High-purity carbon quantum dot material and method for preparing the same.
The use of supercritical water and controlled reaction parameters, combined with soluble dopants and acetonitrile purification, addresses the limitations of existing methods, enabling efficient large-scale production of high-purity carbon quantum dots with adjustable properties.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- WAJIN CAPITAL CO LTD
- Filing Date
- 2024-08-22
- Publication Date
- 2026-07-23
AI Technical Summary
Current methods for synthesizing carbon quantum dots are limited to laboratory-scale due to high equipment costs, harsh reaction conditions, low yield, and inefficient purification processes, making large-scale industrial production challenging.
A method involving supercritical water and controlled reaction parameters, including the use of soluble dopants and acetonitrile for purification, to produce high-purity carbon quantum dots efficiently.
The method enables high yield, consistent production of carbon quantum dots with adjustable size and functional groups, suitable for industrial scale-up with low product loss and improved purification efficiency.
Smart Images
Figure 0007894160000001 
Figure 0007894160000002 
Figure 0007894160000003
Abstract
Description
Technical Field
[0004] , ,
[0001] The present invention relates to the field of carbon nanomaterials and quantum dots, and specifically to an industrially adjustable preparation method for high-purity carbon quantum dots.
Background Art
[0002] Carbon quantum dots generally consist of an sp2 / sp3 carbon core and an outer layer containing functional groups such as oxygen / nitrogen, and refer to monodisperse carbon nanomaterials with a size of 10 nm or less. While having excellent properties similar to those of conventional semiconductor quantum dots, it can effectively overcome the drawback of low biocompatibility. Since the supply source is wide, the synthesis is easy and the functionalization is simple, it is an ideal material to replace conventional semiconductor materials.
[0003] Carbon quantum dots are carbon-based zero-dimensional materials. Carbon quantum dots have many advantages, such as excellent optical properties, good water solubility, environmental friendliness, a wide supply source of raw materials, low cost, and excellent biocompatibility. Since the discovery of carbon quantum dots, many synthesis methods have been developed, such as arc discharge, laser pinning method, electrochemical synthesis method, chemical oxidation method, combustion method, subcritical hydrothermal synthesis method, microwave synthesis method, template method, etc. Carbon quantum dots have good application prospects in many fields, such as medical imaging technology, environmental monitoring, chemical analysis, catalyst preparation, energy development, etc.
[0004] However, each of these methods has its advantages and disadvantages. For example, chemical vapor deposition can produce highly crystalline carbon quantum dots, but the equipment costs are high and the yield is low. Electrochemical methods offer high yields, but the preparation conditions are strict, requiring control over parameters such as electrode spacing. While these methods can produce various types of carbon quantum dots, the reaction processes all involve harsh conditions such as high temperature and high pressure, often resulting in the generation of many byproducts. Therefore, efficiently separating and purifying the carbon quantum dots produced from the reaction solution is an urgent problem that needs to be solved. Currently, the mainstream purification method involves dialyzing an aqueous solution of carbon quantum dots to deposit high molecular weight carbon quantum dots in order to achieve separation and purification. However, this method has a long purification cycle, and the purified product is an aqueous solution of quantum dots, requiring further separation of carbon quantum dots from water to obtain a pure carbon quantum dot product. A very small number of publications mention purification using ethanol centrifugation, but this method requires the use of large amounts of ethanol, and at the same time, most of the product is lost during the separation process, resulting in low purification efficiency and the problem of difficulty in separating the two phases of liquid even after centrifugation. In summary, the above two methods are currently limited to laboratory use and cannot be used for large-scale industrial production. [Overview of the Initiative] [Problems that the invention aims to solve]
[0005] The problem that this invention aims to solve is to provide a high-purity carbon quantum dot material and a method for preparing the same. [Means for solving the problem]
[0006] To solve the above technical problems, the method for preparing high-purity carbon quantum dots according to the present invention is: Step 1: Dissolve soluble carbon-containing organic matter in ultrapure water, and adjust the mass ratio of carbon elements in the soluble carbon-containing organic matter to water to 1:10000 to 1:100. Step 2: Fill the pressure reactor to the brim with the reaction mixture and seal the reactor. Step 3: Start the heating program, rapidly raise the temperature to 380°C, and maintain the pressure inside the reactor at 23 MPa or higher. Step 4: Start the cooling system and cool the reactants in the reactor. Step 5: After cooling, collect and quantify the aqueous solution of the obtained carbon quantum dots. Step 6: Includes separating and purifying the aqueous solution of carbon quantum dots.
[0007] Supercritical water has extremely active chemical properties and, under supercritical conditions, interacts with carbonaceous organic matter containing soluble functional groups, with water molecules interacting with the functional groups and reacting.
[0008] Unlike hydrothermal synthesis, which is generally used to prepare metallic and inorganic nonmetal nanoparticles, the main driving force is the difference in solubility between the soluble precursor or intermediate product and the final product; that is, the reaction proceeds in the direction of decreasing Gibbs free energy. Water is present only as a medium, its grain growth follows crystallization kinetics, and the grain size is adjusted by controlling temperature, pressure, and reaction time. The difference between the preparation of carbon quantum dots by supercritical water and the thermal synthesis of water is that water participates as a reactant, the mechanism that produces quantum dots is a chemical reaction of organic matter, does not follow the laws of crystallization kinetics, the products at different stages are different substances, and the organic matter carbonizes under supercritical conditions for a long time.
[0009] As a further improvement, after step 1, a soluble dopant substance is added to the solution and completely dissolved, wherein the soluble dopant substance is an element containing nitrogen, phosphorus, or sulfur, and the ratio of the dopant element to the carbon source in the soluble dopant substance is 1:1 or less.
[0010] Because carbon quantum dots synthesized using only a carbon source and supercritical water have low stability, it is necessary to add dopants containing elements such as nitrogen, phosphorus, and sulfur to stabilize the structure of the carbon quantum dots and to adjust the carbocyclic structure and functional groups. The soluble carbon source is a soluble organic substance containing six or more carbon atoms in its molecule. The aforementioned soluble dopant substance is dimethyl sulfoxide.
[0011] Preferably, in step 3, the reaction time is 10 to 15 minutes. Supercritical water is highly reactive, and if the reaction is prolonged, the organic matter will carbonize.
[0012] Preferably, the soluble carbon-containing organic substance is an organic molecule such as an organic acid or sugar. Such organic molecules have high solubility and are rich in functional groups, resulting in a fast reaction rate and high quantum dot yield.
[0013] Preferably, the soluble organic acid is one of citric acid, salicylic acid, glutamic acid, or tartaric acid. Preferably, the soluble sugar is one of glucose, glyceraldehyde, or arabinose. Preferably, the reaction temperature is 380°C.
[0014] Preferably, the cooling time after the reaction is 15 minutes or less. Afterward, the mixture is rapidly cooled to room temperature within 15 minutes. This is because the carbon quantum dots are highly active, and natural cooling can cause side reactions, leading to the formation of larger organic particles and a decrease in the quantum dot yield.
[0015] In step 4, the reactor temperature is lowered using an ethylene glycol coolant at -5°C. This cooling method is more effective, resulting in a faster and more uniform cooling rate.
[0016] Preferably, in step 4, the reactor temperature is lowered using a glycol coolant at -5°C. Cooling the reaction product with an ethylene glycol coolant at -5°C can significantly reduce the occurrence of other reactions during spontaneous cooling and improve the yield of quantum dots.
[0017] As a further improvement, step 5 is: 6.1: Add acetonitrile to the solution, shake to mix thoroughly. As a further improvement, the volume ratio of acetonitrile to the aqueous solution of carbon quantum dots is 5:1. 6.2: Let the mixed solution stand in the dispenser for 30 minutes. 6.3: Collect the lower-layer black viscous liquid, dry it to remove trace amounts of residual acetonitrile, and obtain a purified product of carbon quantum dots. This method includes the above steps.
[0018] Carbon quantum dots have a very low solubility in acetonitrile, but acetonitrile has a high solubility for the impurities associated with the synthesis process of carbon quantum dots. Acetonitrile has a stronger binding force with water molecules than carbon quantum dots and will夺取 the water molecules bound to the carbon quantum dots. Therefore, when an organic solvent is added to the aqueous solution of carbon quantum dots, acetonitrile will夺取 the water molecules bound to the carbon quantum dots. As a result, the lack of water molecules that can bind to the carbon quantum dots causes them to precipitate from the solution. A small amount of impurities generated simultaneously during the synthesis process cannot precipitate due to their low content and remain in the solution, achieving the purpose of separation and purification.
[0019] As a further improvement, in step 6.3, after collecting the lower-layer black viscous liquid, add acetonitrile to the black viscous liquid at a ratio of 1:1, shake to mix thoroughly, perform layer separation, then dispense again, and repeat the above steps 5 times until the volume of the lower-layer black viscous liquid no longer changes. Collect the black viscous liquid, dry it to remove trace amounts of residual acetonitrile, and then obtain a purified product of carbon quantum dots.
[0020] The present invention claims to protect the carbon quantum dot material prepared by the above method for preparing carbon quantum dots.
Advantages of the Invention
[0021] Compared with the prior art, the method of the present invention for preparing carbon quantum dots using supercritical water has the following beneficial technical effects.
[0022] (1) The range of raw materials is wide. (2) The preparation process is simple, (3) The yield and consistency are high, (4) The size and functional groups of the carbon quantum dots can be adjusted according to requirements, (5) The purification efficiency is high and the product loss rate is low, (6) It is easy to scale up industrially.
[0023] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of this application and be able to implement it according to the content of the specification, and to more clearly and easily understand the above and other objects, features, and advantages of this application, the preferred embodiments of this application will be described in detail below in conjunction with the accompanying drawings.
[0024] According to the following description that details the specific embodiments of this application in conjunction with the accompanying drawings, those skilled in the art can better understand the above and other objects, advantages, and features of this application.
Brief Description of the Drawings
[0025] To more clearly illustrate the technical solutions in the embodiments or prior art of this application, the accompanying drawings necessary to be used in the description of the embodiments or prior art are briefly described below.
[0026] [Figure 1] It is a TEM photograph of carbon quantum dots of about 8.5 nm prepared in Example 1. [Figure 2] It is the fluorescence excitation spectrum of the carbon quantum dots prepared in Example 1. [Figure 3] It is an image of the yellow fluorescence of the carbon quantum dots prepared in Example 1 under ultraviolet light. [Figure 4] It is a TEM photograph of carbon quantum dots of about 2 nm prepared in Example 2. [Figure 5] It is the fluorescence excitation spectrum of the carbon quantum dots prepared in Example 2. [Figure 6]This is an image of the blue fluorescence of the carbon quantum dots prepared in Example 2 under ultraviolet light. [Figure 7] This figure shows the formation of larger carbon quantum dots, which can be observed after natural cooling. [Figure 8] This figure shows that the sizes of the carbon quantum dots are nearly identical after cooling to room temperature for 15 minutes. [Figure 8a] This is a magnified view of a portion of Figure 8. [Figure 9] This figure shows the effect of cooling rate on quantum dot yield. [Figure 10] This figure shows the effect of reaction time on quantum dot yield. [Figure 11] This figure shows a comparison of the stability of urea and metaphosphate in the dimethyl sulfoxide doping group and the control group. [Figure 12] This figure shows the carbonization of sucrose after reacting under supercritical water conditions for 20 minutes. [Figure 13] This photograph shows the dispensing of acetonitrile and quantum dot solution in different proportions. [Figure 14] This photograph shows the dispensing of different proportions of concentrated solution and acetonitrile after re-purification. [Figure 15] This photograph shows the layer separation results when different solvents are selected. [Modes for carrying out the invention]
[0027] To further clarify the purpose, technical solutions, and advantages of the embodiments of this application, the technical solutions of the embodiments of this application will be described clearly and completely below, together with the accompanying drawings of the embodiments of this application.
[0028] The method for producing high-purity carbon quantum dots according to the present invention comprises the following steps: Step 1: Dissolve soluble carbon-containing organic matter in ultrapure water, and adjust the mass ratio of carbon elements in the soluble carbon-containing organic matter to water to 1:10000 to 1:100. Step 2: Fill the pressure reactor to the brim with the reaction mixture, seal the reactor, Step 3: Start the heating program and rapidly raise the temperature to 380°C, maintaining the pressure inside the reactor at 23 MPa or higher. Step 4: Start the cooling system to cool the reactants in the reactor. Step 5: After cooling, collect and quantify the aqueous solution of the obtained carbon quantum dots. Step 6: Separate and purify the aqueous solution of carbon quantum dots.
[0029] Supercritical water has extremely active chemical properties and, under supercritical conditions, interacts with carbonaceous organic matter containing soluble functional groups, with water molecules interacting with the functional groups and reacting.
[0030] Unlike hydrothermal synthesis, which is generally used to prepare metallic and inorganic nonmetal nanoparticles, the main driving force is the difference in solubility between the soluble precursor or intermediate product and the final product; that is, the reaction proceeds in the direction of decreasing Gibbs free energy. Water is present only as a medium, its grain growth follows crystallization kinetics, and the grain size is adjusted by controlling temperature, pressure, and reaction time. The difference between the preparation of carbon quantum dots by supercritical water and the thermal synthesis of water is that water participates as a reactant, the mechanism that produces quantum dots is a chemical reaction of organic matter, does not follow the laws of crystallization kinetics, the products at different stages are different substances, and the organic matter carbonizes under supercritical conditions for a long time. As a further improvement, after step 1, a soluble dopant substance is added to the solution and completely dissolved, wherein the soluble dopant substance is an element containing nitrogen, phosphorus, or sulfur, and the ratio of the dopant element to the carbon source in the soluble dopant substance is 1:1 or less.
[0031] Because carbon quantum dots synthesized using only a carbon source and supercritical water have low stability, it is necessary to add dopants containing elements such as nitrogen, phosphorus, and sulfur to stabilize the structure of the carbon quantum dots and to adjust the carbocyclic structure and functional groups.
[0032] The soluble carbon source is a soluble organic substance containing six or more carbon atoms in its molecule. Preferably, the soluble dopant substance is an alcoholamine, an amide, a metaphosphate, or a dimethyl sulfoxide.
[0033] Preferably, the soluble alcohol amine is one of monoethanolamine, diethanolamine, or ethylenediamine.
[0034] Preferably, the soluble amide is one of acetamide, acrylamide, or carbomite.
[0035] As the soluble dopant substance, dimethyl sulfoxide is most preferably selected. Preferably, in step 3, the reaction time is 10 to 15 minutes. Supercritical water is highly reactive, and if the reaction is prolonged, the organic matter will carbonize.
[0036] Preferably, the soluble carbon-containing organic substance is an organic molecule such as an organic acid or sugar. Such organic molecules have high solubility and are rich in functional groups, resulting in a fast reaction rate and high quantum dot yield.
[0037] Preferably, the soluble organic acid is one of citric acid, salicylic acid, glutamic acid, or tartaric acid. Preferably, the soluble sugar is one of glucose, glyceraldehyde, or arabinose.
[0038] Preferably, the pressure inside the reactor is 23 MPa. Preferably, the reaction temperature is 380°C. Preferably, the cooling time after the reaction is 15 minutes or less.
[0039] Afterward, the mixture is rapidly cooled to room temperature within 15 minutes. This is because the carbon quantum dots are highly active, and natural cooling can cause side reactions, leading to the formation of larger organic particles and a decrease in the quantum dot yield.
[0040] In step 4, the reactor temperature is lowered using an ethylene glycol coolant at -5°C. This cooling method is more effective, resulting in a faster and more uniform cooling rate.
[0041] Preferably, in step 4, the reactor temperature is lowered using a glycol coolant at -5°C. Cooling the reaction product with an ethylene glycol coolant at -5°C can significantly reduce the occurrence of other reactions during spontaneous cooling and improve the yield of quantum dots.
[0042] As a further improvement, step 5 is: 6.1: Add acetonitrile to the solution, shake to mix completely, and as a further improvement, the volume ratio of acetonitrile to the carbon quantum dot aqueous solution is 5:1. 6.2: The step of letting the mixed solution stand in the dispenser for 30 minutes, 6.3: The step of collecting the lower layer of black viscous liquid, drying it to remove trace amounts of residual acetonitrile, and obtaining a pure product of carbon quantum dots.
[0043] Carbon quantum dots have very low solubility in acetonitrile, but acetonitrile has high solubility for impurities that occur during the synthesis of carbon quantum dots. Organic solvents have a stronger ability to bind water molecules than carbon quantum dots. When an organic solvent is added to an aqueous solution of carbon quantum dots, the organic solvent removes water molecules bound to the carbon quantum dots, resulting in a shortage of water molecules that can bind to the carbon quantum dots, causing them to precipitate from the solution.
[0044] As a further improvement, in step 6.3, after collecting the lower layer of black viscous liquid, acetonitrile is added to the black viscous liquid in a 1:1 ratio, shaken to mix completely, and after layer separation, the liquid is dispensed again, and the above step is repeated 5 times until the volume of the lower layer of black viscous liquid no longer changes. That is, it is preferable to perform the step of "collecting the lower layer of black viscous liquid, adding acetonitrile to the black viscous liquid in a 1:1 ratio, shaking to mix completely, and after layer separation, dispensing again" 6 times. Finally, the black viscous liquid is collected, dried to remove any trace amounts of residual acetonitrile, and a pure product of carbon quantum dots is obtained.
[0045] Example 1 The specific steps are as follows:
[0046] 1) Take 1 liter of pure water, 100 g of citric acid, and 40 g of monoethanolamine, mix well, and dissolve completely. 2) Pour this solution into a 1L reactor, 3) Heat the solution to approximately 380°C, adjust the pressure to 23 MPa or higher, and maintain it for 6 minutes. 4) Start the cooling system and cool to atmospheric pressure / room temperature for 15 minutes, then open the reactor and dispense the reaction mixture into the dispenser. 5) Add 5L of acetonitrile to the dispenser, shake thoroughly to mix, and let stand for 30 minutes. 6) Collect the lower layer of black viscous liquid, quantify its volume, add acetonitrile in a 1:1 ratio, shake to mix completely, separate the layers, and then dispense again. 7) The lower layer of black viscous liquid is collected again, and the above steps are repeated 5 times. During this time, the volume of the lower layer of black viscous liquid remains unchanged, and the total amount of acetonitrile administered is 6 L. 8) Collect the black viscous liquid at the bottom, place it in a vacuum drying oven, and dry it at room temperature for 24 hours to obtain a pure yellow carbon quantum dot product with an emission wavelength of approximately 8.5 nm and 550 nm.
[0047] Figure 1 is a TEM image of carbon quantum dots of approximately 8.5 nm prepared in Example 1. Figure 1 shows multiple carbon quantum dots with a particle size distribution of 7–10 nm. Figure 2 shows the fluorescence excitation spectrum of the carbon quantum dot prepared in Example 1. Figure 3 is a photograph of the yellow fluorescence of the carbon quantum dots prepared in Example 1 under ultraviolet light. Figure 3 demonstrates that the carbon quantum dots provided in this example have good fluorescence properties.
[0048] Figures 1 to 3 show multiple carbon quantum dots, demonstrating that the carbon quantum dots provided in this embodiment have good fluorescence properties, and that the method of the present invention can prepare suitable carbon quantum dots.
[0049] Example 2 The specific steps are as follows: 1) Take 1 liter of pure water, 90 g of glucose, and 30 g of dimethyl sulfoxide, mix well, and dissolve completely. 2) Pour this solution into a 1L reactor, 3) Heat the solution to approximately 380°C, adjust the pressure to 23 MPa or higher, and hold for 10 minutes. 4) Start the cooling device and cool to atmospheric pressure / room temperature for 12 minutes, then transfer the reaction solution to the dispenser. 5) Add 5L of acetonitrile to the dispenser, shake thoroughly to mix, and let stand for 30 minutes. 6) Collect the lower layer of black viscous liquid, quantify its volume, add acetonitrile in a 1:1 ratio, shake to mix completely, separate the layers, and then dispense again. 7) Collect the lower layer of black viscous liquid again, and repeat the above steps until the volume of the lower layer of black viscous liquid no longer changes, at which point the total amount of acetonitrile administered is 6 L. 8) The black viscous liquid at the bottom is collected, placed in a vacuum drying oven, and dried at room temperature for 24 hours to obtain blue carbon quantum dots with a wavelength of approximately 2 nm and an emission wavelength of approximately 450 nm.
[0050] Figure 4 is a TEM image of carbon quantum dots of approximately 2 nm size prepared in Example 2. Figure 4 shows multiple carbon quantum dots with a particle size distribution of approximately 2 nm. Figure 5 shows the fluorescence excitation spectrum of the carbon quantum dots prepared in Example 2.
[0051] Figure 6 is a photograph of the blue fluorescence of the carbon quantum dots prepared in Example 2 under ultraviolet light. Figure 6 demonstrates that the carbon quantum dots provided in this example have good fluorescence performance.
[0052] Figures 4 to 6 show multiple carbon quantum dots, demonstrating that the carbon quantum dots provided in this embodiment have good fluorescence properties, and that the method of the present invention can prepare suitable carbon quantum dots.
[0053] Example 3 1) Take 1 liter of pure water, 90 g of glucose, 10 g of ethylenediamine, and 5 g of metaphosphoric acid, mix well, and dissolve completely. 2) Pour this solution into a 1L reactor, 3) Heat the solution to approximately 380°C, adjust the pressure to 23 MPa or higher, and hold for 10 minutes. 4) Start the cooling device and cool to atmospheric pressure / room temperature for 12 minutes, then transfer the reaction solution to the dispenser. 5) Add 5L of acetonitrile to the dispenser, shake thoroughly to mix, and let stand for 30 minutes. 6) Collect the lower layer of black viscous liquid, quantify its volume, add acetonitrile in a 1:1 ratio, shake to mix completely, separate the layers, and then dispense again. 7) Collect the lower layer of black viscous liquid again, and repeat the above steps until the volume of the lower layer of black viscous liquid no longer changes, at which point the total amount of acetonitrile administered is 6 L. 8) The black viscous liquid at the bottom is collected, placed in a vacuum drying oven, and dried at room temperature for 24 hours to obtain blue carbon quantum dots with a wavelength of approximately 2 nm and an emission wavelength of approximately 450 nm.
[0054] In the method of the present invention, it is preferable that the cooling time after the reaction is within 15 minutes. After the reaction, the cooling system is activated and the reactor temperature is lowered to room temperature within 15 minutes using a -5°C glycol coolant. This is because carbon quantum dots are highly reactive, and spontaneous cooling would cause side reactions, leading to the formation of larger organic particles and a decrease in the quantum dot yield. In this system, because a -5°C glycol coolant is used, the cooling method is more effective, the cooling rate is faster, and the cooling rate is more uniform.
[0055] The inventors conducted comparative experiments to compare natural cooling with the rapid cooling effect of the present invention. Figure 7 is a TEM image of natural cooling, showing that large carbon quantum dots were generated after cooling, which reduced the quantum dot yield. Figure 8 is a TEM image of cooling to room temperature for 15 minutes, showing that after lowering the temperature, the size of the carbon quantum dots was almost the same, and relatively good monodispersity was achieved.
[0056] In the method of the present invention, the preferred reaction time is 10 to 15 minutes. The inventors conducted a series of comparative experiments to test the effect of different reaction times on the yield. Reaction times of 5 minutes, 10 minutes, 12 minutes, 15 minutes, and 17 minutes were selected. As can be seen from Figure 10, the effect is particularly pronounced when the reaction time is 10 to 15 minutes. This is thought to be because supercritical water is extremely active, and prolonged reaction causes organic matter to carbonize. In Figure 12, carbonization occurred in sucrose after reacting for 20 minutes under supercritical water conditions.
[0057] In the method of the present invention, the soluble dopant substance is preferably an alcoholamine, an amide, metaphosphoric acid, or dimethyl sulfoxide. More preferably, the soluble alcoholamine is one of monoethanolamine, diethanolamine, or ethylenediamine, and preferably, the soluble amide is one of acetamide, acrylamide, or carbomite.
[0058] Figure 11 shows a comparison of the stability of dimethyl sulfoxide-doped and control groups urea and metaphosphate. As can be seen from Figure 11, the effect of dimethyl sulfoxide is better.
[0059] In this invention, the proportion of acetonitrile in the initial purification step is optimized, and the experiment was conducted as follows:
[0060] 20 mL of the stock solution of carbon quantum dot aqueous solution was added to a dispensing funnel. Acetonitrile was added to the dispensing funnel in increments of 20 mL to 120 mL, with a volume ratio of stock solution to acetonitrile of 1:1 to 1:6. As shown in the figure, a clear layer separation first appeared in the solution when the volume ratio was 1:2. Subsequently, the volume of acetonitrile gradually increased, reaching a maximum at 1:5. After that, a clear limiting effect began to appear. When acetonitrile was added again to a volume ratio of 1:6, there was no clear change compared to the 1:5 case. Therefore, the amount of acetonitrile added during the initial purification was determined to be stock solution:acetonitrile = 1:5. Figure 13 shows dispensing photographs of acetonitrile and quantum dot solution at different ratios.
[0061] Experiments to determine the proportion of acetonitrile in the subsequent purification process: The lower layer of carbon mass dot concentrate separated during the initial separation was collected and quantified. 20 mL of the stock solution was purified to obtain 2 mL of concentrate, which was placed in a dispensing funnel. Acetonitrile was added to the dispensing funnel in increments of 1:1 to 1:3, from 2 mL to 6 mL. As shown in the figure, after the initial addition at a 1:1 ratio, there was no significant change when acetonitrile was added again. Subsequently, a limiting effect was clearly demonstrated, so the amount of acetonitrile added in subsequent purifications was determined to be concentrate:acetonitrile = 1:1. Figure 14 shows photographs of the liquid-liquid separation when the ratio of concentrate to acetonitrile was changed during the second purification.
[0062] Experimental verification of the selection of purification reagents: Due to the mechanism of the purification process, the organic reagents used in the purification process must have a strong binding affinity to water and be mutually soluble with water in any desired ratio. Several commonly used laboratory organic reagents that meet these conditions, such as ethanol, acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran, were selected and compared. 10 mL of the reaction stock solution was added to each of five centrifuge tubes, and several of the above organic reagents were added to each. After shaking thoroughly, the mixture was allowed to stand for 30 minutes. As can be seen from the comparison results shown in the figure, the acetonitrile group exhibited a clear layer separation phenomenon compared to the other organic reagents. In the ethanol group, which is used in conventional purification methods, centrifugation is not performed, and therefore carbon quantum dots cannot be separated. Thus, acetonitrile was selected as the organic reagent in the purification process of water-soluble carbon quantum dots. Figure 15 is a photograph showing the layer separation situation when different solvents were selected.
[0063] The above description represents only preferred embodiments of the present invention and does not limit other forms of the invention. Those skilled in the art can utilize the technical content disclosed above to modify or reshape equivalent embodiments of the present invention. Any simple modifications, equivalent modifications, and reshaping made to the above embodiments based on the technical substance of the present invention, without departing from the content of the solution of the present invention, shall all be within the scope of protection of the present invention.
Claims
1. Step 1: Mix pure water, glucose, and dimethyl sulfoxide and dissolve completely to obtain the reaction solution. Step 2: Fill the pressure reactor to its maximum capacity with the reaction liquid and seal the reactor. Step 3: Start the heating program, raise the temperature to 380°C, and carry out the reaction for 10 minutes while maintaining the pressure inside the reactor at 23 MPa or higher. Step 4: Activate the cooling system and cool the reactants in the reactor. Step 5: After cooling, collect and quantify the aqueous solution of the obtained carbon quantum dots. A method for preparing high-purity carbon quantum dots, comprising step 6: separating and purifying an aqueous solution of carbon quantum dots, In step 1, the mass ratio of pure water to glucose is 1000:90, and the mass ratio of glucose to dimethyl sulfoxide is 3:
1. A method for preparing high-purity carbon quantum dots, characterized by the following features.
2. The method for preparing high-purity carbon quantum dots according to Claim 1, characterized in that in step 4, the reactants in the reactor are cooled to room temperature within 15 minutes.
3. The method for preparing high-purity carbon quantum dots according to claim 2, characterized in that in step 4, the temperature of the reactor is lowered using a glycol coolant at -5°C.
4. Step 6 is, 6.1: Add acetonitrile to the solution and shake to mix thoroughly, 6.2: The step of letting the mixed solution stand in the dispenser for 30 minutes, 6.3: A method for preparing high-purity carbon quantum dots according to any one of claims 1 to 3, comprising the steps of collecting the lower layer of black viscous liquid, drying it to remove trace amounts of residual acetonitrile, and obtaining a pure product of carbon quantum dots.
5. The method for preparing high-purity carbon quantum dots according to claim 4, characterized in that, in step 6.3, after collecting the lower layer of black viscous liquid, acetonitrile is added to the black viscous liquid in a 1:1 ratio, shaken to mix completely, separate the layers, dispense again, and repeat the above step five times until the volume of the lower layer of black viscous liquid no longer changes, collect the black viscous liquid, dry it to remove trace amounts of residual acetonitrile, and obtain a pure product of carbon quantum dots.