A kind of red fluorescent carbon dots, a preparation method thereof and an application thereof in detecting perfluorooctanoic acid

Abstract

The present invention discloses a kind of red fluorescent carbon dots, a preparation method thereof and an application in detecting perfluorooctanoic acid. Oxalic acid, meso-tetra(4-carboxyphenyl) porphine and ethanolamine are heated in water to 140-220 °C for hydrothermal reaction for 4-20 h, and then the reaction product is filtered. The filtrate obtained by filtration is dialyzed and dried to obtain red fluorescent carbon dots. The red fluorescent carbon dots can be used as a fluorescent probe to detect perfluorooctanoic acid in environmental samples. The present invention uses oxalic acid, meso-tetra(4-carboxyphenyl) porphine and ethanolamine as carbon sources, and synthesizes red fluorescent carbon dots by a hydrothermal method. The preparation method is simple and easy to implement. The red fluorescent carbon dots of the present invention have high monodispersity, good stability, good water solubility and high fluorescence stability. The simple, rapid, highly sensitive and highly selective detection of perfluorooctanoic acid is realized by the static quenching between the red fluorescent carbon dots and perfluorooctanoic acid.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of fluorescent carbon quantum dots and the detection of perfluorooctanoic acid, and particularly relates to a red fluorescent carbon dot, a preparation method thereof, and an application thereof in the detection of perfluorooctanoic acid. Background Art

[0002] Perfluorooctanoic acid (PFOA) is one of the typical perfluorinated compounds in the environment and is also the final product of the transformation of perfluorinated compounds in the environment. Due to its high physical and chemical stability, strong hydrophobic and lipophobic properties, and high surface activity, it is widely used in fields such as textiles, semiconductors, nano-coatings, fire-fighting foams, and medical devices. PFOA has environmental persistence, bioaccumulation, and long-distance migration properties, and can enter the human body through food, air, and water, resulting in organ, immune, endocrine, and reproductive developmental toxicity, seriously threatening the ecological environment and human health. At the same time, the detection ratio of PFOA in perfluorinated compounds is the highest, which has attracted wide social attention. Therefore, establishing a new method for sensitive and rapid detection of PFOA is of great significance for protecting the ecological environment and human health.

[0003] At present, the methods for detecting PFOA mainly include high performance liquid chromatography, gas chromatography-mass spectrometry, high performance liquid chromatography-mass spectrometry, and high performance liquid chromatography-tandem mass spectrometry. However, most of these methods are restricted by conditions such as complex operation, high instrument cost, and long detection cycle, which further affects the application of these methods.

[0004] Fluorescence analysis method has the advantages of high sensitivity, fast detection rate, and simple operation, and is one of the most promising methods. As a new type of carbon nanomaterial, carbon dots have the characteristics of good water solubility, strong fluorescence stability, and environmental friendliness, and gradually become an ideal substitute for fluorescent materials such as organic dyes, quantum dots, and metal nanoclusters. Carbon dots can be used as high-performance fluorescent probes to achieve highly sensitive detection and analysis of target substances.

[0005] Therefore, designing and preparing a new type of fluorescent carbon dot to develop a simple, rapid, and sensitive method for analyzing PFOA has important research and application significance. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a red fluorescent carbon dot and a preparation method thereof, and the red fluorescent carbon dot prepared by this method can be used to detect perfluorooctanoic acid in environmental samples.

[0007] The present invention adopts the following technical solutions to solve the above technical problems. A preparation method of red fluorescent carbon dots is characterized in that oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine are heated in water to 140-220 °C for hydrothermal reaction for 4-20 h, and then the reaction product is filtered. The filtrate obtained by filtration is dialyzed and dried to obtain red fluorescent carbon dots, wherein the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine to ethanolamine is (0.5-1.5):1:5.

[0008] Further, the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine to ethanolamine is 1:1:5.

[0009] Further, the specific process of the filtration is to filter the reaction product through a microporous filter membrane with a pore size of 0.1-0.45 μm; the specific process of the dialysis is to dialyze the filtrate obtained by filtration through a dialysis bag with a cut-off molecular weight of 500-3000 Da for 6-30 h.

[0010] The red fluorescent carbon dots of the present invention are characterized in that the average particle size of the red fluorescent carbon dots is less than 2 nm and the excitation wavelength is 414 nm.

[0011] The red fluorescent carbon dots of the present invention are used as a fluorescent probe for the selective detection of perfluorooctanoic acid in environmental samples.

[0012] The application of the red fluorescent carbon dots of the present invention as a fluorescent probe for the selective detection of perfluorooctanoic acid in environmental water bodies or environmental soil samples is characterized by the following specific steps:

[0013] The red fluorescent carbon dots are respectively added to perfluorooctanoic acid solutions with gradient concentrations for fluorescence quenching reaction to obtain a reaction system to be measured. The fluorescence intensities of different reaction systems to be measured are respectively measured under the conditions of an excitation wavelength of 414 nm, an emission wavelength of 652 nm, and an excitation slit and emission slit width of 5 nm. A standard curve is established according to the linear relationship between the detected fluorescence intensity and the perfluorooctanoic acid concentration. The linear detection range of the perfluorooctanoic acid concentration is 0.001-0.1 μg mL -1 、0.1-0.9 μg mL -1 and 1.0-4.0 μg mL -1 , and the detection limit is 1.2 pg mL -1 ;

[0014] The red fluorescent carbon dots are added to the environmental sample solution to be measured to carry out a fluorescence quenching reaction to obtain the reaction system to be measured. The fluorescence intensity of the reaction system to be measured is measured under the conditions of an excitation wavelength of 414 nm, an emission wavelength of 652 nm, and an excitation slit and emission slit width of 5 nm. The concentration of perfluorooctanoic acid in the environmental sample to be measured is calculated through the established standard curve.

[0015] Further, the concentration of the red fluorescent carbon dots in the reaction system to be measured is 20 μg / mL. -1 .

[0016] Further, the pH value of the reaction system to be measured is 7.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention uses oxalic acid, meso-tetra(4-carboxyphenyl) porphine, and ethanolamine as carbon sources to synthesize red fluorescent carbon dots by a hydrothermal method, and the preparation method is simple and easy to operate. The red fluorescent carbon dots prepared by the present invention have high monodispersity, good stability, good water solubility, and high fluorescence stability. The detection of perfluorooctanoic acid is realized by the static quenching between the fluorescent carbon dots and perfluorooctanoic acid; the red fluorescent carbon dots obtained in the present invention are used as a fluorescent probe to determine perfluorooctanoic acid in environmental water bodies and environmental soil samples, which has a fast response speed, high sensitivity, good selectivity, strong stability, and a wide detection range for perfluorooctanoic acid. The linear detection concentration range for perfluorooctanoic acid is 0.001 - 0.1 μg / mL, -1 0.1 - 0.9 μg / mL, -1 and 1.0 - 4.0 μg / mL, -1 , and the detection limit is 1.2 pg / mL. -1 . The red fluorescent carbon dots as a fluorescent probe have been successfully applied to the detection of perfluorooctanoic acid in environmental water bodies and environmental soil samples, and can realize the trace identification and accurate quantification of perfluorooctanoic acid with different concentrations in complex matrices, and have strong anti-interference ability. The present invention provides a new method for the simple, rapid, and sensitive detection of perfluorooctanoic acid, and has broad application prospects in the actual detection of environmental samples. Description of the Drawings

[0018] Figure 1 is the TEM image of the red fluorescent carbon dots of the present invention;

[0019] Figure 2 is the Fourier transform infrared spectrum of the red fluorescent carbon dots of the present invention;

[0020] Figure 3 is the fluorescence emission spectrum of the red fluorescent carbon dots of the present invention under different excitation wavelengths;

[0021] Figure 4AIt is a graph showing the effect of the mass ratio of oxalic acid, meso-tetrakis(4-carboxyphenyl)porphine and ethanolamine on fluorescence quenching in the present invention;

[0022] Figure 4B It is a graph showing the effect of the synthesis temperature of the red fluorescent carbon dots in the present invention on fluorescence quenching;

[0023] Figure 4C It is a graph showing the effect of the synthesis time of the red fluorescent carbon dots in the present invention on fluorescence quenching;

[0024] Figure 4D It is a graph showing the effect of the dialysis time of the red fluorescent carbon dots in the present invention on fluorescence quenching;

[0025] Figure 5A It is a graph showing the effect of the concentration of fluorescent carbon dots on fluorescence quenching during the detection of PFOA in the present invention;

[0026] Figure 5B It is a graph showing the effect of the pH value of the solution to be measured on the fluorescence intensity of red fluorescent carbon dots during the detection of PFOA in the present invention;

[0027] Figure 5C It is a graph showing the effect of the pH value of the solution to be measured on fluorescence quenching during the detection of PFOA in the present invention;

[0028] Figure 5D It is a graph showing the effect of the reaction time on fluorescence quenching during the detection of PFOA in the present invention;

[0029] Figure 6A It is a graph showing the effect of different concentrations of PFOA on the fluorescence intensity of red fluorescent carbon dots in the present invention;

[0030] Figure 6B It is a graph showing the linear relationship of different concentrations of PFOA (0.001 - 0.1 μg mL -1 ) with respect to fluorescence quenching in the present invention;

[0031] Figure 6C It is a graph showing the linear relationship of different concentrations of PFOA (0.1 - 0.9 μg mL -1 ) with respect to fluorescence quenching in the present invention;

[0032] Figure 6D It is a graph showing the linear relationship of different concentrations of PFOA (1.0 - 4.0 μg mL -1 ) with respect to fluorescence quenching in the present invention;

[0033] Figure 7 It is a fluorescence quenching comparison graph of PFOA and other perfluorinated substances and interfering ions added to the red fluorescent carbon dot solution in the present invention. Detailed implementation mode

[0034] The above content of the present invention will be further described in detail through the following examples. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. Any technology implemented based on the above content of the present invention belongs to the scope of the present invention.

[0035] The reagents, materials, and equipment used in the following examples of the present invention are as follows:

[0036] Oxalic acid, meso-tetra(4-carboxyphenyl)porphine, ethanolamine, perfluorooctanoic acid, perfluoropentanoic acid, perfluorohexanoic acid, perfluoroheptanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorododecanesulfonic acid, and perfluorooctanesulfonic acid were purchased from Shanghai Aladdin Chemical Co., Ltd. Sodium chloride, potassium chloride, nickel chloride, zinc chloride, cobalt nitrate, calcium chloride, copper nitrate, manganese chloride, lead nitrate, magnesium chloride, mercury chloride, chromium nitrate, iron chloride, ferrous chloride, anhydrous sodium acetate, zinc nitrate, sodium phosphate, sodium phosphite, sodium sulfite, sodium sulfate, calcium carbonate, sodium bicarbonate, and hydrofluoric acid were purchased from Beijing Chemical Plant. Sodium hydroxide and hydrochloric acid were purchased from Tianjin De'en Chemical Reagent Co., Ltd. Secondary water was used in the experimental process.

[0037] The main instruments and equipment used in the experiments included a fluorescence spectrometer (Cary Eclipse, Varian, USA); an ultraviolet-visible spectrophotometer (T6 New Century, Beijing Purkinje General Instrument Co., Ltd.); a transmission electron microscope (JEM-2100, JEOL Ltd., Japan); and a Fourier transform infrared spectrometer (Magna IR750, Nicolet Instrument Corporation, USA).

[0038] Example 1

[0039] Preparation of red fluorescent carbon dots (CDs):

[0040] This example provides a method for preparing red fluorescent carbon dots (CDs), which specifically includes the following steps:

[0041] Red fluorescent carbon dots were prepared by a one-step hydrothermal method using oxalic acid, meso-tetra(4-carboxyphenyl)porphine, and ethanolamine. The specific process was as follows:

[0042] First, oxalic acid, meso-tetra(4-carboxyphenyl)porphine, and ethanolamine with a mass ratio of 0.5:1:5, 0.75:1:5, 1:1:5, 1.25:1:5, and 1.5:1:5 were mixed evenly and then transferred to 50 mL high-pressure reaction vessels with a polytetrafluoroethylene inner lining, respectively. They were heated and reacted at 200 °C for 12 h in a forced-air drying oven. After the reaction, they were naturally cooled to room temperature. The obtained products were filtered through a 0.22 μm microporous filter membrane, and then the filtrate was dialyzed for 12 h using a dialysis bag (cut-off molecular weight: 1000 Da). The solution inside the dialysis bag was collected and dried in an oven to obtain red fluorescent carbon dots prepared from raw materials with different mass ratios.

[0043] Prepare a solution of red fluorescent carbon dots with a concentration of 2 mg / mL -1 and store it at 4 °C for later use.

[0044] To obtain better detection effects, the reaction temperature, reaction time, and dialysis time were optimized. Under the optimal reaction mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine, and ethanolamine of 1:1:5, the reaction temperatures of 140 °C, 160 °C, 180 °C, 200 °C, and 220 °C were optimized. Under the optimal reaction mass ratio and reaction temperature, the reaction times of 4 h, 8 h, 12 h, 16 h, and 20 h were respectively optimized. Under the optimal reaction mass ratio, reaction temperature, and reaction time, the dialysis times of 6 h, 12 h, 18 h, 24 h, and 30 h were respectively optimized, and the remaining experimental steps were the same as those described previously.

[0045] Example 2

[0046] Method for laboratory-simulating the detection of perfluorooctanoic acid (PFOA) in environmental samples:

[0047] Add the red fluorescent carbon dot solution prepared under the optimal conditions of Example 1 to PFOA solutions with different gradient concentrations for fluorescence quenching reactions to obtain the reaction systems to be measured, and establish a standard curve based on the linear relationship between the detected fluorescence intensity change and the PFOA concentration;

[0048] Add the red fluorescent carbon dot solution prepared under the optimal conditions of Example 1 to the environmental sample solution to be measured for fluorescence quenching reactions to obtain the reaction systems to be measured, obtain the fluorescence intensity change, and calculate the concentration of PFOA in the environmental sample to be measured through the established standard curve.

[0049] This example studied different carbon dot concentrations, reaction times, and pH values of the reaction system to obtain the characteristics of CDs and the optimal detection conditions. The excitation wavelength of the fluorescent carbon dots is 414 nm, the emission wavelength is 652 nm, and the excitation slit and emission slit widths are both selected as 5 nm. Seven perfluorinated pollutants (perfluoropentanoic acid, perfluorocaproic acid, perfluoroheptanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluorooctane sulfonic acid, perfluorododecane sulfonic acid) and ions (Na + , K + , Ni 2+ , Co 2+ , Ca 2+ , Cu 2+ , Mn 2+ , Pb 2+ , Mg 2+ , Hg 2 + , Cd 2+ , Fe 3+ , Fe 2+ , F- , Cl - , NO3 - , SO4 2- , SO3 2- , CO3 2- , HCO3 2- , CH3COO - , PO4 2- , HPO3 - ) were used as interferents and interfering ions to investigate their effects on the fluorescence intensity of red fluorescent carbon dots, and the selectivity for detecting PFOA was studied. The experimental results and analysis are as follows:

[0050] (1) Characterization of fluorescent carbon dots

[0051] Obtained by TEM Figure 1 showed that the red fluorescent carbon dots were evenly dispersed, with a spherical or approximately spherical appearance. The particle size distribution of the carbon dots mainly concentrated in the range of 1 - 2 nm, and the average particle size was about 1.6 nm.

[0052] Figure 2 This is the infrared spectrum of the red fluorescent carbon dots of the present invention. It can be seen from Figure 2 that the broad characteristic band centered at 3016 cm -1 is attributed to the stretching vibration of O - H / N - H. The peaks at 2929 cm -1 and 2871 cm -1 are for the stretching vibration of C - H. The peak at 1683 cm -1 is for the stretching vibration of C = O, and the peaks at 1589 cm -1 and 1526 cm -1 are for the deformation vibration of N - H. The peaks at 1374 cm -1 and 970 cm -1 are for the deformation vibration of O - H. The peaks at 1269 cm -1 and 1067 cm -1 indicate that the surface of the red fluorescent carbon dots contains C - N and C - O. The peaks at 781 cm -1 and 7127 cm -1 are for the deformation vibration of C - H. The FTIR spectrum shows that the prepared red fluorescent carbon dots have hydroxyl, amino, and carboxyl groups, and these characteristic functional groups not only enhance their water solubility but also further improve their fluorescence performance.

[0053] Figure 3It shows the change of the emission spectrum of red fluorescent carbon dots when the excitation wavelength varies in the range of 389 nm to 424 nm. It can be seen that the fluorescence intensity gradually increases as the excitation wavelength increases from 389 to 414 nm, and then decreases as the excitation wavelength increases from 414 to 424 nm. Therefore, the excitation wavelength of 414 nm is selected as the optimal excitation wavelength of the red fluorescent carbon dots. Moreover, as the excitation wavelength gradually increases, its emission peak does not shift, indicating that the red fluorescent carbon dots have non-excitation wavelength dependence, which may be related to the uniform size of the carbon dots and is also consistent with the TEM results.

[0054] (2) Optimization of the synthesis conditions of red fluorescent carbon dots

[0055] In the present invention, oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine are used as carbon sources, and red fluorescent carbon dots are synthesized by a hydrothermal method. Different synthesis conditions affect the surface state, surface passivation and carbon core of the red fluorescent carbon dots, and thus affect the fluorescence properties of the red fluorescent carbon dots and the subsequent quenching effect. By optimizing the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine, the synthesis temperature, the synthesis time and the dialysis time, PFOA has a better fluorescence quenching effect on the red fluorescent carbon dots.

[0056] The influence of the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine on fluorescence quenching is as Figure 4A shown. When the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine is 1:1:5, the quenching effect of PFOA on the prepared red fluorescent carbon dots is better than that of the red fluorescent carbon dots with other synthesis ratios. The increase in its fluorescence quenching is mainly due to the appropriate proportion of carboxyl groups and amino groups on the surface of the prepared red fluorescent carbon dots.

[0057] The influence of optimizing the reaction temperature on the fluorescence quenching of red fluorescent carbon dots is as Figure 4B shown. It can be seen from the figure that when the reaction temperatures are 140 °C, 160 °C, 180 °C and 200 °C respectively, the quenching of the red fluorescent carbon dots gradually increases. When the reaction temperature is 200 °C, the quenching effect of the red fluorescent carbon dots is the best. When the reaction temperature is 220 °C, the fluorescence quenching of the red fluorescent carbon dots decreases. This is because the reaction temperature of 200 °C is more sufficient. During the synthesis process at 220 °C, the red fluorescent carbon dots may agglomerate to a certain extent.

[0058] The influence of optimizing the reaction time on the fluorescence quenching of red fluorescent carbon dots is as Figure 4C shown. It can be seen from the figure that when the synthesis time is 12 h, the fluorescence quenching of the red fluorescent carbon dots is the best. As the time continues to extend, the fluorescence quenching of the red fluorescent carbon dots decreases significantly. This may be because the longer the carbonization time, the higher the degree of polymerization of the red fluorescent carbon dots.

[0059] The influence of dialysis time on the fluorescence quenching of red fluorescent carbon dots is as follows Figure 4D shown. It can be seen from the figure that when the dialysis time is 12 h, the fluorescence quenching effect of the red fluorescent carbon dots is the best. With the further extension of the dialysis time, the fluorescence quenching of the red fluorescent carbon dots shows a significant downward trend.

[0060] Finally, the mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl) porphine and ethanolamine is optimized to be 1:1:5, the synthesis temperature is 200 °C, the synthesis time is 12 h, and the dialysis time is 12 h as the optimal synthesis conditions for red fluorescent carbon dots.

[0061] (3) Influence of carbon dot concentration on fluorescence quenching during PFOA detection

[0062] In the reaction system to be measured, the carbon dot concentration is closely related to the initial fluorescence intensity and the degree of quenching, and it is a key parameter for the fluorescence probe to detect PFOA. When the carbon dot concentration is low, the sensitivity of detecting the target substance will increase, but the detection range is limited. And the higher the carbon dot concentration, the wider its detection range. However, when the carbon dot concentration is high, self-absorption will occur, affecting the detection result and the sensitivity is low. As Figure 5A shown, when the carbon dot concentration increases, the value of ΔF (ΔF is the difference between the blank fluorescence value F0 and the fluorescence value F after adding PFOA) increases, and when the concentration of fluorescent carbon dots is 20 μg mL -1 , ΔF reaches the maximum value, and then as the carbon dot concentration continues to increase, the value of ΔF decreases significantly. Therefore, 20 μg mL -1 is the optimal concentration of red fluorescent carbon dots for detecting PFOA.

[0063] (4) Influence of the pH value of the solution to be measured on the fluorescence intensity and fluorescence quenching of carbon dots during PFOA detection

[0064] As Figure 5C shown, when the pH value changes between 5 and 9, its quenching value ΔF first increases and then decreases. When the pH value is between 5 and 7, the quenching value gradually increases. When the pH value is between 7 and 9, the quenching value gradually decreases. And the fluorescence intensity of the carbon dots themselves remains stable between 5 and 9 ( Figure 5B ), indicating that neither acidic nor alkaline conditions are conducive to quenching. The experimental results show that when the pH value is 7, the quenching value ΔF reaches the maximum, and pH has an obvious influence on quenching. In this experiment, pH = 7 is selected as the optimal pH value for probe detection.

[0065] (5) Influence of reaction time on carbon dot fluorescence quenching during PFOA detection

[0066] The reaction time is an important parameter for optimizing the fluorescence quenching of carbon dots. If the reaction time is too short, the reaction will be incomplete, resulting in less fluorescence quenching, narrow detection linear range and low sensitivity. If the reaction time is too long, the fluorescence probe will lose its original advantages. The reaction time was optimized within 0 - 10 min, and the results are as Figure 5D shown. After adding PFOA, the fluorescence value was basically stable with no obvious change. This indicates that the reaction rate between carbon dots and PFOA is fast and the fluorescence probe has strong timeliness.

[0067] (6) Sensitivity experiment of the red fluorescent carbon dots in Example 1 for detecting PFOA

[0068] The experiment determined the linear range applicable to the detection of PFOA, and the results are as Figure 6A 、 6B 、6C and 6D shown. It can be seen from Figure 6A that as the concentration of PFOA increases, the fluorescence quenching value of carbon dots increases. From Figure 6B 、 6C and 6D, it is known that when the concentration range of PFOA is 0.001 - 0.1 μg mL -1 、0.1 - 0.9 μg mL -1 and 1.0 - 4.0 μg mL -1 , there is a good linear relationship between the fluorescence quenching value of carbon dots and the concentration of PFOA, and the detection limit is 1.2 pg mL -1 .

[0069] (7) Selectivity experiment of the red fluorescent carbon dots in Example 1 for detecting PFOA

[0070] As shown in Figure 7 , in addition to PFOA, perfluoropentanoic acid, perfluorohexanoic acid, perfluorodecanoic acid, perfluorononanoic acid, perfluorododecanesulfonic acid, perfluoroheptanoic acid, perfluorooctanesulfonic acid, and common ions such as Na + 、K + 、Ni 2+ 、Co 2+ 、Ca 2+ 、Cu 2+ 、Mn 2+ 、Pb 2 + 、Mg 2+ 、Hg 2+ 、Cd 2+ 、Fe 3+ 、Fe 2+ 、F - 、Cl - 、NO3 - 、SO4 2- 、SO3 2- 、CO3 2- 、HCO32- 、CH3COO - 、PO4 2- 、HPO3 - Effect on the fluorescence intensity of red carbon dots.

[0071] In this comparative experiment, PFOA, other perfluorinated compounds and ions were added respectively. In the reaction system, the concentration of PFOA was 0.03 μg mL -1 , the concentrations of perfluoropentanoic acid, perfluorohexanoic acid and perfluorodecanoic acid were 0.18 μg mL -1 , the concentrations of perfluorononanoic acid and perfluorododecane sulfonic acid were 0.15 μg mL -1 , the concentrations of perfluoroheptanoic acid and perfluorooctane sulfonic acid were 0.09 μgmL -1 , Pb 2+ , Mg 2+ , Hg 2+ were 0.4 μg mL -1 , Cd 2+ , Fe 3+ , Fe 2+ , F - were 0.3 μg mL -1 , Mn 2+ was 0.5 μgmL -1 , Ni 2+ , Co 2+ , Ca 2+ , Cu 2+ , Cl - , NO3 - , SO4 2- , SO3 2- , CO3 2- , HCO3 2- , CH3COO - , PO4 2- , HPO3 - were 0.6 μg mL -1 , Na + , K + were 0.7 μg mL -1 . The detection selectivity was compared through their quenching values. As Figure 7 (single) shows, only PFOA has a strong quenching effect on red fluorescent carbon dots, and no obvious fluorescence quenching was observed for other interferences. A mixture of PFOA and the above-mentioned interfering substances was placed in the solution, and the corresponding fluorescence changes were measured. From Figure 7(mixture) It can be seen that the presence of the above interfering ions has no effect on the detection of PFOA by the red fluorescent carbon dots, while some perfluorinated substances with structures similar to PFOA can promote the quenching process. The results show that the prepared red fluorescent carbon dot fluorescent probe has strong specific recognition performance for perfluorooctanoic acid.

[0072] Example 3

[0073] Study on the Detection of PFOA in Actual Environmental Water Bodies and Environmental Soil Samples by Red Fluorescent Carbon Dots

[0074] The red fluorescent carbon dots obtained in Example 1 of the present invention and the method in Example 2 were applied to the detection of PFOA in actual environmental water bodies and environmental soil samples. In this example, 6 water samples and 4 soil samples were collected to detect PFOA. The water samples were taken from the Wei River, a printing and dyeing factory in Xinxiang City, Siyanjing in Hangzhou, the effluent of a textile factory in Xinxiang City, the Yangtze River, and the effluent of a domestic sewage treatment plant in Xi'an. The soil samples were taken from a refinery in Fan County, a chemical plant in Fan County, a sewage treatment plant in Fan County, and a waste treatment plant in Fan County. The fluorescent probe was used to analyze the blank samples and the spiked samples. The experimental results are shown in Table 1. The recovery rates of PFOA in different complex matrices are in the range of 95.4% - 104.9%, and the relative standard deviation (RSD) does not exceed 4.3% (n = 6), indicating that the red fluorescent carbon dots of the present invention can sensitively detect PFOA, and it is feasible to detect PFOA in actual samples. The detection results have high reliability and accuracy, and have broad application prospects in the detection of actual environmental samples.

[0075] Table 1 Detection of PFOA in Actual Environmental Samples

[0076]

[0077]

[0078] In summary, the present invention uses oxalic acid, meso-tetra(4-carboxyphenyl) porphine, and ethanolamine as carbon sources, and synthesizes red fluorescent carbon dots by a hydrothermal method. The detection of PFOA is realized by the static quenching between the fluorescent carbon dots and PFOA; the red fluorescent carbon dots obtained in the present invention are used as a fluorescent probe to determine PFOA in environmental water bodies and soil samples. It has a fast response speed, high sensitivity, good selectivity, strong stability, and a wide detection range for PFOA. The detection concentration range for perfluorooctanoic acid is 0.001 - 0.1 μg mL -1 , 0.1 - 0.9 μg mL -1 and 1.0 - 4.0 μg mL -1 , and the detection limit is 1.2 pg mL -1This fluorescent probe has been successfully applied to the detection of PFOA in environmental water bodies and environmental soil samples, enabling trace identification and accurate quantification of PFOA at different concentrations in complex matrices, and having strong anti-interference ability. The present invention provides a new method for the simple, rapid, and sensitive detection of PFOA, and has broad application prospects in the detection of actual environmental samples.

[0079] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. Application of red fluorescent carbon dots as a fluorescent probe in detecting perfluorooctanoic acid in environmental samples. The specific preparation process of the red fluorescent carbon dots is as follows: Oxalic acid, meso-tetra(4-carboxyphenyl)porphine and ethanolamine are heated in water to 140 - 220 °C for hydrothermal reaction for 4 - 20 h, and then the reaction product is filtered. The filtrate obtained by filtration is dialyzed and dried to obtain red fluorescent carbon dots. The mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine to ethanolamine in the feed is (0.5 - 1.5):1:

5. The average particle size of the red fluorescent carbon dots is less than 2 nm, and its excitation wavelength is 414 nm.

2. The application according to claim 1, wherein: The mass ratio of oxalic acid, meso-tetra(4-carboxyphenyl)porphine to ethanolamine in the feed is 1:1:

5.

3. The application according to claim 1, characterized in that: The specific process of the filtration is to filter the reaction product through a microporous filter membrane with a pore size of 0.1 - 0.45 μm. The specific process of the dialysis is to dialyze the filtrate obtained by filtration through a dialysis bag with a cut-off molecular weight of 500 - 3000 Da for 6 - 30 h.

4. The application according to claim 1, wherein: The red fluorescent carbon dots are used as a fluorescent probe in the detection of perfluorooctanoic acid in environmental water bodies or environmental soil samples.

5. The application according to claim 4, characterized in that The specific steps are as follows: The red fluorescent carbon dots are added to perfluorooctanoic acid solutions with gradient concentrations respectively for fluorescence quenching reaction to obtain the reaction systems to be measured. The fluorescence intensities of different reaction systems to be measured are measured respectively under the conditions of an excitation wavelength of 414 nm, an emission wavelength of 652 nm, and an excitation slit and emission slit width of 5 nm. A standard curve is established according to the linear relationship between the detected fluorescence intensity and the perfluorooctanoic acid concentration. Red fluorescent carbon dots are added to the environmental sample solution to be measured to carry out a fluorescence quenching reaction to obtain the reaction system to be measured. The fluorescence intensity of the reaction system to be measured is measured under the conditions of an excitation wavelength of 414 nm, an emission wavelength of 652 nm, and an excitation slit and emission slit width of 5 nm. The concentration of perfluorooctanoic acid in the environmental sample to be measured is calculated through the established standard curve. The linear detection range of the perfluorooctanoic acid concentration is 0.001 - 0.1 μg mL -1 , 0.1 - 0.9 μg mL -1 and 1.0 - 4.0 μg mL -1 , and the detection limit is 1.2 pg mL -1 .

6. The application according to claim 5, wherein: The concentration of the red fluorescent carbon dots in the reaction system to be measured is 20 μg / mL -1 .

7. The application according to claim 5, characterized in that: The pH value of the reaction system to be measured is 7.

Images