Deep eutectic solvent for preparing covalent organic framework, preparation method and application of deep eutectic solvent to intelligent colorimetric sensor

Abstract

The invention relates to the technical field of analysis and detection, in particular to a eutectic solvent for preparing a covalent organic framework, a preparation method and application of the eutectic solvent to an intelligent colorimetric sensor. The invention relates to a deep eutectic solvent for preparing a covalent organic framework. The deep eutectic solvent comprises glycine betaine and hexafluoroisopropanol; the molar ratio of the betaine to the hexafluoroisopropanol is (1: 2)-(1: 6). Homoporous and heteroporous covalent organic frameworks are commonly synthesized in a deep eutectic solvent based on betaine-hexafluoroisopropanol and are used for intelligent colorimetric sensing. The invention relates to a novel method for synthesizing a COF connected with imide with a same-pore and different-pore structure. By adjusting the molar ratio of betaine-hexafluoroisopropanol in DES and changing the reaction temperature, the imine-connected COF with clover-shaped, quadrilateral, hexagonal and triangular hexagonal holes can be successfully synthesized. This simple strategy does not require additional catalysts or strict experimental conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of analysis and detection, and in particular to a low eutectic solvent for preparing a covalent organic framework, a preparation method and application in an intelligent colorimetric sensor. Background Art

[0002] Several relatively ideal solvents, including water or water with a small amount of organic solvents (e.g., DMSO), PEG-H2O systems, ionic liquids, and deep eutectic solvents (DESs), have been used to synthesize imine-linked COFs (covalent organic frameworks) with high crystallinity. Catalysts are also crucial in influencing crystallinity. In order to obtain highly crystalline imine-linked COFs, catalyst-related parameters such as type, concentration, and dosage must be optimized, which will consume a lot of resources.

[0003] Covalent Organic Frameworks (COFs) are crystalline porous materials formed by organic molecules connected by covalent bonds. The molecular structure of COFs is highly ordered and can form two-dimensional (2D) or three-dimensional (3D) crystal networks. Based on the geometric design of nodes and connectors, the lattice type of COFs (such as hexagonal, square or cubic) can be precisely controlled. COFs usually have highly tunable porosity and pore size. The pore size ranges from micropores (<2 nm) to mesopores (2-50 nm), depending on the choice of its building blocks.

[0004] Covalent organic frameworks (COFs) have unique potential for measuring water content in organic solvents due to their high porosity, tunable chemistry, and selective adsorption of specific molecules. COFs can be designed to contain water-sensitive fluorescent groups. When COFs come into contact with water, the fluorescence signal changes significantly (e.g., intensity changes or wavelength shifts). By measuring the fluorescence changes, the water content can be quantitatively analyzed. Another example is the introduction of functional sites in COFs that react with water to produce color changes. The water concentration is determined by colorimetry.

[0005] To date, most studies have focused solely on measuring the water content in organic solvents, and only a few studies have been able to simultaneously detect water and organic solvents, especially using fluorescent imine-linked COFs for simultaneous detection of water and organic solvents.

[0006] At present, there are relevant literatures to synthesize highly crystalline imine-linked COFs, which effectively promote the synthesis of several imine-linked homoporous COFs and avoid the cumbersome process associated with catalyst selection. However, based on the selection of similar low eutectic solvents, other homoporous (e.g., quadrilateral) and heteroporous imine-linked COFs can be cleverly synthesized; and can be effectively used in colorimetric sensors, but there is no relevant technology to describe it. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a low eutectic solvent for preparing a covalent organic framework, wherein the low eutectic solvent comprises betaine and hexafluoroisopropanol; and the molar ratio of betaine to hexafluoroisopropanol is (1:2) to (1:6).

[0008] As an embodiment of the present invention, the molar ratio of betaine to hexafluoroisopropanol is 1:2, 1:3, 1:4, 1:5, or 1:6.

[0009] The second aspect of the present invention provides a covalent organic framework, which is prepared by using the low eutectic solvent as a solvent and amine compounds and aldehyde compounds as raw materials.

[0010] As an embodiment of the present invention, the pores of the covalent organic framework are clover-shaped, quadrilateral, hexagonal and triangular hexagonal.

[0011] As an embodiment of the present invention, the amine compound is tris(4-aminophenyl)amine (TA), 4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine (TTA), 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (THP), 1,3,5-tris(4-aminophenyl)benzene (TPB), and 3,3'-diaminobenzidine (DAB) having a symmetrical structure.

[0012] As an embodiment of the present invention, the aromatic aldehyde compound with a symmetrical structure is selected from one or more of 2,6-pyridinedicarboxaldehyde (DFP), 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP), terephthalaldehyde (PDA), 2,5-dihydroxyterephthalaldehyde (DHTA), 2,5-divinyl-1,4-benzenedicarbaldehyde (BDD), and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tri[benzaldehyde] (BTT).

[0013] The third aspect of the present invention provides a method for preparing a covalent organic framework, comprising the following steps: Step 1: Add different reaction raw materials into a reaction vessel; Step 2: Add a low eutectic solvent corresponding to different reaction raw materials into the reaction container and dissolve them by ultrasonication; Step 3: After fully dissolved, fill with nitrogen and seal at room temperature for 72 hours or freeze three times by nitrogen circulation and react at 120 °C for 72 hours; Step 4: After the reaction is completed, the product is washed with ethanol at least three times to remove the solvent; Step 5: After washing, place in a 50°C oven to dry.

[0014] As an embodiment of the present invention, when the reaction raw materials are 2,6-pyridinedicarboxaldehyde and tri(4-aminophenyl)amine; or, 2,6-pyridinedicarboxaldehyde and 4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine, the step 3 is: after sufficient dissolution, freezing three times by nitrogen circulation, and reacting at 120°C for 72 hours.

[0015] A fourth aspect of the present invention provides an intelligent colorimetric sensor, which uses the covalent organic framework to detect the water content (v / v%) in various organic solvents.

[0016] By adopting the above technical solution, the present invention has the following beneficial effects: (1) Using a new type of DES (composed of betaine and hexafluoroisopropanol), homoporous and heteroporous COFs were synthesized, including eight COFs of cloverleaf, quadrilateral, hexagonal, and triangular hexagonal shapes.

[0017] (2) DES forms a strong hydrogen-bonding network with the two precursors, which supports the nucleophilic addition of 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (THP) to 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP), leading to the formation of a C-N bond. With the help of DES, the native isomorphous rearrangement of the zwitterionic intermediate produces a neutral alkanolamine intermediate, which then undergoes a β-elimination to produce the desired imine product with simultaneous dehydration.

[0018] (3) Universal synthesis of homo- and hetero-porous covalent organic frameworks in a betaine-hexafluoroisopropanol-based deep eutectic solvent for smart colorimetric sensing. A new method for the synthesis of imide-linked COFs with homo- and hetero-porous structures. By adjusting the molar ratio of betaine-hexafluoroisopropanol in DES and changing the reaction temperature, imide-linked COFs with clover-shaped, tetragonal, hexagonal, and triangular hexagonal pores can be successfully synthesized. This simple strategy does not require additional catalysts or strict experimental conditions.

[0019] (4) In terms of economic development, since this simple strategy does not require additional catalysts or strict experimental conditions, it can save time, reagents, and other related resources; In terms of technical effect, the dynamic hydrogen bond network catalyzed by the alkaline process induced by betaine-hexafluoroisopropanol is used to inhibit the reversible hydrolysis of the imine intermediate. This is different from the traditional acid-catalyzed COF synthesis, thus enriching the exploration of the general synthesis strategy of COF; In terms of social benefits, COF-3 synthesized using 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (THP) to 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP) as a precursor exhibits excellent polarity-dependent fluorescence color changes. It has been successfully applied to intelligent colorimetric sensing in WeChat applets, which can quickly and accurately identify water fractions in organic solvents through RGB analysis with satisfactory accuracy. In addition, the potential of COF-3 in anti-counterfeiting and message encryption has also been demonstrated, highlighting its broad application prospects.

[0020] This patent addresses the previous lack of exploration in base-catalyzed synthesis of COFs and lays the foundation for the development of other general strategies for the synthesis of various types of COFs from betaine-based DESs. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 X-ray diffraction (XRD) patterns of COF-1 to COF-8 (ah).

[0023] Figure 2 PXRD refinement patterns of COF-1 to COF-8 (ah).

[0024] Figure 3 Scanning electron microscope (SEM) images of COF-1 to COF-8 (ah), transmission electron microscope (TEM) images of COF-1 to COF-8 (ip).

[0025] Figure 4 Infrared spectra of COF-1 to COF-8 (ah).

[0026] Figure 5 This is the QR code of the SWMU-AI WeChat applet.

[0027] Figure 6The linear relationship between the G / R value and water content (0%-99.5%) of the samples is (ad) acetonitrile; (eh) ethanol; (IL) isopropanol; (mp) n-propanol; (qt) tetrahydrofuran.

[0028] Figure 7 The photos of COF-3 in water-acetonitrile, water-ethanol, water-isopropanol, water-n-propanol, and water-tetrahydrofuran systems under ultraviolet light (water content 100-0 v / v%) and the color block diagram and its corresponding CIE chromaticity space 1931 (fj).

[0029] Figure 8 The results of SWMU-AI's rapid test of water content in five organic solvents. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The present invention is further explained below in conjunction with specific implementation modes. Example

[0033] The specific ratio of DES solution is shown in Table 1.

[0034] Table 1 Ratios of different DES solutions name Betaine: hexafluoroisopropanol molar ratio DES-1 1：2 DES-2 1：3 DES-3 1：4 DES-4 1：5 DES-5 1：6 The specific preparation method of the DES solution is as follows: (1) Add betaine and hexafluoroisopropanol into the reaction reagent bottle at a molar ratio of 1:2 to 1:6; (2) Stir at 80 °C and 3000 rpm until a uniform and stable liquid is formed, namely DES-1 (1:2), DES-2 (1:3), DES-3 (1:4), DES-4 (1:5), and DES-5 (1:6).

[0035] See Table 2 for the raw materials used to prepare different covalent organic compounds.

[0036] Table 2 Raw materials for the preparation of different covalent organic compounds name Preparation of raw materials Mass (mg / 8mL) Amount of reactant (mol) Feed ratio (mol) Corresponding DES COF-1 DFP / TA 12.2 / 17.4 0.09 / 0.06 3:2 DES-4 COF-2 DFP / TTA 12.2 / 21.3 0.09 / 0.06 3:2 DES-4 COF-3 THP / DMTP 20.2 / 11.7 0.03 / 0.06 1:2 DES-1 COF-4 THP / PDA 20.2 / 8 0.03 / 0.06 1:2 DES-2 COF-5 TPB / BTT 17.6 / 20 0.05 / 0.05 1:1 DES-4 COF-6 TPB / PDA 21.1 / 12.1 0.06 / 0.09 2:3 DES-5 COF-7 DAB / DHTA 17.1 / 18.6 0.08 / 0.16 1:2 DES-3 COF-8 DAB / BDD 17.1 / 30 0.08 / 0.16 1:2 DES-3 The specific preparation methods of the covalent organic compounds COF-1 and COF-2 are as follows: Step 1: Add different preparation raw materials into a reaction container according to corresponding proportions; Step 2: Add the corresponding DES solution into the reaction container and dissolve it by ultrasonication; Step 3: After fully dissolved, freeze three times by nitrogen circulation and react at 120 °C for 72 hours; Step 4: After the reaction is completed, the product is washed with ethanol at least three times to remove the solvent; Step 5: After washing, place in a 50°C oven to dry.

[0037] The specific preparation method of the covalent organic compounds COF-3 to COF-8 is as follows: Step 1: Add different preparation raw materials into a reaction container according to corresponding proportions; Step 2: Add the corresponding DES solution into the reaction container and dissolve it by ultrasonication; Step 3: After sufficient dissolution, fill with nitrogen and seal the reaction chamber at room temperature for 72 hours; Step 4: After the reaction is completed, the product is washed with ethanol at least three times to remove the solvent; Step 5: After washing, place in a 50°C oven to dry.

[0038] 2. Comparison 1. DES general synthetic COF Reference 1 "A General Synthetic Strategy for the Synthesis of Imine-Linked Covalent Organic Frameworks in Choline Chloride–Hexafluoroisopropanol-Based Deep Eutectic Solvents" (10.1021 / acs.macromol.3c01258) uses choline chloride (ChCl)-hexafluoroisopropanol (HIP)-linked deep eutectic solvents (DESs) as general solvents to synthesize five imine-linked homoporous COFs with high yield and high crystallinity.

[0039] First, Document 1 uses 120°C as the synthesis condition and obtains a product with a higher crystalline form by adjusting the DES ratio. The COF-3 to COF-8 of the present invention can obtain a highly crystalline product by reacting only at room temperature, which is more convenient and economical.

[0040] Secondly, document 1 only explores the synthesis results of isoporous hexagonal imine COFs, while the present invention explores four types of imine COFs, namely, cloverleaf, quadrilateral, hexagonal and triangular hexagonal, including isoporous and heteroporous structures.

[0041] Third, the catalytic mechanism of Reference 1 is similar to the acid-catalyzed process in acetic acid, which is similar to the traditional mechanism. The dynamic hydrogen bond network catalyzed by the base process induced by betaine-hexafluoroisopropanol is used to inhibit the reversible hydrolysis of the imine intermediate, expanding the mechanism type of COFs catalysis.

[0042] 2. Fluorescent COF for fluorescence sensing of trace water in organic phases As can be seen from Table 3, fluorescent COF materials have been reported to be used to detect water content in organic phases, but there are some shortcomings: (1) the type of organic solvent detected is single; (2) the linear range is narrow; (3) the detection limit is not low enough; (3) the detection means are not portable enough, and most are limited to laboratory instrument detection. The present invention detects the water fraction in five organic solvents, and the detection limit is low and the linear range is wide, which can realize the detection of trace organic phase in water phase.

[0043] Table 3 Comparison of the present invention with other reported fluorescence sensing technologies

[0044] Among them, ACN (acetonitrile), MeOH (methanol), DMF (N,N-dimethylformamide), EtOH (ethanol), IPA (isopropanol), NPA (n-propanol), Acetone (acetone), THF (tetrahydrofuran) Performance Testing in, Figure 1 X-ray diffraction (XRD) patterns of COF-1 to COF-8 (ah) prepared above. Figure 1 It can be seen that COF-1 to COF-8 can be prepared by the method provided by the present invention, and there are obvious peaks at 2~4°, indicating that the product has good crystallinity, and the COFs crystal form can be made better by adjusting the proportion of DES (i.e., using DES-1~DES-5).

[0045] Figure 2 PXRD refinement diagrams of COF-1 to COF-8 (ah). The figure is obtained by comparing the simulated XRD data with the experimental XRD data using the software Material Studio 2020. The Rwp data is between 1.35% and 13.9%, indicating that the experimental data (red) and the simulated data (black, "AA sim", "AB sim") almost completely match, corresponding to the stacking mode of COFs (AA stacking or AB stacking).

[0046] Figure 3The following are the scanning electron microscope (SEM) images of COF-1 to COF-8 (ah) and the transmission electron microscope (TEM) images of COF-1 to COF-8 (ip). The results of the scanning electron microscope show the microscopic morphology of COFs, which are spherical, short rods or sheets; the images of the transmission electron microscope show a striped lattice, which verifies that COFs have a good crystal form.

[0047] Figure 4 The infrared spectra of COF-1 to COF-8 (ah) are shown in Figure 1. The data show that the characteristic groups of the precursor substances: amino group -NH2 and aldehyde group -CHO, are significantly weakened or disappeared in the formed COFs, and the characteristic chemical bond of imine COFs, imine bond -C=N-, appears.

[0048] IV. Application The covalent organic compounds prepared above are applied to intelligent colorimetric sensors, taking "SWMU-AI" as an example ( Figure 5 ).

[0049] COF-3 composed of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMTP) and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (THP) exhibits polarity-dependent fluorescence color changes. Five organic solvents (acetonitrile ACN, ethanol EtOH, isopropanol IPA, n-propanol NPA, tetrahydrofuran THF) were selected for ratiometric sensors to detect water content in various organic solvents.

[0050] "SWMU-AI" uses the advanced YOLO v5 target recognition algorithm and uses deep learning technology to accurately identify targets in the collected sample images. After recognition, "SWMU-AI" classifies and segments the images to extract the RGB values ​​of the samples. Visually, each organic solvent-water system color transitions from green to red, allowing the G / R value and water content (WATERFRACTION) to explore a linear relationship through "SWMU-AI".

[0051] Specifically, in a fixed volume of aqueous solution (3 mL in total, COF-3 concentration of 2.5 μg mL -1 ) to obtain different ratios of organic solvent-water solutions. The corresponding images were captured under 365 nm UV light, and the "SWMU-AI" was extensively trained. The "SWMU-AI" can accurately determine the RGB values ​​of the sample's luminescent area and establish a stable linear correlation between the G / R value and the water content (ranging from 0% to 99.5%) in five organic solvents ( Figure 6 ). Therefore, the relevant linear equation has been encoded into “SWMU-AI”, enabling it to predict the water ratio in a sample based on the G / R value of the test sample ( Figure 7 , Figure 8 ).

[0052] Regarding the intelligent colorimetric sensor, the specific operation method is: Step 1: Take a picture of the sample solution under 365 nm UV light; Step 2: Select the organic solvent type in "SWMU-AI": ACN, EtOH, IPA, NPA, THF; Step 3: Select a sample image in the album or take a real-time sample image, select the area where the solution is located, and you can predict the water content (v / v%) of the sample.

[0053] Some recycling situations such as Figure 8 The recovery rates of all concentrations were between 82.82% and 118.60%, as shown in Table 4.

[0054] Table 4 Results of using SWMU-AI to detect water content in various organic solvents

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low eutectic solvent for preparing a covalent organic framework, characterized in that: The low eutectic solvent comprises betaine and hexafluoroisopropanol; and the molar ratio of betaine to hexafluoroisopropanol is (1:2) to (1:6).

2. The deep eutectic solvent for preparing a covalent organic framework according to claim 1, characterized in that The molar ratio of betaine to hexafluoroisopropanol is 1:2, 1:3, 1:4, 1:5, and 1:

6.

3. A covalent organic framework, characterized in that The low eutectic solvent according to claim 1 or 2 is used as a solvent, and an amine compound and an aldehyde compound are used as raw materials to prepare the product.

4. A covalent organic framework according to claim 3, characterized in that: The pores are clover-shaped, quadrilateral, hexagonal and triangular hexagonal.

5. A covalent organic framework according to claim 3, characterized in that: The aldehyde compound is an aromatic aldehyde compound with a symmetrical structure; the amine compound is a porphyrin derivative / triphenylamine derivative / biphenyl derivative with a symmetrical structure.

6. A covalent organic framework according to claim 5, characterized in that: The aromatic aldehyde compound with a symmetrical structure is selected from one or more of 2,6-pyridinedicarboxaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-divinyl-1,4-benzenedicarbaldehyde, and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tri[benzaldehyde].

7. A method for preparing a covalent organic framework according to any one of claims 3 to 6, characterized in that: Here are the steps: Step 1: Add different reaction raw materials into a reaction vessel; Step 2: Adding a low eutectic solvent corresponding to different reaction raw materials into the reaction container and dissolving them by ultrasonication; Step 3: After fully dissolved, fill with nitrogen and seal at room temperature for 72 hours or freeze three times by nitrogen circulation and react at 120 °C for 72 hours; Step 4: After the reaction is completed, the product is washed with ethanol at least three times to remove the solvent; Step 5: After washing, place in a 50°C oven to dry.

8. The preparation method according to claim 7, characterized in that: When the reaction raw materials are 2,6-pyridinedicarboxaldehyde and tris(4-aminophenyl)amine; or, 2,6-pyridinedicarboxaldehyde and 4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine, the step 3 is: after fully dissolving, freezing three times by nitrogen circulation, and reacting at 120°C for 72 hours.

9. An intelligent colorimetric sensor, characterized in that: A covalent organic framework as described in any one of claims 3 to 6 is used to detect the water content v / v% in various organic solvents.

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