High-conductivity carbon nanotube and preparation method thereof

Abstract

The invention discloses a high-conductivity carbon nano tube and a preparation method thereof, belongs to the technical field of preparation of carbon nano tubes, and aims to solve the technical problem that the purity and conductivity of the carbon nano tube need to be further improved in the prior art. The hydroximic acid precursor oxidant is utilized to gently introduce active sites in the initial stage, and conditions are created for subsequent functionalization and dispersion of the carbon nanotubes; the quaternized chitosan oligosaccharide dispersing agent realizes dispersion of carbon nanotubes and traction of metal ions through a stable adsorption layer, and the uniformity of a suspension system is maintained; the citramide diacetic acid sulfonyl ligand firmly locks metal ions in the pickling process, secondary deposition of the metal ions on the surface of the carbon nano tube is avoided, a continuous and efficient chain is formed through pretreatment-dispersion-pickling, impurity removal and structure keeping are both considered in dynamic balance, and the service life of the carbon nano tube is prolonged. The finally obtained carbon nano tube is excellent in purity, dispersity and conductive network continuity.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube preparation technology, specifically to a highly conductive carbon nanotube and its preparation method. Background Technology

[0002] Carbon nanotubes, due to their unique structure and excellent physical properties, are considered an important representative of next-generation functional materials. However, in early preparation processes, residual metal catalysts and the formation of amorphous carbon often resulted in insufficient product purity, limiting their application in precision electronics and energy fields. With in-depth research, it has become increasingly clear that high purity is a prerequisite for unlocking the full potential of carbon nanotubes. Therefore, purification and impurity removal technologies have been continuously developed. Simultaneously, improving electrical conductivity has become a key objective. While individual carbon nanotubes possess excellent electrical properties, in macroscopic materials, purity, dispersion, and the uniformity of the network structure directly determine overall conductivity. In recent years, with advancements in preparation and post-processing techniques, carbon nanotubes have gradually achieved stable conductive networks while maintaining high purity, thus demonstrating increasingly prominent application potential in fields such as transparent conductive films, supercapacitors, and high-speed interconnects.

[0003] While existing carbon nanotube fabrication processes have achieved certain scale-up production after years of development, their overall level still has significant shortcomings. Firstly, the purity of the products is generally low, with residual metal catalysts, amorphous carbon, and other impurities difficult to completely remove. These impurities not only affect the application of carbon nanotubes in high-end electronic devices but also reduce their interfacial compatibility in composite materials, thereby weakening their mechanical and electrical properties. Secondly, the purification process often involves damage to the nanotube structure, manifested as reduced diameter, shortened length, or increased wall defects. This makes it difficult to fully realize the inherent superior properties of carbon nanotubes, especially in applications requiring long-range electron transport, where the performance degradation due to structural damage is more significant. In summary, although existing processes can produce carbon nanotube products, they still fall far short of the requirements for high purity, low defects, and high performance.

[0004] Besides issues of purity and structural damage, existing processes also suffer from significant shortcomings in conductivity. While individual carbon nanotubes theoretically possess extremely high electron mobility and excellent conductivity, in actual macroscopic materials, due to uneven dispersion, disordered orientation, and poor inter-tube contact interfaces, the overall conductivity is far lower than theoretically expected. Furthermore, the presence of impurities creates electrical "dead zones," hindering current transmission and leading to discontinuous conductive networks. On the other hand, high production costs and process complexity hinder the large-scale application of high-performance carbon nanotubes in fields such as transparent electrodes, supercapacitors, and flexible electronic devices. These problems significantly limit the progress of carbon nanotubes from the laboratory to industrialization and represent a critical bottleneck that the industry urgently needs to address.

[0005] To address this technical deficiency, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a highly conductive carbon nanotube and its preparation method, in order to solve the technical problem that the purity and conductivity of carbon nanotubes in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A method for preparing highly conductive carbon nanotubes includes the following steps:

[0009] S1. Hydroxyxamic acid precursor oxidant, anhydrous dichloromethane and anhydrous ethanol are mixed and sprayed onto carbon nanotubes and melamine. After standing at room temperature for 15 minutes, they are pre-dried with hot air at 50°C for 30-40 minutes and calcined to obtain an oxidation intermediate.

[0010] The reaction principle for preparing the oxidation intermediate is as follows:

[0011] The carbon nanotubes were treated with a mixture of hydroxamic acid precursor oxidant, anhydrous dichloromethane, and anhydrous ethanol. During calcination, the surface of the carbon nanotubes was gently oxidized and activated to remove amorphous carbon and introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups, thereby improving the hydrophilicity and subsequent dispersibility of the carbon nanotubes. At the same time, the residual metal catalyst was oxidized into metal oxides, reducing its binding force with the carbon nanotubes and laying the foundation for subsequent acid washing to remove the metal. Melamine released nitrogen source fragments during calcination, some of which were adsorbed on the defect sites of the nanotube wall, enhancing the activity of the carbon nanotube surface and providing additional binding sites for dispersion, ultimately preparing an oxidized intermediate.

[0012] S2. Deionized water, anhydrous ethanol and quaternized chitosan oligosaccharide dispersant were added to a high-speed shear mill. The pH of the system was adjusted to 7.5 with sodium bicarbonate and stirred at 300 rpm for 10 min. After adding the oxidation intermediate, the high-speed shear mill was stirred at 8000 rpm for 2-3 h. The post-processing yielded wet carbon nanotube material.

[0013] The reaction principle for preparing wet carbon nanotubes is as follows:

[0014] A low surface tension system was formed using deionized water, anhydrous ethanol, and quaternized chitosan oligosaccharide dispersant. The pH was adjusted with sodium bicarbonate to deprotonate the carboxyl groups on the carbon nanotube surface, forming negative charges that interact with the quaternary ammonium cations in the dispersant, significantly improving the stability of the carbon nanotubes. Subsequently, the tube bundles were untied and uniformly dispersed by high-speed shearing. The dispersant formed an electrostatic barrier and hydrogen bond network on the tube wall surface, preventing the carbon nanotubes from re-agglomerating. At the same time, the oxidized metal ions were weakly complexed or suspended in the dispersion system, reducing the difficulty of subsequent acid washing. Finally, wet carbon nanotube material was prepared.

[0015] S3. Add the wet carbon nanotube material and mixed acid to the reactor. After soaking at room temperature for 15-20 minutes, add citrimidine diacetate sulfonyl ligand to the reactor. Stir at room temperature for 10-15 minutes, then raise the temperature of the reactor to 45-50℃ and keep it at this temperature for 4-6 hours. The carbon nanotubes are then obtained through post-treatment.

[0016] The reaction principle for preparing carbon nanotubes is as follows:

[0017] The wet carbon nanotube material was contacted with a mixed acid consisting of sulfuric acid, nitric acid, and phosphoric acid. It was first impregnated at room temperature to improve permeability. Then, citrimidine diacetate sulfonyl ligand was added to form a stable complex with metal ions to prevent them from redepositing on the carbon nanotube surface. Subsequently, the system was heated, and the residual metal catalyst and amorphous carbon were completely dissolved by the mild etching effect of the three acids. At the same time, the carbon nanotubes were avoided from being over-cut by the buffering effect of phosphoric acid. Finally, carbon nanotubes were prepared.

[0018] Further, in step S1, the ratio of hydroxamic acid precursor oxidant, anhydrous dichloromethane, anhydrous ethanol, carbon nanotubes and melamine is 0.03g:40mL:10mL:2-3g:1g. The calcination operation is as follows: after pre-drying, the mixture is transferred to a tube furnace, air is introduced at an inlet rate of 500-800mL / min, the tube furnace is heated to 320-350℃ at a heating rate of 2-3℃ / min, the temperature is held for 3-4 hours and then the heating is stopped. After the furnace temperature is allowed to cool naturally to 30-40℃, the material is taken out and passed through a 60-mesh sieve to obtain the oxidation intermediate.

[0019] Furthermore, in step S2, the ratio of deionized water, anhydrous ethanol, quaternized chitosan oligosaccharide dispersant and oxidation intermediate is 200mL:50mL:1.0-1.2g:2g. The post-treatment includes: after the reaction is completed, after the reaction vessel is cooled to room temperature, the reaction liquid is filtered to collect the filter cake, and the filter cake is washed 3-5 times with ethyl acetate and deionized water to obtain wet carbon nanotube material.

[0020] Further, in step S3, the ratio of wet carbon nanotubes, mixed acid, and citric acid diacetate sulfonyl ligand is 2g:30mL:0.20-0.25g. The mixed acid is prepared as follows: 98wt% sulfuric acid aqueous solution is added to a stirred tank and stirred. Then, 65wt% nitric acid aqueous solution and 85% phosphoric acid aqueous solution are added along the wall of the stirred tank to obtain mixed acid. The volume ratio of 98wt% sulfuric acid aqueous solution, 65wt% nitric acid aqueous solution, and 85% phosphoric acid aqueous solution is 3:1:1. The post-treatment includes: after the reaction is completed, the reaction tank is cooled to room temperature, the reaction solution is filtered to collect the filter cake, and the filter cake is washed 3-5 times with anhydrous ethanol and deionized water. After obtaining the solid, it is transferred to an 80℃ drying oven and vacuum dried to constant weight to obtain carbon nanotubes.

[0021] Furthermore, in step S1, the preparation method of the hydroxamic acid precursor oxidant includes the following steps:

[0022] A1. Gallic acid and anhydrous dichloromethane were added to a reaction vessel and stirred. After nitrogen protection, thionyl trichloride and dimethylformamide were added dropwise. The temperature of the reaction vessel was controlled to rise to 50-60℃ and stirred for 2-3 hours. The galloyl chloride intermediate was obtained by post-processing.

[0023] A2. Add galloyl chloride intermediate, hydroxylamine hydrochloride and N,N-dimethylformamide to a reaction vessel, add ammonium carbonate to adjust the pH of the reaction system to 8-9, purge with nitrogen for protection, maintain the temperature of the reaction vessel at 20-30℃, stir for 4-5 hours, and then proceed with post-treatment to obtain the hydroxamic acid precursor oxidant.

[0024] The reaction principle for preparing hydroxamic acid precursor oxidants is as follows:

[0025] By using thionyl trichloride catalyzed by dimethylformamide, the carboxyl group of gallic acid is activated into a more reactive acyl chloride structure, thereby significantly improving the efficiency of subsequent nucleophilic substitution reactions. Subsequently, hydroxylamine hydrochloride is introduced as a nucleophile to attack the carbonyl carbon atom in the acyl chloride, resulting in a nucleophilic substitution reaction. The chloride ion is replaced to form a stable hydroxamic acid structural unit. In this process, ammonium carbonate plays a role in regulating and maintaining the reaction system in a weakly alkaline environment, which can both ensure the effective activity of hydroxylamine and inhibit the occurrence of side reactions.

[0026] Further, in step A1, the ratio of gallic acid, anhydrous dichloromethane, thionyl trichloride, and dimethylformamide is 1-2g:80-100mL:2-3g:0.3mL. The post-processing includes: after the reaction is completed, after the temperature of the reaction vessel is reduced to room temperature, the reaction solution is transferred to a rotary evaporator at 80°C and distilled under reduced pressure until no liquid is collected, to obtain galloyl chloride intermediate;

[0027] Furthermore, in step A2, the ratio of galloyl chloride intermediate, hydroxylamine hydrochloride, and N,N-dimethylformamide is 1g:1.2-1.3g:40-50mL. The post-treatment includes: after the reaction is completed, the reaction vessel is cooled to room temperature, the reaction solution is filtered to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water, and the solid is transferred to an 80℃ drying oven for vacuum drying to constant weight to obtain the hydroxyxamic acid precursor oxidant.

[0028] Furthermore, in step S2, the preparation method of the quaternized chitosan oligosaccharide dispersant includes the following steps:

[0029] B1. Add chitosan oligosaccharide, succinic anhydride, anhydrous ethanol and deionized water to a reaction vessel and stir. Adjust the pH of the reaction system to 8-9 using sodium bicarbonate, purge with nitrogen for protection, heat to 30-35℃, keep warm and stir for 4-5 hours, and then process to obtain hemiacylated chitosan oligosaccharide.

[0030] B2. Add hemiacylated chitosan oligosaccharide, hydroxypropyltrimethylammonium chloride and deionized water to a reaction vessel, adjust the pH of the reaction system to 8-9 using sodium bicarbonate, purge with nitrogen for protection, heat to 40-50℃, keep warm and stir for 6-8 hours, cool to room temperature, and then post-process to obtain quaternized chitosan oligosaccharide dispersant.

[0031] The reaction principle for preparing quaternized chitosan oligosaccharide dispersants is as follows:

[0032] The amino groups on the chitosan oligosaccharide molecule undergo an acylation reaction with succinic anhydride, introducing carboxyl substituents to form hemiacylated chitosan oligosaccharide. The essence of this step is to give the chitosan oligosaccharide molecule an active carboxyl side chain through the ring-opening reaction of succinic anhydride, thereby enhancing its reactivity and hydrophilicity.

[0033] The active sites on the hemiacylated chitosan oligosaccharide undergo a substitution reaction with hydroxypropyltrimethylammonium chloride, resulting in the replacement of chloride ions and the introduction of cationized quaternary ammonium groups into the chitosan oligosaccharide molecular backbone. This modification endows the chitosan oligosaccharide with a permanent positive charge, enabling it to enhance its interaction with water and other polar molecules, while improving its dispersion stability.

[0034] Further, in step B1, the ratio of chitosan oligosaccharide, succinic anhydride, anhydrous ethanol and deionized water is 1g:0.30-0.35g:80mL:10-20mL. The post-processing includes: after the reaction is completed, the reaction vessel is cooled to room temperature, the reaction solution is filtered to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water, and the solid is transferred to an 80℃ drying oven for vacuum drying to constant weight to obtain hemiacylated chitosan oligosaccharide.

[0035] Further, in step B2, the ratio of hemiacylated chitosan oligosaccharide, hydroxypropyltrimethylammonium chloride, and deionized water is 1-2g:0.6-1.2g:20mL. The post-processing includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, put the reaction solution into a 3.5kDa dialysis bag, dialyze with deionized water at 4°C for 48h, collect the dialysis product, pre-freeze it at -40°C, and then freeze-dry it at 0.05mbar to constant weight to obtain quaternized chitosan oligosaccharide dispersant.

[0036] Furthermore, in step S3, the preparation method of the citriimide diacetate sulfonyl ligand includes the following steps:

[0037] C1. Add citric acid and anhydrous dichloromethane to a reaction vessel and stir. After purging with nitrogen, add thionyl chloride and dimethylformamide dropwise. Heat to 50-60℃ and keep the reaction at this temperature for 2-3 hours. Then, process the citrate chloride intermediate.

[0038] C2. Add citrate chloride intermediate, imine diacetic acid, triethylamine and anhydrous acetonitrile to a reaction vessel, purge with nitrogen for protection, control the temperature at 0-5℃, add chlorosulfonamide dropwise, raise the temperature of the reaction vessel to 25-35℃, keep it at this temperature and stir for 6-8 hours, and then proceed with post-treatment to obtain citrate imine diacetic acid sulfonyl ligand.

[0039] The reaction principle for preparing citriimide diacetate sulfonyl ligand is as follows:

[0040] Using thionyl trichloride with the assistance of dimethylformamide, the carboxyl group in the citric acid molecule is converted into a more reactive acyl chloride group, thereby generating citrate chloride intermediate. This activation process is essentially a conversion of carboxylic acid to acyl chloride, which greatly enhances the efficiency of subsequent condensation reactions.

[0041] Next, citrate chloride reacts with iminodiacetic acid in an acyl chloride-amino condensation reaction. Iminodiacetic acid, as a nitrogen-containing ligand precursor, exhibits a strong nucleophilicity for the acyl chloride via its amino group. Under the action of triethylamine, the byproduct HCl is neutralized, allowing the reaction to proceed smoothly and forming a stable amide bond structure. Thus, the citric acid backbone and iminodiacetic acid are linked via an amide bond.

[0042] Finally, chlorosulfonamide was introduced at low temperature, and a -SO2NH2 functional group was introduced onto the molecule via sulfonation. The introduction of the sulfonyl group not only improved the polarity and coordination ability of the ligand, but also provided it with additional binding sites and electronic effects for metal ion complexation and catalytic applications.

[0043] Further, in step C1, the ratio of citric acid, anhydrous dichloromethane, thionyl trichloride, and dimethylformamide is 1g:40-50mL:2.0-2.5g:0.3mL. The post-processing includes: after the reaction is completed, after the temperature of the reaction vessel is reduced to room temperature, the reaction solution is transferred to a rotary evaporator at a temperature of 80°C and distilled under reduced pressure until no liquid is collected, to obtain citrate chloride intermediate;

[0044] Further, in step C2, the ratio of citrile chloride intermediate, imine diacetic acid, triethylamine, chlorosulfonamide, and anhydrous acetonitrile is 1 g: 1.0-1.2 g: 1.0-1.2 g: 1.2-1.5 g: 30 mL. The post-treatment includes: after the reaction is completed, the reaction solution is filtered after the reaction vessel is cooled to room temperature, the filter cake is collected, washed 3-5 times with ethyl acetate and deionized water, and the filter cake is transferred to an 80°C drying oven and vacuum dried to constant weight to obtain citrile imine diacetic acid sulfonyl ligand.

[0045] The present invention also discloses a highly conductive carbon nanotube, which is prepared by a method for preparing highly conductive carbon nanotubes.

[0046] The present invention has the following beneficial effects:

[0047] 1. This invention removes amorphous carbon and insulating impurities through the mild oxidation of a hydroxamic acid precursor oxidant, exposing more continuous graphitized tube walls and reducing interfacial contact resistance. Melamine is partially doped with nitrogen during heat treatment, causing nitrogen-containing defect sites to form in the carbon nanotubes, increasing electron density and improving the conductive path of the π-conjugated system. Quaternized chitosan oligosaccharide dispersant achieves uniform unwinding and stable dispersion during the slurry preparation stage, enabling the carbon nanotubes to form a highly interconnected three-dimensional conductive network in the matrix, reducing breakpoints and voids in the conductive pathway. In the acid washing stage, citrimidine diacetate sulfonyl ligand and triacid work synergistically to thoroughly remove residual metal particles and surface impurities, avoiding interfacial scattering and hindered electron migration. Finally, through the process chain of "surface purification - defect control - uniform dispersion - network construction," carbon nanotubes form a conductive framework with low contact resistance and high connectivity in the conductive slurry, thereby significantly improving the overall conductivity and stability of the slurry.

[0048] 2. The hydroxamic acid precursor oxidant of this invention gently activates the carbon nanotube surface, removing amorphous carbon and exposing the interface of the coated metal particles. During the dispersion stage, the electrostatic and steric hindrance effects of the quaternized chitosan oligosaccharide dispersant effectively untether the carbon nanotube bundles, significantly increasing the contact area between the acid solution and the internal metal particles, avoiding "acid shielding" caused by agglomeration. Simultaneously, the positive charge of the dispersant promotes the localized directional enrichment of acid radical ions, accelerating the penetration and wetting of the acidic medium, thereby enhancing the acid washing efficiency. Subsequently, the tri-acid compound solution etches and dissolves the metal catalyst particles, while the citrimimide diacetate sulfonyl ligand, as a multidentate complexing agent, forms stable chelates with metal ions such as Fe, Co, and Ni, preventing secondary deposition or adsorption back onto the carbon nanotube surface. Finally, through the continuous action of surface activation, dispersion and untethering, acid washing and dissolution, and ligand complexation, the residual metal catalyst content is significantly reduced, and the purity of the carbon nanotubes is greatly improved, providing reliable structural and chemical protection for their application in conductive pastes and high-performance applications.

[0049] 3. This invention utilizes hydroxamic acid as a precursor oxidant to surface-activate carbon nanotubes under mild conditions, removing amorphous carbon and residual catalyst. Simultaneously, it introduces oxygen-containing functional groups such as carboxyl and hydroxyl groups into the nanotube wall, transforming its surface from a hydrophobic graphite structure into a polar interface, creating a chemical basis for aqueous dispersion. Secondly, the hemiacylated and further quaternized chitosan oligosaccharide dispersant forms multiple interactions with the oxidized carbon nanotube surface: on one hand, the carboxyl side chain enhances the bond with the oxygen-containing groups on the carbon nanotube surface through hydrogen bonding and electrostatic interactions; on the other hand, the quaternary ammonium groups provide a permanent positive charge. Electrostatic pairing with the negative charge on the carbon nanotube surface creates a stable charge barrier, while its flexible polysaccharide framework forms steric hindrance in the solvent, preventing the carbon nanotubes from re-aggregating. Furthermore, the citric acid imide diacetate sulfonyl ligand introduced in the acid washing process can effectively complex and attract metal ions, preventing their redeposition on the carbon nanotube surface. At the same time, it works synergistically with the mild etching of tri-acids to further remove residual impurities and maintain the integrity of the tubes. Finally, through the functional complementarity between materials and the sequential connection of the process flow, a significant improvement in the surface polarity of carbon nanotubes, enhanced interfacial interaction, and dispersion stability is achieved. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 SEM image of the carbon nanotubes prepared in Example 12;

[0052] Figure 2 This is a SEM image of the carbon nanotubes prepared in Example 12. Detailed Implementation

[0053] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The chitosan oligosaccharide used in this invention was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number C799253; the citric acid used in this invention was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number C805019.

[0055] Example 1

[0056] This embodiment provides a method for preparing a highly conductive carbon nanotube-based standby hydroxamic acid precursor oxidant, comprising the following steps:

[0057] Step (1): Preparation of galloyl chloride intermediate

[0058] Weigh out 10.0 g gallic acid and 800.0 mL anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 20.0 g thionyl trichloride and 3.0 mL dimethylformamide dropwise. Control the temperature of the reaction vessel to rise to 50 °C and keep it at this temperature for 2 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain galloyl chloride intermediate.

[0059] Step 2: Preparation of hydroxamic acid precursor oxidant

[0060] Weigh out 10.0 g of galloyl chloride intermediate, 12.0 g of hydroxylamine hydrochloride and 400.0 mL of N,N-dimethylformamide and add them to the reaction vessel. Add ammonium carbonate to adjust the pH of the reaction system to 8. Purge with nitrogen for protection and keep the temperature of the reaction vessel at 20℃. Stir for 4 h. After the reaction is completed, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. After obtaining the solid, transfer it to an 80℃ drying oven and vacuum dry to constant weight to obtain the hydroxyxamic acid precursor oxidant.

[0061] Example 2

[0062] This embodiment provides a method for preparing a highly conductive carbon nanotube-based standby hydroxamic acid precursor oxidant, comprising the following steps:

[0063] Step (1): Preparation of galloyl chloride intermediate

[0064] Weigh out 20.0 g gallic acid and 1000.0 mL anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 30.0 g thionyl trichloride and 3.0 mL dimethylformamide dropwise. Control the temperature of the reaction vessel to rise to 60 °C and keep it at this temperature for 3 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain galloyl chloride intermediate.

[0065] Step 2: Preparation of hydroxamic acid precursor oxidant

[0066] Weigh out 10.0 g of galloyl chloride intermediate, 13.0 g of hydroxylamine hydrochloride and 500.0 mL of N,N-dimethylformamide and add them to the reaction vessel. Add ammonium carbonate to adjust the pH of the reaction system to 9. Purge with nitrogen for protection and keep the temperature of the reaction vessel at 30℃. Stir for 5 h. After the reaction is completed, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. Transfer the solid to an 80℃ drying oven and vacuum dry to constant weight to obtain the hydroxyxamic acid precursor oxidant.

[0067] Example 3

[0068] This embodiment provides a method for preparing a highly conductive carbon nanotube-based standby hydroxamic acid precursor oxidant, comprising the following steps:

[0069] Step (1): Preparation of galloyl chloride intermediate

[0070] Weigh out 16.0 g gallic acid and 960.0 mL anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 25.0 g thionyl trichloride and 3.0 mL dimethylformamide dropwise. Control the temperature of the reaction vessel to rise to 55 °C and keep it at this temperature for 3 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain galloyl chloride intermediate.

[0071] Step 2: Preparation of hydroxamic acid precursor oxidant

[0072] Weigh out 10.0 g of galloyl chloride intermediate, 12.0 g of hydroxylamine hydrochloride and 450.0 mL of N,N-dimethylformamide and add them to the reaction vessel. Add ammonium carbonate to adjust the pH of the reaction system to 9. Purge with nitrogen for protection and keep the temperature of the reaction vessel at 25℃. Stir for 5 h. After the reaction is completed, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake 4 times with anhydrous ethanol and deionized water. After obtaining the solid, transfer it to an 80℃ drying oven and vacuum dry to constant weight to obtain the hydroxyxamic acid precursor oxidant.

[0073] Example 4

[0074] This embodiment provides a method for preparing a highly conductive carbon nanotube-based quaternized chitosan oligosaccharide dispersant, comprising the following steps:

[0075] Step ①: Preparation of hemiacylated chitosan oligosaccharide

[0076] Weigh out 10.0 g of chitosan oligosaccharide, 3.0 g of succinic anhydride, 800.0 mL of anhydrous ethanol and 100.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and adjust the pH of the reaction system to 8 with sodium bicarbonate. Purge the system with nitrogen for protection and heat it to 30 °C. Keep the mixture at this temperature and stir for 4 h. After the reaction is complete, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. Transfer the solid to an 80 °C drying oven and dry it under vacuum to constant weight to obtain hemiacylated chitosan oligosaccharide.

[0077] Step ②: Preparation of quaternized chitosan oligosaccharide dispersant

[0078] Weigh out 10.0 g of hemiacylated chitosan oligosaccharide, 6.0 g of hydroxypropyltrimethylammonium chloride, and 200.0 mL of deionized water and add them to a reaction vessel. Adjust the pH of the reaction system to 8 using sodium bicarbonate, purge with nitrogen for protection, heat to 40 °C, stir for 6 h, and cool to room temperature. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then put the reaction solution into a 3.5 kDa dialysis bag and dialyze with deionized water at 4 °C for 48 h. Collect the dialysis product, pre-freeze it at -40 °C, and then freeze-dry it at 0.05 mbar to constant weight to obtain quaternized chitosan oligosaccharide dispersant.

[0079] Example 5

[0080] This embodiment provides a method for preparing a highly conductive carbon nanotube-based quaternized chitosan oligosaccharide dispersant, comprising the following steps:

[0081] Step ①: Preparation of hemiacylated chitosan oligosaccharide

[0082] Weigh out 10.0 g of chitosan oligosaccharide, 3.5 g of succinic anhydride, 800.0 mL of anhydrous ethanol and 200.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and adjust the pH of the reaction system to 9 with sodium bicarbonate. Purge the system with nitrogen for protection and heat it to 35 °C. Keep the mixture at this temperature and stir for 5 h. After the reaction is complete, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. Transfer the solid to an 80 °C drying oven and vacuum dry it to constant weight to obtain hemiacylated chitosan oligosaccharide.

[0083] Step ②: Preparation of quaternized chitosan oligosaccharide dispersant

[0084] Weigh out 10.0 g of hemiacylated chitosan oligosaccharide, 12.0 g of hydroxypropyltrimethylammonium chloride, and 200.0 mL of deionized water and add them to the reaction vessel. Adjust the pH of the reaction system to 9 using sodium bicarbonate, purge with nitrogen for protection, heat to 50 °C, stir for 8 h, and cool to room temperature. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then put the reaction solution into a 3.5 kDa dialysis bag and dialyze with deionized water at 4 °C for 48 h. Collect the dialysis product, pre-freeze it at -40 °C, and then freeze-dry it at 0.05 mbar to constant weight to obtain quaternized chitosan oligosaccharide dispersant.

[0085] Example 6

[0086] This embodiment provides a method for preparing a highly conductive carbon nanotube-based quaternized chitosan oligosaccharide dispersant, comprising the following steps:

[0087] Step ①: Preparation of hemiacylated chitosan oligosaccharide

[0088] Weigh out 10.0 g of chitosan oligosaccharide, 3.2 g of succinic anhydride, 800.0 mL of anhydrous ethanol and 160.0 mL of deionized water and add them to the reaction vessel. Stir the mixture and adjust the pH of the reaction system to 9 with sodium bicarbonate. Purge the system with nitrogen and heat it to 32 °C. Keep the mixture at this temperature and stir for 5 h. After the reaction is complete, let the reaction vessel cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake four times with anhydrous ethanol and deionized water. Transfer the solid to an 80 °C drying oven and dry it under vacuum to constant weight to obtain hemiacylated chitosan oligosaccharide.

[0089] Step ②: Preparation of quaternized chitosan oligosaccharide dispersant

[0090] Weigh out 10.0 g of hemiacylated chitosan oligosaccharide, 9.0 g of hydroxypropyltrimethylammonium chloride, and 200.0 mL of deionized water and add them to the reaction vessel. Adjust the pH of the reaction system to 9 using sodium bicarbonate, purge with nitrogen for protection, heat to 45 °C, stir for 7 h, and cool to room temperature. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then put the reaction solution into a 3.5 kDa dialysis bag and dialyze with deionized water at 4 °C for 48 h. Collect the dialysis product, pre-freeze it at -40 °C, and then freeze-dry it at 0.05 mbar to constant weight to obtain quaternized chitosan oligosaccharide dispersant.

[0091] Example 7

[0092] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0093] Step I: Preparation of citrate chloride intermediate

[0094] Weigh out 10.0 g of citric acid and 400.0 mL of anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 20.0 g of thionyl trichloride and 3.0 mL of dimethylformamide dropwise. Heat to 50 °C and maintain the temperature for 2 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain the citrate chloride intermediate.

[0095] Step II: Preparation of citriimide diacetate sulfonyl ligand

[0096] Weigh out 10.0 g of citrate chloride intermediate, 10.0 g of imine diacetic acid, 10.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile and add them to a reaction vessel. Purge with nitrogen for protection and control the temperature at 0 °C. Add 12.0 g of chlorosulfonamide dropwise. Heat the reaction vessel to 25 °C and stir for 6 h. After the reaction is complete, let the reaction vessel cool to room temperature and filter the reaction solution to collect the filter cake. Wash the filter cake three times with ethyl acetate and deionized water. Transfer the filter cake to an 80 °C drying oven and dry it under vacuum to constant weight to obtain citrate imine diacetic acid sulfonyl ligand.

[0097] Example 8

[0098] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0099] Step I: Preparation of citrate chloride intermediate

[0100] Weigh out 10.0 g of citric acid and 500.0 mL of anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 25.0 g of thionyl trichloride and 3.0 mL of dimethylformamide dropwise. Heat to 60 °C and keep the temperature for 3 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain citrate chloride intermediate.

[0101] Step II: Preparation of citriimide diacetate sulfonyl ligand

[0102] Weigh out 10.0 g of citrate chloride intermediate, 12.0 g of imine diacetic acid, 12.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile and add them to a reaction vessel. Purge with nitrogen for protection and control the temperature at 5 °C. Add 15.0 g of chlorosulfonamide dropwise. Heat the reaction vessel to 35 °C and stir for 8 h. After the reaction is complete, let the reaction vessel cool to room temperature and filter the reaction solution to collect the filter cake. Wash the filter cake 5 times with ethyl acetate and deionized water. Transfer the filter cake to an 80 °C drying oven and dry it under vacuum to constant weight to obtain citrate imine diacetic acid sulfonyl ligand.

[0103] Example 9

[0104] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0105] Step I: Preparation of citrate chloride intermediate

[0106] Weigh out 10.0 g of citric acid and 450.0 mL of anhydrous dichloromethane and add them to the reaction vessel. Stir and purge with nitrogen for protection. Then add 21.0 g of thionyl trichloride and 3.0 mL of dimethylformamide dropwise. Heat to 55 °C and keep the temperature for 3 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain citrate chloride intermediate.

[0107] Step II: Preparation of citriimide diacetate sulfonyl ligand

[0108] Weigh out 10.0 g of citrate chloride intermediate, 12.0 g of imine diacetic acid, 10.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile and add them to a reaction vessel. Purge with nitrogen for protection and control the temperature at 3 °C. Add 13.5 g of chlorosulfonamide dropwise. Heat the reaction vessel to 30 °C and stir for 7 h. After the reaction is complete, let the reaction vessel cool to room temperature and filter the reaction liquid to collect the filter cake. Wash the filter cake four times with ethyl acetate and deionized water. Transfer the filter cake to an 80 °C drying oven and dry it under vacuum to constant weight to obtain citrate imine diacetic acid sulfonyl ligand.

[0109] Example 10

[0110] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0111] Step 1: Preparation of oxidation intermediates

[0112] Weigh out 0.3g of the hydroxamic acid precursor oxidant prepared in Example 1, mix it with 400.0mL of anhydrous dichloromethane and 100.0mL of anhydrous ethanol, and spray it onto 20.0g of carbon nanotubes and 10.0g of melamine. After standing at room temperature for 15min, pre-dry it with hot air at 50℃ for 30min. After pre-drying, transfer the mixture to a tube furnace, introduce air at an inlet rate of 500mL / min, and heat the tube furnace to 320℃ at a heating rate of 2℃ / min. After holding the temperature for 3h, stop heating and allow the furnace temperature to cool naturally to 30℃. Take out the material and pass it through a 60-mesh sieve to obtain the oxidation intermediate.

[0113] Step 2: Preparation of wet carbon nanotube material

[0114] Weigh out 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol, and 10.0 g of the quaternized chitosan oligosaccharide dispersant prepared in Example 4 and add them to a high-speed shear press. Adjust the pH of the system to 7.5 with sodium bicarbonate and stir at 300 rpm for 10 min. Then add 20.0 g of the oxidation intermediate and stir at 8000 rpm for 2 h. After the reaction is complete, wait for the reaction vessel to cool to room temperature and then filter the reaction liquid to collect the filter cake. Wash the cake three times with ethyl acetate and deionized water to obtain wet carbon nanotube material.

[0115] Step 3: Preparation of carbon nanotubes

[0116] Weigh out 300.0 mL of 98 wt% sulfuric acid aqueous solution and add it to a stirred tank. Then, add 100.0 mL of 65 wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution along the wall of the stirred tank to obtain a mixed acid.

[0117] Weigh 20.0g of wet carbon nanotubes and 300.0mL of mixed acid and add them to the reaction vessel. After soaking at room temperature for 15min, add 2.0g of citric acid diacetate sulfonyl ligand prepared in Example 7 to the reaction vessel. Stir at room temperature for 10min and then raise the temperature of the reaction vessel to 45℃. Keep it warm and stir for 4h. After the reaction is completed, wait for the reaction vessel to cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake three times with anhydrous ethanol and deionized water. After obtaining the solid, transfer it to an 80℃ drying oven and vacuum dry it to constant weight to obtain carbon nanotubes.

[0118] Example 11

[0119] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0120] Step 1: Preparation of oxidation intermediates

[0121] Weigh out 0.3g of the hydroxamic acid precursor oxidant prepared in Example 2, 400.0mL of anhydrous dichloromethane and 100.0mL of anhydrous ethanol, mix them and spray them onto 30.0g of carbon nanotubes and 10.0g of melamine. Let it stand at room temperature for 15min, then pre-dry it with hot air at 50℃ for 40min. After pre-drying, transfer the mixture to a tube furnace, introduce air at an inlet rate of 800mL / min, and heat the tube furnace to 350℃ at a heating rate of 3℃ / min. After holding the temperature for 4h, stop heating and let the furnace temperature cool naturally to 40℃. Take out the material and pass it through a 60-mesh sieve to obtain the oxidation intermediate.

[0122] Step 2: Preparation of wet carbon nanotube material

[0123] Weigh out 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol, and 12.0 g of the quaternized chitosan oligosaccharide dispersant prepared in Example 5 and add them to a high-speed shear press. Adjust the pH of the system to 7.5 with sodium bicarbonate and stir at 300 rpm for 10 min. Then add 20.0 g of the oxidation intermediate and stir at 8000 rpm for 3 h. After the reaction is complete, wait for the reaction vessel to cool to room temperature and then filter the reaction liquid to collect the filter cake. Wash the filter cake five times with ethyl acetate and deionized water to obtain wet carbon nanotube material.

[0124] Step 3: Preparation of carbon nanotubes

[0125] Weigh out 300.0 mL of 98 wt% sulfuric acid aqueous solution and add it to a stirred tank. Then, add 100.0 mL of 65 wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution along the wall of the stirred tank to obtain a mixed acid.

[0126] Weigh 20.0g of wet carbon nanotubes and 300.0mL of mixed acid and add them to the reaction vessel. After soaking at room temperature for 20min, add 2.5g of citric acid diacetate sulfonyl ligand prepared in Example 8 to the reaction vessel. Stir at room temperature for 15min and then raise the temperature of the reaction vessel to 50℃. Keep it warm and stir for 6h. After the reaction is completed, wait for the reaction vessel to cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake 5 times with anhydrous ethanol and deionized water. After obtaining the solid, transfer it to an 80℃ drying oven and vacuum dry it to constant weight to obtain carbon nanotubes.

[0127] Example 12

[0128] This embodiment provides a method for preparing highly conductive carbon nanotubes containing citric acid diacetate sulfonyl ligands, including the following steps:

[0129] Step 1: Preparation of oxidation intermediates

[0130] Weigh out 0.3g of the hydroxamic acid precursor oxidant prepared in Example 3, 400.0mL of anhydrous dichloromethane and 100.0mL of anhydrous ethanol, mix them and spray them onto 25.0g of carbon nanotubes and 10.0g of melamine. After standing at room temperature for 15min, pre-dry with hot air at 50℃ for 36min. After pre-drying, transfer the mixture to a tube furnace, introduce air at an inlet rate of 650mL / min, and heat the tube furnace to 350℃ at a heating rate of 3℃ / min. After holding at this temperature for 4h, stop heating and allow the furnace temperature to cool naturally to 40℃. Remove the material and pass it through a 60-mesh sieve to obtain the oxidation intermediate.

[0131] Step 2: Preparation of wet carbon nanotube material

[0132] Weigh out 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol, and 12.0 g of the quaternized chitosan oligosaccharide dispersant prepared in Example 6 and add them to a high-speed shear press. Adjust the pH of the system to 7.5 with sodium bicarbonate and stir at 300 rpm for 10 min. Then add 20.0 g of the oxidation intermediate and stir at 8000 rpm for 3 h. After the reaction is complete, wait for the reaction vessel to cool to room temperature and then filter the reaction liquid to collect the filter cake. Wash the filter cake four times with ethyl acetate and deionized water to obtain wet carbon nanotube material.

[0133] Step 3: Preparation of carbon nanotubes

[0134] Weigh out 300.0 mL of 98 wt% sulfuric acid aqueous solution and add it to a stirred tank. Then, add 100.0 mL of 65 wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution along the wall of the stirred tank to obtain a mixed acid.

[0135] Weigh 20.0g of wet carbon nanotubes and 300.0mL of mixed acid and add them to the reaction vessel. After soaking at room temperature for 18min, add 2.4g of citric acid diacetate sulfonyl ligand prepared in Example 9 to the reaction vessel. Stir at room temperature for 12min and then raise the temperature of the reaction vessel to 50℃. Keep it warm and stir for 5h. After the reaction is completed, wait for the reaction vessel to cool to room temperature, filter the reaction liquid and collect the filter cake. Wash the filter cake 4 times with anhydrous ethanol and deionized water. After obtaining the solid, transfer it to an 80℃ drying oven and vacuum dry it to constant weight to obtain carbon nanotubes.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 12 is that the use of hydroxamic acid precursor oxidant was omitted in step one.

[0138] Comparative Example 2

[0139] The difference between this comparative example and Example 12 is that step ② is omitted in the preparation of the quaternized chitosan oligosaccharide dispersant used in step two.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 12 is that the citric acid diacetate sulfonyl ligand is omitted in step three.

[0142] Performance testing:

[0143] The fineness and volume resistivity of the conductive pastes prepared using carbon nanotubes from Examples 10-12 and Comparative Examples 1-3 were tested in accordance with the standard GB / T 33818-2017 "Carbon Nanotube Conductive Paste".

[0144] The residual amounts of metal impurity elements in carbon nanotubes prepared using Examples 10-12 and Comparative Examples 1-3 were tested according to the standard GB / T 35418-2017 "Determination of Impurity Elements in Carbon Nanotubes by Inductively Coupled Plasma Mass Spectrometry"; the specific data are shown in Table 1.

[0145] Table 1 - Performance Test Data for Each Sample

[0146]

[0147] Data Analysis:

[0148] A comparative analysis of the data in Table 1 reveals that the residual amount of metal impurity elements in the carbon nanotubes prepared by this invention is 7.3 mg·kg⁻¹. -1 The slurry has a fineness of 10.5 μm and a volume resistivity of 0.080 Ω·cm. -1 All data points are better than the comparative data, indicating that:

[0149] In Comparative Example 1, the carbon nanotubes failed to undergo directional oxidation modification at low temperatures due to the absence of hydroxamic acid precursor oxidant. The specific structure of hydroxamic acid could normally undergo complexation-oxidation reactions with metal catalyst residues and amorphous carbon during spraying and pre-drying to generate easily desorbed oxides and oxygen-containing groups. Its absence means insufficient activation of surface defects, and the binding force between metal particles and carbon walls remains strong. Subsequent mixed acid requires more intense etching to remove the metal, which can easily cause structural damage. At the same time, the reduction of surface functionalization sites weakens the binding ability with dispersant, resulting in imperfect electrostatic repulsion and hydrogen bond network between tube bundles. Overall, due to the lack of initial chemical activation, the surface modification depth is insufficient, the impurity removal efficiency is reduced, and the dispersion stability and conductive network continuity are all affected.

[0150] In Comparative Example 2, the absence of quaternized chitosan oligosaccharide resulted in the loss of strong electrostatic interactions between the cationic groups and the deprotonated carboxyl groups on the surface of carbon nanotubes. The quaternary ammonium groups were originally able to form a dense and stable cationic adsorption layer during dispersion, which could inhibit the re-aggregation of the tube bundles through electrostatic barriers and hydrogen bonds, and generate weak complexation with metal ions in the solution to maintain their suspension. The absence of this link meant that the adsorption of the dispersant and the tube wall relied more on weak hydrogen bonds and hydrophobic interactions, resulting in insufficient binding force. After shear shutdown, the van der Waals interactions between the tube bundles were restored, and the particles were prone to aggregation and sedimentation. At the same time, the metal ions lacked effective traction in the dispersion medium and were more likely to be redeposited on the surface of the carbon nanotubes in subsequent processing, leading to a decrease in the uniformity of the system.

[0151] When Comparative Example 3 lacks the citric acid sulfonyl ligand, the metal ions released during the mixed acid impregnation process cannot be effectively chelated and stably embedded. They are very likely to be redeposited on carbon nanotube defects, lumens, or intersections before the acid washing is completed. The sulfonated multi-site ligand can originally firmly pull the metal ions to the solution phase through multiple coordination interactions of carboxyl, amide, and sulfonamide groups, preventing them from binding to the carbon nanotube surface again. The lack of this function forces the operator to rely on longer or stronger acid conditions to achieve the metal removal target. As a result, the carbon nanotube wall structure is often subjected to additional etching, the aspect ratio decreases, the conductive path is destroyed, and metal redeposition and excessive structural cutting coexist, resulting in damage to both the purity and structural integrity of the final sample.

[0152] In conclusion, this invention utilizes a hydroxamic acid precursor oxidant to gently introduce active sites in the initial stage, creating conditions for subsequent functionalization and dispersion of carbon nanotubes. Quaternized chitosan oligosaccharide dispersant stabilizes the adsorption layer, achieving dispersion of carbon nanotubes and attraction of metal ions, maintaining the uniformity of the suspension system. Citric acid imide diacetate sulfonyl ligand firmly locks in metal ions during acid washing, preventing secondary deposition on the carbon nanotube surface and reducing structural damage caused by excessive etching. The order and ratio of these three components are rationally designed, forming a continuous and efficient chain of "pretreatment-dispersion-acid washing," achieving a balance between impurity removal and structural stability. The resulting carbon nanotubes exhibit excellent purity, dispersibility, and conductive network continuity, demonstrating the significant advantages of a systematic process. This synergistic approach, from source activation to end-of-life protection, makes the overall process far superior to single methods and provides a clear path for the controllable processing of carbon nanotubes.

[0153] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0154] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0155] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing highly conductive carbon nanotubes, characterized in that, Includes the following steps: S1. Hydroxyxamic acid precursor oxidant, anhydrous dichloromethane and anhydrous ethanol are mixed and sprayed onto carbon nanotubes and melamine. After standing at room temperature for 15 minutes, they are pre-dried with hot air at 50°C for 30-40 minutes and calcined to obtain an oxidation intermediate. S2. Deionized water, anhydrous ethanol and quaternized chitosan oligosaccharide dispersant were added to a high-speed shear mill. The pH of the system was adjusted to 7.5 with sodium bicarbonate and stirred at 300 rpm for 10 min. After adding the oxidation intermediate, the high-speed shear mill was stirred at 8000 rpm for 2-3 h. The post-processing yielded wet carbon nanotube material. S3. Add the wet carbon nanotube material and mixed acid to the reactor. After soaking at room temperature for 15-20 minutes, add citrimidine diacetate sulfonyl ligand to the reactor. Stir at room temperature for 10-15 minutes, then raise the temperature of the reactor to 45-50℃ and keep it at this temperature for 4-6 hours. The carbon nanotubes are then obtained through post-treatment.

2. The method for preparing highly conductive carbon nanotubes according to claim 1, characterized in that, In step S1, the ratio of hydroxamic acid precursor oxidant, anhydrous dichloromethane, anhydrous ethanol, carbon nanotubes, and melamine is 0.03g:40mL:10mL:2-3g:1g; in step S2, the ratio of deionized water, anhydrous ethanol, quaternized chitosan oligosaccharide dispersant, and oxidation intermediate is 200mL:50mL:1.0-1.2g:2g; in step S3, the ratio of wet carbon nanotubes, mixed acid, and citrileimide diacetate sulfonyl ligand is 2g:30mL:0.20-0.25g. The mixed acid is prepared by adding 98wt% sulfuric acid aqueous solution to a stirred tank and stirring, then adding 65wt% nitric acid aqueous solution and 85% phosphoric acid aqueous solution along the wall of the stirred tank to obtain the mixed acid, wherein the volume ratio of 98wt% sulfuric acid, 65wt% nitric acid, and 85% phosphoric acid is 3:1:

1.

3. The method for preparing highly conductive carbon nanotubes according to claim 1, characterized in that, In step S1, the preparation method of the hydroxamic acid precursor oxidant includes the following steps: A1. Gallic acid and anhydrous dichloromethane are added to a reaction vessel and stirred. After nitrogen protection, thionyl trichloride and dimethylformamide are added dropwise. The temperature of the reaction vessel is controlled to rise to 50-60℃ and stirred for 2-3 hours. The hydroxamic acid precursor oxidant is obtained by post-treatment. A2. Add galloyl chloride intermediate, hydroxylamine hydrochloride and N,N-dimethylformamide to a reaction vessel, add ammonium carbonate to adjust the pH of the reaction system to 8-9, purge with nitrogen for protection, maintain the temperature of the reaction vessel at 20-30℃, stir for 4-5 hours, and then proceed with post-treatment to obtain the hydroxamic acid precursor oxidant.

4. The method for preparing highly conductive carbon nanotubes according to claim 3, characterized in that, In step A1, the ratio of gallic acid, anhydrous dichloromethane, thionyl trichloride, and dimethylformamide is 1-2g:80-100mL:2-3g:0.3mL; in step A2, the ratio of galloyl chloride intermediate, hydroxylamine hydrochloride, and N,N-dimethylformamide is 1g:1.2-1.3g:40-50mL.

5. The method for preparing highly conductive carbon nanotubes according to claim 1, characterized in that, In step S2, the preparation method of the quaternized chitosan oligosaccharide dispersant includes the following steps: B1. Add chitosan oligosaccharide, succinic anhydride, anhydrous ethanol and deionized water to a reaction vessel and stir. Adjust the pH of the reaction system to 8-9 using sodium bicarbonate, purge with nitrogen for protection, heat to 30-35℃, keep warm and stir for 4-5 hours, and then process to obtain hemiacylated chitosan oligosaccharide. B2. Add hemiacylated chitosan oligosaccharide, hydroxypropyltrimethylammonium chloride and deionized water to a reaction vessel, adjust the pH of the reaction system to 8-9 using sodium bicarbonate, purge with nitrogen for protection, heat to 40-50℃, keep warm and stir for 6-8 hours, and then process to obtain quaternized chitosan oligosaccharide dispersant.

6. The method for preparing highly conductive carbon nanotubes according to claim 5, characterized in that, In step B1, the ratio of chitosan oligosaccharide, succinic anhydride, anhydrous ethanol, and deionized water is 1g:0.30-0.35g:80mL:10-20mL; in step B2, the ratio of hemiacylated chitosan oligosaccharide, hydroxypropyltrimethylammonium chloride, and deionized water is 1-2g:0.6-1.2g:20mL.

7. The method for preparing highly conductive carbon nanotubes according to claim 1, characterized in that, In step S3, the preparation method of the citriimide diacetate sulfonyl ligand includes the following steps: C1. Add citric acid and anhydrous dichloromethane to a reaction vessel and stir. After purging with nitrogen, add thionyl chloride and dimethylformamide dropwise. Heat to 50-60℃ and keep the reaction at this temperature for 2-3 hours. Post-process to obtain citrate chloride intermediate. C2. Add citrate chloride intermediate, imine diacetic acid, triethylamine and anhydrous acetonitrile to a reaction vessel, purge with nitrogen for protection, control the temperature at 0-5℃, add chlorosulfonamide dropwise, raise the temperature of the reaction vessel to 25-35℃, keep it at this temperature and stir for 6-8 hours, and then proceed with post-treatment to obtain citrate imine diacetic acid sulfonyl ligand.

8. The method for preparing highly conductive carbon nanotubes according to claim 7, characterized in that, In step C1, the ratio of citric acid, anhydrous dichloromethane, thionyl trichloride, and dimethylformamide is 1g:40-50mL:2.0-2.5g:0.3mL; in step C2, the ratio of citrate chloride intermediate, iminodiacetic acid, triethylamine, chlorosulfonamide, and anhydrous acetonitrile is 1g:1.0-1.2g:1.0-1.2g:1.2-1.5g:30mL.

9. A highly conductive carbon nanotube, characterized in that, The highly conductive carbon nanotubes are prepared using a method for preparing highly conductive carbon nanotubes as described in any one of claims 1-8.

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