Intercalation agent for preparing graphene as well as preparation method and application of intercalation agent

Abstract

The invention belongs to the technical field of graphene preparation, and particularly relates to an intercalator for graphene preparation and a preparation method and application thereof. The preparation method of the intercalator for graphene preparation comprises the following steps: (1) providing a sodium cholate aqueous solution as a basic solution; (2) adding a microenvironment regulating agent into the basic solution, and regulating and stabilizing the pH value and / or ionic strength I of the system to a preset target value; (3) dropwise adding an aqueous solution containing calcium ions into the solution obtained in the step (2) under the conditions of continuous stirring and temperature control, and controlling the final molar concentration ratio R of the calcium ions to the sodium cholate to a preset value; and (4) curing the mixed solution obtained in the step (3) at a set temperature to obtain the intercalator for graphene preparation. The intercalator system provided by the invention has definite environmental response and self-adaptive characteristics, and is beneficial to obtaining graphene with narrow layer number distribution and high quality when being used for preparing graphene.

Description

Technical Field

[0001] This invention belongs to the field of graphene preparation technology, specifically relating to an intercalating agent for graphene preparation, its preparation method, and its application. Background Technology

[0002] With the rapid development of high-tech fields such as electronic information, new energy, and composite materials, the demand for two-dimensional materials such as graphene is increasing, especially for few-layer graphene with a specific number of layers (such as single / double layers or 3-5 layers). However, the precise control of the number of graphene layers is a core technological bottleneck for its large-scale and customized applications.

[0003] Currently, the main methods for preparing few-layer graphene include mechanical exfoliation, chemical vapor deposition, and liquid-phase exfoliation. Among these, liquid-phase exfoliation is considered one of the most promising methods due to its relatively simple operation, low cost, and ease of scalability. This method typically uses surfactants or solvents to reduce the van der Waals forces between graphite layers and achieves exfoliation through physical actions such as ultrasound.

[0004] The liquid-phase exfoliation method for preparing graphene mainly involves breaking the van der Waals forces between graphite layers through physical methods such as ultrasound and shearing, thus exfoliating the graphite layers into graphene. To improve exfoliation efficiency, graphite is usually intercalated first to increase the interlayer spacing and weaken the interlayer forces. For example, CN102583351B discloses a method for preparing few-layer graphene, which combines liquid-phase intercalation technology with microwave irradiation technology. First, graphite is placed in a mixture of tetraalkyl-substituted quaternary ammonium cations and OH groups. - The graphite is subjected to ultrasonic treatment in a solution to allow tetraalkyl-substituted quaternary ammonium cations to insert into the graphite interlayers to form intercalation. The treated graphite is then subjected to microwave irradiation to decompose the graphite intercalation, generating a large amount of gas and further increasing the interlayer spacing. Finally, the treated graphite is dispersed in a low-polarity organic solvent and subjected to ultrasonic treatment to exfoliate the graphite and produce graphene.

[0005] CN114735686B discloses a method for preparing graphene aqueous solution and graphene nanosheets. This method uses graphite particles with a particle size of 20 μm or less. A dispersant and graphite particles are added to deionized water, and the mixture is subjected to stirring and shearing treatment, ultrasonic vibration, and high-pressure emulsification to obtain a graphene slurry containing very few-layer graphene, few-layer graphene, multi-layer graphene, and graphene nanosheets. CN103910354B provides a method for large-scale aqueous phase preparation of graphene. This method uses graphite as raw material. First, an intercalating agent is used to intercalate the graphene sheets, increasing the interlayer distance and weakening the interlayer interaction forces. Then, the intercalated graphite is directly treated with ultrasound and exfoliated and uniformly dispersed in an alkaline aqueous solution with a pH of 10-14.

[0006] To control the number of graphene layers, CN111017916A discloses a method for preparing graphene with controllable layer number. This method involves uniformly dispersing large-sized graphite in methylpyrrolidone, adjusting the solution pH to 11, and then ultrasonically dispersing to obtain multilayer graphene. The graphene is then microwave-heated and ultrasonically exfoliated for a certain time, followed by high-speed centrifugation, washing three times, and freeze-drying to obtain few-layer and single-layer graphene materials. CN110980707A discloses a method for mechanically exfoliating to prepare few-layer graphene. This method uses graphite paper as the anode and a graphite plate as the cathode. The anode is electrochemically exfoliated in an electrolyte. The electrochemically treated graphite is then uniformly dispersed in a mixture of dispersant and water, and mechanical stirring and mechanical exfoliation are used to obtain an aqueous dispersion of few-layer graphene.

[0007] However, existing methods using surfactants primarily address the dispersion and initial exfoliation of graphene, but the exfoliation process is random, lacking effective control over the number (thickness) of the final product. This results in products that are typically mixtures of single-layer, double-layer, and multi-layer graphene (more than 10 layers), with a wide layer distribution and inconsistent properties. Consequently, existing methods struggle to guarantee product consistency when faced with varying water quality, raw material batches, or process fluctuations.

[0008] Therefore, there is an urgent need for a novel preparation method and system that can overcome the limitations of existing technologies, not only precisely control the number of graphene layers and ensure high product quality, but also achieve programmable control through clear and simple chemical parameters, and possess adaptive adjustment capabilities to environmental variables. This is not only an inevitable choice to meet the needs of high-end applications, but also a key step in promoting graphene materials from the laboratory to industrialized customized production. Summary of the Invention

[0009] The purpose of this invention is to provide an intercalating agent for graphene preparation, its preparation method, and its application, so as to help solve or improve at least one of the problems existing in the current graphene liquid phase exfoliation technology, namely, uncontrollable number of product layers, random distribution (easily containing more than 10 layers of graphene), and inability to achieve precise and predictable preparation.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing an intercalating agent for graphene preparation, comprising the following steps: (1) providing an aqueous solution of sodium cholate as a base solution; (2) adding a microenvironment regulator to the base solution to adjust and stabilize the pH value and / or ionic strength I of the system to a preset target value; (3) under continuous stirring and temperature control, adding an aqueous solution containing calcium ions dropwise to the solution obtained in step (2) to control the final molar concentration ratio R of calcium ions to sodium cholate to a preset value; (4) aging the mixture obtained in step (3) at a set temperature to obtain an intercalating agent for graphene preparation; in step (2), the preset target value is: pH = 5.5-8.5 and / or ionic strength I = 0.01-0.2M; in step (3), 0 <R≤1.0。

[0011] Preferably, in step (2), the preset target value is: pH=7.0±0.5 and / or ionic strength I=0.05-0.15M; in step (3), 0.25≤R≤0.75.

[0012] Preferably, in step (3), the dripping rate is 0.5-2.0 mL / min, the stirring speed is 300-600 rpm, and the temperature is 25±2℃; in step (4), the aging treatment temperature is 25-35℃ and the time is 1-3 h.

[0013] Preferably, the concentration of sodium cholate in the base solution is 10-100 mM; and the concentration of calcium ions in the calcium-containing aqueous solution is 2.5-75 mM.

[0014] Preferably, the components of the microenvironment regulator include a pH buffer and / or an inert electrolyte; the pH buffer is at least one of a phosphate buffer pair, a Tris-HCl buffer pair, and a carbonate buffer pair; the inert electrolyte is sodium chloride and / or potassium chloride; and the calcium salt in the calcium-containing aqueous solution is at least one of calcium chloride, calcium nitrate, and calcium acetate.

[0015] The present invention also provides an intercalating agent, which adopts the following technical solution: an intercalating agent prepared by the method described above.

[0016] The present invention also provides a method for preparing graphene, which adopts the following technical solution: a method for preparing graphene, comprising the following steps: intercalating graphite raw materials with an intercalating agent as described above.

[0017] Preferably, the process includes the following steps: S1, adding graphite raw material to the dispersion of the intercalating agent and performing intercalation treatment to obtain a first mixture; S2, subjecting the mixture obtained in step (1) to ultrasonic treatment to obtain a second mixture; S3, separating the second mixture obtained in step S2.

[0018] Preferably, the procedure includes the following steps: In step S1, the intercalation treatment is carried out under stirring conditions at room temperature for 6-24 hours; In step S2, the ultrasonic treatment is carried out under ice-water bath conditions, with an ultrasonic power of 400-600W, a frequency of 40kHz, and an ultrasonic treatment time of 2-8 hours; In step S3, the separation method is step centrifugation: first, centrifugation at 800-1200 rpm for 10-20 minutes removes the unexfoliated graphite raw material, and then centrifugation at 3000-5000 rpm for 20-40 minutes collects the supernatant, wherein the graphene is located in the supernatant.

[0019] The present invention also provides a graphene, which adopts the following technical solution: a graphene prepared by the method described above.

[0020] Beneficial effects: (1) The preparation method of the intercalating agent for graphene preparation of the present invention can generate calcium ion-sodium cholate supramolecular aggregates with specific hydrodynamic diameters in solution by synergistically controlling the R value (molar concentration ratio of calcium ions to sodium cholate), pH value and ionic strength I. The size of the aggregate directly determines the number of graphene layers that can be peeled off and stabilized after it is inserted into the graphite interlayer, thereby helping to achieve a fundamental leap from "random peeling" to "on-demand customization" of the number of graphene layers, and providing a new technical route for solving or improving the industry problem of precise control of the number of graphene layers.

[0021] (2) The intercalating agent system of the present invention has clear environmental response and adaptive characteristics. Among them, pH value regulates the generation of primary coordination units by affecting the dissociation state and coordination ability of bile acid ions; ionic strength regulates the growth and final size of the supramolecular aggregates of the intercalating agent through electrostatic shielding effect. This dual response mechanism enables the system to have inherent regulatory dimensions and adaptive capabilities, which transcends the static mode of single-component mixing.

[0022] (3) The graphene prepared by this invention has the outstanding advantages of narrow layer distribution and high quality. Since the size of the intercalating agent can be precisely "programmed" through parameters and is uniformly distributed, the exfoliation process is more selective and consistent. For example, when the R value is set to 0.25, a high-purity product with a single / double layer ratio of more than 80% can be obtained (the graphene product does not contain more than 10 layers of graphene); when the R value is set to 0.75, a uniform few-layer graphene with a 3-5 layer ratio of more than 75% can be obtained (the graphene product does not contain more than 10 layers of graphene). In addition, the graphene product prepared by the method of this invention has few defects and a complete crystal structure.

[0023] (4) The graphene preparation process of the present invention is green, mild, and highly operable. The entire process is carried out in an aqueous phase, without the need for strong acids, strong oxidants, or organic solvents. The reaction conditions are at or near room temperature, resulting in low energy consumption and environmental friendliness. Furthermore, the raw materials used in the present invention are all common chemicals, which are inexpensive, and the process parameters are easy to control and scale up, demonstrating significant potential for large-scale production.

[0024] (5) The graphene with controllable number of layers (few-layer graphene) obtained by the present invention has clear and broad application prospects in high-performance electronic devices (such as transistors and sensors), high-efficiency composite materials, and new-generation energy storage and conversion systems, and can meet the specific requirements of different application scenarios for material thickness. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein: Figure 1 The graphene layer number distribution was characterized using Raman mapping; (a) is the graphene layer number distribution of Example 1, and (b) is the graphene layer number distribution of Comparative Example 1; the more red areas there are, the higher the monolayer ratio, while blue indicates that the graphene is thicker.

[0026] Figure 2 The images show the SEM images of the microstructure of graphene prepared in Example 1 and Comparative Example 1; where (a) is the SEM image of graphene in Example 1 and (b) is the SEM image of graphene in Comparative Example 1.

[0027] Figure 3 Example 1 uses AFM to test the number of graphene layers.

[0028] Figure 4 The Raman spectra data are for Examples 1-4. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0030] The present invention will be described in detail below with reference to embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0031] In view of at least one of the problems existing in the current graphene liquid-phase exfoliation technology, such as uncontrollable product layer number, random distribution, and inability to achieve precise and predictable preparation, the present invention provides a preparation method for an intercalating agent for graphene preparation.

[0032] When solving this technical problem, the inventors recognized that an ideal method for controlling the number of graphene layers should not rely on high-energy-consuming physical processes or destructive chemical reagents, but should be based on precise regulation of the intrinsic physical and chemical properties of the intercalating agent. An ideal intercalating agent should be an entity with precisely "programmable" size, whose size can be preset under mild conditions through simple chemical parameters and play a dominant role in the intercalation and exfoliation processes. Based on this inventive concept, by introducing and synergistically regulating the molar ratio (R) of calcium ions to sodium cholate, the system pH value, and the ionic strength (I), an intelligent intercalating agent system capable of forming supramolecular aggregates with controllable size is constructed, thereby achieving programmable control of the number of graphene layers.

[0033] The preparation method for the intercalating agent for graphene preparation according to the embodiments of the present invention includes the following steps: (1) providing an aqueous sodium cholate solution as a base solution; (2) adding a microenvironment regulator to the base solution to adjust and stabilize the system pH value and / or the ionic strength I to a preset target value; (3) under continuous stirring and temperature control conditions, adding an aqueous solution containing calcium ions dropwise to the solution obtained in step (2), and controlling the final molar concentration ratio R of calcium ions to sodium cholate to a preset value; (4) aging the mixed solution obtained in step (3) at a set temperature to obtain an intercalating agent for graphene preparation; in step (2), the preset target value is: pH = 5.5 - 8.5 (for example, 6.0, 6.5, 7.0, 7.5, or 8.0) and / or ionic strength I = 0.01 - 0.2 M (for example, 0.01 M, 0.05 M, 0.10 M, 0.15 M, or 0.20 M); in step (3), 0 < R ≤ 1.0 (for example, 0.05, 0.1, 0.25, 0.5, 0.75, 0.9, or 1.0). Among them, the ionic strength (I) is calculated by the formula where (where is the molar concentration of ion i, is the charge number of ion i).

[0034] The method for preparing the intercalating agent for graphene preparation of the present invention can "program" calcium ion-sodium cholate supramolecular aggregates with specific hydrodynamic diameters in situ in solution by synergistically controlling the R value, pH value and ionic strength I. The size of the supramolecular aggregates directly determines the number of graphene layers that can be peeled off and stabilized after being inserted into the graphite interlayer.

[0035] The key role of calcium ions in this invention is as follows: as a divalent crosslinking center, they dynamically coordinate with the carboxyl groups of bile acid ions, inducing and stabilizing the formation of supramolecular aggregates; their molar ratio (R value) is the "master switch" controlling the growth of aggregate size. Sodium cholate serves as the assembly framework, with its steroidal ring structure providing hydrophobic interactions and its carboxyl groups providing coordination sites; pH adjustment can be used to stabilize proton concentration, ensuring that bile acid ions are in the optimal coordination state and the repeatability of the aggregation process; the regulation of ionic strength allows for fine adjustment of the interaction forces during the secondary assembly of aggregates through electrostatic shielding effects, serving as a key "fine-tuning knob" for optimizing aggregate size distribution and stability. If calcium ions are omitted, crosslinked aggregates with rigid structures cannot be formed, and effective size programming and layer number control cannot be achieved solely with sodium cholate micelles; if pH is not buffered, the acidity and alkalinity of the system are prone to fluctuations, leading to unstable coordination states of bile acid ions and non-repeatable aggregate sizes; if the regulation of ionic strength is ignored, the final size and monodispersity of the aggregates cannot be optimized, affecting the accuracy of layer number control.

[0036] The core advantage of the intelligent intercalator system of this invention lies in its "programmability" and "responsiveness." By presetting the set of chemical parameters (R, pH, I), the size of supramolecular aggregates can be precisely controlled: a smaller R value (e.g., ~0.25) combined with moderate ionic strength tends to form smaller aggregates (tens of nanometers), which tend to stabilize monolayer or bilayer graphene after exfoliation; a larger R value (e.g., ~0.75) drives the formation of larger aggregates (hundreds of nanometers), which can stabilize graphene structures with more layers (e.g., 3-5 layers) after exfoliation; pH value, by affecting the dissociation and coordination chemistry of bile ions, provides a stable reaction environment for the entire assembly process. The three factors work synergistically to achieve directional and predictable control from "chemical parameter input" to "material microstructure output." If the pH is too low (<6.0), the degree of protonation of bile ions is high, and the coordination ability is weakened; if the pH is too high (>8.5), it may cause slight hydrolysis of calcium ions, interfering with the assembly process.

[0037] Preferably, 0.1 < R < 0.9; if the value of R is too small (e.g., < 0.1), there will be insufficient calcium ion crosslinking points, making it difficult to form effective supramolecular aggregates, resulting in low exfoliation efficiency and a relatively high proportion of thick-layer graphite in the product; if the value of R is too large (e.g., > 0.9), it may lead to an excessive amount of calcium ions, causing the precipitation of sodium cholate or forming overly dense and uneven-sized aggregates, which is instead unfavorable for uniform intercalation and controllable exfoliation, and the layer number distribution of the product becomes wider.

[0038] In a preferred embodiment of the preparation method of the intercalating agent for graphene preparation according to the present invention, in step (2), the preset target values are: pH = 7.0 ± 0.5 and / or ionic strength I = 0.05 - 0.15 M; in step (3), 0.25 ≤ R ≤ 0.75. Among them, when the value of R is about 0.25, the system is most favorable for obtaining graphene mainly composed of single layers and double layers; when the value of R is about 0.75, the system is most favorable for obtaining graphene mainly composed of 3 - 5 layers. The pH value is preferably maintained within the range of 7.0 ± 0.5. Under this condition, the cholate ions are in the best deprotonated state, which is beneficial for coordination with calcium ions, and the chemical environment of the system is stable. The preferred range of the ionic strength I is from 0.05 M to 0.15 M; within this range, the electrostatic shielding effect provided by the electrolyte can not only effectively promote the growth of aggregates driven by hydrophobicity, but also prevent the premature precipitation or instability of aggregates caused by too high salt concentration. If the ionic strength is too low (< 0.01 M), the electrostatic repulsion between aggregates is obvious, the growth is limited, the size is small and may be unstable; if the ionic strength is too high (> 0.20 M), the hydrophobic interaction is too strong, which may lead to the rapid and disordered growth of aggregates, a wide size distribution, and even salting-out phenomena.

[0039] In a preferred embodiment of the method for preparing the intercalating agent for graphene preparation of the present invention, in step (3), the dropping rate is 0.5-2.0 mL / min (e.g., 0.5 mL / min, 1.0 mL / min, 1.5 mL / min or 2.0 mL / min), the stirring speed is 300-600 rpm (e.g., 300 rpm, 400 rpm, 500 rpm or 600 rpm), and the temperature is controlled at 25±2℃ (e.g., 23℃, 24℃, 25℃, 26℃ or 27℃); in step (4), the aging treatment temperature is 25-35℃ (e.g., 25℃, 27℃, 29℃, 31℃, 33℃ or 35℃), and the time is 1-3h (e.g., 1h, 1.5h, 2h, 2.5h or 3h). In step (3), the dropping rate affects the local concentration of calcium ions introduced, thus influencing the formation and growth kinetics of the primary nucleus. If the dropping rate is too fast, it can easily lead to local supersaturation, resulting in aggregates with uneven sizes. If the dropping rate is too slow, the production efficiency will be low. The ripening process in step (4) is crucial for the relaxation of the aggregate structure and the attainment of thermodynamic equilibrium, which helps to obtain intercalating agents with uniform size and stable performance. If the ripening temperature is too high, the aggregate process will run out of control, leading to structural damage. If the ripening temperature is too low, the ripening will be insufficient. If the ripening time is too short, the reaction will not reach equilibrium and the size of the aggregates will be uneven. If the ripening time is too long, over-ripening and aging will occur, and there will also be issues with energy efficiency and cost.

[0040] In a preferred embodiment of the method for preparing the intercalating agent for graphene preparation of the present invention, the concentration of sodium cholate in the base solution is 10-100 mM (e.g., 10 mM, 30 mM, 50 mM, 70 mM, 90 mM or 100 mM); and the concentration of calcium ions in the aqueous solution containing calcium ions is 2.5-75 mM (e.g., 2.5 mM, 5 mM, 10 mM, 20 mM, 30 mM, 40 mM, 50 mM, 60 mM, 70 mM or 75 mM).

[0041] In a preferred embodiment of the method for preparing the intercalating agent for graphene preparation of the present invention, the components of the microenvironment regulator include a pH buffer and / or an inert electrolyte; the pH buffer is at least one of a phosphate buffer pair, a Tris-HCl buffer pair, and a carbonate buffer pair; the inert electrolyte is sodium chloride and / or potassium chloride; and the calcium salt in the aqueous solution containing calcium ions is at least one of calcium chloride, calcium nitrate, and calcium acetate.

[0042] The present invention also proposes an intercalating agent, which is prepared by the method described above in the embodiments of the present invention.

[0043] The present invention also proposes a method for preparing graphene. The method for preparing graphene in the embodiments of the present invention includes the following steps: intercalating graphite raw materials with the intercalating agent as described above.

[0044] The graphene preparation method of this invention is characterized by its green process, simple operation, and high reproducibility. The entire process is carried out in an aqueous phase, requiring no organic solvents or highly corrosive reagents, and under mild conditions. The prepared few-layer graphene has a concentrated layer distribution and a complete crystal structure, demonstrating clear application value in electronic devices, composite materials, and energy fields.

[0045] In a preferred embodiment of the graphene preparation method of the present invention, the graphene preparation method includes the following steps: S1, adding graphite raw material to an intercalating agent and performing intercalation treatment to obtain a mixture; S2, subjecting the mixture obtained in step (1) to ultrasonic treatment and exfoliating to obtain a graphene dispersion; S3, separating the graphene dispersion. In step S1, the intercalation time must be sufficient to ensure that the intercalating agent aggregates can effectively insert into the graphite layers; the ultrasonic treatment in step S2 must be performed under cooling conditions to prevent overheating from causing structural damage to the intercalating agent aggregates or increasing graphene defects.

[0046] Preferably, in step S1, the ratio of graphite raw material to intercalating agent is 2-6 mg / mL (e.g., 2 mg / mL, 3 mg / mL, 4 mg / mL, 5 mg / mL, or 6 mg / mL); wherein the amount of graphite raw material is expressed in mg, and the amount of intercalating agent is expressed in mL. If the proportion of graphite raw material is too high, the intercalation will be incomplete, and the graphene exfoliation effect will be poor; if the proportion of graphite raw material is too low, the utilization rate and economy of the intercalating agent will be poor.

[0047] In a preferred embodiment of the graphene preparation method of the present invention, the following steps are included: In step S1, the intercalation treatment is carried out under stirring conditions at room temperature, with a stirring speed of 250-350 rpm (e.g., 250 rpm, 280 rpm, 300 rpm, 320 rpm, or 350 rpm) and a stirring time of 6-24 h (e.g., 6 h, 12 h, 18 h, or 24 h); In step S2, the ultrasonic treatment is carried out under ice-water bath conditions, with an ultrasonic power of 400-600 W (e.g., 400 W, 450 W, 500 W, 550 W, or 600 W), a frequency of 40 kHz, and an ultrasonic treatment time of 2-8 h (e.g., 2 h, 4 h, 6 h, or 8 h); In step S3, the separation method is stepped centrifugation (step S3 is the key to separating graphene with different layers and removing unreacted raw materials, low speed...). Centrifugation to remove thick sheets and graphite particles, and high-speed centrifugation to collect graphene of the target number of layers: First, centrifuge at 800-1200 rpm (e.g., 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm) for 10-20 min (e.g., 10 min, 12 min, 14 min, 16 min, 18 min or 20 min) to remove unpeeled graphite material. Then, centrifuge at 3000-5000 rpm (e.g., 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm or 5000 rpm) for 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min or 40 min) to collect the supernatant. Graphene is located in the supernatant (the lower precipitate is mainly unpeeled or incompletely peeled thick graphite material). If the speed of high-speed centrifugation is too low, the centrifugal force will be insufficient, and all the unpeeled thick graphene particles and large agglomerates will not be able to settle effectively. If the speed of high-speed centrifugation is too high, the excessive centrifugal force may cause some of the target-size few-layer graphene (here, few-layer graphene refers to graphene with 3-10 layers) to settle prematurely.

[0048] The present invention also proposes a graphene, which is prepared by the method described above in the embodiments of the present invention.

[0049] The intercalating agent for graphene preparation of the present invention, its preparation method, and its application are described in detail below through specific embodiments.

[0050] The sources of the main raw materials used in the following examples are as follows: Sodium cholate: Shanghai Maclean Biochemical, purity ≥99.0%; Calcium chloride: Sinopharm Chemical Reagent Co., Ltd., analytical grade; Sodium chloride: Sigma-Aldrich, analytical grade, used to adjust ionic strength; Disodium hydrogen phosphate / sodium dihydrogen phosphate: Sinopharm, analytical grade, used to prepare phosphate buffer solution with pH=7.4; Natural flake graphite powder: Shanghai Aladdin Biochemical Technology Co., Ltd., model G103951, particle size <20μm, carbon content >99.9%; The experimental water was laboratory-made deionized water.

[0051] Example 1 The preparation method of the intercalating agent for graphene preparation in this embodiment includes the following steps: (1) Weigh 1.944 g of sodium cholate, dissolve and dilute to 100 mL to obtain 40 mM sodium cholate stock solution; (2) Take 25 mL of sodium cholate stock solution into a reaction vessel, add 2.5 mL of 0.2 M PBS buffer (pH=7.4) and 62.5 μL of 2.0 M NaCl solution, and add deionized water to make the total volume about 47.5 mL (the pH of the mixed solution obtained after step (2) is 7.4, and the ionic strength I is 0.05 M). (3) Under stirring conditions of 25℃ and 500rpm, 6.25mL of 40mM calcium chloride solution was slowly added dropwise to the above solution at a rate of 1.0mL / min using a constant flow pump. After the addition was completed, the final R of the system was 0.25.

[0052] (4) The mixture was aged in a constant temperature shaker at 30°C for 2 hours at a speed of 60 rpm to obtain the intercalating agent of this embodiment.

[0053] The method for preparing graphene in this embodiment includes the following steps: S1. Take 200 mL of intercalating agent (prepared according to the above steps (1)-(4)), add 800 mg of natural flake graphite powder, stir at 300 rpm for 24 h at room temperature, and perform intercalation treatment to obtain the first mixture.

[0054] S2. The mixture obtained after intercalation is placed in an ultrasonic reactor cooled by an ice-water bath and ultrasonically treated at 500W power and 40kHz frequency for 6 hours to obtain a second mixture.

[0055] S3. Centrifuge the second mixture at 1000 rpm for 15 min and discard the precipitate; centrifuge the supernatant at 4500 rpm for 30 min, collect the bottom precipitate and redisperse it in 40 mL of deionized water to obtain the graphene dispersion G1 of this embodiment.

[0056] Product characterization: Statistical analysis by atomic force microscopy (AFM) (see...) Figure 3 In dispersion G1, 84% of the graphene sheets had a thickness ≤1.2 nm (single / double layer), with an average thickness of (0.92±0.15) nm. The average Raman spectrum... The value is 1.65 (see Figure 4 The yield based on the initial graphite powder was approximately 11.4%.

[0057] Example 2 In the preparation process of the graphite intercalating agent in this embodiment: the molar concentration ratio of calcium ions to sodium cholate R = 0.75, the pH of the system = 7.4, and the ionic strength I = 0.05M.

[0058] The specific preparation steps are the same as in Example 1, except that the amount of calcium chloride solution added in step (3) is changed to 18.75 mL, so that the final R=0.75. After aging, intercalating agent B is obtained.

[0059] The graphene exfoliation step was the same as in Example 1, using intercalating agent B, and the resulting product was labeled as graphene dispersion G2.

[0060] Product characterization: AFM statistics showed that 80% of the graphene sheets in dispersion G2 had a thickness of 2.0-3.5 nm (3-5 layers), with an average thickness of (2.65±0.30) nm. The average Raman spectrum... The value is 0.75 (see Figure 4 The yield was approximately 15.9%.

[0061] Example 3 In the preparation process of the graphite intercalating agent in this embodiment: the molar concentration ratio of calcium ions to sodium cholate R=0.5, the pH of the system=7.4, and the ionic strength I=0.05M.

[0062] The specific preparation steps are the same as in Example 1, except that the amount of calcium chloride solution added in step (3) is changed to 12.5 mL, so that the final R=0.75. After aging, intercalating agent C is obtained.

[0063] The graphene exfoliation process was the same as in Example 1, using intercalating agent C, and the resulting product was labeled as graphene dispersion G3.

[0064] Product characterization: AFM statistics showed that 76% of the graphene sheets in dispersion G3 had a thickness of 1.5-2.8 nm (2-4 layers). Average Raman spectroscopy... The value is 1.05 (see Figure 4 The yield was approximately 14.2%.

[0065] Example 4 In the preparation process of the graphite intercalating agent in this embodiment: the molar concentration ratio of calcium ions to sodium cholate R=0.5, the pH of the system=7.4, and the ionic strength I=0.10M.

[0066] The only difference between this embodiment and Example 3 is that the ionic strength I is adjusted to 0.10 M. Specifically, in step (2), the amount of NaCl solution added is changed to 125 μL (2.0 M). The remaining steps are exactly the same as in Example 3, and intercalating agent D is obtained.

[0067] The graphene exfoliation process was the same as in Example 1, but intercalating agent D was used, and the resulting product was labeled as graphene dispersion G4.

[0068] Product characterization: Compared with Example 3 (I=0.05M), the layer number distribution of product G4 shifted slightly towards thicker layers, with the proportion of 3-5 layers increasing to approximately 70%, but the distribution width increased slightly (PDI increased). This demonstrates that ionic strength is an important synergistic factor regulating the layer number distribution.

[0069] Product characterization: AFM statistics showed that 70% of the dispersion G4 contained lamellar sheets with a thickness of 2.0-3.5 nm (3-5 layers). Average Raman spectra... The value is 0.85 (see Figure 4 The yield was approximately 12.0%.

[0070] Example 5 In the preparation of the graphite intercalating agent in this embodiment, its construction is based on the following parameters: the molar concentration ratio of calcium ions to sodium cholate R=0.5, the pH of the system=8.0, and the ionic strength I=0.05M.

[0071] The only difference between this embodiment and Embodiment 3 is that the pH of the system is adjusted to 8.0.

[0072] In step (2), the PBS buffer was replaced with Tris-HCl buffer (0.01M) adjusted to pH 8.0 with NaOH. The remaining steps were exactly the same as in Example 3, yielding intercalating agent E and graphene product G5.

[0073] Product characterization: AFM statistics showed that 72% of the graphene sheets in dispersion G5 had a thickness of 1.5-2.8 nm (mainly 2-4 layers). Average Raman spectroscopy... The value is 1.4. The yield is approximately 12.4%.

[0074] Example 6 In the preparation of the graphite intercalating agent in this embodiment, its construction is based on the following parameters: the molar concentration ratio of calcium ions to sodium cholate R=0.3, the pH of the system=7.4, and the ionic strength I=0.08M.

[0075] Based on step (2) of Example 1, the amount of calcium chloride added was adjusted to 7.5 mL (to make R=0.3), and the amount of NaCl added was adjusted to 100 μL (2.0 M). The remaining steps were the same as in Example 1, and intercalating agent F and graphene product G6 were obtained.

[0076] Product characterization: AFM statistics show that 88% of product G6 has a thickness ≤1.5nm (1-3 layers), indicating excellent layer density. The average Raman spectrum... The value is 1.45. The yield is approximately 12.8%, demonstrating good overall performance.

[0077] Comparative Example 1 The only difference between this comparative example and Example 1 is that the step of adding calcium chloride solution is omitted in the preparation of the intercalating agent (step (3)) (i.e., R=0); the rest is the same as Example 1. The intercalating agent in this comparative example is denoted as CP1, and the graphene dispersion is denoted as CG1.

[0078] Test structure: The graphene dispersion CG1 in this comparative example exhibits an extremely wide AFM layer distribution (1-10 layers or more), with single / double layers accounting for only 29%. Raman spectroscopy. Value dispersion (obtained through multiple tests) The values ​​exhibit significant dispersion, ranging from 0.5 to 1.8 in the tests. A large amount of precipitate appeared after the dispersion stood for 24 hours. This demonstrates a lack of calcium ion crosslinking, preventing the formation of an effective intercalation structure. Consequently, when used in the preparation of graphene, the number of graphene layers is uncontrollable.

[0079] Comparative Example 2 The only difference between this comparative example and Example 1 is that R=1.2 (i.e., 30mL of 40mM calcium chloride solution is added in step (3)), and the rest are consistent with Example 1.

[0080] Experimental results: During the process of adding calcium chloride solution in step (3), the system quickly became turbid and produced a large amount of flocculent precipitate, which could not form a stable intercalating agent; consequently, it could not carry out effective intercalation and stripping.

[0081] Comparative Example 3 The only difference between this comparative example and Example 1 is that the pH and ionic strength are not actively controlled (i.e., the PBS buffer and NaCl solution in step (2) of Example 1 are omitted, and 25 mL of sodium cholate stock solution is directly mixed with 2.5 mL of calcium chloride solution in deionized water (final I is very low, pH is about 8.9)). Everything else is the same as Example 1.

[0082] The intercalating agent in this comparative example is denoted as CP3, and the graphene dispersion is denoted as CG3.

[0083] Experimental results: The monolayer / bilayer ratio of product CG3 was 59%, significantly lower than 84% in Example 1. Furthermore, the results of the three repeated experiments showed large fluctuations (55%-70%), indicating poor reproducibility. This demonstrates that stable and reproducible layer number programming cannot be achieved without controlling pH and I.

[0084] Comparative Example 4 The only difference between this comparative example and Example 3 is that the ionic strength I = 0.25M (that is, in step (2), the amount of NaCl solution with a concentration of 2.0M added is changed to 312.5μL). The rest of the steps are the same as in Example 3, and the graphene product CG4 is obtained.

[0085] Results: The stripping yield dropped significantly to approximately 7%. AFM revealed that the product contained both a small number of monolayers and a large number of thick flakes with more than 5 layers, indicating that layer number control had completely failed. This demonstrates that excessively high ionic strength can damage the structure and function of the intercalating agent.

[0086] Comparative Example 5 The only difference between this comparative example and Example 3 is that the pH of the system is 6.0 (specifically, in step (2), PBS buffer with pH adjusted to 6.0 using HCl); the remaining steps are the same as in Example 3, and the product CG5 is obtained.

[0087] Results: The intercalation efficiency was low, with a graphene yield of only about 5%. The resulting graphene sheets were large and thick, and layer number control was ineffective. This demonstrates that excessively low pH inhibited the effective coordination of bile acid ions, hindering the formation of intercalating agent aggregates.

[0088] Comparative Example 6 In the preparation method of the intercalating agent for graphene preparation in this comparative example, the order of adding raw materials is different from that in Example 1 (specifically, 25 mL of 40 mM sodium cholate solution is quickly mixed with 2.5 mL of 40 mM calcium chloride solution first, and then PBS buffer and NaCl solution are added to try to adjust pH and I). The subsequent ripening and exfoliation steps are the same as in Example 1, and the product CG6 is obtained.

[0089] Results: The monolayer / bilayer ratio of the product CG6 was 56%, and the graphene yield was only about 9%. This proves that the order of "mixing reactants first and then adjusting the environment" cannot form graphene with uniform size.

[0090] Comparative Example 7 The difference between this comparative example and Example 1 is that equimolar magnesium chloride is used instead of calcium chloride (2.5 mL of 40 mM magnesium chloride solution is added in step (3)); the remaining steps are exactly the same as in Example 1, and the product CG7 is obtained.

[0091] Results: The stripping yield of this comparative example was low (~6%), and the product layer number distribution was broad (wide layer number distribution obtained by AFM testing, ranging from 1 to 12 layers), similar to Comparative Example 1. This demonstrates that Ca... 2+ It possesses specific coordination and assembly characteristics and cannot be reacted with Mg. 2+ Simple replacement.

[0092] Comparative Example 8 The difference between this comparative example and Example 1 is that an equimolar amount of sodium dodecyl sulfate (SDS) was used instead of sodium cholate, and the addition of calcium ions was omitted; the remaining steps were exactly the same as in Example 1, yielding product CG8.

[0093] Results: The percentage of single / double layers was 22%, and the graphene yield was 7.5%. This demonstrates that conventional single surfactants do not possess the ability to achieve size-controlled assembly through parametric programming, and cannot achieve precise exfoliation of the number of graphene layers.

[0094] Comparative Example 9 The difference between this comparative example and Example 1 is that in step (4), the product is aged in a constant temperature shaker at 45°C; the remaining steps are exactly the same as in Example 1.

[0095] Result: Due to the excessively high aging temperature, a large amount of precipitation occurred in the reaction system, and an intercalating agent that could be used for graphene intercalation could not be obtained.

[0096] The test results of the graphene prepared in the above examples and comparative examples are summarized in Table 1 below: Table 1 Summary of Performance Data

[0097] In Table 1, "the number of dominant graphene layers" refers to the graphene sheets with the highest proportion and a specific range of layers in the final product (graphene dispersion). It is a qualitative and conclusive description.

[0098] "AFM layer percentage" refers to the percentage of a target layer out of the total number of graphene sheets measured directly using atomic force microscopy (AFM). This method involves directly measuring the thickness of a single graphene sheet using AFM, converting the thickness into a layer number based on empirical values, and finally calculating the percentage of the target layer out of the total number of sheets. This is the most direct and quantitative method for characterizing layer distribution.

[0099] “ "" refers to the ratio of the peak intensity of the 2D peak to the G peak in the Raman spectrum of graphene. This ratio is a dimensionless parameter and serves as a key fingerprint feature for determining the number of graphene layers. Its value is negatively correlated with the number of graphene layers.

[0100] "Yield" refers to the percentage by mass of graphene that meets the target number of layers and is successfully exfoliated from the initial input graphite powder and finally collected using this method.

[0101] Table 1 shows that: In Comparative Example 1 (without calcium ions), the intercalating agent lacked the cross-linking and size programming effect of calcium ions, resulting in completely uncontrollable layer number of the exfoliated product, and significant deterioration in both yield and quality; In Comparative Example 2 (excessive R value), the excessive calcium ions (R=1.2) caused the intelligent assembly system to be destroyed and precipitation to occur, completely losing its exfoliation ability; In Comparative Example 3 (without pH / I regulation), the lack of precise control over the microenvironment led to uneven intercalating agent size and poor repeatability, resulting in a significant decrease in layer number control and yield; In Comparative Example 4 (too low ionic strength) and Comparative Example 5 (too low pH), the ionic strength deviated from the optimal range, causing unstable or ineffective aggregation behavior of the intercalating agent, resulting in a significant reduction in layer number control accuracy and exfoliation efficiency; In Comparative Example 6 (incorrect process sequence), the key process sequence of "first regulating the microenvironment, then introducing calcium ions" was violated, resulting in a wide size distribution of the formed intercalating agent, and a decrease in layer number selectivity and yield; In Comparative Example 7 (Mg... 2+ Alternative Ca 2+ This proves that calcium ions have irreplaceable specificity, and their unique coordination ability is a necessary condition for the formation of effective size-programmed intercalating agents. After replacement, the system performance deteriorates sharply.

[0102] In summary, the systematic comparison between the examples and comparative examples fully demonstrates that the molar ratio of calcium ions to sodium cholate (R value), the system pH value, and the ionic strength (I) are three indispensable and synergistically controllable core parameters for achieving efficient, programmable, and repeatable operation of this intelligent intercalating agent system. The absence of any key component, deviation from core parameters, or disorder of the process sequence will lead to the failure of the entire intelligent system or severe performance degradation. This, in turn, strongly confirms the non-obviousness, completeness, and superior effectiveness of the technical solution of this invention.

[0103] The graphene layer number distribution of Example 1 and Comparative Example 1 was characterized using Raman mapping: Test results are as follows Figure 1 As shown; Figure 1 In the figure, (a) is the test result of graphene in Example 1, and (b) is the test result of graphene in Comparative Example 1; where the more red areas there are, the higher the monolayer ratio of graphene, while blue indicates that the graphene is thicker.

[0104] SEM observation The microstructure of the graphene powder samples (obtained from the dried dispersion) prepared in Example 1 (R=0.25) and Comparative Example 1 (without calcium ions) were observed respectively; SEM images are shown below. Figure 2 As shown.

[0105] Figure 2In the middle: (b) is the SEM image of the sample of Comparative Example 1. It can be seen that the stacked sheets are disordered and there are a large number of thick sheets, agglomerates and curled structures. The edges of the sheets are rough and it is difficult to distinguish the clear single-layer or few-layer features, indicating that the peeling is insufficient and the product is not uniform; (a) is the SEM image of the sample of Example 1. It can be seen that the sheets are flat, well spread, and stacked in distinct layers. It is easy to observe the transparent and less wrinkled ultrathin sheet structure, indicating that the product is mainly composed of few-layer (mainly single / double-layer) graphene, the peeling is sufficient and the number of layers is controllable.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an intercalating agent for graphene preparation, characterized in that, Includes the following steps: (1) Provide sodium cholate aqueous solution as the base solution; (2) Add a microenvironment regulator to the base solution to adjust and stabilize the pH value and / or ionic strength I of the system to a preset target value; (3) Under continuous stirring and temperature control, add an aqueous solution containing calcium ions dropwise to the solution obtained in step (2) to control the final molar concentration ratio R of calcium ions to sodium cholate to the preset value. (4) The mixture obtained in step (3) is aged at a set temperature to obtain an intercalating agent for graphene preparation; In step (2), the preset target values ​​are: pH = 5.5-8.5 and / or ionic strength I = 0.01-0.2M; In step (3), 0 <R≤1.0。 2. The method for preparing the intercalating agent for graphene preparation as described in claim 1, characterized in that, In step (2), the preset target values ​​are: pH = 7.0 ± 0.5 and / or ionic strength I = 0.05-0.15 M; In step (3), 0.25≤R≤0.

75.

3. The method for preparing the intercalating agent for graphene preparation as described in claim 1, characterized in that, In step (3), the dropping rate is 0.5-2.0 mL / min, the stirring speed is 300-600 rpm, and the temperature is controlled at 25±2℃; In step (4), the aging process is carried out at a temperature of 25-35°C for 1-3 hours.

4. The method for preparing the intercalating agent for graphene preparation as described in claim 1, characterized in that, The concentration of sodium cholate in the base solution is 10-100 mM; The concentration of calcium ions in the aqueous solution containing calcium ions is 2.5-75 mM.

5. The method for preparing the intercalating agent for graphene preparation as described in claim 1, characterized in that, The components of the microenvironment regulator include pH buffers and / or inert electrolytes; The pH buffer is at least one of a phosphate buffer pair, a Tris-HCl buffer pair, and a carbonate buffer pair; The inert electrolyte is sodium chloride and / or potassium chloride; The calcium salt in the aqueous solution containing calcium ions is at least one of calcium chloride, calcium nitrate, and calcium acetate.

6. An intercalating agent, characterized in that, The intercalating agent is prepared using the method described in any one of claims 1-5.

7. A method for preparing graphene, characterized in that, The process includes the following steps: intercalating graphite raw materials using the intercalating agent as described in claim 6.

8. The method for preparing graphene according to claim 7, characterized in that, Includes the following steps: S1. Add graphite raw material to the intercalating agent and perform intercalation treatment to obtain a first mixture; S2. The mixture obtained in step (1) is subjected to ultrasonic treatment to obtain a second mixture; S3. Separate the second mixture obtained from step S2.

9. The method for preparing graphene as described in claim 8, characterized in that, The process includes the following steps: In step S1, the intercalation treatment is carried out under room temperature stirring conditions for 6-24 hours. In step S2, the ultrasonic treatment is carried out under ice water bath conditions, with an ultrasonic power of 400-600W, a frequency of 40kHz, and an ultrasonic treatment time of 2-8h. In step S3, the separation method is step centrifugation: first, centrifuge at 800-1200 rpm for 10-20 min to remove unpeeled graphite raw material, and then centrifuge at 3000-5000 rpm for 20-40 min to collect the supernatant, wherein the graphene is located in the supernatant.

10. A graphene, characterized in that, The graphene is prepared by the method described in any one of claims 7-9.

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