Novel long afterglow carbon dot and preparation method thereof

Abstract

The invention provides a novel long afterglow carbon dot and a preparation method thereof. The invention belongs to the field of luminescent carbon nanomaterials, and provides a novel matrix enabling carbon dots (CDs) to have long afterglow. According to the method, 2, 4, 6-triphenyl boroxane is directly adopted as a carbon source, biuret is adopted as an additive, water is adopted as a solvent for a synthetic reaction, operation is convenient, no purification step is needed, the solid-state long-afterglow carbon dots capable of emitting light stably can be obtained, and the matrix of the long-afterglow carbon dots is ammonium pentaborate tetrahydrate. The long afterglow carbon dots with the matrix prepared by the invention can obtain blue afterglow under the excitation of ultraviolet wavelength. The CDs prepared by the method belong to solid-state CDs, are stable in phosphorescence luminescence and have strong acid and strong alkali resistance, and the afterglow time can be regulated by regulating and controlling the pH value.

Description

Technical Field

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

[0002] Carbon dots (CDs) are a new type of nanomaterials with an average particle size of less than 10nm, excellent optical properties, low toxicity and biocompatibility. Long afterglow carbon dots refer to carbon dots with long afterglow characteristics. Long afterglow carbon dots combine the excellent optical properties of carbon dots with the long afterglow effect, making them have broad application prospects in fluorescence imaging, biomarkers, sensors, environmental monitoring and other fields.

[0003] In recent years, there has been great interest in developing phosphorescent materials based on CDs. The phosphorescent emission of CDs is greatly affected by the choice of matrix and synthesis method. Various studies have shown that a variety of matrices including polyvinyl alcohol, silicone, aluminum hydroxide, urea, boric acid, boron nitride, cyanuric acid and certain polymers can lead to different phosphorescence phenomena of 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 matrix 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 new long afterglow carbon dot is synthesized by the present invention, and the matrix of the carbon dot is a new matrix. The synthesis process of the long afterglow carbon dot 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 afterglow carbon dots provided by the invention are solid long afterglow carbon dots which are obtained by hydrothermal reaction of biuret and 2,4,6-triphenylboroxine and take 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 them 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 taking it out after cooling to room temperature;

[0010] c. Freeze, dry and grind the solution obtained in step b to obtain solid long afterglow carbon dots with ammonium pentaborate tetrahydrate as the matrix.

[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, in step b, the hydrothermal reaction temperature 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 afterglow carbon dots based on ammonium pentaborate tetrahydrate 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 with ammonium pentaborate tetrahydrate as the matrix obtained by the present invention can change the afterglow time by changing the pH value by using acid or alkali, such as Figure 8 shown.

[0017] The present invention provides a novel long afterglow carbon dot, the afterglow of which comes from a matrix of ammonium pentaborate tetrahydrate. The long afterglow carbon dot prepared by the present invention can obtain a blue afterglow under ultraviolet wavelength excitation. The obtained carbon dot has a phosphorescence excitation dependence characteristic, and under the excitation of 250-370nm excitation wavelength, the emission peak red shifts as the excitation wavelength increases.

[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 solid 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 using acids and alkalis to regulate the pH value. 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 Phosphorescence emission spectra of AB-CDs at different pH values.

[0026] Figure 8 These are 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 the 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, cover and seal it, 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, take it out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain the CDs powder of biuret.

[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 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 h, transfer the solution to a polytetrafluoroethylene reactor, cover and seal it, 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, take it out to 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 and stir for 1 h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal it, 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, 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. "AB" in AB-CDs is the abbreviation of 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 dependence characteristics. Under the excitation of 250-370nm excitation wavelength, the emission peak red-shifts as the excitation wavelength increases. Figure 3 It can be seen that this example successfully generated long afterglow 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, add to 15mL of deionized water and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal, and put into a drying oven. The reaction temperature is 220°C and the reaction time is 5h. After cooling to room temperature, take out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long afterglow 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 in the middle), 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, add to 15mL of deionized water and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal it, put it in a drying oven, and the reaction temperature is 220°C for 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 afterglow 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, add them to 15mL of deionized water and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal it, put it in a drying oven, and the reaction temperature is 220℃ for 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 afterglow 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, 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, add to 15mL of deionized water and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal it, put it in a drying oven, and the reaction temperature is 220°C for 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 afterglow 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, add to 15mL of deionized water and stir for 1h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal, and put into a drying oven. The reaction temperature is 220°C and the reaction time is 5h. After cooling to room temperature, take out to obtain a light yellow transparent solution. The solution is freeze-dried and ground to obtain a long afterglow 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 e curve in the middle), proving 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, and stir for 1 h. Transfer the mixed solution to a polytetrafluoroethylene reactor, cover and seal it, and put it in a drying oven. The reaction temperature is 220°C and the reaction time is 5 h. After cooling to room temperature, take it out to obtain a light yellow transparent solution. Adjust the pH value of the solution with hydrochloric acid and sodium hydroxide solution (pH = 1, 3, 5, 7, 9, 11, 13), sonicate the adjusted solution, and then freeze-dry and grind it 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, 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 365nm flashlight excitation. 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 afterglow carbon dots with ammonium pentaborate tetrahydrate as the matrix.

2. The method for preparing the novel long afterglow carbon dots according to claim 1, characterized in that: 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 is characterized in that: 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 is characterized in that: 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 is characterized in that: 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 is characterized in that: 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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