1. A preparation method of a fused carbon dot is characterized by comprising the following steps: preparing a raw material carbon dot, and then performing solvothermal reaction on the raw material carbon dot in a polar aprotic organic solvent to form the fused carbon dot;

wherein the surface of the raw material carbon dots is provided with active sites, and the active sites comprise one or more of hydroxyl, carboxyl and amino; the particle size of the raw material carbon dots is 1-8 nm; the raw material carbon dots are black solids prepared by a microwave method of organic matters containing hydroxyl or carboxyl or amino acid and urea; the microwave power is 550-650W, the reaction time is 5-10 minutes, and the solvent for preparing the raw material carbon dots is water;

the polar aprotic organic solvent is selected from N, N-dimethylformamide, formamide or acetone; the dosage ratio of the raw material carbon dots to the polar aprotic organic solvent is 0.5 g-13 g: 5 mL-15 mL;

the reaction temperature of the solvothermal reaction is 200-260 ℃.

2. The method of claim 1, wherein the raw carbon dots are prepared by microwave method using citric acid and urea.

3. The method for preparing a fused carbon dot as claimed in claim 2, wherein the mass ratio of citric acid to urea is 1: 1-4.

4. The method for preparing a fused carbon dot as claimed in claim 1, wherein the solvothermal reaction comprises dissolving the raw material carbon dot in a polar aprotic organic solvent, placing the mixture in a reaction vessel, heating, performing the solvothermal reaction, dehydrating, and fusing adjacent carbon dot interfaces with each other to form the fused carbon dot; the solvothermal reaction time is 1-6 hours.

5. The method for producing a fused carbon dot as claimed in claim 4, wherein the raw material carbon dot and the polar aprotic organic solvent are used in a ratio of 0.5g to 3 g: 15 mL.

6. The method for producing a fused carbon dot according to claim 1, further comprising mixing the reaction solution after the solvothermal reaction with an alcohol solvent to precipitate a black solid, and then performing solid-liquid separation.

7. A fused carbon dot produced by the method for producing a fused carbon dot according to any one of claims 1 to 6.

8. The fused carbon dot as claimed in claim 7, wherein the fused carbon dot has characteristic absorption peaks under laser irradiation in the 560-570nm and 650-680nm bands.

9. The fused carbon dot of claim 8, wherein the fused carbon dot has a particle size of 10-30 nm.

10. Use of the fused carbon dot as claimed in any one of claims 7 to 9 for the preparation of a fluorescence imaging material, for the preparation of a photothermal conversion material or for the preparation of a pharmaceutical carrier.

Background

The tumor photothermal therapy has the technical advantages of minimal invasion, high efficiency and low adverse reaction, can inhibit tumor metastasis, and theoretically can effectively treat tumors which fail chemoradiotherapy and generate drug resistance. The basis of photothermal therapy is to obtain water-soluble nanomaterials with high photothermal conversion efficiency. However, the toxicity of the chemical components of the nano-materials themselves, or the structural biotoxicity brought by the larger size (>100nm), is a major obstacle hindering the clinical application thereof. Therefore, the development of novel nano materials with small size (<100nm), no toxicity and high photothermal conversion efficiency is of great significance.

Carbon Dots (CDs) refer to carbon particles with fluorescent properties and small size, and include graphene quantum dots, carbon nanodots, and polymer dots. The carbon nano-dots are a new nano-luminescent material and have the advantages of no toxicity and good biocompatibility. The development of the carbon nanodots with high-efficiency photo-thermal conversion has important great application value. Methods based on carbon nanodot assembly can achieve high photothermal conversion efficiency (Light: Science & Applications 7(1), 1-11). However, these methods of preparing the assembled carbon dots have weak interaction between particles, resulting in unstable structural and optical properties.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The present invention aims to provide a fused carbon dot, a preparation method and an application thereof to solve the technical problems.

The invention is realized by the following steps:

the invention provides a preparation method of a fused carbon dot, which comprises the following steps: preparing raw material carbon dots, and then performing solvothermal reaction on the raw material carbon dots in a polar aprotic organic solvent to form fused carbon dots;

wherein, the surface of the raw material carbon dot is provided with an active site, and the active site comprises one or more of hydroxyl, carboxyl and amino; the particle size of the raw material carbon dots is 1-8 nm; the raw material carbon dots are black solids prepared by a microwave method of organic matters containing hydroxyl or carboxyl or amino acid and urea; the microwave power is 550-650W, the reaction time is 5-10 minutes, and the solvent for preparing the raw material carbon dots is water;

the polar aprotic organic solvent is selected from N, N-dimethylformamide, formamide or acetone; the dosage ratio of the raw material carbon dots to the polar aprotic organic solvent is 0.5 g-13 g: 5 mL-15 mL;

the reaction temperature of the solvothermal reaction is 200-260 ℃.

In the preferred embodiment of the present invention, the raw material carbon dots are prepared by microwave method using citric acid and urea.

In a preferred embodiment of the present invention, the mass ratio of citric acid to urea is 1: 1-4.

In a preferred embodiment of the present invention, the performing the solvothermal reaction includes dissolving the raw material carbon dots in a polar aprotic organic solvent, placing the mixture in a reaction kettle, heating the mixture, performing the solvothermal reaction, dehydrating the mixture, and fusing the adjacent carbon dot interfaces with each other to form fused carbon dots; the solvothermal reaction time is 1-6 hours.

In a preferred embodiment of the present invention, the ratio of the raw material carbon dots to the polar aprotic organic solvent is 0.5 to 3 g: 15 mL.

In a preferred embodiment of the present invention, the preparation method further comprises mixing the reaction solution after the solvothermal reaction with an alcohol solvent to precipitate a black solid, and then performing solid-liquid separation.

In a preferred embodiment of the present invention, the alcohol solvent is absolute ethanol or methanol, and the amount of the alcohol solvent is 1-4 times of the volume of the reaction solution.

The invention also provides a fused carbon dot which is prepared by the preparation method of the fused carbon dot.

In a preferred embodiment of the present invention, the fused carbon dots have characteristic absorption peaks under the irradiation of laser light in the wavelength bands of 560 to 570nm and 650 to 680 nm.

An application of fused carbon dots in preparing fluorescent imaging materials, photothermal conversion materials or drug carriers.

The invention has the following beneficial effects:

the invention provides a preparation method of fused carbon dots, under the condition of high-temperature solvothermal reaction, active functional groups on the surfaces of a plurality of adjacent carbon nanodots are subjected to dehydration condensation in an aprotic polar solvent, the interfaces are fused with each other so as to promote the interaction among nanoparticles, and the fused carbon dots with specific size and specific spectral characteristics are finally formed by controlling the concentration of the carbon dots added as raw materials and the reaction temperature. The fused carbon dot has an enhanced near-infrared emission center, and also has excellent photo-thermal conversion performance and stable structural and optical properties. The preparation method of the fused carbon dots is simple and easy to implement, low in price, easy for large-scale batch preparation, and has good application prospects in the fields of photothermal conversion materials, photothermal therapy, fluorescence imaging and the like.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a TEM image and AFM image of the raw carbon nanodots r-CDs (a), (c) and the fused carbon dots f-CDs (b), (d) in example 1 of the present invention;

FIG. 2 is a graph showing the UV absorption spectra UV (measured in DMF solvent) of solvent thermal reactions conducted with different amounts of raw carbon dots of example 1 and examples 3, 4, and 5 in accordance with the present invention;

FIG. 3 is an emission spectrum (measured in DMF solvent) of raw material carbon dots (r-CDs), unfused carbon dots (h-CDs) obtained by solvothermal reaction at a low carbon dot input concentration, and fused carbon dots (f-CDs) under 589nm laser excitation;

FIG. 4 is an emission spectrum (measured in DMF solvent) of raw material carbon dots (r-CDs), unfused carbon dots (h-CDs) obtained by solvothermal reaction at a low carbon dot input concentration, and fused carbon dots (f-CDs) under 655nm laser excitation;

FIG. 5 is a graph showing the ultraviolet absorption spectra UV of b-CDs and b-f-CDs of comparative example 3 of the present invention;

FIG. 6 is a graph comparing the temperature rise curves of r-CDs of example 1, h-CDs of example 3, f-CDs of example 1, b-CDs of comparative example 3 and b-f-CDs of the present invention under 655nm excitation;

FIG. 7 is a graph of the cycling of an aqueous solution of fused carbon dots of example 1 of the present invention at 655nm excitation.

Detailed Description

Reference will now be made in detail to embodiments of the invention, one or more examples of which are described below. Each example is provided by way of explanation, not limitation, of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment, can be used on another embodiment to yield a still further embodiment.

The invention provides a preparation method of a fused carbon dot, which comprises the following steps: preparing a raw material carbon dot, and then carrying out a solvothermal reaction on the raw material carbon dot in a polar aprotic organic solvent to form a fused carbon dot, wherein the reaction temperature of the solvothermal reaction is 200-260 ℃.

Wherein, the surface of the raw material carbon dot is provided with an active site, and the active site comprises one or more of hydroxyl, carboxyl and amino; the particle size of the raw material carbon dots is 1-8 nm; the raw material carbon dots are black solids prepared by a microwave method of organic matters containing hydroxyl or carboxyl or amino acid and urea; the microwave power is 550-650W, the reaction time is 5-10 minutes, and the solvent for preparing the raw material carbon dots is water.

The polar aprotic organic solvent is selected from N, N-dimethylformamide, formamide or acetone; the dosage ratio of the raw material carbon dots to the polar aprotic organic solvent is 0.5 g-13 g: 5mL to 15 mL. For example, the ratio of the amount of the raw material carbon dots to the amount of the polar aprotic organic solvent is 0.5 g: 5mL, or 1 g: 10mL, or 2 g: 15mL, or 3 g: 15 mL.

The inventor finds that the selection of the solvent, the adding amount of the carbon dots of the reactant raw materials and the solvothermal reaction temperature have great influence on the reaction process in the process of preparing the carbon nano-material by the solvothermal method in the long-term research and practice process.

Specifically, in the process of preparing the fused carbon dots by the solvothermal method, the process of generating the fused carbon dots is a dehydration process, and the carbon nanodots cannot continue to grow due to the existence of water after the fused carbon dots are generated by reaction and due to the adoption of the proton solvent in the original solvothermal reaction. Based on the above, the inventors have conducted extensive research and practice and creatively found that fused carbon dots can be formed after adding carbon nanodots into a polar aprotic solvent to perform a solvothermal reaction, and therefore it is inferred that the reason why the carbon nanodots further react to form the fused carbon dots may be that the solvent system does not contain a protic solvent capable of providing O-H bonds or N-H bonds, and does not contain or contains very little water, and under such conditions, the solvothermal reaction process avoids the influence of the O-H bonds or N-H bonds given by water and the protic solvent on the reaction, so that the carbon nanodots having active sites on the surface, such as hydroxyl groups, carboxyl groups, amino groups, and the like, can further undergo dehydration condensation, continue to fuse and grow, and finally aggregate to form the fused carbon dots.

The effect of the addition of the carbon dots of the reactant feedstocks on the course of the reaction is shown below: after the raw material carbon points are added into the solvent, the surface active sites of the adjacent small-size raw material carbon points are subjected to dehydration condensation in the aprotic polar solvent, the plurality of raw material carbon points are combined pairwise, and the interfaces are fused with each other. Through a large number of experiments, the inventor creatively discovers that when the addition amount of the raw material carbon dots is too low (<0.5g), the concentration of the raw material carbon dots is not enough to meet the minimum concentration of fusion, under the condition of the addition amount of the raw material carbon dots being lower than 0.5g, the carbon nanodots only undergo the change of a carbon core structure in the heating process, the fusion phenomenon cannot be generated, red light/near infrared absorption centers are difficult to appear, and the obtained product carbon dots are unfused carbon dots (h-CDs); when the addition amount of the raw material carbon points is too high (>3g), the raw material carbon points are gathered in a large amount, and the absorption performance of the obtained fused carbon points in a near infrared region is general; fused carbon dots (f-CDs) having a specific particle size (13 to 20nm) can be obtained only when three to five small-sized carbon dots are fused with each other by solvothermal heating when the amount of the raw material carbon dots added is in a specific range, i.e., 0.5g to 3 g. Compared with the small-sized raw material carbon dots, the fused carbon dots have the characteristics of long-wavelength absorption (red/near infrared) and luminescence, and also have more excellent photo-thermal conversion performance. In the present invention, the term "long wavelength" refers to a light wave having a wavelength of 550nm to 680 nm.

The larger the number of active sites on the surface of the small-size raw material carbon dots, the higher the solvothermal reaction temperature (>200 ℃), and the more favorable the dehydration reaction is, the more thorough the dehydration reaction is.

In one embodiment, the active sites include hydroxyl, carboxyl and amino groups, and the carbon nanodots containing three reactive groups are more susceptible to dehydration fusion growth.

In the preferred embodiment of the present invention, the raw material carbon dots are prepared by microwave method using citric acid and urea. The microwave power may be 550W, 580W, 590W, 600W, 620W, 640W, or 650W. The reaction time may be 5 minutes, 6 minutes, 7 minutes, 8 minutes, or 10 minutes.

The raw material carbon dots prepared by the method are spherical or cake-shaped (flat structures), the diameter is 2-6nm, and the core structure is a multi-layer graphene structure. The carbon nanodot edge is rich in a large number of functional groups (hydroxyl, carboxyl and the like), and provides a good active site for further dehydration condensation later.

In a preferred embodiment of the present invention, the mass ratio of citric acid to urea is 1: 1-4.

In a preferred embodiment of the present invention, the performing the solvothermal reaction includes dissolving the raw material carbon dots in a polar aprotic organic solvent, placing the mixture in a reaction kettle, heating the mixture, performing the solvothermal reaction, dehydrating the mixture, and fusing the adjacent carbon dot interfaces with each other to form fused carbon dots; the solvothermal reaction time is 1-6 hours.

In one embodiment, the solvothermal reaction is preferably carried out for 1 to 3 hours, for example, 1 hour, 2 hours or 3 hours, although in other embodiments, the reaction time may be suitably extended for the reaction to be more complete. The temperature of the solvothermal reaction may be 200 ℃, 220 ℃, 240 ℃ or 260 ℃.

The heating mode of the solvothermal reaction is oven heating, and the oven heating is uniform, so that the reaction is favorably carried out. Of course, in other modes, heating methods such as heating jacket, water bath heating, heating pipe heating and the like can also be adopted.

In a preferred embodiment of the present invention, the ratio of the raw material carbon dots to the polar aprotic organic solvent is 0.5 to 3 g: 15 mL. For example, it may be 0.5g, 1g, 1.5g, 2g or 3 g. In this range, the small-sized raw material carbon nanodots can be sufficiently fused, and the obtained fused carbon dots have a specific particle size (13-20nm), have both red/near-infrared absorption characteristics, and have excellent photothermal conversion performance.

In some embodiments, the adding amount is controlled to be between 0 and 13g so as to fully explore the influence of the adding amount of the raw material carbon dots on the optical properties of the fused carbon dots; for example, the amount may be 0.015g, 1g, 3g, 13g, etc.

In a preferred embodiment of the present invention, the preparation method further comprises mixing the reaction solution after the solvothermal reaction with an alcohol solvent to precipitate a black solid, and then performing solid-liquid separation.

Optionally, the solid-liquid separation is a separation method such as centrifugal separation and solvent evaporation. Optionally, after centrifugation, freeze-drying to obtain fused carbon dots in powder particle form.

In a preferred embodiment of the present invention, the alcohol solvent is absolute ethanol or methanol, propanol; the amount of the alcohol solvent is 1 to 4 times the volume of the reaction solution, for example, 1.5 times, 2 times or 3 times the volume of the reaction solution. In order to improve the separation efficiency, the separated solid can be repeatedly mixed with the alcoholic solution, and the solid-liquid separation is carried out for multiple times to improve the yield of the product.

The invention also provides a fused carbon dot which is prepared by the preparation method of the fused carbon dot.

In a preferred embodiment of the present invention, the fused carbon dots have characteristic absorption peaks under the irradiation of laser light in the wavelength bands of 560 to 570nm and 650 to 680 nm. Under the excitation of laser of 589nm and 655nm, the fluorescence emission peak intensity of the fused carbon point is strongest, and the fused carbon point has excellent photo-thermal conversion efficiency. The fused carbon dots have a particle size of 10-30 nm.

An application of fused carbon dots in preparing fluorescent imaging materials, photothermal conversion materials or drug carriers.

The photothermal conversion material such as nanometer fluid and water-gas interface material is used for generating steam, can be used for power generation and sterilization, and solves the problems of water pollution, seawater desalination, energy shortage and the like.

The fused carbon dots can be used to make dust free paper, filter paper, films, aerogels, cellulose, microporous coke, photothermal receivers, and the like.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

This example provides a method for preparing a fused carbon dot, which comprises preparing a raw material carbon dot, and performing a solvothermal reaction on the raw material carbon dot to form the fused carbon dot.

The preparation of the raw material carbon dots comprises the following steps: 1g of citric acid and 1g of urea are dissolved in 10mL of water to obtain a transparent solution, the transparent solution is placed in a microwave oven and reacts for 10 minutes under 650W, and black solids, namely raw material carbon dots (r-CDs), are obtained after the reaction.

Mixing the raw material carbon dots according to the proportion of 1 g: dissolving 15mL of the solution in N, N-dimethylformamide, placing the obtained N, N-dimethylformamide solution in a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 220 ℃ for 2 hours in an oven, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying to obtain black solid powder, namely fused carbon dots (f-CDs).

Example 2

This example provides a method for preparing a fused carbon dot, which comprises preparing a raw material carbon dot, and performing a solvothermal reaction on the raw material carbon dot to form the fused carbon dot.

The preparation of the raw material carbon dots comprises the following steps: dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a microwave oven, reacting for 10 minutes under 650W to obtain a black solid, namely a raw material carbon dot.

Mixing the raw material carbon dots according to the proportion of 1 g: dissolving 15mL of acetone, placing the obtained acetone solution in a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 220 ℃ for 2 hours in an oven, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying to obtain black solid powder, namely a fused carbon dot.

Example 3

Dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a microwave oven, reacting for 10 minutes under 650W to obtain a black solid, namely a raw material carbon dot.

Mixing the carbon nanodots in a ratio of 3 g: dissolving 15mL of the solution into DMF, placing the obtained DMF solution into a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 220 ℃ for 2 hours in an oven heating manner, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying to obtain black solid powder, namely a fused carbon dot.

Example 4

Dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a microwave oven, reacting for 10 minutes under 650W to obtain a black solid, namely a raw material carbon dot.

And (3) mixing the carbon nanodots according to the weight ratio of 13 g: dissolving 15mL of the solution into DMF, placing the obtained DMF solution into a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 220 ℃ for 2 hours in an oven heating manner, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying to obtain black solid powder, namely a fused carbon dot.

Example 5

Dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a microwave oven, reacting for 10 minutes under 650W to obtain a black solid, namely a raw material carbon dot.

Mixing the carbon nanodots in a ratio of 1 g: dissolving 15mL of the solution into DMF, placing the obtained DMF solution into a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 200 ℃ for 2 hours in an oven, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying at-47 ℃ to obtain black solid powder, namely a fused carbon dot.

Example 6

Compared with example 1, the difference is only that the preparation method of the raw material carbon dot is different, the raw material carbon dot is that 1g of lysine and 1g of urea are dissolved in 10mL of water to obtain a transparent solution, the transparent solution is placed in a microwave oven, the reaction is carried out for 10 minutes under 650W, and a black solid, namely the raw material carbon dot, is obtained after the reaction.

Example 7

The only difference compared with example 1 is that the addition ratio of the raw material carbon point to N, N-dimethylformamide is 12 g: 15 mL.

Example 8

Compared with example 1, the difference is only that the preparation method of the raw material carbon dot is different, the raw material carbon dot is that 1g of citric acid and 4g of urea are dissolved in 10mL of water to obtain a transparent solution, the transparent solution is placed in a microwave oven and reacted for 10 minutes under 650W, and a black solid, namely the raw material carbon dot, is obtained after the reaction.

Example 9

Compared with example 1, the difference is only that the preparation method of the raw material carbon dot is different, the raw material carbon dot is that 1g of citric acid and 3g of urea are dissolved in 10mL of water to obtain a transparent solution, the transparent solution is placed in a microwave oven and reacted for 10 minutes under 650W, and a black solid, namely the raw material carbon dot, is obtained after the reaction.

Example 10

Compared with example 1, the difference is only that the preparation method of the raw material carbon dot is different, the raw material carbon dot is that 1g of citric acid and 2g of urea are dissolved in 10mL of water to obtain a transparent solution, the transparent solution is placed in a microwave oven and reacts for 10 minutes under 650W, and a black solid, namely the raw material carbon dot, is obtained after the reaction.

Comparative example 1

The difference from example 1 is only that the microwave power during the solvothermal reaction was 500W, the reaction time was 10 minutes, and other preparation conditions were the same as example 1.

The experimental result shows that different microwave powers have no great influence on the photothermal conversion performance and the stability of optical properties of the fused carbon dots.

Comparative example 2

The difference from example 1 is only that the reaction time during the solvothermal reaction was 3 minutes, and other preparation conditions were the same as in example 1.

Comparative example 3

Compared with example 1, the difference is only in the preparation method of the raw material carbon dots, fused carbon dots (b-f-CDs) are prepared by using dark blue carbon dots, and the conditions of the solvothermal reaction are the same as those of example 1. The raw material carbon dots are prepared by the following steps:

dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a 30mL of polytetrafluoroethylene high-pressure reaction kettle, reacting at 160 ℃ for 5 hours, adding 60mL of ethanol into the reacted solution to obtain a black solid, washing the black solid with water, centrifuging (8000rpm, 5min), and freeze-drying to obtain dark blue powder, namely raw material carbon dots (b-CDs).

Comparative example 4

This example provides a method for preparing a fused carbon dot, which comprises preparing a raw material carbon dot, and performing a solvothermal reaction on the raw material carbon dot to form the fused carbon dot.

The preparation of the raw material carbon dots comprises the following steps: dissolving 1g of citric acid and 1g of urea in 10mL of water to obtain a transparent solution, placing the transparent solution in a microwave oven, reacting for 10 minutes under 650W to obtain a black solid, namely a raw material carbon dot.

Adding the raw material carbon dots according to the proportion of 0.015 g: dissolving 15mL of the solution into DMF, placing the obtained DMF solution into a 30mL polytetrafluoroethylene high-pressure reaction kettle, heating for reaction at 220 ℃ for 2 hours in an oven heating manner, adding 60mL of ethanol into the reacted solution, centrifuging, and freeze-drying to obtain black solid powder, namely unfused carbon dots (h-CDs).

Experimental example 1

Transmission electron microscopy and atomic force microscopy analyses were performed on the small-sized raw material carbon dots and the fused carbon dots of example 1, and a transmission electron microscopy TEM image and an atomic force AFM image are shown in fig. 1, in fig. 1: a is a transmission electron microscope of raw material carbon dots; c is an atomic force picture of the carbon point; b is a TEM image of fused carbon dots; d is an AFM image of the fused carbon dots. As shown in FIG. 1, after the complex fusion growth reaction, the particle size of the fused carbon dots is increased, the particle size is about 13-20nm, and the height is about 7-12 nm.

Experimental example 2

The fluorescence characteristics of the carbon nanodots (r-CDs), the fused carbon dots (f-CDs) and the unfused carbon dots (h-CDs) in example 1 and example 3 were observed by absorption and fluorescence spectrum PL, as shown in FIG. 2, FIG. 3 and FIG. 4. As shown in FIG. 2, after the compounding, when the addition amount of the raw material carbon point is in the range of 0.5g-3g, the fused carbon point obtained after the secondary solvothermal reaction generates new strong absorption peaks at the wavelength bands of 560-570nm and 650-680 nm. Therefore, carbon dots synthesized in an amount of the raw material carbon dots added in the range of 0.5g to 3g are called fused carbon dots (f-CDs). Carbon dots obtained below this addition range are referred to as unfused carbon dots (h-CDs). FIGS. 3 and 4 show that the fused carbon dots have the strongest fluorescence emission peak intensities under laser excitation at 589nm and 655 nm.

Experimental example 3

Observing the change of the absorption curve before and after the fusion of the blue light carbon dots of the comparative example 3 through an absorption spectrum; from fig. 5, it is found that the fused carbon dots obtained after the recombination generate a new strong absorption peak in the long wavelength region. Meanwhile, through the photothermal property test, it is found from fig. 6 that the photothermal property of the blue light carbon dot after fusion is slightly improved.

Experimental example 4

The aqueous solutions of the raw material carbon dots, the fused carbon dots, and the unfused carbon dots of example 1 were irradiated with laser light, and the temperature change thereof was observed with a thermal imager. Laser parameters: 655nm, 1.4W/cm². Carbon nano-meterPoint concentration volume parameter: 200ppm, 1 mL. The same volume concentration of water, carbon nanodots, unfused carbon dots, and fused carbon dots was used as a control. The sample was irradiated with laser light, and the result is shown in fig. 6. FIG. 5 is a graph showing the temperature rise of the material under 655nm laser irradiation, and it is found from FIG. 6 that 200ppm of the fused carbon dot material was heated up to 48 ℃ after 10 minutes of irradiation (the temperature before irradiation was about 25 ℃). Correspondingly, the raw material carbon nano-dots and the unfused carbon dots with the same concentration are heated to about 15 ℃.

The cycling curve under 655nm excitation of 200ppm of the aqueous solution of the fused carbon dots of example 1 with repeated irradiation is shown in FIG. 7. From fig. 7, it is found that the material has a substantially constant temperature rise rate after multiple cycles, and is a good photo-thermal material.

In conclusion, the fused carbon dots provided by the embodiment of the invention have good biological safety and can be applied to the fields of photothermal therapy, drug carriers and the like. In the preparation method, a certain amount of small-size raw material carbon nanodots are subjected to high-temperature solvothermal reaction, active sites (hydroxyl, carboxyl, amino and the like) on the surfaces of the carbon nanodots are dehydrated, fused and grown among particles in an aprotic polar solvent, and finally aggregated into fused carbon dots, so that a novel method for preparing the fused carbon dots is provided, and the fused carbon dots have the characteristics of red light/near infrared absorption and emission relative to the raw material carbon dots, and have more excellent photo-thermal conversion performance. In addition, the preparation method of the fused carbon dots is simple and easy to operate, has low price and is beneficial to large-scale production.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.