CN108690609B

CN108690609B - Synthesis method of water-soluble or oil-soluble carbon dots and fluorescent carbon dots

Info

Publication number: CN108690609B
Application number: CN201810441113.3A
Authority: CN
Inventors: 冯科; 位思梦; 陈彬; 佟振合; 吴骊珠
Original assignee: Technical Institute of Physics and Chemistry of CAS
Current assignee: Technical Institute of Physics and Chemistry of CAS
Priority date: 2018-05-10
Filing date: 2018-05-10
Publication date: 2021-05-14
Anticipated expiration: 2038-05-10
Also published as: CN108690609A

Abstract

The invention discloses a method for synthesizing water-soluble or oil-soluble carbon dots and fluorescent carbon dots, which takes various organic molecules such as organic acid, organic amine, alcohol/phenol, alkene/alkyne, thiophene, pyrrole and the like as carbon sources or heteroatom precursors, adopts an ionothermal method, takes anhydrous zinc chloride as a pyrolysis accelerant in an organic solvent, and prepares the water-soluble or oil-soluble carbon dots in a similar organic synthesis way; by regulating the reaction precursor, different luminescent carbon spots of near ultraviolet, blue, green, yellow, orange, red and the like can be directly obtained. The synthesis method of the water-soluble or oil-soluble fluorescent carbon dots provided by the invention is carried out under normal pressure, is simple and efficient, has high yield, can accurately control reaction conditions and processes, can prepare carbon dots with different properties, realizes standard flow preparation of the carbon dots, and is more beneficial to industrial production of the carbon dots.

Description

Synthesis method of water-soluble or oil-soluble carbon dots and fluorescent carbon dots

Technical Field

The invention relates to the technical field of chemical synthesis, in particular to a synthesis method of water-soluble or oil-soluble carbon dots and fluorescent carbon dots.

Background

Carbon dots, which are nanocarbons having a quasi-spherical/circular structure, have a common size of several to several tens of nanometers, are generally capable of stably emitting light and exhibit a confinement effect similar to quantum dots. On one hand, the carbon dots are different from organic dye micromolecules, the light stability is good, the photobleaching is not easy, and the carbon dots have certain excitation wavelength dependence; on the other hand, the nano-composite material does not contain heavy metal components, is different from typical semiconductor quantum dots (such as CdS, CdSe and the like), is rich in functional groups such as carboxyl, hydroxyl and the like on the surface, and has low toxicity and good biocompatibility; therefore, the carbon dots show good application prospects in the aspects of biological imaging, fluorescence sensing, light emitting diodes, photovoltaic material devices, photocatalysis, medical treatment and the like, and are a research hotspot in the field of current nano material science.

In 2004, Walter A.Scriptens et al (J.Am.chem.Soc.2004,126,12736) of the University of South Carolina (University of South Carolina) in the United states, luminescent carbon nanoparticles were obtained by a first separation in the process of purifying single-walled carbon nanotubes prepared by arc discharge using an electrophoresis method. In 2006, Sunzapine et al (J.Am. chem. Soc.2006,128,7756) at the University of Clemson University (Clemson University) in U.S. bombarded graphite targets by laser ablation (laser ablation), leading to the preparation of fluorescent carbon dots of various colors that can be uniformly dispersed in water. Subsequently, various reports on the preparation method of the carbon spot synthesis are reported. Such as: chengde Mao et al (angel. chem. int. ed.2007,46,6473) at the University of putue University (Purdue University) for the first time used candles to burn to produce soot to prepare fluorescent carbon dots; the first time, The method comprises The steps of preparing water-soluble fluorescent carbon dots by cutting carbon nanotubes by electrochemical oxidation method through The zhifeing Ding et al (J.Am.chem.Soc.2007,129,744) of The University of Western-style University of Canada (The University of Western-style of Western) and synthesizing various water-soluble fluorescent carbon dots by The Emmanuel P.Giannelis et al (chem.Mater.2008,20,4539; Small 2008,4,455) of The University of Cornell (Cornell University) through an organic Small molecule precursor such as amino carboxylic acid sodium surfactant and citric acid under The high-temperature thermal oxidation condition; the blue fluorescent carbon dots are obtained by oxidizing graphite by an electrochemical method through Ponto culture and the like of Wuhan university (chem.Commun.2008,5116) and pool service and the like of Fuzhou university (J.Am.chem.Soc.2009,131, 4564); yangxuirong et al (chem. Commun.2009,5118), a Changchun institute of China, pyrolyzed a glucose-polyethylene glycol solution by a microwave method for the first time to synthesize fluorescent carbon dots; kian Ping Long et al (ACS Nano 2009,3,2367) of the university of Singapore national university strip graphite in ionic liquid by an electrochemical method to prepare water-soluble fluorescent carbon dots; pandan remainder of Shanghai university et al (adv. Mater.2010,22,734) prepared water-soluble fluorescent carbon dots by cutting graphene by a hydrothermal method; liang-shi Li et al (J.Am.chem.Soc.2010,132,5944) of Indiana University (Indiana University) in U.S. firstly uses aromatic molecules as raw materials to synthesize oil-soluble fluorescent carbon dots by stepwise chemistry; liuchun Yan and the like (Eur.J.Inorg.chem.2010,4411) of the Chinese academy of sciences use small organic molecules as raw materials and directly prepare water-soluble fluorescent carbon dots by a hydrothermal method; the pitch carbon fiber is oxidized by mixed acid through Pulickel M.Ajayan of Rice University and Jujun et al (Nano Lett.2012,12,844) of Nanjing University to prepare a large amount of water-soluble fluorescent carbon dots with good crystallinity; guo Saiwu et al (ACS Nano 2012,6,6592) of Shanghai university of transportation uses the UV Fenton method to oxidize graphene oxide to prepare water-soluble fluorescent carbon dots; the water-soluble near-infrared luminescent carbon dots and the like are synthesized by a microwave hydrothermal method by using a glutathione formamide solution as a raw material in the technical field of Ningbo materials of the Chinese academy of sciences and Linchangwei and the like (adv.Mater.2015,27,7782).

In general, the synthetic preparation of fluorescent carbon dots has been reported to be classified into top-down and bottom-up. The former takes a solution chemical method and an electrochemical method as a typical method, and massive graphite, a carbon tube and graphene are oxidized and cut into luminescent carbon dots with nanometer particle size; the latter is represented by a microwave method and a solvothermal method, and small molecules such as carboxylic acid, amine, alcohol and the like, even biomass are used as raw materials, and fluorescent carbon dot materials with various particle sizes are directly synthesized through pyrolysis, polymerization and coking. However, in general, the fluorescent carbon dots are limited by the synthesis method at present, and cannot be prepared in large quantities, so that a simple and practical large-scale carbon dot preparation method is urgent to break the application bottleneck.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for synthesizing water-soluble or oil-soluble carbon dots and fluorescent carbon dots. The invention adopts an organic synthesis mode, and takes organic micromolecular compounds as precursors to synthesize a large amount of water-soluble/oil-soluble carbon dots under a controllable condition.

The core content is that various oxygen-containing reagents such as carboxylic acid, alcohol/phenol, amine, alkene/alkyne, aromatic hydrocarbon and the like, nitrogen-containing reagents, sulfur-containing reagents, phosphorus-containing reagents, silicon-containing reagents, boron-containing reagents, fluorine-containing reagents, chlorine-containing reagents, bromine-containing reagents, iodine-containing reagents, selenium-containing reagents, tellurium-containing reagents, arsenic-containing reagents and other various organic molecules are used as carbon sources or heteroatom precursors, anhydrous zinc chloride is used as a pyrolysis promoter in an organic solvent, an ionothermal method is utilized to prepare water-soluble or oil-soluble carbon points in an organic synthesis thinking mode under the conditions of normal pressure and lower temperature, and the carbon points with different performances are synthesized and prepared by controlling reaction conditions such as feeding proportion, reaction temperature, reaction time, oxidation strength and the like.

The specific scheme of the invention is as follows:

a method for synthesizing water-soluble or oil-soluble carbon dots and fluorescent carbon dots is characterized by comprising the following steps: one or more organic molecules are used as a carbon source or heteroatom precursor, anhydrous zinc chloride is used as a pyrolysis promoter, and the water-soluble or oil-soluble carbon dots are prepared by adopting an ionic thermal reaction in an organic solvent.

The organic molecules include: examples of the organic acid include organic acids, organic amines, alcohols/phenols, alkenes/alkynes, thiophenes, pyrroles, furans, phthalaldehyde, isophthalaldehyde, terephthalaldehyde, 1, 3-dinitrobenzene, 2-hydroxyquinoline, 4-oxoisoquinoline, 4-aminoisoquinoline, 5-hydroxyisoquinoline, 8-hydroxyquinoline, and 8-aminoquinoline, and various oxygen-containing reagents such as nitrogen-containing reagents, sulfur-containing reagents, phosphorus-containing reagents, silicon-containing reagents, boron-containing reagents, fluorine-containing reagents, chlorine-containing reagents, bromine-containing reagents, iodine-containing reagents, selenium-containing reagents, tellurium-containing reagents, and arsenic-containing reagents.

The water-soluble/oil-soluble carbon dots are prepared by adopting an organic synthesis mode, so that the standard flow preparation of the carbon dots can be realized, and the yield of the carbon dots are greatly improved.

The synthesis method provided by the invention is used for preparing the carbon dots by adopting a heating mode under normal pressure, is more mature and adopts an organic synthesis mode to prepare the carbon dots, is simple and efficient, can also be used for more accurately controlling reaction conditions and processes, monitoring the experimental process at any time, is more mature in process flow, can realize standard flow preparation of the carbon dots, greatly improves the yield and yield of the carbon dots, and is more beneficial to industrial production. Compared with the conventional hydrothermal/solvothermal method, the synthesis method has the main advantages that the synthesis is carried out under normal pressure, a pressure reaction kettle is not needed, the operation is simpler, reactants can be added at any time in the reaction process, the reaction process is monitored, and the preparation process of carbon points is more favorably perfected; compared with a microwave method, the synthesis method disclosed by the invention adopts a heating mode to prepare the carbon dots, so that the non-uniformity of carbon dot particles caused by instantaneous high heat of microwaves is overcome, and the heating device is easier to operate and control compared with a microwave reaction kettle.

Preferably, the organic acid is selected from one or more of citric acid, acrylic acid, polyacrylic acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, amino acid, 3, 5-dihydroxybenzoic acid, phthalic anhydride, cinnamic acid, citrazinic acid, pyromellitic dianhydride, oleic acid, and the like.

Preferably, the alcohol/phenol is selected from one or more combinations of sorbitol, glucose, glycerol, m-triphenol, catechol, resorcinol, hydroquinone, 2-aminophenol, 3-aminophenol, 4-nitrophenol, 2,4, 6-trinitrophenol, and the like.

Preferably, the organic amine is selected from one or more of ethylene diamine, propane diamine, diphenylamine, aniline, p-phenylene diamine, o-phenylene diamine, m-phenylene diamine, 2, 6-diaminopyridine, 1, 8-naphthalene diamine, melamine, urea, acrylamide and the like.

Preferably, the reaction temperature is 150-300 ℃; more preferably, the reaction temperature is 180-240 ℃.

The temperature control interval of the synthesis method is expanded to 150-300 ℃, so that conditions are provided for preparing carbon dots with more performances, and the possibility is provided for preparing carbon dots under the optimal reaction conditions. The carbonization temperatures of different precursors are different, so that the carbon dots can be more efficiently prepared by controlling the reaction temperature.

Preferably, the organic solvent is selected from one or more of ethylene glycol, glycerol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 300, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, polyethylene glycol 1000, and the like.

When the synthetic method of the invention uses a mixed solvent system, more kinds of reaction precursors can be dissolved in the system to participate in the reaction, and the selection range of the raw material precursors is greatly widened, which is more beneficial to enriching the kinds of carbon points. In addition, the synthesis method of the invention can adjust the solubility of carbon points by adding different precursors, such as: using molecules with oleophilic groups such as styrene, acetylene, dodecylamine and the like as reaction precursors to obtain oil-soluble carbon dots; the water-soluble carbon dots can be obtained by using molecules having a strong hydrophilic group such as acrylic acid and ethylenediamine as precursors.

Preferably, the ionothermal method in the organic solvent comprises the following specific steps: adding a carbon source or heteroatom precursor and zinc chloride into an organic solvent, stirring at normal temperature until the carbon source or heteroatom precursor and the zinc chloride are fully mixed, slowly heating to 100 ℃ for reaction for 1h, then heating to 210 ℃ for reaction for 4h, cooling to room temperature, and purifying to obtain carbon dots.

Preferably, the size of the prepared carbon dots is 2-20 nm. The carbon dots prepared by the synthesis method have very good crystallinity, and the carbon hexagonal structure of graphite can be observed obviously.

Preferably, the carbon dots are different light-emitting carbon dots with near ultraviolet, blue, green, yellow, orange or red colors, and the light-emitting range is 350-700 nm. The synthesis method can control the fluorescence color of the carbon dots by controlling the types of the reaction precursors.

The invention also provides application of the carbon dots prepared by the preparation method in biomedicine and photocatalytic reaction.

The carbon dots prepared by the synthesis method of the invention have strong fluorescence, such as: the luminous quantum efficiency of the blue fluorescent carbon dots can reach 0.39, the luminous quantum efficiency of the green fluorescent carbon dots can reach 0.23, the luminous quantum efficiency of the orange fluorescent carbon dots can reach 0.32, and meanwhile, the carbon dots are good in light stability and low in cytotoxicity and can be used in the biomedical fields of cell imaging and the like.

In addition, the carbon dots prepared by the synthesis method have good photoresponse characteristics, can generate singlet oxygen and superoxide anion free radicals under the condition of illumination, can replace small-molecule photosensitizers to be applied to photocatalytic reactions, and can be used for catalyzing the self-dimerization reaction of chalcone.

The invention has the advantages of

The synthesis method of the water-soluble or oil-soluble fluorescent carbon dots provided by the invention is carried out under normal pressure, is simple and efficient, can accurately control reaction conditions and processes, prepares carbon dots with different properties, realizes standard flow preparation of the carbon dots, greatly improves the yield and yield of the carbon dots, and is more beneficial to industrial production.

Drawings

Fig. 1 is a TEM image of the carbon dots prepared in example 1.

Fig. 2 is an XRD spectrum of the carbon dots prepared in example 1.

FIG. 3 is a Raman spectrum of the carbon dots prepared in example 1.

FIG. 4 is a FT-IR spectrum of the carbon dots prepared in example 1.

FIG. 5 is a schematic diagram of the preparation of carbon dots in example 1¹H-NMR spectrum.

FIG. 6 is an XPS survey of carbon dots prepared in example 1.

FIG. 7 shows XPS high resolution spectra of C1s, N1 s and O1 s for carbon dots prepared in example 1.

FIG. 8 is a UV-Vis absorption spectrum of the carbon dot prepared in example 1.

Fig. 9 is a luminescence spectrum of a carbon dot prepared in example 1.

FIG. 10 is a graph of the fluorescence lifetime of the prepared carbon dots of example 1 and a fitted curve.

FIG. 11 is a schematic representation of the preparation of carbon dots for biological cell imaging in example 1.

Fig. 12 is a TEM image of the carbon dots prepared in example 2.

Fig. 13 is an XRD spectrum of the prepared carbon dot of example 2.

FIG. 14 is a Raman spectrum of the carbon dots prepared in example 2.

FIG. 15 is a FT-IR spectrum of the carbon dots prepared in example 2.

FIG. 16 is an XPS survey of carbon dots prepared in example 2.

FIG. 17 is a C1s, N1 s and O1 s XPS high resolution spectra of carbon dots prepared in example 2.

FIG. 18 is a schematic view of preparation of carbon dots in example 2¹H-NMR spectrum.

FIG. 19 is a UV-Vis absorption spectrum of the carbon dot prepared in example 2.

Fig. 20 is a luminescence spectrum of a carbon dot prepared in example 2.

FIG. 21 is a graph of the luminescence lifetime of the carbon dots prepared in example 2 and a fitted curve.

FIG. 22 is a schematic representation of the preparation of carbon dots for biological cell imaging in example 2.

Fig. 23 is a TEM image of the carbon dots prepared in example 3.

Fig. 24 is an XRD spectrum of the carbon dots prepared in example 3.

FIG. 25 is a Raman spectrum of the carbon dots prepared in example 3.

FIG. 26 is a FT-IR spectrum of the carbon dots prepared in example 3.

FIG. 27 is an XPS survey of carbon dots prepared in example 3.

FIG. 28 is a XPS high resolution spectra of C1s, N1 s and O1 s for carbon dots prepared in example 3.

FIG. 29 is a schematic view of preparation of carbon dots in example 3¹H-NMR spectrum.

FIG. 30 is a UV-Vis absorption spectrum of the carbon dots prepared in example 3.

Fig. 31 is a luminescence spectrum of a carbon dot prepared in example 3.

FIG. 32 is a graph of the fluorescence lifetime of the carbon dots prepared in example 3 and a fitted curve.

Fig. 33 is a graph of example 3 carbon dots prepared for biological cell imaging.

Fig. 34 is a TEM image of the carbon dots prepared in example 4.

Fig. 35 is an XRD spectrum of the carbon dots prepared in example 4.

FIG. 36 is a Raman spectrum of the carbon dots prepared in example 4.

FIG. 37 is an FT-IR spectrum of a carbon dot prepared in example 4.

FIG. 38 is an XPS survey of carbon dots prepared in example 4.

FIG. 39 shows XPS high resolution spectra of C1s, N1 s and O1 s for carbon dots prepared in example 4.

FIG. 40 is a schematic representation of the preparation of carbon dots in example 4¹H-NMR spectrum.

FIG. 41 is a UV-Vis absorption spectrum of the carbon dot prepared in example 4.

Fig. 42 is a luminescence spectrum of a carbon dot prepared in example 4.

FIG. 43 is a graph of the fluorescence lifetime of the prepared carbon dots of example 4 and a fitted curve.

FIG. 44 is a graph of example 4 carbon dots prepared for biological cell imaging.

Detailed Description

The present invention is described in detail below by way of examples, it should be noted that the examples are only for the purpose of further illustration, and are not to be construed as limiting the scope of the present invention, and that those skilled in the art can make insubstantial modifications and adaptations to the invention in light of the above teachings. The embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

Example 1

A synthesis and purification method of a typical water-soluble blue fluorescent carbon dot comprises the following steps:

adding 217mg (3.0mmol) of acrylic acid and 54mg (0.5mmol) of 2, 6-diaminopyridine into 5.0mL of 0.5M zinc chloride solution of tetraethylene glycol, stirring at normal temperature to mix completely, slowly heating to 100 ℃ for reaction for 1h, heating to 210 ℃ for reaction for 4h, cooling the reaction system to room temperature, diluting with methanol, centrifuging, collecting supernatant, performing rotary evaporation to remove most of the volume of the concentrated solution of methanol to about 20mL, adding a large amount of diethyl ether for precipitation for 3 times, and drying to obtain 160mg of brown black solid powder with the yield of 61%. The yield was 55% when the amount was 150mL, and 4.45g of blue fluorescent carbon dots were obtained.

Solubility tests show that the blue fluorescent carbon dots have good hydrophilicity and can be well dispersed in polar solvents such as water, methanol and the like.

FIG. 1 is a TEM image of blue fluorescent carbon dots, which shows that the carbon dots have good dispersibility, uniform particle distribution and a statistical average particle size of 4.96 nm; meanwhile, the crystallinity of the blue fluorescent carbon dots is very good, and the hexagonal lattice structure of the graphite phase can be obviously distinguished, wherein the spacing between crystal planes of 0.21nm corresponds to the (100) crystal plane of the graphite phase, and the spacing between crystal planes of 0.26nm corresponds to the (020) crystal plane of the graphite phase.

FIG. 2 is an XRD spectrum of blue fluorescent carbon dots, which shows a wider diffraction peak due to the smaller particle size of the carbon dots, 2, a diffraction angle of 22.4 degrees, and a interplanar spacing of about

Corresponding to the (002) crystal plane of the graphite phase.

FIG. 3 is a Raman spectrum of blue fluorescent carbon dots, which shows that the blue fluorescent carbon dots exhibit typical G-band and D-band characteristic absorption of graphite derivatives, and are located at 1588cm^–1And 1364cm^–1Respectively correspond to aromatic carbon sp²Hybrid E_2gVibrating and disordered carbon structure sp³Hybrid A_1gSymmetric vibration, peak ratio I_D/I_G1.10, and a full width at half maximum (FWHM) of the G band of 150cm^–1(ii) a Besides, 2D (2835 cm) of the graphite structure is also obviously observed by Raman spectrum^–1)、D+G(3026cm^–1) And 2G (3233 cm)^–1) A peak; the above results indicate that the blue fluorescent carbon dots have very good crystallinity and may have a graphite-like multilayer ordered structure.

FIG. 4 is an FT-IR spectrum of a blue fluorescent carbon dot, and it can be seen that 3437cm^–1The broad peak at (b) corresponds to the stretching vibration of the hydroxyl group O-H, 2920cm^–1Stretching vibration of C-H bond corresponding to alkyl group, 1720cm^–1Corresponding to stretching vibration of carboxyl group COOH, 1624cm^–1Corresponding to C ═ O stretching vibration, 1429cm^–1Stretching vibration corresponding to C-N bond, 1084cm^–1Corresponding to the stretching vibration of C-O. The control experiment before and after the system reaction shows that the functional groups of carboxyl, amido, alkene and the like in the reaction precursor acrylic acid and the 2, 6-diaminopyridine are greatly reduced, and the likeThe expansion vibration absorption peak of O-H is obviously enhanced, which indicates that the carbon point should have better hydrophilicity on one hand, and ZnCl is also proved from the other side₂Strong pyrolysis promoting effect in the carbonization process of the ionothermal method.

Fig. 5 is an XPS full spectrum of the blue fluorescent carbon dot, and it is clearly seen that the blue fluorescent carbon dot is mainly composed of carbon (285eV), nitrogen (400eV), and oxygen (532eV), and the contents of the respective elements are calculated as C (53.66%), N (8.06%), and O (23.66%) by simple arithmetic. Meanwhile, the results of the elemental analysis showed that the content of each element of the blue fluorescent carbon dots was C (49.00%), N (8.95%), and H (5.55%), which was substantially consistent with the results of XPS full spectrum measurement. Besides, a small amount of marked zinc chloride impurities remain in the blue fluorescent carbon dots, and the ICP-MS analysis result shows that the mass fraction of the remaining zinc elements in the blue fluorescent carbon dots is 5.08%.

FIG. 6 is a high resolution XPS C1s, O1 s and N1 s spectra of blue fluorescent carbon dots. By deconvolution of carbon XPS peaks, XPS C1s spectra can be divided into five peaks, C-C/C ═ C (284.7eV, 41.35%), C-N (285.9eV, 8.51%), C-O (286.2eV, 40.08%), C ═ O (287.1eV, 4.02%) and COOH (288.7eV, 6.05%); by deconvolution of the oxygen XPS peak, the XPS O1 s spectrum can be divided into two peaks, C ═ O (531.9eV) and C — O (533.2eV), respectively; by deconvolution of the nitrogen XPS peak, the XPS N1 s spectrum can be divided into three peaks, pyridine-N (399.0eV), pyrrolic-N (400.1eV), and graphtic-N (401.2eV), indicating the presence of various forms of C-N bonds on the surface of the blue fluorescent carbon dot, consistent with the FT-IR test.

FIG. 7 shows blue fluorescent carbon dots¹An H-NMR spectrum shows that sharp proton peaks of acrylic acid and 2, 6-diaminopyridine which are small molecular compound precursors are completely absent on a blue fluorescent carbon point, all the proton peaks are obviously widened, and a flat peak type similar to a polymer is presented; wherein the proton peaks of aromatic hydrocarbon, olefin and amine types at 7.94 and 6.77ppm are greatly reduced, and some proton peaks of alkoxy, hydroxyl and carboxyl appear only at 4.55, 4.12, 3.48 and 3.39ppm, which shows that the proton-containing groups are mainly concentrated on the surface of carbon points, and oxygen-containing solvents can be partially bondedAmong them, ZnCl in the ionothermal process₂The strong pyrolysis promoting effect can lead the small molecular compound precursor to generate strong oxidation reduction and gradually carbonize.

FIG. 8 is a UV-Vis absorption spectrum of a blue fluorescent carbon dot, and it can be seen that the blue fluorescent carbon dot shows a distinct shoulder-like absorption peak at 335 nm.

FIG. 9 shows the emission spectrum of a blue fluorescent carbon dot, and it can be seen that the excited light of the blue fluorescent carbon dot shows a significant wavelength dependence, and the emission wavelength is also red-shifted from 413nm to 458nm as the excitation wavelength is increased from 345nm to 435 nm.

FIG. 10 is a fluorescence lifetime spectrum and a fitting curve of a blue fluorescent carbon dot, and fitting of a single photon counting decay curve of light emission at 430nm shows that the luminescence lifetime of the blue fluorescent carbon dot shows double exponential decay, which is 1.64ns (73.5%) and 5.11ns (26.5%) respectively, and the average lifetime is 2.56 ns; further, the luminescence quantum efficiency of the blue fluorescent carbon dot was measured to be 0.39.

The blue fluorescent carbon dots in fig. 11 were used for biological cell imaging. The blue fluorescent carbon dots have the characteristic of low toxicity, no obvious cytotoxicity is seen when the co-culture concentration is lower than 50 mu g/mL, and the fluorescent dots have high fluorescence intensity and good light stability; it can be seen that the blue fluorescent carbon dots and the human hepatoma cell Bel-7402 can well enter cytoplasm after being cultured for 4h, and show a certain mitochondrial targeting property, which is closely related to the chemical structure of precursor molecules used in the preparation of the carbon dots.

Example 2

A method for synthesizing and purifying a typical water-soluble green fluorescent carbon dot comprises the following steps:

adding 217mg (3.0mmol) of acrylic acid and 54mg (0.5mmol) of M-phenylenediamine into 5.0mL of 0.5M zinc chloride solution of tetraethylene glycol, stirring at normal temperature to mix completely, slowly heating to 100 ℃ for reaction for 1h, heating to 210 ℃ for reaction for 4h, cooling the reaction system to room temperature, diluting with methanol, centrifuging, collecting supernatant, performing rotary evaporation to remove most of the volume of the methanol concentrated solution to about 20mL, adding a large amount of diethyl ether for precipitation for 3 times, and drying to obtain 135mg of brown black solid powder with the yield of 51%. The yield was 49% when the amount was 150 mL.

Solubility tests show that the green fluorescent carbon dots have good hydrophilicity and can be well dispersed in polar solvents such as water, methanol and the like.

FIG. 12 is a TEM image of green fluorescent carbon dots, which shows that the carbon dots have good dispersibility, uniform particle distribution, and a statistical average particle size of 5.26 nm; meanwhile, the crystallinity of the green fluorescent carbon dots is very good, the hexagonal lattice structure of the graphite phase can be obviously distinguished, wherein the spacing between 0.21nm crystal faces corresponds to the (100) crystal faces of the graphite phase, the spacing between 0.25nm crystal faces corresponds to the (020) crystal faces of the graphite phase, and the fast Fourier transform result of selective area electron diffraction shows that the hexagonal light spots are distributed corresponding to the (100) crystal faces of the graphite phase.

FIG. 13 is an XRD spectrum of green fluorescent carbon dots showing a broad diffraction peak due to the small particle size of the carbon dots, 2, a diffraction angle of 22.7 DEG, and a interplanar spacing of about

Corresponding to the (002) crystal plane of the graphite phase.

FIG. 14 is a Raman spectrum of green fluorescent carbon dots, which shows that the green fluorescent carbon dots exhibit typical G-band and D-band characteristic absorption of graphite derivatives, and are located at 1592cm^–1And 1361cm^–1Respectively correspond to aromatic carbon sp²Hybrid E_2gVibrating and disordered carbon structure sp³Hybrid A_1gSymmetric vibration, peak ratio I_D/I_G0.76, and a full width at half maximum (FWHM) of the G band of 157cm^–1(ii) a Besides, 2D (2832 cm) of the graphite structure is also obviously observed by Raman spectroscopy^–1)、D+G(3036cm^–1) And 2G (3240 cm)^–1) A peak; the results show that the green fluorescent carbon dots have very good crystallinity and may have a graphite-like multilayer ordered structure.

FIG. 15 is an FT-IR spectrum of a green fluorescent carbon dot, and it can be seen that 3437cm^–1The broad peak at (b) corresponds to the stretching vibration of the hydroxyl group O-H, 2928cm^–1Stretching vibration of C-H bond corresponding to alkyl group, 1720cm^–11632cm corresponding to the stretching vibration of carboxyl group COOH^–1Stretching vibration corresponding to C ═ OMoving, 1400cm^–1Stretching vibration, 1090cm, corresponding to C-N bond^–1Corresponding to the stretching vibration of C-O. The contrast experiments before and after the system reaction show that the functional groups such as carboxyl, amido, alkene and the like in the reaction precursor acrylic acid and m-phenylenediamine are greatly reduced, and the stretching vibration absorption peak of O-H is obviously enhanced, which indicates that the carbon point has better hydrophilicity on one hand, and also proves that ZnCl is arranged on the other side surface₂Strong pyrolysis promoting effect in the carbonization process of the ionothermal method.

Fig. 16 is an XPS full spectrum of the green fluorescent carbon dot, and it is clearly seen that the green fluorescent carbon dot is mainly composed of carbon (285eV), nitrogen (400eV), and oxygen (532eV), and the contents of the respective elements are simply calculated in terms of numbers as C (54.23%), N (6.56%), and O (23.91%). Meanwhile, the results of the elemental analysis showed that the content of each element of the green fluorescent carbon dots was C (54.47%), N (5.99%), H (5.89%), which was substantially consistent with the results of XPS full spectrum measurement. Besides, a small amount of marked zinc chloride impurities are remained in the green fluorescent carbon dots, and the ICP-MS analysis result shows that the mass fraction of the residual zinc elements in the green fluorescent carbon dots is 5.37%.

FIG. 17 is a high resolution XPS C1s, O1 s and N1 s spectra of green fluorescent carbon dots. By deconvolution of carbon XPS peaks, XPS C1s spectra can be divided into five peaks, C-C/C ═ C (284.7eV, 52.89%), C-N (285.9eV, 9.87%), C-O (286.2eV, 24.44%), C ═ O (287.1eV, 7.83%) and COOH (288.7eV, 4.97%); by deconvolution of the oxygen XPS peak, the XPS O1 s spectrum can be divided into two peaks, C ═ O (531.9eV) and C — O (533.2eV), respectively; by deconvolution of the nitrogen XPS peak, the XPS N1 s spectrum can be divided into three peaks, pyridine-N (399.0eV), pyrrolic-N (400.1eV), and graphtic-N (401.2eV), indicating the presence of various forms of C-N bonds on the surface of the green fluorescent carbon dot, consistent with the FT-IR test.

FIG. 18 shows green fluorescent carbon dots¹An H-NMR spectrum shows that sharp proton peaks of acrylic acid and m-phenylenediamine which are small molecular compound precursors are not existed on a green fluorescent carbon point, all the proton peaks are obviously widened, and a flat peak type similar to a polymer is presented; at 7.83 and 7.01ppmThe proton peaks of aromatic hydrocarbon, olefin and amine types are greatly reduced, and some proton peaks of alkoxy, hydroxyl and carboxyl appear only at 4.55, 4.16, 3.60, 3.47 and 3.33ppm, which shows that the proton-containing groups are mainly concentrated on the surface of a carbon point, and oxygen-containing solvents can be partially bonded into the carbon point, ZnCl in the ionothermal method₂The strong pyrolysis promoting effect can lead the small molecular compound precursor to generate strong oxidation reduction and gradually carbonize.

FIG. 19 is a UV-Vis absorption spectrum of a green fluorescent carbon dot, which is observed to show a distinct shoulder-like absorption peak at 430 nm.

FIG. 20 is a graph showing the luminescence spectrum of a green fluorescent carbon dot, and it can be seen that the excited light of the green fluorescent carbon dot shows a significant wavelength dependence, and the luminescence wavelength is also red-shifted from 495nm to 546nm as the excitation wavelength is increased from 365nm to 505 nm.

FIG. 21 is a fluorescence lifetime spectrum and a fitting curve of a green fluorescent carbon dot, and fitting of a single photon counting decay curve of luminescence at 525nm shows that the luminescence lifetime of the green fluorescent carbon dot shows double exponential decay, which is 4.21ns (36.7%) and 10.04ns (63.3%) respectively, and the average lifetime is 7.90 ns; the luminescent quantum efficiency of the green fluorescent carbon dot was further measured to be 0.23.

The green fluorescent carbon dots in fig. 22 were used for biological cell imaging. The blue fluorescent carbon dots have the characteristic of low toxicity, no obvious cytotoxicity is observed when the co-culture concentration is lower than 25 mu g/mL, and the fluorescent dots have high fluorescence intensity and good light stability; it can be seen that the green fluorescent carbon dots and the human hepatoma carcinoma cell Bel-7402 can well enter cytoplasm after being co-cultured for 4 hours, and show a certain nuclear targeting property, which is closely related to the chemical structure of precursor molecules used in the preparation of the carbon dots.

Example 3

A synthesis method of a typical yellow fluorescent carbon dot comprises the following steps:

adding 54mg (0.50mmol) of p-phenylenediamine and 61mg (0.50mmol) of L-cysteine into 5.0mL of 0.5M zinc chloride tetraethylene glycol solution, stirring at normal temperature to fully mix, slowly heating to 100 ℃ for reaction for 1h, heating to 210 ℃ for reaction for 4h, cooling the reaction system to room temperature, diluting with methanol, centrifuging, collecting supernatant, performing rotary evaporation to remove most of the volume of the methanol concentrated solution to about 20mL, adding a large amount of diethyl ether for precipitation for 3 times, and drying to obtain 53mg of brown black solid powder with the yield of 47%. The yield was 43%, and the yield was 1.48 g.

Solubility tests show that the yellow fluorescent carbon dots can be well dispersed in polar organic solvents such as methanol.

FIG. 23 is a TEM image of yellow fluorescent carbon dots, which shows that the carbon dots have good dispersibility, uniform particle distribution, and a statistical average particle size of 4.32 nm; meanwhile, the crystallinity of the yellow fluorescent carbon dots is very good, and the hexagonal lattice structure of the graphite phase can be distinguished obviously, wherein the spacing between crystal planes of 0.21nm corresponds to the (100) crystal plane of the graphite phase, and the spacing between crystal planes of 0.25nm corresponds to the (020) crystal plane of the graphite phase.

FIG. 24 is an XRD spectrum of yellow fluorescent carbon dots showing a broad diffraction peak due to the small particle size of the carbon dots, 2, a diffraction angle of 23.5 DEG, and a interplanar spacing of about

Corresponding to the (002) crystal plane of the graphite phase.

FIG. 25 is a Raman spectrum of yellow fluorescent carbon dots, which shows typical G-band and D-band characteristic absorptions of graphite derivatives at 1585cm^–1And 1372cm^–1Respectively correspond to aromatic carbon sp²Hybrid E_2gVibrating and disordered carbon structure sp³Hybrid A_1gSymmetric vibration, peak ratio I_D/I_G0.80, and a full width at half maximum (FWHM) of G-band of 161cm^–1(ii) a Besides, 2D (2824 cm) of the graphite structure is also obviously observed by Raman spectrum^–1) And 2G (3224 cm)^–1) A peak; the results show that the yellow fluorescent carbon dots have very good crystallinity and may have a graphite-like multilayer ordered structure.

FIG. 26 is an FT-IR spectrum of a yellow fluorescent carbon dot, and it can be seen that 3435cm^–1The broad peak at (b) corresponds to the stretching vibration of the hydroxyl group O-H, 2926cm^–1Stretching vibration of 1717cm corresponding to alkyl C-H bond^–1Corresponding to a carboxyl groupStretching vibration of the group COOH, 1624cm^–11383cm for C ═ O stretching vibration^–1Stretching vibration, 1099cm, corresponding to C-N bond^–1Corresponding to the stretching vibration of C-O. The contrast experiments before and after the system reaction show that the functional groups such as carboxyl, amido and the like in the p-phenylenediamine and the L-cysteine as the reaction precursors are greatly reduced, and the stretching vibration absorption peak of O-H is obviously enhanced, which indicates that the carbon point has better hydrophilicity on one hand, and also proves that ZnCl is arranged on the other side surface₂Strong pyrolysis promoting effect in the carbonization process of the ionothermal method.

Fig. 27 is an XPS full spectrum of the yellow fluorescent carbon dot, and it is clearly seen that the yellow fluorescent carbon dot is mainly composed of carbon (285eV), nitrogen (400eV), and oxygen (532eV), and the contents of the respective elements are C (53.97%), N (5.85%), and O (17.72%) by simple arithmetic calculation. Meanwhile, the results of the elemental analysis showed that the content of each element of the yellow fluorescent carbon dots was C (50.39%), N (6.51%), and H (5.30%), which was substantially consistent with the results of XPS full spectrum measurement. In addition, a small amount of marked zinc chloride impurities are remained in the yellow fluorescent carbon dots, and the mass fraction of the residual zinc element in the yellow fluorescent carbon dots is 4.72 percent as shown by an ICP-MS analysis result.

FIG. 28 is a high resolution XPS C1s, O1 s and N1 s spectra of yellow fluorescent carbon dots. By deconvolution of carbon XPS peaks, XPS C1s spectra can be divided into five peaks, C-C/C ═ C (284.7eV, 64.68%), C-N (285.9eV, 22.74%), C-O (286.2eV, 8.55%), C ═ O (287.1eV, 1.62%) and COOH (288.7eV, 2.40%); by deconvolution of the oxygen XPS peak, the XPS O1 s spectrum can be divided into two peaks, C ═ O (531.9eV) and C — O (533.2eV), respectively; by deconvolution of the nitrogen XPS peak, the XPS N1 s spectrum can be divided into three peaks, pyridine-N (399.0eV), pyrrolic-N (400.1eV), and graphtic-N (401.2eV), indicating the presence of various forms of C-N bonds on the surface of the yellow fluorescent carbon dot, consistent with the FT-IR test.

FIG. 29 shows yellow fluorescent carbon dots¹H-NMR spectrum shows that sharp proton peaks of p-phenylenediamine and L-cysteine which are small molecular compound precursors are completely absent on yellow fluorescent carbon dots, and all the proton peaks are clearThe width is widened, and the flat peak shape similar to the polymer is presented; wherein the proton peak of aromatic hydrocarbon and amine type at 7.96ppm is greatly reduced, and some proton peaks of alkoxy, hydroxyl and carboxyl appear only at 3.82, 3.49 and 3.40ppm, which shows that the proton-containing group is mainly concentrated on the surface of carbon point, and oxygen-containing solvent can be partially bonded therein, ZnCl in the ionothermal method₂The strong pyrolysis promoting effect can lead the small molecular compound precursor to generate strong oxidation reduction and gradually carbonize.

FIG. 30 is a UV-Vis absorption spectrum of a yellow fluorescent carbon dot, which shows that the yellow fluorescent carbon dot has absorption in the visible region, but no obvious shoulder-like absorption peak is observed.

FIG. 31 is a luminescence spectrum of a yellow fluorescent carbon dot, and it can be seen that the excited light of the yellow fluorescent carbon dot exhibits a significant wavelength dependence, and as the excitation wavelength is increased from 445nm to 575nm, the luminescence wavelength is also red-shifted from 561nm to 625 nm.

FIG. 32 is a graph and a fitting curve of fluorescence lifetime of a yellow fluorescent carbon dot, and fitting of a single photon counting decay curve of luminescence at 525nm shows that the luminescence lifetime of the yellow fluorescent carbon dot exhibits double exponential decay, which is 2.77ns (36.8%) and 9.69ns (63.2%), respectively, and the average lifetime is 6.90 ns; further, the luminescence quantum efficiency of the yellow fluorescent carbon dot was measured to be 0.074.

The yellow fluorescent carbon dots in fig. 33 were used for biological cell imaging. The yellow fluorescent carbon dots have the characteristic of low toxicity, no obvious cytotoxicity is seen when the co-culture concentration is lower than 50 mu g/mL, and the yellow fluorescent carbon dots have high fluorescence intensity and good light stability; it can be seen that the yellow fluorescent carbon dots and human hepatoma carcinoma cell Bel-7402 can well enter cytoplasm after being co-cultured for 4h, and show a certain mitochondrial targeting property, which is closely related to the chemical structure of precursor molecules used in the preparation of the carbon dots.

Example 4

A synthesis method of a typical orange fluorescent carbon dot comprises the following steps:

adding 54mg (0.50mmol) of p-phenylenediamine and 73mg (0.50mmol) of 8-hydroxyquinoline into 5.0mL of 0.5M zinc chloride tetraethylene glycol solution, stirring at normal temperature to fully mix, slowly heating to 100 ℃ for reaction for 1h, heating to 210 ℃ for reaction for 4h, cooling the reaction system to room temperature, diluting with methanol, centrifuging, collecting supernatant, performing rotary evaporation to remove most of the volume of the methanol concentrated solution to about 20mL, adding a large amount of diethyl ether for precipitation for 3 times, and drying to obtain 64mg of brown black solid powder with the yield of 54%. The yield was 52% when the reaction was carried out to 150mL, and 1.98g of orange fluorescent carbon dots were obtained.

Solubility tests show that the orange fluorescent carbon dots can be well dispersed in polar organic solvents such as methanol.

FIG. 34 is a TEM image of orange fluorescent carbon dots, which shows that the carbon dots have good dispersibility, uniform particle distribution, and a statistical average particle size of 6.03 nm; meanwhile, the crystallinity of the orange fluorescent carbon dot is very good, the hexagonal lattice structure of the graphite phase can be obviously distinguished, wherein the interplanar spacing of 0.21nm corresponds to the (100) crystal face of the graphite phase, the interplanar spacing of 0.25nm corresponds to the (020) crystal face of the graphite phase, and the selective area electron diffraction result shows that two obvious apertures respectively correspond to the (100) crystal face and the (020) crystal face of the graphite phase.

FIG. 35 is an XRD spectrum of orange fluorescent carbon dots showing a broad diffraction peak due to the small particle size of the carbon dots, 2, a diffraction angle of 23.0 DEG, and a interplanar spacing of about

Corresponding to the (002) crystal plane of the graphite phase.

FIG. 36 is a Raman spectrum of the orange fluorescent carbon dot, and it can be seen that the orange fluorescent carbon dot exhibits typical G-band and D-band characteristic absorption of graphite derivatives, and is located at 1582cm^–1And 1369cm^–1Respectively correspond to aromatic carbon sp²Hybrid E_2gVibrating and disordered carbon structure sp³Hybrid A_1gSymmetric vibration, peak ratio I_D/I_G0.94, and a full width at half maximum (FWHM) of the G band of 154cm^–1(ii) a Besides, 2D (2836 cm) of the graphite structure is also obviously observed by Raman spectroscopy^–1)、D+G(3018cm^–1) And 2G (3248 cm)^–1) A peak; the above results indicate that the orange fluorescent carbon dots have very good crystallinity and may have a graphite-like multilayer ordered structure.

FIG. 37 shows orange fluorescent carbon dotsFT-IR spectrum, it can be seen that 3437cm^–1The broad peak at (b) corresponds to the stretching vibration of the hydroxyl group O-H, 2924cm^–1Corresponding to stretching vibration of alkyl C-H bond, 1622cm^–1Corresponding to C ═ O stretching vibration, 1377cm^–1Stretching vibration, 1107cm, corresponding to C-N bond^–1Corresponding to the stretching vibration of C-O. The contrast experiments before and after the system reaction show that the amido functional groups in the reaction precursors of p-phenylenediamine and 8-hydroxyquinoline are greatly reduced, and the stretching vibration absorption peak of O-H is obviously enhanced, which indicates that the carbon point has better hydrophilicity on one hand, and also proves that ZnCl is arranged on the other side surface₂Strong pyrolysis promoting effect in the carbonization process of the ionothermal method.

Fig. 38 is an XPS survey of the orange fluorescent carbon dot, and it is clearly seen that the orange fluorescent carbon dot is mainly composed of carbon (285eV), nitrogen (400eV), and oxygen (532eV), and the contents of the respective elements are calculated as C (62.60%), N (4.92%), and O (16.36%) by simple arithmetic calculation. Meanwhile, the results of the elemental analysis showed that the content of each element of the orange fluorescent carbon dots was C (54.79%), N (7.50%), and H (5.04%), which was substantially consistent with the results of XPS full spectrum measurement. In addition, a small amount of marked zinc chloride impurities are remained in the orange fluorescent carbon dots, and the mass fraction of the residual zinc element in the orange fluorescent carbon dots is 4.68 percent as shown by ICP-MS analysis results.

FIG. 39 is a high resolution XPS C1s, O1 s and N1 s spectra of orange fluorescent carbon dots. By deconvolution of carbon XPS peaks, XPS C1s spectra can be divided into five peaks, C-C/C ═ C (284.7eV, 77.66%), C-N (285.9eV, 7.21%), C-O (286.2eV, 6.93%), C ═ O (287.1eV, 5.62%) and COOH (288.7eV, 2.58%); by deconvolution of the oxygen XPS peak, the XPS O1 s spectrum can be divided into two peaks, C ═ O (531.9eV) and C — O (533.2eV), respectively; by deconvolution of the nitrogen XPS peak, the XPS N1 s spectrum can be divided into three peaks, pyridine-N (399.0eV), pyrrolic-N (400.1eV), and graphtic-N (401.2eV), indicating the presence of various forms of C-N bonds on the surface of the orange fluorescent carbon dot, consistent with FT-IR measurements.

FIG. 40 shows orange fluorescent carbon dots¹H-NMR spectrum, orange color was observedSharp proton peaks of small molecular compound precursors such as p-phenylenediamine and 8-hydroxyquinoline are completely absent on the fluorescent carbon dots, all the proton peaks are obviously widened, and a flat peak type similar to a polymer is presented; wherein the proton peak of aromatic hydrocarbon and amine type at 7.66ppm is greatly reduced, and some proton peaks of alkoxy, hydroxyl and carboxyl appear only at 4.58, 3.47 and 3.34ppm, which shows that the proton-containing group is mainly concentrated on the surface of carbon point, and oxygen-containing solvent can be partially bonded therein, ZnCl in the ionothermal method₂The strong pyrolysis promoting effect can lead the small molecular compound precursor to generate strong oxidation reduction and gradually carbonize.

FIG. 41 is a UV-Vis absorption spectrum of an orange fluorescent carbon dot, which can be seen to exhibit a distinct shoulder-like absorption peak at 536 nm.

FIG. 42 is a graph showing the luminescence spectrum of an orange fluorescent carbon dot, and it can be seen that the excited light of the orange fluorescent carbon dot shows a significant wavelength dependence, and the luminescence wavelength is also red-shifted from 578nm to 635nm as the excitation wavelength is increased from 435nm to 595 nm.

FIG. 43 is a fluorescence lifetime spectrum and a fitting curve of an orange fluorescent carbon dot, and fitting of a single photon counting decay curve of light emission at 525nm shows that the fluorescence lifetime of the orange fluorescent carbon dot shows double exponential decay, which is respectively 3.49ns (31.1%) and 13.00ns (68.9%), and the average lifetime is 10.04 ns; the luminescent quantum efficiency of the orange fluorescent carbon dot was further measured to be 0.32.

The orange fluorescent carbon dots in fig. 44 were used for biological cell imaging. The orange fluorescent carbon dots have the characteristic of low toxicity, no obvious cytotoxicity is seen when the co-culture concentration is lower than 25 mu g/mL, and the fluorescent dots have high fluorescence intensity and good light stability; it can be seen that the orange fluorescent carbon dots and human hepatoma cell Bel-7402 can enter cytoplasm or adhere to cell membranes after being co-cultured for 4 hours, and show certain cell membrane targeting, which is closely related to the chemical structure of precursor molecules used in the preparation of the carbon dots.

Examples 5 to 9

In a system in which the reaction precursor and the solvent are both glycerol, when the reaction temperature is lower than 200 ℃, the carbonization reaction cannot occur, the carbonization degree is increased along with the increase of the reaction temperature, the fluorescence of the carbon point is gradually reduced, and the water solubility is reduced.

Examples 10 to 16

Preparation of fluorescent carbon dots in different solvent systems:

examples 17 to 27

Fluorescent carbon dots doped with different heteroatoms:

examples 28 to 60

Changing the types of reaction precursors, preparing carbon dots with different fluorescence colors:

it is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the scope of the present invention.

Claims

1. A method for synthesizing water-soluble or oil-soluble carbon dots is characterized in that one or more organic molecules are used as a carbon source or heteroatom precursor, anhydrous zinc chloride is used as a pyrolysis promoter, and an ionic thermal reaction is adopted in an organic solvent to prepare the water-soluble or oil-soluble carbon dots;

the ionic thermal reaction comprises the following specific steps: adding a carbon source or heteroatom precursor and zinc chloride into an organic solvent, stirring at normal temperature until the carbon source or heteroatom precursor and the zinc chloride are fully mixed, slowly heating to 100 ℃ for reaction for 1h, then heating to 150-300 ℃ for reaction for 4h, cooling to room temperature, and purifying to obtain carbon dots; the organic molecule is selected from: organic acids, organic amines, alcohols/phenols, styrene, thiophene, pyrrole, trimethylsiloxy-2-furan, o-phthalaldehyde, m-phthalaldehyde, p-phthalaldehyde, 1, 3-dinitrobenzene, 2-hydroxyquinoline, 4-aminoisoquinoline, 8-hydroxyquinoline, and 8-aminoquinoline;

the organic acid is selected from one or more of citric acid, acrylic acid, phthalic acid, isophthalic acid, terephthalic acid, trimesic acid, amino acid, 3, 5-dihydroxybenzoic acid, 3-fluorocinnamic acid, citrazinic acid and oleic acid; the amino acid is glycine, L-cysteine or L-proline;

the alcohol/phenol is one or more of glucose, glycerol, m-triphenyl phenol, catechol, hydroquinone, 2-aminophenol, 3-aminophenol, 4-nitrophenol and 2,4, 6-trinitrophenol;

the organic amine is selected from one or more of ethylenediamine, propylenediamine, diphenylamine, aniline, p-phenylenediamine, o-phenylenediamine, m-phenylenediamine, 2, 6-diaminopyridine, melamine, urea and acrylamide.

2. The synthesis method according to claim 1, wherein the organic solvent is selected from one or more of ethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, polyethylene glycol 200, polyethylene glycol 300, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 800, polyethylene glycol 1000, oleylamine, and trioctylphosphine oxide (TOPO).

3. The synthesis method according to claim 1, wherein the size of the prepared carbon dots is 2-20 nm.

4. The synthetic method according to claim 1, wherein the carbon dots are carbon dots emitting different colors of near ultraviolet, blue, green, yellow, orange or red, and the light emitting range is 350-700 nm.