Highly conductive carbon nanotubes and methods for making the same

Abstract

The application discloses a kind of high-conductive carbon nanotubes and preparation method thereof, belong to carbon nanotube preparation technical field, for solving the technical problem that the purity and conductivity of carbon nanotube in prior art need to be further improved;The application uses hydroxamic acid precursor oxidant to introduce active site mildly in initial stage, to create conditions for subsequent functionalization and dispersion of carbon nanotubes;Quaternary ammonium chitosan oligosaccharide dispersant realizes the dispersion of carbon nanotubes and metal ion traction by stable adsorption layer, maintains the uniformity of suspension system;Sulfonylization malonic imidodiacetic acid multi-tooth complex ligand firmly locks metal ion in pickling process, avoids its secondary deposition on the surface of carbon nanotube, through "pretreatment-dispersion-pickling", forms continuous and efficient chain, impurity removal and structure maintenance are taken into account in dynamic balance, finally obtained carbon nanotube is excellent in purity, dispersity and conductivity network continuity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon nanotube preparation, and particularly relates to a high-conductivity carbon nanotube and a preparation method thereof. BACKGROUND

[0002] Carbon nanotubes are regarded as an important representative of a new generation of functional materials due to their unique structure and excellent physical properties. However, in the early preparation process, the product purity is insufficient due to the generation of amorphous carbon and the residual metal catalyst, which limits the application of carbon nanotubes in precision electronics and energy fields. With the deepening of research, it is gradually realized that high purity is a prerequisite for releasing the performance of carbon nanotubes, so the purification and impurity removal technology is continuously developed. At the same time, the improvement of the conductivity has also become a key target. A single carbon nanotube itself has excellent electrical properties, but in the macro material, the purity, dispersibility and uniformity of the network structure directly determine the overall conductivity. In recent years, with the progress of preparation and post-processing level, carbon nanotubes have gradually realized stable conductive network while maintaining high purity, thereby showing more and more outstanding application potential in transparent conductive films, supercapacitors and high-speed interconnection fields.

[0003] The existing carbon nanotube preparation process has been able to realize production on a certain scale after years of development, but there are still obvious deficiencies in the overall level. Firstly, the product purity is generally low, and the residual metal catalyst, amorphous carbon and other impurities are difficult to completely remove. Such impurities not only affect the application of carbon nanotubes in high-end electronic devices, but also reduce the interfacial compatibility of carbon nanotubes in composite materials, thereby weakening the mechanical and electrical properties. Secondly, the tube structure is often damaged during the purification process, which is manifested as damaged tube diameter, shortened tube length or increased wall defects, so that the inherent excellent performance of carbon nanotubes is difficult to fully reflect, especially in the case of long-range electron transport, the performance attenuation caused by structural damage is more significant. Overall, although the existing process can obtain carbon nanotube products, there is still a big gap from the requirements of high purity, low defects and high performance.

[0004] In addition to the problems of purity and structural damage, the existing process also has obvious deficiencies in the conductivity. A single carbon nanotube theoretically has extremely high electron mobility and excellent conductivity, but in actual macro materials, due to uneven dispersion, disordered orientation and poor contact interface between tubes, the overall conductivity is much lower than the theoretical expectation. At the same time, the existence of impurities also forms an electrical "dead zone", which hinders the transmission of electric current, resulting in discontinuous conductive network. On the other hand, the production cost and process complexity are high, so that high-performance carbon nanotubes are difficult to realize large-scale application in transparent electrodes, supercapacitors and flexible electronic devices, etc. These problems to a large extent limit the pace of carbon nanotubes from the laboratory to the industrialization, and also become a key bottleneck that the current industry urgently needs to solve.

[0005] In view of the technical defects in this aspect, a solution is provided. SUMMARY

[0006] The present application aims to provide a high-conductivity carbon nanotube and a preparation method thereof, and solve the technical problem that the purity and conductivity of the carbon nanotube in the prior art need to be further improved.

[0007] The object of the present application can be achieved by the following technical solutions.

[0008] A preparation method of a high-conductivity carbon nanotube, comprising the following steps:

[0009] S1, spraying a hydroxamic acid precursor oxidant, anhydrous dichloromethane and anhydrous ethanol onto carbon nanotube and melamine after mixing, and placing at room temperature for 15 min, then pre-drying at 50 DEG C hot air for 30-40 min, and calcining to obtain an oxidation intermediate;

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

[0011] Through the mixed spraying treatment of the hydroxamic acid precursor oxidant, the anhydrous dichloromethane and the anhydrous ethanol, and the mild oxidation activation of the carbon nanotube surface in the calcination process, the amorphous carbon is removed and the oxygen-containing functional groups such as carboxyl and hydroxyl are introduced, so as to improve the hydrophilicity and subsequent dispersibility of the carbon tube; at the same time, the residual metal catalyst is oxidized into metal oxide, so as to reduce the binding force with the carbon tube and lay a foundation for the subsequent removal of the metal by acid washing; the nitrogen source fragments released by the melamine in the calcination process are partially adsorbed on the defect sites of the tube wall, so as to enhance the activity of the carbon tube surface and provide additional binding sites for dispersion, and finally the oxidation intermediate is prepared.

[0012] S2, adding deionized water, anhydrous ethanol and quaternary ammonium chitosan oligosaccharide dispersant into a high-speed shearing machine, adjusting the pH of the system to 7.5 by using sodium bicarbonate and stirring at a speed of 300 rpm for 10 min, then adding the oxidation intermediate, and stirring the high-speed shearing machine at a speed of 8000 rpm for 2-3 h, and then treating to obtain carbon nanotube wet material;

[0013] The reaction principle for preparing the carbon nanotube wet material is:

[0014] A low surface tension system is formed by using deionized water, anhydrous ethanol and quaternary ammonium chitosan dispersant, and the pH is adjusted by sodium bicarbonate to partially deprotonate the carboxyl groups on the surface of the carbon tube to form negative charges, which interact with the quaternary ammonium cations in the dispersant to significantly improve the stability of the carbon tube. Then, the bundle of tubes is disentangled and uniformly dispersed by high-speed shearing, and the dispersant forms an electrostatic barrier and a hydrogen bond network on the surface of the tube wall to prevent the carbon tubes from re-agglomerating. At the same time, the metal ions after oxidation are weakly complexed or suspended in the dispersion system, reducing the difficulty of subsequent pickling. Finally, carbon nanotube wet material is prepared.

[0015] S3, adding carbon nanotube wet material and mixed acid to the reaction kettle, immersing at room temperature for 15-20 min, then adding sulfonated citraconimidyl diacetic acid polydentate complexing ligand to the reaction kettle, stirring at room temperature for 10-15 min, then increasing the temperature of the reaction kettle to 45-50℃, and keeping the temperature for 4-6 h. The carbon nanotube is obtained after post-processing.

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

[0017] The carbon nanotube wet material is contacted with a mixed acid composed of sulfuric acid, nitric acid and phosphoric acid. First, it is immersed at room temperature to improve permeability, then a sulfonated citraconimidyl diacetic acid polydentate complexing ligand is added to form a stable complex with metal ions, preventing their redeposition on the surface of the carbon tube. Subsequently, the system is warmed, and the mild etching effect of the three acids is used to completely dissolve the residual metal catalyst and amorphous carbon. At the same time, under the buffering action of phosphoric acid, excessive cutting of the carbon tube is avoided. Finally, carbon nanotubes are prepared.

[0018] Further, in step S1, the amount ratio of hydroxamic acid precursor oxidant, anhydrous dichloromethane, anhydrous ethanol, carbon nanotube crude tube and melamine is 0.03g:40mL:10mL:2-3g:1g. The calcination operation is as follows: after the pre-drying is completed, the mixture is transferred to a tube furnace, air is introduced at a flow rate of 500-800mL / min, the tube furnace is heated at a rate of 2-3℃ / min to 320-350℃, the heating is stopped after the temperature is kept for 3-4h, the material is taken out when the furnace temperature naturally cools down by 30-40℃, and the material is passed through a 60-mesh sieve to obtain an oxidation intermediate;

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

[0020] Further, in step S3, the ratio of the amounts of the carbon nanotube wet material, the mixed acid, and the sulfonated citraconimidyl diacetic acid polydentate complexing ligand is 2 g:30 mL:0.20-0.25 g, the mixed acid is prepared by adding 98 wt% sulfuric acid aqueous solution into a stirred tank, stirring, and then adding 65 wt% nitric acid aqueous solution and 85% phosphoric acid aqueous solution along the stirred tank wall to obtain the mixed acid, wherein the volume ratio of the 98 wt% sulfuric acid aqueous solution, the 65 wt% nitric acid aqueous solution, and the 85% phosphoric acid aqueous solution is 3:1:1, and the post-treatment includes: after the reaction is completed, the reaction kettle is cooled to room temperature, the reaction liquid is filtered to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water to obtain a solid, and the solid is then transferred to a 80°C drying oven for vacuum drying until the weight is constant to obtain the carbon nanotube.

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

[0022] A1, gallic acid and anhydrous dichloromethane are added into a reaction kettle and stirred, nitrogen is introduced for protection, chlorosulfuric acid and dimethylformamide are added dropwise, the temperature of the reaction kettle is controlled to rise to 50-60°C, and the reaction kettle is stirred for 2-3 hours, and the post-treatment obtains a gallic acid chloride intermediate;

[0023] A2, the gallic acid chloride intermediate, hydroxylamine hydrochloride, and N,N-dimethylformamide are added into a reaction kettle, ammonium carbonate is added to adjust the pH of the reaction system to 8-9, nitrogen is introduced for protection, the temperature of the reaction kettle is maintained at 20-30°C, and the reaction kettle is stirred for 4-5 hours, and the post-treatment obtains the hydroxamic acid precursor oxidant.

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

[0025] Under the catalysis of chlorosulfuric acid in dimethylformamide, the carboxyl group of gallic acid is activated into an acyl chloride structure which is more reactive, thereby significantly improving the efficiency of the subsequent nucleophilic substitution reaction; then, hydroxylamine hydrochloride is introduced as a nucleophile to attack the carbonyl carbon atom in the acyl chloride, a nucleophilic substitution reaction occurs, the chloride ion is replaced, and a stable hydroxamic acid structure unit is formed, and in this process, the role of ammonium carbonate is to adjust and maintain the reaction system in a weak alkaline environment, which can not only ensure the effective activity of hydroxylamine, but also inhibit the occurrence of side reactions.

[0026] Further, in step A1, the ratio of the amounts of the gallic acid, anhydrous dichloromethane, chlorosulfuric acid, and dimethylformamide is 1-2 g:80-100 mL:2-3 g:0.3 mL, and the post-treatment includes: after the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, the reaction liquid is transferred to a rotary evaporator with a temperature of 80°C for reduced pressure distillation until no liquid is collected to obtain the gallic acid chloride intermediate;

[0027] Further, in step A2, the ratio of the amounts of gallic acid chloride intermediate, hydroxylamine hydrochloride and N,N-dimethylformamide is 1 g:1.2-1.3 g:40-50 mL, and the post-treatment includes: after the reaction is completed, the reaction kettle is cooled to room temperature, the reaction solution is filtered under suction to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water, the solid is transferred to a 80°C drying oven for vacuum drying until the weight is constant, and the hydroxamic acid precursor oxidant is obtained.

[0028] Further, in step S2, the preparation method of the quaternary ammonium chitosan oligosaccharide dispersant includes the following steps:

[0029] B1, chitosan oligosaccharide, succinic anhydride, anhydrous ethanol and deionized water mixed solvent are added into a reaction kettle and stirred, sodium bicarbonate is used to adjust the pH of the reaction system to 8-9, nitrogen is introduced for protection, the temperature is raised to 30-35°C, and the temperature is kept constant for 4-5 h, and the semi-acylated chitosan oligosaccharide is obtained after post-treatment;

[0030] B2, semi-acylated chitosan oligosaccharide, hydroxypropyltrimethylammonium chloride and deionized water are added into a reaction kettle, sodium bicarbonate is used to adjust the pH of the reaction system to 8-9, nitrogen is introduced for protection, the temperature is raised to 40-50°C, and the temperature is kept constant for 6-8 h, and the quaternary ammonium chitosan oligosaccharide dispersant is obtained after cooling to room temperature and post-treatment.

[0031] The reaction principle for preparing the quaternary ammonium chitosan oligosaccharide dispersant is:

[0032] The amino group on the chitosan oligosaccharide molecule undergoes acylation reaction with succinic anhydride to introduce carboxyl substituent, forming semi-acylated chitosan oligosaccharide. The essence of this step is to introduce active carboxyl side chains on the chitosan oligosaccharide molecule through ring-opening reaction of succinic anhydride, thereby improving its reactivity and hydrophilicity;

[0033] The active site on the semi-acylated chitosan oligosaccharide undergoes substitution reaction with hydroxypropyltrimethylammonium chloride, and chloride ions are replaced, finally introducing cationic quaternary ammonium groups on the chitosan oligosaccharide molecular skeleton. This modification gives chitosan oligosaccharide permanent positive charge, which can enhance its interaction with water and other polar molecules, and improve its dispersion stability.

[0034] Further, in step B1, the ratio of the amounts of chitosan oligosaccharide, succinic anhydride, anhydrous ethanol and deionized water is 1 g:0.30-0.35 g:80 mL:10-20 mL, and the post-treatment includes: after the reaction is completed, the reaction kettle is cooled to room temperature, the reaction solution is filtered under suction to collect the filter cake, the filter cake is washed 3-5 times with anhydrous ethanol and deionized water, the solid is transferred to a 80°C drying oven for vacuum drying until the weight is constant, and the semi-acylated chitosan oligosaccharide is obtained;

[0035] Further, in step B2, the amount of semi-acylated chitosan oligosaccharide, chlorinated hydroxypropyl trimethyl ammonium, and deionized water is 1-2 g: 0.6-1.2 g: 20 mL, and the post-processing includes: after the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, the reaction solution is loaded into a 3.5 kDa dialysis bag, dialyzed with deionized water at 4℃ for 48h, then the dialysis product is collected, pre-frozen at-40℃, and freeze-dried under the condition of 0.05mbar to constant weight to obtain the quaternary ammonium chitosan oligosaccharide dispersant.

[0036] Further, in step S3, the preparation method of the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand includes the following steps:

[0037] C1, citric acid and anhydrous dichloromethane are added to the reaction kettle and stirred, then sulfuric chloride and dimethylformamide are added dropwise after nitrogen protection, the temperature is raised to 50-60℃, and the reaction is kept for 2-3h, and the citraconyl chloride intermediate is obtained after post-processing;

[0038] C2, citraconyl chloride intermediate, imine diacetic acid, triethylamine and anhydrous acetonitrile are added to the reaction kettle, nitrogen protection is carried out, the temperature is controlled at 0-5℃, chlorosulfonamide is added dropwise, the reaction kettle is heated to 25-35℃, and the reaction is kept stirring for 6-8h, and the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand is obtained after post-processing.

[0039] The reaction principle for preparing the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand is:

[0040] Using sulfuric chloride in the presence of dimethylformamide, the carboxyl group in the citric acid molecule is converted into a more reactive acyl chloride group, thereby generating a citraconyl chloride intermediate. This activation process is essentially a conversion of carboxylic acid to acyl chloride, which greatly enhances the efficiency of the subsequent condensation reaction.

[0041] Then, the citraconyl chloride and imine diacetic acid undergo acyl chloride-amino condensation reaction. As a nitrogen-containing ligand precursor, the amino group of imine diacetic acid has strong nucleophilicity towards acyl chloride. Under the action of triethylamine, HCl is neutralized, making the reaction proceed smoothly, forming a stable amide bond structure. At this point, the citric acid skeleton and imine diacetic acid are connected through an amide bond.

[0042] Finally, chlorosulfonamide is introduced under low temperature conditions to introduce -SO2NH2 functional groups on the molecule through sulfonamidation. The introduction of sulfonamide not only improves the polarity and coordination ability of the ligand, but also provides additional binding sites and electronic effects for its metal ion complexation and catalytic applications.

[0043] Further, in step C1, the ratio of citric acid, anhydrous dichloromethane, thionyl chloride, 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 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 sulfonated citrile imine diacetic acid multidentate complex 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 pickling stage, the sulfonated citrate diacetic acid multidentate complexing ligand synergistically works with the triacids 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 the application mildly activates the surface of carbon nanotubes, removes amorphous carbon and exposes the interface of coated metal particles, and then disperses the carbon nanotube bundles through the electrostatic and steric hindrance effects of the quaternary ammonium chitosan oligosaccharide dispersant, effectively unties the carbon nanotube bundles, significantly increases the contact area of the acid solution and the internal metal particles, avoids the "acid solution shielding" caused by agglomeration, and at the same time, the positive charge carried by the dispersant also promotes the directional enrichment of acid ions in the local area, speeds up the penetration and wetting of the acid medium, thereby enhancing the efficiency of pickling; then, the three-acid compounded solution etches and dissolves the metal catalytic particles, and the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand as a multi-dentate complexing agent forms stable chelates with Fe, Co, Ni and other metal ions to prevent their secondary deposition or adsorption back to the surface of carbon nanotubes, and finally through the continuous action of surface activation-dispersing untie-pickling dissolution-ligand complexing, the content of residual metal catalyst is significantly reduced, and the purity of carbon nanotubes is greatly improved, providing reliable structure and chemical guarantee for its application in conductive paste and high-performance applications.

[0049] 3、The application uses hydroxamic acid precursor oxidant to mildly activate the surface of carbon nanotubes, remove amorphous carbon and residual catalyst, and introduce carboxyl, hydroxyl and other oxygen-containing functional groups into the tube wall, so that the surface of the carbon nanotube is converted from a hydrophobic graphite structure to an interface with a certain polarity, creating a chemical basis for aqueous dispersion; secondly, the semi-acylated and further quaternized chitosan oligosaccharide dispersant forms multiple interactions with the oxidized carbon nanotube surface: on the one hand, the carboxyl side chain and the oxygen-containing groups on the surface of the carbon nanotube are enhanced by hydrogen bonding and electrostatic interaction; on the other hand, the quaternary ammonium group provides a permanent positive charge, which electrostatically pairs with the negative charge on the surface of the carbon nanotube, and at the same time, the flexible polysaccharide skeleton forms steric hindrance in the solvent, preventing the carbon nanotube from re-agglomerating; thirdly, the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand introduced in the pickling process can effectively complex and attract metal ions, preventing them from redepositing on the surface of the carbon nanotube, and at the same time, it cooperates with the mild etching of the three acids to further remove residual impurities and maintain the integrity of the tube; finally, through the functional complementation between materials and the sequential connection of the process flow, the surface polarity of the carbon nanotube is improved, the interface interaction is enhanced, and the dispersion stability is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on these drawings.

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

[0052] Figure 2 SEM image of carbon nanotubes prepared for Example 12. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be clearly and completely described below in combination with examples. Obviously, the described examples are only some of the examples of the present application, but not all the examples. Based on the examples in the present application, all the other examples obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0054] The chitosan oligosaccharide used in the present application is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd., and the article number is C799253. The citric acid used in the present application is purchased from Shanghai Maikelin Biochemical Technology Co., Ltd., and the article number is C805019.

[0055] Example 1

[0056] The present embodiment provides a preparation method of a hydroxamic acid precursor oxidant for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0057] Step 1, preparation of galloyl chloride intermediate

[0058] Take 10.0 g of gallic acid and 800.0 mL of anhydrous dichloromethane and add them to the reaction kettle for stirring. After protection by nitrogen gas, 20.0 g of thionyl chloride and 3.0 mL of dimethylformamide are added dropwise. The temperature of the reaction kettle is controlled to rise to 50℃, and the stirring is kept for 2 h. After the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, and the reaction liquid is transferred to a rotary evaporator with a temperature of 80℃ for reduced pressure distillation until no liquid is collected. The galloyl chloride intermediate is obtained.

[0059] Step 2, preparation of hydroxamic acid precursor oxidant

[0060] Take 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 kettle. Add ammonium carbonate to adjust the pH of the reaction system to 8. Protection by nitrogen gas is performed, and the temperature of the reaction kettle is kept at 20℃. The stirring is kept for 4 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction liquid is filtered to collect the filter cake. The filter cake is washed with anhydrous ethanol and deionized water for 3 times, and then transferred to a 80℃ drying box for vacuum drying until the constant weight. The hydroxamic acid precursor oxidant is obtained.

[0061] Example 2

[0062] The present embodiment provides a preparation method of a hydroxamic acid precursor oxidant for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0063] Step 1, preparation of galloyl chloride intermediate

[0064] Weigh: 20.0 g of gallic acid and 1000.0 mL of anhydrous dichloromethane into the reaction kettle, stir, protect with nitrogen, then add 30.0 g of thionyl chloride and 3.0 mL of dimethylformamide dropwise, control the temperature of the reaction kettle to rise to 60℃, and keep stirring for 3 h. After the reaction is completed, when the temperature of the reaction kettle decreases to room temperature, transfer the reaction liquid to a rotary evaporator with a temperature of 80℃, and distill under reduced pressure until no liquid is collected. Gallic chloride intermediate is obtained.

[0065] Step 2, preparation of hydroxamic acid precursor oxidant

[0066] Weigh: 10.0 g of gallic chloride intermediate, 13.0 g of hydroxylamine hydrochloride, and 500.0 mL of N,N-dimethylformamide into the reaction kettle, add ammonium carbonate to adjust the pH of the reaction system to 9, protect with nitrogen, keep the temperature of the reaction kettle at 30℃, and keep stirring for 5 h. After the reaction is completed, when the reaction kettle cools to room temperature, filter the reaction liquid to collect the filter cake, wash the filter cake with anhydrous ethanol and deionized water 5 times, transfer the solid to a 80℃ drying oven, and vacuum dry to constant weight to obtain the hydroxamic acid precursor oxidant.

[0067] Example 3

[0068] The present embodiment provides a preparation method of a hydroxamic acid precursor oxidant for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0069] Step 1, preparation of gallic chloride intermediate

[0070] Weigh: 16.0 g of gallic acid and 960.0 mL of anhydrous dichloromethane into the reaction kettle, stir, protect with nitrogen, then add 25.0 g of thionyl chloride and 3.0 mL of dimethylformamide dropwise, control the temperature of the reaction kettle to rise to 55℃, and keep stirring for 3 h. After the reaction is completed, when the temperature of the reaction kettle decreases to room temperature, transfer the reaction liquid to a rotary evaporator with a temperature of 80℃, and distill under reduced pressure until no liquid is collected. Gallic chloride intermediate is obtained.

[0071] Step 2, preparation of hydroxamic acid precursor oxidant

[0072] Weigh: 10.0 g of gallic chloride intermediate, 12.0 g of hydroxylamine hydrochloride, and 450.0 mL of N,N-dimethylformamide into the reaction kettle, add ammonium carbonate to adjust the pH of the reaction system to 9, protect with nitrogen, keep the temperature of the reaction kettle at 25℃, and keep stirring for 5 h. After the reaction is completed, when the reaction kettle cools to room temperature, filter the reaction liquid to collect the filter cake, wash the filter cake with anhydrous ethanol and deionized water 4 times, transfer the solid to a 80℃ drying oven, and vacuum dry to constant weight to obtain the hydroxamic acid precursor oxidant.

[0073] Example 4

[0074] The embodiment provides a preparation method of a quaternary ammonium chitosan oligosaccharide dispersant for preparing high-conductivity carbon nanotubes.

[0075] Step 1, preparation of semi-acylated chitosan oligosaccharide

[0076] Take 10.0g chitosan oligosaccharide, 3.0g succinic anhydride, 800.0mL anhydrous ethanol and 100.0mL deionized water mixed solvent and add them into a reaction kettle for stirring, use sodium bicarbonate to adjust the pH value of the reaction system to 8, protect by nitrogen, heat to 30 DEG C, and keep stirring for 4h, after the reaction is completed, cool the reaction kettle to room temperature, filter the reaction solution to collect the filter cake, wash the filter cake with anhydrous ethanol and deionized water for 3 times, transfer the obtained solid to a 80 DEG C drying box for vacuum drying until the weight is constant, and semi-acylated chitosan oligosaccharide is obtained.

[0077] Step 2, preparation of quaternary ammonium chitosan oligosaccharide dispersant

[0078] Take 10.0g semi-acylated chitosan oligosaccharide, 6.0g hydroxypropyltrimethylammonium chloride and 200.0mL deionized water, and add them into a reaction kettle, use sodium bicarbonate to adjust the pH value of the reaction system to 8, protect by nitrogen, heat to 40 DEG C, and keep stirring for 6h, after cooling to room temperature, the reaction is completed, when the temperature of the reaction kettle decreases to room temperature, the reaction solution is loaded into a dialysis bag with a molecular weight of 3.5kDa, and dialysis is carried out at 4 DEG C for 48h by using deionized water, then the dialysis product is collected, pre-frozen at -40 DEG C, and freeze-dried under the condition of 0.05mbar until the weight is constant, and quaternary ammonium chitosan oligosaccharide dispersant is obtained.

[0079] Example 5

[0080] The embodiment provides a preparation method of a quaternary ammonium chitosan oligosaccharide dispersant for preparing high-conductivity carbon nanotubes.

[0081] Step 1, preparation of semi-acylated chitosan oligosaccharide

[0082] Take 10.0g chitosan oligosaccharide, 3.0g succinic anhydride, 800.0mL anhydrous ethanol and 100.0mL deionized water mixed solvent and add them into a reaction kettle for stirring, use sodium bicarbonate to adjust the pH value of the reaction system to 8, protect by nitrogen, heat to 30 DEG C, and keep stirring for 4h, after the reaction is completed, cool the reaction kettle to room temperature, filter the reaction solution to collect the filter cake, wash the filter cake with anhydrous ethanol and deionized water for 3 times, transfer the obtained solid to a 80 DEG C drying box for vacuum drying until the weight is constant, and semi-acylated chitosan oligosaccharide is obtained.

[0083] Step 2, preparation of quaternary ammonium chitosan oligosaccharide dispersant

[0084] Take: 10.0 g of semi-acylated chitosan oligosaccharide, 12.0 g of hydroxypropyl trimethylammonium chloride and 200.0 mL of deionized water into the reaction kettle, adjust the pH of the reaction system to 9 using sodium bicarbonate, protect with nitrogen, heat to 50℃, and stir for 8 h. After cooling to room temperature, the reaction is completed. When the temperature of the reaction kettle decreases to room temperature, the reaction liquid is loaded into a 3.5 kDa dialysis bag, dialyzed with deionized water at 4℃ for 48 h, and then collected. The dialysis product is pre-frozen at -40℃, and then freeze-dried under the condition of 0.05 mbar to constant weight to obtain the quaternary ammonium chitosan oligosaccharide dispersant.

[0085] Example 6

[0086] The present embodiment provides a preparation method of quaternary ammonium chitosan oligosaccharide dispersant for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0087] Step 1, preparation of semi-acylated chitosan oligosaccharide

[0088] Take: 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 mixed solvent into the reaction kettle and stir, adjust the pH of the reaction system to 9 using sodium bicarbonate, protect with nitrogen, heat to 32℃, and stir for 5 h. After the reaction is completed, the reaction kettle is cooled to room temperature, the reaction liquid is collected by suction filtration, and the filter cake is washed with anhydrous ethanol and deionized water 4 times. The solid is transferred to a 80℃ drying oven for vacuum drying to constant weight to obtain semi-acylated chitosan oligosaccharide.

[0089] Step 2, preparation of quaternary ammonium chitosan oligosaccharide dispersant

[0090] Take: 10.0 g of semi-acylated chitosan oligosaccharide, 9.0 g of hydroxypropyl trimethylammonium chloride and 200.0 mL of deionized water into the reaction kettle, adjust the pH of the reaction system to 9 using sodium bicarbonate, protect with nitrogen, heat to 45℃, and stir for 7 h. After cooling to room temperature, the reaction is completed. When the temperature of the reaction kettle decreases to room temperature, the reaction liquid is loaded into a 3.5 kDa dialysis bag, dialyzed with deionized water at 4℃ for 48 h, and then collected. The dialysis product is pre-frozen at -40℃, and then freeze-dried under the condition of 0.05 mbar to constant weight to obtain the quaternary ammonium chitosan oligosaccharide dispersant.

[0091] Example 7

[0092] The present embodiment provides a preparation method of sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0093] Step 1, preparation of citraconyl chloride intermediate

[0094] Weighing: 10.0 g of citric acid and 400.0 mL of anhydrous dichloromethane are added to the reaction kettle and stirred, and after nitrogen protection, 20.0 g of chlorosulfoxide and 3.0 mL of dimethylformamide are added dropwise, and the temperature is raised to 50°C, and the reaction is kept for 2 h. After the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, and the reaction liquid is transferred to a rotary evaporator with a temperature of 80°C for vacuum distillation until no liquid is collected. Citryl chloride intermediate is obtained.

[0095] Step II, preparation of sulfonated citraconimidyl diacetic acid multi-dentate complex ligand

[0096] Weighing: 10.0 g of citryl chloride intermediate, 10.0 g of imine diacetic acid, 10.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile are added to the reaction kettle, and nitrogen protection is carried out, and the temperature is controlled at 0°C. 12.0 g of chlorosulfamide is added dropwise, the reaction kettle is heated to 25°C, and stirring is kept for 6 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction liquid is filtered to collect the filter cake, which is washed with ethyl acetate and deionized water for 3 times. The filter cake is transferred to a 80°C drying oven for vacuum drying until the weight is constant. Sulfonated citraconimidyl diacetic acid multi-dentate complex ligand is obtained.

[0097] Example 8

[0098] The present embodiment provides a preparation method of sulfonated citraconimidyl diacetic acid multi-dentate complex ligand for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0099] Step I, preparation of citryl chloride intermediate

[0100] Weighing: 10.0 g of citric acid and 500.0 mL of anhydrous dichloromethane are added to the reaction kettle and stirred, and after nitrogen protection, 25.0 g of chlorosulfoxide and 3.0 mL of dimethylformamide are added dropwise, and the temperature is raised to 60°C, and the reaction is kept for 3 h. After the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, and the reaction liquid is transferred to a rotary evaporator with a temperature of 80°C for vacuum distillation until no liquid is collected. Citryl chloride intermediate is obtained.

[0101] Step II, preparation of sulfonated citraconimidyl diacetic acid multi-dentate complex ligand

[0102] Weighing: 10.0 g of citryl chloride intermediate, 12.0 g of imine diacetic acid, 12.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile are added to the reaction kettle, and nitrogen protection is carried out, and the temperature is controlled at 5°C. 15.0 g of chlorosulfamide is added dropwise, the reaction kettle is heated to 35°C, and stirring is kept for 8 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction liquid is filtered to collect the filter cake, which is washed with ethyl acetate and deionized water for 5 times. The filter cake is transferred to a 80°C drying oven for vacuum drying until the weight is constant. Sulfonated citraconimidyl diacetic acid multi-dentate complex ligand is obtained.

[0103] Example 9

[0104] The embodiment provides a preparation method of a sulfonated citraconimidyl diacetic acid polydentate complex ligand for preparing high-conductivity carbon nanotubes, and comprises the following steps:

[0105] Step I, preparation of citraconyl chloride intermediate

[0106] Take 10.0 g of citric acid and 450.0 mL of anhydrous dichloromethane, stir and protect by introducing nitrogen, then drop 21.0 g of chlorosulfoxide and 3.0 mL of dimethylformamide, heat to 55 DEG C, and keep for 3 h, after the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, the reaction liquid is transferred to a rotary evaporator with a temperature of 80 DEG C, and is distilled under reduced pressure until no liquid is collected, and a citraconyl chloride intermediate is obtained.

[0107] Step II, preparation of sulfonated citraconimidyl diacetic acid polydentate complex ligand

[0108] Take 10.0 g of citraconyl chloride intermediate, 12.0 g of imine diacetic acid, 10.0 g of triethylamine and 300.0 mL of anhydrous acetonitrile into a reaction kettle, protect by introducing nitrogen, control the temperature at 3 DEG C, drop 13.5 g of chlorosulfamide, heat the reaction kettle to 30 DEG C, and keep stirring for 7 h, after the reaction is completed, the reaction kettle is cooled to room temperature, the reaction liquid is collected by filtration, the filter cake is washed with ethyl acetate and deionized water for 4 times, the filter cake is transferred to a 80 DEG C drying oven for vacuum drying until the weight is constant, and a sulfonated citraconimidyl diacetic acid polydentate complex ligand is obtained.

[0109] Example 10

[0110] The embodiment provides a preparation method of a sulfonated citraconimidyl diacetic acid polydentate complex ligand for preparing high-conductivity carbon nanotubes, and comprises the following steps:

[0111] Step I, preparation of citraconyl chloride intermediate

[0112] Take 10.0 g of citric acid and 450.0 mL of anhydrous dichloromethane, stir and protect by introducing nitrogen, then drop 21.0 g of chlorosulfoxide and 3.0 mL of dimethylformamide, heat to 55 DEG C, and keep for 3 h, after the reaction is completed, the temperature of the reaction kettle is reduced to room temperature, the reaction liquid is transferred to a rotary evaporator with a temperature of 80 DEG C, and is distilled under reduced pressure until no liquid is collected, and a citraconyl chloride intermediate is obtained.

[0113] Step II, preparation of sulfonated citraconimidyl diacetic acid polydentate complex ligand

[0114] Weighing: 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol and 10.0 g of quaternary ammonium chitosan oligosaccharide dispersant prepared in Example 4 are added to a high-speed shearing machine, the pH of the system is adjusted to 7.5 using sodium bicarbonate and stirred at a speed of 300 rpm for 10 min, then 20.0 g of oxidation intermediate is added, and the high-speed shearing machine is stirred at a speed of 8000 rpm for 2 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction solution is filtered to collect the filter cake, which is washed with ethyl acetate and deionized water for 3 times to obtain carbon nanotube wet material.

[0115] Step three, preparation of carbon nanotubes

[0116] Weighing: 300.0 mL of 98wt% sulfuric acid aqueous solution is added to a stirred tank, and after stirring, 100.0 mL of 65wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution are added along the stirred tank wall to obtain mixed acid;

[0117] Weighing: 20.0 g of carbon nanotube wet material and 300.0 mL of mixed acid are added to a reaction kettle, and after soaking at room temperature for 15 min, 2.0 sulfonated citraconimide diacetic acid polydentate complexing ligand prepared in Example 7 is added to the reaction kettle, and after stirring at room temperature for 10 min, the temperature of the reaction kettle is increased to 45℃, and the temperature is kept for 4 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction solution is filtered to collect the filter cake, which is washed with anhydrous ethanol and deionized water for 3 times to obtain a solid, which is then transferred to a 80℃ drying oven for vacuum drying to constant weight to obtain carbon nanotubes.

[0118] Example 11

[0119] The present embodiment provides a preparation method of sulfonated citraconimide diacetic acid polydentate complexing ligand for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0120] Step one, preparation of oxidation intermediate

[0121] Weighing: 0.3 g of hydroxamic acid precursor oxidant prepared in Example 2, 400.0 mL of anhydrous dichloromethane and 100.0 mL of anhydrous ethanol are mixed and sprayed onto 30.0 g of carbon nanotube and 10.0 g of melamine, and then placed at room temperature for 15 min. After pre-drying at 50℃ for 40 min, the mixture is transferred to a tube furnace, air is introduced at a rate of 800 mL / min, and the tube furnace is heated to 350℃ at a rate of 3℃ / min. After keeping the temperature for 4 h, the heating is stopped, and the furnace temperature is naturally cooled to 40℃. The material is taken out and passed through a 60 mesh sieve to obtain the oxidation intermediate.

[0122] Step two, preparation of carbon nanotube wet material

[0123] Weighing: 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol and 12.0 g of quaternary ammonium chitosan oligosaccharide dispersant prepared in Example 5 are added to a high-speed shearing machine, the pH of the system is adjusted to 7.5 using sodium bicarbonate and stirred at a speed of 300 rpm for 10 min, then 20.0 g of oxidation intermediate is added, and the high-speed shearing machine is stirred at a speed of 8000 rpm for 3 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction solution is filtered to collect the filter cake, which is washed with ethyl acetate and deionized water for 5 times to obtain carbon nanotube wet material.

[0124] Step three, preparation of carbon nanotubes

[0125] Weighing: 300.0 mL of 98wt% sulfuric acid aqueous solution is added to a stirred tank, and after stirring, 100.0 mL of 65wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution are added along the stirred tank wall to obtain mixed acid;

[0126] Weighing: 20.0 g of carbon nanotube wet material and 300.0 mL of mixed acid are added to a reaction kettle, and after soaking at room temperature for 20 min, 2.5 sulfonated citraconimide diacetic acid polydentate complexing ligand prepared in Example 8 is added to the reaction kettle, and after stirring at room temperature for 15 min, the temperature of the reaction kettle is increased to 50℃, and the stirring is continued for 6 h. After the reaction is completed, the reaction kettle is cooled to room temperature, the reaction solution is filtered to collect the filter cake, which is washed with anhydrous ethanol and deionized water for 5 times to obtain a solid, which is then transferred to a 80℃ drying oven for vacuum drying to constant weight to obtain carbon nanotubes.

[0127] Example 12

[0128] The present embodiment provides a preparation method of sulfonated citraconimide diacetic acid polydentate complexing ligand for preparing high-conductivity carbon nanotubes, comprising the following steps:

[0129] Step one, preparation of oxidation intermediate

[0130] Weighing: 0.3 g of hydroxamic acid precursor oxidant prepared in Example 3, 400.0 mL of anhydrous dichloromethane and 100.0 mL of anhydrous ethanol are mixed and sprayed onto 25.0 g of carbon nanotube and 10.0 g of melamine, and then the mixture is placed at room temperature for 15 min and pre-dried with hot air at 50℃ for 36 min. After pre-drying, the mixture is transferred to a tube furnace, air is introduced at a rate of 650 mL / min, and the tube furnace is heated to 350℃ at a heating rate of 3℃ / min, and then heated for 4 h. After heating is stopped, the furnace is naturally cooled to 40℃, the material is taken out and passed through a 60 mesh sieve to obtain the oxidation intermediate.

[0131] Step two, preparation of carbon nanotube wet material

[0132] Weighing: 2000.0 mL of deionized water, 500.0 mL of anhydrous ethanol and 12.0 g of quaternary ammonium chitosan oligosaccharide dispersant prepared in Example 6 are added to a high-speed shearing machine, the pH of the system is adjusted to 7.5 using sodium bicarbonate and stirred at a speed of 300 rpm for 10 min, then 20.0 g of oxidation intermediate is added, and the high-speed shearing machine is stirred at a speed of 8000 rpm for 3 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction solution is filtered to collect the filter cake, which is washed with ethyl acetate and deionized water for 4 times to obtain carbon nanotube wet material.

[0133] Step three, preparation of carbon nanotubes

[0134] Weighing: 300.0 mL of 98wt% sulfuric acid aqueous solution is added to a stirred tank, and after stirring, 100.0 mL of 65wt% nitric acid aqueous solution and 100.0 mL of 85% phosphoric acid aqueous solution are added along the stirred tank wall to obtain mixed acid;

[0135] Weighing: 20.0 g of carbon nanotube wet material and 300.0 mL of mixed acid are added to a reaction kettle, and after soaking at room temperature for 18 min, 2.4 sulfonated citraconimidyl diacetic acid polydentate complexing ligand prepared in Example 9 is added to the reaction kettle, and after stirring at room temperature for 12 min, the temperature of the reaction kettle is increased to 50℃, and the stirring is continued for 5 h. After the reaction is completed, the reaction kettle is cooled to room temperature, and the reaction solution is filtered to collect the filter cake, which is washed with anhydrous ethanol and deionized water for 4 times to obtain a solid, which is then transferred to a 80℃ drying oven for vacuum drying to constant weight to obtain carbon nanotubes.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 12 is that the hydroxamic acid precursor oxidant is not used in Step one.

[0138] Comparative Example 2

[0139] The difference between this comparative example and Example 12 is that the quaternary ammonium chitosan oligosaccharide dispersant used in Step two is prepared without Step ②.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 12 is that the sulfonated citraconimidyl diacetic acid polydentate complexing ligand is not used in Step three.

[0142] Performance test:

[0143] The slurry fineness and volume resistivity of the conductive paste prepared by using the carbon nanotubes prepared in Examples 10-12 and Comparative Examples 1-3 are tested according to the standard GB / T 33818-2017 "Carbon nanotube conductive paste".

[0144] The metal impurity element residual amount of the carbon nanotubes prepared by using Examples 10-12 and Comparative Examples 1-3 was tested according to the standard GB / T 35418-2017 “Nanotechnology-Determination of impurity elements in carbon nanotubes-Inductively coupled plasma mass spectrometry”; the specific data are shown in Table 1.

[0145]

[0146] Data analysis:

[0147] After comparing and analyzing the data in Table 1, it can be found that the metal impurity element residual amount of the carbon nanotubes prepared by the present application is 7.3 mg·kg -1 , and the volume resistivity is 0.080 Ω·cm -1 , which are all better than those of the comparative examples, which shows that:

[0148] In Comparative Example 1, the surface of the carbon nanotube bundle cannot be directionally oxidized and modified at a low temperature stage due to the lack of hydroxylamine acid precursor oxidant. The specific structure of hydroxylamine acid can selectively complex and oxidize the residual metal catalyst and amorphous carbon to generate oxides and oxygen-containing groups that are easy to be detached during the spraying and pre-baking process. The lack of hydroxylamine acid means that the surface defect activation is insufficient, the binding force between the metal particles and the carbon wall is still strong, and the subsequent mixed acid needs to rely on more severe etching to remove the metal, which is easy to cause structural damage. At the same time, the reduction of surface functionalization sites weakens the binding ability with the dispersant, making the electrostatic repulsion and hydrogen bond network between the tube bundles imperfect. 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 affected.

[0149] In Comparative Example 2, the dispersion system loses the strong electrostatic interaction between the cationic groups and the deprotonated carboxyl groups on the surface of the oxidized carbon tube after the lack of quaternary ammonium chitosan oligosaccharide. The quaternary ammonium group can form a dense and stable cationic adsorption layer during the dispersion process, which can inhibit the re-aggregation of the tube bundle through the electrostatic barrier and hydrogen bond, and can also weakly complex the metal ions in the solution to maintain its suspended state. The lack of this step makes the adsorption of the dispersant on the tube wall mainly rely on weak hydrogen bonds and hydrophobic interactions, which is insufficient in binding force. After the shear stops, the van der Waals interaction between the tube bundles can be restored, and the particles are easy to aggregate and settle. At the same time, the lack of effective traction of the metal ions in the dispersion medium makes them more likely to be deposited on the surface of the carbon tube during subsequent processing, resulting in a decrease in the uniformity of the system.

[0150] In Comparative Example 3, the sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand is absent, and the metal ions released during the mixed acid immersion process cannot be effectively chelated and stably embedded, and are extremely easy to re-deposit on the carbon nanotube defects, lumen or intersection sites before the pickling is completed. The sulfonated multi-site ligand can originally firmly pull the metal ions into the solution phase through the multiple coordination of the carboxyl, amide and sulfonamide groups, preventing their secondary combination with the carbon nanotube surface. The loss of this function forces the operator to rely on longer time or stronger acidic conditions to achieve the demetallization goal, and the result is often that the carbon nanotube wall structure is additionally etched, the aspect ratio is reduced, and the conductive path is damaged, so that the final sample purity and structural integrity are simultaneously damaged.

[0151] Finally, the present application uses hydroxamic acid precursor oxidants to mildly introduce active sites in the initial stage, creating conditions for subsequent functionalization and dispersion of carbon nanotubes. The quaternary ammonium chitosan dispersant achieves dispersion and metal ion traction of carbon nanotubes through a stable adsorption layer, maintaining the uniformity of the suspension system. The sulfonated citraconimidyl diacetic acid multi-dentate complexing ligand firmly locks the metal ions during pickling, preventing their secondary deposition on the carbon nanotube surface, while reducing structural damage caused by excessive etching. The order and ratio of the three are reasonably designed, forming a continuous and efficient chain of "pretreatment-dispersion-pickling", and the impurity removal and structure maintenance are balanced in a dynamic balance. The carbon nanotubes obtained finally exhibit excellent performance in purity, dispersity and continuity of conductive network, showing the significant advantages of systematic processing. This synergistic approach from source activation to end protection makes the overall process effect far superior to a single means, and provides a clear path for the controlled processing of carbon nanotubes.

[0152] The above content is merely an example and description of the structure of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific embodiments, as long as they do not deviate from the structure of the invention or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

[0153] In the description of the present application, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0154] The preferred embodiments of the application disclosed above are only to facilitate the elucidation of the application. The preferred embodiments do not describe all the details of the application and limit the application to the specific embodiments. Obviously, many modifications and variations can be made in light of the teachings above. The description is chosen and described in order to provide the best illustration of the application and its practical application to those skilled in the art and to enable those skilled in the art to utilize the application in its best mode. The application is only limited 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, soak at room temperature for 15-20 min, then add sulfonated citrate diacetic acid multidentate complex ligand to the reactor, stir at room temperature for 10-15 min, then raise the temperature of the reactor to 45-50℃, keep warm and stir for 4-6 h, and then obtain carbon nanotubes through post-treatment. 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 chloride 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 process to obtain the hydroxyoxime acid precursor oxidant. The preparation method of the sulfonated citric acid diacetic acid multidentate complex 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 sulfonated citrate diacetic acid multidentate complex ligand.

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 sulfonated citrate diacetic acid multidentate complexing 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 A1, the ratio of gallic acid, anhydrous dichloromethane, thionyl chloride, 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.

4. 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.

5. The method for preparing highly conductive carbon nanotubes according to claim 4, 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.

6. The method for preparing highly conductive carbon nanotubes according to claim 1, characterized in that, In step C1, the ratio of citric acid, anhydrous dichloromethane, thionyl chloride, 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.

7. 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 1-6.

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