CN113387347B

CN113387347B - Preparation method of powder graphene with adjustable size

Info

Publication number: CN113387347B
Application number: CN202010167294.2A
Authority: CN
Inventors: 张锦; 孙阳勇
Original assignee: Peking University; Beijing Graphene Institute BGI
Current assignee: Peking University; Beijing Graphene Institute BGI
Priority date: 2020-03-11
Filing date: 2020-03-11
Publication date: 2022-07-19
Anticipated expiration: 2040-03-11
Also published as: CN113387347A

Abstract

The invention discloses a preparation method of powder graphene, which regulates and controls the size of gas-phase graphene by controlling nucleation density and/or time of reaction atmosphere flowing through a reaction zone in the growth process. The method is simple and effective, realizes the size regulation of the graphene in the gas phase for the first time, and can control the appropriate increase or decrease of the size of the graphene. And the graphene quantum dots can be directly obtained in a gas phase, and compared with the traditional method, the method is simple and efficient, and the graphene is pure and has high crystallinity.

Description

Preparation method of powder graphene with adjustable size

Technical Field

The invention relates to the technical field of graphene preparation, in particular to a preparation method of powder graphene with adjustable size.

Background

In 2004, professor geodesi and doctor Novoselov prepared single-layer graphene by tape stripping (k.s. Novoselov, et al. science 2004,306,666), and both consequently obtained the 2010 nobel prize of physics, since this triggered a tremendous research hot tide. The graphene has excellent properties, has a very large specific surface area, a very high Young modulus and electron mobility, a highest thermal conductivity and the like, and has a very great application prospect in the fields of sensors, catalysis, energy sources and the like. The preparation of the graphene mainly comprises two methods of growth from bottom to top and stripping from top to bottom. The bottom-up growth method represented by the chemical vapor deposition method can realize roll-to-roll growth of the graphene film, and can obtain the graphene film (b.h.hong, et al.nat. nanotech.2010,5,574) of nearly 30 inches, but the application of expensive metal catalysts and high energy-consuming systems inevitably limits the quantitative preparation of the graphene film. A top-down peeling method represented by Hummers method (w.s.hummers, et al.j.am.chem.soc.1958,80,1339) can be implemented to prepare hundreds of tons of graphene powder at the present stage, but has the problems of poor graphene quality, high oxygen content, complex post-treatment, serious pollution and the like. We developed a vapor phase growth method of graphene, which does not require a catalyst and a substrate and can realize continuous preparation of graphene (chinese patent application No. 201910875607.7). However, in the process of preparing graphene in a gas phase, the size of graphene cannot be controlled, and how to adjust the size of graphene is still a great challenge.

In addition, for obtaining graphene quantum dots, most of the reactions in solution phase (y.b. yan, et al. adv.mater.2019,1808283) include etching of graphene oxide or crystalline flake graphene with strong acid and strong oxidant, or synthesis reaction of small molecules under hydrothermal conditions and the like. The reactions are complicated and time-consuming, the pollution is serious, complicated post-treatment is needed for purification, and the obtained graphene quantum dot surface has a pollution problem. Therefore, how to directly synthesize the graphene quantum dots in a gas phase is extremely important.

Disclosure of Invention

In order to overcome the defects, the invention aims to provide a preparation method of powder graphene.

The invention provides a preparation method of powder graphene, which comprises the following steps: s1, introducing inert gas into the microwave plasma chemical vapor deposition system to generate plasma; and S2, introducing carbon source-nucleation density inhibitor mixed gas into the microwave plasma chemical vapor deposition system to perform vapor phase growth of graphene powder, and directly collecting graphene powder in tail gas.

In some embodiments, the nucleation density inhibitor is selected from one or more of oxygen, water vapor, carbon dioxide, and air.

In some embodiments, when the nucleation density inhibitor is one or more of oxygen, carbon dioxide and air, the amount of species of elemental carbon derived from the carbon source is: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 2; when the nucleation density inhibitor is water vapor, the amount of the substance of carbon element derived from the carbon source: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 1.

in some embodiments, in the step S2, the overall gas flow is controlled to be between 0.01S and 10S.

In some embodiments, it is preferred that the bulk gas stream is passed through the reaction zone for a time in the range of from 0.01s to 0.05 s.

The invention also provides a preparation method of the powder graphene, which comprises the following steps: s1, introducing inert gas into the microwave plasma chemical vapor deposition system to generate plasma; and S2, introducing carbon source gas into the microwave plasma chemical vapor deposition system, controlling the time of the whole gas flow flowing through the reaction interval to be 0.01-0.15S, carrying out vapor phase growth of the graphene powder, and directly collecting the graphene powder in the tail gas.

In some embodiments, in the step S2, the overall gas flow is controlled to pass through the reaction zone for a time period of 0.01S to 0.05S.

In some embodiments, the inert gas is selected from one or more of argon, krypton, and xenon.

In some embodiments, the carbon source is selected from one or more of hydrocarbons, alcohols, ethers, ketones, and phenols.

The method adopts a nucleation density control method, a residence time control method or a combination method of the two to realize the adjustment of the size of the powder graphene in the gas phase, and can directly obtain the graphene quantum dots in the gas phase by controlling proper conditions. The method can realize the size adjustment of the powder graphene, can directly obtain the graphene quantum dots in the gas phase, and has great application prospect.

Drawings

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

Fig. 1A is a TEM image of powder graphene obtained in example 1 of the present invention.

Fig. 1B is a size statistical chart of the graphene powder prepared in example 1 of the present invention.

Fig. 2A is a TEM image of powder graphene obtained in example 2 of the present invention.

Fig. 2B is a size statistical chart of the powder graphene prepared in example 2 of the present invention.

Fig. 3A is a TEM image of powder graphene obtained in example 3 of the present invention.

Fig. 3B is a size statistical chart of the powder graphene prepared in example 3 of the present invention.

Fig. 4A is a TEM image of powder graphene obtained in example 4 of the present invention.

Fig. 4B is a size statistical chart of the powder graphene prepared in example 4 of the present invention.

Fig. 5A is a graph of light emission of the powder graphene dispersion liquid prepared in example 5 of the present invention at 365 nm.

Fig. 5B is a fluorescence test curve of the powder graphene dispersion prepared in example 5 of the present invention.

Detailed Description

The technical solution of the present invention is further explained below according to specific embodiments. The scope of protection of the invention is not limited to the following examples, which are set forth for illustrative purposes only and are not intended to limit the invention in any way.

The method adopts a nucleation density control method, a residence time control method or a combination method of the two to realize the adjustment of the size of the powder graphene, and can directly obtain the graphene quantum dots in a gas phase by controlling proper conditions. To achieve the above objects, the present invention is implemented using a microwave plasma chemical vapor deposition system.

Specifically, the nucleation density control method includes the steps of: s1, introducing inert gas into the microwave plasma chemical vapor deposition system to generate plasma; and S2, introducing carbon source-nucleation density inhibitor mixed gas into the microwave plasma chemical vapor deposition system to perform vapor phase growth of the graphene powder, and directly collecting the graphene powder in the tail gas.

The method for regulating and controlling the size of the gas-phase graphene by adopting a nucleation density control method is characterized in that a nucleation density inhibitor is introduced in the growth process of the graphene to control the nucleation density of the graphene, so that the size is regulated. Through research, the size of the graphene is favorably increased by properly reducing the nucleation density of the graphene, but the addition of excessive nucleation density inhibitor is unfavorable for the size increase of the graphene, and the yield of the graphene is rapidly reduced, so that the concentration of the nucleation density inhibitor needs to be controlled to be proper. When the nucleation density inhibitor is one or more of oxygen, carbon dioxide and air, the amount of the substance of carbon element derived from the carbon source: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 2; amount of substance of carbon element derived from carbon source when the nucleation density inhibitor is water vapor: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 1. if the amount of the substance of carbon element derived from the carbon source: when the ratio of the amount of the oxygen element substances derived from the nucleation density inhibitor is smaller than the corresponding numerical value, the graphene is etched cleanly by oxygen, and the graphene cannot be obtained; within the range, the nucleation density of the graphene is inversely proportional to the increase of the size of the graphene in the growth process, so that the ratio of the carbon source to the nuclear density inhibitor can be controlled to control the nucleation density of the graphene, and further the size of the graphene can be regulated and controlled.

When the size of the gas-phase graphene is regulated and controlled by adopting a residence time control method, the method specifically comprises the following steps: s1, introducing inert gas into the microwave plasma chemical vapor deposition system to generate plasma; and S2, introducing carbon source gas into the microwave plasma chemical vapor deposition system, controlling the time of the whole gas flow flowing through the reaction interval to be 0.01-0.15S, carrying out vapor growth of the graphene powder, and directly collecting the graphene powder in tail gas. According to the method, the time of the whole gas flow flowing through the reaction zone is controlled within a preset range, so that the nucleation sites are more quickly moved out of the reaction system to reduce the size of graphene, the size of the graphene is in direct proportion to the residence time within the preset time range, and therefore the size of the graphene can be regulated and controlled by controlling the flowing time within the time range. In particular, when the residence time is changed to reduce the time for the reaction atmosphere to flow through the reaction space to 0.05s or less, the size of graphene is further reduced, and graphene quantum dots can be obtained. When the residence time exceeds 0.15s, the nucleation density of the graphene is high, and the size change of the graphene controlled by the residence time is not obvious. Controlling the time that the bulk gas stream flows through the reaction zone can be accomplished by controlling the flow rate of the inert gas. The time during which the reaction atmosphere flows through the reaction space is reduced, for example by suitably increasing the flow of inert gas.

The size of the graphene can be adjusted by combining a nuclear density control method and a residence time control method. That is, a predetermined ratio of the carbon source-nucleation density inhibitor mixed gas is introduced at S2 and the time for which the entire gas flow passes through the reaction zone is controlled within a predetermined range. At this time, when the effect of size increase by nucleation density control is superior to the effect of size reduction by residence time control, the graphene size appears to increase, and conversely, decreases. According to the principle, a person skilled in the art can obtain the relationship between the specific residence time and the size of the prepared graphene through limited tests according to the type and the proportion of the selected nucleation inhibitor and the carbon source, so as to achieve the purpose of regulating and controlling the size of the gas-phase graphene. In general, residence times of between 0.01s and 10s are preferred. Furthermore, when the residence time is changed to reduce the time for the reaction atmosphere to flow through the reaction zone to 0.05s or less and the carbon source concentration is small, the size of the graphene can be further reduced, and the graphene quantum dots can be obtained.

The inert gas and carbon source gas for the purposes of the present invention may be any gas suitable for graphene growth. For example, the inert gas may be selected from one or more of argon, krypton, and xenon; the carbon source may be selected from one or more of hydrocarbons, alcohols, ethers, ketones, and phenols.

The principle of three methods for controlling the size of the graphene in the growth process is described in detail, and according to the principle, a person skilled in the art can obtain the relationship between specific operation parameters and the size of the prepared graphene through limited tests, so that the purpose of regulating and controlling the size of the gas-phase graphene is achieved.

The inventive concept of the present invention is explained below with reference to specific embodiments. The experimental procedures used in the following examples are all conventional procedures unless otherwise specified. Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Example 1

The microwave power of the microwave plasma chemical vapor deposition system is adjusted to 500W, and the system is triggered to generate Ar plasma, so that the visible system generates a bright luminous heating phenomenon. The flow rate of the system Ar is controlled to be 1200sccm (sccm, standard condition milliliter per minute), the retention time is 0.8s at the moment, 5sccm of methane is introduced, and at the moment, more graphene drifts away from the system along with the airflow. The graphene was characterized by transmission (FIG. 1A) and was statistically sized to an average graphene size of 175nm (FIG. 1B).

Example 2

The microwave power of the microwave plasma chemical vapor deposition system is adjusted to 500W, and the system is triggered to generate Ar plasma, so that the visible system generates a bright luminous heating phenomenon. The flow rate of the system Ar is controlled to be 1200sccm (sccm, standard condition milliliter per minute), the retention time is 0.8s, 5sccm of methane and 1.45sccm of nucleation inhibitor (oxygen) are introduced, and at this time, more graphene drifts away from the system along with the gas flow. The graphene was characterized by transmission (fig. 2A) and subjected to size statistics to find the average size of the graphene to 240nm (fig. 2B).

Example 3

The microwave power of the microwave plasma chemical vapor deposition system is adjusted to 500W, and the system is triggered to generate Ar plasma, so that the visible system generates a bright luminous heating phenomenon. The flow rate of the system Ar is controlled to be 10SLM (SLM, standard condition liter per minute), the residence time is 0.09s, 5sccm of methane and 1.98sccm of nucleation inhibitor (oxygen) are introduced, and the obtained graphene is subjected to transmission characterization (figure 3A) and size statistics, so that the average size of the graphene is 50nm (figure 3B).

Example 4

The microwave power of the microwave plasma chemical vapor deposition system is adjusted to 300W, and the system is triggered to generate Ar plasma, so that the visible system generates a bright luminous heating phenomenon. Controlling the flow rate of Ar of the system to be 20SLM (SLM, standard condition liter per minute), keeping the residence time to be 0.05s, introducing 2sccm of methane, leading more graphene in the system to drift away from the system along with the airflow, and performing transmission characterization (figure 4A) and size statistics on the obtained graphene to find that the average size of the graphene is 12.1nm (figure 4B).

Example 5

The microwave power of the microwave plasma chemical vapor deposition system is adjusted to 500W, and the system is triggered to generate Ar plasma, so that the visible system generates a bright luminous heating phenomenon. Controlling the flow of the system Ar to be 20SLM (SLM, standard condition liter per minute), ensuring the retention time to be 0.02s, introducing 1sccm of methane, at the moment, more graphene drifts in the system along with the airflow, dispersing the obtained graphene in a dispersing agent, irradiating under a 365nm handheld ultraviolet lamp, and finding that the system has a fluorescence phenomenon (figure 5A), wherein the fluorescence test result shows that the system emits light near-500 nm (figure 5B), and the luminescent graphene quantum dots are obtained.

As can be seen from fig. 1B, 2B, 3B, 4B, and 5B, the nucleation density control method and the residence time control method of the present invention can realize the control of the size of the gas-phase graphene. Comparing example 1 and example 2, it can be seen that the size of graphene can be increased by adding a nucleation inhibitor. Comparing examples 1, 4 and 5, it can be seen that reducing the residence time of the whole gas flow in the reaction zone can reduce the size of graphene, and when the residence time is reduced to a certain time, vapor-phase growth of graphene quantum dots can be realized.

The method is simple and effective, realizes the size regulation of the graphene in the gas phase for the first time, and can control the appropriate increase or decrease of the size of the graphene. And the graphene quantum dots can be directly obtained in a gas phase, and compared with the traditional method, the method is simple and efficient, and the graphene is pure and has high crystallinity.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A preparation method of powder graphene is characterized by comprising the following steps:

s1, introducing inert gas into the microwave plasma chemical vapor deposition system to generate plasma; and

s2, introducing a carbon source-nucleation density inhibitor mixed gas into the microwave plasma chemical vapor deposition system to perform vapor phase growth of graphene powder, and directly collecting graphene powder in tail gas;

wherein the nucleation density inhibitor is selected from one or more of oxygen, water vapor, carbon dioxide and air.

2. The production method according to claim 1, wherein when the nucleation density inhibitor is one or more of oxygen, carbon dioxide and air, the amount of the substance of carbon element derived from the carbon source is: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 2; when the nucleation density inhibitor is water vapor, the amount of the substance of carbon element derived from the carbon source: the amount of species of elemental oxygen derived from the nucleation density inhibitor is greater than 1: 1.

3. the method according to claim 1, wherein in the step S2, the time of the whole gas flow passing through the reaction zone is controlled to be 0.01S-10S.

4. The method of claim 3, wherein the whole gas stream is passed through the reaction zone for a time of 0.01s to 0.05 s.

5. The method according to any one of claims 1 to 4, wherein the inert gas is one or more selected from argon, krypton and xenon.

6. The method according to any one of claims 1 to 4, wherein the carbon source is one or more selected from the group consisting of hydrocarbons, alcohols, ethers, ketones, and phenols.