A two-dimensional covalent organic framework bulk and preparation method and application thereof

Abstract

This invention discloses a two-dimensional covalent organic framework bulk, its preparation method, and its applications, belonging to the field of two-dimensional covalent organic framework technology. The method of this invention includes mixing two monomers required for polymerizing the two-dimensional covalent organic framework with a freezeable solvent, reacting them to obtain a precursor solution; controlling the degree of polymerization through reaction conditions, controlling the macroscopic dimensions of the material through freeze casting, and achieving in-situ crystalline transformation through solvothermal methods, thereby obtaining a two-dimensional covalent organic framework crystalline bulk with atomic orientation that can reach centimeter-scale macroscopic dimensions. This overcomes the shortcomings of existing technologies in simultaneously achieving atomic orientation and material thickness at the centimeter scale. The prepared bulk simultaneously possesses regular oriented nanopores and interlayer stacking structures, which have significant application value in fields such as material separation, energy storage, heterogeneous catalysis, and biosensing.

Description

Technical Field

[0001] This application belongs to the field of two-dimensional covalent organic framework technology, and in particular relates to a two-dimensional covalent organic framework block, its preparation method and application. Background Technology

[0002] Two-dimensional covalent organic frameworks (2DCOFs) consist of well-organized, oriented nanopores and interlayer stacking structures, theoretically enabling directional transport of matter along one-dimensional channels. Therefore, the size and orientation of 2D COFs directly determine their charge and mass transport capabilities. Currently, the preparation methods for 2D COFs are mainly divided into thermodynamic and kinetic approaches. The thermodynamic approach utilizes intermolecular forces between different phase interfaces to achieve the pre-assembly and directional polymerization of precursors, ultimately obtaining oriented 2D COF films. However, limited by the range of phase interface interactions, the film thickness prepared by this method is only at the nanometer scale; further increasing the film thickness significantly reduces its orientation. The kinetic approach bypasses the traditional thermodynamically controlled interfacial polymerization method, using controlled evaporation and crystal transformation of solutions to prepare micron-sized 2D COF films with atomic orientation, but it cannot produce materials with larger dimensions (e.g., centimeter-sized). Furthermore, while colloidal printing methods can obtain thicker materials, their orientation is poor, and the materials are often discontinuous.

[0003] Existing technologies struggle to balance atomic orientation and material thickness when preparing 2D COFs materials: materials with greater thickness cannot achieve atomic-level orientation, while materials with good atomic orientation can only reach the micrometer level in thickness.

[0004] The application of 2D-COF thin films in actual production is very limited. For example, in gas / liquid separation, the films lack gas storage capacity, making in-situ catalytic reactions and large-capacity sieving impossible. Furthermore, in biosensing, the films are fragile, inconvenient to carry out, difficult to assemble, and have limited detection efficiency due to low throughput. If 2D-COF materials could be fabricated in bulk form (centimeter-scale), these problems could be effectively solved.

[0005] Existing technology discloses a low-temperature polymerization-assisted (CryoPAP) technique for producing covalent organic framework (COF) aerogels. The core of this technique lies in the discovery that the aldehyde-amine reaction can proceed at -18°C. Using 1,4-dioxane containing acetic acid as a solvent and freezing template, monomers are confined within ice crystal interstices to undergo low-temperature polymerization, forming an amorphous low-temperature gel with a directional macroporous structure. Subsequently, a crystallization process (transformation from amorphous to crystalline state) yields crystalline COF aerogels. Various two-dimensional and three-dimensional COF aerogels have been successfully prepared. Their hierarchical pore structure endows the materials with excellent volatile organic compound adsorption properties, and they can be molded into rod-shaped products of different diameters, demonstrating good processability and practical application potential. While this preparation method can obtain three-dimensional bulk COF materials, it cannot achieve atomic orientation.

[0006] Therefore, developing a new method to prepare 2D COFs crystalline bulks with atomic orientation at the centimeter scale is of great research significance and application value. Summary of the Invention

[0007] To address the technical problems existing in the prior art, the primary objective of this invention is to provide a method for preparing two-dimensional covalent organic framework blocks.

[0008] Another object of the present invention is to provide a two-dimensional covalent organic framework block prepared by the above method.

[0009] Another objective of this invention is to provide the application of the above-mentioned two-dimensional covalent organic framework in material separation, energy storage, heterogeneous catalysis, and biosensing.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a two-dimensional covalent organic framework block includes the following steps: S1. Mix the organic amine monomers, aldehyde monomers and freezeable solvents required for the polymerization of two-dimensional covalent organic frameworks, react them, and obtain a precursor solution; S2. Add the precursor solution to the casting mold and freeze it unidirectionally to obtain a frozen precursor solution; S3. The frozen precursor solution is freeze-dried to remove the freezeable solvent, resulting in 2D COFs amorphous bulk material; S4. The 2D COFs amorphous bulk material is subjected to in-situ crystallization treatment using a solvothermal method to obtain the 2D COFs crystalline bulk material. Steps S1 to S3 are carried out in the absence of a catalyst, while step S4 is carried out in the presence of a catalyst; the catalyst is a catalyst that catalyzes the Schiff base reaction between amino and aldehyde groups. The reaction time in step S1 is 5 to 300 minutes.

[0011] In step S1 of the present invention, organic amine monomers and aldehyde monomers are mixed and reacted for a period of time without a catalyst. The reaction forms oligomers, which are key to giving the final 2D COFs crystalline bulk atom orientation.

[0012] Cryocasting is a low-temperature forming technique that utilizes the dynamic growth of freezeable solvent crystals as a template to construct porous materials. In step S2, the freezeable solvent grows directionally along the temperature gradient during the unidirectional freezing process, simultaneously displacing the oligomers generated in step S1 into the interstitial regions between the solvent crystals. As the freezing process proceeds, the advancing freezeable solvent front exerts directional constraints through interfacial solute-solvent interactions, organizing the oligomers into pre-oriented amorphous oligomers. This newly formed orientation is subsequently enhanced through entropy-driven π–π stacking and dynamic covalent exchange. In step S3, the crystalline phase is removed by freeze-drying, retaining the oriented oligomer network to obtain a 2D COFs amorphous bulk material with an oriented porous structure corresponding to the solvent crystal morphology.

[0013] If steps S1, S2, and S3 are carried out in the presence of a catalyst, the polymerization reaction will be significant, and the organic amine monomers and aldehyde monomers will form polymers instead of oligomers. This situation will weaken the constraint effect of the freezeable solvent on the polymers, thus preventing the polymers from forming atomically oriented arrangements, and the final COFs material will have no atomic orientation.

[0014] In step S4, the dynamic reversible properties of imine bonds are utilized to activate the dynamic covalent self-correction process through catalyst catalysis and thermal treatment. Under solvothermal conditions, the imine bonds in the 2D COFs amorphous bulk are dynamically chemically bonded and crystallized, transforming these amorphous but pre-oriented networks into atomically ordered crystal frameworks, thus successfully preparing 2D COFs crystalline bulks with atomic orientation. This invention combines three techniques: controlling the polymerization degree through reaction conditions (time and the absence of a catalyst), controlling the macroscopic size of the material through freeze casting, and achieving in-situ crystalline transformation through solvothermal methods. This results in the preparation of two-dimensional covalent organic framework crystalline bulk materials with atomic orientation that can reach centimeter-scale macroscopic dimensions. This overcomes the shortcomings of existing technologies that cannot simultaneously achieve atomic orientation and material thickness at the centimeter scale. The prepared bulk materials also have regular oriented nanopores and interlayer stacking structures, which have important application value in the fields of material separation, energy storage, heterogeneous catalysis, and biosensing.

[0015] In this invention, the two-dimensional covalent organic framework block refers to a two-dimensional covalent organic framework material with macroscopic dimensions reaching the centimeter level.

[0016] Preferably, the size of the two-dimensional covalent organic framework block is on the order of centimeters.

[0017] More preferably, the size (thickness) of the two-dimensional covalent organic framework block is 1~10cm.

[0018] Preferably, in step S1, the freezeable solvent is DMSO.

[0019] Preferably, in step S1, the organic amine monomer is at least one of a triamine or a diamine.

[0020] More preferably, the ternary amine includes, but is not limited to, 1,3,5-tris(4-aminophenyl)benzene.

[0021] More preferably, the diamine includes, but is not limited to, p-phenylenediamine.

[0022] Preferably, in step S1, the aldehyde monomer is at least one of a ternary aldehyde or a dialdehyde.

[0023] More preferably, the ternary aldehyde includes, but is not limited to, pyromellitic aldehyde.

[0024] More preferably, the dialdehyde includes, but is not limited to, terephthalaldehyde and / or 2,5-dimethoxybenzene-1,4-dicarboxaldehyde.

[0025] Preferably, in step S1, the concentration of the amino group from the organic amine monomer in the precursor solution is 0.16~0.20 mol / L.

[0026] Preferably, in step S1, the concentration of aldehyde groups from the aldehyde monomer in the precursor solution is 0.16~0.20 mol / L.

[0027] Preferably, the reaction in step S1 is carried out under stirring conditions.

[0028] More preferably, in step S1, the stirring speed is 250~350 rpm.

[0029] In this invention, unidirectional freezing refers to applying a cold source to the precursor solution from a single direction (e.g., from bottom to top), thereby causing the temperature of the precursor solution to increase from low to high along that direction. During unidirectional freezing, crystals capable of freezing the solvent grow directionally along that direction.

[0030] Preferably, in step S2, the unidirectional freezing time is 8 to 12 minutes.

[0031] Preferably, in step S2, the temperature range of the cold source for unidirectional freezing is -180℃ to -10℃.

[0032] Preferably, in step S3, a freeze-drying step is included before the freeze-drying.

[0033] More preferably, the cryopreservation temperature is -75 to -85°C.

[0034] More preferably, in step S3, the freezing time is 12 to 24 hours.

[0035] Preferably, in step S3, the freeze-drying is carried out in a freeze dryer.

[0036] Preferably, in step S3, the freeze-drying time is 48 to 72 hours.

[0037] Preferably, in step S4, the 2D COFs amorphous bulk material undergoes in-situ crystallization treatment in a crystallization conversion reaction solution.

[0038] Preferably, the conditions for the solvothermal method are: temperature of 80~120℃, inert gas atmosphere, and time of 48~72 hours.

[0039] The crystallization reaction solution was obtained by mixing 1,4-dioxane, mesitylene, and 6M glacial acetic acid in a volume ratio of (7~9):(3~1):1.

[0040] Preferably, in step S4, after the in-situ crystallization treatment, a purification and drying process is also included.

[0041] More preferably, the purification process includes: taking out the crystalline block after cooling to room temperature and soaking it in a detergent.

[0042] More preferably, the drying process includes: transferring the purified crystalline bulk to a vacuum drying oven and drying it overnight at 70~90°C to obtain dried 2D COFs crystalline bulk. Preferably, the detergent is at least one of tetrahydrofuran, anhydrous ethanol, or n-hexane.

[0043] More preferably, the detergent is tetrahydrofuran, anhydrous ethanol, and n-hexane.

[0044] Preferably, the catalyst is acetic acid.

[0045] Compared with the prior art, the present invention has the following beneficial effects: This invention combines three techniques: controlling the polymerization degree through reaction conditions (time and the absence of a catalyst), controlling the macroscopic size of the material through freeze casting, and achieving in-situ crystalline transformation through solvothermal methods. This results in the preparation of two-dimensional covalent organic framework crystalline bulk materials with atomic orientation that can reach centimeter-scale macroscopic dimensions. This overcomes the shortcomings of existing technologies that cannot simultaneously achieve atomic orientation and material thickness at the centimeter scale. The prepared bulk materials also have regular oriented nanopores and interlayer stacking structures, which have important application value in the fields of material separation, energy storage, heterogeneous catalysis, and biosensing. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of cryogenic orientation in Example 1.

[0047] Figure 2 a is a schematic diagram of the X-ray application direction during 2D-WAXS characterization of the two-dimensional covalent organic framework block of Example 1; b is a diagram of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 1; c is a one-dimensional integral diagram of the full-angle 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 1; d is a one-dimensional intensity integral diagram of the (100) crystal plane diffraction ring of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 1.

[0048] Figure 3 This is a schematic diagram of the crystal planes of the two-dimensional covalent organic framework block of Example 1.

[0049] Figure 4 a is a schematic diagram of the X-ray application direction during 2D-WAXS characterization of the two-dimensional covalent organic framework block of Example 2; b is a diagram of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 2; c is a one-dimensional integral diagram of the full-angle 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 2; d is a one-dimensional intensity integral diagram of the (100) crystal plane diffraction ring of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 2.

[0050] Figure 5 This is a schematic diagram of the crystal planes of the two-dimensional covalent organic framework block in Example 2.

[0051] Figure 6 a is a schematic diagram of the X-ray application direction during 2D-WAXS characterization of the two-dimensional covalent organic framework block of Example 3; b is a diagram of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 3; c is a one-dimensional integral diagram of the full-angle 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 3; d is a one-dimensional intensity integral diagram of the (100) crystal plane diffraction ring of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Example 3.

[0052] Figure 7 This is a schematic diagram of the crystal planes of the two-dimensional covalent organic framework block in Example 3.

[0053] Figure 8 The nitrogen adsorption-desorption isotherm and pore size distribution diagram are shown in Example 1.

[0054] Figure 9 The graph shows the methylene blue adsorption kinetics fitting curve for Example 1.

[0055] Figure 10 a is the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Comparative Example 1; b is the one-dimensional intensity integral diagram of the (100) crystal plane diffraction ring of the 2D-WAXS characterization result of the two-dimensional covalent organic framework block of Comparative Example 1.

[0056] Figure 11 The image shows the WAXS pattern of the two-dimensional covalent organic framework block in Comparative Example 3.

[0057] Figure 12 The image shows the PXRD characterization results of the two-dimensional covalent organic framework block in Comparative Example 2.

[0058] Figure 13 The graphs show the X-ray microtomography and micron aperture variation with freezing temperature for Examples 1 and 6-9. Detailed Implementation

[0059] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0060] The casting molds used in each embodiment and comparative example were prepared by self-making: a copper sheet was used as the bottom end cap, and a hollow polytetrafluoroethylene cylindrical sleeve (outer diameter 12mm, inner diameter 10mm, height 10mm) was used as the wall. The bottom of the polytetrafluoroethylene sleeve was brought into contact with the copper sheet, and the end cap was tightly wrapped with sealing film to prepare the casting mold.

[0061] The cold sources used in each embodiment and comparative example were also prepared in-house: (1) A glass culture dish with a diameter of 9 cm was placed on a square foam cover, and liquid nitrogen was added to it as an ice bath to obtain a cold source of -180 ℃; (2) A glass culture dish with a diameter of 9 cm was placed on a square foam cover, and a mixed ice bath of liquid nitrogen and n-pentane was added to it to obtain a cold source of -130 ℃; (3) A glass culture dish with a diameter of 9 cm was placed on a square foam cover, and dry ice / ethanol was added to it to obtain a cold source of -80 ℃; (4) A glass culture dish with a diameter of 9 cm was placed on a square foam cover, and a solvent with a volume ratio of dry ice:ethanol / ethylene glycol mixed solvent = 3:2 was added to it as an ice bath to obtain a cold source of -30 ℃; (5) A glass culture dish with a diameter of 9 cm was placed on a square foam cover, and dry ice and ethylene glycol were added to it as an ice bath to obtain a cold source of -10 ℃.

[0062] Example 1 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk, including the following steps: S1 Weigh 101.28 mg TAPB and 59.04 mg PDA, mix them, add 4.8 mL of dimethyl sulfoxide, and stir at 300 rpm for 10 min at room temperature to obtain the precursor solution.

[0063] S2. After the reaction in step S1 is completed, the precursor solution obtained is quickly added to the casting mold in an amount of 800 μL. The casting mold is then placed in direct contact with a freezing liquid (a cold source at -80 ℃) that just covers the height of the copper sheet. This creates a temperature gradient in the casting mold that gradually increases from bottom to top, causing the dimethyl sulfoxide crystals to grow directionally from bottom to top. Finally, the casting mold is placed on the cold source and frozen unidirectionally for 10 min to stabilize the structure of the directionally grown dimethyl sulfoxide crystals, resulting in a fully frozen precursor solution. S3. The fully frozen precursor solution, along with the casting mold, was placed in a freezer at -80°C for 24 hours; then transferred to a freeze dryer and freeze-dried for 48 hours to obtain TAPB-PDA 2D COFs amorphous bulk with oriented pore structure.

[0064] S4. (1) Preparation of crystal conversion reaction solution: Mix 1,4-dioxane, mesitylene and 6M glacial acetic acid in a volume ratio of 8:2:1 to obtain TAPB-PDA crystal conversion reaction solution; (2) Solvothermal reaction: The amorphous bulk of TAPB-PDA 2D COFs was placed in a high-temperature pressure-resistant bottle with a side arm, and the crystal conversion reaction solution was added until the bulk was completely submerged. After evacuation, nitrogen gas was introduced and the mixture was reacted in an oil bath at 80°C for 72 hours. The bulk was then removed and soaked in tetrahydrofuran, anhydrous ethanol for 1 day each, and then soaked in n-hexane for 5 days. The bulk was then transferred to a vacuum drying oven and dried under vacuum at 80°C overnight to obtain dried crystalline bulk of TAPB-PDA 2D COFs.

[0065] Example 2 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-OMePDA (2,5-dimethoxybenzene-1,4-dicarboxaldehyde) 2D COFs crystalline bulk, including the following steps: The difference between this embodiment and Example 1 is as follows: In step S1, 101.28 mg TAPB and 83.9 mg OMePDA were weighed, mixed, and 4.8 mL of dimethyl sulfoxide was added. The mixture was stirred at 300 rpm for 300 min at room temperature to obtain a precursor solution. In step S2, the temperature of the cold source was -130℃. The corresponding step S4 finally yielded TAPB-OMePDA 2D COFs crystalline bulk.

[0066] Example 3 This embodiment provides a method for preparing LZU-1 2D COFs crystalline bulk, including the following steps: The difference between this embodiment and Example 1 is as follows: In step S1, 76.8 mg of pyromellitic aldehyde and 76.8 mg of p-phenylenediamine were weighed, mixed, and 4.8 mL of dimethyl sulfoxide was added. The mixture was stirred at 300 rpm for 180 min at room temperature to obtain a precursor solution. In step S4, the oil bath reaction temperature was 120 °C. The corresponding step S4 ultimately yielded LZU-1 2D COFs crystalline bulk.

[0067] Example 4 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0068] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the unidirectional freezing time in step S2 is 8 min.

[0069] Example 5 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0070] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the unidirectional freezing time in step S2 is 12 min.

[0071] Example 6 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0072] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the temperature of the cold source in step S2 is -10℃.

[0073] Example 7 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0074] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the temperature of the cold source in step S2 is -30°C.

[0075] Example 8 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0076] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the temperature of the cold source in step S2 is -130°C.

[0077] Example 9 This embodiment provides a method for preparing TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk.

[0078] The preparation method of TAPB (1,3,5-tris(4-aminophenyl)benzene)-PDA (terephthalaldehyde) 2D COFs crystalline bulk in this embodiment differs from that in Example 1 in that the temperature of the cold source in step S2 is -180°C.

[0079] Comparative Example 1 This specification provides a method for preparing 2D COFs materials.

[0080] The preparation method of the comparative example 2D COFs material differs from that of Example 1 in that: in step S1, the mixture is stirred at 300 rpm for 345 min.

[0081] Comparative Example 2 This comparative example provides a method for preparing 2D COFs materials.

[0082] The preparation method of the 2D COFs material in this comparative example differs from that in Example 1 in that step S1 is adjusted to use the traditional solvothermal method to synthesize 2D COFs (refer to Chem. Commun., 2016, 52, 3690-3693), and then add 4.8 mL of dimethyl sulfoxide and sonicate to dissolve it as a precursor solution.

[0083] Comparative Example 3 This comparative example provides a method for preparing 2D COFs materials.

[0084] The preparation method of the 2D COFs material in this comparative example differs from that in Example 1 in that step S2 is omitted; a material with poor thermal conductivity (polytetrafluoroethylene) is wrapped around the outside of the mold to ensure that there is no temperature gradient during cooling, and then step S3 is performed.

[0085] Sample characterization and performance testing Samples prepared in the examples and comparative examples were tested and analyzed using 2D-WAXS (two-dimensional wide-angle X-ray diffraction): 2D-WAXS was performed on a Sinop Xeuss 3.0 fully automated small-angle / wide-angle X-ray scattering instrument using CuKα (λ=1.54189Å). The detector was an Eiger2 R 500K with a pixel size of 75μm×75μm², and the sample was exposed to the beam for 150 seconds. The sample-to-detector distance in 2D-WAXS characterization was 150mm, and all samples were calibrated using the lanthanum hexaboride (LaB6) standard. Subsequently, the obtained two-dimensional diffraction patterns were analyzed using Origin software. One-dimensional diffraction intensity integration and angular intensity integration were analyzed using Fit 2D software.

[0086] Figure 1 The figure shows a schematic diagram of the cryogenic orientation of Example 1. It can be seen from the figure that cryogenic casting has an effect on the pre-arrangement of COF. The schematic diagrams of the cryogenic casting COF arrangement in other examples are similar to those in Example 1.

[0087] (1) Analysis of the TAPB-PDA 2D COFs crystalline bulk prepared in Example 1: The amorphous bulk TAPB-PDA 2D COFs was processed by solvothermal in-situ crystallization to achieve in-situ construction of nanopores inside the bulk. To verify whether the present invention successfully prepared crystalline bulk TAPB-PDA 2D COFs with atomic orientation, the bulk was characterized by 2D-WAXS.

[0088] For example Figure 2 (a) shows the method for loading TAPB-PDA 2D COFs crystalline bulk samples, with the X-ray direction perpendicular to the icing direction. The loading methods for Examples 4-9 are similar to those in Example 1. The characterization results of 2D-WAXS are as follows: Figure 2 As shown in (b), the TAPB-PDA 2D COFs crystalline bulk exhibits clear diffraction rings formed by diffraction from the (100), (110), (200), (210), (220), and (001) crystal planes. The (100), (110), (200), (210), and (220) crystal planes reflect the in-plane structure of the 2D COFs two-dimensional nanolayers, while the (001) crystal plane reflects the π-π stacking structure between the 2D COFs layers. Therefore, the (001) crystal plane is orthogonal to the other five crystal planes in space. This demonstrates that the 2D COFs crystalline bulk simultaneously possesses regular oriented nanopores and an interlayer stacking structure, i.e., atomic orientation. The characterization results of the 2D-WAXS in Examples 4-9 are similar to those in Example 1. A one-dimensional WAXS diffraction intensity map can be obtained by performing a full-angle one-dimensional integration on the two-dimensional WAXS pattern, as shown in the figure. Figure 2 As shown in (c), the diffraction pattern reveals diffraction peaks of the (100), (110), (200), (210), (220), and (001) crystal planes, further demonstrating the crystallinity of the fabricated TAPB-PDA 2D COFs bulk. The one-dimensional WAXS diffraction intensity patterns of Examples 4-9 are similar to those of Example 1. One-dimensional intensity integration of the (100) crystal plane diffraction ring yields the following results: Figure 2 As shown in (d), from Figure 2 (d) It can be seen that the diffraction intensity has a characteristic peak at a position with an azimuth angle difference of about 180°. The peaks are approximately symmetrically distributed and the curves are smooth and noiseless. This indicates that the crystal planes of the TAPB-PDA 2D COFs crystalline bulk are preferentially arranged along a specific direction, which further strongly proves that the technical solution has successfully prepared TAPB-PDA 2D COFs crystalline bulk with atomic orientation. The one-dimensional intensity integration results of the (100) crystal plane diffraction rings in Examples 4 to 9 are similar to those in Example 1.

[0089] Figure 3 This is a schematic diagram of the main crystal planes of Example 1. The spatial relationship of the main crystal planes can be seen from the figure.

[0090] (2) Analysis of TAPB-OMePDA 2D COFs crystalline bulk prepared in Example 2 The amorphous bulk TAPB-OMePDA 2D COFs was post-processed using a solvothermal in-situ crystalline transformation method, which enabled the in-situ construction of nanopores inside the bulk. To verify whether this technique successfully prepared crystalline bulk TAPB-OMePDA 2D COFs with atomic orientation, the bulk was characterized using 2D-WAXS.

[0091] by Figure 4 (a) shows the method for loading TAPB-OMePDA 2D COFs crystalline bulk samples, with the X-ray direction perpendicular to the icing direction; the characterization results of 2D-WAXS are as follows. Figure 4 As shown in (b), the TAPB-OMePDA 2D COFs crystalline bulk exhibits clear diffraction rings formed by diffraction from the (100), (110), (200), (210), (220), and (001) crystal planes. The (100), (110), (200), (210), and (220) crystal planes reflect the in-plane structure of the 2D COFs two-dimensional nanolayers, while the (001) crystal plane reflects the π-π stacking structure between the 2D COFs layers. Therefore, the (001) crystal plane is orthogonal to the other five crystal planes in space. This proves that the 2D COFs crystalline bulk simultaneously possesses regular oriented nanopores and an interlayer stacking structure, i.e., atomic orientation. A one-dimensional WAXS diffraction intensity map can be obtained by performing a full-angle one-dimensional integration of this two-dimensional WAXS pattern, as shown in the image. Figure 4 As shown in (c), the diffraction pattern reveals diffraction peaks on the (100), (110), (200), (210), (220), and (001) crystal planes, further demonstrating the crystallinity of the fabricated TAPB-OMePDA 2D COFs bulk. One-dimensional intensity integration of the (100) crystal plane diffraction ring yields the following results: Figure 4 As shown in (d), from Figure 4 (d) It can be seen that the diffraction intensity has a characteristic peak at a position with an azimuth angle difference of about 180°. The peaks are approximately symmetrically distributed and the curves are smooth and noise-free. This indicates that the crystal planes of the TAPB-OMePDA 2D COFs crystalline bulk are preferentially arranged along a specific direction, which further strongly proves that the present technical solution has successfully prepared TAPB-OMePDA 2D COFs crystalline bulk with atomic orientation.

[0092] Figure 5 This is a schematic diagram of the main crystal planes of Example 2. The spatial relationship of the main crystal planes can be seen from the figure.

[0093] (3) Analysis of LZU-1 2D COFs crystalline bulk prepared in Example 3 The amorphous bulk LZU-1 2D COFs was post-processed using a solvothermal in-situ crystalline transformation method, which enabled the in-situ construction of nanopores inside the bulk. To verify whether this technique successfully prepared LZU-1 2D COFs crystalline bulk with atomic orientation, the bulk was characterized using 2D-WAXS.

[0094] For example Figure 6 (a) shows the method for loading LZU-1 2D COFs crystalline bulk samples, with the X-ray direction perpendicular to the icing direction; the 2D-WAXS characterization results are as follows. Figure 6 As shown in (b), the LZU-1 2D COFs crystalline bulk exhibits clear diffraction rings formed by diffraction from the (100), (110), (200), (210), (220), and (001) crystal planes. The (100), (110), (200), (210), and (220) crystal planes reflect the in-plane structure of the 2D COFs two-dimensional nanolayers, while the (001) crystal plane reflects the π-π stacking structure between the 2D COFs layers. Therefore, the (001) crystal plane is orthogonal to the other five crystal planes in space. This proves that the 2D COFs crystalline bulk simultaneously possesses regular oriented nanopores and an interlayer stacking structure, i.e., atomic orientation. A one-dimensional WAXS diffraction intensity map can be obtained by performing a full-angle one-dimensional integration on this two-dimensional WAXS pattern, as shown in the figure. Figure 6 As shown in (c), the diffraction pattern reveals diffraction peaks on the (100), (110), (200), (210), (220), and (001) crystal planes, further demonstrating the crystallinity of the fabricated LZU-1 2D COFs bulk. One-dimensional intensity integration of the (100) crystal plane diffraction ring yields the following results: Figure 6 As shown in (d), from Figure 6 (d) It can be seen that the diffraction intensity has a characteristic peak at a position with an azimuth angle difference of about 180°. The peaks are approximately symmetrically distributed and the curves are smooth and noiseless. This indicates that the crystal planes of the LZU-1 2D COFs crystalline bulk are preferentially arranged along a specific direction, which further strongly proves that the present technical solution has successfully prepared LZU-1 2D COFs crystalline bulk with atomic orientation.

[0095] Figure 7 This is a schematic diagram of the main crystal planes of Example 3. The spatial relationship of the main crystal planes can be seen from the figure.

[0096] Figure 8 The nitrogen adsorption-desorption isotherm and pore size distribution diagram are shown in Example 1. Figure 8 a is the nitrogen adsorption-desorption isotherm diagram of Example 1. Figure 8 b is the pore size distribution diagram of Example 1, from Figure 8b. It can be seen that the pore size distribution of the block is highly concentrated at about 3.5 nm, which is close to the theoretical pore size of the COF material. The nitrogen adsorption-desorption isotherms and pore size distribution diagrams of other embodiments are similar to those of Embodiment 1.

[0097] Figure 9 The graph shows the methylene blue adsorption kinetics fitting curve for Example 1. Figure 9 a is the first-order kinetic fitting plot of Example 1. Figure 9 b is the second-order kinetic fitting diagram of Example 1. As can be seen from the figure, the adsorption process of this block is more in line with the second-order kinetic model, indicating that the adsorption mechanism is dominated by chemisorption. The methylene blue adsorption kinetic fitting curves of other examples are similar to those of Example 1.

[0098] Figure 10 Figure a shows the 2D-WAXS characterization results of the two-dimensional covalent organic framework block in Comparative Example 1; Figure b shows the one-dimensional intensity integral plot of the 100) crystal plane diffraction ring of the 2D-WAXS characterization results of the two-dimensional covalent organic framework block in Comparative Example 1. As can be seen in 10a, using a prepolymer solution prepared with excessively long stirring time for cryogenic casting and crystal transformation results in a crystalline bulk that, while still possessing crystallinity, exhibits significantly reduced orientation. Figure 10 b shows that if the reaction time in step S1 is too long, polymers will be generated, which will reduce the smoothness of the integral curve, increase its roughness, and produce a lot of noise, further confirming the weak orientation of the bulk.

[0099] Figure 11 The image shows the WAXS pattern of the two-dimensional covalent organic framework block in Comparative Example 3. From... Figure 11 It can be seen that the randomly frozen bulk does not have anisotropy, which indicates that the two-dimensional covalent organic framework bulk prepared in Comparative Example 3 has crystallinity but no atomic orientation.

[0100] Figure 12 The image shows the PXRD characterization results of the two-dimensional covalent organic framework block in Comparative Example 2. From... Figure 12 It can be seen that the bulk material in Comparative Example 2 does not have crystallinity, and therefore does not have atomic orientation, indicating that it is impossible to obtain a bulk material with atomic orientation by directly using readily available 2DCOFs.

[0101] Figure 13 The graphs show the X-ray microtomography and micron aperture variation with freezing temperature for Examples 1 and 6-9. Figure 13 a) is an X-ray microtomographic image of Examples 1 and 6-9, and 13b is a graph showing the trend of micron-sized aperture as a function of freezing temperature for Examples 1 and 6-9. Figure 13As can be seen, lowering the temperature accelerates the freezing process, resulting in finer directional channels. Atomically oriented TAPB-PDA covalent organic framework bulks can be prepared over a wide temperature range (–10°C to –180°C), and the channels tend to expand as the cold source temperature increases. Figure 13 b can be quantitatively observed that the channel width of the TAPB-PDA covalent organic framework block with atomic orientation can be between approximately 20 and 70 μm.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a two-dimensional covalent organic framework block, characterized in that, Includes the following steps: S1. Mix the organic amine monomers, aldehyde monomers and freezeable solvents required for the polymerization of two-dimensional covalent organic frameworks, react them, and obtain a precursor solution; S2. Add the precursor solution to the casting mold and freeze it unidirectionally to obtain a frozen precursor solution; S3. The frozen precursor solution is freeze-dried to remove the freezeable solvent, resulting in 2D COFs amorphous bulk material; S4. The 2D COFs amorphous bulk material is subjected to in-situ crystallization treatment using a solvothermal method to obtain the 2D COFs crystalline bulk material. Steps S1 to S3 are carried out in the absence of a catalyst, while step S4 is carried out in the presence of a catalyst; the catalyst is a catalyst that catalyzes the Schiff base reaction between amino and aldehyde groups. The reaction time in step S1 is 5 to 300 minutes.

2. The preparation method according to claim 1, characterized in that, In step S1, the freezeable solvent is DMSO.

3. The preparation method according to claim 1, characterized in that, In step S1, the organic amine monomer is at least one of a triamine or a diamine.

4. The preparation method according to claim 1, characterized in that, In step S1, the aldehyde monomer is at least one of a ternary aldehyde or a dialdehyde.

5. The preparation method according to claim 1, characterized in that, In step S2, the temperature range of the cold source for unidirectional freezing is -180℃ to -10℃.

6. The preparation method according to claim 1, characterized in that, In step S3, the size of the two-dimensional covalent organic framework block is on the order of centimeters.

7. The preparation method according to claim 1, characterized in that, In step S3, the catalyst is acetic acid.

8. The preparation method according to claim 1, characterized in that, In step S4, the conditions for the solvothermal method are: temperature of 80~120℃, inert gas atmosphere, and time of 48~72 hours.

9. A two-dimensional covalent organic framework block, characterized in that, It is prepared by any of the preparation methods described in claims 1 to 8.

10. The application of the two-dimensional covalent organic framework block according to claim 9 in material separation, energy storage, heterogeneous catalysis, and biosensing.

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