Carbon dots capable of emitting white fluorescence in water and ethanol, and preparation method and application thereof

Abstract

The present invention discloses carbon dots capable of emitting white fluorescence in water and ethanol, as well as a preparation method and application thereof. The preparation method utilizes aniline as a carbon and nitrogen source, ethanol as a solvent, and hydrogen peroxide as an oxidant to produce the carbon dots capable of emitting white fluorescence in water and ethanol through a hydrothermal reaction. The volume ratio of aniline to hydrogen peroxide is 1:1, and the hydrogen peroxide has a hydrogen peroxide concentration of 30 wt%. The carbon dots capable of emitting white fluorescence in water and ethanol prepared by the present invention emit white fluorescence under 365 nm ultraviolet light. Fluorescence spectra and three-dimensional reconstruction of the fluorescence spectra demonstrate that the emission of the material is a composite of three different excitation wavelengths. The excitation wavelength can be controlled by varying the solvent to achieve different emission intensities, thereby controlling the color of the fluorescent solution and ultimately achieving adjustable fluorescence color.

Description

Technical Field

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

[0002] In recent years, carbon dots (Cdots), an emerging class of environmentally friendly, carbon-based luminescent nanomaterials, have attracted widespread attention due to their significant advantages, including facile preparation, environmental friendliness, low cost, low toxicity, long-term storage, tunable luminescence, high photoluminescence quantum yield, and excellent resistance to photobleaching. Due to their excellent tunable photoluminescence, Cdots hold great promise for applications in sensing, bioimaging, photodynamic therapy, optoelectronic devices, and anti-counterfeiting. However, their application in multicolor displays and white light-emitting diodes remains limited. This is because, under UV excitation, Cdots typically emit only a single blue color, lacking longer-wavelength orange-red luminescence, and are susceptible to quenching in the solid state. Their emission peak is typically broadband, exceeding 200 nm in width. White light devices are typically produced using the three primary colors (red, green, and blue) or two complementary colors (yellow and blue) to achieve composite white light. However, most reported white-light emitting devices require complex doping schemes or the assistance of fluorescent organic dyes. This complexity hinders large-scale application.

[0003] To date, most invention patents rely on multiple precursors or multi-element doping to achieve the preparation of white fluorescent materials. For example, Chinese patent application publication number CN110885679A prepares white fluorescent carbon dots by mixing multiple solvents; while Chinese patent application publication number CN117247776A introduces a series of elements such as lanthanum, manganese, tungsten, and thulium to achieve multiple excitations to obtain a composite white-light fluorescent powder. Furthermore, almost all reported white fluorescent materials lack tunable fluorescence properties. Therefore, it is highly desirable to develop a single-precursor, easily synthesized, high-yield, and tunable 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 comprises using aniline as a carbon source and a nitrogen source, ethanol as a solvent, and hydrogen peroxide as an oxidant to obtain the carbon dots capable of emitting white fluorescence in water and ethanol through a hydrothermal reaction. 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%.

[0007] Beneficial effects: In the present invention, aniline is used as the carbon source and nitrogen source, ethanol is used as the solvent, and hydrogen peroxide is used as the oxidant to obtain carbon quantum dots. The carbon quantum dots 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 18 h to 28 h.

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

[0019] The present invention also provides a fluorescent device containing 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 through 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 industrial large-scale 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 fluorescence spectrum and three-dimensional reconstruction of fluorescence spectrum, it is shown that the emission of this material is a composite of three different excitation wavelengths. The excitation wavelength can be controlled by changing the solvent to achieve different emission intensities, thereby controlling the color of the solution and ultimately achieving an adjustable fluorescence color. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0029] Figure 5 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. The inset is an optical image of the carbon dots without (left) and irradiated at a wavelength of 365 nm (right).

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

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

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

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

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

[0038] Figure 14 Optical images of carbon dots in ethanol (carbon dot concentration of 1 mg / ml) without (left) and irradiated at 365 nm wavelength (right) according to Example 1 of the present invention;

[0039] Figure 15 Optical images of carbon dots in chloroform (carbon dot concentration of 1 mg / ml) without (left) and irradiated at 365 nm wavelength (right) according to Example 1 of the present invention;

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

[0041] Figure 17 Optical images of carbon dots in water (carbon dot concentration of 0.5 mg / ml) without (left) and irradiated at 365 nm (right) wavelength for comparative example 2 of the present invention;

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

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments 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 shall fall 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 field 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%), sonicate for 5 minutes, then add 2 mL of hydrogen peroxide solution (AR 30% wt), sonicate for another 5 minutes. The resulting mixed solution is placed in a 25 mL reactor and hydrothermally reacted in a vacuum drying oven at 200°C for 24 hours.

[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: The ethanol solution outside the dialysis bag was collected and fresh anhydrous ethanol was added every 24 hours, and this process was repeated three times. The collected solution was 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%), sonicate for 5 minutes, then add 4 mL of hydrogen peroxide solution (AR 30% wt), sonicate for another 5 minutes. The resulting mixed solution is placed in a 25 mL reactor and hydrothermally reacted in a vacuum drying oven at 180°C for 28 hours.

[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: The ethanol solution outside the dialysis bag was collected and fresh anhydrous ethanol was added every 24 hours, and this process was repeated three times. The collected solution was 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%), sonicate for 5 minutes, then add 2 mL of hydrogen peroxide solution (AR 30% wt), sonicate for another 5 minutes. The resulting mixed solution is placed in a 25 mL reactor and hydrothermally reacted in a vacuum drying oven at 220°C for 18 hours.

[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 was collected and added with new ultrapure water every 24 hours, and repeated three times in total. The collected solution was 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 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%), sonicate for 5 minutes, then add 1 mL of hydrogen peroxide solution (AR 30% wt), sonicate for another 5 minutes. The resulting mixed solution is placed in a 25 mL reactor and hydrothermally reacted in a vacuum drying oven at 220°C for 18 hours.

[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: Every 24 hours, the aqueous solution outside the dialysis bag was collected and fresh ultrapure water was added. This process was repeated three times. The collected solution was vacuum dried to obtain the carbon dots that 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), and sonicate for 5 min. The resulting mixed solution is placed in a 25 mL reactor and hydrothermally reacted 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: Every 24 hours, collect the aqueous solution outside the dialysis bag and add new ultrapure water. Repeat this process three times. The collected solution is vacuum-dried to obtain the carbon dots that emit blue fluorescence in water.

[0071] First, the morphology of the carbon dots collected in Example 1 was characterized. Figure 1 As shown in the left figure, the particle size of the sample is relatively uniform as observed by 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. 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 spectroscopy 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 2 shows that the intensity ratio of the G peak to the D peak 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 figure.

[0077] The carbon dots of Example 1 were dispersed in water to obtain a carbon dot aqueous dispersion. 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 cycloalkenyl molecule. At the same time, the peripheral hexagonal carbon ring is doped with a graphitic nitrogen. This meta-nitrogen doping leads to the red shift of the emission peak of the core cycloalkenyl 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 dot 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 sample on the left side of the inset is under daylight conditions).

[0078] The photoluminescence properties of the carbon quantum dots in Example 1 were studied at different excitation wavelengths. Figure 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 emerges around 500nm. At the same time, as the excitation wavelength continues to increase, this phenomenon reappears. When the excitation wavelength increases from 400nm to 540nm, the emission peak intensity around 500nm gradually decreases, and a new emission peak emerges around 640nm.

[0079] like Figure 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, and combined with the CIE chromaticity diagram ( Figure 10 ) for color positioning. The three emission peaks, from left to right, represent blue, green, and red light emission, respectively, consistent with the three primary colors. For further illustration, under full-wavelength excitation, photometric composite positioning was performed on the CIE chromaticity diagram. It was found that the composite light emitted by Example 1 was located at (0.332, 0.281), and the color was white.

[0080] Figure 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. Figure 12The fluorescence spectrum of the carbon dots in Example 1 in carbon tetrachloride solvent is shown in Figure 2. It can be observed that, while the carbon dots have three emission peaks at 400nm, 480nm, and 640nm in water, they only have emission peaks at 390nm and 650nm in carbon tetrachloride solution. This peak shift effect is caused by the fact that in solvents of different polarities, carbon dots aggregate. When the spacing is close to When the distance (R0) is less than 0.05, the aggregation and absorption overlap of the material will produce energy transfer of short-wavelength emission (340-500nm), thereby weakening it, while the long wavelength is relatively enhanced.

[0082] like Figure 13 As shown, the three-dimensional fluorescence spectrum of Example 1 is reconstructed 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 ( Figure 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 Figure 12 illustration).

[0083] The carbon dots of Example 1 were dispersed in ethanol to obtain an ethanol dispersion of carbon dots. Figure 14 The optical images of the carbon dots in Example 1 dispersed in ethanol under sunlight and under 365 nm ultraviolet light are shown. The carbon dots in Example 1 fluoresce white as can be observed in the UV-light images.

[0084] The carbon dots of Example 1 were dispersed in chloroform to obtain a chloroform dispersion of carbon dots. Figure 15 The optical images are respectively the dispersion of the carbon dots in chloroform under sunlight and the dispersion under 365nm UV light of Example 1. The UV light photo shows that the carbon dots in Example 1 emit yellow fluorescence.

[0085] Figure 16 The following are optical images of the carbon dots in aqueous dispersions of Example 2 and Comparative Example 1, respectively, dispersed under sunlight and under a 365nm UV lamp. The UV-light images show that the carbon dots in Example 2 still fluoresce white, while those in Comparative Example 1 fluoresce green.

[0086] Figure 17 The optical images of the carbon dots in comparative example 2, dispersed under sunlight and under 365 nm ultraviolet light, respectively. The carbon dots in comparative example 2 exhibit blue fluorescence under ultraviolet light.

[0087] Figure 18The fluorescence spectra of the carbon dots of Comparative Example 2 and Comparative Example 1 are shown. Comparison shows 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 they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. 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 various embodiments of the present invention.

Claims

1. A method for preparing carbon dots that emit white fluorescence in water and ethanol, characterized by: The method uses aniline as a carbon source and a nitrogen source, ethanol as a solvent, and hydrogen peroxide as an oxidant to obtain carbon dots capable of emitting white fluorescence in water and ethanol through a hydrothermal reaction. 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, wherein: 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, wherein: 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, wherein: The method further 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, wherein: 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, wherein: The method further 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 emits white fluorescence in water and ethanol, characterized by: 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.

Images