A metalloporphyrin-oxime bimetal site covalent organic framework material and a preparation method and application thereof

Abstract

This invention discloses a metalloporphyrin-oxime bimetallic site covalent organic framework material, its preparation method, and its applications. It relates to the field of electrocatalysis technology. The aforementioned metalloporphyrin-oxime bimetallic site covalent organic framework material has the structure shown in Formula I: ; wherein M1 and M2 are independently selected from Cu or Co, respectively. Through precise molecular-level structural design, this invention's metalloporphyrin-oxime bimetallic site covalent organic framework material constructs spatially ordered porphyrin-coordinating metal sites M1 and oxime-coordinating metal sites M2 within a two-dimensional crystalline covalent organic framework. Based on the intrinsic catalytic differences between the copper and cobalt metal sites, stepwise tandem catalysis of the nitrate reduction to ammonia reaction is achieved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, and in particular to a metalloporphyrin-oxime bimetallic site covalent organic framework material, its preparation method, and its application. Background Technology

[0002] Ammonia, a globally abundant chemical, possesses industrial and energy potential. However, its traditional Haber-Bosch production process is characterized by high energy consumption and emissions, and its low nitrogen fertilizer utilization efficiency in agriculture leads to aquatic ecological crises. Therefore, electrocatalytic conversion of nitrates in water to ammonia under ambient temperature and pressure holds promise as a dual strategy for energy transition and ecological protection in the context of carbon neutrality. Recently, materials based on cobalt, copper, ruthenium, palladium, and titanium have been identified as potential sources of NO3. - Promising electrocatalysts for ammonia production via electrocatalysis demonstrate the feasibility of the aforementioned strategy. However, these electrocatalysts still suffer from problems such as low current density, high overpotential, and low mass transfer efficiency. Notably, in the field of electrocatalytic CO2 reduction reaction (CO2RR), studies have shown that introducing an additional light field into the electrocatalytic system is a highly attractive strategy. This method can not only effectively improve the low current density and high overpotential problems existing in traditional electrocatalysis processes, but also has the potential to reduce energy consumption while improving the overall efficiency of the catalytic system.

[0003] However, due to the lack of suitable catalysts, reports on photo-assisted electrocatalytic nitrate reduction remain scarce. Therefore, developing highly efficient photoelectrocatalysts with clearly defined active sites and precise tunability, and further elucidating the intrinsic relationship between active sites and reaction pathways, is a crucial scientific problem that urgently needs to be solved. It is worth noting that the nitrate (NO3⁻) reduction reaction is a complex electrocatalytic process involving multi-electron transfer and proton coupling; different reaction pathways may produce different byproducts (NO2⁻). - The reaction pathway is highly dependent on the concentration distribution of key species in the catalyst interfacial microenvironment, especially the interfacial concentration of the core intermediate NO2⁻ and its subsequent rapid and continuous protonation, which is crucial for ammonia selectivity. Therefore, improving mass transfer efficiency and intermediate utilization is key to optimizing the reaction pathway and enhancing the selectivity of the target product. Copper-based catalysts, due to the similarity of their d orbitals to the lowest unoccupied π* orbitals in NO3⁻, facilitate the reduction of NO3⁻ to NO2. -The process exhibits significant kinetic advantages. Furthermore, cobalt is considered a typical catalyst for hydrogenation. However, currently, there is no tandem strategy integrating two highly active metal sites, Cu and Co, into a single catalytic system. It is important to emphasize that the key to constructing a tandem catalyst system lies not only in screening for highly active catalytic sites to form high-concentration intermediates (such as NO2⁻ and active hydrogen), but also in designing efficient transport pathways for these intermediates. Optimizing the entire transport pathway from intermediate formation to utilization is expected to significantly improve the reaction efficiency and process optimization level of photoelectrocatalytic ammonia synthesis. Therefore, photoelectrocatalysts for NO3⁻ reduction need to meet the following key characteristics: 1. Good photoelectric conversion capability; 2. Well-defined stepwise catalytic sites for NO3⁻ to NO2 conversion. - Targeted conversion and NO2 - 3. It has efficient hydrogenation of NH3; 4. It has good material transport pathways between catalytic sites; 5. It has good structural stability under the synergistic effect of light radiation and electrical energy.

[0004] Covalent organic frameworks (COFs) are structurally well-defined crystalline porous materials. Due to their excellent light absorption, electron delocalization, and high stability, COFs are widely used in energy storage, heterogeneous catalysis, and other fields. More notably, these superior structural characteristics provide a solid foundation for COFs to achieve highly efficient photoelectrocatalytic reactions as heterogeneous catalysts, including the photoelectrocatalytic reduction of nitrate to ammonia. More importantly, the covalent bonds connecting the building blocks with different active sites not only achieve spatial separation of the active sites but also synergistically construct an ordered conductive network, thereby endowing the catalyst with highly efficient charge transport capabilities. Therefore, COFs have great application potential in the construction of tandem catalysts. However, the use of COFs as highly efficient tandem catalysts for the photoelectrocatalytic reduction of nitrate has not yet been explored, especially in elucidating the synergistic mechanism between active sites and the regulation of reaction pathways at the atomic level.

[0005] Therefore, it is urgent to design and synthesize a class of COFs constructed from conjugated ligands and bimetallic nodes that have efficient electron transport capabilities and excellent structural stability, and to systematically explore their application value in electrocatalytic nitrate reduction under low overpotential and high selectivity conditions. Summary of the Invention

[0006] A metalloporphyrin-oxime bimetallic site covalent organic framework material having the structure shown in Formula I:

[0007] ;

[0008] M1 and M2 are independently selected from Cu or Co, respectively.

[0009] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0010] This invention relates to a metalloporphyrin-oxime bimetallic site covalent organic framework material. Through precise molecular-level structural design, spatially ordered porphyrin-coordinated M1 metal sites and oxime-coordinated M2 metal sites are constructed within a two-dimensional crystalline covalent organic framework. Based on the intrinsic catalytic differences between the copper and cobalt metal sites, stepwise tandem catalysis of the nitrate reduction to ammonia reaction is achieved. The d orbital of the Cu site coordinated at the porphyrin ring center has a similar energy level to the lowest unoccupied molecular π* orbital of the nitrate ion, enabling efficient adsorption and activation of nitrate ions, driving the directional reduction of nitrate to the nitrite core intermediate. Meanwhile, the oxime-coordinated Co site… The sites possess excellent hydrogen adsorption and activation capabilities, enabling the rapid generation of highly active adsorbed hydrogen during the catalytic process. This provides a sufficient active hydrogen source for the continuous multi-step hydrogenation reaction of nitrite intermediates, promoting the directional and efficient conversion of nitrite into ammonia. The spatial separation and synergistic cooperation of the bimetallic sites precisely regulate the reaction pathway of nitrate reduction, fundamentally inhibiting the generation of byproducts such as nitrite, nitrogen, and hydrazine, and significantly improving the selectivity of ammonia products.

[0011] In this invention, the porphyrin group in the metalloporphyrin-oxime bimetallic site covalent organic framework material serves as a strong light-absorbing unit, achieving efficient light absorption across a broad UV-Vis spectral range. Under illumination, it is excited to generate photogenerated electron-hole pairs. Simultaneously, the porphyrin group and the imine bond formed by monomer condensation construct a highly conjugated π-conjugated system, creating a long-range ordered continuous transport channel for photogenerated electrons. This effectively reduces charge transport resistance, significantly suppresses recombination of photogenerated carriers, and achieves highly efficient photoelectric conversion and charge transport. It can rapidly transport photogenerated electrons to the bimetallic catalytic active site, increasing the electron density of the active site, reducing the overpotential of the reaction, accelerating the catalytic reaction kinetics, and achieving excellent photoelectric synergistic catalytic effects. The intramolecular hydrogen bond structure of the oxime ligand constructs a continuous proton transfer pathway from the electrolyte to the catalytic active center in the catalytic system, achieving efficient coupling of electron transfer and proton migration during the catalytic reaction. This significantly accelerates the continuous protonation process of reaction intermediates, further improving the efficiency of the hydrogenation reaction and the kinetic rate of ammonia formation.

[0012] According to one embodiment of the present invention, M1 and M2 may be the same or different. The present invention can optimize catalytic performance by adjusting the metal combination.

[0013] According to one embodiment of the present invention, M1 is Cu and M2 is Co. This combination represents the optimal matching combination of bimetallic sites: the Cu site at the porphyrin center can leverage its intrinsic kinetic advantages to efficiently adsorb and activate NO3. -Targeted reduction to generate NO2 ⁻ The core intermediate; the Co site coordinated with the oxime group can exert its excellent hydrogen adsorption activation ability, for NO2 ⁻ The continuous multi-step hydrogenation of the intermediate provides a sufficient active hydrogen source, driving NO2 production. ⁻ Directed and efficient conversion to NH3. The precise tandem catalytic pathway formed by the two fully leverages the synergistic effect of the two sites. Therefore, CuPor-CoOx-COF (Example 3) exhibits the highest current density and the highest ammonia production Faradaic efficiency (95.00%) in all examples.

[0014] According to one embodiment of the present invention, the metalloporphyrin-oxime bimetallic site covalent organic framework material is a two-dimensional layer-by-layer stacked structure. This layer-by-layer stacking can form an ordered π-π stack, which is beneficial for charge transport.

[0015] According to one embodiment of the present invention, the metalloporphyrin-oxime bimetallic site covalent organic framework material exhibits diffraction peaks at 4.15° and 8.35° in powder X-ray diffraction patterns, corresponding to the (110) and (220) crystal planes, respectively. The positions of these diffraction peaks are consistent with the two-dimensional layer-by-layer stacked structure simulated by Material Studio.

[0016] According to one embodiment of the present invention, the pore size of the metalloporphyrin-oxime bimetallic site covalent organic framework material is 1.65–1.85 nm. The pore size of 1.65–1.85 nm is much larger than the kinetic diameter of nitrate and ammonia molecules, enabling rapid diffusion of substrates and products; simultaneously, the confinement effect of the pores allows NO2 generated at the M1 site to be absorbed. ⁻ The intermediate diffuses rapidly within the pores to the adjacent M2 site, preventing it from diffusing into the bulk solution, thus improving the hydrogenation efficiency of the intermediate, suppressing side reactions, and enhancing the selectivity of ammonia.

[0017] According to one embodiment of the present invention, the metalloporphyrin-oxime bimetallic site covalent organic framework material is formed by the covalent condensation of a tetraaldehyde phenylporphyrin monomer and an oxime metal monomer via imine bonds, wherein the tetraaldehyde phenylporphyrin monomer is 5,10,15,20-tetra(4-aldehydephenyl)-21H,23H-porphyrin. This tetraaldehyde phenylporphyrin has four symmetrical aldehyde reaction sites, which can efficiently condense with the amino group of the oxime monomer to form imine bonds, constructing a two-dimensional conjugated COF framework; simultaneously, the large π structure of the porphyrin ring enables strong light absorption and efficient charge transport, solving the problem of low photoelectric conversion efficiency.

[0018] According to one embodiment of the present invention, the oxime-based metal monomer is named M2Ox, where Ox is derived from the English word oxime, and is abbreviated as Ox.

[0019] According to one embodiment of the present invention, the oxime-based metal monomer M2Ox is a metal-coordinated ethylenedioxime-benzidine diamine compound. This oxime monomer structure simultaneously possesses an ethylenedioxime group capable of coordinating with a metal, an oxime hydroxyl group capable of forming intramolecular hydrogen bonds, and an amino reaction site capable of condensing with an aldehyde group. This allows for simultaneous M2 site anchoring, proton pathway construction, and COF framework polymerization, solving the problem that existing catalysts cannot simultaneously construct active sites and proton transfer pathways.

[0020] According to one embodiment of the present invention, the metalloporphyrin-oxime bimetallic site covalent organic framework material has one of the following structures:

[0021] Formula II Formula III Formula IV Formula V.

[0022] Specifically, the technical solution adopted according to the second aspect of the present invention is as follows:

[0023] A method for preparing the metalloporphyrin-oxime bimetallic site covalent organic framework material includes the following steps:

[0024] S1 mixes tetraaldehyde phenyl porphyrin monomer, oxime M2Ox monomer and acetic acid aqueous solution in solvent, reacts under vacuum conditions, and after washing and drying, obtains crystalline porphyrin-oxime covalent organic framework material precursor;

[0025] S2 disperses the crystalline porphyrin-oxime covalent organic framework material precursor obtained in step S1 in a solvent, adds a metal salt containing M1, and reacts to obtain the metalporphyrin-oxime bimetallic site covalent organic framework material.

[0026] According to embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

[0027] The method of this invention adopts a stepwise preparation design. First, a crystalline porphyrin-oxime covalent organic framework precursor is constructed by solvothermal reaction of tetraaldehyde phenylporphyrin monomer and oxime M2Ox monomer under acetic acid aqueous solution catalysis and vacuum environment. The precursor can complete imine bond condensation under mild and controllable conditions to form a highly conjugated, long-range ordered crystalline porous framework, avoiding the interference of metal ions on the polymerization process, ensuring that the precursor structure is regular, the channels are interconnected and the crystallinity is high, and providing a stable and site-uniform carrier for subsequent metal modification.

[0028] Vacuum reaction conditions can effectively eliminate the interference of oxygen and bubbles in the system, suppress the occurrence of side reactions, and allow the monomers to fully condense to form a continuous two-dimensional conjugated structure. At the same time, the acetic acid aqueous solution, as a proton catalyst, can precisely promote the dehydration condensation of aldehyde and amino groups, efficiently generate imine bonds, and enable the precursor to have a stable framework, good charge transport ability, and proton transfer channels provided by oxime groups.

[0029] Subsequently, the precursor was modified with metallization, and the metal salt M1 was introduced into the porphyrin central cavity for coordination anchoring. Utilizing the strong coordination ability and pore confinement effect of the porphyrin ring, the M1 metal ion was uniformly and stably bound to the porphyrin site, forming a spatially separated and orderly arranged bimetallic active center with the M2 metal site already present on the oxime group. This achieved the precise construction of the two sites without destroying the already formed crystalline framework structure.

[0030] According to one embodiment of the present invention, the tetraaldehyde phenyl porphyrin monomer in step S1 is 5,10,15,20-tetra(4-aldehydephenyl)-21H,23H-porphyrin, and the oxime M2Ox monomer is a metal-coordinated dioxime diphenyl diamine compound, wherein the coordinating metal is M2.

[0031] According to one embodiment of the present invention, the molar ratio of the tetraaldehyde phenylporphyrin monomer, the oxime M2Ox monomer, and acetic acid in step S1 is 1:(1-2):(120-200). Excess acetic acid acts as a catalyst to promote imine bond formation, and an appropriate excess of the oxime monomer is beneficial for complete reaction.

[0032] According to one embodiment of the present invention, the solvent in step S1 is a mixed solution of mesitylene and 1,4-dioxane, preferably, the volume ratio of mesitylene to 1,4-dioxane is 1-2:1-2. The use of the mixed solvent of mesitylene and 1,4-dioxane is beneficial to the growth of COF crystals.

[0033] According to one embodiment of the present invention, the reaction temperature in step S1 is 110-130°C, and / or the reaction time is 3-5 days.

[0034] According to one embodiment of the present invention, the vacuum condition in step S1 is achieved by the following method: a mixture obtained by mixing tetraaldehyde phenylporphyrin monomer, oxime M2Ox monomer, aqueous acetic acid solution and solvent is placed in a reaction flask, subjected to a freeze-thaw cycle in liquid nitrogen, and then sealed after being evacuated; preferably, the freeze-thaw cycle is repeated at least three times; more preferably, the freeze-thaw cycle is repeated three times.

[0035] According to one embodiment of the present invention, the washing in step S1 is to wash the reaction product with tetrahydrofuran and acetone.

[0036] According to one embodiment of the present invention, the drying in step S1 is vacuum drying at 60-90°C for 2-4 hours.

[0037] According to one embodiment of the present invention, the solvent in step S2 is ethanol or tetrahydrofuran. Ethanol or tetrahydrofuran can promote the entry of metal ions into the porphyrin cavity.

[0038] According to one embodiment of the present invention, the metal salt containing M1 in step S2 is cobalt(II) chloride hexahydrate or copper(II) chloride dihydrate.

[0039] According to one embodiment of the present invention, the mass ratio of the crystalline porphyrin-oxime covalent organic framework material precursor to the M1-containing metal salt is 1:(1.2 to 2.0).

[0040] According to one embodiment of the present invention, the reaction temperature in step S2 is 40-50°C; preferably, the reaction time in step S2 is 12-24 hours.

[0041] Another aspect of the present invention provides the application of the aforementioned metalloporphyrin-oxime bimetallic site covalent organic framework material as a catalyst in electrocatalytic nitrate reduction, specifically including the following steps:

[0042] The metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing Nafion solution, water and ethanol, and the dispersion was uniform to obtain catalyst ink;

[0043] The working electrode is prepared by spraying the catalyst ink onto hydrophobic carbon paper.

[0044] A three-electrode system is formed by the working electrode, the reference electrode, and the counter electrode to carry out electrocatalytic nitrate reduction in the electrolyte.

[0045] According to one embodiment of the present invention, the electrolyte in the electrolyte solution comprises at least one of K2SO4 and KNO3.

[0046] According to one embodiment of the present invention, the concentration of the Nafion solution is 5-6 wt%.

[0047] According to one embodiment of the present invention, the volume ratio of the Nafion solution, water and ethanol is 1:45-50:45-50.

[0048] According to one embodiment of the present invention, the volume of the catalyst ink sprayed onto the hydrophobic carbon paper is 100-120 μL.

[0049] According to one embodiment of the present invention, the reference electrode is an AgCl electrode, the counter electrode is a Pt foil, and the three-electrode system is separated into a cathode chamber and an anode chamber by a Nafion 117 film.

[0050] According to one embodiment of the present invention, the electrolyte in the electrolyte solution comprises K2SO4 and KNO3, wherein the concentration ratio of K2SO4 to KNO3 is 0.5-0.6 mol / L: 0.1-0.2 mol / L.

[0051] According to one embodiment of the present invention, the volume of the electrolyte is 30-50 mL.

[0052] Another aspect of the present invention provides the application of the aforementioned metalloporphyrin-oxime bimetallic site covalent organic framework material as a catalyst in photoelectrocatalytic nitrate reduction, comprising the following steps:

[0053] The metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing Nafion solution, water and ethanol, and the dispersion was uniform to obtain catalyst ink;

[0054] The working electrode is prepared by spraying the catalyst ink onto hydrophobic carbon paper.

[0055] A three-electrode system is formed by the working electrode, the reference electrode, and the counter electrode. A light source is introduced into the reaction system to carry out photoelectrocatalytic reduction of nitrate in the electrolyte.

[0056] According to one embodiment of the present invention, the light source is a xenon lamp, and the power of the light source is 300-350W.

[0057] In another aspect, the present invention provides a method for electrocatalytic reduction of nitrate, using the aforementioned metalporphyrin-oxime bimetallic site covalent organic framework material as a catalyst, and performing electrolytic reduction in an electrolyte containing nitrate to reduce nitrate to ammonia.

[0058] In another aspect, the present invention provides a method for photoelectrocatalytic reduction of nitrate, using the aforementioned metalporphyrin-oxime bimetallic site covalent organic framework material as a catalyst, and performing electrolytic reduction in a light-irradiated and nitrate-containing electrolyte to reduce nitrate to ammonia.

[0059] In another aspect, the present invention provides a composition for catalytic nitrate reduction, comprising the metalloporphyrin-oxime bimetallic site covalent organic framework material and a conductive carbon material, wherein the conductive carbon material is hydrophobic carbon paper or carbon cloth.

[0060] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0061] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0062] Figure 1 The flowchart shows the preparation method of the metalloporphyrin-oxime bimetallic site covalent organic framework materials in Examples 1-4.

[0063] Figure 2 MaterialStudio simulations of the metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4.

[0064] Figure 3 The image shows the X-ray diffraction pattern of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 1.

[0065] Figure 4 The image shows the X-ray diffraction pattern of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 2.

[0066] Figure 5 The image shows the X-ray diffraction pattern of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3.

[0067] Figure 6 The image shows the X-ray diffraction pattern of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 4.

[0068] Figure 7 The image shows the infrared spectrum of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 1.

[0069] Figure 8 The infrared spectrum of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 2 is shown.

[0070] Figure 9 The infrared spectrum of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 is shown.

[0071] Figure 10 The infrared spectrum of the metalloporphyrin-oxime bimetallic site covalent organic framework material in Example 4 is shown.

[0072] Figure 11 The linear voltammetric curve is shown for the electrocatalytic nitrate reduction reaction obtained by using the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 as a catalyst.

[0073] Figure 12The graph shows the Faraday efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 as a catalyst in the electrocatalytic reduction of nitrate to ammonia as a function of potential.

[0074] Figure 13 The linear voltammetric curves of the metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 as catalysts for the electrocatalytic reduction of nitrate under light irradiation are shown.

[0075] Figure 14 The graphs show the Faraday efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 as catalysts for the electrocatalytic reduction of nitrate to ammonia under light irradiation, as a function of potential.

[0076] Figure 15 The image shows a Material Studio simulation of the porphyrin-oxime organic framework material in Comparative Example 1.

[0077] Figure 16 The graphs show the Faraday efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 and the porphyrin-oxime organic framework material of Comparative Example 1 as catalysts for photoelectrophotocatalytic reduction of nitrate to ammonia as a function of potential.

[0078] Figure 17 This is a flowchart illustrating the preparation method of the porphyrin organic framework material in Comparative Example 2.

[0079] Figure 18 Material Studio simulation of the porphyrin organic framework material in Comparative Example 2.

[0080] Figure 19 The graphs show the Faraday efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 and the porphyrin organic framework material of Comparative Example 2 as catalysts for photoelectrochemical reduction of nitrate to ammonia as a function of potential. Detailed Implementation

[0081] The terms "preferred," "more preferred," etc., used in this invention refer to embodiments of the invention that provide certain beneficial effects under certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are unavailable, nor is it intended to exclude other embodiments from the scope of this invention.

[0082] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0083] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of the present invention.

[0084] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0085] In the examples and comparative examples, the preparation method of the copper oxime (M2Ox, M = Cu) monomer includes the following steps: In a 250 mL double-necked round-bottom flask, (1E,2E)-1,2-bis(4'-amino-[1,1'-biphenyl]-4-yl)ethane-1,2-dione dioxime (1.0 g, 2.37 mmol) and sodium hydroxide (0.80 g, 20.00 mmol) are added sequentially. After evacuating the system with an oil pump and replacing the gas with high-purity nitrogen three times, the nitrogen atmosphere is maintained, ethanol is added, and the mixture is stirred for 20 minutes. Subsequently, an ethanol solution containing copper(II) dihydrate (201.17 mg, 1.18 mmol) is added dropwise to the reaction system, the temperature is raised to 65°C, and the mixture is refluxed and stirred for 12 hours. After cooling to room temperature, the resulting precipitate is filtered, washed with water and ethanol, and dried under vacuum to obtain a yellowish-brown solid product. The precursor of the above-mentioned oxime monomer, (1E,2E)-1,2-bis(4'-amino-[1,1'-biphenyl]-4-yl)ethane-1,2-dione dioxime, was synthesized according to the method reported in the literature (Angewandte Chemie International Edition. 2022, 61, e202204326).

[0086] In the examples and comparative examples, the preparation method of the cobalt-containing oxime (M2Ox, M = Co) monomer includes the following steps: In a 250 mL double-necked round-bottom flask, (1E,2E)-1,2-bis(4'-amino-[1,1'-biphenyl]-4-yl)ethane-1,2-dione dioxime (1.0 g, 2.37 mmol) and sodium hydroxide (0.80 g, 20.00 mmol) are added sequentially. After evacuating the system with an oil pump and replacing the gas with high-purity nitrogen three times, the nitrogen atmosphere is maintained, ethanol is added, and the mixture is stirred for 20 minutes. Subsequently, an ethanol solution containing cobalt(II) hexahydrate (268.86 mg, 1.18 mmol) is added dropwise to the reaction system, the temperature is raised to 65°C, and the mixture is refluxed and stirred for 12 hours. After cooling to room temperature, the resulting precipitate is filtered, washed with water and ethanol, and dried under vacuum to obtain a yellowish-brown solid product. The precursor of the above-mentioned oxime monomer, (1E,2E)-1,2-bis(4'-amino-[1,1'-biphenyl]-4-yl)ethane-1,2-dione dioxime, was synthesized according to the method reported in the literature (Angewandte Chemie International Edition. 2022, 61, e202204326).

[0087] In the examples and comparative examples, the CAS number of the tetraaldehyde phenylporphyrin monomer is 150805-46-2, and it is named 2HPor in this invention.

[0088] In the examples and comparative examples, the gaseous reduction products were monitored using a gas chromatograph (GC-7920, CEAulight, Beijing) equipped with a thermal conductivity detector (TCD). Ammonia in the liquid products was measured by UV-vis spectrophotometry and compared with a standard curve to calculate the yield of the electrocatalytic product. The UV-vis spectrophotometric method for measuring ammonia involved preparing a mixture at room temperature by mixing 2 mL of electrolyzed electrolyte, 2 mL of a NaOH solution containing 5 wt% salicylic acid and 5 wt% sodium citrate (NaOH concentration 1 mol / L), 1 mL of NaClO (NaClO concentration 50 mmol / L), and 0.2 mL of 1 wt% sodium ferrocyanide (III) dihydrate. After allowing the mixture to stand in the dark for 2 hours, analysis was performed using a UV-Vis spectrophotometer. The peak at λ = 655 nm in the resulting indophenol blue spectrum was then compared with the corresponding standard curve to quantify the ammonia product.

[0089] Example 1

[0090] A metalloporphyrin-oxime bimetallic site covalent organic framework material having the structure shown in Formula II:

[0091] .

[0092] The preparation method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material is shown in the flowchart below. Figure 1 As shown, specifically, it includes the following steps:

[0093] S1. Take a Pyrex glass tube (Beijing Xinweier Glass) with a specification of 19mm (outer diameter) × 65mm (length). Add cobalt M2Ox (M2 = Co) (18.00mg, 0.02mmol), 2HPor (14.54mg, 0.02mmol), mesitylene (0.50mL), and 1,4-dioxane (0.50mL) in sequence. Sonicate for about 20 minutes to disperse it evenly. Add 0.40mL of 6mol / L acetic acid aqueous solution under oscillation conditions and continue sonicating for about 15 minutes. Then, rapidly freeze the resulting mixture in 77K (liquid nitrogen bath). Vacuum the system using an oil pump, and control the vacuum degree of the system at 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freezing-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, place the mixture at 120℃ and heat it for 72 hours. The brownish-yellow precipitate was separated by filtration through a Buchner funnel using 250 nm filter paper and washed with acetone and tetrahydrofuran (THF) until the filtrate was colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120 °C for 12 hours to obtain the crystalline porphyrin-oxime covalent organic framework material precursor 2HPor-CoOx-COF.

[0094] Under a nitrogen atmosphere, 120 mg of 2HPor-CoOx-COF and 200 mg of cobalt(II) chloride hexahydrate were added to a round-bottom flask, followed by 50 mL of ethanol. The resulting suspension was stirred overnight at 40 °C. After the reaction was complete and cooled to room temperature, the product was collected by filtration and washed alternately with deionized water and ethanol, three times each. Finally, the product was vacuum dried at 120 °C for 12 hours to obtain the target product, a metalloporphyrin-oxime bimetallic site covalent organic framework material.

[0095] The method for applying the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in electrocatalytic nitrate reduction includes the following steps:

[0096] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL of Nafion solution (5 wt%), 450 μL of water, and 450 μL of ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen from the solution, followed by electrocatalytic testing.

[0097] The application method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in photoelectrocatalytic nitrate reduction includes the following steps:

[0098] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL Nafion solution (5 wt%), 450 μL water, and 450 μL ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen. A xenon lamp with a power of 300 W was introduced into the reaction system to perform photoelectrochemical nitrate reduction in the electrolyte.

[0099] Example 2

[0100] A metalloporphyrin-oxime bimetallic site covalent organic framework material having the structure shown in Formula III:

[0101] .

[0102] The preparation method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material is shown in the flowchart below. Figure 1 As shown, specifically, it includes the following steps:

[0103] S1. Take a Pyrex glass tube (Beijing Xinweier Glass) with a specification of 19mm (outer diameter) × 65mm (length). Add copper M2Ox (M2 = Cu) (18.00mg, 0.02mmol), 2HPor (14.54mg, 0.02mmol), mesitylene (0.50mL), and 1,4-dioxane (0.50mL) in sequence. Sonicate for about 20 minutes to disperse it evenly. Add 0.40mL of 6mol / L acetic acid aqueous solution under shaking conditions and continue sonicating for about 15 minutes. Then, rapidly freeze the resulting mixture in 77K (liquid nitrogen bath). Vacuum the system using an oil pump, and control the vacuum degree of the system at 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freezing-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, place the mixture at 120℃ and heat it for 72 hours. The brownish-yellow precipitate was separated by filtration through a Buchner funnel using 250 nm filter paper and washed with acetone and tetrahydrofuran (THF) until the filtrate was colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120 °C for 12 hours to obtain the crystalline porphyrin-oxime covalent organic framework precursor 2HPor-CuOx-COF.

[0104] Under a nitrogen atmosphere, 120 mg of 2HPor-CuOx-COF and 200 mg of copper(II) chloride dihydrate were added to a round-bottom flask, followed by 50 mL of ethanol. The resulting suspension was stirred overnight at 40 °C. After the reaction was complete and cooled to room temperature, the product was collected by filtration and washed alternately with deionized water and ethanol, three times each. Finally, the product was vacuum dried at 120 °C for 12 hours to obtain the target product, a metalloporphyrin-oxime bimetallic site covalent organic framework material.

[0105] The method for applying the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in electrocatalytic nitrate reduction includes the following steps:

[0106] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL of Nafion solution (5 wt%), 450 μL of water, and 450 μL of ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen from the solution, followed by electrocatalytic testing.

[0107] The application method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in photoelectrocatalytic nitrate reduction includes the following steps:

[0108] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL Nafion solution (5 wt%), 450 μL water, and 450 μL ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen. A xenon lamp with a power of 300 W was introduced into the reaction system to perform photoelectrochemical nitrate reduction in the electrolyte.

[0109] Example 3

[0110] A metalloporphyrin-oxime bimetallic site covalent organic framework material having the structure shown in Formula IV:

[0111] .

[0112] The preparation method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material is shown in the flowchart below. Figure 1 As shown, specifically, it includes the following steps:

[0113] S1. Take a Pyrex glass tube (Beijing Xinweier Glass) with a specification of 19mm (outer diameter) × 65mm (length). Add cobalt M2Ox (M2 = Co) (18.00mg, 0.02mmol), 2HPor (14.54mg, 0.02mmol), mesitylene (0.50mL), and 1,4-dioxane (0.50mL) in sequence. Sonicate for about 20 minutes to disperse it evenly. Add 0.40mL of 6mol / L acetic acid aqueous solution under oscillation conditions and continue sonicating for about 15 minutes. Then, rapidly freeze the resulting mixture in 77K (liquid nitrogen bath). Vacuum the system using an oil pump, and control the vacuum degree of the system at 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freezing-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, place the mixture at 120℃ and heat it for 72 hours. The brownish-yellow precipitate was separated by filtration through a Buchner funnel using 250 nm filter paper and washed with acetone and tetrahydrofuran (THF) until the filtrate was colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120 °C for 12 hours to obtain the crystalline porphyrin-oxime covalent organic framework material precursor 2HPor-CoOx-COF.

[0114] Under a nitrogen atmosphere, 120 mg of 2HPor-CoOx-COF and 200 mg of copper(II) chloride dihydrate were added to a round-bottom flask, followed by 50 mL of ethanol. The resulting suspension was stirred overnight at 40 °C. After the reaction was complete and cooled to room temperature, the product was collected by filtration and washed alternately with deionized water and ethanol, three times each. Finally, the product was vacuum dried at 120 °C for 12 hours to obtain the target product, a metalloporphyrin-oxime bimetallic site covalent organic framework material.

[0115] The method for applying the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in electrocatalytic nitrate reduction includes the following steps:

[0116] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL of Nafion solution (5 wt%), 450 μL of water, and 450 μL of ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen from the solution, followed by electrocatalytic testing.

[0117] The application method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in photoelectrocatalytic nitrate reduction includes the following steps:

[0118] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL Nafion solution (5 wt%), 450 μL water, and 450 μL ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen. A xenon lamp with a power of 300 W was introduced into the reaction system to perform photoelectrochemical nitrate reduction in the electrolyte.

[0119] Example 4

[0120] A metalloporphyrin-oxime bimetallic site covalent organic framework material having the structure shown in Formula V:

[0121] .

[0122] The preparation method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material is shown in the flowchart below. Figure 1 As shown, specifically, it includes the following steps:

[0123] S1. Take a Pyrex glass tube (Beijing Xinweier Glass) with a specification of 19mm (outer diameter) × 65mm (length). Add copper M2Ox (M2 = Cu) (18.00mg, 0.02mmol), 2HPor (14.54mg, 0.02mmol), mesitylene (0.50mL), and 1,4-dioxane (0.50mL) in sequence. Sonicate for about 20 minutes to disperse it evenly. Add 0.40mL of 6mol / L acetic acid aqueous solution under shaking conditions and continue sonicating for about 15 minutes. Then, rapidly freeze the resulting mixture in 77K (liquid nitrogen bath). Vacuum the system using an oil pump, and control the vacuum degree of the system at 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freezing-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, place the mixture at 120℃ and heat it for 72 hours. The brownish-yellow precipitate was separated by filtration through a Buchner funnel using 250 nm filter paper and washed with acetone and tetrahydrofuran (THF) until the filtrate was colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120 °C for 12 hours to obtain the crystalline porphyrin-oxime covalent organic framework precursor 2HPor-CuOx-COF.

[0124] Under a nitrogen atmosphere, 120 mg of 2HPor-CuOx-COF and 200 mg of cobalt(II) chloride hexahydrate were added to a round-bottom flask, followed by 50 mL of ethanol. The resulting suspension was stirred overnight at 40 °C. After the reaction was complete and cooled to room temperature, the product was collected by filtration and washed alternately with deionized water and ethanol, three times each. Finally, the product was vacuum dried at 120 °C for 12 hours to obtain the target product, a metalloporphyrin-oxime bimetallic site covalent organic framework material.

[0125] The method for applying the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in electrocatalytic nitrate reduction includes the following steps:

[0126] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL of Nafion solution (5 wt%), 450 μL of water, and 450 μL of ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen from the solution, followed by electrocatalytic testing.

[0127] The application method of the above-mentioned metalloporphyrin-oxime bimetallic site covalent organic framework material in photoelectrocatalytic nitrate reduction includes the following steps:

[0128] Four mg of a metalloporphyrin-oxime bimetallic site covalent organic framework material was dispersed in a mixed solution containing 10 μL Nafion solution (5 wt%), 450 μL water, and 450 μL ethanol, and the dispersion was uniform to obtain catalyst ink. 100 μL of the catalyst ink was directly sprayed onto hydrophobic carbon paper to obtain a working electrode. AgCl was used as the reference electrode, Pt foil as the counter electrode, and a Nafion 117 membrane was used to separate the cathode and anode chambers to form a standard three-electrode system. 30 mL of an aqueous solution containing 0.5 mol / L K₂SO₄ and 0.1 mol / L KNO₃ was used as the electrolyte. Argon gas was introduced into the electrolytic cell for 9–12 min to remove dissolved oxygen. A xenon lamp with a power of 300 W was introduced into the reaction system to perform photoelectrochemical nitrate reduction in the electrolyte.

[0129] Comparative Example 1

[0130] The difference between Comparative Example 1 and Example 3 is that the precursor in Comparative Example 1 was not post-modified, that is, the comparative example was only prepared up to 2HPor-CoOx-COF.

[0131] Specifically:

[0132] A method for preparing a porphyrin-oxime-based organic framework material comprises the following steps:

[0133] Take a Pyrex glass tube (Beijing Xinweier Glass) with dimensions of 19 mm (outer diameter) × 65 mm (length), and add cobalt-containing M2Ox (M2 = Co) (18.00 mg, 0.02 mmol), 2HPor (14.54 mg, 0.02 mmol), mesitylene (0.50 mL), and 1,4-dioxane (0.50 mL) sequentially. Sonicate for approximately 20 minutes to achieve uniform dispersion. Add 0.40 mL of a 6 mol / L acetic acid aqueous solution under oscillation conditions, and continue sonicating for approximately 15 minutes. Then, rapidly freeze the resulting mixture in a liquid nitrogen bath at 77 K. Vacuum the system using an oil pump, maintaining a vacuum level of 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freeze-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, place the mixture at 120 °C for 72 hours. The brownish-yellow precipitate was separated by filtration through a Buchner funnel using 250 nm filter paper and washed with acetone and tetrahydrofuran (THF) until the filtrate was colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120 °C for 12 hours to obtain the crystalline porphyrin-oxime covalent organic framework precursor 2HPor-CoOx-COF.

[0134] Comparative Example 2

[0135] The difference between Comparative Example 2 and Example 3 is that in Comparative Example 2, tetraaldehyde phenyl porphyrin (2HPor) monomer and tetra(4-aminobiphenyl)ethylene monomer (TPE; CAS: 2252187-21-4) without oxime metal active centers and intramolecular hydrogen bonds were polymerized using the same solvothermal method as in Example 3 to form a crystalline porphyrin-based covalent organic framework material precursor (2HPor-TPE-COF). The solvents mesitylene and 1,4-dioxane were replaced with pure 1,2-dichlorobenzene. Subsequently, Cu was further coordinated and anchored in the porphyrin-centered cavity of 2HPor-TPE-COF using the same post-modification strategy as in Example 3. 2+ This forms a metalloporphyrin-based crystalline covalent organic framework material (CuPor-TPE-COF).

[0136] Specifically:

[0137] A method for preparing porphyrin organic framework materials, the flowchart is as follows: Figure 17 As shown, the steps are as follows:

[0138] S1. Take a Pyrex glass tube (Beijing Xinweier Glass) with dimensions of 19 mm (outer diameter) × 65 mm (length). Add tetrakis(4-aminobiphenyl)ethylene monomer (0.02 mmol), 2HPor (14.54 mg, 0.02 mmol), and pure 1,2-dichlorobenzene sequentially. Sonicate for about 20 minutes to achieve uniform dispersion. Add 0.40 mL of 6 mol / L acetic acid aqueous solution under shaking conditions and continue sonicating for about 15 minutes. Then, rapidly freeze the resulting mixture in 77 K (liquid nitrogen bath). Vacuum the system using an oil pump, controlling the vacuum degree at 1.33 Pa ~ 0.133 Pa. Degas the system through three consecutive freeze-evacuation-thawing cycles, and then seal the tube under vacuum. After returning to room temperature, heat the mixture at 120 °C for 72 hours. Filter the mixture through a Buchner funnel using 250 nm filter paper to separate the precipitate. Wash the precipitate with acetone and tetrahydrofuran (THF) until the filtrate is colorless. The solid powder was transferred to a Soxhlet extractor and extracted with tetrahydrofuran for 24 hours and acetone for 24 hours, respectively. Finally, the product was dynamically activated under vacuum at 120°C for 12 hours to obtain the precursor 2HPor-TPE-COF;

[0139] Under a nitrogen atmosphere, 120 mg of 2HPor-TPE-COF and 200 mg of copper(II) chloride dihydrate were added to a round-bottom flask, followed by 50 mL of ethanol. The resulting suspension was stirred overnight at 40 °C. After the reaction was complete and cooled to room temperature, the product was collected by filtration and washed alternately with deionized water and ethanol, three times each. Finally, the product was vacuum dried at 120 °C for 12 hours to obtain the target product, the porphyrin organic framework material.

[0140] Performance testing:

[0141] The metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 were simulated using Material Studio software, such as... Figure 2 As shown, the metalloporphyrin-oxime bimetallic site covalent organic framework material is found to be a two-dimensional structure composed of stacked layers, and has a rich pore structure with a pore size of about 1.85 nm.

[0142] The metalloporphyrin-oxime bimetallic site covalent organic framework materials from Examples 1-4 were used, and their crystal structures were characterized by powder X-ray diffraction combined with theoretical simulation using Materials Studio software. The test results are shown in the figures below. Figure 3-6 ,from Figure 3-6The powder X-ray diffraction test results showed that the metal porphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 all showed obvious diffraction peaks at 4.15° and 8.35°, which correspond to the (110) and (220) crystal planes in their repeating stacking arrangement theoretical model, respectively. Furthermore, the Pawley refinement results of the metalloporphyrin-oxime bimetallic site covalent organic framework materials in Examples 1-4 above agree well with the experimental data, converging to Rp = 2.00%, Rwp = 2.65% (CoPor-CoOx-COF), Rp = 0.64%, Rwp = 0.82% (CuPor-CuOx-COF), Rp = 1.33%, Rwp = 1.78% (CuPor-CoOx-COF) and Rp = 0.68%, Rwp = 0.90% (CoPor-CuOx-COF), respectively, confirming the rationality and reliability of the calculation model used.

[0143] The metalloporphyrin-oxime bimetallic site covalent organic framework materials from Examples 1-4 were subjected to infrared spectroscopy tests, and the test results are as follows: Figure 7-10 As shown, from Figure 7-10 As can be seen, in the infrared spectra of the metalporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 of the present invention, the crystalline covalent organic framework materials of the metalporphyrin-oxime bimetallic site all showed a new characteristic stretching vibration peak at 1624 cm⁻¹, which belongs to the imine bond. This indicates that the imine bond has been successfully synthesized, thus proving the successful preparation of the metalporphyrin-oxime bimetallic site covalent organic framework material.

[0144] The metalloporphyrin-oxime bimetallic site covalent organic framework material (CuPor-CoOx-COF) from Example 3 was used as a catalyst in the electrocatalytic reduction of nitrate under both light and dark conditions. The obtained linear voltammetry (LSV) curves are shown below. Figure 11 As shown in the figure, CuPor-CoOx-COF exhibits electrocatalytic nitrate reduction performance under both illuminated and unilluminated conditions. Throughout the entire test potential range, the current density under illuminated conditions is significantly higher than that under unilluminated conditions, and the onset potential for electrocatalytic nitrate reduction is more positive under illuminated conditions. These results indicate that illumination effectively reduces the reaction overpotential, accelerates catalytic kinetics, and further significantly enhances the electrocatalytic nitrate reduction activity of this catalyst, demonstrating excellent photoelectric synergistic effects.

[0145] Figure 12 The graph shows the Faradaic efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material (CuPor-CoOx-COF) from Example 3 as a catalyst in the electrocatalytic reduction of nitrate to ammonia under both illuminated and dark conditions, as a function of potential. Figure 12 It can be seen that CuPor-CoOx-COF exhibits excellent electrocatalytic performance in the reduction of nitrate to ammonia under both illuminated and dark conditions. Furthermore, the Faradaic efficiency under illuminated conditions is significantly higher than that under dark conditions across the entire test potential range. Specifically, under illuminated conditions, CuPor-CoOx-COF achieves its highest Faradaic efficiency of 95.00% at -1.1 V vs. RHE, which is higher than the performance under dark conditions. These results indicate that illumination can effectively improve the ammonia selectivity of CuPor-CoOx-COF in the electrocatalytic reduction of nitrate, achieving a superior photoelectrochemical synergistic catalytic effect.

[0146] Figure 13 The linear voltammetric (LSV) curves of the metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 as catalysts for the electrocatalytic reduction of nitrate under light irradiation are shown. As shown in the figure, all four catalysts exhibited electrocatalytic nitrate reduction performance under illumination. Throughout the entire test potential range, CuPor-CoOx-COF (the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3) consistently exhibited the highest current density, reaching approximately -60 mA cm⁻² at -1.2 V vs. RHE potential, indicating its relatively optimal electrocatalytic nitrate reduction activity under illumination. The current densities of the other three catalysts were in the order of CuPor-CuOx-COF (Example 2) > CoPor-CuOx-COF (Example 4) > CoPor-CoOx-COF (Example 1), demonstrating that the metal matching between the porphyrin and oxime sites significantly regulates catalytic activity and selectivity. Furthermore, only when the combination of the porphyrin Cu site and the oxime Co site matches the intrinsic catalytic properties of the two metals can the optimal tandem catalytic effect be achieved, verifying the rationality of the precise dual-site design of this invention.

[0147] Figure 14The graphs show the Faraday efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework materials of Examples 1-4 as catalysts for the electrocatalytic reduction of nitrate to ammonia under light irradiation, as a function of potential. As shown in the figure, all four catalysts exhibited electrocatalytic performance in the reduction of nitrate to ammonia under illumination. Among them, CuPor-CoOx-COF (the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3) showed the highest Faradaic efficiency throughout the entire test potential range, reaching a peak of approximately 95.00% at -1.1 V vs. RHE, indicating that it had the best selectivity for the electrocatalytic reduction of nitrate to ammonia under illumination. The Faradaic efficiencies of the other three catalysts at -1.1 V vs. RHE were in the following order: CuPor-CuOx-COF (Example 2) > CoPor-CuOx-COF (Example 4) > CoPor-CoOx-COF (Example 1), indicating that the metal species of the metalloporphyrin and oxime group had a significant regulatory effect on the ammonia selectivity.

[0148] The porphyrin-oxime organic framework material of Comparative Example 1 was used, and its crystal structure was characterized by powder X-ray diffraction combined with theoretical simulation using MaterialsStudio software. The characterization results are as follows: Figure 15 As shown in the figure, it exhibits obvious diffraction peaks at 4.15° and 8.35°, which correspond to the (110) and (220) crystal planes in its theoretical model of repeated stacking arrangement, respectively.

[0149] Figure 16 The graphs show the Faradaic efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3 and the porphyrin-oxime organic framework material of Comparative Example 1, as a catalyst for photoelectrophotocatalytic reduction of nitrate to ammonia under illumination, as a function of potential. The graphs show that when the porphyrin center lacks Cu... 2+ At that time, the Faraday efficiency of 2HPor-CoOx-COF (the porphyrin-oxime organic framework material of Comparative Example 1) containing only oxime single metal sites was lower than that of CuPor-CoOx-COF (the metalloporphyrin-oxime bimetallic site covalent organic framework material of Example 3) in the RHE test range of -0.8 V to -1.1 V. This indicates that CuPor-CoOx-COF has better selectivity for photoelectrochemical nitrate reduction to ammonia production compared to the oxime single metal site structure.

[0150] Figure 18For the porphyrin organic framework material of Comparative Example 2, the crystal structure of the above material was characterized by powder X-ray diffraction combined with theoretical simulation using Materials Studio software. As shown in the figure, it has obvious diffraction peaks at 4.15° and 8.35°, which correspond to the (110) and (220) crystal planes in its repeating stacking arrangement theoretical model, respectively.

[0151] Figure 19 The graphs show the Faradaic efficiency of the metalloporphyrin-oxime bimetallic site covalent organic framework material (CuPor-CoOx-COF) in Example 3 and the porphyrin organic framework material (CuPor-TPE-COF) in Comparative Example 2, as catalysts for the photoelectrochemical reduction of nitrate to ammonia under illumination, as a function of potential. The graphs show that within the core potential range of -0.9 V to -1.1 V vs. RHE, the ammonia Faradaic efficiency of the metalloporphyrin-oxime bimetallic site crystalline covalent organic framework material catalyst CuPor-CoOx-COF, which contains oxime-based metal active centers and intramolecular hydrogen bonds, is superior to that of CuPor-TPE-COF, which does not contain oxime-based metal active centers and intramolecular hydrogen bonds. The highest Faradaic efficiency is nearly 95%, further demonstrating the excellent catalytic selectivity advantages brought by the oxime-based metal active centers and intramolecular hydrogen bonds in CuPor-CoOx-COF.

[0152] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A metalloporphyrin-oxime bimetallic site covalent organic framework material, characterized in that: It has the structure shown in Equation I: ； M1 and M2 are independently selected from Cu or Co, respectively.

2. The metalloporphyrin-oxime bimetallic site covalent organic framework material according to claim 1, characterized in that: The metalloporphyrin-oxime bimetallic site covalent organic framework material is a two-dimensional layer-by-layer stacked structure.

3. The metalloporphyrin-oxime bimetallic site covalent organic framework material according to claim 1, characterized in that: The pore size of the metalloporphyrin-oxime bimetallic site covalent organic framework material is 1.65–1.85 nm.

4. The metalloporphyrin-oxime bimetallic site covalent organic framework material according to claim 1, characterized in that: The metalloporphyrin-oxime bimetallic site covalent organic framework material has one of the following structures: Formula II Formula III Formula IV Formula V.

5. A method for preparing a metalloporphyrin-oxime bimetallic site covalent organic framework material as described in any one of claims 1 to 4, characterized in that: Includes the following steps: S1 mixes tetraaldehyde phenyl porphyrin monomer, oxime M2Ox monomer and acetic acid aqueous solution in solvent, reacts under vacuum conditions, and after washing and drying, obtains crystalline porphyrin-oxime covalent organic framework material precursor; S2 disperses the crystalline porphyrin-oxime covalent organic framework material precursor obtained in step S1 in a solvent, adds a metal salt containing M1, and reacts to obtain the metalporphyrin-oxime bimetallic site covalent organic framework material.

6. The method according to claim 5, characterized in that: In step S1, the tetraaldehyde phenyl porphyrin monomer is 5,10,15,20-tetra(4-aldehydephenyl)-21H,23H-porphyrin, and the oxime M2Ox monomer is a metal-coordinated dioxime diphenyl diamine compound, wherein the coordinating metal is M2.

7. The method according to claim 5, characterized in that: In step S1, the molar ratio of tetraaldehyde phenylporphyrin monomer, oxime M2Ox monomer and acetic acid is 1:(1-2):(120-200).

8. The method according to claim 5, characterized in that: The mass ratio of the crystalline porphyrin-oxime covalent organic framework material precursor to the M1-containing metal salt is 1:(1.2~2.0).

9. The application of the metalloporphyrin-oxime bimetallic site covalent organic framework material as described in any one of claims 1 to 4 as a catalyst in the electrocatalytic reduction of nitrate.

10. The application of the metalloporphyrin-oxime bimetallic site covalent organic framework material as described in any one of claims 1 to 4 as a catalyst in photoelectrocatalytic nitrate reduction.

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