CN110615430A - Novel preparation method of primary few-layer graphene - Google Patents
Novel preparation method of primary few-layer graphene Download PDFInfo
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- CN110615430A CN110615430A CN201910990511.5A CN201910990511A CN110615430A CN 110615430 A CN110615430 A CN 110615430A CN 201910990511 A CN201910990511 A CN 201910990511A CN 110615430 A CN110615430 A CN 110615430A
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- C01B32/00—Carbon; Compounds thereof
- C01B32/15—Nano-sized carbon materials
- C01B32/182—Graphene
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- C01B32/19—Preparation by exfoliation
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- C01B32/00—Carbon; Compounds thereof
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- C01B32/182—Graphene
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Abstract
The invention discloses an optimized process for recycling semi-finished graphene waste materials obtained by preparing graphene through a re-stripping liquid-phase ultrasonic stripping method. The method comprises the following specific steps: carrying out ultrasonic treatment on a graphite raw material by a common liquid phase stripping method, and centrifuging to retain a lower-layer precipitate; adding a specified single-component solution, stripping the semi-finished graphene with the aid of multiple micro-interfaces, recovering the interface by recovering the graphene film on the interface, and repeating the process until the semi-finished graphene is completely recovered; after the steps are carried out, optionally, the obtained re-stripped graphene is subjected to means such as freeze drying and the like to remove solution components, so that a pure graphene product is obtained. The method fills the vacancy that the waste cannot be treated in the traditional ultrasonic stripping method, and effectively improves the unit yield, low pollution rate, low cost, high product purity, low hole defect rate and low impurity content of the graphene prepared by the ultrasonic stripping method.
Description
Technical Field
The invention relates to the field of manufacturing of two-dimensional materials, in particular to an optimization technology for preparing graphene by using a surface energy dominant ultrasonic stripping method. The method fills the vacancy that the waste cannot be treated in the traditional ultrasonic stripping method. The graphene product prepared by the method has superior quality and high purity, and is beneficial to industrial application of graphene production by an ultrasonic stripping method.
Background
As a powerful two-dimensional material, graphene has become a popular new favorite in domestic and foreign markets in recent years, but the industrial production of graphene also faces a lot of difficulties, currently, the most common process for industrially preparing graphene is a graphene oxide reduction method, the reduced graphene (rGO) produced by the process has high yield and simple operation, but the defect rate of the rGO is high and unavoidable, the performances of the graphene in the aspects of heat transfer, electricity transmission and the like are seriously influenced, the cost for producing 1g of rGO is not lower than ￥ 40, most products with ￥ 3 yuan or less on the market are false products mixed with a large amount of graphite impurities, the pollution discharge requirement is high, nearly 200g of industrial wastewater needs to be discharged when producing 1g of rGO, and the method is contrary to the industrial development policy of energy conservation, emission reduction and green sustainability in China.
The liquid-phase ultrasonic stripping process is another common graphene production method, and is mostly used for scientific preparation or small-scale production. The process has the characteristics of low production threshold, complete product crystal structure and high product purity, but the high cost caused by low production efficiency even exceeds that of a graphene oxide reduction method, and is a main source for limiting the industrial application of the liquid-phase ultrasonic stripping process. The traditional ultrasonic stripping process has basically the same mode, namely, graphite raw materials are dispersed in a liquid phase, and after ultrasonic treatment is carried out on graphite dispersion liquid in an ultrasonic environment, the centrifuged upper-layer dispersion liquid is a graphene finished product. Under the process mode, the concentration of graphene in the centrifuged upper-layer dispersion liquid reaches 1-2g/mL, namely the upper-layer dispersion liquid is called high-concentration graphene, and the total mass of finished products is not more than 30% of the total mass of raw materials when the graphene is prepared in one pot. We prove that the rest 70-80% of the precipitated solid slag contains a large amount of finished graphene which is already formed but not completely peeled off, and the waste of the part of the finished graphene causes a great proportion of material loss.
In addition, the quality of graphene products on the market is also anxious. Research personnel of national university of singapore have analyzed products of more than 60 graphene production brands all over the world, and the results show that the products of which the content of graphene exceeds 40% and does not exceed 5% are slammed into 'pseudo-graphene' by professionals. Although the properties of all graphene products on the market cannot be represented, the requirement of a novel industrial production means is urgently needed in the current industry, and the requirements of unit cost and graphene quality are met.
Disclosure of Invention
The invention aims to solve the problems and requirements, recover a centrifugal precipitation product after ultrasonic graphite stripping by taking the surface energy of an interface as a main factor, and provide a re-stripping process of semi-finished graphene by combining a micro-interface continuous generation device with simple hardware and various modes.
In the past, the main role of the surface energy of a solvent in a liquid phase stripping process is to provide a solubility parameter principle, namely, an organic solvent with the surface energy similar to that of graphite can provide good solubility parameters for graphite, so that the dispersibility of the graphite in a liquid phase is improved, and the organic solvent is used as a medium to treat a liquid phase graphite dispersion liquid under an ultrasonic environment. Later, the principle is further developed into a selection principle of a graphene dispersant, and researchers also propose a stable film forming phenomenon of graphene on an interface assisted by surface energy, but the principle is not expanded to the direct production aspect of graphene. In fact, the proposition of the principle of solubility parameters, YennyHernandez, has long demonstrated that the surface energy of graphite, i.e., the energy required to overcome van der Waals forces when a unit area of graphite is peeled back to form a thinner new surface, is highly synergistic with the appropriate surface energy for this process. This is a very simple spontaneous process.
Based on the above, the process for stripping the semi-finished graphene from the surface of the interface provided by the invention is sensitive to the surface energy and stable in various interface properties. In a laboratory, the method comprises the following specific steps:
1) ultrasonic treatment of graphite feedstock
And (3) taking a graphite raw material to disperse in a specified dispersing agent system, and placing in an ultrasonic environment for several hours to obtain the graphite-graphene mixed dispersion liquid.
2) Centrifugal separation of ultrasonic exfoliation products
And (3) subpackaging the graphite-graphene mixed dispersion liquid into centrifugal tubes, and performing high-speed centrifugation by using a centrifuge to obtain black upper-layer dispersion liquid and black lower-layer precipitated solid. The upper layer dispersion liquid is a finished product of the prepared perfect graphene, and the lower layer precipitated solid is a semi-finished product of the graphene which is not completely peeled off. When the sonication time is insufficient, the precipitated solid may contain a portion of graphite impurities.
3) Re-peeling of semi-finished graphene
Transferring the finished graphene dispersion liquid to other vessels for storage, collecting the semi-finished graphene in each centrifugal tube into a reaction vessel by using a stable single/double-component solution with appropriate surface energy property, and injecting a certain amount of stable single/double-component solution with appropriate surface energy property as a stripping agent to generate a spontaneous re-stripping process of the semi-finished graphene. At the moment, the phase interface is continuously updated by continuous gas blowing, chemical gas production, manual liquid exchange and other modes, and the process can be effectively amplified.
4) Purification of re-exfoliated graphene
And (3) collecting the re-stripped graphene product on the surface phase interface, freezing at-20 ℃, and then carrying out vacuum freeze drying to remove the stripping agent component to obtain re-stripped graphene dry powder. And different graphene product forms can be obtained by film making, tabletting and other modes according to requirements.
In the step 1), the use amount of the graphite raw material can be flexibly changed according to production requirements, and the requirement of the graphite is met according to the solubility parameter principle.
In the step 1), the type of the dispersant can be flexibly changed according to production requirements.
In the step 2), the centrifugal separation conditions can be flexibly changed according to production requirements.
In the step 3), the type of the stripping agent can be flexibly changed according to production requirements, the requirement is met according to the principle of solubility parameter of graphene, and particularly, when a physical gas generation is adopted to obtain a phase interface, a stable single-component solution with appropriate surface energy is adopted; when chemical gas production is adopted to obtain a phase interface, a stable two-component solution system with appropriate surface energy is adopted; other methods are adopted to obtain the phase interface, and accordingly flexible change is carried out.
The method has the advantages that:
1. fills the vacancy that the centrifugal sediment waste cannot be treated in the traditional ultrasonic stripping method.
2. The unit yield of graphene prepared by the ultrasonic stripping method is effectively improved, the pollution rate is low, and the cost is low.
3. The prepared graphene product contains about 80% of few-layer graphene and about 20% of single-layer and double-layer graphene, and has high product purity, complete crystal structure and low impurity content.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of the product of example 1.
FIG. 2 is a Transmission Electron Microscope (TEM) image of the product of example 1.
FIG. 3 is a graph of the Raman spectrum (Raman) results of the product of example 1
Detailed Description
The concept, technical effect test and the like of the present invention will be clearly described below in conjunction with the embodiments and the accompanying drawings to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
The implementation process of the invention comprises the following steps:
1) ultrasonic treatment of graphite feedstock
And (3) taking a graphite raw material to disperse in a specified dispersing agent system, and placing in an ultrasonic environment for several hours to obtain the graphite-graphene mixed dispersion liquid.
2) Centrifugal separation of ultrasonic exfoliation products
And (3) subpackaging the graphite-graphene mixed dispersion liquid into centrifugal tubes, and performing high-speed centrifugation by using a centrifuge to obtain black upper-layer dispersion liquid and black lower-layer precipitated solid. The upper layer dispersion liquid is a finished product of the prepared perfect graphene, and the lower layer precipitated solid is a semi-finished product of the graphene which is not completely peeled off. When the sonication time is insufficient, the precipitated solid may contain a portion of graphite impurities.
3) Re-peeling of semi-finished graphene
Transferring the finished graphene dispersion liquid to other vessels for storage, collecting the semi-finished graphene in each centrifugal tube into a reaction vessel by using a stable single/double-component solution with appropriate surface energy property, and injecting a certain amount of stable single/double-component solution with appropriate surface energy property as a stripping agent to generate a spontaneous re-stripping process of the semi-finished graphene. At the moment, the phase interface is continuously updated by continuous gas blowing, chemical gas production, manual liquid exchange and other modes, and the process can be effectively amplified.
4) Purification of re-exfoliated graphene
And (3) collecting the re-stripped graphene product on the surface phase interface, freezing at-20 ℃, and then carrying out vacuum freeze drying to remove the stripping agent component to obtain re-stripped graphene dry powder. And different graphene product forms can be obtained by film making, tabletting and other modes according to requirements.
The following specific examples are further illustrative of the methods and techniques provided herein and are not to be construed as limiting the present application.
Example 1: implementation of physical gas production phase interface obtaining method of the invention
Dispersing 250g of graphite powder in a TBA/DMF binary organic system for ultrasonic treatment for 4 hours, centrifugally separating to reserve the components of the lower-layer precipitate, flushing a small amount of deionized water into a 1000mL glass beaker, adding a proper amount of deionized water to ensure that the total volume reaches 400 plus one of 600mL, sinking the nanometer air disc/air bubble stone connected with the air guide tube into the bottom of the beaker, connecting an air flow pump, and blowing air to continuously generate a micro-gas-liquid interface. And then stripping graphene, stopping air blowing when the surface gas-liquid interface is enriched to saturation, standing until the middle layer liquid is clarified, collecting the stripped graphene, recovering the surface gas-liquid interface state, and repeating the air blowing process until the semi-finished graphene is stripped. The collected re-exfoliated graphene is frozen at the temperature of minus 20 ℃, about 200g of graphene dry powder can be obtained after vacuum freeze drying, and SEM, TEM and Raman spectrum characterization is carried out on the graphene dry powder to determine the morphology and purity information of the graphene dry powder. Test results show that the graphene produced by the strategy has good independence, thin lamella and high stripping completion degree (figure 1); the electron diffraction pattern corresponding to single-layer or double-layer graphene can be detected (figure 2); when confocal Raman is adopted for surface scanning (20 scanning points), the spectral curves of 16 detection points show typical characteristic Raman signals of 3-5 layers of few-layer graphene, the spectral curves of 4 detection points show typical characteristic Raman signals of 1-2 layers of graphene, and no other impurity signals are detected.
Example 2: implementation of chemical gas production phase interface to prepare primary few-layer graphene
Dispersing 0.4g of graphite powder in a TBA/DMF binary organic system, carrying out ultrasonic treatment for 4 hours, carrying out centrifugal separation to retain the components of the lower-layer precipitate, quickly washing the lower-layer precipitate into a 10mL glass beaker by using a small amount of hydrogen peroxide, immediately adding a proper amount of hydrogen peroxide water to enable the total volume to reach 4-5mL, and standing for the end of the reaction. And after gas production is finished, collecting and stripping graphene, freezing at the temperature of minus 20 ℃, and carrying out vacuum freeze drying to obtain graphene dry powder.
Example 3: preparation of native few-layer graphene by implementing method on liquid-liquid interface
Dispersing 0.4g of graphite powder in a TBA/DMF (tert-butyl-N-dimethylformamide) binary organic system for ultrasonic treatment for 4 hours, centrifugally separating to keep the components of a lower-layer precipitate, flushing a small amount of deionized water into a 10mL glass beaker, adding 1-2mL of silicone oil to seal the gas-phase contact surface of a semi-finished product graphene, carefully adding 4-5mL of deionized water along the wall, obtaining a soft and fine graphene membrane layer at a water-oil interface after a liquid phase is stabilized, and obtaining the graphene membrane layer after pumping out the silicone oil by using a needle cylinder. The above process is repeated thereafter until the graphene film layer between the water-oil interfaces is no longer produced. And collecting and stripping graphene, freezing at-20 ℃, and carrying out vacuum freeze drying to obtain graphene dry powder.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core ideas. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (5)
1. A novel preparation method of primary few-layer graphene is characterized by comprising the following specific steps:
(1) ultrasonic treatment of graphite raw materials: taking a graphite raw material to disperse in a specified dispersant system, and placing the graphite raw material in an ultrasonic environment for several hours to obtain a graphite-graphene mixed dispersion liquid;
(2) centrifugal separation of ultrasonic stripping product: subpackaging the graphite-graphene mixed dispersion liquid into centrifugal tubes, and performing high-speed centrifugation by using a centrifuge to obtain black upper-layer dispersion liquid and black lower-layer precipitated solid; the upper layer dispersion liquid is a finished product of the prepared perfect graphene, and the lower layer precipitated solid is a semi-finished product of the graphene which is not completely peeled off; when the ultrasonic treatment time is insufficient, a part of graphite impurities may be contained in the precipitated solid;
(3) re-stripping the semi-finished graphene: transferring the finished graphene dispersion liquid to other vessels for storage, collecting the semi-finished graphene in each centrifugal tube into a reaction vessel by using a stable single/double-component solution with appropriate surface energy property, and injecting a certain amount of stable single/double-component solution with appropriate surface energy property as a stripping agent to generate a spontaneous re-stripping process of the semi-finished graphene; at the moment, the phase interface is continuously updated by continuous gas blowing, chemical gas production, manual liquid exchange and other modes, so that the process can be effectively amplified;
(4) and stripping and purifying the graphene: collecting the re-stripped graphene product on the surface phase interface, freezing at-20 ℃, and removing the stripping agent component by vacuum freeze drying to obtain re-stripped graphene dry powder; and different graphene product forms can be obtained by film making, tabletting and other modes according to requirements.
2. The novel preparation method of primary few-layer graphene according to claim 1, wherein in the step (1), the amount of graphite raw material used can be flexibly changed according to production requirements, and the requirement is satisfied with the principle of solubility parameter of graphite.
3. The novel method for preparing native few-layer graphene according to claim 1, wherein in step (1), the type of dispersant can be flexibly changed according to production requirements.
4. The novel method for preparing native graphene with few layers according to claim 1, wherein in the step (2), the conditions of centrifugal separation can be flexibly changed according to production requirements.
5. The novel preparation method of primary few-layer graphene according to claim 1, wherein in the step (3), the type of the stripping agent can be flexibly changed according to production requirements, and the requirement of satisfying the solubility parameter principle of graphene is met, and particularly, when a physical gas generation is adopted to obtain a phase interface, a stable single-component solution with appropriate surface energy is adopted; when chemical gas production is adopted to obtain a phase interface, a stable two-component solution system with appropriate surface energy is adopted; other methods are adopted to obtain the phase interface, and accordingly flexible change is carried out.
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