Graphene reduced by graphene oxide, graphene film and preparation method thereof

Abstract

The present invention belongs to the technical field of graphite oxide reduction, and discloses a graphene reduced by graphene oxide, a graphene film and a preparation method thereof. The method comprises the following steps: dispersing graphene oxide in a mixed solution of triethylene glycol to form a graphene oxide dispersion, irradiating with a laser wavelength of 1000 to 1100 nm, washing and drying after the irradiation to obtain graphene. The present invention combines a laser with a wavelength of 1064 nm with a dispersion based on triethylene glycol, which can provide extremely high transient energy for reactants, thereby promoting a deprotonation process and a reduction process, and the prepared graphene is completely reduced, has a large size and few defects.

Description

Technical Field

[0001] The invention belongs to the technical field of graphite oxide reduction, and in particular relates to graphene reduced by graphene oxide, a graphene film and a preparation method thereof. Background Art

[0002] In view of the promotion and popularization of flexible electronic devices such as foldable mobile phones, computers, and curved displays, there is an urgent need to develop a new type of HDM that is extremely flexible and does not produce creases after repeated folding. Currently, commonly used heat dissipation metals include silver, copper, and aluminum, which are highly rigid and generally have corrosion and oxidation problems, limiting their application in flexible devices or corrosive environments.

[0003] Polymers are another class of materials commonly used in electronic packaging because of their excellent flexibility and low cost. However, their thermal management performance is extremely limited due to their low intrinsic thermal conductivity. In recent years, carbon-based membranes have gradually come into the field of vision of researchers. As an alternative, they have satisfactory thermal conductivity based on effective phonon transmission paths. Among them, graphene membranes have been well developed because of their excellent thermal conductivity under certain harsh conditions. Studies have shown that the larger the size of the graphene sheet, the tighter the structure of the membrane, the smaller the loss during heat transfer, and the better the thermal conductivity. However, some thorny issues in graphene synthesis and film formation technology remain a huge challenge. Traditional synthesis methods, including chemical vapor deposition (CVD) and mechanical exfoliation, usually require high costs to prepare high-quality graphene with low yields. Graphene oxide, as the most commonly used precursor for preparing graphene, has abundant oxygen-containing functional groups, including hydroxyl, carboxyl and epoxy groups. These functional groups can form hydrogen between layers during film formation, thereby forming a better cross-linked structure. Therefore, great efforts have been made on the assembly methods of GO sheets to obtain independent GO membranes, and then GO is reduced to graphene by various methods. Miao et al. grafted GO with PANI by dip coating at 5 °C, and then annealed at 2800 °C to obtain graphene-PI heat dissipation films. However, the structure of the film obtained by direct dip coating or spin coating is very loose, and the large gaps between graphene sheets cause serious scattering of phonons during the transfer process, so the thermal conductivity decreases sharply; Zhang et al. innovatively applied the vacuum filtration strategy to prepare GO membranes with dense and ordered structures, and then obtained graphene by adding hydrogen iodide (HI) as a reducing agent. In addition to HI, hydrazine is also a commonly used effective strong reducing agent, but it is difficult for the internal GO sheets to fully contact the reducing agent, which inevitably leads to incomplete reduction. The residual hydrogen bonds and the imbalance of hydrogen bonds on different sides of the interlayer reduce the flexibility of HDMs, making it easy to leave creases after repeated folding. Not to mention that both HI or hydrazine are highly toxic and will cause serious harm to the environment. Summary of the invention

[0004] The purpose of the present invention is to provide a graphene, a graphene film and a preparation method thereof reduced by graphene oxide in view of the above-mentioned problems existing in the existing method of reducing graphene by a reducing agent. The laser with a wavelength of 1064nm is combined with a dispersion based on triethylene glycol (TEG). TEG has a strong absorption peak at a wavelength near 1000-1100nm, which can provide extremely high transient energy for the reactants, thereby promoting the deprotonation process and the reduction process. The prepared graphene is completely reduced, has a large size and few defects.

[0005] In order to achieve the above purpose, the technical solution adopted in this application is:

[0006] The first object of the present invention is to provide a method for preparing graphene by reducing graphene oxide, comprising the following steps: dispersing graphene oxide in a mixed solution of triethylene glycol to form a graphene oxide dispersion, irradiating with a laser wavelength of 1000 to 1100 nm, and washing and drying after the irradiation to obtain graphene.

[0007] Preferably, the concentration of the graphene oxide dispersion is 0.5-2 mg / mL.

[0008] Preferably, the mixed solution is a mixed solution formed by triethylene glycol and N,N-dimethylformamide.

[0009] Preferably, the volume ratio of triethylene glycol to N,N-dimethylformamide is 1-10:1-10.

[0010] Preferably, the laser irradiation time is 0.25-2h.

[0011] Preferably, the frequency of laser irradiation is 5-20 Hz, and the energy density is 300 mJ-1J.

[0012] The second object of the present invention is to provide graphene prepared by the above method.

[0013] The second object of the present invention is to provide a graphene film, wherein the graphene is dispersed in a solvent to form a graphene dispersion liquid, the dispersion liquid is printed onto a polytetrafluoroethylene substrate, the substrate is heated and after the solution is evaporated to form a graphene film, the dispersion liquid is separated from the substrate to obtain a graphene film.

[0014] Preferably, the concentration of the graphene dispersion is 1 mg / ml, and the solvent is N,N-dimethylformamide.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention combines a laser with a wavelength of 1064nm with a dispersion based on triethylene glycol (TEG) / DMF. TEG has a strong absorption peak at a wavelength near 1000-1100nm, which can provide extremely high transient energy for the reactants, thereby promoting the deprotonation process and the reduction process. In addition, efficient absorption can generate a large amount of plasma in the solution, and the plasma also has a strong reducing effect on GO. DMF is used to reduce the viscosity of the liquid. The prepared graphene is completely reduced. Due to the short irradiation time, the ablation effect caused by the laser can be greatly reduced, so that the prepared graphene has a large size and few defects. The thermal conductivity of the prepared graphene film is 892W / m·k. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the dispersibility of graphene oxide obtained in the present invention under different dispersants;

[0018] Figure 2 This is a scanning electron microscope image of the graphene obtained by the present invention;

[0019] Figure 3 This is a transmission electron microscope image of the graphene obtained by the present invention;

[0020] Figure 4 This is an infrared spectrum of graphene obtained by the present invention;

[0021] Figure 5 This is a cross-sectional scanning electron microscope image of the graphene film obtained by the present invention;

[0022] Figure 6 This is a comparison chart of the thermal conductivity of the graphene film obtained in the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0025] Example 1

[0026] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0027] Graphene oxide was dispersed in a mixed solution of triethylene glycol (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion. The concentration of graphene oxide was 0.5 mg / mL. Laser wavelength was 1064 nm for 15 min. The frequency of laser irradiation was 5 Hz and the energy density was 300 mJ. After the irradiation, it was washed with water and ethanol in turn and dried at 60°C to constant weight to obtain graphene.

[0028] Example 2

[0029] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0030] Graphene oxide was dispersed in a mixed solution of triethylene glycol (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion. The concentration of graphene oxide was 0.5 mg / mL. Laser wavelength was 1064 nm for 30 min. The frequency of laser irradiation was 10 Hz and the energy density was 600 mJ. After the irradiation, it was washed with water and ethanol in turn and dried at 60°C to constant weight to obtain graphene.

[0031] Example 3

[0032] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0033] The graphene oxide was dispersed in a mixed solution of triethylene glycol (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion, the concentration of the graphene oxide was 1 mg / mL, and the laser wavelength was 1064 nm for 60 min. The frequency of the laser irradiation was 15 Hz, and the energy density was 800 mJ. After the irradiation, the graphene was washed with water and ethanol in sequence, and dried at 60° C. to constant weight to obtain graphene;

[0034] Example 4

[0035] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0036] Graphene oxide was dispersed in a mixed solution of triethylene glycol (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion. The concentration of graphene oxide was 2 mg / mL. The sample was irradiated at a laser wavelength of 1064 nm for 120 min. The frequency of the laser irradiation was 20 Hz and the energy density was 1200 mJ. After the irradiation, the sample was washed with water and ethanol in turn and dried at 60°C to constant weight to obtain graphene.

[0037] Comparative Example 1

[0038] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0039] Graphene oxide was dispersed in water to form a graphene oxide dispersion, the concentration of graphene oxide was 0.5 mg / mL, and laser irradiation was performed at a wavelength of 1064 nm for 15 min. The frequency of laser irradiation was 5 Hz, and the energy density was 300 mJ. After the irradiation, the dispersion was washed with water and ethanol in sequence, and dried at 60° C. to constant weight to obtain graphene.

[0040] Comparative Example 2

[0041] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0042] Graphene oxide was dispersed in a mixed solution of triethylene glycol (TEG and DMF were mixed in a volume ratio of 1:1) to form a graphene oxide dispersion. The concentration of graphene oxide was 0.5 mg / mL. Laser wavelength was 532 nm for 30 min. The frequency of laser irradiation was 5 Hz and the energy density was 300 mJ. After the irradiation, it was washed with water and ethanol in turn and dried at 60°C to constant weight to obtain graphene.

[0043] Comparative Example 3

[0044] A method for preparing graphene by reducing graphene oxide comprises the following steps:

[0045] Graphene oxide was dispersed in water to form a graphene oxide dispersion, the concentration of graphene oxide was 0.5 mg / mL, and laser irradiation was performed at a wavelength of 532 nm for 30 min. The frequency of laser irradiation was 5 Hz, and the energy density was 300 mJ. After the irradiation, the dispersion was washed with water and ethanol in sequence, and dried at 60° C. to constant weight to obtain graphene.

[0046] Figure 1 Schematic diagram of the dispersibility of graphene oxide in different dispersants of the present invention, Figure 1 In the formula, a is the dispersant TEG / DMF, and b is the dispersant water. Figure 1 As shown, graphene oxide is mixed uniformly with TEG / DMF dispersant without stratification, while stratification occurs after graphene oxide is mixed with water.

[0047] Figure 2 is a scanning electron microscope image of graphene obtained in the present invention, Figure 2 In the embodiment, a is Example 1, b is Comparative Example 1, c is Comparative Example 2, and d is Comparative Example 3. Figure 2As shown, the graphene sheet size of Example 1 is about 2 μm, and the sheet structure is smooth and complete. The graphene sheet size of Comparative Example 1 is less than 500 nm. Small-sized structures easily cause heat conduction losses and reduce thermal conductivity. The graphene sheet size of Comparative Example 2 is about 400 nm, and obvious wrinkles and agglomeration occur, which are not conducive to heat conduction. The scanning electron microscope image of Comparative Example 4 shows that the sheet size is about 300 nm, a large number of defects and wrinkles are generated on the surface, and the structural flatness is poor, which is not conducive to heat conduction.

[0048] Figure 3 is a transmission electron microscope image of graphene obtained in the present invention, Figure 3 In the figure, a is Example 1, and b is an enlarged view of a. Figure 3 As shown in the figure, we can see that the sheet structure is very flat and complete. Figure 3 b The edge graphene structure can be clearly seen, and the interlayer spacing is the typical graphene spacing of 0.33nm, proving that graphene oxide is well reduced to graphene.

[0049] Figure 4 This is the infrared spectrum of the graphene obtained by the present invention. Figure 4 As shown, the original GO sample has a peak at 3432 cm -1 A broad OH stretching vibration band is shown near 2920-2850cm, so the weakening of the intensity of this peak can be used as a basis for judging whether the GO reduction is completed to a certain extent. According to the spectrum of Example 1, it can be clearly seen that this peak almost disappears. -1 The peak at represents the CH stretching vibration, which may be due to the ring opening of the epoxy group and the protonation of TEG. When the irradiation time is increased to 15 minutes, this peak is almost unobservable, indicating that the CC network structure is constructed by the dehydrogenation reaction. In contrast, Comparative Examples 1-3 show the obvious presence of carboxyl and hydroxyl peaks, indicating that the reaction is far from complete. The above results are consistent with the inferred reaction process, and the reaction is only effective in the TEG / DMF-1064nm system.

[0050] Example 5

[0051] A graphene film, the preparation method comprising the following steps:

[0052] The graphene described in Example 1 was dispersed in N,N-dimethylformamide to form a graphene dispersion liquid, the concentration of the graphene dispersion liquid was 1 mg / mL, the dispersion liquid was screen printed onto a polytetrafluoroethylene substrate, the substrate was heated until the solution was completely volatilized to form a graphene film, and then the substrate was separated to obtain a graphene film, the thickness of the graphene film was 1.83 μm, and it was named LRG-1064. (T / D)-15SP. Before printing, a polytetrafluoroethylene substrate (5 mm thick) was cleaned with ethanol and double distilled water and dried at room temperature. The prepared graphene DMF dispersion was printed on the substrate by pressing. Then, the prepared film was heated in an oven for 30 minutes at 120°C to evaporate the solvent. The dried film fell off automatically.

[0053] Comparative Example 4

[0054] A graphene film, the preparation method comprising the following steps:

[0055] The graphene described in Example 1 was dispersed in N,N-dimethylformamide to form a graphene dispersion liquid, the concentration of the graphene dispersion liquid was 1 mg / mL, the graphene dispersion liquid was evenly dropped on a polytetrafluoroethylene substrate with a smooth surface, the substrate was heated until the solution was completely evaporated to form a graphene film, and then separated from the substrate. The graphene film was named LRG-1064 (T / D) -15DC.

[0056] Comparative Example 5

[0057] A method for preparing a graphene film by reducing graphene oxide comprises the following steps: dispersing graphene in N,N-dimethylformamide to form a graphene dispersion liquid, wherein the concentration of the graphene dispersion liquid is 0.1 mg / ml, using aluminum oxide as filter paper, placing the filter paper in a suction filtration funnel, pouring the graphene oxide dispersion liquid into the suction filtration funnel, depositing to form a graphene oxide film by vacuum filtration, adding ethanol to separate the graphene oxide film from a substrate to obtain a graphene oxide film after the filtration is completed, placing the graphene oxide film in a container, dripping hydroiodic acid on the film in a ratio of 1 ml:5 mg of graphene oxide, heating to 100°C, reacting for 1 hour, and after the reaction is completed, washing with water and ethanol respectively for 3 times to obtain a graphene film; the graphene oxide film is named GO-VF-HI.

[0058] Figure 5 is a cross-sectional scanning electron microscope image of the graphene film obtained by the present invention, Figure 5 In the embodiment, a is Example 5, b is Comparative Example 4, and c is Comparative Example 5. Figure 5 As shown, LRG-1064 obtained in Example 5 (T / D)- The membrane structure prepared by 15-SP is relatively dense, with a thickness of about 1.83 μm; the LRG-1064 obtained in Comparative Example 4 (T / D)- The structure of 15DC is loose; the GO-VF-HI obtained in Comparative Example 5 has a large number of sheets in the middle, which may lead to the problem of incomplete reduction of a large amount of GO.

[0059] Figure 6 The thermal conductivity comparison diagram of the graphene film obtained by the present invention is as follows: Figure 6 As shown, Example 5LRG-1064(T / D)- 15SP heat dissipation film has the highest thermal conductivity of 965W / m·k, compared with 4LRG-1064 (T / D) The thermal conductivity of -15DC and comparative example 5GO-VF-HI heat dissipation films are 643Wm -1 K -1 , and 543Wm -1 K -1 It can be seen that the high-quality graphene reduction and compact deposition film process make the thermal conductivity of the prepared graphene film quite considerable.

[0060] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing graphene by reducing graphene oxide, It is characterized in that The method comprises the following steps: dispersing graphene oxide in a mixed solution of triethylene glycol to form a graphene oxide dispersion, irradiating the dispersion with a laser wavelength of 1000-1100nm, with a laser irradiation frequency of 5-20Hz and an energy density of 300mJ-1J, and washing and drying after the irradiation to obtain graphene.

2. The method for preparing graphene by reducing graphene oxide according to claim 1, It is characterized in that The concentration of the graphene oxide dispersion is 0.5-2 mg / mL.

3. The method for preparing graphene by reducing graphene oxide according to claim 1, It is characterized in that The mixed solution is a mixed solution formed by triethylene glycol and N,N-dimethylformamide.

4. The method for preparing graphene by reducing graphene oxide according to claim 3, It is characterized in that The volume ratio of triethylene glycol to N,N-dimethylformamide is 1-10:1-10.

5. The method for preparing graphene by reducing graphene oxide according to claim 1, It is characterized in that The laser irradiation time is 0.25-2h.

6. Graphene prepared by the method according to any one of claims 1 to 5.

7. A graphene film, It is characterized in that The graphene described in claim 6 is dispersed in a solvent to form a graphene dispersion liquid, the dispersion liquid is printed onto a polytetrafluoroethylene substrate, the substrate is heated and after the solution is completely evaporated to form a graphene film, it is separated from the substrate to obtain a graphene film.

8. The graphene film according to claim 7, It is characterized in that The concentration of the graphene dispersion is 1 mg / ml, and the solvent is N,N-dimethylformamide.

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