Ultra-narrowband deep red fluorescent carbon dots and preparation method thereof

Abstract

The present invention discloses an ultra-narrowband deep red fluorescent carbon dot and a preparation method thereof, belonging to the technical field of carbon dot preparation. The preparation method comprises the following steps: (1) drying a biomass raw material and then grinding it for the first time, dissolving it in water and performing ultrasound, then performing microwave treatment, and finally separating to obtain a solid product; (2) grinding the solid product obtained in step (1) for the second time, then dissolving it in an organic solvent and performing ultrasound and centrifugation, finally taking the supernatant, and drying to obtain the product. The present invention adopts a microwave method to synthesize carbon dots, and the steps are simple and easy to operate; the raw material is a biomass raw material, and the entire preparation process is energy-saving and environmentally friendly; the obtained deep red carbon dots have a luminescence peak at 678nm, a half-peak width of only 20nm, good monochromaticity, high color purity, and high fluorescence intensity, and have good application prospects in the fields of colorful display and biological imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dot preparation, and in particular to an ultra-narrow-band deep red fluorescent carbon dot and a preparation method thereof. Background Art

[0002] Carbon dots are fluorescent carbon nanoparticles with a particle size usually less than 10 nm. They have excellent luminescence properties, good water solubility, low toxicity and biocompatibility, and show great application prospects in biological imaging, environmental monitoring, drug delivery, light-emitting devices, etc.

[0003] Red fluorescent carbon dots, especially ultra-narrowband deep red fluorescent carbon dots (luminescence wavelength > 660nm, half-peak width < 30nm), have the advantages of abundant raw materials, low cost, and low toxicity compared to traditional luminescent materials (organic fluorescent dyes, heavy metal-based quantum dots, and perovskite quantum dots). They have broad application prospects in full-color display and solid-state lighting. Therefore, the preparation of red fluorescent carbon dots has attracted widespread attention. However, the red fluorescent carbon dots reported so far have the following problems: (1) the emission wavelength rarely reaches the deep red region, the emission peak depends on the excitation wavelength, the emission peak is relatively broad, and the color purity is poor; (2) the preparation method is complicated and requires a complex purification process. The raw materials are chemical reagents, which does not conform to the concept of green environmental protection. The existence of these problems has greatly limited the application of red fluorescent carbon dots. Therefore, it is extremely important to invent a simple and easy-to-operate method to prepare deep red fluorescent carbon dots with high color purity. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide an ultra-narrowband deep red fluorescent carbon dot and a preparation method thereof, so as to solve the problems of the existing red carbon dots, such as the luminescence wavelength cannot reach the deep red region, the luminescence peak is relatively wide, the color purity is poor, the preparation method is complicated, and it is not green and environmentally friendly.

[0005] The technical solution of the present invention to solve the above technical problems is as follows:

[0006] A method for preparing ultra-narrow-band deep red fluorescent carbon dots comprises the following steps:

[0007] (1) The biomass raw material is first dried and then ground for the first time, then dissolved in water and subjected to ultrasonic treatment, followed by microwave treatment, and finally separated to obtain a solid product;

[0008] (2) The solid product obtained in step (1) is first ground for a second time, then dissolved in an organic solvent, ultrasonicated, and centrifuged, and finally the supernatant is collected and dried to obtain the product.

[0009] The beneficial effects of the present invention are as follows: the present invention provides a method for preparing ultra-narrow-band deep red fluorescent carbon dots, which are prepared using biomass raw materials. The preparation method is simple and does not require a complicated purification process. The prepared carbon dots have good monochromaticity, narrow half-peak width, high color purity, and high fluorescence intensity.

[0010] Furthermore, the biomass raw material in step (1) includes any one of green tea leaves, coriander, mint, lettuce, amaranth, wood ear vegetable, spinach and bayberry leaves.

[0011] The beneficial effect of adopting the above further technical solution is that the raw materials used in the present invention are green biomass raw materials, without chemical drugs, and conform to the concept of green environmental protection.

[0012] Furthermore, the drying temperature in step (1) is 40-80° C., and the drying is performed until the powder is easy to grind.

[0013] Furthermore, the mass volume ratio of the product after the first grinding in step (1) to water is 1-5 g:20 mL.

[0014] Furthermore, in step (1), the ultrasonic treatment time is 5-20 min; the microwave treatment power is 600-1000 W, and the time is 10-20 min.

[0015] Furthermore, in step (2), the mass volume ratio of the product after the second grinding to the organic solvent is 1-5 g:20 mL, and the organic solvent is anhydrous ethanol.

[0016] Furthermore, in step (2), the ultrasonic time is 5-20 min, the centrifugal speed is 8000-10000 rpm, and the time is 5-20 min.

[0017] Furthermore, the drying method in step (2) is freeze-drying.

[0018] An ultra-narrow-band deep red fluorescent carbon dot is prepared by the above preparation method.

[0019] The ultra-narrowband deep red fluorescent carbon dots are used in the preparation of colorful display devices and as biological imaging materials.

[0020] The present invention has the following beneficial effects:

[0021] (1) The present invention adopts microwave method to synthesize carbon dots, which has simple steps and is easy to operate; the raw materials are biomass raw materials and do not contain chemical drugs, and the entire preparation process is energy-saving and environmentally friendly.

[0022] (2) The deep red carbon dots prepared by the present invention have a luminescence peak at 678 nm, a half-peak width of only 20 nm, good monochromaticity, high color purity, and high fluorescence intensity, and have good application prospects in the fields of colorful display and biological imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a transmission electron micrograph of the deep red fluorescent carbon dots prepared in Example 1;

[0024] Figure 2 Figure 1 is a surface structure characterization of the deep red fluorescent carbon dots prepared in Example 1, where (a) is a Fourier transform infrared absorption spectrum, (b) is a full X-ray photoelectron spectrum, and (c) and (d) are high-resolution spectra of C1s and O1s, respectively.

[0025] Figure 3 The fluorescence emission spectrum of the deep red fluorescent carbon dots prepared in Example 1 changes with the excitation wavelength and photographs under white light and ultraviolet light;

[0026] Figure 4 The color coordinates of the deep red fluorescent carbon dots prepared in Example 1 under 400 nm light excitation;

[0027] Figure 5 This is a photograph of the deep red fluorescent carbon dots prepared in Example 2-3 under 365nm ultraviolet light;

[0028] Figure 6 This is a photograph of the deep red fluorescent carbon dots prepared in Example 4-7 under 365nm ultraviolet light;

[0029] Figure 7 This is the fluorescence emission spectrum of the red fluorescent carbon dots prepared in Comparative Example 1. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0031] Example 1:

[0032] A method for preparing ultra-narrow-band deep red fluorescent carbon dots comprises the following steps:

[0033] (1) placing Qishe green tea leaves in a crucible, drying them in an electric constant temperature drying oven at 80°C for 3 hours, then taking them out and grinding them into powder using an agate mortar to obtain tea powder;

[0034] (2) First, 2 g of the tea powder obtained in step (1) was dissolved in 20 mL of distilled water, ultrasonically treated for 12 min, then poured into a 100 mL conical flask and heated in a household microwave oven at 800 W for 10 min; finally, the solid was removed and separated, and further ground in an agate mortar to a fine powder;

[0035] (3) The powder obtained after grinding in step (2) was first dissolved in 20 mL of ethanol, ultrasonicated for 10 min, and then centrifuged at 9000 rpm for 10 min. The supernatant was collected as a deep red fluorescent carbon dot solution, and finally freeze-dried to obtain a deep red fluorescent carbon dot solid powder.

[0036] Example 2-3:

[0037] A method for preparing ultra-narrow-band deep red fluorescent carbon dots comprises the following steps:

[0038] The preparation method is the same as that of Example 1, except that the Qishe green tea leaves in step (1) are replaced by Huanong green tea leaves and Fenggang green tea leaves, respectively, and the other steps remain unchanged.

[0039] Example 4-7:

[0040] A method for preparing ultra-narrow-band deep red fluorescent carbon dots comprises the following steps:

[0041] The preparation method is the same as that of Example 1, except that the Qishe green tea leaves in step (1) are replaced by coriander, mint, lettuce and amaranth, respectively, and the other steps remain unchanged.

[0042] Comparative Example 1:

[0043] A method for preparing red fluorescent carbon dots comprises the following steps:

[0044] (1) 10 g of fresh tea leaves were chopped and placed in a mortar. 10 mL of water and 10 mL of ethanol were added and ground thoroughly. The ground mixture was centrifuged at 9000 rpm for 10 min to remove the precipitate and debris.

[0045] (2) placing the supernatant obtained after centrifugation in step (2) in a polytetrafluoroethylene-lined autoclave, heating it at 150° C. for 6 h, and then cooling it to room temperature in the oven;

[0046] (3) The final product of step (3) was centrifuged at 9000 rpm for 10 min, and the centrifuged solution was then dialyzed in a dialysis bag with a molecular weight cutoff of 3000 Da for 3 days to obtain a red fluorescent carbon dot solution, which was then freeze-dried to obtain a red fluorescent carbon dot solid powder.

[0047] Test example:

[0048] The ultra-narrow-band deep red fluorescent carbon dots prepared in Example 1 were subjected to morphological characterization, Fourier transform infrared spectroscopy, X-ray photoelectron spectrum, fluorescence emission spectrum and color coordinate measurement under 400 nm light excitation. The ultra-narrow-band deep red fluorescent carbon dots prepared in Examples 1-7 were observed under 365 nm ultraviolet light, and the red fluorescent carbon dots prepared in Comparative Example 1 were subjected to fluorescence emission spectrum measurement.

[0049] The experimental results are as follows Figure 1-Figure 7 shown.

[0050] Depend on Figure 1 The ultra-narrowband deep red fluorescent carbon dots obtained in Example 1 are quasi-spherical nanoparticles with a maximum particle size of 2 nm and are well-dispersed. High-resolution transmission electron microscopy measurements show a lattice spacing of 0.21 nm, corresponding to the (100) interplanar spacing of hexagonal graphite.

[0051] Depend on Figure 2 From the FTIR and XPS results in , it can be seen that a large number of oxygen-containing functional groups such as -OH and -COOH exist on the surface of the ultra-narrow-band deep red fluorescent carbon dots prepared in Example 1.

[0052] Depend on Figure 3 It can be seen that the fluorescence of the ultra-narrowband deep red fluorescent carbon dots prepared in Example 1 does not shift with the change of the excitation wavelength, and the optimal emission peak is located at 678nm; when excited by 400nm light, the half-maximum width of the emission spectrum is about 20nm, and the absolute fluorescence quantum yield is 68.4%. Figure 3 It can also be seen that under 365nm ultraviolet light, the carbon dot solution shows bright red.

[0053] Depend on Figure 4 It can be seen that the CIE coordinates of the ultra-narrow-band deep red fluorescent carbon dot solution prepared in Example 1 under 400 nm light excitation are (0.730, 0.270), indicating that the light emitted by the carbon dots is pure deep red and has good application prospects in colorful displays.

[0054] Depend on Figure 5-Figure 6 It can be seen that the ultra-narrow-band deep red fluorescent carbon dot solutions prepared in Examples 2-7 all emit bright red at 365 nm, similar to Example 1.

[0055] Depend on Figure 7 It can be seen that the fluorescence of the red fluorescent carbon dots prepared in Comparative Example 1 does not shift with the change of laser wavelength, and the optimal emission peak is located at 721 nm. However, when excited by 400 nm light, the half-peak width of the emission spectrum is 62 nm, which is three times wider than that of the ultra-narrow-band deep red fluorescent carbon dots prepared in Example 1 of the present invention. Figure 3 It can be seen that the fluorescence intensity of the ultra-narrow-band deep red fluorescent carbon dots prepared in Example 1 of the present invention is more than 100 times that of the red fluorescent carbon dots prepared in Comparative Example 1.

[0056] 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 ultra-narrow-band deep red fluorescent carbon dots, characterized in that: The following steps are involved: (1) The biomass raw material is first dried and then ground for the first time, then dissolved in water and ultrasonicated, then microwaved, and finally separated to obtain a solid product; (2) The solid product obtained in step (1) is first ground for a second time, then dissolved in an organic solvent, ultrasonicated, and centrifuged, and finally the supernatant is collected and dried to obtain; Wherein, the biomass raw material in step (1) includes any one of green tea leaves, coriander, mint, lettuce and amaranth; the mass volume ratio of the product after the first grinding to water is 1-5 g:20 mL; the ultrasonic time is 5-20 min; the microwave treatment power is 600-1000 W, and the time is 10-20 min; In the step (2), the mass volume ratio of the product after the second grinding to the organic solvent is 1-5 g: 20 mL, and the organic solvent is ethanol; the ultrasonic time is 5-20 min, and the centrifugal speed is 8000-10000 rpm, and the time is 5-20 min.

2. The method for preparing ultra-narrow-band deep red fluorescent carbon dots according to claim 1, wherein: The drying temperature in step (1) is 40-80°C.

3. The method for preparing ultra-narrow-band deep red fluorescent carbon dots according to claim 1, wherein: The drying method in step (2) is freeze drying.

4. An ultra-narrow-band deep red fluorescent carbon dot, characterized in that: The method is prepared according to any one of claims 1 to 3.

5. Use of the ultra-narrowband deep red fluorescent carbon dots according to claim 4 in the preparation of multi-color display devices and as bioimaging materials.

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