Bimetallic covalent organic framework materials, methods of making and applications thereof

Abstract

The present application relates to a bimetallic covalent organic framework material and a preparation method and application thereof, and belongs to the technical field of coordination polymer materials. The technical problem solved by the present application is to provide a bimetallic covalent organic framework material M1TPP-M2QL-COF. The structural formula of the material is shown in the formula. The bimetallic covalent organic framework material obtained by the present application has an ultra-long lifetime exciton of 36000 picoseconds; it can be used as a photocatalytic catalyst and exhibits excellent photocatalytic defluorination and debromination performance on o-dibromide, has a significant conversion efficiency and separation yield in a wide range of substrates, the highest conversion efficiency is 99%, and the catalyst has recyclability. The preparation method of the bimetallic covalent organic framework material of the present application not only realizes a metal occupancy rate of nearly 100% at a predetermined position, but also allows independent coordination of a bimetallic center without structural interference. The process is simple, raw materials are easy to obtain, and large-scale industrial production is possible.

Description

Technical Field

[0001] This invention relates to bimetallic covalent organic framework materials, their preparation methods and applications, and belongs to the field of coordination polymer materials technology. Background Technology

[0002] Utilizing solar energy to drive organic transformations under mild conditions is a key frontier in sustainable chemistry. Among the ever-expanding library of photocatalysts, covalent organic frameworks (COFs) stand out due to their crystallinity and porosity, modular network structure, and highly tunable photoelectric properties. The atomic-level precision of COFs allows for precise tuning of molecular orbitals and band structures, thus providing a multifunctional platform for heterogeneous photocatalysis.

[0003] Although pure organic COFs have shown great potential, their catalytic efficiency is often limited by the inertness of the carbon-based framework and the lack of substrate-specific activation sites. Integrating transition metal active centers into the COF lattice has become a key strategy for bridging the gap between light capture and chemical conversion. While metallization modification of COFs can provide independent catalytic centers, systems relying on single-metal sites often encounter fundamental physicochemical problems. The main bottleneck is that in a single-metal coordination environment, charge carriers are confined within the localized coordination layer, lacking sufficient separation driving force, which often leads to excessively rapid electron-hole recombination. Furthermore, reliance on a single type of metal site is thermodynamically constrained by the Sabatil principle, making it difficult to achieve the optimal balance between reactant adsorption and product desorption in complex organic conversions, and also difficult to meet the different energy requirements of oxidation and reduction half-reactions.

[0004] While theoretical studies have emphasized the necessity of bimetallic site environments for addressing these issues, accurately constructing such structures in a single material remains a significant synthetic challenge. Traditional strategies, such as random doping or ion exchange, are often limited by the random distribution of metals and insufficient spatial control. Excessive heteronuclear spacing hinders synergistic catalysis, while excessive disorder leads to metal aggregation. On the other hand, in-situ introduction of bimetallic precursors to participate in framework self-assembly (e.g., the common Salen COF structure) often results in low crystallinity of bimetallic COFs, making it difficult to guarantee structural precision. Due to subtle differences in arrangement, the synergistic effects between metals can vary significantly, thus limiting the performance stability of COFs in catalytic processes. Furthermore, the alternating use of metal building blocks to construct heterobimetallic COFs with high crystallinity and well-defined metal sites provides an effective strategy for designing bimetallic COF catalysts. However, this method is limited by the finite availability of suitable metal coordination ligand libraries, which poses a challenge to the widespread application and structural diversification of such COFs.

[0005] Therefore, developing a method to precisely introduce a second metal ion into a predetermined coordination site without disrupting the original stable coordination structure, and obtaining a covalent organic framework material with a clearly defined bimetallic center, is of great scientific significance and application value for promoting the development of photocatalytic systems. Summary of the Invention

[0006] To address the above deficiencies, the first technical problem solved by this invention is to provide a bimetallic covalent organic framework material, M1TPP-M2QL-COF. This material possesses ultra-long-lived excitons and can be used as a photocatalyst, exhibiting excellent performance in photocatalytic defluorination and photocatalytic debromination.

[0007] The bimetallic covalent organic framework material of this invention has the following structural formula: As shown:

[0008]

[0009] Mode

[0010] Where M1 is Ni, Co or Cu, and M2 is Fe, Co, Ni, Cu or Zn, and M1 and M2 are different.

[0011] The second technical problem solved by this invention is to provide a method for preparing a bimetallic covalent organic framework material.

[0012] The method for preparing the bimetallic covalent organic framework material of the present invention includes the following steps:

[0013] (1) Using 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde as raw materials, M1TPP-Im-COF was obtained by Schiff-base reaction;

[0014] (2) The M1TPP-Im-COF obtained in step (1) is subjected to the Doebner reaction to convert the imine bond into a quinoline bond, thus obtaining M1TPP-QL-COF;

[0015] (3) The M1TPP-QL-COF obtained in step (2) is stirred and reacted with the second metal source to introduce the second metal ions into the framework and obtain a bimetallic covalent organic framework material; the second metal source is a salt of metal M2.

[0016] In one embodiment of the present invention, in step (1), the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde is 1:1 to 3; preferably, the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde is 1:2.

[0017] In one embodiment of the present invention, the Schiff-base reaction in step (1) is carried out in a solvent under vacuum conditions in the presence of a catalyst; the Doebner reaction in step (2) is carried out in a solvent under vacuum conditions with M1TPP-Im-COF and pyruvate in the presence of an oxidant; and the stirring reaction in step (3) is carried out in a solvent under a protective atmosphere.

[0018] In one embodiment of the invention, the catalyst is acetic acid or isoquinoline; the solvent is independently selected from at least one of n-butanol, o-dichlorobenzene and methanol; the oxidant is at least one of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetrachlorobenzoquinone, and tetrabutylammonium iodide; preferably, the catalyst is acetic acid and the oxidant is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

[0019] In one embodiment of the present invention, the temperature of the Schiff-base reaction in step (1) is 100-160°C and the reaction time is at least 3 days; preferably, the temperature of the Schiff-base reaction is 120°C and the reaction time is 3 days; the temperature of the Doebner reaction in step (2) is 100-160°C and the reaction time is at least 3 days; preferably, the temperature of the Doebner reaction is 120°C and the reaction time is 3 days; the temperature of the stirring reaction in step (3) is 10-80°C and the stirring time is 12-48 h; preferably, the stirring time is 24 h.

[0020] In one embodiment of the present invention, in step (2), the molar ratio of oxidant to M1TPP-Im-COF is controlled to be 1:0.5 to 1; the molar ratio of pyruvate to M1TPP-Im-COF is 1:0.01 to 1; preferably the molar ratio of oxidant to M1TPP-Im-COF is 1:0.5; and the molar ratio of pyruvate to M1TPP-Im-COF is 1:0.03.

[0021] In one embodiment of the present invention, in step (3), the second metal source is at least one of the nitrate, sulfate or chloride salt of M2; preferably the second metal source is the nitrate of M2.

[0022] In one embodiment of the present invention, in step (3), the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:1 to 5; preferably, the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:2.

[0023] The present invention also provides the application of the bimetallic covalent organic framework material described in the present invention or the bimetallic covalent organic framework material prepared by the method of the present invention in photocatalysts.

[0024] This invention relates to a bimetallic covalent organic framework material that can be used as a catalyst in the field of photocatalysis. Specifically, it can be applied to photocatalytic defluorination or photocatalytic debromination reactions.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention provides a bimetallic covalent organic framework material with well-defined bimetallic sites, ultra-long exciton lifetime, single-atom dispersion of the metal in the structure, an M2 metal ion coordination environment exhibiting an M2N2O2 asymmetric structure, and catalytic activity. The bimetallic covalent organic framework material obtained by this invention possesses an ultra-long exciton lifetime of 36,000 picoseconds; it can be used as a photocatalyst and exhibits excellent photocatalytic defluorination and debromination performance of ortho-dibromines. It demonstrates significant conversion efficiency and separation yield across a wide range of substrates, with a maximum conversion efficiency of 99%, and the catalyst is recyclable.

[0027] The present invention provides a method for preparing bimetallic covalent organic framework materials that not only achieves nearly 100% metal occupancy at predetermined sites but also allows for independent coordination of the bimetallic centers without structural interference. The process is simple, the raw materials are readily available, and it can be mass-produced industrially. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the preparation reaction of the bimetallic covalent organic framework material NiTPP-FeQL-COF in Example 1 of the present invention.

[0029] Figure 2 The infrared spectra of NiTPP-Im-COF and NiTPP-QL-COF in Example 1 of this invention are shown.

[0030] Figure 3 The images show the PXRD patterns of NiTPP-Im-COF and NiTPP-QL-COF in Embodiment 1 of the present invention; where a is the PXRD pattern of NiTPP-Im-COF and b is the PXRD pattern of NiTPP-QL-COF.

[0031] Figure 4 The images shown are TEM images of NiTPP-Im-COF, NiTPP-QL-COF, and NiTPP-FeQL-COF from Example 1. In the images, a is a TEM image of NiTPP-Im-COF, b is a TEM image of NiTPP-QL-COF, and c is a TEM image of NiTPP-FeQL-COF.

[0032] Figure 5 The image shown is a HAADF-STEM image of NiTPP-FeQL-COF obtained in Example 1 of this invention.

[0033] Figure 6 The images show the XANES and EXAFS spectra of NiTPP-FeQL-COF obtained in Example 1 of this invention, with the XANES spectrum on the left and the EXAFS spectrum on the right.

[0034] Figure 7 This is the 2D mapped fs-TA spectrum of the NiTPP-FeQL-COF material obtained in Example 1 of the present invention.

[0035] Figure 8 The image shows the kinetic curves of the fs-TA spectra of NiTPP-Im-COF, NiTPP-QL-COF, and NiTPP-FeQL-COF obtained in Example 1 of this invention.

[0036] Figure 9 The diagram shows the performance of NiTPP-FeQL-COF as a photocatalyst in defluorination and debromination reactions in Example 2 of this invention. In the diagram, a represents the conversion efficiency and separation yield of the debromination reaction; b represents the recovery test diagram of NiTPP-FeQL-COF in the debromination reaction; c represents the conversion efficiency and separation yield of the defluorination reaction; and d represents the recovery test diagram of NiTPP-FeQL-COF in the defluorination reaction. Detailed Implementation

[0037] The structural formula of the bimetallic covalent organic framework material M1TPP-M2QL-COF of this invention is as follows: As shown:

[0038]

[0039] Mode

[0040] Where M1 is Ni, Co or Cu, and M2 is Fe, Co, Ni, Cu or Zn, and M1 and M2 are different.

[0041] The M1TPP-M2QL-COF of this invention possesses an ultra-long exciton lifetime and exhibits excellent photocatalytic defluorination and debromination performance of ortho-dibromine.

[0042] This structural formula represents a schematic diagram of a structural unit of M1TPP-M2QL-COF. In fact, the M1TPP-M2QL-COF of the present invention is a layered framework formed by M1 porphyrin building blocks and M2 quinoline building blocks connected by covalent bonds. The M2 metal ion forms an M2N2O2 chelate structure with the nitrogen atoms of two quinolines and the oxygen atom of 2,5-dihydroxyterephthalic acid on the adjacent COF layer through post-synthetic modification, while the M1 metal ion stably occupies the center of the porphyrin ring.

[0043] The second technical problem solved by this invention is to provide a method for preparing a bimetallic covalent organic framework material.

[0044] The method for preparing the bimetallic covalent organic framework material of the present invention includes the following steps:

[0045] (1) Using 5,10,15,20-tetratetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde as raw materials, the first metal-porphyrin imine COF was obtained by Schiff-base reaction, denoted as M1TPP-Im-COF;

[0046] (2) The M1TPP-Im-COF obtained in step (1) is subjected to the Doebner reaction to convert the imine bond into a quinoline bond, resulting in the first metalloporphyrin-quinoline COF, denoted as M1TPP-QL-COF;

[0047] (3) React the M1TPP-QL-COF obtained in step (2) with the second metal source to introduce the second metal ion into the framework and obtain a bimetallic covalent organic framework material, denoted as M1TPP-M2QL-COF; the second metal source is a salt of metal M2.

[0048] This invention is based on 5,10,15,20-tetratetra(4'-triphenylaminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde (DHTA). An imine-linked M1-porphyrin COF (M1TPP-Im-COF) is obtained via a Schiff-base reaction. The first metal introduced in this step exhibits excellent coordination stability with the porphyrin ligand due to the macrocyclic effect. In the second step, the imine bond is converted to a quinoline bond via the Doebner reaction, constructing a first-metal porphyrin-quinoline COF (M1TPP-QL-COF). This step enhances the conjugation of the COF framework, which is beneficial for light absorption. The third step involves introducing a second metal into the COF via post-synthetic modification. This metal forms a strong chelate, M2N2O2, with the nitrogen atoms of the two quinolines and the oxygen atom of 2,5-dihydroxyterephthalic acid on adjacent COF layers, yielding a first metalloporphyrin-second metalloquinoline covalent organic framework (M1TPP-M2QL-COF). Due to the macrocyclic effect of the first metalloporphyrin and the kinetic inertness of the second metal substitution, the second metal is difficult to substitute for the first metal during coordination, resulting in a first metalloporphyrin-second metalloquinoline covalent organic framework with well-defined coordination sites. This method not only achieves nearly 100% metal occupancy at predetermined positions but also allows independent coordination of the bimetallic center without structural interference. The resulting M1TPP-M2QL-COF material exhibits excellent photocatalytic defluorination and debromination performance; it demonstrates significant conversion efficiency and separation yield across a wide substrate range, with a maximum conversion efficiency of 99%.

[0049] In this invention, the structural formulas of M1TPP-Im-COF and M1TPP-QL-COF are as follows:

[0050]

[0051] Each step of the present invention will be explained in detail below.

[0052] 1. Step (1)

[0053] Step (1) is a Schiff-base reaction, in which 5,10,15,20-tetrakis(4'-triphenylaminophenyl)porphyrin-M1 reacts with 2,5-dihydroxyterephthalaldehyde (DHTA). The first metalloporphyrin-imine COF (M1TPP-Im-COF) was obtained by Schiff base reaction.

[0054] The structural formula of 5,10,15,20-tetra(4'-triphenylaminophenyl)porphyrin-M1 is:

[0055] .

[0056] In one embodiment of the present invention, in step (1), the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde is 1:1 to 3; preferably, the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde is 1:2.

[0057] In one embodiment of the invention, the Schiff-base reaction is carried out in a solvent under vacuum conditions in the presence of a catalyst.

[0058] Commonly used Schiff-base reaction catalysts and solvents are suitable for this invention. In some specific embodiments, the catalyst is acetic acid or isoquinoline, and the solvent is at least one selected from n-butanol, o-dichlorobenzene, or methanol. Preferably, the catalyst is acetic acid, and the solvent is n-butanol and o-dichlorobenzene. More preferably, the volume ratio of n-butanol to o-dichlorobenzene is 0.5–2:1, and even more preferably, the volume ratio is 1:1.

[0059] To ensure the reaction materials are mixed as evenly as possible and to maintain a vacuum environment, the following specific procedures are preferred: 5,10,15,20-tetrakis(4'-triphenylaminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde are dispersed in a solvent and sonicated for 5–120 s; then the catalyst is added, and the air in the reaction apparatus is purged through at least three cycles of freezing-vacuuming-thawing; then the apparatus is sealed with a flame gun at 600–1200 °C; and then the Schiff-base reaction is carried out.

[0060] In one embodiment of the invention, the Schiff-base reaction is carried out at a temperature of 100–160°C for at least 3 days. Preferably, the Schiff-base reaction is carried out at a temperature of 120°C for 3 days.

[0061] After the reaction, the mixture was cooled to room temperature, washed, and dried to obtain the first metalloporphyrin-imine COF, denoted as M1TPP-Im-COF. Washing can be performed using conventional methods in the art. In one specific embodiment of the invention, the mixture was washed with acetone, methanol, and tetrahydrofuran, followed by Soxhlet extraction with acetone, methanol, and tetrahydrofuran for 24 hours with each solvent.

[0062] 2. Step (2)

[0063] Step (2) is the Doebner reaction, which converts the imine bond in M1TPP-Im-COF obtained in step (1) into a quinoline bond to obtain the first metalloporphyrin-quinoline COF, denoted as M1TPP-QL-COF;

[0064] In one embodiment of the invention, the Doebner reaction involves reacting M1TPP-Im-COF and pyruvic acid in the presence of an oxidizing agent. The oxidizing agent is at least one selected from 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetrachlorobenzoquinone, and tetrabutylammonium iodide; preferably, the oxidizing agent is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

[0065] In one embodiment of the present invention, the molar ratio of oxidant to M1TPP-Im-COF is controlled to be 1:0.5-1; the molar ratio of pyruvic acid to M1TPP-Im-COF is controlled to be 1:0.01-1.

[0066] In one specific embodiment of the present invention, the molar ratio of oxidant to M1TPP-Im-COF is 1:0.5; the molar ratio of pyruvic acid to M1TPP-Im-COF is 1:0.03.

[0067] In one embodiment of the invention, the Doebner reaction is carried out in a solvent under vacuum conditions. Commonly used solvents are suitable for this invention; in some specific embodiments, the solvent is at least one selected from n-butanol, o-dichlorobenzene, or methanol. Preferably, the solvent is n-butanol and o-dichlorobenzene. More preferably, the volume ratio of n-butanol to o-dichlorobenzene is 0.5–2:1, and even more preferably, the volume ratio is 1:1.

[0068] Similar to step (1), in order to better mix the reaction raw materials and ensure the vacuum environment, step (2) preferably adopts the following specific operation: M1TPP-Im-COF, pyruvic acid and oxidant are dispersed in a solvent and ultrasonically treated for 5 to 120 s; the air in the reaction device is exhausted after at least three cycles of freezing-vacuuming-thawing; then the tube is sealed with a flame gun at 600 to 1200°C; finally, the reaction is carried out in a sealed container.

[0069] In one embodiment of the invention, the Doebner reaction is carried out at a temperature of 100–160°C for at least 3 days. Preferably, the Doebner reaction is carried out at a temperature of 120°C for 3 days.

[0070] After the reaction, the mixture was cooled to room temperature, washed, and dried to obtain the first metalloporphyrin-quinoline COF, denoted as M1TPP-QL-COF. Washing can be performed using conventional methods in the art. In one specific embodiment of the invention, the mixture was washed with acetone, methanol, and tetrahydrofuran, followed by Soxhlet extraction with acetone, methanol, and tetrahydrofuran for 24 hours with each solvent.

[0071] (3) Step 3

[0072] Step (3) reacts M1TPP-QL-COF with a second metal source to introduce the second metal ions into the framework to form coordination, thereby obtaining the bimetallic covalent organic framework material M1TPP-M2QL-COF.

[0073] In one specific embodiment of the present invention, in step (3), the second metal source is at least one of the nitrate, sulfate or chloride salt of M2; preferably, the second metal source is the nitrate of M2.

[0074] In one specific embodiment of the invention, the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:1 to 5. In a preferred embodiment, the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:2. The ratio of metal ion M1 to M2 in the COF material is close to the theoretical value of 1:2, indicating that the quinoline sites are coordinated to and saturated by M2 ions. Importantly, the significant localized orbital hybridization between the M1 porphyrin and M2 quinoline regions indicates that these two metal centers do not operate in isolation, but are connected through a low-impedance pathway, thereby promoting directional electron migration.

[0075] In one specific embodiment of the present invention, the reaction in step (3) is carried out under a protective atmosphere and stirred in a solvent at 10–80°C.

[0076] In some specific embodiments, the solvent is at least one selected from n-butanol, o-dichlorobenzene, or methanol. Methanol is preferred as the solvent.

[0077] In one specific embodiment of the present invention, the stirring time is 12 to 48 hours. Preferably, the stirring time is 24 hours.

[0078] In one specific embodiment of the present invention, the specific operation of step (3) is as follows: M1TPP-QL-COF and the second metal source are dispersed in a solvent, ultrasonically treated for 5 to 120 s, and stirred and reacted at 60 °C for 24 hours under argon protection.

[0079] After the reaction, the material is washed and dried to obtain the bimetallic covalent organic framework material M1TPP-M2QL-COF. Washing and drying can both be performed using conventional methods in the art; in one specific embodiment of the invention, washing is performed with methanol and deionized water.

[0080] This invention relates to a bimetallic covalent organic framework material that can be used as a catalyst in the field of photocatalysis. Specifically, it can be applied to photocatalytic defluorination or photocatalytic debromination reactions.

[0081] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products. In this embodiment of the invention, 5,10,15,20-tetra(4'-aminophenyl)porphyrin nickel (NiTPP-4NH2), 2,5-dihydroxyterephthalaldehyde (DHTA), pyruvic acid, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), transition metal salt ferric nitrate nonahydrate (Fe(NO3)3∙9H2O), 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylic acid ester (HEH), tetramethylethylenediamine (TMEDA), N,N-diisopropylethylamine (DIPEA), o-dichlorobenzene, n-butanol, acetic acid, acetone, methanol, and tetrahydrofuran were purchased from Adamas-beta.

[0082] Example 1: Preparation and Characterization of NiTPP-FeQL-COF

[0083] Preparation of NiTPP-FeQL-COF:

[0084] 1) A mixture of NiTPP-4NH2 (16.2 mg, 0.022 mmol), DHTA (7.4 mg, 0.044 mmol), 6 M acetic acid (100 μL), o-dichlorobenzene (0.5 mL), and n-butanol (0.5 mL) was placed in a 10 mL Pyrex tube. The mixture was sonicated for 2 minutes, degassed by three freeze-thaw cycles, vacuum sealed, and heated at 120 °C for 3 days. The reaction mixture was cooled to room temperature. The product was collected by filtration, washed several times with acetone, methanol, and tetrahydrofuran, and then Soxhlet extracted with acetone, methanol, and tetrahydrofuran (24 hours for each solvent). After vacuum drying at 80 °C for 12 hours, the target product NiTPP-Im-COF was obtained.

[0085] 2) A mixture of NiTPP-Im-COF (30 mg, 0.03 mmol), pyruvate (75 μL, 1 mmol), DDQ (15 mg, 0.06 mmol), o-dichlorobenzene (0.5 mL), and n-butanol (0.5 mL) was placed in a 10 mL Pyrex tube. The mixture was sonicated for 2 minutes, degassed by three freeze-thaw cycles, vacuum sealed, and heated at 120 °C for 3 days. The reaction mixture was cooled to room temperature. The product was collected by filtration, washed several times with acetone, methanol, and tetrahydrofuran, and then Soxhlet extracted with acetone, methanol, and tetrahydrofuran (24 hours for each solvent). After vacuum drying at 80 °C for 12 hours, the target product NiTPP-QL-COF was obtained.

[0086] 3) A mixture of NiTPP-QL-COF (200 mg, 0.88 mmol), Fe(NO3)3∙9H2O (355.5 mg, 0.88 mmol), and methanol (90 mL) was placed in a 250 mL round-bottom flask. The mixture was sonicated for 2 minutes and stirred at 60 °C for 24 hours under argon protection. The product was collected by filtration, washed several times with methanol and deionized water, and then dried under vacuum at 80 °C for 12 hours to obtain the target product NiTPP-FeQL-COF.

[0087] Structural characterization:

[0088] 1) Infrared images of covalent organic framework samples obtained using amino monomers and aldehyde monomers.

[0089] The obtained sample was first dried in a vacuum oven at 60°C, and then infrared spectroscopy was performed on the sample. The results are shown in [Figure number missing]. Figure 2 As shown in the figure, the C=O stretching vibration peak disappears in all products, and the characteristic peak of the imine bond is at 1592 cm⁻¹. −1 The presence of this feature indicates the formation of an imine bond in the reaction. Additionally, the presence of 1717 cm⁻¹ in the nickel porphyrin-quinoline covalent organic framework further supports this. −1 The characteristic peak at the point is attributed to the stretching vibration of the C=O group in the carboxylic acid on the quinoline ring, confirming the conversion of imine to quinoline.

[0090] 2) The crystallography of the covalent organic framework sample was measured using X-ray diffraction (PXRD).

[0091] Powder X-ray diffraction (PXRD) measurements were performed on a Rigaku SmartLab X-ray diffractometer using Cu-Kα radiation (λ = 1.54178 Å) in the 2θ range, from 2° to 30°, at a scan rate of 5° min. -1 The results are shown in Figure 3 . Figure 3In the figure, a is the PXRD pattern of NiTPP-Im-COF, and b is the PXRD pattern of NiTPP-QL-COF. As can be seen from the figure, the experimental PXRD patterns agree well with the simulated patterns. Strong peaks appear at 3.52° and 7.06° in the nickel porphyrin-imine covalent organic framework (NiTPP-Im-COF), corresponding to the (100) and (200) crystal planes, respectively. The proposed model was refined using the Pawley refinement method, yielding the following cell parameters: a = b = 25.8516 Å, c = 3.9075 Å, α = β = γ = 90°, R wp = 5.31%, and R p = 5.18%. Furthermore, the experimental PXRD pattern of the nickel porphyrin-quinoline covalent organic framework (NiTPP-QL-COF) showed good consistency with the simulated pattern, maintaining high crystallinity. Strong peaks appeared at 3.51° and 7.09°, corresponding to the (100) and (200) crystal planes, respectively. The proposed model was refined using the Pawley refinement method, yielding the following cell parameters: a = b = 25.9011 Å, c = 3.8785 Å, α = β = γ = 90°, R wp = 6.92%, and R p = 6.67%.

[0092] 3) TEM images of covalent organic framework samples obtained by field emission transmission electron microscopy.

[0093] Field emission scanning electron microscopy (FE-TEM) images were acquired on a Talos F200S and then performed using high-resolution transmission electron microscopy (HR-TEM). The results are shown in [Figure number missing]. Figure 4 As shown in the figure, NiTPP-Im-COF, NiTPP-QL-COF, and NiTPP-FeQL-COF exhibit good crystallinity.

[0094] 4) The atomic distribution of the covalent organic framework sample was obtained using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).

[0095] Images obtained from a Spectra Ultra 60-300 microscope with an accelerating voltage of 200 kV, using dual Cs-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), are detailed below. Figure 5 As shown in the figure, the metal exhibits a single-atom dispersion in its structure.

[0096] 5) XANES / EXAFS plots of covalent organic framework samples obtained by XAFS testing and software fitting.

[0097] XAFS measurements of transition metal iron were performed at station BL17B of the Shanghai Synchrotron Radiation Facility (SSRF). The SSRF's electron storage ring operated at 3.5 GeV with a maximum current of 200 mA. Metal K-edge XAFS data were acquired using a fixed-exit Si(111) dual-crystal monochromator. Fluorescence signals were collected using a Wright detector, and the energy was calibrated using a metal foil.

[0098] The obtained EXAFS data were analyzed using the ATHENA module of the IFEFFIT software package according to standard procedures. The EXAFS contributions of different coordination layers were separated using the Hanning window. Subsequently, quantitative curve fitting was performed in R space and Fourier transform k space using the ARTEMIS module of IFEFFIT.

[0099] The results are shown in Figure 6 In the XANES spectrum shown in the left figure, compared with the spectra of the comparative example and the two standard references (Fe foil and FePc), the XANES curves of NiTPP-FeQL-COF show similar contours, indicating that they have similar local coordination geometry. In the EXAFS spectrum shown in the right figure, the Fe-N / O peaks of NiTPP-FeQL-COF are close to those of Fe2O3 and FePc. At the same time, NiTPP-FeQL-COF has no Fe-Fe, showing its single-atom dispersion characteristics.

[0100] 6) Femtosecond transient absorption spectroscopy (fs-TA) measurement of covalent organic framework samples

[0101] Femtosecond transient absorption spectroscopy (fs-TA) measurements were performed using a self-made femtosecond pump-probe setup. A Ti:sapphire femtosecond laser system provided the laser pulses for the femtosecond transient absorption measurements. A regenerative amplifier (Spectra Physics, Spitfire) equipped with a mode-locked Ti:sapphire laser (Spectra Physics, Tsunami) output a laser pulse at a wavelength of 800 nm (150 fs, 1 kHz), which was then split into two parts using a 9:1 beam splitter. The primary part was fed into a TOPAS Prime (LightConversion) to generate a pump pulse (350 nm, 150 fs, 1 kHz). The secondary part was further attenuated and focused onto a 3 mm calcium fluoride plate to generate a probe pulse. An ultraviolet filter was inserted into the probe beam to select the ultraviolet-visible probe beam (360–680 nm). The time delay between the pump beam and the probe beam was adjusted using a computer-controlled motorized translation stage in the pump beam. The time resolution between the pump pulse and the probe pulse was determined to be ~150 fs (FWHM). Transmitted light was detected using a CMOS linear image sensor. The excitation pulse energy measured at the sampling point was approximately 0.4 μJ cm⁻¹.−2 Spectrophotometry was used to check sample stability before and after each experiment. The kinetic trajectory obtained from time-resolved spectroscopy was analyzed, and a nonlinear least-squares fitting method was used to deconvolve the instrument response function (IRF) to obtain a general exponential function. All spectroscopic measurements were performed at room temperature. See details. Figure 7 and Figure 8 .

[0102] Depend on Figure 7 It can be seen that after excitation at 400 nm, the initially recorded fs-TA spectrum in the NiTPP-FeQL-COF film consists of a negative band in the range of 410 to 780 nm and a positive band that peaks at 500 nm; the former negative band is attributed to ground-state bleaching (GSB). This is consistent with the comparison of the steady-state absorption spectrum, while the positive band is related to excited-state absorption (ESA).

[0103] Depend on Figure 8 It can be seen that by fitting the kinetic curve at 500 nm, the estimated ESA lifetimes of NiTPP-FeQL-COF, NiTPP-QL-COF and NiTPP-Im-COF are approximately 36000 ps, ​​30000 ps and 7500 ps, ​​respectively.

[0104] Example 2: Photocatalytic debromination and photocatalytic defluorination

[0105] 1. General procedure for photocatalytic debromination reaction (taking NiTPP-FeQL-COF as photocatalyst as an example):

[0106] A mixture of NiTPP-FeQL-COF (3 mg) and meso-1,2-dibromo-1,2-diphenylethane (68 mg, 0.2 mmol) was placed in a 10 mL Schlenk tube. The tube was completely degassed with argon and purged for 3 cycles. TMEDA (60 μL, 0.4 mmol) and dry DMF (1 mL) were injected into the Schlenk tube. The reaction mixture was irradiated with a blue LED lamp (420–430 nm, 45 W) for 2 h and cooled with an electric fan to maintain a constant reaction temperature of 25 °C. After the reaction was complete, all liquid phases were collected and quantitatively analyzed using gas chromatography-mass spectrometry (GC-MS) with n-dodecane as an internal standard. The structure of the product was confirmed by comparing the retention times with those of the standard. GC-MS analysis was performed using a quadrupole mass spectrometer equipped with an HP-5 MS column (30 m × 0.25 mm × 0.25 μm) and helium (He) as the carrier gas.

[0107] 2. General procedure for photocatalytic defluorination reaction (taking NiTPP-FeQL-COF as a photocatalyst as an example):

[0108] A mixture of NiTPP-FeQL-COF (3 mg), 2-fluoro-1-phenylethyl ketone (27.6 mg, 0.2 mmol), and HEH (55.7 mg, 0.22 mmol) was placed in a 10 mL Schlenk tube. The tube was completely degassed with argon and purged for three cycles. DIPEA (70 μL, 0.4 mmol) and dry DMF (1 mL) were injected into the Schlenk tube. The reaction mixture was reacted under a blue LED lamp (420–430 nm, 45 W) for 30 h, cooled by an electric fan to maintain a constant reaction temperature of 25 °C. After the reaction, all liquid phases were collected and quantitatively analyzed by GC-MS, using n-dodecane as an internal standard. The structure of the product was confirmed by comparing the retention times with those of a standard. GC-MS analysis was performed using a quadrupole mass spectrometer equipped with an HP-5 MS column (30 m × 0.25 mm × 0.25 μm) and helium as the carrier gas.

[0109] 3. Results Analysis

[0110] The performance of COF photocatalysts in defluorination and debromination reactions is shown in [reference needed]. Figure 9 .

[0111] a) shows the conversion efficiency and isolated yield of the debromination reaction; the NiTPP-Im-COF group uses NiTPP-Im-COF as the photocatalyst, the NiTPP-QL-COF group uses NiTPP-QL-COF as the photocatalyst, the NiTPP-FeQL-COF group uses NiTPP-FeQL-COF as the photocatalyst, the air group uses NiTPP-FeQL-COF in an air atmosphere as the catalyst, the no catalyst group is the control group without photocatalyst, the no TMEDA group is the control group without TMEDA injection, and the no light group is the control group without light. It can be seen that NiTPP-FeQL-COF as the photocatalyst has the highest conversion efficiency and isolated yield in the debromination reaction. b) shows the recovery test diagram of the NiTPP-FeQL-COF debromination reaction, indicating that the conversion efficiency and isolated yield do not change significantly after five cycles, and the catalyst is recyclable. Conversion rate refers to the amount of raw material converted, while separation yield refers to the amount of product obtained.

[0112] c represents the conversion efficiency and separation yield of the defluorination reaction. It is evident that NiTPP-FeQL-COF, as the photocatalyst, exhibits the highest conversion efficiency and separation yield in the defluorination reaction. d shows the recovery test results of the NiTPP-FeQL-COF defluorination reaction, indicating that the conversion efficiency and separation yield do not change significantly after five cycles, demonstrating the recyclability of the catalyst.

Claims

1. A bimetallic covalent organic framework material, characterized in that: The structural formula of the bimetallic covalent organic framework material is as follows: As shown: Mode Where M1 is Ni, Co or Cu, and M2 is Fe, Co, Ni, Cu or Zn, and M1 and M2 are different.

2. The method for preparing the bimetallic covalent organic framework material according to claim 1, characterized in that, Includes the following steps: (1) Using 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 and 2,5-dihydroxyterephthalaldehyde as raw materials, M1TPP-Im-COF was obtained by Schiff-base reaction; (2) The M1TPP-Im-COF obtained in step (1) is subjected to the Doebner reaction to convert the imine bond into a quinoline bond, thus obtaining M1TPP-QL-COF; (3) The M1TPP-QL-COF obtained in step (2) is stirred and reacted with the second metal source to introduce the second metal ions into the framework and obtain a bimetallic covalent organic framework material; the second metal source is a salt of metal M2.

3. The method for preparing the bimetallic covalent organic framework material according to claim 2, characterized in that: In step (1), the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 to 2,5-dihydroxyterephthalaldehyde is 1:1 to 3; preferably, the molar ratio of 5,10,15,20-tetra(4'-aminophenyl)porphyrin-M1 to 2,5-dihydroxyterephthalaldehyde is 1:

2.

4. The method for preparing the bimetallic covalent organic framework material according to claim 2, characterized in that: The Schiff-base reaction in step (1) was carried out in a solvent under vacuum in the presence of a catalyst; The Doebner reaction in step (2) is carried out in a solvent under vacuum conditions, with M1TPP-Im-COF and pyruvate in the presence of an oxidant. The stirring reaction in step (3) is carried out in a solvent under a protective atmosphere.

5. The method for preparing the bimetallic covalent organic framework material according to claim 4, characterized in that: The catalyst is acetic acid or isoquinoline; the solvent is independently selected from at least one of n-butanol, o-dichlorobenzene and methanol; the oxidant is at least one of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, tetrachlorobenzoquinone, and tetrabutylammonium iodide; preferably, the catalyst is acetic acid and the oxidant is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

6. The method for preparing the bimetallic covalent organic framework material according to claim 5, characterized in that: The Schiff-base reaction in step (1) is carried out at a temperature of 100–160°C for at least 3 days; preferably, the Schiff-base reaction is carried out at a temperature of 120°C for 3 days. The temperature of the Doebner reaction in step (2) is 100-160°C, and the reaction time is at least 3 days; preferably, the temperature of the Doebner reaction is 120°C, and the reaction time is 3 days. The temperature of the stirring reaction in step (3) is 10-80°C, and the stirring time is 12-48 h; preferably, the stirring time is 24 h.

7. The method for preparing the bimetallic covalent organic framework material according to claim 5, characterized in that: In step (2), the molar ratio of oxidant to M1TPP-Im-COF is controlled to be 1:0.5 to 1; the molar ratio of pyruvate to M1TPP-Im-COF is 1:0.01 to 1; preferably, the molar ratio of oxidant to M1TPP-Im-COF is 1:0.5; and the molar ratio of pyruvate to M1TPP-Im-COF is 1:0.

03.

8. The method for preparing the bimetallic covalent organic framework material according to claim 2, characterized in that: In step (3), the second metal source is at least one of the nitrate, sulfate or chloride salt of M2; preferably the second metal source is the nitrate of M2.

9. The method for preparing the bimetallic covalent organic framework material according to claim 2, characterized in that: In step (3), the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:1 to 5; preferably, the molar ratio of metal ion M1 in M1TPP-QL-COF to metal ion M2 in the second metal source is 1:

2.

10. The application of the bimetallic covalent organic framework material according to claim 1 or the bimetallic covalent organic framework material prepared by any one of claims 2 to 9 in photocatalysts.

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