Application of choline-type rare earth fluorescent probe in detection of nitro compounds in ionic liquid and water

Abstract

The application belongs to the technical field of rare earth fluorescent probes, and particularly relates to application of a choline type rare earth fluorescent probe in detection of nitro compounds in ionic liquids and nitro compounds in water. The application synthesizes a choline type rare earth fluorescent probe [choline]3[Eu(dpa)3] (wherein choline is choline, and DPA is 2,6-pyridine dicarboxylic acid) which has good solubility and stability in ionic liquids and aqueous solutions. The synthesized choline type rare earth fluorescent probe is used as a rare earth fluorescent probe for detecting nitro compounds, and the fluorescence detection performance of the choline type rare earth fluorescent probe on various nitro compounds in water and 1-butyl-3-methyl imidazole hexafluorophosphate (BmimPF6) ionic liquids is explored. The application fills a blank of substance detection of rare earth fluorescent probes in ionic liquid solvents, and has important application value for realizing detection of nitro compounds in ionic liquids.

Description

Technical Field

[0001] This invention belongs to the field of rare earth fluorescent probe technology, specifically relating to the application of choline-type rare earth fluorescent probes in the detection of nitro compounds in ionic liquids and water. Background Technology

[0002] Nitro compounds are an important class of chemical raw materials; however, most nitro compounds are highly toxic and hazardous, posing a serious threat not only to human health but also to the safety of the ecological environment and public health. With increasing awareness of ecological protection and safety, the ability to sensitively identify and detect nitro compounds in target analytes has become a growing concern for researchers both domestically and internationally.

[0003] Currently, the main methods for detecting nitro compounds include spectrometry, chromatography, and electrochemical analysis. Among these, fluorescence spectroscopy, a spectroscopic method, offers advantages such as high detection sensitivity, cost-effectiveness, and ease of operation. The preparation of fluorescent probe molecules that can accurately detect trace amounts of nitro compounds and effectively eliminate background interference has long been a focus of research. In the field of fluorescence detection, choline-type rare-earth fluorescent probes not only possess a large Stokes shift, effectively avoiding self-absorption during sample detection, but their unique decay lifetime can also effectively distinguish background interference during detection. Compared with major fluorescent labels such as small organic molecules, quantum dots, and fluorescent proteins, choline-type rare-earth fluorescent probes exhibit sharp-line spectra and possess advantages such as good selectivity and rapid detection. Therefore, rare-earth fluorescent probes are considered ideal materials for preparing fluorescent probes. How to prepare rare-earth fluorescent probes that can rapidly identify and detect nitro aromatic compounds is a hot topic of research both domestically and internationally.

[0004] However, due to the forbidden transition of the inner 4f electrons in a single rare earth ion, direct excitation of rare earth ions suffers from low luminescence efficiency. This is primarily mitigated through the energy transfer effect (i.e., antenna effect) between the organic ligand and the rare earth ion. Therefore, the blocking of the energy transfer effect in choline-type rare earth fluorescent probes by the analyte can achieve the fluorescence quenching response of these probes. The detection of nitro compounds by choline-type rare earth fluorescent probes follows this principle.

[0005] With the increasing demand for high-performance and environmentally friendly materials, ionic liquids, as emerging green solvents, are gradually gaining attention. Ionic liquids are salt solvents composed of organic cations and organic or inorganic anions, existing as liquids at or near room temperature. Unlike traditional water and organic solvents, ionic liquids possess advantages such as a wide liquid temperature range, non-volatility, non-flammability, excellent electrical and thermal conductivity, and thermodynamic stability. This makes them a superior alternative to traditional solvents, gradually emerging in various high-tech and new energy fields. Given the further promotion and application of ionic liquids, the detection of toxic and pollutant substances will inevitably extend beyond water and organic solvent environments, including nitro compounds. This presents new challenges for rare-earth fluorescent probes in ionic liquids to detect nitro compounds. Furthermore, existing research indicates that the type of solvent significantly affects the detection of nitro compounds by choline-based rare-earth fluorescent probes. For example, Mondal's research group at Visva-Bharati University of India discovered that rare-earth terbium complexes of 2,6-pyridinedicarboxylic acid exhibit quenching effects on various nitro compounds, and found that the detection sensitivity depends on the type of solvent; rare-earth fluorescent probes show different sensitivities and detection limits in water and different organic solvents (water, methanol, acetonitrile, and tetrahydrofuran). However, the detection performance of rare-earth fluorescent probes in ionic liquids has not yet been reported.

[0006] Currently, researchers both domestically and internationally have conducted some studies on the luminescence properties of rare earth ions and their complexes in ionic liquids. Results show that, firstly, ionic liquids do not interfere with the rare earth spectra in the visible and near-infrared regions; secondly, compared with traditional solvents, ionic liquids exhibit weak coordination and weak solvation of solute molecules; furthermore, it has been found that rare earth ions and their complexes possess higher fluorescence intensity and lifetime in ionic liquids. This not only fundamentally avoids the probability of fluorescence quenching of rare earth fluorescent probes caused by solvent coordination, reducing the influence of solvents on probe response performance during detection, but also helps maintain the stability of the coordination structure of rare earth fluorescent probes, thereby improving the fluorescence performance and stability of rare earth fluorescent probes.

[0007] In recent years, research has demonstrated that ionic liquids can serve as ideal dispersion media for rare-earth luminescent materials. Furthermore, studies have shown that the imidazole cations in ionic liquids can not only form hydrogen bonds with rare-earth fluorescent probes, stabilizing them and enhancing their photostability, but also exhibit energy transfer effects, further improving their fluorescence quantum yield and lifetime. Moreover, the unique compositional structure of the anions and cations in ionic liquids is a major factor influencing the solubility and other functional properties of complexes within them. Whether these unique solvent properties affect the detection performance of rare-earth fluorescent probes remains a mystery. Therefore, how to prepare rare-earth fluorescent probes and detect nitro compounds in ionic liquid solvents will become a key technical issue in solving the detection of nitro compounds in novel solvents and further expanding the application fields of rare-earth fluorescent probes. Summary of the Invention

[0008] To address the shortcomings of the existing technology, the purpose of this invention is to provide an application of choline-type rare-earth fluorescent probes for the detection of nitro compounds in ionic liquids and water. This invention synthesizes a choline-type rare-earth fluorescent probe, [choline]3[Eu(dpa)3] (wherein choline is choline and DPA is 2,6-pyridinedicarboxylic acid), which exhibits good solubility and stability in both ionic liquids and aqueous solutions. The rare-earth europium ion possesses excellent fluorescence monochromaticity, and the DPA ligand can effectively transfer energy to the rare-earth europium ion, increasing its fluorescence intensity. The choline ion, as the counterion of the complex, effectively enhances its solubility in ionic liquids and strengthens its fluorescence stability. This invention utilizes a synthesized choline-type rare-earth fluorescent probe as a rare-earth fluorescent probe for detecting nitro compounds, exploring its fluorescence detection performance for various nitro compounds in water and imidazole ionic liquids. This invention fills the gap in the detection of substances using rare-earth fluorescent probes in ionic liquid solvents, and has important theoretical significance for further enriching and realizing the detection applications of rare-earth fluorescent probes in different solvents and environments. At the same time, it will have important application value for the detection of nitro compounds in ionic liquids.

[0009] This invention is achieved through the following technical solution:

[0010] Application of choline-type rare earth fluorescent probe in the detection of nitro compounds in ionic liquids and water, wherein the choline-type rare earth fluorescent probe is [choline]3[Eu(DPA)3], wherein choline is choline and DPA is 2,6-pyridinedicarboxylic acid.

[0011] Preferably, the nitro compounds include, but are not limited to, p-nitrophenol, nitrobenzene, p-nitrotoluene, and m-dinitrobenzene.

[0012] Preferably, the method for preparing the detection probe for nitro compounds in ionic liquids is as follows:

[0013] The choline-type rare earth fluorescent probe sample was dispersed in an ionic liquid to obtain a dispersion.

[0014] Different concentrations of nitro compounds were prepared, and a dispersion was added to them. The fluorescence intensity at the excitation wavelength of 293 nm and the emission wavelength of 616 nm was then measured. A standard curve was constructed, and the linear relationship between fluorescence intensity and nitro compound concentration and the limit of detection were determined by fitting.

[0015] Preferably, when testing the sample, the fluorescence intensity at the excitation wavelength of 293 nm and the emission wavelength of 616 nm is measured, and the concentration of the sample is determined based on the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

[0016] The preferred method for preparing the detection method for nitro compounds in water is as follows:

[0017] The choline-type rare earth fluorescent probe sample was dispersed in water to obtain a dispersion.

[0018] Nitro compounds of different concentrations were prepared, and a dispersion was added to them. The fluorescence intensity was then measured at an excitation wavelength of 287 nm and an emission wavelength of 616 nm. A standard curve was constructed, and the linear relationship between fluorescence intensity and nitro compound concentration and the limit of detection were determined by fitting.

[0019] Preferably, when testing the sample, the fluorescence intensity at the excitation wavelength of 287 nm and the emission wavelength of 616 nm is measured, and the concentration of the sample is determined based on the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

[0020] Preferably, the choline-type rare-earth fluorescent probe is prepared according to the following steps:

[0021] S1. Dissolve 2,6-pyridinedicarboxylic acid and choline hydroxide in methanol solution in water, then adjust the pH to neutral to obtain a mixture;

[0022] S2. Heat the mixture from step S1 to 70-75℃ and add an aqueous solution of EuCl3·6H2O dropwise. Stir the mixture at 70-75℃ for 2-3 hours, then evaporate the solvent to obtain a powder product. Remove the residual choline hydroxide from the powder product to obtain a choline-type rare earth fluorescent probe.

[0023] Preferably, the molar ratio of 2,6-pyridinedicarboxylic acid, choline hydroxide, and EuCl3·6H2O is 3:6:1; and the mass fraction of choline hydroxide in the methanol solution of choline hydroxide in step S1 is 47-50%.

[0024] Preferably, in step S1, the volume ratio of water to choline hydroxide is 3-4:1, and the pH is adjusted using a 1 mol / L sodium hydroxide solution or potassium hydroxide solution.

[0025] Preferably, the method for removing residual solvent of choline hydroxide in step S2 is to wash the powder product with methanol.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention prepares a choline-type rare-earth fluorescent probe [choline]3[Eu(DPA)3] (where choline is choline and DPA is 2,6-pyridinedicarboxylic acid), and for the first time applies it to the detection of nitro compounds. Its fluorescence detection performance for nitro compounds in water and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid was studied. The results show that the choline-type rare-earth fluorescent probe exhibits both static and dynamic quenching of nitro compounds in both water and ionic liquids. The quenching performance of the choline-type rare-earth fluorescent probe for different nitro compounds in aqueous solution is: p-nitrophenol > nitrobenzene > p-nitrotoluene > m-dinitrobenzene; the quenching performance for different nitro compounds in ionic liquid is: p-nitrotoluene > p-nitrophenol > nitrobenzene > m-dinitrobenzene. Meanwhile, the quenching efficiencies of p-nitrotoluene, m-dinitrobenzene, and nitrobenzene are higher in ionic liquids than in aqueous solutions, while the quenching efficiency of p-nitrophenol is lower in ionic liquids than in aqueous solutions. This research will contribute to the detection of nitro compounds in non-traditional solvents and will further broaden the application fields of rare-earth fluorescent probes, possessing significant theoretical importance and practical value.

[0028] 2. The present invention mainly utilizes the fact that when choline is used as the counterion of rare earth complexes, it can increase the solubility of rare earth complexes in ionic liquids and is beneficial to improving the quenching efficiency of rare earth fluorescent probes on nitro compounds. Attached Figure Description

[0029] Figure 1 The fluorescence excitation (top) and emission spectra (bottom) of [choline]3[Eu(DPA)3] in aqueous solution and ionic liquid of Example 1 of the present invention are shown.

[0030] Figure 2 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] in aqueous solution with different concentrations of p-nitrophenol are shown in Example 1 of this invention.

[0031] Figure 3The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] in aqueous solution with different concentrations of nitrobenzene are shown in Example 1 of this invention.

[0032] Figure 4 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] in aqueous solution with different concentrations of m-dinitrobenzene are shown in Example 1 of this invention.

[0033] Figure 5 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] in aqueous solution with different concentrations of p-nitrotoluene are shown in Example 1 of this invention.

[0034] Figure 6 Bar chart showing the percentage quenching of different nitro compounds in aqueous solution;

[0035] Figure 7 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] with different concentrations of p-nitrophenol added to the ionic liquid solution of Example 1 of the present invention are shown.

[0036] Figure 8 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] with different concentrations of p-nitrotoluene added to the ionic liquid solution of Example 1 of the present invention are shown.

[0037] Figure 9 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] with different concentrations of nitrobenzene added to the ionic liquid solution are shown in Example 1 of the present invention.

[0038] Figure 10 The fluorescence emission spectrum (top) and fluorescence quenching curve (bottom) of the choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3] with different concentrations of m-dinitrobenzene added to the ionic liquid solution of Example 1 of the present invention are shown.

[0039] Figure 11 Bar chart showing the percentage of quenching of different nitro compounds in ionic liquids. Detailed Implementation

[0040] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0041] Example 1

[0042] The preparation method of choline-type rare earth fluorescent probes includes the following steps:

[0043] S1. Dissolve 5.014 g of 2,6-pyridinedicarboxylic acid (Hdpa, 3 eq) and 15.47 g of choline hydroxide (47%, 6 eq) in a methanol solution in 54.15 mL of water (volume ratio of water to choline hydroxide is 7:2).

[0044] After adjusting the pH of the solution to neutral with a 1 mol / L sodium hydroxide aqueous solution, the solution was heated to 70°C, and then 10 mL of a 1 mol / L EuCl3·6H2O (1 eq) aqueous solution was added dropwise to obtain a mixed solution.

[0045] S2. After stirring the mixture from step S1 at 70°C for 2 hours, most of the water was removed by rotary evaporation to obtain a white powder product. The product was washed with methanol to remove residual choline hydroxide and dried under vacuum at 50°C to obtain a choline-type rare earth fluorescent probe sample.

[0046] Example 2

[0047] The preparation method of choline-type rare earth fluorescent probes includes the following steps:

[0048] S1. Dissolve 5.014 g of 2,6-pyridinedicarboxylic acid (Hdpa, 3 eq) and 16.12 g of choline hydroxide (49%, 6 eq) in a methanol solution in 46.5 mL of water (volume ratio of water to choline hydroxide is 6:2).

[0049] After adjusting the pH of the solution to neutral with a 1 mol / L sodium hydroxide aqueous solution, the solution was heated to 73°C, and then 10 mL of a 1 mol / L EuCl3·6H2O (1 eq) aqueous solution was added dropwise to obtain a mixed solution.

[0050] S2. After stirring the mixture from step S1 at 75°C for 2.5 hours, most of the water was removed by rotary evaporator to obtain a white powder product. The product was washed with methanol to remove residual choline hydroxide and dried under vacuum at 50°C to obtain a choline-type rare earth fluorescent probe sample.

[0051] Example 3

[0052] The preparation method of choline-type rare earth fluorescent probes includes the following steps:

[0053] S1. Dissolve 5.014 g of 2,6-pyridinedicarboxylic acid (Hdpa, 3 eq) and 16.46 g of choline hydroxide (50%, 6 eq) in a methanol solution in 61.88 mL of water (volume ratio of water to choline hydroxide is 8:2).

[0054] After adjusting the pH of the solution to neutral with a 1 mol / L sodium hydroxide aqueous solution, the solution was heated to 75°C, and then 10 mL of a 1 mol / L EuCl3·6H2O (1 eq) aqueous solution was added dropwise to obtain a mixed solution.

[0055] S2. After stirring the mixture from step S1 at 72°C for 3 hours, most of the water was removed by rotary evaporator to obtain a white powder product. The product was washed with methanol to remove residual choline hydroxide and dried under vacuum at 50°C to obtain a choline-type rare earth fluorescent probe sample.

[0056] Examples 1-3 of this invention all yielded choline-type rare-earth fluorescent probe samples suitable for detecting nitro compounds in water and ionic liquids, with parallel results. The following study uses the choline-type rare-earth fluorescent probe sample prepared in Example 1 as an example, with specific methods and results shown below:

[0057] I. Preparation of quenching solutions for nitro compounds of different concentrations:

[0058] Preparation of quenching solutions for nitro compounds of different concentrations:

[0059] (1) Rare earth complexes were prepared by adding quenching solutions of nitro compounds of different concentrations to water, and the mixing ratios in Table 1 and Table 2 were used for low and high concentrations, respectively:

[0060] Table 1. Preparation of quenching solutions for low concentrations of nitro compounds in water.

[0061]

[0062] Table 2. Preparation of quenching solutions for high concentrations of nitro compounds in water.

[0063]

[0064] (2) Rare earth complexes were prepared by adding quenching solutions of nitro compounds of different concentrations to BmimPF6 ionic liquid, and the mixing ratios in Table 3 and Table 4 were used for low and high concentrations, respectively:

[0065] Table 3. Preparation of quenching solutions for low concentrations of nitro compounds in ionic liquids.

[0066]

[0067] Table 4. Preparation of high-concentration nitro compound quenching solutions in ionic liquids.

[0068]

[0069] Among them, the “rare earth complexes” in Tables 1-4 are the choline-type rare earth fluorescent probes prepared in Example 1 of this invention, and the “BmimPF6” in Tables 3-4 are 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) ionic liquid.

[0070] II. Data Processing:

[0071] Stern–Volmer (SV) equation: (I0 / I) = K sv [C]+1, where I0 and I are the fluorescence intensities before and after the addition of the nitro-explosive analyte, [C] is the molar concentration of the analyte, and K... sv It is the quenching constant.

[0072] Quenching percentage W: W = (I0 - I) / I0, where I0 and I are the fluorescence intensities before and after the addition of the nitro explosive analyte.

[0073] Detection limit: LOD = 3σ / s, where σ is the standard deviation of the intercept, and s is K. sv Constant value.

[0074] III. Results and Discussion

[0075] 1. Fluorescence properties of the rare earth fluorescent probe [choline]3 [Eu(DPA)3]

[0076] Figure 1 The images show the fluorescence excitation and emission spectra of [choline]3[Eu(DPA)3] at a concentration of 1 mg / mL in water and ionic liquids. The optimal emission wavelength was 616 nm. The strongest excitation peak in the spectrum corresponds to the ligand-to-metal charge transition (LMCT) of the choline-type rare-earth fluorescent probe, which occurs at 287 nm in water and 293 nm in ionic liquids. In aqueous solution, the choline-type rare-earth fluorescent probe itself exhibits an energy transfer absorption peak at 395 nm, while this excitation peak disappears in ionic liquids. This indicates that the energy transfer efficiency of the ligand-to-central ion is higher in ionic liquids, and the complex is more stable.

[0077] At optimal excitation wavelengths of 287 nm and 293 nm, respectively, the choline-type rare-earth fluorescent probes in both aqueous and ionic liquid solutions exhibited the strongest emission peak at 616 nm. This is a characteristic peak of the complex, and the emission peak is associated with Eu. 3+ The 5D0→7F2 electric dipole transition (or ultrasensitive transition) is related to the coordination environment of the choline-type rare-earth fluorescent probe. Additionally, the emission peak at 596 nm is Eu. 3+ The magnetic dipole transition from 5D0 to 7F1, the intensity of which is independent of the coordination environment of the choline-type rare earth fluorescent probe.

[0078] Unlike electric dipole transitions, the intensity of the absorption peak in magnetic dipole transitions is essentially unaffected by Eu. 3+ The influence of the surrounding environment. Generally, the magnetic dipole transition from 5D0 to 7F1 is used as the standard. The coordination symmetry and fluorescence monochromaticity of the europium system can be judged by the intensity ratio of the two characteristic emission peaks. The larger the intensity ratio of the two characteristic emission peaks, the lower the symmetry of the europium ion coordination layer, and the better the fluorescence monochromaticity of the system. In aqueous solution, the 5D0→7F2 electric dipole transition (or ultrasensitive transition) of choline-type rare earth fluorescent probes is about four times stronger than the 5D0→7F1 magnetic dipole transition, while in ionic liquids, the complex Eu... 3+ The electric dipole transition from 5D0 to 7F2 is about three times stronger than the magnetic dipole transition from 5D0 to 7F1, indicating that the coordination structure of choline-type rare earth fluorescent probes changes in water and ionic liquids. Furthermore, the coordination structure of choline-type rare earth fluorescent probes is more asymmetric and exhibits better fluorescence monochromaticity in aqueous solutions.

[0079] 2. Detection of nitro compounds using rare earth fluorescent probes

[0080] (1) Fluorescence quenching performance of rare earth fluorescent probes on nitro compounds in aqueous solution:

[0081] Figure 2 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in 1 mg / mL choline-type rare earth fluorescent probe aqueous solution with different concentrations of p-nitrophenol, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of p-nitrophenol increases from 3 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 2(Inset in the upper middle figure). The linear relationship is ln(I0 / I)=64259[C]-0.18262, the correlation is 0.97422, and the fluorescence quenching constant Ksv=6.43×10 from the slope. 4 The calculated limit of detection (LOD) for the choline-type rare-earth fluorescent probe against p-nitrophenol is 6.41 × 10⁻⁶. -6 mg / L.

[0082] Furthermore, the change in fluorescence intensity with increasing concentration conforms to a nonlinear exponential fit (…). Figure 2 (See the lower figure), the fitted equation is y = 0.00248e 129519x +4.44812(R 2 =0.99943). This indicates that the fluorescence quenching of p-nitrophenol involves both static and dynamic quenching. This is mainly because when the concentration of p-nitrophenol is high, the collision probability between the choline-type rare earth fluorescent probe and the nitro compound increases, thus causing dynamic quenching of the complex, at which point the fluorescence quenching pattern is nonlinear.

[0083] Figure 3 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in a 1 mg / mL aqueous solution of a choline-type rare-earth fluorescent probe with different concentrations of nitrobenzene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of nitrobenzene increases from 3 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 3 (Inset in the upper middle figure). The linear relationship is y = 36033x - 0.03051, the correlation is 0.93948, and the fluorescence quenching constant Ksv can be obtained from the slope as 3.60 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 1.34 × 10⁻⁶. -5 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 3 (See the lower figure), the fitted equation is y = 0.00005361e 114038x +3.85251(R 2 =0.99871), indicating that the fluorescence quenching of nitrobenzene also involves both static and dynamic quenching.

[0084] Figure 4The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in a 1 mg / mL aqueous solution of a choline-type rare-earth fluorescent probe with different concentrations of m-dinitrobenzene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of m-dinitrobenzene increases from 20 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 4 (Inset in the upper middle figure). The linear relationship is y = 14510x + 0.02621, the correlation is 0.99306, and the fluorescence quenching constant Ksv can be obtained from the slope as 1.45 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 9.57 × 10⁻⁶. -6 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 4 (See the lower figure), the fitted equation is y = 0.80394e 16056x +0.29434(R 2 =0.99448), indicating that the fluorescence quenching of m-dinitrobenzene also involves both static and dynamic quenching.

[0085] Figure 5 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in a 1 mg / mL aqueous solution of a choline-type rare earth fluorescent probe with different concentrations of p-nitrotoluene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of p-nitrotoluene increases from 20 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 3-5 (Inset in the upper middle figure). The linear relationship is y = 21481x - 0.03091, the correlation is 0.99378, and the fluorescence quenching constant Ksv can be obtained from the slope as 2.15 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 9.06 × 10⁻⁶. -6 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 3-5 (See the lower figure), the fitted equation is y = 0.28134e 29615x +1.75357(R 2=0.99213), indicating that the fluorescence quenching of p-nitrotoluene also involves both static and dynamic quenching.

[0086] By comparing the quenching constants (Ksv) of different nitro compounds in aqueous solution (see Table 5), the detection sensitivity of choline-type rare-earth fluorescent probes for p-nitro compounds can be determined as follows: p-nitrophenol > nitrobenzene > p-nitrotoluene > m-dinitrobenzene. The detection limits for different nitro compounds are: nitrobenzene > m-dinitrobenzene > p-nitrotoluene > p-nitrophenol.

[0087] Table 5. Fluorescence quenching constants and detection limits of different nitro compounds in aqueous solutions.

[0088] Nitro compounds Ksv(L / mg) Limit of detection (LOD) (mg / L) p-Nitrophenol <![CDATA[6.43×10 4 ]]> <![CDATA[6.41×10 -6 ]]> Nitrobenzene <![CDATA[3.60×10 4 ]]> <![CDATA[1.34×10 -5 ]]> m-Dinitrobenzene <![CDATA[1.45×10 4 ]]> <![CDATA[9.57×10 -6 ]]> p-Nitrotoluene <![CDATA[2.15×10 4 ]]> <![CDATA[9.06×10 -6 ]]>

[0089] Quenching titration of four nitro compounds in aqueous solution with [choline]3[Eu(DPA)3] showed that when the nitro compound was added at a concentration of 100 mg / L, [choline]3[Eu(DPA)3] exhibited quenching rates of 99.90%, 94.62%, 88.33%, and 75.13% for PNP, NB, NT, and DNB, respectively (see [link to titration]). Figure 6 Among them, when p-nitrophenol and nitrobenzene were added at a concentration of 100 mg / L, the fluorescence of the choline-type rare earth fluorescent probe was basically completely quenched.

[0090] (2) Fluorescence quenching performance of rare earth fluorescent probes in ionic liquids against nitro compounds:

[0091] Figure 7 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in 1 mg / mL choline-type rare-earth fluorescent probe ionic liquid with different concentrations of p-nitrophenol, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of p-nitrophenol increases from 5 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 7 (Inset in the upper middle figure). The linear relationship is y = 53928x - 0.15458, the correlation is 0.97221, and the fluorescence quenching constant Ksv can be obtained from the slope as 5.39 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 1.01 × 10⁻⁶. -5 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 7 (See the lower figure), the fitted equation is y = 0.3783e89808x +2.8678(R 2 =0.99935), indicating that the fluorescence quenching of p-nitrophenol also involves both static and dynamic quenching.

[0092] Figure 8 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in 1 mg / mL choline-type rare-earth fluorescent probe ionic liquid with different concentrations of p-nitrotoluene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of p-nitrotoluene increases from 5 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 8 (Inset in the upper middle figure). The linear relationship is y = 47305x + 0.18323, the correlation is 0.99557, and the fluorescence quenching constant Ksv can be obtained from the slope as 4.73 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 4.00 × 10⁻⁶. -6 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 8 (See the lower figure), the fitted equation is y = 2.33041e 39513x +0.23936(R 2 =0.99994), indicating that the fluorescence quenching of p-nitrotoluene also involves both static and dynamic quenching.

[0093] Figure 9 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in a choline-type rare-earth fluorescent probe ionic liquid with different concentrations of nitrobenzene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of nitrobenzene increases from 5 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 9 (Inset in the upper middle figure). The linear relationship is y = 12237x + 0.14181, the correlation is 0.96908, and the fluorescence quenching constant Ksv can be obtained from the slope as 1.22 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 2.04 × 10⁻⁶. -5mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 9 (See the lower figure), the fitted equation is y = 15.10552e 2321x -14.7010(R 2 =0.97273), indicating that the fluorescence quenching of nitrobenzene also involves both static and dynamic quenching.

[0094] Figure 10 The figures show the fluorescence emission spectra of [choline]3[Eu(DPA)3] in a choline-type rare-earth fluorescent probe ionic liquid at 1 mg / mL with different concentrations of m-dinitrobenzene, and the fluorescence quenching curves obtained from the changes in the fluorescence emission peak intensity at 616 nm. The figures show that as the concentration of m-dinitrobenzene increases from 5 mg / L to 160 mg / L, the fluorescence intensity of [choline]3[Eu(DPA)3] in the aqueous solution gradually decreases while the I0 / I ratio gradually increases. Plotting the logarithm of the fluorescence intensity lnI0 / I against the concentration of the nitro compound yields a working curve with a good linear relationship (see...). Figure 10 (Inset in the upper middle figure). The linear relationship is y = 9220x - 0.07817, the correlation is 0.99477, and the fluorescence quenching constant Ksv can be obtained from the slope as 9.22 × 10⁻⁶. 4 The calculated limit of detection (LOD) for choline-type rare-earth fluorescent probe against nitrobenzene is 8.30 × 10⁻⁶. -6 mg / L. The change in fluorescence intensity with increasing concentration also conforms to a nonlinear exponential fit (mg / L). Figure 10 (See the lower figure), the fitted equation is y = 1.45584e 7131x -0.6026(R 2 =0.99403), indicating that the fluorescence quenching of m-dinitrobenzene also involves both static and dynamic quenching.

[0095] By comparing the quenching constants Ksv values ​​of different nitro compounds in ionic liquids (see Table 6), the detection sensitivity of choline-type rare-earth fluorescent probes for p-nitro compounds can be determined as follows: p-nitrophenol > p-nitrotoluene > nitrobenzene > m-dinitrobenzene. Furthermore, the detection limits for different nitro compounds are: nitrobenzene > p-nitrophenol > m-dinitrobenzene > p-nitrotoluene.

[0096] Table 6. Fluorescence quenching constants of different nitro compounds in ionic liquid solutions.

[0097] Nitro compounds Ksv(L / mg) Limit of detection (LOD) (mg / L) p-Nitrophenol <![CDATA[5.39×10 4 ]]> <![CDATA[1.01×10 -5 ]]> p-Nitrotoluene <![CDATA[4.72×10 4 ]]> <![CDATA[4.00×10 -6 ]]> Nitrobenzene <![CDATA[1.22×10 4 ]]> <![CDATA[2.04×10 -5 ]]> m-Dinitrobenzene <![CDATA[9.22×10 3 ]]> <![CDATA[8.30×10 -6 ]]>

[0098] Quenching titrations of four nitro compounds with [choline]3[Eu(DPA)3] in ionic liquids showed that, at an addition level of 100 mg / L, [choline]3[Eu(DPA)3] exhibited quenching rates of 99.67%, 99.16%, 77.48%, and 55.48% for PNP, NT, NB, and DNB, respectively (see [link to titration]). Figure 11 Among them, when p-nitrophenol and nitrobenzene were added at a concentration of 100 mg / L, the fluorescence of the rare earth complexes was basically completely quenched.

[0099] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, it is intended to include any modifications and variations that fall within the scope of the claims and their equivalents.

Claims

1. The application of choline-type rare earth fluorescent probes in the detection of nitro compounds in ionic liquids and water, characterized in that, The choline-type rare earth fluorescent probe [choline]3[Eu(DPA)3], where choline is choline and DPA is 2,6-pyridinedicarboxylic acid; The nitro compounds include, but are not limited to, p-nitrophenol, nitrobenzene, p-nitrotoluene, and m-dinitrobenzene; The choline-type rare-earth fluorescent probe was prepared according to the following steps: S1. Dissolve 2,6-pyridinedicarboxylic acid and choline hydroxide in methanol solution in water, then adjust the pH to neutral to obtain a mixture; S2. Heat the mixture from step S1 to 70-75℃ and add an aqueous solution of EuCl3·6H2O dropwise. Stir the reaction at 70-75℃ for 2-3 hours, then evaporate the solvent to obtain a powder product. Remove the residual choline hydroxide from the powder product to obtain a choline-type rare earth fluorescent probe. The 2,6-pyridinedicarboxylic acid, choline hydroxide, and EuCl3·6H2O The molar ratio is 3:6:1; and the mass fraction of choline hydroxide in the methanol solution of choline hydroxide in step S1 is 47-50%. In step S1, the volume ratio of water to choline hydroxide is 3-4:1, and the pH is adjusted using a 1 mol / L sodium hydroxide solution or potassium hydroxide solution. Using choline as the counterion of rare earth complexes increases the solubility of rare earth complexes in ionic liquids and enhances the quenching efficiency of rare earth fluorescent probes for nitro compounds.

2. The application of the choline-type rare earth fluorescent probe according to claim 1 in the detection of nitro compounds in ionic liquids and water, characterized in that, The application method for detecting nitro compounds in ionic liquids is as follows: The choline-type rare earth fluorescent probe sample was dispersed in an ionic liquid to obtain a dispersion. Different concentrations of nitro compounds were prepared, and a dispersion was added to them. The fluorescence intensity at the excitation wavelength of 293 nm and the emission wavelength of 616 nm was then measured. A standard curve was constructed, and the linear relationship between fluorescence intensity and nitro compound concentration and the limit of detection were determined by fitting.

3. The application of the choline-type rare earth fluorescent probe according to claim 2 in the detection of nitro compounds in ionic liquids and water, characterized in that, When testing the sample, the fluorescence intensity at the excitation wavelength of 293 nm and the emission wavelength of 616 nm is measured, and the concentration of the sample is determined based on the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

4. The application of the choline-type rare earth fluorescent probe according to claim 1 in the detection of nitro compounds in ionic liquids and nitro compounds in water, characterized in that, The application method for detecting nitro compounds in water is as follows: The choline-type rare earth fluorescent probe sample was dispersed in water to obtain a dispersion. Nitro compounds of different concentrations were prepared, and a dispersion was added to them. The fluorescence intensity was then measured at an excitation wavelength of 287 nm and an emission wavelength of 616 nm. A standard curve was constructed, and the linear relationship between fluorescence intensity and nitro compound concentration and the limit of detection were determined by fitting.

5. The application of the choline-type rare earth fluorescent probe according to claim 4 in the detection of nitro compounds in ionic liquids and nitro compounds in water, characterized in that, When testing the sample, the fluorescence intensity at the excitation wavelength of 287 nm and the emission wavelength of 616 nm is measured, and the concentration of the sample is determined based on the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

6. The application of the choline-type rare earth fluorescent probe according to claim 1 in the detection of nitro compounds in ionic liquids and water, characterized in that, The method for removing residual solvent of choline hydroxide in step S2 is to wash the powdered product with methanol.

Images