Pyrimidyl full-conjugated structure covalent organic framework material, catalyst containing pyrimidyl full-conjugated structure covalent organic framework material, and preparation method and application thereof

Abstract

The invention relates to a pyrimidyl full-conjugated structure covalent organic framework material, a catalyst containing the pyrimidyl full-conjugated structure covalent organic framework material and a preparation method and application thereof. The preparation method of the pyrimidyl full-conjugated structure covalent organic framework material comprises the following steps: (1) dissolving an aldehyde precursor and a methyl precursor containing a bipyrimidine structure in an organic mixed solvent, fully dispersing, and adding a catalyst to obtain a mixed solution; the organic mixed solvent is composed of mesitylene, 1, 4-dioxane and acetonitrile, and the catalyst is trifluoroacetic acid; (2) sequentially carrying out liquid nitrogen freezing-vacuumizing-unfreezing cyclic operation, vacuum sealing and secondary unfreezing on the obtained mixed solution to room temperature, and reacting at the temperature of 120-150 DEG C to obtain a crude product; and (3) deblocking the reaction system of the obtained crude product, and then carrying out solid-liquid separation, washing, Soxhlet extraction and drying to obtain the pyrimidyl covalent organic framework material with the fully conjugated structure.

Description

Technical Field

[0001] The present invention belongs to the field of covalent organic framework material preparation and catalyst preparation, and relates to a covalent organic framework material with a pyrimidine-based fully conjugated structure, a catalyst containing the same, and a preparation method and application thereof. Background Art

[0002] Single-atom catalysts (SACs) have attracted extensive research interest in recent years due to their advantages over both homogeneous and heterogeneous catalysts. However, on the other hand, limited by a single, isolated active site, single-atom catalysts cannot be applied to complex chemical reactions involving multiple intermediates. In contrast, bimetallic single-atom catalysts (DSACs) not only have electronic interactions between atomic-level sites, but also exhibit synergistic catalytic functions. Compared with traditional single-atom catalysts, the two metal atoms in bimetallic single-atom catalysts can work synergistically to reduce thermal / kinetic reaction energy barriers, regulate reaction pathways, and break the linear proportional relationship that limits the activity limit of multi-intermediate reactions. However, the current precise synthesis strategies for bimetallic single-atom catalysts are very scarce, which seriously affects the application progress of bimetallic single-atom catalysts.

[0003] As an emerging two-dimensional material, covalent organic frameworks (COFs) are composed of lightweight elements such as carbon, hydrogen, oxygen, and nitrogen. They offer diverse structural units, high specific surface area, good chemical stability, and adjustable pore size, making them effective supports for anchoring active metals. Prior research has explored the use of COFs as effective supports for single atoms in the preparation of catalysts. For example, a Chinese patent (publication number CN113322474A) discloses the use of 1,3,6,8-tetrakis(4-formaldehydephenyl)pyrene as an aldehyde precursor and 2,2'-([2,2'-bipyridine]-5,5'-diyl)diacetonitrile as a cyano precursor to prepare a fully conjugated COF material to achieve the loading of single-atom metal cobalt. Although the performance of the catalyst in the electrochemical catalytic oxygen evolution reaction can be improved, when 2,2'-([2,2'-bipyridine]-5,5'-diyl)diacetonitrile containing a cyano group is used as the structural unit of the fully conjugated COF, one bipyridine group can only coordinately bond with one metal atom, resulting in a low single-atom metal loading and a small number of metal active sites, which limits the further improvement of the catalytic performance. Summary of the Invention

[0004] In view of the problems existing in the above-mentioned prior art, the object of the present invention is to provide a novel covalent organic framework material with a pyrimidine-based fully conjugated structure, a catalyst containing the same, and a preparation method and application thereof.

[0005] Another object of the present invention is to provide a pyrimidine-based conjugated COF-supported metal single atom pair catalyst with simple synthesis process, low cost, and environmental protection, as well as its preparation method and application.

[0006] The first aspect of the present invention provides a covalent organic framework material with a pyrimidine-based fully conjugated structure, wherein the covalent organic framework material with a pyrimidine-based fully conjugated structure is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds, wherein the covalent organic framework material has a bipyrimidine structure and has a fully conjugated structure connected by carbon-carbon double bonds.

[0007] Preferably, the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde, and the methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine.

[0008] Preferably, the half-peak width of the covalent organic framework material with a fully conjugated pyrimidine structure is 0.5 to 2.0 degrees, preferably 0.8 to 1.5 degrees;

[0009] Preferably, the specific surface area of ​​the pyrimidine-based fully conjugated covalent organic framework material is 60 to 600 m 2 / g, preferably 200 to 600 m 2 / g, more preferably 400 to 600 m 2 / g.

[0010] Preferably, the covalent organic framework material of the pyrimidine-based fully conjugated structure comprises a repeating unit represented by formula (1) and / or a repeating unit represented by formula (2):

[0011]

[0012]

[0013] The second aspect of the present invention provides a method for preparing a covalent organic framework material with a pyrimidine-based fully conjugated structure, comprising the following steps:

[0014] (1) dissolving an aldehyde precursor and a methyl precursor containing a bipyrimidine structure in an organic mixed solvent, fully dispersing them, and then adding a catalyst to obtain a mixed solution; the organic mixed solvent comprises mesitylene, 1,4-dioxane, and acetonitrile, and the catalyst is trifluoroacetic acid;

[0015] (2) subjecting the obtained mixed solution to a cycle of liquid nitrogen freezing-vacuuming-thawing, vacuum sealing, secondary thawing to room temperature, and then reacting at a temperature of 120-150° C. to obtain a crude product;

[0016] (3) The reaction system of the crude product is unsealed, and then solid-liquid separation, washing, Soxhlet extraction and drying are performed to obtain a covalent organic framework material with a fully conjugated pyrimidine structure.

[0017] Based on the use of an aldehyde precursor and a methyl precursor containing a bipyrimidine structure as monomers, the present invention creatively employs a specific composition of an organic mixed solvent (composed of mesitylene, 1,4-dioxane, and acetonitrile) and a specific composition of a catalyst (trifluoroacetic acid). Under the combined action of a specific type and ratio of solvent and catalyst, a covalent organic framework material with a pyrimidine-based fully conjugated structure is prepared with high crystallinity and a high specific surface area. Moreover, the reaction of the present application is an aldol condensation reaction, which does not require further quenching reaction.

[0018] Preferably, in step (1): the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde, and the methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine;

[0019] Preferably, in step (1), the concentration of the aldehyde precursor in the mixed solution is 0.1 to 0.2 mol / L, and the concentration of the methyl precursor containing a bipyrimidine structure in the mixed solution is 0.05 to 0.1 mol / L, preferably, the concentration of the aldehyde precursor is twice the concentration of the methyl precursor containing a bipyrimidine structure;

[0020] Preferably, in step (1): the ratio of the total volume of mesitylene and 1,4-dioxane to the volume of acetonitrile in the organic mixed solvent is 2:(0.09-0.12), wherein the volume ratio of mesitylene and 1,4-dioxane is (1-4):(4-1), preferably (1-2):(2-1).

[0021] Preferably, in step (1), the volume ratio of the organic mixed solvent to the catalyst is (2-6):1, preferably (4-6):1, and more preferably 5.25:1.

[0022] Preferably, in step (2), the reaction is a constant temperature reaction; and the time of the constant temperature reaction is 72 to 120 hours.

[0023] Preferably, in step (3): the Soxhlet extraction is performed using tetrahydrofuran; preferably, the Soxhlet extraction time is 12 to 36 hours.

[0024] Preferably, the drying is vacuum drying; preferably, the temperature of the vacuum drying is 100 to 120° C., and the time is 12 to 24 hours.

[0025] The third aspect of the present invention provides a pyrimidine-based conjugated COF-supported metal single atom pair catalyst, wherein the pyrimidine-based conjugated COF-supported metal single atom pair catalyst comprises:

[0026] A covalent organic framework material with a pyrimidine-based fully conjugated structure, wherein the covalent organic framework material with a pyrimidine-based fully conjugated structure is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds, wherein the covalent organic framework material has a bipyrimidine structure and has a fully conjugated structure connected by carbon-carbon double bonds; and

[0027] A plurality of metal single atom pairs are connected to the covalent organic framework material via coordination bonds, wherein the two metal atoms in each metal single atom pair are respectively coordinated and bonded to the two bidentate N sites in the same bipyrimidine group in the form of ions.

[0028] Preferably, each metal single atom pair is selected from one of platinum atoms, manganese atoms, iron atoms, cobalt atoms, nickel atoms, copper atoms, zinc atoms, ruthenium atoms, rhodium atoms, palladium atoms and iridium atoms.

[0029] Preferably, the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde; and the methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine.

[0030] Preferably, the covalent organic framework material of the pyrimidine-based fully conjugated structure comprises a repeating unit represented by formula (1) and / or a repeating unit represented by formula (2):

[0031]

[0032]

[0033] Preferably, the loading amount of the metal atoms is 2 to 20 wt%, preferably 10 to 20 wt%.

[0034] Preferably, the distance between two metal atoms in the metal single atom pair is 0.7 to 0.9 nanometers (eg, 0.79 nanometers).

[0035] The fourth aspect of the present invention provides a method for preparing the above-mentioned pyrimidine-based conjugated COF-loaded metal single atom pair catalyst, comprising: mixing a covalent organic framework material with a pyrimidine-based fully conjugated structure, a soluble metal salt and a solvent, heating while stirring to achieve the coordination loading of metal ions on the covalent organic framework material, and then separating and purifying to obtain a pyrimidine-based conjugated COF-loaded metal single atom pair catalyst.

[0036] Preferably, the molar ratio of the covalent organic framework material of the pyrimidine-based fully conjugated structure to the soluble metal salt is 1:2 to 1:3;

[0037] And / or, the soluble metal salt is selected from at least one of metal nitrate, ethylenediamine nitrate metal ion salt, metal chloride and metal bromide; preferably, the metal ion in the soluble metal salt is selected from one of platinum ion, manganese ion, iron ion, cobalt ion, nickel ion, copper ion, zinc ion, ruthenium ion, rhodium ion, palladium ion and iridium ion;

[0038] And / or, the solvent is selected from at least one of water, acetonitrile, methanol, ethanol, 10% hydrobromic acid aqueous solution and 10% HCl aqueous solution, or a combination thereof.

[0039] Preferably, the soluble metal salt is selected from ethylenediamine platinum nitrate, manganese chloride, ferric chloride, cobalt chloride, and nickel chloride.

[0040] Preferably, the solvent is a mixed solution of water / acetonitrile; water / methanol; or 10% HCl aqueous solution / ethanol.

[0041] Preferably, the stirring speed is 400 to 800 rpm, more preferably 400 to 600 rpm.

[0042] Preferably, the heating temperature is 60-70°C.

[0043] Preferably, the heating time is 6 to 8 hours.

[0044] Preferably, the heating is performed under a nitrogen atmosphere and / or an inert atmosphere; more preferably, the inert atmosphere is an argon atmosphere.

[0045] The fifth aspect of the present invention provides an application of the above-mentioned pyrimidine-based conjugated COF-loaded metal single atom pair catalyst in the field of electrocatalysis, wherein the electrocatalytic field is electrochemical catalytic oxygen reduction reaction, electrocatalytic hydrogen evolution reaction or electrocatalytic carbon dioxide reduction reaction.

[0046] Beneficial effects of the present invention:

[0047] (1) In the present invention, a covalent organic framework material with a pyrimidine-based fully conjugated structure having excellent crystallinity and specific surface area was prepared for the first time.

[0048] (2) This invention proposes for the first time a strategy for preparing catalysts by loading monodisperse metal single atom pairs (e.g., Pt single atom pairs) on the surface of fully conjugated carbon-carbon double-bonded carbon-fiber (COF) materials. Specifically, by fixing metal active sites at bipyrimidine sites on the COF material skeleton, the structure and concentration of the active center can be controlled, which can significantly increase the loading of metal single atoms. In addition, the fully conjugated structure connected by carbon-carbon double bonds can provide a fast electron transfer channel, providing a guarantee for the electrochemical application of the catalyst.

[0049] (3) The present invention provides a method for synthesizing pyrimidine-based conjugated COF-supported metal single atom pairs, which exhibit significant advantages. Synergistic metal single atom pairs can be prepared, altering the oxygen adsorption configuration, achieving cleavage of the O-O bond, and improving the efficiency and selectivity of the oxygen reduction reaction. Furthermore, the method is scalable and universal, and can be widely applied to different transition metal species. A variety of catalysts with different functions can be prepared as needed. In particular, by using different metals, synergistic bimetallic single atom pairs can be achieved on COFs.

[0050] (4) Unlike the traditional high-temperature calcination and pyrolysis methods for preparing catalysts, the preparation method of the pyrimidine-based conjugated COF-loaded metal single atom catalyst of the present invention not only has mild conditions, high yield, cheap and readily available raw materials, an environmentally friendly production process, low energy consumption, and green environmental protection, but can be produced and applied on a large scale, and has good economic benefits and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a flow chart for the preparation of the Pmd-PA-MXn catalyst in Example 10.

[0052] Figure 2 This is a flow chart for the preparation of the Pmd-BDPA-MXn catalyst in Example 11.

[0053] Figure 3 This is the X-ray diffraction pattern of the Pmd-PA-COF material in Example 1.

[0054] Figure 4 This is the X-ray diffraction pattern of the Pmd-BDPA-COF material in Example 2.

[0055] Figure 5 Schematic diagram of the structure of the Pmd-PA-COF material in Example 1.

[0056] Figure 6 Schematic diagram of the structure of the Pmd-BDPA-COF material in Example 2.

[0057] Figure 7This is the spherical aberration corrected electron microscope image of the Pmd-PA-PtN4 material in Example 10.

[0058] Figure 8 This is the LSV curve of the electrochemical catalytic oxygen reduction of the Pmd-PA-PtN4 material in Example 10.

[0059] Figure 9 Nitrogen adsorption and desorption test curves of the materials obtained in Examples 3-11 DETAILED DESCRIPTION

[0060] The present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, those skilled in the art will be able to make several changes and improvements without departing from the scope of the present invention, all of which fall within the scope of protection of the present invention.

[0061] In the present disclosure, the covalent organic framework material with a fully conjugated pyrimidine structure is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds. Preferably, the molar ratio of the structural units derived from the aldehyde precursor and the structural units derived from the methyl precursor containing a bipyrimidine structure is 2:1. According to X-ray diffraction, the half-peak width of the covalent organic framework material with a fully conjugated pyrimidine structure is 0.5 to 2.0 degrees, preferably 0.8 to 1.5 degrees. According to nitrogen adsorption and desorption tests, the specific surface area of ​​the covalent organic framework material with a fully conjugated pyrimidine structure is 60 to 600 m 2 / g, preferably 200 to 600 m 2 / g, more preferably 400 to 600 m 2 The pyrimidine-based fully conjugated covalent organic framework material of the present invention has a porous structure. When the crystallinity is poor, the pore structure collapses and the specific surface area is low. Therefore, there is a positive correlation between the crystallinity (half-maximum width) and the specific surface area.

[0062] In one embodiment of the present invention, the pyrimidine-based fully conjugated covalent organic framework material is obtained by reacting 1,4-terephthalaldehyde or 4,4'-biphenyldicarboxaldehyde as an aldehyde precursor and 4,4',6,6'-tetramethyl-2,2'-bipyrimidine as a methyl precursor containing a bipyrimidine structure. The structure of the pyrimidine-based fully conjugated covalent organic framework material is shown in Formula (1) and / or Formula (2):

[0063]

[0064]

[0065] In one embodiment of the present invention, a bipyrimidine structural building block containing an active methyl group is first prepared through organic synthesis, and then a pyrimidine-based fully conjugated covalent organic framework material is prepared through an Aldol condensation reaction. The following is an exemplary method for preparing a pyrimidine-based fully conjugated covalent organic framework material.

[0066] An aldehyde precursor and a methyl precursor containing a bipyrimidine structure are dissolved in an organic mixed solvent, and after being fully dispersed, a catalyst is added (for example, dropped) to obtain a mixed solution. Preferably, the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde. The methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine. In the mixed solution, the concentration of the aldehyde precursor is 0.1 to 0.2 mol / L, and the concentration of the methyl precursor is 0.05 to 0.1 mol / L, and the concentration of the aldehyde precursor is preferably controlled to be twice the concentration of the methyl precursor containing the bipyrimidine structure. For example, the concentration of the aldehyde precursor is 0.1 mol / L, and the concentration of the methyl precursor is 0.05 mol / L. The organic mixed solvent consists of mesitylene, 1,4-dioxane and acetonitrile. The catalyst is trifluoroacetic acid.

[0067] In a preferred embodiment of the present invention, the total volume of mesitylene and 1,4-dioxane is 2 mL and the volume ratio is (1-4): (4-1), preferably (1-2): (2-1), and most preferably 1:1, and the volume of acetonitrile is 0.09-0.12 mL, preferably 0.1 mL. If the mesitylene content is too high or the acetonitrile content is too low, the polarity of the mixed solvent is small, the reaction monomer cannot be completely dissolved, and the resulting material has poor crystallinity, resulting in a poor specific surface area. If the mesitylene content is too low or the acetonitrile content is too high, the polarity of the mixed solvent is large, nucleation is difficult during the crystallization process, and the resulting material has no crystallinity, resulting in a poor specific surface area.

[0068] In a preferred embodiment of the present invention, the volume ratio of the organic mixed solvent to the catalyst is (2-6):1, preferably (4-6):1, and more preferably 5.25:1, so that the resulting pyrimidine-based fully conjugated covalent organic framework material has excellent crystallinity and specific surface area. If the catalyst content is too high, the reaction rate is too fast and the crystallinity is poor, resulting in a poor specific surface area. If the catalyst content is too low, the reaction cannot proceed fully, and a periodic network structure cannot be formed, and its crystallinity is poor, resulting in a poor specific surface area.

[0069] The mixed solution is subjected to a cycle of liquid nitrogen freezing, vacuuming, and thawing, vacuum-sealed, and thawed to room temperature for a second time. The solution is then placed in an oven for a period of isothermal reaction to obtain a crude product. The isothermal reaction temperature is 120-150°C. The isothermal reaction time is 72-120 hours, preferably 72-96 hours. The liquid nitrogen freezing time is 300-600 seconds. After the reaction system is frozen, the system is evacuated to a vacuum degree of less than 100 Pa and maintained under vacuum for 10-15 minutes. The solution is then thawed to room temperature to allow the dissolved oxygen in the solution to precipitate. This liquid nitrogen freezing, vacuuming, and thawing cycle is repeated at least three times. The vacuum degree of the vacuum seal is less than 100 Pa. The parameters for the second thawing to room temperature are: thawing at room temperature.

[0070] The reaction system of the crude product is unsealed, and then subjected to solid-liquid separation, solid washing, Soxhlet extraction, and subsequent drying to obtain a covalent organic framework material (or fully conjugated COF material, fully conjugated COF solid powder, or COF material) with a carbon-carbon double bond-connected pyrimidine-based fully conjugated structure. The solid-liquid separation is centrifugation or filtration. The solvent for washing the solid contains at least one of acetone, tetrahydrofuran, and methanol, for example, acetone, tetrahydrofuran, and methanol in that order. Tetrahydrofuran is preferably used for Soxhlet extraction, the purpose of which is to replace the organic mixed solution in the crude product while removing unreacted monomers. The Soxhlet extraction time is 12 to 36 hours. The drying is vacuum drying. The temperature of the vacuum drying is 100 to 120°C, and the time is 12 to 24 hours.

[0071] In one embodiment of the present invention, the pyrimidine-based conjugated covalent organic framework-supported single atom pair catalytic material comprises: a pyrimidine-based fully conjugated covalent organic framework material (referred to as fully conjugated COF material) and a metal single atom pair. Wherein, the pyrimidine-based fully conjugated covalent organic framework material is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by a carbon-carbon double bond. The metal atom pair is loaded in the skeleton of the covalent organic framework in the form of ions, wherein the two metal atoms in each metal atom pair are coordinately bonded to the same bipyrimidine group, that is, the metal atoms are in the form of bimetallic single atom pairs.

[0072] In one embodiment of the present invention, the fully conjugated covalent organic framework material is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds, wherein the molar ratio of the structural units derived from the aldehyde precursor and the structural units derived from the methyl precursor containing a bipyrimidine structure is 2:1.

[0073] In one embodiment of the present invention, each metal single atom pair includes, but is not limited to, one of a platinum atom, a manganese atom, an iron atom, a cobalt atom, a nickel atom, a copper atom, a zinc atom, a ruthenium atom, a rhodium atom, a palladium atom, and an iridium atom. Since the metal atom pairs are supported in the form of ions, each metal single atom pair can also be referred to as each metal ion pair, and each metal ion pair includes, but is not limited to, a platinum ion, a manganese ion, an iron ion, a cobalt ion, a nickel ion, a copper ion, a zinc ion, a ruthenium ion, a rhodium ion, a palladium ion, and an iridium ion.

[0074] In one embodiment of the present invention, the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde. The methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine.

[0075] In the present invention, the bipyrimidine structure is introduced into the COF skeleton, which can realize the construction of a bimetallic single atom pair. The two bidentate N sites in each bipyrimidine group can bind to two metal ions to form a metal single atom pair. Moreover, the binuclear complex of the bipyrimidine structure has a planar configuration, which is conducive to full contact between the substrate and the metal site, thereby improving the mass transfer rate. In addition, the present invention utilizes a fully conjugated COF skeleton connected by a carbon-carbon double bond, which is conducive to improving its electron transport performance. In particular, the bipyrimidine structure is evenly distributed in the COF skeleton, providing evenly distributed metal coordination sites, which is conducive to the anchoring and loading of monodisperse metal sites, showing excellent performance in the field of electrocatalysis and has good application prospects.

[0076] In one embodiment of the present invention, the pyrimidine-based conjugated COF-supported metal single atom pair catalyst comprises a spherical carbon-carbon double-bonded fully conjugated pyrimidine-based COF material and a monodispersed metal single atom pair supported on the COF material. The carbon-carbon double-bonded fully conjugated COF material is prepared by an aldol condensation reaction of a 4,4',6,6'-tetramethyl-2,2'-bipyrimidine precursor containing an active methyl group and a 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde precursor containing an aldehyde group.

[0077] In one embodiment of the present invention, the distance between the two metal ions in each metal atom pair is 0.7 to 0.9 nanometers, preferably 0.79 nanometers, and is measured using synchrotron radiation.

[0078] In one embodiment of the present invention, the loading amount of the metal single atom pairs is 2 to 20 wt%, preferably 10 to 20 wt%.

[0079] In one embodiment of the present invention, a pyrimidine-based fully conjugated covalent organic framework (COF) material and a soluble metal salt are dispersed in a solvent using a liquid-phase impregnation method. The resulting material is then stirred, heated, separated, and purified to produce a pyrimidine-based conjugated covalent organic framework (COF)-supported single-atom pair catalytic material. By manipulating the type of soluble metal salt and solvent, the present invention can further control the structure and coordination configuration of the metal single-atom pairs.

[0080] In one embodiment of the present invention, the preparation method of the pyrimidinyl conjugated COF-supported bimetallic single atom pair catalyst is simple and efficient, covers a wide range of metal types, has mild preparation conditions, is low cost, has a simple process, has controllable active site structure and concentration, has high yield, and can easily control reaction process conditions. The following exemplifies the preparation method of the pyrimidinyl conjugated COF-supported bimetallic single atom pair catalyst provided by the present invention.

[0081] The COF material, a soluble metal salt (or soluble metal complex), and a suitable solvent are mixed and heated while stirring for liquid phase loading (i.e., coordination loading) to obtain a product. Preferably, the soluble metal salt is selected from at least one of metal nitrates, ethylenediamine metal nitrates, metal chlorides, and metal bromides; the metal ions in the soluble metal salt are selected from one of platinum ions, manganese ions, iron ions, cobalt ions, nickel ions, copper ions, zinc ions, ruthenium ions, rhodium ions, palladium ions, and iridium ions. For example, the soluble metal salt is one of ethylenediamine platinum nitrate, manganese chloride, iron chloride, cobalt chloride, nickel chloride, copper chloride, zinc chloride, ruthenium chloride, rhodium chloride, palladium chloride, iridium chloride, platinum chloride, etc. The suitable solvent is at least one of methanol, water, 10% hydrochloric acid solution, 10% hydrobromic acid solution, acetonitrile, or a combination thereof. For example, the solvent is a water / acetonitrile mixed solution, a water / methanol mixed solution, or a 10% HCl aqueous solution / ethanol mixed solution. The combination of soluble metal salts and solvents is optimized, specifically as follows: a combination of ethylenediamine platinum nitrate and a water / acetonitrile mixed solution, a combination of metal chloride and a 10% HCl aqueous solution / ethanol mixed solution, and a combination of metal chloride and a water / methanol mixed solution. The stirring speed is 400 to 800 rpm, preferably 400 to 600 rpm. The molar ratio of the fully conjugated covalent organic framework material and the soluble metal salt is 1:2 to 1:3. The heating temperature is 60 to 70°C. The heating and stirring are carried out simultaneously, and the heating (stirring) time is 6 to 8 hours. The heating is carried out under a nitrogen atmosphere and / or an inert atmosphere; preferably, the inert atmosphere is an argon atmosphere.

[0082] The product is separated and purified to obtain a carbon-carbon double-bonded pyrimidine-based conjugated COF-supported metal single atom pair catalyst. The separation method is filtration. The purification method is washing with at least one of acetone, tetrahydrofuran, and methanol. Preferably, the product is dried after purification. The drying method is vacuum drying, etc. The filtration, purification, and drying are all conventional methods in the art.

[0083] In one embodiment of the present invention, the pyrimidine-based covalent organic framework-loaded metal single atom pair catalytic material can be used to construct a catalyst system, which has high potential industrial application value in the field of energy catalysis and is preferably suitable for electrocatalytic hydrogen evolution reaction, oxygen reduction reaction, and carbon dioxide reduction reaction.

[0084] In a preferred embodiment of the present invention, a pyrimidine-based conjugated COF material negative metal single atom pair catalyst can be used for the electrochemical oxygen reduction reaction. The specific steps are: the pyrimidine-based fully conjugated COF-loaded metal single atom pair catalyst is mixed with conductive carbon black, ethanol, and Nafion binder, and then ultrasonically dispersed to obtain a catalyst ink; a certain amount of this ink is evenly coated on the surface of carbon paper using a pipette, and dried to obtain a working electrode; the electrochemical oxygen reduction performance is then tested in a three-electrode system, wherein a carbon rod serves as the counter electrode, a Hg / HgO electrode serves as the reference electrode, and a 0.1M KOH solution serves as the electrolyte.

[0085] Example 1

[0086] (1) Accurately weigh 26.8 mg (0.2 mmol) of 1,4-terephthalaldehyde and 23.8 mg (0.11 mmol) of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine and add them to a reaction tube. Then, add 1 mL of mesitylene and 1 mL of 1,4-dioxane. After ultrasonically dispersing the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution.

[0087] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 72 hours to obtain a crude product;

[0088] (3) After the reaction, the reaction system was unsealed and subjected to solid-liquid separation. The solid was washed with acetone, tetrahydrofuran, and methanol in sequence. The solid was separated by filtration and wrapped with filter paper. It was then Soxhlet extracted with tetrahydrofuran for 12 h and then vacuum dried at 100 °C for 12 h to obtain a fully conjugated COF solid powder connected by carbon-carbon double bonds.

[0089] The X-ray diffraction pattern of the fully conjugated COF solid powder connected by carbon-carbon double bonds in Example 1 is as follows: Figure 3As shown in the figure, it can be seen that the COF has good crystallinity (half-peak width is 1.5 degrees). The structural schematic diagram of the COF obtained by structural simulation is shown in Figure 5 As shown in the figure, it can be seen that the COF presents an AA stacking structure.

[0090] Example 2

[0091] (1) Accurately weigh 42.05 mg (0.2 mmol) of 4,4'-biphenyldicarboxaldehyde and 23.8 mg (0.11 mmol) of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0092] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 72 hours to obtain a crude product;

[0093] (3) After the reaction is completed, the reaction system is unsealed, the solid and the liquid are separated, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and wrapped with filter paper. It is then Soxhlet extracted with tetrahydrofuran for 12 hours, and then vacuum dried at 100°C for 24 hours to obtain a COF solid powder connected by a carbon-carbon double bond.

[0094] The X-ray diffraction pattern of the COF solid powder connected by carbon-carbon double bonds in Example 2 is as follows: Figure 4 As shown in the figure, it can be seen that the COF has good crystallinity (half-peak width is 0.8 degrees). The structural schematic diagram of the COF obtained by structural simulation is shown in Figure 6 As shown in the figure, it can be seen that the COF presents an AA stacking structure.

[0095] Example 3

[0096] Example 3 A COF solid powder with carbon-carbon double bonds was prepared by a method substantially the same as that of Example 2, except that 1.33 mL of mesitylene and 0.67 mL of 1,4-dioxane were used in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in No. 1.

[0097] Example 4

[0098] Example 4 A COF solid powder with carbon-carbon double bonds was prepared by a method substantially the same as that of Example 2, except that 1.5 mL of mesitylene and 0.5 mL of 1,4-dioxane were used in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in No. 2.

[0099] Example 5

[0100] Example 5 A COF solid powder with carbon-carbon double bonds was prepared by the same method as in Example 2, except that 700 μL trifluoroacetic acid was used in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 3.

[0101] Example 6

[0102] Example 7 A COF solid powder with carbon-carbon double bonds was prepared by the same method as in Example 2, except that 525 μL trifluoroacetic acid was used in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 4.

[0103] Example 7

[0104] Example 7 A COF solid powder with carbon-carbon double bonds was prepared by a method substantially the same as that of Example 2, except that 350 μL of trifluoroacetic acid was used in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 5.

[0105] Example 8

[0106] Example 8 COF solid powder was prepared by the same method as Example 2, except that: in step (1), 1.6 mL of mesitylene and 0.4 mL of 1,4-dioxane were added, and the nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 6.

[0107] Example 9

[0108] Example 9 uses the same method as Example 2 to prepare COF solid powder, except that 0.67 mL of mesitylene and 1.33 mL of 1,4-dioxane are added in step (1). The nitrogen adsorption-desorption curve is as follows: Figure 9 As shown in number 7.

[0109] Example 10

[0110] Example 10: COF solid powder was prepared by the same method as Example 2, except that 0.4 mL of mesitylene and 1.6 mL of 1,4-dioxane were added in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 8.

[0111] Example 11

[0112] Example 11 COF solid powder was prepared by the same method as Example 2, except that 1050 μL trifluoroacetic acid was added in step (1). The nitrogen adsorption-desorption curve was as follows: Figure 9 As shown in number 9.

[0113] Comparative Example 1

[0114] Comparative Example 1: A carbon-carbon double bond-connected COF solid powder was prepared using a method substantially the same as that of Example 2, with the only difference being that 50 μL of acetonitrile solution was used in step (1), and no solid product was obtained upon completion of the reaction.

[0115] Comparative Example 2

[0116] Comparative Example 2: A COF solid powder connected by carbon-carbon double bonds was prepared by a method substantially the same as that of Example 2, with the only difference being that 75 μL of acetonitrile solution was used in step (1), and no solid product was obtained upon completion of the reaction.

[0117] Comparative Example 3

[0118] Comparative Example 3: COF solid powder was prepared by a method substantially the same as that of Example 2, except that 400 μL of trifluoroacetic acid was added in step (1) and no acetonitrile solution was added, and no solid product was obtained at the end of the reaction.

[0119] Comparative Example 4

[0120] Comparative Example 4: COF solid powder was prepared by a method substantially the same as that of Example 2, with the only difference being that 150 μL of acetonitrile solution was added in step (1), and no solid product was obtained at the end of the reaction.

[0121] Comparative Example 5

[0122] Comparative Example 5: COF solid powder was prepared using a method substantially the same as that of Example 2, with the only difference being that 400 μL of KOH aqueous solution (1 M) was added in place of trifluoroacetic acid in step (1). A block solid was obtained upon completion of the reaction, and the crystallinity and specific surface area could not be tested.

[0123] Comparative Example 6

[0124] Comparative Example 6: COF solid powder was prepared by a method substantially the same as that of Example 2, except that 400 μL of 1 M NaOH aqueous solution was added in place of trifluoroacetic acid in step (1). A block solid was obtained upon completion of the reaction, and the crystallinity and specific surface area could not be tested.

[0125] The crystallinity and specific surface area of ​​the COF materials prepared in the above examples and comparative examples were measured, and the results are shown in Table 1.

[0126] Table 1: Preparation conditions and performance parameters of COF materials prepared in the examples and comparative examples of the present invention

[0127]

[0128] “ / ” in the table means “not tested”.

[0129] Comparing Example 10, Example 9, Example 2, Example 3, Example 4 and Example 81, it can be seen that as the ratio of mesitylene and 1,4-dioxane increases, the crystallinity and specific surface area of ​​the covalent organic framework material with the obtained pyrimidine-based fully conjugated structure tend to first increase and then decrease (among which Examples 3, 4 and 8 have similar specific surface areas, but instead form an increasing trend, which should be caused by measurement errors). Example 2 achieves excellent crystallinity and high specific surface area, and Example 2 is the best. In Example 10 and Example 9, the difference in specific surface area caused by the low content of mesitylene is due to the large polarity of the mixed solvent, which makes nucleation more difficult during the crystallization process and the resulting material does not have crystallinity. In Example 8, the difference in specific surface area caused by the high content of mesitylene is due to the low polarity of the mixed solvent, the inability of the reaction monomer to be completely dissolved, and the poor crystallinity of the resulting material.

[0130] Comparison of Example 7, Example 2, Example 6, Example 5, and Example 11 shows that as the ratio of the organic mixed solvent to the catalyst increases, the crystallinity and specific surface area of ​​the resulting pyrimidine-based fully conjugated covalent organic framework material first increase and then decrease. Example 2 achieves excellent crystallinity and high specific surface area, and Example 2 is the best. However, in Examples 7 and 11, the high catalyst content results in excessively fast reaction rates, poor crystallinity, and thus poor specific surface area.

[0131] Comparing Comparative Example 3, Comparative Example 1, Comparative Example 2, Example 2, and Comparative Example 4, it can be seen that with the increase of acetonitrile content, a crystalline covalent organic framework material with a fully conjugated pyrimidine structure having an excellent specific surface area is prepared only at about 2: (0.9 to 1.2) (Example 2). However, in Comparative Examples 1-3, the acetonitrile content is too low, the mixed solvent has a small polarity, the reaction monomer cannot be completely dissolved, the degree of polymerization is low, and no solid product is obtained after Soxhlet extraction. In Comparative Example 4, the acetonitrile content is too high, the mixed solvent has a large polarity, nucleation is difficult during the crystallization process, and no solid product is obtained after Soxhlet extraction.

[0132] Comparison of Comparative Examples 5 and 6 with Example 2 reveals that the solid product obtained using conventional alkaline solution catalysts is a blocky solid, and its crystallinity and specific surface area cannot be measured, indicating that it lacks a porous structure and crystallinity. The present invention utilizes trifluoroacetic acid to prepare a fully conjugated pyrimidine-based covalent organic framework material with excellent crystallinity and a high specific surface area.

[0133] Example 12

[0134] (1) Accurately weigh 26.8 mg (0.2 mmol) of 1,4-terephthalaldehyde and 23.8 mg (0.1 mmol) of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine and add them to a reaction tube. Then, add 1 mL of mesitylene and 1 mL of 1,4-dioxane. After ultrasonically dispersing the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution.

[0135] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 72 hours to obtain a crude product;

[0136] (3) After the reaction is completed, the reaction system is unsealed and subjected to solid-liquid separation. The solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper. It is then subjected to Soxhlet extraction with tetrahydrofuran for 12 hours and then vacuum dried at 100°C for 12 hours to obtain a fully conjugated COF solid powder connected by carbon-carbon double bonds.

[0137] (4) 41 mg of the prepared fully conjugated COF solid powder (0.1 mmol) and 83 mg of ethylenediamine platinum nitrate (0.22 mmol) were mixed with 10 mL of water / acetonitrile (water:acetonitrile volume ratio 1:1). The mixture was heated to 60°C under an argon atmosphere for 6 h to obtain the product. The product was then filtered and washed with acetone, tetrahydrofuran, and methanol. After vacuum drying, the pyrimidine-based covalent organic framework-supported platinum metal single atom pair catalyst was obtained.

[0138] The synthesis diagram of the pyrimidine-based covalent organic framework-supported platinum metal single atom pair catalyst in Example 10 is shown in FIG. Figure 1 ,from Figure 1 It can be seen that the COF presents a fully conjugated structure connected by carbon-carbon double bonds, which is beneficial to improving its electron transport performance. In addition, the pyrimidine rings are evenly distributed in the COF skeleton, which is conducive to the anchoring and loading of monodisperse platinum metal single atom pairs.

[0139] 5 mg of the fully conjugated COF material loaded with metal (monodispersed Pt) single atom pair catalyst prepared in Example 10 was ultrasonically mixed with 2 mg of conductive carbon black, 490 μL of ethanol, and 10 μL of Nafion binder to obtain catalyst ink. 10 μL of the catalyst ink was evenly coated on the surface of carbon paper using a pipette and dried to obtain a working electrode. The electrochemical oxygen evolution performance was then tested under a three-electrode system, in which a carbon rod was used as a counter electrode, a Hg / HgO electrode was used as a reference electrode, and a 0.1 M KOH solution was used as an electrolyte. The resulting linear sweep voltammetry curve is shown in FIG. Figure 8 It is shown that the catalyst has good electrocatalytic performance.

[0140] Example 13

[0141] (1) Accurately weigh 42.05 mg (0.2 mmol) of 4,4'-biphenyldicarboxaldehyde and 23.8 mg (0.1 mmol) of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0142] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 72 hours to obtain a crude product;

[0143] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a COF solid powder connected by a carbon-carbon double bond;

[0144] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder (0.1 mmol), 83 mg of ethylenediamine platinum nitrate (0.22 mmol), and mix them with 10 mL of water / acetonitrile (1:1). Heat to 60 ° C under nitrogen environment and react for 6 h. Then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported platinum metal single atom pair catalyst is obtained.

[0145] The synthesis diagram of the pyrimidine-based covalent organic framework-supported platinum metal single atom pair catalyst in Example 11 is shown in FIG. Figure 2 ,from Figure 2 It can be seen that the COF presents a carbon-carbon double bond conjugated structure, which is beneficial to improving its electron transport performance. In addition, the bipyrimidine rings are evenly distributed in the COF skeleton, which is conducive to the anchoring and loading of monodisperse platinum metal single atom pairs.

[0146] The spherical aberration diagram of the pyrimidine-based covalent organic framework-supported platinum metal single atom catalyst in this Example 11 is shown in FIG. Figure 7 There are no obvious metal particles on the catalyst of the pyrimidine-based covalent organic framework-loaded platinum metal single atom pair. Monodispersed platinum atoms can be clearly seen in the spherical aberration electron microscopy image, which shows that the platinum atoms are distributed in the COF in the form of single atoms.

[0147] Example 14

[0148] (1) Accurately weigh 42.05 mg of 4,4'-biphenyldicarboxaldehyde and 23.8 mg of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0149] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 120 hours to obtain a crude product;

[0150] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a COF solid powder connected by a carbon-carbon double bond;

[0151] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder (0.1 mmol), 26.8 mg of copper chloride dihydrate (0.24 mmol), and mix them with 10 mL of 10% hydrochloric acid solution / ethanol (1:1). Heat to 70 ° C. under nitrogen environment and react for 8 h. Then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported copper metal single atom pair catalyst is obtained.

[0152] Example 15

[0153] (1) Accurately weigh 42.05 mg of 4,4'-biphenyldicarboxaldehyde and 23.8 mg of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0154] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 120 hours to obtain a crude product;

[0155] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a solid powder of COF material connected by carbon-carbon double bonds;

[0156] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder and 26.0 mg of cobalt chloride hexahydrate (0.24 mmol), mix with 10 mL of 10% hydrochloric acid solution / ethanol (1:1), heat to 70 ° C under nitrogen environment to react for 8 h, then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported cobalt metal single atom pair catalyst is obtained.

[0157] Example 16

[0158] (1) Accurately weigh 42.05 mg of 4,4'-biphenyldicarboxaldehyde and 23.8 mg of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0159] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 120 hours to obtain a crude product;

[0160] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a solid powder of COF material connected by carbon-carbon double bonds;

[0161] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder and 52.2 mg of ruthenium chloride trihydrate (0.24 mmol), mix with 10 mL of 10% hydrochloric acid solution / ethanol (1:1), heat to 70 ° C under nitrogen environment to react for 8 hours, then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported ruthenium metal single atom pair catalyst is obtained.

[0162] Example 17

[0163] (1) Accurately weigh 42.05 mg of 4,4'-biphenyldicarboxaldehyde and 23.8 mg of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0164] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 120 hours to obtain a crude product;

[0165] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a solid powder of COF material connected by carbon-carbon double bonds;

[0166] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder, 53.2 mg of palladium dibromide (0.24 mmol), and mix with 10 mL of 10% hydrobromic acid solution / ethanol (1:1). Heat to 70 ° C. under nitrogen environment and react for 8 h. Then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported palladium metal single atom pair catalyst is obtained.

[0167] Example 18

[0168] (1) Accurately weigh 42.05 mg of 4,4'-biphenyldicarboxaldehyde and 23.8 mg of 4,4',6,6'-tetramethyl-2,2'-bipyrimidine, add them to a reaction tube, add 1 mL of mesitylene and 1 mL of 1,4-dioxane, ultrasonically disperse the solvent, add 100 μL of acetonitrile solution and 400 μL of trifluoroacetic acid, and mix again to obtain a mixed solution;

[0169] (2) The mixed solution was subjected to a liquid nitrogen freeze-vacuum-thaw cycle in sequence, the reaction tube was sealed with a flame gun under vacuum, thawed to room temperature for a second time, and then placed in an oven at 150°C for 120 hours to obtain a crude product;

[0170] (3) After the reaction is completed, the reaction system is unsealed, the solid-liquid separation is performed, and the solid is washed with acetone, tetrahydrofuran, and methanol in sequence. The solid is separated by filtration and then wrapped with filter paper and subjected to Soxhlet extraction with tetrahydrofuran for 12 hours. Subsequently, the solid is vacuum-dried at 100°C for 24 hours to obtain a solid powder of COF material connected by carbon-carbon double bonds;

[0171] (4) Weigh 57.2 mg of the prepared carbon-carbon double bond connected COF solid powder and 67.4 mg of platinum chloride (0.24 mmol), mix with 10 mL of methanol / water (1:1), heat to 70 ° C under nitrogen environment for 8 h, then filter the product and wash it with acetone, tetrahydrofuran, and methanol. After vacuum drying, a pyrimidine-based covalent organic framework-supported platinum metal single atom pair catalyst is obtained.

[0172] The metal ion loadings of the catalysts prepared in the above examples and comparative examples and the distances between two metal atoms in the metal single atom pairs were measured, and the results are shown in Table 2.

[0173] Table 2: Composition and properties of catalysts prepared in Examples of the present invention and Comparative Examples

[0174]

[0175] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a covalent organic framework material with a pyrimidine-based fully conjugated structure, characterized in that: The preparation method comprises the following steps: (1) dissolving an aldehyde precursor and a methyl precursor containing a bipyrimidine structure in an organic mixed solvent, fully dispersing them, and then adding a catalyst to obtain a mixed solution; the organic mixed solvent comprises mesitylene, 1,4-dioxane, and acetonitrile, and the catalyst is trifluoroacetic acid; (2) subjecting the obtained mixed solution to a cycle of liquid nitrogen freezing-vacuuming-thawing, vacuum sealing, secondary thawing to room temperature, and then reacting at a temperature of 120-150° C. to obtain a crude product; (3) The reaction system of the crude product is unsealed, and then solid-liquid separation, washing, Soxhlet extraction and drying are performed to obtain a covalent organic framework material with a fully conjugated pyrimidine structure.

2. The preparation method according to claim 1, characterized in that In step (1), the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde, and the methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine.

3. The preparation method according to claim 1, characterized in that In step (1): the concentration of the aldehyde precursor in the mixed solution is 0.1 to 0.2 mol / L, and the concentration of the methyl precursor containing a bipyrimidine structure in the mixed solution is 0.05 to 0.1 mol / L. Preferably, the concentration of the aldehyde precursor is twice the concentration of the methyl precursor containing a bipyrimidine structure.

4. The preparation method according to claim 1, characterized in that In step (1), the ratio of the total volume of mesitylene and 1,4-dioxane to the volume of acetonitrile in the organic mixed solvent is 2:(0.09-0.12), wherein the volume ratio of mesitylene and 1,4-dioxane is (1-4):(4-1), preferably (1-2):(2-1).

5. The preparation method according to claim 1, characterized in that In step (1), the volume ratio of the organic mixed solvent to the catalyst is (2-6):1, preferably (4-6):1, and more preferably 5.25:

1.

6. The preparation method according to claim 1, characterized in that In step (2): the reaction is a constant temperature reaction; the constant temperature reaction time is 72 to 120 hours.

7. The preparation method according to claim 1, characterized in that In step (3): the Soxhlet extraction is performed using tetrahydrofuran; preferably, the Soxhlet extraction time is 12 to 36 hours; And / or, the drying is vacuum drying; preferably, the vacuum drying temperature is 100-120° C., and the time is 12-24 hours.

8. A covalent organic framework material with a pyrimidine-based fully conjugated structure, characterized in that: The covalent organic framework material with a fully conjugated pyrimidine structure is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds, wherein the covalent organic framework material has a bipyrimidine structure and has a fully conjugated structure connected by carbon-carbon double bonds; preferably, the aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde, and the methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine; Preferably, the half-peak width of the covalent organic framework material with a fully conjugated pyrimidine structure is 0.5 to 2.0 degrees, preferably 0.8 to 1.5 degrees; Preferably, the specific surface area of ​​the pyrimidine-based fully conjugated covalent organic framework material is 60 to 600 m 2 / g, preferably 200 to 600 m 2 / g, more preferably 400 to 600 m 2 / g.

9. The covalent organic framework material with a pyrimidine-based fully conjugated structure according to claim 8, characterized in that: The covalent organic framework material of the pyrimidine-based fully conjugated structure includes a repeating unit represented by formula (1) and / or a repeating unit represented by formula (2):

10. A pyrimidine-based conjugated COF-supported metal single atom pair catalyst, characterized in that: The pyrimidine-based conjugated COF-supported metal single atom pair catalyst comprises: A covalent organic framework material with a pyrimidine-based fully conjugated structure, wherein the covalent organic framework material with a pyrimidine-based fully conjugated structure is composed of structural units derived from an aldehyde precursor and structural units derived from a methyl precursor containing a bipyrimidine structure connected by carbon-carbon double bonds, wherein the covalent organic framework material has a bipyrimidine structure and has a fully conjugated structure linked by carbon-carbon double bonds; as well as A plurality of metal single atom pairs are connected to the covalent organic framework material via coordination bonds, wherein the two metal atoms in each metal single atom pair are respectively coordinated and bonded to the two bidentate N sites in the same bipyrimidine group in the form of ions.

11. The pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to claim 10, characterized in that: Each of the metal single atom pairs is selected from one of platinum atoms, manganese atoms, iron atoms, cobalt atoms, nickel atoms, copper atoms, zinc atoms, ruthenium atoms, rhodium atoms, palladium atoms and iridium atoms.

12. The pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to claim 10, characterized in that: The aldehyde precursor is 1,4-terephthalaldehyde and / or 4,4'-biphenyldicarboxaldehyde; The methyl precursor containing a bipyrimidine structure is 4,4',6,6'-tetramethyl-2,2'-bipyrimidine.

13. The pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to claim 10, characterized in that: The fully conjugated covalent organic framework material comprises a repeating unit represented by formula (1) and / or a repeating unit represented by formula (2):

14. The pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to claim 10, characterized in that: The loading amount of the metal atoms is 2 to 20 wt%, preferably 10 to 20 wt%.

15. The pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to claim 10, characterized in that: The distance between two metal atoms in the metal single atom pair is 0.7 to 0.9 nanometers.

16. A method for preparing the pyrimidine-based conjugated COF-supported metal single atom catalyst according to claim 10, characterized in that: The preparation method comprises: A pyrimidine-based fully conjugated covalent organic framework material, a soluble metal salt and a solvent are mixed, and heated while stirring to achieve the coordination loading of metal ions on the covalent organic framework material. The mixture is then separated and purified to obtain a pyrimidine-based conjugated COF-loaded metal single atom pair catalyst.

17. The preparation method according to claim 16, characterized in that The molar ratio of the covalent organic framework material of the pyrimidine-based fully conjugated structure to the soluble metal salt is 1:2 to 1:3; And / or, the soluble metal salt is selected from at least one of metal nitrate, ethylenediamine metal nitrate, metal chloride and metal bromide; preferably, the metal ion in the soluble metal salt is selected from one of platinum ion, manganese ion, iron ion, cobalt ion, nickel ion, copper ion, zinc ion, ruthenium ion, rhodium ion, palladium ion and iridium ion; more preferably, the soluble metal salt is selected from at least one of ethylenediamine platinum nitrate, manganese chloride, iron chloride, cobalt chloride and nickel chloride; And / or, the solvent is selected from at least one of water, acetonitrile, methanol, ethanol, 10% hydrobromic acid aqueous solution and 10% HCl aqueous solution or a combination thereof. Preferably, the solvent is a mixed solution of water / acetonitrile; water / methanol; or 10% HCl aqueous solution / ethanol.

18. The preparation method according to claim 16, characterized in that The stirring speed is 400 to 800 rpm, preferably 400 to 600 rpm; And / or, the heating temperature is 60-70° C.; the heating time is 6-8 hours; the heating is carried out under a nitrogen atmosphere and / or an inert atmosphere; preferably, the inert atmosphere is an argon atmosphere.

19. Use of the pyrimidine-based conjugated COF-supported metal single atom pair catalyst according to any one of claims 10 to 18 in the field of electrocatalysis, characterized in that: The electrocatalytic field is electrochemical catalytic oxygen reduction reaction, electrocatalytic hydrogen evolution reaction or electrocatalytic carbon dioxide reduction reaction.

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