阅读说明：本技术 一种高氮含量掺杂石墨烯量子点的制备方法 (Preparation method of high-nitrogen-content doped graphene quantum dots ) 是由 姜文静 朱伟 马宏明 蒋炎 黄荣庆 罗振扬 于 2020-12-30 设计创作，主要内容包括：本发明公开了一种高氮含量掺杂石墨烯量子点的制备方法,属于石墨烯量子点技术领域。该方法为：将氨基石墨烯分散在强酸溶液中,得到产物A；将产物A加热反应,得到产物B；除去产物B中的强酸,得到产物C；将产物C分散在氨水中,得到产物D；将产物D加热加压使其反应,得到产物E；将产物E提纯、干燥,得到高氮含量掺杂石墨烯量子点。本发明的制备方法在生产工艺上简单可控,所制得的高氮含量掺杂石墨烯量子点的尺寸大小均一,产率高,氮含量高,表面富含官能团,在水及其他有机溶剂中具有良好的分散性,同时还具有优异的光学性能。(The invention discloses a preparation method of a high-nitrogen-content doped graphene quantum dot, and belongs to the technical field of graphene quantum dots. The method comprises the following steps: dispersing amino graphene in a strong acid solution to obtain a product A; heating the product A for reaction to obtain a product B; removing the strong acid in the product B to obtain a product C; dispersing the product C in ammonia water to obtain a product D; heating and pressurizing the product D to react to obtain a product E; and purifying and drying the product E to obtain the high-nitrogen-content doped graphene quantum dot. The preparation method is simple and controllable in production process, and the prepared high-nitrogen-content doped graphene quantum dots are uniform in size, high in yield and high in nitrogen content, have high dispersibility in water and other organic solvents and excellent optical performance, and the surface of the high-nitrogen-content doped graphene quantum dots is rich in functional groups.)

1. A preparation method of a high-nitrogen-content doped graphene quantum dot is characterized by comprising the following steps:

step 1, dispersing amino graphene in a strong acid solution to obtain a product A;

step 2, heating the product A for reaction to obtain a product B;

step 3, removing the strong acid in the product B to obtain a product C;

step 4, dispersing the product C in ammonia water to obtain a product D;

step 5, heating and pressurizing the product D to react to obtain a product E;

and 6, purifying and drying the product E to obtain the high-nitrogen-content doped graphene quantum dot.

2. The method for preparing the doped graphene quantum dot with the high nitrogen content according to claim 1, wherein the strong acid is nitric acid.

3. The preparation method of the high-nitrogen-content doped graphene quantum dot according to claim 1 or 2, wherein the strong acid solution is a strong acid aqueous solution with a concentration of 3-8 mol/L.

4. The method for preparing the doped graphene quantum dot with the high nitrogen content according to claim 1, wherein the amino graphene is prepared by adopting a method disclosed in Chinese patent 2018102122660.

5. The method for preparing the doped graphene quantum dot with the high nitrogen content according to claim 1 or 2, wherein in the step 1, the concentration of the amino graphene in the strong acid solution is 2% to 5%.

6. The preparation method of the high-nitrogen-content doped graphene quantum dot according to claim 1 or 2, wherein in the step 1, the amino graphene is dispersed in a strong acid solution in an ultrasonic mode, the ultrasonic power is 100W, and the ultrasonic time is 0.1-1 hour.

7. The preparation method of the doped graphene quantum dot with high nitrogen content according to claim 1, wherein in the step 2, the heating reaction is carried out at 60-80 ℃ for 6-10 hours.

8. The method for preparing the high-nitrogen-content doped graphene quantum dot according to claim 1, wherein in the step 4, the method for dispersing the product C in ammonia water comprises the following steps: and dispersing the product C in water, and then adding ammonia water to adjust the pH value to 8-9.

9. The method for preparing the doped graphene quantum dot with high nitrogen content according to claim 1, wherein in the step 5, the method for heating and pressurizing the product D to react comprises the following steps: and transferring the product D into a reaction kettle, setting the reaction temperature to be 160-220 ℃, and setting the reaction time to be 6-12 hours.

10. The method for preparing the doped graphene quantum dot with high nitrogen content according to claim 1, wherein in the step 6, the method for purifying the product E comprises the following steps: and carrying out suction filtration on the product E by using a microporous filter membrane, collecting filtrate, and putting the collected filtrate into a dialysis bag for dialysis to obtain dialysis filtrate, namely finishing the purification of the product E.

Technical Field

The invention belongs to the technical field of graphene quantum dots, and particularly relates to a preparation method of a high-nitrogen-content doped graphene quantum dot.

Background

The graphene quantum dots are derived from physical research of graphene, have a similar carbon structure to graphene, and are another novel zero-dimensional carbon nanomaterial discovered after zero-dimensional carbon nanomaterials such as fullerene, one-dimensional carbon nanotubes and two-dimensional graphene are reported. From the appearance, the graphene quantum dots have strong quantum confinement effect and edge effect, and the effect is more obvious when the size is smaller. The graphene quantum dots are rich in surface functional groups, so that the graphene quantum dots have excellent water dispersion property. Meanwhile, the graphene quantum dots also have the advantages of conductivity, luminescence, no toxicity, low preparation cost and the like, and are widely applied to the fields of photoelectricity, catalysis, biomedicine and the like at present.

At present, the preparation of graphene quantum dots mainly comprises two methods, namely a top-down method and a bottom-up method, wherein carbon materials with larger sizes, such as graphite, are used as raw materials from top to bottom, the graphene quantum dots are obtained by cutting, stripping or decomposing through a physical and chemical method, and the physical and chemical denudation of the graphite is usually carried out through a hydrothermal method, a solvothermal method, a hydrazine hydrate reduction method, an electrochemical method and the like. The method from bottom to top mainly uses small molecules as precursors, and finally obtains the graphene quantum dots through a series of chemical reactions.

However, the commonly synthesized graphene quantum dots often have the defects of single surface functional group, low fluorescence quantum yield and the like, and the application of the graphene quantum dots in multiple fields is limited. In recent years, researchers find that doping heteroatoms in quantum dots can effectively regulate and control the structure and the performance of graphene quantum dots. Among them, nitrogen-doped graphene quantum dots are receiving wide attention due to their unique photoelectric and catalytic properties. Because the nitrogen element and the carbon element are positioned in the same period of the periodic table of the elements and the atomic radii are close, the doping is relatively easy to realize. And the nitrogen atoms have strong electron-withdrawing induction effect, and can change the density of pi electron cloud so as to change the band gap width of the graphene quantum dots, thereby changing the properties of the graphene quantum dots.

Chinese patent 2019103475382, published as 2019, 6 and 28, discloses a method for preparing nitrogen-doped graphene quantum dots by a hydrothermal method, wherein butanediamine and hydrogen peroxide are added, and graphene oxide is cut by the hydrothermal method to obtain the nitrogen-doped graphene quantum dots, and the nitrogen-doped graphene quantum dots have good dispersibility and uniform particles. However, in the method disclosed in the above patent, the graphene quantum dots are prepared by a hydrothermal method, the graphene oxide and the reduction product thereof are used as raw materials, a large amount of reagents are required to be added in the reduction process, and the time consumption is long.

Chinese patent 2017114945611, published as 2018, 4 and 6, discloses a preparation method of a nitrogen-doped graphene quantum dot material, wherein reduced graphene oxide is dispersed in concentrated nitric acid, the reduced graphene oxide is heated to 140-160 ℃ in a magnetic stirring oil bath, the constant-temperature reaction is carried out for 12-18 h under the condensation of circulating water, a solvent is evaporated, and the nitrogen-doped graphene quantum dot is obtained through dialysis, so that the luminous stability of the nitrogen-doped graphene quantum dot is improved to a certain extent. However, the nitrogen-doped graphene quantum dots obtained by the method have the problems of complex preparation process, long time consumption, low nitrogen content and the like.

Disclosure of Invention

Aiming at the problems of low yield, low nitrogen content, more impurities and complex preparation of graphene quantum dots in the prior art, the invention aims to provide a preparation method of high-nitrogen-content doped graphene quantum dots.

In order to solve the problems, the technical scheme adopted by the invention is as follows:

a preparation method of a high-nitrogen-content doped graphene quantum dot comprises the following steps:

step 1, dispersing amino graphene in a strong acid solution to obtain a product A;

step 2, heating the product A for reaction to obtain a product B;

step 3, removing the strong acid in the product B to obtain a product C;

step 4, dispersing the product C in ammonia water to obtain a product D;

step 5, heating and pressurizing the product D to react to obtain a product E;

and 6, purifying and drying the product E to obtain the high-nitrogen-content doped graphene quantum dot.

Further, the strong acid is nitric acid.

Further, the strong acid solution is a strong acid aqueous solution with the concentration of 3-8 mol/L.

Further, the amino graphene is prepared by adopting a method disclosed in Chinese patent 2018102122660.

Further, in the step 1, the concentration of the amino graphene in the strong acid solution is 2% -5%.

Further, in the step 1, dispersing the amino graphene in a strong acid solution in an ultrasonic mode, wherein the ultrasonic power is 100W, and the ultrasonic time is 0.1-1 hour.

Further, in the step 2, the heating reaction is carried out for 6-10 hours at 60-80 ℃.

Further, in step 4, the method for dispersing the product C in ammonia water is as follows: and dispersing the product C in water, and then adding ammonia water to adjust the pH value to 8-9.

Further, in step 5, the method of heating and pressurizing the product D to react comprises: and transferring the product D into a reaction kettle, setting the reaction temperature to be 160-220 ℃, and setting the reaction time to be 6-12 hours.

Further, in step 6, the method for purifying the product E comprises the following steps: and carrying out suction filtration on the product E by using a microporous filter membrane, collecting filtrate, and putting the collected filtrate into a dialysis bag for dialysis to obtain dialysis filtrate, namely finishing the purification of the product E.

Compared with the prior art, the invention has the beneficial effects that:

the high-nitrogen-content doped graphene quantum dot prepared by the invention is simple and controllable in production process, the amino graphene with rich nitrogen content is selected as a carbon source, nitric acid is preferably selected as a strong oxidant, ammonia water is selected as a nitrogen source, and the nitrogen content is improved while other impurity ions are prevented from being introduced. The prepared high-nitrogen-content doped graphene quantum dot has the advantages of uniform size, high yield, high nitrogen content, no other impurity ions, rich functional groups on the surface, good dispersibility in water and other organic solvents, capability of emitting bright green fluorescence under 365nm ultraviolet illumination and excellent optical performance.

Drawings

Fig. 1 is a schematic flow chart of a preparation method of a high nitrogen-doped graphene quantum dot according to the present invention;

fig. 2 is an infrared spectrum of the nitrogen-doped graphene quantum dot of example 1;

fig. 3 is an atomic force picture of the nitrogen-doped graphene quantum dot of example 1;

fig. 4 is a picture of nitrogen-doped graphene quantum dots under a 365nm ultraviolet lamp in example 1;

fig. 5 is a picture of the nitrogen-doped graphene quantum dots of comparative example 1 under a 365nm ultraviolet lamp.

Detailed Description

The invention is further described with reference to specific examples.

The following amino graphene used in each example was prepared according to example 1 of chinese patent 2018102122660.

The rest raw materials are all commercial products.

Example 1

Referring to the schematic flow chart shown in fig. 1, the preparation method of the high nitrogen-doped graphene quantum dot of the present embodiment is as follows:

1. 205mL of deionized water is taken in a beaker, and then 65-68% of HNO is weighed₃45mL of the aqueous solution is added into deionized water, and the mixture is stirred while being inverted to prepare 250mL of 4mol/L nitric acid aqueous solution;

2. 1g of amino graphene powder is dispersed in the prepared solution, and the ultrasonic dispersion is uniform, wherein the ultrasonic power is 100W, and the ultrasonic time is 0.5 hour;

3. transferring the solution with uniform ultrasonic dispersion into an oil bath pan, heating to 60 ℃, and carrying out condensation reflux for 10 hours;

4. after the reaction is finished, taking out the reaction solution, and heating and steaming to remove the nitric acid solution in the product to obtain a tan solid;

5. ultrasonically dispersing the obtained tan solid in 100mL of deionized water, wherein the ultrasonic power is 100W, the ultrasonic time is 0.5 hour, and then adding ammonia water (25-28%) to adjust the pH value to 8.03;

6. transferring the solution with the adjusted pH value to a reaction kettle, and reacting for 12 hours at 160 ℃;

7. cooling to room temperature after the reaction is finished, performing suction filtration by using a 0.22 mu m microporous filter membrane, and collecting filtrate;

8. putting the collected filtrate into a dialysis bag for dialysis, wherein the cut-off molecular weight of the dialysis bag is 3500, the dialysis frequency is 5 times, and each time lasts for 2 hours;

9. and (4) carrying out vacuum drying on the obtained filtrate, wherein the dried powdery sample is the high-nitrogen-content doped graphene quantum dot.

The obtained nitrogen-content-doped graphene quantum dot can emit bright green fluorescence under 365nm ultraviolet illumination.

Example 2

Referring to fig. 1, the preparation method of the high nitrogen-doped graphene quantum dot of the present embodiment is as follows:

1. 185mL of deionized water is taken in a beaker, and then 65-68% of HNO is weighed₃65mL of the solution is added into deionized water, and the solution is stirred while being inverted to prepare 250mL of 6mol/L nitric acid aqueous solution;

2. 1g of amino graphene powder is dispersed in the prepared solution, and the ultrasonic dispersion is uniform, wherein the ultrasonic power is 100W, and the ultrasonic time is 0.5 hour;

3. transferring the solution with uniform ultrasonic dispersion into an oil bath pan, heating to 70 ℃, and carrying out condensation reflux for 8 hours;

4. after the reaction is finished, taking out the reaction solution, heating and steaming to remove the nitric acid solution in the product to obtain a tan solid;

5. ultrasonically dispersing the obtained tan solid in 100mL of deionized water, wherein the ultrasonic power is 100W, the ultrasonic time is 0.5 hour, and adding ammonia water (25-28%) to adjust the pH value to 8.56;

6. transferring the solution with the adjusted pH value to a reaction kettle, and reacting for 10 hours at 180 ℃;

7. cooling to room temperature after the reaction is finished, performing suction filtration by using a 0.22 mu m microporous filter membrane, and collecting filtrate;

8. putting the collected filtrate into a dialysis bag for dialysis, wherein the cut-off molecular weight of the dialysis bag is 3500, the dialysis frequency is 5 times, and each time lasts for 2 hours;

9. and (3) carrying out vacuum drying on the filtrate obtained by dialysis, wherein the dried powdery sample is the doped graphene quantum dot with high nitrogen content.

The obtained nitrogen-content-doped graphene quantum dot can emit bright green fluorescence under 365nm ultraviolet illumination.

Example 3

1. 160mL of deionized water is taken in a beaker, and then 65-68% of HNO is weighed₃Adding 90mL of the solution into deionized water, and stirring while pouring to prepare 250mL of 8mol/L nitric acid aqueous solution;

2. 1g of amino graphene powder is dispersed in the prepared solution, and the ultrasonic dispersion is uniform, wherein the ultrasonic power is 100W, and the ultrasonic time is 0.5 hour;

3. transferring the solution with uniform ultrasonic dispersion into an oil bath pan, heating to 80 ℃, and carrying out condensation reflux for 6 hours;

4. after the reaction is finished, taking out the reaction solution, heating and steaming to remove the nitric acid solution in the product to obtain a tan solid;

5. ultrasonically dispersing the obtained tan solid in 100mL of deionized water, wherein the ultrasonic power is 100W, the ultrasonic time is 0.5 hour, and adding ammonia water (25-28%) to adjust the pH value to 8.93;

6. transferring the solution with the adjusted pH value to a reaction kettle, and reacting for 8 hours at 200 ℃;

7. cooling to room temperature after the reaction is finished, performing suction filtration by using a 0.22 mu m microporous filter membrane, and collecting filtrate;

8. putting the collected filtrate into a dialysis bag for dialysis, wherein the cut-off molecular weight of the dialysis bag is 3500, the dialysis frequency is 5 times, and each time lasts for 2 hours;

9. and (4) carrying out vacuum drying on the filtrate obtained by dialysis, wherein the dried powdery sample is the doped graphene quantum dot with high nitrogen content.

The obtained nitrogen-content-doped graphene quantum dot can emit bright green fluorescence under 365nm ultraviolet illumination.

Comparative example 1

The preparation method of the nitrogen-doped graphene quantum dot in the comparative example is substantially the same as that in example 1, except that in the comparative example 1, graphene oxide is directly used as a raw material to perform a reaction without performing an amination reaction.

Comparative example 2

This comparative example is substantially the same as example 1 except that the reaction was carried out using graphene as a raw material without carrying out an amination reaction.

Fig. 2 is an infrared spectrum of the nitrogen-doped graphene quantum dot in example 1. As can be seen, 3342.9cm^-1Is NH stretching vibration peak, 1486.77cm^-1OH bending vibration peak at 1352.79cm^-1Is C-N stretching vibration peak, 1003.35cm^-1Is C-C stretching vibration peak, 695.20cm^-1Is NH₂And an out-of-plane rocking peak proves that the surface of the material is rich in functional groups and has good dispersibility in water and other organic solvents.

Fig. 3 is an atomic force picture of the nitrogen-doped graphene quantum dot in example 1, and as can be seen from fig. 3, the prepared nitrogen-doped graphene quantum dot is uniform in distribution, small in particle size, and favorable for fluorescence luminescence stability.

Fig. 4 is a picture of the nitrogen-doped graphene quantum dots of example 1 under a 365nm ultraviolet lamp.

Fig. 5 is a picture of the nitrogen-doped graphene quantum dots of comparative example 1 under a 365nm ultraviolet lamp.

As can be seen from comparison between fig. 4 and fig. 5, the fluorescence intensity of the nitrogen-doped graphene quantum dot prepared by the method under a 365nm ultraviolet lamp is higher than that of the graphene quantum dot prepared from graphene without amination.

The nitrogen content of the nitrogen-doped graphene quantum dots obtained in each example and comparative example was tested, and the results are shown in table 1.

As can be seen from table 1, the nitrogen content of the nitrogen-doped graphene quantum dot prepared by the method is significantly higher than that of the graphene quantum dot prepared by directly using graphite oxide and graphene, and the method is favorable for fluorescence luminescence stability.

TABLE 1N content test of different examples and comparative examples

Sample (I)	N content (%)
		Example 1	6.86
Example 2	6.55
		Example 3	6.32
Comparative example 1	3.21
		Comparative example 2	2.32