High-stability covalent organic framework fluorescent probe for identifying hydrazine hydrate and preparation method of high-stability covalent organic framework fluorescent probe

Abstract

The invention provides a high-stability covalent organic framework fluorescent probe for identifying hydrazine hydrate and a preparation method of the high-stability covalent organic framework fluorescent probe, and belongs to the technical field of covalent organic materials. The fluorescence quenching characteristic of the material is reduced by utilizing a hydrazone bond and an N-H single bond pair on a skeleton pore channel. Methoxyl in the framework is used as an electron donor, electron cloud is delocalized from the tail end to a hydrazone bond through p-pi conjugation, and the stability of SEH-COFs is enhanced. Meanwhile, rich N and O atoms in the SEH-COFs framework are used as interaction sites, so that effective interaction with recognized molecules of an object is facilitated, and fluorescence quenching is achieved. And the quenching efficiency can be up to 82%. Based on the characteristic, the fluorescent probe provided by the invention has very high sensitivity and selectivity on hydrazine hydrate, the detection limit in water is extremely low and is 0.78 nM, the pH stability is good, and the sensing capability is maintained under different pH conditions, so that the reliable performance in various environment settings is ensured.

Description

Technical Field

[0001] The invention relates to the technical field of covalent organic material applications, and in particular to the preparation of a high-intensity emission covalent organic framework and its application in the field of identifying hydrated hydrazine. Technical Background

[0002] Hydrazine is a highly flammable and explosive molecule widely used in missile and rocket propulsion, but it poses potential health hazards to humans in daily life, especially at high environmental concentrations, where it has teratogenic and carcinogenic effects.

[0003] The current method for detecting the hydrazine content in water is to use the reaction of hydrazine and dimethylaminobenzaldehyde under acidic conditions to generate a yellow azo compound, and the depth of the yellow color is proportional to the hydrazine content within the measurement range. A spectrophotometer is used to detect the content of the azo compound at an absorption wavelength of 454 nm.

[0004] Since hydrazine is easily oxidized under alkaline conditions, especially oxidants such as chlorine, bromine, and iodine will reduce the test results. In addition, turbid water samples and water samples with pigments will also interfere with the test results. In addition, aromatic amines in water samples will also interfere with the test results of hydrazine. Therefore, a detection method that is not affected by pH conditions and interfering ions is an important issue that needs to be solved at present.

[0005] Covalent organic frameworks (COFs) are a class of porous materials that have attracted much attention due to their unique properties and wide range of applications. COFs are constructed by connecting organic building units by covalent bonds to form a crystalline structure. Due to these characteristics, COFs exhibit low weight density and stable structure. COFs offer tunable properties in terms of their topology and pore structure, that is, the geometry and size of the organic building units can be adjusted to create a variety of covalent organic framework structures with different properties and applications. Previously, COFs have been widely studied and applied, including gas absorption, catalysis, energy storage and emission sensors. In addition, luminescent materials also have a wide range of practical applications, including material detection, optical electronic devices, laser dyes and organic electroluminescent devices. These materials play a vital role in various technologies and industries. A large number of studies have demonstrated the effectiveness of luminescent COFs in detecting hazardous explosives, metal ions and anions, providing the possibility of building a hydrazine sensor. However, traditional COFs often lack sufficient detection sites, which may lead to the omission of certain analytes, increasing the technical difficulty of using COFs as effective hydrazine sensors. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a high-stability covalent organic framework fluorescent probe for identifying hydrated hydrazine and a preparation method thereof. The technical solution adopted by the present invention is as follows: The highly stable covalent organic framework fluorescent probe for identifying hydrated hydrazine is a covalent organic framework porous polymer based on hydrazone connection, which has a molecular structure shown in SEH-COF-1 or SEH-COF-2: .

[0007] The preparation method of the covalent organic framework porous polymer SEH-COF-1 and SEH-COF-2 based on hydrazone connection, the synthesis route is as follows:

[0008] It is prepared by the Schiff base reaction of 1,3,5-tris(3'-methoxy-4'-acylhydrazonephenyl)benzene (TMHB) and 2,4,6-trimethoxy-1,3,5-benzenetricarboxaldehyde (TPB-OMe) or 1,3,5-tris(3'-methoxy-4'-benzaldehydephenyl)benzene (TFPB-OMe). The specific steps are: 1) At room temperature and pressure, add equal amounts of TMHB and TPB-OMe or TFPB-OMe into a reaction tube, add o-dichlorobenzene and n-butanol under a nitrogen atmosphere, slowly dropwise add 6 mol / L acetic acid aqueous solution and sonicate for 2-10 min; the volume ratio of o-dichlorobenzene, n-butanol, and acetic acid aqueous solution is (7.5-15):(7.5-15):(1.5-3); 2) Place the reaction tube into a reactor and place it at 120°C in a nitrogen atmosphere for 24 to 120 hours; 3) Filter in a sand core funnel, wash with acetone and ethanol 2 to 3 times respectively during the filtration process, then use tetrahydrofuran as a solvent for Soxhlet extraction for 24 hours, and place in a vacuum oven at 90°C for 12 hours to obtain a powder of a covalent organic framework porous polymer SEH-COF-1 or SEH-COF-2 based on hydrazone linkage.

[0009] The covalent organic framework porous polymers SEH-COF-1 and SEH-COF-2 connected by hydrazones are applied as fluorescent probes for identifying hydrated hydrazine.

[0010] The method for using the hydrazone-linked covalent organic framework porous polymers SEH-COF-1 and SEH-COF-2 to identify hydrated hydrazine fluorescent probes is as follows: 1) Accurately weigh 2.4 mg of SEH-COF-1 or SEH-COF-2 and add it to 40 mL of deionized water, and fully disperse it by ultrasound to obtain a covalent organic bone porous polymer dispersion; 2) Measure 3.0 mL of the covalent organic bone porous polymer dispersion prepared in step 1) and put it into a beaker. Then transfer 3.0 mL of the sample to be tested. Mix the two and shake them evenly. Then place them in the sample cell of the fluorescence spectrometer and test the fluorescence intensity under light excitation at a wavelength of 365 nm.

[0011] Beneficial effects of the present invention: 1. The fluorescent probe involved in the present invention is a crystalline covalent organic framework porous polymer prepared by Schiff base reaction. The design of SEH-COFs is subject to several considerations. First, the hydrazone bond containing a single-bonded -NH group helps to reduce aggregation-induced fluorescence quenching. The methoxy group acts as an electron donor, delocalizing the electron cloud from the vertex to the hydrazone bond through p-π conjugation, thereby enhancing the stability of SEH-COFs. In addition, the conjugated structure and nitrogen atoms give it strong fluorescence properties. The nitrogen and oxygen atoms present on the framework wall combine with guest molecules, making SEH-COFs an innovative molecular sensor.

[0012] 2. The present invention has experimentally confirmed the excellent detection of SEH-COFs for hydrated hydrazine, which exceeds many other materials with active sites. The experiment also confirmed the high sensitivity and selective recognition ability of SEH-COFs for hydrated hydrazine. In the pH range of 4 to 10, the fluorescence intensity of SEH-COFs remains relatively stable, and the pH stability is good. Maintaining its sensing ability under different pH conditions ensures reliable performance in various environmental settings. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Fourier transform infrared spectra of two covalent organic framework porous polymers SEH-COFs and the corresponding synthetic monomers; a: infrared spectrum of SEH-COF-1, b: infrared spectrum of SEH-COF-2 Figure 2 Solid-state NMR spectra of two covalent organic framework porous polymers SEH-COFs and the corresponding synthetic monomers; a: solid-state NMR spectrum of SEH-COF-1, b: solid-state NMR spectrum of SEH-COF-2.

[0015] Figure 3 X-ray diffraction patterns of two covalent organic framework porous polymers SEH-COFs; a: X-ray diffraction pattern of SEH-COF-1, b: X-ray diffraction pattern of SEH-COF-2; Figure 4These are the nitrogen adsorption / desorption curves of two covalent organic framework porous polymers SEH-COFs: a: nitrogen adsorption / desorption curve of SEH-COF-1; b: nitrogen adsorption / desorption curve of SEH-COF-2.

[0016] Figure 5 The nonlocal density function theoretical diagrams of two covalent organic framework porous polymers SEH-COFs: a: The nonlocal density function theoretical diagram of SEH-COF-1; b: The nonlocal density function theoretical diagram of SEH-COF-2.

[0017] Figure 6 Field emission scanning electron microscopy images of two covalent organic framework porous polymers SEH-COFs; a: Field emission scanning electron microscopy image of SEH-COF-1, b: Field emission scanning electron microscopy image of SEH-COF-2 Figure 7 UV-visible spectra of two covalent organic framework porous polymers SEH-COFs and synthetic raw materials. a: SEH-COF-1, b: SEH-COF-2; Figure 8 Solid fluorescence emission images of two covalent organic framework porous polymers SEH-COFs under 365 nm excitation, a: solid fluorescence emission image of SEH-COF-1, b: solid fluorescence emission image of SEH-COF-2; Fig. 9 The regular and gradual quenching of fluorescence of covalent organic framework porous polymer dispersion by hydrated hydrazine. a: SEH-COF-1, b: SEH-COF-2; Fig.10 Selective bar graph of SEH-COFs covalent organic framework porous polymer for hydrated hydrazine fluorescence detection, a: SEH-COF-1, b: SEH-COF-2; Fig.11 The effect of pH on the selectivity of covalent organic framework porous polymer SEH-COFs for hydrated hydrazine fluorescence detection, a: SEH-COF-1, b: SEH-COF-2; Fig.12 Linear fitting diagram of ion concentration and fluorescence intensity, a: SEH-COF-1, b: SEH-COF-2. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0020] Sources of raw materials for the following examples: 1,3,5-tris(3'-methoxy-4'-acylhydrazonephenyl)benzene (Tab, 5 g 95%), 2,4,6-trimethoxy-1,3,5-benzenetricarboxaldehyde (Tab, 5 g 97%), and 1,3,5-tris(3'-methoxy-4'-benzaldehydephenyl)benzene (Tab, 5 g 93%), n-butanol (n-BuOH, 500 mL 99%), o-dichlorobenzene (o-DCB, 100 mL 98%) were purchased from Aladdin Chemistry (Shanghai, China).

[0021] Example 1 (Synthesis of Covalent Organic Framework Porous Polymer SEH-COF-1) 1) At room temperature and pressure, place 0.1 mmol (57.1 mg) of 1,3,5-tris(3'-methoxy-4'-acylhydrazophenyl)benzene and 0.1 mmol (25.2 mg) of 2,4,6-trimethoxy-1,3,5-benzenetricarboxaldehyde in a 10 mL reaction tube. Add 0.75 mL of o-dichlorobenzene and 0.75 mL of n-butanol under nitrogen atmosphere, slowly drop 0.2 mL of 6 mol / L acetic acid aqueous solution and ultrasonicate for 10 min. The two monomers react completely with ultrasonication and the solution is mixed evenly. 2) Place the reaction tube into a reactor and place it at 120°C in a nitrogen atmosphere for 24 hours; 3) Filter in a sand core funnel, wash with acetone and ethanol 2-3 times respectively during the filtration process, then use tetrahydrofuran as a solvent for Soxhlet extraction for 24 hours, and place in a vacuum oven at 90°C for 12 hours to obtain a covalent organic framework porous polymer powder, which is recorded as SEH-COF-1.

[0022] Example 2 (Synthesis of Covalent Organic Framework Porous Polymer SEH-COF-2) 1) At room temperature and pressure, 0.1 mmol (57.1 mg) of 1,3,5-tris(3'-methoxy-4'-acylhydrazonephenyl)benzene and 0.1 mmol (48.1 mg) of 1,3,5-tris(3'-methoxy-4'-benzaldehydephenyl)benzene were placed in a 10 mL reaction tube. 0.75 mL of o-dichlorobenzene and 0.75 mL of n-butanol were added under nitrogen atmosphere. 0.2 mL of 6 mol / L acetic acid aqueous solution was slowly added dropwise and ultrasonicated for 10 min. 2) Place the reaction tube into a reactor and place it at 120°C in a nitrogen atmosphere for 24 hours; 3) Filter in a sand core funnel, wash with acetone and ethanol for 2-3 times respectively during the filtration process, then use tetrahydrofuran as a solvent for Soxhlet extraction for 24 hours, and place in a vacuum oven at 90°C for 12 hours to obtain a covalent organic framework porous polymer powder, which is recorded as SEH-COF-2.

[0023] The FT-IR spectra of SEH-COF-1 and SEH-COF-2 (collectively referred to as SEH-COFs) show a peak at 1617 cm - ¹ and 1619 cm - The characteristic stretching vibration bands at 1697 cm⁻¹, corresponding to the formation of hydrazone bonds, are absent due to the aldehyde groups in TFB-OMe and TFB-OMe. This confirms the complete condensation of the monomers into COFs. This indicates that the aldehyde groups have completely reacted to form imine bonds, which is essential for the COF structure. In addition, the FT-IR signals observed in the range of 2800-3000 cm⁻¹ confirm the presence of methoxy groups in SEH-COFs ( Figure 1 ).

[0024] Solid-state carbon-13 NMR ( 13 C NMR spectroscopy further elucidated the structural integrity of SEH-COF-1 and SEH-COF-2. This technique provides detailed information on the carbon environment within the COF structure, which is essential for verifying the formation and integrity of the covalent network. 13C NMR spectroscopy showed that the carbon signals of SEH-COF-1 and SEH-COF-2 were 158 and 157 ppm, respectively, corresponding to the carbon atoms that form the hydrazone bonds between the organic building blocks ( Figure 2 In addition, signals of methoxy (-OMe) groups were observed at 56 ppm and 55 ppm for SEH-COF-1 and SEH-COF-2, respectively, confirming their incorporation into COFs. The detection of keto carbon at 168 ppm further supported the successful condensation reaction and confirmed the structural features of COFs.

[0025] Powder X-ray diffraction (PXRD) analysis helps to elucidate the crystalline nature of SEH-COF-1 and SEH-COF-2. SEH-COF-1 has obvious PXRD peaks at 4.66°, 8.12°, 9.40°, 12.42°, and 25.14°, corresponding to the (100), (110), (200), (300), and (001) planes, respectively. Figure 3 (a)). Similarly, the PXRD peaks of SEH-COF-2 are located at 4.52°, 5.86°, 6.80°, 8.96°, and 24.72°, corresponding to the same plane ( Figure 3 (b)). Pawley refinement of the unit cell validates the structural model, showing that the AA stacking model, characterized by the COF layer arrangement, closely agrees with the experimental PXRD data, confirming its accuracy. In contrast, the AB stacking model is inconsistent with the experimental results, indicating that the AA model more accurately reflects the actual structure of COFs.

[0026] The nitrogen adsorption and desorption test showed the porous characteristics of SEH-COFs. SEH-COFs showed a nitrogen adsorption isotherm of type ( Figure 4 ). This type of isotherm is characteristic of microporous materials, indicating significant porosity, and a large amount of nitrogen absorption can be noticed at low pressures (P / P0) up to 0.1. As can be seen from the figure, the specific surface area of ​​SEH-COF-1 is 316 m² / g, and the specific surface area of ​​SEH-COF-2 is 187 m² / g. In addition, the pore sizes of SEH-COF-1 and SEH-COF-2 are centered at 1.6 nm and 2.0 nm, respectively ( Figure 5 ).

[0027] Field Emission Scanning Electron Microscope (FE-SEM) Figure 6 , showing a uniform stacking structure. Both SEH-COF-1 and SEH-COF-2 exhibit consistent ribbon structures, illustrating the uniformity of the synthesis process.

[0028] The electronic absorption properties of SEH-COFs were analyzed by UV-visible spectroscopy. SEH-COF-1 showed an absorption band centered at 395 nm ( Figure 7 (a) ), with respect to the red shift of the absorption maximum of its constituent units. This red shift indicates the conjugation effect of SEH-COFs. Similarly, SEH-COF-2 exhibits an absorption band at 406 nm ( Figure 7 (b)). The absorption properties of SEH-COF-2 are affected by the structure. The presence of triphenylbenzene units weakens the conjugated system of SEH-COF-2 by making the structure less rigid compared to the linear benzene rings. This curvature can disrupt the delocalization of π-electrons on the framework, leading to a shift in the observed absorption maximum.

[0029] Through solid-state fluorescence spectroscopy analysis, SEH-COF-1 and SEH-COF-2 both showed good photoluminescence properties under 365 nm excitation ( Figure 8 (a) and (b)). SEH-COF-1 fluoresces at 460 nm, while SEH-COF-2 fluoresces at 575 nm.

[0030] Example 3 (Construction of fluorescent probe) 2.4 mg of the covalent organic bone porous polymers SEH-COF-1 and SEH-COF-2 synthesized in Example 1 and Example 2 were accurately weighed and dissolved in 40 mL of deionized water, respectively, and fully dispersed by ultrasound to obtain a covalent organic bone porous polymer dispersion. The obtained covalent organic bone porous polymer dispersion was almost transparent.

[0031] Example 4 (Sensitivity of fluorescent probe) Take 3.0 mL of the covalent organic bone porous polymer dispersion prepared in step 1) and put it into a beaker. Then take 3.0 mL of the 1×10 -3 mol / L hydrated hydrazine solution. Mix the two and place them in the sample pool of the fluorescence spectrometer, and test the fluorescence intensity under the excitation of light at a wavelength of 365nm.

[0032] The detection limit of SEH-COFs-1 was as low as 0.78 nM, and the detection limit of SEH-COFs-2 was as low as 0.95 nM. Fig. 9 . Comparison of all the fluorescence spectra obtained revealed that the fluorescence intensity gradually decreased with the increase of hydrated hydrazine concentration. In addition, fluorescence titration experiments characterized the sensitivity of SEH-COFs to hydrated hydrazine detection. The Stern-Volmer constant (Ksv) of SEH-COF-1 and SEH-COF-2 was 2.3 × 10 5 M - ¹( Fig.10 (a) and (b). The high Ksv value also confirms the excellent detectability of SEH-COFs for hydrated hydrazine.

[0033] Example 5 (Selectivity of fluorescent probe) Measure 3.0 mL of the covalent organic bone porous polymer dispersion prepared in step 1) of Example 3 and put it into a beaker. Then transfer 5.0 μL of the 1×10 -2 mol / L hydrated hydrazine solution. After mixing and shaking, place them in the sample pool of the fluorescence spectrometer, test the fluorescence intensity under the excitation of light at a wavelength of 365 nm, and add 2× 10 -5M different metal ion solutions as interfering components (sodium chloride, potassium chloride, barium chloride, calcium chloride, nickel chloride, cobalt chloride, copper chloride and zinc chloride).

[0034] After the introduction of these typical interfering components, the fluorescence emission intensity of SEH-COFs is still very small (e.g. Fig.11 (a) and (b) as shown by orange bars). In contrast, after the addition of hydrazine, the fluorescence intensity decreased significantly (as shown in Fig.11 This significant decrease confirms the high sensitivity and selective recognition ability of SEH-COFs towards hydrated hydrazine.

[0035] Example 6 (Effect of different pH conditions on fluorescent probes) Measure 3.0 mL of the covalent organic bone porous polymer dispersion prepared in step 1) of Example 3 and put it into a small beaker. Then transfer 5.0 μL of the 1×10 -2 mol / L hydrated hydrazine solution. Mix the two and place them in the sample pool of the fluorescence spectrometer. Test the fluorescence intensity under the excitation of light at a wavelength of 365nm. Add hydrochloric acid and sodium hydroxide solution to adjust the pH value.

[0036] like Fig.12 As shown in (a) and (b), the fluorescence intensity of SEH-COFs remains relatively stable in the pH range of 4 to 10, with good pH stability. This stability is critical for practical applications where sensors may encounter fluctuating pH environments. Within this pH range, the fluorescence intensity fluctuates only slightly after the addition of hydrated hydrazine, further demonstrating that SEH-COFs maintain their sensing ability under different pH conditions. They maintain good sensitivity in both harsh acidic and alkaline environments, ensuring reliable performance in a variety of environments.

Claims

1. A highly stable covalent organic framework fluorescent probe for identifying hydrated hydrazine, characterized in that: The fluorescent probe is a covalent organic framework porous polymer based on hydrazone connection, which has a molecular structure shown in SEH-COF-1 or SEH-COF-2: 。 2. The method for preparing a high-stability covalent organic framework fluorescent probe for identifying hydrated hydrazine according to claim 1, characterized in that: The covalent organic framework porous polymer based on hydrazone connection is prepared by reacting 1,3,5-tris(3'-methoxy-4'-acylhydrazonephenyl)benzene with 2,4,6-trimethoxy-1,3,5-benzenetricarboxaldehyde or 1,3,5-tris(3'-methoxy-4'-benzaldehydephenyl)benzene through a Schiff base reaction.

3. The method for preparing a high-stability covalent organic framework fluorescent probe for identifying hydrated hydrazine according to claim 2, characterized in that: The steps of preparing the covalent organic framework porous polymer based on hydrazone connection by Schiff base reaction are: 1) At room temperature and pressure, add equal amounts of 1,3,5-tris(3'-methoxy-4'-acylhydrazonephenyl)benzene and 2,4,6-trimethoxy-1,3,5-benzenetricarbaldehyde or 1,3,5-tris(3'-methoxy-4'-benzaldehydephenyl)benzene into a reaction tube, add o-dichlorobenzene and n-butanol under a nitrogen atmosphere, slowly add 6 mol / L acetic acid aqueous solution dropwise and sonicate for 2-10 min; the volume ratio of o-dichlorobenzene, n-butanol and acetic acid aqueous solution is (7.5-15):(7.5-15):(1.5-3); 2) Place the reaction tube into a reactor and place it at 120°C in a nitrogen atmosphere for 24 to 120 hours; 3) Filtration was performed in a sand core funnel, and the mixture was washed with acetone and ethanol for 2 to 3 times respectively during the filtration process. Then, Soxhlet extraction was performed with tetrahydrofuran as a solvent for 24 h. The mixture was placed in a vacuum oven and dried at 90°C for 12 h to obtain a powder of a covalent organic framework porous polymer based on hydrazone linkage.

4. The method for preparing a high-stability covalent organic framework fluorescent probe for identifying hydrated hydrazine according to claim 3, characterized in that: The volume ratio of o-dichlorobenzene, n-butanol and acetic acid aqueous solution in step 1) is 7.5:7.5:

2.

5. The method for preparing a high-stability covalent organic framework fluorescent probe for identifying hydrated hydrazine according to claim 3, characterized in that: In step 1), ultrasonic treatment was performed for 10 min.

6. The method for preparing a highly stable covalent organic framework fluorescent probe for identifying hydrated hydrazine according to claim 3, characterized in that: In step 2), the reaction was carried out in a nitrogen atmosphere for 24 h.

7. Use of the high-stability covalent organic framework fluorescent probe according to claim 1 as a fluorescent probe for identifying hydrated hydrazine.

8. The use of the high-stability covalent organic framework fluorescent probe according to claim 7 as a fluorescent probe for identifying hydrated hydrazine, characterized in that: 1) Accurately weigh 2.4 mg of hydrazone-linked covalent organic framework porous polymer powder and add it to 40 mL of deionized water, and fully disperse it by ultrasound to obtain a covalent organic framework porous polymer dispersion; 2) Take 3.0 mL of the covalent organic framework porous polymer dispersion prepared in step 1) and put it into a beaker. Then take 3.0 mL of the sample to be tested, mix the two and shake them evenly. Then put them into the sample cell of the fluorescence spectrometer and test its fluorescence intensity under light excitation at a wavelength of 365 nm.

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