Graphene quantum dot and preparation method and application thereof, graphene film slurry and preparation method thereof, graphene film and LED

Abstract

The invention provides a graphene quantum dot and a preparation method and application thereof, graphene film slurry and a preparation method thereof, a graphene film and an LED, and the preparation method comprises the following steps: adding sodium persulfate and graphite into concentrated sulfuric acid to obtain expanded graphite; adding potassium permanganate and concentrated sulfuric acid into the expanded graphite to obtain graphene oxide; and adding ammonia water and hydrogen peroxide into the graphene oxide to obtain the graphene quantum dots.

Description

Technical Field

[0001] This invention relates to the field of graphene films, and in particular to a graphene quantum dot and its preparation method, applications, graphene film slurry and its preparation method, graphene films, and LEDs. Background Technology

[0002] With the continuous development of fields such as artificial intelligence, autonomous driving, 5G communication, and avionics, the demand for improved chip performance is also constantly increasing. However, improving chip performance often requires increasing transistor density, which leads to localized heat accumulation and subsequent thermal failure. Meanwhile, graphene films, due to their lightweight, flexibility, and high thermal conductivity, are widely used in chip heat dissipation to reduce the occurrence of thermal failures.

[0003] Graphene films are typically produced by high-temperature heat treatment of graphene oxide films to remove internal oxygen-containing groups and restore sp. 2 The graphene film is obtained after the structural domains are removed, so it usually has structural defects introduced when oxygen atoms are removed, which limits the improvement of the thermal conductivity of the final graphene film.

[0004] Therefore, some existing technologies attempt to add additives to graphene film slurries in the hope of filling the vacancies generated during high-temperature heat treatment. However, in reality, most additives actually increase defects in the graphene film and cause phonon scattering, thus reducing the thermal conductivity of the graphene film. While a few additives can improve the thermal conductivity of the graphene film, they often require special solvents or additional surface functionalization treatments, resulting in high costs and limiting large-scale use. Summary of the Invention

[0005] Therefore, it is necessary to address the problem that existing technologies cannot improve the thermal conductivity of graphene films at a low cost by providing a graphene quantum dot and its preparation method, its application, a graphene film slurry and its preparation method, a graphene film, and an LED.

[0006] The technical solution provided by this invention is as follows:

[0007] A method for preparing graphene quantum dots, comprising:

[0008] Sodium persulfate and graphite are added to concentrated sulfuric acid to obtain expanded graphite;

[0009] Potassium permanganate and concentrated sulfuric acid were added to the expanded graphite to obtain graphene oxide;

[0010] Ammonia and hydrogen peroxide are added to the graphene oxide to obtain the graphene quantum dots.

[0011] In some embodiments of this application, when graphene oxide, ammonia, and hydrogen peroxide are mixed, the mass of graphene oxide is 14.4 k, the volume of ammonia is 12 k, and the volume of hydrogen peroxide is 300 k, where k is a positive number, the mass unit of graphene oxide is mg, and the volume units of ammonia and hydrogen peroxide are mL.

[0012] In some embodiments of this application, the temperature during the reaction of graphene oxide, ammonia, and hydrogen peroxide is 70°C-80°C.

[0013] A graphene quantum dot is prepared by the aforementioned method for preparing graphene quantum dots.

[0014] Application of graphene quantum dots in the preparation of graphene films.

[0015] A graphene film slurry comprising graphene oxide and graphene quantum dots.

[0016] In some embodiments of this application, the mass fraction of graphene quantum dots in the graphene film slurry is no more than 15%.

[0017] A method for preparing a graphene film, comprising:

[0018] The graphene film slurry is coated onto a substrate and dried to obtain a composite film;

[0019] The composite membrane was carbonized in an argon atmosphere at 1200℃-1400℃.

[0020] The composite film is graphitized in an argon atmosphere at 3000℃-3300℃ to obtain the graphene film.

[0021] A graphene film is prepared using the method described above.

[0022] An LED includes a light-emitting chip, a heat sink, and a graphene film, wherein the graphene film is located between the light-emitting chip and the heat sink.

[0023] The beneficial effects of this invention are as follows:

[0024] The graphene quantum dots provided in this application have a simple and low-cost preparation method, good dispersibility in water, and strong interaction with graphene oxide. They can be mixed with graphene oxide to form a graphene film slurry without relying on special solvents.

[0025] The excellent dispersibility of graphene quantum dots and their interaction with graphene oxide enable them to fully penetrate the interlayer of graphene oxide in composite films obtained by coating graphene film slurry. This provides a good foundation for graphene quantum dots to act as bridges between adjacent layered structures in graphene oxide during subsequent heat treatment.

[0026] Furthermore, although the graphene quantum dots in this application slightly affect the orderliness of the layered structure in the graphene oxide composite film, the precursor used in its preparation is graphene oxide, which has a relatively complete six-membered ring lattice structure in the lateral direction, similar to the lattice structure of the composite film. Therefore, during the heat treatment stage, it can effectively promote the migration and rearrangement of carbon atoms, while also acting as a carbon source to fill and repair vacancies generated during heat treatment. Moreover, the small amount of nitrogen atoms within the graphene quantum dots can also promote defect repair and grain growth. During heat treatment, the graphene quantum dots can effectively interconnect adjacent layered structures, constructing continuous heat conduction paths conducive to phonon transport and improving the orderliness of the layered structure stacking. Based on these two reasons, the graphene quantum dots in this application can actually significantly improve the thermal conductivity of the final graphene film. Attached Figure Description

[0027] Figure 1 This is a SEM image of graphene oxide in Example 1 of the present invention;

[0028] Figure 2 This is a lateral size distribution diagram of graphene oxide in Example 1 of the present invention;

[0029] Figure 3 The image shown is the AFM image of graphene oxide in Example 1 of this invention.

[0030] Figure 4 for Figure 3 The height curve at the position of the dashed line;

[0031] Figure 5 This is a SEM image of the graphene quantum dots in Example 2 of the present invention;

[0032] Figure 6 This is a lateral size distribution diagram of the graphene quantum dots in Example 2 of the present invention;

[0033] Figure 7 This is a TEM image of the graphene quantum dots in Example 2 of the present invention;

[0034] Figure 8 This is a zeta potential diagram of the graphene quantum dots in Example 2 of the present invention;

[0035] Figure 9 The XPS spectrum of the graphene quantum dots in Example 2 of this invention;

[0036] Figure 10 The FTIR spectrum of the graphene quantum dots in Example 2 of this invention;

[0037] Figure 11 This is a flowchart illustrating the preparation process of the graphene film in Example 3 of the present invention.

[0038] Figure 12 The images show cross-sectional SEM images of the composite membranes in Embodiment 3 and Comparative Example 1 when x represents different values. Figure 12 c- Figure 12 The x values ​​of i are 0, 2.5, 5, 7.5, 10, 12.5, and 15 respectively.

[0039] Figure 13 These are photographs of the composite films in Embodiment 3 and Comparative Example 1 of the present invention when x represents different values. Figure 13 a- Figure 13 f is f(x) = 0, 10, 20, 30, 40, 50.

[0040] Figure 14 The Raman spectra of the composite films in Example 3 and Comparative Example 1 of the present invention are for different values ​​of x (x from top to bottom are 15, 12.5, 10, 7.5, 5, 2.5, 0).

[0041] Figure 15 for Figure 14 I corresponding to each Raman spectrum D / I G ;

[0042] Figure 16 The Raman spectra of graphene films in Example 3 and Comparative Example 1 of the present invention are for different values ​​of x (x from top to bottom are 15, 12.5, 10, 7.5, 5, 2.5, 0).

[0043] Figure 17 for Figure 16 P corresponding to each Raman spectrum disorder ;

[0044] Figure 18 These are photographs of the graphene films in Example 3 and Comparative Example 1 of the present invention when x represents different values. Figure 18 a- Figure 18 The x values ​​of g are 0, 2.5, 5, 7.5, 10, 12.5, and 15 respectively.

[0045] Figure 19 for Figure 18 The I corresponding to different positions on each of the photos D / I G Numerical diagram ( Figure 19 a- Figure 19The x values ​​of g are 0, 2.5, 5, 7.5, 10, 12.5, and 15 respectively. Detailed Implementation

[0046] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0047] Example 1:

[0048] This embodiment provides a graphene oxide preparation method including the following steps:

[0049] Step 101: Add 50g sodium persulfate (Na2S2O8) and 5g flake graphite to 450mL concentrated sulfuric acid (H2SO4, 98%), and stir at room temperature for 1h to allow the flake graphite to gradually expand and obtain expanded graphite.

[0050] Step 102: Subsequently, under a water bath at 35°C, 20g of potassium permanganate (KMnO4) and 150mL of concentrated sulfuric acid (H2SO4) are added to the expanded graphite to gradually oxidize the expanded graphite and obtain graphene oxide.

[0051] Specifically, after the expanded graphite reacts for 6 hours, the oxidation reaction is terminated by adding 1 L of an ice-water mixture to the reaction solution, followed by the addition of 1 L of deionized water and 10 mL of hydrogen peroxide (H2O2) to remove unreacted manganese ions (Mn). 7+ ).

[0052] Step 103: Continue to add 60 mL of HCl solution (10%) to the solution, stir gently for 30 min, then add a large amount of deionized water to dilute, remove impurities by natural sedimentation and repeated replacement of deionized water, and then obtain solid graphene oxide by centrifugation at a speed of 1500 rpm for 30 min.

[0053] A dispersion of graphene oxide (solid content 3.6 wt%) was obtained by adding deionized water to graphene oxide and sonicating for 30 min. The graphene oxide dispersion was then homogenized and sheared using a high-pressure homogenizer at a shear rate of 2700 rpm for 60 min, a homogenization pressure of 2400 bar, and 6 homogenization cycles.

[0054] The morphology of the graphene oxide dispersion was then examined after being dropped onto silica. For example... Figure 1 and Figure 2 As shown, graphene oxide exhibits a typical sheet-like morphology with an average lateral dimension of approximately 0.38 μm. Figure 3 and Figure 4 As shown, the height of the graphene oxide is approximately 1.2 nm, matching the thickness of a single layer. This confirms that the sheet-like structure of the graphene oxide in this embodiment has a small size, making it easier to release internal gases during the subsequent film-forming and annealing process, avoiding the formation of pores inside the film, and facilitating the formation of a dense and orderly stacked layered structure within the film.

[0055] Example 2:

[0056] This embodiment provides a graphene quantum dot, the preparation method of which includes the following steps:

[0057] Step 201: Weigh 400g of the graphene oxide dispersion (solid content 3.6wt%) prepared in Example 1, add 12mL of ammonia and 300mL of hydrogen peroxide (H2O2) in a water bath at 75℃, and react for 15h at a stirring speed of 300r / min to obtain graphene quantum dots.

[0058] Step 202: The graphene quantum dots are precipitated and washed with ethanol as a weak solvent, and then freeze-dried at -50°C to obtain solid powder of the graphene quantum dots.

[0059] like Figure 5 and Figure 6 As shown, the graphene quantum dots prepared in this embodiment are smaller in size than the graphene oxide in Example 1, with an average diameter of only about 56 nm. Figure 7 The single-layer atomic structure and nanometer-scale lateral diameter (<100nm) of the graphene quantum dots in this embodiment are clearly shown, which fully confirms that the graphene quantum dots in this embodiment possess the structural characteristics of quantum dots.

[0060] like Figure 8 As shown, the graphene quantum dots in this embodiment exhibit a zeta potential of -46.1 mV in deionized water, indicating that the graphene quantum dots demonstrate good dispersion stability in water. This is because the graphene quantum dots in this embodiment possess a large number of oxygen- and nitrogen-containing functional groups (such as hydroxyl, carboxyl, and amine groups), as specifically demonstrated below. Figure 9 and Figure 10 As shown.

[0061] based on Figure 9It is known that the graphene quantum dots contain 54.7% C atoms, 37.4% O atoms, and 7.2% N atoms. Peaks corresponding to CC (284.8 eV), CN / CO (286.8 eV), and C=O (289.2 eV) appear in the C 1s spectrum; a peak corresponding to amine groups (401.7 eV) appears in the N 1s spectrum. Based on... Figure 10 It can be known that 3400 cm -1 The absorption band at 1571 cm⁻¹ corresponds to NH₃. -1 1405cm -1 1315cm -1 The peaks at these locations correspond to C=C, CN, and CO, respectively. These functional groups are important active sites for the graphene quantum dots in participating in interfacial interactions, and are the key basis for the graphene quantum dots to play a bridging role.

[0062] Example 3:

[0063] This embodiment provides a graphene film slurry, including the graphene oxide prepared in Example 1 and the graphene quantum dots prepared in Example 2.

[0064] The graphene film slurry was prepared by mixing the graphene quantum dots from Example 2 with the graphene oxide dispersion from Example 1, and stirring at 800 rpm-1200 rpm for 1 hour. The mass fraction of the graphene quantum dots in the graphene film slurry was x%.

[0065] In the graphene film slurry, as mentioned above, graphene quantum dots have good dispersibility in water, and their abundant active sites (nitrogen-containing groups and oxygen-containing groups) can be linked with hydroxyl and carboxyl groups on graphene oxide through hydrogen bonds or amide bonds, thereby further inhibiting aggregation behavior in water, thus jointly improving the dispersibility of graphene quantum dots and graphene oxide in water.

[0066] like Figure 11 As shown, this embodiment further provides a method for preparing a graphene film, which includes the following steps in sequence:

[0067] Step 301: The graphene film slurry is coated onto the substrate, dried at 55°C for 12 hours, and then peeled off from the substrate to obtain a composite film with a thickness of more than 100 μm.

[0068] Step 302: Heat the multiple laminated composite films at 80℃-230℃ for 16 hours to remove residual moisture and partially eliminate oxygen-containing functional groups.

[0069] Step 303: Carbonize the aforementioned multi-layered composite membrane for 2 hours in an argon atmosphere at 1300°C to remove oxygen-containing functional groups and promote structural reorganization.

[0070] Step 304: Graphitize the aforementioned multi-layered composite film in an argon atmosphere at 3150°C for 2 hours to promote defect healing and grain growth, thereby obtaining a graphene film.

[0071] Step 305: After the graphene film cools to room temperature, remove it and then perform cyclic rolling at a pressure of 5 MPa using a pressure roller to make the density of the graphene film exceed 2.0 g / cm³. 3 .

[0072] Comparative Example 1:

[0073] The difference between this comparative example and Example 3 is that the graphene film slurry does not contain the graphene quantum dots of Example 2, i.e., x=0.

[0074] Figure 12 , Figure 13 , Figure 14 and Figure 15 The sample in the sample corresponds to the composite film that was not heat-treated in step 301.

[0075] Firstly, as Figure 13 As shown, x gradually increases from 0. When x increases to 20, cracks and wrinkles begin to appear on the surface of the composite film. Furthermore, with further increases in x, these cracking and wrinkling phenomena intensify. This phenomenon arises because graphene quantum dots not only act as nanometer-sized spacers between graphene oxide layers, inhibiting interlayer slippage, but also cause localized stress concentration, leading to strain mismatch. Simultaneously, as mentioned earlier, the excellent dispersibility of graphene quantum dots in the graphene film slurry and their interaction with graphene oxide allow them to fully penetrate the interlayer spaces within the composite film, further exacerbating the aforementioned phenomena.

[0076] As supporting evidence, such as Figure 12 As shown, when x=0, the composite membrane exhibits a highly ordered layered structure. As x gradually increases to 12.5, the orderliness of the layered structure inside the composite membrane does not change significantly. However, when x further increases to 15, the layered structure inside the composite membrane begins to show slight disorder and wrinkles.

[0077] Based on the above characterization, in order to ensure the quality of the final graphene film, x ≤ 15 should be satisfied.

[0078] like Figure 14 As shown, 1350cm -1 The D peak at 1580 cm⁻¹ can be associated with lattice distortion and edge defects. -1The G peak at that location can be associated with sp. 2 Vibrations in the hybrid carbon domain, and the corresponding D peak intensity I D and G peak intensity I G The ratio between these values ​​is an important indicator for measuring the quality of internal defects in graphene films. For example... Figure 15 As shown, as x gradually increases from 0 to 15, I D / I G The values ​​are relatively stable with very small fluctuations, indicating that the addition of small amounts of graphene quantum dots does not lead to significant changes in the defect level within the graphene oxide layer.

[0079] Figure 16 , Figure 17 , Figure 18 and Figure 19 The corresponding samples were all graphene films rolled in step 305.

[0080] By comparison Figure 14 and Figure 16 It can be seen that the composite film undergoes a significant structural change after being heat-treated to become a graphene film. Specifically, compared to the composite film, the D peak intensity of the graphene film is significantly reduced, while the G peak becomes sharper, indicating that the crystallinity of the graphene film is improved and defects are reduced after heat treatment. Furthermore, the graphene film exhibits higher crystallinity at 2700 cm⁻¹. -1 A distinct G' peak appeared at the point, indicating that sp 2 The carbon conjugated structure was restored. Furthermore, the degree of disordered stacking between graphene oxide layers was determined based on the asymmetric shape of the G' peak. This disordered stacking resulted in a peak at 2700 cm⁻¹. -1 G' is generated nearby 2D Peak (intensity I) G'2D ), AB Bernal accumulation leads to 2680cm -1 G' is generated at the location 3DA Peak and at 2720cm -1 G' is generated at the location 3DB Peak (intensity I) G'3DB ).

[0081] Among them, disordered stacking accounts for P disorder =I G'2D / (I G'2D +I G'3DB ).like Figure 17 As shown, when x=0, P disorder =7.7%, while by adding a small amount (x≤15) of graphene quantum dots, P can be increased. disorder A significant decrease. Specifically, as x increases from 0 to 12.5, P... disorder It continues to decrease, and when x=12.5, P disorderIt reaches a minimum value of 2.45%, and when x increases from 12.5 to 15, although P... disorder It rebounded to 3.58%, but remained below 7.7%. This indicates that graphene quantum dots can enhance the ordered stacking of the layered structure within the graphene film, a phenomenon consistent with... Figure 12 The graphene quantum dots exhibit completely opposite effects in the composite film.

[0082] like Figure 18 and Figure 19 As shown, for the graphene film corresponding to x=0, its I D / I G The average value is approximately 0.0080, mainly because the composite film loses oxygen-containing groups and releases gas during heat treatment, resulting in vacancy defects and damage inside the final graphene film. Figure 19 In Figure 19 a- Figure 19 g corresponds to I D / I G The average values ​​are shown in Table 1.

[0083] Table 1

[0084]

[0085] Based on Table 1 and Figure 19 It is known that a small amount of graphene quantum dots can reduce defects inside the final graphene film (reduce Ig). D / I G (the average value). As x gradually increases from 0 to 15, I D / I G The average value generally shows a trend of first decreasing and then increasing. Meanwhile, when x=12.5, I... D / I G The average value reached a minimum of 0.0073, and this trend is consistent with... Figure 17 The trends shown are consistent.

[0086] The reason why graphene quantum dots in this application can repair internal defects in graphene films lies in the fact that the precursor used in their preparation is graphene oxide, which has a relatively complete six-membered ring lattice structure in the lateral direction, similar to the lattice structure of the composite film. Therefore, during the heat treatment stage, it can effectively promote the migration and rearrangement of carbon atoms, and at the same time act as a carbon source to fill and repair the vacancies generated during the heat treatment process. Furthermore, a small number of nitrogen atoms within the graphene quantum dots can also promote defect repair and grain growth. During heat treatment, graphene quantum dots can effectively interconnect adjacent layered structures, constructing continuous heat conduction paths conducive to phonon transport. However, when the graphene quantum dot content is too high (e.g., x≥15), on the one hand, it will cause the graphene quantum dots to aggregate between layers, hindering grain growth; on the other hand, during the heat treatment process, the oxygen-containing and nitrogen-containing groups inherent in the graphene quantum dots will lead to the generation of more gaseous byproducts, causing some damage to the structure.

[0087] Table 2 shows the thermal diffusivity and thermal conductivity data of the graphene film when x represents different values.

[0088] Table 2

[0089]

[0090] Table 2 shows that as x increases from 0 to 15, both the thermal diffusivity and thermal conductivity of the graphene film exhibit a trend of first increasing and then decreasing, reaching their maximum values ​​at x = 12.5. This trend is consistent with... Figure 17 Consistent with the trend shown in Table 1, this confirms that the repair effect of graphene quantum dots on internal defects in graphene films significantly improves the thermal conductivity of the graphene films themselves.

[0091] Comparative Example 2:

[0092] This comparative example provides an LED, including a light-emitting chip and a heat sink. The LED has a power of 50W, and a thermocouple is used to monitor the temperature of the light-emitting chip.

[0093] The temperature of the light-emitting chip reached 83.4℃ after running for 300 seconds.

[0094] Comparative Example 3:

[0095] The difference between this comparative example and Comparative Example 2 is that the LED also includes a graphene film with x=0, and the graphene film is placed between the light-emitting chip and the heat sink.

[0096] The temperature of the light-emitting chip reached 76.2℃ after running for 300 seconds.

[0097] Example 4:

[0098] The difference between this embodiment and Comparative Example 3 is that x=12.5 for the graphene film.

[0099] The temperature of the light-emitting chip reached 70.4℃ after running for 300 seconds.

[0100] By comparing Comparative Example 2, Comparative Example 3 and Example 4, it can be found that the graphene film with improved thermal conductivity can effectively conduct heat and improve heat dissipation efficiency.

[0101] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing graphene quantum dots, characterized in that, include: Sodium persulfate and graphite are added to concentrated sulfuric acid to obtain expanded graphite; Potassium permanganate and concentrated sulfuric acid were added to the expanded graphite to obtain graphene oxide; Ammonia and hydrogen peroxide are added to the graphene oxide to obtain the graphene quantum dots.

2. The preparation method according to claim 1, characterized in that, When graphene oxide, ammonia, and hydrogen peroxide are mixed, the mass of graphene oxide is 14.4 k, the volume of ammonia is 12 k, and the volume of hydrogen peroxide is 300 k, where k is a positive number, the mass of graphene oxide is in mg, and the volumes of ammonia and hydrogen peroxide are in mL.

3. The preparation method according to claim 1, characterized in that, The reaction temperature of graphene oxide, ammonia, and hydrogen peroxide is 70℃-80℃.

4. A graphene quantum dot, characterized in that, Graphene quantum dots are prepared by the method described in claim 1, 2, or 3.

5. The application of graphene quantum dots as described in claim 4 in the preparation of graphene films.

6. A graphene film slurry, characterized in that, This includes graphene oxide and graphene quantum dots as described in claim 4.

7. The graphene film slurry according to claim 6, characterized in that, The mass fraction of graphene quantum dots in graphene film slurry is no more than 15%.

8. A method for preparing a graphene film, characterized in that, include: The graphene film slurry as described in claim 6 is coated onto a substrate and dried to obtain a composite film; The composite membrane was carbonized in an argon atmosphere at 1200℃-1400℃. The composite film is graphitized in an argon atmosphere at 3000℃-3300℃ to obtain the graphene film.

9. A graphene film, characterized in that, The graphene film was prepared using the method described in claim 8.

10. An LED, characterized in that, It includes a light-emitting chip, a heat sink, and a graphene film as described in claim 9, wherein the graphene film is located between the light-emitting chip and the heat sink.

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