A copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode and its preparation method and application

Abstract

The present invention provides a copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode, its preparation method and application, which solve the deficiency that the prior art cannot fully exert the potential ability of the metal-organic framework as a catalyst for nitrate reduction to ammonia. The present invention utilizes a hydrogen-substituted graphdiyne nano-thin layer coated on the surface of a copper hydroxide nanowire array to construct a dual-template composite nanoarray that combines the dual advantages of a copper hydroxide chemical template and a hydrogen-substituted graphdiyne physical template. Through an anion exchange reaction with trimesic acid at room temperature, the one-dimensional growth of the copper-based metal-organic framework is achieved, and a copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode with high electrocatalytic activity for nitrate reduction to ammonia is prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite nanomaterials, and particularly relates to a copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode, and a preparation method and application thereof. Background Art

[0002] In the process of industrial and agricultural production, ammonia is an important "zero-carbon" energy carrier. However, its consumption will lead to the accumulation of nitrate in groundwater and gradually become a global water pollutant, seriously affecting human health. Therefore, among many ammonia production technologies, the selective hydrogenation of nitrate to ammonia by electrochemical methods is a green way to close the "nitrogen cycle". Therefore, the development and preparation of functional electrocatalysts have become the key factors restricting its development.

[0003] In nature, nitrate reductase is the most efficient catalyst for reducing nitrate to ammonia, which is composed of a molybdenum active center and a bridging ligand. At the same time, theoretical and experimental studies have shown that the adsorption of reactants at the active sites of the catalyst is also one of the key factors affecting the catalyst efficiency. In view of this, the development of a transition metal-based mimetic enzyme electrocatalyst has great theoretical significance and practical value for the development of artificial electroreduction of nitrate to ammonia.

[0004] Metal-organic frameworks (MOFs), as crystalline materials with an ordered porous structure composed of transition metal ions and organic bridging ligands, not only have a similar composition structure to nitrate reductase in nature, but also have a high density of exposed metal active sites compared with traditional inorganic semiconductor materials. At the same time, these metal active sites can act as Lewis acid catalytic sites to adsorb reactants with Lewis acid-base properties, making them shine in organic catalytic reactions; in addition, theoretically, the unsaturated metal sites in MOFs have an adsorption effect on nitrate ions (Lewis bases), thereby promoting the catalytic conversion of nitrate at the metal sites of MOFs, and it is a potential catalyst for nitrate reduction to ammonia; however, due to the poor conductivity of MOFs, the nodes between metal ions and ligands are prone to structural damage in an electrochemical negative voltage operating environment, resulting in poor electrochemical stability, which severely limits its application potential in electrocatalysis. At present, researchers mostly prepare MOF derivatives by high-temperature calcination for use in electrocatalysis, which seriously destroys the crystal structure of MOFs and is not conducive to the development of its intrinsic electrochemical functionality. At the same time, MOFs are mostly powder materials with a polyhedral structure, and when used, conductive agents, binders, etc. need to be added and coated on the electrode, which not only is not conducive to the diffusion of nitrate ions inside the electrode, but also is prone to falling off during the reaction process, with poor stability, severely limiting the application potential of the intrinsic catalytic activity of MOFs.

[0005] In response to the above problems, the present invention explores an ammonia production catalyst with great application prospects based on a metal-organic framework. Summary of the Invention

[0006] The purpose of the present invention is to address the shortcomings of the existing technology in that it cannot fully utilize the potential of metal organic frameworks as catalysts for nitrate reduction to ammonia, and to provide a copper-based metal organic framework@hydrogen-substituted graphene one-dimensional composite nanoarray electrode and its preparation method and application, which also has catalytic function.

[0007] The concept of the present invention:

[0008] Given that metal organic frameworks (MOFs) have advantages in all aspects as potential catalysts for nitrate reduction to ammonia, the research team of this application has conducted in-depth research on them, trying to change the shortcomings that limit their intrinsic catalytic activity and "modify" them; the research team of this application took into account that hydrogen-substituted graphyne (HsGDY) is a type of organic microporous polymer material with a highly conjugated system composed of benzene rings and diacetylene bonds, which has good chemical stability, conductivity and ion diffusivity, making it promising as a support carrier to solve the conductivity and stability problems faced by MOFs in electrochemical applications. At the same time, since hydrogen-substituted graphyne can form a conformal microporous coating with controllable thickness on the surface of many material substrates during the process of monomer copolymerization; this coating can serve as a conductive channel to improve the conductivity of the material on the one hand; on the other hand, it can serve as a rigid skeleton to improve the stability of the material. Therefore, the present invention designs and develops a one-dimensional nanoarray structure of MOFs and hydrogen-substituted graphyne composites for the electroreduction of nitrate to ammonia.

[0009] To achieve the above objectives, the technical solutions provided by the present invention are:

[0010] A copper-based metal-organic framework@hydrogen-substituted graphene one-dimensional composite nanoarray (Cu3(BTC)2@HsGDY), which is unique in that it includes a conductive copper substrate and a one-dimensional composite nanowire array with a core-shell structure neatly arranged and grown on the copper substrate;

[0011] Each composite nanowire includes an inner layer of a copper metal organic framework (Cu3(BTC)2) with a face-centered cubic structure and a hierarchical porous structure with a diameter of 200-300 nanometers, and an outer layer of a microporous hydrogen-substituted graphyne (HsGDY) nanolayer with a large conjugated structure uniformly coated on the inner layer and a thickness of 20-30 nanometers. The length of each composite nanowire is 5-10 microns.

[0012] Furthermore, the inner layer of the copper metal organic framework is distributed with micropores of 0.5 nm, 0.8 nm and 1.2 nm, and mesopores of 4.0 nm;

[0013] The inner part of the outer layer of the hydrogen-substituted graphdiyne nanosheet has micropores with a size of 1.3 nanometers;

[0014] The copper substrate is made of copper foam with three-dimensional interconnected pores.

[0015] The preparation method of the above copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray is characterized in that it includes the following steps:

[0016] 1) Pretreatment

[0017] The copper substrate is pretreated to remove organic impurities and oxide layers on the surface, and then dried for later use;

[0018] 2) Preparation of copper hydroxide nanowire array

[0019] Sodium hydroxide and ammonium persulfate are dissolved in ultrapure water, and the copper substrate pretreated in step 1) is placed therein. After standing at room temperature (20 - 25 °C) for 12 - 16 minutes (preferably 15 minutes), a copper hydroxide (Cu(OH)2) nanowire array is obtained on the surface of the copper substrate;

[0020] 3) Preparation of copper hydroxide @ hydrogen-substituted graphdiyne composite nanoarray double template

[0021] 3.1) Copper(I) iodide and bis(triphenylphosphine)palladium(II) chloride are stirred and dispersed in a mixed solution of triethylamine and tetrahydrofuran at room temperature; an eggplant-shaped flask can be used for this operation;

[0022] 3.2) The copper substrate with the copper hydroxide nanowire array obtained in step 2) is fixed in the mixed solution obtained in step 3.1). After introducing an inert gas (such as high-purity argon, nitrogen) to remove oxygen in the mixed solution, 1,3,5-triethynylbenzene copolymer monomer is quickly added. Under the protection of an inert gas (such as high-purity argon, nitrogen), it is stirred at a speed of 300 - 1000 revolutions per minute (stirring can promote the uniform cross-linking of the copolymer monomer on the surface of the nanowire array) and heated to 60 °C for reaction for 12 - 24 hours. Under such mild reaction conditions, the 1,3,5-triethynylbenzene copolymer monomer can be uniformly copolymerized and cross-linked on the surface of the copper hydroxide nanowire array through Glaser coupling reaction to form a hydrogen-substituted graphdiyne nano-coating layer, and a copper hydroxide @ hydrogen-substituted graphdiyne (Cu(OH)2@HsGDY) composite nanoarray double template with a core-shell structure is obtained on the copper substrate;

[0023] 4) Preparation of copper metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode

[0024] The copper substrate with the copper hydroxide@hydrogen-substituted graphdiyne composite nanoarray obtained in step 3) was placed in a mixed solution of ethanol and water containing trimesic acid, and left standing at room temperature (20 - 25 °C) for 6 - 10 hours to obtain a copper-based metal-organic framework@hydrogen-substituted graphdiyne (Cu3(BTC)2@HsGDY) one-dimensional composite nanoarray electrode.

[0025] Further, step 1) specifically is:

[0026] The copper substrate was ultrasonically treated successively with acetone and 3M hydrochloric acid to remove organic impurities and oxide layers on the surface, and then washed clean with water and ethanol successively and dried.

[0027] Further, in step 2), the molar ratio of sodium hydroxide to ammonium persulfate is 20∶1, and the molar concentration of sodium hydroxide after dissolution is 2.67 mol / L.

[0028] Further, in step 3.1), the mass ratio of cuprous iodide to bis(triphenylphosphine)palladium(II) chloride is 1.1∶4.2; the volume ratio of triethylamine to tetrahydrofuran is 2∶1; in the mixed solution of triethylamine and tetrahydrofuran, the mass concentration of cuprous iodide is 0.05 - 0.10 g / L, and the mass concentration of bis(triphenylphosphine)palladium(II) chloride is 0.19 - 0.38 g / L;

[0029] In step 3.2), the mass concentration of 1,3,5-triethynylbenzene comonomer is 0.16 - 0.33 g / L, and the thickness of the hydrogen-substituted graphdiyne coating layer can be adjusted by regulating the mass concentration of the comonomer. The higher the concentration, the thicker the layer;

[0030] The stirring speed is 600 revolutions per minute.

[0031] In step 4), the volume ratio of ethanol to water is 23∶9, and the mass concentration of trimesic acid is 0.02 - 0.05 g / mL.

[0032] Meanwhile, the present invention also provides the application of the above-mentioned copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode as both a cathode electrode and a catalyst (that is, this electrode simultaneously takes into account the functions of the cathode and the catalyst) in the electrocatalytic reduction of nitrate to ammonia.

[0033] And, a method for electrocatalytic reduction of nitrate to ammonia using the above-mentioned copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode, which is characterized in that:

[0034] In an H-type electrolytic cell, a three-electrode system is adopted. The copper metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode is directly used as the cathode electrode and placed in a 0.5 M neutral aqueous solution of sodium sulfate containing 200 ppm potassium nitrate. A voltage range of -0.5 to -0.9 V vs RHE is applied, and the test duration is 2 h to conduct the electroreduction of nitrate to ammonia reaction. The best ammonia production Faraday efficiency (90.1%) is achieved at -0.7 V vs RHE, and the ammonia production rate is 4.2 mg h -1 cm -2 。

[0035] Furthermore, a silver / silver chloride electrode is used as the reference electrode, and a platinum sheet is used as the counter electrode.

[0036] The mechanism of the present invention:

[0037] The present invention utilizes a hydrogen-substituted graphdiyne nano-thin layer coated on the surface of copper hydroxide nanowire arrays to construct a dual-template composite nanoarray that combines the dual advantages of the chemical template of copper hydroxide and the physical template of hydrogen-substituted graphdiyne. Through an anion exchange reaction with trimesic acid at room temperature, the one-dimensional growth of copper-based metal-organic frameworks is realized, and a copper-based metal-organic framework @ hydrogen-substituted graphdiyne (Cu3(BTC)2@HsGDY) one-dimensional composite nanoarray electrode with high electrocatalytic reduction activity of nitrate to ammonia is prepared.

[0038] The beneficial effects of the present invention are:

[0039] 1. The copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode is synthesized for the first time and successfully used for electrocatalytic nitrate reduction to ammonia, achieving the best ammonia production Faraday efficiency (90.1%) at -0.7 V vs RHE, and the yield is 4.2 mg h -1 cm -2 。

[0040] 2. In the present invention, the copper-based metal-organic framework (Cu3(BTC)2) can act as a Lewis acid catalyst to provide more catalytic active sites, regulate the distribution of adsorbed nitrate (*NO3) and adsorbed hydrogen (*H) at the copper active sites, and enhance the activity and selectivity of electroreduction of nitrate to ammonia.

[0041] 3. In the present invention, the hydrogen-substituted graphdiyne coating layer can, on the one hand, provide a micro reaction space to guide the synthesis of one-dimensional copper-based metal-organic frameworks; on the other hand, it can act as an electron transport layer and a rigid skeleton to shorten the electron transport distance inside the copper-based metal-organic frameworks, reduce the damage of electrons to the nodes between metal ions and ligands, and enhance its catalytic kinetic activity and the stability of the overall electrode material.

[0042] 4. Compared with the powder material, the one-dimensional nanoarray structure of the present invention is neatly arranged on the conductive substrate. On the one hand, it can be directly used as a working electrode, thus effectively avoiding the agglomeration of the catalyst; on the other hand, it is conducive to the mass transfer of nitrate and improves the kinetic activity of the catalytic reaction. In summary, the development of the one-dimensional MOFs nanoarray structure with a composite conductive layer has important development prospects for improving its kinetic activity and stability and expanding its practical application in the electroreduction of nitrate to ammonia. Description of the Drawings

[0043] Figure 1 It is a scanning electron microscope (SEM) photograph of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention.

[0044] Figure 2 It is a transmission electron microscope (TEM) photograph of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention.

[0045] Figure 3 It is an X-ray diffraction (XRD) pattern of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention.

[0046] Figure 4 It is the N2 adsorption-desorption curve and pore size distribution diagram of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention.

[0047] Figure 5 It is a linear sweep voltammogram of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention in the presence / absence of nitrate solution.

[0048] Figure 6 The ammonia production rate and Faraday efficiency diagram of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray prepared by the present invention at different potentials. Detailed Description of the Invention

[0049] The following further describes the content of the present invention in detail with reference to the drawings and specific examples:

[0050] Example 1:

[0051] Step 1: Take 2×3 cm 2 of copper foam, and ultrasonically treat it successively with acetone and 3M hydrochloric acid to remove the organic impurities and oxide layer on the surface, and then wash it clean with water and ethanol in turn and dry it.

[0052] Step 2: Weigh 0.16 mol of sodium hydroxide and 8 mmol of ammonium persulfate, dissolve them in a beaker containing 60 mL of ultrapure water at room temperature, then put the copper foam from Step 1 into it, let it stand and react at room temperature for 15 minutes, and after washing, Cu(OH)2 nanowire arrays are obtained.

[0053] Step 3: Weigh 4.4 mg of cuprous iodide and 16.8 mg of bis(triphenylphosphine)palladium(II) chloride and disperse them in a Schlenk flask containing a mixed solution of 40 mL of triethylamine and 20 mL of tetrahydrofuran. Fix the Cu(OH)2 nanowire arrays obtained in Step 2 in the Schlenk flask, purge with argon for 15 minutes to remove the oxygen in the mixed solution, quickly add 14 mg of 1,3,5-triethynylbenzene co-monomer, and under argon protection, react in an oil bath at 60 °C with a rotation speed of 600 rpm for 12 hours. After washing, a copper hydroxide@hydrogen-substituted graphdiyne (Cu(OH)2@HsGDY) composite nanowire array double template is obtained.

[0054] Step 4: Dissolve 1.05 g of benzene-1,3,5-tricarboxylic acid in a beaker containing 23 mL of ethanol and 9 mL of water, then place the copper hydroxide@hydrogen-substituted graphdiyne composite nanowire arrays obtained in Step 3 into it and let it stand at room temperature for 6 hours. After washing, a copper metal-organic framework@hydrogen-substituted graphdiyne (Cu3(BTC)2@HsGDY) one-dimensional composite nanowire array is obtained.

[0055] Example 2:

[0056] The reaction is carried out using the method of Example 1, except that the reaction time in Step 3 is 18 hours.

[0057] Example 3:

[0058] The reaction is carried out using the method of Example 1, except that the reaction time in Step 3 is 24 hours.

[0059] Example 4:

[0060] The reaction is carried out using the method of Example 1, except that the addition amount of 1,3,5-triethynylbenzene co-monomer in Step 3 is 10 mg.

[0061] Example 5:

[0062] The reaction is carried out using the method of Example 1, except that the addition amount of 1,3,5-triethynylbenzene co-monomer in Step 3 is 20 mg.

[0063] Example 6:

[0064] The reaction is carried out using the method of Example 1, except that the mass of benzene-1,3,5-tricarboxylic acid added in Step 4 is 0.64 g.

[0065] Example 7:

[0066] The reaction was carried out using the method of Example 1, except that 1.6 g of trimesic acid was added in Step 4.

[0067] Example 8:

[0068] The reaction was carried out using the method of Example 1, except that the reaction time in Step 4 was 10 h.

[0069] Result analysis

[0070] As Figure 1 and Figure 2 shown, the morphology of the copper metal-organic framework@hydrogen-substituted graphdiyne (Cu3(BTC)2@HsGDY) composite nanorod arrays prepared in Example 1 was characterized by SEM and TEM. The copper metal-organic framework@hydrogen-substituted graphdiyne was a one-dimensional composite nanorod array structure uniformly grown on the copper foam substrate. Among them, the overall length of the composite nanorod array was 5-10 μm, the thickness of the outer hydrogen-substituted graphdiyne (HsGDY) shell was 20-30 nm, and the diameter of the inner copper metal-organic framework (Cu3(BTC)2) was 200-300 nm.

[0071] As Figure 3 shown, XRD analysis indicated that Cu(OH)2 encapsulated inside HsGDY was successfully and completely converted into face-centered cubic phase Cu3(BTC)2.

[0072] As Figure 4 shown, through the nitrogen adsorption-desorption isotherm and pore size distribution analysis, the copper metal-organic framework@hydrogen-substituted graphdiyne composite nanorod array was a hierarchical porous nanostructure containing micropores and mesopores (Cu3(BTC)2: micropores of 0.5 nm, 0.8 nm and 1.2 nm, and mesopores of 4.0 nm; HsGDY: micropores of 1.3 nm).

[0073] The specific steps for testing the electrocatalytic reduction of nitrate to ammonia using the copper metal-organic framework@hydrogen-substituted graphdiyne composite nanorod arrays prepared in the present invention were as follows: The electrocatalytic reduction of nitrate to ammonia reaction was carried out in an H-type electrolytic cell containing a proton exchange membrane (Nafion-117) using a three-electrode system. The electrolyte was 0.5 M sodium sulfate + 200 ppm potassium nitrate solution (0.5 M sodium sulfate solution was used as a blank control). The copper metal-organic framework@hydrogen-substituted graphdiyne composite nanorod array was directly used as the working electrode, the silver / silver chloride electrode was used as the reference electrode, and the platinum sheet was used as the counter electrode. The test was carried out using a CHI electrochemical workstation. As Figure 5 shown in the linear sweep voltammogram, the copper metal-organic framework@hydrogen-substituted graphdiyne composite nanorod array had electrocatalytic reduction activity for nitrate, as Figure 6As shown, in a 0.5 M sodium sulfate + 200 ppm potassium nitrate solution, the copper metal-organic framework @ hydrogen-substituted graphdiyne composite nanoarray has an ammonia production rate in the range of 4.0 - 4.5 mg h -1 cm -2 , and a Faraday efficiency of 85 - 90%.

[0074] Similarly, for the target products prepared in Examples 2 - 8, observations and performance tests were carried out, and they all had the same effects as the examples. Therefore, the practical application of the present invention in the electroreduction of nitrate to ammonia has important development prospects.

[0075] The above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode, characterized in that: It includes a copper substrate and an array of composite nanowires with a core-shell structure that are neatly arranged and grown on the copper substrate; Each composite nanowire includes an inner layer of copper metal-organic framework with a hierarchical porous structure having a diameter of 200 - 300 nanometers, and an outer layer of a microporous hydrogen-substituted graphdiyne nanothin layer with a thickness of 20 - 30 nanometers uniformly coated on the inner layer, and the length of each composite nanowire is 5 - 10 micrometers; The copper metal-organic framework is Cu3(BTC)2.

2. The copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanowire array electrode according to claim 1, characterized in that: Micropores with diameters of 0.5 nanometers, 0.8 nanometers, and 1.2 nanometers and mesopores with a diameter of 4.0 nanometers are distributed inside the inner layer of the copper metal-organic framework; Micropores with a diameter of 1.3 nanometers are distributed inside the outer layer of the hydrogen-substituted graphdiyne nanothin layer; The copper substrate uses copper foam.

3. The preparation method of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode according to any one of claims 1 or 2, characterized in that, It includes the following steps: 1) Pretreatment The copper substrate is pretreated to remove organic impurities and oxide layers on the surface, and then dried for standby; 2) Preparation of copper hydroxide nanowire array Sodium hydroxide and ammonium persulfate are dissolved in ultrapure water, and the copper substrate pretreated in step 1) is placed therein, and left standing at room temperature for 12 - 16 minutes to obtain an array of neatly arranged copper hydroxide nanowires on the copper substrate surface; 3) Preparation of copper hydroxide@hydrogen-substituted graphdiyne composite nanowire array double template 3.1) Copper iodide and bis(triphenylphosphine)palladium(II) chloride are stirred and dispersed in a mixed solution of triethylamine and tetrahydrofuran at room temperature; 3.2) The copper substrate with the copper hydroxide nanowire array obtained in step 2) is fixed in the mixed solution obtained in step 3.1), after introducing an inert gas to remove oxygen in the mixed solution, 1,3,5-triethynylbenzene copolymer monomer is added, and under the protection of an inert gas, it is stirred and heated to 60°C at a rotation speed of 300 - 1000 revolutions per minute for 12 - 24 hours to obtain a copper hydroxide@hydrogen-substituted graphdiyne composite nanowire array double template with a core-shell structure on the copper substrate; 4) Preparation of copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanowire array electrode The copper substrate with the copper hydroxide@hydrogen-substituted graphdiyne composite nanowire array obtained in step 3) is placed in a mixed solution of ethanol and water containing trimesic acid, and left standing at room temperature for 6 - 10 hours to obtain a copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanowire array electrode.

4. The preparation method of the copper-based metal-organic framework @ hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode according to claim 3, wherein Step 1) specifically is: The copper substrate is ultrasonically treated successively with acetone and 3M hydrochloric acid to remove organic impurities and oxide layers on the surface, and then washed clean with water and ethanol successively and dried.

5. The preparation method of the copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanowire array electrode according to claim 3 or 4, characterized in that: In step 2), the molar ratio of sodium hydroxide to ammonium persulfate is 20∶1, and the molar concentration of sodium hydroxide after dissolution is 2.67 mol / L.

6. The preparation method of the copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanowire array according to claim 5, characterized in that: In step 3.1), the mass ratio of cuprous iodide to bis(triphenylphosphine)palladium(II) chloride is 1.1∶4.2; the volume ratio of triethylamine to tetrahydrofuran is 2∶1; in the mixed solution of triethylamine and tetrahydrofuran, the mass concentration of cuprous iodide is 0.05 - 0.10 g / L, and the mass concentration of bis(triphenylphosphine)palladium(II) chloride is 0.19 - 0.38 g / L; In step 3.2), the mass concentration of 1,3,5-triethynylbenzene comonomer is 0.16 - 0.33 g / L; The stirring speed is 600 revolutions per minute.

7. The preparation method of the copper-based metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode according to claim 6, wherein: In step 4), the volume ratio of ethanol to water is 23∶9, and the mass concentration of trimesic acid is 0.02 - 0.05 g / mL.

8. The application of the copper metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode according to claim 1 or 2 as both a cathode electrode and a catalyst in the electrocatalytic reduction of nitrate to ammonia.

9. A method for electrocatalytic reduction of nitrate to ammonia using the copper metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode according to claim 1 or 2, wherein: In an H-type electrolytic cell, a three-electrode system is adopted. The copper metal-organic framework@hydrogen-substituted graphdiyne one-dimensional composite nanoarray electrode is used as the cathode electrode, and a 0.5 M neutral aqueous solution of sodium sulfate containing 200 ppm potassium nitrate is used as the electrolyte. The applied voltage range is -0.5 to -0.9 V vs RHE, and the test duration is 2 h for the electroreduction reaction of nitrate to ammonia.

10. The method according to claim 9, wherein: A silver / silver chloride electrode with an internal 3 M potassium chloride solution is used as the reference electrode, and a platinum sheet is used as the counter electrode.

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