CN113881428B - Method for solid-phase synthesis of high-quality fluorescent carbon dots in air by taking mesoporous molecular sieve as template - Google Patents
Method for solid-phase synthesis of high-quality fluorescent carbon dots in air by taking mesoporous molecular sieve as template Download PDFInfo
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- C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
- C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
- C09K11/65—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing carbon
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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- B—PERFORMING OPERATIONS; TRANSPORTING
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Abstract
The invention provides a method for synthesizing high-quality fluorescent carbon dots in solid phase in air by taking a mesoporous molecular sieve as a template, taking organic micromolecules as a single carbon source, filling the mesoporous molecular sieve as the template into pore channels of the molecular sieve by an impregnation method, directly heating in the air for reacting for a plurality of hours, cooling, and then extracting and eluting by water, ethanol or other solvents to collect product carbon dots. The synthesis method is simple, convenient and quick, does not need a reaction condition of a solvent and high pressure, has high safety, and is suitable for preparing a large number of carbon points with consistent size morphology, composition structure, property and function. The molecular sieve is internally provided with Lewis acid catalytic sites, so that high yield can be realized in a short time; meanwhile, the molecular sieve has good thermal stability, and can be recycled through high-temperature calcination after reaction, so that the preparation cost is greatly reduced. Ethanol or other solvents for extracting carbon points can be recycled through distillation, so that the discharge of waste liquid is reduced, and the method accords with the basic principle of green chemistry.
Description
Technical Field
The invention belongs to the field of nano material preparation, and in particular relates to a method for solid-phase synthesis of fluorescent carbon dots in air by taking a mesoporous molecular sieve as a template.
Background
The carbon dots are quasi-spherical nano particles with diameters of 1-10 nanometers and generally have photoluminescence characteristics by taking carbon elements as main components. As an emerging carbon nano luminescent material, compared with the traditional semiconductor quantum dot, the carbon dot has the unique advantages of excellent light stability, biocompatibility, low toxicity, low cost, water solubility, chemical inertness and the like, and has wide application prospects in multiple fields of biosensing, nano medicine, biological imaging, photoelectric devices, energy storage and the like. At present, the main obstacle for preventing industrialization and practical application of carbon dots is that the existing carbon dot synthesis preparation method cannot meet the practical requirements. Development of a carbon dot preparation method which is efficient, safe, environment-friendly, excellent in performance, low in cost and good in quality is a key challenge in the field.
The synthesis methods of carbon dots can be mainly classified into two types: "top-down" and "bottom-up" methods. "top-down" refers to a method of stripping carbon dots from a larger carbon block material, including graphite arc methods, laser cutting of carbon materials, electrochemical etching of graphite electrodes or carbon tube carbon cloths, oxidative strong acid decomposition of various carbon materials, and the like. "bottom-up" refers to the preparation of carbon dots from small organic molecules, polymers, biomass, etc. as raw materials by pyrolysis carbonization routes, such as combustion/pyrolysis, microwave digestion, hydrothermal/solvothermal treatment, etc. The carbon dots obtained from top to bottom have uneven particle size and inconsistent physical and chemical properties, particularly generally poor luminescence properties, and are often required to be subjected to surface chemical treatment to be stably dispersed in a solvent. Although the carbon dots with uniform particle size, controllable physical and chemical properties and excellent luminescence performance can be obtained from bottom to top, the reaction process is complex, the impurities are more, the yield and the productivity are very low, the multi-step separation and purification treatment is needed, the whole production period is long, and finally, the high-quality carbon dots are high in cost and cannot be practically applied. In addition, for the synthetic method which requires a large amount of solvent or strong acid, strong alkali and strong oxidant, no matter from top to bottom or from bottom to top, the synthetic method can cause potential safety hazard, pollute the environment and poison health.
We consider solid phase synthesis as the fundamental approach to overcome many of the disadvantages of liquid phase synthesis. However, solid phase synthesis is generally difficult to control the size of carbon dots, and the product is prone to agglomeration. In addition, it is also important to select an appropriate carbon source, and various small molecules or biomasses react in the nano space to generate separation and phase separation, so that a uniform product cannot be obtained, and a single small organic molecule carbon source is adopted, so that polymerization carbonization can be generated to form carbon points. The control of the reaction time and temperature is also important, and too low a temperature or too short a time cannot form carbon dots, and too high a temperature or too long a time results in poor light emitting performance of the carbon dots.
Disclosure of Invention
The invention aims to solve the problems and provide a novel method for solid-phase synthesis of fluorescent carbon dots in air by taking a mesoporous molecular sieve as a template, taking organic small molecules as a reaction precursor and taking a mesoporous silica molecular sieve as a template agent, so that a large amount of high-quality fluorescent carbon dots can be efficiently, safely and environmentally-friendly.
The aim of the invention is achieved by the following technical scheme:
a method for synthesizing fluorescent carbon dots in solid phase in air by using mesoporous molecular sieve as template, using small organic molecule as single carbon source, using mesoporous molecular sieve as template, filling carbon source into pore canal of mesoporous molecular sieve by impregnation method, directly heating in air for reacting for several hours, cooling, extracting and eluting, collecting fluorescent carbon dots.
According to the invention, a carbon source is filled into pore channels of the mesoporous molecular sieve, fluorescent carbon dots with various colors can be generated by heating in the air for a plurality of hours, carbon dot products with uniform particle size and high-efficiency luminescence can be obtained by extracting with water, ethanol or other organic solvents, further separation and purification are not needed, the organic solvents can be recycled through distillation, and the mesoporous molecular sieve template can be recycled through high-temperature calcination.
The method comprises the following steps:
(1) Dissolving an organic micromolecular carbon source into a solvent to form a saturated solution, filling the carbon source into pore channels of a mesoporous molecular sieve by adopting an impregnation method, and volatilizing to remove the solvent;
(2) Heating mesoporous molecular sieve powder filled with a carbon source, and naturally cooling to room temperature after the reaction is finished;
(3) Mixing the solvent with the reacted product, extracting, washing and decarbonizing the product, evaporating the solution of the carbon dots to obtain carbon dot powder, and recycling the condensed organic solvent;
(4) The used mesoporous molecular sieve is calcined in air, residues are removed, and the calcined template is reused.
The method can recycle the organic solvent and the molecular sieve template, greatly saves the cost, reduces the environmental pollution and accords with the basic principle of green chemistry. The template and the solvent which are repeatedly used can not obviously influence the quality and the yield of the final carbon dot product.
Preferably, the organic small molecule carbon source of step (1) includes, but is not limited to, saccharides, alcohols, amines, phenols, carboxylic acids, amino acids, such as phloroglucinol, o-phenylenediamine, citric acid, glutamic acid, rhodamine B, 1-aminoanthraquinone, and the like. These organics themselves must be solid at ambient temperature and have a high melting point, a high solubility in solvents, and the catalytic pyrolysis of a single carbon source can form carbon sites. The reaction temperature and time are optimized for different carbon sources, and fluorescent carbon points with yield exceeding 50%, high-efficiency luminescence and various colors can be obtained. The proper solvent extraction is selected for different carbon point products, so that not only can the yield be improved, but also the purity can be improved.
Preferably, the solvent includes, but is not limited to, methanol, ethanol, acetone, toluene, chloroform, tetrahydrofuran, and more preferably, the solvent is ethanol.
Preferably, the mesoporous molecular sieve has uniform one-dimensional pore canal, pore diameter of 2-50 nanometers and stable structure at high temperature. Lewis acid sites are usually arranged in the pore channels of the molecular sieves, so that the molecular sieves can catalyze the condensation reaction of small molecules, accelerate the formation of carbon points, and the one-dimensional pore channels are favorable for filling of carbon sources and elution of the carbon points. Because a single organic micromolecular carbon source and a molecular sieve template agent with consistent pore diameter are used, the obtained carbon dot particles are uniform, and the particle diameter error is less than 1 nanometer; the composition structure of the carbon dots is highly consistent, the fluorescence emission spectrum of the carbon dots is only single-peak, the peak width is narrow, and the carbon dots do not move along with the change of the excitation wavelength; the fluorescence of the final product is only dependent on the carbon source and the reaction conditions, and the product has high reproducibility, and the luminous wavelength can be modulated as required in the visible light region.
Preferably, the mesoporous molecular sieve comprises, but is not limited to, mesoporous silica SBA-15, and the mesoporous molecular sieve uses SBA-15 with the aperture of 8 nanometers as a template, so that the obtained carbon dots have the particle diameters of about 2.7 nanometers, the product particles are uniform, and the particle diameter error is less than 1 nanometer.
Preferably, in the step (2), the mesoporous molecular sieve powder filled with the carbon source is placed in air at 100-300 ℃ and heated for 1-10 hours, and the heating process in the air greatly simplifies the process of synthesizing carbon points and improves the production safety.
Preferably, the reaction equipment includes, but is not limited to, a forced air drying oven, an electric furnace, a muffle furnace, a tube furnace, an electric hot plate.
Preferably, the mesoporous molecular sieve in the step (4) is calcined in air at 500-700 ℃.
The operation of recycling the organic solvent and the molecular sieve template greatly saves cost, reduces environmental pollution and accords with the basic principle of green chemistry.
Compared with the prior art, the invention has the following beneficial effects:
the invention uses a single organic micromolecular carbon source and a molecular sieve template agent with consistent aperture, and the route finally obtains high-quality fluorescent carbon dots, which is specifically expressed in the following aspects:
firstly, SBA-15 with the aperture of 8 nanometers is used as a template, the grain diameter of the obtained carbon dots is about 2.7 nanometers, the product particles are uniform, the grain diameter error is less than 1 nanometer, and the index is far beyond the common carbon dot synthesis route.
Second, the composition structure of the carbon dots is highly consistent, the fluorescence emission spectrum is only single-peak, the peak width is narrow, and the carbon dots do not move along with the change of the excitation wavelength.
Third, the fluorescence of the product depends on the carbon source and the reaction conditions, the luminescence peak is randomly modulated from blue to red in the visible light region, the luminous efficiency is also selected to be different, and the reproducibility is high.
Fourth, other properties of the product, such as water solubility or alcohol solubility, may be selected based on the characteristics of the carbon source.
Fifth, this patent cannot be exemplified one by one due to thousands of alternative carbon sources, but it can be speculated that the carbon dot performance obtained using the method of the invention of this patent is extremely rich.
Drawings
FIG. 1 is a transmission electron microscope image of carbon dots prepared in example 1 of the present invention.
FIG. 2 is a high resolution transmission electron microscope image of carbon dots prepared in example 1 of the present invention.
FIG. 3 is a graph showing the particle size distribution of carbon dots prepared in example 1 of the present invention.
Fig. 4 shows fluorescence emission spectra of four typical luminescent carbon dots in the examples of the present invention, and sample A, B, C, D is the fluorescence emission spectra of the samples of example 6, example 7, example 9, and example 10, respectively.
FIG. 5 is a schematic flow chart of the carbon dot preparation method.
Detailed Description
For a better illustration of the present invention, the following description will further illustrate the present invention with reference to specific examples, example results and corresponding drawings, but the examples should not be construed as limiting the scope of the invention.
A method for solid-phase synthesis of fluorescent carbon dots in air by using mesoporous molecular sieve as template, the flow chart is shown in figure 5, and the specific steps are as follows:
(1) Dissolving an organic micromolecular carbon source into ethanol or other organic solvents to form a saturated solution, filling the carbon source into pore channels of mesoporous silica SBA-15 by adopting an impregnation method, and naturally airing.
(2) And (3) placing the SBA-15 powder filled with the carbon source into a blast drying oven at 100-300 ℃ for heating reaction for 1-10 hours. And naturally cooling to room temperature after the reaction is finished.
(3) Mixing water, ethanol or other organic solvents with the reacted product, extracting carbon dots, evaporating the solution of the carbon dots to obtain carbon dot powder, and recycling the condensed organic solvents.
(4) The used SBA-15 is calcined in the air at 500-700 ℃ for several hours, the residue in the template is removed, and the calcined template can be reused.
The following are specific examples:
example 1
0.7738 g of phloroglucinol is dissolved in 4 ml of absolute ethanol to make the concentration of the phloroglucinol in the ethanol nearly saturated, 0.5 g of SBA-15 with the aperture of 8 nanometers is added into the ethanol, and the mixture is naturally dried at room temperature. The phloroglucinol-loaded SBA-15 was then transferred to a beaker and placed in a forced air drying oven for reaction at 200℃for 6 hours. After the reaction is finished, deionized water is used for washing for a plurality of times to remove impurities. Then, SBA-15 is added into absolute ethyl alcohol, and ultrasonic dissolution is carried out, thus obtaining carbon point ethanol solution. The morphology and the optical characteristics of the ethanol solution of the carbon point are carried out, fig. 1 is a transmission electron microscope image of the prepared carbon point, fig. 2 is a high-resolution transmission electron microscope image of the prepared carbon point, fig. 3 is a particle size distribution diagram of the prepared carbon point, and the result shows that the obtained carbon point is a monodisperse spherical nanoparticle with the average particle size of 2.7 nanometers, and a wide diffraction peak corresponding to a graphite (002) plane exists near 23 degrees of an XRD pattern. The carbon dot solution has bright blue fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 480 nanometers, and the quantum yield is 56 percent.
Example 2
The preparation was the same as in example 1, except that the reaction temperature was changed to 220℃and the reaction time was changed to 8 hours, with the other conditions unchanged. The characterization of the product was essentially the same as in example 1, except that the luminescence was weakened and the quantum yield was 42%.
Example 3
The preparation was the same as in example 1, except that the reaction temperature was changed to 180℃and the reaction time was changed to 4 hours, with the other conditions unchanged. The characterization of the product was essentially the same as in example 1, except that the luminescence was weakened and the quantum yield was 41%.
Example 4
The preparation was the same as in example 1, except that the reaction temperature was changed to 160℃and the reaction time was changed to 2 hours, with the other conditions unchanged. The characterization of the product was essentially the same as in example 1, except that the luminescence was weakened and the quantum yield was 24%.
Example 5
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.6635 g of resorcinol, and the other conditions were unchanged. The characterization result of the product shows that the carbon points are monodisperse spherical nano particles, the average particle diameter is 2.7 nanometers, and diffraction peaks exist near 23 degrees of XRD patterns. The carbon dot solution has bright yellow fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 572 nanometers, and the quantum yield is 35 percent.
Example 6
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.6240 g of o-phenylenediamine, and the other conditions were unchanged. In fig. 4, a is a fluorescence emission spectrum of a carbon dot, and a characterization result of a product shows that the carbon dot is a monodisperse spherical nanoparticle, the average particle size is 2.7 nanometers, and a diffraction peak exists near 23 degrees of an XRD pattern. The carbon dot solution has bright green fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 544nm, and the quantum yield is 21%.
Example 7
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.8018 g of citric acid, and the other conditions were unchanged. In fig. 4, B is a fluorescence emission spectrum of a carbon dot, and a characterization result of the product shows that the carbon dot is a monodisperse spherical nanoparticle, the average particle diameter is 2.7 nm, and a diffraction peak exists near 23 ° of the XRD pattern. The carbon dot solution has blue fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 473 nanometers, and the quantum yield is 6%.
Example 8
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.7332 g of glutamic acid, and the other conditions were unchanged. The characterization result of the product shows that the carbon points are monodisperse spherical nano particles, the average particle diameter is 2.7 nanometers, and diffraction peaks exist near 23 degrees of XRD patterns. The carbon dot solution has blue fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 460 nanometers, and the quantum yield is 13 percent.
Example 9
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.4108 g rhodamine B, and the other conditions were unchanged. In fig. 4, C is the fluorescence emission spectrum of carbon dots, and the characterization result of the product shows that the carbon dots are monodisperse spherical nanoparticles, the average particle diameter is 2.7 nm, and diffraction peaks exist near 23 ° of the XRD pattern. The carbon dot solution has bright yellow fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 564 nanometers, and the quantum yield is 83 percent.
Example 10
The preparation was the same as in example 1, except that the starting material was changed to a saturated solution of 0.7228 g of 1-aminoanthraquinone, and the other conditions were unchanged. In fig. 4, D is a fluorescence emission spectrum of a carbon dot, and a characterization result of the product shows that the carbon dot is a monodisperse spherical nanoparticle, the average particle diameter is 2.7 nm, and a diffraction peak exists near 23 ° of the XRD pattern. The carbon dot solution has bright red fluorescence under the irradiation of an ultraviolet lamp, the fluorescence emission peak is positioned at 607 nanometers, and the quantum yield is 15 percent.
Table 1 example sample reaction materials, reaction conditions and fluorescent Property test results
| Examples | Reaction raw materials | Reaction conditions | Fluorescence emission wavelength | Fluorescence quantum yield |
| 1 | Phloroglucinol | 200℃6h | 480nm | 56％ |
| 2 | Phloroglucinol | 220℃8h | 480nm | 42％ |
| 3 | Phloroglucinol | 180℃4h | 480nm | 41％ |
| 4 | Phloroglucinol | 160℃2h | 480nm | 24％ |
| 5 | Resorcinol | 200℃6h | 572nm | 35％ |
| 6 | O-phenylenediamine | 200℃6h | 544nm | 21％ |
| 7 | Citric acid | 200℃6h | 473nm | 6％ |
| 8 | Glutamic acid | 200℃6h | 460nm | 13％ |
| 9 | Rhodamine B | 200℃6h | 564nm | 83％ |
| 10 | 1-aminoanthraquinone | 200℃6h | 607nm | 15％ |
The previous description of the embodiments is provided to facilitate a person of ordinary skill in the art in order to make and use the present invention. It will be apparent to those skilled in the art that various modifications can be readily made to these embodiments and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above-described embodiments, and those skilled in the art, based on the present disclosure, should make improvements and modifications without departing from the scope of the present invention.
Claims (7)
1. A method for synthesizing high-quality fluorescent carbon dots in solid phase in air by taking a mesoporous molecular sieve as a template is characterized in that organic micromolecules are taken as a single carbon source, the mesoporous molecular sieve is taken as the template, the carbon source is filled into pore channels of the mesoporous molecular sieve through an impregnation method, the mesoporous molecular sieve is directly heated in the air for reacting for a plurality of hours, and the fluorescent carbon dots are extracted and eluted after cooling and collected;
the mesoporous molecular sieve has uniform one-dimensional pore canal, and the aperture is 2-50 nanometers;
the mesoporous molecular sieve has stable structure at high temperature;
the mesoporous molecular sieve comprises, but is not limited to, mesoporous silica SBA-15;
the method comprises the following steps:
(1) Dissolving an organic micromolecular carbon source into a solvent to form a saturated solution, filling the carbon source into pore channels of a mesoporous molecular sieve by adopting an impregnation method, and volatilizing to remove the solvent;
(2) Heating mesoporous molecular sieve powder filled with a carbon source, and naturally cooling to room temperature after the reaction is finished;
(3) Mixing the solvent with the reacted product, extracting, washing and decarbonizing the product, evaporating the solution of the carbon dots to obtain carbon dot powder, and recycling the condensed organic solvent;
(4) The used mesoporous molecular sieve is calcined in air, residues are removed, and the calcined template is reused.
2. The method for solid-phase synthesis of fluorescent carbon dots in air using mesoporous molecular sieve as template according to claim 1, wherein the organic small molecule carbon source in step (1) includes, but is not limited to, saccharides, alcohols, amines, phenols, and carboxylic acids.
3. The method for solid phase synthesis of fluorescent carbon dots in air using mesoporous molecular sieve as template according to claim 1, wherein the solvent includes but is not limited to methanol, ethanol, acetone, toluene, chloroform, and tetrahydrofuran.
4. A method for solid phase synthesis of fluorescent carbon dots in air using mesoporous molecular sieve as template according to claim 3, wherein the solvent is ethanol.
5. The method for solid-phase synthesis of fluorescent carbon dots in air by using a mesoporous molecular sieve as a template according to claim 1, wherein the step (2) is to heat mesoporous molecular sieve powder filled with a carbon source in air at 100-300 ℃ for 1-10 hours.
6. The method for solid phase synthesis of fluorescent carbon dots in air using mesoporous molecular sieve as template according to claim 5, wherein the reaction equipment comprises but is not limited to a blast drying oven, an electric furnace, a muffle furnace, a tube furnace, and an electric plate.
7. The method for solid-phase synthesis of fluorescent carbon dots in air by using a mesoporous molecular sieve as a template according to claim 6, wherein the mesoporous molecular sieve in the step (4) is calcined at 500-700 ℃ in air.
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