CN114457354A - Preparation method of nitrogen-doped carbon quantum dots - Google Patents

Abstract

The invention discloses a method for preparing nitrogen-doped carbon quantum dots. The method comprises the following steps: Step S1. Electrolyte configuration: use deionized water as solvent and amino acid as electrolyte to configure electrolyte; step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out liquid-phase plasma oxidation synthesis under the pulse voltage lower than 500V; step S3. Separation: centrifuge the reacted electrolyte and dry it Then carbon quantum dot powder is obtained. The method for preparing nitrogen-doped carbon quantum dots provided by the present invention adopts amino acid as the nitrogen source of the carbon source, water as the solvent, and liquid-phase plasma oxidation to synthesize carbon quantum dots, which not only has high production efficiency and yield, but also has low pulse voltage. , very safe, simple to operate, easy to implement, and can be popularized and applied in actual production. The prepared carbon quantum dots have good water solubility, small particle size, narrow particle size distribution, good quantum effect, and good application prospect.

Description

A kind of preparation method of nitrogen-doped carbon quantum dots

technical field

The invention relates to the technical field of carbon quantum dots, in particular to a preparation method of nitrogen-doped carbon quantum dots.

Background technique

Fluorescent chemical sensors have a wide range of applications in analytical chemistry, biochemistry, cell biology and many other fields due to their advantages of simple operation, good selectivity, high sensitivity, strong immediacy, and low detection limit. Fluorescent molecular probes have attracted much attention. Carbon nanodots (C-dots) are a new type of fluorescent nanomaterials based on carbon elements. In a wide range of visible light and near-infrared light, carbon quantum dots can achieve strong fluorescence up-conversion through single-photon and two-photon absorption. , and can act as electron donor or acceptor to generate photoinduced charge transfer. At the same time, carbon quantum dots have the characteristics of good biocompatibility and non-toxicity. Therefore, it has important application value in the fields of biological detection, photovoltaic devices and catalysis.

At present, the synthesis methods of carbon quantum dots include arc discharge method, laser irradiation method, thermal decomposition method, wet oxidation, ultrasonic synthesis, microwave assisted, electrochemical etching, hydrothermal method and so on. For example, Chinese invention patent CN201510903400.8 discloses a method for preparing carbon quantum dots by electrochemical etching; Chinese invention patent CN201310021590.1 discloses a method of hydrothermal synthesis or high-pressure microwave synthesis to prepare carbon quantum dots with fluorescent properties The Chinese invention patent with the application number of 201810285560.4 discloses a method for synthesizing carbon quantum dots by gas-phase detonation. Although the above method can realize the preparation of carbon quantum dots, there are generally defects such as low yield of carbon quantum dots, poor water solubility of the produced carbon quantum dots, and low fluorescence quantum yield, which makes the prepared carbon quantum dots suitable for use in electronic devices. , optoelectronic devices and biological markers and other fields are restricted.

Heteroatom doping is currently the main method to improve the fluorescence properties of carbon quantum dots. The study found that nitrogen (N) element doping into carbon quantum dots can promote the formation of various new surface states of carbon quantum dots, resulting in high photostability, surface passivation and good quantum yield. Chinese invention patent 201910164360.8 discloses a method for synthesizing nitrogen-doped carbon quantum dots based on ionic liquids; Chinese invention patent 202111253892.2 discloses a method for high-pressure hydrothermal synthesis of nitrogen-doped carbon quantum dots. The quantum probe realizes the detection of Fe ³⁺ with high selectivity and high sensitivity; Chinese invention patent 202111193402.4 discloses a method for high-pressure hydrothermal synthesis of nitrogen-doped carbon quantum dots; Chinese invention patent 2020103888835.4 discloses a high-pressure solvothermal method Methods for the synthesis of nitrogen-doped carbon quantum dots. Although the above method can realize nitrogen doping, it has the defects of low yield of carbon quantum dots, low fluorescence quantum ratio and complicated operation. Therefore, finding a new synthesis method with high yield, simple operation and high fluorescence quantum yield is the only way to realize the application of nitrogen-doped carbon quantum dots in the field of biofluorescence labeling.

In order to improve the yield of nitrogen-doped carbon quantum dots, the Chinese invention patent with the application number of 201410241942.9 discloses a method for preparing carbon quantum dots by a liquid-phase plasma discharge method. The method uses absolute ethanol as a solvent and aluminum nitrate as a solvent. Electrolyte, carbon quantum dots are synthesized by high voltage and short-time discharge, which have the characteristics of high yield and fast synthesis speed. However, this method uses anhydrous ethanol as a solvent, which is easy to cause fire during the plasma discharge process and lacks safety. In addition, the carbon quantum dots prepared by this method are oil-soluble carbon quantum dots, which lack stability in the aqueous phase. The Chinese invention patent with the application number CN202010374407.6 discloses a method and device for preparing carbon quantum dots based on the action of liquid-phase pulsed plasma. The method adopts urea and ascorbic acid as the reaction solution, and the voltage is 15-30kV and the frequency is 30 Nitrogen-doped carbon quantum dots are prepared by performing liquid-phase pulse plasma action under the condition of ~40 Hz. However, the voltage used in this method is 15-30kV, which is as high as the voltage at the time of lightning strike, which is extremely unsafe. It is easy to break down the equipment during the preparation process, and it is easy to generate electric sparks during the high-voltage discharge process. Therefore, the discharge environment is very demanding. It needs to be carried out under vacuum conditions. Once the air is humid, it is easy to break down the air and cause fire or explosion under the action of electric sparks. Therefore, this method requires special equipment and is simply impossible to implement in practical production applications.

It can be seen that the existing technology still needs to be improved and improved.

SUMMARY OF THE INVENTION

In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing nitrogen-doped carbon quantum dots, aiming to solve the problem of preparing nitrogen-doped carbon quantum dots by liquid plasma action in the prior art. rate and reduce its voltage to improve production safety.

In order to achieve the above object, the present invention has adopted the following technical solutions:

A method for preparing nitrogen-doped carbon quantum dots, wherein the method comprises the following steps:

Step S1. Configuration of the electrolyte: use deionized water as the solvent and amino acid as the electrolyte to configure the electrolyte;

Step S2. Synthesis: insert the cathode and the anode of the liquid plasma oxidation device into the electrolyte, and carry out liquid plasma oxidation synthesis under the pulse voltage lower than 500V;

Step S3. Separation: centrifuging the reacted electrolyte, and drying to obtain carbon quantum dot powder.

In the method for preparing nitrogen-doped carbon quantum dots, the concentration of amino acids in the electrolyte is 5-20 g/L.

In the method for preparing nitrogen-doped carbon quantum dots, the amino acid is serine or lysine.

In the method for preparing nitrogen-doped carbon quantum dots, in the step S2, the conditions for liquid-phase plasma oxidation synthesis are: a pulse voltage of 200V to 300V, a pulse frequency of 50Hz to 1000Hz, and a duty cycle of 10% to 10%. 35%, and the electrolyte temperature is 20°C to 40°C.

In the method for preparing nitrogen-doped carbon quantum dots, in the step S2, the liquid-phase plasma oxidation treatment time is 10-30 minutes.

In the preparation method of nitrogen-doped carbon quantum dots, in the step S1, the amino acid is serine, and the concentration of the serine is 16 g/L; in the step S2, the synthesis conditions are: the pulse voltage is 260V, The pulse frequency was 600 Hz, the duty ratio was 22%, the electrolyte temperature was 30° C., and the treatment time was 18 min.

In the method for preparing nitrogen-doped carbon quantum dots, in step S3, the rotational speed of the centrifuge is greater than 20,000 rpm during the centrifugation, and the centrifugation time is 3-10 minutes.

In the preparation method of nitrogen-doped carbon quantum dots, both the cathode and the anode of the liquid-phase plasma oxidation are stainless steel plates.

Beneficial effects:

The invention provides a method for preparing nitrogen-doped carbon quantum dots. The method adopts amino acid as a carbon source and can introduce nitrogen source at the same time. Therefore, the prepared carbon quantum dots contain nitrogen and have better fluorescence properties; Moreover, since amino acids are easily soluble in water, water can be used as a solvent. Compared with organic solvents, the water system has better safety. The pulse voltage during liquid-phase plasma oxidation is greatly reduced, so that when the carbon quantum dots are prepared by liquid-phase plasma technology in the prior art, it needs to be prone to breakdown under high-voltage conditions, causing safety problems such as fire or explosion. Liquid-phase plasma oxidation to prepare carbon ion dots not only has high efficiency and yield, but also is simple to operate and easy to implement, and can be popularized and applied in practical production.

The above preparation method of nitrogen-doped carbon quantum dots not only has a high yield of carbon quantum dots, but also the prepared carbon quantum dots have small particle size, narrow particle size distribution, and have better quantum effects. The water solubility is also good, which can make the subsequent application in the preparation of fluorescent probes more convenient, so it has better application prospects.

Description of drawings

1 is a transmission electron microscope image of the carbon quantum dots prepared in Example 1.

FIG. 2 is the XRD pattern of the carbon quantum dots prepared in Example 1. FIG.

FIG. 3 is a particle size distribution diagram of the carbon quantum dots prepared in Example 1. FIG.

Figure 4 is the full spectrum of the X-ray fluorescence spectrum of carbon quantum dots.

FIG. 5 is an upconversion characteristic spectrum of carbon quantum dots.

Detailed ways

The present invention provides a method for preparing nitrogen-doped carbon quantum dots. In order to make the purpose, technical solution and effect of the present invention clearer and clearer, the present invention is further described in detail with examples below. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

The invention discloses a method for preparing nitrogen-doped nitrogen-doped carbon quantum dots, which comprises the following steps:

Step S1. Electrolyte configuration: Deionized water is used as the solvent, and amino acid is used as the electrolyte to configure the electrolyte. Wherein, the electrolyte adopts a system using deionized water as a solvent. Compared with the organic solvent system in the prior art, in the process of plasma oxidation, no inert gas protection is required, which reduces the requirements for equipment and thus has better safety. performance. At the same time, the electrolyte uses amino acid as electrolyte, preferably water-soluble amino acid. Said amino acid is used as carbon source and nitrogen source. Under the oxidation of plasma, nitrogen-doped carbon quantum dots can be obtained. At the same time, because amino acid is a small molecular organic acid with good electrical conductivity, a large electric field can be obtained at a lower voltage, so the liquid plasma discharge voltage required is smaller, which can reduce energy consumption and improve the safety of the production process. sex.

Step S2. Synthesis: insert the cathode and anode of the liquid plasma oxidation device into the electrolyte, carry out liquid plasma oxidation synthesis under the pulse voltage lower than 500V, and obtain nitrogen-doped nitrogen through liquid plasma oxidation. Carbon quantum dots. The synthesis of carbon quantum dots by liquid-phase plasma oxidation has the characteristics of simple operation and high production efficiency, and the production process does not require atmosphere protection or vacuum conditions, which is a low-cost and high-efficiency synthesis method. In addition, since amino acid is used as carbon source and water is used as solvent, it has good electrical conductivity, so the oxidation voltage of liquid plasma is lower, and the production safety is greatly improved.

Step S3. Separation: centrifuging the reacted electrolyte, separating the supernatant liquid, and drying the lower layer powder to obtain carbon quantum dot powder. The synthesized carbon quantum dots can be separated from water by centrifugation. The separation steps are simple and easy to implement.

As an embodiment, in the above-mentioned preparation method of nitrogen-doped nitrogen-doped carbon quantum dots, in the electrolyte, the concentration of amino acid is 5-20 g/L. The concentration of amino acid is a key factor affecting the yield, particle size and particle size distribution of carbon quantum dots. Fluorescence properties of quantum dots are quenched. When the concentration of amino acid is low, although carbon quantum dots with small particle size can be obtained, the yield is low and it is difficult to obtain by centrifugation. When the concentration of amino acid is 5-20 g/L, carbon quantum dots with small particle size and narrow particle size distribution can be obtained, which do not agglomerate and have better fluorescence properties.

As a preferred embodiment, in the above-mentioned preparation method of nitrogen-doped carbon quantum dots, the amino acid is serine or lysine, and the serine and lanolin are small molecular amino acids, which are easily soluble in water and have electrical conductivity. Good, and the nitrogen content in the molecule is high, carbon quantum dots with high nitrogen doping content can be prepared, and the fluorescent performance is good, and the yield of carbon quantum dots can be improved.

In some preferred embodiments, in the method for preparing nitrogen-doped carbon quantum dots, the synthesis conditions in step S2 are: a pulse voltage of 200V to 300V, a pulse frequency of 50Hz to 1000Hz, and a duty cycle of 10%. ~ 35%, electrolyte temperature is 20 ℃ ~ 40 ℃.

In the above synthesis conditions, the higher the pulse voltage, the faster the synthesis speed of carbon quantum dots, which can improve the generation efficiency. However, the faster the reaction speed is, the larger the particle size of the obtained carbon quantum dots will be, which is easy to cause fluorescence. Performance quenching. This is because the higher the voltage, the greater the probability of collision between ions, and the faster the reaction speed. However, when the reaction speed is too fast, the generated carbon quantum dots are more likely to agglomerate, which in turn makes the particle size of the carbon quantum dots larger. , resulting in a decrease in the fluorescence performance of carbon quantum dots. Therefore, in order to improve the fluorescence performance, it is usually necessary to reduce the pulse voltage so that the reaction speed is not too fast. When the selected pulse voltage is 200V-300V, it not only has a better reaction speed, but also can obtain carbon quantum dots with smaller particle size. The pulse frequency, duty cycle and electrolyte temperature will also affect the synthesis speed of carbon quantum dots. The lower the frequency, the larger the duty cycle, and the higher the temperature, the faster the synthesis speed of carbon quantum dots, but the faster the synthesis speed. , the particle size of the obtained carbon quantum dots will be larger, and the larger the particle size of the carbon quantum dots, the lower the quantum efficiency. This is because, when the particle size of the carbon quantum dots is larger, the possibility of light passing through the carbon quantum is less, and the possibility of refraction and diffraction recombination of light of a certain wavelength is less, thus reducing the quantum efficiency. When the pulse voltage is 200V～300V, the pulse frequency is 50Hz～1000Hz, the duty ratio is 10%～35%, and the electrolyte temperature is 20℃～40℃, it not only has a faster synthesis speed, but also the synthesized carbon quantum The dot particle size is small, the particle size distribution is narrow, and it has better fluorescence performance.

Preferably, under the above synthesis conditions, the reaction time of the liquid phase plasma oxidation is 10-30 min. Since the oxidation reaction time will affect the yield and particle size of the carbon quantum dots, the longer the reaction time, the higher the yield. However, if the time is too long, the prepared carbon quantum dots tend to agglomerate and increase the particle size. Therefore, when the pulse voltage is 200V～300V, the pulse frequency is 50Hz～1000Hz, the duty ratio is 10%～35%, and the electrolyte temperature is 20℃～40℃, the reaction time is controlled to be 10～30min, which can obtain higher yield and smaller particle size.

In some embodiments, in the above method for preparing nitrogen-doped carbon quantum dots, the electrode is a stainless steel plate, that is, both the cathode and the anode of the liquid-phase plasma discharge are stainless steel plates. Using a stainless steel plate as an electrode not only has good electrical conductivity and low cost, but also does not affect the fluorescence properties of carbon quantum dots.

Preferably, in the above-mentioned preparation method of nitrogen-doped carbon quantum dots, in the step S3, the rotational speed of the centrifuge is greater than 20,000 rpm during the centrifugation, and the centrifugation time is 3-10 minutes. Due to the small particle size of the synthesized carbon quantum dots, a high centrifuge speed is required to separate the carbon quantum dots from water, otherwise the yield of the carbon quantum dots will be affected.

As a preferred method for preparing nitrogen-doped carbon quantum dots, in the step S1, the electrolyte is serine, and the concentration of serine is 16 g/L, and in the step S2, the liquid-phase plasma oxidation synthesis conditions are: The pulse voltage was 260V, the pulse frequency was 600Hz, the duty ratio was 22%, the electrolyte temperature was 30°C, and the treatment time was 18min. The method has high yield of carbon quantum dots, and the obtained carbon quantum dots have a small particle size, the particle size is mainly distributed in 4-6 nm, the quantum efficiency is high, and the nitrogen doping amount is high, and the fluorescence performance is good.

The above-mentioned preparation method of nitrogen-doped nitrogen-doped carbon quantum dots adopts an aqueous solution system. Compared with the existing organic solution system, in the plasma oxidation process, no special vacuum conditions are required, and no inert gas protection is required. Fire is safer; amino acid is used as carbon source and nitrogen source. Since amino acid is a small molecular organic acid, it has good water solubility and conductivity, which can reduce the pulse voltage, thereby reducing the requirements for liquid plasma oxidation equipment, and making the synthesis conditions It is safer and easier to implement, and can then be applied in actual production; using a lower synthesis voltage, the excess voltage of 15-30kV in the prior art is reduced to 200-300v, so it can reduce energy consumption and improve the safety of the synthesis process. At the same time, ordinary DC or AC power supply can be achieved without a high-voltage power supply system, thereby reducing the dependence on special equipment.

The above-mentioned preparation method of nitrogen-doped carbon quantum dots not only has a high yield of carbon quantum dots, but also the prepared carbon quantum dots have small particle size and narrow particle size distribution, have better quantum effect, and at the same time, have good water solubility. , which can make the subsequent application in the preparation of fluorescent probes more convenient, so it has better application prospects.

To further illustrate the preparation method of nitrogen-doped carbon quantum dots provided by the present invention, the following examples are provided.

Example 1

A preferred method for preparing nitrogen-doped carbon quantum dots, the method includes the following steps: Step S1. Electrolyte configuration: using deionized water as a solvent and serine as an electrolyte to configure an electrolyte, wherein the concentration of serine is 16g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty cycle is 22%, The electrolyte temperature is 30°C, and the treatment time is 18min;

Step S3. Separation: Centrifuge the reacted electrolyte, the rotating speed of the centrifuge is 25000 rpm, the centrifugation time is 5min, the supernatant is discarded after centrifugation, and the solid is dried to obtain carbon quantum dot powder.

Example 2

A preparation method of nitrogen-doped carbon quantum dots, the method comprises the following steps:

Step S1. the configuration of the electrolyte: use deionized water as a solvent, use serine as an electrolyte, configure an electrolyte, wherein the concentration of serine is 5g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 200V, the pulse frequency is 50Hz, the duty cycle is 35%, The temperature of the electrolyte is 40° C., and the liquid-phase plasma oxidation treatment time is 10 minutes; Step S3. Separation: centrifuge the reacted electrolyte, the rotating speed of the centrifuge is 30,000 rpm, the centrifugation time is 10 minutes, and the centrifugation is discarded. The supernatant was removed, and the solid was dried to obtain carbon quantum dot powder.

Example 3

A preparation method of nitrogen-doped carbon quantum dots, the method comprises the following steps:

Step S1. The configuration of the electrolyte: take deionized water as the solvent, and use the serine as the electrolyte to configure the electrolyte, wherein the concentration of the serine is 20g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 300V, the pulse frequency is 1000Hz, the duty ratio is 10%, The temperature of the electrolyte is 20°C, and the liquid-phase plasma oxidation treatment time is 30 minutes; Step S3. Separation: centrifuging the reacted electrolyte, the rotating speed of the centrifuge is 20,000 rpm, and the centrifugation time is 10 minutes, and discarded after centrifugation. The supernatant was removed, and the solid was dried to obtain carbon quantum dot powder.

Example 4

A preparation method of nitrogen-doped carbon quantum dots, the method comprises the following steps:

Step S1. The configuration of the electrolyte solution: take deionized water as the solvent and lysine as the electrolyte to configure the electrolyte solution, wherein the concentration of lysine is 15g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 250V, the pulse frequency is 500Hz, the duty cycle is 25%, The temperature of the electrolyte is 30° C., and the liquid-phase plasma oxidation treatment time is 15 minutes; step S3. Separation: centrifuge the reacted electrolyte, the rotating speed of the centrifuge is 30,000 rpm, the centrifugation time is 5 minutes, and the centrifugation is discarded. The supernatant was removed, and the solid was dried to obtain carbon quantum dot powder.

Example 5

A preferred preparation method of nitrogen-doped carbon quantum dots, the method comprises the following steps: Step S1. Electrolyte configuration: using deionized water as a solvent and lysine as an electrolyte to configure an electrolyte, wherein serine The concentration is 10g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 230V, the pulse frequency is 200Hz, the duty cycle is 15%, The temperature of the electrolyte is 25° C., and the liquid-phase plasma oxidation treatment time is 25 minutes; step S3. Separation: centrifuging the reacted electrolyte, the rotating speed of the centrifuge is 25,000 rpm, and the centrifugation time is 8 minutes, and discarded after centrifugation. The supernatant was removed, and the solid was dried to obtain carbon quantum dot powder.

Example 6

A preferred method for preparing nitrogen-doped carbon quantum dots, the method includes the following steps: Step S1. Electrolyte configuration: using deionized water as a solvent and glycine as an electrolyte to configure an electrolyte, wherein the concentration of glycine is is 16g/L;

Step S2. Synthesis: insert the cathode and the anode of the liquid-phase plasma oxidation device into the electrolyte, and carry out the liquid-phase plasma oxidation synthesis. The synthesis conditions are: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty cycle is 22%, The electrolyte temperature is 30°C, and the treatment time is 18min;

Step S3. Separation: Centrifuge the reacted electrolyte, the rotating speed of the centrifuge is 25000 rpm, the centrifugation time is 5min, the supernatant is discarded after centrifugation, and the solid is dried to obtain carbon quantum dot powder.

Characterization and Performance Testing

Carry out standard characterization and performance test with the carbon quantum dots prepared in Example 1, and the specific test results are as follows:

1 is a transmission electron microscope image of the carbon quantum dots prepared in Example 1. As can be seen from the figure, the particle size of the carbon quantum dots prepared by the present invention is 3-8 nm, which is very small, and therefore has good fluorescence properties.

Figure 2 is the XRD pattern of the carbon quantum dots prepared in Example 1. As can be seen from the figure, a mandolin peak appears in the diffraction pattern near 25 degrees, which corresponds to the (002) crystal plane of graphite, which proves that the prepared carbon quantum dots The dots are graphitized carbon quantum dots with good quantum effects.

Figure 3 is a particle size distribution diagram of the carbon quantum dots prepared in Example 1. It can be seen from the figure that the particle size of the carbon quantum dots is small and the distribution is narrow, mainly between 4.5-6.5. Has good fluorescence properties.

Figure 4 is the full spectrum of the X-ray fluorescence spectrum of carbon quantum dots. It can be seen from the figure that the carbon quantum dots are mainly composed of carbon, oxygen and nitrogen elements, wherein the atomic content of carbon is about 90%, and the atomic content of oxygen is about 70%. %, the atomic content of nitrogen is about 3%. It can be seen that nitrogen element is doped into the carbon quantum dots, thereby improving the fluorescence properties of the carbon quantum dots.

Figure 5 is the up-conversion characteristic spectrum of carbon quantum dots. It can be seen from the figure that the synthesized carbon quantum dots have typical fluorescence up-conversion characteristics. The wavelengths of the emitted light are 420nm, 440nm, 460nm, 480nm, and 500nm respectively, which shows that when the light passes through the carbon quantum dots, the wavelengths become smaller through the up-conversion of the carbon quantum dots. In practical applications, the energy of short wavelengths is greater. Therefore, when light of long wavelengths passes through the carbon quantum dots, the energy of the waves can be increased, which has a wide range of applications in biomedicine.

To sum up, the present invention discloses a method for preparing nitrogen-doped carbon quantum dots. The method adopts amino acid as a carbon source, and nitrogen source can be introduced at the same time. Therefore, the prepared carbon quantum dots contain nitrogen, and have relatively high performance. good fluorescence performance; and, because amino acids are easily soluble in water, water can be used as a solvent. Compared with organic solvents, the water system has better safety. At the same time, amino acids with small molecular structure are used as electrolytes. It can greatly reduce the pulse voltage during liquid-phase plasma oxidation, and solve the problem that when carbon quantum dots are prepared by liquid-phase plasma technology in the prior art, it needs to be easily broken down under high pressure conditions, causing fire or explosion. In addition, the use of liquid-phase plasma oxidation to prepare carbon ion dots not only has high efficiency and yield, but also is simple to operate and easy to implement, which can be popularized and applied in actual production.

It can be understood that for those of ordinary skill in the art, equivalent replacements or changes can be made according to the technical solutions of the present invention and the inventive concept thereof, and all these changes or replacements should belong to the protection scope of the appended claims of the present invention.

Claims (8)

1. a preparation method of nitrogen-doped carbon quantum dots, is characterized in that, described method comprises the following steps: Step S1. Configuration of the electrolyte: use deionized water as the solvent and amino acid as the electrolyte to configure the electrolyte; Step S2. Synthesis: insert the cathode and the anode of the liquid plasma oxidation device into the electrolyte, and carry out liquid plasma oxidation synthesis under the pulse voltage lower than 500V; Step S3. Separation: centrifuging the reacted electrolyte, and drying to obtain carbon quantum dot powder. 2 . The method for preparing nitrogen-doped carbon quantum dots according to claim 1 , wherein the concentration of amino acid in the electrolyte is 5-20 g/L. 3 . 3 . The method for preparing nitrogen-doped carbon quantum dots according to claim 2 , wherein the amino acid is serine or lysine. 4 . 4 . The method for preparing nitrogen-doped carbon quantum dots according to claim 1 , wherein, in the step S2 , the conditions for liquid-phase plasma oxidation synthesis are: a pulse voltage of 200V to 300V and a pulse frequency of 50Hz. 5 . ~1000Hz, duty cycle of 10% to 35%, and electrolyte temperature of 20°C to 40°C. 5 . The method for preparing nitrogen-doped carbon quantum dots according to claim 1 , wherein, in the step S2 , the liquid-phase plasma oxidation treatment time is 10-30 min. 6 . 6. The method for preparing nitrogen-doped carbon quantum dots according to claim 1, wherein in the step S1, the amino acid is serine, and the concentration of the serine is 16 g/L; in the step S2 , the synthesis conditions are: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty cycle is 22%, the electrolyte temperature is 30°C, and the treatment time is 18min. 7 . The method for preparing nitrogen-doped carbon quantum dots according to claim 1 , wherein, in the step S3 , the rotation speed of the centrifuge is greater than 20,000 rpm during centrifugation, and the centrifugation time is 3-10 minutes. 8 . 8 . The method for preparing nitrogen-doped carbon quantum dots according to claim 1 , wherein the cathode and the anode of the liquid-phase plasma oxidation are both stainless steel plates. 9 .

Images