A novel long-lasting carbon dot and its preparation method

Abstract

The present invention provides a novel long-afterglow carbon dot and a preparation method thereof. The present invention belongs to the field of luminescent carbon nanomaterials and proposes a novel matrix that enables carbon dots (CDs) to have a long afterglow. The present invention directly uses 2,4,6-triphenylboroxine as a carbon source, biuret as an additive, and water as a solvent for a synthesis reaction. The operation is convenient and no purification step is required to obtain solid-state long-afterglow carbon dots with stable luminescence. The matrix of the long-afterglow carbon dots is ammonium pentaborate tetrahydrate. The long-afterglow carbon dots prepared by the present invention with the matrix can obtain a blue afterglow under ultraviolet wavelength excitation. The CDs prepared by the present invention are solid-state CDs, have stable phosphorescence, are resistant to strong acids and alkalis, and can also adjust the afterglow time by controlling the pH value.

Description

Technical Field

[0001] The present invention relates to the field of luminescent carbon nanomaterials, in particular to a novel long-lasting-glow carbon dot and a preparation method thereof. Background Art

[0002] Carbon dots (CDs) are a new type of nanomaterial with an average particle size of less than 10 nm. They exhibit excellent optical properties, low toxicity, and biocompatibility. Long-lasting carbon dots (CDs) are carbon dots that exhibit a long afterglow. Combining the excellent optical properties of CDs with the long afterglow effect, these CDs hold broad application prospects in fluorescence imaging, biomarkers, sensors, and environmental monitoring.

[0003] In recent years, there has been great interest in the development of phosphorescent materials based on CDs. The phosphorescence emission of CDs is significantly affected by the choice of host and synthesis method. Various studies have shown that a variety of hosts, including polyvinyl alcohol, silicone, aluminum hydroxide, urea, boric acid, boron nitride, cyanuric acid, and certain polymers, can lead to different phosphorescence phenomena in CDs. This host-guest strategy effectively reduces the intersystem crossing (ISC) of the energy gap, suppresses the non-radiative decay of triplet excitons, and induces room-temperature phosphorescence (RTP). Therefore, the host is of great significance for long-lasting carbon dots. Summary of the Invention

[0004] The purpose of the present invention is to provide a novel long-afterglow carbon dot and a preparation method thereof. The present invention synthesizes new long-afterglow carbon dots, and the matrix of the carbon dots is a new matrix. The synthesis process of the long-afterglow carbon dots is simple, and CDs with stable long afterglow can be obtained without further modification.

[0005] The present invention is achieved in that:

[0006] The novel long-lasting carbon dots provided by the present invention are solid-state long-lasting carbon dots obtained by hydrothermal reaction of biuret and 2,4,6-triphenylboroxine and taking ammonium pentaborate tetrahydrate as a matrix.

[0007] The preparation method of the novel long afterglow carbon dots is as follows:

[0008] a. Weigh 2,4,6-triphenylboroxine and biuret in a mass ratio of 0.3:(0.06-3), add the weighed raw materials into deionized water to dissolve, and stir in a stirrer; wherein 2,4,6-triphenylboroxine is a carbon source, biuret is an additive, and water is a solvent;

[0009] b. placing the mixed solution in a reactor for hydrothermal reaction, and then cooling it to room temperature before taking it out;

[0010] c. Freeze, dry, and grind the solution obtained in step b to obtain solid long-lasting carbon dots based on ammonium pentaborate tetrahydrate.

[0011] Preferably, in step a, the mass of the biuret is 0.06 g, the mass of 2,4,6-triphenylboroxine is 0.3 g, and the stirring time is 60 min.

[0012] Preferably, the hydrothermal reaction temperature in step b is 220° C. and the reaction time is 5 h.

[0013] The obtained product was detected by X-ray diffractometer to obtain the XRD spectrum (see Figure 3 ), it can be clearly seen that the peak position corresponds to the standard card of ammonium pentaborate tetrahydrate, proving that long-lasting carbon dots with ammonium pentaborate tetrahydrate as the matrix are generated.

[0014] The long afterglow carbon dots formed are rich in C, N, B, and O functional groups, and contain NH bonds and BO bonds, such as Figure 4-Figure 6 shown.

[0015] There is no afterglow for the carbon dots generated only with biuret, and there is no afterglow for the carbon dots generated only with 2,4,6-triphenylboroxine. Only the carbon dots generated with biuret and 2,4,6-triphenylboroxine have afterglow. Figure 1 shown.

[0016] The long afterglow carbon dots based on ammonium pentaborate tetrahydrate obtained in the present invention can change the afterglow time by changing the pH value using acid or alkali. Figure 8 shown.

[0017] The present invention provides a novel long-lasting carbon dot, the afterglow of which is derived from its matrix, ammonium pentaborate tetrahydrate. The long-lasting carbon dots prepared by the present invention exhibit a blue afterglow under ultraviolet excitation. Furthermore, the resulting carbon dots exhibit excitation-dependent phosphorescence, with the emission peak red-shifting as the excitation wavelength increases under excitation wavelengths of 250-370 nm.

[0018] Compared with other carbon dots, the long afterglow carbon dots in the present invention are, on the one hand, a new type of carbon dots and are solid-state carbon dots; on the other hand, the preparation process of the carbon dots is simple, and solid-state long afterglow carbon dots with stable luminescence can be obtained without any purification; thirdly, the carbon dots are resistant to strong acids and alkalis, and the luminescence intensity of the long afterglow carbon dots is different under different pH conditions; fourthly, the carbon dots have an adjustable afterglow time characteristic, and the afterglow time can be changed by controlling its pH value using acids and alkalis. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The phosphorescence emission spectra of CDs generated by the reaction of biuret and 2,4,6-triphenylboroxine in different ratios.

[0020] Figure 2 The phosphorescence emission spectra of the long afterglow carbon dots obtained in Example 1 under different excitations.

[0021] Figure 3 This is the X-ray diffraction spectrum of the long afterglow carbon dots obtained in Example 1.

[0022] Figure 4 This is the XPS overall spectrum of the long afterglow carbon dots obtained in Example 1.

[0023] Figure 5 This is the XPS fine spectrum of the long afterglow carbon dots obtained in Example 1.

[0024] Figure 6 This is a comparison chart of the Fourier red light spectra of the long afterglow carbon dots obtained in Example 1.

[0025] Figure 7 Figure 2 shows the phosphorescence emission spectra of AB-CDs at different pH values.

[0026] Figure 8 Actual photos of AB-CDs with different pH values ​​under 365nm flashlight excitation. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, further description will be given below with reference to relevant drawings.

[0028] Comparative Example 1: Preparation of solid CDs generated by biuret reaction at 220°C.

[0029] (1) Weigh 1 g of biuret and add it to 15 mL of deionized water. After stirring for 1 hour, transfer the solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220°C and the reaction time is 5 hours. After cooling to room temperature, remove the solution and obtain a light yellow transparent solution. This solution is freeze-dried and ground to obtain the biuret CDs powder.

[0030] (2) The phosphorescence emission spectrum was measured using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 1 As shown, it can be seen that there is no phosphorescence (corresponding to Figure 1 h curve).

[0031] Comparative Example 2: Preparation of solid CDs generated by the reaction of 2,4,6-triphenylboroxine at 220°C.

[0032] (1) Weigh 0.3 g of 2,4,6-triphenylboroxine and add it to 15 mL of deionized water. After stirring for 1 hour, transfer the solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220°C and the reaction time is 5 hours. After cooling to room temperature, remove the solution and obtain a transparent solution. The solution is freeze-dried and ground to obtain the CDs powder of 2,4,6-triphenylboroxine.

[0033] (2) The phosphorescence emission spectrum was measured using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 1 As shown, it can be seen that there is no phosphorescence (corresponding to Figure 1 middle g curve).

[0034] Example 1: Preparation of a long afterglow CDs powder (0.06 g) at 220°C.

[0035] (1) Weigh 0.3 g of 2,4,6-triphenylboroxine and 0.06 g of biuret and add them to 15 mL of deionized water. Stir for 1 h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220°C and the reaction time is 5 h. After cooling to room temperature, remove the mixture to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. "AB" in AB-CDs is the abbreviation for ammonium pentaborate.

[0036] (2) The phosphorescence emission spectrum was measured using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 1 As shown, the emission peak appears at 456nm, proving that it has afterglow, and the emission peak intensity is the strongest at this concentration ratio (corresponding to Figure 1 (a curve in the middle).

[0037] (3) The obtained carbon dots were subjected to laser spectroscopy and XRD tests, and the results were as follows: Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the carbon dots prepared in this embodiment have phosphorescence excitation-dependent characteristics. Under the excitation wavelength of 250-370nm, the emission peak red-shifts as the excitation wavelength increases. Figure 3 It can be seen that this embodiment successfully generated long-lasting carbon dots based on ammonium pentaborate tetrahydrate.

[0038] (4) In order to perform elemental analysis on AB-CDs, they were characterized by X-ray photoelectron spectroscopy, such as Figure 4 and Figure 5 As shown, the AB-CDs material contains C, N, O, and B elements.

[0039] (5) At the same time, in order to explore the functional group information of AB-CDs, the material was tested by Fourier transform infrared spectroscopy. The results are as follows: Figure 6 As shown. Figure 6 It can be seen that there are BO, OBO, and NH bonds in AB-CDs, which correspond to the functional groups of ammonium pentaborate tetrahydrate.

[0040] Example 2: Preparation of a long afterglow CDs powder (0.15 g of biuret) at 220°C.

[0041] Weigh 0.3g of 2,4,6-triphenylboroxine and 0.15g of biuret and add them to 15mL of deionized water, and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220℃ and the reaction time is 5h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. Use a fluorescence spectrophotometer (F-7000, Hitachi) to test the phosphorescence emission spectrum. Figure 1 As shown, the emission peak appears at 456nm (corresponding to Figure 1 b curve), proving that it has afterglow.

[0042] Example 3: Preparation of a long afterglow CDs powder (0.3 g of biuret) at 220°C.

[0043] Weigh 0.3g of 2,4,6-triphenylboroxine and 0.3g of biuret and add them to 15mL of deionized water, and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220℃ and the reaction time is 5h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. Use a fluorescence spectrophotometer (F-7000, Hitachi) to test the phosphorescence emission spectrum. Figure 1 As shown, the emission peak appears at 456nm (corresponding to Figure 1 The c curve in the middle proves that it has afterglow.

[0044] Example 4: Preparation of a long afterglow CDs powder (1 g of biuret) at 220°C.

[0045] Weigh 0.3g of 2,4,6-triphenylboroxine and 1g of biuret and add them to 15mL of deionized water, stirring for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220℃ and the reaction time is 5h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. The phosphorescence emission spectrum is tested using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 1 As shown, phosphorescence appears slightly (corresponding to Figure 1 f curve in the middle).

[0046] Example 5: Preparation of a long afterglow CDs powder (1.5 g of biuret) at 220°C.

[0047] Weigh 0.3g of 2,4,6-triphenylboroxine and 1.5g of biuret and add them to 15mL of deionized water, and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220℃ and the reaction time is 5h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. Use a fluorescence spectrophotometer (F-7000, Hitachi) to test the phosphorescence emission spectrum. Figure 1 As shown, the emission peak appears at 456nm (corresponding to Figure 1 The d curve in the middle proves that it has afterglow.

[0048] Example 6: Preparation of a long afterglow CDs powder (3 g of biuret) at 220°C.

[0049] Weigh 0.3g of 2,4,6-triphenylboroxine and 3g of biuret and add them to 15mL of deionized water, and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220℃ and the reaction time is 5h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long-lasting CDs powder (AB-CDs) based on ammonium pentaborate tetrahydrate. Use a fluorescence spectrophotometer (F-7000, Hitachi) to test the phosphorescence emission spectrum. Figure 1 As shown, the emission peak appears at 456nm (corresponding to Figure 1 The e curve in the middle proves that it has afterglow.

[0050] Example 7: Preparation of AB-CDs at different pH values.

[0051] (1) Weigh 0.3 g of 2,4,6-triphenylboroxine and 0.06 g of biuret and add them to 15 mL of deionized water. Stir for 1 h. Transfer the mixed solution to a polytetrafluoroethylene reactor, seal it with a lid, and place it in a drying oven. The reaction temperature is 220°C and the reaction time is 5 h. After cooling to room temperature, remove the solution to obtain a light yellow transparent solution. The pH value of the solution is adjusted with hydrochloric acid and sodium hydroxide solution (pH = 1, 3, 5, 7, 9, 11, 13). The adjusted solution is sonicated, freeze-dried, and then ground to obtain AB-CDs with different pH values.

[0052] The phosphorescence emission spectrum was measured using a fluorescence spectrophotometer (F-7000, Hitachi). Figure 7 As shown in Figure 3, as the pH value increases, the phosphorescence emission peak also changes from weak to strong. Figure 7 In the figure, curve a corresponds to the product in Example 1, and its pH value is 8.5.

[0053] (2) Use a mobile phone to take pictures of the sample under the excitation of a 365nm flashlight. Figure 8 As shown, it can be seen that as the pH value increases, the afterglow time also increases from short to long.

Claims

1. A novel method for preparing long afterglow carbon dots, characterized in that: The steps include: a. Weigh 2,4,6-triphenylboroxine and biuret in a mass ratio of 0.3:(0.06-3), add the weighed raw materials into deionized water to dissolve, and stir; b. placing the mixed solution in a reactor for hydrothermal reaction, and then taking it out after cooling to room temperature; c. Freeze, dry, and grind the solution obtained in step b to obtain solid long-lasting carbon dots based on ammonium pentaborate tetrahydrate.

2. The method for preparing the novel long afterglow carbon dots according to claim 1, wherein: In step b, the temperature of the hydrothermal reaction is 220° C. and the reaction time is 5 h.

3. The method for preparing the novel long afterglow carbon dots according to claim 1, wherein: In step a, the mass ratio of 2,4,6-triphenylboroxine to biuret is 0.3:0.

06.

4. The method for preparing the novel long afterglow carbon dots according to claim 1, wherein: After step b and before step c, the method further includes adjusting the pH value of the solution obtained in step b by using hydrochloric acid and sodium hydroxide solution.

5. The method for preparing the novel long afterglow carbon dots according to claim 4, wherein: The pH value of the solution obtained in step b is adjusted to 1-13 using hydrochloric acid and sodium hydroxide solution.

6. The method for preparing the novel long afterglow carbon dots according to claim 1, wherein: The stirring time in step a is 1 h.

7. A novel long afterglow carbon dot prepared by the method according to any one of claims 1 to 6.

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