A method for grading extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation

Abstract

The application discloses a method for extracting carbon nanomaterials with different particle sizes by combining ultrasonic-assisted crushing with gradient centrifugation and anti-solvent precipitation. The method comprises the following steps: firstly, ultrasonic treatment is performed on an initial solution; then, four times of graded centrifugation with increasing rotation speed are sequentially performed, and the supernatant is taken as the mother liquor for the next time of centrifugation, so that dispersions with different size gradients are obtained. Then, the dispersions are mixed with a specific proportion of n-hexane (a precipitant) and isopropyl alcohol (a cosolvent), and after standing, centrifugation and vacuum drying, the final product is obtained. The method realizes high-precision size grading of carbon nanomaterials through a standardized centrifugal gradient, and effectively widens the utilization rate of raw materials. Meanwhile, the mixed anti-solvent system is used to remove the high-boiling-point NMP solvent at low temperature, and irreversible agglomeration of nanosheets is avoided.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial separation and purification technology, specifically involving a method for graded extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation. Background Technology

[0002] Liquid-phase exfoliation is currently the mainstream process for the large-scale preparation of high-quality carbon nanomaterials. N-methylpyrrolidone (NMP) is widely used as a dispersion medium due to its surface energy matching that of carbon materials. However, existing NMP dispersions for carbon nanomaterials face two major technical bottlenecks in post-processing and product extraction: First, the size distribution is wide and lacks precise classification. Traditional ultrasonic exfoliation products have a very wide size range. Conventional single centrifugation can only roughly remove large particles that have not been exfoliated, and cannot achieve precise exfoliation and classification of nanosheets with extremely fine size differences in the dispersion. This seriously limits the application of carbon nanomaterials in high-end fields that are sensitive to size (such as microelectronic devices, high-transmittance conductive films, etc.).

[0003] Secondly, high-boiling-point solvents are difficult to remove and are prone to irreversible aggregation. NMP has a boiling point of about 202°C. Direct heating and evaporation for drying not only consumes a lot of energy, but also, due to capillary contraction during solvent evaporation, carbon nanosheets are prone to irreversible "π-π" stacking and aggregation, resulting in the failure of the exfoliation effect. If conventional single-type flocculant is used for precipitation, it often leads to excessively violent flocculation, which cannot effectively wash away the NMP molecules between the layers, making it difficult to redisperse the product agglomerates.

[0004] Therefore, there is an urgent need for a method that can achieve high-precision dimensional classification, as well as gently and efficiently remove NMP solvent and obtain high-purity powder products. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for graded extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for graded extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation, characterized in that it includes: The initial solution was subjected to ultrasonic depolymerization and assisted disruption. The ultrasonicated solution was subjected to four fractional centrifugations. After each centrifugation, the upper 2 / 3 of the clear liquid was used as the mother liquor for the next centrifugation, and finally a dispersion was obtained. The dispersion was mixed evenly with the precipitant and co-solvent, sealed and allowed to stand to obtain the precipitate solution; The precipitate solution was centrifuged, the precipitate was collected, and vacuum dried to obtain the extracted carbon nanomaterials.

[0009] In a preferred embodiment of the method described in this invention, the ultrasonic power is 200~600W and the duration is 4~6 hours.

[0010] As a preferred embodiment of the method described in this invention, the centrifugation speeds are sequentially 3000-5000 rpm for the first stage, 7000-9000 rpm for the second stage, 11000-13000 rpm for the third stage, and 14000-16000 rpm for the fourth stage, with each centrifugation lasting 10-40 minutes.

[0011] In a preferred embodiment of the method described in this invention, the volume of the dispersion accounts for 10-25% of the total volume of the precipitate solution.

[0012] In a preferred embodiment of the method described in this invention, the volume ratio of the precipitant to the co-solvent is 1.5 to 2.5:1.

[0013] In a preferred embodiment of the method described in this invention, the precipitant is a C5-C8 alkane solvent; the co-solvent is a C1-C3 alcohol solvent.

[0014] In a preferred embodiment of the method described in this invention, the sealing and standing time is 2 to 5 days.

[0015] In a preferred embodiment of the method described in this invention, the centrifugation of the precipitate solution is carried out at a speed of 4000-8000 rpm for a time of 10-50 minutes.

[0016] As a preferred embodiment of the method described in this invention, the vacuum drying conditions are: drying at 80℃~120℃ for 8~12 hours.

[0017] Another objective of this invention is to overcome the shortcomings of the prior art and provide a carbon nanomaterial extracted by a graded extraction method based on ultrasonic depolymerization and multi-level gradient centrifugation, characterized in that: the lateral dimension of the carbon nanomaterial is 20-40 nanometers and the average thickness is 2 nm.

[0018] Beneficial effects of this invention: (1) Achieving high-precision size classification: This invention constructs a standardized and streamlined carbon nanomaterial size classification system by setting specific centrifugation gradient parameters (4000 rpm, 8000 rpm, 12000 rpm, 15000 rpm) and fixed processing time (30 minutes per stage), avoiding the problem of wide product particle size distribution caused by traditional single centrifugation. Combined with characterization data such as SEM, TEM, and AFM, it can be seen that CNano1 is mainly distributed at the 200 nm level and has a large thickness; CNano4 separated at 15000 rpm has a significantly reduced lateral size to 5-20 nm, and AFM test shows that its average thickness is only 2 nm, proving that this method can achieve size classification with nanometer-level precision.

[0019] (2) Effective collection of products with multiple particle sizes and improved raw material utilization: Through continuous operation of extracting the upper 2 / 3 of the clear liquid in stages, four carbon nanosheet products with different particle sizes and physicochemical properties can be obtained, which greatly improves the post-processing efficiency and high added value utilization of the dispersion; BET test results show that the specific surface area of ​​CNano1 to CNano4 generally shows a regular increase, and the specific surface area of ​​CNano4 reaches 180.4 m. 2 / g, verifying the ability of different centrifugation gradients to precisely control the specific surface area of ​​carbon nanosheets.

[0020] (3) Mild and efficient removal of high-boiling-point NMP solvent: Using a mixed antisolvent system with hexane as precipitant and isopropanol as cosolvent, combined with static precipitation and low-speed centrifugation collection, NMP can be effectively eluted under low temperature conditions, avoiding high energy consumption caused by high-temperature evaporation and the problem of irreversible "π-π" stacking and agglomeration of carbon nanosheets. The resulting powder is easy to redisperse and retains the structural characteristics of the nanosheets after exfoliation.

[0021] (4) The process parameters of this invention are clear, the steps are simple, the standardization is high, and the repeatability is strong, which makes it easy to promote and industrialize on a large scale. It is especially suitable for the preparation of raw materials in high-end application fields such as size-sensitive microelectronic devices and high-transmittance conductive films. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments 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. Wherein: Figure 1 This is a schematic diagram of the differential centrifugation process in an embodiment of the present invention; Figure 2 The images show a comparison of scanning electron microscope (SEM) images of the four graphene nanosheets (CNano1-4) prepared in Example 1 of this invention. Figure 3 The thickness characterization images of the graphene nanosheets (CNano3-4) prepared in Example 1 of this invention are obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). Figure 4 The infrared (IR) spectra of four types of graphene nanosheets prepared in Example 1 of this invention are shown below. Figure 5 The nitrogen adsorption-desorption isotherms and BET specific surface areas of the four graphene nanosheets (CNano1-4) prepared in Example 1 of this invention are compared.

[0023] Figure 6 The particle size distribution diagrams of the four graphene nanosheets (CNano1-4) prepared in this embodiment are shown.

[0024] Figure 7 These are comparative photographs of the states of the systems obtained in Example 1 and Comparative Example 3 after centrifugation. The carbon nanosheets that have completely settled into a dense black precipitate are from Example 1, while those that are still layered and have not formed a dense precipitate are from Comparative Example 3. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0028] The raw materials used in this invention are: waste graphite after high-energy ball milling at 28 Hz for 24 h and CNano0, which is the product of SiC-assisted ball milling.

[0029] The instruments used in this embodiment of the invention are: Shumei KQ-400DM silent ultrasonic cleaner and Xiangyi H1750 centrifuge.

[0030] Test method in this embodiment of the invention: (1) Morphological and dimensional characterization (SEM / TEM): The surface morphology and aggregation state of the product were observed using a field emission scanning electron microscope (SEM, model: Zeiss Sigma 300). The extracted carbon nanomaterial powder was redispersed in water, drop-coated onto a silicon wafer surface, and dried. The lateral dimensions of the nanosheets were observed using a transmission electron microscope (TEM, model: Talos F200X G2). The dispersion was diluted and then dropped onto an ultrathin carbon-supported film electron microscope grid.

[0031] (2) Thickness characterization (AFM): An atomic force microscope (AFM, model Bruker Dimension Icon) was used. In Tapping Mode, height maps were acquired on the silicon wafer surface, and the average thickness of at least 100 nanosheets was statistically analyzed using random sampling.

[0032] (3) Aperture and specific surface area test (BET): A fully automated physical adsorption analyzer (model: Autosorb-IQ3) was used. Before testing, the samples were degassed under vacuum at 120°C for 8–12 hours. The specific surface area was calculated using the BET equation based on the nitrogen adsorption-desorption isotherm at 77 K.

[0033] (4) Chemical structure and solvent residue testing (FT-IR): A Fourier transform infrared spectrometer (Thermo Scientific Nicolet 6700) was used. ATR mode was employed, with a scan range of 4000–400 cm⁻¹. -1 The focus of the investigation is on 1670 cm. -1 The intensity of the characteristic absorption peaks near the C=O bond in NMP.

[0034] Example 1 This embodiment provides a method for the graded extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation, such as... Figure 1 As shown, the specific steps include: (1) Pre-processing: A graphene NMP dispersion with a concentration of 40 ppm was placed in an ultrasonic device and subjected to ultrasonic depolymerization and assisted fragmentation at a power of 400W for 5 hours to ensure that the carbon nanomaterials were fully exfoliated and the aggregates were broken up in the liquid phase.

[0035] (2) Fractional centrifugation: The sonicated solution was subjected to fractional centrifugation at 4000 rpm, 8000 rpm, 12000 rpm, and 15000 rpm, with each centrifugation lasting 30 minutes. After each centrifugation, the upper 2 / 3 of the supernatant was strictly extracted as the mother liquor for the next centrifugation stage.

[0036] Through this continuous operation, the first-stage CNano1, second-stage CNano2, third-stage CNano3, and fourth-stage CNano4 dispersions of the corresponding size gradients can be intercepted and obtained respectively.

[0037] (3) Solvent precipitation: Add 8 mL of the separated CNano target dispersion to a 50 mL standard centrifuge tube. Then, slowly add 4 mL of premixed hexane as the precipitant and 2 mL of isopropanol as the co-solvent, and shake well initially.

[0038] Next, the centrifuge tube was filled with a mixture of hexane and isopropanol in a 2:1 volume ratio, sealed, and left to stand for 5 days to allow the carbon nanomaterials to fully aggregate and precipitate under the action of the antisolvent.

[0039] (4) Drying and collecting: Place the centrifuge tubes that have completed the settling process into a centrifuge and centrifuge at 6000 rpm for 30 minutes. Pour off the supernatant and collect the solid precipitate at the bottom.

[0040] Finally, the precipitate is transferred to a vacuum drying oven, where it is baked at 120°C for 8 hours, depending on the heat sensitivity of the actual material, to obtain a high-purity dry sample product.

[0041] Figure 2 The images show a comparison of scanning electron microscope (SEM) images of the four graphene nanosheets (CNano1-4) prepared in this embodiment. It can be seen that as the centrifugation speed increases, the particle size of the obtained products decreases significantly, and the aggregates become finer and more dispersed.

[0042] Figure 3 The thickness characterization images of the graphene nanosheets (CNano3-4) prepared in this embodiment are obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). It can be seen that CNano4 separated at 15000 rpm has a significantly reduced lateral size to 20-40 nm. The AFM results show that its average thickness is only 2 nm, proving that this method has successfully achieved high-precision size grading.

[0043] Figure 4 Infrared (IR) spectra of the four graphene nanosheets prepared in this embodiment.

[0044] Figure 5 Nitrogen adsorption-desorption isotherms and BET specific surface areas of four graphene nanosheets (CNano1-4) prepared in the embodiments of this invention are shown in the figure. The BET bar chart clearly shows the specific surface area values ​​of CNano1 to CNano4, with CNano4 having the highest and CNano1 the lowest. The regular change strongly demonstrates the precise control of the specific surface area of ​​the products by gradient centrifugation. The adsorption isotherms further show the pore structure characteristics of different fractions of materials. CNano4 has the highest adsorption capacity in the high-pressure section, which corresponds to its largest specific surface area.

[0045] Figure 6 The particle size distribution of the four graphene nanosheets (CNano1-4) prepared in this embodiment shows a highly significant and regular decrease and narrowing trend in the lateral size of the products as the centrifugation speed increases (corresponding to CNano1 to CNano4 fractions). Specifically, the CNano1 fraction retained at low speeds has a wider size distribution, with a median size (D50) of 243.6 nm and a D90 of 588.1 nm; while the CNano4 fraction separated by high-speed centrifugation at 15000 rpm has a significantly reduced median size (D50) to 31.0 nm, and the particle size distribution range is extremely concentrated (D90 is only 53.8 nm). This data change spanning orders of magnitude and with a concentrated distribution strongly demonstrates that this method successfully overcomes the defect of wide particle size distribution in traditional single centrifugation and achieves high-precision size classification at the nanoscale.

[0046] Furthermore, the aspect ratio distribution data reveals another important advantage of this process. Despite the significant differences in absolute lateral dimensions between CNano1 and CNano4, the median aspect ratio of the four fractions remained highly stable within a narrow range of 1.41 to 1.48. This clearly demonstrates that the specific ultrasonic depolymerization parameters employed in this invention, combined with a mild antisolvent precipitation extraction process, achieve efficient exfoliation and sizing while perfectly preserving the original two-dimensional sheet morphology of the carbon nanomaterials, without damaging the material's fundamental microstructure.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that the four gradient centrifugations (4000 rpm, 8000 rpm, 12000 rpm, 15000 rpm, 30 min each) in step (2) are simplified to one centrifugation at 12000 rpm for 30 min. The upper 2 / 3 of the clear liquid is taken directly into step (3) for subsequent solvent precipitation and drying. The other raw materials, parameters and steps are the same as in Example 1.

[0048] Testing revealed that the obtained product had a wide particle size distribution and contained a mixture of nanosheets of different sizes, resulting in a significantly inferior fractionation effect compared to Example 1, and a significantly lower yield of the effective product. More seriously, due to the lack of buffering and sieving through prior low-speed centrifugation, a large number of coarse particles in the system experienced a strong "entrainment effect" during direct high-speed centrifugation at 12000 rpm. During the rapid settling of the coarse particles, a large number of originally free small-sized nanosheets were physically encapsulated or carried along, being pulled into the sediment at the bottom of the tube. This further led to a significant decrease in the overall yield of high-quality, small-sized carbon nanomaterials extracted from the upper 2 / 3 of the supernatant compared to Example 1 (the sum of CNano1 to CNano4).

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that ultrasonic treatment is not performed in step (1); the other raw materials, parameters and steps are the same as in Example 1.

[0050] The dispersion without ultrasonic depolymerization contained a large number of unexfoliated graphite particles and aggregates. After four gradient centrifugations, the first two stages (4000 rpm, 8000 rpm) produced abnormally thick precipitates, with almost all coarse particles in the system being removed prematurely by the first two stages; the supernatant concentration of the last two stages (12000 rpm, 15000 rpm) was extremely low, making it practically impossible to obtain effective CNano3 and CNano4 products.

[0051] Comparative Example 3 The difference between this comparative example and Example 1 is that the solvent precipitation step in step (3) is replaced with a single solvent system. That is, only 12 mL of n-hexane (without isopropanol) is added to 8 mL of CNano target dispersion, and the remaining steps and parameters are exactly the same as in Example 1.

[0052] Because n-hexane is a strong nonpolar solvent and has extremely poor miscibility with highly polar NMP, its addition immediately results in a clear liquid-liquid phase separation—the upper layer is a transparent n-hexane phase, and the lower layer is a dark polar phase containing NMP. Most of the carbon nanosheets either remain suspended at the interface between the two phases or are retained in the lower NMP phase, unable to form a uniform and controllable solid-phase flocculant under the action of the anti-solvent. After being sealed and allowed to stand for 5 days, the system still maintains the two-phase separation state.

[0053] To visually compare the effects of antisolvent precipitation, the systems from Example 1 and this comparative example were centrifuged under the same conditions after standing. The results are as follows: Figure 7As shown: In the system obtained in Example 1, the carbon nanosheets were completely flocculated and settled to the bottom of the centrifuge tube, forming a black solid precipitate, and the upper liquid was clear; while in this comparative example, after the same centrifugation, the carbon nanosheets still maintained a layered state, and the carbon nanosheets failed to form a dense precipitate. Only a small amount of loose flocculent matter was seen at the bottom of the tube, and no effective solid product could be obtained.

[0054] This comparative example demonstrates that, in the absence of a polar co-solvent as a "bridging medium," it is impossible to achieve effective displacement of NMP and controllable aggregation and precipitation of carbon nanosheets.

[0055] Comparative Example 4 The difference between this comparative example and Example 1 is that the solvent precipitation step in step (3) is replaced with a single solvent system. That is, only 12 mL of isopropanol (without adding n-hexane) is added to 8 mL of CNano target dispersion, and the remaining steps and parameters are exactly the same as in Example 1.

[0056] Isopropanol and NMP are well miscible. After its addition, the system remained in a uniform and stable suspension, and no visible flocculation or sedimentation of carbon nanosheets was observed. After being sealed and left to stand for 5 days, the color and clarity of the dispersion remained basically unchanged. In step (4), after centrifugation at 6000 rpm for 30 min, only a very small amount of extremely fine particles (possibly a few large particles that were not stably dispersed) were found at the bottom of the centrifuge tube, and the concentration of the supernatant was still relatively high. In fact, it was impossible to obtain an effective solid-phase precipitation product. This comparative example proves that relying solely on highly polar isopropanol cannot provide sufficient antisolvent driving force. Non-polar n-hexane must be used as the main precipitant to induce mild and controllable aggregation of carbon nanosheets within 2 to 5 days.

[0057] NMP is a strongly polar aprotic solvent (dielectric constant approximately 32), while n-hexane is a typical nonpolar solvent (dielectric constant approximately 1.9). Their polarity difference is too great, resulting in extremely poor miscibility. When n-hexane is used alone, liquid-liquid phase separation occurs directly, failing to form a uniform antisolvent environment (Comparative Example 3). Although isopropanol exhibits good miscibility with NMP, its polarity (dielectric constant approximately 18) is insufficient to significantly reduce the system's solvation ability for carbon nanosheets, thus failing to provide an effective driving force for aggregation (Comparative Example 4). This invention, using n-hexane as the main precipitant and isopropanol as the co-solvent in a 2:1 volume ratio, utilizes isopropanol as a "polar bridging medium" to enable n-hexane and NMP to become miscible at the molecular scale. This allows for a uniform antisolvent effect throughout the system, gently and controllably inducing the flocculation and precipitation of carbon nanosheets.

[0058] Example 2 This embodiment aims to verify the applicability of the graded extraction method to other two-dimensional carbon materials with different interlayer interactions. Specifically, it includes the following steps: (1) Pretreatment: Commercially available graphite was used to replace waste graphite, and an NMP dispersion with a concentration of 40 ppm was prepared. Since the interlayer spacing of the expanded graphite had been partially opened, the ultrasonic power was adjusted to 300W, and the ultrasonic depolymerization time was shortened to 4 hours.

[0059] (2) Fractional centrifugation: The sonicated solution was subjected to fractional centrifugation at 4000 rpm, 8000 rpm, 12000 rpm and 15000 rpm in sequence, with each centrifugation taking 30 minutes. The upper 2 / 3 of the clear liquid was extracted each time as the mother liquor for the next centrifugation.

[0060] (3) Solvent precipitation and drying collection: The subsequent addition of mixed precipitant (hexane:isopropanol volume ratio 2:1) and drying conditions are consistent with those in Example 1.

[0061] Compared to Example 1, the overall yield of carbon nanosheets in each dispersion (especially CNano3 and CNano4) is expected to be significantly improved due to the easier exfoliation of expanded graphite. After the same gradient centrifugation, the resulting products still exhibit a regular trend of decreasing lateral size.

[0062] This embodiment demonstrates that the method of the present invention also exhibits excellent high-precision size classification and mild antisolvent extraction capabilities for easily exfoliated two-dimensional carbon materials.

[0063] Example 3 The difference between this embodiment and embodiment 1 is that the ultrasonic power in step (1) is replaced with 200W, while the rest of the steps are the same as in embodiment 1.

[0064] Because the ultrasonic power is at a lower limit, the cavitation effect within the system is weakened, and the degree of deagglomeration of the original graphite particles is slightly lower than in Example 1. This is reflected in the fractional centrifugation process, where the proportion of coarse particle agglomerates retained in the first two stages (CNano1 and CNano2) increases, while the yield of small-sized, oligolayer graphene nanosheets entering the fourth stage (CNano4) dispersion decreases. This demonstrates that the core process route of this invention remains effective at 200W power, achieving high-precision size fractionation.

[0065] Example 4 The difference between this embodiment and embodiment 1 is that the ultrasonic power in step (1) is replaced with 600W, while the rest of the steps are the same as in embodiment 1.

[0066] Under high-power ultrasound of 600W, liquid-phase exfoliation was very thorough. During fractionation centrifugation, the yields of smaller fractions such as CNano3 and CNano4 were improved. However, excessively high ultrasonic energy could also lead to an increase in in-plane lattice defects or excessive edge fragmentation in some carbon nanosheets. Despite slight structural damage, the final dry powder obtained at this upper limit still possessed an extremely high specific surface area, and the antisolvent precipitation process could still efficiently elute NMP. This indicates that 600W is an effective working boundary for balancing high exfoliation efficiency and nanosheet structural integrity.

[0067] Example 5 The difference between this embodiment and Example 1 is that the volume ratio of the mixed precipitate of n-hexane and isopropanol in step (3) is replaced with 1.5:1, while the rest of the steps are the same as in Example 1.

[0068] During the settling period, the system exhibited significant flocculation and sedimentation. After centrifugation, a solid precipitate was visible at the bottom of the centrifuge tube, and the supernatant was significantly clearer than the initial dispersion, indicating that the antisolvent effect was effectively achieved. The obtained powder could be redispersed after vacuum drying without significant agglomeration. Since the fractionation centrifugation steps in this embodiment were completely consistent with those in Example 1, the size fractionation pattern of CNano1 to CNano4 obtained was the same as in Example 1.

[0069] Example 6 The difference between this embodiment and Example 1 is that the volume ratio of the mixed precipitate of n-hexane and isopropanol in step (3) is replaced with 2.5:1, while the rest of the steps are the same as in Example 1.

[0070] During the settling period, uniform flocculation and precipitation also occurred in the system. After centrifugation, the solid phase at the bottom of the tube was dense, and the supernatant was clear. The liquid-liquid phase separation phenomenon observed in Comparative Example 3 did not occur, indicating that isopropanol at a ratio of 2.5:1 can still provide sufficient "polar bridging" to maintain a uniform antisolvent environment in the system; the obtained powder can be easily redispersed. Similarly, since the fractionation centrifugation procedure is the same as in Example 1, the size fractionation pattern of CNano1 to CNano4 is the same as in Example 1.

[0071] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for graded extraction of carbon nanomaterials based on ultrasonic depolymerization and multi-stage gradient centrifugation, characterized in that: include, The initial solution is subjected to ultrasonic treatment to achieve depolymerization and assisted fragmentation; The ultrasonicated solution was subjected to four fractional centrifugations. After each centrifugation, the upper 2 / 3 of the clear liquid was used as the mother liquor for the next centrifugation, and finally a dispersion was obtained. The dispersion was mixed evenly with the precipitant and co-solvent, sealed and allowed to stand to obtain the precipitate solution; The precipitate solution was centrifuged, the precipitate was collected, and vacuum dried to obtain the extracted carbon nanomaterials. The initial solution is a dispersion of carbon nanomaterials with a concentration of 20-60 ppm.

2. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The ultrasonic power is 200~600W, and the duration is 4~6 hours.

3. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The centrifugation speeds for the stages are 3000–5000 rpm for the first stage, 7000–9000 rpm for the second stage, 11000–13000 rpm for the third stage, and 14000–16000 rpm for the fourth stage, with each centrifugation lasting 10–40 minutes.

4. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The volume of the dispersion accounts for 10-25% of the total volume of the precipitate solution.

5. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The volume ratio of the precipitant to the co-solvent is 1.5 to 2.5:

1.

6. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The precipitant is a C5-C8 alkane solvent; the co-solvent is a C1-C3 alcohol solvent.

7. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The sealing and settling time is 2 to 5 days.

8. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The precipitate solution is centrifuged, wherein the centrifugation speed is 4000-8000 rpm and the centrifugation time is 10-50 minutes.

9. The method for graded extraction of carbon nanomaterials as described in claim 1, characterized in that: The vacuum drying conditions are 80℃~120℃ for 8~12 hours.

10. The carbon nanomaterials extracted by the fractional extraction method for carbon nanomaterials according to any one of claims 1 to 9, characterized in that: The carbon nanomaterial has a lateral dimension of 20–40 nanometers and an average thickness of 2 nm.

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