Nitrogen-sulfur co-doped carbon dot fluorescent probes based on seven-membered cucurbit rings: their preparation and application

Abstract

This invention discloses a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring, its preparation, and its application. The nitrogen-sulfur co-doped carbon dot fluorescent probe of this invention is prepared by a high-temperature, high-pressure hydrothermal reaction of a seven-membered cucurbit ring and mercaptosuccinic acid. It can be used to detect nitroaniline, and the preparation method is simple and industrially feasible. Furthermore, the detection process is simple, rapid, sensitive, has strong anti-interference ability, and a low detection limit, which is of great significance for the efficient and rapid detection of nitroaniline in water.

Description

Technical Field

[0001] This invention relates to a carbon dot fluorescent probe, its preparation and application, and in particular to a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring, its preparation and application. Background Technology

[0002] With the rapid development of the global chemical industry, the discharge of industrial wastewater has increased, and monitoring and removing pollutants from wastewater has become a major challenge facing the world.

[0003] Nitroaniline (p-NA) is an important intermediate in the production of dyes, pesticides, pharmaceuticals, fuel additives, antioxidants, anti-aging agents, light stabilizers, and developers.

[0004] In particular, p-nitroaniline is one of the most abundant organic pollutants in wastewater. Therefore, rapid and efficient detection of whether the discharge of p-nitroaniline in wastewater meets the standards is essential for environmental protection and public health.

[0005] Currently reported methods for the determination of p-nitroaniline include high-performance liquid chromatography (HPLC), spectrophotometry, and electrochemical methods. However, these methods have drawbacks such as complex sample preparation processes, long processing times, and expensive raw materials and detection equipment.

[0006] Therefore, it is urgent to develop an efficient and simple analytical method to quickly and accurately determine the content of p-NA in polluted wastewater. Summary of the Invention

[0007] The purpose of this invention is to provide a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring, its preparation, and its application. The carbon dot fluorescent probe of this invention can be used to detect nitroaniline, and its preparation method is simple and industrially feasible. Furthermore, the detection process is simple, rapid, sensitive, has strong anti-interference ability, and a low detection limit, which is of great significance for the efficient and rapid detection of nitroaniline in water.

[0008] One of the technical solutions of the present invention is to provide a method for preparing a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring, which is prepared by a high-temperature and high-pressure hydrothermal reaction of a seven-membered cucurbit ring and mercaptosuccinic acid.

[0009] Specifically, the aforementioned method for preparing nitrogen-sulfur co-doped carbon dot fluorescent probes based on seven-membered cucurbit rings is as follows:

[0010] S1. Weigh out the seven-membered cucurbitacin solution and the mercaptosuccinic acid solution according to the molar ratio of seven-membered cucurbitacin: mercaptosuccinic acid ≥ 1:2;

[0011] S2. Mix the seven-membered cucurbitacin solution and mercaptosuccinic acid solution, then disperse them evenly in ultrapure water, and then transfer them to a polytetrafluoroethylene high-pressure reactor for a closed hydrothermal reaction at 160-200℃ for 10-15 hours.

[0012] S3. After the reaction is complete, the sample is cooled to room temperature, filtered, centrifuged, dialyzed, and rotary evaporated to obtain a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring.

[0013] Specifically, in the aforementioned method for preparing nitrogen-sulfur co-doped carbon fluorescent probes based on seven-membered cucurbit rings, the concentration of the seven-membered cucurbit ring solution is 1.0 × 10⁻⁶. -3 mol.L -1 .

[0014] Specifically, in the aforementioned method for preparing nitrogen-sulfur co-doped carbon fluorescent probes based on seven-membered cucurbit rings, the concentration of the MSA solution is 2.0 × 10⁻⁶. -3 mol.L -1 .

[0015] Specifically, in the aforementioned method for preparing nitrogen-sulfur co-doped carbon fluorescent probes based on a seven-membered cucurbit ring, the molar ratio of the seven-membered cucurbit ring to mercaptosuccinic acid is 1:2.

[0016] Specifically, in the aforementioned method for preparing nitrogen-sulfur co-doped carbon fluorescent probes based on seven-membered cucurbit rings, the reaction temperature in step S2 is 180℃ and the reaction time is 12h.

[0017] The second technical solution of the present invention is to provide a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring prepared according to the aforementioned method.

[0018] The third technical solution of the present invention provides an application of a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline, an organic pollutant in water.

[0019] Specifically, the aforementioned application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water includes the following steps:

[0020] S1. Dissolve the carbon dot fluorescent probe in ultrapure water to obtain a concentration of 400 μg / mL. -1 Fluorescent probe solution;

[0021] S2. Add solutions containing different concentrations of nitroaniline to the fluorescent probe solution of S1, mix them thoroughly and react for 2 min, then measure the fluorescence emission spectrum at a fixed excitation wavelength of 365 nm, and plot the fluorescence intensity change curve at an emission wavelength of 460 nm.

[0022] S3. Based on the curve in S2, calculate the intensity change of the fluorescence emission spectrum at 460m before and after adding the nitroaniline solution to obtain the standard curve;

[0023] S4. Add the sample to be tested to the fluorescent probe solution in S1, and perform fluorescence emission with a fixed excitation wavelength of 365nm. Observe the fluorescence intensity at 460nm, and then perform qualitative and quantitative tests on nitroaniline in the sample according to the standard curve.

[0024] Specifically, regarding the application of the aforementioned nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water, the specific testing method for S4 is as follows: if the fluorescence intensity at the emission wavelength of 460 nm decreases significantly, it indicates that the sample contains p-nitroaniline; if no significant change occurs, it indicates that the sample does not contain p-nitroaniline or its content is below the detection limit of the probe. Alternatively, if the color of the probe solution in the quartz fluorescent cuvette is observed to quench under ultraviolet light, it indicates that the detection solution contains p-nitroaniline; if no quenching is observed, it indicates that the water does not contain p-nitroaniline or its content is below the detection limit of the probe.

[0025] Beneficial effects of the present invention

[0026] 1. The fluorescent probe prepared by this invention is a novel nitrogen-sulfur co-doped carbon dot probe based on a seven-membered cucurbit ring, which can detect nitroaniline, an organic pollutant in water.

[0027] 2. The fluorescent probe of this invention has the advantages of high sensitivity, simple sample processing, convenient operation, rapid measurement, low analysis cost, and low manufacturing cost.

[0028] 3. The raw materials of the fluorescent probe of the present invention are characterized by low cost and easy availability.

[0029] 4. Combining the seven-membered cucurbitacin with mercaptosuccinic acid and quantum dots improves the solubility of the seven-membered cucurbitacin and increases the physical and chemical stability of the carbon dots.

[0030] 5. The fluorescent probe of this invention has the advantages of strong anti-interference ability and low detection limit, with a detection limit of 5.89 × 10⁻⁶. - 7 mol.L -1 . Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the synthesis steps of the nitrogen-sulfur co-doped carbon dot (hereinafter referred to as Q[7]-CDs) fluorescent probe based on the seven-membered cucurbit ring and the detection of p-nitroaniline (hereinafter referred to as p-NA);

[0032] Figure 2The fluorescence emission spectrum and ultraviolet-visible absorption spectrum of Q[7]-CDs are shown, where (a) is the fluorescence emission spectrum of Q[7]-CDs at different wavelengths in the range of 235nm-395nm, and (b) is the ultraviolet-visible absorption spectrum of Q[7]-CDs as well as the optimal fluorescence excitation spectrum and the optimal fluorescence emission spectrum.

[0033] Figure 3 The Fourier transform infrared spectrum of Q[7]-CDs;

[0034] Figure 4 X-ray photoelectron spectrum of Q[7]-CDs;

[0035] Figure 5 (a) is a bar chart of the fluorescence quenching efficiency of 16 benzene ring-substituted organic pollutants for selective recognition of Q[7]-CDs, and (b) is a graph of fluorescence changes under ultraviolet light after adding equal amounts of 16 different benzene-substituted organic pollutants to the Q[7]-CDs solution.

[0036] Figure 6 The fluorescence color change of Q[7]-CDs under ultraviolet light when different concentrations of p-NA were added;

[0037] Figure 7 (a) is the fluorescence titration spectrum of p-NA solution of different concentrations gradually added to Q[7]-CDs solution, and (b) is the curve of p-NA concentration versus I0-I standard curve based on the curve change in (a).

[0038] Figure 8 (a) shows the UV absorption spectra of p-NA and Q[7]-CDs@p-NA, as well as the optimal fluorescence excitation and emission spectra of Q[7]-CDs. Figure 8 (b) is a UV absorption titration diagram of adding different concentrations of p-NA to Q[7]-CDs solution;

[0039] Figure 9 The proton NMR spectrum of pure p-NA;

[0040] Figure 10 The 1H NMR spectra of mercaptosuccinic acid, Q[7]-CDs, p-NA, and Q[7]-CDs@p-NA are shown.

[0041] Figure 3 and Figure 4 The successful synthesis of Q[7]-CDs was confirmed, and the functional groups such as -COOH and -SH give Q[7]-CDs good water solubility, physical and chemical stability, which is convenient for practical application.

[0042] Figure 5The bar chart of quenching efficiency shows that the quenching rate is the highest after adding p-NA, indicating that it has a good specific recognition ability for p-NA.

[0043] Figure 5 b and Figure 6 It can be seen that the luminescence of the Q[7]-CDs solution under ultraviolet light darkened after the addition of p-NA;

[0044] Figure 7 It can be seen that as p-NA is continuously added, the fluorescence intensity of Q[7]-CDs at 460nm gradually decreases until it remains unchanged.

[0045] Figure 7 The standard curve of b can be used to calculate the detection limit of Q[7]-CDs for p-NA as 5.89×10. -7 mol.L -1 .

[0046] Figure 8 It can be seen that the UV-Vis absorption peak of p-NA has a significant overlap with the fluorescence excitation spectrum of Q[7]-CDs, indicating that the energy used to excite Q[7]-CDs was not absorbed by p-NA, and the quenching mechanism may have an internal filtering effect.

[0047] Depend on Figure 8 b shows that when different concentrations of p-NA are added to the Q[7]-CDs solution, the peaks of the ultraviolet absorption spectrum do not change. Therefore, there is no chemical change in our system that generates host-guest complexes. It is speculated that there may be a static quenching mechanism of charge transfer.

[0048] Depend on Figure 9 and Figure 10 It can be seen that by comparing the proton NMR spectra of mercaptosuccinic acid [MSA], Q[7]-CDs, p-NA, and Q[7]-CDs@p-NA, it can be seen that for Q[7]-CDs@p-NA, compared with pure p-NA, the proton peak signal near the -NH2 position shifts to a higher field, while the hydrogen signal peak near the -NO2 benzene ring shifts slightly to a lower field due to the deshielding effect of the cucurbit ring port. This indicates that the -NH2 end of p-NA enters the hydrophobic cavity of Q[7], and the protons and -NO2 near the -NO2 position should be located outside the cavity port. Based on the summary of the reported literature, in addition to the internal filtering effect, the quenching mechanism should be the photoinduced charge transfer between Q[7]-CDs and p-nitroaniline. Detailed Implementation

[0049] The present invention will be further described below with reference to embodiments, but these embodiments are not intended to limit the scope of the invention.

[0050] Embodiments of the present invention

[0051] Example 1:

[0052] The preparation method of each reagent in the analytical method of this invention is as follows:

[0053] (1) Accurately weigh an appropriate amount of seven-membered cucurbitacin, dissolve it in 60 mL of ultrapure water (18.25 MΩ·cm) by heating and sonication to obtain a concentration of 1.0 × 10⁻⁶. -3 mol.L -1 A seven-membered cucurbitacin ring solution;

[0054] (2) Accurately weigh an appropriate amount of mercaptosuccinic acid, dissolve it in 60 mL of ultrapure water by heating and sonication to obtain a concentration of 2.0 × 10⁻⁶. -3 mol.L -1 A solution of mercaptosuccinic acid;

[0055] (3) The obtained nitrogen-sulfur co-doped carbon dot solid powder based on the seven-membered cucurbit ring was prepared with ultrapure water to a concentration of 400 μg / mL. -1 Solution for later use;

[0056] (4) Preparation of standard solutions for 16 benzene-substituted organic pollutants: Accurately weigh the required analytical grade standards of the organic compounds and prepare solutions with ultrapure water, each with a concentration of 1.0 × 10⁻⁶. -3 mol.L -1 The standard solution.

[0057] Example 2:

[0058] A method for preparing a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring is as follows:

[0059] The seven-membered cucurbitacin solution and mercaptosuccinic acid solution from Example 1 were mixed in a molar ratio of seven-membered cucurbitacin: mercaptosuccinic acid = 1:2. The mixture was heated and sonicated for 1 hour to achieve homogeneity, then transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 180°C for 12 hours. After the reaction was completed and the high-pressure reactor cooled to room temperature, the reaction solution was filtered. The filtered solution was then subjected to a high-pressure reactor at 10,000 rpm. -1 Centrifuge for 20 minutes, take the supernatant and put it into a 1000kDa dialysis bag for dialysis for 24 hours. Change the water every 10 hours to obtain a pure Q[7]-CDs aqueous solution. Then, evaporate the solution in the dialysis bag at 70℃ to remove the solvent and obtain a yellowish-brown solid powder, which is the nitrogen-sulfur co-doped carbon dot fluorescent probe based on the seven-membered cucurbit ring.

[0060] Example 3:

[0061] A method for preparing a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring is as follows:

[0062] The seven-membered cucurbitacin solution and mercaptosuccinic acid solution from Example 1 were mixed in a molar ratio of seven-membered cucurbitacin: mercaptosuccinic acid = 1:5. The mixture was heated and sonicated for 1 hour to achieve homogeneity, then transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 160°C for 15 hours. After the reaction was completed and the high-pressure reactor cooled to room temperature, the reaction solution was filtered. The filtered solution was then subjected to a high-pressure reactor at 10,000 rpm. -1 Centrifuge for 20 minutes, take the supernatant and put it into a 1000kDa dialysis bag for dialysis for 24 hours. Change the water every 10 hours to obtain a pure Q[7]-CDs aqueous solution. Then, evaporate the solution in the dialysis bag at 70℃ to remove the solvent and obtain a yellowish-brown solid powder, which is the nitrogen-sulfur co-doped carbon dot fluorescent probe based on the seven-membered cucurbit ring.

[0063] Example 4:

[0064] A method for preparing a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring is as follows:

[0065] The seven-membered cucurbitacin solution and mercaptosuccinic acid solution from Example 1 were mixed in a molar ratio of seven-membered cucurbitacin: mercaptosuccinic acid = 1:10. The mixture was heated and sonicated for 1 hour to achieve homogeneity. Then, it was transferred to a polytetrafluoroethylene-lined high-pressure reactor and hydrothermally reacted at 200°C for 10 hours. After the reaction was completed and the high-pressure reactor cooled to room temperature, the reaction solution was filtered. The filtered solution was then subjected to a high-pressure reactor at 10,000 rpm. -1 Centrifuge for 20 minutes, take the supernatant and put it into a 1000kDa dialysis bag for dialysis for 24 hours. Change the water every 10 hours to obtain a pure Q[7]-CDs aqueous solution. Then, evaporate the solution in the dialysis bag at 70℃ to remove the solvent and obtain a yellowish-brown solid powder, which is the nitrogen-sulfur co-doped carbon dot fluorescent probe based on the seven-membered cucurbit ring.

[0066] Example 5:

[0067] A method for detecting p-nitroaniline, an organic pollutant in water, using a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring is described below:

[0068] (1) Determination of the standard curve:

[0069] Take eight 5mL volumetric flasks and add 2500μL of a 400μg / mL solution to each flask. -1 The fluorescent carbon dot solution was mixed with 1.0 × 10⁻⁶ ppm. -3The p-NA (0 μL, 20.0 μL, 40.0 μL, 60.0 μL, 80.0 μL, 100.0 μL, 120.0 μL, 140 μL) were added to eight volumetric flasks, diluted with ultrapure water, and shaken well before use. Fluorescence emission spectroscopy was performed with a fixed excitation wavelength of 365 nm. The concentration of p-NA was used as the abscissa, and the difference between the fluorescence emission intensity (I0) of the Q[7]-CDs probe at 460 nm without p-NA and the fluorescence emission intensity (I) with different concentrations of p-NA was used as the ordinate to plot a standard curve. The detection limit of the probe for p-NA was calculated by the slope k of the standard curve and the standard deviation σ of the 11 blank values ​​measured, according to the detection limit calculation formula (3σ / k).

[0070] (2) Sample testing:

[0071] Take an aqueous solution containing an unknown concentration of p-NA, add the prepared fluorescent probe standard solution to it, and observe the change in fluorescence intensity at 460 nm under an excitation wavelength of 365 nm. If the fluorescence intensity at 460 nm decreases significantly, it indicates that the water sample contains p-NA. If there is no significant change in fluorescence intensity at 460 nm, it indicates that the water sample does not contain p-NA or the content is lower than the detection limit of the fluorescent carbon dot probe.

[0072] Example 6:

[0073] A method for detecting p-NA in water using a fluorescent carbon dot probe based on a seven-membered cucurbit ring is described below:

[0074] (1) Determination of the standard curve:

[0075] Take a quartz fluorescence cuvette and add 400 μg / mL of the solution. -1 2500 μL of fluorescent probe solution was added, and then 1.0 × 10⁻⁶ μL of the solution was accurately added to each sample. -3 20 μL of p-NA standard solution was reacted for 2 min, and fluorescence emission spectroscopy was performed with a fixed excitation wavelength of 365 nm. Following the above procedure, 20 μL of p-NA standard solution was continuously added to the above 2500 μL probe solution, and a series of fluorescence curves were measured at an excitation wavelength of 365 nm. The titration operation was stopped when the value of the vertical axis of the fluorescence curve changed slowly. Then, a standard curve was obtained with p-NA concentration as the abscissa and the difference between the fluorescence emission intensity I0 of the probe at 460 nm and the fluorescence emission intensity I after adding different concentrations of p-NA (I0-I) as the ordinate. The detection limit of the probe for p-NA was calculated using the slope k of the standard curve and the standard deviation σ of 11 blank values, according to the detection limit calculation formula (3σ / k).

[0076] (2) Sample testing:

[0077] Take an aqueous solution containing an unknown concentration of p-NA, add the prepared fluorescent probe standard solution to it, and observe at an excitation wavelength of 365 nm. If a significant decrease in fluorescence intensity is observed at 460 nm, it indicates the presence of p-NA in the water sample. If no significant change in fluorescence intensity is observed at 460 nm, it indicates the absence of p-NA in the water sample or that its content is below the detection limit of the fluorescent carbon dot probe. Alternatively, if quenching of the luminescence of the probe solution in the fluorescent cuvette is observed under ultraviolet light, it indicates the presence of p-NA in the test solution. If no significant change occurs, it indicates the absence of p-NA in the water or that its content is below the detection limit of the probe. The detection limits are shown in the attached figure. Figure 7 As shown.

[0078] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An application of a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water, characterized in that, The specific method for using the fluorescent probe is as follows: S1. Weigh out the seven-membered cucurbitacin solution and the mercaptosuccinic acid solution according to the molar ratio of seven-membered cucurbitacin: mercaptosuccinic acid ≥ 1:2; S2. Mix the seven-membered cucurbitacin solution and mercaptosuccinic acid solution, then disperse them evenly in ultrapure water, and then transfer them to a polytetrafluoroethylene high-pressure reactor for a closed hydrothermal reaction at 160-200℃ for 10-15 hours. S3. After the reaction is complete, the sample is cooled to room temperature, filtered, centrifuged, dialyzed, and rotary evaporated to obtain a nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring.

2. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water as described in claim 1, characterized in that: The concentration of the seven-membered cucurbitacin solution is 1.0 × 10⁻⁶. -3 mol.L -1 .

3. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water as described in claim 1, characterized in that: The concentration of the mercaptosuccinic acid solution is 2.0 × 10⁻⁶. -3 mol.L -1 .

4. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring in the detection of p-nitroaniline in water as described in claim 1, characterized in that: The molar ratio of the seven-membered cucurbitacin to mercaptosuccinic acid is 1:

2.

5. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring according to claim 1 in the detection of p-nitroaniline in water, characterized in that: The reaction temperature for S2 is 180℃, and the reaction time is 12h.

6. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring according to claim 1 in the detection of p-nitroaniline in water, characterized in that, The detection includes the following steps: S1. Dissolve the carbon dot fluorescent probe in ultrapure water to obtain a concentration of 400 μg / mL. -1 Fluorescent probe solution; S2. Add solutions containing different concentrations of nitroaniline to the fluorescent probe solution of S1, mix them thoroughly and react for 2 min, then measure the fluorescence emission spectrum at a fixed excitation wavelength of 365 nm, and plot the fluorescence intensity change curve at an emission wavelength of 460 nm. S3. Based on the curve in S2, calculate the intensity change of the fluorescence emission spectrum at 460m before and after adding the nitroaniline solution to obtain the standard curve; S4. Add the sample to be tested to the fluorescent probe solution in S1, and perform fluorescence emission with a fixed excitation wavelength of 365nm. Observe the fluorescence intensity at 460nm, and then perform qualitative and quantitative tests on nitroaniline in the sample according to the standard curve.

7. The application of the nitrogen-sulfur co-doped carbon dot fluorescent probe based on a seven-membered cucurbit ring according to claim 6 in the detection of p-nitroaniline in water, characterized in that, The specific testing method for S4 is as follows: if the fluorescence intensity at the emission wavelength of 460 nm decreases significantly, it indicates that the sample contains nitroaniline; if no significant change occurs, it indicates that the sample does not contain nitroaniline or its content is below the detection limit of the probe. Alternatively, if the color of the probe solution in the quartz fluorescent cuvette is observed to quench under ultraviolet light, it indicates that the test solution contains nitroaniline; if no quenching is observed, it indicates that the water does not contain nitroaniline or its content is below the detection limit of the probe.

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