A compact graphene-carbon nanotube composite film and a preparation method thereof

Abstract

The application discloses a compact graphene-carbon nanotube composite film and a preparation method thereof. The preparation method comprises the following steps: S1, mixing graphene oxide aqueous solution and carbon nanotube solution, uniformly dispersing, and preparing graphene oxide-carbon nanotube mixed solution; S2, performing solid-liquid separation on the graphene oxide-carbon nanotube mixed solution by suction filtration; drying the filter membrane covered with the graphene oxide-carbon nanotube composite film, and peeling off the graphene oxide-carbon nanotube composite film from the filter membrane; and S3, performing heat reduction treatment on the graphene oxide-carbon nanotube composite film, and obtaining the graphene-carbon nanotube composite film. The carbon nanotube network structure in the composite film is uniformly dispersed between adjacent graphene layers, plays a role of a heat conduction bridge, and has the potential to improve the longitudinal thermal conductivity of graphene.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology research, specifically to a dense graphene-carbon nanotube composite film and its preparation method. Background Technology

[0002] Since its discovery in 2004, graphene has been recognized for its extremely high in-plane thermal conductivity (~5000 W / m²). -1 K -1 Graphene has attracted widespread attention and is widely used in the preparation of high thermal conductivity thin films. However, the longitudinal thermal conductivity of graphene thermal conductive films is relatively low. In particular, when graphene oxide (GO) is used as the starting material to prepare graphene thermal conductive films, the oxygen-containing functional groups (-COOH, -OH, and -COC) of GO decompose during the thermal reduction process. This leads to an increase in the interlayer spacing of the graphene film due to the gas generated by the decomposition of oxygen-containing functional groups, which can increase from 30 nm to more than 300 nm. Consequently, the longitudinal thermal conductivity of the subsequently prepared graphene thermal conductive films is low, making it difficult to meet the longitudinal heat dissipation requirements of high-power devices. Therefore, how to improve the longitudinal thermal conductivity of graphene films has become a key scientific and technological challenge in this field.

[0003] In current techniques, Alexandr V. et al. (Applied Surface Science, 2016, 361: 213-220) studied the effect of thermal reduction temperature on the structure of reduced graphene oxide (rGO), controlling the content of oxygen functional groups and the thermal reduction process by changing the heat treatment temperature. They found that at 300°C... o C-thermal reduction leads to the disruption of the internal structure of graphene and the expansion of interlayer pores, which is very detrimental to improving the longitudinal thermal conductivity of graphene. Moreover, the influence and importance of the heating rate on the density and interlayer spacing of reduced graphene oxide films have not been considered.

[0004] Carbon nanotubes, as allotropes of carbon, also possess excellent thermal conductivity (3500 W / m²). -1 K -1Combining graphene with carbon nanotubes (CNTs) is expected to leverage the combined advantages of both to prepare thermally conductive films with higher longitudinal thermal conductivity. In the prior art, CN111154461A discloses a graphene-carbon nanotube composite thermally conductive film and its preparation method. Its main technical feature is the loading of metal nanoparticles between the layers of the graphene oxide film, using these as a catalyst to grow carbon nanotubes in situ, thereby forming a graphene-carbon nanotube composite film. However, this method does not address the control of the heating rate during the reduction process below 200℃ and between 200-600℃, and therefore cannot control the interlayer spacing of the graphene. CN116789110A discloses a method for preparing a graphene / carbon nanotube composite solution. This involves uniformly mixing graphene oxide and carbon nanotubes, chemically reducing the graphene oxide, and then using a dispersant to uniformly disperse the graphene / carbon nanotubes in the solution. This method does not involve a dense graphene-carbon nanotube composite film or its preparation method. The chemically reduced graphene oxide prepared by this invention has many structural defects, which is detrimental to its application in the field of thermal conductivity. Therefore, there is an urgent need to develop a dense composite film based on graphene / carbon nanotubes and its preparation method. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a dense graphene-carbon nanotube composite film and its preparation method. This invention achieves the preparation of a dense film by controlling the decomposition rate of graphene functional groups during thermal reduction to suppress interlayer expansion. Simultaneously, the high thermal conductivity of carbon nanotubes acts as a bridge between the graphene sheet layers, further improving the longitudinal thermal conductivity of the graphene film.

[0006] <First Aspect> A method for preparing a dense graphene-carbon nanotube composite film includes the following steps: S1. A mixture of graphene oxide aqueous solution and carbon nanotube solution was prepared by uniformly dispersing them to form a graphene oxide-carbon nanotube mixed solution. S2. The graphene oxide-carbon nanotube mixed solution is filtered to separate solid and liquid components; the filter membrane coated with the graphene oxide-carbon nanotube composite film is dried and peeled off from the filter membrane to obtain the graphene oxide-carbon nanotube composite film. S3. The graphene oxide-carbon nanotube composite film is subjected to thermal reduction treatment to obtain the graphene-carbon nanotube composite film.

[0007] In step S3, the thermal reduction treatment step is as follows: the graphene oxide-carbon nanotube composite film from step S2 is heated from the ambient temperature to a preset temperature of 180-300℃ at a heating rate of 1-6℃ / min under a protective atmosphere; after reaching the preset temperature, the temperature is kept constant for 1-3 hours to allow the graphene oxide to undergo a thermal reduction reaction, thereby obtaining the graphene-carbon nanotube composite film.

[0008] By leveraging the high thermal conductivity of carbon nanotubes, they are anchored between the layered structures of graphene sheets to act as bridges, thereby improving the longitudinal thermal conductivity of graphene.

[0009] In S1, the carbon nanotubes include one or more of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs). In S1, the mass ratio of graphene oxide to carbon nanotubes in the graphene oxide-carbon nanotube mixed solution is 1:0.02-1:0.8.

[0010] In S1, the carbon nanotube aqueous solution is prepared by dispersing carbon nanotubes in an aqueous solution containing 0.5-1.0 wt% surfactant to obtain the carbon nanotube solution; the concentration of carbon nanotubes in the solution is 0.5-1 mg / mL.

[0011] The surfactant includes one or more of the following: anionic sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and cationic hexadecyltrimethylammonium bromide (CTAB).

[0012] In S1, the concentration of the graphene oxide aqueous solution is 2-5 mg / mL.

[0013] In S1, the dispersion is ultrasonic dispersion, and the ultrasonic conditions are: 40-60 kHz, ultrasonic time 30-60 min.

[0014] In S2, the drying conditions are natural drying at ambient temperature for 15-20 hours.

[0015] In S2, vacuum filtration is performed using a microporous membrane with a pore size of 2-5 μm; the filtration pressure is -0.1 to -0.2 MPa.

[0016] In S2, the filtration conditions are: vacuum filtration, filtration time 1~8 h.

[0017] As one embodiment of the present invention, the preparation method of the graphene-carbon nanotube composite film includes the following steps: A. A mixture of graphene oxide aqueous solution and carbon nanotube solution was prepared by uniformly dispersing them. B. Disperse the graphene oxide-carbon nanotube mixture evenly in an ice-water bath, dilute with diluent, and further disperse by ultrasonication to obtain a graphene-carbon nanotube dispersion. C. Filter the graphene oxide-carbon nanotube dispersion to separate the solid and liquid components; dry the filter membrane coated with the graphene-carbon nanotube composite membrane, and peel the obtained graphene oxide-carbon nanotube composite film off the filter membrane. D. The graphene oxide-carbon nanotube composite film is subjected to thermal reduction treatment to obtain the dense graphene-carbon nanotube composite film.

[0018] In step B, deionized water can be used as the diluent, with a dilution ratio of 5-10 times, in order to facilitate vacuum filtration and membrane formation.

[0019] Furthermore, in step B, the cell disruptor has a power of 500 W and a disruption time of 1-2 hours.

[0020] Furthermore, in step B, the ultrasonic conditions are: 40-60 kHz, ultrasonic time 30-60 min.

[0021] Furthermore, in step B, the temperature of the ice-water bath is 1~10℃ to prevent carbon nanotubes from agglomerating at ~40℃.

[0022] <Second aspect> The graphene-carbon nanotube composite film prepared by the method described above is also within the scope of protection of this invention.

[0023] The final product obtained by this invention is a graphene-carbon nanotube composite film with carbon nanotubes anchored to a graphene sheet layer structure and oriented.

[0024] The key features of this invention are: (1) In the process of thermal reduction treatment, the present invention controls the heating rate, thereby regulating the decomposition rate of oxygen-containing functional groups (such as hydroxyl, carboxyl, etc.) on the surface of graphene oxide, suppressing the interlayer expansion in the film, and finally realizing the preparation of dense film. (2) The innovative heating strategy adopted in this invention can also ensure the uniform distribution of carbon nanotubes between graphene layers, better play the anchoring and bridging role, and ultimately improve the longitudinal thermal conductivity of graphene-carbon nanotube composite film. (3) The present invention prepares a graphene-carbon nanotube composite film in which carbon nanotubes are uniformly anchored and intercalated between graphene sheets, acting as a bridge between adjacent layers, effectively optimizing the phonon transport path, and having the potential to improve the longitudinal thermal conductivity of the graphene film. Due to the anchoring effect of carbon nanotubes between graphene sheets and the precise control of process parameters during the preparation of the composite film, the composite film has good structural stability. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a cross-sectional SEM image of the graphene-carbon nanotube composite film prepared in experimental group 4 of Example 1; Figure 2This is a cross-sectional SEM image of the graphene oxide film in Comparative Example 1. Figure 3 The thermogravimetric analysis of the graphene oxide film in Comparative Example 1 at heating rates of 5–60 °C / min is shown; where a is the thermogravimetric curve under different heating rates, and b is the thermogravimetric differential curve corresponding to a. Figure 4 Schematic diagrams of GO and 4% MWCNTs-GO prepared in test group 2 of the present invention; (a) physical image of the composite film with a diameter of approximately 45 mm; (b) cross-sectional SEM image with a magnification of 1 k; (c) magnification of 50 k. Detailed Implementation

[0026] The present invention will be described in detail below with reference to embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several adjustments and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0027] Example 1 Example 1 is a dense graphene-carbon nanotube composite film. This example optimizes the ratio of graphene oxide to carbon nanotubes (multi-walled carbon nanotubes are used in this example). The specific preparation steps are as follows: Step 1: First, select 100 mL of uniformly dispersed graphene oxide aqueous solution in a beaker, add MWCNTs dispersion containing 1.0 wt% sodium dodecyl sulfate (SDS) to it, and perform pre-ultrasonic treatment. The ultrasonic frequency is 40 kHz and the ultrasonic time is 30 min to obtain graphene oxide-carbon nanotube mixture. The concentration of the graphene oxide aqueous solution was 2 mg / mL; the concentration of MWCNTs in the MWCNTs dispersion was 0.5 mg / mL; the mass ratios of graphene oxide and carbon nanotubes were set as shown in Table 1. Table 1

[0028] Step 2: The graphene oxide-carbon nanotube mixtures obtained from each experimental group in Step 1 were placed in a cell ultrasonic disruptor under an ice-water bath. The ultrasonic power was 500 W, and the ultrasonic dispersion time was 2 h. Then, ultrapure water was added to dilute it 5 times, followed by ultrasonic dispersion at a frequency of 40 kHz for 30 min to obtain a graphene oxide-carbon nanotube dispersion.

[0029] Step 3: 40 mL of the graphene oxide-carbon nanotube dispersion from each experimental group in Step 2 was subjected to solid-liquid separation using a vacuum filter with a filter membrane. The filter membrane had a pore size of 5 μm and a diameter of 50 mm, resulting in a filter membrane coated with a graphene oxide-carbon nanotube composite film. The membrane was then allowed to dry naturally at ambient temperature and peeled off. This process yielded the graphene oxide-carbon nanotube composite film. The filtration time was 2 h and the filtration pressure was -0.1 MPa.

[0030] Step 4: Perform thermal reduction treatment on the graphene oxide-carbon nanotube composite films prepared in each experimental group in Step 3. The specific steps are as follows: The graphene oxide-carbon nanotube composite film was placed in a tube furnace, and the furnace temperature was increased from room temperature to 300°C at a rate of 2°C / min under inert gas protection (nitrogen or argon). After reaching the target temperature, the temperature was maintained constant for 3 hours to allow the graphene oxide to undergo a complete thermal reduction reaction. After the reaction was completed, the heating device was turned off, and the composite film was allowed to cool naturally to room temperature under inert gas protection. The thermally reduced graphene-carbon nanotube composite film was then removed for later use.

[0031] The study found that when the mass ratio was 1:0.04 (corresponding to 4%), carbon nanotubes were able to anchor very uniformly between graphene sheets compared to other ratios, forming a good bridging structure, such as... Figure 1 (SEM image of test group 4 in Example 1) is shown. It not only ensures the structural integrity of the composite membrane, but also facilitates phonon transmission, and has the potential to achieve high longitudinal thermal conductivity.

[0032] In samples with 2%, 4%, 6%, 8%, and 10% (corresponding to experimental groups 1-5), fine and uniform MWCNTs were found intercalated between graphene sheets. At this point, the graphene interlayers were "filled" with entangled MWCNTs with a diameter of ~10 nm, acting as bridges connecting adjacent graphene layers. When the MWCNT content was 10% (corresponding to experimental group 5), a slightly excessive amount of carbon nanotube network overflowed outside the sheets, resulting in a weakening of the interlayer compactness of the composite film. This disrupted the heat transfer path and may affect the longitudinal phonon transport efficiency, thereby reducing the longitudinal thermal conductivity of the composite film. Therefore, it is necessary to strictly control the amount of MWCNTs used in the composite.

[0033] Figure 4 Schematic diagrams of GO and 4% MWCNTs-GO prepared in test group 2 of the present invention; (a) physical image of the composite film with a diameter of approximately 45 mm; (b) cross-sectional SEM image with a magnification of 1 k; (c) magnification of 50 k.

[0034] Therefore, the preferred mass ratio of graphene oxide to carbon nanotubes is 1:0.02 to 1:0.08; more preferably 1:0.04.

[0035] Example 2 Example 2 is a graphene-carbon nanotube composite film. This example focuses on optimizing the filtration process parameters, and single-walled carbon nanotubes are used in this example. The specific preparation steps are as follows: Step 1: The graphene oxide-carbon nanotube mixture prepared according to the dosage of experimental group (2) in Example 1 was placed in a cell ultrasonic disruptor under an ice-water bath. After 2 hours, it was taken out and diluted 5 times with ultrapure water. Then, it was ultrasonically dispersed at a frequency of 40 kHz for 30 minutes to obtain a graphene oxide-carbon nanotube dispersion.

[0036] Step 2: The graphene oxide-carbon nanotube dispersion is subjected to solid-liquid separation by passing it through a vacuum filter with a filter membrane diameter of 50 mm to obtain a filter membrane coated with a graphene oxide-carbon nanotube composite film. The filter membrane is then allowed to dry naturally at ambient temperature and peeled off to obtain the graphene oxide-carbon nanotube composite film. The filtration process parameters are shown in Table 2.

[0037] Step 3: Same as step 4 in Example 1.

[0038] Table 2 .

[0039] Example 3 Example 3 focuses on optimizing the conditions of the thermal reduction step. In this example, double-walled carbon nanotubes are used; the specific preparation steps are as follows: Steps 1 and 2: Same as in Experimental Group 2 of Example 1; Step 3: Same as test group 8 in Example 2; Step 4: Perform thermal reduction treatment on the graphene oxide-carbon nanotube composite film prepared in Step 3. The specific steps are as follows: Five mg of graphene oxide-carbon nanotube composite film was placed in a tube furnace, and the furnace temperature was increased from room temperature to 300°C under inert gas protection (nitrogen or argon) at different heating rates (see Table 3). After reaching the target temperature, the temperature was kept constant for 3 hours to allow the graphene oxide to undergo a complete thermal reduction reaction.

[0040] Table 3 .

[0041] Comparative Example 1: The comparative example is a graphene oxide film, whose specific preparation steps are as follows: Step 1: First, select 50 mL of uniformly dispersed graphene oxide aqueous solution in a beaker, add ultrapure water to dilute it 10 times, and perform ultrasonic treatment to mix it evenly.

[0042] Step 2: Place the graphene oxide aqueous solution obtained in Step 1 into a cell disruptor and remove it after 1 hour.

[0043] Step 3: Pass 40 mL of the uniform graphene oxide aqueous solution from Step 2 through a vacuum filter with a filter membrane of 5 μm to separate the solid and liquid components. The resulting filter membrane contains graphene oxide. Allow it to dry naturally at ambient temperature and then peel it off from the filter paper to obtain the prepared graphene oxide membrane.

[0044] Figure 2 This is a cross-sectional SEM image of the graphene oxide film in Comparative Example 1.

[0045] Performance testing TGA testing The graphene oxide-carbon nanotube composite film of Experimental Group 2 in Example 1 and the graphene oxide film of Comparative Example 1 were placed in the TGA test chamber and the temperature was raised from room temperature to 300°C at different heating rates under inert gas protection (nitrogen or argon).

[0046] Figure 3 The thermogravimetric analysis of the graphene oxide film in Comparative Example 1 at heating rates of 5–60 °C / min is shown; where a is the thermogravimetric curve under different heating rates, and b is the thermogravimetric differential curve corresponding to a.

[0047] Within the temperature range of 100℃ to 200℃, the graphene oxide film sample exhibits a sharp weight loss peak at approximately 180℃, corresponding to the decomposition of oxygen-containing functional groups related to the graphene oxide end groups, such as -COOH, -OH, and COC. At this point, GO is thermally reduced to rGO, with a thermal reduction temperature of approximately 180℃. Furthermore, as the heating rate gradually increases from 5℃ / min to 60℃ / min, i.e., when the thermal reduction rate increases significantly, the thermal reduction temperature decreases with increasing heating rate. Simultaneously, the interlayer spacing of the graphene oxide film increases with increasing heating rate. The drastic thermal reduction rate significantly affects the interlayer structure of graphene oxide; the increased interlayer spacing makes it difficult for heat (phonons) to be conducted longitudinally, affecting its longitudinal thermal conductivity.

[0048] In contrast, the graphene oxide-carbon nanotube composite film in Example 2, due to the presence of carbon nanotubes between the graphene layers, plays a certain anchoring role, suppressing the increase in the interlayer spacing of graphene during the reduction process to some extent. Although cracks gradually appeared at 8℃ / min, it did not exhibit the sharp weight loss peaks seen in the graphene oxide film. This indicates that the addition of carbon nanotubes not only optimizes the structural stability of the composite film but also positively impacts its thermal reduction behavior, reducing the interference of heat (phonon) conduction in the longitudinal direction and improving the longitudinal thermal conductivity to some extent. This provides a superior performance foundation for its application in fields such as thermal management.

[0049] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can 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 preparing a dense graphene-carbon nanotube composite film, characterized in that, Includes the following steps: S1. A mixture of graphene oxide aqueous solution and carbon nanotube solution was prepared by uniformly dispersing them to form a graphene oxide-carbon nanotube mixed solution. S2. The graphene oxide-carbon nanotube mixed solution is filtered to separate solid and liquid components; the filter membrane coated with the graphene oxide-carbon nanotube composite film is dried and peeled off from the filter membrane to obtain the graphene oxide-carbon nanotube composite film. S3. The graphene oxide-carbon nanotube composite film is subjected to thermal reduction treatment to obtain the graphene-carbon nanotube composite film. In step S3, the thermal reduction treatment step is as follows: the graphene oxide-carbon nanotube composite film from step S2 is heated from the ambient temperature to a preset temperature of 180-300℃ at a heating rate of 1-6℃ / min under a protective atmosphere; after reaching the preset temperature, it is kept at the temperature for 1-3 hours; and a dense graphene-carbon nanotube composite film is obtained. In S1, the carbon nanotubes include one or more of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. And / or, in S1, the mass ratio of graphene oxide to carbon nanotubes in the graphene oxide-carbon nanotube mixed solution is 1:0.02-1:0.8; In S1, the method for preparing the carbon nanotube aqueous solution is to disperse carbon nanotubes in an aqueous solution containing 0.5-1.0 wt% surfactant to obtain the carbon nanotube solution; the concentration of carbon nanotubes in the solution is 0.5-1 mg / mL. The surfactant includes one or more of the following: anionic sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), and cationic hexadecyltrimethylammonium bromide (CTAB).

2. The preparation method according to claim 1, characterized in that, In S1, the concentration of the aqueous solution of graphene oxide is 2-5 mg / mL.

3. The preparation method according to claim 1, characterized in that, In S1, the dispersion is ultrasonic dispersion, and the ultrasonic conditions are: 40-60 kHz, ultrasonic time 30-60 min.

4. The preparation method according to claim 1, characterized in that, In S2, the drying conditions are natural drying at ambient temperature for 15-20 hours.

5. The preparation method according to claim 1, characterized in that, In S2, vacuum filtration is performed using a microporous membrane with a pore size of 2-5 μm; the filtration pressure is -0.1 to -0.2 MPa; and the filtration time is 1 to 8 h.

6. A graphene-carbon nanotube composite film prepared by the preparation method according to any one of claims 1-5.

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