CN109970047B - Method for preparing graphene quantum dots from carbon nanohorns - Google Patents

Abstract

The invention discloses a method for preparing graphene quantum dots from carbon nanohorns, and belongs to the technical field of carbon nanomaterial preparation. The method of the invention adopts the direct current arc method to prepare nitrogen-doped carbon nanohorns: graphite rods are used as the cathode and anode of the arc, and the cathode and anode are placed vertically. After the electric arc furnace is evacuated, the buffer gas is charged and the arc is started. , collecting the deposits on the inner wall of the reaction chamber is the nitrogen-doped carbon nanohorn; putting the nitrogen-doped carbon nanohorn into the tube furnace, calcining under the set atmosphere and temperature, and the collected product is the graphene quantum dot. It is determined by TEM that the calcined product is graphene quantum dots, and the size is 5-15 nm; the method of the invention adopts the DC arc method to prepare nitrogen-doped carbon nanohorns and convert them into graphene quantum dots, which has the advantages of safety, reliability, low cost, The operation process is simple, which opens up a new idea for the preparation of graphene quantum dots.

Description

A kind of method for preparing graphene quantum dots from carbon nanohorns

technical field

The invention discloses a method for preparing graphene quantum dots from carbon nanohorns, and belongs to the field of carbon nanomaterial preparation.

Background technique

In recent years, graphene has received increasing attention due to its unique properties, such as large specific surface area, high carrier mobility, excellent mechanical flexibility, good thermal/chemical stability, and environmentally friendly features, etc. Compared with two-dimensional graphene nanosheets (graphene nanosheets, GNSs) and one-dimensional graphene nanoribbons (graphenenanoribbons, GNRs), zero-dimensional graphene quantum dots (graphene quantum dots, GQDs) due to its size below 10nm performance stronger quantum confinement and boundary effects. At present, graphene quantum dots have (1) no highly toxic metal elements, and are environmentally friendly quantum dot materials; (2) stable structure, resistant to strong acid, strong alkali and photocorrosion; (3) adjustable band gap width; (4) The surface functionalization is easy to achieve (5) The thickness can be as thin as a single atom, chemical stability and other characteristics. Therefore, it has more attractive application prospects in many fields such as solar photovoltaic devices, biomedicine, light-emitting diodes and sensors.

Although GQDs have become the focus of attention of scientists in various fields in recent years, and their preparation is still in their infancy, the synthesis of carbon nanocrystals (including carbon nanotubes, graphene, nanocarbons, nanocarbon dots, collectively referred to as carbon dots) can be traced back to Longer ago. At present, there are two methods to prepare GQDs with controllable properties, namely top-down and white bottom-up methods. The top-down method refers to cutting large-sized graphene flakes into small-sized GQDs by physical or chemical methods, including hydrothermal method, electrochemical method, and chemical exfoliation of carbon fibers, etc.; the bottom-up method is It refers to the preparation of GQDs with small molecules as precursors through a series of chemical reactions, mainly solution chemistry, ultrasonic and microwave methods.

However, there is still a long way to go to prepare high-yield, high-quality GQDs. However, the above-mentioned preparation methods all have certain defects. For example, the top-down method has relatively simple steps and high yield, but cannot precisely control the morphology and size of GQDs. Most of the bottom-up methods are more controllable, but the steps are cumbersome to operate. Therefore, it is very important to propose a method for preparing graphene quantum dots with a simple process and large-scale preparation, which is very important to promote the further research of graphene quantum dots. The invention adopts a direct current arc method, and can efficiently prepare nitrogen-doped graphene in a nitrogen-containing atmosphere, which is the key to converting carbon nanohorns into graphene quantum dots by calcining at high temperature, so as to solve the problem of efficient and simple preparation. Technical difficulties of graphene quantum dots.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for preparing graphene quantum dots by carbon nanohorn, which can efficiently and simply prepare graphene quantum dots, and specifically comprises the following steps:

(1) Preparation of nitrogen-doped carbon nanohorns by DC arc method: graphite rods are used as the cathode and anode of the arc, and the cathode and anode are placed vertically. After the arc furnace is evacuated, the buffer gas is charged and the arc is started. After the reaction is completed, the collection The deposits on the inner wall of the reaction chamber are nitrogen-doped carbon nanohorns.

(2) Put the nitrogen-doped carbon nanohorns prepared in step (1) into a tube furnace, calcined under a set atmosphere and temperature, and the collected products are graphene quantum dots.

Preferably, the conditions for preparing nitrogen-doped carbon nanohorns in step (1) of the present invention are: the diameter of the electrode graphite rod is 10-30 mm, the distance between the two poles is 1-3 mm, and the arc discharge current is 100-250 A , the arc discharge time is 5 ~ 30min, and the pressure of the buffer gas is 40 ~ 80 KPa.

Preferably, the buffer gas in step (1) of the present invention is nitrogen.

Preferably, the calcination atmosphere in step (2) of the present invention is one of air and oxygen or a mixture of the two gases.

Preferably, in step (2) of the present invention, the calcination temperature is 600-800° C., and the calcination time is 30-240 min.

Beneficial effects of the present invention:

(1) The present invention adopts a DC arc method to prepare carbon nanohorns, and the prepared carbon nanohorns are calcined to prepare graphene quantum dots. The equipment is simple, the process is simple, the production cost is low, the production efficiency is high, and it is green and pollution-free.

(2) For the nitrogen-doped carbon nanohorns prepared by the present invention, the diameter of the carbon nanohorn monomers is 2-5 nm through transmission electron microscopy, and they aggregate into spherical aggregates with a diameter of 50-100 nm. The product is graphene quantum dots with a size of 5-15 nm.

(3) Compared with other methods for preparing graphene quantum dots, the method can be completed in one step, the conditions are controllable, the steps are simple, etc., and the prepared graphene quantum dots have high purity and uniform structure and size. The particle size distribution is uniform and has excellent fluorescence characteristics.

Description of drawings

1 is a transmission electron microscope image of nitrogen-doped carbon nanohorns in Example 1;

Fig. 2 is the X-ray photoelectron spectrogram of nitrogen-doped carbon nanohorn in Example 1;

Fig. 3 is the transmission electron microscope of graphene quantum dots in embodiment 1;

Fig. 4 is the transmission electron microscope of graphene quantum dots in embodiment 2;

Fig. 5 is the transmission electron microscope of graphene quantum dots in embodiment 3;

Fig. 6 is the transmission electron microscope of graphene quantum dots in embodiment 4;

7 is a transmission electron microscope of the graphene quantum dots in Example 5.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content.

Example 1

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) The prepared nitrogen-doped carbon nanohorns were placed in a tube furnace, calcined in an air atmosphere at a temperature of 600 °C for 240 min, and the products collected when cooled to room temperature were graphene quantum dots.

The transmission electron microscope image of the carbon nanohorns prepared in this example is shown in Figure 1, and it can be seen from the figure that 'dahlia'-shaped carbon nanohorns are prepared; the X-ray photoelectron spectrum is shown in Figure 2, from the figure It can be seen that the prepared carbon nanohorns are doped with nitrogen elements; the diameter of the individual particles is 2-5 nm and aggregates into spherical aggregates with a diameter of 30-100 nm.

The transmission electron microscope image of graphene quantum dots is shown in Figure 3. It can be seen from the figure that the obtained graphene quantum dots have a size of 5-15 nm, no impurities and have a good monodisperse structure. Graphene quantum dots have a strong fluorescence effect.

Example 2

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) The prepared nitrogen-doped carbon nanohorns were placed in a tube furnace, calcined in an air atmosphere at a temperature of 800 °C for 30 min, and the products collected when cooled to room temperature were graphene quantum dots.

The transmission electron microscope image of the graphene quantum dots prepared in this example is shown in FIG. 4 . It can be seen from the figure that the obtained graphene quantum dots have a size of 5-15 nm, no impurities and a good monodisperse structure. At the same time, the graphene quantum dots prepared by this method have a strong fluorescence effect.

Example 3

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) The prepared nitrogen-doped carbon nanohorns were placed in a tube furnace, calcined in an air atmosphere at a temperature of 700 °C for 90 min, and the products collected when cooled to room temperature were graphene quantum dots.

The transmission electron microscope image of the graphene quantum dots prepared in this example is shown in Figure 5. It can be seen from the figure that the obtained graphene quantum dots have a size of 5-15 nm, no impurities and a good monodisperse structure. At the same time, the graphene quantum dots prepared by this method have a strong fluorescence effect.

Example 4

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10mm, the distance between the two poles is 1mm, and the cathode and anode poles are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A. Charged with 70 KPa nitrogen and started the arc, after 5 min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) The prepared nitrogen-doped carbon nanohorns were placed in a tube furnace, calcined in an oxygen atmosphere at a temperature of 650 °C for 120 min, and the products collected when cooled to room temperature were graphene quantum dots.

The transmission electron microscope image of the graphene quantum dots prepared in this example is shown in Figure 6. It can be seen from the figure that the size of the graphene quantum dots obtained is 5-15 nm, free of impurities and has a good monodisperse structure.

Example 5

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, and calcine them in a mixed atmosphere of oxygen and air at a temperature of 700 °C for 120 min. After cooling to room temperature, the collected product is the graphene quantum point.

The transmission electron microscope image of the graphene quantum dots prepared in this example is shown in Figure 7. It can be seen from the figure that the size of the graphene quantum dots obtained is 5-15 nm, free of impurities and has a good monodisperse structure.

Example 6

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, calcined in a mixed atmosphere of oxygen and air at a temperature of 750 °C for 60 min, and the collected product after cooling to room temperature is the graphene quantum point.

The graphene quantum dots prepared in this example have a size of 5-15 nm, are free of impurities and have a good monodisperse structure.

Example 7

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, and calcinate them in a mixed atmosphere of oxygen and air at a temperature of 650 °C for 200 min. After cooling to room temperature, the collected product is the graphene quantum point.

The graphene quantum dots prepared in this example have a size of 5-15 nm, are free of impurities and have a good monodisperse structure.

Example 8

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, calcined in a mixed atmosphere of oxygen and air at a temperature of 800 °C for 100 min, and the product collected when cooled to room temperature is the graphene quantum point.

The graphene quantum dots prepared in this example have a size of 5-15 nm, are free of impurities and have a good monodisperse structure.

Example 9

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, calcined in a mixed atmosphere of oxygen and air at a temperature of 800 °C for 30 min, and the product collected when cooled to room temperature is the graphene quantum point.

The graphene quantum dots prepared in this example have a size of 5-15 nm, are free of impurities and have a good monodisperse structure.

Example 10

A method for preparing graphene quantum dots by carbon nanohorn, specifically comprising the following steps:

(1) The graphite rod is used as the anode and cathode of the arc. The diameter of the graphite rod is 10 mm, the distance between the two poles is 1 mm, and the anode and cathode are placed vertically. After the electric arc furnace is pumped to a vacuum of 3Pa, the DC arc discharge current is 200A , charged with 70KPa nitrogen and started the arc, after 5min of discharge, the sediments on the inner wall of the reaction chamber were collected as nitrogen-doped carbon nanohorns.

(2) Put the prepared nitrogen-doped carbon nanohorns into a tube furnace, calcined in an air atmosphere at a temperature of 700 °C for 60 min, and the products collected when cooled to room temperature are graphene quantum dots; The graphene quantum dots prepared in the examples have a size of 5-15 nm, are free of impurities and have a good monodisperse structure.

Claims (2)

1. A method for preparing graphene quantum dots from carbon nanohorns is characterized by specifically comprising the following steps of:

(1) preparing nitrogen-doped carbon nanohorns by a direct-current arc method: using graphite rods as the anode and the cathode of an electric arc, vertically placing the cathode and the anode, filling buffer gas and starting the electric arc after the electric arc furnace is vacuumized, and collecting sediment on the inner wall of a reaction cavity after the reaction is finished, namely the nitrogen-doped carbon nanohorn;

(2) putting the nitrogen-doped carbon nanohorn prepared in the step (1) into a tube furnace, calcining at a set atmosphere and temperature, and collecting a product, namely the graphene quantum dot; wherein the calcination temperature is 600-800 ℃, and the size of the graphene quantum dots is 5-15 nm;

the diameter of the electrode graphite rod is 10-30 mm, the distance between two electrodes is 1-3 mm, the arc discharge current is 100-250A, the arc discharge time is 5-30 min, and the pressure of buffer gas nitrogen is 40-80 kPa;

in the step (1), the buffer gas is nitrogen;

the calcining atmosphere is one of air and oxygen or the mixture of the two gases.

2. The method of preparing graphene quantum dots from carbon nanohorns as claimed in claim 1, wherein: the calcination time is 30-240 min.

Images