CN108622886A - A kind of liquid nitrogen auxiliary prepares the method for high-quality graphene and high-quality graphene obtained - Google Patents

Abstract

The present invention relates to a kind of liquid nitrogen auxiliary to prepare the method for high-quality graphene and high-quality graphene obtained, and graphene of the invention has the characteristics that oxygen content is low, defect is few, few layer graphene (being less than 5 layers) content is high and big with two-dimensional slice size.The present invention method be：Quasiflake graphite is placed in liquid nitrogen, high-speed stirred, makes liquid nitrogen volatilization to get to graphene powder after the completion of to be mixed.The method of the present invention rapidly and efficiently, safety and environmental protection and at low cost, and obtained graphene is high-quality, oxygen content is below 8%, and in the Raman spectrum of the graphene, the peak intensity ratio at the peaks D and the peaks G is below 0.8, for the peak intensity ratio at the peaks 2D and the peaks G 0.2 or more, method of the invention can be applied to the production of extensive high-quality graphene.

Description

A liquid nitrogen-assisted method for preparing high-quality graphene and the prepared high-quality graphene Graphene

technical field

The invention belongs to the technical field of carbon materials, and relates to a kind of graphene and its preparation method, especially a kind of high-quality graphene and its preparation method. More specifically, the invention relates to a liquid nitrogen-assisted method for preparing high-quality graphene Method and high-quality graphene obtained.

Background technique

Graphene is a hexagonal honeycomb-like two-dimensional structure material formed by carbon atoms with sp ² hybrid orbitals, and has many excellent properties. Graphene has ultra-high light transmittance, high thermal conductivity, high electron mobility, high electrical conductivity, room temperature quantum Hall effect, adjustable energy band gap, excellent mechanical properties, efficient hydrogen storage performance, singular magnetic chemical properties and perfect charge-to-charge interactions. Because of its unparalleled properties, graphene is considered to be the material of choice in the fields of next-generation microelectronic devices, organic optoelectronic materials, high-efficiency energy storage materials, multifunctional composite materials, and biomaterials. However, the low-cost macro-preparation of high-quality graphene still faces difficulties, which greatly limits its development and application.

So far, graphene has been prepared in a variety of ways, which can be mainly divided into two categories: top-down method and bottom-up method. The former is to construct a two-dimensional honeycomb structure of graphene by forming covalent bonds with the help of small molecule chemical reactions; the latter is to prepare two-dimensional graphene by exfoliating three-dimensional bulk graphite materials. More representative methods include CVD method, SiC epitaxial growth method, redox method, mechanical stripping method, liquid phase stripping method and other methods.

Among these methods, some methods prepare high-quality graphene, but are expensive and complicated to operate; some methods are simple to operate, but the prepared graphene is of poor quality. Therefore, there is still a need for research on methods that are simple to operate, low in cost, and can quickly prepare high-quality graphene.

Contents of the invention

Aiming at the problems existing in the prior art, the object of the present invention is to provide a kind of high-quality graphene and its preparation method, and the present invention is committed to providing a kind of high-quality (low oxygen content, low defect) graphene.

In addition, the present invention seeks to provide a method for the preparation of graphene, which is of high quality, in particular by an economical, efficient and low-risk process.

The "high-quality graphene" of the present invention refers to: the oxygen content of the graphene is below 8%, and in the Raman spectrum of the graphene, the peak intensity ratio of the D peak to the G peak is below 0.8, and the ratio of the 2D peak to the G peak is below 0.8. The peak intensity ratio of the G peak is above 0.2.

The graphene of the present invention not only has low oxygen content, few defects, few layers, but also has the characteristics of large two-dimensional sheet size. In the graphene of the present invention, the mass content of few-layer graphene (the number of layers is less than 5) is 10%. -15%, such as 10%, 11%, 11.5%, 12%, 13%, 13.5%, 14%, 14.3%, 14.6% or 15%.

The "few-layer graphene" in the present invention means that the number of layers is less than 5.

For reaching above-mentioned purpose, the present invention adopts following technical scheme:

In a first aspect, the present invention provides a method for liquid nitrogen-assisted preparation of graphene, especially a method for liquid nitrogen-assisted preparation of high-quality graphene, the method comprising:

The worm-like graphite is placed in liquid nitrogen, stirred, and the liquid nitrogen is volatilized after the stirring is completed to obtain graphene powder.

In the present invention, the way to volatilize the liquid nitrogen can be to stand still to volatilize the remaining liquid nitrogen naturally, or to heat the remaining liquid nitrogen to evaporate to dryness, but it is not limited to the above two ways, and other ways to volatilize the liquid nitrogen can also be used in the present invention.

Preferably, the amount of liquid nitrogen used is 100ml-800ml for every 1g of worm-like graphite, such as 100ml, 200ml, 225ml, 250ml, 300ml, 350ml, 400ml, 450ml, 500ml, 550ml, 600ml, 650ml, 700ml, 750ml, 780ml or 800ml, etc., preferably 400ml.

Preferably, the stirring speed is 2000r/min-25000r/min, such as 2000r/min, 4000r/min, 6000r/min, 8000r/min, 10000r/min, 12500r/min, 15000r/min, 17000r/min , 18500r/min, 20000r/min, 21000r/min, 22000r/min, 23000r/min, 24000r/min or 25000r/min, etc., preferably 8000r/min-20000r/min, more preferably 20000r/min.

Preferably, the stirring time is 5min-60min, such as 5min, 10min, 15min, 20min, 25min, 28min, 30min, 35min, 40min, 42min, 45min, 50min, 55min or 60min, etc.

As a preferred technical scheme of the method of the present invention, since liquid nitrogen volatilizes during the stirring process, it is preferable to continuously replenish liquid nitrogen during the stirring process, so that the total amount of liquid nitrogen relative to 1g of worm-like graphite after filling is completed. 100ml-800ml.

Preferably, the amount of added liquid nitrogen is equal to the amount of liquid nitrogen volatilized during the stirring process.

Preferably, the equipment used for the stirring is a high-speed mechanical stirrer.

Preferably, during the stirring process using a high-speed mechanical stirrer, the diameter of the stirring knife rotor is not less than 16 mm, preferably 32 mm.

Preferably, during the stirring process using a high-speed mechanical stirrer, the gap between the stator and the rotor of the stirring tool is not greater than 1mm, preferably 0.5mm.

As a preferred technical solution of the method of the present invention, the worm-like graphite is prepared by the following method: first intercalate the graphite raw material, and then heat the intercalated graphite raw material to expand to obtain the worm-like graphite.

Preferably, the volume of worm-like graphite converted from 1 g of graphite raw material is 300ml-600ml, such as 300ml, 350ml, 400ml, 450ml, 500ml, 520ml, 550ml, 575ml or 600ml.

Preferably, the graphite raw material includes any one or a combination of at least two of flake graphite, graphite powder, expanded graphite, fullerene, carbon nanotube, carbon nanobelt, carbon black, mesoporous carbon or activated carbon, but It is not limited to the materials listed above, and other graphite raw materials commonly used in this field can also be used in the present invention.

Preferably, the intercalation agent used in the intercalation is any one of acid, alkali metal, alkaline earth metal or salt, preferably acid.

Preferably, the heating method is any one or a combination of at least two of furnace heating or microwave heating, preferably microwave heating.

More preferably, the worm-like graphite is prepared by the following method:

(1) use acid to carry out intercalation to graphite raw material, obtain the graphite raw material of intercalation;

(2) Under the protection of an inert gas, the intercalated graphite raw material is irradiated with microwaves to obtain worm-like graphite.

The worm-like graphite prepared by this preferred technical solution is fluffy worm-like graphite, and the volume of the worm-like graphite converted from every 1g of graphite raw material is 300ml-600ml.

Preferably, during the step (1) of preparing the intercalated graphite raw material, the graphite raw material is placed in an acid solution, stirred, and solid-liquid separated to obtain the intercalated graphite raw material.

Preferably, the mass fraction of the acid solution is any one or at least two of perchloric acid with a mass fraction of 30%-72%, sulfuric acid with a mass fraction of 50%-98%, and nitric acid with a mass fraction of 50%-98%. The mixture of two kinds, preferably any one of 72% perchloric acid, 98% sulfuric acid or 98% nitric acid or a mixture of at least two, more preferably 72% perchloric acid, or 98% sulfuric acid and 98% nitric acid mixture.

In the present invention, the mass fraction is 30%-72% perchloric acid, for example, the mass fraction is 30%, 33%, 35%, 37.5%, 40%, 43%, 46%, 50%, 52%, 55%, 58%, 60%, 65%, 68%, 70% or 72%, etc., preferably 72%.

In the present invention, the mass fraction is 50%-98% sulfuric acid, such as 50%, 55%, 58%, 60%, 63%, 65%, 70%, 72%, 76%, 78% , 82%, 85%, 90%, 92%, 94%, 96% or 98%, etc.

In the present invention, the mass fraction is 50%-98% nitric acid, for example, the mass fraction is 50%, 53%, 58%, 60%, 65%, 66%, 68%, 70%, 73%, 75% , 77%, 78%, 80%, 84%, 88%, 90%, 93%, 96% or 98%, etc.

Preferably, the stirring time is 1min-36h, such as 1min, 2min, 3min, 5min, 8min, 10min, 12min, 15min, 20min, 25min, 28min, 0.5h, 0.8h, 1h, 2h, 3h, 4h , 5h, 7h, 10h, 12h, 15h, 17h, 18h, 20h, 24h, 25h, 27h, 30h, 32h, 34h, 35h or 36h, etc. For different acid solutions, the preferred stirring time is different. For example, when the acid solution is perchloric acid with a mass fraction of 30%-72%, the preferred stirring time is 1min-5min; when the acid solution is a mass fraction of 50% -98% sulfuric acid or nitric acid with a mass fraction of 50%-98% or a mixture of both, the preferred stirring time is 12h-36h.

The stirring in the present invention is carried out at room temperature.

In the present invention, the amount of the acid solution used in step (1) is not specifically limited, as long as the graphite raw material can be completely immersed in the acid solution.

As a preferred technical solution of the method of the present invention, the acid solution is perchloric acid with a mass fraction of 72%, and relative to 1g of graphite raw material, the amount of the acid solution is 100ml, and the stirring time is 3min.

As a preferred technical scheme of the method of the present invention, the acid solution is 98% sulfuric acid and/or nitric acid with a mass fraction of 98%, and with respect to 1g graphite raw material, the consumption of the acid solution is 25ml- 60ml, the stirring time is 12h-36h.

In the present invention, the "sulfuric acid with a mass fraction of 98% and/or nitric acid with a mass fraction of 98%" refers to: it can be sulfuric acid with a mass fraction of 98%, or nitric acid with a mass fraction of 98%. It is a mixture of sulfuric acid with a mass fraction of 98% and nitric acid with a mass fraction of 98%.

In the present invention, after the intercalation step in step (1), the acid solution can be recovered and reused.

Preferably, the inert gas in step (2) is any one or a combination of at least two of nitrogen, argon, helium, neon, krypton or xenon, preferably any one of nitrogen or argon .

Preferably, the power of the microwave radiation in step (2) is 100W-1200W, such as 100W, 200W, 300W, 400W, 600W, 700W, 800W, 950W, 1000W, 1100W or 1200W, etc., preferably 700W-1000W.

Preferably, the microwave radiation time in step (2) is 10s-300s, such as 10s, 20s, 30s, 40s, 45s, 50s, 60s, 65s, 70s, 80s, 90s, 100s, 110s, 130s, 135s, 150s, 160s, 180s, 200s, 215s, 230s, 245s, 260s, 270s, 280s or 300s, etc., preferably 90s-300s.

As a preferred technical solution of the method of the present invention, a method for preparing graphene comprises the following steps:

(1) The graphite raw material is placed in the perchloric acid of 72% by mass fraction, the graphite raw material is fully immersed in the perchloric acid of 72% by mass fraction, stirred for 1min-5min, solid-liquid separation, to obtain perchloric acid intercalated graphite raw materials;

(2) under the protection of nitrogen, carry out the microwave radiation of 180s-300s to the graphite material of perchloric acid intercalation, obtain worm-shaped graphite;

(3) According to the dosage standard of 1g worm-like graphite/(400ml-600ml) liquid nitrogen, put the worm-like graphite in liquid nitrogen, use a high-speed mechanical stirrer to stir for 5min-60min, and add and volatilize continuously during the stirring process The same amount of liquid nitrogen as liquid nitrogen is left to stand after stirring to allow the liquid nitrogen to volatilize naturally to obtain graphene powder.

As another preferred technical solution of the method of the present invention, a method for preparing graphene comprises the following steps:

(1) the graphite raw material is placed in the nitric acid of 98% and/or the sulfuric acid of 98% by mass fraction, the nitric acid of 98% and/or the mass fraction of graphite raw material is completely immersed in said mass fraction is 98% In the sulfuric acid, stir 12h-36h, solid-liquid separation, obtain the graphite raw material of intercalation;

(2) Under the protection of argon gas, microwave radiation of 180s-300s is carried out to the graphite raw material of intercalation, obtains worm-like graphite;

(3) According to the dosage standard of 1g worm-like graphite/(400ml-600ml) liquid nitrogen, put the worm-like graphite in liquid nitrogen, use a high-speed mechanical stirrer to stir for 5min-60min, and add and volatilize continuously during the stirring process The same amount of liquid nitrogen as liquid nitrogen is left to stand after stirring to allow the liquid nitrogen to volatilize naturally to obtain graphene powder.

In the second aspect, the present invention provides graphene prepared by the method described in the first aspect, the average size of the two-dimensional plane of the graphene is 2 μm-5 μm, for example, 2 μm, 2.5 μm, 3 μm, 3.2 μm, 3.4 μm μm, 3.5μm, 3.8μm, 4μm, 4.3μm, 4.5μm, 4.7μm or 5μm, etc.

In the present invention, the "average size of the two-dimensional plane of graphene" refers to the average value of the sizes in each direction passing through the center of the two-dimensional plane.

Preferably, the graphene has an oxygen content below 8% or even lower, such as 8%, 7.5%, 7%, 6.5%, 6%, 5% or 4%, preferably below 5%.

In the present invention, in the Raman spectrum of graphene, the peak intensity ratio (ID/IG) of the _D peak to the _G peak is below 0.8, such as 0.8, 0.75, 0.7, 0.6, 0.55, 0.5, 0.4, 0.3 or 0.2 or the like, preferably 0.5 or less, more preferably 0.2. The ID/ _IG of the _graphene of the present invention is below 0.8, indicating that it has few defects and good quality.

In the present invention, in the Raman spectrum of graphene, the peak intensity ratio of the 2D peak to the G peak is above 0.2, such as 0.2, 0.3, 0.4 or 0.8, preferably above 0.5, more preferably 0.8.

The G peak of graphene, which is a peak generally shown in graphite-based materials, is shown in the range of about 1500 cm ⁻¹ to about 1700 cm ⁻¹ . The G peak is caused by a mode in which a hexagonal carbon atom vibrates in the opposite direction to its neighbors, thus having E _2g symmetry, where the vibrational mode is Raman-allowed for the Raman-scattered Raman that is allowed by this symmetry case, this can be observed in primary scattering. In general, weak intensities are observed when the number of graphene layers is small.

The D peak of graphene, which is caused by the A ₁ ' vibrational mode in which the hexagonal carbon atom vibrates in the opposite direction to the atoms facing the carbon atom, is shown in the range of about 1250 cm ⁻¹ to about 1450 cm ⁻¹ out of the peak. Due to the symmetry of Raman scattering, this A1 _′ vibrational mode is not observed in the lattice structure of intact single-layer graphene, whereas when defects occur in the hexagonal structure, or when the edge part of the graphene is exposed to Externally, the A ₁ ' vibrational mode is observed.

The 2D peak of graphene is caused by rescattering of two photons emitted in the above-mentioned A ₁ ' vibrational mode, and is a peak exhibited in the range of about 2600 cm ⁻¹ to about 2800 cm ⁻¹ . The scattering is referred to as double resonance Raman scattering due to the fact that two resonances are generated during the scattering process, and due to the effect of this resonance, the scattering is shown prominently in the spectrum.

In particular, the 2D peaks are completely different between single-layer graphene and multi-layer graphene. In single-layer graphene, the peak has a Lorentzian line shape, narrow width and high intensity; meanwhile, in graphene of two or more layers, a plurality of peaks overlap each other to have a broad peak, and thus, the single-layer Graphene can be distinguished by the shape of its peaks.

In the method for preparing graphene of the present invention, graphene is exfoliated from graphite and micronized so that the intensity of the G peak becomes smaller and the intensity of the 2D peak increases as the number of graphene layers to be exfoliated decreases. Therefore, as graphene is effectively exfoliated from graphite, the I _2D / _IG value increases, and the relative degree of exfoliation of graphene can be evaluated by using this value, the higher the I _2D / _IG , the better the exfoliation , the higher the mass content of the exfoliated few-layer graphene is.

The I _2D / _IG value of general commercial graphene is about 0.1 to about 0.15; and the I _2D / _IG of the graphene of the present invention is significantly improved to about 0.2 or greater, which means that the graphene phase of the present invention Compared with commercial graphene, which is more effectively exfoliated, so that the graphene in a few-layer state has a high content, in the graphene of the present invention, the mass content of few-layer graphene (less than 5 layers) is 10%-15%.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The present invention provides a method for preparing high-quality graphene quickly, efficiently, economically, safely, and with low risk using liquid nitrogen assistance. The method is very simple, and only needs to place worm-like graphite in liquid nitrogen , stirring at high speed, and then evaporating liquid nitrogen, high-quality graphene powder with low oxygen content, few defects, and few layers can be obtained. The method of the present invention can be applied to large-scale production of high-quality graphene.

(2) In the method of the present invention, liquid nitrogen is used to assist the preparation of graphene. After high-speed stirring is completed, high-purity graphene powder can be directly obtained by evaporation of liquid nitrogen, which eliminates the need for washing, drying, etc. in the method of the prior art. For processing steps, the method of the present invention is more convenient and suitable for industrial production.

(3) The average size of the two-dimensional plane of the graphene of the present invention is 2 μm-5 μm, the oxygen content is below 8%, and in the Raman spectrum of the graphene, the peak intensity ratio of the D peak and the G peak is below 0.8 , the peak intensity ratio of 2D peak to G peak is above 0.2, and the mass content of few-layer graphene (less than 5 layers) is 10%-15%.

Description of drawings

Fig. 1 obtains the high-resolution transmission electron microscope photo of graphene for embodiment 1;

Fig. 2 is the scanning electron micrograph of the graphene that embodiment 1 obtains;

Fig. 3 obtains the Raman scattering spectrum of graphene for embodiment 1;

Fig. 4 is the X-ray diffraction spectrum of the graphene that embodiment 1 obtains.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

The present invention will be described in detail through examples below, but the present invention is not limited to the following examples.

The following examples and comparative examples adopt a transmission electron microscope (Tecnai G2 20 S-TWIN) to measure the microstructure of graphene.

The following examples and comparative examples adopt a scanning electron microscope (Hitachi S4800+EDS) to measure the morphology of graphene.

The following examples and comparative examples use an elemental analyzer to measure the carbon and oxygen element content of graphene, thereby obtaining the oxygen content of graphene.

The following examples and comparative examples use a laser Raman spectrometer (Renishaw inVia plus) to determine the structure of graphene.

The following examples and comparative examples adopt X-ray diffractometer (D/MAX-TTRIIII (CBO)) to determine the structure of graphene.

Example 1

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 3min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 600ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/mi, the time was 20min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 6.8% by weight, the ID/ _IG is 0.25, the I _2D / _IG is _0.6 , and the average size of the two-dimensional plane of the graphene is 2 μm-5 μm.

Fig. 1 obtains the transmission electron micrograph of graphene for embodiment 1, as can be seen from the figure, the graphene that peels off is thinner, and number of layers is less.

FIG. 2 is a scanning electron micrograph of the graphene obtained in Example 1. It can be seen from the figure that the average size of the two-dimensional plane of the exfoliated graphene is 2 μm-5 μm.

Fig. 3 obtains the Raman scattering spectrum of graphene for embodiment 1, as can be seen from the figure, I _D / I _G is 0.25, illustrates that the graphene defect that exfoliation obtains is less; I _2D / I _G is 0.6, illustrates that exfoliation obtains The number of graphene layers is less.

Fig. 4 is the X-ray diffraction spectrum of the graphene that embodiment 1 obtains, as can be seen from the figure, the diffraction spectrum does not have obvious graphite peak, illustrates that stripping effect is better.

Example 2

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml of concentrated sulfuric acid (purchased from Beijing Chemical Plant, mass concentration was 98%), stirred at room temperature for 2 God, filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 320ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/min, the time was 20min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 8.0% by weight, the ID/ _IG is 0.4, the I _2D / _IG is _0.5 , and the average size of the two-dimensional plane of the graphene is 2 μm-5 μm.

Example 3

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich company, 50 mesh, purity 99% by weight, the same below) was added to 50ml of concentrated nitric acid and concentrated sulfuric acid mixed acid (the volume ratio of concentrated nitric acid and concentrated sulfuric acid was 3:2, and the concentrated nitric acid Purchased from Beijing Chemical Plant, the mass concentration is 98%, concentrated sulfuric acid was purchased from Beijing Chemical Plant, the mass concentration was 98%), stirred at room temperature for 2 days, and filtered.

The filtered graphite was placed in a corundum crucible, filled with nitrogen and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 480ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/min, the time was 20min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 6.8% by weight, the ID/ _IG is 0.5, the I _2D / _IG is _0.5 , and the average size of the two-dimensional plane of the graphene is 2 μm-5 μm.

Example 4

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 3min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 1.5min, take it out after cooling, and obtain 450ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 500ml beaker, add 400ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/min, the time was 20min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 7.2% by weight, ID/ _IG is 0.4, I _2D / _IG is _0.6 , and the average size of the two-dimensional plane of graphene is 2 μm-5 μm.

Example 5

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 3min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 600ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 10000r/min, the time was 30min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 7.0% by weight, the ID/ _IG is 0.5, the I _2D / _IG is _0.6 , and the average size of the two-dimensional plane of the graphene is 2 μm-5 μm.

Example 6

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of graphite powder (purchased from AlfaAesar company, -20 to +80 mesh, purity of 99% by weight, the same below) was added to 50ml of perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature 3min, filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 520ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/min, the time was 30min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 7.5% by weight, the ID/I _G is 0.5, the I _2D /I _G is 0.5, and the average size of the two _- dimensional plane of the graphene is 2 μm-5 μm.

Example 7

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 3min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 600ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 15000r/min, the time was 60min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 6.3% by weight, ID/ _IG is 0.3, I _2D / _IG is _0.6 , and the average size of the two-dimensional plane of graphene is 2 μm-5 μm.

Example 8

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 3min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 600ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 600ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 8000r/min, the time was 60min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 6.4% by weight, ID/ _IG is 0.3, I _2D / _IG is _0.5 , and the average size of the two-dimensional plane of graphene is 2 μm-5 μm.

Example 9

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich Company, 50 mesh, purity 99% by weight, the same below) was added to 50ml perchloric acid (purchased from Beijing Chemical Plant, mass concentration was 72%), stirred at room temperature for 5min ,filter.

The filtered graphite was placed in a corundum crucible, filled with argon and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 5 minutes, take it out after cooling, and obtain 600ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave in a 500ml beaker, add 200ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 8000r/min, the time was 60min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 7.8% by weight, the ID/I _G is 0.5, the I _2D /I _G is 0.5, and the average size of the two _- dimensional plane of the graphene is 2 μm-5 μm.

Example 10

This example is used to illustrate the preparation of high-quality graphene assisted by liquid nitrogen.

1g of flake graphite (purchased from Sigma-Aldrich company, 50 mesh, purity 99% by weight, the same below) was added to 50ml of concentrated nitric acid and concentrated sulfuric acid mixed acid (the volume ratio of concentrated nitric acid and concentrated sulfuric acid was 3:2, and the concentrated nitric acid Purchased from Beijing Chemical Plant, the mass concentration is 98%, concentrated sulfuric acid was purchased from Beijing Chemical Plant, the mass concentration was 98%), stirred at room temperature for 2 days, and filtered.

The filtered graphite was placed in a corundum crucible, filled with nitrogen and sealed. Put the crucible in a microwave oven (Galanz domestic microwave oven, 700W power), microwave for 3 minutes, take it out after cooling, and obtain 480ml fluffy worm-like graphite.

Put the worm-like graphite obtained by microwave into a 1000ml beaker, add 800ml of liquid nitrogen, and then use a high-speed mechanical stirrer to stir (the instrument was purchased from IKA, T 18 digital ULTRA-TURRAX, S 18N-19G dispersing cutter head). The rotation speed was set at 18000r/min, the time was 40min, and liquid nitrogen was continuously replenished during the stirring period. After the stirring is completed, the graphene powder can be obtained after the liquid nitrogen volatilizes completely.

It is determined that the oxygen content of the graphene prepared by the method is 7.7% by weight, ID/ _IG is _0.4 , I _2D / _IG is 0.5, and the average size of the two-dimensional plane of graphene is 2 μm-5 μm.

Comparative example 1

Except that the liquid nitrogen was replaced by deionized water, and the steps of filtering and drying were carried out after the stirring was completed, other preparation methods and conditions were the same as in Example 10.

It is determined that the oxygen content of the graphene prepared by the method is 8.0% by weight, the ID/ _IG is 1.0, the I _2D / _IG is _0.2 , and the average size of the two-dimensional plane of the graphene is 100nm-600nm.

Comparative example 2

Except that liquid nitrogen was replaced by ethanol, and the steps of filtering, washing and drying were carried out after the stirring was completed, other preparation methods and conditions were the same as in Example 10.

It is determined that the oxygen content of the graphene prepared by the method is 7.8% by weight, the ID/ _IG is 1.2, the I _2D / _IG is _0.1 , and the average size of the two-dimensional plane of the graphene is 50nm-200nm.

From Comparative Example 1 and Comparative Example 2, it can be seen that replacing liquid nitrogen with deionized water or ethanol cannot obtain large two-dimensional sheets of graphene, and the I _D / I _G value is significantly increased, and the I _2D / The _IG value obviously drops, indicating that the peeling effect becomes worse, and the content of few-layer graphene is obviously lower than the content of few-layer graphene in the graphene of the present invention. Moreover, the scheme of using water or ethanol can only obtain graphene powder after post-processing steps such as filtration and drying, which is more complicated than the method of the present invention and is not conducive to industrial production.

The applicant declares that the present invention illustrates the detailed methods of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed methods, that is, it does not mean that the present invention must rely on the above-mentioned detailed methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. a method for preparing graphene assisted by liquid nitrogen, is characterized in that, described method comprises the following steps: The worm-like graphite is placed in liquid nitrogen, stirred, and the liquid nitrogen is volatilized after the stirring is completed to obtain graphene powder. 2. The method according to claim 1, characterized in that, relative to every 1g of worm-like graphite, the amount of said liquid nitrogen is 100ml-800ml; Preferably, the amount of liquid nitrogen is 400ml for every 1g of worm-like graphite; Preferably, the stirring speed is 2000r/min-25000r/min, preferably 8000r/min-20000r/min, more preferably 20000r/min; Preferably, the stirring time is 5min-60min; Preferably, liquid nitrogen is continuously added during the stirring process, so that the total amount of liquid nitrogen is 100ml-800ml for every 1g of worm-like graphite; Preferably, the amount of liquid nitrogen added is equal to the amount of liquid nitrogen volatilized during the stirring process; Preferably, the equipment used for the stirring is a high-speed mechanical stirrer; Preferably, during the stirring process using a high-speed mechanical stirrer, the diameter of the stirring cutter rotor is not less than 16mm, preferably 32mm; Preferably, during the stirring process using a high-speed mechanical stirrer, the gap between the stator and the rotor of the stirring tool is not greater than 1mm, preferably 0.5mm. 3. The method according to claim 1 or 2, wherein the worm-like graphite is prepared by the following method: first intercalate the graphite raw material, and then heat the intercalated graphite raw material to expand to obtain worm-like graphite. Shaped graphite; Preferably, the volume of the vermicular graphite converted from every 1g of graphite raw material is 300ml-600ml. 4. The method according to claim 3, wherein the graphite raw material comprises flake graphite, graphite powder, expanded graphite, fullerenes, carbon nanotubes, carbon nanobelts, carbon black, mesoporous carbon or activated carbon. Any one or a combination of at least two of Preferably, the intercalation agent used in the intercalation is any one of acid, alkali metal, alkaline earth metal or salt, preferably acid; Preferably, the heating method is any one or a combination of at least two of furnace heating or microwave heating, preferably microwave heating. 5. according to the described method of claim 3 or 4, it is characterized in that, described vermicular graphite is prepared by following method: (1) use acid to carry out intercalation to graphite raw material, obtain the graphite raw material of intercalation; (2) Under the protection of an inert gas, the intercalated graphite raw material is irradiated with microwaves to obtain worm-like graphite. 6. method according to claim 5, is characterized in that, the process of the graphite raw material of step (1) preparation intercalation is: graphite raw material is placed in acid solution, stirs, and solid-liquid separation obtains the graphite raw material of intercalation ; Preferably, the acid solution is any one or at least two of perchloric acid with a mass fraction of 30%-72%, sulfuric acid with a mass fraction of 50%-98%, and nitric acid with a mass fraction of 50%-98%. The mixture of two kinds, preferably any one of 72% perchloric acid, 98% sulfuric acid or 98% nitric acid or a mixture of at least two, more preferably 72% perchloric acid, or 98% sulfuric acid and 98% nitric acid mixture; Preferably, the stirring time is 1min-36h; Preferably, the acid solution is perchloric acid with a mass fraction of 72%, and relative to 1g of graphite raw material, the amount of the acid solution is 100ml, and the stirring time is 3min; Preferably, the acid solution is sulfuric acid with a mass fraction of 98% and/or nitric acid with a mass fraction of 98%, and relative to 1g of graphite raw material, the amount of the acid solution is 25ml-60ml, and the stirring time is 12h-36h. 7. The method according to claim 5 or 6, wherein the inert gas in step (2) is any one or at least two of nitrogen, argon, helium, neon, krypton or xenon A combination of, preferably any one of nitrogen or argon; Preferably, the power of the microwave radiation in step (2) is 100W-1200W, preferably 700W-1000W; Preferably, the microwave irradiation time in step (2) is 10s-300s, preferably 90s-300s. 8. The method according to any one of claims 1-7, characterized in that the method comprises the following steps: (1) The graphite raw material is placed in perchloric acid with a mass fraction of 72%, and the graphite raw material is completely immersed in the perchloric acid with a mass fraction of 72%, stirred for 1min-5min, solid-liquid separation, to obtain perchloric acid Graphite raw material for acid intercalation; (2) under the protection of nitrogen, carry out the microwave radiation of 180s-300s to the graphite material of perchloric acid intercalation, obtain worm-shaped graphite; (3) According to the dosage standard of 1g worm-like graphite/(400ml-600ml) liquid nitrogen, put the worm-like graphite in liquid nitrogen, use a high-speed mechanical stirrer to stir for 5min-60min, and add and volatilize continuously during the stirring process The same amount of liquid nitrogen as liquid nitrogen is left to stand after stirring to allow the liquid nitrogen to volatilize naturally to obtain graphene powder. 9. The method according to any one of claims 1-7, characterized in that the method comprises the following steps: (1) the graphite raw material is placed in the nitric acid of 98% and/or the sulfuric acid of 98% by mass fraction, the nitric acid of 98% and/or the mass fraction of graphite raw material is completely immersed in said mass fraction is 98% In the sulfuric acid, stir 12h-36h, solid-liquid separation, obtain the graphite raw material of intercalation; (2) Under the protection of argon gas, microwave radiation of 180s-300s is carried out to the graphite raw material of intercalation, obtains worm-like graphite; (3) According to the dosage standard of 1g worm-like graphite/(400ml-600ml) liquid nitrogen, put the worm-like graphite in liquid nitrogen, use a high-speed mechanical stirrer to stir for 5min-60min, and add and volatilize continuously during the stirring process The same amount of liquid nitrogen as liquid nitrogen is left to stand after stirring to allow the liquid nitrogen to volatilize naturally to obtain graphene powder. 10. The graphene prepared by the method according to any one of claims 1-9, wherein the average size of the two-dimensional plane of the graphene is at 2 μm-5 μm; Preferably, the oxygen content of the graphene is below 8%, preferably below 5%; Preferably, in the Raman spectrum of the graphene, the peak intensity ratio of the D peak to the G peak is below 0.8, preferably below 0.5, more preferably 0.2; Preferably, in the Raman spectrum of the graphene, the peak intensity ratio of the 2D peak to the G peak is above 0.2, preferably above 0.5, more preferably 0.8; Preferably, in the graphene, the mass content of the few-layer graphene with the number of layers less than 5 is 10%-15%.