A method for detecting Fe in environmental water bodies by using nitrogen-doped carbon dots as a fluorescent probe 3+ ​

Abstract

The application discloses a method for detecting Fe 3+ in environmental water bodies by using nitrogen-doped carbon dots as a fluorescent probe and belongs to the field of analysis and detection. The application uses cysteine and ethylenediamine as precursors, synthesizes stable blue-light carbon dots as a fluorescent probe through one-step hydrothermal method, and experiments show that the fluorescence intensity of the carbon dots will obviously be quenched with the increase of the concentration of Fe 3+ in the system. A linear model is constructed by using the relationship between the fluorescence intensity of the solution and the concentration of Fe 3+ , so that the concentration of Fe 3+ contained in the environmental water sample can be quantitatively detected. Compared with traditional detection methods, the application is simple to operate, safe, low in cost and high in sensitivity, and establishes a new method for detecting Fe 3+ in environmental water bodies.

Description

TECHNICAL FIELD

[0001] The application relates to a method for detecting Fe 3+ in environmental water bodies by using nitrogen-doped carbon dots as fluorescent probes, and belongs to the field of analysis and detection. BACKGROUND

[0002] Iron ions (Fe 3+ ) play an important role in maintaining normal physiological activities of the human body, such as exchange and tissue of the respiratory process, detoxification of drugs in cells, cell proliferation and differentiation, synthesis of DNA and RNA, and gene regulation, etc. However, excessive iron storage in the body can induce the enhancement of lipid peroxidation reaction, leading to imbalance of the oxidation and antioxidant systems of the body, direct damage to DNA, and induction of mutations, which are related to tumors of various organs such as the liver, lungs and esophagus. One of the reasons for the abnormal content of Fe 3+ in the human body is that there may be excessive metal ions in drinking water. Water is a basic guarantee for maintaining normal life activities of the human body, and metal pollution entering water circulation can directly cause great harm to the human body. Therefore, high-sensitivity detection of Fe 3+ in water bodies is of great significance to the environment and biological systems.

[0003] Traditional Fe 3+ detection methods mainly include atomic absorption spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry and electrochemical methods, etc. These methods use expensive instruments, have relatively harsh detection conditions, and are complicated in sample pretreatment, and are not generally applicable to on-site sensitive detection.

[0004] The fluorescence method has the advantages of high sensitivity, simple operation, low cost and time saving. The use of fluorescent nanomaterials as fluorescent probes greatly improves the detection sensitivity, and the detection has the advantages of simple operation, short detection time and high sensitivity. At present, fluorescence spectroscopy technology has been widely applied in the fields of environment, chemistry, medicine and food, and some scholars have proposed to use fluorescence spectroscopy technology to detect Fe 3+ in water bodies. However, the operation method and sensitivity in the related research reports are not as good as those of the traditional detection methods. SUMMARY

[0005] [TECHNICAL PROBLEM]

[0006] At present, the methods for detecting Fe 3+ mainly include atomic absorption spectrometry, atomic emission spectrometry, inductively coupled plasma mass spectrometry and electrochemical methods, etc. Most of the detection methods are time-consuming and involve complex sample processing procedures, or require professional technical personnel and expensive costs. The research on the use of fluorescence spectroscopy to detect Fe 3+ in environmental water bodies needs to be further developed.

[0007] [Technical Solution]

[0008] To address the aforementioned problems, this invention provides a method for detecting Fe in environmental water using nitrogen-doped carbon dots as fluorescent probes. 3+ This invention proposes a method based on the internal filtration effect and intermolecular electrostatic interactions, using nitrogen-doped carbon dots as fluorescent probes for the detection of Fe in environmental water. 3+ The detection method enables convenient, safe, and sensitive quantitative detection of Fe in environmental water bodies. 3+ .

[0009] This invention provides a method for quantitative detection of Fe in water using nitrogen-doped carbon dots as fluorescent probes. 3+ A method for determining the content, the method comprising the following steps:

[0010] (1) Add cysteine ​​and ethylenediamine to water, mix well, and obtain a mixture; then add the mixture to a high-pressure reactor and heat to carry out a hydrothermal reaction; after the reaction is completed, concentrate the reaction solution and purify it by column chromatography to obtain a purified solution, further concentrate it to obtain N-CDs concentrate, and then dilute it with water to obtain a carbon dot solution.

[0011] (2) A series of known Fe salts were prepared by adding soluble iron salts to water. 3+ The concentration of the standard water sample is then added to the carbon dot solution obtained in step (1), mixed and allowed to stand, and then the corresponding fluorescence emission spectrum is measured.

[0012] (3) Fe was not added during collection. 3+ The fluorescence intensity peak F0 at 383 nm in the time-varying fluorescence emission spectrum, and a series of known Fe 3+ The fluorescence intensity peak F at 383 nm wavelength in the fluorescence emission spectrum of standard water samples of different Fe concentrations was calculated. 3+ The quenching degree of concentration C = (F0 - F) / F0; using the quenching degree C and Fe 3+ A linear detection model was constructed based on concentration.

[0013] In one embodiment of the present invention, in step (1), the dosage of cysteine ​​relative to ethylenediamine is (0.1-0.5) g / mL; specifically, 0.2 g / mL may be selected.

[0014] In one embodiment of the present invention, in step (1), the concentration of cysteine ​​in the mixture is 0.01-0.05 g / mL; specifically, 0.02 g / mL may be selected.

[0015] In one embodiment of the present invention, the temperature of the hydrothermal reaction in step (1) is 200-220°C; specifically, 210°C may be selected.

[0016] In an embodiment of the present application, the time for the hydrothermal reaction in step (1) is 8-15 hours; specifically, 10 hours can be selected.

[0017] In an embodiment of the present application, the hydrothermal reaction in step (1) is carried out in an autoclave containing a tetrafluoroethylene lining.

[0018] In an embodiment of the present application, in step (1), the purified liquid is further concentrated to a degree of concentration to one fourth of the volume of the purified liquid.

[0019] In an embodiment of the present application, in step (1), the parameters for the purification by column chromatography are: the stationary phase is silica gel, and the mobile phase is a mixture of methanol and dichloromethane, and the volume ratio of methanol to dichloromethane is 1:8.

[0020] In an embodiment of the present application, in step (1), the N-CDs concentrate is diluted with water at a dilution factor of 100 times.

[0021] In an embodiment of the present application, in step (2), the volume ratio of the carbon dot solution to the standard water sample is 1:2.

[0022] In an embodiment of the present application, in step (2), the soluble iron salt is selected from: ferric chloride hexahydrate.

[0023] In an embodiment of the present application, in step (2), the water body is deionized water, tap water, or lake water, etc.

[0024] In an embodiment of the present application, in step (2), the deionized water standard water sample containing Fe 3+ is configured to have a concentration of Fe 3+ of 0-100 μM, the tap water standard water sample has a concentration of Fe 3+ of 0-60 μM, and the lake water standard water sample has a concentration of Fe 3+ of 0-150 μM.

[0025] In an embodiment of the present application, in step (4), the fluorescence emission spectrum is measured using a FLS980 fluorescence spectrometer produced by Edinburg, UK, the excitation wavelength is 315 nm, the peak wavelength is 383 nm, and the excitation and emission slit widths are 2.5 nm and 2.5 nm, respectively.

[0026] In an embodiment of the present application, the method specifically comprises:

[0027] (1) adding cysteine and ethylenediamine into water, mixing to obtain a mixture; then adding the mixture into an autoclave, and heating from room temperature to 210°C in an electric furnace and maintaining for 10 hours to obtain a carbon dot stock solution;

[0028] (2) After the reaction is completed, purification is carried out to obtain nitrogen-doped carbon dots (N-CDs); the obtained N-CDs are diluted to a required concentration to obtain a carbon dot aqueous solution, and are stored in a refrigerator (4℃) for subsequent use;

[0029] (3) Fe 3+ is added to deionized water, filtered tap water and lake water to prepare a series of standard water samples with known Fe 3+ concentrations, and then the N-CDs in step (2) are added to the series of standard water samples with known Fe 3+ concentrations, and after standing, the corresponding fluorescence emission spectra are measured;

[0030] (4) The fluorescence intensity peak value F0 at 383 nm in the fluorescence emission spectrum when Fe 3+ is not added, and the fluorescence intensity peak value F at 383 nm in the fluorescence emission spectrum of a series of standard water samples with known Fe 3+ concentrations are collected; the quenching degree C = (F0-F) / F0 of different Fe 3+ concentrations is calculated; and a linear detection model is constructed by using the quenching degree C and the Fe 3+ concentration.

[0031] The application provides application of the above method in the field of environmental detection.

[0032] [Advantages]:

[0033] 1. The fluorescence emission of the N-CDs used in the application is in the ultraviolet band, the Stokes shift is small, and the energy utilization rate is high. Moreover, the fluorescence excitation of the N-CDs has a large degree of overlap with the absorption of Fe 3+ , thereby providing a good basis for realizing detection of Fe 3+ .

[0034] 2. The concentration of the N-CDs used in the application is optimized, and the N-CDs have good effects when directly added to filtered actual water samples, thereby increasing the sensitivity of detection.

[0035] 3. The method realizes quantitative detection of Fe 3+ in environmental water bodies by using the N-CDs fluorescent probe synthesized by using cysteine and ethylenediamine as raw materials for the first time, and the detection operation is simple, and only a few solutions need to be mixed, stood and then measured for the fluorescence emission spectrum.

[0036] 4. The application first constructs a linear model in deionized water, the linear range is 0.3-20 μM, and the standard curve equation is C = 0.02782I + 0.0282 (C is the quenching degree of carbon dot fluorescence and I is the Fe 3+ concentration), and the determination coefficient R 2=0.998, with a detection limit as low as 0.069 μM. When the detection scheme was applied to actual water samples, the limit was 1-30 μM in tap water, and the standard curve equation was C = 0.01849I + 0.06783 (where C is the quenching degree of carbon point fluorescence and I is the Fe...). 3+ Concentration), coefficient of determination R 2 =0.997, detection limit as low as 0.21 μM; in lake water, it is 2-30 μM, and the standard curve equation is C = 0.04544I + 0.01466 (C is the quenching degree of carbon point fluorescence and I is the Fe...). 3+ Concentration), coefficient of determination R 2 =0.965, with a detection limit as low as 0.59 μM. The method showed recoveries of 96.6%-103.3% in tap water and lake water, demonstrating good detection accuracy and suitability for monitoring Fe in environmental water bodies. 3+ The issue of excessive levels of certain substances is of great significance. Attached Figure Description

[0037] Figure 1 For the detection of Fe in environmental water samples by N-CDs 3+ The flowchart.

[0038] Figure 2 The absorption spectrum, fluorescence excitation spectrum, and emission spectrum of the N-CDs aqueous solution in Example 1 are shown.

[0039] Figure 3 (a) For Fe in a deionized water sample 3+ N-CDs / Fe at concentrations of 0-100 μM 3+ Fluorescence emission spectrum of the solution (excitation wavelength 315 nm); (a) Inset: Fluorescence quenching degree ((F0-F) / F0) versus Fe 3+ Scatter plot of concentration (Fe) 3+ The concentration is 0-100 μM, and F0 and F are the presence and absence of Fe, respectively. 3+ (a) Peak intensity of the solution at time; (b) Degree of quenching and Fe 3+ Linear fitting plots for concentrations ranging from 0.3 to 20 μM.

[0040] Figure 4 (a) For Fe in tap water samples 3+ N-CDs / Fe at concentrations of 0-60 μM 3+ Fluorescence emission spectrum of the solution (excitation wavelength 315 nm); (a) Inset: Fluorescence quenching degree ((F0-F) / F0) versus Fe 3+ Scatter plot of concentration (Fe) 3+ The concentration ranges from 0 to 60 μM, with F0 and F representing the absence and presence of Fe, respectively. 3+ (a) Peak intensity of the solution at time; (b) Degree of quenching and Fe3+ Linear fitting plot of the fluorescence quenching degree ((F0-F) / F0) versus Fe

[0041] Figure 5 (a) In lake water samples, Fe 3+ N-CDs / Fe 3+ Fluorescence emission spectra of the solution (excitation wavelength: 315 nm); (a) inset: scatter plot of the fluorescence quenching degree ((F0-F) / F0) versus Fe 3+ concentration (Fe 3+ F0 and F are the peak intensities of the solution in the absence and presence of Fe 3+ respectively); (b) quenching degree versus Fe 3+ Linear fitting plot of the fluorescence quenching degree ((F0-F) / F0) versus Fe

[0042] Figure 6 To compare the anti-interference ability of N-CDs for Fe 3+ Fluorescence quenching degree curves of 5 μM and 10 μM Fe

[0043] Figure 7 To compare the anti-interference ability of N-CDs for Fe 3+ Results plot of the anti-interference ability of N-CDs for Fe DETAILED DESCRIPTION

[0044] The embodiments of the present application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application.

[0045] Example 1 Preparation of nitrogen-doped carbon dots

[0046] The preparation of nitrogen-doped carbon dots includes the following steps:

[0047] (1) Mix 0.8 g of cysteine in 4 mL of ethylenediamine, and add ultrapure water to the total volume of the mixed solution to 40 mL. Move the mixture to a 100-mL tetrafluoroethylene-lined autoclave and heat from room temperature to 210°C in an electric furnace and keep for 10 hours.

[0048] (2) After the heating is completed, cool the reaction product to room temperature, concentrate the product to one-fifth of the original volume under vacuum; then purify; the purification of N-CDs is carried out by column chromatography (the purification parameters are: the stationary phase is silica gel, and the mobile phase is a mixture of methanol and dichloromethane at a volume ratio of 1:8), to obtain a purified liquid; concentrate to one-fourth of the original volume of the purified liquid to obtain an N-CDs concentrate;

[0049] (3) The N-CDs concentrate obtained by purification and concentration was diluted 100 times with water to obtain a carbon dot solution, which was stored in a 4°C refrigerator for subsequent use.

[0050] (4) The absorption spectrum, fluorescence excitation spectrum and emission spectrum of the N-CDs are shown in Figure 2 .

[0051] Construction of a detection model in Example 2

[0052] A method for detecting Fe 3+ in environmental water bodies based on the nitrogen-doped carbon dots as a fluorescent probe described in Example 1 includes the following steps for constructing a standard curve:

[0053] (1) Deionized water, or tap water and lake water samples filtered with a 0.22 μm microporous membrane, respectively, were used as solvents, and Fe 3+ (hexahydrated ferric chloride) was added to the solvents to prepare a series of deionized water-Fe 3+ standard samples with Fe 3+ concentrations of 0-100 μM, tap water-Fe 3+ standard samples with Fe 3+ concentrations of 0-60 μM, and lake water-Fe 3+ standard samples with Fe 3+ concentrations of 0-150 μM.

[0054] 1 mL of the carbon dot solution obtained in Example 1 was mixed with 2 mL of each of the deionized water-Fe 3+ standard sample, tap water-Fe 3+ standard sample or lake water-Fe 3+ standard sample, and was allowed to stand at room temperature.

[0055] (2) The samples in (1) were subjected to fluorescence spectrum detection, and the scanning conditions were as follows: the excitation wavelength was 315 nm, the emission wavelength scanning range was 330-530 nm, the scanning interval was 1 nm, and the slit width was set to 2.5 / 2.5 nm (excitation slit / emission slit). The fluorescence intensity peak value F at 383 nm was obtained. The fluorescence spectrum detection was performed on the Fe 3+ concentration 0 standard sample to obtain the fluorescence intensity peak value F0 at 383 nm. The quenching degree C of different Fe 3+ concentrations was calculated by the following formula: C = (F0-F) / F0.

[0056] (3) The relationship between the fluorescence intensity of the carbon dots in the deionized water standard sample solution with different Fe 3+ concentrations and the Fe 3+ concentration is shown in Figure 3 (a), and the quenching degree C and the Fe 3+The fitted curve of concentration I is as follows Figure 3 (b). From Figure 3 (a)(b) shows that when Fe 3+ Within the concentration range of 0.3-20 μM, the quenching degree of carbon points C and Fe 3+ The concentration I shows a linear relationship, with the linear regression equation being C = 0.02782I + 0.0282, and the coefficient of determination R0. 2 =0.998, detection limit is 0.069μM.

[0057] (4) Add different Fe 3+ The fluorescence intensity and fluorescence quenching degree of carbon dots in the standard tap water sample solution of different concentrations are related to Fe. 3+ The relationship of concentration is as follows Figure 4 As shown in (a), the quenching degree C and Fe 3+ The fitted curve of concentration I is as follows Figure 4 (b). From Figure 4 (a)(b) shows that when Fe 3+ The quenching degree of carbon points C and Fe in the concentration range of 1-30 μM 3+ The concentration I shows a linear relationship, with the linear regression equation being C = 0.01849I + 0.06783, and the coefficient of determination R0. 2 =0.997, detection limit is 0.21μM.

[0058] (5) Add different Fe 3+ The fluorescence intensity and fluorescence quenching degree of carbon dots in lake water standard sample solutions of varying concentrations are related to Fe. 3+ The relationship of concentration is as follows Figure 5 As shown in (a), the quenching degree C and Fe 3+ The fitted curve of concentration I is as follows Figure 5 (b). From Figure 5 (a)(b) shows that when Fe 3+ The quenching degree of carbon points C and Fe in the concentration range of 2-30 μM 3+ The concentration I shows a linear relationship, with the linear regression equation being C = 0.04544I + 0.01466, and the coefficient of determination R0. 2 =0.965, detection limit is 0.59μM.

[0059] Example 3: Spiked Recovery Verification

[0060] Mix 1 mL of the carbon dot solution obtained in Example 1 with 2 mL of samples with different spiking concentrations shown in Table 1, and let stand at room temperature. Determine the concentration using the same method as in Example 2. Specific detection results are shown in Table 1.

[0061] As can be seen from Table 1, the test results are accurate and feasible.

[0062] Table 1. The recovery and RSD of N-CDs method for detecting Fe in environmental water samples 3+

[0063]

[0064] Example 4. The change of carbon dot concentration on detection

[0065] In order to make the detection method more sensitive and accurate, the concentration of N-CDs, i.e. the dilution multiple, was optimized.

[0066] The N-CDs stock solution was diluted to 10, 40, 70, 100, 150 and 200 times, respectively. Equal amounts of deionized water, 5 μM and 10 μM Fe 3+ were added to each portion, respectively. The fluorescence degree of the mixed solution was measured and the quenching degree was calculated, and the results are shown in Figure 6 The image shows that the quenching degree is the largest when the N-CDs stock solution is diluted 100 times. It is inferred that when the dilution degree is too low, the concentration of N-CDs is too high, and the lower concentration of Fe 3+ has less effect on N-CDs, and cannot play a role in sensitive detection. When the concentration of N-CDs is too low, the fluorescence intensity of N-CDs itself is weak, and the quenching effect is also weakened. Therefore, the N-CDs is diluted 100 times as the experimental condition.

[0067] Example 5. Anti-interference ability of the detection model in the system

[0068] The fluorescence quenching of N-CDs mixed with 14 kinds of common metal ions was measured to verify the anti-interference ability of N-CDs for detecting Fe 3+ . As shown in Figure 7 , when N-CDs was incubated with various metal ions at the same concentration, although individual ions also had a slight effect on carbon dots, the comparison showed that Fe 3+ had the most obvious fluorescence quenching effect on carbon dots, indicating that carbon dots had relatively high selectivity for Fe 3+ ions. This also laid a good foundation for the practical application of N-CDs for detecting Fe 3+ in environmental water.

[0069] Comparative Example 1

[0070] The detection model of the present application was compared with the currently published detection scheme, and the results are shown in Table 2.

[0071] Table 2. Comparison of detection range and detection limit of different carbon dot methods for detecting Fe 3+

[0072] ​​

[0073]

[0074] The comparison results show that, compared with the method using other raw materials, the detection method using cysteine and ethylenediamine as raw materials can obtain a lower detection limit, and has a greater progress in sensitivity. Compared with two patent methods for detecting Fe 3+ using nitrogen-doped carbon dots, the method of the present application can simultaneously obtain a wider detection range and a lower detection limit at a low concentration, which is beneficial to improve the accuracy and reliability in actual detection.

Claims

1. A method for quantitative detection of Fe in water using nitrogen-doped carbon dots as fluorescent probes. 3+ A method for determining the content, the method comprising the following steps: (1) Add cysteine ​​and ethylenediamine to water, mix well, and obtain a mixture; then add the mixture to a high-pressure reactor and heat to carry out a hydrothermal reaction; after the reaction is completed, concentrate the reaction solution and purify it by column chromatography to obtain a purified solution, further concentrate it to obtain N-CDs concentrate, and then dilute it with water to obtain a carbon dot solution. (2) A series of known Fe salts were prepared by adding soluble iron salts to water. 3+ The concentration of the standard water sample is then added to the carbon dot solution obtained in step (1), mixed and allowed to stand, and then the corresponding fluorescence emission spectrum is measured. (3) Collection without adding Fe 3+ The fluorescence intensity peak F0 at 383 nm in the time-varying fluorescence emission spectrum, and a series of known Fe 3+ The fluorescence intensity peak F at 383 nm wavelength in the fluorescence emission spectrum of standard water samples of different Fe concentrations was calculated. 3 + The quenching degree of concentration C = (F0 - F) / F0; using the quenching degree C and Fe 3+ A linear detection model was constructed based on concentration.

2. The method according to claim 1, characterized in that, In step (1), the dosage of cysteine ​​relative to ethylenediamine is (0.1-0.5) g / mL.

3. The method according to claim 1, characterized in that, In step (1), the concentration of cysteine ​​in the mixture is 0.01-0.05 g / mL.

4. The method according to claim 1, characterized in that, The temperature of the hydrothermal reaction in step (1) is 200-220℃.

5. The method according to claim 1, characterized in that, The hydrothermal reaction time in step (1) is 8-15 hours.

6. The method according to claim 1, characterized in that, In step (1), the parameters for purification by column chromatography are: the stationary phase is silica gel, the mobile phase is a mixture of methanol and dichloromethane, and the volume ratio of methanol to dichloromethane is 1:

8.

7. The method according to claim 1, characterized in that, In step (1), the N-CDs concentrate is diluted with water by a factor of 100.

8. The method according to claim 1, characterized in that, In step (2), the volume ratio of the carbon dot solution to the standard water sample is 1:

2.

9. The method according to any one of claims 1-8, characterized in that, In step (2), the water body is deionized water, tap water, or lake water.

10. The application of the method according to any one of claims 1-9 in the field of environmental monitoring.

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