Method for improving hydrogen storage properties of covalent organic framework compounds and their use for hydrogen storage

Abstract

The present invention provides a method for improving the hydrogen storage properties of a covalent organic framework compound, comprising the step of forming a covalent organic framework compound by dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer, wherein the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the covalent organic framework compound has a two-dimensional or three-dimensional structure.

Description

[Technical Field]

[0001] The present invention relates to the technical field of hydrogen storage materials, and in particular to a method for improving the hydrogen storage properties of covalent organic framework compounds and the use of fluorinated covalent organic framework compounds as hydrogen storage media. [Background technology]

[0002] As humankind's energy demand and use increases, non-renewable energy sources such as fossil fuels (coal, oil, and natural gas) are becoming increasingly scarce, and the large-scale development and utilization of renewable energy has become an important component of the energy strategies of countries around the world. Hydrogen energy is the most ideal energy source for the future, as it is abundantly available, environmentally friendly, renewable, and has high energy density. One of the biggest technical obstacles to using hydrogen energy as fuel is its storage. Hydrogen is in a gaseous state at room temperature and pressure, and its density is only 1 / 14 that of air. A car needs to consume approximately 5 to 13 kg of hydrogen to travel 482.7 km (300 miles), and 5 kg of hydrogen at room temperature and pressure can store 56 m 3 Therefore, hydrogen vehicle applications require more practical and feasible hydrogen storage methods.

[0003] Currently, various hydrogen storage methods have been proposed, with the most common being compressed gas storage and liquid hydrogen storage. While these methods are easy to implement and the technologies are mature, they each have drawbacks that are difficult to overcome. For example, storing and transporting high-pressure hydrogen gas in cylinders poses a risk because the high-pressure hydrogen can dissolve and penetrate the steel walls of the storage cylinder, potentially causing hydrogen embrittlement. This poses a significant safety risk for long-term hydrogen storage, as well as small hydrogen storage capacity and high costs. While liquid hydrogen is denser than hydrogen gas, its storage temperature is -252.8°C, which means that storage requires significant energy consumption and good insulation, resulting in high equipment requirements and high costs. Therefore, finding new hydrogen storage materials and storage and transportation methods is crucial, and porous materials have become one of the recent hot spots in materials exploration.

[0004] Adsorption is the partial retention of gas after contact with a solid. It can be divided into two categories: chemisorption and physisorption, depending on the adsorption strength, heat of adsorption, adsorption rate, selectivity, adsorption temperature, and pressure. The main chemical hydrogen storage materials are metal hydrides. Chemisorption is usually associated with an activation energy, which means that for adsorption to be complete, molecules attracted to the surface must first pass an energy barrier and firmly bond with the surface. Therefore, most chemisorption processes have high reaction activation energies, the desorption process is slow, and some metal hydrides are irregenerate. Physisorption hydrogen storage involves accumulating gas molecules on the surface of a material without chemical reaction with the material, and adsorbing and storing the gas through molecular interactions between the gas and the material. Because the force between the hydrogen molecules and the pore surface of the adsorbent is very weak, physisorption hydrogen storage has fast adsorption and desorption rates and is typically operated at low temperatures and high pressures. The main physical hydrogen storage materials include porous materials such as zeolites, activated carbon, carbon nanotubes, and metal-organic frameworks.

[0005] Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) are both crystalline porous materials that have been rapidly developing in recent years. MOFs are three-dimensional network crystalline structures composed of porous organic ligands, primarily aromatic acid or base nitrogen and oxygen, hybridized with inorganic metal centers through coordination bonds. Therefore, MOFs are also known as porous coordination polymers (PCPs). Their pore structure resembles that of zeolites, but their flexible frameworks mean they are also called "soft zeolites." The first generation of MOF materials was synthesized in the mid-1990s. At that time, the pore structure of MOF materials required the support of guest molecules. When the guest molecules were removed, the framework collapsed, resulting in a stable pore structure. Subsequently, researchers began assembling anionic, cationic, and neutral ligands into coordination polymers, synthesizing a new generation of MOF materials. The organic ligands in this type of MOF material are primarily carboxyl-containing organic anionic ligands, sometimes mixed with nitrogen-containing heterocyclic organic neutral ligands. This generation of MOF materials overcomes the shortcomings of previous generations by allowing the framework structure to change to some extent when guest molecules are introduced or removed, or when certain external stimuli (such as pressure) are applied, but not to collapse. Covalent organic frameworks are a new type of framework material recently synthesized that can have a variety of 1D, 2D, and 3D crystal structures. The frameworks of these materials contain only organic structural units, connected by very strong covalent bonds (e.g., C-C, C-O, B-O). Three of these materials, COF-6, COF-8, and COF-10, have a layered 2D structure similar to graphite. The other three, COF-102, COF-105, and COF-108, have a 3D structure formed by introducing triangular and tetrahedral nodes. This type of material has the advantages of large porosity and specific surface area, good thermal stability, and ease of functionalization. Compared to MOFs, COFs have a lower crystalline density, which increases the possibility of their effective use in gas storage.At the same time, the materials have greater stability and potential for further modification, since the covalent bonds connecting the COF building blocks are more stable than the coordinate bonds of MOFs.

[0006] Currently, for physical hydrogen storage materials, MOF / COF materials mainly improve the hydrogen storage properties of the material in terms of increasing its specific surface area and pore volume.

[0007] For example, MOF-5 is a representative example of many MOF compounds, and its framework [Zn4O(bdc)3] consists of Zn4O(-COO)6 units and terephthalate bdc 2- It is a three-dimensional network with a pcu topology formed by interconnecting these. Patent document WO2005003622A1 discloses a hydrogen storage container to which MOF-5 material is added, and shows that under a pressure of 3 bar, the hydrogen storage weight of the container to which MOF-5 is added increases by 1.46 times compared to a container to which MOF-5 is not added.

[0008] However, physical hydrogen storage materials have a trade-off between large specific surface area and material stability. MOF / COF materials with large specific surface area are always produced by highly reversible reactions, which means they have a high tendency to decompose (low chemical stability). In addition, pore collapse is also an unavoidable problem for MOF / COF materials with large specific surface area. For example, a MOF / COF with a BET specific surface area of ​​5000 m 2 For MOFs exceeding 800 / g, the activation process is always complicated and requires methods such as supercritical CO2. This shows that a large specific surface area can cause problems with both chemical stability and pore structure collapse. Furthermore, even the current 7200 MOF materials cannot meet the hydrogen storage density requirements proposed by the US Department of Energy for hydrogen storage systems. Therefore, finding solutions other than increasing the BET specific surface area has become a worthwhile research direction for MOF / COF-type physical hydrogen storage materials.

[0009] Because all COF materials contain aromatic ring structures (a requirement for rigid structural elements), these building blocks are difficult to functionalize, and further pore modification is always required for functionalization. Regarding hydrogen storage properties, aromatic ring structures typically have very high heats of adsorption (~4 kJ / mol), making it difficult to provide effective adsorption sites. Therefore, an effective method is needed to improve the hydrogen storage properties of materials by improving the heat of adsorption of the adsorption sites. Summary of the Invention [Problem to be solved by the invention]

[0010] As mentioned above, combining the properties of physical and chemical hydrogen storage materials is the key to developing effective hydrogen storage materials, and is also a major challenge in the field of hydrogen storage.After extensive research, the inventors unexpectedly discovered that the heat of hydrogen adsorption and the hydrogen storage capacity of covalent organic framework (COF) compounds can be significantly increased by fluorinating specific sites on the aromatic rings of the COF. [Means for solving the problem]

[0011] According to a first aspect of the present invention, there is provided a method for improving the hydrogen storage properties of a covalent organic framework compound, comprising the step of dehydration polycondensing an aromatic polyamino monomer and an aromatic polyaldehyde monomer to form a covalent organic framework compound, wherein the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the covalent organic framework compound has a two-dimensional or three-dimensional structure.

[0012] According to a second aspect of the present invention, there is provided a use of a fluorinated covalent organic framework compound as a hydrogen storage medium, wherein the fluorinated covalent organic framework compound is formed by dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer, the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the fluorinated covalent organic framework compound has a two-dimensional or three-dimensional structure.

[0013] In some embodiments, the fluorinated aromatic ring is selected from a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, or a pyrene ring.

[0014] In some embodiments, the fluorinated aromatic ring is a benzene ring.

[0015] In some embodiments, the aromatic polyaldehyde monomer contains one of the fluorinated aromatic rings, the fluorinated aromatic ring contains two paraldehyde groups, and the aromatic polyamino monomer has the following structure: TIFF2026503827000002.tif94170R is an amino group or a 4-aminophenyl group.

[0016] In some embodiments, the aromatic polyamino monomer contains one of the fluorinated aromatic rings, the fluorinated aromatic ring contains two para-amino groups, and the aromatic polyaldehyde monomer has the structure: TIFF2026503827000003.tif95170R is an aldehyde group or a 4-aldehyde phenyl group.

[0017] In some embodiments, the aromatic polyamino monomer is 1,3,5-tris(4-aminophenyl)benzene or tetrakis(4-aminophenyl)methane.

[0018] In some embodiments, the aromatic polyaldehyde monomer is 2,5-difluoroterephthalaldehyde. [Effects of the Invention]

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. In the prior art, modification treatments of hydrogen storage materials usually involve increasing the specific surface area of ​​the material or doping the material to improve the material's hydrogen storage properties, which requires complicated operations and high costs. In comparison, the present invention advantageously solves the problem of low hydrogen storage capacity of existing hydrogen storage materials by controlling the adsorption induction force of covalent organic framework compounds through simple structural modification.

[0021] 2. The low heat of adsorption of covalent organic framework compounds in the prior art has hindered their widespread use and application as hydrogen storage media. The present invention increases the heat of hydrogen adsorption of covalent organic framework compounds by fluorinating specific sites on the aromatic rings of COFs, thereby further increasing the hydrogen storage capacity of COF compounds, which is beneficial for promoting the practical application and development of covalent organic frameworks in the field of hydrogen storage.

[0022] 3. The method of the present invention is versatile and can be effectively applied to covalent organic framework compounds of different structures and dimensions.

[0023] 4. In the prior art, all methods for modifying hydrogen storage materials are limited to milligram-level laboratory scale. In comparison, the method of the present invention can be scaled up for production, which is advantageous for industrial application. [Brief explanation of the drawings]

[0024] The present invention will be further described below in conjunction with the drawings and embodiments. [Figure 1(a)] 1 is a schematic diagram of a synthesis process for a two-dimensional covalent organic framework compound provided by the present invention. [Figure 1(b)]1 is a schematic diagram of a synthesis process for a three-dimensional covalent organic framework compound provided by the present invention. [Figure 2(a)-(g)] 1 shows X-ray diffraction (XRD) patterns of the covalent organic framework compounds provided by Production Examples 1 to 7 of the present invention, respectively. [Figure 3(a)] 1 shows the nitrogen adsorption-desorption isotherm of the two-dimensional covalent organic framework compound provided by Preparation Example 1 of the present invention. [Figure 3(b)] 1 shows the nitrogen adsorption-desorption isotherm of the three-dimensional covalent organic framework compound provided by Preparation Example 2 of the present invention. [Figure 4(a)] 1 shows hydrogen adsorption-desorption isotherms of the two-dimensional covalent organic framework compound of the present invention. [Figure 4(b)] 1 shows hydrogen adsorption-desorption isotherms of the three-dimensional covalent organic framework compound of the present invention. [Figure 4(c)] 1 shows the hydrogen adsorption-desorption isotherm of the two-dimensional covalent organic framework compound provided by Preparation Example 4 of the present invention. [Figure 5(a)-(b)] 1 is a graph showing the relationship between the amount of hydrogen adsorption and pressure (bar) for two-dimensional and three-dimensional covalent organic framework compounds, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0025] As used herein, the terms covalent organic framework, covalent organic framework, and COF can be used interchangeably.

[0026] In order to make the technical solutions and advantages of the present invention clearer and easier to understand, the present invention will be clearly and completely described below through examples in conjunction with the drawings, whereby, provided that there are no contradictions between them, each embodiment or each technical feature described below can be arbitrarily combined to form a new embodiment.

[0027] It should also be noted that terms such as "exemplary" or "for example" are used herein to indicate an example, instance, or illustration. An embodiment or design described as "exemplary" or "for example" herein is not to be construed as preferred or more advantageous over other embodiments or designs. Rather, the use of terms such as "exemplary" or "for example" is intended to concretely illustrate the relevant concept.

[0028] In the present invention, "at least one" means one or more, and "multiple" means two or more. "And / or" describes a relationship between related objects and indicates that a three-way relationship may exist. For example, A and / or B can represent the singular presence of A, the simultaneous presence of A and B, or the singular presence of B, where A and B may be singular or plural. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or multiple items. For example, "at least one of a, b, or c" can represent a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c are singular or plural. It should be noted that "at least one" can be interpreted as "one or multiple items."

[0029] In the present invention, the term "fluorinated aromatic ring" means that H on an aromatic ring is substituted with F, and a ring in which H on a substituent connected to an aromatic ring is substituted with F does not belong to the "fluorinated aromatic ring" of the present invention.

[0030] As described above, the present invention provides a method for improving the hydrogen storage properties of a covalent organic framework compound, comprising the step of forming a covalent organic framework compound by dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer, wherein the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the covalent organic framework compound has a two-dimensional or three-dimensional structure.

[0031] According to the present invention, the aromatic polyamino monomer is an aromatic compound containing two or more amino groups, for example, the aromatic polyamino monomer can be selected from substituted or unsubstituted p-phenylenediamine, substituted or unsubstituted triaminobenzene and other substituted or unsubstituted polyamino aromatic compounds, substituted or unsubstituted diamino heterocyclic compounds, substituted or unsubstituted triamino heterocyclic compounds, or substituted or unsubstituted polyamino heterocyclic compounds.

[0032] According to the present invention, the aromatic polyaldehyde monomer is an aromatic compound containing two or more aldehyde groups, for example, the polyaldehyde monomer is selected from substituted or unsubstituted terephthalaldehyde, substituted or unsubstituted biphenyldicarboxaldehyde, substituted or unsubstituted p-thiophenedicarboxaldehyde and other substituted or unsubstituted polyaldehyde-based aromatic compounds, substituted or unsubstituted dialdehyde-based heterocyclic compounds, substituted or unsubstituted trialdehyde-based heterocyclic compounds, or substituted or unsubstituted polyaldehyde-based heterocyclic compounds.

[0033] According to one preferred embodiment of the present invention, the aromatic polyaldehyde monomer contains one of the fluorinated aromatic rings, and the fluorinated aromatic ring contains two paraldehyde groups, and the aromatic polyamino monomer has the following structure: TIFF2026503827000004.tif90170R is an amino group or a 4-aminophenyl group.

[0034] In a preferred embodiment, the aromatic polyamino monomer contains one of the fluorinated aromatic rings, the fluorinated aromatic ring contains two para-amino groups, and the aromatic polyaldehyde monomer has the following structure: TIFF2026503827000005.tif94170R is an aldehyde group or a 4-aldehyde phenyl group.

[0035] According to the present invention, the two-dimensional or three-dimensional structure refers to a structure having periodically repeated two-dimensional or three-dimensional crystal structure units.

[0036] The two-dimensional structure may be a two-dimensional sheet-like structure in which polygonal structural units having pores therein are horizontally arranged. The polygons may be, for example, equilateral triangles, scalene triangles, squares, pentagons, hexagons, or a combination thereof, and have pores therein. In consideration of the stability of the chemical structure, the polygons may be, for example, equilateral triangles, squares, pentagons, regular hexagons, or a combination thereof, or, for example, regular pentagons, regular hexagons, or a combination thereof, or, for example, regular hexagons.

[0037] The three-dimensional structure may be any three-dimensional crystalline structure present in an overlapping stacked structure, an alternating stacked structure, a unidirectional stacked structure or a random stacked structure, and has pores therein.

[0038] According to the present invention, the step of dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer to form a covalently bonded organic framework compound may be any dehydration polycondensation reaction known in the art. For example, the dehydration polycondensation is carried out by reacting a polyamino monomer and a polyaldehyde monomer as reactants in a mixed solvent and catalyzed by a catalyst. Typically, the reaction is carried out at 100 to 150°C, preferably 100 to 130°C, more preferably 110°C, 112°C, 114°C, 116°C, 118°C, or 120°C, and most preferably 120°C. The catalyst may be selected from any catalyst known in the art. For example, the catalyst may be selected from one or more of formic acid, acetic acid, p-toluenesulfonic acid, oxalic acid, lactic acid, hydrochloric acid, sulfuric acid, and pyrrolidine. Preferably, the catalyst is selected from acetic acid. The mixed solvent can be selected from any mixed solvent known in the art. For example, the mixed solvent may be any of ethylene glycol + cyclohexane, mesitylene + dioxane, n-butanol + dioxane, o-dichlorobenzene + n-butanol, and mesitylene + n-butanol. In the mixed solvent, the volume ratio of the former to the latter is 9:1 to 1:9, for example, 5:1 to 1:5, 3:1 to 1:3, and preferably the volume ratio of the two liquids is 1:1.

[0039] According to the present invention, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine. Preferably, the fluorinated aromatic ring is a fluorinated benzene ring. More preferably, the fluorinated aromatic ring is a fluorinated benzene ring, and the aromatic polyaldehyde monomer contains the fluorinated benzene ring, while the aromatic polyamino monomer does not contain the fluorinated benzene ring.

[0040] According to the present invention, the fluorinated aromatic ring has two para-aldehyde groups or two para-amino groups connected thereto, at least one hydrogen atom of which is substituted with fluorine, and the fluorinated aromatic ring has a hydrogen atom not substituted with fluorine, preferably, the fluorinated aromatic ring has two para-aldehyde groups connected thereto, at least one hydrogen atom of which is substituted with fluorine, and the fluorinated aromatic ring has a hydrogen atom not substituted with fluorine, more preferably, the fluorinated aromatic ring has two para-aldehyde groups connected thereto, and one, two, or three hydrogen atoms of which are substituted with fluorine, and most preferably, the fluorinated aromatic ring has two para-aldehyde groups connected thereto, and the fluorinated aromatic ring is partially fluorinated.

[0041] The inventors unexpectedly discovered that COF compounds containing monofluorofluorinated aromatic rings, difluorofluorinated aromatic rings, and trifluorofluorinated aromatic rings have superior hydrogen storage properties compared to COF compounds containing fully fluorinated aromatic rings and non-fluorinated COF compounds. In particular, compared to COF compounds containing partially fluorofluorinated aromatic rings and COF compounds containing perfluorofluorinated aromatic rings, COF compounds containing partially fluorofluorinated aromatic rings have a much larger specific surface area and higher hydrogen storage capacity. Furthermore, to increase hydrogen storage capacity, the fluorinated moiety must be located on the aromatic ring (e.g., benzene ring) and cannot be located on other substituents connected to the aromatic ring (e.g., benzene ring).

[0042] Formula I shows a part of the molecular structure unit of the two-dimensional COF compound in the production example of the present invention, and the substituent R 1 ~R 4are independently selected from H, OCH3, and F. The inventors conducted theoretical studies and found that the dipole moments (molecular polarization index) of different substituents are shown in Table 1. As can be seen from Table 3, the introduction of monofluoro, partially fluoro, and trifluoro substituents increases the polarity of the substitution site on the benzene ring. The inventors discovered that introducing highly polar groups to specific sites on the aromatic ring can adjust the environment within the pores of COFs and increase their interaction with hydrogen molecules. This is an effective strategy for improving the heat of adsorption of the material, thereby favoring the hydrogen storage properties of COF materials.

[0043] TIFF2026503827000007.tif129170

[0044] Preferred conditions of the present invention will be further described below with reference to the drawings in conjunction with examples. It should be understood that the preferred examples described herein are merely for the purpose of explaining and interpreting the present invention, and are not intended to limit the present invention.

[0045] All raw materials or reagents used in the following preparation examples are commercially available or self-made.

[0046] [Manufacturing Example 1] Synthesis of two-dimensional fluorinated covalent organic framework compound TPB-DFTP-COF 1,3,5-Tris(4-aminophenyl)benzene (TPB) (0.1 mmol) and 2,5-difluoroterephthalaldehyde (DFTP) (0.15 mmol) were added to a 1 mL o-dichlorobenzene + n-butanol (o-DCB + n-BuOH, 1:1 volume ratio) mixed solvent and dissolved in the mixed solvent to obtain a mixture. Acetic acid (6 mol / L, 0.1 mL) was added to the mixture, which was then heated to 120 °C and incubated for 3 days. The reaction product was filtered, washed, and purified to obtain a fluorinated 2D COF named TPB-DFTP-COF. A schematic diagram of the synthesis process is shown in Figure 1(a).

[0047] [Manufacturing Example 2] Synthesis of three-dimensional fluorinated covalent organic framework compounds (3D-F-COFs) Tetrakis(4-aminophenyl)methane (0.1 mmol) and 2,5-difluoroterephthalaldehyde (0.2 mmol) were added to a dioxane + 1,3,5-trimethylbenzene (1 mL, 1:1 volume ratio) mixed solvent and dissolved in the mixed solvent to obtain a mixture. Acetic acid was added to the mixture, and the mixture was heated to 120 °C and incubated for 3 days. The reaction product was centrifuged and purified by Soxhlet extraction with tetrahydrofuran to obtain a fluorinated 3D-COF, named 3D-F-COF. A schematic diagram of the synthesis process is shown in Figure 1(b).

[0048] [Manufacturing Example 3 (Comparison)] Synthesis of two-dimensional methoxylated covalent organic framework compound TPB-DMTP-COF 1,3,5-Tris(4-aminophenyl)benzene (0.1 mmol) and 2,5-dimethoxyterephthalaldehyde (DMTP) (0.15 mmol) were added to a mixed solvent of o-dichlorobenzene and n-butanol (1 mL, 1:1 volume ratio) and dissolved in the mixed solvent to obtain a mixture. Acetic acid was added to the mixture, which was then heated to 120 °C and incubated for 3 days. The reaction product was filtered, washed, and purified to obtain a two-dimensional methoxylated COF named TPB-DMTP-COF. A schematic diagram of the synthesis process is shown in Figure 1(a).

[0049] [Manufacturing Example 4 (Comparison)] Synthesis of two-dimensional perfluorinated covalent organic framework compound TPB-TFTP-COF 1,3,5-Tris(4-aminophenyl)benzene (0.1 mmol) and 2,3,5,6-tetrafluoroterephthalaldehyde (0.15 mmol) were added to a 1 mL (1:1 volume ratio) mixed solvent of o-dichlorobenzene and n-butanol to obtain a mixture. Acetic acid was added to the mixture, which was then heated to 120 °C and incubated for 3 days. The reaction product was filtered, washed, and purified to obtain a two-dimensional perfluorinated COF named TPB-TFTP-COF.

[0050] [Production Example 5 (Comparison)] Synthesis of unsubstituted two-dimensional covalent organic framework compounds 1,3,5-tris(4-aminophenyl)benzene (0.1 mmol) and terephthalaldehyde (0.15 mmol) were added to a mixed solvent of o-dichlorobenzene and n-butanol (1 mL, 1:1 volume ratio) and dissolved in the mixed solvent to obtain a mixture. Acetic acid was added to the mixture, and the mixture was heated to 120 °C and incubated for 3 days. The reaction product was filtered, washed, and purified to obtain a two-dimensional fluorine-free COF named 2D-F-less-COF.

[0051] [Production Example 6 (Comparison)] Synthesis of three-dimensional methoxylated covalent organic framework compound 3D-MeO-COF Tetrakis(4-aminophenyl)methane (0.1 mmol) and 2,5-dimethoxyterephthalaldehyde (0.2 mmol) were dissolved in a dioxane + 1,3,5-trimethylbenzene (1 mL, 1:1 volume ratio) mixture. Acetic acid was added to the mixture, which was then heated to 120 °C and incubated for 3 days. The reaction product was centrifuged and purified by Soxhlet extraction with tetrahydrofuran to obtain a fluorinated 3D methoxylated COF, designated 3D-MeO-COF, as shown in Figure 1(b).

[0052] [Production Example 7 (Comparison)] Synthesis of unsubstituted three-dimensional covalent organic framework compound COF-300 Tetrakis(4-aminophenyl)methane (0.1 mmol) and terephthalaldehyde (0.2 mmol) were dissolved in a dioxane + 1,3,5-trimethylbenzene (1 mL, 1:1 volume ratio) mixture. Acetic acid was added to the mixture, which was then heated to 120 °C and incubated for 3 days. The reaction product was centrifuged and purified by Soxhlet extraction with tetrahydrofuran to obtain a fluorinated 3D COF named COF-300, shown in Figure 1(b).

[0053] Table 2 shows the properties and state of the compounds obtained in Production Examples 1 to 7, and their crystal structures were analyzed using powder crystal X-ray diffraction (XRD). The results are shown in Figures 2(a) to 2(g).

[0054] TIFF2026503827000008.tif112170

[0055] 2(a) and 2(c), a comparison of the powder crystal X-ray diffraction results of TPB-DMTP-COF and TPB-DFTP-COF indicates that there is no significant difference in the crystal structure of 2D covalent organic frameworks containing fluorine groups compared to 2D covalent organic frameworks containing methoxy groups. Referring to Fig. 2(b) and 2(f), a comparison of the powder crystal X-ray diffraction results of 3D-F-COF and 3D-MeO-COF further indicates that the introduction of fluorine groups does not significantly affect the crystal structure of 3D covalent organic frameworks.

[0056] Figure 2(e) shows the X-ray diffraction spectrum of the two-dimensional fluorine-free covalent organic framework compound obtained in Preparation Example 5. There are no clear crystalline characteristic peaks, indicating that the crystallinity of the 2D-F-free-COF is poor.

[0057] Example 1 (BET specific surface area measurement and hydrogen storage capacity measurement) A portion of the obtained covalent organic framework compound was subjected to BET specific surface area measurement and hydrogen storage capacity measurement using a gas adsorption apparatus.

[0058] The atmospheric pressure gas adsorption apparatus used was a BELSORP-max II manufactured by MicrotracBEL.

[0059] The high-pressure hydrogen adsorption apparatus used was a Micromerics Instrument Corporation HPVA-100 high-pressure volumetric analyzer.

[0060] The BET specific surface area was determined from the N2 adsorption isotherm at 77 K, and the surface area of ​​the material was calculated using the BET (Brunauer-Emmett-Teller) equation.

[0061] The hydrogen storage capacity at 77K under atmospheric pressure was measured by using an atmospheric pressure gas adsorption analyzer and determining the hydrogen adsorption isotherm by the dynamic volumetric method.

[0062] The hydrogen storage capacity at 77K and high pressure was measured by using a high-pressure gas adsorption analyzer to obtain the high-pressure adsorption isotherm of hydrogen by the static volumetric method.

[0063] The measured BET specific surface area, hydrogen storage capacity at 77 K under normal pressure, and hydrogen storage capacity at 77 K under high pressure (80 bar) are shown in Table 3.

[0064] TIFF2026503827000009.tif147170

[0065] As shown in Figures 4(a) to 4(c), the inventors discovered that the specific surface area of ​​partially fluorinated COFs is not significantly different from that of methoxylated COFs and fully fluorinated COFs, regardless of whether the COFs are 2D or 3D COFs, and the hydrogen adsorption capacity is significantly increased. This indicates that the improvement in the hydrogen adsorption properties of COF compounds obtained by fluorination treatment using partial fluorination is not due to an increase in the specific surface area, but rather to the introduction of partial fluoro substituents. Therefore, fluorination treatment to introduce partial fluoro substituents is a simple, versatile, and effective strategy for improving the hydrogen storage properties of COF compounds.

[0066] Referring to Figures 5(a) and 5(b), the fluorination treatment method of the present invention significantly increased the hydrogen storage capacity of the two-dimensional and three-dimensional covalent organic framework compounds under high-pressure hydrogen storage conditions.

[0067] The inventors of the present invention performed simulation calculations on the adsorption energy of the material obtained by the method of the present invention, and the results are shown in Table 4 to evaluate the influence of the method of the present invention on the hydrogen adsorption properties of the material. The simulation calculations were performed using the CASTEP module built into the materials calculation software Materials Studio (commercially available from Accelrys, Inc., USA). The results of the simulation calculations show that the fluorination treatment method by introducing partial fluoro substituents can significantly improve the adsorption energy.

[0068] TIFF2026503827000010.tif176170

[0069] Industrial Practicality The covalent organic framework compounds obtained by the processing method of the present invention can store hydrogen at a practical level, making it easier to use hydrogen, and will have more general practical value as the hydrogen society comes about.

Claims

1. A method for improving the hydrogen storage properties of a covalent organic framework compound, comprising: forming a covalent organic framework compound by dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer, wherein the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the covalent organic framework compound has a two-dimensional or three-dimensional structure.

2. 1. Use of a fluorinated covalent organic framework compound as a hydrogen storage medium, wherein the fluorinated covalent organic framework compound is formed by dehydration polycondensation of an aromatic polyamino monomer and an aromatic polyaldehyde monomer, the aromatic polyamino monomer and / or the aromatic polyaldehyde monomer contains at least one fluorinated aromatic ring, at least one hydrogen atom on the fluorinated aromatic ring is substituted with fluorine, and the fluorinated aromatic ring has hydrogen atoms that are not substituted with fluorine, and the fluorinated covalent organic framework compound has a two-dimensional or three-dimensional structure.

3. 3. The method according to claim 1 or the use according to claim 2, wherein the fluorinated aromatic ring is selected from a benzene ring, a naphthalene ring, an anthracene ring, a phenanthrene ring, or a pyrene ring.

4. 3. The method according to claim 1 or the use according to claim 2, wherein the fluorinated aromatic ring is a benzene ring.

5. The aromatic polyaldehyde monomer contains one of the fluorinated aromatic rings, and the fluorinated aromatic ring contains two paraldehyde groups, and the aromatic polyamino monomer has the following structure:

3. The method according to claim 1 or the use according to claim 2, wherein R is an amino group or a 4-aminophenyl group.

6. The aromatic polyamino monomer contains one of the fluorinated aromatic rings, and the fluorinated aromatic ring contains two para-amino groups. The aromatic polyaldehyde monomer has the following structure:

3. The method according to claim 1 or the use according to claim 2, wherein R is an aldehyde group or a 4-aldehyde phenyl group.

7. The method according to claim 1 or the use according to claim 2, wherein the aromatic polyamino monomer is 1,3,5-tris(4-aminophenyl)benzene or tetrakis(4-aminophenyl)methane.

8. The method according to claim 1 or the use according to claim 2, wherein the aromatic polyaldehyde monomer is 2,5-difluoroterephthalaldehyde.

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