CN108529592B - Preparation method of double-emission fluorescent carbon dots with high quantum yield and application of double-emission fluorescent carbon dots in PFOS detection - Google Patents

Preparation method of double-emission fluorescent carbon dots with high quantum yield and application of double-emission fluorescent carbon dots in PFOS detection Download PDF

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CN108529592B
CN108529592B CN201810459565.4A CN201810459565A CN108529592B CN 108529592 B CN108529592 B CN 108529592B CN 201810459565 A CN201810459565 A CN 201810459565A CN 108529592 B CN108529592 B CN 108529592B
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谭克俊
朱盼盼
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Abstract

The invention relates to the field of nano materials, in particular to a preparation method of a dual-emission fluorescent carbon dot with high quantum yield and application thereof in PFOS detection, wherein the dual-emission fluorescent carbon dot is synthesized by 2, 4-diaminotoluene, ethylenediamine and phosphoric acid through a hydrothermal method. The carbon dots prepared by the method can emit fluorescence with two wavelengths under the excitation of light with the wavelengths of 280nm and 340nm, and have fluorescence emission at the positions of 350nm and 515nm under the excitation of the light with the wavelength of 280 nm; under the excitation of 340nm light, the fluorescence emission is carried out at 434nm and 502nm, and the fluorescence quantum yield of two emission centers can reach more than 44%. When the carbon spot is used for measuring PFOS, under two excitation wavelengths, the fluorescence intensity ratio of the two emission wavelengths of the carbon spot and the concentration of the PFOS are in a linear relationship, so that two results can be obtained and mutually verified, and the accuracy of the measurement result is improved.

Description

Preparation method of double-emission fluorescent carbon dots with high quantum yield and application of double-emission fluorescent carbon dots in PFOS detection
Technical Field
The invention relates to the field of nano materials, in particular to a preparation method of a double-emission fluorescent carbon dot with high quantum yield and application thereof in PFOS detection.
Background
The carbon dots serving as a fluorescent carbon nano material discovered in recent years have remarkable advantages such as good biocompatibility, proper size, adjustable excitation and emission wavelengths, good light stability and the like. The synthesis method of the fluorescent carbon dots has been greatly developed, and the advantage of low cost and wide application range also attracts the wide attention of more and more researchers.
So far, fluorescent carbon dots are mostly divided into single-emitting carbon dots and double-emitting carbon dots, i.e., only one or two fluorescent emissions under single wavelength excitation. Dual-emission fluorescent carbon dots have many advantages over single-emission carbon dots. The dual-emission carbon dots can be used as a ratio sensor, and can effectively overcome interference from factors unrelated to the object to be measured so as to improve the accuracy and sensitivity of the measuring method. However, the quantum yield of both the single-emission fluorescent carbon dot and the dual-emission fluorescent carbon dot is low, so that the application of the fluorescent carbon quantum dot is difficult to popularize.
PFOS (perfluorooctane sulfonate) is ubiquitous in the environment as a persistent and highly biologically toxic organic substance, is difficult to degrade and can be accumulated in the organism, further accumulates and amplifies with the food chain, and has a strong carcinogenic effect on the human body, so it is important to detect the concentration of environmental PFOS.
Disclosure of Invention
The invention provides a method for preparing a dual-emission fluorescent carbon dot with high quantum yield, which can emit fluorescence with two wavelengths under the excitation of light with the wavelengths of 280nm and 340nm, and has fluorescence emission at the positions of 350nm and 515nm under the excitation of light with the wavelength of 280 nm; under the excitation of 340nm light, the fluorescence emission is carried out at 434nm and 502nm, and the fluorescence quantum yield of the two emission centers is higher.
In order to achieve the above objects, the present invention provides a method for preparing a dual-emission fluorescent carbon dot with high quantum yield, which is characterized in that 2, 4-diaminotoluene, ethylenediamine and phosphoric acid are synthesized by a hydrothermal method.
Preferably, the preparation method comprises the following steps:
(1) placing 2, 4-diaminotoluene, ethylenediamine and phosphoric acid in a closed reactor, and adding water as a solvent to obtain a reaction system, wherein the mass ratio of the 2, 4-diaminotoluene, the ethylenediamine and the phosphoric acid is 0.5-3: 1-5: 1-10, and the addition amount of the water enables the mass concentration of the ethylenediamine to be not higher than 3.7425 mol/L;
(2) heating the reaction system to 180-210 ℃, and reacting for 7-11 h;
(3) and cooling the reaction system to room temperature, centrifuging to remove large particles, dialyzing, cooling and drying the double-emission fluorescent carbon dots.
Preferably, in step (1), the mass ratio of 2, 4-diaminotoluene, ethylenediamine and phosphoric acid is 0.5:4: 8.
Preferably, in step (1), the amount of water added is 4 mL.
Preferably, in step (1), the closed reactor is an autoclave lined with polytetrafluoroethylene.
Preferably, the reaction temperature in the step (2) is 195 ℃.
Preferably, the reaction time in step (2) is 9.5 h.
Preferably, the dialysis membrane with a molecular cut-off of 300(MWCO) is used in the dialysis in step (3). Specifically, the cellulose ester dialysis membrane is selected as the dialysis membrane.
The invention also provides the dual-emission fluorescent carbon dot prepared by the method, and the dual-emission fluorescent carbon dot has dual fluorescence emission under the excitation of 280nm or 340nm light.
Preferably, the dual-emission fluorescent carbon dot has fluorescence emission at 350nm and 515nm under the excitation of 280nm light, and has fluorescence emission at 434nm and 502nm under the excitation of 340nm light.
The application of the double-emission fluorescent carbon spot in PFOS detection also belongs to the protection scope of the invention.
The invention has the beneficial effects that:
1. the preparation method provided by the invention is simple and easy to operate, the raw materials are cheap and easy to obtain, and the quantum yield of two emission centers is up to 44%;
2. the double-emission fluorescence peak of the carbon dot provided by the invention has a longer wavelength distance, and can better avoid experimental errors caused by the strength of mutual influence between two peaks.
3. The carbon dot provided by the invention has two emission centers, when PFOS is measured, under the excitation of 280nm light, the emitted fluorescence ratio of 350nm to 515nm is in direct proportion to the concentration of PFOS, the linear range is 10 mu mol/L-300 mu mol/L, the detection limit is 3.4170 mu mol/L, under the excitation of 340nm light, the emitted fluorescence ratio of 434nm to 502nm is also in direct proportion to the concentration of PFOS, the linear range is 4 mu mol/L-100 mu mol/L, and the detection limit is 2.9275 mu mol/L. The results measured under the light conditions with different excitation wavelengths can be mutually verified, and the accuracy of the measurement result is improved.
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FIG. 1a is a graph of the fluorescence spectrum of carbon dots prepared in example 1 under excitation at 280nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 1b is a graph of the fluorescence spectrum of carbon dots prepared in example 1 under excitation at 340nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 2a is a graph of the fluorescence spectrum of carbon dots prepared in example 2 under excitation at 280nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 2b is a graph of the fluorescence spectrum of carbon dots prepared in example 2 under excitation at 340nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 3a is a graph of the fluorescence spectrum of carbon dots prepared in example 3 under excitation at 280nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 3b is a graph of the fluorescence spectrum of carbon dots prepared in example 3 under excitation at 340nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 4a is a graph of the fluorescence spectrum of carbon dots prepared in example 4 under excitation at 280nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 4b is a graph of the fluorescence spectrum of carbon dots prepared in example 4 under excitation at 340nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 5a is a graph of the fluorescence spectrum of carbon dots prepared in example 5 under excitation at 280nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 5b is a graph of the fluorescence spectrum of carbon dots prepared in example 5 under excitation at 340nm, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 6a is a graph of the fluorescence spectrum of carbon dots prepared in example 6 at 280nm excitation, with wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 6b is a plot of the fluorescence spectrum of carbon dots prepared in example 6 at 340nm excitation, wavelength on the abscissa and fluorescence intensity on the ordinate;
FIG. 7 is a TEM image of the carbon dot prepared in example 7, wherein the inset is a TEM image;
FIG. 8 is an infrared spectrum of a carbon dot prepared in example 7;
FIG. 9 is a graph of the salt tolerance spectrum of the carbon dots prepared in example 7, with the concentration of sodium chloride in the solution on the abscissa and the fluorescence intensity on the ordinate;
FIG. 10 is a graph of a photobleaching spectrum of carbon dots prepared in example 7 with time on the abscissa and fluorescence intensity on the ordinate;
FIG. 11 is a graph of fluorescence spectra of carbon dot solutions containing PFOS at different concentrations prepared in example 9 under excitation at 280nm, with the abscissa as wavelength and the ordinate as fluorescence intensity;
FIG. 12 is 280nm excited linear relationship of carbon dot solutions containing PFOS of different concentrations prepared in example 9Graph with the abscissa representing the concentration of PFOS and the ordinate representing the ratio of the fluorescence intensity differences (where Fa 0Initial fluorescence intensity at 350nm, FaIs the fluorescence intensity of a 350nm equilibrium solution, Fb 0Initial fluorescence intensity of 515nm, FbIs the fluorescence intensity of the equilibrium solution at a wavelength of 515 nm);
FIG. 13 is a graph of the fluorescence spectra of carbon dot solutions containing PFOS at different concentrations prepared in example 9 under excitation at 340nm, with the abscissa as wavelength and the ordinate as fluorescence intensity;
FIG. 14 is a plot of the 340nm excitation linearity of carbon dot solutions containing PFOS at various concentrations prepared in example 9, with PFOS concentration on the abscissa and fluorescence intensity difference ratio on the ordinate (where F isc 0Initial fluorescence intensity, F, of 434nmcIs the fluorescence intensity of the equilibrium solution at 434nm, Fd 0Is the initial fluorescence intensity at 502nm, FdIs the fluorescence intensity of the equilibrium solution at a wavelength of 502 nm).
Detailed Description
The 2, 4-diaminotoluene, ethylenediamine and phosphoric acid used in the examples are all commercially available in analytically pure form.
EXAMPLE 1 Effect of the ethylene diamine and phosphoric acid ratio on carbon Point
Eight parts of 3mmol 2, 4-diaminotoluene and 200. mu.L ethylenediamine were accurately weighed into eight 25mL polytetrafluoroethylene reaction vessels, respectively, and then the volume ratios of ethylenediamine: phosphoric acid 1: (0, 1, 1.5, 2, 2.5, 3, 4, 6) 0, 200. mu.L, 300. mu.L, 400. mu.L, 500. mu.L, 600. mu.L, 800. mu.L, 1200. mu.L of the phosphoric acid solution was measured in each of the respective reaction vessels, and then 4mL of water was added to each of the eight reaction vessels. Then the closed reaction kettle is placed in an air-blast drying oven to be heated and reacted for 10 hours at the temperature of 200 ℃. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
Diluting the obtained carbon dots with water to obtain carbon dot mother liquor with concentration of 1mg/mL, taking 200 μ L, diluting with water to 1mL, measuring fluorescence spectrum with F-7000 fluorescence spectrophotometer, obtaining fluorescence spectrum diagram (figure 1a) when excitation wavelength is 280nm, and obtaining fluorescence spectrum diagram (figure 1b) when excitation wavelength is 340 nm. As shown in FIG. 1a, when the amount ratio of 2, 4-diaminotoluene, ethylenediamine and phosphoric acid substances is 1:1:1.5, the fluorescence of the carbon dots under 280nm excitation starts to appear obvious double-wave peaks, and when the amount ratio of the raw material substances is 1:1:2, the double-emission fluorescence peak intensities of the carbon dots are both stronger and equivalent, and the trough fluorescence intensity is relatively lowest. As shown in FIG. 1b, when the ratio of 2, 4-diaminotoluene, ethylenediamine and phosphoric acid was 1:1:2, the fluorescence emission of the carbon spot at 340nm excitation began to appear bimodal and bimodal was most pronounced, with still weak bimodal at the ratios of 1:1:2.5 and 1:1: 3.
Example 2 Effect of ethylene diamine and phosphoric acid volume on carbon Point
Accurately weighing five parts of 3mmol 2, 4-diaminotoluene in five 25mL polytetrafluoroethylene reaction kettles respectively, and then adding the following components in volume ratio of ethylenediamine: the volume of phosphoric acid is increased synchronously with the proportion of 1:2, and then the phosphoric acid is added into a reaction kettle, namely 200 mu L, 400 mu L, 600 mu L, 800 mu L and 1000 mu L of ethylenediamine are respectively measured, and the volume of the corresponding phosphoric acid is 400 mu L, 800 mu L, 1200 mu L, 1600 mu L and 2000 mu L. Then 4mL of water is added into the reaction kettle respectively, and then the closed reaction kettle is placed in an air-blowing drying oven to be heated and reacted for 10 hours at 200 ℃. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The fluorescence spectra were obtained in the same manner as in example 1 (FIGS. 2a and b). As shown in FIG. 2a and FIG. 2b, the fluorescence intensity of the carbon dots increases in sequence with the simultaneous volume expansion of ethylenediamine and phosphoric acid, and when the ratio of 2, 4-diaminotoluene, ethylenediamine and phosphoric acid is 1:4:8, the fluorescence intensity of the double-emission trough is lowest compared with the peak at this ratio.
Example influence of 32, 4-diaminotoluene on the carbon Point
First, 0, 1.5mmol, 3mmol, 4.5mmol, 6mmol, 7.5mmol, 9mmol2, 4-diaminotoluene was weighed into a reaction vessel (the ratio of the amounts of the corresponding substances was 2, 4-diaminotoluene to ethylenediamine to phosphoric acid was 0:4:8, 0.5:4:8, 1:4:8, 1.5:4:8, 2:4:8, 2.5:4:8, 3:4:8), and then 1600 μ L seven parts of ethylenediamine 800 μ L phosphoric acid was accurately weighed into seven 25mL polytetrafluoroethylene reaction vessels, respectively. Then 4mL of water is added into the reaction kettle respectively, and then the closed reaction kettle is placed in an air-blowing drying oven to be heated and reacted for 10 hours at 200 ℃. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The fluorescence spectra were obtained in the same manner as in example 1 (FIGS. 3a and b). As shown in FIGS. 3a and 3b, when the ratio of raw materials is 0.5:4:8, the carbon point fluorescence under the excitation of 280nm and 340nm begins to generate double emission, and the double emission still exists along with the increase of the mass of the 2, 4-diaminotoluene, and when the ratio is 0.5:4:8 in combination with FIGS. 3a and 3b, the fluorescence intensity under the two excitations is relatively strong.
Example 4 Effect of reaction temperature on carbon Point
1.5mmol of 2 and 4-diaminotoluene were weighed respectively, and 800. mu.L of ethylenediamine and 1600. mu.L of phosphoric acid were weighed into four 25mL polytetrafluoroethylene reaction kettles. Then 4mL of water was added to the reaction vessel, and the reaction vessel was placed in a forced air drying oven to react at 180 ℃, 190 ℃, 200 ℃ and 210 ℃ for 10 hours. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The fluorescence spectra were obtained in the same manner as in example 1 (FIGS. 4a and b). As shown in the figure, the synthesized carbon dots have double-emission fluorescence at four temperatures, and the fluorescence intensity of the synthesized carbon dots is strongest at 190 ℃, and the wave trough is most obvious.
Example 5 Effect of reaction time on carbon Point
1.5mmol of 2 and 4-diaminotoluene are weighed respectively, and five parts of 800 mu L of ethylenediamine and 1600 mu L of phosphoric acid are weighed into five 25mL polytetrafluoroethylene reaction kettles. Then 4mL of water is added into the reaction kettle respectively, and then the closed reaction kettle is placed in a forced air drying oven to react for 7h, 8h, 9h, 10h and 11h at 190 ℃. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The fluorescence spectra were obtained in the same manner as in example 1 (FIGS. 5a and b). As shown in the figure, when the reaction time is more than or equal to 8h, the fluorescence peak of the carbon dot is double-emission under two-wave excitation (280nm and 340nm), and when the reaction time is 10h, the double-emission peak under two excitation is most obvious, and the fluorescence intensity is strongest.
Example 6 orthogonal optimization of synthetic carbon dots
The raw materials in the amounts shown in Table 1 were loaded into the reaction vessel and the reaction was heated at the corresponding temperatures and times. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The fluorescence spectra were obtained in the same manner as in example 1 (FIGS. 6a and b). As shown in the figure, the synthesized nine sample carbon dots have obvious dual-emission characteristics under the excitation of 280nm and 340nm, and the carbon dots under the condition of serial number 6 with the lowest fluorescence intensity of the trough are combined with the carbon dots in the graph of FIG. 6a and b.
EXAMPLE 7 preparation of carbon dots
A polytetrafluoroethylene reactor was charged with 0.1829g of 2, 4-diaminotoluene, 800. mu.L of ethylenediamine, 1600. mu.L of phosphoric acid, 4mL of water. Then the closed reaction kettle is placed in a forced air drying oven to be heated and reacted for 570min at the temperature of 195 ℃. After the reaction is finished, the reaction kettle is naturally cooled to room temperature, and the product is centrifugally dialyzed, frozen and dried to obtain the carbon point solid.
The finally synthesized carbon dots were characterized by a Transmission Electron Microscope (TEM) High Resolution TEM (HRTEM) and an infrared spectrometer, and the results are shown in fig. 7 and fig. 8, respectively, where the average size of the carbon dots was 5.36nm, and the lattice spacing was 0.24nm (corresponding to the (1120) plane of graphite). And measuring fluorescence quantum yield at the fluorescence emission wavelengths of 350nm and 515nm to obtain phi350nm＝44.21％,Φ515nm＝46.10％。
Example 8 salt tolerance examination of carbon dots
The carbon dots prepared in example 7 were diluted with water to prepare 1mg/mL carbon dot solution, 200 μ L of 1mg/mL carbon dot solution was put into seven centrifugal tubes, an appropriate amount of briutan-Robinson (BR) buffer solution with pH 5.2 was added, sodium chloride solutions of different concentrations were added into the centrifugal tubes, the final salt concentrations were adjusted to 1mL with water, fluorescence measurements were performed with F-7000 fluorescence spectrophotometer, and the final experiments showed that the fluorescence peak intensities at four wavelengths excited at 280nm and 340nm were almost not changed greatly, and the results are shown in fig. 9, indicating that the carbon dots had good salt tolerance.
TABLE 1 reaction conditions for orthogonal optimization of synthetic carbon sites
Figure BDA0001660544470000071
Example 9 evaluation of photobleaching Properties of carbon dots
Diluting the carbon dots prepared by the method in example 7 with water to prepare a 1mg/mL carbon dot solution, adding 200 μ L of water into a centrifuge tube, adding water to a constant volume of 1mL, and performing a photobleaching experiment at an excitation wavelength of 280nm, emission wavelengths of 350nm and 515nm, an excitation wavelength of 340nm, and emission wavelengths of 434nm and 502nm by using an F-7000 fluorescence spectrophotometer, wherein the final experiment shows that the fluorescence intensities at four emission wavelengths are not greatly changed, and the result is shown in FIG. 10, which shows that the carbon dots have excellent photobleaching resistance.
EXAMPLE 10 method for determining PFOS by carbon Point
The carbon dot prepared in example 7 was diluted with water to prepare a 1mg/mL carbon dot solution, 200. mu.l of the carbon dot solution was put into a centrifuge tube, 100. mu.l of birutan-Robinson (Britton-Robinson, BR) buffer solution having a pH of 5.2 was added, PFOS solutions of different concentrations were added, and the volume was adjusted to 1mL with water. Then transferring the sample to a cuvette for fluorescence measurement under the excitation of 280nm and 340nm, and finding that PFOS has a remarkable effect on the carbon spot through experiments, wherein the ratio fluorescence signal and the concentration of PFOS are in a linear relation in a certain range, thereby establishing a ratio fluorescence spectrum analysis method for detecting PFOS (figures 11,12,13 and 14). The method is successfully used for measuring PFOS in Yangling river water and tap water in the three gorges reservoir area, and RSD is less than or equal to 5%.

Claims (10)

1. The preparation method of the dual-emission fluorescent carbon dot with high quantum yield is characterized in that the dual-emission fluorescent carbon dot is synthesized by a hydrothermal method from 2, 4-diaminotoluene, ethylenediamine and phosphoric acid, and comprises the following steps:
(1) placing 2, 4-diaminotoluene, ethylenediamine and phosphoric acid in a closed reactor, and adding water as a solvent to obtain a reaction system, wherein the mass ratio of the 2, 4-diaminotoluene, the ethylenediamine and the phosphoric acid is 0.5-3: 1-5: 1-10, and the addition amount of the water enables the mass concentration of the ethylenediamine to be not higher than 3.7425 mol/L;
(2) heating the reaction system to 180-210 ℃, and reacting for 7-11 h;
(3) and cooling the reaction system to room temperature, centrifuging to remove large particles, dialyzing, cooling and drying to obtain the dual-emission fluorescent carbon dots.
2. The method according to claim 1, wherein in the step (1), the mass ratio of 2, 4-diaminotoluene, ethylenediamine and phosphoric acid is 0.5:4: 8.
3. The method according to claim 1, wherein in the step (1), water is added in an amount of 4 mL.
4. The method according to claim 1, wherein in the step (2), the reaction temperature is 195 ℃.
5. The method according to claim 1, wherein in the step (2), the reaction time is 9.5 hours.
6. The method according to claim 1, wherein in the step (3), a dialysis membrane having a molecular cut-off of 300(MWCO) is used for dialysis.
7. The method according to claim 6, wherein the dialysis membrane is a cellulose ester dialysis membrane.
8. The dual-emission fluorescent carbon dot prepared by the preparation method of any one of claims 1 to 7, wherein the dual-emission fluorescent carbon dot has dual fluorescence emission under the excitation of 280nm or 340nm light.
9. The dual-emission fluorescent carbon dot of claim 8, wherein the dual-emission fluorescent carbon dot has fluorescence emissions at both 350nm and 515nm when excited by 280nm light, and at both 434nm and 502nm when excited by 340nm light.
10. Use of the dual emission fluorescent carbon spot according to claim 8 or 9 for detecting PFOS.
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