Carbon dots capable of emitting white fluorescence in water and ethanol as well as preparation method and application of carbon dots

Abstract

The invention discloses a carbon dot capable of emitting white fluorescence in water and ethanol and a preparation method and application thereof.The preparation method comprises the steps that aniline serves as a carbon source and a nitrogen source, ethanol serves as a solvent, hydrogen peroxide serves as an oxidizing agent, and the carbon dot capable of emitting white fluorescence in water and ethanol is obtained through a hydrothermal reaction; wherein the volume ratio of aniline to hydrogen peroxide is 1: 1; the concentration of the hydrogen peroxide is 30wt%. The prepared carbon dots capable of emitting white fluorescence in water and ethanol have the capability of emitting white fluorescence under the irradiation of 365nm ultraviolet light; through a fluorescence spectrum and three-dimensional reconstruction of the fluorescence spectrum, the emission of the material is formed by compounding three different excitation wavelengths, and the excitation wavelengths can be regulated and controlled by changing a solvent so as to achieve different emission intensities, so that the color of a fluorescence solution is regulated and controlled, and finally, the purpose of adjusting the fluorescence color is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer material preparation, and in particular to a carbon dot capable of emitting white fluorescence in water and ethanol, and a preparation method and application thereof. Background Art

[0002] In recent years, carbon dots, as an emerging class of environmentally friendly carbon-based luminescent nanomaterials, have attracted widespread attention from the academic community due to their obvious advantages such as simple preparation, environmental protection, low cost, low toxicity, long-term storage, adjustable luminescence, high photoluminescence quantum yield, and excellent resistance to photobleaching. Based on the excellent tunable photoluminescence property, carbon dots have good application prospects in sensing, bioimaging, photodynamic therapy, optoelectronic devices, anti-counterfeiting, etc. However, its application in multicolor displays and white light-emitting diodes is still limited. This is because under ultraviolet light excitation, carbon dots usually have only a single blue luminescence color and lack longer-wavelength orange-red luminescence, and the luminescence is easily quenched in the solid state. Its emission peak is generally a broadband peak with a width greater than 200nm. The production method of white light devices is usually based on three primary colors (red, green, and blue) or two complementary colors (yellow and blue) to achieve composite white light. However, most of the white light emitting devices reported so far require complex doping schemes or the assistance of fluorescent organic dyes. This complexity is not conducive to large-scale application.

[0003] So far, most invention patents rely on multi-precursors or multi-element doping to achieve the preparation of white fluorescent materials. For example, the Chinese patent application document with publication number CN110885679A completes the preparation of white fluorescent carbon dots by mixing multiple solvents; and the Chinese patent application document with publication number CN117247776A achieves multiple excitations by introducing a series of elements such as lanthanum, manganese, tungsten, and thulium to obtain fluorescent powder compounded into white light. In addition, almost all reported white fluorescent materials do not have adjustable fluorescence properties. Therefore, it is very necessary to develop a single-precursor, easy-to-synthesize, high-yield, and adjustable optical property white fluorescent carbon dot material. Summary of the invention

[0004] The technical problem to be solved by the present invention is how to improve the fluorescence performance of carbon dots.

[0005] The present invention solves the above technical problems through the following technical means:

[0006] A method for preparing carbon dots capable of emitting white fluorescence in water and ethanol, wherein aniline is used as a carbon source and a nitrogen source, ethanol is used as a solvent, and hydrogen peroxide is used as an oxidant, and the carbon dots capable of emitting white fluorescence in water and ethanol are obtained through a hydrothermal reaction; wherein the volume ratio of the aniline to the hydrogen peroxide is 1:1; and the hydrogen peroxide is a hydrogen peroxide having a hydrogen peroxide concentration of 30 wt%.

[0007] Beneficial effects: In the present invention, aniline is used as a carbon source and a nitrogen source, ethanol is used as a solvent, and hydrogen peroxide is used as an oxidant to obtain carbon quantum dots, which are small in size, have good white fluorescence in both water and ethanol, and their fluorescence color is adjustable.

[0008] Preferably, the volume ratio of aniline to ethanol is ≤1:3.

[0009] Preferably, the aniline is AR with a purity of 99.5%.

[0010] Preferably, the temperature of the hydrothermal reaction is 180-220° C.; the time of the hydrothermal reaction is 18h-28h.

[0011] Preferably, the method further comprises dialyzing and drying the product after the hydrothermal reaction; the dialysis comprises water dialysis, ethanol dialysis or a combination of the two.

[0012] Preferably, dialysis is performed in 3000D-14000D dialysis bags.

[0013] Preferably, the method further comprises dispersing the dried carbon dots in a mixture of one or more of water, ethanol, chloroform and carbon tetrachloride.

[0014] Preferably, the method further comprises dispersing the dried carbon dots in water, ethanol or a mixture of both.

[0015] The present invention also provides a carbon dot capable of emitting white fluorescence in water and ethanol, which is prepared by using the method for preparing the carbon dot capable of emitting white fluorescence in water and ethanol.

[0016] The present invention also proposes an application of the carbon dots capable of emitting white fluorescence in water and ethanol as fluorescent dyes.

[0017] Preferably, the carbon dots exhibit different fluorescent colors when mixed with different solvents.

[0018] The invention also provides a fluorescent dye containing the carbon dots capable of emitting white fluorescence in water and ethanol.

[0019] The invention also provides a fluorescent device, which contains the carbon dots capable of emitting white fluorescence in water and ethanol.

[0020] The advantages of the present invention are:

[0021] (1) The present invention generates nitrogen-doped carbon dots in one step by reacting aniline with hydrogen peroxide via a hydrothermal reaction.

[0022] (2) Compared with other methods, the present invention uses low-cost raw materials, short synthesis time, simpler steps, and can quickly synthesize a large number of carbon quantum dots in a short time. It is green and environmentally friendly and has great prospects for application in large-scale industrial manufacturing in the future.

[0023] (3) The present invention prepares nitrogen-doped carbon dots, which have fluorescence responses in different solvents and are color-adjustable fluorescent dyes.

[0024] The carbon dots prepared by the present invention have the ability to emit white fluorescence under 365nm ultraviolet light. Through the fluorescence spectrum and the three-dimensional reconstruction of the fluorescence spectrum, it is shown that the emission of the material is a composite of three different excitation wavelengths, and the excitation wavelength can be adjusted by changing the solvent to achieve different emission intensities, thereby adjusting the solution color and finally achieving an adjustable fluorescence color. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Transmission microscopy characterization (left figure, inset is particle size statistical analysis) and high-resolution transmission microscopy characterization (right figure) of carbon dots in Example 1 of the present invention;

[0026] Figure 2 Atomic force microscopy characterization of carbon dots in Example 1 of the present invention;

[0027] Figure 3 This is the infrared characterization of the carbon dots in Example 1 of the present invention;

[0028] Figure 4 Raman characterization of carbon dots in Example 1 of the present invention;

[0029] Figure 5 is the X-ray photoelectron spectrum of the carbon dots in Example 1 of the present invention;

[0030] Figure 6 The C1s spectrum of the carbon dots X-ray photoelectron spectrum in Example 1 of the present invention;

[0031] Figure 7 The N1s spectrum of the carbon dots X-ray photoelectron spectrum in Example 1 of the present invention;

[0032] Figure 8 The UV-visible absorption and emission spectra of the carbon dots in water in Example 1 of the present invention are characterized, and the inset is an optical image of the carbon dots without (left side) / with 365 nm wavelength irradiation (right side);

[0033] Fig. 9 The fluorescence spectrum of the carbon dots in Example 1 of the present invention (the carbon dots concentration is 1 mg / ml) dissolved in water under the wide range of 340-540 nm;

[0034] Fig.10The three-dimensional reconstructed fluorescence spectrum and CIE chromaticity diagram of the carbon dots in Example 1 of the present invention (carbon dots concentration is 1 mg / ml) dissolved in water under excitation in a wide range of 300-620 nm;

[0035] Fig.11 The stability of the fluorescence intensity of the carbon dots in Example 1 of the present invention dissolved in water (the carbon dots concentration is 1 mg / ml) and irradiated with 365 nm fluorescence for one hour.

[0036] Fig.12 The fluorescence spectrum of carbon dots dissolved in carbon tetrachloride (carbon dots concentration is 1 mg / ml) in Example 1 of the present invention under wide range excitation of 320-560 nm and the optical image of carbon dots irradiated at a wavelength of 365 nm (inset);

[0037] Fig.13 The three-dimensional reconstructed fluorescence spectrum and CIE chromaticity diagram of the carbon dots dissolved in carbon tetrachloride (carbon dots concentration is 1 mg / ml) excited in a wide range of 280-560 nm in Example 1 of the present invention;

[0038] Fig.14 Optical images of carbon dots dispersion in ethanol (carbon dots concentration is 1 mg / ml) without (left side) / with 365 nm wavelength irradiation (right side) according to Example 1 of the present invention;

[0039] Fig.15 Optical images of carbon dots dispersion in chloroform (carbon dots concentration is 1 mg / ml) without (left side) / with 365 nm wavelength irradiation (right side) according to Example 1 of the present invention;

[0040] Fig.16 Optical images of carbon dots dispersion of Example 2 of the present invention and Comparative Example 1 carbon dots in water (carbon dots concentration is 1 mg / ml) without (left side) / with 365 nm wavelength irradiation (right side);

[0041] Fig.17 Optical images of carbon dots dispersion in water (carbon dots concentration is 0.5 mg / ml) without (left side) / with 365 nm wavelength irradiation (right side) of comparative example 2 of the present invention;

[0042] Fig.18 The fluorescence spectra of the carbon dots of Comparative Example 1 and Comparative Example 2 dissolved in water (the concentration of the carbon dots is 1 mg / ml) of the present invention are shown. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0044] Unless otherwise specified, the test materials and reagents used in the following examples can be obtained from commercial sources.

[0045] If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the art or according to the product instructions.

[0046] Example 1

[0047] A method for preparing carbon dots that can emit white fluorescence in water and ethanol comprises the following steps:

[0048] Step 1: Weigh 2 mL of aniline (AR 99.5%) solution, add 16 mL of anhydrous ethanol (AR 99.5%), add 2 mL of hydrogen peroxide solution (AR 30% wt) after ultrasonic treatment for 5 min, and ultrasonic treatment for another 5 min. The obtained mixed solution is placed in a 25 mL reactor and subjected to hydrothermal reaction at 200° C. in a vacuum drying oven for 24 h.

[0049] Step 2: After the reaction is completed, cool the reactor to room temperature, transfer the solution inside to a 14000D dialysis bag, and dialyze it in anhydrous ethanol.

[0050] Step 3: Every 24 hours, the ethanol solution outside the dialysis bag is collected and fresh anhydrous ethanol is added, which is repeated three times in total. The collected solution is vacuum dried to obtain the carbon dots that can emit white fluorescence in water and ethanol.

[0051] Example 2

[0052] A method for preparing carbon dots that can emit white fluorescence in water and ethanol comprises the following steps:

[0053] Step 1: Weigh 4 mL of aniline (AR 99.5%) solution, add 12 mL of anhydrous ethanol (AR 99.5%), add 4 mL of hydrogen peroxide solution (AR 30% wt) after ultrasonic treatment for 5 min, and ultrasonic treatment for another 5 min. The obtained mixed solution is placed in a 25 mL reactor and subjected to hydrothermal reaction at 180° C. in a vacuum drying oven for 28 h.

[0054] Step 2: After the reaction is completed, cool the reactor to room temperature, transfer the solution inside to a 3000D dialysis bag, and dialyze it in anhydrous ethanol.

[0055] Step 3: Every 24 hours, the ethanol solution outside the dialysis bag is collected and fresh anhydrous ethanol is added, which is repeated three times in total. The collected solution is vacuum dried to obtain the carbon dots that can emit white fluorescence in water and ethanol.

[0056] Example 3

[0057] A method for preparing carbon dots that can emit white fluorescence in water and ethanol comprises the following steps:

[0058] Step 1: Weigh 2 mL of aniline (AR 99.5%) solution, add 16 mL of anhydrous ethanol (AR 99.5%), add 2 mL of hydrogen peroxide solution (AR 30% wt) after ultrasonic treatment for 5 min, and ultrasonic treatment for another 5 min. The obtained mixed solution is placed in a 25 mL reactor and subjected to hydrothermal reaction at 220° C. in a vacuum drying oven for 18 h.

[0059] Step 2: After the reaction is completed, cool the reactor to room temperature, transfer the solution inside to a 3000D dialysis bag, and dialyze it in ultrapure water.

[0060] Step 3: The aqueous solution outside the dialysis bag is collected and added with new ultrapure water every 24 hours, and this process is repeated three times in total. The collected solution is vacuum dried to obtain the carbon dots that can emit white fluorescence in water and ethanol.

[0061] Comparative Example 1

[0062] A method for preparing carbon dots that can emit green fluorescence in water specifically comprises the following steps:

[0063] Step 1: Weigh 2 mL of aniline (AR 99.5%) solution, add 17 mL of anhydrous ethanol (AR 99.5%), add 1 mL of hydrogen peroxide solution (AR 30% wt) after ultrasonic treatment for 5 min, and ultrasonic treatment for another 5 min. The obtained mixed solution is placed in a 25 mL reactor and subjected to hydrothermal reaction at 220° C. in a vacuum drying oven for 18 h.

[0064] Step 2: After the reaction is completed, cool the reactor to room temperature, transfer the solution inside to a 3000D dialysis bag, and dialyze it in ultrapure water.

[0065] Step 3: Collect the aqueous solution outside the dialysis bag and add new ultrapure water every 24 hours. Repeat this process three times in total. Vacuum dry the collected solution to obtain the carbon dots that can emit green fluorescence in water.

[0066] Comparative Example 2

[0067] A method for preparing carbon dots capable of emitting blue fluorescence in water comprises the following steps:

[0068] Step 1: Weigh 18 mL of anhydrous ethanol (AR 99.5%) solution, add 2 mL of hydrogen peroxide solution (AR 30% wt), ultrasonicate for 5 min, put the obtained mixed solution into a 25 mL reactor, and hydrothermally react in a vacuum drying oven at 220° C. for 18 h.

[0069] Step 2: After the reaction is completed, cool the reactor to room temperature, transfer the solution inside to a 3000D dialysis bag, and dialyze it in ultrapure water.

[0070] Step 3: Collect the aqueous solution outside the dialysis bag and add new ultrapure water every 24 hours. Repeat this process three times in total. Vacuum dry the collected solution to obtain the carbon dots that can emit blue fluorescence in water.

[0071] First, the carbon dots collected in Example 1 were characterized by morphology. Figure 1 As shown in the left figure, the particle size of the sample is relatively uniform through transmission electron microscopy. After statistical Gaussian fitting distribution analysis, the main size of the carbon dot sample is about 12-14nm ( Figure 1 Illustration). Figure 1 As shown in the right figure, through high-resolution imaging, lattice fringes representing the carbon (020) crystal plane can be observed.

[0072] like Figure 2 As shown, the thickness of the carbon dots in Example 1 was determined to be 6-7 nm by atomic force microscopy, and combined with the data obtained by transmission electron microscopy, it was shown that the shape of the prepared carbon dots was quasi-pie-shaped.

[0073] The carbon dots of Example 1 were tested by infrared using a Fourier transform infrared spectrometer to obtain an infrared spectrum of Example 1. The absorption peak positions of different wavelengths in the spectrum represent the different functional group bond positions. Figure 3 As shown, the material mainly has expansion or stretching vibrations of chemical bonds such as carbon-oxygen bonds, carbon-hydrogen bonds, carbon-nitrogen bonds, and nitrogen-hydrogen bonds.

[0074] Figure 4 The Raman spectrum in Figure 1 shows the intensity ratio of the G peak to the D peak, which is 1.053, indicating that the material contains a large number of sp2 carbon vacancy defects.

[0075] Figure 5 The X-ray photoelectron spectrum of the carbon dots of Example 1 was obtained by testing, and it was found that the carbon content in the carbon dots was 85.1%, the oxygen content was 6.0%, and the nitrogen content was 8.9%.

[0076] Figure 6 , 7 The C1s and N1s peaks of the X-ray photoelectron spectrum of the carbon dots in Example 1 were separated, and the corresponding bond positions were marked in the picture.

[0077] The carbon dots of Example 1 are dispersed in water to obtain a water dispersion of carbon dots. Figure 8 This is the superposition of the ultraviolet absorption spectrum, excitation spectrum and fluorescence spectrum of the carbon dot water dispersion in Example 1. The absorption peak at 230nm in the ultraviolet absorption spectrum is attributed to π-π * The broad absorption bands at 281nm and 430nm are attributed to the pyrrolic nitrogen doping in the cycloolefin molecule. At the same time, the hexagonal carbon ring on the periphery also has a graphitic nitrogen doping. This meta-nitrogen doping leads to the red shift of the emission peak of the core cycloolefin structure. Therefore, the photoluminescence (PL) spectrum shows emission (400nm, 480nm and 640nm) under excitation (340nm, 400nm and 540nm), respectively. When the aqueous dispersion of carbon dots (carbon dots concentration is 1mg / ml) is exposed to ultraviolet light with a wavelength of 365nm, white fluorescence ( Figure 8 As shown in the upper left inset, the left side of the inset is the sample under daylight conditions).

[0078] The photoluminescence properties of the carbon quantum dots in Example 1 were studied at different excitation wavelengths. Fig. 9 As shown in the figure, when the excitation wavelength increases from 340nm to 400nm, the emission peak intensity around 400nm gradually decreases, and a new emission peak will emerge around 500nm. At the same time, as the excitation wavelength continues to increase, this phenomenon will reappear. When the excitation wavelength increases from 400nm to 540nm, the emission peak intensity around 500nm gradually decreases, and a new emission peak will emerge around 640nm.

[0079] like Fig.10 As shown, by reconstructing the three-dimensional fluorescence spectrum of Example 1 for intuitive explanation, it can be clearly observed from the figure that the carbon dots have three independent emission peaks. Combined with the CIE chromaticity diagram ( Fig.10 ) for color positioning, the three emission peaks represent blue light emission, green light emission, and red light emission from left to right, which are consistent with the three primary colors. For further explanation, under full-wavelength excitation, photometric composite positioning is performed in the CIE chromaticity diagram, and it is found that the composite light position emitted by Example 1 is (0.332, 0.281), and the color is white.

[0080] Fig.11 This indicates that the carbon dots still have good fluorescence stability within 60 minutes under 365nm light irradiation.

[0081] The carbon dots of Example 1 were dispersed in carbon tetrachloride. Fig.12The fluorescence spectrum of the carbon dots in Example 1 in carbon tetrachloride solvent is shown in Figure 2. It can be observed that compared with the three emission peaks of the carbon dots in water at 400nm, 480nm, and 640nm, the carbon dots in carbon tetrachloride solution only have emission peaks at 390nm and 650nm. The reason for this peak shift effect is that in solvents of different polarities, carbon dots aggregate. When the spacing is close to When the distance (R0) is smaller than 0.1, the aggregation and absorption overlap of the material will produce energy transfer of short-wavelength emission (340-500nm), which will be weakened, while the long wavelength will be relatively enhanced.

[0082] like Fig.13 As shown, by reconstructing the three-dimensional fluorescence spectrum of Example 1 for intuitive explanation, it can be clearly observed from the figure that in carbon tetrachloride solution, the carbon dots have two independent emission peaks. Combined with the CIE chromaticity diagram ( Fig.13 ) for color positioning, the two emission peaks represent blue light emission and red light emission from left to right, so that the final composite color is orange-red (such as Fig.12 illustration).

[0083] The carbon dots of Example 1 were dispersed in ethanol to obtain an ethanol dispersion of carbon dots. Fig.14 They are respectively the optical images of the carbon dots in Example 1 dispersed in ethanol under sunlight and dispersed under 365 nm ultraviolet light. From the photos under ultraviolet light, it can be observed that the carbon dots in Example 1 are white fluorescent.

[0084] The carbon dots of Example 1 were dispersed in chloroform to obtain a chloroform dispersion of carbon dots. Fig.15 They are respectively the optical images of the chloroform dispersion of the carbon dots in Example 1 dispersed under sunlight and the optical images of the dispersion under 365nm ultraviolet light. From the photos under ultraviolet light, it can be observed that the carbon dots in Example 1 are yellow fluorescent.

[0085] Fig.16 The optical images of the dispersion of the carbon dots in water under sunlight and under 365 nm ultraviolet light are shown respectively for Example 2 and Comparative Example 1. From the photo under ultraviolet light, it can be observed that the carbon dots in Example 2 still have white fluorescence, while the carbon dots in Comparative Example 1 have green fluorescence.

[0086] Fig.17 They are respectively the optical images of the dispersion of carbon dots in water under sunlight and the optical images of the dispersion under 365nm ultraviolet light of comparative example 2. From the photos under ultraviolet light, it can be observed that the carbon dots in comparative example 2 are blue fluorescent.

[0087] Fig.18The fluorescence spectra of the carbon dots of comparative example 2 and comparative example 1 are shown. By comparison, it is found that the absorption peaks at 280nm and 460nm of comparative example 1 are attenuated, which affects the emission intensity of the green and red fluorescence of comparative example 1, thereby changing the fluorescence color.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon dots that can emit white fluorescence in water and ethanol, characterized in that: Aniline is used as a carbon source and a nitrogen source, ethanol is used as a solvent, and hydrogen peroxide is used as an oxidant to obtain the carbon dots capable of emitting white fluorescence in water and ethanol through a hydrothermal reaction; wherein the volume ratio of the aniline to the hydrogen peroxide is 1:1; and the hydrogen peroxide has a hydrogen peroxide concentration of 30 wt%.

2. The method for preparing carbon dots capable of emitting white fluorescence in water and ethanol according to claim 1, characterized in that: The volume ratio of aniline to ethanol is ≤1:

3.

3. The method for preparing carbon dots capable of emitting white fluorescence in water and ethanol according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 180-220° C.; the time of the hydrothermal reaction is 18h-28h.

4. The method for preparing carbon dots capable of emitting white fluorescence in water and ethanol according to claim 1, characterized in that: The method also includes dialyzing and drying the product after the hydrothermal reaction; the dialysis includes one or a combination of water dialysis and ethanol dialysis.

5. The method for preparing carbon dots capable of emitting white fluorescence in water and ethanol according to claim 4, characterized in that: Dialysis was performed in 3000D-14000D dialysis bags.

6. The method for preparing carbon dots capable of emitting white fluorescence in water and ethanol according to claim 4 or 5, characterized in that: The method also includes dispersing the dried carbon dots in a mixture of one or more of water, ethanol, chloroform, and carbon tetrachloride.

7. A carbon dot that can emit white fluorescence in water and ethanol, characterized in that: The carbon dots are prepared by the method for preparing carbon dots capable of emitting white fluorescence in water and ethanol as described in any one of claims 1 to 6.

8. Use of the carbon dots capable of emitting white fluorescence in water and ethanol as claimed in claim 7 as fluorescent dyes.

9. A fluorescent dye, characterized in that: Contains the carbon dots capable of emitting white fluorescence in water and ethanol as claimed in claim 7.

10. A fluorescent device, characterized in that: Contains the carbon dots capable of emitting white fluorescence in water and ethanol as claimed in claim 7.

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