CN111498836A - Preparation method of nitrogen-doped reduced graphene oxide field emission cathode - Google Patents

Abstract

The invention discloses a preparation method of a nitrogen-doped reduced graphene oxide field emission cathode, which comprises the steps of adding graphene oxide into an organic solution, and adhering the graphene oxide to one end of a conductive graphite rod; and placing the conductive graphite rod stained with the graphene oxide in a quartz tube, carrying out chemical vapor deposition with excessive chitosan, and introducing hydrogen for reduction to obtain the nitrogen-doped redox graphene. Can be used for preparing the cathode of a field emission device. By doping nitrogen atoms, the invention can reduce the work function and introduce more emission sites on the surface of the graphene, effectively reduce the starting voltage of field emission, improve the emission enhancement factor, and can be used for electron sources in field emission flat-panel displays, field emission light sources, vacuum electronic devices and the like.

Description

Preparation method of nitrogen-doped reduced graphene oxide field emission cathode

technical field

The invention relates to field emission technology, in particular to a method for preparing a nitrogen-doped reduced graphene oxide field emission cathode and a nitrogen-doped reduced graphene oxide field emission cathode.

Background technique

Graphene is a new type of two-dimensional carbon nanomaterial, which is composed of carbon atoms tightly packed into a hexagonal honeycomb lattice, and has good electrical conductivity and thermal conductivity. In theory, graphene has a large field enhancement factor, rich edge structure, and strong field emission capability. It is expected to be used in field emission fields such as field emission flat panel displays, field emission light sources, and vacuum electronic devices. However, the field emission current intensity obtained by simply using graphene as the field emission cathode is not high, and the field enhancement factor is not large. Through research, it is found that doping nitrogen atoms into graphene can appropriately increase the emission site, reduce the turn-on voltage, and improve the field enhancement factor, thereby increasing the field emission current intensity of nitrogen-doped redox graphene. It is beneficial to the application of graphene materials in the field emission field.

At present, the method for producing nitrogen-doped graphene mainly includes chemical vapor deposition (CVD). However, the nitrogen content of nitrogen-doped graphene obtained by the traditional method of using nitrogen precursors and carbon precursor catalyst surfaces in a high-temperature furnace for chemical vapor deposition is not high, resulting in insufficient effective emission sites. There is still room for improvement in terms of improvement, and at the same time, the graphene on the substrate needs to be subjected to a complex transfer process, which is not conducive to the actual device fabrication of graphene field emission cathodes.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing a nitrogen-doped reduced graphene oxide field emission cathode, which effectively increases the nitrogen content of graphene and provides more emission sites for field emission.

The concrete technical scheme that realizes the object of the present invention is:

A method for preparing a nitrogen-doped reduced graphene oxide field emission cathode, the method comprising the following specific steps:

Step 1: Preparation of Graphene Oxide Dispersion

Mix ethyl cellulose and terpineol with a mass ratio of 1:5-20 in a water bath at 60-100 ° C for 2-6 hours, and stir with a magnetic controller for 2-4 hours to obtain an organic binder; Graphene and an organic binder are mixed in a mass ratio of 1:10-20 to obtain a graphene oxide paste, ultrasonically dispersed and dissolved for 0.5-2h to form a graphene oxide dispersion; one end of a graphite rod is dipped into the dispersion;

Step 2: Nitrogen Doping

Place the graphite rod of step 1 in a vacuum environment with drying conditions of 60-120 ° C for 30 minutes; after drying, the graphite rod with graphene oxide at one end and chitosan are placed in a quartz tube, and then placed in a tube. In the furnace, the opening direction of the quartz tube is opposite to the direction of the air inlet; a small tube containing chitosan is placed in the quartz tube, and one end is closed; the graphite rod with graphene oxide at one end is placed on the closed end of the quartz tube, which is equipped with chitosan. The small tube of sugar is placed on the open end of the quartz tube and faces the graphite rod; argon gas is introduced at a temperature of 300-800 ° C, and the chitosan is thermally decomposed to produce a nitrogen-containing product, which reacts with graphene oxide to perform nitrogen atom doping; wherein, Argon flow is 10-200sccm;

Step 3: Reduction of Nitrogen-Doped Graphene Oxide

The graphite rod of step 2 is placed in a quartz boat, put into a high-temperature furnace of 600-1000 ° C, and fed with 5-100 sccm of hydrogen, and a reduction reaction is carried out under a hydrogen atmosphere of 5-100 Pa to obtain the nitrogen-doped reduced graphene oxide. Field emission cathode; wherein: the chitosan is powder, and the mass is 0.1-5g.

The graphene oxide was prepared by Hummer.

Compared with the existing scheme, the beneficial effects of the present invention are:

(1) Compared with the traditional nitrogen doping method, the nitrogen doping method of the present invention effectively increases the nitrogen content of graphene, provides more emission sites for field emission, and at the same time obtains an appropriate amount of defects, which is conducive to reducing the emission power The function improves the field emission capability of the cathode, while reducing the turn-on voltage, increasing the field enhancement factor, and significantly increasing the field emission current.

(2) Compared with the traditional CVD method to prepare nitrogen-doped graphene, chitosan is naturally non-toxic and environmentally friendly. Using chitosan as a nitrogen precursor is safer and avoids environmental pollution. At the same time, the reaction conditions of the present invention have lower requirements on temperature, are more safe and effective, have low cost and have good controllability.

Description of drawings

Fig. 1 is the nitrogen-doped reduced graphene oxide field emission cathode preparation flow schematic diagram of the present invention;

2 is a graph showing the variation of the emission current density J with the electric field E of the field emission cathode of the present invention and the common graphene field emission cathode.

FIG. 3 is a characterization diagram of nitrogen element doping in the present invention.

Detailed ways

The present invention will be further described in detail below through specific implementation methods in conjunction with the accompanying drawings.

Referring to Figure 1, the present invention specifically includes:

Graphene oxide is mixed with organic solvent to obtain graphene oxide dispersion and one end of graphite rod 2 is used to dip the dispersion, after vacuum drying, put into high temperature heating furnace together with chitosan 4, pass into argon 1, chitosan 4 Thermal decomposition produces nitrogen-containing products, which react with graphene oxide 3 for nitrogen atom doping;

The obtained sample is then placed in a quartz boat in a high-temperature furnace, and a reduction reaction is carried out under the atmosphere of hydrogen 5 to obtain a nitrogen-doped reduced graphene oxide 6 field emission cathode.

The oxygen content of the graphene oxide is 56%, and it is prepared by the improved Hummers method.

The preparation steps are as follows: mixing ethyl cellulose and terpineol in a water bath at 6-100° C. for 2-6 hours at a mass ratio of 1:5-20, and then stirring with a magnetic controller for 2-4 hours to prepare organic compounds. Binder; graphene oxide is mixed with an organic binder in a mass ratio of 1:10-20 to obtain a graphene oxide paste, and ultrasonically dispersed and dissolved for 0.5-2h to form a graphene oxide dispersion.

The drying conditions of the dispersion liquid are drying in a vacuum environment of 60-120° C. for 0.5 h.

The chitosan is powder with a mass of 0.1-5g.

The specific operation of the nitrogen atom doping reaction is as follows: the graphite rod 1 and the chitosan 4 are respectively placed in a quartz tube; the chitosan 4 is placed at the bottom of the small test tube, the opening is at the bottom of the large test tube, and the graphite rod 2 is placed in the bottom of the small test tube. Bottom of large test tube.

The reaction conditions of the process of reducing nitrogen-doped graphene oxide with hydrogen are as follows: in a high temperature furnace of 600-1000° C., feeding 5-100 sccm of hydrogen, and carrying out the reduction reaction in a hydrogen atmosphere of 5-100 Pa.

Example 1

1) Preparation of graphene oxide dispersion

Mix ethyl cellulose and terpineol in a water bath at 80°C for 4 hours at a mass ratio of 1:20, and stir with a magnetron for 4 hours to prepare an organic binder; add 1 g of graphene oxide to 19 g of organic binder In the agent, ultrasonically disperse and dissolve for 0.5h to form a graphene oxide dispersion, and dip a small amount of the dispersion at one end with a graphite rod to obtain a graphene oxide dispersion sample;

2) Nitrogen atom doping

The graphite rod was dried in a vacuum environment of 80 degrees Celsius for 0.5 h. The dried sample and 0.5 g of chitosan were placed in a quartz tube as shown in Figure 1, then placed in a high-temperature furnace, the valve was closed, the vacuum was slowly evacuated, and an argon gas with a flow rate of 20 sccm was introduced. Raise the temperature to 500°C in 50 minutes, keep at 500°C for half an hour, and take out the sample after the temperature drops to room temperature;

3) Reduction of oxygen atoms

The sample was placed in a quartz boat and then placed in a high-temperature furnace. After the tube was evacuated, the reduction reaction was carried out under a hydrogen atmosphere of 900 °C and 50 Pa for 1 h. After cooling to room temperature, a nitrogen-doped reduced graphene oxide field emission cathode was obtained.

Example 2

1) Preparation of graphene oxide dispersion

Mix ethyl cellulose and terpineol in a water bath at 80°C for 4 hours at a mass ratio of 1:20, and stir with a magnetic controller for 4 hours to prepare an organic adhesive; add 0.5 g of graphene oxide to 10 g of organic adhesive. In the mixture, ultrasonically disperse and dissolve for 0.5h to form a graphene oxide dispersion, and dip a small amount of the dispersion at one end with a graphite rod to obtain a graphene oxide dispersion sample;

2) Nitrogen atom doping

The graphite rod was placed in a vacuum environment of 70 °C to dry for 0.5 h. The dried sample and 0.5 g of chitosan were placed in a quartz tube as shown in Figure 1, then placed in a high-temperature furnace, the valve was closed, the vacuum was slowly evacuated, and an argon gas with a flow rate of 20 sccm was introduced. Raise the temperature to 600°C in 60 minutes, keep at 600°C for half an hour, and take out the sample after the temperature drops to room temperature;

3) Reduction of oxygen atoms

The sample was placed in a quartz boat and then placed in a high-temperature furnace. After the tube was evacuated, the reduction reaction was carried out under a hydrogen atmosphere of 900 °C and 50 Pa for 1 h. After cooling to room temperature, a nitrogen-doped redox graphene field emission cathode was obtained.

Comparative Example 3

1) Preparation of graphene oxide dispersion

Mix ethyl cellulose and terpineol in a water bath at 80°C for 4 hours at a mass ratio of 1:20, and stir with a magnetron for 4 hours to prepare an organic binder; add 1 g of graphene oxide to 19 g of organic binder In the agent, ultrasonically disperse and dissolve for 0.5h to form a graphene oxide dispersion, and dip a small amount of the dispersion at one end with a graphite rod to obtain a graphene oxide dispersion sample;

2) Traditional nitrogen-doped redox graphene

The graphite rod was dried in a vacuum environment of 80 degrees Celsius for 0.5 h. Put the dried sample in a high-temperature furnace to vacuumize, pass 10Pa hydrogen, heat up to 1000°C for 1.5h, keep it at 1000°C for 30 minutes, pass 45PaC ₂ H ₃ N to react for 1 hour, and cool to room temperature Then nitrogen-doped graphene oxide is obtained;

3) Reduction of oxygen atoms

The sample was placed in a quartz boat and then placed in a high-temperature furnace. After the tube was evacuated, the reduction reaction was carried out under a hydrogen atmosphere of 900 °C and 50 Pa for 1 h. After cooling to room temperature, a nitrogen-doped redox graphene field emission cathode was obtained.

Field emission performance test of the prepared field emission cathode:

Using ITO glass as cathode and anode, the graphite rod obtained in Example 1 and Comparative Example was fixed on the cathode ITO glass as an emitter through conductive tape to obtain a device that can be used to measure field emission performance, and the field emission of different emitters were measured respectively. Emission performance, turn-on voltage, field enhancement factor. As can be seen from FIG. 2 , the nitrogen-doped reduced graphene oxide field emission cathode prepared by the present invention has stronger field emission capability, lower turn-on voltage, significantly enhanced emission current and stronger field emission performance. FIG. 3 is the XPS characterization of Example 1, and the doping ratio of nitrogen element is as high as 4%.

The above content is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be considered that the specific implementation of the present invention is limited to these descriptions. Under the premise, simple deductions or substitutions can also be made.

Claims (2)

1. a preparation method of nitrogen-doped reduced graphene oxide field emission cathode, is characterized in that, the method comprises the following concrete steps: Step 1: Preparation of Graphene Oxide Dispersion Mix ethyl cellulose and terpineol with a mass ratio of 1:5-20 in a water bath at 60-100 ° C for 2-6 hours, and stir with a magnetic controller for 2-4 hours to obtain an organic binder; Graphene oxide and organic binder are mixed in a mass ratio of 1:10-20 to obtain a graphene oxide paste, ultrasonically dispersed and dissolved for 0.5-2h to form a graphene oxide dispersion; one end of a graphite rod is dipped into the dispersion; Step 2: Nitrogen Doping Place the graphite rod of step 1 in a vacuum environment with drying conditions of 60-120 ° C for 30 minutes; after drying, the graphite rod with graphene oxide at one end and chitosan are placed in a quartz tube, and then placed in a tube. In the furnace, the opening direction of the quartz tube is opposite to the direction of the air inlet; a small tube containing chitosan is placed in the quartz tube, and one end is closed; the graphite rod with graphene oxide at one end is placed on the closed end of the quartz tube, which is equipped with chitosan. The small tube of sugar is placed on the open end of the quartz tube and faces the graphite rod; argon gas is introduced at a temperature of 300-800 ° C, and the chitosan is thermally decomposed to produce a nitrogen-containing product, which reacts with graphene oxide to perform nitrogen atom doping; wherein, Argon flow is 10-200 sccm; Step 3: Reduction of Nitrogen-Doped Graphene Oxide The graphite rod of step 2 is placed in a quartz boat, put into a high-temperature furnace of 600-1000 ° C, and fed with 5-100 sccm hydrogen, and a reduction reaction is carried out under a hydrogen atmosphere of 5-100 Pa to obtain the nitrogen-doped reduced graphite oxide An ene field emission cathode; wherein: the chitosan is powder, and the mass is 0.1-5g. 2. The preparation method of nitrogen-doped reduced graphene oxide field emission cathode as claimed in claim 1, wherein the graphene oxide is obtained by Hummer.

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