CN113930788B - Double-peak fluorescence emission graphene quantum dot, preparation method and adjustment method - Google Patents
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Abstract
The invention discloses a bimodal fluorescence emission graphene quantum dot, a preparation method and an adjusting method. The preparation method comprises the following steps: inserting a carbon source working electrode, a counter electrode and a reference electrode into the electrolyte, and adjusting and maintaining the temperature of the electrolyte to 50-80 ℃; and performing cyclic voltammetry scanning to obtain a solution dispersed with the bimodal fluorescence emission graphene quantum dots, and performing suction filtration, dialysis and freeze drying to obtain the water-soluble bimodal fluorescence emission graphene quantum dots. According to the preparation method provided by the invention, the bimodal fluorescence emission graphene quantum dots are prepared by electrochemical oxidation under the assistance of heat, and under the coupling action of an electric field and a temperature field, epoxy groups are subjected to ring-opening addition to introduce carbonyl fluorescence sites, so that the water-soluble bimodal fluorescence emission graphene quantum dots are prepared. The preparation method and the adjusting method provided by the invention are green, environment-friendly, simple and safe, and have large-scale production potential.
Description
Technical Field
The invention belongs to the technical field of graphene quantum dots, and particularly relates to a double-peak fluorescence emission graphene quantum dot, a preparation method and an adjustment method.
Background
The graphene quantum dot is a novel fluorescent carbon nano material with the size of less than 10nm, and mainly comprises an internal carbon core and a surface functional group. In recent years, due to the advantages of unique fluorescence property, good biocompatibility, nanometer size, high specific surface area, excellent solubility, photobleaching resistance and the like, the graphene quantum dots attract great attention in the fields of biological imaging, analytical sensing, tumor treatment, drug delivery, energy storage and transformation.
In order to explore wider application range of the graphene quantum dots and promote the graphene quantum dots to be industrially and practically applied, researchers focus on preparing the high-quantum-yield graphene quantum dots, the long-wave emission graphene quantum dots and the bi/multimodal fluorescence emission graphene quantum dots by a safe, economic and simple method. The existing preparation methods of graphene quantum dots can be divided into two main categories according to the size of a carbon source precursor: top-down and bottom-up. Patent document CN105565297a discloses a graphene quantum dot prepared by electrochemical oxidation cutting of a carbon fiber tip face and a method thereof, and discloses a method for preparing the graphene quantum dot by electrochemical oxidation, expansion, dissociation and cutting of a microcrystalline graphite sheet layer on the carbon fiber tip face at normal temperature. The prepared graphene quantum dots can be stably dispersed in water, and the particle size distribution is uniform. But the carbon fiber raw material is expensive, the preparation efficiency is low, and the industrial production is difficult. In the method for preparing the graphene quantum dots by the ultraviolet light etching dry method in patent document CN102208755a, the graphene on the mica sheet is etched by ultraviolet light to obtain the graphene quantum dots, but the method is large in energy consumption, harmful to radiation and small in preparation amount. Patent document CN103265020a is a method for macro preparation of graphene quantum dot powder, in which natural crystalline flake graphite is used as a carbon source, the natural crystalline flake graphite is converted into first-order intercalation nano graphite oxide, and then the first-order intercalation nano graphite oxide is further subjected to heat treatment to obtain graphene quantum dot powder, but the preparation process is complex, long in time consumption, serious in pollution, and difficult to regulate and control product properties. In the method for preparing the graphene quantum dots under the coupling effect of the electric field and the ultrasonic field in patent document CN109594097B, graphite is used as a carbon source, an electrolytic cell is placed in the ultrasonic cell, and the graphene quantum dots are prepared under the coupling effect of the electric field and the ultrasonic field. In addition, the graphene quantum dots prepared by the methods are similar to most literature reports and show unimodal fluorescence emission. However, fluorescence sensing with unimodal fluorescence emission graphene quantum dots as the nanoprobe is mainly realized through a linear relationship between the concentration of an analyte and the fluorescence intensity, but the fluorescence intensity of the unimodal fluorescence emission graphene quantum dots is interfered by factors such as local environment change, light source power fluctuation, optical path change and photo-bleaching, and the accuracy of the unimodal fluorescence emission graphene quantum dot nanoprobe is limited to a certain extent.
The ratio type fluorescent probe realizes fluorescent sensing through the linear relation between the concentration of an analyte and the intensity ratio of bimodal fluorescent emission, has certain self-correction on environmental interference, and is more accurate in fluorescent detection. At present, researchers compound graphene quantum dots with fluorescent substances with other fluorescence emission peak positions, such as semiconductor quantum dots, organic dyes, fluorescent proteins and the like, to prepare the double-peak fluorescence emission nano probe. However, the preparation of the composite type bimodal fluorescence emission nanoprobe faces the defects of complex preparation process, organic dye leakage, heavy metal pollution and the like. Therefore, the method for preparing the graphene quantum dots with intrinsic double-peak fluorescence emission has important significance.
In order to prepare graphene quantum dots with intrinsic bimodal fluorescence emission, some research teams adopt organic dyes and the like with intrinsic bimodal fluorescence emission as carbon sources, such as basic fuchsin, calcein and the like. By means of hydrothermal treatment, new fluorescence sites are introduced by hydrothermal carbonization while the fluorescence property of part of the precursor is maintained, and the graphene quantum dots with intrinsic double-peak fluorescence emission are prepared. However, these methods require organic fluorescent dyes as precursors, and the preparation process requires high temperature and high pressure, which is not suitable for large-scale preparation.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a bimodal fluorescence emission graphene quantum dot, a preparation method and an adjustment method, and aims to solve the technical problems that an organic fluorescent dye is required to be used as a precursor at present, and the preparation process requires high temperature and high pressure, so that the bimodal fluorescence emission graphene quantum dot is not beneficial to large-scale preparation by controlling the temperature of an electrolyte.
In order to achieve the above object, according to an aspect of the present invention, there is provided a method for preparing a bimodal fluorescence emission graphene quantum dot, including: inserting a carbon source working electrode, a counter electrode and a reference electrode into the electrolyte, and adjusting and maintaining the temperature of the electrolyte to 50-80 ℃; and performing cyclic voltammetry scanning to obtain a solution dispersed with the bimodal fluorescence emission graphene quantum dots, and performing suction filtration, dialysis and freeze drying to obtain the water-soluble bimodal fluorescence emission graphene quantum dots.
Preferably, the temperature of the electrolyte is adjusted to 50-80 ℃, specifically, the electrolyte is filled into a double-layer electrolytic cell, and circulating water is introduced into an interlayer of the double-layer electrolytic cell, so that the temperature of the electrolyte is adjusted and maintained to 50-80 ℃. Specifically, the temperature of the electrolyte is adjusted and maintained at any temperature of 50 to 80 ℃, for example, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ and the like.
Preferably, the carbon source working electrode is a graphite rod, the counter electrode is a platinum sheet, and the reference electrode is a mercury/mercury oxide electrode.
Preferably, the electrolyte is a potassium hydroxide solution with the concentration of 0.1-3 mol/L.
Preferably, the cyclic voltammetry scan is performed, specifically: under the conditions that the voltage is 0-2V and the scanning rate is 0.06-0.2 mV/s, the cyclic voltammetry scanning is carried out for 120-1000 circles.
Preferably, the suction filtration, dialysis, freeze drying comprises: carrying out suction filtration on the solution dispersed with the bimodal fluorescence emission graphene quantum dots through a microporous filter membrane to obtain a filtrate, then dialyzing the filtrate to be neutral in a dialysis bag with the molecular weight cutoff of 1000-12000 Da, and removing redundant salt ions to obtain a bimodal fluorescence emission graphene quantum dot dispersion liquid; the dispersion was freeze-dried at-60 ℃ under a vacuum of 4Pa for 48 hours.
According to another aspect of the invention, the bimodal fluorescence emission graphene quantum dot prepared by the preparation method is provided, and the average particle size of the bimodal fluorescence emission graphene quantum dot is 1.4-2.1nm.
According to a further aspect of the present invention, in the preparation method, the average particle size of the bimodal fluorescence emission graphene quantum dots is adjusted by adjusting the temperature of the electrolyte, and the average particle size of the bimodal fluorescence emission graphene quantum dots decreases with the increase of the temperature of the electrolyte.
According to still another aspect of the present invention, in the above preparation method, the fluorescence emission peak of the bimodal fluorescence emission graphene quantum dot is adjusted by adjusting the temperature of the electrolyte, the distance between two fluorescence emission peaks of the bimodal fluorescence emission graphene quantum dot under excitation of 300nm at room temperature increases with the increase of the temperature of the electrolyte, and the intensity ratio of the fluorescence emission peak with a larger wavelength to the fluorescence emission peak with a smaller wavelength increases. Here, the distance between the two fluorescence emission peaks refers to the distance between the peak tops of the two fluorescence emission peaks, i.e., the difference between the wavelengths corresponding to the two fluorescence intensity maxima.
According to another aspect of the invention, the application of the bimodal fluorescence emission graphene quantum dot in a ratio type fluorescence probe is provided.
In general, at least the following advantages can be obtained by the above technical solution contemplated by the present invention compared to the prior art.
(1) According to the preparation method provided by the invention, the bimodal fluorescence emission graphene quantum dots are prepared by electrochemical oxidation under the assistance of heat, under the coupling action of an electric field and a temperature field, the original nuclear fluorescence sites and partial surface oxygen-containing functional groups are retained, and meanwhile, the epoxy groups formed by electrochemical oxidation at graphite defects are subjected to ring-opening addition to introduce carbonyl fluorescence sites, so that the water-soluble bimodal fluorescence emission graphene quantum dots are prepared. The preparation process does not need harsh conditions such as high temperature and high pressure, and organic fluorescent dye is not needed as a precursor, so that the problems of complex preparation process, organic dye leakage, heavy metal pollution and the like in the prior art are solved.
(2) The invention can realize the regulation and control of the preparation of the bimodal fluorescence emission graphene quantum dots with low cost and high efficiency, and can realize the regulation of the average particle size of the bimodal fluorescence emission graphene quantum dots, the distance between two fluorescence emission peaks and the intensity ratio of the two fluorescence emission peaks by regulating and controlling the condition of heating assistance.
(3) The preparation method and the adjusting method provided by the invention are green, environment-friendly, simple and safe, and have large-scale production potential.
Drawings
Fig. 1 is a TEM image of a bimodal fluorescence emission graphene quantum dot prepared in example 1 of the present invention;
fig. 2 is a particle size distribution statistical chart of bimodal fluorescence emission graphene quantum dots prepared in example 1 of the present invention;
fig. 3 is an HRTEM image of a bimodal fluorescence emission graphene quantum dot prepared in example 1 of the present invention;
FIG. 4 is a fluorescence emission spectrum of a bimodal fluorescence emission graphene quantum dot prepared in example 1 of the present invention under room temperature 300nm excitation;
fig. 5 is a fluorescence emission spectrum of the bimodal fluorescence emission graphene quantum dot prepared in embodiment 2 of the present invention under room temperature 300nm excitation;
FIG. 6 is a fluorescence emission spectrum of a bimodal fluorescence emission graphene quantum dot prepared in example 3 of the present invention under room temperature 300nm excitation;
FIG. 7 is a fluorescence emission spectrum of the graphene quantum dot prepared in comparative example 1 of the present invention under room temperature 300nm excitation;
FIG. 8 is a fluorescence emission spectrum of the graphene quantum dot prepared in comparative example 2 of the present invention under room temperature 300nm excitation;
fig. 9 is a graph showing changes in average particle diameters of the graphene quantum dots prepared in examples 1 to 3 according to the present invention and comparative examples 1 to 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention. In addition, the technical features involved in the respective embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
The embodiment provides a preparation method of a bimodal fluorescence emission graphene quantum dot and the bimodal fluorescence emission graphene quantum dot prepared by the method, and the preparation method comprises the following steps:
a. dissolving 56.1g of potassium hydroxide in 500mL of deionized water to prepare electrolyte with the concentration of 2 mol/L;
b. in the electrolyte double-layer electrolytic cell configured in the step a, a graphite electrode with the purity of 99.99 percent is taken as a working electrode, a platinum sheet electrode is taken as a counter electrode, a mercury/mercury oxide electrode is taken as a reference electrode, and the electrodes are parallelly inserted into electrolyte to assemble an electrochemical reaction device;
c. b, introducing circulating water of 80 ℃ into the interlayer of the double-layer electrolytic cell in the step b, keeping the temperature of the electrolyte at 80 ℃, setting the voltage range to be 0-2V, setting the scanning rate to be 0.06-0.2 mV/s, and performing cyclic voltammetry scanning for 120 circles under the action of heat assistance to obtain a bimodal fluorescence emission graphene quantum dot solution;
d. c, carrying out suction filtration on the solution obtained in the step c through a 0.22-micron microporous filter membrane to obtain a filtrate, then dialyzing the filtrate to be neutral in a dialysis bag with the molecular weight cutoff of 3500Da, and removing redundant salt ions to obtain a dispersion liquid of the bimodal fluorescence emission graphene quantum dots;
e. and d, freeze-drying the bimodal fluorescence emission graphene quantum dot dispersion liquid obtained in the step d to obtain the water-soluble bimodal fluorescence emission graphene quantum dot.
Fig. 1 is a TEM image of a bimodal fluorescence emission graphene quantum dot prepared in this embodiment, fig. 2 is a statistical graph of a particle size distribution of the bimodal fluorescence emission graphene quantum dot prepared in this embodiment, fig. 3 is an HRTEM image of the bimodal fluorescence emission graphene quantum dot prepared in this embodiment, and fig. 4 is a fluorescence emission spectrum of the bimodal fluorescence emission graphene quantum dot prepared in this embodiment under excitation at room temperature of 300 nm. It can be seen that the bimodal fluorescence emission graphene quantum dot prepared in the embodiment is bimodal fluorescence emission under the excitation of 300nm at room temperature, the average particle size of the bimodal fluorescence emission graphene quantum dot is about 1.4nm, the size distribution is uniform, the bimodal fluorescence emission graphene quantum dot can be stably dispersed in water, and the fluorescence emission is adjustable. The carbon quantum dot prepared by the embodiment has good biocompatibility, low cytotoxicity and adjustable fluorescence emission, and has wide application prospect in the aspects of biological imaging, analytical sensing, energy storage and transformation.
According to the preparation method provided by the embodiment, the fluorescent carbon quantum dots are prepared through electrochemical oxidation under the assistance of heat, graphite which is cheap and easy to obtain is selected as a carbon source, a potassium hydroxide aqueous solution is used as an electrolyte, and the water-soluble double-peak fluorescence emission graphene quantum dots are prepared under the coupling effect of an electric field and a temperature field. The method can regulate and control the preparation of the bimodal fluorescence emission graphene quantum dots with low cost and high efficiency, achieves the process of regulating and controlling the conversion of the graphite raw material into the bimodal fluorescence emission graphene quantum dots by regulating and controlling the electrochemical reaction conditions and applying the heat auxiliary conditions, and opens up a new way for regulating and controlling the preparation of the bimodal fluorescence emission graphene quantum dots by using the low-cost carbon source.
Example 2
In this embodiment, a preparation method identical to that in embodiment 1 is used to prepare the bimodal fluorescence emission graphene quantum dot, except that in step c, 60 ℃ circulating water is introduced into the interlayer of the double-layer electrolytic cell, so that the temperature of the electrolyte is maintained at 60 ℃.
Referring to fig. 5, a fluorescence emission spectrum of the bimodal fluorescence emission graphene quantum dot prepared in this embodiment under excitation of 300nm is shown. It can be seen that the bimodal fluorescence emission graphene quantum dot prepared in the embodiment is bimodal fluorescence emission under the excitation of 300nm at room temperature.
The average particle size of the bimodal fluorescence emission graphene quantum dot prepared in the embodiment is about 1.7 nm.
Example 3
In this embodiment, a preparation method identical to that in embodiment 1 is adopted to prepare the bimodal fluorescence emission graphene quantum dot, except that in step c, 50 ℃ circulating water is introduced into the interlayer of the double-layer electrolytic cell, so that the temperature of the electrolyte is kept at 50 ℃.
Referring to fig. 6, a fluorescence emission spectrum of the bimodal fluorescence emission graphene quantum dot prepared in this embodiment under excitation of 300nm is shown. It can be seen that the bimodal fluorescence emission graphene quantum dot prepared in the embodiment is bimodal fluorescence emission under the excitation of 300nm at room temperature.
The average particle size of the bimodal fluorescence emission graphene quantum dot prepared in the embodiment is about 2.1nm.
Example 4
In this embodiment, a bimodal fluorescence emission graphene quantum dot is prepared by the same preparation method as in example 1, except that in step c, cyclic voltammetry scanning is performed for 480 cycles under the thermal assistance effect.
Comparative example 1
The comparative example adopts the same preparation method as that of the example 1 to prepare the graphene quantum dots, and is different in that circulating water of 20 ℃ is introduced into the interlayer of the double-layer electrolytic cell in the step c, so that the temperature of the electrolyte is kept at 20 ℃.
Referring to fig. 7, the fluorescence emission spectrum of the graphene quantum dot prepared in this comparative example under 300nm excitation is shown. It can be seen that the graphene quantum dots prepared by the comparative example have monomodal fluorescence emission under the excitation of 300nm at room temperature.
The average particle size of the graphene quantum dots prepared by the comparative example is about 3.7 nm.
Comparative example 2
The comparative example adopts the same preparation method as that of the example 1 to prepare the graphene quantum dots, except that circulating water of 40 ℃ is introduced into the interlayer of the double-layer electrolytic cell in the step c, so that the temperature of the electrolyte is kept at 40 ℃.
Referring to fig. 8, the fluorescence emission spectrum of the graphene quantum dot prepared in this comparative example under 300nm excitation is shown. It can be seen that the graphene quantum dot prepared by the comparative example has a single-peak fluorescence emission under the excitation of 300nm at room temperature.
The average particle size of the graphene quantum dots prepared by the comparative example is about 2.5 nm.
From the results of examples 1-3 and comparative examples 1-2, it can be seen that fig. 9 is a graph showing the change of the average particle size of the graphene quantum dots prepared by the methods of the comparative examples and different examples, and as the temperature of the electrolyte is increased from 20 ℃ to 80 ℃, the average size of the product is reduced from 3.7nm to about 1.4nm, which illustrates that the method of the present invention can adjust and control the average size of the bimodal fluorescence emission graphene quantum dots with low cost and high efficiency.
Referring to fig. 4 to 6, it can be seen that according to the preparation method provided by the present invention, as the temperature of the electrolyte increases from 50 ℃ to 80 ℃, the distance between two fluorescence emission peaks of the bimodal fluorescence emission graphene quantum dot under the excitation of 300nm at room temperature increases, and the intensity ratio of the fluorescence emission peak with a larger wavelength to the fluorescence emission peak with a smaller wavelength increases.
Application examples
In this embodiment, the bimodal fluorescence emission graphene quantum dot prepared in example 1 is applied to a ratiometric fluorescent probe, and fluorescence sensing is realized through a linear relationship between the concentration of an analyte and the intensity ratio of bimodal fluorescence emission.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A preparation method of a bimodal fluorescence emission graphene quantum dot is characterized by comprising the following steps:
inserting a carbon source working electrode, a counter electrode and a reference electrode into the electrolyte, and adjusting and maintaining the temperature of the electrolyte to 50-80 ℃;
performing cyclic voltammetry scanning to obtain a solution dispersed with the bimodal fluorescence emission graphene quantum dots, and performing suction filtration, dialysis and freeze drying to obtain water-soluble bimodal fluorescence emission graphene quantum dots;
under the coupling action of an electric field and a temperature field, while original nuclear fluorescence sites and partial surface oxygen-containing functional groups are kept, epoxy groups formed by electrochemical oxidation at graphite defects are subjected to ring-opening addition to introduce carbonyl fluorescence sites, so that water-soluble bimodal fluorescence emission graphene quantum dots are obtained;
the electrolyte is a potassium hydroxide solution with the concentration of 0.1 to 3mol/L;
the cyclic voltammetry scanning is carried out, and specifically comprises the following steps: and performing cyclic voltammetry scanning for 120 to 1000 circles under the conditions that the voltage is 0-2V and the scanning rate is 0.06 to 0.2mV/s.
2. The preparation method according to claim 1, wherein the temperature of the electrolyte is adjusted to 50 to 80 ℃, specifically, the electrolyte is filled into a double-layer electrolytic cell, circulating water is introduced into an interlayer of the double-layer electrolytic cell, and thus the temperature of the electrolyte is adjusted to 50 to 80 ℃.
3. The method of claim 1, wherein the carbon source working electrode is a graphite rod, the counter electrode is a platinum sheet, and the reference electrode is a mercury/mercury oxide electrode.
4. The method of claim 1, wherein the filtering, dialyzing, and freeze-drying comprises: carrying out suction filtration on the solution dispersed with the bimodal fluorescence emission graphene quantum dots through a microporous filter membrane to obtain a filtrate, then dialyzing the filtrate to be neutral in a dialysis bag with the molecular weight cutoff of 1000-12000Da, and removing redundant salt ions to obtain a bimodal fluorescence emission graphene quantum dot dispersion liquid; the dispersion was freeze-dried at-60 ℃ under a vacuum of 4Pa for 48 hours.
5. The bimodal fluorescence emission graphene quantum dot prepared by the preparation method of any one of claims 1 to 4, wherein the average particle size of the bimodal fluorescence emission graphene quantum dot is 1.4-2.1nm.
6. A method for adjusting the average particle size of the bimodal fluorescence emission graphene quantum dots, wherein in the preparation method of any one of claims 1 to 4, the average particle size of the bimodal fluorescence emission graphene quantum dots is adjusted by adjusting the temperature of the electrolyte, and the average particle size of the bimodal fluorescence emission graphene quantum dots decreases with the increase of the temperature of the electrolyte.
7. A method for adjusting the fluorescence emission peak of a bimodal fluorescence emission graphene quantum dot, which is characterized in that in the preparation method of any one of claims 1 to 4, the fluorescence emission peak of the bimodal fluorescence emission graphene quantum dot is adjusted by adjusting the temperature of the electrolyte, the distance between two fluorescence emission peaks of the bimodal fluorescence emission graphene quantum dot under the excitation of 300nm at room temperature is increased along with the increase of the temperature of the electrolyte, and the intensity ratio of the fluorescence emission peak with a larger wavelength to the fluorescence emission peak with a smaller wavelength is increased.
8. Use of the bimodal fluorescently emitting graphene quantum dot of claim 5 in a ratiometric fluorescent probe.
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