Ultramicroporous fluorine-rich two-dimensional covalent organic framework material and its preparation method and application

Abstract

The present invention discloses a fluorine-rich two-dimensional covalent organic framework material with ultramicroporous properties, as well as a preparation method and application thereof. The present invention uses six-connected node molecules with hexagonal symmetry and three-connected node molecules with fluorinated trigonal symmetry to obtain an orderly extended trigonally symmetrical two-dimensional topological network structure through [6+3] imine condensation, and a framework compound with fluorinated groups. The material has high crystallinity and a unique ultramicroporous pore structure, which enables this novel two-dimensional covalent organic framework compound to produce rich specific gas screening properties, and has good application prospects in industrial gas separation and purification.

Description

Technical Field

[0001] The present invention belongs to the field of covalent organic framework (COFs) materials, and specifically relates to a class of ultramicroporous fluorine-rich two-dimensional covalent organic framework materials and a preparation method thereof, as well as applications in the field of gas separation. Background Art

[0002] As an important chemical raw material, acetylene is widely used in fields such as petrochemical and electronics industries. However, acetylene produced by processes such as petroleum distillation and cracking often contains some impurities, such as methane and carbon dioxide, which seriously affect its subsequent use benefits. Since the boiling points and kinetic sizes of acetylene (C2H2), carbon dioxide (CO2) and methane (CH4) molecules are very close, their separation is extremely challenging. Therefore, achieving selective adsorption separation of C2H2 / CO2 and C2H2 / CH4 is particularly important for reducing energy consumption, purifying energy and achieving "carbon neutrality". Traditional adsorption materials are difficult to meet the market's growing demand for high-performance adsorption separation materials due to their drawbacks such as poor adsorption separation effects. Therefore, it is necessary to study porous materials with controllable pore size, excellent adsorption separation selectivity and high stability.

[0003] Covalent organic frameworks (COFs), as an emerging porous material, are widely used in energy, catalysis, and separation due to their tunable regular pore structure, rich and designable active sites, and high specific surface area. The nanosheets formed by two-dimensional COFs have atomic-level thickness and extremely low mass transfer resistance, and have become a research hotspot in the field of high-throughput gas separation. Introducing functional sites, such as fluorine groups (-F), into the COFs skeleton can enhance the binding affinity for C2H2. Therefore, the development of a fluorine-functionalized two-dimensional COF material can provide a new research perspective for the adsorption separation of C2H2 / CO2 and other substances. Summary of the Invention

[0004] The present invention provides a two-dimensional covalent organic framework material with an ultramicroporous fluorine-rich structure, as well as its preparation method and application. The present invention successfully synthesized a series of fluorinated two-dimensional COFs by assembling a hexagonal, six-node molecule with a fluorinated trigonal, three-node molecule. The material's high crystallinity and unique ultramicroporous structure offer promising applications in industrial gas separation and purification, such as industrial helium separation and acetylene or methane purification.

[0005] The technical solutions of the present invention are as follows:

[0006] A fluorine-rich two-dimensional covalent organic framework material with ultra-microporous structure, which is formed by covalently connecting six hexagonal symmetric nodes and three fluorinated trigonal symmetric nodes on a two-dimensional level and stacking in three dimensions;

[0007] In at least a portion of the two-dimensional covalent organic framework material, each hexagonal six-connected node is connected to six adjacent fluorinated three-connected nodes, and each fluorinated three-connected node is connected to three adjacent hexagonal six-connected nodes, forming a two-dimensional topological network structure.

[0008] in,

[0009] The six-connected nodes of hexagonal symmetry and the three-connected nodes of fluorinated trigonal symmetry are shown in formula (1) and formula (2), respectively:

[0010]

[0011] In formula (1) and formula (2),

[0012] R is one or more of H, OH, SH, and halogen (F, Cl, Br, I);

[0013] “---” indicates a connection.

[0014] The BET specific surface area of ​​the ultramicroporous fluorine-rich two-dimensional covalent organic framework material of the present invention is 100 to 2000 m 2 / g, pore size is 0.4~1.0nm.

[0015] In at least a portion of the ultramicroporous fluorine-rich two-dimensional covalent organic framework material of the present invention, the molar ratio of six hexagonal symmetric connection nodes to three fluorinated trigonal symmetric connection nodes is (0.5-1.5): (0.75-2.25), preferably 1:2.

[0016] The ultramicroporous fluorine-rich two-dimensional covalent organic framework material of the present invention comprises a two-dimensional topological network structure with trigonal symmetry.

[0017] The connecting group of the ultramicroporous fluorine-rich two-dimensional covalent organic framework material described in the present invention contains a dynamic covalent bond, and the connection mode is selected from one of -C=N-, -C=NN=C-, -C=N-NH-, -C=C-, and -C=C(CN)-, preferably -C=N- (reversible imine covalent bond).

[0018] When the connection mode is -C=N-, the ultramicroporous fluorine-rich two-dimensional covalent organic framework material includes a skeleton unit shown in formula (3):

[0019]

[0020] In formula (3),

[0021] R is one or more of H, OH, SH, and halogen (F, Cl, Br, I);

[0022] “---” indicates the connection bit.

[0023] The method for preparing the ultramicroporous fluorine-rich two-dimensional covalent organic framework material of the present invention comprises:

[0024] The hexagonal symmetric six-connected node molecule, the fluorinated trigonal symmetric three-connected node molecule, the reaction solvent, and the catalyst are mixed, and after degassing by freeze-thaw cycle, the mixture is sealed and heated to 80-180° C. for reaction for 72-168 hours, and the reaction mixture is post-treated to obtain the ultramicroporous fluorine-rich two-dimensional covalent organic framework material;

[0025] The molar ratio of the hexagonal symmetric six-connected node molecule to the fluorinated trigonal symmetric three-connected node molecule is (0.5-1.5): (0.75-2.25), preferably 1:2;

[0026] The reaction solvent is selected from one of the following mixed solvents: o-dichlorobenzene / n-butanol, anisole / n-butanol, N,N-dimethylacetamide / n-butanol;

[0027] The catalyst is acetic acid or trifluoroacetic acid;

[0028] The preferred reaction temperature is 120°C and the reaction time is 3 days;

[0029] The specific post-treatment method is as follows: after the reaction is completed, the product is cooled to room temperature, and the solid product is collected by centrifugation. The solid product is first soaked in N,N-dimethylacetamide for 6 hours, repeated twice, and then soaked in acetone for 6 hours, repeated twice, and then Soxhlet extraction is performed with tetrahydrofuran and acetone for 24 to 48 hours respectively. The solid product is then placed in a vacuum drying oven and dried at 100°C to 20 mTorr for 24 hours to obtain the target product.

[0030] The hexagonal symmetric six-connected node molecule and the fluorinated trigonal symmetric three-connected node molecule are shown in formula (4) and formula (5), respectively:

[0031]

[0032] In formula (4) and formula (5),

[0033] One of R1 and R2 is an aldehyde group (-CHO), and the other is an amino group (-NH2); preferably, R1 is an aldehyde group and R2 is an amino group;

[0034] R3 and R4 are each independently H, OH, SH, or halogen (F, Cl, Br, I); preferably, R3 and R4 are both H.

[0035] The ultramicroporous fluorine-rich two-dimensional covalent organic framework material of the present invention can be applied to the separation and purification of industrial gases.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention provides a design strategy for a two-dimensional covalent organic framework compound with a novel interlayer staggered stacking. It adopts six-connected node molecules with hexagonal symmetry and three-connected node molecules with fluorinated trigonal symmetry, and obtains an orderly extended trigonally symmetrical two-dimensional topological network structure through [6+3] imine condensation, and the framework compound has a fluorinated group.

[0038] The two-dimensional covalent organic framework compound of the present invention has high crystallinity and a unique ultramicroporous pore structure, which enables this new two-dimensional covalent organic framework compound to produce rich specific gas screening properties and has good application prospects in industrial gas separation and purification. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 : Schematic diagram of the topological structure of the fluorine-rich two-dimensional covalent organic framework compound in Example 1 of the present invention.

[0040] Figure 2 : Schematic diagram of the synthesis of the fluorine-rich two-dimensional covalent organic framework compound in Example 1 of the present invention.

[0041] Figure 3 : Powder X-ray (PXRD) test spectrum and simulation spectrum of the fluorine-rich two-dimensional covalent organic framework compound in Example 1 of the present invention.

[0042] Figure 4 : Infrared (FT-IR) spectrum of the fluorine-rich two-dimensional covalent organic framework compound in Example 1 of the present invention.

[0043] Figure 5 : Scanning electron microscope photograph of the fluorine-rich two-dimensional covalent organic framework compound in Example 1 of the present invention.

[0044] Figure 6 : The adsorption performance diagram (a) of the fluorine-rich two-dimensional covalent organic framework compound for acetylene, ethylene and carbon dioxide at 298K and the acetylene / carbon dioxide and acetylene / ethylene separation performance diagram (b) in Example 1 of the present invention. DETAILED DESCRIPTION

[0045] The objectives, technical solutions and advantages of the present invention are further described in detail below in conjunction with the embodiments and drawings. The specific embodiments described are only used to explain the present invention and are not intended to limit the present invention.

[0046] In the following examples,

[0047] The raw materials hexaaldehyde benzene (HFPB) and 1,3,5-trifluoro-2,4,6-tris(4-aminophenyl)benzene (TAFB) had a purity of >95% and were purchased from Shanghai Tengqian Biotechnology Co., Ltd.

[0048] Example 1

[0049] (1) Synthesis of TFB-COF

[0050] See Figure 2 In a glass ampoule, hexaformaldehyde benzene (HFPB) (14 mg, 20 mmol) and 1,3,5-trifluoro-2,4,6-tris(4-aminophenyl)benzene (TAFB) (16 mg, 40 mmol) were added to a mixed solvent of anisole (0.48 mL) and n-butanol (0.12 mL). After sonication for 5 minutes, a pale yellow turbid solution was obtained. 9 M acetic acid (60 μL) was added to the glass ampoule as a catalyst. The glass ampoule was quickly frozen at 77 K in a liquid nitrogen bath and degassed by freeze-pump-thaw cycles three times before being sealed. The glass ampoule was placed in an oven at 120°C for 3 days. The purple-white solid was isolated by centrifugation and washed with N,N-dimethylacetamide (2 × 10 mL) and acetone (2 × 10 mL). The resulting precipitate was filtered and then thoroughly washed with tetrahydrofuran and acetone by Soxhlet extraction for 48 h, respectively. The sample was then transferred to a vacuum chamber, evacuated to 20 mTorr at 100° C., and dried for 24 h to obtain TFB-COF as a light yellow powder (yield: 20 mg, 66%).

[0051] (2) Product characterization

[0052] See Figure 3 Through PXRD measurements, TFB-COF showed diffraction peaks at 6.58, 10.56, 11.72, 12.62, 13.50, 15.02, 15.90, 16.50, 17.94, 20.48, 21.96, and 22.94. Structural simulations using Materials Studio software revealed the crystal structure of TFB-COF. The simulated PXRD pattern generated by the corresponding two-dimensional topological network structure of the fluorinated structure matched well with the experimental PXRD pattern, confirming the correctness of the structure.

[0053] See Figure 4 The Fourier transform infrared (FT-IR) spectrum showed that the required monomers and the corresponding product TFB-COF were -1 The characteristic stretching vibration of the C=N bond was generated, proving the successful synthesis of TFB-COF.

[0054] See Figure 5 , Scanning electron microscopy (SEM) pattern, showing that TFB-COF has a blocky morphology.

[0055] See Figure 6The adsorption performance of acetylene, ethylene and carbon dioxide of TFB-COF was tested using a gas adsorption instrument (ASAP 2020) at 298K. The results showed that TFB-COF showed the best adsorption capacity for acetylene at 298K, reaching 55cm 3 / g, and the corresponding acetylene / carbon dioxide separation factor reaches 3.

[0056] Comparative Example

[0057] Our research group previously disclosed a similar two-dimensional COFs material without fluorine functional groups in the application CN 115894947A. Under the same gas adsorption and separation performance test conditions, the results showed that its adsorption capacity for acetylene was only 30 cm 3 / g, and the corresponding acetylene / carbon dioxide separation factor was only 1.5, which fully demonstrated the effectiveness of the introduction of fluorinated functional groups in the present invention. This is also consistent with a previous research work reported by our research group (New Journal of Chemistry 2023, 47, 6759-6764).

[0058] The embodiments described above only express the preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of protection of the present invention. The various technical features of the embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the various technical features in the above embodiments are described, but as long as there are no contradictions in these combinations involved, they should be considered to be within the scope of this specification. For those of ordinary skill in the art, several modifications and changes can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be based on the appended claims.

Claims

1. A fluorine-rich two-dimensional covalent organic framework material with ultramicropores, characterized in that: It is formed by six connecting nodes of hexagonal symmetry and three connecting nodes of fluorinated trigonal symmetry connected by covalent bonds on the two-dimensional level and formed by three-dimensional stacking; In at least a portion of the two-dimensional covalent organic framework material, each hexagonal six-connected node is connected to six adjacent fluorinated three-connected nodes, and each fluorinated three-connected node is connected to three adjacent hexagonal six-connected nodes, forming a two-dimensional topological network structure. in, The six-connected nodes of hexagonal symmetry and the three-connected nodes of fluorinated trigonal symmetry are shown in formula (1) and formula (2), respectively: The connection mode of the ultra-microporous fluorine-rich two-dimensional covalent organic framework material is -C=N-, and includes the skeleton unit shown in formula (3): （3） In formula (1), formula (2), and formula (3), R is H; "---" indicates a connection.

2. The ultramicroporous fluorine-rich two-dimensional covalent organic framework material according to claim 1, characterized in that: The BET specific surface area of ​​this material is 100~2000m 2 / g, pore size is 0.4~1.0nm.

3. The ultra-microporous fluorine-rich two-dimensional covalent organic framework material according to claim 1, characterized in that: In at least a portion of the material, a molar ratio of hexagonal six-linked nodes to fluorinated trigonal three-linked nodes is (0.5-1.5):(0.75-2.25).

4. The method for preparing the ultramicroporous fluorine-rich two-dimensional covalent organic framework material according to claim 1, wherein: The preparation method comprises: The hexagonal symmetric six-connected node molecule, the fluorinated trigonal symmetric three-connected node molecule, the reaction solvent, and the catalyst are mixed, and after freeze-thaw cycle degassing, the mixture is sealed and heated to 80-180° C. for reaction for 72-168 hours. The reaction mixture is post-treated to obtain the ultramicroporous fluorine-rich two-dimensional covalent organic framework material; The reaction solvent is selected from one of the following mixed solvents: o-dichlorobenzene / n-butanol, anisole / n-butanol, N,N-dimethylacetamide / n-butanol; The catalyst is acetic acid or trifluoroacetic acid; The hexagonal symmetric six-connected node molecule and the fluorinated trigonal symmetric three-connected node molecule are shown in formula (4) and formula (5), respectively: In formula (4) and formula (5), One of R1 and R2 is an aldehyde group, and the other is an amino group; R3 and R4 are both H.

5. The preparation method according to claim 4, wherein The molar ratio of the hexagonal symmetric six-connected node molecule to the fluorinated trigonal symmetric three-connected node molecule is (0.5~1.5): (0.75~2.25).

6. The preparation method according to claim 4, wherein The post-treatment method is as follows: after the reaction is completed, cool to room temperature, collect the solid product by centrifugation, soak it in N, N-dimethylacetamide for 6 hours, repeat twice, then soak it in acetone for 6 hours, repeat twice, then use tetrahydrofuran and acetone for Soxhlet extraction for 24 to 48 hours respectively, then place it in a vacuum drying oven, evacuate to 20 mTorr at 100°C and dry it for 24 hours to obtain the target product.

7. Use of the ultramicroporous fluorine-rich two-dimensional covalent organic framework material as claimed in claim 1 in the separation and purification of industrial gases.

8. The use according to claim 7, characterized in that The ultra-microporous fluorine-rich two-dimensional covalent organic framework material is used for the adsorption separation of acetylene / carbon dioxide.

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