CN108249425B - Method for preparing graphene quantum dots by using molecular sieve - Google Patents
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- CN108249425B CN108249425B CN201810062764.1A CN201810062764A CN108249425B CN 108249425 B CN108249425 B CN 108249425B CN 201810062764 A CN201810062764 A CN 201810062764A CN 108249425 B CN108249425 B CN 108249425B
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Abstract
The invention provides a method for preparing graphene quantum dots by using a molecular sieve, which is characterized by comprising the following steps of: step one, mixing a precursor and a molecular sieve according to a certain proportion to obtain a mixed solution; step two, treating the mixed solution by a hydrothermal method to obtain a compound; centrifuging the composition to obtain the graphene quantum dot-molecular sieve containing the graphene quantum dots; and fourthly, stirring the graphene quantum dot-molecular sieve at the temperature of 70-100 ℃, and desorbing the graphene quantum dot. The graphene quantum dots prepared by the method are uniform in size distribution, high in purity and high in quantum yield, and the problems of nonuniform particle size distribution and high impurity content of the graphene quantum dots prepared by a hydrothermal method are solved. The method is simple in process and easy to operate, and the graphene quantum dots with different particle sizes can be prepared according to actual needs.
Description
Technical Field
The invention relates to a method for preparing graphene quantum dots, in particular to a method for preparing graphene quantum dots by using a molecular sieve.
Background
The graphene quantum dots are quasi-zero-dimensional nano materials, have the size of 1-10 nm, have obvious quantum confinement effect and boundary effect, show good chemical inertness, biocompatibility and lower biotoxicity, and are applied to the fields of biological imaging, disease detection, photoelectric devices, energy correlation and the like.
The hydrothermal method is one of the commonly used preparation methods of graphene quantum dots. Compared with other preparation methods, the hydrothermal method has simple preparation process and does not need corrosive liquid such as strong acid, strong alkali and the like. However, the graphene quantum dots prepared by the hydrothermal method have the problems of uneven particle size distribution and high impurity content. This problem not only degrades the quality of the graphene quantum dots, but also affects the quantum yield of the graphene quantum dots.
Disclosure of Invention
The invention aims to solve the problems of uneven particle size distribution and high impurity content of graphene quantum dots prepared by a hydrothermal method, and aims to provide a method for preparing the graphene quantum dots by using a molecular sieve.
The invention provides a method for preparing graphene quantum dots by using a molecular sieve, which is characterized by comprising the following steps of: step one, mixing a precursor and a molecular sieve according to a certain proportion to obtain a mixed solution; step two, treating the mixed solution by a hydrothermal method to obtain a compound; centrifuging the composition to obtain the graphene quantum dot-molecular sieve containing the graphene quantum dots; and fourthly, stirring the graphene quantum dot-molecular sieve at the temperature of 70-100 ℃, and desorbing the graphene quantum dot.
The method for preparing the graphene quantum dots by using the molecular sieve provided by the invention can also have the following characteristics: wherein the pore size of the molecular sieve is any one of 3nm, 5nm, 8nm and 10 nm.
The method for preparing the graphene quantum dots by using the molecular sieve provided by the invention can also have the following characteristics: wherein the molecular sieve is any one of MCM-41 molecular sieve, SBA-15 molecular sieve and FDU-12 molecular sieve.
The method for preparing the graphene quantum dots by using the molecular sieve provided by the invention can also have the following characteristics: wherein the precursor and the molecular sieve are mixed in any mass ratio within the range of 1: 1-1: 10.
The method for preparing the graphene quantum dots by using the molecular sieve provided by the invention can also have the following characteristics: wherein the treatment temperature of the hydrothermal method is 160 ℃, and the treatment time is 15 h.
The method for preparing the graphene quantum dots by using the molecular sieve provided by the invention can also have the following characteristics: wherein, the heating mode of the step four is direct water bath heating or heating by adopting a condensing reflux mode.
Action and Effect of the invention
According to the method for preparing the graphene quantum dots by using the molecular sieve, the molecular sieve is added into the precursor, so that the graphene quantum dots obtained after the treatment by the hydrothermal method can enter the pores of the molecular sieve to form the graphene quantum dot-molecular sieve only if the pore size of the graphene quantum dots is similar to that of the molecular sieve, and thus the graphene quantum dots and impurities with other scales in the solution can be separated. And centrifuging to obtain the graphene quantum dot-molecular sieve. Graphene quantum dots in the graphene quantum dot-molecular sieve can be desorbed from the inside of pores of the molecular sieve at 70-100 ℃ so as to obtain the graphene quantum dots. Therefore, the graphene quantum dots prepared by the method are uniform in size distribution, high in purity and high in quantum yield.
The method is simple in process and easy to operate, desorption can be achieved at the low temperature of 70-100 ℃, and energy consumption is low.
Drawings
Fig. 1 is a Transmission Electron Microscope (TEM) spectrum of nitrogen-doped graphene quantum dots obtained in an example of the present invention;
fig. 2 is a fluorescence spectrum of the original nitrogen-doped graphene quantum dot in the present example and the nitrogen-doped graphene quantum dot prepared in the example.
Detailed Description
In order to make the technical means, the creation features, the achievement purposes and the effects of the present invention easy to understand, the following embodiments specifically describe the method for preparing the graphene quantum dots by using the molecular sieve in the present invention with reference to the accompanying drawings.
The method for preparing the graphene quantum dots by using the molecular sieve can be used for preparing the graphene quantum dots and can also be used for preparing element-doped graphene quantum dots. In this embodiment, the preparation of the nitrogen-doped graphene quantum dot is taken as an example for detailed description.
Step one, weighing 1g of MCM-41 molecular sieve with the average pore diameter of 3 nm.
Step two, cleaning the MCM-41 molecular sieve: firstly, 100ml of deionized water is added, and ultrasonic dispersion is carried out for 20 minutes; then 100ml of absolute ethyl alcohol is added, and ultrasonic dispersion is carried out for 20.
And step three, weighing 0.5g of precursor citric acid and 0.55g of dopant urea. Citric acid and urea were mixed and dissolved by adding 30ml of distilled water.
And step four, adding the cleaned MCM-41 molecular sieve into the dissolved citric acid and urea, stirring for 30min to obtain a mixed solution, and transferring the mixed solution into a hydrothermal reaction kettle.
And step five, treating the mixed solution in a hydrothermal reaction kettle by a hydrothermal method to obtain a composition, wherein the treatment temperature is 160 ℃, and the treatment time is 15 hours. The composition comprises nitrogen-doped graphene quantum dots-molecular sieves, nitrogen-doped graphene quantum dots of other sizes, and impurities.
And step six, centrifuging the composition to obtain the nitrogen-doped graphene quantum dot-molecular sieve containing the nitrogen-doped graphene quantum dots.
And step seven, washing the nitrogen-doped graphene quantum dot-molecular sieve by using 100ml of ethanol, and centrifuging to remove the ethanol.
And step eight, adding 30ml of distilled water into the cleaned nitrogen-doped graphene quantum dot-molecular sieve while stirring, directly heating in a water bath to 95 ℃, keeping the temperature for 5 hours, and continuously stirring during the heating period to desorb the nitrogen-doped graphene quantum dots.
In this embodiment, the average pore diameter of the molecular sieve is 3nm, and in practical applications, the average pore diameter of the molecular sieve may be any one of 5nm, 8nm and 10 nm.
In this example, the molecular sieve is MCM-41 molecular sieve, and in practical application, the molecular sieve may also be SBA-15 molecular sieve or FDU-12 molecular sieve.
In this embodiment, the mass ratio of the precursor to the MCM-41 molecular sieve is 1:2, and in practical applications, the mass ratio of the precursor to the molecular sieve may be any value within a range of 1:1 to 1: 10.
In this embodiment, the heating manner in step eight is direct water bath heating, and in practical application, the heating manner may also be a condensing reflux manner. .
In this embodiment, the heating temperature in the step eight is 95 ℃, and in practical application, the heating temperature in the step eight is an arbitrary value within a range of 70 to 100 ℃.
Fig. 1 is a Transmission Electron Microscope (TEM) spectrum of nitrogen-doped graphene quantum dots obtained in an example of the present invention.
As shown in FIG. 1, the nitrogen-doped graphene quantum dots obtained in the embodiment are spherical, the average diameter of the particles is 3nm, and the particle size distribution is 2-4 nm.
Fig. 2 is a fluorescence spectrum of the original nitrogen-doped graphene quantum dot in the present example and the nitrogen-doped graphene quantum dot prepared in the example.
As shown in fig. 2, the abscissa represents wavelength, the ordinate represents fluorescence intensity, the solid line in the graph is the fluorescence spectrum of the nitrogen-doped graphene quantum dot prepared in the example, and the dotted line is the fluorescence spectrum of the original nitrogen-doped graphene quantum dot. As can be seen from fig. 2, the fluorescence intensity of the nitrogen-doped graphene quantum dot prepared by the present example is significantly increased compared to the original nitrogen-doped graphene quantum dot prepared by the hydrothermal method in the prior art.
Meanwhile, the quantum yield of the nitrogen-doped graphene quantum dot prepared by the embodiment is as high as 75%, while the quantum yield of the original nitrogen-doped graphene quantum dot prepared by a hydrothermal method in the prior art is only 49%.
Effects and effects of the embodiments
According to the method for preparing the graphene quantum dots by using the molecular sieve, the molecular sieve is added into the precursor, so that the graphene quantum dots obtained after the treatment by the hydrothermal method can enter the pores of the molecular sieve to form the graphene quantum dot-molecular sieve only if the pore size of the graphene quantum dots is similar to that of the molecular sieve, and thus the graphene quantum dots and impurities with other scales in the solution can be separated. And centrifuging to obtain the graphene quantum dot-molecular sieve. Graphene quantum dots in the graphene quantum dot-molecular sieve can be desorbed from the inside of pores of the molecular sieve at 70-100 ℃ so as to obtain the graphene quantum dots. Therefore, the graphene quantum dots prepared by the method are uniform in particle size distribution, high in purity and high in quantum yield, the problems that the graphene quantum dots prepared by a hydrothermal method in the prior art are not uniform in particle size distribution and high in impurity content are solved, and the quantum yield is improved.
The method is simple in process and easy to operate, desorption can be achieved at the low temperature of 70-100 ℃, and energy consumption is low.
The method can also obtain corresponding graphene quantum dots with uniform particle sizes by changing the pore size of the molecular sieve, so that the graphene quantum dots with different particle sizes can be prepared according to actual needs.
The method can be used for preparing the graphene quantum dots and can also be used for preparing the element-doped graphene quantum dots.
The above embodiments are preferred examples of the present invention, and are not intended to limit the scope of the present invention.
Claims (4)
1. A method for preparing graphene quantum dots by using a molecular sieve is characterized by comprising the following steps:
step one, mixing a precursor and a molecular sieve according to a certain proportion to obtain a mixed solution;
step two, treating the mixed solution by a hydrothermal method to obtain a composition;
centrifuging the composition to obtain a graphene quantum dot-molecular sieve containing the graphene quantum dots;
stirring the graphene quantum dot-molecular sieve at 70-100 ℃ to desorb the graphene quantum dot,
wherein the pore size of the molecular sieve is any one of the sizes of 3nm, 5nm, 8nm and 10nm,
the molecular sieve is any one of an MCM-41 molecular sieve, an SBA-15 molecular sieve and an FDU-12 molecular sieve.
2. The method for preparing graphene quantum dots by using the molecular sieve as claimed in claim 1, wherein the method comprises the following steps:
wherein the precursor and the molecular sieve are mixed in any mass ratio within the range of 1: 1-1: 10.
3. The method for preparing graphene quantum dots by using the molecular sieve as claimed in claim 1, wherein the method comprises the following steps:
wherein the treatment temperature of the hydrothermal method is 160 ℃, and the treatment time is 15 h.
4. The method for preparing graphene quantum dots by using the molecular sieve as claimed in claim 1, wherein the method comprises the following steps:
wherein, the heating mode of the step four is direct water bath heating or heating by adopting a condensing reflux mode.
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