Ratio-type fluorescent probe based on carbon quantum dot hybrid covalent organic framework and preparation method of ratio-type fluorescent probe

Abstract

The invention discloses a ratio type fluorescent probe based on a carbon quantum dot hybrid covalent organic framework and a preparation method thereof, and the fluorescent probe comprises nitrogen-doped biological carbon quantum dots synthesized by using waste durian shells as a carbon source, and nitrogen-doped biological carbon quantum dots synthesized by using 2, 5-bis (allyloxy) terephthaloyl hydrazide and 4 ', 5-bis (allyloxy) terephthaloyl hydrazide as a carbon source. A three-dimensional hydrazide-imine type covalent organic framework is generated through a hydrothermal reaction of 4, 4 '', 4'' '', 4'' '''-(ethylene-1, 1, 2, 2-tetrayl) tetra (([[1, 1'-biphenyl]-4-formaldehyde)), and ratio type fluorescence is synthesized through bulk polymerization. A carbon quantum dot hybrid covalent organic framework is adopted to prepare the ratio-type fluorescent probe, two fluorescence emission signals with different wavelengths are formed based on the carbon quantum dot and the covalent organic framework, errors caused by factors such as signal drift and instrument change in an experiment are reduced, a three-dimensional hydrazide-imine covalent organic framework is adopted as a substrate, and the ratio-type fluorescent probe can be prepared by using the three-dimensional hydrazide-imine covalent organic framework as a substrate. Through fluorescence resonance energy transfer between the carbon quantum dots and the carbon quantum dots, self-quenching of the carbon quantum dots is reduced, and the strong adsorption capacity of the covalent organic framework synthesized by the carbon quantum dots to a target compound is utilized.

Description

Technical Field

[0001] The present invention belongs to the field of fluorescence sensing technology, and in particular, relates to a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework and a preparation method thereof, which can be used in the field of environmental analysis and testing. Background Art

[0002] At present, the development of fluorescent nanomaterials has been widely used in the fields of sensing and bio-imaging. Carbon quantum dots, especially biomass carbon quantum dots, as a new type of fluorescent nanomaterial, have attracted widespread attention due to their low raw material cost, simple synthesis method, good biocompatibility and low toxicity. [1] In addition, its physicochemical properties can be further tuned by heteroatom doping. For example, doping carbon quantum dots with N heteroatoms can passivate their surface states, achieve a transition from excitation-related emission to excitation-independent emission, and improve their ability to detect metal ion fluorescence. [2] Studies have found that carbon quantum dots are prone to self-aggregation during use, causing fluorescence quenching. In order to improve their practical application performance, they are often doped with other materials.

[0003] Covalent organic frameworks (COFs) have attracted extensive attention due to their excellent structural tunability, high specific surface area, good chemical stability, and rich functionalization potential. Extended π-conjugation in the COF backbone can produce useful luminescent properties. [3] , is one of the potential fluorescent materials. Moreover, the high porosity of the covalent organic framework makes it an excellent carrier, which can not only effectively avoid the fluorescence quenching effect caused by the self-aggregation of carbon quantum dots, but also increase the mass transfer rate of the target compound, thereby further improving the efficiency of fluorescence detection. [4] .

[0004] Therefore, it is planned to dope the covalent organic framework material with carbon quantum dots through bulk polymerization to develop a ratiometric fluorescent probe based on covalent organic framework carbon quantum dots. This can not only maintain the excellent optical properties of quantum dots, but also regulate the surface properties of the probe through the structural advantages of the covalent organic framework and enhance the selective binding ability with the target analyte.

[0005] References

[0006] [1]TC Wareing,P.Gentile,ANPhan.Biomass-Based CarbonDots:CurrentDevelopmentandFuturePerspectives.ACSNano 15(2021)15471-15501.

[0007] [2]J.Ju,W.Chen.Synthesis of highly fluorescent nitrogen-dopedgraphene quantum dots for sensitive,label-free detection ofFe(III)inaqueousmedia.BiosensorsandBioelectronics58(2014)219-225.

[0008] [3]HWKral,MEM,WER,MPLThe luminescent and photophysicalproperties of covalent organic frameworks.Chem.Soc.Rev.49(2020)839-864.

[0009] [4] S. Wang, N. Liang, X. Hu, W. Li, Z. Guo, X. Zhang, X. Huang, Z. Li, Summary of the invention

[0010] In order to solve the complex process of sample pretreatment and instrumental analysis required in the prior art, the present invention provides a method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, which realizes the visual detection of α-dicarbonyl compounds in food.

[0011] The present invention is achieved through the following technical solutions:

[0012] The invention discloses a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework. The fluorescent probe comprises nitrogen-doped biocarbon quantum dots synthesized by using waste durian shells as a carbon source and a three-dimensional hydrazide-imine covalent organic framework generated by a hydrothermal reaction of 2,5-bis(allyloxy)terephthaloyl hydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)). The ratiometric fluorescence is synthesized by bulk polymerization, wherein the ratio of the nitrogen-doped biocarbon quantum dots to the three-dimensional hydrazide-imine covalent organic framework is 2:1-3:1.

[0013] As a further improvement, the present invention also discloses a method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, which uses carbon quantum dots and a covalent organic framework as fluorescent materials and is prepared by curing and cross-linking.

[0014] As a further improvement, the carbon quantum dots described in the present invention are nitrogen-doped carbon quantum dots generated by hydrothermal reaction of waste durian shell powder and ethylenediamine.

[0015] As a further improvement, the covalent organic framework described in the present invention is a hydrazide-imine type covalent organic framework generated by the hydrothermal reaction of 2,5-bis(allyloxy)terephthaloylhydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)).

[0016] As a further improvement, the specific preparation steps of the present invention are:

[0017] 1) ultrasonically dispersing an appropriate amount of 2,5-bis(allyloxy)terephthaloyl hydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) in toluene, and adding acetic acid to obtain a uniform reaction solution;

[0018] 2) reacting the reaction solution obtained in 1) for a period of time under sealed conditions, and centrifuging to obtain a yellow powder, which is the covalent organic framework;

[0019] 3) drying the durian peel at 80° C. overnight to remove as much moisture as possible, and then grinding the durian peel into durian peel powder;

[0020] 4) mixing the durian peel powder obtained in 3) with ethylenediamine in water, and then transferring the mixture to a reaction vessel for hydrothermal reaction at a certain temperature to obtain a light yellow solution;

[0021] 5) Centrifuging the light yellow solution obtained in step 4) at high speed to obtain carbon quantum dots;

[0022] 6) adding the covalent organic framework obtained in 2) and the carbon quantum dots obtained in 5) into ethanol, adding acrylamide after ultrasonication and stirring evenly, then adding ethylene glycol dimethacrylate and azobisisobutyronitrile, sealing under nitrogen conditions and heating and stirring.

[0023] As a further improvement, in step 1) of the present invention, the concentration of 2,5-bis(allyloxy)terephthaloylhydrazide is 9 mg / mL-10 mg / mL, the concentration of 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) is 21 mg / mL-23 mg / mL, the concentration of acetic acid is 2 mol / L-3 mol / L, the reaction temperature in step 2) is 120°C-140°C, and the reaction time is 60h-72h.

[0024] As a further improvement, in step 4) of the present invention, the concentration of the durian peel powder is 7 mg / mL-10 mg / mL, the volume ratio of ethylenediamine to water is 5:100-15:100, the reaction temperature is 160° C.-180° C., and the reaction time is 5 h-7 h.

[0025] As a further improvement, in step 6) of the present invention, the concentration of the covalent organic framework is 0.1 mg / mL-0.3 mg / mL, the concentration of the carbon quantum dots is 0.05 mg / mL-0.1 mg / mL, the concentration of acrylamide is 16 mg / mL-18 mg / mL, the volume ratio of ethylene glycol dimethacrylate to ethanol is 1:10-1.5:10, the concentration of azobisisobutyronitrile is 8 mg / mL-12 mg / mL, the reaction temperature is 150°C-170°C, and the reaction time is 20h-30h.

[0026] The present invention has the following advantages and effects:

[0027] 1. The present invention uses carbon quantum dots hybridized covalent organic framework to prepare a ratiometric ratiometric fluorescent probe, which forms two fluorescence emission signals of different wavelengths based on carbon quantum dots and covalent organic framework, thereby reducing errors caused by factors such as signal drift and instrument changes in the experiment.

[0028] 2. The present invention adopts a three-dimensional hydrazide-imine type covalent organic framework as a substrate, and reduces the self-quenching of carbon quantum dots through fluorescence resonance energy transfer between the three-dimensional hydrazide-imine type covalent organic framework and the quantum dots.

[0029] 3. 2,5-Bis(allyloxy)terephthaloylhydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) were selected as reaction monomers, and the strong adsorption ability of the synthesized covalent organic framework for the target compound was utilized to improve the detection speed of the ratiometric fluorescent probe.

[0030] 4. The present invention adopts ethylenediamine doping to prepare nitrogen-doped carbon quantum dots to improve their fluorescence response ability.

[0031] 5. The present invention uses discarded durian peel to prepare nitrogen-doped carbon quantum dots, which is green and environmentally friendly.

[0032] 6. The present invention realizes visual detection of α-dicarbonyl compounds in videos based on the color change of ratiometric fluorescent probes in α-dicarbonyl compounds of different concentrations.

[0033] 7. The present invention adopts a bulk curing method to prepare a carbon quantum dot hybrid covalent organic framework fluorescent probe, so that strong π-π conjugation and hydrogen bonds are formed between the carbon quantum dots and the covalent organic framework, thereby improving the stability of the material and extending its service life.

[0034] 8. In the process of preparing carbon quantum dots, the concentration of durian peel powder is controlled to be 7 mg / mL-10 mg / mL, the volume ratio of ethylenediamine to water is 5:100-15:100, the reaction temperature is 160°C-180°C, and the reaction time is 5h-7h, so that the synthesized nitrogen-doped carbon quantum dots have a suitable size, thereby showing the best fluorescence response value.

[0035] 9. In the preparation of fluorescent probes, the present invention controls the concentration of the covalent organic framework to 0.1 mg / mL-0.3 mg / mL, and the concentration of carbon quantum dots to 0.05 mg / mL-0.1 mg / mL, so that the final response value ratio of the fluorescent probe at 510 nm and 670 nm shows a good linear relationship with the concentration of the target and exhibits a lower detection limit. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the preparation method of ratiometric fluorescent probe based on carbon quantum dot hybrid covalent organic framework. DETAILED DESCRIPTION

[0037] The present invention discloses a method for preparing a ratio-type fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, wherein the covalent organic framework and carbon quantum dots are dispersed in ethanol, acrylamide is added and stirred for a period of time, and then ethylene glycol dimethacrylate and azobisisobutyronitrile are added, and the mixture is sealed under nitrogen conditions and heated and stirred. The ratio-type fluorescent probe based on the carbon quantum dot hybrid covalent organic framework can be obtained by washing with methanol and then drying. The specific preparation steps are as follows:

[0038] 1) ultrasonically dispersing an appropriate amount of 2,5-bis(allyloxy)terephthaloyl hydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) in toluene, adding an appropriate amount of acetic acid to obtain a uniform reaction solution, wherein the concentration of 2,5-bis(allyloxy)terephthaloyl hydrazide is 9 mg / mL-10 mg / mL, the concentration of 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) is 21 mg / mL-23 mg / mL, and the concentration of acetic acid is 2 mol / L-3 mol / L;

[0039] 2) transferring the reaction solution obtained in 1) to a reaction vessel, reacting at 120° C. for 72 h, and centrifuging to obtain a yellow powder, which is a covalent organic framework;

[0040] 3) drying the durian peel at 80° C. overnight to remove as much moisture as possible, and then grinding the durian peel into durian peel powder;

[0041] 4) mixing the durian peel powder obtained in 3) with ethylenediamine in water, then transferring to a reactor, and hydrothermally reacting at 180° C. for 5 h to obtain a light yellow solution, wherein the concentration of the durian peel powder is 7 mg / mL-10 mg / mL, and the volume ratio of ethylenediamine to water is 5:100-15:100;

[0042] 5) The solution obtained in step 4) was centrifuged at 10000 r / min for 20 min, and then dried at 60 degrees Celsius to obtain nitrogen-doped carbon quantum dots.

[0043] 6) The covalent organic framework obtained in step 2) and the carbon quantum dots obtained in step 5) are added to ethanol, ultrasonicated for 10 minutes, stirred for 30 minutes after adding acrylamide, and then ethylene glycol dimethacrylate and azobisisobutyronitrile are added, and the mixture is sealed and heated and stirred under nitrogen conditions. The concentration of the covalent organic framework is 0.1 mg / mL-0.3 mg / mL, the concentration of the carbon quantum dots is 0.05 mg / mL-0.1 mg / mL, the concentration of acrylamide is 16 mg / mL-18 mg / mL, the volume ratio of ethylene glycol dimethacrylate to ethanol is 1:10-1.5:10, the concentration of azobisisobutyronitrile is 8 mg / mL-12 mg / mL, the reaction temperature is 150°C-170°C, and the reaction time is 20h-30h.

[0044] Under 365nm ultraviolet light, the ratiometric fluorescent probe based on the carbon quantum dot hybrid covalent organic framework appears purple; if it is placed in a low concentration of α-dicarbonyl compound and then irradiated with 365nm ultraviolet light, the ratiometric fluorescent probe appears lavender or blue-gray. As the concentration of the α-dicarbonyl compound increases, the color of the ratiometric fluorescent probe turns green. This is due to the strong π-π conjugation between the target compound, the carbon quantum dot aggregate and the covalent organic framework, which limits the rotation of the covalent organic framework and enhances its fluorescence response. The detection method established using the ratiometric fluorescent probe based on the carbon quantum dot hybrid covalent organic framework can complete adsorption and fluorescence response in 15 minutes, and the detection limit for α-dicarbonyl compounds can reach 0.1μg / kg.

[0045] The detection method established using a fluorescent probe based on ionic liquid-doped covalent organic frameworks completed adsorption and fluorescence response in 18 minutes, and the detection limit for α-dicarbonyl compounds was 0.31 μg / kg.

[0046] Comparing these two fluorescent probes, it can be seen that carbon quantum dots can more effectively fill the pores of the covalent organic framework, reduce its interlayer stacking, and enhance its fluorescence properties. Therefore, the ratiometric fluorescent probe based on the carbon quantum dot hybrid covalent organic framework has a faster response speed and lower detection limit for α-dicarbonyl compounds.

[0047] As a comparison, the covalent organic framework obtained in step 2) and the carbon quantum dots obtained in step 5) were added to N, N-dimethylformamide and stirred for 2 hours to directly obtain a carbon quantum dot hybrid covalent organic framework. After adsorption-elution 4 times, the fluorescence response value of the material was reduced to 80% of the initial use value. The carbon quantum dot hybrid covalent organic framework prepared by the method of the present invention was used more than 8 times before its fluorescence response value was reduced to 80% of the initial use value. It can be seen that the bulk polymerization method can effectively hybridize carbon quantum dots to the surface of the covalent organic framework, thereby improving the stability and reusability of the material.

[0048] The detection limits of ratiometric fluorescent probes for α-dicarbonyl compounds at different covalent organic framework concentrations are shown in Table 1:

[0049] Table 1

[0050]

[0051]

[0052] As can be seen from Table 1, with the increase of the concentration of the covalent organic framework, the detection limit first decreases and then increases. This may be because the concentration of the covalent organic framework is too high, the quantum dots cannot effectively fill its pores, its interlayer stacking is serious, and the degree of self-quenching increases, so the ratio of the emission spectrum intensity at 510nm and 670nm decreases. From the data in Table 1, it can be seen that the fluorescent probe prepared when the concentration of the covalent organic framework is 0.1mg / mL-0.3mg / mL has a lower detection limit and higher practical application value.

[0053] The emission peak intensity results of the ratiometric fluorescent probe at 510nm and 670nm under different nitrogen-doped carbon quantum dot concentrations are shown in Table 2:

[0054] Table 2

[0055]

[0056] It can be seen from Table 2 that with the increase of carbon quantum dot concentration, the emission peak intensity of the ratiometric fluorescent probe at 510nm remains basically unchanged, and the emission peak at 670nm first increases and then remains unchanged. According to the experimental results, it can be seen that the carbon quantum dot concentration is best in the range of 0.05mg / mL-0.1mg / mL.

[0057] The technical solution of the present invention is further described below in conjunction with the accompanying drawings:

[0058] The present invention prepares a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, and realizes the visual detection of α-dicarbonyl compounds in food through the specific adsorption of the covalent organic framework on α-dicarbonyl compounds and the dual fluorescence response of the covalent organic framework and carbon quantum dots.

[0059] Figure 1 The figure is a schematic diagram of a preparation method of a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework. The specific preparation process is as follows:

[0060] 18 mg of 2,5-bis(allyloxy)terephthaloyl hydrazide and 42 mg of 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) were ultrasonically dispersed in 2 mL of toluene, and 1 mL of 6 mol / L acetic acid was added to obtain a uniform reaction solution, which was then transferred to a reactor and reacted at 120°C for 72 h. Yellow powder was obtained by centrifugation, which was the covalent organic framework. Durian peel was dried at 80°C overnight to remove as much moisture as possible, and then ground into durian peel powder. 200 mg of durian peel powder and 2.5 mL of ethylenediamine were mixed in 25 mL of water, and then Transfer the reaction vessel and perform hydrothermal reaction at 180°C for 5 hours to obtain a light yellow solution. Centrifuge at 10,000 r / min for 20 minutes and then dry at 60 degrees Celsius to obtain nitrogen-doped carbon quantum dots. Add 1.0 mg of the covalent organic framework and 0.35 mg of carbon quantum dots to 5 mL of ethanol, ultrasonicate for 10 minutes, add 85 mg of acrylamide and stir for 30 minutes, then add 0.6 mL of ethylene glycol dimethacrylate and 50 mg of azobisisobutyronitrile, seal and heat at 160°C under nitrogen conditions with stirring for 24 hours, centrifuge, wash 3 times with methanol and dry to obtain a ratiometric fluorescent probe based on the carbon quantum dot hybrid covalent organic framework.

[0061] Finally, it should be noted that the above examples are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, characterized in that: The fluorescent probe comprises nitrogen-doped biocarbon quantum dots synthesized by using discarded durian shells as a carbon source and a three-dimensional hydrazide-imine type covalent organic framework generated by a hydrothermal reaction of 2,5-bis(allyloxy)terephthaloyl hydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)), and a ratio-type fluorescence is synthesized by bulk polymerization, wherein the ratio of the nitrogen-doped biocarbon quantum dots to the three-dimensional hydrazide-imine type covalent organic framework is 2:1-3:

1.

2. A method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework, characterized in that: Carbon quantum dots and covalent organic frameworks are used as fluorescent materials, and a ratiometric fluorescent probe based on carbon quantum dots hybridized covalent organic framework is prepared by curing and cross-linking.

3. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 1, characterized in that: The carbon quantum dots are nitrogen-doped carbon quantum dots generated by hydrothermal reaction of waste durian shell powder and ethylenediamine.

4. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 2 or 3, characterized in that: The covalent organic framework is a hydrazide-imine type covalent organic framework generated by the hydrothermal reaction of 2,5-bis(allyloxy)terephthaloylhydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)).

5. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 4, characterized in that: The specific preparation steps are: 1) ultrasonically dispersing an appropriate amount of 2,5-bis(allyloxy)terephthaloyl hydrazide and 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) in toluene, and adding acetic acid to obtain a uniform reaction solution; 2) reacting the reaction solution obtained in 1) for a period of time under sealed conditions, and centrifuging to obtain a yellow powder, which is the covalent organic framework; 3) drying the durian peel at 80° C. overnight to remove as much moisture as possible, and then grinding the durian peel into durian peel powder; 4) mixing the durian peel powder obtained in 3) with ethylenediamine in water, and then transferring the mixture to a reaction vessel for hydrothermal reaction at a certain temperature to obtain a light yellow solution; 5) Centrifuging the light yellow solution obtained in step 4) at high speed to obtain carbon quantum dots; 6) adding the covalent organic framework obtained in 2) and the carbon quantum dots obtained in 5) into ethanol, adding acrylamide after ultrasonication and stirring evenly, then adding ethylene glycol dimethacrylate and azobisisobutyronitrile, sealing under nitrogen conditions and heating and stirring.

6. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 5, characterized in that: In the step 1), the concentration of 2,5-bis(allyloxy)terephthaloylhydrazide is 9 mg / mL-10 mg / mL, the concentration of 4',4"',4""',4"""'-(ethylene-1,1,2,2-tetrayl)tetrakis(([[1,1'-biphenyl]-4-carboxaldehyde)) is 21 mg / mL-23 mg / mL, the concentration of acetic acid is 2 mol / L-3 mol / L, the reaction temperature in step 2) is 120°C-140°C, and the reaction time is 60h-72h.

7. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 6, characterized in that: In the step 4), the concentration of the durian peel powder is 7 mg / mL-10 mg / mL, the volume ratio of ethylenediamine to water is 5:100-15:100, the reaction temperature is 160° C.-180° C., and the reaction time is 5 h-7 h.

8. The method for preparing a ratiometric fluorescent probe based on a carbon quantum dot hybrid covalent organic framework according to claim 5, 6 or 7, characterized in that: In the step 6), the concentration of the covalent organic framework is 0.1 mg / mL-0.3 mg / mL, the concentration of the carbon quantum dots is 0.05 mg / mL-0.1 mg / mL, the concentration of acrylamide is 16 mg / mL-18 mg / mL, the volume ratio of ethylene glycol dimethacrylate to ethanol is 1:10-1.5:10, the concentration of azobisisobutyronitrile is 8 mg / mL-12 mg / mL, the reaction temperature is 150°C-170°C, and the reaction time is 20h-30h.

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