CN111718713B

CN111718713B - Carbon dot, preparation method and application thereof, and solid luminescent forming material

Info

Publication number: CN111718713B
Application number: CN202010706792.XA
Authority: CN
Inventors: 赵丹; 郝健
Original assignee: South Central University for Nationalities
Current assignee: South Central Minzu University
Priority date: 2020-07-21
Filing date: 2020-07-21
Publication date: 2022-11-29
Anticipated expiration: 2040-07-21
Also published as: CN111718713A

Abstract

The invention discloses a carbon dot, a preparation method and application thereof, and a solid luminescent forming material. The preparation method of the carbon dots comprises the following steps: dissolving and mixing the carbon dot preparation raw materials in a solvent, and removing the solvent capable of reacting with the dehydrating agent. Adding a dehydrating agent into the uniform mixture, and reacting at the temperature of 80-200 ℃; the carbon dot preparation raw materials contain hydrophilic groups, the carbon dot preparation raw materials are fully and uniformly mixed in a dissolving mode, basic conditions are provided for reaction effects, in addition, in the reaction process, the hydrophilic groups contained in the raw materials are subjected to condensation polymerization under the action of the dehydrating agent, water-soluble and hydrophobic carbon dots can be simultaneously generated in the reaction process, and the synthesis ratio of the water-soluble and hydrophobic carbon dots can be realized by controlling the using amount and the type of the dehydrating agent. In addition, the whole preparation process is simple to operate, the wavelength of the synthesized hydrophobic carbon dots is long and adjustable, and the fluorescence quantum yield of the carbon dots is high.

Description

Carbon dot, preparation method and application thereof, and solid luminescent forming material

Technical Field

The invention relates to the technical field of nano materials, in particular to a carbon dot, a preparation method and application thereof, and a solid luminescent forming material.

Background

Carbon Dots (CDs) are a novel fluorescent nano material, and are widely concerned by researchers due to the fact that the surface of the CDs is easy to functionalize, the biocompatibility is good, the chemical property is stable, the photobleaching resistance is strong, the raw materials are rich and the preparation is easy. Carbon dots have increasingly shown potential to replace conventional quantum dots in applications in the fields of drug delivery, medical diagnostics, two-photon imaging, ion detection and catalysis.

Most of the CDs synthesized so far are water-soluble CDs. However, due to the limitation of surface groups, such CDs are prone to fluorescence quenching after aggregation (ACQ phenomenon), and are difficult to be applied to organic electronics, thin film applications, or sensors in hydrophobic environments, and the like. Therefore, hydrophobic Carbon Dots (HCDs) have become a new subject of research by researchers.

At present, the methods for synthesizing carbon dots mainly include arc discharge, laser ablation, chemical oxidation in strong acid and electrochemical synthesis, where allotropes of carbon, such as carbon nanotubes, nanodiamonds or graphite, are pulverized until the product yields the properties of fluorescent nanoparticles. The method for preparing the hydrophobic carbon dots mainly comprises the following steps: firstly, water-soluble CDs (WCDs) are synthesized, and then the WCDs are converted into HCDs through surface modification, or the HCDs are prepared through high-temperature one-step reaction in strong acid, strong base or organic reagent. The preparation methods have the defects of complicated operation steps, long time consumption, low quantum yield, strong toxicity and corrosivity of selected solvents and the like. In addition, the prior art also lacks a carbon dot preparation method which can simultaneously prepare water-soluble and hydrophobic carbon dots.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a carbon dot, a preparation method and application thereof and a solid luminescent forming material, so as to solve the problems.

The invention is realized by the following steps:

in a first aspect, an embodiment of the present invention provides a method for preparing carbon dots, including:

adding a dehydrating agent into the uniform mixture of the carbon dot preparation raw materials, and reacting at the temperature of 100-200 ℃; wherein, the carbon dot preparation raw material contains hydrophilic groups, and the uniform mixture is mainly prepared by the following preparation steps: dissolving and mixing the carbon dot preparation raw materials in a solvent, and removing the solvent capable of reacting with the dehydrating agent.

In a second aspect, the embodiment of the present invention further provides a carbon dot prepared by the above preparation method, and optionally, the carbon dot is a hydrophobic carbon dot separated after the reaction.

In a third aspect, the embodiment of the invention also provides an application of the carbon dots in preparation of a fluorescent material.

In a fourth aspect, the present invention further provides an application of the carbon dot in preparation of a solid lighting device, a display, or a solid light-emitting forming material, where the carbon dot is a hydrophobic carbon dot separated after reaction, and optionally, the hydrophobic carbon dot is an N, S co-doped hydrophobic carbon dot with a fluorescence emission wavelength of 450 to 580 nm.

In a fifth aspect, the embodiment of the present invention further provides a solid luminescent excipient, wherein the raw material components of the solid luminescent excipient contain the hydrophobic carbon dots.

The invention has the following beneficial effects: the method comprises the steps of dissolving the carbon dot preparation raw materials firstly and then removing a solvent capable of reacting with the dehydrating agent, so that the carbon dot preparation raw materials can be fully and uniformly mixed, basic conditions are provided for the reaction effect generated by the carbon dots, then the dehydrating agent is added into the uniform mixture, and in the process of generating the carbon dots through reaction, carboxyl, amino or hydroxyl and other hydrophilic groups contained in the carbon dot preparation raw materials can be subjected to condensation polymerization under the action of the dehydrating agent, so that water-soluble carbon dots and hydrophobic carbon dots can be generated in the reaction process at the same time. And the synthesis ratio of the water-soluble carbon points and the hydrophobic carbon points can be realized by controlling the using amount and the type of the dehydrating agent. In addition, the whole preparation process is simple to operate, the wavelength of the synthesized hydrophobic carbon dots is long and adjustable, and the fluorescence quantum yield of the carbon dots is high.

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 photograph (mixture of hydrophilic and hydrophobic carbon dots) of a solid product synthesized in the second step of example 1 of the present invention;

FIG. 2 is a photograph of a solid product (mixture of hydrophilic and hydrophobic carbon dots) synthesized in the second step of example 2 of the present invention;

FIG. 3 is a photograph of a solid product (mixture of hydrophilic and hydrophobic carbon dots) synthesized in the second step of example 3 according to the present invention;

FIG. 4 is a photograph of a hydrophobic carbon dot solution of example 1 of the present invention under 365nm UV irradiation;

FIG. 5 is a graph showing fluorescence emission of the hydrophobic carbon dots synthesized in example 1 of the present invention;

FIG. 6 is a UV-VIS absorption spectrum of the hydrophobic carbon dots synthesized in example 1 of the present invention;

FIG. 7 shows an XPS scan spectrum (i) of a hydrophobic carbon dot, a peak spectrum (ii) of C1S XPS, a peak spectrum (iii) of N1S XPS, a peak spectrum (iV) of O1S XPS, and a peak spectrum (V) of S2p XPS synthesized in example 1 of the present invention;

FIG. 8 is a photograph of a hydrophilic carbon dot solution synthesized in example 1 according to the present invention under 365nm UV irradiation;

FIG. 9 is a graph showing fluorescence emission of hydrophilic carbon dots synthesized in example 1 of the present invention;

FIG. 10 is a graph showing UV-VIS absorption spectra of hydrophilic carbon dots synthesized in example 1 of the present invention;

FIG. 11 is a photograph of a hydrophobic carbon dot solution in comparative example 1 of the present invention under 365nm ultraviolet light irradiation;

FIG. 12 is a graph showing fluorescence emission of the hydrophobic carbon dot synthesized in comparative example 1 according to the present invention;

FIG. 13 is a photograph of a hydrophilic carbon dot solution synthesized in comparative example 1 according to the present invention under 365nm UV irradiation;

FIG. 14 is a graph showing fluorescence emission of a hydrophilic carbon dot synthesized in comparative example 1 according to the present invention;

FIG. 15 is a white light LED lamp constructed by using the synthesized hydrophobic carbon dots of example 1 as one of the light source components;

FIG. 16 is a graph of the electroluminescence spectrum of the white light emitting LED lamp of FIG. 12;

fig. 17 contains a picture of a solid state epoxy device bearing the hydrophobic carbon dots of example 1 in natural light;

fig. 18 is a photograph of a solid state epoxy device loaded with hydrophobic carbon dots of example 1 under 365nm uv light;

FIG. 19 is a photograph comparing a hydrophilic carbon dot solution in example 2 of the present invention under irradiation of natural light and 365nm ultraviolet light;

FIG. 20 is a fluorescence emission spectrum of the synthesized hydrophobic carbon dots of example 2;

FIG. 21 is a photograph showing a comparison of the hydrophobic carbon dot solution of example 3 of the present invention under irradiation of natural light and 365nm ultraviolet light.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of 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 conventional products which are not indicated by manufacturers and are commercially available.

The carbon dots, the preparation method and the application thereof, and the solid luminescent forming material provided by the present invention are specifically described below.

The inventors have analyzed the carbon dot preparation method of the prior art and found that there is a lack of a synthesis method capable of easily simultaneously producing water-soluble carbon dots and hydrophobic carbon dots. The preparation methods of the hydrophobic carbon dots mainly comprise two types, one is to synthesize hydrophilic CDs (WCDs) and then convert the WCDs into HCDs by surface modification. For example, shang and his colleagues dissolve WCDs in toluene and oleylamine under heating reflux at 130 ℃ in an oil bath environment, and after 6 hours, orange HCDs are obtained, the emission wavelength (lambda em) of which is red-shifted by 20nm compared with the WCDs; after obtaining WCDs by Varisco et al, ethylenediamine or dodecylamine was added and stirred at 115 ℃ for 4 hours to obtain HCDs with unchanged wavelength. Such methods are complicated and time consuming to operate, and may result in reduced quantum yields. Another type is the preparation of HCDs by high temperature one-step reactions in strong acids, bases or organic reagents. The commonly used reaction reagents comprise strong acid and strong alkali such as phosphoric acid, nitric acid, sodium hydroxide and the like or organic reagents such as toluene, 1-octadecene and the like as solvents. And the reaction temperature of most experiments is between 160 and 280 ℃, and the reaction time is different from 20min to 12h. However, the solvent selected by the method has the characteristics of strong toxicity and corrosivity, is not environment-friendly and does not accord with the characteristic of green synthesis.

Therefore, it is one of the main objects of the present invention to develop a solid phase synthesis method with simple and fast operation and green process (with or without strong acid, strong base and organic reagent) to obtain HCDs emitting light of long wavelength. Therefore, based on the defects existing in the current carbon dot preparation, the inventor creatively proposes the following technical scheme through a great deal of research and practice on the basis of the prior art.

Some embodiments of the present invention provide a method of preparing a carbon dot, including: adding a dehydrating agent into the uniform mixture of the carbon dot preparation raw materials, and reacting at the temperature of 100-200 ℃. Wherein, the carbon dot preparation raw material contains hydrophilic groups, and the uniform mixture is mainly prepared by the following preparation steps: dissolving and mixing the carbon dot preparation raw materials in a solvent, and removing the solvent capable of reacting with the dehydrating agent.

The carbon dot preparation raw materials are dissolved firstly, and then the solvent capable of reacting with the dehydrating agent is removed, so that the carbon dot preparation raw materials can be fully and uniformly mixed, and the solvent can not react with the dehydrating agent to influence the synthesis process of the carbon dots. It should be noted that the solvent removal in the embodiment of the present invention may also be a basic removal, and it should be ensured that a small amount of residual solvent does not affect the carbon dot synthesis process, and preferably, the solvent removal is a complete removal. When the solvent is not reacted with the dehydrating solvent, the removal step of the solvent is not an essential step.

Furthermore, in the process of generating the carbon dots through the reaction, the dehydrating agent can promote condensation polymerization of hydrophilic groups such as carboxyl, amino or hydroxyl contained in the raw materials for preparing the carbon dots, promote the synthesis of the carbon dots, realize the preparation of water-soluble carbon dots and hydrophobic carbon dots, and the water-soluble carbon dots and the hydrophobic carbon dots are synthesized simultaneously in the synthesis process, but the main bodies of the water-soluble carbon dots and the hydrophobic carbon dots are hydrophobic carbon dots. The synthesis ratio of the water-soluble carbon dots and the hydrophobic carbon dots and the wavelength of the hydrophobic carbon dots can be realized by adjusting the amount and the type of the dehydrating agent. That is, the more dehydrating agents are used, the less water-soluble carbon dots are synthesized, the more hydrophobic carbon dot ratio is increased and the wavelength is red-shifted.

The longer the reaction time and the higher the reaction temperature are, the more advantageous the preparation of the long-wavelength hydrophobic carbon dot is.

Specifically, some embodiments of the present invention provide a method for preparing a carbon dot, which includes the steps of:

s1, dissolving and mixing the carbon dot preparation raw materials in a solvent, and removing the solvent capable of reacting with a dehydrating agent.

In some embodiments, the carbon site preparation feedstock includes, but is not limited to, a carbon source and a nitrogen and sulfur co-dopant. Further, the carbon source includes, but is not limited to, at least one of citric acid, oxalic acid, sodium citrate, sodium oxalate, glucose. Nitrogen, sulfur co-dopants include, but are not limited to, at least one of D, L-homocysteine, L-methionine, L-cysteine hydrochloride, D-cysteine, glutathione, N-acetyl-L-cysteine, beta-mercaptoethylamine, and thioacetamide.

In some preferred embodiments, the nitrogen and sulfur co-dopant comprises at least one of L-cysteine, L-cysteine hydrochloride, and N-acetyl-L-cysteine. In some preferred embodiments, the mass ratio of the carbon source to the nitrogen and sulfur co-doping agent is 1:0.5 to 10.

Or the carbon dot preparation raw materials comprise ethylenediamine, polyethyleneimine, phenol and the like.

In some embodiments, the solvent used for dissolving the carbon dot preparation raw material is water, and removing the solvent after dissolving and mixing the carbon dot preparation raw material in the solvent comprises: the carbon dot preparation raw materials are dissolved in water, and then react for 6 to 15 hours at the temperature of between 60 and 80 ℃, and the water is preferably ultrapure water. Namely, after completely dissolving the carbon dot preparation raw material, preferably powder, in water, and evaporating the water by heating, a solid homogeneous mixture containing no water or a slurry homogeneous mixture containing a small amount of water is obtained.

In some embodiments, the vessel for dissolving and removing the solvent is selected from any one of a polytetrafluoroethylene reaction liner, a beaker, and a round-bottom flask. Preferably, the vessel is a polytetrafluoroethylene reaction liner.

S2, adding a dehydrating agent into the uniform mixture of the carbon dot preparation raw materials, and reacting at the temperature of 80-200 ℃.

In some embodiments, the reaction is carried out for a time period of 10 to 360min, preferably 20 to 200min, more preferably 20 to 80min. The above reaction time can be controlled to allow the preparation raw materials to react sufficiently to obtain carbon dots with better quality.

Further, depending on the proportion of hydrophobic carbon sites desired and the mass requirements, in some embodiments, the amount of dehydrating agent may be from 0.1 to 1g.

Further, in some embodiments, dehydrating agents include, but are not limited to, polyphosphoric acid, N' -Dicyclohexylcarbodiimide (DCC), 1- (3-dimethylaminopropyl) -3-Ethylcarbodiimide (EDC), 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride (EDCI), N-dimethylformamide, 2-dichloro-5- (2-phenylethyl) -4- (trimethylsilyl) -3-furanone (DPTF), 1, 3-dimethyl-2-imidazolidinone (P-DMI), bis (trichloromethyl) carbonate (BTC), thionyl chloride-dimethylformamide (SOCl) ₂ -DMF), 2-chloro-1, 3 dimethylimidazolium chloride (DMC), phosphorus pentachloride, phosphorus oxychloride and phosphorus pentoxide.

In some preferred embodiments, the dehydrating agent is N, N' -dicyclohexylcarbodiimide, 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide or 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride.

Specifically, the dehydrating agent is mostly solid, and therefore, in order to allow sufficient contact between the dehydrating agent and the raw material for manufacturing carbon dots, in some embodiments, the dehydrating agent is added in the form of an organic solution, and preferably, the organic solvent for dissolving the dehydrating agent is acetonitrile, but the amount of the organic solvent for dissolving the dehydrating agent is very small, only 100 to 1000uL, and does not substantially affect the reaction system, and the process of uniformly preparing the raw material for manufacturing carbon dots with water, removing water, and then adding the dehydrating agent to perform the reaction is not performed in the organic solvent as a whole. Further, when the dehydrating solvent is selected to be a liquid dehydrating solvent, it is not necessary to add an organic solvent to dissolve the dehydrating solvent.

Further, in some embodiments, the reaction vessel for preparing the carbon dots is selected from any one of a hydrothermal reaction kettle, a beaker and a round-bottom flask, and in a preferred embodiment, the reaction vessel is a hydrothermal reaction kettle.

In some embodiments, the heating vessel for heating to maintain the reaction temperature is selected from any one of a water bath, an oil bath, and an electrically heated constant temperature forced air drying oven. In a preferred embodiment, the heating container is an electric heating constant temperature air blowing drying oven.

Further, since the carbon dots directly generated by the synthesis reaction are solid in a consolidated state in which water-soluble carbon dots and hydrophobic carbon dots are mixed, some embodiments may further include the step of selectively:

and S3, dissolving the carbon dot solid obtained by the reaction with a solvent to obtain a carbon dot solution.

In some embodiments, since the carbon dot solid includes both water-soluble carbon dots and hydrophobic carbon dots, the carbon dot solid is dissolved with a water-soluble solvent and a hydrophobic solvent, respectively, to obtain a solution of water-soluble carbon dots and a solution of hydrophobic carbon dots, and then the water-soluble carbon dots and the hydrophobic carbon dots are obtained by removing the solvents, respectively. When the solvent is water, the carbon dots in the carbon dot solution are hydrophilic carbon dots, and the residual solid is extracted by the corresponding solvent to obtain hydrophobic carbon dots; when the hydrophobic carbon dots are dissolved by using a hydrophobic solvent capable of dissolving the hydrophobic carbon dots, the obtained carbon dot solution is the hydrophobic carbon dot solution, and the remaining solid is extracted by pure water and the like to obtain the water-soluble carbon dots. Therefore, the water-soluble carbon dots and the hydrophobic carbon dots can be separated by means of solvent dissolution extraction, and the separate water-soluble carbon dots and hydrophobic carbon dots are obtained.

The method of removing the solvent from the carbon dot solution to obtain the carbon dots includes, but is not limited to, rotary evaporation, freeze drying, and the like.

Specifically, in some embodiments, the water soluble solvent is water and the hydrophobic solvent is an organic solvent including, but not limited to, at least one of cyclohexane, carbon tetrachloride, chloroform, tetrahydrofuran, and methanol. Preferably, the hydrophobic solvent is chloroform.

It should be noted that, when water is selected to be used as a solvent for preparing the raw material at the carbon point in the embodiment, the use of an organic solvent is avoided in the whole synthesis process, and the method is environment-friendly and green. In contrast, in other existing synthesis methods, an organic solution is used and needs to be heated, and the organic solution is easy to volatilize when being heated, so that the potential safety hazard problem exists. The embodiment of the invention needs to be dissolved by organic solvent extraction in the separation stage, but does not need heating.

Some embodiments of the present invention also provide a carbon dot prepared by the method for preparing a carbon dot according to any one of the preceding embodiments. In some preferred embodiments, the carbon sites are hydrophobic carbon sites isolated after the reaction. Furthermore, the hydrophobic carbon dot can also be an N and S co-doped hydrophobic carbon dot with the fluorescence emission wavelength of 450-540 nm.

Some embodiments of the invention also provide application of the carbon dots in preparation of fluorescent materials.

Some embodiments of the present invention also provide the use of carbon dots, which are hydrophobic carbon dots separated after reaction, in the preparation of solid lighting devices, displays or solid luminescent excipient materials.

Some embodiments of the present invention also provide a solid luminescent excipient, which contains the above hydrophobic carbon dots in the raw material components.

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

Example 1

(1) Citric acid and L-cysteine hydrochloride were placed in a polytetrafluoroethylene liner, and 2mL of ultrapure water was added to the liner to dissolve and mix uniformly, the amount of citric acid was 0.4mmoL and the amount of L-cysteine hydrochloride was 0.5mmoL. The lining is placed in an electric heating constant temperature air blast drying oven to react for 12 hours at 70 ℃.

(2) And (2) adding 0.3g of N, N' -Dicyclohexylcarbodiimide (DCC) into the lining in the step (1), putting the lining into a hydrothermal reaction kettle, placing the hydrothermal reaction kettle into an electric heating constant-temperature air blowing drying box, and reacting for 40min at 180 ℃ to obtain a dark brown solid product (shown in figure 1).

(3) And ultrasonically dissolving the solid product by using trichloromethane to obtain a hydrophobic carbon dot solution, and then performing rotary evaporation to obtain a hydrophobic carbon dot solid. And (3) ultrasonically extracting the solid insoluble in the trichloromethane for multiple times by using 10ml of pure water to obtain a hydrophilic carbon dot aqueous solution, and freeze-drying to obtain the hydrophilic carbon dot solid.

Example 2

(1) Sodium citrate and D, L-homocysteine were placed in a beaker, and 2mL of ultrapure water was added to the beaker to dissolve and mix them uniformly, the amount of the sodium citrate material was 0.6mmoL, and the amount of the D, L-homocysteine material was 1mmoL. The beaker is placed in an electric heating constant temperature blast drying oven to react for 6 hours at 70 ℃.

(2) And (2) adding 0.5g of 1- (3-dimethylaminopropyl) -3-Ethylcarbodiimide (EDC) into the beaker in the step (1), and continuously placing the beaker in an electric heating constant temperature air drying oven to react for 10min at 200 ℃ to obtain a yellow solid (shown in figure 2). Dissolving the yellow solid by pure water with multi-step ultrasound to obtain blue luminous hydrophilic carbon dot solution, and freeze-drying to obtain hydrophilic carbon dot solid. And (3) completely dissolving part of products which cannot be dissolved in pure water by using methanol to obtain a hydrophobic carbon dot solution, and performing rotary evaporation to obtain a hydrophobic carbon dot solid.

Example 3

(1) Oxalic acid and N-acetyl-L-cysteine were placed in a round-bottomed flask, and 2mL of ultrapure water was added to the round-bottomed flask to dissolve and mix them uniformly, the amount of oxalic acid was 1.2mmoL and the amount of N-acetyl-L-cysteine was 1mmoL. The beaker is placed in an electric heating constant temperature air blast drying oven to react for 10 hours at 70 ℃.

(2) And (2) adding 0.5g of 1, 3-dimethyl-2-imidazolidinone into the round-bottom flask obtained in the step (1), and placing the mixture in a water bath kettle to react for 5 hours at the temperature of 100 ℃ to obtain a brown yellow solid (shown in figure 3). And ultrasonically dissolving the solid by using trichloromethane for multiple times to obtain a hydrophobic carbon dot solution, adding methanol into the solution, and centrifuging to obtain the hydrophobic carbon dot solid. Dissolving the solid which cannot be dissolved in the trichloromethane solution in pure water to obtain a hydrophilic carbon dot aqueous solution, adding isopropanol into the aqueous solution, and centrifuging at 8000 rpm to obtain the hydrophilic carbon dot solid.

Example 4

(1) Citric acid and polyethyleneimine are placed in a round-bottom flask, 2mL of mixed reagent of ultrapure water and ethanol which are mixed in a one-to-one mode are added into the round-bottom flask, so that the raw materials are dissolved and mixed uniformly, the mass of the citric acid is 1.0mmoL, and the mass of the polyethyleneimine is 2.8mmoL. The round-bottom flask is placed in an electric heating constant-temperature forced air drying oven to react for 3 hours at 70 ℃.

(2) And (2) adding 0.2g of bis (trichloromethyl) carbonate (BTC) into the round-bottom flask obtained in the step (1), placing the round-bottom flask into an oil bath kettle, reacting for 2 hours at 170 ℃ to obtain a dark brown solid, dissolving the dark brown solid with trichloromethane to obtain a hydrophobic carbon dot solution, adding acetonitrile, and centrifuging to obtain the hydrophobic carbon dot solid. The carbon dots emit yellow light, the optimal emission wavelength is 543nm, and the quantum yield is 18%. And dissolving the residual insoluble solid in a pure water solution to obtain a blue luminescent hydrophilic carbon dot aqueous solution, adding acetonitrile into the aqueous solution, and centrifugally drying to obtain the hydrophilic carbon dot solid, wherein the optimal emission wavelength is 431nm, and the quantum yield is 22%.

Comparative example 1

(1) Citric acid and L-cysteine hydrochloride were placed in a polytetrafluoroethylene liner and mixed thoroughly with a glass rod with the amount of citric acid being 0.4mmoL and the amount of L-cysteine hydrochloride being 0.5mmoL.

(2) And (2) adding 0.3g of N, N' -Dicyclohexylcarbodiimide (DCC) into the lining in the step (1), putting the lining into a hydrothermal reaction kettle, and placing the hydrothermal reaction kettle in an electric heating constant-temperature air-blowing drying oven to react for 40min at 180 ℃ to obtain a light yellow solid product. And ultrasonically dissolving the solid product by using trichloromethane to obtain a hydrophobic carbon dot solution, and then performing rotary evaporation to obtain a hydrophobic carbon dot solid. Dissolving the residual insoluble solid with water to obtain blue luminescent water-soluble carbon dot solution, and freeze drying to obtain water-soluble carbon dot solid.

Comparative example 2

This comparative example is different from example 1 only in that the reaction temperature of step (2) is 60 degrees, the reaction time is 30 minutes, and a pale yellow solid product can be prepared, and the solid product can be ultrasonically dissolved in water and fluoresces blue, that is, only hydrophilic carbon dots can be prepared.

In the above examples and comparative examples, when the dehydrating agent was a solid, it was dissolved in 200. Mu.L of acetonitrile and then added to the reaction vessel.

Comparative example 3

This comparative example differs from example 1 only in that in step (2), the reaction was carried out without adding a dehydrating agent. The product is a brownish yellow solid, and the carbon dots are only hydrophilic carbon dots which emit blue light.

Test example 1

The hydrophobic carbon dot solution of example 1 was irradiated under 365nm ultraviolet light, as shown in fig. 4, to emit yellow light, and a fluorescence emission pattern and an ultraviolet-visible absorption spectrum pattern of the hydrophobic carbon dot of example 1 were obtained, as shown in fig. 5 and 6, in this order, and it was revealed that the hydrophobic carbon dot optimally emitted 540nm in wavelength and 352nm in maximum absorption wavelength, but had broad absorption at 400nm to 500nm and a fluorescence quantum yield of 30%. Then, the hydrophobic carbon dots in example 1 were subjected to elemental analysis by X-ray photoelectron spectroscopy (XPS), and the results are shown in fig. 7, which indicates that the carbon dots contain four elements: C. n, O and S belong to N and S codoped hydrophobic carbon dots. The hydrophilic carbon dot solution in example 1 was irradiated with 365nm ultraviolet light, and it emitted blue light as shown in fig. 8. The fluorescence spectrogram and the ultraviolet-visible absorption spectrogram are shown in fig. 9 and fig. 10, the optimal emission wavelength is 450nm, the maximum absorption wavelength is 352nm, and the quantum yield is 34%.

When the carbon dot of comparative example 1 was analyzed, as shown in fig. 11, the hydrophobic carbon dot exhibited blue luminescence, and as can be seen from the fluorescence emission spectrum of the hydrophobic carbon dot of comparative example 1 shown in fig. 12, the maximum emission wavelength was 440nm, and the quantum yield was 11%, as can be seen from the photograph and the fluorescence emission spectrum of the hydrophilic carbon dot solution of the water-soluble carbon dot of comparative example 1 shown in fig. 13 and 14 under 365nm ultraviolet light irradiation, blue luminescence, the maximum emission wavelength was 448nm, and the quantum yield was 14%.

As can be seen from the comparison between example 1 and comparative example 1, if the carbon source and the N, S doping agent are fully dissolved and uniformly mixed in the first step without adding a solvent, the synthesis of the N, S co-doped carbon dots is not facilitated when the dehydrating agent is directly added for reaction (most of the dehydrating agent reacts with only one raw material), the synthesis efficiency is low, the emission wavelength of the prepared hydrophobic carbon dots is obviously shortened, and the quantum yield is low.

Test example 2

The hydrophobic carbon dots obtained in example 1 show excellent fluorescence for use in solid state lighting and displays. As shown in fig. 15, a white light illumination LED lamp was constructed using hydrophobic carbon dots as one of the light source components. Fig. 16 is a graph of the electroluminescence spectrum of the fabricated white LED device. Consists of two emission bands: blue λ em at 450nm, from blue GaN-based chips, and 575nm from broad yellow emission from hydrophobic carbon dots. The two emission bands mix to produce white light. The prepared white light LED has the CIE (0.2637, 0.2255) and falls within the white light region. These results indicate that the hydrophobic carbon dots based on yellow luminescence successfully fabricated white LEDs.

Test example 3

Application of the hydrophobic carbon dots of example 1 to the production of a solid-state light-emitting forming material. Mixing transparent epoxy resin A and epoxy resin B according to the mass ratio of 3:1, adding a proper amount of hydrophobic carbon dot solution, uniformly mixing again, pouring into a mold, and standing at room temperature for 24 hours to obtain the solid luminescent forming material shown in figures 17 and 18. The material was a hard solid material, with a tan color observable in daylight (as shown in fig. 17). Under 365nm ultraviolet light, the solid fluoresced yellow (as shown in FIG. 18).

Test example 4

The hydrophilic carbon dot solution in example 2 was irradiated with 365nm ultraviolet light, and blue light was emitted as shown in fig. 19. The hydrophobic carbon dot solid in example 2 was subjected to a fluorescence emission spectrum, as shown in fig. 20, the fluorescence emission wavelength was 490nm, and the fluorescence quantum yield was 19%. The hydrophobic carbon dot solution of example 3 was irradiated under 365nm uv light to emit green light as shown in fig. 21, with an optimal emission wavelength of 530nm and a quantum yield of 21%. The hydrophilic carbon dot of example 3 was also obtained as blue light emission, with an optimal emission wavelength of 426nm and a quantum yield of 33%.

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.

Claims

1. A method for producing a carbon dot, comprising:

adding a dehydrating agent into a uniform mixture of carbon dot preparation raw materials, and reacting at the temperature of 100-200 ℃;

wherein the carbon dot preparation raw material contains hydrophilic groups, and the uniform mixture is mainly prepared by the following preparation steps: dissolving carbon dot preparation raw materials in water, and reacting at 60 to 80 ℃ for 6 to 15h;

the carbon point preparation raw material comprises a carbon source and a nitrogen and sulfur co-doping agent, wherein the carbon source is at least one of citric acid, oxalic acid and sodium citrate and sodium oxalate; the nitrogen and sulfur co-doping agent is at least one of D, L-homocysteine, L-cysteine hydrochloride, D-cysteine, glutathione and N-acetyl-L-cysteine; the mass ratio of the carbon source to the nitrogen and sulfur co-doping agent is 1:0.5 to 10;

the dehydrating agent is at least one of N, N' -dicyclohexylcarbodiimide, 1- (3-dimethylaminopropyl) -3-ethylcarbodiimide hydrochloride, 1, 3-dimethyl-2-imidazolidinone and bis (trichloromethyl) carbonate; the dosage of the dehydrating agent is 0.1-1g.

2. The method according to claim 1, wherein the reaction is carried out for 10 to 360 min.

3. The production method according to claim 1, wherein the dehydrating solvent is added in the form of an organic solution.

4. The production method according to claim 3, wherein the organic solvent used for dissolving the dehydrating solvent is acetonitrile.

5. The method according to claim 1, wherein the reaction vessel for preparing the carbon dots is selected from any one of a hydrothermal reaction kettle, a beaker, and a round-bottomed flask.

6. The production method according to claim 1, wherein the heating vessel for heating to maintain the reaction temperature is selected from any one of a water bath, an oil bath, and an electric heating constant temperature forced air drying oven.

7. The production method according to claim 1, wherein the water is ultrapure water.

8. The method of claim 1, wherein the vessel for dissolving and removing the solvent is selected from any one of a polytetrafluoroethylene reaction lining, a beaker, and a round-bottomed flask.

9. The production method according to any one of claims 1 to 6, further comprising dissolving the carbon-point solid obtained by the reaction with a solvent to obtain a carbon-point solution.

10. The method according to claim 9, further comprising removing the solvent from the carbon dot solution to obtain a carbon dot powder.

11. The production method according to claim 10, wherein the carbon dot solid is dissolved with a water-soluble solvent and a hydrophobic solvent to obtain a solution of water-soluble carbon dots and a solution of hydrophobic carbon dots, respectively, and then the solvents are removed to obtain water-soluble carbon dots and hydrophobic carbon dots, respectively.

12. The method according to claim 11, wherein the water-soluble solvent is pure water, a buffer solution, and the hydrophobic solvent is an organic solvent including at least one of cyclohexane, carbon tetrachloride, chloroform, tetrahydrofuran, and methanol.

13. A carbon dot produced by the production method according to any one of claims 1 to 12.

14. The carbon dot of claim 13, wherein the carbon dot is a hydrophobic carbon dot separated after a reaction.

15. The carbon dot according to claim 14, wherein the hydrophobic carbon dot is an N, S co-doped hydrophobic carbon dot having a fluorescence emission wavelength of 450 to 580 nm.

16. Use of the carbon dot according to any one of claims 13 to 15 in the preparation of a fluorescent material.

17. Use of the carbon dot of claim 16, which is a hydrophobic carbon dot separated after reaction, in the production of a solid illumination device, a display, or a solid luminescent excipient.

18. A solid luminescent excipient characterized in that the raw material components thereof contain the hydrophobic carbon dots according to any one of claims 14 to 15.