A three-dimensional covalent organic framework material, its preparation method and application

Abstract

The present invention relates to the technical field of covalent organic framework materials, and particularly to a three-dimensional covalent organic framework material, a preparation method thereof, and an application thereof; the three-dimensional covalent organic framework material has a structural formula including a repeating unit shown in Formula I. The three-dimensional covalent organic framework material of the present invention has a rich porous structure and hydroxyl functional groups, is very sensitive to humidity, is less affected by temperature and humidity, has good cycle stability, and can be used as a humidity sensing material in the field of humidity sensing; moreover, its preparation method has simple process, low cost, and good controllability.

Description

Technical Field

[0001] The present invention relates to the technical field of covalent organic framework materials, and in particular to a three-dimensional covalent organic framework material and a preparation method and application thereof. Background Art

[0002] Human survival and social activities are closely related to humidity. Humidity monitoring is particularly important for some environments that require strict humidity control, such as drugs that are very sensitive to moisture, chemicals that are prone to explosion or deterioration when exposed to water, and the storage of precision instruments.

[0003] Due to different application fields, the technical requirements for humidity sensors are also different. At present, conventional humidity detection is mostly carried out using humidity-sensitive elements. During use, humidity-sensitive elements need to be in the test environment for a long time, and their anti-pollution performance is poor. Their service life and detection accuracy will gradually decrease. They are also greatly affected by the ambient temperature, prone to time drift and temperature drift, and have poor stability. In addition, the original price of full humidity detection is also relatively expensive and the cost is high. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a three-dimensional covalent organic framework material and a preparation method and application thereof, so as to solve the problem of poor stability of humidity-sensitive elements in the prior art that they need to be in the test environment for a long time.

[0005] To achieve the above objectives and other related objectives, the present invention is obtained by including the following technical solutions.

[0006] The present invention provides a three-dimensional covalent organic framework material, the structural formula of which includes a repeating unit as shown in Formula I:

[0007]

[0008] In formula I, the wavy lines represent several omitted repeating units.

[0009] Preferably, the number of repeating units of the three-dimensional covalent organic framework material is 2×10^7-2×10^9.

[0010] Preferably, the three-dimensional covalent organic framework material is a single crystal structure.

[0011] Preferably, the grain size of the three-dimensional covalent organic framework material is 1 to 4 μm.

[0012] Preferably, the grain morphology of the three-dimensional covalent organic framework material is prismatic.

[0013] Preferably, the three-dimensional covalent organic framework material has a hydrochromic property; specifically, after absorbing water, the three-dimensional covalent organic framework material changes from orange to brown-black.

[0014] Preferably, the hydrochromic property of the three-dimensional covalent organic framework material is reversible.

[0015] Preferably, the pore volume of the three-dimensional covalent organic framework material is 0.5 - 0.75 cm 3 / g.

[0016] Preferably, the three-dimensional covalent organic framework material is synthesized from the compound shown in Formula II and the compound shown in Formula III as raw materials:

[0017]

[0018] The present invention also discloses a preparation method of a three-dimensional covalent organic framework material. The Schiff base condensation reaction of the compound shown in Formula II and the compound shown in Formula III in a reaction medium yields the three-dimensional covalent organic framework material.

[0019] The synthesis route of the three-dimensional covalent organic framework material of the present invention is as follows:

[0020]

[0021] Preferably, the reaction system of the Schiff base condensation reaction further contains a template agent.

[0022] Preferably, the template agent is aniline, and the molar ratio of the compound shown in Formula II, the compound shown in Formula III, and the template agent is 1:(2 - 3):(12 - 13).

[0023] On the one hand, the addition of excessive aniline can compete with the compound shown in Formula II to react with the compound shown in Formula III, thereby reducing the rate of the formation of imine bonds between the compound shown in Formula II and the compound shown in Formula III and regulating the nucleation and crystallization rate of the covalent organic framework material (COFs); on the other hand, aniline forms a model molecule with imine bonds with the compound shown in Formula III, and the imine exchange reaction of the model molecule with the product obtained from Formula II and Formula III also plays a role in regulating the crystal state. This model molecule will be washed away by an organic solvent after the reaction and will not appear on the final COFs structural molecule.

[0024] Preferably, the reaction system of the Schiff base condensation reaction further contains a catalyst, and the catalyst is an acid solution.

[0025] Preferably, the acid solution is an aqueous solution of acetic acid.

[0026] Preferably, the molar ratio of the compound shown in Formula II, the compound shown in Formula III, and acetic acid is 1:(2 - 3):(22 - 24).

[0027] Acetic acid acts as a catalyst to accelerate the formation of imine bonds. At an appropriate catalyst concentration, an appropriate amount of imine, and a certain temperature, it increases the reversibility of the imine bond formation process, regulates the thermodynamic and kinetic processes of the reaction, and gives the crystal sufficient time for defect repair, thereby obtaining a COFs crystal material with high crystallinity.

[0028] Preferably, in step (1), the reaction medium is a mixture of o-dichlorobenzene and 1,3,5-trimethylbenzene;

[0029] More preferably, the volume ratio of o-dichlorobenzene to 1,3,5-trimethylbenzene is 1:1.

[0030] Preferably, in step (1), the temperature of the Schiff base condensation reaction is 75-100 °C; specifically, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C.

[0031] Preferably, it further includes a post-treatment step, and the post-treatment step includes purification and / or impurity removal.

[0032] Purification is carried out by centrifugal washing and Soxhlet extraction. The Soxhlet extraction method can effectively remove the model molecules generated during the reaction of aniline and aldehyde and the unreacted raw materials. The target product COFs is a polymer and is insoluble in organic solvents, while the model molecules and unreacted raw materials can be dissolved in organic solvents and removed.

[0033] Preferably, the solvent used for purification is tetrahydrofuran.

[0034] Preferably, during impurity removal, the purification solvent and other high-boiling solvents in the pores are removed.

[0035] More preferably, vacuum heating degassing is used for impurity removal: the purified product is heated and degassed under vacuum conditions. More preferably, the temperature of heating degassing is 100-120 °C, specifically 100 °C, 105 °C, 110 °C, 115 °C, 120 °C. More preferably, impurity removal is carried out until no gas is generated under vacuum heating conditions; specifically, impurity removal is carried out until the pressure change of the system does not exceed 15 mTorr, and more preferably, until the pressure change of the system does not exceed 1 mTorr.

[0036] The commonly used activation temperature is 100-120 °C, but high-temperature and long-time high-vacuum heating degassing at relatively high temperatures will damage the crystal state. Since after long-time washing and replacement with the low-boiling solvent THF, it can be considered that there are no other high-boiling solvents in the pores except for the Soxhlet extraction solvent (THF) and water, so activation at 100 °C is more appropriate.

[0037] The purification and impurity removal processes are very important. If there are other organic solvents such as solvents (THF) in the pores of the COFs, the pores of the material cannot fully absorb water molecules, affecting the color display range, and the presence of model molecules and raw materials interferes with the color display effect.

[0038] The present invention also discloses an application of a three-dimensional covalent organic framework material as a humidity sensing material in the field of humidity sensing.

[0039] More preferably, the three-dimensional covalent organic framework material in the present application is used as an environmental humidity indicator for indicating whether there is water in the environment. Specifically, it can be used in environments that require strict humidity control, such as drugs that are very sensitive to moisture, chemicals that are prone to explosion or deterioration when exposed to water, and the storage of precision instruments.

[0040] As described above, the three-dimensional covalent organic framework material, its preparation method, and application of the present invention have the following beneficial effects:

[0041] The three-dimensional covalent organic framework material of the present invention has a rich porous structure and hydroxyl functional groups, is very sensitive to humidity, is less affected by temperature and humidity, has good cycle stability, and can be used as a humidity sensing material in the field of humidity sensing; and its preparation method has simple technology, low cost, and good controllability. Description of the Drawings

[0042] Figure 1 The infrared spectra of the three-dimensional covalent organic framework material prepared in Example 1 after adsorbing water, the compound shown in Formula II, the compound shown in Formula III, and the model molecule are shown.

[0043] Figure 2 The PXRD comparison diagrams of the three-dimensional covalent organic framework material prepared in Example 1, the raw materials, and the model molecule after adsorbing dioxane are shown.

[0044] Figure 3 The SEM image of the three-dimensional covalent organic framework material prepared in Example 1 at a low magnification is shown.

[0045] Figure 4 The SEM image of the three-dimensional covalent organic framework material prepared in Example 1 at a high magnification is shown.

[0046] Figure 5 The grain size distribution diagram of the three-dimensional covalent organic framework material prepared in Example 1 is shown.

[0047] Figure 6 The TGA curve of the three-dimensional covalent organic framework material prepared in Example 1 after absorbing water in the air is shown.

[0048] Figure 7The PXRD patterns of the three-dimensional covalent organic framework prepared in Example 1 after treatment with 2M HCl or 2M NaOH are shown.

[0049] Figure 8 The diagrams showing the changes in the structural crystallinity and symmetry of the three-dimensional covalent organic framework prepared in Example 1 under different conditions are shown.

[0050] Figure 9 The N2 isothermal adsorption curve of the three-dimensional covalent organic framework prepared in Example 1 at 77K is shown.

[0051] Figure 10 The isothermal adsorption curve of 1,4-dioxane vapor of the three-dimensional covalent organic framework prepared in Example 1 at 298K is shown.

[0052] Figure 11 The water-induced color change effect when the three-dimensional covalent organic framework prepared in Example 1 undergoes water adsorption is shown (left ordinate: adsorption amount, right ordinate: number of water molecules adsorbed per mol of ST-301).

[0053] Figure 12 The diffuse reflectance spectra (DRS) of the activated phase of ST-301 and samples with different amounts of water vapor introduced are shown.

[0054] Figure 13 The in-situ water adsorption process PXRD spectra at equilibrium and transition states under different humidities are shown.

[0055] Figure 14 The in-situ water desorption process PXRD spectra at equilibrium and transition states under different humidities are shown.

[0056] Figure 15 The change in the full width at half maximum of the main peak of the equilibrium state PXRD under different humidities is shown. Detailed implementation mode

[0057] The following specific examples illustrate the implementation mode of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0058] It should be noted that the process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art. In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between the clearly mentioned steps, unless otherwise specified; it should also be understood that the combined connection relationship between one or more devices / devices mentioned in the present invention does not exclude the existence of other devices / devices before and after the combined devices / devices or the insertion of other devices / devices between the two clearly mentioned devices / devices, unless otherwise specified. Moreover, unless otherwise specified, the numbers of each method step are only convenient tools for identifying each method step, rather than limiting the arrangement order of each method step or the scope of implementation of the present invention. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present invention.

[0059] Example 1

[0060] Prepare a three-dimensional covalent organic framework material (denoted as ST-301) according to the following synthetic route:

[0061]

[0062] (1) Weigh tetra(4-aminophenyl)methane (TAM, 50 mg, 0.13 mmol) and 2,5-dihydroxyterephthalaldehyde (dhTPA, 43.5 mg, 0.26 mmol) into a 20 ml glass bottle. After adding 5 ml of ortho-dichlorobenzene and 5 ml of 1,3,5-trimethylbenzene respectively, ultrasonically disperse for 3 min, then add 0.15 ml of aniline (1.64 mmol), and finally add 0.5 ml of 6 mol / L acetic acid aqueous solution. Place it in an oven at 85 °C and react for 3 days. An orange solid powder is obtained at the bottom of the bottle;

[0063] (2) Centrifuge and wash the orange solid powder obtained in step (1) with tetrahydrofuran (THF) multiple times until the supernatant is clear and transparent. Then, use THF as the washing solvent and further wash it by Soxhlet extraction for at least 5 days; After that, transfer the sample to an adsorption tube and place it on a vacuum degassing station. Slowly pump down the pressure to 10 torr, then start fast pumping, and slowly heat to 100 °C for degassing for 24 h. When the final pressure is below 15 mTorr and no longer rises, the activation is completed, and the three-dimensional covalent organic framework material is obtained.

[0064] Perform basic characterization on the three-dimensional covalent organic framework material (ST-301) prepared in this example.

[0065] As Figure 1 shown, the aldehyde group at 1663 cm -1 in dhTPA and 3396 cm -1The stretching vibration peaks of amino groups all disappeared completely in the synthesized products, and a stretching vibration peak of imine bonds appeared at 1611 cm -1 −1, indicating the occurrence of the Schiff base reaction for synthesizing COFs and the complete conversion of raw materials. The model molecule is a structural analogue of ST-301, and its infrared spectrum is similar to but not exactly the same as that of ST-301. There is a common characteristic peak of imine bonds at 1611 cm -1 −1, further indicating the occurrence of the Schiff base reaction. At the same time, it also further proves that after Soxhlet extraction, the target product ST-301 is not the model molecule.

[0066] As Figure 2 shown, the sharp peak shape of solvated ST-301 indicates good crystallinity, and the positions of each peak do not overlap with those of the raw materials and the model molecule. It is preliminarily judged that the synthesized product is a covalent organic framework material with good crystallinity.

[0067] Figure 3 、 Figure 4 The SEM images of Figure 6 and the size distribution diagram of

[0068] show that the crystal particles of ST-301 are regular prismatic, and most of the grain sizes are 1 - 4 μm in length and 0.8 - 1 μm in thickness, and the product is pure without impurity phases. Figure 6 shown, Figure 6 it shows that the decomposition temperature of ST-301 can reach 397 °C, and the weight loss between room temperature and 120 °C is the water in the pores. The same mass of ST-301 was immersed in 1 ml of 2 M NaOH for 1, 3, and 7 days, and in 2 M HCl for 1 and 3 days respectively. The specific TGA curves are as Figure 7 shown. It can be seen from Figure 7 that ST-301 can maintain partial crystallinity in 2 M NaOH for up to 7 days.

[0069] The above characterizations show that ST-301 in this example is highly crystalline, has a regular morphological structure, a relatively uniform size distribution, and at the same time has good thermal stability and alkali resistance.

[0070] The crystal phase structures of the activated phase, hydrated phase, and expanded phase of the three-dimensional covalent organic framework material (ST-301) prepared in this example were analyzed: When there are no guest molecules in the pores, the unit cell is smaller and is called the activated phase (ST-301-Activated). When water is absorbed in the pores, the unit cell expands by 2.9% and is called the hydrated phase (ST-301-Hydrated). When an organic solvent is adsorbed, it will expand by 62.8% and is called the expanded phase (ST-301-Expanded(THF)).

[0071] The three crystal phase structures of ST-301 under different environments were analyzed by combining three-dimensional electron diffraction (3D ED) and powder diffraction Rietveld refinement. The corresponding refinement parameters and structure information are as Figure 8 shown in Table 1:

[0072] Table 1. Statistical results of Rietveld refinement of the three-phase structure of ST-301

[0073]

[0074] In Table 1, Z is the number of the smallest asymmetric structural units in the unit cell.

[0075] Figure 8 Rietveld refinement of three-dimensional electron diffraction (3D ED) and synchrotron radiation powder diffraction data was used to determine the changes in the crystallinity and symmetry of the ST-301 structure. Figure 8 In it, a, b, and c are the projections of the three-dimensional reciprocal lattices of the expanded phase, activated phase, and hydrated phase of the reconstructed ST-301 along the

[001] ,

[010] , and

[010] directions, respectively. Figure 8 In it, d, e, and f are schematic diagrams of the crystal structures of the expanded phase, activated phase, and hydrated phase of ST-301, respectively. Figure 8 In it, g, h, and i are the powder diffraction data of the expanded phase, activated phase, and hydrated phase of ST-301 obtained by Rietveld refinement results. Due to the overlap of diffraction peaks, the indexing results are not unique.

[0076] It can also be clearly seen from Table 1 and Figure 8 that in the three-dimensional covalent organic framework material (ST-301), the rotation of the C-N single bond in the imine COF, the displacement between different atomic interpenetrating layers, and the change in the angle between the C-C single bonds of the TAM nodes make the ST-301 structure have dynamic changes and different structures in different environments.

[0077] The pore properties of the three-dimensional covalent organic framework material (ST-301) prepared in this example were characterized:

[0078] The pore properties of the material can be detected by using different guest molecules as probes. In this application, the N2 isothermal adsorption curve and the isothermal adsorption of 1,4-dioxane vapor are used for testing respectively. The test results are as Figure 9 and Figure 10 shown. It is known from Figure 9 that the theoretical pore volume of ST-301 is 0.71 cm 3 / g, and the measured pore volume is 0.57 cm 3 / g. Figure 9 The measured pore volume tested in Figure 10 is similar to the pore volume of 0.58 cm 3 / g obtained by the dioxane vapor adsorption test in Figure 9 . The measured pore volume is 80% of the theoretical pore volume. For the flexible material ST-301, it can be considered that the pores are basically opened at this time. However, there are differences in the adsorption behaviors of the two curves: Figure 10 In Figure 9 , the isothermal adsorption curve of ST-301 in nitrogen at 77K shows a three-stage step shape, indicating that the pores of ST-301 are opened step by step and the structure is flexible. Figure 10 In

[0079] , the dioxane vapor adsorption curve shows a two-stage step shape. Thus, it can be explained that ST-301 has different response behaviors to different guest molecules. Due to the strong hydrogen bond interaction of the hydroxyl functional group with water molecules, the adsorption behavior in the water environment is more exploratory and specific.

[0079] Observe the water-induced color change effect and the corresponding structural changes of the three-dimensional covalent organic framework material (ST-301) prepared in this example:

[0080] It is observed that the color of the ST-301 sample will quickly change from orange to brown-black after being exposed to air. When the sample is activated again by using dry air or heating and vacuum pumping, it can turn orange again. Comparing with the structurally similar material COF-300, it is found that COF-300 does not have such a significant color change phenomenon. Only after introducing hydroxyl groups into ST-301 does it show water-sensitive characteristics. Therefore, the applicant believes that water absorption is the inducement for its color change. The water adsorption curve of ST-301 in an environment containing only water at 298K is tested and it is found that different color changes occur under different water vapor pressures.

[0081] Furthermore, the applicant quantified the color change by testing the diffuse reflectance spectrum (DRS) with a UV-visible spectrometer. For details, see Figure 11 、 Figure 12 and Table 2. It is known from Figure 11 and Figure 12It can be seen that the diffuse reflectance spectrum of ST-301 shows two energy bands of 1.8 eV and 2.2 eV. However, the 2.2 eV energy band is only obvious when P / P0 ≤ 0.49. As the water absorption increases, the absorption edge undergoes a red shift, indicating that the color becomes significantly darker at this time. After P / P0 > 0.49, the 1.8 eV energy band becomes dominant.

[0082] The structural color change during the water-induced color change process was analyzed by in-situ PXRD. The in-situ PXRD of ST-301 during the water adsorption process is as Figure 13 and Figure 14 shown. It can be seen from Figure 13 and Figure 14 that as the water absorption increases and the humidity is greater than 1%, the diffraction peaks shift slightly towards lower angles, indicating that the unit cell expands to a certain extent when absorbing water. When desorbing, the diffraction peaks shift slightly towards higher angles, indicating that the unit cell contracts during desorption. The diffraction peak intensity is strong at high humidity. Measuring the PXRD spectra at equilibrium states under different humidities, the results are shown in Figures 15 and Table 3. It can be found that as the humidity increases, the full width at half maximum (FWHM) of the main peak gradually becomes narrower, indicating that the entry of water molecules into the pore environment improves the structural order. According to the water adsorption and powder diffraction refinement data, it is calculated that when ST-301 is in the water-saturated state, every 1 mol of ST-301 will adsorb 4 mol of water molecules.

[0083] Table 2. Energy bands corresponding to the absorption edge of ST-301 under different water vapor pressures.

[0084]

[0085] Table 3. Changes in the full width at half maximum (FWHM) of the main peak of the equilibrium state PXRD under different humidities

[0086]

[0087] It can be seen from the above that the three-dimensional covalent organic framework material of the present invention has imine bonds and hydroxyl groups in its structure. Water molecules can form intramolecular hydrogen bonds with the three-dimensional covalent organic framework material. The more fully the water is adsorbed, the more conducive it is to the formation of a complete hydrogen bond network in the structure. The water molecules induce the adjustment of the atomic positions of the framework through hydrogen bond interactions, improving the crystallinity, and also making the internal electronic state of the structure more unified and the energy band narrower, resulting in a darker color.

[0088] The present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0089] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A three-dimensional covalent organic framework material, characterized in that, Its structural formula includes repeating units shown in Formula I: ； The number of repeating units in the three-dimensional covalent organic framework material is 2×10 ^ 7 - 2×10 ^ 9; The three-dimensional covalent organic framework material is a single crystal structure; The crystal grain morphology of the three-dimensional covalent organic framework material is prismatic; The crystal grain size of the three-dimensional covalent organic framework material is 1 - 4 µm; The three-dimensional covalent organic framework material is synthesized from the compound shown in Formula II and the compound shown in Formula III as raw materials through a Schiff base condensation reaction: ； The reaction system of the Schiff base condensation reaction further contains a template agent, the template agent is aniline, and the molar ratio of the compound shown in Formula II, the compound shown in Formula III, and the template agent is 1:(2 - 3):(12 - 13).

2. The three-dimensional covalent organic framework material according to claim 1, wherein: The three-dimensional covalent organic framework material has a water-induced color change property; And / or: The water-induced color change property of the three-dimensional covalent organic framework material is reversible; and / or: the pore volume of the three-dimensional covalent organic framework material is 0.5 to 0.75 cm 3 / g.

3. A preparation method of a three-dimensional covalent organic framework material according to any one of claims 1 - 2, wherein: The compound shown in Formula II and the compound shown in Formula III are subjected to a Schiff base condensation reaction in a reaction medium to obtain the three-dimensional covalent organic framework material; ， ； The reaction system of the Schiff base condensation reaction further contains a template agent, the template agent is aniline, and the molar ratio of the compound shown in Formula II, the compound shown in Formula III, and the template agent is 1:(2 - 3):(12 - 13).

4. The preparation method according to claim 3, characterized in that: The reaction system of the Schiff base condensation reaction further contains a catalyst, and the catalyst is an acid solution.

5. The preparation method according to claim 4, characterized in that, The acid solution is an aqueous solution of acetic acid.

6. The preparation method according to claim 3, characterized in that, The reaction medium is a mixture of o-dichlorobenzene and 1,3,5-trimethylbenzene; And / or: The temperature of the Schiff base condensation reaction is 75 - 100 °C; And / or: It further includes a post-treatment step, and the post-treatment step includes purification and / or impurity removal; And / or: The solvent used for purification is tetrahydrofuran.

7. Application of a three-dimensional covalent organic framework material according to any one of claims 1 - 2 as a humidity sensing material in the field of humidity sensing.

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