CN114457354A - Preparation method of nitrogen-doped carbon quantum dots - Google Patents
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Abstract
The invention discloses a preparation method of nitrogen-doped carbon quantum dots, which comprises the following steps: s1, preparing electrolyte: preparing an electrolyte by taking deionized water as a solvent and amino acid as an electrolyte; step S2, synthesis: inserting a cathode and an anode of a liquid phase plasma oxidation device into electrolyte, and performing liquid phase plasma oxidation synthesis under a pulse voltage lower than 500V; s3, separation: and centrifuging the reacted electrolyte, and drying to obtain carbon quantum dot powder. The preparation method of the nitrogen-doped carbon quantum adopts amino acid as a nitrogen source of a carbon source, water as a solvent and liquid-phase plasma for oxidation synthesis of the carbon quantum dots, and has the advantages of high production efficiency and yield, low pulse voltage, safety, simple operation, easy realization and popularization and application in actual production. The prepared carbon quantum dots have the advantages of good water solubility, small particle size, narrow particle size distribution, good quantum effect and good application prospect.
Description
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
The fluorescence chemical sensor has the advantages of simple operation, good selectivity, high sensitivity, strong instantaneity, low detection limit and the like, is widely applied to various fields of analytical chemistry, biochemistry, cell biology and the like, and is concerned by people in designing and synthesizing various effective fluorescent molecular probes. The carbon nano-dots (C-dots) are a novel fluorescent nano-material taking carbon elements as main bodies, can realize strong fluorescence up-conversion by single photon and two-photon absorption in a wide visible light and near infrared light range, and can be used as an electron donor or an acceptor to generate photoinduced charge transfer. Meanwhile, the carbon quantum dots have the characteristics of good biocompatibility, no toxicity and the like. Therefore, the method 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 methods, laser radiation methods, thermal decomposition methods, wet oxidation, ultrasonic synthesis, microwave assistance, electrochemical etching, hydrothermal methods and the like. For example, chinese invention patent CN201510903400.8 discloses a method for preparing carbon quantum dots by electrochemical etching; the Chinese invention patent CN201310021590.1 discloses a method for preparing carbon quantum dots with fluorescence characteristic by adopting hydrothermal synthesis or high-pressure microwave synthesis; the chinese patent application No. 201810285560.4 discloses a method for synthesizing carbon quantum dots by a gas phase detonation method. Although the method can realize the preparation of the carbon quantum dots, the method generally has the defects of low yield of the carbon quantum dots, poor water solubility of the generated carbon quantum dots, low fluorescence quantum yield and the like, and further limits the application of the prepared carbon quantum dots in the fields of electronic devices, photoelectric devices, biomarkers and the like.
Heteroatom doping is the main method currently used to improve the fluorescence properties of carbon quantum dots. Research shows that nitrogen (N) element is doped into the carbon quantum dots, so that the carbon quantum dots can be promoted to form a plurality of new surface states, and high light stability, surface passivation and good quantum yield are achieved. Chinese patent 201910164360.8 discloses a method for synthesizing nitrogen based on ionic liquidA method of doping carbon quantum dots; chinese patent 202111253892.2 discloses a method for synthesizing nitrogen-doped carbon quantum dots by high-pressure hydrothermal method, and the nitrogen-doped carbon quantum dots synthesized by the method realize Fe-doping3+High selectivity and high sensitivity detection; the chinese invention patent 202111193402.4 discloses a method for high pressure hydrothermal synthesis of nitrogen-doped carbon quantum dots; the chinese invention patent 2020103888835.4 discloses a method for high pressure solvothermal synthesis of nitrogen-doped carbon quantum dots. Although the method can realize nitrogen doping, the method has the defects of low yield of carbon quantum dots, low fluorescence quantum ratio and complex operation. Therefore, the search for a new synthesis method with high yield, simple operation and high fluorescence quantum yield is a necessary way for realizing the application of the nitrogen-doped carbon quantum dots in the field of biological fluorescence labeling.
In order to improve the yield of nitrogen-doped carbon quantum dots, the chinese patent application No. 201410241942.9 discloses a method for preparing carbon quantum dots by a liquid-phase plasma discharge method, which synthesizes carbon quantum dots by high-voltage short-time discharge using absolute ethyl alcohol as a solvent and aluminum nitrate as an electrolyte, and has the characteristics of high yield, high synthesis speed and the like. However, this method uses absolute ethyl alcohol as a solvent, easily causes fire during plasma discharge, and lacks safety, and in addition, the carbon quantum dots prepared by this method are oil-soluble carbon quantum dots, and lack stability in aqueous phase. The Chinese patent with the application number of CN202010374407.6 discloses a method and a device for preparing carbon quantum dots based on the action of liquid-phase pulse plasma, wherein urea and ascorbic acid are used as reaction liquid, and the liquid-phase pulse plasma action is carried out under the conditions that the voltage is 15-30 kV and the frequency is 30-40 Hz to prepare the nitrogen-doped carbon quantum dots. However, the voltage adopted by the method is 15-30 kV, is extremely unsafe as high as the voltage in lightning stroke, and is easy to break down equipment in the preparation process, and electric sparks are easy to generate in the high-voltage discharge process, so that the method has extremely high requirements on the discharge environment, needs to be carried out under the vacuum condition, is easy to break down air once the air is moist, and causes fire or explosion under the action of the electric sparks. Therefore, the method requires special equipment and cannot be realized at all in practical production application.
It is seen that improvements and enhancements to the prior art are needed.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide a preparation method of nitrogen-doped carbon quantum dots, and aims to solve the problems that in the prior art, the yield of the nitrogen-doped carbon quantum dots prepared by adopting the liquid phase plasma effect is high, the voltage of the nitrogen-doped carbon quantum dots is reduced, and the production safety is improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of nitrogen-doped carbon quantum dots comprises the following steps:
s1, preparing electrolyte: preparing an electrolyte by taking deionized water as a solvent and amino acid as an electrolyte;
step S2, synthesis: inserting a cathode and an anode of a liquid phase plasma oxidation device into electrolyte, and performing liquid phase plasma oxidation synthesis under a pulse voltage lower than 500V;
s3, separation: and centrifuging the reacted electrolyte, and drying to obtain carbon quantum dot powder.
In the preparation method of the nitrogen-doped carbon quantum dot, the concentration of amino acid in the electrolyte is 5-20 g/L.
In the preparation method of the nitrogen-doped carbon quantum dot, the amino acid is serine or lysine.
In the preparation method of the nitrogen-doped carbon quantum dot, in the step S2, the conditions of the liquid-phase plasma oxidation synthesis are as follows: the pulse voltage is 200V-300V, the pulse frequency is 50 Hz-1000 Hz, the duty ratio is 10% -35%, and the temperature of the electrolyte is 20-40 ℃.
In the preparation method of the nitrogen-doped carbon quantum dot, in the step S2, the liquid-phase plasma oxidation treatment time is 10-30 min.
In the preparation method of the nitrogen-doped carbon quantum dot, in the step S1, the amino acid is serine, and the concentration of the serine is 16 g/L; in step S2, the synthesis conditions are: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty ratio is 22%, the temperature of the electrolyte is 30 ℃, and the processing time is 18 min.
In the preparation method of the nitrogen-doped carbon quantum dot, in the step S3, the rotation speed of a centrifuge during centrifugation is greater than 20000 revolutions per minute, and the centrifugation time is 3-10 min.
In the preparation method of the nitrogen-doped carbon quantum dot, the cathode and the anode of the liquid phase plasma oxidation are both stainless steel plates.
Has the advantages that:
the invention provides a preparation method of nitrogen-doped carbon quantum, which adopts amino acid as a carbon source and can introduce a nitrogen source simultaneously, so that the prepared carbon quantum dot contains nitrogen and further has better fluorescence performance; and because the amino acid is easy to dissolve in water, a water system has better safety compared with an organic solvent, meanwhile, the amino acid with a small molecular structure is used as an electrolyte, the amino acid has better conductivity, the pulse voltage during liquid phase plasma oxidation can be greatly reduced, the safety problems that in the prior art, when the carbon quantum dots are prepared by adopting a liquid phase plasma technology, breakdown is easy to occur under a high pressure condition to cause fire or explosion and the like are solved, and the carbon ion dots are prepared by adopting the liquid phase plasma oxidation, so that the efficiency and the yield are high, the operation is simple, the implementation is easy, and the carbon ion dots can be popularized and applied in actual production.
The preparation method of the nitrogen-doped carbon quantum dot has the advantages that the yield of the carbon quantum dot is high, the prepared carbon quantum dot is small in particle size and narrow in particle size distribution, and has a good quantum effect, and meanwhile, the carbon quantum dot is good in water solubility, so that the subsequent application in preparation of a fluorescent probe is more convenient, and the preparation method has a better application prospect.
Drawings
FIG. 1 is a transmission electron micrograph of a carbon quantum dot prepared in example 1.
Fig. 2 is an XRD pattern of the carbon quantum dot prepared in example 1.
Fig. 3 is a particle size distribution diagram of carbon quantum dots prepared in example 1.
FIG. 4 is a full spectrum of X-ray fluorescence spectrum of carbon quantum dots.
Fig. 5 is an upconversion characteristic spectrum of a carbon quantum dot.
Detailed Description
The invention provides a preparation method of nitrogen-doped carbon quantum dots, and in order to make the purpose, technical scheme and effect of the invention clearer and clearer, the invention is further described in detail by the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention discloses a preparation method of nitrogen-doped carbon quantum dots, which comprises the following steps:
s1, preparing electrolyte: deionized water is used as a solvent, and amino acid is used as an electrolyte to prepare an electrolyte. The electrolyte adopts a system with deionized water as a solvent, and compared with the organic solvent system in the prior art, the electrolyte does not need inert gas protection in the plasma oxidation process, reduces the requirement on equipment and further has better safety performance. Meanwhile, the electrolyte takes amino acid as electrolyte, preferably water-soluble amino acid, and the amino acid is taken as a carbon source and a nitrogen source, so that the carbon quantum dots doped with nitrogen can be obtained under the oxidation action of plasma. Meanwhile, as the amino acid is a small molecular organic acid, the conductivity is good, and a larger electric field can be obtained at a lower voltage, the discharge voltage of the required liquid phase plasma is smaller, so that the energy consumption can be reduced, and the safety of the production process can be improved.
Step S2, synthesis: inserting a cathode and an anode of a liquid phase plasma oxidation device into electrolyte, performing liquid phase plasma oxidation synthesis under the pulse voltage lower than 500V, and obtaining the nitrogen-doped carbon quantum dots through the liquid phase plasma oxidation. The method for synthesizing the carbon quantum dots by adopting the liquid-phase plasma oxidation has the characteristics of simple operation and high production efficiency, does not need atmosphere protection or vacuum condition in the production process, and is a low-cost and high-efficiency synthesis method. In addition, as amino acid is used as a carbon source and water is used as a solvent, the conductive performance is better, so that the oxidation voltage of the liquid phase plasma is lower, and the production safety is greatly improved.
S3, separation: and (3) centrifuging the reacted electrolyte, separating supernatant liquor, and drying lower-layer powder to obtain carbon quantum dot powder. The carbon quantum dots obtained by synthesis can be separated from water by centrifugal separation. The separation steps are simple and easy to realize.
In one embodiment, in the method for manufacturing the nitrogen-doped and nitrogen-doped carbon quantum dot, the concentration of the amino acid in the electrolyte is 5 to 20 g/L. The concentration of amino acid is a key factor influencing the yield, the particle size and the particle size distribution of the carbon quantum dots, and the yield of the carbon quantum dots is higher when the concentration is higher, but the carbon quantum dots are easy to agglomerate to form the carbon quantum dots with larger particle sizes, so that the fluorescence characteristics of the carbon quantum dots are quenched. When the concentration of the amino acid is low, carbon quantum dots having a small particle size can be obtained, but the yield is low and it is difficult to obtain the carbon quantum dots by centrifugation. When the concentration of the amino acid is 5-20 g/L, carbon quantum dots with small particle size and narrow particle size distribution can be obtained, and the carbon quantum dots do not agglomerate and have good fluorescence characteristics.
As a preferred embodiment, in the above method for preparing nitrogen-doped carbon quantum dots, the amino acid is serine or lysine, the serine and the lysine are small-molecule amino acids, and are easily soluble in water, have good conductivity, and have a high nitrogen content in a molecule, so that carbon quantum dots with a high nitrogen-doped content can be prepared, have good fluorescence properties, and can improve the yield of the carbon quantum dots.
In some preferred embodiments, in the method for preparing nitrogen-doped carbon quantum dots, the synthesis conditions of step S2 are as follows: the pulse voltage is 200V-300V, the pulse frequency is 50 Hz-1000 Hz, the duty ratio is 10% -35%, and the temperature of the electrolyte is 20-40 ℃.
Under the above-mentioned conditions, the higher the pulse voltage, the higher the rate of synthesizing the carbon quantum dots, and the higher the production efficiency, however, the higher the reaction rate, the larger the particle size of the obtained carbon quantum dots, and the more easily the fluorescence properties are quenched. This is because the higher the voltage, the higher the probability of ion collision, the faster the reaction rate, but when the reaction rate is too high, the more easily the formed carbon quantum dots are agglomerated, and further the larger the particle size of the carbon quantum dots, the lower the fluorescence performance of the carbon quantum dots, so that in order to improve the fluorescence performance, it is generally necessary to reduce the pulse voltage so that the reaction rate is not too high. When the pulse voltage is selected to be 200V-300V, the reaction speed is better, and carbon quantum dots with smaller particle size can be obtained. The pulse frequency, duty ratio and electrolyte temperature also influence the synthesis speed of the carbon quantum dots, the lower the frequency, the larger the duty ratio and the higher the temperature, the faster the synthesis speed of the carbon quantum dots is, but the faster the synthesis speed is, the larger the particle size of the obtained carbon quantum dots is, and the larger the particle size of the carbon quantum dots is, the lower the quantum efficiency is. This is because, when the particle size of the carbon quantum dot is large, the probability that light passes through the carbon quantum is small, the probability that light of a certain wavelength is refracted and diffracted and recombined is small, and the quantum efficiency is further reduced. When the pulse voltage is 200V-300V, the pulse frequency is 50 Hz-1000 Hz, the duty ratio is 10% -35%, and the temperature of the electrolyte is 20-40 ℃, the synthesis speed is high, and the synthesized carbon quantum dots have small particle size, narrow particle size distribution and good fluorescence performance.
Preferably, under the synthesis conditions, the liquid phase plasma oxidation reaction time is 10-30 min. Since the time of the oxidation reaction affects the yield and the particle size of the carbon quantum dots, the yield is higher the longer the reaction time is, but the longer the reaction time is, the agglomeration of the prepared carbon quantum dots is easily caused, and the particle size is increased. Therefore, when the pulse voltage is 200V-300V, the pulse frequency is 50 Hz-1000 Hz, the duty ratio is 10% -35%, and the temperature of the electrolyte is 20-40 ℃, the reaction time is controlled to be 10-30 min, and higher yield and smaller particle size can be obtained.
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. The stainless steel plate is used as an electrode, so that the conductive performance is better, the cost is low, and the fluorescence performance of the carbon quantum dots is not influenced.
Preferably, in the above method for preparing nitrogen-doped carbon quantum dots, in step S3, the rotation speed of the centrifuge during the centrifugation is greater than 20000 rpm, and the centrifugation time is 3-10 min. The carbon quantum dots obtained by synthesis have small particle size, so that the carbon quantum dots and water can be separated by a high centrifuge rotating speed, otherwise, the yield of the carbon quantum dots is influenced.
As a preferred method for preparing nitrogen-doped carbon quantum dots, in step S1, the electrolyte is serine, and the concentration of the serine is 16g/L, and in step S2, the conditions of the liquid-phase plasma oxidation synthesis are that the pulse voltage is 260V, the pulse frequency is 600Hz, the duty ratio is 22%, the temperature of the electrolyte is 30 ℃, and the treatment time is 18 min. The method has the advantages of high yield of the carbon quantum dots, small particle size of the obtained carbon quantum dots, high quantum efficiency, high nitrogen doping amount and good fluorescence performance, and the particle size of the obtained carbon quantum dots is mainly distributed in the range of 4-6 nm.
Compared with the existing organic solution system, the preparation method of the nitrogen-doped carbon quantum dot adopts the aqueous solution system, does not need special vacuum condition and inert gas protection in the plasma oxidation process, does not generate fire and is safer; amino acid is used as a carbon source and a nitrogen source, and because the amino acid is a micromolecular organic acid, the water solubility and the conductivity are good, the pulse voltage can be reduced, the requirement on liquid-phase plasma oxidation equipment is further reduced, the synthesis condition is safer and easier to realize, and the amino acid can be applied to actual production; the lower synthetic voltage is adopted, the voltage is reduced to 200-300 v from the voltage exceeding 15-30 kV in the prior art, so that the energy consumption can be reduced, the safety of the synthetic process is improved, meanwhile, a high-voltage power supply system is not needed, a common direct current or alternating current power supply can be realized, and the dependence on special equipment is further reduced.
The preparation method of the nitrogen-doped carbon quantum dot has the advantages that the yield of the carbon quantum dot is high, the prepared carbon quantum dot is small in particle size and narrow in particle size distribution, and has a good quantum effect, meanwhile, the water solubility is good, and the subsequent application in preparation of a fluorescent probe is more convenient, so that the preparation method has a better application prospect.
To further illustrate the preparation method of the nitrogen-doped carbon quantum dot provided by the present invention, the following examples are provided.
Example 1
A preferred method of fabricating nitrogen doped carbon quantum dots, the method comprising the steps of: s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and serine as electrolyte, wherein the concentration of the serine is 16 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty ratio is 22%, the temperature of the electrolyte is 30 ℃, and the processing time is 18 min;
s3, separation: and centrifuging the reacted electrolyte at the rotating speed of 25000 r/min for 5min, discarding supernatant liquor after centrifugation, and drying the solid to obtain the carbon quantum dot powder.
Example 2
A preparation method of nitrogen-doped carbon quantum dots comprises the following steps:
s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and serine as electrolyte, wherein the concentration of the serine is 5 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 200V, the pulse frequency is 50Hz, the duty ratio is 35 percent, the temperature of the electrolyte is 40 ℃, and the oxidation treatment time of the liquid-phase plasma is 10 min; s3, separation: and (3) centrifuging the reacted electrolyte at the rotation speed of 30000 r/min for 10min, discarding supernatant liquor after centrifugation, and drying the solid to obtain the carbon quantum dot powder.
Example 3
A preparation method of nitrogen-doped carbon quantum dots comprises the following steps:
s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and serine as electrolyte, wherein the concentration of the serine is 20 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 300V, the pulse frequency is 1000Hz, the duty ratio is 10%, the electrolyte temperature is 20 ℃, and the liquid-phase plasma oxidation treatment time is 30 min; s3, separation: and (3) centrifuging the reacted electrolyte, wherein the rotating speed of a centrifuge is 20000 revolutions per minute, the centrifuging time is 10min, discarding supernatant liquid after centrifuging, and drying the solid to obtain carbon quantum dot powder.
Example 4
A preparation method of nitrogen-doped carbon quantum dots comprises the following steps:
s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and lysine as electrolyte, wherein the concentration of the lysine is 15 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 250V, the pulse frequency is 500Hz, the duty ratio is 25%, the temperature of the electrolyte is 30 ℃, and the oxidation treatment time of the liquid-phase plasma is 15 min; s3, separation: and (3) centrifuging the reacted electrolyte, wherein the rotating speed of a centrifuge is 30000 r/min, the centrifuging time is 5min, discarding supernatant liquid after centrifuging, and drying the solid to obtain carbon quantum dot powder.
Example 5
A preferred method of fabricating nitrogen doped carbon quantum dots, the method comprising the steps of: s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and lysine as electrolyte, wherein the concentration of serine is 10 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 230V, the pulse frequency is 200Hz, the duty ratio is 15%, the temperature of the electrolyte is 25 ℃, and the oxidation treatment time of the liquid-phase plasma is 25 min; s3, separation: and (3) centrifuging the reacted electrolyte, wherein the rotating speed of a centrifuge is 25000 r/min, the centrifuging time is 8min, discarding supernatant liquor after centrifuging, and drying the solid to obtain carbon quantum dot powder.
Example 6
A preferred method for preparing nitrogen-doped carbon quantum dots comprises the following steps: s1, preparing electrolyte: preparing electrolyte by taking deionized water as a solvent and glycine as electrolyte, wherein the concentration of the glycine is 16 g/L;
step S2, synthesis: inserting a cathode and an anode of a liquid-phase plasma oxidation device into electrolyte, and carrying out liquid-phase plasma oxidation synthesis under the synthesis conditions: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty ratio is 22%, the temperature of the electrolyte is 30 ℃, and the processing time is 18 min;
s3, separation: and (3) centrifuging the reacted electrolyte at the rotating speed of 25000 r/min for 5min, discarding supernatant liquid after centrifugation, and drying the solid to obtain carbon quantum dot powder.
Characterization and Performance testing
The carbon quantum dots prepared in example 1 were used for calibration characterization and performance testing, and the specific test results were as follows:
FIG. 1 is a transmission electron microscope image of the carbon quantum dot prepared in example 1, and it can be seen that the carbon quantum dot prepared by the method has a particle size of 3-8nm, which is very small, and thus has a good fluorescence property.
Fig. 2 is an XRD spectrum of the carbon quantum dot prepared in example 1, and it can be seen from the graph that a stramonium peak appears near 25 degrees in the diffraction spectrum, which corresponds to the (002) crystal plane of graphite, which proves that the prepared carbon quantum dot is a graphitized carbon quantum dot and has a good quantum effect.
FIG. 3 is a graph showing the particle size distribution of the carbon quantum dots prepared in example 1, wherein the carbon quantum dots have a small particle size and a narrow distribution, mainly ranging from 4.5 to 6.5, and have a small particle size, thus having a good fluorescent property.
Fig. 4 is a full spectrum of X-ray fluorescence spectrum of the carbon quantum dot, which shows that the carbon quantum dot is mainly composed of carbon, oxygen and nitrogen elements, wherein the atomic content of carbon is about 90%, the atomic content of oxygen is about 7% and the atomic content of nitrogen is about 3%. Therefore, nitrogen is doped into the carbon quantum dots, and the fluorescence performance of the carbon quantum dots can be improved.
Fig. 5 is an upconversion characteristic spectrum of a carbon quantum dot, and it is understood from the graph that the synthesized carbon quantum dot has typical fluorescent upconversion characteristics, and wavelengths of outgoing light are 420nm, 440nm, 460nm, 480nm and 500nm respectively when wavelengths of incident light are 830nm, 860nm, 890nm, 920nm, 950nm and 980nm respectively, thereby showing that when light passes through the carbon quantum dot, wavelengths are all reduced by upconversion action of the carbon quantum dot. In practical applications, the energy of short wave is larger, so that when light with long wavelength passes through the carbon quantum dots, the energy of the wave can be increased, which has wide application in biomedicine.
In summary, the invention discloses a method for preparing nitrogen-doped carbon quantum, which adopts amino acid as a carbon source and can introduce a nitrogen source simultaneously, so that the prepared carbon quantum dot contains nitrogen and has better fluorescence performance; and because the amino acid is easy to dissolve in water, a water system can have better safety compared with an organic solvent, meanwhile, the amino acid with a small molecular structure is used as an electrolyte, the conductivity is better, the pulse voltage during liquid phase plasma oxidation can be greatly reduced, the safety problems that in the prior art, when the carbon quantum dots are prepared by adopting a liquid phase plasma technology, breakdown is easy to occur under a high pressure condition to cause fire or explosion and the like are solved, and the carbon ion dots are prepared by adopting the liquid phase plasma oxidation, so that the efficiency and the yield are high, the operation is simple, the implementation is easy, and the carbon ion dots can be popularized and applied in actual production.
It should be understood that equivalents and modifications of the technical solution and inventive concept thereof may occur to those skilled in the art, and all such modifications and alterations should fall within the scope of the appended claims.
Claims (8)
1. A preparation method of nitrogen-doped carbon quantum dots is characterized by comprising the following steps:
s1, preparing electrolyte: preparing an electrolyte by taking deionized water as a solvent and amino acid as an electrolyte;
step S2, synthesis: inserting a cathode and an anode of a liquid phase plasma oxidation device into electrolyte, and performing liquid phase plasma oxidation synthesis under a pulse voltage lower than 500V;
s3, separation: and 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 acids in the electrolyte is 5-20 g/L.
3. The method for preparing nitrogen-doped carbon quantum dots according to claim 2, wherein the amino acid is serine or lysine.
4. The method for preparing nitrogen-doped carbon quantum dots according to claim 1, wherein in the step S2, the conditions of the liquid-phase plasma oxidation synthesis are as follows: the pulse voltage is 200V-300V, the pulse frequency is 50 Hz-1000 Hz, the duty ratio is 10% -35%, and the temperature of the electrolyte is 20-40 ℃.
5. The method of claim 1, wherein in step S2, the liquid phase plasma oxidation treatment time is 10-30 min.
6. The method of claim 1, wherein in step S1, the amino acid is serine, and the concentration of the serine is 16 g/L; in step S2, the synthesis conditions are: the pulse voltage is 260V, the pulse frequency is 600Hz, the duty ratio is 22%, the temperature of the electrolyte is 30 ℃, and the processing time is 18 min.
7. The method of claim 1, wherein in step S3, the rotation speed of the centrifuge during the centrifugation treatment is greater than 20000 rpm, and the centrifugation time is 3-10 min.
8. The method of claim 1, wherein the cathode and the anode of the liquid phase plasma oxidation are both stainless steel plates.
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