CN115791738A - Application of Choline Rare Earth Fluorescent Probes in the Detection of Nitro Compounds in Ionic Liquids and Water - Google Patents

Abstract

The invention 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 liquid and nitro compounds in water] ₃ [Eu(dpa) ₃ ](wherein choline is choline, DPA is 2, 6-pyridinedicarboxylic acid), and the synthesized choline type rare earth fluorescent probe is used as a rare earth fluorescent probe for detecting nitro compounds, so that the detection of the nitro compounds in water and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF) is explored ₆ ) The invention fills the blank that the rare earth fluorescent probe realizes the material detection in the ionic liquid solvent, and simultaneously generates important application value for realizing the detection of the nitro compound in the ionic liquid.

Description

Nitrolation of nitro compounds in ionic liquids and water with choline-type rare earth fluorescent probes compound detection applications

technical field

The invention belongs to the technical field of rare earth fluorescent probes, in particular to the application of choline type rare earth fluorescent probes in the detection of nitro compounds in ionic liquids and in water.

Background technique

Nitro compounds are an important class of chemical raw materials. However, most nitro compounds are highly toxic and dangerous, which not only seriously threaten human health, but also seriously threaten the safety of human ecological environment and public health. With the increasing awareness of ecological protection and safety, how to sensitively identify and detect nitro compounds in target detection substances has attracted more and more attention from researchers at home and abroad.

The methods currently used to detect nitro compounds mainly include spectroscopy, chromatography and electrochemical analysis. Among them, the fluorescence spectroscopic analysis method in the spectroscopic method has the advantages of high detection sensitivity, cost-effectiveness, and simple operation. How to prepare fluorescent probe molecules that can accurately detect trace nitro compounds and effectively eliminate the influence of background interference has always been a challenge for scientific researchers. the focus of our attention. In the field of fluorescence detection, the choline-type rare earth fluorescent probe not only has a large Stokes shift, which can effectively avoid the self-absorption problem during sample detection, but also its special attenuation life can effectively distinguish background interference in detection, and it is different from organic small Compared with the main fluorescent markers such as molecules, quantum dots, and fluorescent proteins, the detection signal of choline-type rare earth fluorescent probes is a sharp line spectrum, and has the advantages of good selectivity, convenience and speed, so rare earth fluorescent probes are considered to be Ideal material for the preparation of fluorescent probes. How to prepare rare-earth fluorescent probes that can quickly identify and detect nitroaromatic compounds is a hot topic of domestic and foreign researchers.

However, since the inner 4f electrons of a single rare earth ion are forbidden transitions, the direct excitation of rare earth ions has the disadvantage of low luminous efficiency, and the improvement is mainly through the energy transfer effect between organic ligands and rare earth ions (that is, the antenna effect). to fulfill. Therefore, the blocking of the energy transfer effect in the choline-type rare earth fluorescent probe by the analyte can be used to realize the purpose of the fluorescence quenching response of the choline-type rare-earth fluorescent probe, and the choline-type rare-earth fluorescent probe can detect nitro The process of compounds follows this principle.

With the demand for high performance and environmental protection in the field of materials, ionic liquids have gradually entered people's field of vision as emerging green solvents. Ionic liquid is a salt solvent composed of organic cations and organic or inorganic anions, which is liquid at room temperature or near room temperature; different from traditional water and organic solvents, ionic liquid has a wide range of liquid temperature, non-volatile, non-combustible , electrical and thermal conductivity and excellent thermodynamic stability, etc., which make ionic liquids an advantageous substitute for traditional solvents, and gradually emerge in various high-tech and new energy fields. In view of the further in-depth promotion and application of ionic liquids, it is inevitable that the detection of toxic and pollutants is not limited to the environment of water and organic solvents, and nitro compounds are also included. Whether the detection of nitro compounds can be realized in liquid has put forward new requirements. At the same time, the studies that have been carried out also show that the type of solvent has a significant impact on the detection of nitro compounds by choline-type rare earth fluorescent probes. For example, the Mondal research group of Indian International University found that the rare earth terbium complex of 2,6-pyridinedicarboxylic acid has a quenching effect on various nitro compounds, and found that the sensitivity of detection depends on the type of solvent, in water and Rare earth fluorescent probes have different sensitivities and detection limits in different organic solvents (water, methanol, acetonitrile and tetrahydrofuran). However, there is no report on the detection performance of rare earth fluorescent probes in ionic liquids.

At present, researchers at home and abroad have carried out some research on the luminescent properties of rare earth ions and their complexes in ionic liquids. The results show that, first of all, in the visible and near-infrared regions, ionic liquids do not interfere with the spectrum of rare earths; secondly, compared with traditional solvents, ionic liquids have the characteristics of weak coordination and weak solvation for solute molecules; in addition, rare earth ions and Its complexes have higher fluorescence intensity and lifetime in ionic liquids, which not only fundamentally avoids the probability of fluorescence quenching of rare earth fluorescent probes caused by solvent coordination, but also reduces the influence of solvents on the response performance of probes during the detection process. , and it is also beneficial to maintain the stability of the coordination structure of the rare earth fluorescent probe in it, thereby improving the fluorescence performance and stability of the rare earth fluorescent probe.

In recent years, studies have proved that ionic liquids can be used as an ideal dispersion medium for rare earth luminescent materials. In addition, studies have also shown that the imidazolium cations of ionic liquids can not only form hydrogen bonds with rare earth fluorescent probes, but also stabilize rare earth fluorescent probes and enhance their light resistance. There is an energy transfer effect between rare earth fluorescent probes, which can further improve their fluorescence quantum yield and lifetime; in addition, the special composition and structure of ionic liquid anions and cations is the main reason that affects the dissolution of complexes and other functional properties. These special solvents Whether the properties affect the detection performance of rare earth fluorescent probes is still an unsolved mystery. Therefore, how to realize the preparation of rare earth fluorescent probes and the detection of nitro compounds in ionic liquid solvents will become a key technical problem to solve the detection of nitro compounds in new solvents and to further expand the application field of rare earth fluorescent probes.

Contents of the invention

For above-mentioned deficiencies in the prior art, the object of the present invention is to provide the application of the detection of nitro compounds in ionic liquid and water nitro compounds of choline type rare earth fluorescent probe, the present invention has synthesized in ionic liquid and aqueous solution all have good Solubility and stability of the choline-type rare earth fluorescent probe [choline] ₃ [Eu(dpa) ₃ ] (wherein, choline is choline, and DPA is 2,6-pyridinedicarboxylic acid). Among them, rare earth europium ion has excellent fluorescence monochromaticity, DPA ligand can produce effective energy transfer to rare earth europium ion, improve its fluorescence intensity, choline ion as the counter ion of the complex can effectively enhance its fluorescence in ionic liquid Solubility and enhance its fluorescence stability. Utilize the synthesized choline-type rare earth fluorescent probe as a rare earth fluorescent probe for detecting nitro compounds, and explore its fluorescence detection performance for various nitro compounds in water and imidazole ionic liquids. The present invention fills the rare earth fluorescent probe in ion The gap in the detection of substances in liquid solvents has important theoretical significance for further enriching and realizing the detection and application of rare earth fluorescent probes in different solvents and environments. At the same time, it will have important applications for the detection of nitro compounds in ionic liquids value.

The present invention is achieved through the following technical solutions:

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

Preferably, the nitro compounds include but not limited to p-nitrophenol, nitrobenzene, p-nitrotoluene, m-dinitrobenzene.

Preferably, the application method for preparing the nitro compound detection probe in the ionic liquid is:

Dispersing the choline-type rare earth fluorescent probe sample in the ionic liquid to obtain a dispersion;

Prepare different concentrations of nitro compounds, add dispersion liquid to them, then measure the fluorescence intensity at the excitation wavelength of 293nm and emission wavelength of 616nm, make a standard curve, and fit to determine the linear relationship between the fluorescence intensity and the concentration of nitro compounds and the minimum detection limit.

Preferably, when detecting the sample to be tested, measure its fluorescence intensity at an excitation wavelength of 293nm and an emission wavelength of 616nm, and determine the concentration of the sample to be tested according to the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

Preferably, the application method for the detection of nitro compounds in preparation water is:

Dispersing the choline-type rare earth fluorescent probe sample in water to obtain a dispersion;

Prepare different concentrations of nitro compounds, add dispersion liquid to them, then measure the fluorescence intensity at the excitation wavelength of 287nm and emission wavelength of 616nm, make a standard curve, and fit to determine the linear relationship between the fluorescence intensity and the concentration of nitro compounds and The lowest detection limit.

Preferably, when detecting the sample to be tested, measure its fluorescence intensity at an excitation wavelength of 287nm and an emission wavelength of 616nm, and determine the concentration of the sample to be tested according to the linear relationship between the fluorescence intensity and the concentration of the nitro compound.

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

S1. Dissolving the methanol solution of 2,6-pyridinedicarboxylic acid and choline hydroxide in water, and then adjusting the pH to neutral to obtain a mixed solution;

S2. Heating the mixed solution in step S1 to 70-75°C, and adding an aqueous solution of EuCl ₃ ·6H ₂ O dropwise thereto, stirring and reacting at 70-75°C for 2-3 hours, evaporating the solvent to obtain a powder product, and The powder product removes residual choline hydroxide to obtain a choline-type rare earth fluorescent probe.

Preferably, the molar ratio of 2,6-pyridinedicarboxylic acid, choline hydroxide, and EuCl ₃ ·6H ₂ O is 3:6:1; and in the methanol solution of choline hydroxide in step S1, hydrogen The mass fraction of oxidized choline is 47-50%.

Preferably, in the step S1, the volume ratio of water to choline hydroxide is 3-4:1, and 1 mol/L sodium hydroxide solution or potassium hydroxide solution is used to adjust the pH.

Preferably, the method for removing the residual solvent of choline hydroxide in the step S2 is: washing the powder product with methanol.

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

1. The present invention has prepared a choline-type rare earth fluorescent probe [choline] ₃ [Eu(DPA) ₃ ] (wherein, choline is choline, and DPA is 2,6-pyridinedicarboxylic acid), and it is applied to nitric acid for the first time. Based on the detection of nitro compounds, the fluorescence detection performance of nitro compounds in water and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid was studied. The research results showed that both static quenching and dynamic quenching coexisted for nitro compounds in water and ionic liquids. The quenching properties of choline-type rare earth fluorescent probes for different nitro compounds in aqueous solution are p-nitrophenol>nitrobenzene>p-nitrotoluene>m-dinitrobenzene; the quenching performance of different nitro compounds in ionic liquid The quenching performance is p-nitrotoluene>p-nitrophenol>nitrobenzene>m-dinitrobenzene. Meanwhile, the quenching efficiencies of p-nitrotoluene, m-dinitrobenzene, and nitrobenzene were higher in ionic liquids than in aqueous solutions, while the quenching efficiencies of p-nitrophenol were lower in ionic liquids than in aqueous solutions. The development of the research work will help to realize the detection of nitro compounds in non-traditional solvents, and will further broaden the detection application field of rare earth fluorescent probes, which has important theoretical significance and certain practical value.

2. The present invention mainly uses choline as the counter ion of the rare earth complex, which can increase the solubility of the rare earth complex in the ionic liquid, and is beneficial to improve the quenching efficiency of the rare earth fluorescent probe to the nitro compound.

Description of drawings

Fig. 1 is the fluorescence excitation (upper figure) and emission spectrum (lower figure) of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution and ionic liquid in Example 1 of the present invention;

Figure 2 is the fluorescence emission spectrum (upper figure) and fluorescence quenching of the choline-type rare earth fluorescent probe of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution with different concentrations of p-nitrophenol in Example 1 of the present invention Curve (below);

Fig. 3 is the fluorescence emission spectrum (upper figure) and the fluorescence quenching curve of the choline-type rare earth fluorescent probe of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution with different concentrations of nitrobenzene added in Example 1 of the present invention Figure (below);

Fig. 4 is the fluorescence emission spectrum (upper figure) and the fluorescence quenching of [choline] ₃ [Eu(DPA) ₃ ] in the aqueous solution of [choline] 3 [Eu(DPA) 3 ] with different concentrations of m-dinitrobenzene in the aqueous solution. Annihilation curve (below);

Figure 5 is the fluorescence emission spectrum (upper figure) and fluorescence quenching of the choline-type rare earth fluorescent probe of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution with different concentrations of p-nitrotoluene in Example 1 of the present invention Curve (below);

Fig. 6 is a histogram of quenching percentage of different nitro compounds in aqueous solution;

Fig. 7 is the fluorescence emission spectrum (upper figure) and the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in the ionic liquid solution of Example 1 of the present invention with different concentrations of p-nitrophenol added to the choline-type rare earth fluorescent probe. Quenching curve (below);

Fig. 8 is the fluorescence emission spectrum (upper figure) and the fluorescence emission spectrum of the choline-type rare earth fluorescent probe of [choline] ₃ [Eu(DPA) ₃ ] added to the ionic liquid solution with different concentrations of p-nitrotoluene in Example 1 of the present invention. Quenching curve (below);

Fig. 9 is the fluorescence emission spectrum (upper figure) and the fluorescence quenching of the choline-type rare earth fluorescent probe of [choline] ₃ [Eu(DPA) ₃ ] in the ionic liquid solution of Example 1 of the present invention with different concentrations of nitrobenzene added. Annihilation curve (below);

Figure 10 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in the ionic liquid solution of Example 1 of the present invention with different concentrations of m-dinitrobenzene added to the fluorescence emission spectrum of the choline-type rare earth fluorescent probe (upper figure) and Fluorescence quenching curve (below);

Figure 11 is a histogram of quenching percentages of different nitro compounds in ionic liquids.

Detailed ways

Specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention. The experimental methods described in the various embodiments of the present invention are conventional methods unless otherwise specified.

Example 1

The preparation method of choline type rare earth fluorescent probe comprises the steps:

S1, 5.014g of 2,6-pyridinedicarboxylic acid (Hdpa, 3eq) and 15.47g of choline hydroxide (47%, 6eq) in methanol were dissolved in 54.15mL of water (and choline hydroxide The volume ratio is 7:2);

After adjusting the pH of the solution to neutral with a 1mol/L aqueous sodium hydroxide solution, heat the solution to 70°C, and then add 10mL of a 1mol/L EuCl ₃ ·6H ₂ O (1eq) aqueous solution dropwise to obtain a mixed solution;

S2. After the mixed solution in step S1 was stirred and reacted at 70°C for 2 hours, most of the water was removed by a rotary evaporator to obtain a white powder product, which was washed with methanol to remove residual choline hydroxide, and dried in vacuum at 50°C , to obtain a choline-type rare earth fluorescent probe sample.

Example 2

The preparation method of choline type rare earth fluorescent probe comprises the steps:

S1, 5.014g of 2,6-pyridinedicarboxylic acid (Hdpa, 3eq) and 16.12g of choline hydroxide (49%, 6eq) in methanol were dissolved in 46.5mL of water (and choline hydroxide The volume ratio is 6:2);

After adjusting the pH of the solution to neutral with a 1mol/L aqueous sodium hydroxide solution, heat the solution to 73°C, and then add 10mL of a 1mol/L EuCl ₃ ·6H ₂ O (1eq) aqueous solution dropwise to obtain a mixed solution;

S2. After the mixed solution in step S1 was stirred and reacted at 75°C for 2.5h, most of the water was removed with a rotary evaporator to obtain a white powder product, which was washed with methanol to remove residual choline hydroxide, and then vacuumized at 50°C dried to obtain a choline-type rare earth fluorescent probe sample.

Example 3

The preparation method of choline type rare earth fluorescent probe comprises the steps:

S1, 5.014g of 2,6-pyridinedicarboxylic acid (Hdpa, 3eq) and 16.46g of choline hydroxide (50%, 6eq) in methanol were dissolved in 61.88mL of water (and choline hydroxide The volume ratio is 8:2);

After adjusting the pH of the solution to neutral with a 1mol/L aqueous sodium hydroxide solution, heat the solution to 75°C, and then add 10mL of a 1mol/L EuCl ₃ ·6H ₂ O (1eq) aqueous solution dropwise to obtain a mixed solution;

S2. After the mixed solution in step S1 was stirred and reacted at 72°C for 3 hours, most of the water was removed by a rotary evaporator to obtain a white powder product, which was washed with methanol to remove residual choline hydroxide, and dried in vacuum at 50°C , to obtain a choline-type rare earth fluorescent probe sample.

Examples 1-3 of the present invention all produce choline-type rare earth fluorescent probe samples that can be applied to the detection of nitro compounds in water and ionic liquids, and the effects are parallel. The choline-type rare earth prepared in Example 1 below Taking the fluorescent probe sample as an example, the following research is carried out. The specific research methods and results are as follows:

1. Preparation of quenching solutions of different concentrations of nitro compounds:

Preparation of quenching solutions of different concentrations of nitro compounds:

(1) Quenching solutions of rare earth complexes added with different concentrations of nitro compounds in water, and configured according to the mixing ratios in Table 1 and Table 2 respectively at low and high concentrations:

The preparation of the nitro compound quenching solution of low concentration in water of table 1

The preparation of high concentration nitro compound quenching solution in water of table 2

(2) Quenching solutions of nitro compounds of different concentrations are added to BmimPF ₆ ionic liquid for rare earth complexes, and are configured according to the mixing ratios in Table 3 and Table 4 under low concentration and high concentration respectively:

The preparation of the nitro compound quenching solution of low concentration in the ionic liquid of table 3

The preparation of the high-concentration nitro compound quenching solution in the ionic liquid of table 4

Among them, the "rare earth complex" in Table 1-Table 4 is the choline-type rare earth fluorescent probe prepared in Example 1 of the present invention, and the "BmimPF ₆ " in Table 3-Table 4 is 1-butyl-3-methanol imidazolium hexafluorophosphate (BmimPF ₆ ) ionic liquid.

2. Data processing:

Stern–Volmer (SV) equation: (I ₀ /I)=K _sv [C]+1, where I ₀ and I are the fluorescence intensity before and after the addition of the nitro explosive analyte , [C] is the molar concentration of the analyte, and K _sv is the quenching constant.

Quenching percentage W: W=(I ₀ −I)/I ₀ , where I ₀ and I are the fluorescence intensity before and after addition of nitro explosive analyte.

Limit of detection: LOD = 3σ/s, where σ is the standard deviation of the intercept and s is the K _sv constant value.

3. Results and Discussion

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

Figure 1 is the fluorescence excitation and emission spectra of [choline] ₃ [Eu(DPA) ₃ ] at a concentration of 1 mg/mL in water and ionic liquids. When the optimal emission wavelength is 616nm, the excitation spectrum of [choline] ₃ [Eu(DPA) ₃ ] is measured, in which the strongest excitation peak in the spectrum corresponds to the central metal europium ion from the ligand of the choline-type rare earth fluorescent probe The transfer transition peak (LigandtoMetalChargeTranstation, LMCT), in water and ionic liquids were 287nm and 293nm. In the aqueous solution, the energy transfer absorption peak of the choline-type rare earth fluorescent probe itself appeared at 395nm, but this excitation peak disappeared in the ionic liquid, indicating that the ligand of the choline-type rare earth fluorescent probe in the ionic liquid moves toward the central ion. The energy transfer efficiency is higher and the complex is more stable.

When the optimum excitation wavelengths were 287nm and 293nm respectively, the choline-type rare earth fluorescent probes in the aqueous solution and the ionic liquid all showed the strongest peak at the emission wavelength of 616nm, which is the characteristic peak of the complex, and the emission peak is The electric dipole transition (or ultrasensitive transition) of 5D ₀ →7F ₂ of Eu ³⁺ is related to the coordination environment of the choline-type rare earth fluorescent probe. In addition, the emission peak at 596nm is the magnetic dipole transition of 5D ₀ →7F ₁ of Eu ³⁺ , and the peak intensity has nothing to do with the coordination environment of the choline-type rare earth fluorescent probe.

For the transition within the configuration, unlike the electric dipole transition, the intensity of the absorption peak of the magnetic dipole transition is basically not affected by the surrounding environment of Eu ³⁺ . Generally, the magnetic dipole transition of 5D ₀ → 7F ₁ is used as the standard. The coordination symmetry of the europium system and the strength of fluorescence monochromaticity can be judged by the intensity ratio of the two characteristic emission peaks. The larger the intensity ratio, the lower the symmetry of the europium ion coordination layer, and the better the fluorescence monochromaticity of the system. In aqueous solution, the 5D ₀ → 7F ₂ electric dipole transition (or ultrasensitive transition) of the choline-type rare earth fluorescent probe is about four times stronger than the 5D ₀ → 7F ₁ magnetic dipole transition, while in ionic liquid The 5D ₀ → 7F ₂ electric dipole transition of the complex Eu ³⁺ is about three times stronger than the 5D ₀ → 7F ₁ magnetic dipole transition, indicating the coordination structure of choline-type rare earth fluorescent probes in water and ionic liquids The change occurs, and the asymmetry of the coordination structure of the choline-type rare earth fluorescent probe in the aqueous solution is higher, and the fluorescence monochromaticity is better.

2. Detection of nitro compounds with rare earth fluorescent probes

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

Figure 2 is [choline] ₃ [Eu(DPA) ₃ ] in 1mg/mL choline-type rare earth fluorescent probe aqueous solution, adding different concentrations of p-nitrophenol fluorescence emission spectrum, and the fluorescence emission peak intensity at 616nm Change the resulting fluorescence quenching curve. It can be seen from the figure that as the concentration of p-nitrophenol increases from 3mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ / I gradually increases. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in Figure 2). The linear relationship is ln(I ₀ /I)=64259[C]-0.18262, the correlation is 0.97422, and the fluorescence quenching constant Ksv=6.43×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe for p-nitrophenol was 6.41×10 ^-6 mg/L.

In addition, the change of fluorescence intensity with increasing concentration conforms to nonlinear exponential fitting (lower graph in Fig. 2), and the fitting equation is y=0.00248e ^129519x +4.44812 (R ² =0.99943). This shows that the fluorescence quenching of p-nitrophenol exists both static quenching and dynamic quenching. This is mainly because when the concentration of p-nitrophenol is high, the collision probability between the cholinergic rare earth fluorescent probe and the nitro compound increases, which causes the dynamic quenching of the complex, and the fluorescence quenching diagram shows a non- linear.

Figure 3 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1 mg/mL choline-type rare earth fluorescent probe aqueous solution, adding different concentrations of nitrobenzene, and the change of fluorescence emission peak intensity at 616nm The resulting fluorescence quenching curve. It can be seen from the figure that as the concentration of nitrobenzene increases from 3mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ /I Gradually increase. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in Fig. 3). The linear relationship is y=36033x-0.03051, the correlation is 0.93948, and the fluorescence quenching constant Ksv=3.60×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 1.34×10 ^-5 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (lower figure in Figure 3), and the fitting equation is y=0.00005361e ^114038x +3.85251 (R ² =0.99871), indicating that the fluorescence quenching of nitrobenzene also There are static quenching and dynamic quenching.

Figure 4 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1mg/mL choline-type rare earth fluorescent probe aqueous solution, adding different concentrations of m-dinitrobenzene, and the fluorescence emission peak at 616nm Fluorescence quenching curves obtained from intensity changes. It can be seen from the figure 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 aqueous solution decreases gradually and I ₀ /I increases gradually. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in Figure 4). The linear relationship is y=14510x+0.02621, the correlation is 0.99306, and the fluorescence quenching constant Ksv=1.45×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 9.57×10 ^-6 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (lower figure in Fig. 4), and the fitting equation is y=0.80394e ^16056x +0.29434 (R ² =0.99448), indicating that the fluorescence quenching of m-dinitrobenzene There are also static quenching and dynamic quenching at the same time.

Figure 5 is [choline] ₃ [Eu(DPA) ₃ ] in 1 mg/mL choline-type rare earth fluorescent probe aqueous solution, adding different concentrations of p-nitrotoluene fluorescence emission spectrum, and the fluorescence emission peak intensity at 616nm Change the resulting fluorescence quenching curve. It can be seen from the figure that as the concentration of p-nitrotoluene increases from 20mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ / I gradually increases. Plotting the logarithmic value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in Figure 3-5). The linear relationship is y=21481x-0.03091, the correlation is 0.99378, and the fluorescence quenching constant Ksv=2.15×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 9.06×10 ^-6 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (lower figure in Fig. 3-5), and the fitting equation is y=0.28134e ^29615x +1.75357 (R ² =0.99213), which shows that the fluorescence quenching of p-nitrotoluene There are both static quenching and dynamic quenching.

By comparing the quenching constant Ksv values (see Table 5) of different nitro compounds in aqueous solution, it can be drawn that the detection sensitivity of the p-nitro compounds of the choline-type rare earth fluorescent probe is p-nitrophenol > nitrobenzene > p-nitrophenol Nitrotoluene > m-dinitrobenzene. The detection limits of different nitro compounds were nitrobenzene > m-dinitrobenzene > p-nitrotoluene > p-nitrophenol.

Fluorescence quenching constants and detection limits of different nitro compounds in aqueous solution of table 5

Nitro compound type Ksv(L/mg) Detection limitLOD(mg/L) p-Nitrophenol 6.43×10⁴ 6.41×10^-6 Nitrobenzene 3.60×10⁴ 1.34×10^-5 m-dinitrobenzene 1.45×10⁴ 9.57×10^-6 p-Nitrotoluene 2.15×10⁴ 9.06×10^-6

Quenching titration of [choline] ₃ [Eu(DPA) ₃ ] for four nitro compounds in aqueous solution showed that when the amount of nitro compound added was 100 mg/L, [choline] ₃ [Eu(DPA) ₃ ] It showed 99.90%, 94.62%, 88.33% and 75.13% quenching of PNP, NB, NT and DNB in water (see Figure 6). Among them, when the addition amount of p-nitrophenol and nitrobenzene is 100 mg/L, the fluorescence of the choline-type rare earth fluorescent probe is basically quenched completely.

(2) Fluorescence quenching performance of rare earth fluorescent probes on nitro compounds in ionic liquids:

Figure 7 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1mg/mL choline-type rare earth fluorescent probe ionic liquid, adding different concentrations of p-nitrophenol, and the fluorescence emission peak at 616nm Fluorescence quenching curves obtained from intensity changes. It can be seen from the figure that as the concentration of p-nitrophenol increases from 5mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ / I gradually increases. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in FIG. 7 ). The linear relationship is y=53928x-0.15458, the correlation is 0.97221, and the fluorescence quenching constant Ksv=5.39×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 1.01×10 ^-5 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (lower figure in Fig. 7), and the fitting equation is y=0.3783e ^89808x +2.8678 (R ² =0.99935), indicating that the fluorescence quenching of p-nitrophenol is also There are both static quenching and dynamic quenching.

Figure 8 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1mg/mL choline-type rare earth fluorescent probe ionic liquid, adding different concentrations of p-nitrotoluene, and the fluorescence emission peak at 616nm Fluorescence quenching curves obtained from intensity changes. It can be seen from the figure that as the concentration of p-nitrotoluene increases from 5mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ / I gradually increases. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in FIG. 8 ). The linear relationship is y=47305x+0.18323, the correlation is 0.99557, and the fluorescence quenching constant Ksv=4.73×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 4.00×10 ^-6 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (the lower figure in Fig. 8), and the fitting equation is y=2.33041e ^39513x +0.23936 (R ² =0.99994), which shows that the fluorescence quenching of p-nitrotoluene is also There are both static quenching and dynamic quenching.

Figure 9 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1mg/mL choline-type rare earth fluorescent probe ionic liquid, adding different concentrations of nitrobenzene, and the fluorescence emission peak intensity at 616nm Change the resulting fluorescence quenching curve. It can be seen from the figure that as the concentration of nitrobenzene increases sequentially from 5mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ /I Gradually increase. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in FIG. 9 ). The linear relationship is y=12237x+0.14181, the correlation is 0.96908, and the fluorescence quenching constant Ksv=1.22×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 2.04×10 ^-5 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (the lower figure in Figure 9), and the fitting equation is y=15.10552e ^2321x -14.7010 (R ² =0.97273), indicating that the fluorescence quenching of nitrobenzene is also There are static quenching and dynamic quenching.

Figure 10 is the fluorescence emission spectrum of [choline] ₃ [Eu(DPA) ₃ ] in 1 mg/mL choline-type rare earth fluorescent probe ionic liquid, adding different concentrations of m-dinitrobenzene, and the fluorescence emission at 616nm Fluorescence quenching curves obtained from peak intensity changes. It can be seen from the figure that as the concentration of m-dinitrobenzene increases from 5mg/L to 160mg/L, the fluorescence intensity of [choline] ₃ [Eu(DPA) ₃ ] in aqueous solution decreases gradually and I ₀ /I increases gradually. Plotting the logarithm value lnI ₀ /I of the fluorescence intensity against the concentration of the nitro compound can obtain a working curve with a good linear relationship (see the inset of the upper panel in FIG. 10 ). The linear relationship is y=9220x-0.07817, the correlation is 0.99477, and the fluorescence quenching constant Ksv=9.22×10 ⁴ can be known from the slope. The calculated LOD of the choline-type rare earth fluorescent probe p-nitrobenzene was 8.30×10 ^-6 mg/L. The change of fluorescence intensity with the increase of concentration is also in line with nonlinear exponential fitting (lower figure in Figure 10), and the fitting equation is y=1.45584e ^7131x -0.6026 (R ² =0.99403), which shows that the fluorescence quenching of m-dinitrobenzene There are also static quenching and dynamic quenching at the same time.

By comparing the quenching constant Ksv values of different nitro compounds in ionic liquids (see Table 6), it can be concluded that the detection sensitivity of the nitro compounds of the choline-type rare earth fluorescent probe is p-nitrophenol > p-nitrotoluene >Nitrobenzene>m-dinitrobenzene. And the detection limit of different nitro compounds is nitrobenzene>p-nitrophenol>m-dinitrobenzene>p-nitrotoluene.

The fluorescence quenching constant table of different nitro compounds in the ionic liquid solution of table 6

Nitro compound type Ksv(L/mg) Detection limitLOD(mg/L) p-Nitrophenol 5.39×10⁴ 1.01×10^-5 p-Nitrotoluene 4.72×10⁴ 4.00×10^-6 Nitrobenzene 1.22×10⁴ 2.04×10^-5 m-dinitrobenzene 9.22×10³ 8.30×10^-6

Quenching titration of [choline] ₃ [Eu(DPA) ₃ ] for four nitro compounds in ionic liquid showed that when the amount of nitro compound added was 100 mg/L, [choline] ₃ [Eu(DPA) ₃ ] showed 99.67%, 99.16%, 77.48% and 55.48% quenching of PNP, NT, NB and DNB in ionic liquids (see Figure 11). Among them, when the addition amount of p-nitrophenol and nitrobenzene is 100mg/L, the fluorescence of the rare earth complex is basically quenched completely.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. In this way, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, it is also intended to include these modifications and variations.

Claims (10)

1. The application of choline type rare earth fluorescent probe in the detection of nitro compounds in ionic liquid and water nitro compound, it is characterized in that, described choline type rare earth fluorescent probe is [choline] ₃ [Eu(DPA) ₃ ] , wherein, choline is choline, and DPA is 2,6-pyridinedicarboxylic acid. 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 nitro compounds, is characterized in that, said nitro compounds include but are not limited to p-nitrophenol, Nitrobenzene, p-nitrotoluene, m-dinitrobenzene. 3. 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 nitro compounds is characterized in that the application method of nitro compounds detection in ionic liquids is: Dispersing the choline-type rare earth fluorescent probe sample in the ionic liquid to obtain a dispersion; Prepare different concentrations of nitro compounds, add dispersion liquid to them, then measure the fluorescence intensity at the excitation wavelength of 293nm and emission wavelength of 616nm, make a standard curve, and fit to determine the linear relationship between the fluorescence intensity and the concentration of nitro compounds and the minimum detection limit. 4. the application of the choline-type rare earth fluorescent probe according to claim 3 in the detection of nitro compounds in ionic liquids and water nitro compounds is characterized in that, when detecting the sample to be tested, measure it at excitation wavelength 293nm, emission Fluorescence intensity at a wavelength of 616nm, and according to the linear relationship between the fluorescence intensity and the concentration of the nitro compound, determine the concentration of the sample to be tested. 5. 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 nitro compounds is characterized in that the application method for the detection of nitro compounds in water is: Dispersing the choline-type rare earth fluorescent probe sample in water to obtain a dispersion; Prepare different concentrations of nitro compounds, add dispersion liquid to them, then measure the fluorescence intensity at the excitation wavelength of 287nm and emission wavelength of 616nm, make a standard curve, and fit to determine the linear relationship between the fluorescence intensity and the concentration of nitro compounds and The lowest detection limit. 6. the application of the choline type rare earth fluorescent probe according to claim 5 in the detection of nitro compounds in ionic liquids and water nitro compounds, is characterized in that, when detecting the sample to be tested, measure it at excitation wavelength 287nm, emission Fluorescence intensity at a wavelength of 616nm, and according to the linear relationship between the fluorescence intensity and the concentration of the nitro compound, determine the concentration of the sample to be tested. 7. the application of choline type rare earth fluorescent probe according to claim 1 in the detection of nitro compound in ionic liquid and water nitro compound is characterized in that, described choline type rare earth fluorescent probe is prepared according to the following steps: S1. Dissolving the methanol solution of 2,6-pyridinedicarboxylic acid and choline hydroxide in water, and then adjusting the pH to neutral to obtain a mixed solution; S2. Heating the mixed solution in step S1 to 70-75°C, and adding an aqueous solution of EuCl ₃ ·6H ₂ O dropwise thereto, stirring and reacting at 70-75°C for 2-3 hours, evaporating the solvent to obtain a powder product, and The powder product removes residual choline hydroxide to obtain a choline-type rare earth fluorescent probe. 8. the application of the choline type rare earth fluorescent probe according to claim 7 in the preparation of nitro compounds in ionic liquids and water nitro compound detection probes, is characterized in that, the 2,6-pyridinedicarboxylic acid, The molar ratio of choline hydroxide to EuCl ₃ ·6H ₂ O is 3:6:1; and in the methanol solution of choline hydroxide in step S1, the mass fraction of choline hydroxide is 47-50%. 9. the application of the choline-type rare earth fluorescent probe according to claim 7 in the detection of nitro compounds in ionic liquids and water nitro compounds, is characterized in that, in the step S1, the volume of water and choline hydroxide The ratio is 3-4:1, using 1mol/L sodium hydroxide solution or potassium hydroxide solution to adjust the pH. 10. the application of the choline-type rare earth fluorescent probe according to claim 7 in the detection of nitro compounds in ionic liquids and water nitro compounds, is characterized in that, in the step S2, the removal method of choline hydroxide residual solvent For: using methanol to wash the powder product.

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