Preparation method of aqueous single-walled carbon nanotube dispersion liquid

Abstract

The invention belongs to the technical field of carbon nanotube dispersion, and particularly relates to a preparation method of a water-based single-walled carbon nanotube dispersion liquid. The preparation method comprises the following steps: adding a single-walled carbon nanotube into an organic solvent, uniformly stirring, carrying out dispersion treatment, adding a first surfactant into the obtained pretreated slurry A, uniformly stirring, carrying out ultrasonic dispersion to obtain slurry B, carrying out vacuum filtration on the slurry B, washing, and baking a collected filter cake to obtain the single-walled carbon nanotube composite material. The single-walled carbon nanotube C, a second surfactant and water are subjected to dispersion treatment, and the carbon nanotube adsorption material is obtained. The water-insoluble first surfactant is introduced to form a dry powder intermediate, so that secondary agglomeration is effectively inhibited, efficient and stable dispersion is realized while the structural integrity of the carbon nanotubes is maintained, and the preparation process is simple and suitable for industrial popularization and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon nanotube dispersion, and particularly relates to a preparation method of an aqueous single-walled carbon nanotube dispersion liquid. BACKGROUND

[0002] Single-walled carbon nanotubes are one-dimensional tubular nanomaterials of single-layer graphene curling. Since their discovery, they have attracted widespread attention due to their unique and excellent performance in optics, electricity and mechanics. Single-walled carbon nanotubes have shown excellent application performance and potential in the fields of memory, biosensors, optical elements, batteries and composite materials. However, due to the one-dimensional structural characteristics of single-walled carbon nanotubes, such as large specific surface area, large aspect ratio and strong intermolecular force between carbon nanotubes, the state of single-walled carbon nanotubes is mostly in the form of bundled aggregates, which is difficult to disperse, greatly restricting the exertion of their excellent performance and practical application. Therefore, the dispersion of single-walled carbon nanotubes has been an important technical issue of concern for scientists and business people.

[0003] Like multi-walled carbon nanotubes, the preparation method of the aqueous dispersion liquid of single-walled carbon nanotubes mainly includes physical modification of non-covalent coating and chemical modification of covalent modification. Non-covalent coating mainly uses PVP, NaCMC, sodium polystyrene sulfonate, conjugated molecule-containing polymers and other substances as dispersants, and uses sand milling, high-frequency ultrasonic, high-pressure homogenization and high-pressure microjet for mechanical shearing treatment, so as to obtain a single-walled carbon nanotube dispersion liquid. This method needs high-energy external force shearing because the dispersant is a rigid macromolecular substance and has poor wetting ability for single-walled carbon nanotubes. Therefore, this method often cuts and breaks single-walled carbon nanotubes, which destroys the advantage of the aspect ratio of single-walled carbon nanotubes. Covalent modification mainly uses strong alkali, strong acid and strong oxidizing substances to etch the surface of single-walled carbon nanotubes to produce hydrophilic groups, so as to obtain a dispersion liquid. However, this method has a certain destructive effect on the structure of single-walled carbon nanotubes, which affects the mechanical and electrical properties of carbon nanotubes, thereby affecting the use and application fields of carbon nanotubes.

[0004] In view of the above problems, some researchers use m-cresol, chlorosulfonic acid, strong polar solvents and the like to wet, dissolve and disperse the single-walled carbon nanotube bundles, or further use small molecular weight polymers in the form of polymer grafting to disperse the single-walled carbon nanotube bundles. This method can disperse the single-walled carbon nanotube bundles while retaining the one-dimensional structure of the single-walled carbon nanotubes with high aspect ratio to the greatest extent, but has the problems of long polymerization reaction process and secondary aggregation in the process of filtration and drying.

[0005] Therefore, it is urgent to provide a preparation method of an aqueous single-walled carbon nanotube dispersion liquid to solve the above problems. SUMMARY

[0006] Based on the above technical background, the main objective of this invention is to provide a method for preparing an aqueous single-walled carbon nanotube dispersion. This method, while maintaining the integrity of the single-walled carbon nanotubes as much as possible, solves the shortcomings of complex processes such as filtration, drying, secondary aggregation, and graft polymerization, and obtains an aqueous single-walled carbon nanotube dispersion with simple preparation process and high dispersibility, thus overcoming the deficiencies in the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The first aspect of this invention is to provide a method for preparing an aqueous single-walled carbon nanotube dispersion, the method comprising the following steps: Step 1: Add single-walled carbon nanotubes to an organic solvent, stir until homogeneous, and then disperse to obtain pretreated slurry A; Step 2: Add the first surfactant to the pretreated slurry A, stir evenly, and then disperse ultrasonically to obtain slurry B; Step 3: After vacuum filtration of slurry B, wash it and bake the collected filter cake to obtain single-walled carbon nanotubes C adsorbed with the first surfactant. Step 4: Stir the single-walled carbon nanotubes C, the second surfactant, and water evenly, and then disperse them to obtain an aqueous single-walled carbon nanotube dispersion.

[0008] The steps described above are described in detail below.

[0009] In step 1, the mass ratio of the single-walled carbon nanotubes to the organic solvent is (0.05-0.2):(99.5-99.99).

[0010] Preferably, the mass ratio of the single-walled carbon nanotubes to the organic solvent is 0.1:99.8.

[0011] The organic solvent is miscible with water and has good affinity with carbon nanotubes.

[0012] The organic solvent is selected from one or more of N,N-dimethylpyrrolidone (NMP), N,N-dimethylformamide, formamide, N,N-dimethylacetamide, acetamide, and acetonitrile.

[0013] Preferably, the organic solvent is N,N-dimethylpyrrolidone (NMP) or formamide.

[0014] The dispersion treatment conditions are: dispersion treatment for 30 to 60 minutes at an ultrasonic power of 100 to 200 W.

[0015] Preferably, the dispersion treatment conditions are: dispersion treatment for 40 min at an ultrasonic power of 150 W.

[0016] In step 2, the mass ratio of the first surfactant to the pretreated slurry A is (0.05~0.2):(99.5~100).

[0017] Preferably, the mass ratio of the first surfactant to the pretreated slurry A is 0.1:99.9.

[0018] The first surfactant is selected from one or more of Span 80, Span 60, and Span 20.

[0019] Preferably, the first surfactant is Span 80.

[0020] This invention involves coating single-walled carbon nanotubes with a water-insoluble first surfactant before the removal of organic solvents, forming a stable dry powder intermediate after drying. The physical protective layer formed by the first surfactant effectively prevents the single-walled carbon nanotubes from re-contacting due to the loss of solvent support during the removal of organic solvents and drying process, thereby significantly inhibiting the secondary aggregation of single-walled carbon nanotubes. Finally, with the assistance of a water-soluble second surfactant, a high-quality aqueous dispersion with uniform dispersion and high stability is obtained.

[0021] The conditions for ultrasonic dispersion are: ultrasonic dispersion for 10 to 30 minutes at an ultrasonic power of 100 to 200 W.

[0022] Preferably, the ultrasonic dispersion conditions are: ultrasonic dispersion for 20 min at an ultrasonic power of 150 W.

[0023] This invention employs relatively gentle physical dispersion methods such as low-power ultrasound and high-pressure homogenization throughout the process, avoiding the damage to the aspect ratio of single-walled carbon nanotubes caused by high-energy shearing and the damage to the conjugated structure on the surface of carbon nanotubes caused by chemical modification, thereby preserving the inherent excellent properties of single-walled carbon nanotubes to the greatest extent.

[0024] In step 3, the conditions for vacuum filtration are: vacuum filtration of slurry B using a microporous filter membrane.

[0025] Preferably, the vacuum filtration conditions are as follows: vacuum filtration of slurry B is performed using a microporous filter membrane with a pore size of 15 μm.

[0026] After vacuum filtration of slurry B, it is washed multiple times with deionized water until the filtrate becomes clear.

[0027] The baking conditions are: baking at 100–140°C for 5–15 minutes.

[0028] Preferably, the baking conditions are: baking at 120°C for 10 minutes.

[0029] In step 4, the mass ratio of the single-walled carbon nanotube C, the second surfactant, and water is (0.5-1):(0.5-1):(98-99).

[0030] Preferably, the mass ratio of the single-walled carbon nanotubes C, the second surfactant, and water is 0.8:0.8:98.4.

[0031] The second surfactant is selected from one or more of Tween 80, Tween 60, Tween 20, and tallow amine polyoxyethylene ether.

[0032] Preferably, the second surfactant is Tween 80 or tallow amine polyoxyethylene ether.

[0033] The conditions for the dispersion treatment are: the dispersion treatment pressure is 200-400 bar, and the dispersion treatment is performed 4-8 times.

[0034] Preferably, the conditions for the dispersion treatment are: a dispersion treatment pressure of 300 bar and a dispersion treatment number of 5 times.

[0035] This invention utilizes the synergistic effect of two surfactants to construct a smooth transition path from the organic phase to the aqueous phase. The process flow is clear and simple, easy to operate and scale up for production. Furthermore, by preparing a stable dry powder intermediate, it facilitates product storage, transportation, and subsequent use, demonstrating excellent industrial applicability.

[0036] A second aspect of the present invention is to provide an aqueous single-walled carbon nanotube dispersion prepared by the preparation method described in the first aspect of the present invention.

[0037] The beneficial effects of this invention are as follows: (1) The present invention uses a small molecule organic solvent and a flexible first surfactant that have strong affinity, wetting and penetrating power for single-walled carbon nanotubes, and uses low power and low pressure to treat single-walled carbon nanotubes. While breaking up the single-walled carbon nanotube bundles, the one-dimensional structure of the single-walled carbon nanotubes with high aspect ratio is preserved to the maximum extent.

[0038] (2) This invention utilizes the adsorption and encapsulation properties of the first surfactant to avoid secondary aggregation of single-walled carbon nanotubes during filtration and drying. Moreover, the first surfactant has poor solubility in water, and during water washing, it can be more firmly adsorbed onto the surface of single-walled carbon nanotubes through phase change, thus weakening the intermolecular forces between the single-walled carbon nanotubes. At the same time, the second surfactant has a good compatibilizing effect on the first surfactant. Adding the second surfactant to the aqueous solution allows for the preparation of highly dispersed single-walled carbon nanotube dispersions under relatively low homogenization pressure. Attached Figure Description

[0039] Figure 1 SEM images of single-walled carbon nanotube powder before treatment are shown; Figure 2 SEM images of the single-walled carbon nanotube dispersion prepared in Example 1 are shown. Figure 3 SEM images of the single-walled carbon nanotube dispersion prepared in Example 2 are shown. Figure 4 SEM images of the single-walled carbon nanotube dispersion prepared in Example 3 are shown. Figure 5 SEM images of the single-walled carbon nanotube dispersion prepared in Example 4 are shown. Figure 6 SEM images of the single-walled carbon nanotube dispersion prepared in Example 5 are shown. Figure 7 SEM images of the single-walled carbon nanotube dispersion prepared in Comparative Example 1 are shown. Figure 8 The image shows a SEM image of the single-walled carbon nanotube dispersion prepared in Comparative Example 2. Detailed Implementation

[0040] The present invention will now be described in detail, and its features and advantages will become clearer and more apparent from these descriptions.

[0041] Example The present invention is further illustrated below with specific examples. These embodiments are merely illustrative and not intended to limit the scope of the invention. All raw materials used in the embodiments of the present invention are commercially available.

[0042] Example 1 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of NMP (N-methylpyrrolidone). Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 40 min to obtain pretreated slurry A.

[0043] Weigh 0.1 g of the first surfactant Span 80 and add it to slurry A. Stir well and continue ultrasonic dispersion for 20 min. The ultrasonic dispersion power is 150 W to obtain slurry B.

[0044] Slurry B was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water until the filtrate was clear. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C adsorbed with the first surfactant.

[0045] Weigh 0.8 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant Tween 80, and 98.4 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion.

[0046] Example 2 Weigh 0.2 g of single-walled carbon nanotubes and add them to 99.6 g of NMP. Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 50 min to obtain pretreated slurry A.

[0047] Weigh 0.2 g of the first surfactant Span 80 and add it to slurry A. Stir well and continue ultrasonic dispersion for 20 min. The ultrasonic dispersion power is 150 W to obtain slurry B.

[0048] Slurry B was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water until the filtrate was clear. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C adsorbed with the first surfactant.

[0049] Weigh 0.8 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant Tween 80 and 98.4 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Example 3 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of formamide. Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 40 min to obtain pretreated slurry A.

[0050] Weigh 0.1 g of the first surfactant Span 80 and add it to slurry A. Stir well and continue ultrasonic dispersion for 20 min. The ultrasonic dispersion power is 150 W to obtain slurry B.

[0051] Slurry B was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water until the filtrate was clear. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C adsorbed with the first surfactant.

[0052] Weigh 0.8 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant Tween 80 and 98.4 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Example 4 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of formamide. Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 40 min to obtain pretreated slurry A.

[0053] Weigh 0.1 g of the first surfactant Span 80 and add it to slurry A. Stir well and continue ultrasonic dispersion for 20 min. The ultrasonic dispersion power is 150 W to obtain slurry B.

[0054] Slurry B was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water until the filtrate was clear. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C adsorbed with the first surfactant.

[0055] Weigh 0.8 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant tallow amine NE-1815, and 98.4 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Example 5 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of NMP. Stir well and disperse using a 20 KH ultrasonic disperser at a power of 150 W for 40 min to obtain pretreated slurry A.

[0056] Weigh 0.1 g of the first surfactant Span 60 and add it to slurry A. Stir well and continue ultrasonic dispersion for 20 min at a power of 150 W to obtain slurry B.

[0057] Slurry B was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water until the filtrate was clear. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C adsorbed with the first surfactant.

[0058] Weigh 0.8 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant Tween 60 and 98.4 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Comparative Example Comparative Example 1 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of NMP. Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 60 min to obtain pretreated slurry A.

[0059] Slurry A was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C.

[0060] Weigh 0.4 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant Tween 80 and 98.8 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Comparative Example 2 Weigh 0.1 g of single-walled carbon nanotubes and add them to 99.8 g of formamide. Stir well and disperse using a 20 KH ultrasonic disperser with a power of 150 W for 60 min to obtain pretreated slurry A.

[0061] Slurry A was vacuum filtered using a microporous membrane with a pore size of 15 μm and washed multiple times with deionized water. The filter cake was collected and baked at 120℃ for 10 min to obtain single-walled carbon nanotubes C.

[0062] Weigh 0.4 g of single-walled carbon nanotubes C, 0.8 g of the second surfactant tallow amine NE-1815, and 98.8 g of deionized water by weight, stir evenly, and then disperse using a high-pressure homogenizer at a pressure of 300 bar for 5 times to obtain an aqueous single-walled carbon nanotube dispersion. Experimental Example Experiment Example 1: SEM Testing Scanning electron microscopy (SEM) tests were performed on untreated single-walled carbon nanotube powder, single-walled carbon nanotube dispersions prepared in Examples 1-5, Comparative Examples 1 and 2, respectively. The test results are shown below. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5, Figure 6 , Figure 7 and Figure 8 As shown.

[0063] from Figure 1 It can be seen that the single-walled carbon nanotube powder exhibits aggregates of large filament bundles, with the carbon nanotubes intertwined and aggregated. From Figures 2-6 It can be seen that the carbon nanotubes in the single-walled carbon nanotube dispersions prepared in Examples 1 to 5 are uniformly dispersed in the dispersion, and more than 95% maintain a single dispersed state, thus retaining a one-dimensional structure with a high aspect ratio. Figure 7 and Figure 8 It can be seen that the carbon nanotubes in the dispersion are severely entangled, with large filament bundles, and are not effectively dispersed. These results indicate that ultrasonic dispersion of the pretreated slurry A with the first surfactant helps improve the dispersion uniformity of single-walled carbon nanotubes in the dispersion, and also helps maintain the integrity of the single-walled carbon nanotubes in the dispersion. These results demonstrate that the single-walled carbon nanotube dispersion prepared by the method described in this invention has the advantage of high dispersion uniformity and exhibits a one-dimensional structure with a high aspect ratio.

[0064] Experimental Example 2: Viscosity Test Viscosity tests were conducted on the aqueous single-walled carbon nanotube dispersions prepared in Examples 1-5 and Comparative Examples 1-2, respectively. The test conditions were as follows: the viscosity of the aqueous carbon nanotube dispersions before and after being placed at room temperature (25±1℃) for 2 weeks was measured using a Brookfield viscometer (rotor No. 6). The comparative data are shown in Table 1.

[0065] Table 1. Viscosities of aqueous carbon nanotube dispersions before and after 2 weeks of storage.

[0066] The data in Table 1 show that the viscosity of the aqueous single-walled carbon nanotube dispersions prepared in Examples 1-5 is 695-1007 cp (lower viscosity indicates better dispersibility). After 14 days, the viscosity increases to 853-1362 cp. The viscosity of the aqueous single-walled carbon nanotube dispersions prepared in Comparative Examples 1-2 is 1893-1908 cp. After 14 days, the viscosity increases to 3505-3563 cp. The comparison shows that the viscosity of the aqueous single-walled carbon nanotube dispersions prepared in Examples 1-5 is much lower than that of Comparative Examples 1-2. Moreover, after 14 days, the increase in viscosity of Examples 1-5 is also much lower than that of Comparative Examples 1-2 (a lower increase in viscosity indicates better stability).

[0067] The above results show that the dispersion degree of the carbon nanotube dispersions prepared in Examples 1-5 is much higher than that in Comparative Examples 1-2, and the stability of the carbon nanotube dispersions prepared in Examples 1-5 is also much higher than that in Comparative Examples 1-2. This indicates that adding a poorly water-soluble first surfactant to the pretreated slurry A can better pre-disperse the single-walled carbon nanotubes, resulting in a low-viscosity, stable aqueous single-walled carbon nanotube dispersion. In contrast, the aqueous carbon nanotube dispersions obtained in Comparative Examples 1 and 2 have high viscosity and poor storage stability due to the lack of a pre-dispersion step with the first surfactant.

[0068] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for producing an aqueous single-walled carbon nanotube dispersion, characterized by, The preparation method comprises the following steps: Step 1, adding single-walled carbon nanotubes into an organic solvent, stirring uniformly, and then performing a dispersion treatment to obtain a pretreatment slurry A; Step 2, adding a first surfactant into the pretreatment slurry A, stirring uniformly, and then performing an ultrasonic dispersion to obtain a slurry B; Step 3, after vacuum filtration of the slurry B, performing a washing, and baking the collected filter cake to obtain single-walled carbon nanotubes C adsorbed with the first surfactant; Step 4, stirring the single-walled carbon nanotubes C, a second surfactant and water uniformly, and then performing a dispersion treatment to obtain an aqueous single-walled carbon nanotube dispersion.

2. The production method according to claim 1, characterized by, In step 1, The mass ratio of the single-walled carbon nanotubes to the organic solvent is (0.05-0.2):(99.5-99.99).

3. The preparation method according to claim 1, characterized in that, In step 1, The organic solvent is selected from one or more of N,N-dimethylpyrrolidone (NMP), N,N-dimethylformamide, formamide, N,N-dimethylacetamide, acetamide and acetonitrile.

4. The production method according to claim 1, characterized by, In step 1, The dispersion treatment is performed under an ultrasonic power of 100-200 W for 30-60 min.

5. The preparation method according to claim 1, characterized in that, In step 2, The mass ratio of the first surfactant to the pretreatment slurry A is (0.05-0.2):(99.5-100).

6. The method of claim 1, wherein, In step 2, The first surfactant is selected from one or more of Span 80, Span 60 and Span 20.

7. The preparation method according to claim 1, characterized in that, In step 2, The ultrasonic dispersion is performed under an ultrasonic power of 100-200 W for 10-30 min.

8. The method of claim 1, wherein, In step 3, The baking is performed at 100-140℃ for 5-15 min.

9. The method of claim 1, wherein, In step 4, The mass ratio of the single-walled carbon nanotubes C, the second surfactant and water is (0.5-1):(0.5-1):(98-99); and / or, The second surfactant is selected from one or more of Tween 80, Tween 60, Tween 20 and a polyoxyethylene lauryl ether; and / or, The dispersion treatment is performed at a pressure of 200-400 bar for 4-8 times.

10. An aqueous single-walled carbon nanotube dispersion prepared by the preparation method according to any one of claims 1-9.

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