Method for modifying surface of carbon nano tube

Abstract

The invention discloses a carbon nano tube surface modification method which comprises the following steps: S1, dispersing a carbon nano tube in a mixed acid solution to obtain an acidified carbon nano tube; s2, adding the acidified carbon nano tube into a Fenton reagent, so as to obtain a hydroxylated carbon nano tube; s3, mixing the hydroxylated carbon nanotube with a coupling agent to obtain a coupling agent modified carbon nanotube; s4, polymerizing on the surface of the coupling agent modified carbon nanotube to form a polydopamine layer to obtain a carbon nanotube precursor; and S5, carrying out acidification treatment on the carbon nano tube precursor to obtain the modified carbon nano tube. The modification method comprises the following steps: carrying out surface modification on a long-chain coupling agent, carrying out polymerization and wrapping on the surface modified with the long-chain coupling agent to form polydopamine, anchoring the modified coupling agent by a polydopamine layer, and finally partially decomposing the polydopamine through special acid treatment to expose active functional groups of the coupling agent, so as to obtain the polydopamine-modified coupling agent. The dispersion performance of the modified carbon nanotube in an organic phase is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanotube materials, and specifically to a method for surface modification of carbon nanotubes. Background Art

[0002] Carbon nanotubes (CNTs) are graphite sheets formed by the arrangement and curling of sp2 hybridized carbon atoms. They are one-dimensional tubular structures at the nanoscale with high modulus, high strength, and extremely excellent mechanical, electrical, and thermal properties. Based on these properties, carbon nanotubes are widely used as reinforcing agents for composite materials and are prepared by compounding with other materials to obtain composite materials. Among them, polymer-based composite materials prepared by compounding with polymer resins are widely used in dielectric materials, electromagnetic materials, and other fields due to their high dielectric constant. Due to the reinforcing effect of carbon nanotubes, the mechanical strength, glass transition temperature, and dielectric properties of polymer composites are improved to varying degrees. However, carbon nanotubes have a high aspect ratio and hydrophobicity, and a high surface energy, which leads to a strong self-agglomeration phenomenon of carbon nanotubes and makes it difficult to interact with other materials. The above problems have posed certain challenges to the widespread application of carbon nanotubes.

[0003] In order to improve the dispersion performance of carbon nanotubes, some surface modification methods for carbon nanotubes are described in the prior art, such as the modification methods described in references 1-3:

[0004] Reference 1: Chinese patent document with publication number CN112811413A

[0005] Reference 1 records a modification method of carbon nanotubes, modified carbon nanotubes and their applications. The modification method comprises the following steps: step 1, stirring the carboxyl carbon nanotubes and the acylation agent at -30 to 150°C for 1 to 100 hours, filtering, washing, and obtaining acylated carbon nanotubes; step 2, adding sucrose and its derivatives, solvents, and organic bases to the acylated carbon nanotubes, reacting at -30 to 120°C for 1 to 300 hours, filtering, washing, and drying to obtain modified carbon nanotubes. This method solves the problem of poor dispersibility of carbon nanotubes in aqueous systems and unstable dispersion solutions, and the modification process is simple and easy to operate, and is suitable for industrial production.

[0006] Reference 2: Chinese patent document with publication number CN105819417A

[0007] Reference 2 records a method for dispersing multi-walled carbon nanotubes by modifying them with a surfactant, wherein β-cyclodextrin is used as a surfactant to modify the self-made multi-walled carbon nanotubes, thereby achieving uniform dispersion of the multi-walled carbon nanotubes. The carbon nanotube particles in the solution become smaller and finer, presenting a uniform and stable black suspension. It can be seen from the transmission electron microscope image magnified 30,000 times that at the same magnification, the carbon nanotubes before modification are entangled and tangled. After modification with β-CD in this experiment, the carbon nanotube bundles distributed in the field of view are better dispersed.

[0008] Reference 3: Chinese patent document with publication number CN109052370A

[0009] Reference 3 records a method for surface modification of carbon nanotubes: (1) purifying untreated carbon nanotubes with Fenton's reagent; (2) calcining the carbon nanotubes treated in step (1) at high temperature to further purify them; (3) coating the carbon nanotubes treated in step (2) with polydopamine; (4) modifying the carbon nanotubes treated in step (3) with a coupling agent. The surface modification method of carbon nanotubes of the present invention coats the surface of the carbon nanotubes with polydopamine, and the outer layer of the polydopamine is adsorbed with a coupling agent, so that the carbon nanotubes can be stably dispersed in water or an organic solvent. Compared with the prior art, the dispersion performance of the carbon nanotubes can be improved without destroying their own structure, and the method has the advantages of simple operation, no toxic reagents involved, no pollution, and good dispersion effect. The method is applicable to both single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0010] References 1-3 all record technical solutions for improving the dispersion performance of carbon nanotubes by surface modification. However, the modification methods that can improve the dispersion performance of carbon nanotubes are not limited to the above technical ideas. Based on this, the applicant proposes a carbon nanotube surface modification method that is different from the prior art. Summary of the invention

[0011] The purpose of the present invention is to provide a method for surface modification of carbon nanotubes which has a technical concept different from that of the prior art.

[0012] In order to solve the above technical problems, the present invention adopts a technical solution: a method for surface modification of carbon nanotubes, comprising the following steps:

[0013] S1, uniformly dispersing carbon nanotubes in a mixed acid solution and subjecting the mixture to ultrasonic treatment, transferring the mixture to a water bath for stirring after the ultrasonic treatment, filtering out a solid phase from the mixed solution after the stirring treatment and washing the mixture to neutrality to obtain acidified carbon nanotubes for later use;

[0014] S2, adding the acidified carbon nanotubes to Fenton's reagent and ultrasonically treating the mixture, filtering out the solid phase from the ultrasonically treated mixture and washing it to neutrality, and drying it to obtain hydroxylated carbon nanotubes for later use;

[0015] S3, dispersing the hydroxylated carbon nanotubes in deionized water, adjusting the pH value to 8.0-9.0 and subjecting to ultrasonic stirring, after ultrasonic stirring, slowly adding the long-chain silane coupling agent to the mixed solution, stirring at room temperature, centrifuging and subjecting to a second ultrasonic treatment after the stirring treatment, and finally washing the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use;

[0016] S4, dispersing the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and subjecting the solution to ultrasonic treatment, adding dopamine hydrochloride and Tris buffer to the solution after the ultrasonic treatment, stirring the solution at room temperature, and after the stirring is completed, centrifuging and washing the solution to obtain a carbon nanotube precursor for later use;

[0017] S5, placing the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment, after the low-speed stirring treatment, transferring the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment, after the stirring is completed, centrifugally separating, washing and drying to obtain modified carbon nanotubes.

[0018] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the mixed acid solution in step S1 is a mixture of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1.

[0019] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the temperature of the water bath in step S1 is controlled at 40-45° C., and the stirring treatment is performed for 1-2 hours.

[0020] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the ultrasonic frequency of the ultrasonic treatment in step S2 is 20-25 kHz, the ultrasonic power is 300-400 W, and the ultrasonic time is 0.5-2 h.

[0021] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the Fenton reagent in step S2 is a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1.

[0022] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the long-chain silane coupling agent in step S3 is a long-chain quaternary ammonium salt organic silane coupling agent or a long-chain alkane silane coupling agent.

[0023] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: in the step S3, the long-chain silane coupling agent is 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride, 3-(trimethoxysilyl)propyldimethyldodecylammonium chloride, tridecafluorooctyltrimethoxysilane, hexadecyltrimethoxysilane or octadecyltriethoxysilane.

[0024] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: in step S4, Tris buffer is added to make the pH value of the mixed solution reach 8.5-9.0.

[0025] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the dilute acid in step S5 is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 20-35%, the rotation speed of the low-speed stirring is controlled to 500-800 r / min, and the stirring time is 30-60 min.

[0026] As a further optimization of the method for surface modification of carbon nanotubes of the present invention: the concentrated acid in step S5 is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 95-98%, the speed of high-speed stirring is controlled to be 2000-3000r / min, and the stirring time is 5-10min.

[0027] The invention has the following beneficial effects: the modification method of the invention is to firstly perform surface modification of a long-chain coupling agent, then polymerize and wrap the surface modified with the long-chain coupling agent to form polydopamine, the polydopamine layer can also anchor the modified coupling agent, and finally partially decompose the polydopamine through special acid treatment to expose the active functional groups of the coupling agent, thereby obtaining modified carbon nanotubes, whose dispersion performance in an organic phase is significantly improved. DETAILED DESCRIPTION

[0028] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0029] A method for surface modification of carbon nanotubes comprises the following steps:

[0030] S1. Dispersing carbon nanotubes uniformly in a mixed acid solution and subjecting the mixture to ultrasonic treatment. After the ultrasonic treatment, the mixture is transferred to a water bath for stirring. The solid phase is filtered out of the mixed solution after stirring and washed to neutrality to obtain acidified carbon nanotubes for later use.

[0031] The mixed acid solution is a mixture of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1.

[0032] The temperature of the water bath is controlled at 40-45°C, and the stirring treatment is performed for 1-2 hours.

[0033] S2. Add the acidified carbon nanotubes into Fenton's reagent and perform ultrasonic treatment. Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained for later use.

[0034] The ultrasonic frequency of the ultrasonic treatment is 20-25kHz, the ultrasonic power is 300-400W, and the ultrasonic time is 0.5-2h.

[0035] Among them, Fenton's reagent is a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1.

[0036] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.0-9.0 and perform ultrasonic stirring. After the ultrasonic stirring, slowly add the long-chain silane coupling agent to the mixture and stir at room temperature. After the stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0037] The long-chain silane coupling agent is a long-chain quaternary ammonium salt organic silane coupling agent or a long-chain alkane silane coupling agent, and specifically can be: 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride, 3-(trimethoxysilyl)propyldimethyldodecylammonium chloride, tridecafluorooctyltrimethoxysilane, hexadecyltrimethoxysilane or octadecyltriethoxysilane.

[0038] S4. Disperse the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 8.5-9.0) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0039] S5, placing the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment, after the low-speed stirring treatment, transferring the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment, after the stirring is completed, centrifugally separating, washing and drying to obtain modified carbon nanotubes.

[0040] The dilute acid is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 20-35%, the rotation speed of the low-speed stirring is controlled to be 500-800r / min, and the stirring time is 30-60min.

[0041] The concentrated acid is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 95-98%, the rotation speed of the high-speed stirring is controlled to be 2000-3000r / min, and the stirring time is 5-10min.

[0042] Example 1

[0043] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 42°C and the stirring treatment is performed for 1.5 hours). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0044] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 22 kHz, ultrasonic power is 350 W, and ultrasonic time is 1 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained for later use.

[0045] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.5 and perform ultrasonic stirring. After ultrasonic stirring, slowly add a long-chain silane coupling agent (3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride) into the mixture and stir at room temperature. After stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0046] S4. Disperse the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 8.8) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0047] S5. Place the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment (the dilute acid is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 30%, the speed of low-speed stirring is controlled to 600r / min, and the stirring time is 45min). After the low-speed stirring treatment, transfer the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment (the concentrated acid is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 97%, the speed of high-speed stirring is controlled to 2500r / min, and the stirring time is 6min). After the stirring is completed, centrifugal separation, washing and drying are performed to obtain the modified carbon nanotubes.

[0048] Example 2

[0049] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 40°C and the stirring treatment is performed for 2 hours). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0050] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 20 kHz, ultrasonic power is 400 W, and ultrasonic time is 0.5 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained for later use.

[0051] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 9.0 and perform ultrasonic stirring. After ultrasonic stirring, slowly add a long-chain silane coupling agent (3-(trimethoxysilyl)propyldimethyldodecylammonium chloride) into the mixture and stir at room temperature. After stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0052] S4. Disperse the coupling agent-modified carbon nanotubes in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 8.5) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0053] S5. Place the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment (the dilute acid is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 35%, the speed of low-speed stirring is controlled to be 500r / min, and the stirring time is 60min). After the low-speed stirring treatment, transfer the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment (the concentrated acid is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 95%, the speed of high-speed stirring is controlled to be 3000r / min, and the stirring time is 5min). After the stirring is completed, centrifugal separation, washing and drying are performed to obtain the modified carbon nanotubes.

[0054] Example 3

[0055] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 45°C and the stirring treatment is performed for 1 hour). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0056] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 25 kHz, ultrasonic power is 300 W, and ultrasonic time is 2 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained and set aside.

[0057] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.0 and perform ultrasonic stirring. After ultrasonic stirring, slowly add a long-chain silane coupling agent (tridecafluorooctyltrimethoxysilane) into the mixture and stir at room temperature. After stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0058] S4. Disperse the coupling agent-modified carbon nanotubes in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 9.0) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0059] S5. Place the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment (the dilute acid is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 20%, the speed of low-speed stirring is controlled to 800r / min, and the stirring time is 30min). After the low-speed stirring treatment, transfer the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment (the concentrated acid is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 98%, the speed of high-speed stirring is controlled to 2000r / min, and the stirring time is 10min). After the stirring is completed, centrifugal separation, washing and drying are performed to obtain the modified carbon nanotubes.

[0060] Example 4

[0061] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 40°C and the stirring treatment is performed for 1 hour). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0062] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 25 kHz, ultrasonic power is 400 W, and ultrasonic time is 1 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained and set aside.

[0063] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.5 and perform ultrasonic stirring. After the ultrasonic stirring, slowly add the long-chain silane coupling agent (octadecyltriethoxysilane) into the mixture and stir at room temperature. After the stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0064] S4. Disperse the coupling agent-modified carbon nanotubes in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 9.0) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0065] S5. Place the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment (the dilute acid is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 25%, the speed of low-speed stirring is controlled to 600r / min, and the stirring time is 35min). After the low-speed stirring treatment, transfer the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment (the concentrated acid is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 98%, the speed of high-speed stirring is controlled to 2200r / min, and the stirring time is 7min). After the stirring is completed, centrifugal separation, washing and drying are performed to obtain the modified carbon nanotubes.

[0066] Comparative Example 1

[0067] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 42°C and the stirring treatment is performed for 1.5 hours). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0068] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 22 kHz, ultrasonic power is 350 W, and ultrasonic time is 1 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained for later use.

[0069] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.5 and perform ultrasonic stirring. After ultrasonic stirring, slowly add a long-chain silane coupling agent (3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride) into the mixture and stir at room temperature. After stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0070] S4. Disperse the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 8.8) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0071] Comparative Example 2

[0072] S1. Disperse the carbon nanotubes uniformly in a mixed acid solution (the mixed acid solution is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:1) and perform ultrasonic treatment. After the ultrasonic treatment, transfer to a water bath for stirring treatment (the temperature of the water bath is controlled at 42°C and the stirring treatment is performed for 1.5 hours). After the stirring treatment, filter out the solid phase from the mixed solution and wash it to neutrality to obtain acidified carbon nanotubes for standby use.

[0073] S2. Add the acidified carbon nanotubes to Fenton's reagent (a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:1) and ultrasonically treat the mixture (ultrasonic frequency is 22 kHz, ultrasonic power is 350 W, and ultrasonic time is 1 h). Filter the solid phase from the mixed solution after ultrasonic treatment and wash it to neutrality. After drying, hydroxylated carbon nanotubes are obtained for later use.

[0074] S3. Disperse the hydroxylated carbon nanotubes in deionized water, adjust the pH value to 8.5 and perform ultrasonic stirring. After ultrasonic stirring, slowly add a long-chain silane coupling agent (3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride) into the mixture and stir at room temperature. After stirring, centrifuge and perform a second ultrasonic treatment. Finally, rinse the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use.

[0075] S4. Disperse the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and perform ultrasonic treatment. After the ultrasonic treatment, add dopamine hydrochloride and Tris buffer solution (the pH value of the mixed solution reaches 8.8) to the solution, stir at room temperature, and after the stirring is completed, centrifuge and wash to obtain a carbon nanotube precursor for use.

[0076] S5. placing the carbon nanotube precursor in a concentrated acid solution for high-speed stirring treatment (the concentrated acid is a concentrated sulfuric acid solution with a concentration of 97%, the speed of high-speed stirring is controlled to be 2500r / min, and the stirring time is 6min). After the stirring is completed, the modified carbon nanotubes are obtained by centrifugal separation, washing and drying.

[0077] <Dispersion Test>

[0078] The carbon nanotubes prepared in Examples 1-4 and Comparative Examples 1-2 were dispersed in ethanol to prepare a 0.03 mg / ml dispersion. The absorbance of the dispersion was characterized by a UV-visible spectrometer. The results are as follows: Experimental Group Absorbance (au) Example 1 0.625 Example 2 0.618 Example 3 0.588 Example 4 0.606 Comparative Example 1 0.456 Comparative Example 2 0.515

[0079] From the results in the above table, it can be seen that the dispersion performance of the modified carbon nanotubes prepared in Examples 1-4 is significantly better than that of Comparative Examples 1 and 2. The applicant believes that this is due to the special modification method of the present invention, which first modifies the surface of the long-chain coupling agent, and then polymerizes and wraps the surface modified with the long-chain coupling agent to form polydopamine. The polydopamine layer can also anchor the modified coupling agent. Finally, the polydopamine is partially decomposed by a special acid treatment to expose the active functional groups of the coupling agent, thereby obtaining modified carbon nanotubes, which have significantly improved dispersion performance in the organic phase. Comparative Example 1 did not perform the final acid treatment, resulting in most of the active functional groups of the coupling agent being wrapped, and failed to achieve the corresponding modification effect. Comparative Example 2 did not perform a dilute acid treatment before the concentrated acid treatment, resulting in a reduced effect of the acid treatment.

[0080] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for surface modification of carbon nanotubes, characterized in that: The following steps are involved: S1, uniformly dispersing carbon nanotubes in a mixed acid solution and subjecting the mixture to ultrasonic treatment, transferring the mixture to a water bath for stirring after the ultrasonic treatment, filtering out a solid phase from the mixed solution after the stirring treatment and washing the mixture to neutrality to obtain acidified carbon nanotubes for later use; S2, adding the acidified carbon nanotubes to Fenton's reagent and ultrasonically treating the mixture, filtering out the solid phase from the ultrasonically treated mixture and washing it to neutrality, and drying it to obtain hydroxylated carbon nanotubes for later use; S3, dispersing the hydroxylated carbon nanotubes in deionized water, adjusting the pH value to 8.0-9.0 and subjecting to ultrasonic stirring, after ultrasonic stirring, slowly adding the long-chain silane coupling agent to the mixed solution, stirring at room temperature, centrifuging and subjecting to a second ultrasonic treatment after the stirring treatment, and finally washing the precipitate with water and ethanol to obtain carbon nanotubes modified with the coupling agent for later use; S4, dispersing the carbon nanotubes modified with the coupling agent in a beaker of anhydrous ethanol and performing ultrasonic treatment, adding dopamine hydrochloride and Tris buffer to the solution after the ultrasonic treatment, stirring at room temperature, and after the stirring is completed, centrifuging and washing to obtain a carbon nanotube precursor for standby use; S5, placing the carbon nanotube precursor in a dilute acid solution for low-speed stirring treatment, after the low-speed stirring treatment, transferring the carbon nanotube precursor to a concentrated acid solution for high-speed stirring treatment, after the stirring is completed, centrifugally separating, washing and drying to obtain modified carbon nanotubes.

2. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: The mixed acid solution in step S1 is a mixed solution of sulfuric acid and nitric acid, the concentration of sulfuric acid is 98%, the concentration of nitric acid is 65%, and the volume ratio of sulfuric acid to nitric acid is 3:

1.

3. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: In step S1, the temperature of the water bath is controlled at 40-45° C., and the stirring treatment is performed for 1-2 hours.

4. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: The ultrasonic frequency of the ultrasonic treatment in step S2 is 20-25 kHz, the ultrasonic power is 300-400 W, and the ultrasonic time is 0.5-2 h.

5. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: In step S2, the Fenton reagent is a mixture of hydrogen peroxide and ferrous sulfate in a mass ratio of 5:

1.

6. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: In step S3, the long-chain silane coupling agent is a long-chain quaternary ammonium salt organic silane coupling agent or a long-chain alkane silane coupling agent.

7. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: In step S3, the long-chain silane coupling agent is 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride, 3-(trimethoxysilyl)propyldimethyldodecylammonium chloride, tridecafluorooctyltrimethoxysilane, hexadecyltrimethoxysilane or octadecyltriethoxysilane.

8. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: In step S4, Tris buffer is added to make the pH value of the mixed solution reach 8.5-9.

0.

9. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: The dilute acid in step S5 is a dilute nitric acid solution, the concentration of the dilute nitric acid solution is 20-35%, the rotation speed of the low-speed stirring is controlled to be 500-800 r / min, and the stirring time is 30-60 min.

10. A method for surface modification of carbon nanotubes as claimed in claim 1, characterized in that: The concentrated acid in step S5 is a concentrated sulfuric acid solution, the concentration of the concentrated sulfuric acid solution is 95-98%, the speed of high-speed stirring is controlled to be 2000-3000r / min, and the stirring time is 5-10min.