KR101254173B1 - Fabrication method for graphene sheet or graphene particle using supercritical fluid - Google Patents

Abstract

The present invention relates to a method for producing a graphene sheet or graphene particles, the method for producing a graphene sheet or graphene particles of the present invention (a) graphene oxide dispersed in an alcohol solvent to form a graphene oxide dispersion solution (B) reducing the graphene oxide dispersion solution under supercritical conditions to form graphene sheets or graphene particles formed by agglomeration of graphene sheets; and (c) the graphene sheets or graphene particles. It comprises the steps of separating and washing and drying, the method for producing a graphene film of the present invention is to prepare a graphene film in the form of a thin film using a graphene sheet or graphene particles prepared according to the above method.

Description

Fabrication method for graphene sheet or graphene particles using supercritical fluids {Fabrication method for graphene sheet or graphene particle using supercritical fluid}

The present invention relates to a method for producing a graphene sheet or graphene particles, and more particularly to a method for producing graphene using supercritical conditions.

Graphene is a material with a single atomic thickness consisting of hexagonal lattice of carbon atoms in a two-dimensional plane. It has various characteristics due to its amazing properties such as excellent electrical mobility, thermal conductivity, mechanical strength, quantized transparency according to thickness, and high specific surface area. Materials of great interest from the field (Park et al., Nature Nanotechnology, 2010, 4, 217-224; Geim, Science, 2009, 324, 1530-1534; Allen et al., Chemical Reviews, 2010, 110, 132-145). Graphene is now widely used in automotive, energy, marine, aerospace, architecture, electronics, medicine, military, and telecommunications, including next-generation energy storage materials, silicon alternatives, supercapacitors, lightweight structural components, electromagnetic shielding materials, sensors, and displays. (Stankovich et al., Nature, 2006, 442, 282-286; Stoller et al., Nano Letters, 2008, 8, 3498-3502; Dikin et al., Nature, 2006, 448, 457-460 Ramanathan et al., Nature Nanotechnology, 2008, 3, 327-331; Blake et al., Nano Letters, 2008, 8, 1704-1708; Bunch et al., Science, 2007, 315, 490-493).

In order for graphene to be applied to various fields in the future, it is essential to develop a method for manufacturing graphene in a mass-produced, economical, fast and easy manner. Current methods for preparing graphene include chemical vapor deposition, stripping of graphene monolayers from graphite multilayer sheets using adhesive tape ("Scotch-tape" or "Peel off" method), and carbonization. The method of stacking graphene crystals on silicon (SiC) substrates (epitaxial growth), cutting carbon nanotubes, thermal exfoliation of graphite (thermal exfoliation), chemical reduction (chemical reduction), etc. It is. Among these, the chemical reduction method is capable of mass production compared to other graphene production methods, and is relatively economical and has advantages of introducing various chemical functional groups (Kaner et al., Science, 2008, 320, 1170-1171). ). In addition, the production of graphene sheets that are well dispersed in a suitable medium has attracted a lot of attention because it can be applied to various fields such as paper structure, thin film coating on various substrates, polymer nanocomposites.

According to the method for preparing graphene by chemical reduction, graphene oxide flakes are prepared by first oxidizing graphite with a strong oxidizing agent. Graphene oxide flakes have a single atomic layer structure and are produced by oxidation such as epoxy groups (epoxide, -O-), carboxyl groups (carboxyl, -COOH), carbonyl (-C = O), hydroxyl groups (hydroxyl, -OH), etc. Because of its hydrophilicity, it has excellent dispersibility in water. However, graphene oxide does not have a hexagonal structure inherent to graphene because of the functional group, and thus has little electrical conductivity. Therefore, it is essential to convert from graphene oxide to graphene with excellent electrical conductivity by proper deoxygenation or reduction.

Several chemical methods have been tried to produce graphene by deoxygenation or reduction of graphene oxide. The most popular of these are hydrazine (hydrazine, NH ₂ NH ₂ ), dimethylhydrazine (dimethylhydrazine, CH ₃ NHNHCH ₃ ), hydroquinone (hydroquinone, HOC ₆ H ₄ OH), sodium borohydride (NaBH ₄ ), And methods of using strong reducing agents such as hydrogen sulfide (H ₂ S) have been proposed (Tung et al., Nature Nanotechnology, 2008, 4, 25-29; Lomeda et al., Journal of American Chemical Society, 2008, 130, 16201-16206; Stankovich et al., Nature, 2006, 442, 282-286; Wang et al., Journal of Physical Chemistry C, 2008, 112, 8192-8195; Si et al., Nano Letters, 2008, 8, 1679-1682; Hofman et al., Kolloid-Zeitschrift, 1934, 68, 149-151).

The use of the reducing agent has the advantage of relatively effective removal of oxygen to produce a graphene having a relatively high electrical conductivity, while most of the strong reducing agent is very corrosive and explosive, very toxic to the human body and cause environmental pollution Because of the disadvantages, there is a problem in that the process cost increases when manufacturing a large amount of graphene. In addition, when hydrazine, which is known as the most effective reducing agent for the deoxygenation of graphene oxide, is used, the resulting graphene contains nitrogen, which has a drawback that the electrical conductivity is much lower than that of graphite (Shin et al., Advanced Functional Materials, 2009, 19, 1987-1992). As a problem, a method of using a relatively weak reducing agent such as sugar and vitamin C has been proposed (Zhu et al, ACS Nano, 2010, 4, 2429-2437; Gao et al, Chemistry of Materials, 2010, 22, 2213-2218). When the weak reducing agent is used, there is an advantage that it is environmentally friendly and harmless to the human body, while the reducing power of the reducing agent is weak so that oxygen cannot be effectively removed from graphene oxide. In addition, when the weak reducing agent is used, the graphene does not have a hexagonal lattice shape inherent to form a defect in graphene, resulting in low electrical conductivity, which results in lower quality. In addition, in order to remove more oxygen from the graphene oxide dispersed in the aqueous solution by using a reducing agent, the reaction time is 6 to 24 hours, which is relatively long, and the reaction proceeds in a batch form.

Therefore, in order to apply graphene to a wide range of fields in the future, the deoxygenation reaction of graphene oxide is more effective, thereby producing high-quality graphene, and the deoxygenation reaction is more environmentally friendly and harmless to humans. There is an urgent need to develop methods that can reduce additional process costs. In addition, it is necessary to develop a graphene production method in which the deoxygenation of graphene oxide proceeds at a very high speed.

An object of the present invention is to produce a high-quality graphene sheet or graphene particles with excellent electrical conductivity by the deoxygenation of graphene oxide without using a reducing agent in an environmentally friendly, easy to mass production, uniform quality and excellent productivity And to provide a method for producing a graphene film comprising a graphene sheet or graphene particles thus formed.

Another object of the present invention to provide a graphene sheet or graphene particles and graphene film prepared by the method for producing graphene from graphene oxide using the supercritical fluid.

Graphene sheet or method for producing a graphene particle of the present invention comprises the steps of (a) dispersing the graphene oxide in an alcohol solvent to form a graphene oxide dispersion solution, (b) the graphene oxide dispersion solution in supercritical conditions Reducing the graphene sheet or the graphene sheet by the graphene sheet is formed by agglomeration and (c) separating and cleaning and drying the graphene sheet or graphene particles, the graphene of the present invention The manufacturing method of the film is to prepare a graphene film in the form of a thin film using a graphene sheet or graphene particles prepared according to the above method.

According to the present invention, a high-quality graphene sheet or graphene particles having excellent electrical conductivity through a deoxygenation reaction of graphene oxide under supercritical fluid conditions and a graphene film including the same may be prepared. Since the graphene sheet or graphene particle manufacturing method of the present invention is environmentally friendly due to the high corrosiveness, explosiveness, human toxicity, environmental pollution, etc. when using a strong reducing agent in the method for producing graphene from the existing graphene oxide The increase in process costs can be solved, resulting in lower equipment and operating costs. In addition, since the deoxygenation of graphene oxide proceeds very effectively under supercritical fluid conditions, it is possible to solve the problem of low quality graphene, which is accompanied by low electrical conductivity, by using a conventional weak reducing agent.

In addition, since the deoxygenation of graphene oxide in the supercritical fluid proceeds at a very high speed, graphene production time can be shortened, production is easy, quality is uniform, mass production is possible and economical.

In order to overcome the disadvantage of preparing graphene by deoxygenation using a conventional reducing agent, when oxygen is produced in a deoxygenation reaction without using a reducing agent under supercritical fluid conditions, oxygen is effectively reduced within a very short time of 2 hours or less. As a result, it is possible to produce high quality graphene sheets or graphene particles with high electrical conductivity, and also to produce graphene sheets or graphene particles in an environmentally friendly manner since no reducing agent is used. It was confirmed that the present invention was completed. In addition, the present invention can produce a high-quality graphene sheet or graphene particles in a continuous process because the deoxygenation reaction of graphene oxide in a supercritical fluid condition is made at a very fast rate even without using a reducing agent.

1 is a graph of FT-IR measurement results of graphene prepared in supercritical methanol using the batch supercritical fluid process of Example 1. FIG.
Figure 2 is a graph of XPS measurement results of graphene prepared in supercritical methanol using the batch type supercritical fluid process of Example 1.
3 is a graph of TGA measurement results of graphene prepared in supercritical methanol using the batch type supercritical fluid process of Example 1. FIG.
4 is a TEM photograph of graphene prepared in supercritical methanol using the batch supercritical fluid process of Example 1. FIG.
FIG. 5 is a graph showing XPS measurement results of graphene prepared in supercritical methanol using the continuous supercritical fluid process of Example 10.
6 is a TEM image of graphene prepared in supercritical methanol using the continuous supercritical fluid process of Example 10.

Graphene sheet or method for producing a graphene particle of the present invention comprises the steps of (a) dispersing the graphene oxide in an alcohol solvent to form a graphene oxide dispersion solution, (b) the graphene oxide dispersion solution in supercritical conditions Reducing the graphene sheet or the graphene sheet to form graphene particles formed by agglomeration; and (c) separating and cleaning and drying the graphene sheet or graphene particles. The graphene sheet refers to a single layer of graphite structure separated from graphite, and constitutes the graphene particles when the graphene sheets are piled up together.

First, step (a) is to disperse the graphene oxide in alcohol. Graphene oxide may be prepared by treating graphite particles with an oxidizing agent such as potassium permanganate (KMnO ₄ ) and a strong acid such as concentrated sulfuric acid or nitric acid. Graphene oxide has a single atomic layer structure in the form of flakes, and epoxy groups (epoxide, -O-), carboxyl groups (carboxyl, -COOH), carbonyl (-C = O), and hydroxyl groups (hydroxyl, -OH) formed during oxidation Because of its hydrophilicity due to functional groups such as), it is excellent in dispersibility in water or alcohol. Meanwhile, in order to disperse the prepared graphene oxide in alcohol, a general dispersion method such as ultrasonic wave may be used.

Prior to step (a), (a ') may further comprise the step of treating the graphite with a strong acid and an oxidizing agent to form graphene oxide.

The graphene oxide may be in the form of flakes having a single atomic layer structure, and the graphene oxide may include at least one functional group selected from the group consisting of an epoxy group, a carboxyl group, a carbonyl group, and a hydroxyl group in water or an alcohol solvent. Dispersibility may be excellent.

The alcohol solvent may be an alcohol solvent including one or more hydroxyl groups in the main chain having 1 to 10 carbon atoms. More preferably, alcohol having one or more hydroxyl groups bonded to the main chain having 1 to 7 carbon atoms may be used, but the present invention is not limited thereto.

The concentration of graphene oxide in the graphene oxide dispersion solution may be 0.1 g / L to 1000 g / L. More preferably, it may be 1 g / L to 500 g / L. When the concentration of graphene oxide in the graphene oxide dispersion solution is less than 0.1 g / L, the concentration is too thin, so that the amount of graphene sheets or graphene particles produced in unit time is low and economic efficiency is low, and the amount of graphene oxide is 1,000 If g / l is exceeded, the concentration is too high to effectively deoxygenate the reaction from graphene oxide, and the uniformity may deteriorate and the quality may be degraded.

Step (b) may be in a batch reactor or continuous process reactor. The use of a continuous process reactor has the advantage of maintaining quality stability during mass production.

Step (b) may be at 100-600 ° C. and 20-600 bar. It is more preferable that reaction temperature is 300-500 degreeC, and reaction pressure is 100-500 bar. When the reaction temperature is less than 100 ℃ and the reaction pressure is less than 20 bar may reduce the reducing power of the supercritical alcohol may not effectively proceed with the deoxygenation reaction of the graphene oxide may produce a low electrical conductivity graphene, reaction If the temperature exceeds 600 ° C and the reaction pressure exceeds 600 bar, the economical efficiency is lowered due to the cost of maintaining a high temperature and high pressure.

The residence time in the reactor in step (b) is not particularly limited, but is preferably from 10 seconds to 6 hours, more preferably from 1 minute to 4 hours. If the residence time in the reactor is less than 10 seconds, because the residence time is short, the deoxygenation of graphene oxide in supercritical alcohol does not proceed effectively, there is a problem that low-quality graphene with low electrical conductivity can be produced, 6 hours If exceeded, the increase in the residence time in the conditions of high temperature and high pressure may lead to a decrease in productivity and deterioration of economic efficiency.

The alcohol solvent is methanol (critical temperature = 239 ° C; critical pressure = 81 bar), ethanol (critical temperature = 241 ° C; critical pressure = 63 bar), propanol (critical temperature = 264 ° C; critical pressure = 52 bar), Isopropyl alcohol (critical temperature = 307 ° C; critical pressure = 41 bar), butanol (critical temperature = 289 ° C; critical pressure = 45 bar), isobutanol (critical temperature = 275 ° C; critical pressure = 45 bar), 2- Butanol (critical temperature = 263 ° C; critical pressure = 42 bar), tert-butanol (critical temperature = 233 ° C; critical pressure = 40 bar), n-pentanol (critical temperature = 307 ° C; critical pressure = 39 bar), Isopentyl alcohol (critical temperature = 306 ° C; critical pressure = 39 bar), 2-methyl-1-butanol (critical temperature = 302 ° C; critical pressure = 39 bar), neopentyl alcohol (critical temperature = 276 ° C; critical pressure = 40 bar), diethyl kebinol (critical temperature = 286 ° C; critical pressure = 39 bar), methyl propyl kebinol (critical temperature = 287 ° C; critical pressure = 37 bar), methyl isopropyl Kebinol (critical temperature = 283 ° C; critical pressure = 39 bar), dimethyl ethyl kebinol (critical temperature = 271 ° C; critical pressure = 37 bar), 1-hexanol (critical temperature = 337 ° C; critical pressure = 34 bar ), 2-hexanol (critical temperature = 310 ° C; critical pressure = 33 bar), 3-hexanol (critical temperature = 309 ° C; critical pressure = 34 bar), 2-methyl-1-pentanol (critical temperature = 331 ° C; critical pressure = 35 bar), 3-methyl-1-pentanol (critical temperature = 387 ° C; critical pressure = 30 bar), 4-methyl-1-pentanol (critical temperature = 330 ° C; critical pressure = 30 bar), 2-methyl-2-pentanol (critical temperature = 286 ° C; critical pressure = 36 bar), 3-methyl-2-pentanol (critical temperature = 333 ° C; critical pressure = 36 bar), 4- Methyl-2-pentanol (critical temperature = 301 ° C .; Critical pressure = 35 bar), 2-methyl-3-pentanol (critical temperature = 303 ° C; critical pressure = 35 bar), 3-methyl-3-pentanol (critical temperature = 302 ° C; critical pressure = 35 bar) , 2,2-dimethyl-1-butanol (critical temperature = 301 ° C .; critical pressure = 35 bar), 2,3-dimethyl-1-butanol (critical temperature = 331 ° C .; critical pressure = 35 bar), 2,3 -Dimethyl-2-butanol (critical temperature = 331 ° C; critical pressure = 35 bar), 3,3-dimethyl-1-butanol (critical temperature = 331 ° C; critical pressure = 35 bar), 2-ethyl-1-butanol (Critical temperature = 307 ° C; critical pressure = 34 bar), 1-heptanol (critical temperature = 360 ° C; critical pressure = 31 bar), 2-heptanol (critical temperature = 335 ° C; critical pressure = 30 bar), At least one selected from the group consisting of 3-heptanol (critical temperature = 332 ° C; critical pressure = 30 bar) and 4-heptanol (critical temperature = 329 ° C; critical pressure = 30 bar), the second Critical conditions are the critical temperature and the critical pressure of the alcohol.

Step (c) is a step of separating the prepared graphene sheet or graphene particles from the alcohol. The graphene sheet or graphene particles formed through the reduction process in step (b) are separated from alcohol and dried. Separation may use centrifugation or filtering, and the nanoparticle and the unreacted precursor solution may be separated.

After step (c), the graphene sheet or graphene particles of (c ') may be further comprising the step of purifying by centrifugation after dispersing in a solvent. At this time, the solvent may be alcohol, acetone, tetrahydrofuran and the like, but is not limited to the graphene sheet or graphene particles formed can be dispersed.

The graphene film manufacturing method of the present invention is to prepare a graphene film in the form of a thin film using the graphene sheet or graphene particles prepared according to the above method, the graphene sheet or graphene particles are dispersed in a solvent By forming a graphene particle dispersion solution, and separating the graphene particle dispersion solution using a filter to separate the graphene film formed on the filter from the filter to obtain a graphene film.

Examples and Comparative Examples

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. However, this is only a few embodiments, the present invention is not limited thereto. Hereinafter, the graphene term is used interchangeably with graphene sheets or graphene particles.

Graphene Characterization

Deoxygenation of graphene oxide using a transmission electron microscopy (hereinafter referred to as 'TEM') of EFI Co., Ltd. to analyze the morphology of the graphene prepared by the production method of the present invention. Fourier transform infrared spectroscopy from Thermo Electron (FT-IR) and X-ray Photoelectron Spectroscopy (Physical Electronic) XPS) and Thermo Scientific's elemental analyzer (hereinafter referred to as 'EA') were used. In addition, the thermal properties of the graphene was measured using a thermogravimetric analysis (Thermogravimetric Analysis, hereinafter 'TGA') of DuPont. The electrical conductivity of graphene was first measured using a four-point probe made by Jandel, after making a free-standing graphene film. Free-standing graphene film is dispersed on a supercritical alcohol graphene on methylene chloride (methylene chloride, CH ₂ Cl ₂ ) and then the film on the filter by a vacuum filtration method using a porous alumina filter of Millipore (Millipore) Was formed and dried in air and then separated from the filter.

Example  1: Batch Supercritical Fluid Process Graphene  Manufacturing (1)

Graphene oxide was prepared using a modified Hummers method in which graphite powder was treated with concentrated sulfuric acid, K ₂ S ₂ O ₈ , P ₂ O _5, and treated with KMnO ₄ , H ₂ O ₂ . 1 g of graphene oxide was dispersed in 50 ml of methanol to adjust the graphene oxide concentration to 20 g / l, and 3.5 ml of graphene oxide dispersed methanol solution was made of a 10 ml alloy (Hastelloy C276). It was introduced into a high temperature high pressure reactor. The reactor was introduced into a salt bath maintained at 400 ° C. to a pressure of 300 bar and then deoxygenated for 2 hours while maintaining this condition. The resulting graphene solution was cooled with 10 ° C. water and filtered through a filter to separate and recover the graphene. The recovered graphene was dried in a vacuum oven at 60 ° C. for one day to remove methanol. 1 is a graph of the FT-IR results of the graphene thus formed. 2 is XPS results of the graphene prepared in Example 1, Figure 3 is the TGA results of the graphene prepared in Example 1, Figure 4 is a TEM image of the graphene prepared in Example 1.

As shown in FIG. 1, the FT-IR spectrum of graphene oxide shows hydroxyl groups (OH, 3446 cm ⁻¹ ), carbonyl groups (C═O, 1731 cm ⁻¹ ), and C═C groups (1621 cm ^{− 1} ), alcohol group (C-OH, 1386 cm ^-1 ), epoxy group (COC, 1220 cm ^-1 ), ether group (CO, 1060 cm ^-1 ) can be confirmed that the oxidation was present. When deoxygenation of graphene oxide was carried out using supercritical methanol to reduce the permeability by oxygen-bonded functional groups such as hydroxyl group, carbonyl group, alcohol group, epoxy group and ether group It can be seen that the decrease. On the other hand, the graphene reduced in supercritical methanol increased the transmittance (1569 cm ^-1 ) corresponding to the intrinsic skeletal vibration. This suggests that supercritical methanol is very effective for the deoxygenation of graphene oxide.

As shown in FIG. 2, oxygen is almost absent in the XPS spectrum of the graphite powder, but it can be seen that oxygen is present in graphene oxide due to a large increase in the oxygen peak. On the other hand, when the graphene oxide is deoxidized by using a supercritical methanol in Example 1, it can be seen that the oxygen peak is greatly reduced. Table 1 shows the results of calculating the C / O ratio by quantifying the XPS oxygen and carbon peaks. In the case of the graphite powder, the C / O ratio was very large as 97.47, and it was confirmed that there was almost no oxygen. In the case of graphene oxide, the C / O ratio was 1.95. In the case of graphene reduced graphene oxide by deoxygenation using supercritical methanol, it was confirmed that much oxygen was removed as the C / O ratio measured by XPS was 11.89. After measuring the amount of carbon, oxygen, and hydrogen by EA, the C / O ratio was calculated and the results are shown in Table 1. The C / O ratio measured by EA also tended to be very similar to the C / O ratio measured by XPS.

3 is a TGA graph of the graphene prepared in Example 1. In the case of graphite powder, since the oxygen is almost absent, the weight is hardly reduced even when heated to 800 ° C., but the graphene oxide is reduced by 66% of the original weight when heated to 800 ° C. This is because oxygen present in the graphene oxide is gasified in the form of CO or CO ₂ . In the case of the graphene prepared in Example 1 it was confirmed that the deoxygenation proceeded effectively by reducing the weight by 13% when heated to 800 ℃.

Figure 4 is an HR-TEM image of the graphene prepared in Example 1. The image and electron scattering results measured by the selective area diffraction pattern. Graphene has a structure in the form of a single layer or a multi-layered nano-sheet structure in which two or three graphene sheets overlap and can be seen that it is very transparent. Therefore, it can be seen that graphene reduced with supercritical methanol has a flaky structure. Electron scattering showed electrons scattered on the (1100) plane of graphene to the first ring and electrons scattered on the (1120) plane of graphene to the second ring. It is also shown that the scattered pattern on the (0001) side of graphene is marked by bright spots with a regular hexagonal structure in the first and second rings, indicating that the crystallinity of graphene prepared by the batch process in supercritical methanol is very good. Can be.

In Example 1, a film was prepared from the reduced graphene nanosheets by deoxygenation of graphene oxide using supercritical methanol, and electrical conductivity was measured by a four-point probe method. It was found that the electrical conductivity of the graphene film was very high at 3,247 S / m. Therefore, when the graphene oxide was reduced with supercritical methanol, the deoxygenation reaction proceeded effectively, and since the graphene nanosheets were prepared, when the graphene nanosheets were prepared as a free standing film, the graphene nanosheets prepared by the van der Waals attraction were closely attached to each other. It is believed that the conductivity is high.

Example  2: using a batch supercritical fluid process Grapina  Manufacturing (2)

Graphene was prepared in the same manner as in Example 1, except that the reaction time of Example 1 was changed to 1 hour instead of 2 hours. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  3: using a batch supercritical fluid process Grapina  Manufacture (3)

Graphene was prepared in the same manner as in Example 1, except that the reaction time of Example 1 was 30 minutes instead of 2 hours. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  4: using a batch supercritical fluid process Grapina  Manufacture (4)

Graphene was prepared in the same manner as in Example 1, except that the reaction time of Example 1 was 15 minutes instead of 2 hours. The prepared graphene was analyzed by XPS in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  5: Batch Supercritical Fluid Process Grapina  Manufacture (5)

Graphene was prepared in the same manner as in Example 1, except that the dispersion reaction time of Example 1 was 5 minutes instead of 2 hours. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  6: using batch supercritical fluid process Grapina  Manufacture (6)

Graphene was prepared in the same manner as in Example 1 except that the graphene oxide concentration of Example 1 was 40 g / L instead of 20 g / L. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  7: using a batch supercritical fluid process Grapina  Manufacture (7)

Graphene was prepared in the same manner as in Example 1 except that the graphene oxide concentration of Example 1 was changed to 286 g / L instead of 20 g / L. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  8: using batch supercritical fluid process Grapina  Manufacture (8)

Graphene was prepared in the same manner as in Example 1 except that ethanol was used instead of methanol as the reaction solvent of Example 1. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  9: using a batch supercritical fluid process Grapina  Manufacture (9)

Graphene was prepared in the same manner as in Example 1, except that propanol was used instead of methanol as the reaction solvent of Example 1. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

Example  10: using a batch supercritical fluid process Grapina  Manufacture (10)

Graphene was prepared in the same manner as in Example 1, except that butanol was used instead of methanol as the reaction solvent of Example 1. The prepared graphene was analyzed by XPS and EA in the same manner as in Example 1, and the results are shown in Table 1 below.

division menstruum Graphene Oxide Concentration (g / ℓ) Reaction time C / O ratio
by EA C / O ratio
by XPS Example 1 Supercritical methanol 20 2 hours 11.10 11.89 Example 2 Supercritical methanol 20 1 hours 10.18 10.03 Example 3 Supercritical methanol 20 30 minutes 9.25 9.17 Example 4 Supercritical methanol 20 15 mins 8.18 8.78 Example 5 Supercritical methanol 20 5 minutes 6.01 6.25 Example 6 Supercritical methanol 40 2 hours 13.52 13.79 Example 7 Supercritical methanol 286 2 hours 12.58 13.08 Example 8 Supercritical ethanol 20 2 hours 12.04 11.56 Example 9 Supercritical propanol 20 2 hours 10.21 10.15 Example 10 Supercritical butanol 20 2 hours 9.56 9.09 Graphene oxide - - - 2.31 1.95 black smoke - - - > 98 97.47

As shown in Table 1, as the reaction time was decreased from 2 hours to 5 minutes in Examples 1 to 4, the C / O ratio measured by XPS decreased from 11.89 to 6.25, and the deoxygenation was decreased as the reaction time decreased. The degree was reduced. However, in Example 5, even when the reaction time was very short as 5 minutes, the C / O ratio was 6.25, indicating that the deoxygenation of graphene oxide in supercritical methanol proceeds effectively. In addition, when the concentration of graphene oxide dispersed in supercritical methanol in Examples 1 and 5 was increased from 20 g / L to 40 g / L, the C / O ratio increased from 11.89 to 13.79. It was found that an effective deoxygenation reaction proceeded. In addition, although the concentration of graphene oxide dispersed in supercritical methanol in Examples 5 and 6 was increased from 40 g / L to 286 g / L, the C / O ratio was hardly changed. Although the oxide was used, it was found that the deoxygenation reaction proceeded effectively. In addition, in the case of using supercritical ethanol, supercritical propanol and supercritical butanol instead of supercritical methanol as the supercritical alcohol in Examples 1 and 7 to 9, the C / O ratio of the prepared graphene was 11.89 to 9.09 It can be seen that a sufficient deoxygenation reaction proceeded in each solvent because the C / O ratio of graphene oxide before the reduction was higher than 1.95. Therefore, it was found that the alcohol in the supercritical state is very effective for the deoxygenation reaction in the graphene oxide because of the reducing power.

Example  11: Continuous  Using a supercritical fluid process Grapina  Produce

Methanol was introduced into a 1000 ml glass vessel, and 10 g of graphene oxide was introduced thereto to adjust the dispersed graphene concentration to 20 g / l. The methanol solution in which the graphene oxide was dispersed was pressurized to 250 bar by pumping at a rate of 3 g / min at room temperature using a high pressure pump. Methanol was introduced into another 20 l plastic vessel, pumped at a rate of 9 g / min using a high pressure pump, pressurized to 250 bar and transferred to the preheater. The pressurized precursor mixed solution and methanol were transferred to a high temperature high pressure reactor where the temperature was maintained at 400 ° C. for 15 minutes. The resulting solution of graphene particles was cooled using a cooler, and then the graphene particles were separated and recovered using a filter. The separated graphene was dried in a vacuum oven at 60 ° C. for one day to remove methanol and analyzed in the same manner as in Example 1. 5 is XPS results of graphene prepared in a continuous process using the supercritical methanol of Example 10. As shown in Figure 5, it can be seen that the oxygen peak is significantly reduced compared to the graphene oxide. In addition, the C / O ratio measured by XPS was 8.43, and even in the case of using the continuous process, it was found that the effective deoxygenation reaction was performed in the graphene oxide similarly to the case of using the batch process.

6 shows HR-TEM results of graphene prepared by deoxygenation from graphene oxide in a continuous process using supercritical methanol and electron scattering results measured by selective area diffraction pattern. Similar to the case of using the batch process, it was found that a single layer of graphene sheet was prepared. Electron scattering showed electrons scattered on the (1100) plane of graphene to the first ring and electrons scattered on the (1120) plane of graphene to the second ring. In addition, the scattered pattern on the (0001) side of the graphene is marked by bright dots with a regular hexagonal structure in the first and second rings, indicating that the crystallinity of graphene produced by a continuous process in supercritical methanol is very good. Can be. In addition, it can be seen that the graphene prepared by the deoxygenation reaction from the graphene oxide in a continuous process using supercritical methanol has high electrical conductivity of 1,523 S / m, thereby producing high quality graphene. As a result, it was confirmed that even when the continuous process was used, graphene nanosheets having excellent electrical conductivity could be manufactured similarly to the case where the batch process was used.

Claims (12)

(a) dispersing graphene oxide in an alcohol solvent to form a graphene oxide dispersion solution;
(b) reducing the graphene oxide dispersion solution under supercritical conditions to form graphene sheets or graphene particles formed by agglomeration of the graphene sheets; And
(c) separating and cleaning and drying the graphene sheet or graphene particles
Graphene sheet or a graphene particle manufacturing method comprising a. The method of claim 1, wherein before step (a),
(a ') A method for producing a graphene sheet or graphene particles further comprising the step of forming a graphene oxide by treating a strong acid and an oxidizing graphite. The method of claim 1, wherein the graphene oxide is in the form of flakes having a single atomic layer structure. The graphene sheet or graphene particles of claim 1, wherein the graphene oxide has at least one functional group selected from the group consisting of an epoxy group, a carboxyl group, a carbonyl group, and a hydroxyl group, and is excellent in dispersibility in an alcohol solvent. Manufacturing method. The method of claim 1, wherein the alcohol solvent is an alcohol solvent including at least one hydroxyl group in a main chain having 1 to 10 carbon atoms. The method of claim 1, wherein the concentration of graphene oxide in the graphene oxide dispersion solution is 0.1 g / L to 1000 g / L. The method of claim 1, wherein step (b) is performed in a batch reactor or a continuous process reactor. The method of claim 1, wherein step (b) is made of graphene sheet or graphene particles is made at 100 ~ 600 ℃ and 20 ~ 600 bar. The method of claim 1, wherein the alcohol solvent is methanol (critical temperature = 239 ℃; critical pressure = 81 bar), ethanol (critical temperature = 241 ℃; critical pressure = 63 bar), propanol (critical temperature = 264 ℃; critical Pressure = 52 bar), isopropyl alcohol (critical temperature = 307 ° C; critical pressure = 41 bar), butanol (critical temperature = 289 ° C; critical pressure = 45 bar), isobutanol (critical temperature = 275 ° C; critical pressure = 45 bar), 2-butanol (critical temperature = 263 ° C; critical pressure = 42 bar), tert-butanol (critical temperature = 233 ° C; critical pressure = 40 bar), n-pentanol (critical temperature = 307 ° C; critical Pressure = 39 bar), isopentyl alcohol (critical temperature = 306 ° C; critical pressure = 39 bar), 2-methyl-1-butanol (critical temperature = 302 ° C; critical pressure = 39 bar), neopentyl alcohol (critical temperature = 276 ° C; critical pressure = 40 bar), diethyl kebinol (critical temperature = 286 ° C; critical pressure = 39 bar), methyl propyl kebinol (critical temperature = 287 ° C; critical pressure = 37 bar), Methyl isopropyl kebinol (critical temperature = 283 ° C; critical pressure = 39 bar), dimethyl ethyl kebinol (critical temperature = 271 ° C; critical pressure = 37 bar), 1-hexanol (critical temperature = 337 ° C; critical pressure = 34 bar), 2-hexanol (critical temperature = 310 ° C; critical pressure = 33 bar), 3-hexanol (critical temperature = 309 ° C; critical pressure = 34 bar), 2-methyl-1-pentanol ( Critical temperature = 331 ° C., critical pressure = 35 bar), 3-methyl-1-pentanol (critical temperature = 387 ° C .; critical pressure = 30 bar), 4-methyl-1-pentanol (critical temperature = 330 ° C.); Critical pressure = 30 bar), 2-methyl-2-pentanol (critical temperature = 286 ° C; critical pressure = 36 bar), 3-methyl-2-pentanol (critical temperature = 333 ° C; critical pressure = 36 bar) , 4-methyl-2-pentanol (critical temperature = 301 ° C .; Critical pressure = 35 bar), 2-methyl-3-pentanol (critical temperature = 303 ° C; critical pressure = 35 bar), 3-methyl-3-pentanol (critical temperature = 302 ° C; critical pressure = 35 bar) , 2,2-dimethyl-1-butanol (critical temperature = 301 ° C .; critical pressure = 35 bar), 2,3-dimethyl-1-butanol (critical temperature = 331 ° C .; critical pressure = 35 bar), 2,3 -Dimethyl-2-butanol (critical temperature = 331 ° C; critical pressure = 35 bar), 3,3-dimethyl-1-butanol (critical temperature = 331 ° C; critical pressure = 35 bar), 2-ethyl-1-butanol (Critical temperature = 307 ° C; critical pressure = 34 bar), 1-heptanol (critical temperature = 360 ° C; critical pressure = 31 bar), 2-heptanol (critical temperature = 335 ° C; critical pressure = 30 bar), At least one selected from the group consisting of 3-heptanol (critical temperature = 332 ° C; critical pressure = 30 bar) and 4-heptanol (critical temperature = 329 ° C; critical pressure = 30 bar),
The supercritical condition is a graphene sheet or a method for producing graphene particles that are above the critical temperature and critical pressure of the alcohol. The method of claim 1, wherein after step (c),
Dispersing the graphene sheet or graphene particles of (c ') in a solvent and then centrifuging to purify the graphene sheet or a method for producing the graphene particles. A graphene film manufacturing method for preparing a graphene film in the form of a thin film using a graphene sheet or graphene particles prepared according to any one of claims 1 to 10. The graphene formed on the filter of claim 11, wherein the graphene sheet or the graphene particles are dispersed in a solvent to form a graphene particle dispersion solution, and the graphene particle dispersion solution is separated using a filter to form graphene. Method for producing a graphene film is to separate the film from the filter to obtain a graphene film.

Images