A colorful carbon quantum dot and its preparation method and application

Abstract

The present invention provides a method for preparing colorful carbon quantum dots. The method comprises taking phthalonitrile and an organic molecule, dissolving them in a solvent, and obtaining a reaction precursor solution. The reaction precursor solution is placed in an autoclave and reacted under heating conditions. After the reaction is completed, the solution is naturally cooled to room temperature. The pH of the product solution is then adjusted to 7 with a corresponding acid solution or alkaline solution. The solution is then concentrated under reduced pressure or filtered and washed. Finally, the colorful carbon quantum dots are obtained by drying. The present invention also provides carbon quantum dots, wherein the carbon quantum dots are blue carbon quantum dots having an emission peak at a wavelength of 441 nm, or cyan carbon quantum dots having an emission peak at a wavelength of 498 nm, or green carbon quantum dots having an emission peak at a wavelength of 520 nm, or red carbon quantum dots having an emission peak at a wavelength of 629 nm. In addition, the present invention also provides an application of the colorful carbon quantum dots. The preparation method of the present invention is simple and easy to implement, and the prepared carbon quantum dots have good luminescence performance and high quantum yield.

Description

Technical Field

[0001] The present invention relates to the field of carbon quantum dots, and in particular to colorful carbon quantum dots and a preparation method and application thereof. Background Art

[0002] Carbon quantum dots (CQDs) are a class of fluorescent carbon nanomaterials that have emerged as promising alternatives to traditional quantum dots and organic dyes in applications such as bioimaging, sensing, and optoelectronics. In recent years, fluorescent nanomaterials based on CQDs have attracted widespread interest among researchers. They possess numerous advantages, including excellent optical properties, good water solubility, a wide range of raw material sources, low cost, and good biocompatibility, and are widely used in photocatalysis, bioimaging, analytical sensing, and other fields. Not only do they exhibit optical properties comparable to those of semiconductor quantum dots, but they also possess advantages such as high biocompatibility, easy accessibility, low cost, and ease of surface functionalization that is difficult to achieve with semiconductor quantum dots. CQDs possess unique optical properties, such as tunable emission, ease of synthesis, and low toxicity, making them attractive for many applications in biology, medicine, and the environment. The synthesis of CQDs can be achieved through a variety of methods, including bottom-up and top-down approaches, involving the use of different carbon sources and surface functionalization strategies, and can also be produced through a variety of synthetic processes, including hydrothermal treatment, laser ablation, pyrolysis, and microwave technology. Although their synthetic routes differ, all CQDs share the same sp 2 core, which may contain nitrogen as part of the aromatic ring, and carbon-, nitrogen-, and oxygen-rich moieties have been proposed to exist on the surface of carbon quantum dots.

[0003] Although multicolor carbon quantum dots have been widely studied in recent years, there have been few reports on the synthesis of full-color carbon quantum dots based on the same reaction precursor, and there are also few reports on the preparation method of full-color fluorescent carbon quantum dots based on the same reaction precursor. More importantly, the emission peak of carbon quantum dots is concentrated in the red region, which is of great significance for various applications. Although the existing technology also provides red-emitting carbon quantum dots with higher fluorescence quantum yield through sophisticated chemical synthesis and silicon column chromatography, its synthesis process is complicated and has poor controllability. At present, there is still a great need for a relatively simple synthesis route to produce efficient red-emitting carbon quantum dots.

[0004] Given that practical applications, such as in vivo animal imaging, white light-emitting diodes, and functional fluorescent materials with anti-counterfeiting properties, require bright full-color emission from blue to red, it is very important and urgent to develop a simple and high-yield method to prepare high fluorescence intensity, high quantum yield, and color-tunable carbon quantum dots across the entire visible spectrum. Summary of the Invention

[0005] The present invention aims to address the deficiencies of the prior art and provide a method for preparing and applying colorful carbon quantum dots. Based on the above-mentioned problems, the present invention proposes a method for preparing and applying colorful carbon quantum dots, which is simple, economical, and easy to implement. Furthermore, the prepared carbon quantum dots have good luminescence performance and high quantum yield, and the fluorescence spectrum shows that the emission peak covers the entire visible spectrum.

[0006] The technical solution of the present invention is achieved as follows:

[0007] A method for preparing colorful carbon quantum dots comprises the following steps:

[0008] Phthalonitrile and organic molecules are taken in a certain proportion and dissolved in a solvent to obtain a reaction precursor solution; the reaction precursor solution is placed in a stainless steel autoclave with a polytetrafluoroethylene liner and reacted under heating conditions; after the reaction is completed, it is naturally cooled to room temperature; the pH of the product solution is then adjusted to 7 with a corresponding acid solution or alkaline solution; then it is concentrated under reduced pressure by a rotary evaporator or filtered and washed; and finally, the colorful carbon quantum dots are obtained by drying.

[0009] In the above-mentioned method for preparing colorful carbon quantum dots, the organic molecule is any one of organic acid, organic amine, and phenol.

[0010] In the above-mentioned method for preparing colorful carbon quantum dots, the organic acid is any one of citric acid, tartaric acid, malic acid, oxalic acid, ascorbic acid, and salicylic acid.

[0011] In the above-mentioned method for preparing colorful carbon quantum dots, the organic amine is any one of ethylenediamine, o-phenylenediamine, propylenediamine, butylenediamine, and diethylenetriamine.

[0012] In the above-mentioned method for preparing colorful carbon quantum dots, the phenol is any one of phenol, resorcinol, catechol, hydroquinone, and phloroglucinol.

[0013] According to the above-mentioned method for preparing colorful carbon quantum dots, the organic molecule is an organic acid, the organic acid is citric acid, and the mass ratio (g / g) of the phthalonitrile and the citric acid is (0.05~1):1; or, preferably, the organic molecule is an organic amine, the organic amine is ethylenediamine, and the mass volume ratio (g / μL) of the phthalonitrile and ethylenediamine is 1:(50~1500); or, preferably, the organic molecule is a phenol, the phenol is resorcinol, and the mass ratio (g / g) of the phthalonitrile and resorcinol is 5:(0.8~5); or, preferably, the organic molecule is an organic amine, the organic amine is o-phenylenediamine, and the molar ratio of the phthalonitrile and o-phenylenediamine is 5:(7~10).

[0014] In the above-mentioned method for preparing colorful carbon quantum dots, the solvent is any one of water, sodium hydroxide and sulfuric acid.

[0015] In the above-mentioned method for preparing colorful carbon quantum dots, the heating reaction conditions are: reaction temperature is 160° C. to 220° C., and reaction time is 6 h to 12 h.

[0016] Based on the same inventive concept, the present invention also provides a colorful carbon quantum dot, which is a blue light carbon quantum dot having an emission peak at a wavelength of 441nm, or a cyan light carbon quantum dot having an emission peak at a wavelength of 498nm, or a green light carbon quantum dot having an emission peak at a wavelength of 520nm, or a red light carbon quantum dot having an emission peak at a wavelength of 629nm.

[0017] Based on the same inventive concept, the present invention also provides colorful carbon quantum dots prepared by the preparation method described above or the application of the colorful carbon quantum dots described above, and the colorful quantum dots can be applied to photocatalysis, bioimaging, analytical sensing and functional fluorescent materials with anti-counterfeiting properties.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention provides a method for preparing colorful carbon quantum dots, which provides a simple and high-yield method for synthesizing full-color carbon quantum dots, so that the luminescence of carbon quantum dots covers the entire visible light spectrum, providing a broader application for the practical application of carbon quantum dots.

[0020] 2. The present invention provides a method for preparing colorful carbon quantum dots, which can obtain effective luminescence under ultraviolet light. The quantum yield of blue light carbon quantum dots can reach 35.69%, the quantum yield of cyan light can reach 56.64%, the quantum yield of green light can reach 71.56%, and the quantum yield of red light can reach 15.78%. In addition, the raw materials are cheap, easy to obtain, and environmentally friendly.

[0021] 3. The colorful carbon quantum dots in blue, cyan, green and red prepared by the present invention have good luminescence properties, are easy to synthesize and have low toxicity. They are not only attractive in many applications in biology, medicine and the environment, but are also widely used in photocatalysis, bioimaging, analytical sensing and functional fluorescent materials with anti-counterfeiting properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The fluorescence spectra of the carbon quantum dots prepared in Example 1, Comparative Example 1 and Comparative Example 2 and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 1 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 1 and the luminescence photo under ultraviolet light irradiation, Figure 1B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 2 and the luminescence photo under ultraviolet light irradiation, Figure 1 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 1 and the luminescence photograph under ultraviolet light irradiation;

[0023] Figure 2 Transmission electron microscopy image and particle size statistical distribution diagram of B-CDs prepared in Example 1;

[0024] Figure 3 This is the X-ray diffraction spectrum of the B-CDs prepared in Example 1;

[0025] Figure 4 : This is a comparison chart of the Fourier transform infrared spectra of B-CDs prepared in Example 1 and the raw material phthalonitrile;

[0026] Figure 5 Normalized UV-visible absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of B-CDs prepared in Example 1;

[0027] Figure 6 The full fluorescence emission spectrum of B-CDs prepared in Example 1 and the luminescence photograph under UV light irradiation;

[0028] Figure 7 This is the fluorescence lifetime decay diagram of B-CDs prepared in Example 1;

[0029] Figure 8 The fluorescence spectra of the carbon quantum dots prepared in Example 17 and Comparative Examples 3 and 4 and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 8 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 3 and the luminescence photo under ultraviolet light irradiation, Figure 8 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 4 and the luminescence photo under ultraviolet light irradiation, Figure 8 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 17 and the luminescence photograph under ultraviolet light irradiation;

[0030] Figure 9 Transmission electron microscopy image and particle size statistical distribution diagram of G1-CDs prepared in Example 17;

[0031] Figure 10 This is the X-ray diffraction spectrum of G1-CDs prepared in Example 17;

[0032] Figure 11 : This is a comparison chart of the Fourier transform infrared spectra of G1-CDs prepared in Example 17 and the raw material phthalonitrile;

[0033] Figure 12Normalized ultraviolet-visible absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of G1-CDs prepared in Example 17;

[0034] Figure 13 The full fluorescence emission spectrum of G1-CDs prepared in Example 17 and a luminescence photograph under UV light irradiation;

[0035] Figure 14 This is the fluorescence lifetime decay graph of G1-CDs prepared in Example 17;

[0036] Figure 15 The fluorescence spectra of the carbon quantum dots prepared in Example 32 and Comparative Examples 5 and 6 and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 15 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 5 and the luminescence photo under ultraviolet light irradiation, Figure 15 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 6 and the luminescence photo under ultraviolet light irradiation, Figure 15 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 32 and a luminescence photograph under ultraviolet light;

[0037] Figure 16 Transmission electron microscopy image and particle size statistical distribution diagram of G2-CDs prepared in Example 32;

[0038] Figure 17 This is the X-ray diffraction spectrum of G2-CDs prepared in Example 32;

[0039] Figure 18 3. Comparison of Fourier transform infrared spectra of G2-CDs prepared in Example 32 and the raw material phthalonitrile;

[0040] Figure 19 Normalized ultraviolet-visible absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of G2-CDs prepared in Example 32;

[0041] Figure 20 The full fluorescence emission spectrum of G2-CDs prepared in Example 32 and a luminescence photograph under UV light irradiation;

[0042] Figure 21 This is the fluorescence lifetime decay graph of G2-CDs prepared in Example 32;

[0043] Figure 22 The fluorescence spectra of the carbon quantum dots prepared in Example 47, Comparative Examples 7 and 8 and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 22 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 7 and the luminescence photo under ultraviolet light irradiation, Figure 22B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 8 and the luminescence photo under ultraviolet light irradiation, Figure 22 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 47 and a luminescence photograph under ultraviolet light;

[0044] Figure 23 This is a comparison chart of the absolute quantum yields of red fluorescent carbon quantum dots prepared in Comparative Example 7 and Example 47 measured using FLS-1000;

[0045] Figure 24 Transmission electron micrograph and particle size statistical distribution diagram of R-CDs prepared in Example 47;

[0046] Figure 25 This is the X-ray diffraction spectrum of the R-CDs prepared in Example 47;

[0047] Figure 26 This is the Fourier transform infrared spectrum of the R-CDs prepared in Example 47;

[0048] Figure 27 Normalized ultraviolet-visible absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of the R-CDs prepared in Example 47;

[0049] Figure 28 The full fluorescence emission spectrum of the R-CDs prepared in Example 47 and a luminescence photograph under UV light irradiation;

[0050] Figure 29 This is the fluorescence lifetime decay diagram of R-CDs prepared in Example 47. DETAILED DESCRIPTION

[0051] The following will be combined with the contents of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0052] Unless otherwise defined, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are intended solely for the purpose of describing specific embodiments and are not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0053] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0054] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0055] A method for preparing colorful carbon quantum dots comprises the following steps:

[0056] Phthalonitrile and organic molecules are taken in a certain proportion and dissolved in a solvent to obtain a reaction precursor solution; the reaction precursor solution is placed in a stainless steel autoclave with a polytetrafluoroethylene liner and reacted under heating conditions; after the reaction is completed, it is naturally cooled to room temperature; the pH of the product solution is then adjusted to 7 with a corresponding acid solution or alkaline solution; then it is concentrated under reduced pressure by a rotary evaporator or filtered and washed; and finally, the colorful carbon quantum dots are obtained by drying.

[0057] Preferably, the reactants are purified after naturally cooling to room temperature. Purification methods include dialysis using a dialysis membrane, ultrapure water washing, etc. In the present invention, the role of dialysis is to diffuse salts and small molecules out of the dialysis bag, and to retain large molecular weight substances in the solution within the bag; the role of ultrapure water washing is to wash away impurities remaining on the surface of the carbon quantum dots.

[0058] Preferably, in some embodiments of the present invention, drying is performed by freeze drying; in other embodiments, drying is performed by oven drying at 60°C. Freeze drying eliminates the effects of surface tension during drying, preventing sample deformation. Oven drying is simple to operate and provides a viable alternative for samples that cannot be freeze-dried, such as G1-CDs.

[0059] In the above-mentioned method for preparing colorful carbon quantum dots, the organic molecule is any one of an organic acid, an organic amine, and a phenol.

[0060] Preferably, the organic acid is any one of citric acid, tartaric acid, malic acid, oxalic acid, ascorbic acid, and salicylic acid. Of course, the organic acid is not limited to the above-mentioned ones. Preferably, the organic acid is citric acid. In some embodiments of the present invention, preferably, the mass ratio (g / g) of the phthalonitrile to the citric acid is (0.05-1):1. When the mass ratio (g / g) of the phthalonitrile to the citric acid is less than 0.05:1, the nitrogen source provided in the reaction system is insufficient, and the fluorescence quantum yield and fluorescence intensity of the synthesized blue light carbon quantum dots are low; when the mass ratio (g / g) of the phthalonitrile to the citric acid is greater than 1:1, the fluorescence quantum yield and fluorescence intensity of the obtained blue light carbon quantum dots are also reduced. More preferably, the mass ratio of the phthalonitrile to the citric acid is 0.08:1. Under this condition, the quantum yield of the blue light carbon quantum dots is the highest.

[0061] Alternatively, preferably, the organic amine is any one of ethylenediamine, o-phenylenediamine, propylenediamine, butylenediamine, and diethylenetriamine, although the organic amines are not limited to the aforementioned ones. Preferably, the organic amine is ethylenediamine. In some embodiments of the present invention, preferably, the mass volume ratio (g / μL) of o-phthalonitrile to ethylenediamine is 1:(50-1500). More preferably, the mass volume ratio (g / μL) of o-phthalonitrile to ethylenediamine is 1:200. Under these conditions, the quantum yield of the cyan carbon quantum dots is the highest.

[0062] Alternatively, preferably, the organic amine is o-phenylenediamine. In some other embodiments of the present invention, preferably, the molar ratio of o-phenylenediamine to o-phenylenediamine is 5:(7-10); more preferably, the molar ratio of o-phenylenediamine to o-phenylenediamine is 5:7. Under this condition, the quantum yield of its red light carbon quantum dots is the highest. Moreover, the applicant unexpectedly discovered that the red fluorescence intensity and quantum yield of the red fluorescence of the red carbon quantum dots prepared only by o-phenylenediamine are low, and the target product red carbon quantum dots cannot be obtained by only using o-phenylenediamine. The red carbon quantum dots prepared by the joint action of o-phenylenediamine and o-phenylenediamine under acidic conditions have significantly improved red fluorescence intensity and quantum yield compared with the red carbon quantum dots prepared by o-phenylenediamine.

[0063] Alternatively, the phenol is any one of phenol, resorcinol, catechol, hydroquinone, and phloroglucinol. Preferably, the phenol is resorcinol. In some embodiments of the present invention, preferably, the mass ratio (g / g) of the phthalonitrile to resorcinol is 5: (0.8-5). More preferably, the mass ratio of the phthalonitrile to resorcinol is 5: (1.5-3). Under this condition, the fluorescence quantum yield of its green light carbon quantum dots exceeds 70%; most preferably, the mass ratio of the phthalonitrile to resorcinol is 5: 3. Under this condition, the fluorescence quantum yield of its green light carbon quantum dots is 71.56%, which is higher than that of blue light carbon quantum dots, cyan light carbon quantum dots, and red light carbon quantum dots.

[0064] The principle of the present invention is as follows: using o-phthalonitrile with a conjugated structure, and then introducing small molecules such as citric acid or ethylenediamine to increase its surface functionalization to prepare carbon quantum dots, which can avoid a complex polymerization process and easily regulate short-wavelength emission of carbon quantum dots. Unlike citric acid and ethylenediamine, resorcinol is known as an aromatic compound with a conjugated structure. When resorcinol is used as a reaction precursor, green-emitting carbon quantum dots can be prepared. By introducing a nitrogen-containing precursor (o-phenylenediamine), the maximum emission of the resulting carbon quantum dots turns to red light. The applicant unexpectedly discovered that by selecting a precursor with a conjugated structure and a nitrogen-containing group, the red shift of the carbon quantum dot emission peak can be achieved. The fluorescence spectrum of the carbon quantum dots synthesized by the present invention shows that the emission peak covers the entire visible spectrum, and subsequent characterization shows that the blue, cyan, green, and red carbon quantum dots are caused by the size of the conjugated domain and the increase in the number of carbonyl and amino groups. These characteristics are consistent with the characteristics of the selected precursor, indicating that the structural portion of the precursor is retained in the resulting carbon quantum dots.

[0065] In the above-mentioned method for preparing colorful carbon quantum dots, the solvent is any one of water, sodium hydroxide and sulfuric acid.

[0066] In some embodiments of the blue light-emitting carbon quantum dots of the present invention, preferably, the solvent is sodium hydroxide, and the concentration of the sodium hydroxide solution is 0.5 M to 1.2 M; more preferably, the concentration of the sodium hydroxide solution is 0.8 M. NaOH solution is used as the solvent because it can accelerate the decomposition of phthalonitrile, resulting in faster decomposition, carbonization, and nucleation of organic matter.

[0067] In some embodiments of the cyan carbon quantum dots of the present invention, preferably, the solvent is ultrapure water. Water is used as the solvent here to introduce oxygen into the reaction system for doping and increase surface defects.

[0068] In some embodiments of the green light carbon quantum dots of the present invention, preferably, the solvent is sodium hydroxide, and the concentration of the sodium hydroxide solution is 0.5M to 1.4M; more preferably, the concentration of the sodium hydroxide solution is 1.2M. The use of NaOH solution as a solvent here can accelerate the decomposition, carbonization and nucleation of organic matter, increase the reaction rate, and promote the faster synthesis of carbon quantum dots. On the other hand, phthalonitrile and resorcinol in OH - The presence of α-HBr better activates its condensation reaction.

[0069] In some embodiments of the red light carbon quantum dots of the present invention, preferably, the solvent is sulfuric acid. Under acidic conditions, o-phenylenediamine and o-phthalonitrile are carbonized and polymerized into conjugated planes, followed by continuous accumulation inside the carbon core. A flexible polymer shell is formed outside the carbon core, which has a relatively rich surface polymer chain. The surface of the carbon quantum dots has nitrogen, oxygen and sulfur-containing functional groups, which not only increases its sp2 The red carbon quantum dots synthesized by the conjugated structure and the introduction of nitrogen sources have high fluorescence intensity and the spectrum shows excitation independence.

[0070] In the above-described method for preparing colorful carbon quantum dots, the heating reaction conditions are: a reaction temperature of 160°C to 220°C and a reaction time of 6 to 12 hours. Under these conditions, temperatures above 220°C can cause excessive carbonization of the organic matter, thereby affecting the fluorescence quantum yield and the photoluminescence of the carbon quantum dots; temperatures below 160°C can result in incomplete carbonization of the organic matter, preventing the formation of carbon cores; reaction times exceeding 12 hours can cause excessive reaction of the organic matter, resulting in a large number of byproducts, thereby affecting the fluorescence quantum yield; and reaction times less than 6 hours can result in insufficient reaction of the organic matter, thereby affecting the fluorescence quantum yield and the photoluminescence of the carbon quantum dots. Preferably, the heating reaction conditions are: a temperature of 180°C to 200°C and a time of 8 to 10 hours. In some embodiments of the blue-emitting carbon quantum dots of the present invention, the heating reaction conditions are more preferably: a temperature of 180°C for 8 hours. In some embodiments of the cyan-emitting carbon quantum dots and green-emitting carbon quantum dots of the present invention, the heating reaction conditions are more preferably: a temperature of 200°C for 8 hours. In the embodiment of the red light carbon quantum dots of the present invention, the heating reaction conditions are: temperature 200° C., time 10 h.

[0071] Based on the same inventive concept, the present invention also provides a colorful carbon quantum dot, which is a blue light carbon quantum dot having an emission peak at a wavelength of 441nm, or a cyan light carbon quantum dot having an emission peak at a wavelength of 498nm, or a green light carbon quantum dot having an emission peak at a wavelength of 520nm, or a red light carbon quantum dot having an emission peak at a wavelength of 629nm.

[0072] Based on the same inventive concept, the present invention also provides colorful carbon quantum dots prepared by the preparation method as described above or the application of the colorful carbon quantum dots as described above. The colorful quantum dots can be applied to photocatalysis, biological imaging, analytical sensing, and functional fluorescent materials with anti-counterfeiting properties, etc.

[0073] Example 1:

[0074] Preparation of blue light carbon quantum dots: 0.08 g of phthalonitrile and 1.0 g of citric acid were dissolved in 20.0 mL of 0.8 M sodium hydroxide solution. Subsequently, the solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and hydrothermally heated at 180 ° C for 8 hours. After naturally cooling to room temperature, the light yellow solution was neutralized with dilute hydrochloric acid solution. The neutralized product was dialyzed against ultrapure water for 8 hours through a dialysis membrane with a molecular weight cutoff of 1000 Da, and then concentrated by a rotary evaporator at 65 ° C and reduced pressure. Finally, the blue light carbon quantum dots (blue light carbon quantum dots hereinafter referred to as B-CDs) powder was collected by freeze drying.

[0075] The B-CDs of this example were prepared by the above preparation method.

[0076] The fluorescence spectrometer 7000 was used for testing, and the test conditions were as follows: the voltage of the photomultiplier tube detector (PMT voltage) was controlled to 400 V, the excitation light and emission light slit widths were both 5 nm, the fluorescence spectrum measured in Example 1 of the present invention, the UV-visible absorption spectrum, and the concentration of the blue light carbon quantum dots used for the quantum yield were all 4 mg / mL, and the maximum fluorescence intensity of the blue light carbon quantum dots prepared in Example 1 of the present invention was tested. The maximum fluorescence intensity of the blue light carbon quantum dots prepared in Example 1 of the present invention was 5762 (au); the Edinburgh-fluorescence spectrometer FLS1000 was used to test the fluorescence quantum yield of the blue light carbon quantum dots prepared in Example 1 of the present invention. The fluorescence quantum yield of the blue light carbon quantum dots prepared in Example 1 of the present invention was 35.69%.

[0077] Example 2:

[0078] The method is basically the same as that in Example 1, except that 0.05 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0079] Example 3:

[0080] The method is basically the same as that in Example 1, except that 0.15 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0081] Example 4:

[0082] The method is basically the same as that in Example 1, except that 0.3 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0083] Example 5:

[0084] The method is basically the same as that in Example 1, except that 0.6 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0085] Example 6:

[0086] The method is basically the same as that in Example 1, except that 0.8 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0087] Example 7:

[0088] The method is basically the same as that in Example 1, except that 1.0 g of phthalonitrile is used. The quantum yield is measured using the method in Example 1, and the results are shown in Table 1.

[0089] Example 8:

[0090] The method is basically the same as Example 1, except that the concentration of NaOH used is 0.5 M. The quantum yield is tested using the method of Example 1, and the results are shown in Table 2.

[0091] Example 9:

[0092] The method is basically the same as Example 1, except that the concentration of NaOH used is 1.0 M. The quantum yield is tested using the method of Example 1, and the results are shown in Table 2.

[0093] Example 10:

[0094] The method is basically the same as Example 1, except that the concentration of NaOH used is 1.2 M. The quantum yield is tested using the method of Example 1, and the results are shown in Table 2.

[0095] Example 11:

[0096] The method is basically the same as that in Example 1, except that the reaction temperature is 160° C. The quantum yield is measured using the method in Example 1, and the results are shown in Table 3.

[0097] Example 12:

[0098] The process is basically the same as that of Example 1, except that the reaction temperature is 200° C. The quantum yield is measured using the same method as in Example 1, and the results are shown in Table 3.

[0099] Example 13:

[0100] The method is basically the same as that in Example 1, except that the reaction temperature is 220° C. The quantum yield is measured using the method in Example 1, and the results are shown in Table 3.

[0101] Example 14:

[0102] The method is basically the same as that in Example 1, except that the reaction time is 6 h. The quantum yield is measured using the method in Example 1, and the results are shown in Table 4.

[0103] Example 15:

[0104] The method is basically the same as that in Example 1, except that the reaction time is 10 h. The quantum yield is measured using the method in Example 1, and the results are shown in Table 4.

[0105] Example 16:

[0106] The method is basically the same as that in Example 1, except that the reaction time is 12 h. The quantum yield is measured using the method in Example 1, and the results are shown in Table 4.

[0107] Example 17:

[0108] Preparation of cyan carbon quantum dots: 1.0 g of phthalonitrile and 200 μL of ethylenediamine were dissolved in 15.0 mL of ultrapure water. Subsequently, the solution was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and hydrothermally heated at 200°C for 8 h. After naturally cooling to room temperature, the yellow-green solution was neutralized with dilute hydrochloric acid solution and the pH was adjusted to 7. It was then concentrated under reduced pressure at 65°C using a rotary evaporator. Finally, the cyan carbon quantum dots (hereinafter referred to as G1-CDs) powder was collected by freeze drying.

[0109] The G1-CDs of this example were prepared by the above preparation method.

[0110] The fluorescence spectrum, ultraviolet-visible absorption spectrum, and quantum yield of the cyan carbon quantum dots measured in Example 17 of the present invention are all at a concentration of 4 mg / mL. The measurement method of Example 1 is used to test that the maximum fluorescence intensity of the cyan carbon quantum dots prepared in Example 17 of the present invention is 1522 (au); the measurement method of Example 1 is used to test that the fluorescence quantum yield of the cyan carbon quantum dots prepared in this example is 56.64%.

[0111] Example 18:

[0112] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 50 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0113] Example 19:

[0114] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 100 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0115] Example 20:

[0116] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 300 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0117] Example 21:

[0118] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 400 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0119] Example 22:

[0120] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 500 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0121] Example 23:

[0122] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 900 μL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0123] Example 24:

[0124] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 1.2 mL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0125] Example 25:

[0126] The method is basically the same as Example 17, except that the volume of ethylenediamine used is 1.5 mL. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0127] Example 26:

[0128] The reaction was basically the same as Example 17, except that the reaction temperature was 160° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 6.

[0129] Example 27:

[0130] The reaction was basically the same as Example 17, except that the reaction temperature was 180° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 6.

[0131] Example 28:

[0132] The reaction was basically the same as Example 17, except that the reaction temperature was 220° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 6.

[0133] Example 29:

[0134] The reaction was basically the same as Example 17, except that the reaction time was 6 h. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 7.

[0135] Example 30:

[0136] The results are basically the same as those in Example 17, except that the reaction time is 10 h and the quantum yield is tested using the determination method of Example 1. The results are shown in Table 7.

[0137] Example 31:

[0138] The reaction was essentially the same as Example 17, except that the reaction time was 12 h. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 7.

[0139] Example 32:

[0140] Preparation of green light carbon quantum dots: 0.5g of phthalonitrile and 0.3g of resorcinol were dissolved in 15.0mL of 1.2M sodium hydroxide solution. Subsequently, it was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and solvent-thermally heated at 200°C for 8h. After naturally cooling to room temperature, it was neutralized with a certain concentration of dilute hydrochloric acid solution to adjust the pH to 7. The neutralized product was dialyzed against ultrapure water for 8 hours through a dialysis membrane with a molecular weight cutoff of 1000Da, and then concentrated under reduced pressure by a rotary evaporator at 65°C. Finally, the green light carbon quantum dots (hereinafter referred to as G2-CDs) powder was collected by freeze drying.

[0141] The G2-CDs of this example were prepared by the above preparation method.

[0142] The test was conducted using a fluorescence spectrometer 7000, and the test conditions were as follows: the voltage of the photomultiplier tube detector (PMT voltage) was controlled to 400 V, the slit widths of the excitation light and the emission light were both 2.5 nm, the fluorescence spectrum measured in Example 32 of the present invention, the ultraviolet-visible absorption spectrum, and the concentration of the green light carbon quantum dots used for the quantum yield were all 4 mg / mL, and the maximum fluorescence intensity of the green light carbon quantum dots prepared in Example 32 of the present invention was 517 (au); the determination method of Example 1 was used, and the fluorescence quantum yield of the green light carbon quantum dots prepared in the test example was 71.56%.

[0143] Example 33:

[0144] The same as Example 32, except that 0.08 g of resorcinol was used. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 8.

[0145] Example 34:

[0146] The same method as Example 32 was used, except that 0.15 g of resorcinol was used. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 8.

[0147] Example 35:

[0148] The same as Example 32, except that 0.4 g of resorcinol was used. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 8.

[0149] Example 36:

[0150] The same method as Example 32 was used, except that 0.5 g of resorcinol was used. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 8.

[0151] Example 37:

[0152] The method is basically the same as Example 32, except that the concentration of NaOH used is 0.5 M. The quantum yield is measured using the method of Example 1, and the results are shown in Table 9.

[0153] Example 38:

[0154] The method is basically the same as Example 32, except that the concentration of NaOH used is 0.8 M. The quantum yield is measured using the method of Example 1, and the results are shown in Table 9.

[0155] Example 39:

[0156] The method is basically the same as Example 32, except that the concentration of NaOH used is 1.0 M. The quantum yield is measured using the method of Example 1, and the results are shown in Table 9.

[0157] Example 40:

[0158] The method is basically the same as Example 32, except that the concentration of NaOH used is 1.4 M. The quantum yield is measured using the method of Example 1, and the results are shown in Table 9.

[0159] Example 41:

[0160] The reaction was basically the same as Example 20, except that the reaction temperature was 160° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 10.

[0161] Example 42:

[0162] The reaction was basically the same as Example 32, except that the reaction temperature was 180° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 10.

[0163] Example 43:

[0164] The reaction was basically the same as Example 32, except that the reaction temperature was 220° C. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 10.

[0165] Example 44:

[0166] The reaction was essentially the same as in Example 32, except that the reaction time was 6 h. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 11.

[0167] Example 45:

[0168] The reaction was essentially the same as Example 32, except that the reaction time was 10 h. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 11.

[0169] Example 46:

[0170] The reaction was substantially the same as in Example 32, except that the reaction time was 12 h. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 11.

[0171] Example 47:

[0172] Preparation of red-light carbon quantum dots: 0.320g of o-phthalonitrile and 0.378g of o-phenylenediamine were dissolved in 9.2mL of ultrapure water. Subsequently, 800μL of concentrated sulfuric acid was slowly added and the mixture was transferred to a stainless steel autoclave lined with polytetrafluoroethylene and solvent-thermally heated at 200°C for 10h. After cooling naturally to room temperature, the blue-green solution was precipitated with sodium hydroxide to precipitate carbon quantum dots, i.e., the product solution was neutralized to a pH of 7.0, and then a simple purification process was performed, i.e., washing with ultrapure water several times. Finally, after drying in an oven at 60°C, the final solid product, red-light carbon quantum dots (hereinafter referred to as R-CDs), was obtained.

[0173] The R-CDs of this embodiment were prepared by the above preparation method.

[0174] The test was conducted using a fluorescence spectrometer 7000, and the test conditions were as follows: the voltage of the photomultiplier tube detector (PMT voltage) was controlled to 400 V, the slit widths of the excitation light and the emission light were both 10 nm, the fluorescence spectrum measured in Example 47 of the present invention, the ultraviolet-visible absorption spectrum, and the absorbance of the red light carbon quantum dots used for the quantum yield were all 0.95, and the maximum fluorescence intensity of the red light carbon quantum dots prepared in Example 47 of the present invention was 2963 (au); the determination method of Example 1 was used to test that the fluorescence quantum yield of the red light phosphor prepared in this example was 15.78%.

[0175] Comparative Example 1:

[0176] The preparation method of blue carbon quantum dots in this comparative example is basically the same as that in Example 1, except that phthalonitrile is not added in the preparation step of blue carbon quantum dots. The quantum yield is tested using the method of Example 1, and the results are shown in Table 1.

[0177] Comparative Example 2:

[0178] The preparation method of blue light carbon quantum dots in this comparative example is basically the same as that in Example 1, except that citric acid is not added in the preparation step of the blue light carbon quantum dots.

[0179] Comparative Example 3:

[0180] The preparation method of the cyan carbon quantum dots used in this comparative example is basically the same as that of Example 17, except that no phthalonitrile is added in the preparation step of the cyan carbon quantum dots.

[0181] Comparative Example 4:

[0182] The preparation method for preparing cyan carbon quantum dots in this comparative example is basically the same as that in Example 17, except that ethylenediamine is not added during the preparation step of the cyan carbon quantum dots. The quantum yield is measured using the method of Example 1, and the results are shown in Table 5.

[0183] Comparative Example 5:

[0184] The preparation method of green carbon quantum dots used in this comparative example is basically the same as that in Example 32, except that phthalonitrile is not added in the preparation step of the green carbon quantum dots.

[0185] Comparative Example 6:

[0186] This comparative example used a method for preparing green carbon quantum dots that was essentially the same as that used in Example 32, except that resorcinol was not added during the preparation of the green carbon quantum dots. The quantum yield was measured using the same method as in Example 1, and the results are shown in Table 8.

[0187] Comparative Example 7:

[0188] The preparation method of the red light carbon quantum dots used in this comparative example is basically the same as that of Example 47, except that no phthalonitrile is added in the preparation step of the red light carbon quantum dots.

[0189] Comparative Example 8:

[0190] The preparation method of the red light carbon quantum dots used in this comparative example is basically the same as that of Example 47, except that o-phenylenediamine is not added in the preparation step of the red light carbon quantum dots.

[0191] Table 1 shows the effect of different masses of phthalonitrile on the quantum yield of blue light carbon quantum dots. It can be seen from Table 1 that when preparing blue light carbon quantum dots, the amount of citric acid is 1.0g and the amount of phthalonitrile is 0.08g, and the quantum yield is the highest.

[0192] Table 1 Effect of different masses of phthalonitrile on the quantum yield of blue light carbon quantum dots

[0193]

[0194]

[0195] Table 2 shows the effect of different NaOH solution concentrations on the quantum yield of blue light carbon quantum dots. It can be seen from Table 2 that when preparing blue light carbon quantum dots, the concentration of NaOH solution is 0.8 M and the quantum yield is the highest.

[0196] Table 2 Effect of different NaOH solution concentrations on the quantum yield of blue light carbon quantum dots

[0197]

[0198] Table 3 shows the effect of different reaction temperatures on the quantum yield of blue light carbon quantum dots. It can be seen from Table 3 that when preparing blue light carbon quantum dots, the quantum yield is the highest when the reaction temperature is 180°C.

[0199] Table 3 Effect of different reaction temperatures on the quantum yield of blue light carbon quantum dots

[0200]

[0201] Table 4 shows the effect of different reaction times on the quantum yield of blue light carbon quantum dots. It can be seen from Table 4 that when preparing blue light carbon quantum dots, the quantum yield is the highest when the reaction time is 8 h.

[0202] Table 4 Effect of different reaction times on the quantum yield of blue light carbon quantum dots

[0203]

[0204] Table 5 shows the effect of different volumes of ethylenediamine on the quantum yield of cyan carbon quantum dots. It can be seen from Table 5 that when preparing cyan carbon quantum dots, the amount of phthalonitrile is 1.0 g and the amount of ethylenediamine is 200 μL, and the quantum yield is the highest.

[0205] Table 5 Effect of different volumes of ethylenediamine on the quantum yield of cyan carbon quantum dots

[0206]

[0207] Table 6 shows the effect of different reaction temperatures on the quantum yield of cyan carbon quantum dots. It can be seen from Table 6 that when preparing cyan carbon quantum dots, the quantum yield is the highest when the reaction temperature is 200°C.

[0208] Table 6 Effect of different reaction temperatures on the quantum yield of cyan carbon quantum dots

[0209]

[0210] Table 7 shows the effect of different reaction times on the quantum yield of cyan carbon quantum dots. It can be seen from Table 7 that when preparing cyan carbon quantum dots, the quantum yield is the highest when the reaction time is 8 h.

[0211] Table 7 Effect of different reaction times on the quantum yield of cyan carbon quantum dots

[0212]

[0213] Table 8 shows the effect of different resorcinol masses on the quantum yield of green light carbon quantum dots. It can be seen from Table 8 that when preparing green light carbon quantum dots, the amount of phthalonitrile is 0.5 g and the amount of resorcinol is 0.3 g, and the quantum yield is the highest.

[0214] Table 8 Effect of different resorcinol masses on the quantum yield of green light carbon quantum dots

[0215]

[0216]

[0217] Table 9 shows the effect of different NaOH solution concentrations on the quantum yield of green light carbon quantum dots. It can be seen from Table 9 that when preparing green light carbon quantum dots, the quantum yield is highest when the concentration of NaOH solution is 1.2 M.

[0218] Table 9 Effect of different NaOH solution concentrations on the quantum yield of green light carbon quantum dots

[0219]

[0220] Table 10 shows the effects of different reaction temperatures on the quantum yield of green light carbon quantum dots. It can be seen from Table 10 that when preparing green light carbon quantum dots, the quantum yield is highest when the reaction temperature is 200°C.

[0221] Table 10 Effect of different reaction temperatures on the quantum yield of green light carbon quantum dots

[0222]

[0223] Table 11 shows the effects of different reaction times on the quantum yield of green light carbon quantum dots. It can be seen from Table 11 that when preparing green light carbon quantum dots, the quantum yield is the highest when the reaction time is 8 h.

[0224] Table 11 Effect of different reaction times on the quantum yield of green light carbon quantum dots

[0225]

[0226] Figure 1 The fluorescence spectra of the carbon quantum dots prepared in Example 1 and Comparative Examples 1 and 2 (all tested under the same conditions: PMT 400V, slit width 5nm) and luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 1 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 1 and the luminescence photo under ultraviolet light irradiation, Figure 1 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 2 and the luminescence photo under ultraviolet light irradiation, Figure 1 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 1 and the luminescence photo under ultraviolet light. Figure 1 As can be seen from A, in the absence of phthalonitrile, that is, when the reactant is only citric acid, the fluorescence intensity of the carbon quantum dots synthesized is extremely weak, with an intensity of only 33.08 (au), and the spectrum shows excitation independence. The luminescence photos under ultraviolet light also show that its fluorescence is very weak; Figure 1 As can be seen from B, the fluorescence intensity of the carbon quantum dots synthesized when the reactant is only phthalonitrile is only 116 (au), and the spectrum shows excitation dependence. The luminescence photo under ultraviolet light also shows that its fluorescence is very weak. Figure 1As can be seen from C, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized by the joint action of citric acid and phthalonitrile is significantly increased, with an intensity of 5762 (au), and the spectrum shows excitation independence. The luminescence photograph under ultraviolet light can be seen to have very bright blue fluorescence. Therefore, it can be concluded that phthalonitrile plays an indispensable role in Example 1 of the present invention, and it can also explain the importance of phthalonitrile as a nitrogen source with a conjugated structure to blue light carbon quantum dots with high fluorescence intensity and high quantum yield. At the same time, citric acid provides more functional groups for surface functionalization of carbon quantum dots, avoiding a complex polymerization process, and easily regulating short-wavelength emission carbon quantum dots, thereby successfully preparing the blue light carbon quantum dots of this Example 1.

[0227] Figure 2 The transmission electron micrograph and particle size distribution diagram of the B-CDs prepared in Example 1 are used to characterize the morphology of the B-CDs. Figure 2 From the transmission electron microscopy image of A, it can be seen that the B-CDs are uniform and nearly spherical, with good dispersion. Figure 2 The particle size statistics of B show that the average particle size of the B-CDs is between 6.64±0.11nm.

[0228] Figure 3 This is the X-ray diffraction spectrum of the B-CDs prepared in Example 1. As can be seen from the figure, B-CDs has a relatively obvious broad peak at 2θ of 18°, corresponding to the 002 plane of graphitic carbon, showing the amorphous structure of carbon quantum dots.

[0229] Figure 4 The comparison of Fourier infrared spectra of B-CDs prepared in Example 1 and raw material phthalonitrile is shown in the figure. It can be seen that phthalonitrile has a wavelength of 2232 cm -1 The sharp absorption peak at 1567 cm is attributed to the stretching vibration of -CN. -1 and 3037cm -1 The absorption peak is attributed to the stretching vibration of C=C and CH on the benzene ring; and the Fourier infrared spectrum of B-CDs can be found at 2232cm -1 -CN disappears at 1567cm -1 The stretching vibration of C=N appears at 3356cm -1 The strong stretching vibration peak of -OH is shown at 1391cm -1 The absorption peak at 1243 cm is caused by the stretching vibration of -COO-. -1 and 1057cm -1 The absorption peaks at correspond to the stretching vibrations of COC and CO, respectively.

[0230] Figure 5Figure 1 shows the normalized UV-Vis absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of the B-CDs prepared in Example 1. The figure shows that the B-CDs exhibit absorption in the short-wavelength region (284 nm), attributed to the π–π* transition of C=C / C=N, while exhibiting strong absorption in the long-wavelength region (336 nm), attributed to the n–π* transition of C=O. Furthermore, the maximum excitation wavelength of the B-CDs prepared in Example 1 is 368 nm, corresponding to an emission wavelength of 441 nm.

[0231] Figure 6 The full fluorescence emission spectrum of the B-CDs prepared in Example 1 and a photo of the fluorescence under UV light are shown. As can be seen from the figure, under different excitation conditions, the fluorescence emission peak is concentrated at 441 nm, with no excitation wavelength dependence. The photo of the fluorescence under UV light also shows that the carbon quantum dots emit bright blue fluorescence under UV light.

[0232] Figure 7 This is the fluorescence lifetime decay diagram of the B-CDs prepared in Example 1. From the figure, it can be seen that the fluorescence lifetime of B-CDs under 368nm excitation is 7.28ns.

[0233] Figure 8 The fluorescence spectra of the carbon quantum dots prepared in Example 17 and Comparative Examples 3 and 4 (all tested under the same conditions: PMT 400V, slit width 5nm) and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 8 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 3 and the luminescence photo under ultraviolet light irradiation, Figure 8 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 4 and the luminescence photo under ultraviolet light irradiation, Figure 8 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 17 and the luminescence photo under ultraviolet light. Figure 8 As can be seen from A, in the absence of phthalonitrile, that is, when the reactant is only ethylenediamine, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized is 489 (au), the optimal excitation is 360nm, the corresponding emission wavelength is 439nm, and the spectrum shows excitation dependence; Figure 8 As can be seen from B, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized when the reactant is only phthalonitrile is 424 (au), the optimal excitation is 340nm, the corresponding emission wavelength is 394nm, and the spectrum shows excitation dependence; Figure 8It can be seen from C that the fluorescence intensity of the cyan fluorescent carbon quantum dots synthesized by the joint action of ethylenediamine and phthalonitrile is not only significantly enhanced to 1522 (au), but also the emission is red-shifted to 498nm, and the spectrum shows excitation independence; therefore, it can be seen that the conjugated structure of phthalonitrile and the surface functionalization of the carbon quantum dots by providing nitrogen-containing functional groups by introducing ethylenediamine cause the emission wavelength to be red-shifted, thereby successfully preparing the cyan carbon quantum dots of Example 17.

[0234] Figure 9 The transmission electron micrograph and particle size distribution diagram of G1-CDs prepared in Example 17 are used to characterize the morphology of G1-CDs. Figure 9 From the transmission electron microscopy image of A, it can be seen that the G1-CDs are uniform and nearly spherical, with good dispersion. Figure 9 From the particle size statistics diagram of Figure B, it can be seen that the average particle size of the G1-CDs is between 3.16±0.02nm.

[0235] Figure 10 This is the X-ray diffraction spectrum of G1-CDs prepared in Example 17. As can be seen from the figure, G1-CDs has a relatively obvious broad peak at 2θ of 25.2°, corresponding to the 002 plane of graphitic carbon, which not only shows the amorphous structure of carbon quantum dots, but also indicates that it has an obvious conjugated structure.

[0236] Figure 11 The comparison of Fourier infrared spectra of G1-CDs prepared in Example 17 and raw material phthalonitrile shows that phthalonitrile has a wavelength of 2232 cm -1 The sharp absorption peak at 1567 cm is attributed to the stretching vibration of -CN. -1 and 3037cm -1 The absorption peak is attributed to the stretching vibration of C=C and CH on the benzene ring; and the Fourier infrared spectrum of G1-CDs can be found at 2232cm -1 -CN disappears at 1548cm -1 The stretching vibration of C=N appears at 3192 cm -1 The stretching vibration peak of NH is strong at 1381 cm -1 The absorption peak at 1148 cm is caused by the stretching vibration of C=C / CN. -1 The absorption peak corresponds to the stretching vibration of CO.

[0237] Figure 12Figures 2 and 3 show the normalized UV-visible absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of G1-CDs prepared in Example 17. The figure shows strong absorption in the short-wavelength region (320 nm) of G1-CDs, attributed to the π–π* transition of C═C / C═N. Broader absorption occurs in the long-wavelength region (395 nm and 416 nm), attributed to the n–π* transition of C═O. Furthermore, the maximum excitation wavelength of G1-CDs prepared in Example 17 is 423 nm, corresponding to an emission wavelength of 498 nm.

[0238] Figure 13 The full fluorescence emission spectrum of G1-CDs prepared in Example 17 and a photo of the fluorescence emission under UV light are shown. As can be seen from the figure, under different excitation conditions, the fluorescence emission peak is concentrated at 498 nm, with no excitation wavelength dependence. The photo of the fluorescence emission under UV light also shows that the carbon quantum dots emit bright cyan fluorescence under UV light.

[0239] Figure 14 This is the fluorescence lifetime decay diagram of G1-CDs prepared in Example 17. From the figure, it can be seen that the fluorescence lifetime of G1-CDs under 423nm excitation is 6.26ns.

[0240] Figure 15 The fluorescence spectra of the carbon quantum dots prepared in Example 32 and Comparative Examples 5 and 6 (all tested under the same conditions: PMT 400V, slit width 2.5nm) and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 15 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 5 and the luminescence photo under ultraviolet light irradiation, Figure 15 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 6 and the luminescence photo under ultraviolet light irradiation, Figure 15 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 32 and the luminescence photo under ultraviolet light. Figure 15 As can be seen from A, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized in the absence of phthalonitrile, that is, when the reactant is only resorcinol, is 43.36 (au), and the fluorescence under ultraviolet light can be seen to be relatively weak; Figure 15 As can be seen from B, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized when the reactant is only phthalonitrile is 11 (au). From the luminescence photos under ultraviolet light, it can be seen that the luminescence is extremely weak; Figure 15C shows that the fluorescence intensity of the green fluorescent carbon quantum dots synthesized by the joint action of resorcinol and phthalonitrile is significantly increased, with an intensity of 517 (au), the emission wavelength is red-shifted from the blue light region to the green light region, and the spectrum shows excitation independence, and the half-peak width of the spectrum is narrow, showing excellent photoluminescence, and from the luminescence photograph under ultraviolet light, it can be seen that its green fluorescence is very bright; According to Comparative Examples 5 and 6, it can be seen that green light carbon quantum dots cannot be synthesized. After adding phthalonitrile, Example 32 can successfully obtain bright green light carbon quantum dots. On the basis of phthalonitrile, by introducing the aromatic compound resorcinol with a conjugated structure, the two work together to increase sp 2 The nitrogen / oxygen related surface defects of the structural domains and carbon quantum dots caused the fluorescence emission to red-shift, thereby successfully preparing the green light carbon quantum dots of Example 32.

[0241] Figure 16 The transmission electron micrograph and particle size distribution diagram of G2-CDs prepared in Example 32 are used to characterize the morphology of G2-CDs. Figure 16 From the transmission electron microscopy image of A, it can be seen that the G2-CDs are uniform and nearly spherical, with good dispersion and uniform particle size; Figure 16 From the particle size statistics diagram of B, it can be seen that the average particle size of the G1-CDs is between 9.43±0.16nm.

[0242] Figure 17 This is the X-ray diffraction spectrum of G2-CDs prepared in Example 32. It can be seen from the figure that G2-CDs has a relatively obvious broad peak at 2θ of 24.6°, corresponding to the 002 plane of graphite carbon. Compared with the half-peak width of G1-CDs, the half-peak width of G2-CDs is narrower, indicating that the carbon core of G2-CDs is sp 2 The close packing of conjugated structures also means a higher degree of graphitization.

[0243] Figure 18 The comparison of Fourier infrared spectra of G2-CDs prepared in Example 32 and raw material phthalonitrile shows that phthalonitrile has a wavelength of 2232 cm -1 The sharp absorption peak at 1567 cm is attributed to the stretching vibration of -CN. -1 and 3037cm -1 The absorption peak is attributed to the stretching vibration of C=C and CH on the benzene ring; and the Fourier infrared spectrum of G2-CDs can be found at 2232cm -1 -CN disappears at 1545cm -1 The stretching vibration of C=N appears at 3384 cm -1 The strong OH stretching vibration peak is at 1379 cm-1 The absorption peak at 1147 cm is caused by the stretching vibration of CN / C=C. -1 The absorption peak corresponds to the stretching vibration of CO.

[0244] Figure 19 The normalized UV-Vis absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of G2-CDs prepared in Example 32 are shown. The optical properties of G2-CDs are shown in the figure. G2-CDs exhibit strong absorption in the short-wavelength region (293 nm), attributing to the π–π* transition of C=C / C=N. Furthermore, a relatively weaker but equally pronounced absorption band exists in the long-wavelength region (489 nm), attributing to the n–π* transition of C=O. The maximum excitation wavelength of G1-CDs prepared in Example 32 is 496 nm, corresponding to an emission wavelength of 520 nm. Furthermore, it can be seen that there is only minimal overlap between the absorption and emission spectra, effectively avoiding self-absorption and achieving strong luminescence emission.

[0245] Figure 20 The full fluorescence emission spectrum of the G2-CDs prepared in Example 32 and a photo of their fluorescence under UV illumination are shown. As can be seen from the figure, under different excitation conditions, the fluorescence emission peak is concentrated at 520 nm, showing no dependence on the excitation wavelength. The narrow half-width of the spectrum indicates good luminescence performance. The photo of the fluorescence under UV illumination also shows that the carbon quantum dots emit a bright sea-green fluorescence under UV illumination.

[0246] Figure 21 This is the fluorescence lifetime decay diagram of G2-CDs prepared in Example 32. From the figure, it can be seen that the fluorescence lifetime of G1-CDs under 496nm excitation is 4.44ns.

[0247] Figure 22 The fluorescence spectra of the carbon quantum dots prepared in Example 47 and Comparative Examples 7 and 8 (all tested under the same conditions: PMT 400V, slit width 10nm) and the luminescence photos under ultraviolet light irradiation are shown, wherein: Figure 22 A is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 7 and the luminescence photo under ultraviolet light irradiation, Figure 22 B is the fluorescence spectrum of the carbon quantum dots prepared in Comparative Example 8 and the luminescence photo under ultraviolet light irradiation, Figure 22 C is the fluorescence spectrum of the carbon quantum dots prepared in Example 47 and the luminescence photo under ultraviolet light. Figure 22 As can be seen from A, in the absence of o-phthalonitrile, that is, when the reactant is only o-phenylenediamine, the fluorescence intensity of the red fluorescent carbon quantum dots synthesized is 593 (au), and the luminescence photo under ultraviolet light can show that its fluorescence is relatively weak; Figure 22As can be seen from B, the fluorescence intensity of the blue fluorescent carbon quantum dots synthesized when the reactant is only phthalonitrile is 5429 (au), and its emission wavelength is 4210nm. From the luminescence photograph under ultraviolet light, it can be seen that it emits blue fluorescence; Figure 22 C can be seen that the fluorescence intensity of the red fluorescent carbon quantum dots synthesized by the joint action of o-phenylenediamine and o-phthalonitrile is significantly increased, with an intensity of 2963 (au), and the spectrum shows excitation independence, and from the luminescence photograph under ultraviolet light irradiation, it can be seen that its red fluorescence is very bright; According to Comparative Example 7, it can be seen that the fluorescence intensity and quantum yield of its red fluorescence are both low. After adding o-phthalonitrile, the red fluorescence intensity and quantum yield in Example 47 are significantly improved, which shows that o-phthalonitrile has a necessary effect on Example 47 of the present invention. After adding o-phthalonitrile, o-phenylenediamine and o-phthalonitrile are carbonized and polymerized under acidic conditions, and the carbon quantum dots have nitrogen, oxygen and sulfur-containing functional groups on the surface, which not only increases its sp 2 The conjugated structure was further enhanced by introducing a nitrogen source, thereby successfully preparing the red light carbon quantum dots of Example 47.

[0248] Figure 23 This is a comparison chart of the absolute quantum yields of red fluorescent carbon quantum dots prepared in Comparative Example 7 and Example 47 measured using FLS-1000, wherein: Figure 23 A is the absolute quantum yield of the red fluorescent carbon quantum dots prepared in Example 47, Figure 23 B is the absolute quantum yield of the red fluorescent carbon quantum dots prepared in Comparative Example 7. The quantum yield measurements show that the quantum yield measured in Comparative Example 7 is 3.91%, while the quantum yield measured in Example 47 is 15.78%. This indicates that phthalonitrile plays an indispensable role in improving red fluorescence intensity and quantum yield.

[0249] Figure 24 The transmission electron micrograph and particle size distribution diagram of the R-CDs prepared in Example 47 are used to characterize the morphology of the R-CDs. Figure 24 From the transmission electron microscopy image of A, it can be seen that the R-CDs are uniform and nearly spherical, with good dispersion and uniform particle size; Figure 24 From the particle size statistics of Figure B, it can be seen that the average particle size of the R-CDs is between 6.06±0.11nm.

[0250] Figure 25 The X-ray diffraction spectrum of the R-CDs prepared in Example 47 shows not only a typical broad peak around 21.98°, indicating amorphous carbon, but also numerous sharp, narrow peaks, more resembling the diffraction pattern of an ordered polymer structure. Therefore, XRD indicates that the R-CDs contain not only a certain degree of carbon core structure but also a significant amount of surface polymer structure.

[0251] Figure 26 This is the Fourier infrared spectrum of R-CDs prepared in Example 47. It can be seen from the figure that at 1455 cm -1 The stretching vibration of C=C appears at 3433cm -1 The strong NH stretching vibration peak at 1630 cm -1 The absorption peak at 1100 cm is caused by the stretching vibration of C=N / C=O. -1 The absorption peak corresponds to the stretching vibration of COC. In addition, the absorption peak at 619 cm -1 There is stretching vibration of SC.

[0252] Figure 27 Figure 47 shows the normalized UV-Vis absorption (UV-Vis), excitation (PLE), and emission (PL) spectra of the R-CDs prepared in Example 47. The optical properties of the R-CDs are shown in the figure. The two absorption peaks at 563 nm and 613 nm are due to the n→π* transition of the CNC and the complex state of the carbon dot surface. The maximum excitation wavelength of the R-CDs prepared in Example 47 is 607 nm, and the corresponding emission wavelength is 629 nm.

[0253] Figure 28 The full fluorescence emission spectrum of the R-CDs prepared in Example 47 and a photograph of their luminescence under UV illumination are provided to investigate their optical properties. As shown, when the excitation wavelength increases from 460 nm to 600 nm, the emission spectrum of the R-CDs exhibits distinct excitation-independent properties, with a maximum emission wavelength at 629 nm and a shoulder peak at 681 nm.

[0254] Figure 29 This is the fluorescence lifetime decay diagram of the R-CDs prepared in Example 47. From the figure, it can be seen that the fluorescence lifetime of R-CDs under 607nm excitation is 1.67ns.

[0255] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing colorful carbon quantum dots, characterized in that: The following steps are involved: Phthalonitrile and an organic molecule are dissolved in a solvent in a certain ratio to obtain a reaction precursor solution; the reaction precursor solution is placed in a stainless steel autoclave lined with polytetrafluoroethylene and reacted under heating conditions; after the reaction is completed, the solution is naturally cooled to room temperature; the pH of the product solution is then adjusted to 7 with a corresponding acid solution or alkaline solution; the solution is then concentrated under reduced pressure using a rotary evaporator or filtered and washed; and finally, the colorful carbon quantum dots are obtained by drying. The organic molecule is any one of organic acid, organic amine, and phenol; The organic acid is any one of citric acid, tartaric acid, malic acid, oxalic acid, ascorbic acid, and salicylic acid; The organic amine is any one of ethylenediamine, o-phenylenediamine, propylenediamine, butylenediamine, and diethylenetriamine; The phenols are any one of phenol, resorcinol, catechol, hydroquinone and phloroglucinol.

2. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The organic molecule is an organic acid, the organic acid is citric acid, and the mass ratio (g / g) of the phthalonitrile to the citric acid is (0.05-1):

1.

3. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The organic molecule is an organic amine, the organic amine is ethylenediamine, and the mass volume ratio (g / μL) of the phthalonitrile to ethylenediamine is 1:(50-1500).

4. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The organic molecules are phenols, the phenols are resorcinol, and the mass ratio (g / g) of the phthalonitrile to resorcinol is 5:(0.8-5).

5. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The organic molecule is an organic amine, the organic amine is o-phenylenediamine, and the molar ratio of o-phthalonitrile to o-phenylenediamine is 5:(7-10).

6. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The solvent is any one of water, sodium hydroxide solution and sulfuric acid.

7. The method for preparing colorful carbon quantum dots according to claim 1, wherein: The heating reaction conditions are: reaction temperature is 160° C. to 220° C., and reaction time is 6 h to 12 h.

8. A colorful carbon quantum dot prepared according to the preparation method according to any one of claims 1 to 7, characterized in that: The carbon quantum dots are blue light carbon quantum dots with an emission peak at a wavelength of 441 nm, or cyan light carbon quantum dots with an emission peak at a wavelength of 498 nm, or green light carbon quantum dots with an emission peak at a wavelength of 520 nm, or red light carbon quantum dots with an emission peak at a wavelength of 629 nm.

9. A use of the colorful carbon quantum dots prepared by the preparation method according to any one of claims 1 to 7 or the colorful carbon quantum dots according to claim 8, characterized in that: The colorful quantum dots can be applied to photocatalysis, biological imaging, analytical sensing and functional fluorescent materials with anti-counterfeiting properties.

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