Algae-based three-color fluorescent carbon quantum dot as well as preparation method and application thereof

Abstract

The invention provides an algae-based three-color fluorescent carbon quantum dot as well as a preparation method and application thereof. According to the algae-based three-color fluorescent carbon quantum dot and the preparation method thereof, the polar aprotic solvent N, N-dimethylformamide is used, the dehydration and carbonization process in the reaction is accelerated, the reaction time is shortened, and meanwhile, the carbon quantum dot with more uniform particle size distribution is obtained. The generated algae-based carbon quantum dots have relatively strong fluorescence characteristics, low cytotoxicity, high cell absorption efficiency and high-contrast biological imaging potential, and respectively present red, orange and green fluorescence in N, N-dimethylformamide solvent / ethanol solvent / hydrosolvent under the irradiation of a 365nm ultraviolet lamp, so that the application range of the algae-based carbon quantum dots is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of carbon quantum dots, and particularly to an algal-based three-color fluorescent carbon quantum dot, a preparation method thereof, and an application thereof. Background Art

[0002] Carbon quantum dots are small carbon nanoparticles (<10 nm) with strong photoluminescence characteristics, good electrochemical characteristics, low toxicity, environmental friendliness, low cost, simple synthesis routes, etc. They have good application prospects in many fields such as medical imaging technology, environmental monitoring, chemical analysis, catalyst preparation, and energy development, and have received extensive attention from scholars all over the world. Microalgae have outstanding characteristics such as not occupying arable land for artificial cultivation, short cultivation cycles, and strong carbon fixation ability, and are considered to be a promising renewable biological raw material.

[0003] At present, the preparation methods of carbon quantum dots mainly include two types: the bottom-up method and the top-down method. The top-down method is more suitable for industrial production due to the wide source and low price of raw materials. The precursors used in the top-down method to prepare biomass carbon quantum dots are usually plants such as vegetables, fruits, tree leaves and stems and their derivatives, and a small part uses animal hair, bones, etc. Compared with other biomass precursors, microalgae are small in size, have good dispersibility without being broken, and the reaction is more sufficient.

[0004] At present, the main method for preparing carbon quantum dots from microalgae is the hydrothermal method. However, the hydrothermal method has low reaction efficiency and long reaction time, which greatly increases the preparation cost and delays the preparation time, and is not suitable for large-scale industrial production. At the same time, the algal-based carbon quantum dots prepared by the hydrothermal method mostly exhibit blue-green fluorescence, and the uneven particle size distribution results in impure fluorescence color, severely limiting their applications.

[0005] Based on the current defects in the preparation of carbon quantum dots from microalgae, it is necessary to improve this. Summary of the Invention

[0006] In view of the above-mentioned disadvantages or improvement requirements of the prior art, the present invention provides an algal-based three-color fluorescent carbon quantum dot, a preparation method thereof, and an application thereof. By using N,N-dimethylformamide, a polar aprotic solvent, the dehydration carbonization process in the reaction is accelerated, the reaction time is reduced, and at the same time, carbon quantum dots with a more uniform particle size distribution are obtained. The generated algal-based carbon quantum dots have strong fluorescence characteristics, low cytotoxicity, high cell absorption efficiency, have the potential for high-contrast bioimaging, and under the irradiation of a 365 nm ultraviolet lamp, exhibit red, orange, and green three-color fluorescence in N,N-dimethylformamide solvent / ethanol solvent / water solvent respectively, broadening the application range of algal-based carbon quantum dots.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing algal-based three-color fluorescent carbon quantum dots, comprising the following steps:

[0009] Add microalgae and N,N-dimethylformamide solvent into a reaction kettle, and obtain a mixture through a solvothermal reaction;

[0010] Centrifuge the mixture and collect the upper layer liquid;

[0011] Filter the upper layer liquid to obtain a carbon quantum dot solution;

[0012] Add the carbon quantum dot solution into a dialysis bag for dialysis purification to obtain a purified carbon quantum dot solution;

[0013] Freeze-dry the purified carbon quantum dot solution to obtain algal-based three-color fluorescent carbon quantum dots.

[0014] Preferably, the temperature of the solvothermal reaction is 180-260 °C and the time is 4-12 h.

[0015] Preferably, the microalgae include at least one of Chlorella pyrenoidosa and Nannochloropsis oculata.

[0016] Preferably, the mass ratio of the microalgae to the alcohol solvent is 1:(1-200).

[0017] Preferably, centrifuge the mixture at a rotation speed of 2000-8000 rpm for 5-20 min and collect the upper layer liquid;

[0018] Filter the upper layer liquid with a microporous filter membrane with a pore size of 0.1-0.45 μm to obtain a carbon quantum dot solution.

[0019] Preferably, the cut-off molecular weight of the dialysis bag is 500-3500 Da;

[0020] The dialysis solution used during dialysis includes at least one of N,N-dimethylformamide, ethanol, and deionized water.

[0021] Preferably, add microalgae and N,N-dimethylformamide solvent into a reaction kettle, introduce an inert gas into the reaction kettle, and carry out a solvothermal reaction at a rotation speed of 300-4000 rpm to obtain a mixture.

[0022] Preferably, after adding microalgae and N,N-dimethylformamide solvent into a reaction kettle, add a weak acid into the reaction kettle; the weak acid includes at least one of formic acid and acetic acid;

[0023] The freeze-drying temperature is -40 °C to -80 °C.

[0024] In a second aspect, the present invention also provides an algal-based three-color fluorescent carbon quantum dot, which is prepared by using the described preparation method.

[0025] In a third aspect, the present invention also provides the application of the algal-based three-color fluorescent carbon quantum dot prepared by the described preparation method or the algal-based three-color fluorescent carbon quantum dot in the fields of biological imaging, environmental detection, and energy catalysis.

[0026] The preparation method of the algal-based three-color fluorescent carbon quantum dot of the present invention has the following beneficial effects compared with the prior art:

[0027] 1. Compared with other biomass precursors, the microalgae used in the preparation method of the algal-based three-color fluorescent carbon quantum dot of the present invention are small in size, have good dispersibility without being broken, the reaction is more sufficient, and the high nitrogen content of the microalgae is beneficial to improving the yield of carbon quantum dots. The generated algal-based carbon quantum dots have strong fluorescence characteristics, low cytotoxicity, high cell absorption efficiency, and the potential for high-contrast biological imaging.

[0028] 2. In the preparation method of the algal-based three-color fluorescent carbon quantum dot of the present invention, N,N-dimethylformamide is used as an aprotic solvent, which accelerates the dehydration reaction. In the same time, the reaction is more sufficient compared with the hydrothermal method. The generated algal-based carbon quantum dots have strong fluorescence characteristics, and under the irradiation of a 365 nm ultraviolet lamp, they show red, orange, and green three-color fluorescence in N,N-dimethylformamide solvent / ethanol solvent / water solvent respectively, broadening the application channels of the product.

[0029] 3. In the preparation method of the algal-based three-color fluorescent carbon quantum dot of the present invention, N,N-dimethylformamide is used as a solvent, and an additional N element participating in the reaction is added to regulate the red shift of the fluorescence color. At the same time, as a polar solvent, it helps the uniform dispersion and carbonization of carbon source molecules during the reaction, and carbon quantum dots with a more uniform size distribution can be obtained. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0031] Figure 1 It is the transmission electron microscope (FTEM) image of the microalgae-based carbon quantum dot prepared in Example 1;

[0032] Figure 2Dark box diagrams of the algal-based three-color fluorescent carbon quantum dots prepared in Example 1 and the algal-based fluorescent carbon quantum dots prepared in Comparative Examples 1-3, dissolved separately in the preparation solvents (methanol / ethanol / n-butanol / N,N-dimethylformamide), ethanol, and deionized water and irradiated under 365 nm ultraviolet light illumination conditions;

[0033] Figure 3 Ultraviolet-visible absorption spectrum, fluorescence excitation and emission spectra of the algal-based carbon quantum dots prepared in Example 1;

[0034] Figure 4 Fourier transform infrared (FT-IR) spectrum of the microalgal-based carbon quantum dots prepared in Example 1;

[0035] Figure 5 X-ray photoelectron spectroscopy (XPS) spectrum of the carbon quantum dots prepared in Example 1. Detailed implementation manners

[0036] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all of the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0037] In the description of the present invention, it should be understood that the relationships indicating orientations or positions such as "upper" are based on the orientations or positions shown in the drawings, or the orientations or positions in which the products of the present invention are usually placed during use, or the orientations or positions commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the indicated devices or elements must have specific orientations, be constructed and operated in specific orientations, and thus should not be construed as limiting the present invention.

[0038] The description order of the following embodiments does not limit the preferred order of the embodiments. Additionally, in the description of this application, the term "comprising" means "including but not limited to". The various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of the present invention; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0039] An embodiment of this application provides a method for preparing algal-based three-color fluorescent carbon quantum dots, comprising the following steps:

[0040] S1. Add microalgae and N,N-dimethylformamide solvent to a reaction kettle, and obtain a mixture through solvothermal reaction;

[0041] S2. Centrifuge the mixture and collect the upper layer liquid;

[0042] S3. Filter the upper layer liquid to obtain a carbon quantum dot solution;

[0043] S4. Add the carbon quantum dot solution into a dialysis bag for dialysis purification to obtain a purified carbon quantum dot solution;

[0044] S5. Freeze-dry the purified carbon quantum dot solution to obtain algal-based three-color fluorescent carbon quantum dots.

[0045] The method for preparing algal-based three-color fluorescent carbon quantum dots of the present invention uses microalgae to prepare algal-based three-color fluorescent carbon quantum dots; compared with other biomass precursors, microalgae are small in size, have good dispersibility without the need for crushing, the reaction is more sufficient, and the high nitrogen content of microalgae is beneficial to improving the yield of carbon quantum dots. The generated algal-based carbon quantum dots have strong fluorescence emission characteristics, low cytotoxicity, high cell absorption efficiency, and the potential for high-contrast bioimaging; using N,N-dimethylformamide, a polar aprotic solvent, can accelerate the dehydration carbonization process in the reaction, reduce the reaction time, and simultaneously obtain carbon quantum dots with a more uniform particle size distribution. The generated algal-based carbon quantum dots have strong fluorescence characteristics, low cytotoxicity, high cell absorption efficiency, and the potential for high-contrast bioimaging, and under irradiation with a 365 nm ultraviolet lamp, they exhibit red, orange, and green three-color fluorescence in N,N-dimethylformamide solvent / ethanol solvent / water solvent respectively, broadening the application range of algal-based carbon quantum dots.

[0046] Specifically, using N,N-dimethylformamide as a solvent, algal-based carbon quantum dots are prepared by a solvothermal method. During the preparation process, microalgae are decomposed into small molecules and then dehydrated, carbonized and polymerized into spherical nanoparticles, which are the carbon quantum dots. The main components of the carbon quantum dots are the carbon source core and its outer organic functional groups, with a particle size of 1-5 nm. Under the irradiation of 365 nm ultraviolet light, red, orange, and green fluorescence is presented in N,N-dimethylformamide solvent / ethanol solvent / water solvent respectively.

[0047] In some embodiments, the mixture is centrifuged and the upper layer liquid is collected, and the lower layer solid product is obtained after centrifugation; the upper layer liquid is filtered to obtain a carbon quantum dot solution, and the solid product after filtration is obtained; the lower layer solid product obtained after centrifugation and the solid product after filtration are used as by-product biochar together.

[0048] In some embodiments, the time and temperature of the solvothermal reaction will affect the yield and performance of the final product carbon quantum dots. Too short a time or too low a temperature will result in too low a yield of carbon quantum dots, and too long a time or too high a temperature will change the fluorescence characteristics of the carbon quantum dots; the temperature of the solvothermal reaction is 180-260 °C and the time is 4-12 h.

[0049] In some embodiments, the microalgae include at least one of Chlorella pyrenoidosa and Nannochloropsis oculata.

[0050] In some embodiments, the mass ratio of microalgae to alcohol solvent is 1:(1-200), and further preferably 1:(5-20). Too much N,N-dimethylformamide solvent will result in too low a concentration of the reaction mixture, increasing the filtration and freeze-drying time, while too little N,N-dimethylformamide solvent will result in insufficient reaction and a reduction in the yield of carbon quantum dots.

[0051] In some embodiments, the mixture is centrifuged at a speed of 2000-8000 rpm for 5-20 min, and the upper layer liquid is collected;

[0052] The upper layer liquid is filtered using a microporous membrane with a pore size of 0.1-0.45 μm to obtain a carbon quantum dot solution.

[0053] In some embodiments, the carbon quantum dot solution is added into a dialysis bag for dialysis purification to remove small molecule substances. The cut-off molecular weight of the dialysis bag is 500-3500 Da; preferably, the cut-off molecular weight of the dialysis bag is 500-1000 Da.

[0054] In some embodiments, the dialysis solution used for dialysis includes at least one of N,N-dimethylformamide, ethanol, and deionized water, and the dialysis time is 12-24 h.

[0055] In some embodiments, microalgae and N,N-dimethylformamide solvent are added into a reaction kettle, an inert gas is introduced into the reaction kettle, and a solvothermal reaction is carried out at a rotation speed of 300-4000 rpm to obtain a mixture; the inert gas includes nitrogen, helium, neon, argon, etc.

[0056] In some embodiments, after adding microalgae and N,N-dimethylformamide solvent into the reaction kettle, a weak acid is further added into the reaction kettle; the weak acid includes at least one of formic acid and acetic acid; adding weak acids such as formic acid and acetic acid to regulate the fluorescence color.

[0057] In some embodiments, the freeze-drying temperature is -40°C to -80°C. If the temperature is too high, incomplete freezing will occur, resulting in loss of thermosensitive components. If the temperature is too low, the drying time will be too long and the sublimation rate will decrease, greatly increasing the cost.

[0058] The preparation method of the algal-based three-color fluorescent carbon quantum dots of the present invention has the following advantages:

[0059] 1. Compared with other biomass precursors, microalgae are small in size, have good dispersibility without being crushed, the reaction is more sufficient, and the high nitrogen content of microalgae is beneficial to improving the yield of carbon quantum dots. The generated algal-based carbon quantum dots have strong fluorescence characteristics, low cytotoxicity, high cell absorption efficiency, and the potential for high-contrast bioimaging.

[0060] 2. As an aprotic solvent, N,N-dimethylformamide accelerates the dehydration reaction. In the same time, the reaction is more sufficient compared with the hydrothermal method; the generated algal-based carbon quantum dots have strong fluorescence characteristics, and under the irradiation of a 365 nm ultraviolet lamp, they show red, orange, and green three-color fluorescence in N,N-dimethylformamide solvent / ethanol solvent / water solvent respectively, broadening the application channels of the product.

[0061] 3. As a solvent, N,N-dimethylformamide additionally adds N element participating in the reaction, regulating the red shift of the fluorescence color. At the same time, as a polar solvent, it helps the uniform dispersion and carbonization of carbon source molecules during the reaction, and carbon quantum dots with more uniform size distribution can be obtained.

[0062] Based on the same inventive concept, the present invention also provides an algal-based three-color fluorescent carbon quantum dot prepared by the above preparation method.

[0063] Based on the same inventive concept, the present invention also provides an application of the algal-based three-color fluorescent carbon quantum dot prepared by the above preparation method or the above algal-based three-color fluorescent carbon quantum dot in the fields of bioimaging, environmental detection, and energy catalysis.

[0064] The preparation method of the algal-based three-color fluorescent carbon quantum dots of the present application will be further described below with specific examples. This part further illustrates the content of the present invention in combination with specific examples, but should not be construed as a limitation to the present invention. Unless otherwise specified, the technical means adopted in the examples are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0065] Example 1

[0066] The embodiment of the present application provides a preparation method of algal-based three-color fluorescent carbon quantum dots, including the following steps:

[0067] S1. Add 15 g of microalgae (specifically Chlorella pyrenoidosa) and 135 g of N,N-dimethylformamide (DMF) solvent into a reaction kettle, and under an argon atmosphere, carry out a solvothermal reaction at 240 °C and under magnetic stirring at 300 rpm for 6 h to obtain a reaction mixture;

[0068] S2. Centrifuge the mixture in S1 at a speed of 4000 rpm for 10 min, and collect the upper layer liquid.

[0069] S3. Filter the upper layer liquid with a microporous filter membrane with a pore size of 0.22 μm to obtain a carbon quantum dot solution;

[0070] S4. Add the carbon quantum dot solution into a dialysis bag for dialysis purification to obtain a purified carbon quantum dot solution; the cut-off molecular weight of the dialysis bag is 1000 Da; the dialysis solution used during dialysis is N,N-dimethylformamide, and the dialysis time is 12 h;

[0071] S5. Freeze-dry the purified carbon quantum dot solution to obtain algal-based three-color fluorescent carbon quantum dots; the freeze-drying temperature is -60 °C.

[0072] According to the same method as in Example 1 above, provide the preparation methods of algal-based three-color fluorescent carbon quantum dots in Examples 2 to 9. The specific preparation process parameters are shown in Table 1 below, and the process parameters not listed are the same as those in Example 1.

[0073] Table 1 - Reaction parameters in Examples 2 to 9

[0074]

[0075]

[0076] Comparative Example 1

[0077] This comparative example provides a method for preparing algal-based fluorescent carbon quantum dots. It is the same as Example 1, except that 135 g of ethanol solvent is used instead of 135 g of N,N-dimethylformamide solvent, and the remaining process parameters are the same as those in Example 1.

[0078] Comparative Example 2

[0079] This comparative example provides a method for preparing algal-based fluorescent carbon quantum dots. It is the same as Example 1, except that 135 g of methanol solvent is used instead of 135 g of N,N-dimethylformamide solvent, and the remaining process parameters are the same as those in Example 1.

[0080] Comparative Example 3

[0081] This comparative example provides a method for preparing algal-based fluorescent carbon quantum dots. It is the same as Example 1, except that 135 g of n-butanol solvent is used instead of 135 g of N,N-dimethylformamide solvent, and the remaining process parameters are the same as those in Example 1.

[0082] Performance Characterization

[0083] Figure 1 It is the transmission electron microscope (FTEM) image of the microalgae-based carbon quantum dots prepared in Example 1. As can be seen from the figure, the product carbon quantum dots are uniformly spherical, with a relatively uniform size distribution. The particle size is between 1 and 5 nm, and the average particle size is 2.23 ± 0.56 nm. Magnifying a single carbon quantum dot particle, obvious lattice fringes can be seen, and the lattice spacing is about 0.20 nm, corresponding to the (100) crystal plane of graphite, indicating good crystallization and nucleation.

[0084] The algal-based three-color fluorescent carbon quantum dots prepared in Example 1 and the algal-based fluorescent carbon quantum dots prepared in Comparative Examples 1-3 were respectively dissolved in the preparation solvents (methanol / ethanol / n-butanol / N,N-dimethylformamide), ethanol, and deionized water and placed in a dark box under 365 nm ultraviolet light irradiation. The results are as Figure 2 shown.

[0085] Figure 2 In the first figure, the preparation solvent environments are ethanol (representing Comparative Example 1), DMF (representing Example 1), methanol (representing Comparative Example 2), and n-butanol (representing Comparative Example 3). The carbon quantum dots prepared with the corresponding preparation solvents were dissolved in the same solvent (for example, the preparation solvent in Example 1 is DMF, and the prepared carbon quantum dots were dissolved in DMF accordingly), and placed in a dark box under 365 nm ultraviolet light irradiation.

[0086] Figure 2The second figure in the text shows a dark box diagram of dissolving carbon quantum dots prepared with ethanol (representing Comparative Example 1), DMF (representing Example 1), methanol (representing Comparative Example 2), and n-butanol (representing Comparative Example 3) as the preparation solvent environments in water and irradiating them under the illumination of a 365 nm ultraviolet lamp.

[0087] Figure 2 The third figure in the text shows a dark box diagram of dissolving carbon quantum dots prepared with ethanol (representing Comparative Example 1) as the preparation solvent environment in DMF and irradiating them under the illumination of a 365 nm ultraviolet lamp.

[0088] Figure 2 The fourth figure in the text shows a dark box diagram of dissolving carbon quantum dots prepared with DMF (representing Example 1) as the preparation solvent environment in ethanol and irradiating them under the illumination of a 365 nm ultraviolet lamp.

[0089] From Figure 2 It can be seen that the carbon quantum dots prepared with N,N-dimethylformamide solvent in Example 1 emit deeper red fluorescence in the N,N-dimethylformamide solution, show bright orange fluorescence in the ethanol solvent, and emit obvious green fluorescence in the aqueous solution. This is because the polarity of the solvent changes the dominant luminescent functional groups on the surface of the carbon quantum dots. Compared with the carbon quantum dots prepared with conventional alcohol solvents such as ethanol, methanol, and n-butanol, N,N-dimethylformamide significantly causes a red shift in the fluorescence color, broadening the application channels of the carbon quantum dots.

[0090] Figure 3 It is the ultraviolet-visible absorption spectrum (UV-vis), fluorescence excitation (PLE, i.e., Excitation in the figure), and emission (PL, i.e., Emission in the figure) spectra of the algal-based carbon quantum dots prepared in Example 1. From the UV curve, it can be seen that there are two absorption peaks at 268 nm and 400 nm, corresponding to the superposition of the π-π* transition and n-π* transition of the sp 2 carbon domain and the absorption of defect states, indicating that the surface product carbon quantum dots have a rich surface state / defect state structure. The PL spectrum of the product carbon quantum dot solution has obvious multi-peak emission characteristics, with three emission peaks at 434 nm, 616 - 639 nm, and 681 nm, corresponding to blue light, orange light, and red light emissions respectively. There are also three corresponding absorption peaks in the PLE curve. Since the intensity of red and orange light is higher than that of blue light, it shows red fluorescence under the excitation of 365 nm ultraviolet light. The red shift of the excitation peak and emission peak broadens the application field of E-BCDs. The low-energy long-wavelength red light can penetrate deeper into organisms and biological tissues compared with blue-green fluorescence, and has less light damage, making it more suitable for application in the field of biomedical imaging and having good application prospects. Further, two or more excitation peaks endow it with the potential to be used as a high-precision ratio probe.

[0091] Figure 4 It is the Fourier transform infrared (FT-IR) spectrum of the microalgae-based carbon quantum dots prepared in Example 1. It can be seen that both types of carbon quantum dots have a large number of unsaturated double bonds and rich surface functional groups, which endow them with good solubility and photoluminescence properties. The choice of N,N-dimethylformamide solvent significantly leads to an increase in nitrogen-containing functional groups on the surface. Among them, pyridine nitrogen reduces the band gap by introducing new surface defect states, while graphitic nitrogen enhances the stability of the π-π* conjugate system. The protonation of amino groups further changes the electronic energy band structure of the carbon core, thus triggering the occurrence of high-purity red fluorescence. In addition to red fluorescence, the broad-spectrum absorption and multi-peak emission of the product carbon quantum dots make them have broad prospects in the fields of biological imaging, environmental detection, and energy catalysis.

[0092] Figure 5 It is the X-ray photoelectron spectroscopy (XPS) spectrum of the carbon quantum dots prepared in Example 1. It can be seen that the carbon quantum dots have a nitrogen-doped sp 2 carbon skeleton structure and are rich in oxygen-containing functional groups on the surface. The full spectrum (Figure a) shows the characteristic peaks of C1s (284.8 eV), O1s (531.5 eV), and N1s (399.8 eV), and exhibits high oxidation characteristics. The C 1s fine spectrum (Figure b) reveals the chemical environment of the carbon core through peak fitting: sp 2 / sp 3 hybridized carbon (284.8 eV), C-O / C-N (285.7 eV), carbonyl and carboxylate groups (287.5 eV). Among them, the high C-C / C═C content indicates a partially graphitized structure, which is consistent with the lamellar structure observed by TEM. The O 1s spectrum (Figure c) shows that carboxyl groups (531.2 eV) and hydroxyl / ether groups (532.6 eV) are dominant, endowing the material with hydrophilicity and tunable fluorescence properties. The coexistence of pyridine nitrogen (398.6 eV), pyrrole nitrogen (399.5 eV), and oxidized nitrogen (401.3 eV) in the N 1s spectrum (Figure d) indicates that nitrogen doping narrows the band gap through the conjugation effect, resulting in a red shift of fluorescence and enhanced photocatalytic activity.

[0093] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of algal-based three-color fluorescent carbon quantum dots, characterized in that, It includes the following steps: Add microalgae and N,N-dimethylformamide solvent into a reaction kettle, and obtain a mixture through solvothermal reaction; Centrifuge the mixture and collect the upper-layer liquid; Filter the upper-layer liquid to obtain a carbon quantum dot solution; Add the carbon quantum dot solution into a dialysis bag for dialysis purification to obtain a purified carbon quantum dot solution; Freeze-dry the purified carbon quantum dot solution to obtain algae-based tri-color fluorescent carbon quantum dots.

2. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, The temperature of the solvothermal reaction is 180-260°C and the time is 4-12 h.

3. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, wherein, The microalgae includes at least one of Chlorella pyrenoidosa and Nannochloropsis oculata.

4. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, The mass ratio of the microalgae to the alcohol solvent is 1:(1-200).

5. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, Centrifuge the mixture at a rotation speed of 2000-8000 rpm for 5-20 min and collect the upper-layer liquid; Filter the upper-layer liquid with a microporous membrane with a pore size of 0.1-0.45 μm to obtain a carbon quantum dot solution.

6. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, The cut-off molecular weight of the dialysis bag is 500-3500 Da; The dialysis solution used during dialysis includes at least one of N,N-dimethylformamide, ethanol, and deionized water.

7. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, Add microalgae and N,N-dimethylformamide solvent into a reaction kettle, introduce an inert gas into the reaction kettle, and perform solvothermal reaction at a rotation speed of 300-4000 rpm to obtain a mixture.

8. The preparation method of the algal-based three-color fluorescent carbon quantum dots according to claim 1, characterized in that, After adding microalgae and N,N-dimethylformamide solvent into a reaction kettle, add a weak acid into the reaction kettle; the weak acid includes at least one of formic acid and acetic acid; The freeze-drying temperature is -40°C to -80°C.

9. A kind of algal-based three-color fluorescent carbon quantum dots, characterized in that, It is prepared by using the preparation method according to any one of claims 1-8.

10. Application of the algae-based tri-color fluorescent carbon quantum dots prepared by using the preparation method according to any one of claims 1-8 or the algae-based tri-color fluorescent carbon quantum dots according to claim 9 in the fields of biological imaging, environmental detection, and energy catalysis.

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