Fluorescent carbon dots with room-temperature phosphorescence performance and preparation method and application thereof

Abstract

The application provides fluorescent carbon dots with room-temperature phosphorescence performance and a preparation method and application thereof, and belongs to the technical field of carbon dots. The preparation method provided by the application comprises the following steps: (1) mixing polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution; (2) performing hydrothermal reaction on the mixed solution obtained in the step (1) to obtain fluorescent carbon dots with room-temperature phosphorescence performance. The carbon dots prepared by using polyethyleneimine and thiamine hydrochloride as raw materials have both fluorescent and phosphorescent characteristics, and have high fluorescent intensity and long phosphorescent afterglow time.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of carbon dots, and particularly relates to fluorescent carbon dots with room-temperature phosphorescence performance as well as a preparation method and application thereof. BACKGROUND

[0002] The fluorescent carbon dots are a kind of carbon nanomaterials with excellent optical performance, and have important roles in the fields of biological medicine, optoelectronic devices, sensors and the like. According to the differences in carbon cores and surface states, the carbon dots can be divided into graphene quantum dots, carbon nanodots and carbonized polymer dots. The carbonized polymer dots not only integrate the excellent chemical stability and high luminescent performance of traditional carbon dots, but also can avoid the self-quenching effect of the luminescent center due to aggregation by forming a high molecular chain outer layer structure. The carbonized polymer dots prepared in the prior art generally only have fluorescent properties and low fluorescent intensity, or have phosphorescence effect but short phosphorescence time, thereby limiting the application thereof. Therefore, how to obtain carbon dots with both fluorescent and phosphorescent properties and high fluorescent intensity and long phosphorescence time has become a problem in the prior art. SUMMARY

[0003] The application aims to provide fluorescent carbon dots with room-temperature phosphorescence performance as well as a preparation method and application thereof. The carbon dots prepared by the application have both fluorescent and phosphorescent properties, and high fluorescent intensity and long phosphorescence time.

[0004] In order to achieve the above-mentioned application purposes, the application provides the following technical solutions.

[0005] The application provides a preparation method of fluorescent carbon dots with room-temperature phosphorescence performance, comprising the following steps:

[0006] (1) mixing polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution;

[0007] (2) performing hydrothermal reaction on the mixed solution obtained in the step (1) to obtain the fluorescent carbon dots with room-temperature phosphorescence performance.

[0008] Preferably, the weight-average molecular weight of the polyethyleneimine in the step (1) is 600-70000.

[0009] Preferably, the mass ratio of the polyethyleneimine to the thiamine hydrochloride in the step (1) is 0.5:(0.02-1.6).

[0010] Preferably, the pH value of the mixed solution in the step (1) is 5-10.

[0011] Preferably, the mass ratio of the polyethyleneimine to water in the step (1) is 1:(20-40).

[0012] Preferably, the temperature of the hydrothermal reaction in step (2) is 120-200℃, and the time of the hydrothermal reaction is 2-16h.

[0013] Preferably, the temperature of the hydrothermal reaction is 180℃, and the time of the hydrothermal reaction is 14h.

[0014] The application further provides the fluorescent carbon dots with room-temperature phosphorescence prepared by the preparation method.

[0015] The application further provides the application of the fluorescent carbon dots with room-temperature phosphorescence in the preparation of luminescent materials, biological medicines, photoelectric devices and sensors.

[0016] Preferably, the luminescent material comprises carbon dot-boron oxide composite material or carbon dot-polymer composite film.

[0017] The application provides a preparation method of fluorescent carbon dots with room-temperature phosphorescence, comprising the following steps: (1) mixing polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution; (2) performing hydrothermal reaction on the mixed solution obtained in step (1) to obtain fluorescent carbon dots with room-temperature phosphorescence. The carbon dots prepared by the application have both fluorescent and phosphorescent characteristics, and have high fluorescent intensity and long phosphorescent afterglow time. The results of the examples show that the carbon dot solution prepared by the application emits blue fluorescence with a wavelength of 458nm under excitation of a 335nm light source, and the carbon dot-boron oxide composite material solid powder prepared by the application displays blue fluorescence under a 365nm lamp and emits green phosphorescence at 525nm, has high fluorescent intensity, and can continuously emit room-temperature phosphorescence for nearly 7s after the 365nm ultraviolet lamp is turned off for 2s. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The fluorescence spectrum of the carbon dot solution prepared in Examples 1-4 is shown in the figure;

[0019] Figure 2 The fluorescence spectrum of the carbon dot solution prepared in Examples 1, 5-9 is shown in the figure;

[0020] Figure 3 The fluorescence spectrum of the carbon dot solution prepared in Examples 1, 18-22 is shown in the figure;

[0021] Figure 4 The fluorescence spectrum of the carbon dot solution prepared in Examples 1, 23-30 is shown in the figure;

[0022] Figure 5 The fluorescence spectrum of the carbon dot solution prepared in Examples 1, 31-34 is shown in the figure;

[0023] Figure 6Fluorescence spectrum of the carbon dot solution prepared in Example 1, Comparative Examples 1 to 4;

[0024] Figure 7 Fluorescence spectrum of the carbon dot solution prepared in Example 1 diluted 10 times;

[0025] Figure 8 UV absorption spectrum of the carbon dot solution prepared in Example 1 diluted 100 times;

[0026] Figure 9 Transmission scanning electron microscope image of the carbon dot solution prepared in Example 1;

[0027] Figure 10 Particle size distribution graph of the carbon dot solution prepared in Example 1;

[0028] Figure 11 Fluorescence spectrum of the carbon dot solution prepared in Example 1 diluted 10 times under different excitation wavelengths;

[0029] Figure 12 Graph of different excitation wavelengths and fluorescence intensity of the carbon dot solution prepared in Example 1 diluted 10 times;

[0030] Figure 13 Fluorescence spectrum of the carbon dot solution prepared in Example 1 diluted 10 times under different time irradiation;

[0031] Figure 14 Fluorescence spectrum of the carbon dot solution prepared in Example 1 under different pH buffer solutions;

[0032] Figure 15 Phosphorescence spectrum of the carbon dot boron oxide composite material prepared in Application Example 1 under different temperatures;

[0033] Figure 16 Phosphorescence lifetime curve of the carbon dot boron oxide composite material prepared in Application Example 1 under different temperatures;

[0034] Figure 17 Phosphorescence spectrum of the carbon dot boron oxide composite material prepared in Application Example 1 reversibility with temperature graph;

[0035] Figure 18 Macrograph of the carbon dot boron oxide composite material prepared in Application Example 1 under visible light, 254 nm and 365 nm ultraviolet lamp irradiation for 2 s, and different time after the ultraviolet lamp is turned off;

[0036] Figure 19 Macrograph of the carbon dot boron oxide composite material prepared in Application Example 1 and the materials prepared in Comparative Application Examples 1 to 7 under 365 nm ultraviolet lamp irradiation for 2 s, and different time after the ultraviolet lamp is turned off;

[0037] Figure 20 Tensile stress-strain curves of the films prepared for Application Example 2 and Comparative Application Example 8;

[0038] Figure 21 Macrographs of the films prepared for Application Example 2 and Comparative Application Example 8 after stretching under UV lamp and sunlight. DETAILED DESCRIPTION

[0039] The application provides a preparation method of fluorescent carbon dots with room-temperature phosphorescence performance, comprising the following steps:

[0040] (1) mixing polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution;

[0041] (2) performing hydrothermal reaction on the mixed solution obtained in the step (1) to obtain fluorescent carbon dots with room-temperature phosphorescence performance.

[0042] Unless otherwise specified, the source of each raw material is not particularly limited in the application, and commercially available products known to those skilled in the art can be used.

[0043] The application mixes polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution.

[0044] In the application, the weight average molecular weight of the polyethyleneimine is preferably 600-70000, more preferably 1800-10000, and further preferably 1800. Controlling the weight average molecular weight of the polyethyleneimine within the above range can further improve the luminescence intensity of the carbon dots.

[0045] In the application, the mass ratio of the polyethyleneimine to the thiamine hydrochloride is preferably 0.5:(0.02-1.6), more preferably 0.5:(0.04-0.8), further preferably 0.5:(0.08-0.5), and most preferably 0.5:0.08. Controlling the mass ratio of the polyethyleneimine to the thiamine hydrochloride within the above range can further improve the luminescence intensity of the carbon dots.

[0046] In the application, the mass ratio of the polyethyleneimine to water is preferably 1:(20-40), and more preferably 1:30. Controlling the mass ratio of the polyethyleneimine to water within the above range can fully dissolve the raw materials.

[0047] In the application, the pH value of the mixed solution is preferably 5-10, more preferably 6-9, and further preferably 7-8. Controlling the pH value of the mixed solution within the above range can further improve the luminescence intensity of the carbon dots.

[0048] In the present application, when the pH value of the mixed solution is not within the above range, the present application preferably adds acid or base to adjust the pH value of the mixed solution. In the present application, the acid is preferably hydrochloric acid; the base is preferably sodium hydroxide solution. The present application does not have special limitations on the concentration and amount of the acid or base, as long as the pH value of the mixed solution is within the above range.

[0049] In the present application, the mixing of the polyethyleneimine, thiamine hydrochloride and water is preferably carried out under ultrasonic conditions. The present application does not have special limitations on the power and time of the ultrasonic, as long as the technical solutions known to those skilled in the art are used to ensure that the raw materials are fully dissolved and uniformly mixed.

[0050] After obtaining the mixed solution, the present application carries out hydrothermal reaction on the mixed solution to obtain fluorescent carbon dots with room-temperature phosphorescence performance.

[0051] In the present application, the temperature of the hydrothermal reaction is preferably 120-200℃, more preferably 140-180℃, and further preferably 160-180℃; the time of the hydrothermal reaction is preferably 2-16h, more preferably 4-14h, and further preferably 10-14h. Controlling the temperature and time of the hydrothermal reaction within the above range can further improve the luminescence intensity of the carbon dots.

[0052] After the hydrothermal reaction is completed, the present application preferably sequentially carries out filtration, dialysis, concentration and drying on the product of the hydrothermal reaction to obtain fluorescent carbon dots with room-temperature phosphorescence performance.

[0053] In the present application, the filtration preferably uses a water filter needle filter; the pore size of the water filter needle filter is preferably 0.4-0.5μm, and more preferably 0.45μm. The present application does not have special limitations on the model of the water filter needle filter, and any model known to those skilled in the art can be used.

[0054] In the present application, the molecular weight cut-off during dialysis is preferably 450-550Da, and more preferably 500Da.

[0055] In the present application, the time of dialysis is preferably 40-50h, and more preferably 48h.

[0056] In the present application, the concentration temperature is preferably 70-90℃, and more preferably 80℃; the concentration is preferably carried out under vacuum conditions. The present application does not have special limitations on the vacuum degree of the vacuum conditions and the time of concentration, and any technical solution known to those skilled in the art can be used.

[0057] The present application does not have special limitations on the temperature and time of drying, and any technical solution known to those skilled in the art can be used.

[0058] The carbon dots prepared from polyethyleneimine and thiamine hydrochloride have both fluorescence and phosphorescence properties, high fluorescence intensity and long phosphorescence afterglow time.

[0059] The application also provides the fluorescent carbon dots with room-temperature phosphorescence prepared by the preparation method.

[0060] The carbon dots prepared by the application are yellow solids in a highly dispersed spherical shape, have uniform size, an average particle size of about 4.28 nm, are soluble in water to form a uniform transparent yellow solution, have a positive surface charge state under different pH conditions, a zeta potential value of +19.07 mV under the condition of pH=2.87 aqueous solution, show blue fluorescence under a 365 nm lamp, an optimal excitation wavelength of 335 nm, an emission wavelength of 458 nm, and green phosphorescence emission at 525 nm, and have a phosphorescence intensity decreasing with increasing temperature, a temperature reversibility of 20-80 DEG C, stable light-emitting performance, good excitation wavelength independence and spectral stability, a fluorescence quantum yield of 18.87%, and film-forming property.

[0061] The application also provides application of the fluorescent carbon dots with room-temperature phosphorescence in preparation of luminescent materials, biological medicines, optoelectronic devices and sensors.

[0062] In the application, the luminescent material preferably comprises carbon dot boron oxide composite materials or carbon dot polymer composite films.

[0063] The application is not specially limited to the preparation method of the carbon dot boron oxide composite materials or carbon dot polymer composite films, and a technical solution known to those skilled in the art can be used.

[0064] In the embodiment of the application, the preparation method of the carbon dot boron oxide composite material is as follows: 2.0 g of boric acid is dissolved in 40 mL of ultrapure water, then 2 mL of a carbon dot aqueous solution with a concentration of 60 mg / mL is added, ultrasonic mixing is performed for 10 min, an aluminum foil is used to cover the mouth of the beaker, the beaker is placed in an oven at 180 DEG C for heating for 5 h, and natural cooling is performed to room temperature to obtain an amorphous glassy carbon dot boron oxide composite material.

[0065] In the embodiment of the application, the preparation method of the carbon dot polymer composite film is as follows: 1 g of PVA is weighed in a dry beaker, 1 mL of a carbon dot aqueous solution with a concentration of 60 mg / mL is added, ultrapure water is used to make up to 10 mL, stirring is performed in a 90 DEG C water bath for 30 min until the PVA is completely dissolved, the mixture is uniformly mixed until the bubbles disappear, the mixture is poured on a film preparation glass plate, a film with a thickness of 0.05 mm is prepared by using an adjustable film preparation device, the film preparation glass plate is placed in an oven for drying at 35 DEG C for 2 h, and cooling is performed to form a carbon dot polymer composite film.

[0066] The carbon dot aqueous solution prepared by the application has positive zeta potential and can be dispersed in an anionic polymer solution, and is used for preparing a carbon dot polymer composite film.

[0067] The carbon dots prepared by the application have excellent luminescent performance, and the prepared luminescent material also has excellent luminescent performance.

[0068] The technical solutions in the application will be clearly and completely described below in combination with the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0069] Embodiment 1

[0070] (1) 0.5 g of polyethyleneimine (PEI) with a weight average molecular weight of 1800, 0.08 g of thiamine hydrochloride (TH) and water were mixed (the mass ratio of polyethyleneimine and thiamine hydrochloride was 0.5:0.08, and the mass ratio of polyethyleneimine and water was 1:30), and then placed in an ultrasonic oscillator until completely dissolved. Then, a sodium hydroxide solution was used to adjust the pH value to 8, to obtain a mixed solution;

[0071] (2) The mixed solution was transferred and sealed in the inner liner of a reaction kettle polytetrafluoroethylene, and then placed in an oven at 180 DEG C for 14 h. After the reaction, the product was filtered by using a 0.45 μm water-based filter membrane needle filter, to obtain a yellow and clear carbon dot solution. After 500 Da permeable membrane dialysis for 48 h and 80 DEG C vacuum concentration, freeze-drying was performed to obtain a yellow paste solid, which was fluorescent carbon dots with room temperature phosphorescence performance, and was recorded as PEI-TH-CPDs.

[0072] Embodiment 2

[0073] In the embodiment 1 step (1), the weight average molecular weight of polyethyleneimine was replaced by 600, and other parameters were the same as those in the embodiment 1.

[0074] Embodiment 3

[0075] In the embodiment 1 step (1), the weight average molecular weight of polyethyleneimine was replaced by 10000, and other parameters were the same as those in the embodiment 1.

[0076] Embodiment 4

[0077] In the embodiment 1 step (1), the weight average molecular weight of polyethyleneimine was replaced by 70000, and other parameters were the same as those in the embodiment 1.

[0078] The carbon dot solutions prepared in the embodiments 1-4 were subjected to fluorescence spectrum scanning, and the results were as follows:Figure 1 The results are shown in Table 1. It can be seen from Table 1 that the fluorescence intensity is the highest when the weight average molecular weight of the polyethyleneimine is 1800. Figure 1

[0079] Example 5

[0080] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.02 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.02 at this time, and other parameters are the same as those in Example 1.

[0081] Example 6

[0082] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.04 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.04 at this time, and other parameters are the same as those in Example 1.

[0083] Example 7

[0084] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.16 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.16 at this time, and other parameters are the same as those in Example 1.

[0085] Example 8

[0086] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.32 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.32 at this time, and other parameters are the same as those in Example 1.

[0087] Example 9

[0088] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.35 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.35 at this time, and other parameters are the same as those in Example 1.

[0089] The carbon dot solution prepared in Examples 1, 5-9 is subjected to fluorescence spectrum scanning, and the results are shown in Table 1. It can be seen from Table 1 that the fluorescence intensity is the highest when the amount of polyethyleneimine is 0.5 g, the amount of thiamine hydrochloride is 0.08 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.08. Figure 2 Figure 2

[0090] Example 10

[0091] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.4 g, and the mass ratio of polyethyleneimine to thiamine hydrochloride is 0.5:0.4 at this time, and other parameters are the same as those in Example 1.

[0092] Example 11

[0093] ​​​The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.48 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:0.48, and other parameters are the same as those in Example 1.

[0094] Example 12

[0095] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.5 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:0.5, and other parameters are the same as those in Example 1.

[0096] Example 13

[0097] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.55 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:0.55, and other parameters are the same as those in Example 1.

[0098] Example 14

[0099] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.64 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:0.64, and other parameters are the same as those in Example 1.

[0100] Example 15

[0101] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 0.8 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:0.8, and other parameters are the same as those in Example 1.

[0102] Example 16

[0103] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 1.12 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:1.12, and other parameters are the same as those in Example 1.

[0104] Example 17

[0105] The amount of thiamine hydrochloride in step (1) of Example 1 is replaced by 1.6 g, at this time the mass ratio of polyethyleneimine and thiamine hydrochloride is 0.5:1.6, and other parameters are the same as those in Example 1.

[0106] Example 18

[0107] The pH value of the mixed solution in step (1) of Example 1 is replaced by 5, and other parameters are the same as those in Example 1.

[0108] Example 19

[0109] The pH value of the mixed solution in step (1) of Example 1 is replaced by 6, and other parameters are the same as those in Example 1.

[0110] Example 20

[0111] The pH value of the mixed solution in step (1) of Example 1 was replaced with 7, and the other parameters were the same as those in Example 1.

[0112] Example 21

[0113] The pH value of the mixed solution in step (1) of Example 1 was replaced with 9, and the other parameters were the same as those in Example 1.

[0114] Example 22

[0115] The pH value of the mixed solution in step (1) of Example 1 was replaced with 10, and the other parameters were the same as those in Example 1.

[0116] Fluorescence spectrum scanning was performed on the carbon dot solutions prepared in Examples 1 and 18 to 22. The results were as follows: Figure 3 As shown. Figure 3 It can be seen that the fluorescence intensity is highest when the pH value of the mixed solution is 8.

[0117] Example 23

[0118] The reaction time in step (2) of Example 1 was replaced by 2 h, and the other parameters were the same as those in Example 1.

[0119] Example 24

[0120] The reaction time in step (2) of Example 1 was replaced by 4 h, and the other parameters were the same as those in Example 1.

[0121] Example 25

[0122] The reaction time in step (2) of Example 1 was replaced with 6 h, and the other parameters were the same as those in Example 1.

[0123] Example 26

[0124] The reaction time in step (2) of Example 1 was replaced by 7 h, and the other parameters were the same as those in Example 1.

[0125] Example 27

[0126] The reaction time in step (2) of Example 1 was replaced with 8 h, and the other parameters were the same as those in Example 1.

[0127] Example 28

[0128] The reaction time in step (2) of Example 1 was replaced with 10 h, and the other parameters were the same as those in Example 1.

[0129] Example 29

[0130] The reaction time in step (2) of Example 1 was replaced with 12 h, and the other parameters were the same as those in Example 1.

[0131] Example 30

[0132] The reaction time in step (2) of Example 1 was replaced with 16 h, and the other parameters were the same as those in Example 1.

[0133] Fluorescence spectrum scanning was performed on the carbon dot solutions prepared in Examples 1 and 23 to 30. The results are as follows: Figure 4 As shown. Figure 4 It can be seen that the fluorescence intensity is the highest when the reaction time is 14 h.

[0134] Example 31

[0135] The reaction temperature in step (2) of Example 1 was replaced with 120° C., and the other parameters were the same as those in Example 1.

[0136] Example 32

[0137] The reaction temperature in step (2) of Example 1 was replaced with 140° C., and the other parameters were the same as those in Example 1.

[0138] Example 33

[0139] The reaction temperature in step (2) of Example 1 was replaced with 160° C., and the other parameters were the same as those in Example 1.

[0140] Example 34

[0141] The reaction temperature in step (2) of Example 1 was replaced with 200° C., and the other parameters were the same as those in Example 1.

[0142] Fluorescence spectrum scanning was performed on the carbon dot solutions prepared in Examples 1 and 31 to 34. The results are as follows: Figure 5 As shown. Figure 5 It can be seen that the fluorescence intensity is highest when the reaction temperature is 180℃.

[0143] Comparative Example 1

[0144] The thiamine hydrochloride in step (1) of Example 1 was replaced by phthalic acid, and the other parameters were the same as those in Example 1.

[0145] Comparative Example 2

[0146] The thiamine hydrochloride in step (1) of Example 1 was replaced by thioglycolic acid, and the other parameters were the same as those in Example 1.

[0147] Comparative Example 3

[0148] The thiamine hydrochloride in step (1) of Example 1 is replaced by cystine, and other parameters are the same as those of Example 1.

[0149] Comparative Example 4

[0150] The thiamine hydrochloride in step (1) of Example 1 is replaced by sulfuric acid, and other parameters are the same as those of Example 1.

[0151] Comparative Example 5

[0152] The thiamine hydrochloride in step (1) of Example 1 is replaced by citric acid, and other parameters are the same as those of Example 1.

[0153] The carbon dot solution prepared in Example 1 and Comparative Examples 1-4 is subjected to fluorescence spectrum scanning, and the results are shown in Table 1. Figure 6 As can be seen from Table 1, the carbon dots prepared in Example 1 using thiamine hydrochloride as raw material have the highest fluorescence intensity. Figure 6 The carbon dot solution prepared in Example 1 is diluted 10 times with purified water, and the fluorescence emission spectrum and fluorescence excitation spectrum in the scanning range of 220-650 nm are determined, and the results are shown in Table 2.

[0154] Figure 7

[0155] The carbon dot solution prepared in Example 1 is diluted 100 times with purified water, and the ultraviolet absorption spectrum in the range of 200-600 nm is scanned with purified water as a reference, and the solution photos under sunlight and 365 nm ultraviolet light are taken, and the results are shown in Table 3. Figure 8 As can be seen from Table 3, the carbon dot aqueous solution has a stable blue fluorescence emission signal at 458 nm under excitation at a wavelength of 335 nm. Figures 7-8

[0156] The carbon dot solution prepared in Example 1 is dialyzed for 24 h through a 500 Da osmotic membrane, and the dialysate is dropped onto a copper mesh with a porous carbon film, and then naturally dried, and the morphology and structure thereof are characterized by field emission transmission electron microscopy, and the transmission scanning electron microscope image obtained is shown in Table 4. Figure 9

[0157] The carbon dot solution prepared in Example 1 is dialyzed for 24 h through a 500 Da osmotic membrane, and the transmission scanning electron microscope image thereof is determined, and the particle size distribution is analyzed by using Nano Measurer software, and the particle size distribution graph obtained is shown in Table 5. Figure 10

[0158] As can be seen from Table 5, the carbon dots are in a highly dispersed spherical-like state, and the size is relatively uniform, and the average particle size is about 4.28 nm. Figures 9-10

[0159] ​​​​​​The carbon dot solution prepared in Example 1 was diluted 10 times with purified water, and the excitation wavelength was changed to 290-380 nm. The fluorescence spectra at different excitation wavelengths were measured. The results are as follows: Figure 11 As shown, Figure 11 The corresponding emission wavelength and intensity change curve is as follows Figure 12 shown.

[0160] Take 1 mL of the carbon dot solution prepared in Example 1, dilute it 10 times with purified water, and irradiate it under a UV lamp at 365 nm. Scan the optimal excitation wavelength and the optimal emission wavelength every 5 minutes. Measure continuously for 1 hour. The results are as follows: Figure 13 shown.

[0161] 400 μL of the carbon dot solution prepared in Example 1 was added to each of 12 10 mL centrifuge tubes. 1.2 mL of prepared BR buffer solutions with different pH values ​​(pH = 1.81, 2.87, 3.78, 4.78, 5.72, 6.80, 7.96, 8.95, 9.91, 10.88, 11.82) and aqueous solutions were added to each centrifuge tube. The fluorescence spectra of the carbon dots under different pH buffer solutions and aqueous solutions are shown in Figure 3. Figure 14 As shown. Figures 11-14 As can be seen from the figure, the carbon dot solution prepared by the present invention exhibits stable fluorescence emission under different pH solution environments and different irradiation times of 365nm light source. It also exhibits stable fluorescence emission under excitation of different light sources with wavelengths of 290-380nm, with the emission peak position at 458nm.

[0162] Application Example 1

[0163] 2.0 g of boric acid was dissolved in 40 mL of ultrapure water, and then 2 mL of a 60 mg / mL aqueous solution of carbon dots prepared in Example 1 was added. The mixture was ultrasonically mixed for 10 min. The mouth of the beaker was covered with aluminum foil, and the mixture was placed in an oven at 180°C and heated for 5 h. The mixture was naturally cooled to room temperature to obtain an amorphous glassy carbon dot-boron oxide composite material, which was designated as PEI-thiamine hydrochloride CPDs@B2O3.

[0164] Comparative Application Example 1

[0165] The carbon dot aqueous solution in Application Example 1 was replaced with pure water to obtain B2O3.

[0166] Comparative Application Example 2

[0167] The aqueous solution of carbon dots prepared in Example 1 in Application Example 1 was replaced with the aqueous solution of carbon dots prepared in Comparative Example 1, and other parameters were the same as those in Application Example 1 to obtain PEI-phthalic acid CPDs@B2O3.

[0168] Comparative Application Example 3

[0169] The water solution of carbon dots prepared in Example 1 in Application Example 1 was replaced by the water solution of carbon dots prepared in Comparative Example 2, and other parameters were the same as in Application Example 1, to obtain PEI-thioglycolic acid CPDs@B2O3.

[0170] Comparative Application Example 4

[0171] The water solution of carbon dots prepared in Example 1 in Application Example 1 was replaced by the water solution of carbon dots prepared in Comparative Example 3, and other parameters were the same as in Application Example 1, to obtain PEI-cystine CPDs@B2O3.

[0172] Comparative Application Example 5

[0173] The water solution of carbon dots prepared in Example 1 in Application Example 1 was replaced by the water solution of carbon dots prepared in Comparative Example 4, and other parameters were the same as in Application Example 1, to obtain PEI-sulfuric acid CPDs@B2O3.

[0174] Comparative Application Example 6

[0175] The water solution of carbon dots prepared in Example 1 in Application Example 1 was replaced by the water solution of carbon dots prepared in Comparative Example 5, and other parameters were the same as in Application Example 1, to obtain PEI-citric acid CPDs@B2O3.

[0176] Comparative Application Example 7

[0177] The water solution of carbon dots prepared in Example 1 in Application Example 1 was replaced by molybdenum disulfide quantum dots, and other parameters were the same as in Application Example 1, to obtain molybdenum disulfide quantum dots QDs@B2O3.

[0178] The solid of Application Example 1 was ground into powder, phosphorescence spectrum scanning was carried out at different temperatures, and afterglow videos and photos were taken under a 356 nm ultraviolet lamp, and the phosphorescence spectrum at different temperatures obtained is shown in Figure 15 , and the corresponding phosphorescence lifetime curve is shown in Figure 16 . It can be seen from Figures 15-16 that the intensity of the phosphorescence spectrum decreases with the increase of temperature, and the corresponding luminescence lifetime also decreases.

[0179] The solid of Application Example 1 was ground into powder, and repeated heating and cooling cycles were carried out at 20℃ and 80℃, and the phosphorescence spectrum is shown in Figure 17 . It can be seen from Figure 17 that the composite material prepared by the carbon dots has temperature reversibility of 20-80℃.

[0180] The solid of Application Example 1 was ground into powder, and irradiated under visible light, 254 nm and 365 nm ultraviolet light for 2 s, respectively, and then the afterglow pictures at different light-off times were taken after the light was turned off, and the results are shown in Figure 18 . It can be seen from Figure 18As can be seen from the table, the composite material prepared from the carbon dots can continuously emit room temperature phosphorescence for nearly 7s after the 365nm ultraviolet lamp is turned off for 2s.

[0181] The solids in application example 1 and comparative application examples 1-7 were ground into powder, and the phosphorescence pictures under different light-off times were taken after irradiation for 2s under a 365nm ultraviolet lamp, and the results are shown in Figure 19 Figure 19 As can be seen from the table, the phosphorescence time of the composite material prepared from the carbon dots is longer.

[0182] Application Example 2

[0183] 1g of PVA was weighed into a dry beaker, 1mL of the carbon dot aqueous solution prepared in example 1 with a concentration of 60mg / mL was added, and the volume was made up to 10mL with ultrapure water. The mixture was stirred in a 90℃ water bath for 30min until the PVA was completely dissolved and the bubbles disappeared. Then the mixture was poured onto a film-making glass plate and prepared into a thin film with a film thickness of 0.05mm using an adjustable film maker. The film-making glass plate was placed in an oven and dried at 35℃ for 2h, and then cooled to form a carbon dot polymer composite thin film, which was recorded as CPDs@PVA thin film.

[0184] Comparative Application Example 8

[0185] The carbon dot aqueous solution in application example 2 was omitted to obtain a PVA thin film.

[0186] The thin films prepared in application example 2 and comparative application example 8 were cut into long strip shapes with a size of 100*16.4mm, and their tensile properties were tested, and the photos were taken under a 365nm ultraviolet lamp. The tensile stress-strain curves are shown in Figure 20 The macroscopic pictures of the thin films prepared in application example 2 and comparative application example 8 after stretching under the ultraviolet lamp and sunlight are shown in Figure 21 Figure 21 In the figure, (a) is the macroscopic picture under sunlight, and (b) is the macroscopic picture under the ultraviolet lamp. As can be seen from the figure, Figures 20-21 The tensile resistance of the thin film prepared in application example 2 is nearly 3 times higher than that of the PVA thin film.

[0187] In summary, the carbon dots prepared in the application have both fluorescence and phosphorescence properties, and have high luminous intensity and long phosphorescence afterglow time.

[0188] The above only describes the preferred embodiments of the application, and it should be noted that those of ordinary skill in the art can make several improvements and refinements without departing from the principles of the application, and these improvements and refinements should also be considered within the protection scope of the application.​​

Claims

1. A method for preparing fluorescent carbon dots with room temperature phosphorescence properties, comprising the following steps: (1) mixing polyethyleneimine, thiamine hydrochloride and water to obtain a mixed solution; (2) subjecting the mixed solution obtained in step (1) to a hydrothermal reaction to obtain fluorescent carbon dots having room temperature phosphorescence properties.

2. The preparation method according to claim 1, characterized in that The weight average molecular weight of the polyethyleneimine in the step (1) is 600 to 70,000.

3. The preparation method according to claim 1, characterized in that The mass ratio of polyethyleneimine to thiamine hydrochloride in the step (1) is 0.5: (0.02-1.6).

4. The preparation method according to claim 1, characterized in that The pH value of the mixed solution in step (1) is 5-10.

5. The preparation method according to claim 1, characterized in that The mass ratio of polyethyleneimine to water in the step (1) is 1:(20-40).

6. The preparation method according to claim 1, characterized in that The temperature of the hydrothermal reaction in step (2) is 120-200° C., and the time of the hydrothermal reaction is 2-16 hours.

7. The preparation method according to claim 6, characterized in that The temperature of the hydrothermal reaction is 180° C., and the time of the hydrothermal reaction is 14 h.

8. Fluorescent carbon dots with room temperature phosphorescence prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the fluorescent carbon dots with room temperature phosphorescence properties according to claim 8 in the preparation of luminescent materials, biomedicine, optoelectronic devices and sensors.

10. The use according to claim 9, characterized in that The luminescent material includes a carbon dot-boron oxide composite material or a carbon dot-polymer composite film.

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