Carbon nanotube with zwitterionic surface microstructure and preparation method thereof

Abstract

The invention discloses a carbon nanotube with a zwitterionic surface microstructure and a preparation method of the carbon nanotube, and belongs to the technical field of preparation of carbon nanotubes. According to the method, a styrene-maleic anhydride copolymer (SMA) with specific molecular weight and anhydride content or polyethyleneimine / polyvinylamine with specific molecular weight and amino content is grafted on the surface of an aminated / carboxylated carbon nanotube to construct the zwitterionic microstructure. The preparation method comprises the following steps: 1) preparing a modified solution of SMA or polyvinylamine polymer, and 2) dispersing the carbon nanotubes in the solution, carrying out ultrasonic treatment, freeze-drying and purifying to obtain the product. The method utilizes the zwitter-ion microstructure to enhance the dispersibility of the carbon nanotubes in the composite material while maintaining the high conductivity of the composite material, and is suitable for preparing the high-conductivity composite material.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon nanotube preparation, and particularly relates to a carbon nanotube with a zwitterionic surface microstructure and a preparation method thereof. Background Art

[0002] In recent years, organic-inorganic composite conductive materials have demonstrated significant advantages in applications such as battery shielding and electrically assisted membrane separation. Carbon nanotubes (CNTs) are ideal for preparing these composites due to their high electrical conductivity, excellent mechanical properties, and thermal stability. However, strong van der Waals forces between CNTs cause them to easily aggregate in organic solvents or polymer matrices, severely degrading the structural integrity and functionality of the composites.

[0003] To improve dispersibility, existing techniques typically involve functionalizing the carbon nanotube surface (e.g., grafting organic molecular chains) and supplementing it with ultrasonic dispersion. However, this approach has inherent drawbacks: while grafting insulating organic chains improves dispersibility, it significantly reduces the intrinsic conductivity of the carbon nanotubes. The performance of composite conductive materials depends on low interfacial resistance and the formation of continuous electrical percolation pathways. While surface grafting can facilitate path formation, insulating molecular chains significantly increase interfacial resistance, hindering electron transport.

[0004] Therefore, improving the dispersion of carbon nanotubes while maintaining their high electrical conductivity has become a technical bottleneck in the preparation of high-performance composite conductive materials. Existing surface modification technologies are unable to achieve both, and new methods are urgently needed to synergistically optimize dispersion and conductivity. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a carbon nanotube with a zwitterionic surface microstructure and a preparation method thereof, which utilizes the zwitterionic microstructure to enhance the dispersion of the carbon nanotube in the composite material while maintaining its high electrical conductivity, thereby solving at least one technical problem involved in the background technology.

[0006] In order to solve the above-mentioned technical problems, the present invention is achieved as follows: An embodiment of the present invention provides a method for preparing carbon nanotubes having a zwitterionic surface microstructure, comprising the following steps: Step 1, preparation of modified solution: SMA (Styrene-Maleic Anhydride copolymer) with a molecular weight of 1000-3000 and an anhydride content of 25-45 wt% is mixed with deionized water and sodium hydroxide in a certain mass ratio, and heated and stirred at 50-80°C for 5-24 hours to obtain a uniform solution A; Alternatively, polyethyleneimine with a molecular weight of 1,000 to 5,000 and an amino content of 25 to 45 wt%, or polyethyleneamine with a molecular weight of 50,000 to 100,000 and an amino content of 30 to 50 wt%, is added to deionized water at 50 to 80° C. and stirred for 1 to 5 hours to obtain a uniform solution B; Step 2: Construction of zwitterionic microstructure: A certain mass of amino-treated carbon nanotubes is dispersed in the homogeneous solution A under ultrasound assistance; or a certain mass of carboxylated carbon nanotubes is dispersed in the homogeneous solution B under ultrasound assistance; the ultrasonic treatment is continued for 30 to 90 minutes, the solvent is removed by freeze drying, and then purified with deionized water to obtain carbon nanotubes with a zwitterionic surface microstructure.

[0007] Optionally, in step 1, the homogeneous solution A is prepared by mixing SMA, sodium hydroxide and deionized water in a mass ratio of (1-30):(1-5):100.

[0008] Optionally, in step 1, the concentration of the uniform solution A and the uniform solution B is 1 to 30 wt %.

[0009] Optionally, in step 2, the amount of the amino-treated carbon nanotubes or carboxylated carbon nanotubes added is 1 to 3 wt % of the total mass of the solution.

[0010] Optionally, in step 2, the ultrasonic power of the ultrasonic-assisted dispersion and ultrasonic treatment is 30 to 70 W.

[0011] The present invention also provides a carbon nanotube with a zwitterionic surface microstructure, which is prepared by the method.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention significantly enhances the dispersion of carbon nanotubes in composite materials through covalent or non-covalent bonding between the surface molecular chains (amino / carboxylation) of carbon nanotubes and the polymer molecular chains (SMA / polyethyleneimine / polyvinylamine). Furthermore, the electron transport function of the zwitterionic microstructure constructed on the surface effectively alleviates the conductivity loss caused by the introduction of insulating polymer molecular chains.

[0013] 2. The zwitterionic microstructure of the present invention not only promotes uniform dispersion of carbon nanotubes, building a complete electropermeation pathway, but also accelerates electron transport, reducing interfacial resistance and forming a highly efficient conductive network. Data from the examples show that the conductivity of zwitterionic-modified carbon nanotubes (up to 6.67 S / cm) is significantly higher than that of single charge-modified carbon nanotubes (only 1.96–2.03 S / cm in Comparative Examples 1-2).

[0014] 3. This invention overcomes the prior art limitation that improving dispersibility requires sacrificing conductivity. Comparative Examples 1-2 demonstrate that incorrect combinations of carbon nanotubes and polymers (e.g., carboxylated CNTs + SMA or amino-modified CNTs + PEI) result in a single-charge surface, resulting in significantly lower conductivity than zwitterionic structures.

[0015] 4. The synergistic effect of the present invention makes it possible to prepare composite conductive materials with uniform structure and high conductivity on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive work, among which: Figure 1 This is a surface morphology of the carbon nanotube with zwitterionic surface microstructure prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] The terms "first," "second," and the like in the specification and claims of the present invention are used to distinguish similar objects, and are not used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the present invention can be implemented in an order other than that illustrated or described herein, and that the objects distinguished by "first," "second," and the like are generally of the same type, and do not limit the number of objects. For example, the first object can be one or more. In addition, the term "and / or" in the specification and claims refers to at least one of the connected objects, and the character " / " generally indicates that the objects connected are in an "or" relationship.

[0019] The present invention also provides a method for preparing carbon nanotubes having a zwitterionic surface microstructure, comprising the following steps: Step 1, preparation of modified solution: SMA with a molecular weight of 1000-3000 and an anhydride content of 25-45 wt% is mixed with deionized water and sodium hydroxide in a mass ratio of (1-30):(1-5):100, and heated and stirred at 50-80° C. for 5-24 hours to obtain a uniform solution A with a concentration of 1-30 wt%; or Add polyethyleneimine with a molecular weight of 1000-5000 and an amino content of 25-45 wt%, or polyethyleneamine with a molecular weight of 50000-100000 and an amino content of 30-50 wt%, to deionized water at 50-80°C and stir for 1-5 hours to obtain a uniform solution B with a concentration of 1-30 wt%; Step 2: Construction of zwitterionic microstructure: Dispersing 1 to 3 wt% of amino-modified carbon nanotubes, which account for 1 to 3 wt% of the total mass of the solution, into the uniform solution A under the assistance of ultrasound at an ultrasonic power of 30 to 70 W; or Dispersing 1 to 3 wt% of carboxylated carbon nanotubes, which account for 1 to 3 wt% of the total mass of the solution, into the uniform solution B under the assistance of ultrasound at an ultrasonic power of 30 to 70 W; The treatment is continued at an ultrasonic power of 30 to 70 W for 30 to 90 minutes, the solvent is removed by freeze drying, and then the mixture is purified with deionized water to obtain carbon nanotubes with a zwitterionic surface microstructure.

[0020] The present invention also provides a carbon nanotube with a zwitterionic surface microstructure, which is prepared by the method.

[0021] The following is a detailed description of the method for preparing the carbon nanotubes with zwitterionic surface microstructures provided by the present invention using specific examples.

[0022] Example 1 Example 1 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: SMA with a molecular weight of 1600 and an anhydride content of 26 wt% was mixed with sodium hydroxide and deionized water in a mass ratio of 5:1:100 at 55°C while heating and stirring for 6 h to obtain a uniform solution A. Step 2: Construction of zwitterionic microstructure: 1 wt% of amino-modified carbon nanotubes were uniformly dispersed in the above-mentioned uniform solution A under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 30 minutes and then freeze-dried to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0023] Example 2 This embodiment 2 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: SMA with a molecular weight of 2300 and an anhydride content of 31 wt% was mixed with sodium hydroxide and deionized water in a mass ratio of 15:3:100 at 65°C while heating and stirring for 15 h to obtain a uniform SMA solution. Step 2: Construction of zwitterionic microstructure: 2 wt % of amino-modified carbon nanotubes were uniformly dispersed in the homogeneous SMA solution under ultrasound assistance, and then the ultrasonic treatment was continued for 60 min before freeze-drying to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0024] Example 3 This embodiment 3 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: SMA with a molecular weight of 2800 and an anhydride content of 42 wt% was mixed with sodium hydroxide and deionized water in a mass ratio of 25:5:100 at 75°C while heating and stirring for 24 h to obtain a uniform SMA solution. Step 2: Construction of zwitterionic microstructure: 3 wt% of amino-modified carbon nanotubes were uniformly dispersed in the homogeneous SMA solution under ultrasound assistance, and then the ultrasonic treatment was continued for 90 min before freeze-drying to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0025] Example 4 This embodiment 4 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: Polyethyleneimine with a molecular weight of 2000 and an amino content of 30 wt% was added to deionized water at a temperature of 60°C and stirred for 2 hours to form a polyethyleneimine solution with a concentration of 10 wt%; Step 2: Construction of zwitterionic microstructure: 1 wt% of carboxylated carbon nanotubes were uniformly dispersed in the polyethyleneimine solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 60 minutes and then freeze-dried to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0026] Example 5 This embodiment 5 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: Polyethyleneimine with a molecular weight of 4000 and an amino content of 41 wt% was added to deionized water at a temperature of 70° C. and stirred for 4 hours to form a uniform polyethyleneimine solution with a concentration of 25 wt%.

[0027] Step 2: Construction of zwitterionic microstructure: 2.5 wt% of carboxylated carbon nanotubes were uniformly dispersed in the polyethyleneimine solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 90 minutes and then freeze-dried to remove the solvent; The grafted carbon nanotubes were placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures. The surface morphology of the carbon nanotubes is as follows: Figure 1 As shown, it can be seen that the surface structure of carbon nanotubes is uniform.

[0028] Example 6 This embodiment 6 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: Polyethyleneimine with a molecular weight of 60,000 and an amino content of 25 wt% was added to deionized water at a temperature of 60°C and stirred for 3 hours to form a uniform polyethyleneimine solution with a concentration of 10 wt%; Step 2: Construction of zwitterionic microstructure: 1 wt% of carboxylated carbon nanotubes were uniformly dispersed in the polyethyleneimine solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 60 minutes and then freeze-dried to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0029] Example 7 This embodiment 7 provides a method for preparing carbon nanotubes with zwitterionic surface microstructures, comprising the following steps: Step 1, preparation of modified solution: Polyethyleneimine with a molecular weight of 80,000 and an amino content of 43 wt% was added to deionized water at a temperature of 80° C. and stirred for 5 hours to form a uniform polyethyleneimine solution with a concentration of 25 wt%.

[0030] Step 2: Construction of zwitterionic microstructure: 2.5 wt% of carboxylated carbon nanotubes were uniformly dispersed in the polyethyleneimine solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 90 minutes and then freeze-dried to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with zwitterionic surface microstructures.

[0031] Comparative Example 1 According to the preparation method in Example 3, the amino-treated carbon nanotubes are replaced with carboxyl-treated carbon nanotubes, which specifically includes the following steps: Step 1, preparation of modified solution: SMA with a molecular weight of 2800 and an anhydride content of 42 wt% was mixed with deionized water and sodium hydroxide in a mass ratio of 25:5:100 at 75°C while heating and stirring for 24 h to form a uniform SMA solution; Step 2: Construction of zwitterionic microstructure: 3 wt% carboxylated carbon nanotubes were uniformly dispersed in the SMA solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 90 minutes before freeze-drying to remove the solvent. The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with negatively charged surface microstructures.

[0032] Comparative Example 2 According to the preparation method in Example 5, the styrene maleic anhydride copolymer grafted on the surface of the amino-treated carbon nanotubes was replaced with polyethyleneimine, which specifically includes the following steps: Step 1, preparation of modified solution: Polyethyleneimine with a molecular weight of 4000 and an amino content of 41 wt% was added to deionized water at a temperature of 70°C and stirred for 4 hours to form a uniform polyethyleneimine solution with a concentration of 25 wt%; Step 2: Construction of zwitterionic microstructure: 2.5 wt% of amino-modified carbon nanotubes were uniformly dispersed in the polyethyleneimine solution under ultrasound assistance, and then the solution was subjected to ultrasound treatment for 90 minutes and then freeze-dried to remove the solvent; The grafted modified carbon nanotubes are placed in deionized water for purification and freeze-dried again to obtain carbon nanotubes with a positively charged surface microstructure.

[0033] The grafting rates and electrical conductivity of the carbon nanotubes with zwitterionic, negatively charged, and positively charged surface microstructures prepared by the carbon nanotube surface modification methods provided in Examples 1-7 and Comparative Examples 1-2 are shown in Table 1. The specific testing methods are as follows: Grafting rate: The residual carbon weight of unmodified carboxylated carbon nanotubes, amino-modified carbon nanotubes, zwitterionic, negatively charged, and positively charged microstructured carbon nanotubes at 500°C was determined by thermogravimetric analysis, and then the grafting rate was calculated according to formula (1).

[0034] (1) Wherein, R is the grafting rate, unit: %; C1 is the residual carbon weight ratio of carbon nanotubes with zwitterionic, negatively charged, and positively charged microstructures, unit: %; C0 is the residual carbon weight ratio of carboxylated and amino-treated carbon nanotubes, unit: %.

[0035] Conductivity: The resistivity was tested using a four-probe resistivity tester (ST2258C multifunctional digital four-probe tester, Suzhou Jingge Electronics Co., Ltd.).

[0036] Table 1 It can be found from Examples 1-7 that the increase in the grafting rate of styrene maleic anhydride copolymer, polyethyleneimine or polyvinylamine on the surface of carbon nanotubes will lead to the formation of more zwitterionic microstructures, which rapidly improve the electrical conductivity of carbon nanotubes by accelerating electron transport. The electrical conductivity of carbon nanotubes with negatively charged surface microstructures prepared by replacing carboxylated carbon nanotubes with the amination carbon nanotubes in Example 3 is significantly reduced. Similarly, the electrical conductivity of carbon nanotubes with positively charged surface microstructures prepared by replacing amination carbon nanotubes with the carboxylated carbon nanotubes in Example 5 is also significantly reduced. This shows that the technical route proposed in this application to enhance its dispersion in composite materials and reduce interfacial resistance by constructing zwitterionic microstructures on the surface of carbon nanotubes has obvious feasibility.

[0037] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0038] Furthermore, it should be noted that the scope of the methods and systems of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in reverse order, depending on the functions involved. For example, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Furthermore, features described with reference to certain examples may be combined in other examples.

[0039] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing carbon nanotubes with zwitterionic surface microstructures, characterized in that: The steps include: Step 1, preparation of modified solution: SMA with a molecular weight of 1000-3000 and an anhydride content of 25-45 wt% is mixed with deionized water and sodium hydroxide in a certain mass ratio, heated and stirred at 50-80° C. for 5-24 hours to obtain a uniform solution A; Alternatively, polyethyleneimine with a molecular weight of 1,000 to 5,000 and an amino content of 25 to 45 wt%, or polyethyleneamine with a molecular weight of 50,000 to 100,000 and an amino content of 30 to 50 wt%, is added to deionized water at 50 to 80° C. and stirred for 1 to 5 hours to obtain a uniform solution B; Step 2: Construction of zwitterionic microstructure: A certain mass of amino-treated carbon nanotubes is dispersed in the homogeneous solution A under ultrasound assistance; or a certain mass of carboxylated carbon nanotubes is dispersed in the homogeneous solution B under ultrasound assistance; the ultrasonic treatment is continued for 30 to 90 minutes, the solvent is removed by freeze drying, and then purified with deionized water to obtain carbon nanotubes with a zwitterionic surface microstructure.

2. The method according to claim 1, characterized in that In step 1, the homogeneous solution A is prepared by mixing SMA, sodium hydroxide and deionized water in a mass ratio of (1-30):(1-5):

100.

3. The method according to claim 1, characterized in that In step 1, the concentration of the homogeneous solution A and the homogeneous solution B is 1 to 30 wt %.

4. The method according to claim 1, wherein In step 2, the amount of the amino-modified carbon nanotubes or carboxylated carbon nanotubes added is 1 to 3 wt % of the total mass of the solution.

5. The method according to claim 1, wherein In step 2, the ultrasonic power for ultrasonic-assisted dispersion and ultrasonic treatment is 30 to 70 W.

6. A carbon nanotube having a zwitterionic surface microstructure, characterized in that: The method is prepared by any one of claims 1 to 5.

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