TWI796609B - Method for preparing graphene sheet by using supercritical fluid intercalation step and microwave expansion step - Google Patents

Abstract

A method for preparing a graphene sheet by using a supercritical fluid intercalation step and a microwave expansion step, comprising: providing graphite oxide or expandable graphite; performing a supercritical fluid intercalation step, wherein the graphite oxide or the expandable graphite and the urea aqueous solution are intercalated by a supercritical fluid, and then stir by nitric acid with ultrasonically oscillated and filtered. The urea nitrate intercalation graphite can be obtained. Finally it performs a microwave expansion step, wherein the graphene is obtained by the urea nitrate intercalated graphite at a predetermined temperature by microwave heating, and is pulverized by a pulverizer to obtain a graphene sheet.

Description

Method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps

The invention relates to a method for preparing graphene sheets, in particular to a method for preparing graphene sheets by supercritical fluid intercalation and microwave expansion steps.

Nanocarbon-based materials such as nanographites (NGs), nanocarbons (NCs), carbon nanotubes (CNTs) and graphene-based materials (graphene-based materials) , NCBMs) have excellent physical and chemical properties such as heat transfer, electrical, and mechanical properties, and therefore, methods for fabricating these materials have been extensively studied in recent years.

The current methods for preparing graphene include: mechanical exfoliation method, epitaxial growth method, redox method, chemical vapor deposition method and so on. Various preparation methods have their advantages and disadvantages. For example, the mechanical exfoliation method can obtain a few-layer or multi-layer graphene with a complete crystal structure, but its production efficiency is not high and cannot be applied on a large scale. The redox method is to oxidize graphite into graphite oxide first, and then reduce it to obtain graphene. This method can be used for large-scale industrial production of graphene, but the structure of graphene is greatly damaged and has many defects. A large amount of acid solution and Strong oxidizing agents are easy to cause damage to the environment.

However, the above-mentioned methods often require the use of expensive equipment or under a specific ambient atmosphere to carry out the manufacture of nanocarbon-based materials (NCBMs), and some methods also require multiple and large quantities of Only chemicals can react, and the use of a large amount of chemicals will lead to problems in the disposal of waste liquid and waste. Therefore, when preparing carbon nanomaterials (NCBMs), considering the manufacturing cost, the friendliness to the environment, and the scalability of the manufacturing process is a subject that relevant technical personnel in this technical field must break through.

In view of the above-mentioned problems in the prior art, an object of the present invention is to provide a method for preparing graphene sheets utilizing supercritical fluid intercalation and microwave expansion steps. Supercritical fluid has similar gas diffusion properties and compressibility, and can Effusion occurs like a gas, has fluidity similar to a liquid, and generally has a density between 0.1 and 1.0 g/ml. Supercritical fluid is a state of matter. When the matter exceeds the critical temperature and critical pressure, the properties of gas and liquid will tend to be similar, and finally a homogeneous fluid will be achieved. Among them, carbon dioxide, one of the supercritical fluids, has mild critical conditions, such as critical temperature 31.1°C, critical pressure 7.38MPA, non-toxic, low price, and easy to separate from the product. It is widely used in the preparation of nano-composite materials. For example, it is directly applied to the preparation of graphene, which can avoid the use of a large amount of organic solvents and strong acids and alkalis. It is a green and environmentally friendly application technology.

In order to achieve the aforementioned purpose, the present invention proposes a method for preparing graphene sheets utilizing supercritical fluid intercalation and microwave expansion steps, comprising: providing graphite oxide or expandable graphite; carrying out a supercritical fluid intercalation step, wherein the graphite oxide Or expandable graphite and urea aqueous solution are intercalated by supercritical fluid carbon dioxide, then use nitric acid to stir at room temperature, undergo ultrasonic vibration and filter and dry to obtain urea nitrate intercalated graphite; and carry out a microwave expansion step, wherein by adding nitric acid The urea-intercalated graphite is microwave-heated at a predetermined temperature to obtain graphene, and is pulverized by a pulverizer to obtain graphene sheets.

Wherein, graphite oxide is obtained by performing a graphite oxidation step, and the graphite oxidation step includes an acid solution mixing step, a flake graphite mixing step, a first ultrasonic vibration step and A filtering step, an acid solution mixing step is to mix a first acid solution, a second acid solution and potassium permanganate to obtain a mixed acid, and a flake graphite mixing step is to mix the flake graphite and the mixed acid to obtain a mixed acid Solution, the first ultrasonic vibration step is to ultrasonically vibrate the mixed solution with a first power and a first time to obtain a first intermediate, and the filtering step is to obtain graphite oxide after filtering the first intermediate.

Wherein, the first power may be in the range of 200W to 900W, and the first time may be, for example, more than 20 minutes.

Among them, the ratio of the first acid solution to the second acid solution is in the range of 2:1 to 1:2, and the first acid solution is acetic anhydride or nitric acid, the second acid solution is phosphoric acid or acetic anhydride, permanganic acid The ratio of potassium to flake graphite is in the range of 1.6:1 to 0.8:1.

Wherein, the first acid solution is acetic anhydride or nitric acid, and the second acid solution is phosphoric acid or acetic anhydride.

Wherein, the supercritical fluid intercalation step includes a first supercritical fluid intercalation step, a second ultrasonic vibration step and a filtration drying step, and the first supercritical fluid intercalation step is by putting supercritical carbon dioxide in the reaction tank The temperature is 40 to 60°C, carbon dioxide is at a critical temperature of 50 to 80°C, and a critical pressure of 2500 to 3500psi, carrying urea aqueous solution to intercalate graphite oxide or expandable graphite to form a second intermediate, and the second ultrasonic vibration step is to convert the second intermediate Mix with nitric acid and perform ultrasonic vibration with a second power and a second time to obtain a third intermediate. The filtration and drying step is to filter and dry the third intermediate to obtain urea nitrate intercalated graphite.

Wherein, in the second ultrasonic vibration step, nitric acid is added dropwise into the second intermediate and stirred to uniformly mix the second intermediate and nitric acid.

Wherein, the second power is in the range of 200W to 900W, and the second time is more than 60 minutes.

Among them, the urea aqueous solution is made by mixing urea and deionized water in a ratio ranging from 1:9.4 to 1:12.5, and the ratio of the second intermediate to nitric acid in the second ultrasonic oscillation step is 1:4 to 1: Mixed in a ratio of 6.

Wherein, the predetermined temperature is in the range of 100°C to 400°C.

Wherein, the microwave expansion step is to obtain graphene sheets by pulverizing graphene with a pulverizer at 25,000 to 30,000 revolutions per minute. Preferably, graphene sheets are obtained by pulverizing graphene at 28,000 revolutions per minute.

Based on the above, according to the method for preparing graphene sheets utilizing supercritical fluid intercalation and microwave expansion steps of the present invention, it may have one or more of the following advantages:

(1) The method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps of the present invention uses supercritical carbon dioxide intercalation steps to intercalate graphite oxide and urea aqueous solution and mix nitric acid with ultrasonic vibration and The urea nitrate intercalated graphite is obtained by filtration, and finally the microwave thermal expansion step is performed to microwave the urea nitrate intercalated graphite at a predetermined temperature to obtain graphene, which is pulverized by a pulverizer to obtain graphene sheets.

(2) The method of utilizing supercritical fluid intercalation and microwave expansion steps of the present invention to prepare graphene sheet adopts supercritical fluid mode to carry supercritical carbon dioxide to intercalate graphite with urea aqueous solution and mix them uniformly with nitric acid, so that nitric acid enters In the interlayer of graphite oxide, it reacts with urea in intercalated graphite to form urea nitrate salts in the interlayer of graphite oxide, and then microwaves the urea nitrate intercalated graphite to expand to obtain graphene, which is pulverized by a pulverizer. to obtain graphene sheets.

Herein, in order to make Jun Shen have a further understanding and understanding of the technical characteristics of the present invention and the technical effects that can be achieved, the preferred embodiment and detailed description are as follows.

S10, S20, S30, S12, S14, S16, S18, S22, S24, S26: steps

Fig. 1 is a schematic flow chart of the method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps of the present invention.

Fig. 2 is the schematic flow chart of graphite oxidation step in the present invention.

Fig. 3 is a schematic flow chart of the supercritical fluid intercalation step in the present invention.

FIG. 4 is a photographic view of graphene sheets prepared in an ultrasonic manner.

Fig. 5 is a photographic view of graphene sheet prepared by supercritical fluid in the present invention.

In order to facilitate the understanding of the technical features, content and advantages of this creation and the effects it can achieve, this creation is hereby combined with the drawings and described in detail in the form of embodiments as follows, and the ideas used in it are only for the purpose of For the purpose of illustration and auxiliary instructions, it may not be the true proportion and precise configuration of this creation after its implementation. Therefore, the scale and configuration relationship of the attached drawings should not be interpreted or limited to the scope of rights of this creation in actual implementation. In addition, for ease of understanding, the same elements in the following embodiments are described with the same symbols.

Please refer to FIG. 1 . FIG. 1 is a schematic flow chart of a method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps of the present invention. As shown in FIG. 1 , the method for preparing graphene sheet using supercritical fluid intercalation and microwave expansion steps of the present invention includes at least steps S10 , S20 and S30 . In step S10, graphite oxide (expandable graphite can also be provided) is provided, wherein graphite oxide can be obtained, for example, by performing a graphite oxidation step (the graphite oxidation step will be described in detail below). In step S20, a supercritical fluid intercalation step is carried out, wherein graphite oxide and urea aqueous solution are intercalated with supercritical fluid, mixed with nitric acid, ultrasonically oscillated and filtered to obtain urea nitrate intercalated graphite. In step S30, carry out microwave expansion step step, wherein the graphene obtained by heating the urea nitrate-intercalated graphite with a microwave at a predetermined temperature and pulverized by a pulverizer is obtained to obtain a graphene sheet.

As shown in FIG. 2 , the graphite oxidation step (step S10 ) may, for example, include steps S12 , S14 , S16 and S18 . In step S12 , an acid solution mixing step is performed. The acid solution mixing step is to mix a first acid solution, a second acid solution and potassium permanganate to obtain a mixed acid. In step S14 , a graphite flake mixing step is performed. The graphite flake mixing step is to mix graphite flakes and mixed acids to obtain a mixed solution. In step S16 , a first ultrasonic vibration step is performed. The first ultrasonic vibration step is to ultrasonically vibrate the mixed solution with a first power and a first time to obtain a first intermediate. Wherein, the first power may be in the range of 200W to 900W, for example. Preferably, the first power may range from 400W to 600W, for example. More preferably, the first power may range from 500W to 600W, for example. In an embodiment, the first power may be, for example, 400W. The first time may be, for example, 20 minutes or more than 20 minutes. The first power and the first time are not limited to the values or ranges mentioned above. Any ultrasonic oscillation parameters that can be obtained by ultrasonic oscillation of the mixed solution containing flake graphite and mixed acid are all the parameters of the present invention. The first power and the first time for which protection is requested. In step S18, a filtering step is performed, and the filtering step is to obtain graphite oxide after filtering the first intermediate. The filtering step may be, for example, suction filtration, but is not limited thereto.

The ratio of the first acid solution to the second acid solution may, for example, be in the range of 2:1 to 1:2. For example, the ratio of the first acid solution to the second acid solution may be 2:1, or 1:1, or 1:2. The ratio of potassium permanganate to flake graphite may, for example, be in the range of 1.6:1 to 0.8:1. For example, the ratio of potassium permanganate to flake graphite may be 1.6:1 or 0.8:1. The first acid solution can be, for example, acetic anhydride or nitric acid, and the second acid solution can be, for example, phosphoric acid or acetic anhydride. The above first acid solution and The ratio and type of the second acid solution and the ratio of potassium permanganate to flake graphite are just examples, and users can adjust the type and ratio according to actual needs.

As shown in FIG. 3 , the supercritical fluid intercalation step (step S20 ) includes steps S22 , S24 and S26 . In step S22, a supercritical carbon dioxide intercalation step is carried out, in which supercritical carbon dioxide is carried by urea aqueous solution for intercalation reaction and mixed with graphite oxide to obtain a second intermediate. In step S24, the second ultrasonic shock step is carried out. The second ultrasonic shock step is to mix the second intermediate with nitric acid and carry out ultrasonic shock with a second power and a second time to obtain a third intermediate. In step S26, a filtering and drying step is performed. The filtering and drying step is to obtain urea nitrate intercalated graphite after filtering and drying the third intermediate.

In performing the second ultrasonic vibration step (step S24 ), nitric acid may, for example, be added dropwise to the second intermediate and stirred to uniformly mix the second intermediate and nitric acid. Alternatively, nitric acid may also be directly added to the second intermediate and stirred to uniformly mix the second intermediate and nitric acid.

The second power may be in the range of 200W to 900W, and the second time may be, for example, more than 5 minutes. Preferably, the second power may range from 400W to 600W, for example. More preferably, the second power may range from 500W to 600W, for example. In one embodiment, the second power can be, for example, 200W, and the second time can be, for example, 10 minutes. In the present invention, the second power and the second time are not limited to the values or ranges mentioned above. Any ultrasonic oscillation parameters that allow the urea aqueous solution and graphite oxide to be uniformly mixed together are the second claimed protection of the present invention. power and second time.

The aqueous urea solution can be formed by mixing urea and deionized water at a ratio ranging from 1:9.4 to 1:12.5, for example. Preferably, the ratio of urea to deionized water is 1:10. The ratio of the second intermediate to nitric acid can be mixed in a ratio ranging from 1:4 to 1:6, for example. Preferably, the The ratio of the two intermediates to nitric acid is 1:5. The above ratios of urea and deionized water and the ratio of the second intermediate and nitric acid are just examples, and users can adjust the ratios according to actual needs.

In step S30, the predetermined temperature may be in the range of 100°C to 400°C, for example. Preferably, the predetermined temperature may range from 150°C to 400°C, for example. More preferably, the predetermined temperature may range from 150°C to 300°C, for example. For example, the predetermined temperature may be above 100°C, such as 150°C, 200°C or 300°C. In the present invention, the predetermined temperature for heating the urea nitrate intercalation graphite in step S30 is not limited to the aforementioned range and/or numerical value, any heating temperature that can heat the urea nitrate intercalation graphite to make graphene is all basic The predetermined temperature for which the invention is claimed. In the present invention, the time for carrying out the microwave expansion step (step S30) is very short, that is, the urea nitrate intercalation graphite can be expanded to obtain graphene, and the graphene sheet can be obtained after pulverizing by a pulverizer at 25,000 to 30,000 revolutions per minute .

The present invention prepares the method for graphene sheet by supercritical fluid intercalation and microwave expansion step and can for example carry out in the following manner: first, carry out graphite oxidation step (step S10): mix 6 grams of acetic anhydride and 30 grams of nitric acid with 12.7 grams Potassium permanganate (the concentration of acetic anhydride is 98wt%, the concentration of nitric acid is 70wt%, and the purity of potassium permanganate is 99%) is mixed together to obtain mixed acid (i.e. acid solution mixing step, step S12); 6 Gram flake graphite (purity 95%) joins in mixed acid and continues to stir more than 1 minute so that flake graphite and mixed acid evenly mix together and obtain mixed solution (ie flake graphite mixing step, step S14); The container (such as a beaker) is sealed and placed in an ultrasonic oscillator with a power of 600W for more than 1 hour to obtain the first intermediate (i.e. the first ultrasonic oscillation step, step S16); finally, perform suction filtration to obtain graphite oxide (i.e. filtering step, step S18).

Next, perform the supercritical fluid intercalation step (step S20): add 1.5 grams of urea (99% purity) into 15 grams of deionized water and stir until dissolved to obtain an aqueous urea solution, and then add the aforementioned step S18 Gained graphite oxide was added to the sample tank and carried out supercritical carbon dioxide intercalation for 3 hours so that aqueous urea solution entered between the layers of graphite oxide to obtain the second intermediate (i.e. supercritical carbon dioxide intercalation step, step S22); 30 milliliters of nitric acid ( Concentration is 70wt%) dropwise and slowly add in the second intermediate and keep stirring, so that nitric acid and urea in the graphite oxide layer react to form energetic salts between the graphite oxide layers and carry out ultrasonic vibration for 60 minutes And get the third intermediate (i.e. the second ultrasonic vibration step, step S24); finally, after the third intermediate is washed with deionized water, carry out suction filtration and dry the filtrate to obtain urea nitrate intercalated graphite (ie filter drying step, step S26).

Finally, carry out the microwave expansion step (step S30): put the urea nitrate intercalated graphite into a microwave oven for 3 minutes and the temperature reaches 250° C., so that the urea nitrate intercalated graphite is heated and expanded to obtain graphene, and the 28,000 rpm crushing to obtain graphene sheets. Therefore, compared with the graphene sheet prepared by ultrasonic method ( FIG. 4 ), the graphene sheet prepared by supercritical fluid in the present invention has the characteristics shown in FIG. 5 .

To sum up, the method of the present invention for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps uses supercritical fluid intercalation steps to prepare graphite oxide, urea aqueous solution, and nitric acid through ultrasonic vibration and filtration. The urea nitrate intercalated graphite is obtained, and finally the microwave expansion step is carried out to heat the urea nitrate intercalated graphite at a predetermined temperature to obtain graphene. The present invention adopts supercritical carbon dioxide intercalation method to uniformly mix graphite oxide and urea together, so that urea enters the interlayer of graphite oxide, and then reacts nitric acid with urea that enters the interlayer of graphite oxide to form nitric acid in the interlayer of graphite oxide Urea salts, and then heat the urea nitrate intercalated graphite to expand to obtain graphene, and then pulverize it with a pulverizer to obtain graphene sheets.

The above descriptions are illustrative only, not restrictive. Any equivalent modification or change made without departing from the spirit and scope of the present invention shall be included in the scope of the appended patent application.

S10, S20, S30: steps

Claims (6)

A method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps, comprising: providing graphite oxide or expandable graphite; performing a supercritical fluid intercalation step, including performing a supercritical carbon dioxide intercalation step, a first Two ultrasonic oscillation steps and one filter drying step, the supercritical carbon dioxide intercalation step is to intercalate supercritical carbon dioxide with urea aqueous solution into graphite oxide or expandable graphite to obtain a second intermediate, the second ultrasonic oscillation step is Mixing the second intermediate with nitric acid and ultrasonically vibrating with a second power and a second time to obtain a third intermediate, the filtering and drying step is obtained after filtering and drying the third intermediate Urea nitrate intercalated graphite, wherein the second power is 600W, and the second time is more than 60 minutes; and a microwave expansion step is carried out, wherein graphene is obtained by microwave heating of urea nitrate intercalated graphite with a predetermined temperature, The graphene sheet is obtained after pulverizing by a pulverizer, wherein the predetermined temperature is in the range of 100°C to 400°C. The method for preparing graphene sheet using supercritical fluid intercalation and microwave expansion steps as described in claim 1, wherein the graphite oxide is obtained by performing a graphite oxidation step, and the graphite oxidation step includes performing an acid liquid mixing step , a flake graphite mixing step, a first ultrasonic vibration step and a filtering step, the acid solution mixing step is to mix a first acid solution, a second acid solution and potassium permanganate to obtain a mixed acid, the scale The graphite mixing step is to mix flake graphite and the mixed acid together to obtain a mixed solution, and the first ultrasonic vibration step is to perform ultrasonic vibration on the mixed solution with a first power and a first time to obtain a first An intermediate, the filtration step is the first An intermediate is filtered to obtain the graphite oxide, wherein the first power is 600W, and the first time is more than 60 minutes. The method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps as described in claim 2, wherein the ratio of the first acid solution to the second acid solution is in the range of 2:1 to 1:2 , The ratio of potassium permanganate to flake graphite is in the range of 1.6:1 to 0.8:1. The method for preparing graphene sheet using supercritical fluid intercalation and microwave expansion steps as described in claim 3, wherein the first acid solution is acetic anhydride or nitric acid, and the second acid solution is phosphoric acid or acetic anhydride. The method for preparing graphene sheet by supercritical fluid intercalation and microwave expansion steps as described in Claim 1, wherein the aqueous urea solution is formed by mixing urea and deionized water in a ratio ranging from 1:9.4 to 1:12.5, In the second ultrasonic vibration step, the ratio of the second intermediate to nitric acid is mixed in a ratio ranging from 1:4 to 1:6. The method for preparing graphene sheets using supercritical fluid intercalation and microwave expansion steps as described in Claim 1, wherein the microwave expansion step is to obtain graphene sheets by pulverizing graphene with a pulverizer at 25,000 to 30,000 revolutions per minute.

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