CN112391163B - Nitrogen-doped yellow carbon quantum dot and preparation method thereof - Google Patents

Abstract

The invention discloses a nitrogen-doped yellow carbon quantum dot and a preparation method thereof, wherein the particle size range of the yellow carbon quantum dot fluorescent material is 3-6 nm. The yellow carbon quantum can emit bright yellow fluorescence under the excitation of light with the wavelength of 320-550 nm, and the fluorescence quantum efficiency can reach 38 percent at most. The preparation method takes 2,4,6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source and tin salt as a catalyst, so that the synthesis time for synthesizing the yellow carbon quantum dots is greatly shortened, and the absolute fluorescence quantum efficiency of the synthesized yellow carbon quantum dots is high. The yellow carbon quantum dots prepared by the method have stable fluorescence performance in an ethanol solution, and no fluorescence intensity reduction is observed within 35 days. The preparation method greatly simplifies the synthesis process of synthesizing the yellow carbon quantum dots, improves the preparation efficiency and greatly reduces the preparation cost.

Description

Nitrogen-doped yellow carbon quantum dots and preparation method thereof

technical field

The invention relates to a carbon quantum dot and a preparation method thereof, in particular to a yellow carbon quantum dot and a preparation method thereof, which are applied in the technical field of carbon nanomaterials.

Background technique

Carbon quantum dots are a class of spherical nanomaterials with a particle size of less than 10 nm. In addition to the luminous performance and small size characteristics of traditional quantum dots, carbon quantum dots also have good water solubility, stable luminescent performance, and good compatibility with biomolecules. The method has the advantages of simple method and low cost. These characteristics make it have broad application prospects in the fields of bioimaging, luminescent labeling of biomedical molecules, and fluorescent sensors.

There are many methods for synthesizing carbon quantum dots, such as hydrothermal method, solvothermal method, microwave method, etc. Among them, the carbon quantum dot luminescent material synthesized by the solvothermal method has the advantages of narrow particle size distribution and high fluorescence quantum efficiency. However, the reaction time of the currently reported solvothermal synthesis of carbon quantum dots takes a long time, and most of the quantum efficiencies are not high. It is reported in the literature that the yellow-green carbon quantum dots (maximum emission wavelength 555nm, maximum excitation wavelength 393nm) can be synthesized by microwave method with resorcinol as carbon source and o-phenylenediamine as nitrogen source. The quantum efficiency of yellow-green carbon quantum dots is 62.2% (Pei Yang, Ziqi Zhu, Xinghui Li, et al. J. Alloys Compd. 2020, 834: 154399.). Using citric acid as carbon source, urea as nitrogen source, manganese acetate as catalyst, and toluene as solvent, yellow-green carbon quantum dots (maximum emission wavelength 555nm, maximum excitation wavelength 450nm) were synthesized by solvothermal method, and the quantum luminous efficiency Reached 68.6% (Yingbo Liu, Daiyong Chao, Liang Zhou, et al. Carbon, 2018, 135:253-259.). Therefore, it is of great research significance and practical value to find a new preparation method of carbon quantum dot luminescent material that is green, environmentally friendly, short synthesis time, low cost, uniform particle size distribution, and high quantum efficiency for the wide and practical application of carbon quantum dots. Because of the penetrability and damage to biological tissues of fluorescence emitted by short wavelengths, its application in the biological field is limited. Therefore, the synthesis of carbon quantum dots with longer wavelength excitation and longer wavelength emission is of great significance and has become a technical problem to be solved urgently.

Contents of the invention

In order to solve the problems of the prior art, the object of the present invention is to overcome the deficiencies in the prior art, and provide a nitrogen-doped yellow carbon quantum dot and its preparation method. The fluorescence performance of the yellow carbon quantum dot in the present invention is stable in ethanol solution , no decrease in fluorescence intensity was observed within 35 days. The preparation method of the invention can synthesize high-quality nitrogen-doped yellow carbon quantum dot materials with long excitation wavelength and uniform particle size, greatly simplifies the synthesis process of yellow carbon quantum dots, improves preparation efficiency, and greatly reduces preparation cost.

In order to achieve the above invention creation purpose, the present invention adopts the following technical solutions:

A nitrogen-doped yellow carbon quantum dot, the particle size of which ranges from 3 to 6 nm, can emit yellow fluorescence under light excitation of 320 to 550 nm; the nitrogen-doped yellow carbon quantum dot is dispersed in an ethanol solution In 35 days, no decline in fluorescence intensity occurred.

Preferably, the maximum excitation wavelength for the nitrogen-doped yellow carbon quantum dots of the present invention to emit yellow fluorescence is 525 nm.

Preferably, the nitrogen-doped yellow carbon quantum dots of the present invention can emit yellow fluorescence when excited by light of 336-525 nm.

Preferably, the nitrogen-doped yellow carbon quantum dots emit yellow fluorescence with a maximum emission wavelength of 568 nm.

Preferably, -COOH, -OH and _-NH2 groups are bound to the surface of the nitrogen-doped yellow carbon quantum dots.

A method for preparing nitrogen-doped yellow carbon quantum dots of the present invention, using 2,4,6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source, and metal tin salt as a catalyst, using solvothermal Method, synthesized yellow light carbon quantum dots, including the following steps:

a. According to the molar ratio of metal tin salt and 2,4,6-trihydroxybenzoic acid 1: (1~2), the ratio of raw materials is mixed, and the metal tin salt and 2,4,6-trihydroxybenzoic acid are dissolved in In ethanol, add a certain amount of m-phenylenediamine to form a mixed solution; the molar ratio of the m-phenylenediamine and 2,4,6-trihydroxybenzoic acid is 1: (1～2); adjust the pH of the mixed solution The value is 4~6, stir at 40~70°C for 30~60 minutes to make the solution evenly mixed;

b. Put the uniformly mixed mixed solution into a polytetrafluoroethylene reactor, react at 160-200°C for 2-4 hours, and then cool to room temperature to obtain a product solution;

c. Centrifuge the product solution to remove tin oxide, and dialyze with a membrane with a molecular weight of 3500Da for at least 1 day to remove small molecular substances, thereby obtaining nitrogen-doped yellow carbon quantum dots.

Preferably, yellow light carbon quantum dots with high fluorescence quantum efficiency can be synthesized, and the highest absolute fluorescence quantum efficiency can reach 38%.

Preferably, in the step a, the tin salt is any one of SnCl ₄ ·5H ₂ O, SnCl ₄ , SnCl ₂ ·2H ₂ O, SnCl ₂ and SnF ₂ or any mixed salt of several kinds.

Preferably, in the step a, 1-2 mmol of 2,4,6-trihydroxybenzoic acid and tin salt are dissolved in at least 20 mL of ethanol.

Preferably, in the step b, the reaction is carried out at 160-180°C.

Preferably, in the step c, the concentration of the obtained nitrogen-doped yellow carbon quantum dot solution is not lower than 23 mg/mL.

Compared with the prior art, the present invention has the following obvious outstanding substantive features and significant advantages:

1. The present invention uses 2,4,6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source, and a metal tin compound as a catalyst. By doping nitrogen atoms in carbon quantum dots, the emission wavelength is red-shifted to Yellow light-emitting area, and improve the luminous efficiency of carbon quantum dots; the present invention uses metal tin compound as catalyst, greatly shortens the synthesis time of carbon quantum dots, greatly reduces the synthesis cost of carbon quantum dots; the synthesis time used is shorter than the time reported in literature Shortened by more than 50%, the quantum efficiency of yellow light carbon quantum dots synthesized in 2 hours can reach 38%;

2. The synthetic method of the present invention is carried out in the air, does not need complicated synthetic equipment, does not need chromatographic separation; The synthetic method has the high efficiency of synthesis, the advantage that cost is low; The inventive method does not use sulfur-containing chemical reagent, is a kind of Green synthetic method;

3. The yellow carbon quantum dot fluorescent material synthesized by the present invention has very stable fluorescence performance in ethanol solution, and no decline in its fluorescence intensity has been observed within 35 days; the luminescence performance does not weaken in the air, and under the light excitation of 320～550nm, Bright yellow fluorescence is emitted, and the maximum emission wavelength is 568nm; the stability of the luminescence performance of the yellow carbon quantum dots at room temperature is good; the method of the invention is simple, easy to implement, and low in cost, and is suitable for popularization and use.

Description of drawings

Fig. 1 is the fluorescent emission spectrum of the yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention respectively under the excitation of 336nm, 380nm and 525nm light, and the inset is a photo of yellow fluorescent emission under the irradiation of a 365nm lamp.

Fig. 2 is the excitation spectrum of the yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention at a detection wavelength of 568 nm.

Fig. 3 is the ultraviolet-visible absorption spectrum of the ethanol solution of yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention, and the illustration is a photo of it under natural light.

Fig. 4 is a high-resolution transmission electron microscope image of yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention, and the inset is the characteristic lattice diffraction fringes of carbon quantum dots.

Fig. 5 is a particle size distribution diagram of yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention.

Fig. 6 is an infrared spectrum diagram of yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention.

Fig. 7 is a time-varying curve of the fluorescence intensity of the yellow fluorescent carbon quantum dots obtained in Example 1 of the present invention at an emission wavelength of 568 nm.

8 is a schematic flow chart of a method for preparing nitrogen-doped yellow carbon quantum dots according to Embodiment 1 of the present invention, and the illustration is a photograph of yellow fluorescence emitted by a 365nm lamp.

Detailed ways

Below in conjunction with specific implementation example, above-mentioned scheme is described further, and preferred embodiment of the present invention is described in detail as follows:

Embodiment one:

In this example, see Figure 7, a method for preparing nitrogen-doped yellow carbon quantum dots, using 2,4,6-trihydroxybenzoic acid as the carbon source, m-phenylenediamine as the nitrogen source, and metal Tin salt is used as a catalyst, and a yellow-light carbon quantum dot is synthesized by a solvothermal method, including the following steps:

a. Weigh 1mmol of SnCl ₄ 5H ₂ O and 1mmol of 2,4,6-trihydroxybenzoic acid, dissolve them in 15mL of absolute ethanol, and raise the temperature to 40°C under magnetic stirring to obtain the carbon source reactant solution; then 2mmol of m-phenylenediamine was dissolved in 5mL of absolute ethanol to form a nitrogen source reactant solution; the nitrogen source reactant solution was added dropwise to the carbon source reactant solution, and the pH value of the solution was adjusted to 6; Continue to stir at 40°C for 60 minutes to make the solution evenly mixed;

b. Put the homogeneously mixed mixed solution into a polytetrafluoroethylene reactor, react at 180°C for 2 hours, and then naturally cool to room temperature to obtain a product solution;

c. Centrifuge the product solution at a speed of 10,000 rpm to remove the tin oxide nanoparticles generated by the reaction, and dialyze with a membrane with a molecular weight of 3500Da for 1 day to remove small molecular substances, thereby obtaining nitrogen-doped yellow light carbon A nitrogen-doped yellow light carbon quantum dot solution with a quantum dot concentration of 23 mg/mL.

Experimental test analysis:

The nitrogen-doped yellow light carbon quantum dot solution prepared in this embodiment was used as a test sample for analytical testing and property inspection.

After the yellow light carbon quantum dots prepared in this example were diluted 100 times with ethanol, their fluorescence emission spectra were measured with a steady-state transient fluorescence spectrometer FLS1000 under light excitation of 336nm, 380nm and 525nm, respectively, see FIG. 1 . The maximum emission of the yellow light carbon quantum dot is at 568nm, the maximum emission wavelength does not change with the excitation wavelength, and emits characteristic yellow fluorescence.

At a detection wavelength of 568nm, the ethanol dilute solution of yellow carbon quantum dots has three excitation absorption peaks at 336nm, 380nm and 525nm, see Figure 2, which shows that it can obtain bright yellow fluorescence under the excitation of 320nm-550nm light.

Fig. 3 is the ultraviolet-visible absorption spectrum of the yellow light carbon quantum dots prepared in this example, showing that it mainly has three absorption peaks, which are respectively located at 273nm, 293nm and 425nm. Fig. 4 is a high-resolution electron microscope HRTEM image of the yellow light carbon quantum dots prepared in this embodiment, which has characteristic lattice diffraction fringes of carbon quantum dots. FIG. 5 is a particle size distribution diagram of the yellow fluorescent carbon quantum dots obtained in this embodiment, indicating that the particle size range of the carbon quantum dots is 3-6 nm. Fig. 6 is the infrared absorption spectrum of the yellow carbon quantum dots obtained in this embodiment, which shows that there are more -COOH and -OH groups on the surface of the carbon quantum dots, and a small amount of _-NH2 groups on the surface. Fig. 7 is the time-dependent curve of the fluorescence intensity of the yellow fluorescent carbon quantum dots obtained in this example at an emission wavelength of 568 nm, indicating that the yellow carbon quantum dots have good fluorescence stability in ethanol solution.

In this implementation method, yellow fluorescent carbon quantum dots are prepared by 180°C with a reaction time of 2 hours. In this example, 2,4,6-trihydroxybenzoic acid is used as a carbon source, m-phenylenediamine is used as a nitrogen source, and a metal tin compound is used as a catalyst. , by doping nitrogen atoms in the carbon quantum dots, the luminous wavelength is red-shifted to the yellow luminous region, and the luminous efficiency of the carbon quantum dots is improved; this embodiment uses a metal tin compound as a catalyst, greatly shortening the synthesis time of the carbon quantum dots , greatly reducing the synthesis cost of carbon quantum dots; the synthesis time used is more than 50% shorter than that reported in the literature, and the quantum efficiency of yellow light carbon quantum dots synthesized in 2 hours can reach 38%.

Embodiment two:

This embodiment is basically the same as Embodiment 1, especially in that:

In this example, a method for preparing nitrogen-doped yellow carbon quantum dots uses 2,4,6-trihydroxybenzoic acid as the carbon source, m-phenylenediamine as the nitrogen source, and metal tin salt as the catalyst , using a solvothermal method to synthesize yellow light carbon quantum dots, including the following steps:

a. Weigh 1mmol of SnCl ₄ 5H ₂ O and 1mmol of 2,4,6-trihydroxybenzoic acid, dissolve them in 15mL of absolute ethanol, and raise the temperature to 40°C under magnetic stirring to obtain the carbon source reactant solution; then 2mmol of m-phenylenediamine was dissolved in 5mL of absolute ethanol to form a nitrogen source reactant solution; the nitrogen source reactant solution was added dropwise to the carbon source reactant solution, and the pH value of the solution was adjusted to 6; Continue to stir at 40°C for 60 minutes to make the solution evenly mixed;

b. Put the homogeneously mixed mixed solution into a polytetrafluoroethylene reactor, react at 160°C for 2 hours, and then naturally cool to room temperature to obtain a product solution;

c. Centrifuge the product solution at a speed of 10,000 rpm to remove the tin oxide nanoparticles generated by the reaction, and dialyze with a membrane with a molecular weight of 3500Da for 1 day to remove small molecular substances, thereby obtaining nitrogen-doped yellow light carbon A nitrogen-doped yellow light carbon quantum dot solution with a quantum dot concentration of 23 mg/mL.

In this implementation method, yellow fluorescent carbon quantum dots are prepared by 160°C with a reaction time of 2 hours. In this example, 2,4,6-trihydroxybenzoic acid is used as a carbon source, m-phenylenediamine is used as a nitrogen source, and a metal tin compound is used as a catalyst. , by doping nitrogen atoms in the carbon quantum dots, the luminous wavelength is red-shifted to the yellow luminous region, and the luminous efficiency of the carbon quantum dots is improved; this embodiment uses a metal tin compound as a catalyst, greatly shortening the synthesis time of the carbon quantum dots , greatly reducing the synthesis cost of carbon quantum dots; the synthesis time used is shortened by more than 50% compared with the time reported in the literature, and the quantum efficiency of yellow light carbon quantum dots synthesized in 2 hours can reach 16.4%.

Embodiment three:

This embodiment is basically the same as the previous embodiment, and the special features are:

In this example, a method for preparing nitrogen-doped yellow carbon quantum dots uses 2,4,6-trihydroxybenzoic acid as the carbon source, m-phenylenediamine as the nitrogen source, and metal tin salt as the catalyst , using a solvothermal method to synthesize yellow light carbon quantum dots, including the following steps:

a. Weigh 1mmol of SnCl ₄ 5H ₂ O and 1mmol of 2,4,6-trihydroxybenzoic acid, dissolve them in 15mL of absolute ethanol, and raise the temperature to 40°C under magnetic stirring to obtain the carbon source reactant solution; then 2mmol of m-phenylenediamine was dissolved in 5mL of absolute ethanol to form a nitrogen source reactant solution; the nitrogen source reactant solution was added dropwise to the carbon source reactant solution, and the pH value of the solution was adjusted to 6; Continue to stir at 40°C for 60 minutes to make the solution evenly mixed;

b. Put the homogeneously mixed mixed solution into a polytetrafluoroethylene reactor, react at 200°C for 2 hours, and then naturally cool to room temperature to obtain a product solution;

c. Centrifuge the product solution at a speed of 10,000 rpm to remove the tin oxide nanoparticles generated by the reaction, and dialyze with a membrane with a molecular weight of 3500Da for 1 day to remove small molecular substances, thereby obtaining nitrogen-doped yellow light carbon A nitrogen-doped yellow light carbon quantum dot solution with a quantum dot concentration of 23 mg/mL.

In this implementation method, yellow fluorescent carbon quantum dots are prepared by 200°C with a reaction time of 2 hours. In this example, 2,4,6-trihydroxybenzoic acid is used as the carbon source, m-phenylenediamine is used as the nitrogen source, and a metal tin compound is used as the catalyst. , by doping nitrogen atoms in the carbon quantum dots, the luminous wavelength is red-shifted to the yellow luminous region, and the luminous efficiency of the carbon quantum dots is improved; this embodiment uses a metal tin compound as a catalyst, greatly shortening the synthesis time of the carbon quantum dots , greatly reducing the synthesis cost of carbon quantum dots; the synthesis time used is shortened by more than 50% compared with the time reported in the literature, and the quantum efficiency of yellow light carbon quantum dots synthesized in 2 hours can reach 18%.

Comparative example:

In this comparative example, a method for preparing carbon quantum dots, using 2,4,6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source, and metal tin salt as a catalyst, adopts a solvothermal method , synthesized composite carbon quantum dots, including the following steps:

a. Weigh 1mmol of SnCl ₄ 5H ₂ O and 1mmol of 2,4,6-trihydroxybenzoic acid, dissolve them in 15mL of absolute ethanol, and raise the temperature to 40°C under magnetic stirring to obtain the carbon source reactant solution; then 2mmol of m-phenylenediamine was dissolved in 5mL of absolute ethanol to form a nitrogen source reactant solution; the nitrogen source reactant solution was added dropwise to the carbon source reactant solution, and the pH value of the solution was adjusted to 6; Continue to stir at 40°C for 60 minutes to make the solution evenly mixed;

b. Put the homogeneously mixed mixed solution into a polytetrafluoroethylene reactor, react at 140°C for 2 hours, and then naturally cool to room temperature to obtain a product solution;

c. Centrifuge the product solution at a speed of 10,000 rpm to remove the tin oxide nanoparticles generated by the reaction, and dialyze with a membrane with a molecular weight of 3500Da for 1 day to remove small molecular substances, thereby obtaining a composite carbon quantum dot solution.

In this implementation method, the composite carbon quantum dots are prepared by using a reaction time of 2 hours at 140°C.

See Table 1 for the comparison of the quantum efficiencies of the carbon quantum dots prepared in the above examples and comparative examples.

Table 1 Quantum efficiency of yellow carbon quantum dots synthesized at different reaction temperatures

comparative example Embodiment two Embodiment one Embodiment Three temperature/℃ 140 160 180 200 Absolute Fluorescence Quantum Efficiency 4.1% 16.4% 38.0% 18.0%

It can be seen from Table 1 that the quantum efficiency of the synthesis of yellow carbon quantum dots is greater than 16% when the reaction is carried out at 160-200°C for 2 hours, while the quantum efficiency of the synthesis of yellow carbon quantum dots at 140°C for 2 hours is only 4.1%. Therefore, the temperature condition is a key technical condition element of the present invention.

A method for preparing nitrogen-doped yellow carbon quantum dots, in the step a, the tin salt is any one of SnCl ₄ 5H ₂ O, SnCl ₄ , SnCl ₂ 2H ₂ O, SnCl ₂ and SnF ₂ Salt or any mixed salt of several kinds is used as a catalyst to shorten the synthesis time of carbon quantum dots and greatly reduce the synthesis cost of carbon quantum dots.

Based on the above examples, it can be seen that the particle size range of the yellow carbon quantum dot fluorescent material prepared in the above examples is 3-6 nm. The yellow carbon quantum can emit bright yellow fluorescence under the light excitation of 320-550nm, and the fluorescence quantum efficiency can reach up to 38%. The preparation method of the above example uses 2,4,6-trihydroxybenzoic acid as the carbon source, m-phenylenediamine as the nitrogen source, and tin salt as the catalyst, so that the synthesis time of the synthetic yellow carbon quantum dots is greatly shortened, and the synthesized yellow carbon quantum dots The absolute fluorescent quantum efficiency of the carbon quantum dot reaches 38%, and the concentration is not lower than 23mg/mL. The fluorescence performance of the yellow carbon quantum dots prepared by the method in the above example is very stable in ethanol solution, and no decrease in fluorescence intensity was observed within 35 days. The preparation method greatly simplifies the synthesis process for synthesizing the yellow carbon quantum dots, improves the preparation efficiency, and greatly reduces the preparation cost.

The embodiment of the present invention has been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned embodiment, and various changes can also be made according to the purpose of the invention of the present invention. The changes, modifications, substitutions, combinations or simplifications should all be equivalent replacement methods, as long as they meet the purpose of the invention, as long as they do not deviate from the technical principle and inventive concept of the invention, they all belong to the protection scope of the invention.

Claims (10)

1. A nitrogen-doped yellow carbon quantum dot is characterized in that: the particle size range of the fluorescent powder is 3-6 nm, and the fluorescent powder can emit yellow fluorescence under the excitation of light with the wavelength of 320-550 nm; dispersing the nitrogen-doped yellow carbon quantum dots in an ethanol solution, wherein the fluorescence intensity is not reduced within 35 days; the preparation method comprises the following steps of synthesizing the nitrogen-doped yellow carbon quantum dot by using 2,4, 6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source and a metal tin salt as a catalyst by adopting a solvothermal method:

the method for synthesizing the yellow carbon quantum dots by using the solvothermal method and taking 2,4, 6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source and metallic tin salt as a catalyst comprises the following steps:

a. according to the molar ratio of the metallic tin salt to the 2,4, 6-trihydroxybenzoic acid of 1: (1-2), dissolving metal tin salt and 2,4, 6-trihydroxybenzoic acid in ethanol, and adding a certain amount of m-phenylenediamine to form a mixed solution; the mol ratio of the m-phenylenediamine to the 2,4, 6-trihydroxybenzoic acid is 1: (1-2); adjusting the pH value of the mixed solution to 4-6, and stirring for 30-60 minutes at 40-70 ℃ to uniformly mix the solution;

b. putting the uniformly mixed solution into a polytetrafluoroethylene reaction kettle, reacting for 2-4 hours at 160-200 ℃, and then cooling to room temperature to obtain a product solution;

c. and (3) carrying out centrifugal separation treatment on the product solution, removing tin oxide, dialyzing by using a membrane with the molecular weight of 3500Da for at least 1 day, and removing small molecular substances, thereby obtaining the nitrogen-doped yellow carbon quantum dots.

2. The nitrogen-doped yellow carbon quantum dot of claim 1, wherein: the maximum excitation wavelength for the nitrogen-doped yellow carbon quantum dots to emit yellow fluorescence is 525nm.

3. The nitrogen-doped yellow carbon quantum dot of claim 2, wherein: under the excitation of light of 336-525 nm, yellow fluorescence can be emitted.

4. The nitrogen-doped yellow carbon quantum dot of claim 1, wherein: the maximum emission wavelength of yellow fluorescence is 568nm.

5. The nitrogen-doped yellow carbon quantum dot of claim 1, wherein: the surface of which is bonded with-COOH, -OH and-NH ₂ A group.

6. A method for preparing nitrogen-doped yellow carbon quantum dots according to claim 1, wherein the method comprises the following steps: the method for synthesizing the yellow carbon quantum dots by using the solvothermal method and taking 2,4, 6-trihydroxybenzoic acid as a carbon source, m-phenylenediamine as a nitrogen source and metallic tin salt as a catalyst comprises the following steps:

a. according to the molar ratio of the metallic tin salt to the 2,4, 6-trihydroxybenzoic acid of 1: (1-2), dissolving metal tin salt and 2,4, 6-trihydroxybenzoic acid in ethanol, and adding a certain amount of m-phenylenediamine to form a mixed solution; the mol ratio of the m-phenylenediamine to the 2,4, 6-trihydroxybenzoic acid is 1: (1-2); adjusting the pH value of the mixed solution to 4-6, and stirring for 30-60 minutes at 40-70 ℃ to uniformly mix the solution;

b. putting the uniformly mixed solution into a polytetrafluoroethylene reaction kettle, reacting for 2-4 hours at 160-200 ℃, and then cooling to room temperature to obtain a product solution;

c. and (3) carrying out centrifugal separation treatment on the product solution, removing tin oxide, dialyzing by using a membrane with the molecular weight of 3500Da for at least 1 day, and removing small molecular substances, thereby obtaining the nitrogen-doped yellow carbon quantum dots.

7. The method for preparing nitrogen-doped yellow carbon quantum dots according to claim 6, wherein the method comprises the following steps: the yellow carbon quantum dots with high fluorescence quantum efficiency are synthesized, and the highest absolute fluorescence quantum efficiency reaches 38%.

8. The method for preparing nitrogen-doped yellow carbon quantum dots according to claim 6, wherein the method comprises the following steps: in the step a, snCl is adopted as the tin salt ₄ ·5H ₂ O、SnCl ₄ 、SnCl ₂ ·2H ₂ O、SnCl ₂ And SnF ₂ Any one salt or a mixed salt of any several salts; or dissolving 1-2 mmol of 2,4, 6-trihydroxybenzoic acid and tin salt in at least 20mL ethanol.

9. The method for preparing nitrogen-doped yellow carbon quantum dots according to claim 6, wherein the method comprises the following steps: in the step b, the reaction is carried out at 160 to 180 ℃.

10. The method for preparing nitrogen-doped yellow carbon quantum dots according to claim 6, wherein the method comprises the following steps: in the step c, the concentration of the obtained nitrogen-doped yellow light carbon quantum dot solution is not less than 23mg/mL.

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