CN102491317B - Preparation method of graphene - Google Patents

Abstract

The invention provides a preparation method of graphene, comprising: dispersing graphite oxide in water under the condition of ultrasonic vibration to obtain a colloid; under acidic or alkaline conditions, using zinc as a reducing agent to reduce the graphite oxide to obtain Graphene; the weight ratio of graphite oxide to zinc is 1: (5.5-6.5). The present invention uses zinc as a reducing agent. Zinc has good reducing performance on graphite oxide, is cheap and non-toxic, does not damage the health of operators, and has high environmental protection performance. Using zinc as a reducing agent will not introduce other functional groups , which is conducive to maintaining the good electrical properties of graphene. More importantly, zinc is an amphoteric metal, so that the above method can prepare graphene under both acidic and alkaline conditions. Therefore, the above method can be used to flexibly select the preparation conditions according to requirements.

Description

The preparation method of graphene

technical field

The invention relates to the field of graphene, in particular to a preparation method of graphene. the

Background technique

Graphene is a new type of carbon material in which a single layer of carbon atoms is tightly packed into a two-dimensional honeycomb structure. It is the basic unit of other dimensional carbon materials, such as zero-dimensional fullerenes, one-dimensional carbon nanotubes, and three-dimensional graphite. . the

In addition to its special structure, graphene also has many unique properties, most notably thermal conductivity and mechanical strength. Graphene is a good conductor that can dissipate heat quickly, and electrons pass through graphene with almost no resistance, and the heat generated is very small. Graphene is very strong and hard, its hardness is higher than that of diamond, and its strength is better than that of steel. The ideal strength can reach 110-130GPa. At the same time, graphene is a very excellent semiconductor material with a much higher carrier mobility than silicon. Graphene is also currently known as the material with the best electrical conductivity at room temperature, and the movement speed of electrons in it is higher than that of ordinary conductors. This feature makes it have great application prospects in the fields of nanoelectronic components, sensors, transistors and batteries. Graphene also has good light transmission and is a potential substitute for traditional ITO films. the

The preparation methods of graphene mainly include chemical reduction method, micro-mechanical exfoliation method and chemical vapor deposition method. The latter two methods have low output and high process requirements. Therefore, the chemical reduction method is mainly used at present. The chemical reduction method uses graphite oxide as a raw material, and usually uses dimethylhydrazine, hydroquinone, and sodium borohydride as reducing agents to reduce graphite oxide to obtain graphene. However, these reducing agents are highly toxic or flammable, which is not conducive to the health of operators and is inconvenient to operate, and will introduce other functional groups to affect the electrical properties of graphene. the

Contents of the invention

The technical problem solved by the present invention is to provide a preparation method of graphene, which does not use toxic raw materials, has high environmental protection, and does not introduce other functional groups to affect the electrical properties of graphene. the

In view of this, the invention provides a kind of preparation method of graphene, comprising:

a), under the condition of ultrasonic vibration, graphite oxide is dispersed in water to obtain a colloid;

b) Under acidic or alkaline conditions, using zinc as a reducing agent to reduce the graphite oxide to obtain graphene; the weight ratio of the graphite oxide to zinc is 1: (5.5-6.5). the

Preferably, the step b) is carried out under alkaline conditions, specifically:

b1), in the colloid, adding zinc and alkali successively in a molar ratio of 1: (10～15) to obtain graphene; the alkali is sodium hydroxide or potassium hydroxide, and the weight ratio of graphite oxide to zinc is It is 1: (5.5～6.5). the

Preferably, the weight ratio of sodium hydroxide or potassium hydroxide to graphite oxide is (15-30):1. the

Preferably, the reaction time of the step b1 is 5h-8h. the

Preferably, the reaction temperature in step b1 is 80°C to 100°C. the

Preferably, the step b) is carried out under acidic conditions, specifically:

b2), in the colloid, add zinc and acid solution successively, obtain graphene; Described acid solution is the hydrochloric acid or the sulfuric acid solution that concentration is 0.5mol/L～2mol/L, and the weight ratio of described graphite oxide and zinc is 1: (5.5～6.5). the

The weight ratio of HCl or sulfuric acid in the hydrochloric acid to graphite oxide is (15-50):1. the

The reaction time of the step b2 is 5h-8h. the

The concentration of graphite oxide in the colloid is 0.8g/L-1.2g/L. the

The invention provides a preparation method of graphene, which is obtained by firstly dispersing graphite oxide in water to obtain graphite oxide colloid, and then using zinc as a reducing agent to reduce graphite oxide under acidic or alkaline conditions. The present invention uses zinc as a reducing agent. Zinc has good reducing performance on graphite oxide, is cheap and non-toxic, does not damage the health of operators, and has high environmental protection performance. Using zinc as a reducing agent will not introduce other functional groups , which is conducive to maintaining the good electrical properties of graphene. More importantly, zinc is an amphoteric metal, so that the above method can prepare graphene under acidic conditions and alkaline conditions. Under acidic conditions, the product has higher purity, simple purification steps, and easy post-treatment. ; Prepared under alkaline conditions, the degree of reduction is high, and the modification of graphene can be realized while reducing graphite oxide. Therefore, the above method can be used to flexibly select the preparation conditions according to the needs. the

Description of drawings

Fig. 1 is the ultraviolet-visible spectrum of graphite oxide solution;

Fig. 2 is the XRD figure of a, b, c, d;

Fig. 3 is the XRD figure of e, f, g, h;

Fig. 4 is the infrared spectrogram of a, b, c, d;

Fig. 5 is the infrared spectrogram of e, f, g, h. the

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention. the

The embodiment of the present invention discloses a kind of preparation method of graphene, comprises the following steps:

a), under the condition of ultrasonic vibration, graphite oxide is dispersed in water to obtain a colloid;

b) Under acidic or alkaline conditions, using zinc as a reducing agent to reduce the graphite oxide to obtain graphene; the weight ratio of the graphite oxide to zinc is 1: (5.5-6.5). the

The above method is to disperse graphite oxide in water by ultrasonic vibration to obtain colloid, and then use zinc as a reducing agent to reduce graphite oxide. Since zinc is an amphoteric metal, it can play a reducing role in acidic or alkaline conditions. The reduction reaction can be carried out under both acidic and basic conditions. The advantage of preparing graphene under acidic conditions is that the product has high purity, simple purification steps, and easy post-treatment; the advantage of preparing graphene under alkaline conditions is that the degree of reduction is high, and the reduction of graphene oxide can be achieved at the same time. Graphene is modified. Therefore, the above method can be used to flexibly select the preparation conditions according to the needs. And the zinc reducing agent used is non-toxic, more environmentally friendly, and will not introduce other functional groups to affect the electrical properties of graphene. the

In the above-mentioned preparation method, step a is the process of dispersing graphene in an aqueous medium. Graphene oxide can be prepared according to the Hummer method. In order to ensure that graphite is fully oxidized, graphite oxide is preferably prepared according to the following method:

S1), mix the graphite and concentrated sulfuric acid and place in an ice bath to stir for 15min to 20min;

S2), adding potassium permanganate to the mixture obtained in step S1, and incubating at 30°C to 40°C for 25min to 40min;

S3), adding distilled water to the mixture obtained in step S2 for dilution, placing it in an oil bath at 95° C. to 100° C. for 10 to 20 minutes, and then adding hydrogen peroxide solution;

S4), the product is centrifuged, washed with hydrochloric acid, and then washed with deionized water until the pH value reaches 5, and dried. the

In order to make the reduction reaction of step b more fully, the present invention preferably controls the concentration of graphite oxide in the colloid to be 0.8g/L-1.2g/L. the

Step b is a process of reducing graphite oxide with zinc as a reducing agent. The reason why the present invention selects zinc as a reducing agent is that: first, zinc is a cheap and non-toxic reducing agent, and using it as a reducing agent will not cause operator inconvenience. It poses harm to health and has good environmental protection performance; secondly, zinc is an amphoteric metal, which can reduce graphite oxide no matter in acidic or alkaline conditions, and the preparation conditions can be flexibly selected; compared with other amphoteric metals, gallium, The price of germanium and indium is relatively expensive, and the production cost is too high; the electrode potential of tin is low, and the reducibility is not as good as that of zinc. If tin is used as the reducing agent, the reaction conditions will be too harsh, or the product reduction will be insufficient, and the product purity will be low; Although the electrode potential is relatively high, the inventors have found through research that: when it is applied to the reduction of graphite oxide, its reducing performance is inferior to that of zinc. For this reason, the present invention selects zinc as the reducing agent, to improve the environmental performance of the reaction, the flexible selectivity of the preparation conditions and the product purity. the

In the process of reducing graphite oxide, in order to ensure that graphite oxide is fully reduced, the present invention controls the weight ratio of graphite oxide to zinc to be 1: (5.5-6.5), preferably 1: (5.6-6.0), more preferably 1 : (5.7～5.8). the

Zinc can realize the reduction of graphite oxide under acidic conditions and under alkaline conditions, if the reaction is carried out under alkaline conditions, then step b is preferably carried out as follows:

b1), at 60°C to 100°C, add zinc and alkali successively to the colloid, the alkali is NaOH or KOH, and the weight ratio of graphite oxide to zinc is 1: (5.5 to 6.5) to obtain graphene. the

In the above steps, in order to improve the purity of the product, the reaction temperature is preferably set at 80° C. to 100° C., and the reduction reaction time is preferably set at 5 h to 8 h. On the one hand, the alkali is used to react with zinc, and on the other hand, it is used to disperse the colloid. If the amount of alkali added is too low, the reaction rate will be too slow and the reduction will not be sufficient, thus prolonging the reaction time; Alkali residues increase the number of times the product is subsequently washed. For this reason, the present invention preferably controls the molar ratio of alkali and zinc to be (11～13):1. The weight ratio of graphite oxide to sodium hydroxide or potassium hydroxide is preferably 1: (15-30). the

The advantage of reducing graphite oxide under alkaline conditions is that the degree of reduction is high and it is convenient to modify graphene. Under alkaline conditions, graphite oxide is easier to exfoliate to obtain a stable negatively charged colloid, which can be electrostatically assembled with positively charged sheet molecules, and this molecular level assembly is better than the existing physical mixing effect. Therefore, the graphene with excellent modification effect can be prepared in one step by introducing guest molecules during the reduction reaction by using the above method. the

The introduced guest molecule is a compound that exists stably under alkaline conditions and can react with -OH, -O-, -COOH on the surface of graphite oxide, which can be: metal oxides, such as Fe ₃ O ₄ magnetic nanoparticles , ZnO or _TiO2 , etc.; small biological molecules, such as oligonucleotides, etc.; small organic molecules, such as pyridine, etc.; layered compounds, such as layered double metal hydroxides, etc. If the guest molecules are metal oxides or hydroxides, a composite material of metal oxides and graphene can be obtained after high-temperature vacuum calcination and reduction.

In addition, preparing graphene under alkaline conditions and at a temperature range of 80° C. to 100° C. can also increase the reduction degree of graphene oxide, and the product has a higher purity. the

If the reduction reaction is carried out under acidic conditions, then step b is preferably carried out as follows:

b2), add zinc and acid solution successively to above-mentioned colloid, obtain graphene, and described acid solution is the hydrochloric acid or sulfuric acid solution that concentration is 0.5mol/L～2mol/L, and the weight ratio of graphite oxide and zinc is 1:( 5.5～6.5). the

The advantages of preparing graphene under acidic conditions are: high product purity, simple purification steps, and easy post-processing. In the above steps, in order to fully reduce the graphite oxide, the temperature of the reduction reaction is preferably set at 60° C. to 100° C., and the time is preferably set at 5 h to 8 h. If the concentration of the acid solution is too low, the reaction rate is too slow and the reduction is not sufficient, so the reaction time needs to be prolonged; if the concentration of the acid solution is too high, there will be too much acid residue, which increases the number of subsequent washings of the product. For this reason, the present invention preferably controls the concentration of the acid solution to be 0.5 mol/L-2 mol/L. The weight ratio of HCl in hydrochloric acid or sulfuric acid to graphite oxide is preferably (15-50):1. the

After filtering the reaction solution according to the above method, washing with hydrochloric acid to remove unreacted zinc, washing with water the zinc salt attached to the surface of the product, and drying to obtain graphene. the

As can be seen from the above results, the method provided by the present invention is used to prepare graphene, which uses cheap and non-toxic zinc as a reducing agent, and has good environmental protection performance; it will not introduce other functional groups to affect the electrical properties of graphene; at the same time, it can be used in acidic conditions. Graphene can be prepared under alkaline conditions, and the product purity is higher under acidic conditions, the purification steps are simple, and the post-treatment is easy; under alkaline conditions, graphite oxide can be reduced and graphene can be modified at the same time. Therefore, the above method can be used to flexibly select the preparation conditions according to the needs. the

In order to further understand the present invention, the preparation method of graphene provided by the present invention is described below in conjunction with examples, and the protection scope of the present invention is not limited by the following examples. the

Embodiment 1 prepares graphite oxide

1. Rinse the graphite powder with distilled water, pour off the suspended matter in the upper layer, filter and dry;

2. Take 5g of dried graphite and 230mL of 98% concentrated sulfuric acid, mix them in an ice bath, stir for 15 minutes, and make them fully mixed. Weigh 30g of KMnO ₄ and add the above mixture to continue stirring for 2 hours, then transfer it to a medium-temperature water bath at 35°C Continue to stir for 30 minutes, slowly add 460ml of distilled water into the reaction system, then place it in a 98°C oil bath for 15 minutes, then add 1400ml of warm water, then add 100ml of 30% H ₂ O ₂ , centrifuge the product, and wash it with 2L of 5% HCl solution Washing, and then washing with water to pH ≈ 5, and drying to obtain graphite oxide.

Adopt ultrasonic vibration to disperse 120mg graphite oxide in 150ml water, as shown in Figure 1, be the ultraviolet-visible spectrum of this graphite oxide solution, graphite oxide solution has a characteristic peak at wavelength 230nm place, has a characteristic peak at about 300nm, thus It can be seen that graphite oxide was successfully prepared. the

The graphite oxide used in the following examples is all prepared by this example. the

Example 2

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 120ml water to obtain a colloid;

2. Add 655mg zinc powder and 30ml 2.0mol/L hydrochloric acid successively to the colloid obtained in step 1, finish the reaction after reacting at room temperature for 6 hours, filter the mixture obtained by the reaction, wash with water, and dry to obtain graphene. the

Example 3

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 120ml water to obtain a colloid;

2. Add 658mg zinc powder and 30ml 2.0mol/L hydrochloric acid successively to the colloid obtained in step 1, finish the reaction after reacting at 60°C for 6 hours, filter the mixture obtained by the reaction, wash with water, and dry to obtain graphene. the

Example 4

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 120ml water to obtain a colloid;

2. Add 662mg zinc powder and 30ml 2.0mol/L hydrochloric acid successively to the colloid obtained in step 1, finish the reaction after reacting at 80°C for 6 hours, filter the mixture obtained by the reaction, wash with water, and dry to obtain graphene. the

Example 5

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 120ml water to obtain a colloid;

2. Add 658mg of zinc powder and 30ml of 2.0mol/L hydrochloric acid successively to the colloid obtained in step 1, finish the reaction after reacting at 100°C for 6 hours, filter the mixture obtained by the reaction, wash with water, and dry to obtain graphene. the

Example 6

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 150ml water to obtain a colloid;

2. Add 654mg zinc powder and 4.8g NaOH successively to the colloid obtained in step 1, finish the reaction after 6 hours of constant temperature reaction at room temperature, filter the mixture obtained by the reaction, wash with hydrochloric acid and water successively, and dry to obtain graphene. the

Example 7

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 150ml water to obtain a colloid;

2. Add 655 mg of zinc powder and 4.8 g of NaOH to the colloid obtained in step 1, and finish the reaction after a constant temperature reaction at 60°C for 6 hours, filter the reaction mixture, wash with hydrochloric acid and water in turn, and dry to obtain graphene . the

Example 8

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 150ml water to obtain a colloid;

2. Add 655mg of zinc powder and 4.8g of NaOH to the colloid obtained in step 1, and finish the reaction after 6 hours of constant temperature reaction at 80°C, filter the reaction mixture, wash with hydrochloric acid and water in turn, and dry to obtain graphene . the

Example 9

1. Use ultrasonic vibration to disperse 120mg graphite oxide in 150ml water to obtain a colloid;

2. Add 655mg of zinc powder and 4.8g of NaOH to the colloid obtained in step 1 in sequence, and finish the reaction after 6 hours of constant temperature reaction at 100°C, filter the reaction mixture, wash with hydrochloric acid and water in turn, and dry to obtain graphene . the

Get respectively the graphene powder prepared by embodiment 2～5, numbering is successively a, b, c, d, get the graphene powder prepared by embodiment 6～9, numbering is successively e, f, g, h; above-mentioned material Carry out X-ray powder diffraction analysis, infrared spectroscopic analysis and quantitative elemental analysis in turn, and the analysis results are as follows:

[XRD Powder Diffraction Analysis]

Figure 2 is the XRD pattern of a, b, c, and d, as can be seen from the figure, as the temperature increases, the diffraction peak at 2θ=11.8° (corresponding to d=0.75nm) gradually becomes weaker, when It disappears completely when the temperature is 100°C; while the diffraction peak at 2θ=23.5° (corresponding to d=0.38nm) gradually increases, and reaches the extreme value when the temperature is 100°C. Figure 3 shows the XRD patterns of e, f, g, and h. During the temperature increase from room temperature to 100°C, there is no diffraction peak at 2θ=11.8°, only a single peak at 2θ=23.5°. Since the interlayers of graphite oxide contain functional groups such as carbonyl groups and epoxy groups, the interlayer spacing can reach 0.60-0.90nm. After being reduced to graphene, the interlayer functional groups disappear, and the interlayer spacing is reduced to about 0.30nm. Combined with the XRD pattern, it can be shown that under acidic conditions, with the increase of reaction temperature, the reduction degree of graphite oxide increases, and it is the most sufficient at 100 ° C. It can be determined that graphite oxide has been reduced to graphene, while under alkaline conditions , a good reduction effect can be achieved at room temperature. the

[Infrared spectrum analysis]

Figure 4 is the infrared spectrograms of a, b, c, and d, and Figure 5 is the infrared spectrograms of e, f, g, and h. From the comparison ^of a, b, c, and d, it can ^be seen that the reduction of GO under acidic conditions has a great influence on the degree of reduction by temperature. There is no decrease, and the wave numbers at 1727cm ^-1 , 1384cm ^-1 , 1226cm ^-1 , and 1064cm ^-1 respectively represent the CO stretching vibrations of C=O, CO, COC, and alcohols still obviously exist, indicating that the reduction of GO is not complete at room temperature; As the temperature rises, at 80°C, the strength at 3430cm ^-1 and 1614cm ^-1 becomes weaker, respectively representing the reduction of the stretching and bending vibration of the hydroxyl group, and the weakening of water absorption. The wave numbers are at 1727cm ^-1 , 1384cm ^-1 , 1226cm ^-1 , The absorption peak at 1064cm ^-1 disappeared or decreased obviously; at 100°C, the absorption intensity continued to weaken, indicating that the degree of reduction further increased; through the comparison of Zn-NaOH and Zn-HCl reduction of GO, it can be seen that the extreme value of Zn-HCl reduction appeared At 100°C, Zn-NaOH can be reduced very well at room temperature, and the reduction is most thorough at 100°C.

[Quantitative elemental analysis]

The test results are listed in Table 1:

Table 1 elemental analysis test results

The results of elemental analysis show that compared with the raw material GO, a, b, c, d data show that under acidic conditions, with the increase of temperature, GO is more and more fully reduced, e, f, g, h show that in Reduction at room temperature under alkaline conditions has a better reduction effect, and the reduction is most thorough at 100°C. the

The descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. the

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. the

Claims (5)

1. a preparation method of graphene, comprising: a), under the condition of ultrasonic vibration, graphite oxide is dispersed in water to obtain colloid; b) Under alkaline conditions, the graphite oxide is reduced with zinc as a reducing agent to obtain graphene; the weight ratio of graphite oxide to zinc is 1: (5.5-6.5); The step b) is carried out under alkaline conditions, specifically: b1), sequentially adding zinc and alkali with a molar ratio of 1: (10-15) to the colloid to obtain graphene; the alkali is sodium hydroxide or potassium hydroxide. 2. The preparation method according to claim 1, characterized in that the weight ratio of the sodium hydroxide or potassium hydroxide to graphite oxide is (15-30):1. 3. The preparation method according to claim 1, characterized in that, the reaction time of the step b1 is 5h-8h. 4. The preparation method according to claim 1, characterized in that, the reaction temperature in the step b1 is 80°C-100°C. 5. The preparation method according to claim 1, characterized in that the concentration of graphite oxide in the colloid is 0.8g/L˜1.2g/L.

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