CN106006609A - Method for preparing graphene with step-by-step purification method - Google Patents

Abstract

The invention discloses a method for preparing graphene by a step-by-step purification method. The technical problem to be solved is the rapid separation and purification of graphene oxide, an intermediate product, so as to facilitate large-scale industrial production. Compared with the prior art, the present invention can completely remove impurities in two steps through ammonia water and acid solution. Since the water solubility of the product and impurities is always different in this process, the filtration and washing speed is greatly accelerated, and continuous operation is possible. , suitable for large-scale production of high-quality graphene.

Description

A kind of step-by-step purification method prepares the method for graphene

technical field

The invention relates to the field of graphene, specifically treating the graphene oxide mixture obtained by the Hummers method with ammonia water and acid solution, removing impurities through simple suction filtration or low-speed centrifugation, and finally reducing to prepare high-quality graphene.

technical background

Graphene (also known as single-layer graphite or two-dimensional graphite) is a two-dimensional carbon atom crystal with a thickness of one atom. Since the single-layer graphene was successfully obtained by the Geim group of the University of Manchester in the United Kingdom in 2004, graphene has attracted much attention for its unique physical and chemical properties. It has excellent light transmission and thermal conductivity. It is a known It is the thinnest, hardest, and least resistive material, and its discoverer won the Nobel Prize in 2010. Graphene has a series of excellent properties such as high specific surface area, outstanding thermal conductivity and mechanical properties, and its extraordinary electron transfer performance. achieve a wide range of applications. In recent years, the large-scale preparation of graphene has become a hot spot in the field of new material research.

At present, the Hummers method is the most commonly used chemical method for preparing graphene at this stage. The typical preparation process is that graphite is oxidized and peeled into graphene oxide under the oxidation of a strong oxidant; impurity ions (such as Mn ⁴⁺ , SO ₄ ^2- , Na ⁺ , NO ^3- , etc.) to obtain graphene oxide; then adding a reducing agent to reduce the oxygen-containing functional groups to finally obtain graphene. Because this method has a wide range of raw materials, short reaction time, and stable quality of graphene obtained, the Hummers method and its improved methods have been increasingly favored in recent years. For example, the patent with the publication number CN200910187298 is based on the modified Hummers method to oxidize graphite and then ultrasonically peel it off, and obtain high-quality graphene after reduction.

However, in the process of preparing graphene by the Hummers method, the intermediate product - graphene oxide has a large number of hydrophilic groups such as carboxyl and hydroxyl groups, resulting in the Zeta potential of graphene oxide in aqueous solution as high as -40mV, forming a very stable decentralized system. At the same time, impurities such as Mn ⁴⁺ , SO ₄ ^2- , Na ⁺ , and NO ^3- in the solution are also very water-soluble ions. Therefore, it is very difficult to separate water-soluble graphene oxide from water-soluble impurities. The traditional filtration method must use a high-vacuum oil pump to filter and wash, and the separation speed is slow, resulting in low production efficiency. Centrifugal separation is another separation method, but the graphene oxide can only be precipitated by ultra-high-speed centrifuge with a speed of more than 10,000 rpm for a long time. This is not only cumbersome to operate, but also increases the cost, which is not conducive to large-scale production. In addition, impurity ions can be removed by dialysis, but dialysis bags are expensive, and the dialysis process often takes up to a week. At present, this method is only suitable for the micro-production of graphene for laboratory use. It can be seen that the efficient separation of graphene oxide is a key step in the preparation of graphene, and has become a core issue restricting the large-scale production of graphene.

Contents of the invention

The purpose of the present invention is to develop a high-efficiency, low-cost graphene preparation method to solve the problems of high cost, low efficiency and difficult purification in the prior art.

Technical scheme of the present invention is:

A high-efficiency, fast and low-cost method for preparing graphene. The graphene oxide mixture obtained by the Hummers method is treated separately with ammonia water and acid solution. After removing impurities by simple suction filtration or low-speed centrifugation, high-quality graphite is prepared through a reduction step. alkene. The specific scheme is as follows: firstly, the graphene oxide mixture obtained by the traditional Hummers method. Then add ammonia water, adjust the pH of the system to above 7, and fully react for 0.5-10 hours under the condition of 0-100°C. At this time, there are two main reactions in the solution: (1) under low acidity conditions, Mn ⁴⁺ will generate Mn (OH) ₄ precipitation; (2) graphene oxide will generate water-insoluble partially reduced graphene precipitation under the reduction of ammonia water. The two precipitates from the previous step were simply filtered or washed by low-speed centrifugation (less than 5000 rpm) to remove water-soluble ions. Next, acid solution is added to adjust the pH of the system to below 7, so that Mn(OH) ₄ is precipitated to regenerate water-soluble Mn ⁴⁺ , and the Mn ⁴⁺ is removed by filtration to obtain pure partially reduced graphene. Partially reduced graphene undergoes reduction and drying steps to obtain high-quality graphene powder.

In the present invention, ammonia solution is used to adjust alkalinity.

The acid solution used includes an aqueous solution of one or more mixed acids such as hydrochloric acid, sulfuric acid or nitric acid.

Advantages of the present invention:

Compared with the conventional purification process, the present invention aims at the difficulty of graphene oxide separation and time-consuming purification, and proposes a step-by-step purification scheme for high-efficiency separation, using different pH conditions to remove different impurity ions, and then performing the reduction step, only needing low-speed centrifugation Or simple filtration, it is expected to be used in the rapid purification of graphene oxide and the efficient preparation of graphene, which greatly reduces the production cycle and cost of graphene. This not only provides innovative technical support for the large-scale production of graphene, but also creates favorable conditions for the large-scale application of graphene in energy, materials, medicine and other fields.

Description of drawings

Fig. 1 is the X-ray diffraction pattern of graphene obtained in Example 1 of the present invention.

Figure 2 is an atomic force microscope image of the graphene obtained in Example 1 of the present invention.

Fig. 3 is a transmission electron microscope image of graphene obtained in Example 1 of the present invention.

detailed description

Graphene preparation method of the present invention, comprises the following steps:

1. Preparation of Graphene Oxide Mixture

Graphene oxide was prepared by the Hummers method of literature (Hummers S; Offeman R.Preparation of graphitic oxide.J.Am.Chem.Soc., 1958,80:1339-1339) to obtain Mn ⁴⁺ , SO ₄ ^2- , Graphene oxide mixed solution with Na ⁺ , NO ^3- and other impurities. This process can expand the distance between graphite layers from 0.34nm to 0.78nm, but it also generates a large number of carboxyl, hydroxyl and epoxy groups on the surface of graphene oxide. This leads to very stable dispersion of graphene oxide in aqueous solution, which is not conducive to filtration and centrifugation.

2. Ammonia treatment

Dilute the graphene mixed solution obtained above, and slowly add ammonia water to adjust the pH of the mixture to be greater than 7 under stirring. After 10 hours, after 0.5 to 5 hours of standing, the upper part of the solution becomes clear, and the lower layer is a precipitated layer. By any one of the methods of filtration, centrifugation, and liquid separation, the precipitate is separated and washed to remove water-soluble impurity ions.

3. Acid treatment

Put the precipitate obtained above into water for ultrasonication to make a suspension with a solid content of 0.01-500%, add acid solution, the amount of ammonia water is about 0.5-5 times the mass of graphene, adjust the pH of the system to below 7, and heat After stirring for 0.5-5 hours, Mn(OH) ₄ is precipitated to regenerate water-soluble Mn ⁴⁺ , and Mn ⁴⁺ is removed by centrifugation, liquid separation or filtration to obtain pure partially reduced graphene.

4. Reduction of graphene

The partially reduced graphene obtained in the previous step is ultrasonically dispersed in water again, and a reducing agent is added for further reduction and drying to obtain high-quality graphene powder.

Example 1:

Use the method of Hummers to prepare a mixed solution of graphite oxide containing impurities. According to the quality of graphite oxide in the solution, add one times the mass of ammonia solution, adjust the pH to 10, stir at a temperature of 100°C for 0.5 hours, and then let it stand for 1 hour , centrifuged at 3000 rpm, washed three times with dilute hydrochloric acid, washed three times with distilled water, dried in an oven, and finally obtained black graphene oxide and Mn(OH) ₄ Mixed precipitates.

The mixed precipitate was ultrasonically redispersed in water to prepare a 1% suspension, and an equal mass of hydrochloric acid was added, heated to 100°C for 2 hours to dissolve manganese ions, filtered and washed to obtain pure partially reduced graphene.

Redisperse the partially reduced graphene obtained above in water, add an equal mass of hydrazine hydrate, react in a water bath at 90°C for 2 hours, filter and wash, and then freeze-dry to obtain black graphene powder.

Example 2

Utilize the method of Hummers to prepare the impurity-containing graphite oxide mixed solution, according to the quality of graphite oxide in the solution, add twice the mass of ammonia water, adjust the pH to 13, stir for 1 hour, then stand for 2 hours, filter the precipitate, and wash with dilute hydrochloric acid Washed three times, then washed three times with distilled water, freeze-dried, and finally obtained black graphene oxide and Mn(OH ₎ mixed precipitate.

The mixed precipitate was ultrasonically redispersed in water to prepare a 5% suspension, adding twice the mass of sulfuric acid, heated to 100°C for 2 hours to dissolve the manganese ions, filtered and washed to obtain pure partially reduced graphene.

The partially reduced graphene obtained above was redispersed in water, and an equal mass of hydrazine hydrate was added, reacted in a water bath at 90° C. for 2 hours, filtered and washed, and then freeze-dried to obtain black graphene powder.

Example 3

Utilize the method of Hummers to prepare impurity-containing graphite oxide mixed solution, according to the quality of graphite oxide in the solution, add three times the mass of ammonia water, stir for 1 hour, after standing for 3 hours, separate the liquid to obtain the lower layer solution, wash with dilute hydrochloric acid three times , and washed three times with distilled water, freeze-dried, and finally obtained black graphene oxide and Mn(OH) ₄ mixed precipitates.

The mixed precipitate was ultrasonically redispersed in water to prepare a 1% suspension, and three times the mass of nitric acid was added, heated to 100°C for 2 hours to dissolve manganese ions, filtered and washed to obtain pure partially reduced graphene.

Redisperse the partially reduced graphene obtained above in water, add an equal mass of hydrazine hydrate, react in a water bath at 90°C for 2 hours, filter and wash, and then freeze-dry to obtain black graphene powder.

Example 4

Utilize the method of Hummers to prepare impurity-containing graphite oxide mixed solution, according to the quality of graphite oxide in the solution, add ammonia water with five times the mass, stir for 0.5 hour, after standing for 0.5 hour, filter under low vacuum, wash twice with dilute hydrochloric acid , and then washed twice with distilled water, dried in an oven at 110 degrees, and finally obtained a black mixed precipitate of graphene oxide and manganese hydroxide.

The mixed precipitate was ultrasonically redispersed in water to prepare a 1% suspension, adding one-time mass of nitric acid, heating to 100°C for 15 minutes to dissolve manganese ions, filtering and washing to obtain pure partially reduced graphene.

The partially reduced graphene obtained above was redispersed in water, and an equal mass of hydrazine hydrate was added, reacted in a water bath at 90° C. for 5 hours, filtered and washed, and then freeze-dried to obtain black graphene powder.

Claims (5)

1. the method that a substep method of purification prepares Graphene, it is characterised in that: comprise the following steps: Ammonia is added in the graphene oxide mixture solution with a large amount of impurity prepared by Hummers method, Regulation system pH, to more than 7, is fully reacted 0.5～10 hour under conditions of 0～100 DEG C, is then led to Filter, any one of centrifugal, separatory operational approach method, separating, washing precipitates, and removes and dissolves The foreign ion of property, obtains the mixed precipitation of partial reduction Graphene and manganous hydroxide；Again to mixed precipitation Middle addition acid solution, regulation system pH to less than 7, make Mn (OH)₄Precipitation regenerates water miscible Mn⁴⁺, filter and remove Mn⁴⁺Pure partial reduction Graphene can be obtained；Partial reduction Graphene is through entering One step reduction and drying steps, i.e. can get high-quality graphene powder.

The method that substep method of purification the most according to claim 1 prepares Graphene, it is characterised in that: Described graphene oxide mixture is prepared by existing chemical oxidization method or Hummers method.

The method that substep method of purification the most according to claim 1 prepares Graphene, is characterized in that making Processing graphene oxide mixture in two steps by ammonia and acid solution, wherein acid solution is hydrochloric acid, nitric acid or sulphuric acid In one or more.

The method that substep method of purification the most according to claim 1 prepares Graphene, is characterized in that leading to Filter, any one of centrifugal, separatory operational approach method, separating, washing precipitates, and removes metal Impurity and other impurity, obtain the graphene oxide of higher degree.

The method that substep method of purification the most according to claim 1 prepares Graphene, is characterized in that The high-purity partial reduction Graphene arrived can generate high-quality graphite through further conventional reduction process Alkene product.