-80℃ for 1-2 hours under nitrogen protection, and then perform post-treatment to obtain a deep eutectic reaction solution.

[0043] The reaction principle for preparing a deep eutectic reaction solution is as follows:

[0044] A framework is established through borate esterification reaction, and then betaine and ammonium formate are used to participate in hydrogen bonding complexation to form a stable composite liquid with low melting point, strong hydrogen bond network and high ionic conductivity.

[0045] Relying on hydrogen bonding and self-assembly between small molecules, boric acid and glycerol undergo esterification between hydroxyl and boron atoms to generate a stable borate ester structure in the system. This borate ester skeleton can provide electron acceptor sites while maintaining a certain degree of flexibility and solubility, thus providing a foundation for the subsequent construction of hydrogen bond networks.

[0046] Based on this, the introduction of betaine and ammonium formate further enriches the types of hydrogen bond donors and acceptors. The quaternary ammonium salt cation and carboxylic acid anion in the betaine molecule have a dual role: their positive charge can stabilize the overall ionic environment of the system, while the carboxyl group participates in hydrogen bond interactions. Ammonium formate provides both amino hydrogen bond donors and formate hydrogen bond acceptors, making the hydrogen bond interactions in the system more diversified and stable.

[0047] Through the synergistic effect between the molecules mentioned above, the original single components with high melting points are combined to form a deep eutectic system with a significantly lower melting point that can be liquid at room temperature. This system combines the high ionic conductivity of ionic liquids with the good wettability of ordinary solvents, providing an efficient electron / ion transfer environment during arc exfoliation and graphene doping, while also providing chemical reaction sites for the introduction and stabilization of heteroatoms.

[0048] Furthermore, in step C1, the ratio of boric acid to glycerol is 1g:2-3g;

[0049] Furthermore, in step C2, the ratio of borate ester mother liquor, betaine and ammonium formate is 1.0-1.2g:0.3-0.5g:0.2-0.3g. The post-treatment includes: after the reaction is completed, after the reaction solution is cooled to room temperature, it is degassed with nitrogen for 10-20 minutes and filtered through a 0.22μm filter membrane to obtain a deep eutectic reaction solution.

[0050] The present invention has the following beneficial effects:

[0051] 1. The deep eutectic reaction solution prepared in this invention forms a highly ionicly conductive and stable microenvironment through hydrogen bonding complexation between the borate ester framework and betaine and ammonium formate. This effectively buffers the local high-energy impact during arc discharge, reducing structural damage caused by excessive ablation of the graphite layer from the source. Simultaneously, the Schiff base coating anode forms active sites after phosphoric acid etching. The multifunctional groups in the coating undergo hydrogen bonding and π–π interactions with the graphite surface, making the arc action more uniform. During the discharge process, nitrogen, phosphorus, and other heteroatoms are released, which passivate and stabilize the defect edges. On the other hand, in the subsequent heat treatment stage, urea and hypophosphoric acid decompose to release reducing species, which repair and heal the defects generated during the arc process in a mild atmosphere. The material provides chemical stability and doping sources, and the process provides uniform exfoliation and mild repair. The coupling effect of the two ultimately achieves a significant reduction in the defect density of graphene, and the lattice integrity is significantly better than that of traditional methods.

[0052] 2. The Schiff base-coated anode prepared by this invention can stabilize the electrode interface and ensure uniform discharge during the arc exfoliation process, while also releasing heteroatom sources such as nitrogen and phosphorus. These heteroatoms are in situ incorporated into the graphene lattice under high-energy conditions, which not only adjusts the local band structure but also effectively improves the carrier concentration and migration channels. On the other hand, the deep eutectic reaction solution provides high ionic conductivity and wettability, making the arc discharge process more stable and avoiding serious defects caused by local overheating, thereby obtaining sheets with higher crystallinity and fewer defects. Subsequently, the reducing atmosphere generated by urea and hypophosphoric acid during the heat treatment stage can further repair defect points in the conductive path, reduce interface scattering, and improve electron transport efficiency. Thus, the material itself provides doping and a stable interface, and the process ensures uniform exfoliation and defect repair. The coupling of these two aspects gives graphene a more complete π-conjugated structure and continuous electron channels, thereby exhibiting a significantly improved conductivity.

[0053] 3. The deep eutectic reaction solution prepared by this invention has low melting point, high wettability, and strong hydrogen bond network characteristics. During arc discharge, it can uniformly disperse energy, avoid excessive agglomeration of graphite layers, and make the exfoliated graphene sheets thinner and more dispersed. At the same time, the Schiff base-coated anode provides a uniform and stable reaction interface. Its surface multifunctional groups form hydrogen bonds and π–π interactions with the graphite sheets, which not only helps to uniformly exfoliate the sheets, but also inhibits interlayer recombination to a certain extent. On the other hand, the subsequent mild heat treatment with urea and hypophosphoric acid releases polar species while repairing defects, further improving the interfacial affinity of the graphene sheets and reducing the van der Waals attraction between sheets, thereby maintaining a high degree of sheet dispersion. By providing chemical functional groups and interface regulation at the material end, and achieving mild exfoliation and defect repair at the process end, the two work together to give graphene a larger specific surface area and more available active sites.

[0054] 4. In this process, the preparation not only focuses on optimizing material properties but also takes into account environmental friendliness. The reaction medium used is stable and has low toxicity, avoiding the large-scale use of strong acids, strong alkalis, or organic solvents in traditional processes, thus reducing potential secondary pollution at the source. At the same time, the arc discharge reaction can be carried out under normal pressure conditions, making the process simple and energy-efficient. It eliminates the need for long-term high-temperature calcination or multiple complex processing steps, which helps to reduce overall energy consumption. Moreover, the reaction byproducts are few in variety and easy to handle, resulting in a lighter environmental burden. Through this approach, graphene materials with low defect concentration, high conductivity, and large specific surface area are obtained, and the preparation process exhibits more mild and sustainable characteristics, providing favorable conditions for subsequent large-scale application and green development. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 This is a SEM image of the graphene prepared in Example 9. Detailed Implementation

[0057] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] In this application, the graphite electrode used has a fixed carbon content of not less than 99.9 wt%, an ash content of less than 0.05 wt%, and metallic impurities controlled below 10 ppm. The electrode used is a cylindrical rod with a bulk density of 1.82-1.88 g·cm³. -3 The resistivity is about 8-12 μΩ·m, the average grain size is 10-15 μm, and the electrode with a diameter of 6 mm and a length of 150 mm is preferably used. The anode end is processed into a hemispherical or conical blunt end, and the cathode end is a flat end or a slightly concave structure.

[0059] Example 1

[0060] This embodiment provides a reactive deep eutectic solution for a green graphene preparation process based on arc discharge, including the following steps:

[0061] Step I: Preparation of borate ester mother liquor

[0062] Weigh out 10.0g of boric acid and 20.0g of glycerol and add them to the reaction vessel. Under nitrogen protection, react under reduced pressure at 90-110℃ for 2 hours to obtain boric ester mother liquor.

[0063] Step II: Preparation of deep eutectic reaction solution

[0064] Weigh out 10.0g of borate ester mother liquor, 3.0g of betaine and 2.0g of ammonium formate and add them to the reaction vessel. Under nitrogen protection, react at 60℃ for 1h. After the reaction is completed, wait for the reaction solution to cool to room temperature, degas it with nitrogen for 10min and filter it with a 0.22μm filter membrane to obtain the deep eutectic reaction solution.

[0065] Example 2

[0066] This embodiment provides a reactive deep eutectic solution for a green graphene preparation process based on arc discharge, including the following steps:

[0067] Step I: Preparation of borate ester mother liquor

[0068] Weigh out 10.0g of boric acid and 30.0g of glycerol and add them to the reaction vessel. Under nitrogen protection, react under reduced pressure at 90-110℃ for 3 hours to obtain borate ester mother liquor.

[0069] Step II: Preparation of deep eutectic reaction solution

[0070] Weigh out 12.0g of borate ester mother liquor, 5.0g of betaine and 3.0g of ammonium formate and add them to the reaction vessel. Under nitrogen protection, react at 80℃ for 2h. After the reaction is completed, wait for the reaction solution to cool to room temperature, degas it with nitrogen for 20min and filter it with a 0.22μm filter membrane to obtain the deep eutectic reaction solution.

[0071] Example 3

[0072] This embodiment provides a reactive deep eutectic solution for a green graphene preparation process based on arc discharge, including the following steps:

[0073] Step I: Preparation of borate ester mother liquor

[0074] Weigh out 10.0g of boric acid and 25.0g of glycerol and add them to the reaction vessel. Under nitrogen protection, react under reduced pressure at 90-110℃ for 3 hours to obtain borate ester mother liquor.

[0075] Step II: Preparation of deep eutectic reaction solution

[0076] Weigh out 12.0g of borate ester mother liquor, 4.0g of betaine and 3.0g of ammonium formate and add them to the reaction vessel. Under nitrogen protection, react at 80℃ for 2h. After the reaction is completed, wait for the reaction solution to cool to room temperature, degas it with nitrogen for 16min and filter it with a 0.22μm filter membrane to obtain the deep eutectic reaction solution.

[0077] Example 4

[0078] This embodiment provides a Schiff base-coated anode for a green graphene preparation process based on arc discharge, comprising the following steps:

[0079] Step ①: Preparation of phosphate phenol prepolymer

[0080] Weigh out 60.0 mL of deionized water and 60.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0081] Weigh out 1.0 g phytic acid, 2.5 g dopamine and 100.0 mL mixed solvent and add them to the reaction vessel. Stir and purge with nitrogen. Adjust the pH to 4 with glacial acetic acid, then add 0.08 g succinic acid and 0.2 g sorbitol. Stir at 70 °C for 2 h. After the reaction is complete, cool to room temperature and pour the reaction solution into 2 times the volume of anhydrous ethanol to precipitate the solid. After precipitation is complete, filter and collect the filter cake. Wash the filter cake 3 times with anhydrous ethanol and deionized water and place it in an 80 °C drying oven to constant temperature to obtain phosphate phenol prepolymer.

[0082] Step 2: Preparation of Schiff base coating

[0083] Weigh out 1.0 g of phosphate phenol prepolymer and 80 mL of 50 wt% ethanol aqueous solution and add them to the reaction vessel and stir. Under nitrogen protection, add 0.3 g of 40 wt% glyoxal aqueous solution and stir at 60 °C for 2 h to obtain Schiff base coating.

[0084] Step 3: Preparation of etched graphite anode

[0085] Weigh 20.0g of graphite anode and 200.0mL of 10wt% phosphoric acid solution and add them to the reaction vessel. Let stand for 8 minutes. After standing, take out the graphite electrode, wash it 3 times with deionized water, and transfer it to a drying oven at 80℃ to vacuum dry to constant weight to obtain etched graphite anode.

[0086] Step 4: Preparation of Schiff base coated anode

[0087] Weigh out 10.0g of etched graphite anode and dip it into a reactor containing 50.0mL of Schiff base coating. Form a uniform film at a pull-out speed of 2mm / s. Dry in an 80℃ drying oven for 30min. After curing, a Schiff base coated anode with a thickness of 3μm is formed.

[0088] Example 5

[0089] This embodiment provides a Schiff base-coated anode for a green graphene preparation process based on arc discharge, comprising the following steps:

[0090] Step ①: Preparation of phosphate phenol prepolymer

[0091] Weigh out 60.0 mL of deionized water and 60.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0092] Weigh out 1.0 g phytic acid, 3.0 g dopamine and 100.0 mL mixed solvent and add them to the reaction vessel. Stir and purge with nitrogen. Adjust the pH to 5 with glacial acetic acid, then add 0.10 g succinic acid and 0.4 g sorbitol. Stir at 85 °C for 3 h. After the reaction is complete, cool to room temperature and pour the reaction solution into 2 times the volume of anhydrous ethanol to precipitate the solid. After precipitation is complete, filter and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water and place it in a drying oven at 100 °C to vacuum dry to a constant temperature to obtain phosphate phenol prepolymer.

[0093] Step 2: Preparation of Schiff base coating

[0094] Weigh out 1.0 g of phosphate phenol prepolymer and 80.0 mL of 50 wt% ethanol aqueous solution and add them to the reaction vessel. Under nitrogen protection, add 0.5 g of 40 wt% glyoxal aqueous solution and stir at 70 °C for 3 h to obtain Schiff base coating.

[0095] Step 3: Preparation of etched graphite anode

[0096] Weigh 20.0g of graphite anode and 200.0mL of 10wt% phosphoric acid solution and add them to the reaction vessel. Let stand for 10min. After standing, take out the graphite electrode, wash it 5 times with deionized water, and transfer it to a drying oven at 100℃ to vacuum dry to constant weight to obtain etched graphite anode.

[0097] Step 4: Preparation of Schiff base coated anode

[0098] Weigh 10.0g of etched graphite anode and dip it into a reactor containing 80.0mL of Schiff base coating. Form a uniform film at a pull-out speed of 5mm / s. Dry in a 100℃ drying oven for 30min. Repeat the operation until a Schiff base coating anode with a thickness of 5μm is formed after curing.

[0099] Example 6

[0100] This embodiment provides a Schiff base-coated anode for a green graphene preparation process based on arc discharge, comprising the following steps:

[0101] Step ①: Preparation of phosphate phenol prepolymer

[0102] Weigh out 60.0 mL of deionized water and 60.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0103] Weigh out 1.0 g phytic acid, 2.8 g dopamine and 100.0 mL mixed solvent and add them to the reaction vessel. Stir and purge with nitrogen. Adjust the pH to 4 with glacial acetic acid, then add 0.09 g succinic acid and 0.3 g sorbitol. Stir at 80 °C for 3 h. After the reaction is complete, cool to room temperature and pour the reaction solution into 2 times the volume of anhydrous ethanol to precipitate the solid. After precipitation is complete, filter and collect the filter cake. Wash the filter cake 4 times with anhydrous ethanol and deionized water and place it in a drying oven at 90 °C for vacuum drying to a constant temperature to obtain phosphate phenol prepolymer.

[0104] Step 2: Preparation of Schiff base coating

[0105] Weigh out 1.0 g of phosphate phenol prepolymer and 100 mL of 50 wt% ethanol aqueous solution and add them to the reaction vessel. Under nitrogen protection, add 0.5 g of 40 wt% glyoxal aqueous solution and stir at 65 °C for 3 h to obtain Schiff base coating.

[0106] Step 3: Preparation of etched graphite anode

[0107] Weigh 20.0g of graphite anode and 200.0mL of 10wt% phosphoric acid solution and add them to the reaction vessel. Let stand for 9min. After standing, take out the graphite electrode, wash it 4 times with deionized water, and transfer it to a drying oven at 90℃ to vacuum dry to constant weight to obtain etched graphite anode.

[0108] Step 4: Preparation of Schiff base coated anode

[0109] Weigh out 10.0g of etched graphite anode and dip it into a reactor containing 70.0mL of Schiff base coating. Pull out the coating at a speed of 3mm / s to form a uniform film. Dry the film in a 90℃ oven for 30min. Repeat the process until a Schiff base coating anode with a thickness of 4μm is formed after curing.

[0110] Example 7

[0111] This embodiment provides a green graphene preparation process based on arc discharge, including the following steps:

[0112] Step 1: Preparation of conductive dielectric liquid

[0113] Anhydrous ethanol and deionized water were mixed at a ratio of 1 mL:4 mL to obtain a conditioning agent, which was then collected for later use.

[0114] Add the regulator dropwise to 1.0 g of the deep eutectic reaction solution prepared in Example 1 until the conductivity reaches 4 mS·cm. -1 A conductive dielectric liquid is obtained.

[0115] Step 2: Preparation of graphene

[0116] The Schiff base-coated anode and graphite cathode prepared in Example 4 were inserted into a conductive dielectric liquid and subjected to DC arc discharge with a current of 40A, a voltage of 30V, an electrode spacing of 1.2mm, and a system temperature of 36℃. The reaction was carried out for 16 minutes. After the reaction was completed, the temperature of the reaction solution was allowed to drop to room temperature. The reaction solution was filtered to collect the filter cake. The filter cake was washed once each with 0.2mol / L ammonium bicarbonate solution and anhydrous ethanol to obtain graphene.

[0117] Step 3: Preparation and purification of graphene

[0118] Weigh out 0.8g of graphene and spread it evenly in an alumina boat. Place the boat in the central temperature zone of a single-temperature zone quartz tube furnace (Φ40mm). Place another alumina boat 5cm upstream of the first boat. Add 0.50g of urea and 0.4mL of 50wt% hypophosphite aqueous solution. Purge with high-purity nitrogen at 300mL / min for 10min to replace the air. Keep the nitrogen flow through and raise the temperature to 260℃ at 10℃ / min. Hold the temperature for 20min. After the treatment, continue to purge with nitrogen and cool to 60℃. Remove the sample and add it to anhydrous ethanol. Sonicate for 3min. Filter and collect the filter cake. Rinse the filter cake twice with deionized water. Finally, vacuum dry in an 80℃ drying oven to constant weight to obtain purified graphene.

[0119] Example 8

[0120] This embodiment provides a green graphene preparation process based on arc discharge, including the following steps:

[0121] Step 1: Preparation of conductive dielectric liquid

[0122] Anhydrous ethanol and deionized water were mixed at a ratio of 1 mL:4 mL to obtain a conditioning agent, which was then collected for later use.

[0123] Add the regulator dropwise to 1.0 g of the deep eutectic reaction solution prepared in Example 2 until the conductivity reaches 6 mS·cm. -1 A conductive dielectric liquid is obtained.

[0124] Step 2: Preparation of graphene

[0125] The Schiff base-coated anode and graphite cathode prepared in Example 5 were inserted into a conductive dielectric liquid and subjected to DC arc discharge with a current of 45A, a voltage of 36V, an electrode spacing of 1.5mm, and a system temperature of 45℃. The reaction was carried out for 20min. After the reaction was completed, the temperature of the reaction solution was allowed to drop to room temperature. The reaction solution was filtered to collect the filter cake. The filter cake was washed twice each with 0.2mol / L ammonium bicarbonate solution and anhydrous ethanol to obtain graphene.

[0126] Step 3: Preparation and purification of graphene

[0127] Weigh out 1.0g of graphene and spread it evenly in an alumina boat. Place the boat in the central temperature zone of a single-temperature zone quartz tube furnace (Φ60mm). Place another alumina boat 8cm upstream of the first boat. Add 0.50g of urea and 0.6mL of 50wt% hypophosphite aqueous solution. Purge with high-purity nitrogen at 500mL / min for 15min to replace the air. Keep the nitrogen flow through and raise the temperature to 280℃ at 10℃ / min. Hold the temperature for 30min. After treatment, continue to purge with nitrogen and cool to 60℃. Remove the sample and add it to anhydrous ethanol. Sonicate for 5min. Filter and collect the filter cake. Rinse the filter cake three times with deionized water. Finally, vacuum dry in an 80℃ drying oven to constant weight to obtain purified graphene.

[0128] Example 9

[0129] This embodiment provides a green graphene preparation process based on arc discharge, including the following steps:

[0130] Step 1: Preparation of conductive dielectric liquid

[0131] Anhydrous ethanol and deionized water were mixed at a ratio of 1 mL:4 mL to obtain a conditioning agent, which was then collected for later use.

[0132] Add the regulator dropwise to 1.0 g of the deep eutectic reaction solution prepared in Example 3 until the conductivity reaches 5 mS·cm. -1 A conductive dielectric liquid is obtained.

[0133] Step 2: Preparation of graphene

[0134] The Schiff base-coated anode and graphite cathode prepared in Example 6 were inserted into a conductive dielectric liquid and subjected to DC arc discharge with a current of 45A, a voltage of 36V, an electrode spacing of 1.5mm, and a system temperature of 40℃. The reaction was carried out for 18 minutes. After the reaction was completed, the temperature of the reaction solution was allowed to drop to room temperature. The reaction solution was filtered to collect the filter cake. The filter cake was washed twice each with 0.2mol / L ammonium bicarbonate solution and anhydrous ethanol to obtain graphene.

[0135] Step 3: Preparation and purification of graphene

[0136] Weigh out 1.0g of graphene and spread it evenly in an alumina boat. Place the boat in the central temperature zone of a single-temperature zone quartz tube furnace (Φ50mm). Place another alumina boat 7cm upstream of the first boat. Add 0.50g of urea and 0.5mL of 50wt% hypophosphite aqueous solution. Purge with high-purity nitrogen at 400mL / min for 12min to replace the air. Keep the nitrogen gas flowing and raise the temperature to 280℃ at 10℃ / min. Hold the temperature for 25min. After the treatment, continue to purge with nitrogen and cool to 60℃. Remove the sample and add it to anhydrous ethanol. Sonicate for 5min. Filter and collect the filter cake. Rinse the filter cake three times with deionized water. Finally, vacuum dry in an 80℃ drying oven to constant weight to obtain purified graphene.

[0137] Comparative Example 1

[0138] The difference between this comparative example and Example 9 is that in step two, a graphite anode is used to replace the Schiff base-coated anode in equal amounts.

[0139] The difference between this comparative example and Example 9 is that the deep eutectic reaction solution was omitted in step one, and a 1wt% Na2SO4 aqueous solution was used to adjust the conductivity to 5 mS·cm. -1 Then, replace the conductive dielectric liquid in step two with an equal amount.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 9 is that step three is omitted.

[0142] Performance testing:

[0143] The defect concentration of the purified graphene prepared in Examples 7-9 and Comparative Examples 1-3 was determined according to the standard GB / T 43341-2023 "Defect Concentration Measurement of Graphene in Nanotechnology - Raman Spectroscopy".

[0144] The conductivity of the purified graphene prepared in Examples 7-9 and Comparative Examples 1-3 was determined according to standard DB32 / T 4027-2021 "Dynamic Four-Probe Method for Determination of Electrical Conductivity of Graphene Powder".

[0145] The specific surface area of ​​the purified graphene prepared in Examples 7-9 and Comparative Examples 1-3 was determined according to the standard GB / T 42310-2023 "Determination of Specific Surface Area of ​​Nanotechnology Graphene Powder - Argon Adsorption Static Capacitance Method". The specific data are shown in Table 1.

[0146] Table 1 - Performance Test Data for Each Sample

[0147]

[0148] Data Analysis:

[0149] Comparative analysis of the data in Table 1 revealed that the defect concentration of the purified graphene prepared in this invention is 2.6 × 10⁻⁶. 10 cm -2 The electrical conductivity is 77 S·cm -1 At the same time, the specific surface area is 1020m² 2 ·g -1 All data points are better than the comparative data, indicating that:

[0150] In Comparative Example 1, without the use of a Schiff base-coated anode, the graphite electrode surface lacks homogenization and buffering, and the energy distribution during the arc discharge process tends to be concentrated. The local high temperature and high-energy ion bombardment are significantly enhanced. This non-uniform energy effect makes the graphite sheet peeling no longer smooth, producing more edge cracks and point defects, resulting in damage to the lattice continuity. At the same time, the lack of in-situ passivation of defect edges by multifunctional groups and conjugated networks means that some defects cannot be stabilized in high-energy impacts, thus forming carrier scattering centers and destroying charge migration channels. The increase in defect density not only reduces electron transport efficiency but also makes it easier for the sheets to recombine, thereby reducing the effective specific surface area and ultimately resulting in a significant decline in overall composite performance.

[0151] When the deep eutectic reaction solution was replaced with ordinary ethanol / water electrolyte in Comparative Example 2, the system lost the multiple hydrogen bond network and ion conduction framework constructed by borate ester skeleton, betaine and ammonium formate. As a result, the arc discharge process lacked uniform energy distribution and a stable ionic environment. The unstable discharge led to a decrease in graphite exfoliation efficiency, uneven sheet thickness and more structural damage. At the same time, the ion wettability and electrode interface matching were weakened, and the van der Waals interactions between sheets were more likely to cause agglomeration, which significantly reduced the specific surface area. The uneven energy distribution and the difficulty in timely passivation of defects combined to form more carrier scattering points, which blocked the electron migration path and significantly reduced the conductivity. The accumulation of lattice defects and the aggravation of sheet overlap jointly led to the deterioration of the overall performance of the final sample.

[0152] In Comparative Example 3, without the repair of urea and hypophosphite heat treatment, the point defects and edge cracks generated during the arc stripping stage could not be repaired in subsequent stages. The vacancies, broken bonds, and oxygen-containing groups remaining in the graphene lattice remained at a high concentration. These structural defects became scattering centers for charge migration, which severely disrupted the continuity of electron transport. At the same time, the unpassivated edge defects led to stronger interlayer interactions, causing partial agglomeration of graphene during drying and collection, resulting in a decrease in specific surface area. The cumulative effect of defects not only reduced structural integrity but also weakened the effective extension of the π-conjugated network, making the conductive channels less continuous. In the end, the sample showed a significant decrease in defect concentration, conductivity, and specific surface area, and its overall performance was much worse than that of the material obtained by the complete process.

[0153] In conclusion, this invention provides a stable ionic environment and energy buffer during arc discharge using a deep eutectic reaction solution, enabling uniform exfoliation of graphite sheets and suppressing excessive agglomeration. The Schiff base-coated anode introduces multifunctional groups and heteroatom sources at the reaction interface, promoting stable dispersion between sheets and timely passivation of defect edges during discharge. Subsequently, the reducing species released by mild heat treatment repair point defects generated by the arc, maintaining the continuity of the π-conjugated structure. These three elements form a complementary chain of action: the front end suppresses defect generation, the middle section regulates doping and interfacial interactions, and the end end completes repair and stabilization. The resulting graphene exhibits significant advantages in defect concentration, conductivity, and specific surface area, demonstrating balanced and stable performance. Compared with single control methods, this approach not only avoids the trade-off effect between indicators but also reflects the overall improvement under the synergistic effect of multiple factors, providing a new path for the control of graphene performance.

[0154] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0155] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0156] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A green preparation process for graphene based on arc discharge method, characterized in that, Includes the following steps: S1. Add the regulator dropwise to the deep eutectic reaction solution until the conductivity reaches 4-6 mS·cm. -1 A conductive dielectric liquid is obtained; S2. Insert the Schiff base-coated anode and graphite cathode into a conductive dielectric liquid, discharge by DC arc with a current of 40-45A, a voltage of 30-36V, an electrode spacing of 1.2-1.5mm, a system temperature of 36-45℃, and react for 16-20min. Then, after post-treatment, graphene is obtained. S3. After heat treatment of graphene, purified graphene is obtained. The method for preparing the Schiff base coated anode includes the following steps: A1. Immerse the graphite anode in a 10wt% phosphoric acid solution and let it stand for 8-10 minutes. Then, perform post-treatment to obtain an etched graphite anode. A2. Dip the etched graphite anode into Schiff base coating and form a uniform film at a pull-out speed of 2-5 mm / s. Then, perform post-treatment on the Schiff base coated anode. The preparation method of the deep eutectic reaction solution includes the following steps: C1. After mixing boric acid and glycerol, the mixture is reacted under reduced pressure at 90-110℃ for 2-3 hours under nitrogen protection to obtain boric ester mother liquor. C2. After mixing the borate ester mother liquor, betaine and ammonium formate, react them at 60-80℃ for 1-2 hours under nitrogen protection, and then perform post-treatment to obtain a deep eutectic reaction solution.

2. The green graphene preparation process based on arc discharge method according to claim 1, characterized in that, In step S1, the regulator is a mixture of anhydrous ethanol and deionized water at a ratio of 1 mL:4 mL. In step S3, the heat treatment includes: spreading graphene evenly in an alumina boat, placing it in the central temperature zone of a single-temperature zone quartz tube furnace (Φ40-60 mm), placing another alumina boat 5-8 cm upstream, adding urea and a 50 wt% hypophosphite aqueous solution, purging with high-purity nitrogen at 300-500 mL / min for 10-15 min to replace the air, maintaining nitrogen flow, and heating at 10°C. The temperature is increased to 260-280℃ by 1 / min and held at that temperature for 20-30 min. After the treatment, nitrogen gas is continuously introduced to cool the sample to 60℃. The sample is then removed and added to anhydrous ethanol and sonicated for 3-5 min. After filtration, the filter cake is collected and rinsed with deionized water 2-3 times. Finally, the sample is vacuum dried in an 80℃ drying oven to constant weight to obtain purified graphene. The ratio of graphene, urea and 50wt% hypophosphite aqueous solution is 0.8-1.0g:0.50g:0.4-0.6mL.

3. The green graphene preparation process based on arc discharge method according to claim 1, characterized in that, In step A1, the ratio of graphite anode to 10wt% phosphoric acid solution is 2g:20mL; in step A2, the ratio of etched graphite anode to Schiff base coating is 1g:5-8mL.

4. The green graphene preparation process based on arc discharge method according to claim 1, characterized in that, The preparation method of the Schiff base coating includes the following steps: B1. Add phytic acid and dopamine to a mixed solvent and stir. After purging with nitrogen, add glacial acetic acid to adjust the pH to 4-5, then add succinic acid and sorbitol. Stir at 70-85℃ for 2-3 hours. Post-treatment yields phosphate phenol prepolymer. B2. Disperse the phosphate phenol prepolymer in a 50wt% ethanol aqueous solution, add a 40wt% glyoxal aqueous solution under nitrogen protection, and stir at 60-70℃ for 2-3 hours to obtain a Schiff base coating.

5. The green graphene preparation process based on arc discharge method according to claim 4, characterized in that, In step B1, the ratio of phytic acid, dopamine, mixed solvent, succinic acid, and sorbitol is 1g:2.5-3.0g:100mL:0.08-0.10g:0.2-0.4g, wherein the mixed solvent is obtained by mixing deionized water and anhydrous ethanol in a ratio of 1mL:1mL; in step B2, the ratio of phosphate phenol prepolymer, 50wt% ethanol aqueous solution, and 40wt% glyoxal aqueous solution is 1g:80-100mL:0.3-0.5g.

6. The green graphene preparation process based on arc discharge method according to claim 1, characterized in that, In step C1, the ratio of boric acid to glycerol is 1g:2-3g; in step C2, the ratio of borate ester mother liquor, betaine and ammonium formate is 1.0-1.2g:0.3-0.5g:0.2-0.3g.

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