KR20130121294A - Method for preparing hydrophilic graphene and composite containing the prepared hydrophilic graphene - Google Patents

Abstract

The present invention relates to a technique for reforming graphene prepared by reducing graphite oxide to make it hydrophilic. Hydrophilicity in which ammonium ions, which are hydrophilic cations, are present on the graphene surface by reacting graphene with an amine, followed by halogenated hydrocarbon reaction. Provided is a method of modifying with graphene.
Hydrophilic graphene produced by the present invention is stably dispersed in water, when used in the production of nanocomposites with hydrophilic polymers, graphene is efficiently dispersed and effectively contribute to the improvement of electrical conductivity, thermal conductivity, High performance nanocomposites with improved mechanical properties can be prepared.

Description

Method for preparing hydrophilic graphene and Composite containing the prepared hydrophilic graphene}

The present invention relates to the modification technique and the use of hydrophilic graphene to make the graphene hydrophilic.

As a new nano material having excellent properties of graphene, researches for applications in various fields have recently been conducted. That is, excellent properties such as modulus of 1 TPa, electrical conductivity of 10 ⁶ S / cm, thermal conductivity of 5000 W / mK, and large surface area of 2600 m ² / g can be applied in various fields.

Until 2004, graphene was known to be a material that could not exist independently. Only theoretical studies have been conducted, but since the Geim Group at the University of Manchester in 2004 confirmed the existence of graphene, graphene is a new conductive nanomaterial. In the spotlight, various studies are being conducted worldwide. Graphene can be prepared in several ways. That is, a method of reducing graphite oxide, a chemical vapor deposition method of generating graphene by adsorbing rearrangement of precursors on a substrate, and a method of mechanically separating each layer of graphite are utilized in graphene production. Among these methods, the graphene manufacturing method by reduction of graphite oxide has an advantage that industrial mass production is possible. However, since graphene is a hydrophobic material, it is difficult to stably disperse in water or a hydrophilic medium. Therefore, in order to obtain graphene for various uses using graphene in a hydrophilic medium, it is necessary to modify the prepared graphene to have hydrophilicity. However, when the graphene is modified to have hydrophilicity, excellent properties of graphene are often lowered. Therefore, there is a need for a modification technique that gives hydrophilicity while minimizing the degradation of the inherent physical properties of graphene.

The present invention is to provide a modification technique for obtaining high performance graphene having maximum hydrophilicity and expressing graphene intrinsic physical properties.

In addition, the present invention is to provide a technique for producing a nanocomposite material having excellent physical properties by using hydrophilic graphene.

In order to minimize the degradation of the properties of the graphene when the hydrophilic modification of the graphene, the present inventors utilize a method of modifying hydrophilicity by using a reactive group remaining on the graphene surface prepared from graphite oxide, and using the modified hydrophilic graphene A method of preparing high performance nanocomposites has been studied and the present invention has been completed.

According to the present invention, 1) stirring the heating in the amine compound solution of 50 to 1000 times by weight based on the graphene graphene in the presence of an acid or base catalyst; And 2) adding a halogenated hydrocarbon to graphene after step 1) is provided to modify the graphene hydrophilically to have ammonium ions as cations.

In addition, the present invention provides a high performance nanocomposite composition comprising 100 parts by weight of a polymer and 0.1 to 10 parts by weight of the modified graphene powder.

The composition ratio in the nanocomposite composition is based on solids and the solvents and dispersions used in the preparation of the composition are considered to be evaporated off (dry) in the final nanocomposite.

      Graphene used for modification includes all graphenes prepared by reducing graphite oxide. Most graphenes prepared from graphite oxide have functional groups containing oxygen, and by modifying the hydrophilicity by using this, it is possible to minimize the degradation of the inherent properties of the graphene. Various methods can be utilized to reduce the graphite oxide. For example, a thermal reduction method prepared by swelling and peeling the layers constituting the graphite oxide by heating the graphite oxide to a high temperature instantaneously, a chemical reduction method of dispersing the graphite oxide in a liquid medium and then reducing it using a reducing agent such as hydrazine, etc. There is this. In the thermal reduction method, when graphite oxide is heated to a high temperature of 300 or more instantaneously, gaseous products such as carbon dioxide generated by reduction and decomposition of functional groups on the surface generated by oxidation are vaporized instantaneously, and each layer of graphite oxide is peeled off to form graphene. . The degree of peeling varies depending on the degree of oxidation of the graphite oxide used for peeling, and the degree of peeling may be improved by further ultrasonication. The functional groups attached to the graphite oxide are decomposed and decomposed to generate carbon dioxide and exist as a functional group containing some oxygen. Many of these remaining functional groups exist in the form of an epoxy group, and they are used for hydrophilic modification.

The graphite oxide is prepared by oxidizing graphite powder using nitric acid, NaClO ₃ , KClO ₃ , KMnO ₄ , or other oxidizing agents alone or in combination, and may be prepared by oxidizing by electrochemical method. The ratio of the number of carbon / oxygen in the graphite oxide powder may be in the range of 1 to 20/1 but may be smaller or larger than this depending on the degree of oxidation. Graphite oxide powders usually have peaks around 2 = 13 in the wide-angle X-ray diffraction analysis because the distance between layers is about 7, but the values may vary depending on the degree of oxidation and absorption of moisture.

      The reforming reaction is carried out with stirring and heating of the graphene prepared as shown in Fig. 1 to an amine compound in the presence of an acid or base catalyst. In this process, the first stage reaction of Figure 1 occurs. At this time, the amine compound is reacted by dispersing alone or in a suitable solvent. In this case, the total amount of the amine compound and the solvent should be 50 weight times or more of graphene to be less than 1000 weight times to have proper fluidity and economic efficiency. The range of 200 to 300 times by weight is appropriate. Primary amines, secondary amines and the like can be used. Considering steric hindrance with graphene, primary amines are advantageous for the reaction. The amount of catalyst used is economically less than 30% of the amount of the amine compound. Higher reaction temperatures are advantageous in terms of reaction rate, but excessively high values are not economical and may impair the stability of the product. The graphene reacted with the amine is subjected to the second step reaction of the halogenated hydrocarbon with the second step shown in Figure 1 to prepare a hydrophilic graphene having an ammonium cation. The hydrocarbon group of a halogenated hydrocarbon can use various things, such as a saturated hydrocarbon, unsaturated hydrocarbon, and a hydrocarbon containing an aromatic ring. When the number of carbons is high, the prepared hydrophilic graphene can be minimized to reaggregate due to steric hindrance, but since hydrophilicity is reduced, hydrocarbon groups having 25 or less carbon atoms are preferable. Halogen can be chlorine, bromine or iodine.

      Hydrophilic graphene can be effectively dispersed in water, hydrophilic solvents, hydrophilic polymers, and the like, and can be used for various applications. For example, nanocomposites having improved electrical conductivity, thermal conductivity, and mechanical properties can be manufactured by adding to water-soluble or water-dispersible polymer products.

The polymer encompasses all kinds of polymers such as condensation polymers such as polyurethane, epoxy resins, polyesters, polyamides, addition polymers such as polyvinyl alcohol, and natural polymers such as starch, and the like, and nanocomposites include stabilizers and flame retardants in addition to these polymers. It may also include additives for improving the performance of the polymer. The amount of the modified graphene added preferably includes 0.1 to 10 parts by weight of graphene powder based on 100 parts by weight of the polymer.

According to the present invention, a high-performance graphene having hydrophilicity can be prepared, and graphene is effectively dispersed by using the graphene, thereby preparing a graphene / hydrophilic polymer nanocomposite material in which the contribution to improvement of physical properties is maximized.

Figure 1 schematically shows the reaction of graphene with ethanolamine followed by n -butyl bromide
2 is XPS spectrum of AAG
Figure 3 shows graphs of graphene dispersed in water, respectively: (a) PG, (b) AGM, (c) AG, and (d) AAG.
Figure 4 is a photograph of the shape of the graphene dispersed in the nanocomposites observed with an optical microscope, respectively: (a) N10, (b) N20, (c) N30

By the following examples illustrate the invention in detail. However, the scope of the present invention should not be construed as being limited to these examples.

Graphene  Produce

10 g of graphite powder (expanded graphite, average particle size 280 m) and 200 mL of fuming nitric acid were added to a 500 mL reaction tank equipped with a stirrer, a thermometer, and the like, followed by stirring while maintaining 0, followed by 85 g of potassium chlorate for 2 hours. After slow addition, the graphite was oxidized with stirring at room temperature for 24 hours. The oxidized graphite was filtered off and washed with distilled water until the pH was about 6. The filtered graphite oxide was dried for 2 days at 100 vacuum. The elemental analysis showed that the atomic composition was C ₁₀ O _3.45 H _1.58 .

The dried graphite oxide prepared by the above method was put in a quartz tube, flowed with nitrogen gas, and then put into a 1100 electric furnace for 1 minute, thereby obtaining graphene in which each layer of graphite was thinly thin. The atomic composition of graphene was C ₁₀ O _0.78 H _0.38 , the average particle size was 8.3 m and the surface area measured from the nitrogen adsorption behavior by BET method was 428 m ² / g.

Example  1: (hydrophilic Graphene  Produce)

      For the first step of Figure 1, 1 part of graphene was dispersed in 150 parts of ethanolamine, sonicated for 30 minutes, 23 parts of ammonium chloride as a catalyst was added, and reacted with stirring at 120 to 2 days in a nitrogen atmosphere. The reacted graphene was filtered, washed with water and acetone, and dried at 40 vacuum for 2 days. The raw graphene was named PG, and the graphene reacted with ethanolamine was named AG.

Subsequently, for the second stage reaction of Figure 1, 1 part of AG was dispersed in 100 parts of n -butyl bromide, sonicated for 30 minutes, and then reacted for 2 days at 90 nitrogen atmosphere. The reacted graphene was filtered, washed with water and acetone, and dried at 40 vacuum for 2 days. The graphene reacted in this way was named AAG.

Comparative Example  1: (hydrophilic Graphene  Produce)

Except for reacting at room temperature without adding ammonium chloride as a catalyst, graphene and ethanolamine were reacted in the same manner as in the first step of Example 1, and the reacted graphene was washed and dried. The graphene thus obtained was named AGM.

Example  2 (Manufacture of Nanocomposite Materials)

AAG was dispersed at 5 mg / mL in water and sonicated for 45 minutes, and then mixed with an aqueous solution of 10% by weight of polyvinyl alcohol (PVA), followed by stirring for an additional day. The mixed solution was poured into a Teflon dish and allowed to stand at room temperature for 3 days to evaporate water, and then to stand at 60 vacuum for 2 days to completely remove water to prepare an AAG / PVA nanocomposite material. The content of AAG per 100 parts of PVA was 0.4 parts, 0.7 parts, 1.0 parts, 2.0 parts, and 3.0 denier nanocomposites respectively named N4, N7, N10, N20, N30.

Analysis

Table 1 shows the results of elemental analysis of the graphenes, whereas PG is composed of carbon, oxygen and hydrogen, while AG contains nitrogen and the contents of oxygen and hydrogen are increased than PG. This is considered to be because graphene and ethanolamine reacted. In addition, AAG can be seen that the content of carbon and hydrogen increased by the reaction with n -butyl bromide. On the other hand, the change in elemental composition of AGM compared to PG is not as clear as AG, which indicates that the amount of ethanolamine attached to AGM by physical adsorption or chemical reaction is not high.

The graphenes were analyzed by XPS in Fig. 2 and Table 2, where AAG showed O _1s peak at 532.7 eV, N _1s peak at 400.0 eV, C _1s peak at 284.3 eV, and Br _3d at 68.5 eV. It can be seen that it has a peak. In contrast, the peak of Br _3d could not be observed in the XPS spectrum of AG, and the PG did not have both the N _1s peak and the Br _3d peak. These results are consistent with the results predicted in the response shown in Figure 1. In addition, it can be seen that the peak ratio of O _1s / C _1s is increased by the reaction with ethanolamine in Table 2. In Table 2, the C _1s peak of carbon is the peak of carbon (CC carbon) bonded to carbons near 284 eV, the peak of carbon (CO carbon) single-bonded with oxygen near 286 eV, and the carbon double-bonded with oxygen near 288 eV ( C = O carbon) shows the results of the separation, AG compared with PG can be seen that the carbon dioxide and CN carbon by the reaction with ethanolamine increases the CC carbon and C = O carbon decreases. In AAG, it can be seen that CC carbon is increased again by reaction with n -butyl bromide. As shown in Figure 2, the asymmetric peaks of N _1s can be divided by the contribution of neutral and cationic nitrogen. The presence of neutral nitrogen as well as cationic nitrogen shows that not all nitrogen reacted with n -butyl bromide with the fact that the Br _3d / N _1s ratio value in Table 2 was less than 1.

    After dispersing the graphene at 0.1 mg / mL in water and sonicating for 45 minutes, the graphene was left at room temperature for one day, and the graphene dispersion state was photographed. It can be seen from Fig. 5 that the dispersion of AG in water is better than in AGM and AGM rather than in PG, but almost all of the graphene is sinking in all three samples. In contrast, AAG has been stable in water for more than six months. These results show that AAG has stable cations in water because of the presence of cations on the surface, which is hydrophilic and electrostatically repellent, and has large functional groups attached to it, thereby avoiding entanglement due to steric hindrance.

    In order to see the dispersion of AAG in AAG / PVA nanocomposites, the result of observation with optical microscope after casting into 30m thick film is shown in Figure 4, which shows that the graphene is uniformly dispersed. .

Table 3 shows the measured tensile properties of AAG / PVA nanocomposites, and the modulus and yield stress increased significantly as the graphene content increased. You can see the increase. These results show that graphene is stably dispersed in hydrophilic PVA to effectively express a reinforcing effect.

 Elemental composition of graphene sample Furtherance
PG


AGM


AG


AAG

C ₁₀ O _{0 .78} H _{0 .38}


C ₁₀ O _{0 .83} H _{0 .62} N _{0 .03}


C ₁₀ O _{0 .96} H _{1 .19} N _{0 .13}


C ₁₀ O _{0 .92} H _{1 .32} N _{0 .12}

Graphene XPS Analysis Results sample O _{1 s} Of C _{1 s}

Peak intensity rain Br _3d Of N _{1 s}

Peak intensity rain C _1s analysis C-C carbon C-O and

C-N carbon C = O carbon peak
( eV ) area
(%) peak
( eV ) area
(%) peak
( eV ) area
(%)
PG
AG
AAG
0.123

0.147

0.144
-

-

0.467
284.6

284.4

284.4
64.9

59.6

62.3
286.0

285.6

285.7
25.9

32.9

30.6
288.5

288.5

288.5
9.2

7.5

7.1

Tensile Properties of Graphene / PVA Nanocomposites Sample
Modulus

(MPa)
Yield stress

(MPa)
Shindo

(%)
PVA

N4

N7

N10

N20

N30

N10A

N20A

N30A
616 + 38

875 + 25

1296 + 41

1454 + 32

1864 + 45

1855 + 51

1360 + 49

1498 + 43

1331 + 57

30.1 + 2.2

35.6 + 1.7

44.7 + 2.5

52.7 + 1.9

65.8 + 2.8

51.7 + 3.1

49.1 + 1.4

61.8 + 3.3

48.6 + 2.9
208 + 26

132 + 17

142 + 25

125 + 19

40 + 15

15 + 6

91 + 16

33 + 9

10 + 4

Claims (7)

1) stirring and heating graphene in a presence of an acid or base catalyst in a solution of 50 to 1000 times by weight of the amine compound based on the graphene; And 2) hydrophilic modification of graphene, comprising the step of adding a halogenated hydrocarbon to graphene after step 1). The method of claim 1, wherein the graphene is hydrophilic to modify the graphene prepared by reducing the graphite oxide with a thermal shock or a reducing agent The method according to claim 2, wherein the amine compound solution in step 1) uses 200 to 300 times by weight of graphene, and is modified to hydrophilic graphene, which is heated in the range of 30 to 200. The graphene of claim 2, wherein the amine compound in step 1) is a primary amine compound and the halogenated hydrocarbon in step 2) is a hydrocarbon containing a saturated hydrocarbon, unsaturated hydrocarbon, or aromatic ring of chlorine, bromine or iodine. To modify hydrophilicly The method according to claim 4, wherein the halogenated hydrocarbon is hydrophilically modified with graphene having from 1 to 25 carbon atoms. Nanocomposite material comprising 100 parts by weight of the polymer and 0.1 to 10 parts by weight of the graphene powder modified by the method of claim 1 The nanocomposite material according to claim 6, wherein the polymer is selected from the group consisting of polyurethane, epoxy resin, polyester, polyamide, polystyrene, polyacrylonitrile, polyethylene, polypropylene, and mixtures thereof.

Images