An environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy

Abstract

The application discloses an environmentally-friendly and efficient carbon nanotube dispersion method based on a crystal engineering strategy, which comprises the following steps: carboxylation pretreatment of carbon nanotubes; melt mixing and cooling crystallization; mechanical crushing; repeating the above steps for two to three times; water phase dissociation and dispersion. The application innovatively uses the crystal engineering strategy: erythritol is mixed with the carboxylated carbon nanotubes in a molten state, and in the cooling crystallization process, the growth of erythritol crystals can physically "open up" and isolate the entangled carbon nanotube bundles, realizing the pre-dispersion in the solid state scale; the whole dispersion process uses water and biocompatible erythritol as the main medium, avoiding the use of a large amount of toxic surfactants or organic solvents, and the post-processing is simple and environmentally friendly; the method can obtain a carbon nanotube dispersion liquid which is uniformly dispersed and has good structural integrity, and is beneficial to the application in high-end composite materials.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial processing technology, and in particular to an environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy that is simple in process, environmentally friendly, and has high dispersion efficiency. Background Technology

[0002] Carbon nanotubes have broad application prospects in composite materials, electronic devices, and energy storage due to their excellent mechanical, electrical, and thermal properties. However, due to their huge specific surface area and strong van der Waals forces, commercial carbon nanotubes usually exist in entangled and aggregated bundles or ropes, which severely limits their performance and applications.

[0003] Currently, common methods for dispersing carbon nanotubes mainly include: Chemical covalent functionalization: introducing carboxyl, hydroxyl, and other groups onto the surface of carbon nanotubes through strong acid oxidation to improve their hydrophilicity. However, this method often involves harsh conditions, easily damaging the intrinsic structure of carbon nanotubes, introducing numerous defects, and leading to a decline in performance. Surfactant-assisted ultrasonication: utilizing the steric hindrance or electrostatic repulsion of surfactants to stabilize dispersed carbon nanotubes. However, the introduction of surfactants may affect the performance of subsequent composite materials, is difficult to remove, and the process is not environmentally friendly. Polymer encapsulation: using polymer chains to separate carbon nanotubes, but polymers are also difficult to remove and may be insulating, making them unsuitable for applications requiring conductivity.

[0004] Existing technologies generally suffer from the following problems: cumbersome processes, use of harmful chemicals, low dispersion efficiency, significant damage to carbon nanotube structures, or introduction of dispersants that are difficult to remove. Therefore, developing a green, efficient dispersion method that can maximize the preservation of carbon nanotube integrity is a pressing technical challenge in this field. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide an environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategies, which is simple in process, environmentally friendly, and has high dispersion efficiency.

[0006] Technical solution: The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy described in this invention includes the following steps:

[0007] Step 1: Carboxylation pretreatment of carbon nanotubes;

[0008] Step 2: Melting, mixing, and cooling for crystallization;

[0009] Step 3: Mechanical crushing;

[0010] Step 4: Repeat steps 2 and 3 two to three times;

[0011] Step 5: Aqueous phase dissociation and dispersion.

[0012] Further, step 1 includes subjecting commercial entangled carbon nanotubes to low-temperature acidification and reflux treatment, and grafting carboxyl functional groups onto their surface to obtain carboxylated carbon nanotubes.

[0013] Further, step 2 includes melting and mixing the carboxylated carbon nanotubes obtained in step 1 with erythritol in a mass ratio, stirring until a homogeneous mixture is formed; then cooling the mixture to room temperature to allow erythritol to crystallize, forming carbon nanotube or erythritol composite crystals.

[0014] Furthermore, the carboxylated carbon nanotubes and erythritol are in a mass ratio of 1:33.

[0015] Furthermore, the stirring temperature is set to 120℃-150℃.

[0016] Furthermore, step 3 includes mechanically grinding the carbon nanotube or erythritol composite crystals obtained in step 2 to obtain micron- or nano-sized composite powders.

[0017] Furthermore, step 5 includes dissolving the composite powder obtained in step 3 in deionized water and then subjecting it to ultrasonic treatment. Erythritol rapidly dissolves in water, releasing the carbon nanotubes that were isolated by it, thereby achieving stable dispersion of carbon nanotubes in water.

[0018] Furthermore, the erythritol recovery method includes filtering the dispersed carbon nanotube suspension and collecting the filtrate; evaporating and concentrating the filtrate under reduced pressure at 60℃-80℃ until it reaches saturation, and then cooling it to room temperature to allow erythritol to crystallize out; filtering and collecting the crystals, and drying them to obtain the recovered erythritol.

[0019] Furthermore, the carbon nanotube dispersion obtained in step 5 is characterized in the following ways: stability, dispersion concentration, and morphology.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0021] (1) Innovative crystal engineering strategy was used: erythritol was mixed with carboxylated carbon nanotubes in the molten state. During the cooling crystallization process, the growth of erythritol crystals could physically "spread out" and isolate the entangled carbon nanotube bundles, thus achieving pre-dispersion on the solid scale.

[0022] (2) Green and environmentally friendly: The entire dispersion process uses water and biocompatible erythritol as the main medium, avoiding the use of large amounts of toxic surfactants or organic solvents. The post-processing is simple and environmentally friendly.

[0023] (3) High efficiency and minimal damage: Due to the effect of solid pre-dispersion, only mild ultrasound or shearing is needed in the aqueous phase to achieve good dispersion of carbon nanotubes, which greatly shortens the high-intensity ultrasound time and effectively reduces the mechanical damage to the aspect ratio and structure of carbon nanotubes caused by long-term ultrasound.

[0024] (4) High dispersion quality: This method can obtain carbon nanotube dispersions with uniform dispersion and good structural integrity, which is beneficial for their application in high-end composite materials;

[0025] (5) Simple process and low cost: The raw materials used are readily available, the process flow is simple, it is easy to scale up, and it has the potential for industrial production.

[0026] (6) Erythritol can be recycled and reused: Erythritol can be efficiently recovered through evaporation, concentration and cooling crystallization, with a recovery rate of over 80%, which significantly reduces raw material costs and further improves the environmental friendliness and economy of the method. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the method of the present invention;

[0028] Figure 2 Comparison of digital photographs of carbon nanotube aqueous solutions before and after dispersion;

[0029] Figure 3 This is a transmission electron microscope image of dispersed carbon nanotubes.

[0030] Figure 4 Fourier transform infrared spectrum;

[0031] Figure 5 The images show the original carbon nanotubes and the Raman spectra after processing. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, this invention provides an environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategies, comprising the following steps:

[0034] Step 1: Carboxylation pretreatment of carbon nanotubes: Commercial entangled carbon nanotubes are subjected to low-temperature acidification and reflux treatment, and carboxyl functional groups are grafted onto their surface to obtain carboxylated carbon nanotubes.

[0035] Step 2: Melting and Cooling Crystallization: The carboxylated carbon nanotubes obtained in Step 1 are melt-mixed with erythritol at a mass ratio of 1:33 and stirred at 120℃-150℃ until a homogeneous mixture is formed; then the mixture is cooled to room temperature to allow erythritol to crystallize, forming carbon nanotube / erythritol composite crystals.

[0036] Step 3: Mechanical grinding: The carbon nanotube / erythritol composite crystals obtained in Step 2 are mechanically ground to obtain micron- or nano-sized composite powders;

[0037] Step 4: Repeat steps 2 and 3 two to three times;

[0038] Step 5: Aqueous phase dissociation and dispersion: The composite powder obtained in step 3 is dissolved in deionized water and then subjected to ultrasonic treatment. Erythritol dissolves rapidly in water, releasing the carbon nanotubes that were isolated by it, thereby achieving stable dispersion of carbon nanotubes in water.

[0039] Example 1

[0040] 1. Carboxylation pretreatment: Take 100 mg of multi-walled carbon nanotubes and add 100 mL of a mixture of concentrated nitric acid and concentrated sulfuric acid (volume ratio 1:3). Reflux at 80 °C for 4 hours. After the reaction is complete, cool, filter, wash until neutral, and dry to obtain carboxylated carbon nanotubes.

[0041] 2. Melting and Crystallization: Weigh 10 mg of the above carboxylated carbon nanotubes and 330 mg of erythritol, place them in a beaker, heat in an oil bath at 130°C to melt, and mechanically stir for 30 minutes to ensure uniform mixing. Then, remove the mixture and allow it to cool at room temperature until the erythritol is completely crystallized.

[0042] 3. Mechanical grinding: The cooled hard blocky composite material is placed in a mortar and ground manually, or pulverized using a ball mill, and then passed through a 200-mesh sieve to obtain fine powder;

[0043] 4. Repeat the melting-mixing-cooling-crystallization-mechanical pulverization steps twice, for a total of three cycles; (e.g.) Figure 3 The images shown are transmission electron microscope (TEM) images of dispersed carbon nanotubes, where (a) are untreated carbon nanotubes; (b) are carbon nanotubes dispersed once by this method; (c) are carbon nanotubes dispersed twice by this method; and (d) are carbon nanotubes dispersed three times by this method.

[0044] 5. Aqueous phase dissociation and dispersion: 100 mg of the above composite powder was added to 100 mL of deionized water and treated with a 500 W ultrasonic cell disruptor for 10 minutes to obtain a black, uniform carbon nanotube dispersion. Figure 2 The images show a comparison of digital photographs of carbon nanotube aqueous solutions before and after dispersion (left: original carbon nanotubes; right: dispersion by the method of this invention), where (a) is a comparison of the dispersion state after 5 minutes of sonication; and (b) is a comparison of the dispersion state after 1 hour of standing.

[0045] Effect verification

[0046] The carbon nanotube dispersion prepared in Example 1 of this invention was characterized as follows:

[0047] (1) Stability: No obvious precipitation was observed after standing for 7 days, indicating good dispersion stability.

[0048] (2) Dispersion concentration: The absorbance at 500 nm was measured by UV-Vis spectrophotometer, and the dispersion concentration was calculated to be 0.12 mg / mL.

[0049] (3) Morphological characterization: Transmission electron microscopy showed that carbon nanotubes existed in a single or small aggregated state, maintained good length, and showed no obvious shortening phenomenon.

[0050] like Figure 4 The image shows a Fourier transform infrared (FTIR) spectrum. FTIR analysis reveals a clear intermolecular interaction between erythritol and carbon nanotubes. The strongest evidence comes from a significant redshift of the OH peak by 94.1 cm⁻¹. This significant value indicates a decrease in the vibrational frequency of chemical bonds and a weakening of bond energy, meaning enhanced hydrogen bonding. This suggests that the hydroxyl groups of erythritol form stronger hydrogen bonds with the oxygen-containing functional groups or π-electron clouds on the surface of carbon nanotubes. This molecular-level interaction directly reflects the good dispersion of carbon nanotubes. Supporting evidence is the significant broadening of the OH peak, with the full width at half maximum (FWHM) increasing from 271.6 cm⁻¹ to 278.6 cm⁻¹, a broadening of 7.0 cm⁻¹. This indicates that the chemical environment of the hydroxyl groups becomes heterogeneous—partially interacting with carbon nanotubes and partially uninterrupted. This is a typical characteristic of a complex system, rather than a simple physical mixture. Furthermore, the CO peaks also exhibited a redshift. The 13.0 cm⁻¹ redshift of CO₂ peak-2 is independent evidence of the interaction, while the 1.5 cm⁻¹ redshift of CO₂ peak-1, though consistent in direction, supports the conclusion of an interaction. The most direct evidence comes from the appearance of characteristic peaks of carbon nanotubes: the mixture shows a strong peak at 1632 cm⁻¹, close to the G band of carbon nanotubes (approximately 1580 cm⁻¹), while pure erythritol has no absorption peak in this region. This not only proves that carbon nanotubes are indeed present in the mixture, but also that their peak position is blue-shifted by approximately 50 cm⁻¹, indicating that the electronic structure or environment of the carbon nanotubes has changed due to the interaction with erythritol, as shown in Table 1.

[0051] Table 1: Fourier Transform Infrared Spectral Peaks

[0052]

[0053] like Figure 5The images show the Raman spectra of the original carbon nanotubes and the treated ones. The ID / IG ratio is approximately 1.077, indicating fewer structural defects in the carbon nanotubes, which is superior to the samples treated with traditional strong acid reflux. The ID / IG ratio shows only a slight change, indicating that the sp2 structure integrity is maintained. The decrease in the full width at half maximum (FWHM) of the 2D peak reflects the homogenization of the carbon nanotube vibrational environment. The redshift of the 2D peak directly corresponds to the weakening of van der Waals coupling between the nanotubes. These three indicators collectively confirm that we have achieved effective dissociation and dispersion of carbon nanotubes through physical methods.

[0054] Table 2: Peak shifts of raw carbon nanotubes and treated carbon nanotubes

[0055]

[0056] Comparative Example

[0057] Using a conventional surfactant (SDBS) to directly ultrasonically disperse an equal amount of raw carbon nanotubes, the ultrasonic time required to achieve a similar dispersion concentration was 60 minutes, which is 6 times that of this method; and TEM showed that the carbon nanotube length was significantly shortened and the structural damage was more significant.

[0058] Erythritol recovery method

[0059] The dispersed carbon nanotube suspension was filtered, and the filtrate was collected. The filtrate was concentrated to saturation by vacuum evaporation at 60-80℃, and then cooled to room temperature, where erythritol crystallized out. The crystals were collected by filtration and dried to obtain recovered erythritol, with a recovery rate of over 80%, as shown in Table 3.

[0060] Table 3: Comparison of Erythritol's Recyclability and Reuse

[0061]

[0062] The highly intact and highly dispersible carbon nanotube aqueous dispersion prepared by this method can be widely used in:

[0063] 1. High-performance conductive composite materials and thermally conductive composite materials;

[0064] 2. Flexible electronics, sensors, and transparent conductive films;

[0065] 3. Energy storage devices (lithium batteries, supercapacitor electrodes);

[0066] 4. Biomedical materials, water treatment membrane materials, and other fields.

Claims

1. An environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy, characterized in that, Includes the following steps: Step 1: Carboxylation pretreatment of carbon nanotubes; Step 2: Melting, mixing, and cooling for crystallization; Step 3: Mechanical crushing; Step 4: Repeat steps 2 and 3 two to three times; Step 5: Aqueous phase dissociation and dispersion.

2. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, Step 1 includes subjecting commercial entangled carbon nanotubes to low-temperature acidification and reflux treatment, and grafting carboxyl functional groups onto their surface to obtain carboxylated carbon nanotubes.

3. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, Step 2 includes melting and mixing the carboxylated carbon nanotubes obtained in step 1 with erythritol in a mass ratio, stirring until a homogeneous mixture is formed; then cooling the mixture to room temperature to allow erythritol to crystallize, forming carbon nanotube or erythritol composite crystals.

4. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 3, characterized in that, The carboxylated carbon nanotubes and erythritol are in a mass ratio of 1:

33.

5. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 3, characterized in that, The stirring temperature is set to 120℃-150℃.

6. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, Step 3 includes mechanically grinding the carbon nanotube or erythritol composite crystals obtained in step 2 to obtain micron- or nano-sized composite powders.

7. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, Step 5 involves dissolving the composite powder obtained in step 3 in deionized water and then subjecting it to ultrasonic treatment. Erythritol rapidly dissolves in water, releasing the carbon nanotubes that were isolated by it, thereby achieving stable dispersion of carbon nanotubes in water.

8. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, The erythritol recovery method includes filtering the dispersed carbon nanotube suspension and collecting the filtrate; evaporating and concentrating the filtrate under reduced pressure at 60℃-80℃ until it reaches saturation, and then cooling it to room temperature to allow erythritol to crystallize out; filtering and collecting the crystals, and drying them to obtain the recovered erythritol.

9. The environmentally friendly and efficient carbon nanotube dispersion method based on crystal engineering strategy according to claim 1, characterized in that, The carbon nanotube dispersion obtained in step 5 is characterized by the following aspects: stability, dispersion concentration, and morphology.

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