KR20130052245A - Manufacturing of graphene nanosheet for carbon dioxide adsorbent - Google Patents

Abstract

PURPOSE: A graphene nanosheet for a carbon dioxide adhesive and a manufacturing method thereof are provided to improve a selective absorptivity with respect to carbon dioxide and to prevent adsorption of various gases as well as obtaining the selective adsorptivity by providing an appropriate interlayer structure suitable for carbon dioxide adsorption. CONSTITUTION: A manufacturing method of a graphene nanosheet for a carbon dioxide adhesive comprises the steps of: mixing graphite to a sulfuric acid and potassium permanganate and reacting at a temperature of 30 to 40°C for 1 to 3 hours; adding distilled water to the mixture, increasing a temperature to 95 to 100°C and maintaining for 10 to 20 minutes; adding distilled water; adding hydrogen peroxide; removing a sulfate ion and a chlorine ion from the mixture by centrifuging using a 5wt% hydrochloric acid solution; washing the resultant with acetone and drying in an oven to prepare a graphite oxide; and heat-treating the graphite oxide in a vacuum atmosphere at a temperature of 100 to 1200°C. [Reference numerals] (AA) Graphite oxide; (BB) Graphene nanosheet

Description

Manufacturing method of graphene nanosheet for carbon dioxide adsorbent {MANUFACTURING OF GRAPHENE NANOSHEET FOR CARBON DIOXIDE ADSORBENT}

The present invention relates to a method for producing graphene nanosheets for carbon dioxide adsorbents using graphite oxide, and more particularly, to thermally expand graphite oxide by heat-expansion by heat treatment in a vacuum atmosphere and at different temperatures. It relates to a method for producing graphene nanosheets for carbon dioxide adsorbents having a suitable interlayer structure.

Research into recovering the emitted carbon dioxide, which is the main cause of global warming, is being actively conducted around the world, and the collection technology that has been used so far is mainly focused on absorption, adsorption, and membrane separation methods. Absorption method is the most widely used method for the collection and storage of carbon dioxide, but requires a large amount of energy in the separation process, and the process becomes very complicated because the purification process of the used amine is essential. Wastewater treatment and operating costs are the highest.

In addition, the membrane currently manufactured in the membrane separation method has a problem that the price is very high, the equipment cost of the pretreatment device for the purification of the combustion gas is very high, and the replacement cost due to contamination of the separator is very high.

In order to solve the problems of the absorption method and the membrane separation method, research on the storage and separation of carbon dioxide using the adsorption method is in progress, and the adsorption method is mainly the pressure swing adsorption (PSA) using zeolite as the carbon dioxide adsorbent. To achieve. Therefore, researches for improving the selectivity and adsorption capacity of the carbon dioxide adsorbent used in the PSA process are being actively conducted. Although many studies have been conducted to develop adsorbents having excellent carbon dioxide adsorption capacity such as Na-X and Y zeolites, silica-amine-bonded adsorbents, MCM-41-polymer-bonded adsorbents, MOF, and carbon-based adsorbents, If utilized, there is a limit to reducing the energy consumed for carbon dioxide recovery, as there is a large pressure loss in the reaction tower. Therefore, to reduce carbon dioxide recovery energy, a new type of adsorbent with high adsorption capacity and low pressure loss is required.

Korean Patent Laid-Open Publication No. 2008-0103670 discloses a three-dimensional solid structure consisting of Al ₂ O ₃ and SiO ₂ tetrahedron, having micropores and channels, and having a spherical sample size of 2 mm to 5 mm in the shape of a granular zeolite or the A carbon dioxide adsorbent was prepared by depositing lithium hydroxide or soda lime on zeolite. However, the adsorbent thus prepared is a physical adsorbent that can be used at low temperature and low pressure, and thus is limited to use at higher high temperature and high pressure. Currently, various materials are being developed as carbon dioxide adsorption materials, but current technologies are insufficient to sufficiently remove carbon dioxide emitted in the industry.

Recently, one or more layers of graphene nanosheets were stripped from graphite oxide, and the properties of the sheets were examined. As a result, very useful properties different from existing materials were found. This material is much more stable than carbon nanotubes, and is expected to be used for computer electrodes, ultrafast transistors, and gas adsorbents, which have a much larger storage capacity than silicon semiconductors, as well as transparent electrodes and anti-static conductive materials.

However, although the graphene sheet has very useful properties, an economical and reproducible method for producing a large area graphene sheet has not been developed. As a method of synthesizing the graphene material, mechanical exfoliation (also known as scotch tape method), epitaxial growth on SiC substrate, chemical vapor deposition (CVD), and chemical synthesis have been developed. Among them, a chemical method that is easy to mass-produce is the most promising method for producing high quality graphene that can be industrially used. However, the graphite oxide prepared in this way has a narrow interlayer spacing and certain limitations in the separation between layers, and the graphite pretreatment method used conventionally is not environmentally friendly.

Therefore, the demand for eco-friendly, economical and mass production methods is inevitable.

Disclosure of Invention An object of the present invention is to solve the above problems and to be devised by the necessity of the above, the technical problem to be achieved by the present invention provides a method for producing a graphene nanosheets for carbon dioxide adsorbent that can improve the adsorption efficiency of carbon dioxide. It is.

In order to achieve the above object, the present invention (1) mixing graphite with sulfuric acid (H ₂ SO ₄ ) and potassium permanganate (KMnO ₄ ), and reacting for 1 to 3 hours at 30 to 40 ℃; and (2 ) Adding distilled water to the mixture according to the step (1), the temperature is raised to 95 to 100 ℃ and maintained for 10 to 20 minutes; and (3) adding distilled water to the mixed solution according to the step (2) And (4) adding hydrogen peroxide to the mixed solution of step (3); and (5) sulfuric acid and chlorine ions by centrifugation using the 5 wt% hydrochloric acid solution of the mixed solution of step (4). Removing, washing with acetone, and drying in a vacuum oven to prepare graphite oxide; And (6) heat treating the graphite oxide prepared by the step (5) in a vacuum atmosphere and at 100 to 1200 ° C. to provide graphene nanosheets for the carbon dioxide adsorbent.

It characterized in that the heat treatment for 1 to 60 minutes in the step (6).

The temperature increase rate during the heat treatment in step (6) is characterized in that 10 to 120 ℃ / min.

Heat treatment at 900 to 1100 ℃ 1 to 10 minutes in the step (6), the temperature increase rate is characterized in that 120 ℃ / min.

In another aspect, the present invention provides a graphene nanosheets, characterized in that the specific surface area is 14 to 2500 m2 / g, carbon dioxide adsorption efficiency is 250 to 3500 mg / g (25 ℃, 3MPa). .

According to the present invention as described above, it is possible to obtain a graphene nanosheet for carbon dioxide adsorbent with improved selective adsorption capacity for carbon dioxide.

By using graphite oxide as a raw material and thermally expanding graphite oxide in a vacuum atmosphere and low temperature to prepare graphene nanosheets to provide an interlayer structure suitable for carbon dioxide adsorption, it is possible to obtain a selective adsorption effect of carbon dioxide and to adsorb various gases. It can prevent it beforehand.

Figure 1 shows the manufacturing process of the graphene nanosheets according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for producing a graphene nanosheet (graphene nanosheet) for a high efficiency carbon dioxide adsorbent using graphite oxide (graphite oxide). More particularly, the present invention relates to a method for preparing expanded graphene nanosheets for carbon dioxide adsorbents by heat treating graphite oxide in a vacuum atmosphere and at different temperatures.

Graphite oxide as a starting material used in the present invention is preferred, and the wide interlayer structure and the oxygen functional groups on the surface of graphite oxide are effective for preparing expanded graphene nanosheets.

In addition, the heat treatment (thermal expansion) process of the graphite oxide is preferably carried out at a temperature of 100 to 1200 ℃. If the activation temperature is less than 100 ℃ graphite oxide is not thermal expansion, if it exceeds 1200 ℃ has the disadvantage that the energy cost increases. At this time, the temperature increase rate is preferably 10 to 120 ℃ / min. Productivity will fall when a temperature increase rate is 10 degrees C / min or less.

In addition, in the heat treatment (thermal expansion) step, the activation time is preferably 1 minute to 60 minutes. Although the graphene nanosheet for carbon dioxide adsorbent having an excellent specific surface area is obtained even after the thermal expansion temperature is reached for a short time, that is, after 10 minutes of activation and cooling, there is no improvement in physical properties when it exceeds 60 minutes. It is not desirable when considering economics.

In addition, the present invention has a high carbon yield by the above method, and the interlayer spacing of the graphene nanosheets may be developed to be useful as a carbon dioxide adsorbent.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these examples are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples.

In the present invention, graphene nanosheets were used as carbon dioxide adsorbents, and graphene nanosheets were prepared using graphite oxide as described in the following Examples and Comparative Examples, and then used as carbon dioxide adsorbents to evaluate the adsorption capacity of carbon dioxide.

Comparative Example 1

1 g of graphite (graphite flake, purity 99.999%) was mixed with 2 ml 98 wt% sulfuric acid and 3 g potassium permanganate at 0 ° C., and then reacted at 35 ° C. for 2 hours. 46 ml of distilled water was slowly poured, the temperature was raised to 98 ° C., and maintained for 15 minutes. Then, 140 ml of distilled water was added again to give a golden or reddish brown solution. 10 ml of 30 wt% hydrogen peroxide was added to react with the remaining potassium permanganate. The final mixed solution obtained by the above method was washed with 5wt% hydrochloric acid solution until there was no sulfate ion and chlorine ion by centrifugation, washed once with acetone and dried in a vacuum oven at 60 ° C. for 24 hours. .

Comparative Example 2

Graphite oxide was prepared in the same process as in Comparative Example 1, and then thermally expanded at 300 ° C. under nitrogen atmosphere at room temperature to prepare graphene nanosheets.

Comparative Example 3

Graphite oxide was prepared in the same process as in Comparative Example 1, and then thermally expanded for 10 minutes at 10 ° C./min in a vacuum atmosphere and 100 ° C. to prepare graphene nanosheets.

Example 1.

Graphite oxide was prepared in the same process as in Comparative Example 1, and then thermally expanded for 30 minutes at 30 ° C./min at 150 ° C. in a vacuum atmosphere to prepare graphene nanosheets.

Example 2.

Graphite oxide was prepared in the same process as in Comparative Example 1, and then thermally expanded for 30 minutes at 60 ° C / min in a vacuum atmosphere and at 200 ° C to prepare graphene nanosheets.

Example 3.

Graphite oxide was prepared in the same process as in Comparative Example 1. The graphene nanosheet was prepared by thermal expansion at 60 ° C./min for 30 minutes at 300 ° C. in a vacuum atmosphere.

Example 4.

Graphite oxide was prepared in the same process as in Comparative Example 1. The graphene nanosheet was prepared by thermal expansion at 60 ° C./min for 30 minutes at 400 ° C. in a vacuum atmosphere.

Example 5.

Graphite oxide was prepared in the same process as in Comparative Example 1. The graphene nanosheet was prepared by thermal expansion at 120 ° C./min for 30 minutes at 500 ° C. in a vacuum atmosphere.

Example 6.

Graphite oxide was prepared in the same process as in Comparative Example 1, and then thermally expanded for 5 minutes at 120 ° C./min at 700 ° C. in a vacuum atmosphere to prepare graphene nanosheets.

Example 7.

Graphite oxide was prepared in the same process as in Comparative Example 1. The graphene nanosheet was prepared by thermal expansion at 120 ° C./min for 10 minutes at 900 ° C. in a vacuum atmosphere.

Example 8.

Graphite oxide was prepared in the same process as in Comparative Example 1. Then, the graphene nanosheet was prepared by thermal expansion at 120 ° C./min for 1 minute at 1100 ° C. in a vacuum atmosphere.

In the present invention, each characteristic value was measured by the following method.

Experimental Example 1. Measurement of the specific surface area of the surface-modified graphene nanosheets

(1) Pore Structure of Synthetic Graphene Nanosheets

About 0.2 g of the sample was taken in a 77 K liquid nitrogen atmosphere, and the adsorption amount was measured using nitrogen gas as an adsorbate. The pretreatment of the sample was degassed for about 12 hours at 573 K until the residual pressure in the sample became 10 to 3 torr or lower. After nitrogen isothermal adsorption test, P / P0 (P is partial pressure, P0 is saturated vapor pressure) shows the slope of the straight line with respect to the adsorption amount from about 0.1 to 0.3. From this, BET specific surface area, total pore volume, micropore volume, etc. Was obtained.

(2) CO2 Adsorption Efficiency of Graphene Nanosheets

Each sample was degassed for 6 hours while maintaining the residual pressure at 10 ⁻³ torr or lower at 373 K, and then the amount of carbon dioxide adsorption was measured at 298 K and 30 atm using BEL-HP (BEL Japan). One-time average sample amount was 0.01 g.

As a result, as shown in Table 1, it can be seen that the graphene nanosheets prepared by the method of the present invention exhibited higher BET specific surface area, higher pore volume, and developed pore fraction than graphite oxide. In addition, the trend of pore structure changes showed a significant effect on carbon dioxide adsorption behavior.

[Table 1]

As described above, specific portions of the contents of the present invention have been described in detail, and for those skilled in the art, these specific techniques are merely preferred embodiments, and the scope of the present invention is not limited thereto. Will be obvious. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (5)

(1) mixing graphite with sulfuric acid (H ₂ SO ₄ ) and potassium permanganate (KMnO ₄ ) and reacting at 30 to 40 ° C. for 1 to 3 hours;
(2) adding distilled water to the mixture according to the step (1), increasing the temperature to 95 to 100 ℃ and maintaining for 10 to 20 minutes;
(3) adding distilled water to the mixed liquid according to step (2);
(4) adding hydrogen peroxide to the mixed solution of step (3);
(5) The sulfuric acid and chlorine ions are removed by centrifugation using the 5 wt% hydrochloric acid solution, washed with acetone, and dried in a vacuum oven to remove graphite oxide (graphite oxide). Preparing a; And
(6) heat-treating the graphite oxide (graphite oxide) prepared by the step (5) at a vacuum atmosphere and 100 to 1200 ℃; manufacturing method of the graphene nanosheets for carbon dioxide adsorbent comprising a.
The method of claim 1,
Method of producing a graphene nanosheets for carbon dioxide adsorbent, characterized in that the heat treatment for 1 to 60 minutes in the step (6). The method of claim 1,
Method of producing a graphene nanosheets for carbon dioxide adsorbent, characterized in that the temperature increase rate during the heat treatment in step (6) is 10 to 120 ℃ / min.
The method of claim 1,
Heat treatment at 900 to 1100 ℃ for 1 to 10 minutes in the step (6), the temperature rising rate is a manufacturing method of graphene nanosheets for carbon dioxide adsorbent, characterized in that 120 ℃ / min.
The graphene nanosheets are prepared by the method of claim 1, wherein the specific surface area is 14 to 2500 m 2 / g, and the carbon dioxide adsorption efficiency is 250 to 3500 mg / g (25 ° C., 3 MPa).

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