A method for purifying an oligowall carbon nanotube-based single-walled carbon composite material

Abstract

The present application relates to carbon nanomaterial purification technical field, specifically to a kind of oligowall carbon nanotube-based single-hole carbon composite material purification method, comprising the following steps: S1, the oligowall carbon nanotube-based single-hole carbon composite material to be purified is added into deionized water, ultrasonic dispersion is carried out, and dispersion liquid is obtained;S2, copper salt solution is added to the dispersion liquid, and hydrothermal displacement reaction is carried out at a temperature of 80~200°C, so that copper salt and metal catalyst impurities in the composite material wrapped by graphite carbon layer occur displacement reaction;S3, the product after step S2 reaction is carried out solid-liquid separation, and the obtained solid is added into dilute acid solution, and stirred and pickled at 40~80°C;The present application carries out displacement reaction under hydrothermal conditions (≤200°C), without high temperature (>1800°C) or strong oxidizing acid treatment, avoid the destruction of high temperature and strong oxidizing environment to oligowall carbon nanotube structure, experimental results show that the ID / IG ratio of carbon nanotube after purification is basically flat with before purification, and structural defect is not significantly increased.

Description

Technical Field

[0001] This invention relates to the field of carbon nanomaterial purification technology, specifically to a purification method for oligowalled carbon nanotube-based monoporous carbon composite materials. Background Technology

[0002] Oligowalled carbon nanotubes (OLTs) are carbon nanotubes with 2 to 5 wall layers. They combine the high specific surface area and high aspect ratio of single-walled carbon nanotubes with the good structural stability of multi-walled carbon nanotubes, and have broad application prospects in fields such as conductive additives for lithium-ion batteries, reinforcing phases of composite materials, and catalyst supports.

[0003] However, the preparation of carbon nanotubes typically requires the use of metal catalysts (such as Fe, Co, Ni, etc.), which inevitably exist as impurities in the product. These metal impurities in the crude product not only affect the purity of the carbon nanotubes but may also cause internal short circuits and promote lithium dendrite growth in subsequent applications (such as lithium-ion batteries), posing safety hazards. Therefore, efficient purification of carbon nanotubes is a necessary prerequisite for their industrial application.

[0004] Existing methods for purifying carbon nanotubes have the following main shortcomings: First, metallic impurities encased in graphite carbon layers are difficult to remove. Some metal catalyst nanoparticles are tightly encased in graphite carbon layers during carbon nanotube growth, making conventional acid washing methods ineffective as the acid solution cannot reach the encased metal. Although some studies have attempted to use strong oxidizing acids to oxidize and peel away the carbon layers to expose the internal metal, these acids severely damage the spline structure of the carbon nanotubes. 2 The carbon framework structure introduces numerous structural defects, which is particularly detrimental to oligowalled carbon nanotubes with few wall layers.

[0005] Second, high-temperature treatment methods are energy-intensive and require demanding equipment. Some existing technologies use high-temperature heat treatment (above 1800°C) or high-temperature chlorine treatment to remove metal impurities, but these methods are extremely energy-intensive, require expensive equipment investment, and have small batch processing capacity, making it difficult to meet the needs of large-scale industrial production.

[0006] Third, existing medium-temperature oxidation-acid leaching methods have limited effectiveness. Some technical solutions use a combination of medium-temperature air oxidation and acid leaching (such as 400°C oxidation + acid washing), but due to the low oxidation temperature, the ability to damage the graphite carbon layer is limited, and the encapsulated metal impurities are still difficult to remove effectively. In view of this, we propose a purification method for oligowalled carbon nanotube-based monoporous carbon composite materials. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings mentioned in the background art and provide a purification method for oligowalled carbon nanotube-based monoporous carbon composite materials.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A purification method for oligowalled carbon nanotube-based monoporous carbon composite materials includes the following steps: Step 1: Dispersion Pretreatment The oligowalled carbon nanotube-based monoporous carbon composite material to be purified was added to deionized water and ultrasonically dispersed for 10-30 min to obtain a uniform dispersion. The solid-liquid ratio of the oligowalled carbon nanotube-based monoporous carbon composite material to deionized water was 1:50-1:200 (g / mL), and the ultrasonic power was 200-500 W.

[0009] The purpose of dispersion pretreatment is to uniformly disperse carbon nanotubes in the liquid phase, increase the contact area between carbon nanotubes and copper salt solution, and improve the efficiency of the displacement reaction.

[0010] Step 2: Metal Salt Displacement Reaction A copper salt solution is added to the dispersion obtained in step one, and a hydrothermal displacement reaction is carried out at a temperature of 80-200°C for 2-12 hours. The copper salt is selected from at least one of CuCl2 or Cu(NO3)2, preferably CuCl2. The amount of copper salt added is in a molar ratio of copper salt:coated metal = 2:1-5:1, preferably 3:1.

[0011] The chemical principle of displacement reaction is as follows: Fe+Cu 2+ →Fe 2+ +Cu↓; Co+Cu 2+ →Co 2+ +Cu↓; Ni+Cu 2+ →Ni 2+ +Cu↓; Metal nanoparticles (Fe, Co, Ni) encapsulated in a graphite carbon layer react with Cu in solution. 2+ A displacement reaction occurs, and the metallic element is oxidized to soluble metal ions (Fe). 2+ Co 2+ Ni 2+ ), while Cu 2+ It is reduced to elemental copper. Under hydrothermal conditions (80~200°C), Cu in the solution... 2+ It can diffuse into the interior of the encapsulation layer through naturally occurring defects, grain boundaries, or interlayer gaps in the graphite carbon layer, and undergo a displacement reaction with the metal; the metal ions and elemental copper generated in the reaction can diffuse out through the same path. Unlike treatment with strong oxidizing acids, the displacement reaction takes place under mild conditions and can achieve the conversion and removal of internal metals without destroying the main structure of the graphite carbon layer.

[0012] Step 3: Acid washing to remove The product from step two is subjected to solid-liquid separation. The obtained solid is added to a dilute acid solution and acid-washed by stirring at 40-80°C for 1-4 hours. The dilute acid solution is dilute hydrochloric acid or dilute nitric acid with a concentration of 0.5-2 mol / L, preferably 1 mol / L hydrochloric acid. The purpose of acid washing is to remove the metal ions (Fe2+) generated in the displacement reaction. 2+ Co 2+ Ni 2+ The metal impurities are completely removed by fully dissolving some unreacted metals and the generated elemental copper.

[0013] Step 4: Wash and dry The purified oligowalled carbon nanotube-based monoporous carbon composite material was obtained by repeatedly washing with deionized water until neutral (pH=6.5~7.5) and vacuum drying at 60~100°C for 6~24h.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention conducts the displacement reaction under hydrothermal conditions (≤200°C), eliminating the need for high-temperature (>1800°C) or strong oxidizing acid treatment, thus avoiding the damage to the oligowalled carbon nanotube structure caused by high-temperature and strong oxidizing environments. Experimental results show that the ID / IG ratio of the purified carbon nanotubes is basically the same as that before purification, and the structural defects are not significantly increased.

[0015] 2. This invention utilizes Cu 2+ The substitution reaction with Fe, Co, and Ni facilitates ion diffusion through defects and grain boundaries in the graphite carbon layer, effectively removing the encapsulated metal catalyst without damaging the main structure of the graphite carbon layer. Experimental results show that the total metal removal rate can reach over 88%.

[0016] 3. This invention only requires two core purification steps: displacement reaction and acid washing. It does not require complex processes such as high-temperature reduction and high-temperature vacuum treatment. It is simple to operate, has low equipment requirements, and is suitable for industrial-scale production.

[0017] 4. This invention does not use strong corrosive acids such as concentrated sulfuric acid and concentrated nitric acid. The waste liquid is mainly a dilute acid salt solution containing copper, iron, cobalt and nickel ions, which is easy to treat and environmentally friendly. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. 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.

[0019] The raw material information used in each embodiment of the present invention is as follows: Crude oligowalled carbon nanotube-based monoporous carbon composite material, with 2-5 tube wall layers, prepared by CVD method, purchased from Jiangsu Tiannai Technology Co., Ltd.; Copper dichloride (CuCl2·2H2O), analytical grade (AR), purity ≥99.0%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Hydrochloric acid (HCl), analytical grade (AR), concentration 36%-38%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Nitric acid (HNO3), analytical grade (AR), concentration 65%-68%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Concentrated sulfuric acid (H2SO4), analytical grade (AR), concentration 95%-98%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Deionized water, resistivity ≥18.2 MΩ·cm.

[0020] The present invention will describe the above technical solution in detail through the following embodiments: Example 1

[0021] This embodiment provides a purification method for oligowalled carbon nanotube-based monoporous carbon composite materials, including the following steps: (1) Dispersion pretreatment Weigh 10g of the oligowalled carbon nanotube-based monoporous carbon composite material to be purified (prepared by CVD method, with 2-5 tube wall layers, initial Fe content of 2.8wt% and Ni content of 0.7wt%, provided by Jiangsu Tiannai Technology Co., Ltd.), add it to 1000mL of deionized water (solid-liquid ratio of 1:100g / mL), and ultrasonically disperse it at an ultrasonic power of 300W for 20min to obtain a uniform dispersion.

[0022] (2) Metal salt displacement reaction Add CuCl2·2H2O (Sinopharm Chemical Reagent Co., Ltd., analytical grade, purity ≥99.0%) to the above dispersion. Based on the initial metal impurity content determined by ICP-OES (Fe 2.8wt%, Ni 0.7wt%, total 3.5wt%), and calculating according to the CuCl2:coated metal molar ratio of 3:1, weigh approximately 7.5g of CuCl2·2H2O. Dissolve CuCl2·2H2O in 50mL of deionized water beforehand to form a solution, then add it to the dispersion. Transfer the mixture to a hydrothermal reactor and perform a hydrothermal displacement reaction at 150°C for 6 hours.

[0023] (3) Pickling removal The product from step (2) was cooled to room temperature and centrifuged at 8000 r / min for 10 min, and the supernatant was discarded. The obtained solid was added to 500 mL of 1 mol / L hydrochloric acid solution (prepared from analytical grade hydrochloric acid from Sinopharm Chemical Reagent Co., Ltd.) and stirred and acid-washed for 2 h in a 60°C water bath.

[0024] (4) Washing and drying The acid-washed product was centrifuged at 8000 r / min for 10 min, the supernatant was discarded, and the product was washed repeatedly with deionized water 3-5 times until the pH of the washing solution was 6.5-7.5. The washed product was then vacuum-dried at 80°C for 12 h to obtain the purified oligowalled carbon nanotube-based monoporous carbon composite material.

[0025] Example 2

[0026] The difference between this embodiment and Example 1 is that: in step (2), the temperature of the hydrothermal replacement reaction is 120°C and the reaction time is 8h; in step (3), the dilute acid is a 1mol / L nitric acid solution (prepared from analytical grade nitric acid from Sinopharm Chemical Reagent Co., Ltd.), the acid washing temperature is 50°C, and the acid washing time is 3h. The remaining steps and parameters are the same as in Example 1.

[0027] Example 3

[0028] The difference between this embodiment and Example 1 is that: in step (2), the copper salt is Cu(NO3)2·3H2O (China National Pharmaceutical Group Chemical Reagent Co., Ltd., analytical grade), the temperature of the hydrothermal replacement reaction is 180°C, the reaction time is 4h, and the ratio of Cu(NO3)2 to the coated metal is 4:1 (molar ratio). The remaining steps and parameters are the same as in Example 1.

[0029] Example 4

[0030] The difference between this embodiment and Example 1 is as follows: In step (1), the solid-liquid ratio is 1:50 g / mL (10 g of composite material is added to 500 mL of deionized water), the ultrasonic power is 500 W, and the ultrasonic time is 10 min; in step (2), the hydrothermal replacement reaction temperature is 200°C, the reaction time is 2 h, and the CuCl2:coated metal ratio is 2:1 (molar ratio); in step (3), the hydrochloric acid concentration is 2 mol / L, the pickling temperature is 80°C, and the pickling time is 1 h; in step (4), the drying temperature is 100°C, and the drying time is 6 h. The remaining steps and parameters are the same as in Example 1.

[0031] Comparative Example 1 Weigh 10g of the same batch of oligowalled carbon nanotube-based monoporous carbon composite material as in Example 1, add it to 200mL of a mixed acid solution of concentrated sulfuric acid / concentrated nitric acid (volume ratio 3:1, both concentrated sulfuric acid and concentrated nitric acid are analytical grade from Sinopharm Chemical Reagent Co., Ltd.), and reflux at 120°C in an oil bath for 4h. After the reaction is complete, cool to room temperature, dilute with a large amount of deionized water, centrifuge at 8000r / min for 10min, discard the supernatant, wash repeatedly with deionized water until neutral (pH=6.5~7.5), and vacuum dry at 80°C for 12h.

[0032] Comparative Example 2 Weigh 10g of the same batch of oligowalled carbon nanotube-based monoporous carbon composite material as in Example 1, place it in a tube furnace, and oxidize it at 400°C in air for 2 hours (heating rate 5°C / min). After oxidation, cool to room temperature, add the sample to 500mL of 1mol / L hydrochloric acid solution, and stir and acid wash for 2 hours in a 60°C water bath. After acid washing, centrifuge at 8000r / min for 10 minutes, discard the supernatant, wash repeatedly with deionized water until neutral (pH=6.5~7.5), and vacuum dry at 80°C for 12 hours.

[0033] Comparative Example 3 Weigh 10g of the same batch of oligowalled carbon nanotube-based monoporous carbon composite material as in Example 1, place it in a high-temperature vacuum furnace, and heat it under a vacuum degree ≤10. -3 Under Pa conditions, the temperature was increased to 1800°C at a rate of 10°C / min, held for 5 hours, and then allowed to cool naturally to room temperature before the sample was removed.

[0034] Experimental Example Based on Examples 1-4 and Comparative Examples 1-3 above, samples were prepared and their performance was tested. The specific performance test items were as follows: I. Determination of Metal Impurity Content (1) Measurement method The determination was performed according to the national standard GB / T35418-2017 "Determination of Impurity Elements in Carbon Nanotubes by Inductively Coupled Plasma Mass Spectrometry".

[0035] The specific steps are as follows: Sample digestion: Accurately weigh approximately 50 mg (accurate to 0.1 mg) each of the purified and unpurified carbon nanotube samples, place them in a microwave digestion vessel, add 5 mL of concentrated nitric acid (Sinopharm Chemical Reagent Co., Ltd., analytical grade, 65%~68%) and 2 mL of concentrated hydrochloric acid (Sinopharm Chemical Reagent Co., Ltd., analytical grade, 36%~38%), and digest according to the following microwave digestion procedure: raise the temperature from room temperature to 180°C (heating time 15 min), and maintain at 180°C for 20 min. After digestion, cool to room temperature, transfer the digest to a 50 mL volumetric flask, dilute to the mark with deionized water, and mix well. Simultaneously prepare a blank control sample.

[0036] Instrumental measurements: Measurements were performed using an inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7900). The instrument operating conditions were: RF power 1550W, nebulizer flow rate 1.0 L / min, auxiliary gas flow rate 1.2 L / min, and cooling gas flow rate 15.0 L / min. Measurements were then performed separately. 57 Fe and 60 The mass spectrometry signal intensity of Ni was quantified using the external standard method. Standard curves were plotted using mixed standard solutions (Fe and Ni concentrations of 0, 10, 50, 100, and 500 μg / L, respectively). The linear correlation coefficient R0 was calculated. 2 ≥0.999.

[0037] Results calculation: The concentrations of Fe and Ni in the digestion solution were calculated based on the standard curve, and the contents of Fe and Ni in the sample (wt%) were calculated based on the sample mass and the final volume.

[0038] The measurement results are shown in Table 1 below.

[0039] Table 1

[0040] As shown in Table 1, the total metal removal rate of Example 1 reached 88.6%, significantly better than Comparative Example 1 (65.7%), Comparative Example 2 (45.7%), and Comparative Example 3 (77.1%). This indicates that the present invention can effectively remove metal catalyst impurities encapsulated by the graphite carbon layer through a displacement reaction, and its removal efficiency is significantly better than existing technologies such as strong oxidizing acid treatment, medium-temperature oxidation + acid leaching, and high-temperature heat treatment. Although Comparative Example 3 (high-temperature heat treatment) can also achieve a certain removal effect (77.1%), its energy consumption is extremely high and its equipment requirements are stringent, making it unsuitable for large-scale industrial applications.

[0041] II. Evaluation of the structural integrity of carbon nanotubes (1) Measurement method The determination was performed according to the national standard GB / T32871-2016 "Raman Spectroscopy for Characterization of Single-Wall Carbon Nanotubes".

[0042] The specific operating steps are as follows: The carbon nanotube samples, both before and after purification, are evenly spread on a glass slide, and Raman spectroscopy is performed using a RenishawinVia instrument. The excitation wavelength is 532 nm, the laser power is 5 mW (to avoid thermal damage to the sample), and the scanning range is 100–3500 cm⁻¹. -1 The grating is 1800 lines / mm, the cumulative scan count is 3, and the integration time for each scan is 10 seconds. The D peak is approximately 1350 cm⁻¹. -1 The G peak (approximately 1580 cm⁻¹) represents the defects and disordered structure of carbon materials. -1 The value represents the degree of order in the graphitized structure. Baseline correction and peak area fitting were performed on the D and G peaks using the instrument's software, and the ID / IG ratio was calculated.

[0043] The measurement results are shown in Table 2 below.

[0044] III. Purity Evaluation (1) Measurement method The measurements were performed according to the national standard GB / T32868-2025 "Thermogravimetric Characterization Method of Carbon Nanotubes in Nanotechnology".

[0045] The specific operating steps are as follows: A thermogravimetric analyzer (model: NETZSCHSTA449F3) was used for determination. Approximately 5-10 mg (accurate to 0.01 mg) of carbon nanotube samples before and after purification were accurately weighed and placed in an alumina crucible. Under air atmosphere (flow rate 50 mL / min), the temperature was increased from room temperature to 800°C at a rate of 10°C / min, and the weight loss curve (TG curve) and differential thermal analysis (DSC curve) of the samples were recorded. Carbon nanotubes undergo oxidative decomposition in air at approximately 500-700°C, and the residues are mainly inorganic impurities such as metal oxides. Purity is expressed as the content (mass fraction) of carbon nanotubes in the sample at 600°C, calculated using the formula: Purity (wt%) = (Initial sample mass - Mass of residue at 600°C) / Initial sample mass × 100%.

[0046] The measurement results are shown in Table 2 below.

[0047] Table 2

[0048] As shown in Table 2, the ID / IG ratios of Examples 1-4 (0.14-0.15) were essentially the same as before purification (0.12), indicating that the method of this invention introduces almost no additional structural defects. The ID / IG ratio of Comparative Example 1 significantly increased to 0.35, indicating that the strong oxidizing acid treatment caused severe damage to the carbon nanotube structure. Although the ID / IG ratio of Comparative Example 2 (0.18) was lower than that of Comparative Example 1, it was still higher than that of the examples of this invention. The ID / IG ratio of Comparative Example 3 (0.13) was close to that before purification, indicating that the high-temperature heat treatment caused less damage to the carbon nanotube structure, but it had extremely high energy consumption and demanding equipment requirements. These results demonstrate that this invention can effectively remove metal impurities while protecting the structural integrity of oligowalled carbon nanotubes, possessing the dual advantages of purification efficiency and structural protection.

[0049] The purity of Example 1 reached 97.5%, higher than that of Comparative Example 1 (95.1%), Comparative Example 2 (92.8%), and Comparative Example 3 (96.3%), indicating that the purification effect of this invention on oligowalled carbon nanotube-based monoporous carbon composite materials is superior to existing technologies. It is worth noting that although Comparative Example 3 (high-temperature heat treatment) can also achieve a purity of 96.3%, it requires high temperature (1800°C) and vacuum conditions, resulting in extremely high energy consumption, large equipment investment, and small batch processing capacity, making it difficult to achieve large-scale industrial application. In contrast, this invention can achieve a higher purity (97.5%) under mild conditions (≤200°C), demonstrating significant advantages for industrialization.

[0050] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for purifying oligowalled carbon nanotube-based monoporous carbon composite materials, characterized in that: Includes the following steps: S1. The oligowalled carbon nanotube-based monoporous carbon composite material to be purified is added to deionized water and ultrasonically dispersed to obtain a dispersion. S2. Add a copper salt solution to the dispersion and carry out a hydrothermal replacement reaction at a temperature of 80~200°C, so that the copper salt reacts with the metal catalyst impurities wrapped by the graphite carbon layer in the composite material. S3. Separate the product from step S2 into solid and liquid phases. Add the obtained solid to a dilute acid solution and stir and wash it at 40-80°C. S4. Wash with deionized water until neutral, dry, and obtain purified oligowalled carbon nanotube-based monoporous carbon composite material.

2. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S1, the ultrasonic dispersion time is 10~30 min and the ultrasonic power is 200~500 W; the solid-liquid ratio of the oligowalled carbon nanotube-based monoporous carbon composite material to deionized water is 1:50~1:200 g / mL.

3. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S2, the copper salt is selected from at least one of CuCl2 or Cu(NO3)2.

4. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S2, the amount of copper salt added is in a molar ratio of copper salt to coated metal = 2:1 to 5:

1.

5. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S2, the temperature of the hydrothermal replacement reaction is 150°C, and the reaction time is 2~12h.

6. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S3, the dilute acid solution is dilute hydrochloric acid or dilute nitric acid with a concentration of 0.5~2 mol / L.

7. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S3, the pickling temperature is 60°C and the pickling time is 1~4h.

8. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: In step S4, the drying is vacuum drying, the drying temperature is 60~100°C, and the drying time is 6~24h.

9. The purification method for oligowalled carbon nanotube-based monoporous carbon composite materials as described in claim 1, characterized in that: The impurity in the metal catalyst is at least one of Fe, Co, and Ni.

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