CN103408000B - Preparation method for oxidized grapheme in large sheet - Google Patents

Abstract

The invention relates to a preparation method for oxidized graphene in a large sheet. The method comprises the following steps: uniformly mixing natural scale graphite with the mixed acid of concentrated nitric acid or nitric acid and sulfuric acid in a reactor; adding hydrogen peroxide from the bottom of the reactor; reacting under mixing for 10-60 min; washing with water and drying to obtain layered graphite; mixing the layered graphite with strong acid; adding strong oxidant slowly; performing ultrasound-assisted oxidation reaction in an ice-water bath for 30-60 min after uniform mixing; heating the reaction mixture to 50-60 DEG C and continuing mixing for 6-12 h; adding deionized water and performing ultrasound-assisted mixing reaction for 10-30 min; cleaning the obtained product first with mixed solution of diluted hydrochloric acid and hydrogen perhydrol, then with deionized water; performing centrifugal separation to obtain oxidized graphene. The method provided by the invention is simple in operation, high in oxidation efficiency and free from environment pollution; the prepared oxidized graphene has a high peeling rate and a high specific surface area.

Description

Preparation method of large sheet graphene oxide

technical field

The invention relates to a method for preparing graphene oxide, in particular to a method for preparing large sheets of graphene oxide.

Background technique

Since graphene was first prepared by the AK Geim group of the University of Manchester in 2004 by mechanically exfoliating graphite, graphene, as a new type of two-dimensional nano-carbon material, has attracted people's attention because of its unique structure and properties. . Graphene is a hexagonal lattice honeycomb two-dimensional structure material composed of carbon atoms with sp2 hybrid orbitals. The thickness of the single layer is 0.35nm, and the CC bond length is 0.142nm. It is a component of fullerene, carbon nanotubes and graphite. The basic unit has excellent electrical, thermal, mechanical and electrochemical properties. The theoretical specific surface area of single atomic layer graphene material is as high as 2630m ² /g, the intrinsic electron mobility of semiconductor is about 2×10 ⁵ cm ² /V·s, the resistivity is about 10 ^-6 Ω·cm, and the thermal conductivity is as high as 5000W /m·K, the Young's modulus is 1100GPa, the breaking strength is 125GPa, and the light transmittance is as high as 97.7%. Based on the above characteristics, graphene has very broad application prospects in the fields of electronics, information, energy, biology, and medicine.

The main preparation methods of graphene at home and abroad include micromechanical exfoliation method, epitaxial growth method, chemical vapor deposition method, redox method, liquid phase exfoliation method, etc. The redox method is a relatively common low-cost and high-efficiency method for preparing large-area thin-layer graphene materials. In this method, high-purity natural graphite is oxidized by oxidation technology to obtain graphene oxide with a basic molecular structure of C hexagon and a large number of hydroxyl, carboxyl, epoxy and other groups on the surface and edges, and the graphene oxide is washed to medium properties, and then remove the oxygen-containing groups on its molecular structure by reduction, and finally obtain the method of graphene material. In the preparation process of graphene by chemical redox method, the preparation technology of large sheets and thin layers of graphene oxide is particularly critical. The oxidation methods of graphite mainly include three methods: Brodie, Staudenmaier and Hummers. Thoroughly mix Brodie graphite and NaClO ₄ in a beaker, add concentrated HNO ₃ in an ice bath, heat the mixture to 60°C after mixing evenly, continue to stir for 24 hours, then filter the obtained graphite oxide solid, wash with 5% HCI solution, Filter and dry. The degree of oxidation of graphite oxide obtained after washing is relatively low, and multiple oxidation treatments are required to increase the degree of oxidation, and the reaction time is relatively long. The advantage of this method is that the degree of oxidation can be controlled by the oxidation time, and the synthesized graphite oxide has high crystallinity. However, due to the use of perchlorate as an oxidant, the risk is greater, and more toxic gases will be produced during the reaction. The Staudenmaier method uses concentrated sulfuric acid system, perchlorate and fuming nitric acid as oxidants, and the temperature of the reaction system needs to be kept at 0°C. The degree of oxidation increases with the increase of reaction time, and the final degree of oxidation of graphite can be controlled by controlling the reaction time. Its disadvantage is that the reaction time is long, the degree of oxidation is low, and multiple oxidation treatments are required. Generally, the graphite diffraction peak does not appear in the XRD diagram of the product obtained after oxidation for 56 hours. In addition, more toxic gas substance _Cl2 is produced during the reaction. The Hummers method uses concentrated sulfuric acid and nitrate system, with permanganate as oxidant, and prepares graphite oxide through three reaction stages of low temperature (below 4°C), medium temperature (about 35°C) and high temperature (below 98°C). In this method, the oxidation time is shorter, the oxidation degree of the product is higher, the crystal structure of the product is more regular, and the product is easy to swell and delaminate in water. At present, there have been patent reports on the preparation of graphene oxide by using graphite micropowder or expanded graphite as raw material by the improved Hummers method. However, when using small particle size graphite micropowder as raw material, its oxidation efficiency is higher. When using large flake graphite as raw material, Its oxidation efficiency and the exfoliation degree of graphite oxide are poor; when expanded graphite is used as raw material, although the expanded worm-like graphite provides more contact area for strong acid and strong oxidant, which improves the oxidation efficiency, however, the huge The expansion volume requires more acid for the oxidation reaction. In addition, in the process of preparing expanded graphite by high temperature expansion, the energy consumption is high, and the released sulfide or nitride will cause serious pollution to the environment.

Contents of the invention

In order to overcome the above-mentioned defects in the prior art, the present invention provides a method for preparing large sheets of graphene oxide. The preparation method is to firstly pre-treat graphite to prepare layered graphite, and then use ultrasonic-assisted oxidation to prepare graphene oxide. The method has the advantages of simple operation, high oxidation efficiency and no environmental pollution, and the prepared graphene oxide has high exfoliation degree and large specific surface area.

For reaching above-mentioned purpose, the preparation method of a kind of large sheet graphene oxide of the present invention, it may further comprise the steps:

(1) Mix natural flake graphite with concentrated nitric acid or a mixed acid composed of nitric acid and sulfuric acid evenly in the reactor, add hydrogen peroxide from the bottom of the reactor (if it is added from the top, hydrogen peroxide is easy to decompose, which is not conducive to the reaction), and stir the reaction 10-60min, after washing with water and drying, delaminated graphite is obtained;

(2) Mix delaminated graphite with strong acid, slowly add strong oxidant, mix evenly, and conduct ultrasonic-assisted oxidation reaction in ice-water bath for 30-60min;

(3) Heat the reaction mixture in step (2) to 50-60°C and keep stirring for 6-12h, add deionized water (preferably the ratio of layered graphite to deionized water is 1g: 100mL) and stir for 10 -30min, the obtained product was first washed with a mixed solution of dilute hydrochloric acid and hydrogen peroxide, then washed with deionized water, and centrifuged to obtain graphene oxide.

The higher the purity of graphite raw materials, the better, but the cost of high-purity graphite raw materials is higher. Existing methods for preparing graphene generally require raw materials to be high-purity graphite. The method of the present invention is not limited to high-purity graphite raw materials, and is also very suitable for non-high-purity graphite raw materials. The smaller the particle size of the graphite raw material, the better, the larger the particle size, the lower the oxidation efficiency, and the smaller the particle size, the higher the oxidation efficiency, but the smaller the graphene sheet obtained. Therefore, the present invention has no requirements on the purity and particle size of graphite, but from the perspective of improving production efficiency and reducing production cost, the preferred graphite has a purity of 75-99.9% and a particle size of 150-270 μm.

In the method of the present invention, the natural flake graphite in the step (1) is preferred: concentrated nitric acid or mixed acid of nitric acid and sulfuric acid: hydrogen peroxide=1g: 3-5mL: 0.5-1mL.

In the method of the present invention, preferably, the volume ratio of nitric acid to sulfuric acid in the mixed acid is (8-9):1.

In the method of the present invention, preferably, the nitric acid concentration is 85% (mass percentage), the sulfuric acid concentration is 98% (mass percentage), and the hydrogen peroxide concentration is 60% (mass percentage).

In the method of the present invention, it is preferred that the strong acid used in the ultrasonic-assisted oxidation reaction in the step (2) is concentrated sulfuric acid, concentrated nitric acid, perchloric acid or their mixed acids in any proportion, and the strong oxidant is potassium permanganate, nitric acid Sodium, potassium dichromate, potassium nitrate or their mixture in any proportion.

In the method of the present invention, preferably, the ratio of layered graphite to strong acid in the step (2) is 1g:25-50mL, and the weight ratio of layered graphite to strong oxidant is 1:(3-5), and the specific ratio is based on The particle size of the layered graphite depends on the particle size of the layered graphite. The larger the particle size of the layered graphite, the greater the amount of strong acid and strong oxidant required.

In the method of the present invention, the ultrasonic power of the ultrasonic-assisted oxidation reaction in the step (2) and step (3) is preferably 40-50 kHz.

In the method of the present invention, preferably, the mixed solution of dilute hydrochloric acid and hydrogen peroxide in step (3) is obtained by mixing dilute hydrochloric acid with a mass percentage of 10% and hydrogen peroxide with a mass percentage of 1% at a volume ratio of 1:1.

The present invention also relates to graphene oxide obtained by the above method.

The difference from the prior art is that the present invention firstly prepares layered graphite through an intercalation reaction in which hydrogen peroxide replaces a solid oxidant, and then uses ultrasonic-assisted oxidation to prepare graphene oxide. Not only can the oxidation efficiency of graphite be greatly improved, but also the ultrasonic-assisted reaction makes the prepared graphite oxide unnecessary to be peeled off, and the prepared graphene has a high degree of peeling and a large specific surface area. The method for preparing graphene oxide of the invention has the advantages of simple operation, low energy consumption and no environmental pollution.

The preparation method of the large-scale graphene oxide of the present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is the SEM characterization photo of the layered graphite that the example of the present invention 1 makes;

Fig. 2 is the XRD characterization spectrogram of the layered graphite and graphite oxide that example 1 of the present invention makes;

Fig. 3 is the FTIR characterization spectrogram of the graphite oxide that example 1 of the present invention makes;

Fig. 4 is the TEM characterization photograph of the graphene oxide that example 1 of the present invention makes;

Fig. 5 is the TEM characterization photograph of the graphene oxide that example 2 of the present invention makes;

6 is a TEM characterization photo of graphene oxide prepared in Example 3 of the present invention.

Detailed ways

The following are examples and test data thereof, etc., but the content of the present invention is not limited to the scope of these examples.

Example 1

Mix 10g of natural flake graphite with a purity of 99% and a particle size of 150μm with 30mL of concentrated nitric acid, add 5mL of hydrogen peroxide with a concentration of 60% from the bottom of the reactor, stir and react for 20min, wash with water, and dry to obtain delaminated graphite; weigh 2g Mix layered graphite with 80mL of concentrated sulfuric acid, slowly add 6g of potassium permanganate, mix evenly, and conduct an ultrasonic-assisted oxidation reaction in an ice-water bath for 30min with an ultrasonic power of 40kHz; raise the temperature of the mixture to 50°C and keep stirring for 10h, then add 200mL to Stirring and reacting for 20 minutes under the assistance of ionized water ultrasound, the obtained product was first centrifuged with a mixed solution of 10% (mass percentage) dilute hydrochloric acid and 1% (mass percentage) hydrogen peroxide at a volume ratio of 1:1, and then washed with deionized water and centrifuged. Separated to obtain graphene oxide.

The SEM characterization of the layered graphite obtained by this embodiment (using MX2600FE scanning electron microscope, British Camscan company. The dry layered graphite powder is evenly bonded to the conductive tape for direct testing) with reference to accompanying drawing 1, from Figure 1 It can be seen that after the natural flake graphite is pretreated by acidification and oxidation, part of the graphite flakes are peeled off, showing a flower-like graphite structure. This structure of graphite has a larger specific surface area, which is conducive to further oxidation of graphite.

XRD characterization of layered graphite and graphite oxide (Germany D8Advance diffractometer is used for XRD characterization of materials. The X-ray source is Cu–Kα ray (λ=0.15406nm), voltage 40kV, current 40mA, scanning range 2θ is 5°～ Between 70°, scanning speed is 6°/min, scanning step is 0.02°, and the detector is a scintillation counter. The dry layered graphite powder and the graphene oxide sample dried at 40°C are directly tested.) Referring to Figure 2, It can be seen from Figure 2 that the layered graphite (spectrum a) still retains obvious graphite diffraction peaks at 2θ=25.9°, and the position of the diffraction peaks has shifted to the left, and double peaks appear, mainly because In the pre-treatment process of acidification and oxidation, new substances are inserted into the interlayer of graphite, and the crystal structure changes. However, the re-oxidized graphite oxide (spectrum b) has a strong graphene oxide diffraction peak at 2θ=11°, and the graphite diffraction peak disappears completely, indicating that the oxidation of graphite is relatively complete, and the obtained graphite oxide has a high degree of oxidation.

FTIR characterization of graphene oxide samples (using FTIR-8400s Fourier Transform Infrared Spectrometer of Shimadzu Corporation of Japan to test the samples, scanning range: 4000～500cm ^-1 ; KBr tablet method for sample preparation) refer to attached drawing 3, the results It shows that the CO stretching vibration in the epoxy group, the stretching vibration of C-OH, the bending vibration of OH and the stretching vibration peak of C=O appear in the spectrum, and the intensity is relatively large, while the vibration of C=C is greatly weakened , further indicating that graphite oxide has a higher degree of oxidation.

TEM characterization of graphene oxide samples (using TECNAI G2F30 field emission transmission electron microscope) Graphene oxide was dispersed in absolute ethanol solvent, ultrasonically treated for 20 minutes, sampled with a disposable needle, and dropped onto a copper grid for testing. Referring to accompanying drawing 4 for the photo, it can be seen from Fig. 4 that the graphene oxide sheet is relatively thin, the sheet area is large, and there are folds and stacks.

Example 2

Mix 10g of natural flake graphite with a purity of 99% and a particle size of 180μm with 40mL of concentrated nitric acid, add 7mL of hydrogen peroxide from the bottom of the reactor, stir and react for 30min, wash with water, and dry to obtain delaminated graphite; weigh 2g of delaminated graphite and 100mL Mix concentrated sulfuric acid, slowly add 8g of potassium permanganate, mix well, and then conduct ultrasonic-assisted oxidation reaction in an ice-water bath for 30min, with an ultrasonic power of 50kHz; heat the mixture to 60°C and keep stirring for 12h, then add deionized water and stir under ultrasonic assistance After reacting for 40 minutes, the obtained product was first centrifugally cleaned with a 1:1 mixed solution of 10% dilute hydrochloric acid and 1% hydrogen peroxide, then washed with deionized water, and centrifuged to prepare graphene oxide.

The TEM characterization photos of the graphene oxide samples obtained in this example refer to Figure 5 (the test method is the same as that in Example 1). From Figure 5, it can be seen that the graphene oxide sheets are relatively thin, with a large layer area and wrinkled stacks. .

Example 3

Mix 10g of natural flake graphite with a purity of 90% and a particle size of 270μm with 50mL of concentrated nitric acid, add 10mL of hydrogen peroxide from the bottom of the reactor, stir and react for 60min, wash with water, and dry to obtain delaminated graphite; weigh 2g of delaminated graphite and 90mL Mix concentrated sulfuric acid, slowly add 8g of potassium permanganate, mix well, and conduct ultrasonic-assisted oxidation reaction in an ice-water bath for 30min, with an ultrasonic power of 40kHz; heat the mixture to 60°C and continue stirring for 12h, then add deionized water and ultrasonically assist in stirring After reacting for 30 minutes, the obtained product was first centrifugally cleaned with a 1:1 mixed solution of 10% dilute hydrochloric acid and 1% hydrogen peroxide, then washed with deionized water, and centrifuged to prepare graphene oxide.

The TEM characterization photos of graphene samples obtained by examples refer to accompanying drawing 6 (the test method is the same as in Example 1), it can be seen from the figure that there are few folds in the graphene sheet, the graphene oxide sheet is thinner, and the sheet area is larger , showing stacked folds and curled edges.

Example 4

The preparation method is basically the same as in Example 1, except that the purity of the natural flake graphite used is 75%, and the particle size is 200 μm; when preparing layered graphite, replace the concentrated nitric acid with the mixed acid of 100ml nitric acid and sulfuric acid, wherein the mixed acid contains nitric acid and sulfuric acid The ratio is 8:1. The obtained graphene oxide was characterized by TEM, and the graphene oxide sheet was relatively thin, and the sheet area was large, showing wrinkle stacking, which was similar to the characteristics of Example 1.

Example 5

The preparation method is basically the same as in Example 1, except that when the layered graphite is ultrasonically assisted in an ice-water bath, the strong acid used is a mixed acid of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 3:1, and the strong oxidant used is heavy Potassium chromate can also obtain the same degree of exfoliation as in Example 1, large sheets of graphene oxide with a large specific surface area.

Example 6

The preparation method is basically the same as in Example 1, except that when the layered graphite is oxidized by ultrasonic in an ice-water bath, the strong acid used is perchloric acid, and the strong oxidant used is sodium nitrate and permanganese with a mass ratio of 1:1. Potassium acid mixture, can obtain the same exfoliation degree as embodiment 1 equally high, the large sheet of graphene oxide that specific surface area is big.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. Variations and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (3)

1. a preparation method of large sheet graphene oxide, is characterized in that, comprises the following steps: (1) Mix natural flake graphite with concentrated nitric acid or a mixed acid composed of nitric acid and sulfuric acid in the reactor, add hydrogen peroxide from the bottom of the reactor, stir and react for 10-60min, wash and dry to obtain delaminated graphite; (2) Mix the layered graphite with a strong acid, slowly add a strong oxidizing agent, mix well, and conduct an ultrasonic-assisted oxidation reaction in an ice-water bath for 30-60 minutes; (3) Warm up the reaction mixture in step (2) to 50-60°C and keep stirring for 6-12h, then add deionized water and ultrasonically assist to stir and react for 10-30min, and the obtained product is first washed with a mixed solution of dilute hydrochloric acid and hydrogen peroxide , and then washed with deionized water, and centrifuged to obtain graphene oxide; The purity of the natural flake graphite is 75% or 90%, and the particle size is 150-270 μm; Natural flake graphite in the step (1): concentrated nitric acid or the mixed acid of nitric acid and sulfuric acid: hydrogen peroxide=1g: 3-5mL: 0.5-1mL; The mass concentration of nitric acid is 85%, the mass concentration of sulfuric acid is 98%, and the mass concentration of hydrogen peroxide is 60%; The ratio of layered graphite to strong acid in the step (2) is 1g:25-50mL, and the weight ratio of layered graphite to strong oxidant is 1:(3-5); The ultrasonic power of the ultrasonic-assisted oxidation reaction in the step (2) and the step (3) is 40-50kHz; The mixed solution of dilute hydrochloric acid and hydrogen peroxide in the step (3) is obtained by mixing dilute hydrochloric acid with a mass percentage of 10% and hydrogen peroxide with a mass percentage of 1% at a volume ratio of 1:1. 2. The method according to claim 1, characterized in that: the volume ratio of nitric acid and sulfuric acid in the mixed acid is (8-9):1. 3. method according to claim 1, it is characterized in that: in described step (2), the used strong acid of ultrasonic assisted oxidation reaction is vitriol oil, concentrated nitric acid, perchloric acid or their mixed acid mixed in any proportion, strong The oxidizing agent is potassium permanganate, sodium nitrate, potassium dichromate, potassium nitrate or their mixture in any proportion.