CN112779007A - N, S-doped carbon quantum dot based on choline ionic liquid and preparation method thereof - Google Patents
N, S-doped carbon quantum dot based on choline ionic liquid and preparation method thereof Download PDFInfo
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Abstract
The invention discloses an N, S doped carbon quantum dot based on choline ionic liquid and a preparation method thereof. The preparation method is simple and rapid, the raw materials are not easy to volatilize, the environment is friendly, and the prepared carbon quantum dots have the advantages of uniform particle size distribution, high fluorescence intensity and good stability, and have good development prospect in rapid analysis and detection.
Description
Technical Field
The invention relates to a preparation method of a carbon quantum dot, in particular to an N, S doped carbon quantum dot based on choline ionic liquid and a preparation method thereof.
Background
Carbon Quantum Dots (CQDs) are carbon-based zero-dimensional materials. The carbon quantum dots have the characteristics of excellent optical properties, good water solubility, environmental friendliness, good biocompatibility and the like, and have the advantages of wide sources of preparation raw materials and low synthesis cost. The carbon quantum dot has good application prospects in the fields of biological imaging, environmental monitoring, fluorescent probes, catalyst preparation, heavy metal, organic pollutant and pesticide residue detection and the like.
Since the first discovery of carbon quantum dots, various methods for preparing carbon quantum dots have been reported, and are classified into two major types, i.e., a "top-down" method and a "bottom-up" method. The "top-down" synthesis method refers to a method of physically or chemically stripping a large-size carbon source to obtain a small-size carbon quantum dot, and generally decomposing a carbon-rich substance by means of arc discharge, laser ablation, electrochemical synthesis and the like to finally form the carbon quantum dot. The "bottom-up" synthesis method is opposite to the "top-down" synthesis method in that carbon quantum dots are synthesized from a carbon material having a very small size such as a molecular or ionic state. The synthesis method from bottom to top includes chemical oxidation, combustion, hydrothermal synthesis, microwave synthesis, template method, etc.
Chinese patent CN104059644A discloses a simple and rapid preparation method of nitrogen-doped carbon quantum dots, which adopts alcamines organic matters as raw materials to prepare the carbon quantum dots by pyrolysis, and the method has short preparation time and high yield. Chinese patent CN107746710A discloses a carbon nitride quantum dot and its preparation method and application, wherein the carbon quantum dot is prepared by high temperature cracking method using raw materials containing carbon and nitrogen such as melamine as precursor, and the method also belongs to simple and rapid preparation method. However, the carbon quantum dots prepared by the high temperature cracking method have unsatisfactory dispersibility, uneven particle size distribution, weak fluorescence intensity and poor stability.
Disclosure of Invention
In view of the problems in the prior art, the invention provides an N, S doped carbon quantum dot based on choline ionic liquid and a preparation method thereof, wherein the choline ionic liquid and the thio-betaine compound which are environment-friendly and biocompatible are used as raw materials, and the carbon quantum dot is prepared by combining a high-temperature cracking method and a chemical oxidation method, so that the carbon quantum dot with uniform particle size distribution, strong fluorescence characteristic and good stability is obtained.
In order to achieve the technical purpose, the invention provides the following technical scheme:
a preparation method of N, S doped carbon quantum dots based on choline ionic liquid comprises the following steps:
mixing choline ionic liquid with a thio-betaine compound, adding water for dissolving, drying after mixing uniformly, and carrying out pyrolysis at the temperature of 350-400 ℃ for 2-3h under an anaerobic condition to obtain a solid mixture; and adding aqueous hydrogen peroxide solution, carrying out ultrasonic treatment, centrifuging, taking supernatant, filtering, dialyzing, and carrying out vacuum freeze drying to obtain the N and S doped carbon quantum dots based on the choline ionic liquid.
Further, the choline ionic liquid is one of D-choline tartrate, L-choline tartrate, choline dihydrogen citrate and choline bitartrate.
Further, the sulfobetaine compound is sulfobetaine 8 or sulfobetaine 10.
Furthermore, the molar ratio of the choline ionic liquid to the thio-betaine compound is 1 (1-1.2).
Further, the mass volume ratio of the solid mixture to the aqueous hydrogen peroxide solution is (30-50) mg (40-50) ml.
Further, the aqueous hydrogen peroxide solution has a volume concentration of 50%.
Further, the ultrasonic time is 2-5 h.
Further, the rotation speed during centrifugation is 10000-12000r/min, and the centrifugation time is 5-15 min.
Further, the dialysis conditions are: the specification of the dialysis bag is more than or equal to 1000Da, the dialysis time is 24h, and water is changed every 4 h.
Furthermore, the freeze drying condition is that the temperature is-40 ℃ to-45 ℃ and the time is 10-12 h.
The invention also provides the N, S doped carbon quantum dot based on the choline ionic liquid prepared by the preparation method.
Compared with the prior art, the invention has the beneficial effects that:
the invention takes the mixture of the choline ionic liquid and the thio-betaine compound as a precursor, the choline ionic liquid has the characteristics of difficult volatilization, difficult combustion, chemical and thermodynamic stability, no environmental pollution is generated in the preparation of the carbon quantum dot, and the prepared carbon quantum dot has high fluorescence intensity, long fluorescence service life and good stability, is doped with the thio-betaine compound and can be used for preparing the carbon quantum dot doped with N and S heteroatoms. The invention combines the high-temperature cracking method and the oxidation method, overcomes the defects that the carbon quantum dots are prepared only by the high-temperature cracking method, the higher fluorescence emission intensity can be obtained only under extreme preparation conditions, and the quantum yield is reduced along with the overhigh cracking temperature, and the quantum dots with high fluorescence intensity can be prepared at the cracking temperature of 350-400 ℃ by combining the high-temperature cracking method and the oxidation method. The two methods are combined, and the problem of poor hydrophilicity of the prepared quantum dots exists, so the method adopts the hydrogen peroxide aqueous solution for oxidation after high-temperature cracking, the oxidation condition is relatively mild, the oxidation is carried out in a homogeneous solution, the prepared quantum dots have good hydrophilicity, the prepared quantum dots do not precipitate in the aqueous solution, the dispersity and the granularity uniformity (the granularity is less than 10nm) of the carbon quantum dots are also improved, the high-purity N and S doped carbon quantum dots can be obtained after purification and drying, the preparation process of the carbon quantum dots is simplified, the cost is reduced, and the method is simpler, more convenient and more feasible.
The carbon quantum dots prepared by the method are green and nontoxic, the biocompatibility is good, and the maximum emission peak is about 480 nm. And the fluorescent material has the characteristics of high fluorescence, stable fluorescence intensity, long service life, good dispersibility in aqueous solution, uniform particle size distribution and good application potential in organic pollutant analysis and detection.
Drawings
FIG. 1 is a graph showing fluorescence intensities of carbon quantum dot solutions prepared in example 1 after storage for various periods of time;
FIG. 2 is a Transmission Electron Microscope (TEM) image of the carbon quantum dots prepared in example 1;
FIG. 3 is a fluorescence spectrum of carbon quantum dots prepared in example 1 at different excitation wavelengths.
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The specification and examples are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
The choline ionic liquid in the invention refers to: the cation is choline ion, such as one of D-choline tartrate, L-choline tartrate, choline dihydrogen citrate and choline bitartrate.
In the following examples:
the aqueous hydrogen peroxide solution is prepared by mixing hydrogen peroxide and water according to the volume ratio of 1:1, and the volume concentration of the obtained aqueous hydrogen peroxide solution is 50%.
Example 1
Weighing L-choline tartrate and thiobetaine 8 according to a molar ratio of 1:1 to prepare an aqueous solution, drying to remove a solvent, adding the aqueous solution into a 50ml crucible, putting the crucible into a muffle furnace, carrying out pyrolysis at 380 ℃ for 2.5h under an anaerobic condition, and taking out the crucible after cooling to obtain a solid mixture A;
adding 50mg of solid mixture A into 50ml of hydrogen peroxide aqueous solution, carrying out ultrasonic treatment for 3h, transferring the mixture solution into a centrifuge tube, centrifuging for 10min at 11000r/min, taking supernatant after the centrifugation is finished, filtering again until no solid remains on filter paper, transferring the solution obtained by filtering into a 1200Da dialysis bag after the pretreatment is finished, starting dialysis, wherein the dialysis solution is distilled water, the dialysis time is 24h, water is changed every 4h, a carbon quantum dot solution is obtained after the dialysis is finished, and carrying out freeze drying for 11h at-45 ℃ to obtain the N, S doped carbon quantum dots based on the choline ionic liquid.
The prepared carbon quantum dot solution is kept still at-4 ℃ for more than 30 days, and no insoluble substances are separated out and no significant change in fluorescence intensity is observed every day (see figure 1), and as can be seen from figure 1: the carbon quantum dots prepared by the method have longer fluorescence lifetime.
The result of transmission electron microscope analysis of the N, S doped carbon quantum dots based on the choline ionic liquid prepared in this example is shown in fig. 2, which shows that the carbon quantum dots have uniform particle size distribution and good dispersibility.
Fluorescence spectrum analysis was performed on the N, S-doped carbon quantum dots based on the choline ionic liquid prepared in this example, and the results of fluorescence spectra of the prepared carbon quantum dots with excitation wavelengths of 360nm,380nm,400nm and 420nm are shown in fig. 3. It can be seen from the figure that different excitation wavelengths can significantly affect the emission wavelength and fluorescence intensity of the carbon quantum dots, wherein the emission peak is maximum when the excitation wavelength is 400nm, which can reach about 480nm, and the fluorescence intensity emitted by the quantum dots is maximum when the excitation wavelength is at this wavelength.
Example 2
Weighing choline bitartrate and sulfobetaine 8 according to a molar ratio of 1:1.2 to prepare an aqueous solution, drying to remove a solvent, adding the aqueous solution into a 50ml crucible, putting the crucible into a muffle furnace, carrying out pyrolysis at 350 ℃ for 2h under an anaerobic condition, and taking out after the crucible is cooled to obtain a solid mixture A;
adding 30mg of solid mixture A into 40ml of hydrogen peroxide aqueous solution, carrying out ultrasonic treatment for 3h, transferring the mixture solution into a centrifuge tube, centrifuging for 5min at 10000r/min, taking supernatant after centrifugation, filtering again until no solid remains on filter paper, transferring the solution obtained by filtering into a 1000Da dialysis bag after pretreatment, starting dialysis, wherein dialysate is distilled water, the dialysis time is 24h, water is changed every 4h, a carbon quantum dot solution is obtained after dialysis, and freeze-drying is carried out for 10h at-40 ℃ to obtain the N, S doped carbon quantum dots based on the choline ionic liquid.
Example 3
D-choline tartrate and thiobetaine 10 are mixed according to a mol ratio of 1:1.2, weighing, preparing an aqueous solution, drying to remove a solvent, adding the aqueous solution into a 50ml crucible, putting the crucible into a muffle furnace, carrying out pyrolysis at 400 ℃ for 3 hours under an anaerobic condition, and taking out the crucible after cooling to obtain a solid mixture A;
adding 45mg of solid mixture A into 45ml of hydrogen peroxide aqueous solution, carrying out ultrasonic treatment for 3h, transferring the mixture solution into a centrifuge tube, carrying out centrifugation for 15min, taking supernatant after the centrifugation is finished, filtering again until no solid remains on filter paper, transferring the solution obtained by filtering into a 1200Da dialysis bag after the pretreatment, starting dialysis, wherein the dialysis solution is distilled water, the dialysis time is 24h, water is changed every 4h, a carbon quantum dot solution is obtained after the dialysis is finished, and carrying out freeze drying for 12h at-45 ℃ to obtain the N, S doped carbon quantum dots based on the choline ionic liquid.
Example 4:
weighing 10 mol ratio of choline dihydrogen citrate and thio-betaine at 1:1 to prepare aqueous solution, drying to remove solvent, adding into a 50ml crucible, placing the crucible into a muffle furnace, calcining at 350 ℃ for 5h under anaerobic condition, and taking out after the crucible is cooled to obtain a solid mixture A.
Adding 40mg of the solid mixture A into 50ml of hydrogen peroxide solution, carrying out ultrasonic treatment for 3h, transferring the mixture solution into a centrifuge tube, centrifuging for 10min at 10000r/min, taking supernatant after the centrifugation is finished, filtering again until no solid remains on filter paper, transferring the solution obtained by filtering into a 1000Da dialysis bag after the pretreatment, and starting dialysis, wherein the dialysis solution is distilled water, the dialysis time is 24h, and water is changed every 4 h. And obtaining a carbon quantum dot solution after dialysis. And (3) carrying out freeze drying for 10h at the temperature of minus 45 ℃ to obtain the N, S doped carbon quantum dots based on the choline ionic liquid.
The carbon quantum dot solutions prepared in examples 2 to 4 were subjected to the same detection method as in example 1, and as a result, it was found that the carbon quantum dot solutions prepared in examples 2 to 4 did not cause precipitation of insoluble substances and did not cause significant change in fluorescence intensity; n, S doped carbon quantum dots based on choline ionic liquid have uniform particle size distribution and good dispersibility.
Comparative example 1
The difference from example 1 is that pyrolysis was carried out at 300 ℃.
As a result, it was found that: the prepared N, S doped carbon quantum dots based on the choline ionic liquid have uneven particle size distribution, the average particle size is more than 20nm, the fluorescence intensity of the quantum dots is obviously lower than that of the quantum dots prepared at the temperature of more than 350 ℃, and the stability is poor.
Comparative example 2
The difference from example 1 is that pyrolysis is carried out at 450 ℃.
As a result, it was found that: the fluorescence intensity of the prepared N, S doped carbon quantum dots based on the choline ionic liquid is not obviously improved, but the yield is obviously reduced, and the yield of the quantum dots is less than 0.2%.
Comparative example 3
The same as example 1 except that an aqueous hydrogen peroxide solution was prepared by mixing hydrogen peroxide with water in a volume ratio of 1:2, the resulting aqueous hydrogen peroxide solution had a volume concentration of 33%.
As a result, it was found that: the prepared N, S doped carbon quantum dots based on the choline ionic liquid have poor dispersibility and uneven particle size distribution, and the fluorescence intensity of the prepared quantum dots is obviously reduced.
Comparative example 4
The same as example 1, except that the choline-based ionic liquid and the aqueous solution of the thiobetaine-based compound were mixed in a molar ratio of 1: 2.
As a result, it was found that: the prepared N, S doped carbon quantum dots based on the choline ionic liquid have obviously weakened fluorescence intensity and reduced fluorescence lifetime.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. A preparation method of N, S doped carbon quantum dots based on choline ionic liquid is characterized by comprising the following steps:
mixing choline ionic liquid with a thio-betaine compound, adding water for dissolving, drying after mixing uniformly, and carrying out pyrolysis at the temperature of 350-400 ℃ for 2-3h under an anaerobic condition to obtain a solid mixture; and adding aqueous hydrogen peroxide solution, carrying out ultrasonic treatment, centrifuging, taking supernatant, filtering, dialyzing, and carrying out vacuum freeze drying to obtain the N and S doped carbon quantum dots based on the choline ionic liquid.
2. The method according to claim 1, wherein the choline-based ionic liquid is one of choline D-tartrate, choline L-tartrate, choline dihydrogen citrate, and choline bitartrate.
3. The method according to claim 1, wherein the thio-betaine compound is thio-betaine 8 or thio-betaine 10.
4. The preparation method according to claim 1, wherein the molar ratio of the choline-based ionic liquid to the thio-betaine-based compound is 1 (1-1.2).
5. The method according to claim 1, wherein the mass-to-volume ratio of the solid mixture to the aqueous hydrogen peroxide solution is (30-50) mg (40-50) ml.
6. The method according to claim 5, wherein the aqueous hydrogen peroxide solution has a volume concentration of 50%.
7. The method as claimed in claim 1, wherein the rotation speed during centrifugation is 10000-12000r/min, and the centrifugation time is 5-15 min.
8. The method of claim 1, wherein the dialysis conditions are: the specification of the dialysis bag is more than or equal to 1000Da, the dialysis time is 24h, and water is changed every 4 h.
9. N, S doped carbon quantum dots based on choline ionic liquids prepared according to the preparation method of any one of claims 1 to 8.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115448291A (en) * | 2022-10-13 | 2022-12-09 | 宁夏中星显示材料有限公司 | Carbon oxide quantum dot, carbon oxide quantum dot/sepiolite composite material, and preparation method and application thereof |
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- 2021-01-06 CN CN202110011046.3A patent/CN112779007A/en active Pending
Non-Patent Citations (1)
| Title |
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| HAITAO LI ET AL.: "Long lifetime photoluminescence in N, S co-doped carbon quantum dots from an ionic liquid and their applications in ultrasensitive detection of pesticides", 《CARBON》 * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115448291A (en) * | 2022-10-13 | 2022-12-09 | 宁夏中星显示材料有限公司 | Carbon oxide quantum dot, carbon oxide quantum dot/sepiolite composite material, and preparation method and application thereof |
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Application publication date: 20210511 |