One-pot synthesis of multicolor fluorescent carbon dots using fangfeng as carbon source

Abstract

This invention belongs to the field of luminescent carbon nanomaterials and provides a one-pot method for synthesizing multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as the carbon source. The method uses *Saposhnikovia divaricata* as the carbon source, p-phenylenediamine as the nitrogen source, and ethanol and hydrochloric acid as solvents for the synthesis reaction, making it convenient to operate. The resulting multicolor fluorescent carbon dots exhibit extremely high stability and are not excitation-dependent, with emission spectra covering the entire visible light region. Complete separation of different fluorescent colors can be achieved using only column chromatography.

Description

Technical Field

[0001] This invention belongs to the field of luminescent carbon nanomaterials, specifically relating to a method for one-pot synthesis of multicolor fluorescent carbon dots using Saposhnikovia divaricata as a carbon source. Background Technology

[0002] In the field of materials science today, carbon dots (CDs), as a novel type of nanomaterial, have attracted widespread attention and in-depth research due to their unique optical properties, good biocompatibility, and low toxicity. However, traditional methods for synthesizing carbon dots often suffer from problems such as cumbersome procedures, high costs, and the use of toxic and harmful chemical reagents, which to some extent limit their large-scale application and development.

[0003] With the increasing pursuit of sustainable development and green chemistry, the use of biomass as a carbon source to synthesize carbon dots has gradually become a research hotspot. Biomass resources are abundant, renewable, and environmentally friendly, making them an ideal alternative carbon source. However, existing biomass-based technologies for synthesizing carbon dots (CDs) have several limitations, such as difficulty in achieving full-color control, complex synthesis processes, unstable product performance, low fluorescence intensity, excitation dependence, and difficulty in purification.

[0004] The demand for multicolor fluorescent carbon dots is increasingly prominent in many fields, such as display technology, bioimaging, and photocatalysis. Therefore, providing a new biomass method to synthesize carbon dots with full-color luminescence properties will greatly promote the application expansion of carbon dot materials and bring new development opportunities to related industries. Summary of the Invention

[0005] The purpose of this invention is to provide a method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source. The method is simple to implement and requires no further modification to obtain multicolor fluorescent carbon dots with stable emission and coverage of the visible light region.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for one-pot synthesis of multicolor fluorescent carbon dots using Saposhnikovia divaricata as a carbon source includes the following steps:

[0008] Saposhnikovia divaricata and p-phenylenediamine were dissolved in a mixed solvent of ethanol and hydrochloric acid, stirred evenly, and transferred to a reaction vessel for solvothermal reaction. After the solvothermal reaction was completed, the reaction product was cooled to room temperature and removed for separation by column chromatography to obtain multicolor fluorescent carbon dots.

[0009] Furthermore, the mass ratio of the windproof material to p-phenylenediamine is (0.24-0.66):0.33, preferably (0.33-0.42):0.33.

[0010] Furthermore, the windproof material is a windproof sheet or powder.

[0011] Furthermore, the volume ratio of ethanol to hydrochloric acid in the mixed solvent is 9:(0.5-2).

[0012] Furthermore, the mass-to-volume ratio of the sum of the masses of the wind-proof and p-phenylenediamine to the mixed solvent of ethanol and hydrochloric acid is (0.57-0.99) g : (9.5-11) ml.

[0013] Furthermore, the temperature of the solvothermal reaction is 160-220℃, and the reaction time is 8-12h.

[0014] Furthermore, the eluent used in the column chromatography method has a polarity that increases gradually from low to high, changing as the carbon points are separated. Preferably, petroleum ether, ethyl acetate, acetone, and ethanol are used sequentially as eluents for separation by column chromatography.

[0015] The present invention also provides multicolor fluorescent carbon dots prepared by the above method.

[0016] The carbon dots prepared by this invention exhibit multiple fluorescent colors. Fluorescent carbon dots with emission peaks in the range of 430-750 nm can be separated by column chromatography, covering the visible light region and including blue, light blue, green, yellow, and red fluorescence. These multicolor fluorescent carbon dots are liquid and possess relatively stable emission wavelengths. Under excitation wavelengths of 250-700 nm, the emission peaks show virtually no red-shift or blue-shift with increasing excitation wavelength. Furthermore, they are soluble in most solvents, including petroleum ether, ethyl acetate, butyl acetate, ethanol, and toluene.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention utilizes a novel biomass, *Saposhnikovia divaricata*, as a carbon source, p-diphenylamine as a nitrogen source, and ethanol and hydrochloric acid as solvents to synthesize multicolor fluorescent carbon dots in a one-pot process. The method yields inexpensive raw materials, a simple preparation process, and can synthesize all carbon dots covering the visible light region in a single step, saving costs and significantly reducing the time required for various modulations to change the fluorescence color. The resulting multicolor fluorescent carbon dots exhibit extremely high stability and are excitation-independent, with emission spectra covering the entire visible light region. Complete separation of different fluorescence colors can be achieved using only column chromatography. Attached Figure Description

[0019] Figure 1 The normalized emission spectra of the multicolor fluorescent carbon dot solution prepared in Example 1 at different excitation wavelengths (excitation wavelengths from left to right are 380 nm, 380 nm, 450 nm, 463 nm, 513 nm, and 620 nm).

[0020] Figure 2The images show the blue, green, yellow, and red fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1 under typical sunlight (Fig. a) and under flashlight excitation at different excitation levels (Fig. b). From left to right, they are blue, green, yellow, and red fluorescent carbon dots.

[0021] Figure 3 The figures show the stability test results of the blue, green, yellow, and red fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1 under continuous irradiation by an external light source for 12 hours. Figures (a), (b), (c), and (d) show the emission spectrum changes of the blue, green, yellow, and red fluorescent carbon dots at different irradiation times (t = 0, 1.5, 3, 4.5, 6, 7.5, 9, 10.5, and 12 hours, respectively); Figures (e), (f), (g), and (h) show the emission intensity changes of the blue, green, yellow, and red fluorescent carbon dots, respectively.

[0022] Figure 4 The emission spectra of the blue (Fig. a), green (Fig. b), yellow (Fig. c), and red (Fig. d) fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1 under different excitations are shown.

[0023] Figure 5 The XPS spectra of the blue, green, yellow, and red fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1 are shown.

[0024] Figure 6 The Fourier transform infrared spectra of the blue, green, yellow, and red fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1 are shown.

[0025] Figure 7 The fluorescence lifetime fitting diagrams are of the blue (Fig. a), green (Fig. b), yellow (Fig. c), and red (Fig. d) fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in Example 1.

[0026] Figure 8 The emission spectra of multicolor fluorescent carbon dots prepared under different feed ratios under ultraviolet light excitation at a wavelength of 380 nm are shown. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the present invention...

[0028] All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0029] Example 1

[0030] Weigh 0.33 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 0.5–2 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene (PTFE) reactor, seal it, and place it in a drying oven at 160–220 °C for 8–12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation. Separate the solution by column chromatography, using petroleum ether, ethyl acetate, acetone, and ethanol as eluents in sequence. Evaporate the separated solution to dryness by rotary evaporation and redissolve it in acetone for further characterization.

[0031] The emission spectra of the multicolor fluorescent carbon dot solution were measured using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 1 As shown, the multicolor fluorescent carbon dot solution can separate fluorescent carbon dots with emission peaks in the range of 430-750 nm, covering the entire visible light region, including blue, light blue, green, yellow, and red fluorescence.

[0032] Carbon dots exhibiting four typical fluorescence colors—blue, green, yellow, and red—were further subjected to the following detailed emission spectrum tests.

[0033] like Figure 2 The image shown is a photograph of the blue, green, yellow, and red fluorescent carbon dots separated from the multicolor fluorescent carbon dots prepared in this embodiment under typical sunlight and under excitation by flashlights at different excitation levels.

[0034] Stability test: Carbon dot solutions with different fluorescent colors were continuously irradiated under an external light source (each with its own optimal excitation wavelength) for 12 hours. Figure 3 and Figure 4 As shown, the emission peak positions and fluorescence intensity of these carbon dots are stable, and the fluorescence peaks exhibit excitation-independent emission characteristics.

[0035] Elemental Composition: To explore the elemental composition of these carbon dots in more detail, XPS tests were performed on the material, such as... Figure 5 As shown, these carbon dots mainly contain three elements: C, N, and O.

[0036] Functional group information: To investigate the functional group information of these carbon dots, Fourier transform infrared spectroscopy was performed on the material, such as... Figure 6 As shown, these carbon dots contain a large number of functional groups such as C=C, C=O, and CO bonds, proving that their surface states are extremely abundant.

[0037] Fluorescence lifetime testing: such as Figure 7 As shown, these carbon dots have a fluorescence lifetime on the order of nanoseconds and do not exhibit phosphorescence or afterglow.

[0038] Example 2

[0039] Weigh 0.42 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0040] Example 3

[0041] Weigh 0.60 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0042] Example 4

[0043] Weigh 0.18 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0044] Example 5

[0045] Weigh 0.12 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0046] Example 6

[0047] Weigh 0.06 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0048] Example 7

[0049] Weigh 0.24 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0050] Example 8

[0051] Weigh 0.66 g of Saposhnikovia divaricata and 0.33 g of p-phenylenediamine and add them to 9 mL of ethanol and 1 mL of hydrochloric acid, stirring for 15 min. Transfer the mixture to a polytetrafluoroethylene reactor, seal it, and place it in a drying oven at 200 °C for 12 h. After the reaction product cools to room temperature, remove it to obtain a black turbid solution. Measure its fluorescence intensity under 380 nm ultraviolet light excitation.

[0052] like Figure 8 The figures shown are emission spectra of multicolor fluorescent carbon dots prepared under different feed ratios in Examples 1-8 under ultraviolet light excitation at a wavelength of 380 nm. It can be seen that when the mass ratio of *Saposhnikovia divaricata* to p-phenylenediamine is (0.33-0.66):0.33, the fluorescence intensity of the prepared multicolor fluorescent carbon dots is stronger.

Claims

1. A method for one-pot synthesis of multicolor fluorescent carbon dots using Saposhnikovia divaricata as a carbon source, characterized in that, Includes the following steps: Saposhnikovia divaricata and p-phenylenediamine were dissolved in a mixed solvent of ethanol and hydrochloric acid, stirred evenly, and transferred to a reaction vessel for solvothermal reaction. After the reaction product was cooled to room temperature, it was taken out and separated by column chromatography to obtain multicolor fluorescent carbon dots.

2. The method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source according to claim 1, characterized in that, The mass ratio of the windproof material to p-phenylenediamine is (0.24-0.66):0.

33.

3. The method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source according to claim 1, characterized in that, The volume ratio of ethanol to hydrochloric acid in the mixed solvent is 9:(0.5-2).

4. The method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source according to claim 1, characterized in that, The mass-to-volume ratio of the sum of the masses of the windproof and p-phenylenediamine to the mixed solvent of ethanol and hydrochloric acid is (0.57-0.99) g : (9.5-11) ml.

5. The method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source according to claim 1, characterized in that, The temperature of the solvothermal reaction is 160-220℃, and the reaction time is 8-12h.

6. The method for one-pot synthesis of multicolor fluorescent carbon dots using *Saposhnikovia divaricata* as a carbon source according to claim 1, characterized in that, The eluents used in the column chromatography method are, in order, petroleum ether, ethyl acetate, acetone, and ethanol.

7. Multicolor fluorescent carbon dots prepared by any one of claims 1-6.

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