A naphthalene tetracarboximide-based metal-organic framework semiconductor material, a preparation method therefor and applications thereof

Abstract

The application belongs to the technical field of metal organic framework materials and electrocatalytic materials, and particularly relates to a metal organic framework semiconductor material based on 1,4,5,8-naphthalene tetracarboxylic diimide and a preparation method and application thereof. The material is represented by a formula M(Py-NDI)2(Cl)2, wherein M=Co, Ni; the material is a single crystal material, has a two-dimensional layered structure, belongs to a monoclinic system, a p21 / c space group, a node is a M-N4 structure, one M(II) is coordinated with two chlorine ions and four pyridine groups in a ligand, the two-dimensional layered structure is formed by AB stacking to form a 3D M-cMOF single crystal structure, and the material prepared by the application has simple synthesis steps, mild required conditions, and the obtained two-dimensional sheet structure single crystal material has high conductivity, high stability and high efficient electrocatalytic oxygen reduction activity.

Description

Technical Field

[0001] This invention belongs to the technical field of metal-organic framework materials and electrocatalytic materials, and in particular relates to a metal-organic framework semiconductor material based on 1,4,5,8-naphthalenetetracarboxydiimide, its preparation method and application. Background Technology

[0002] Metal-organic frameworks (MOFs) have been extensively studied in electrocatalysis, as they have in other catalytic fields, due to their homogeneous structure which imparts high selectivity. A major obstacle to the electrocatalytic application of MOFs is their poor stability in aqueous solutions, especially in strongly alkaline solutions; and / or poor electrochemical stability at the reaction potential, which often leads to the reduction or decomposition of MOFs into metals, metal oxides, or metal hydroxides. Therefore, it is essential to develop MOF materials with high electrocatalytic stability to ensure stable electrocatalysis for hundreds of hours at commercial current densities.

[0003] According to the hard-soft acid-base theory, MOFs constructed through coordination between soft bases and soft acids exhibit strong base stability. Studies have shown that constructing conductive MOFs to ensure effective electron conduction during electrocatalysis can not only improve the activity of MOF catalysts but also prevent structural reconstruction before and after the reaction. However, traditional MOF materials are generally insulating due to their poor conductivity. Therefore, preparing metal-organic framework materials with high stability and high conductivity has become a new challenge. Summary of the Invention

[0004] To address the problem of poor stability of current metal-organic framework electrocatalysts, this invention aims to improve chemical stability under alkaline conditions by enhancing coordination bonds and improving electrochemical stability by accelerating charge conduction. This invention provides a metal-organic framework semiconductor material based on naphthalene tetradiimide, its preparation method, and its applications.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] The first aspect of this invention provides a metal-organic framework semiconductor material based on naphthalene tetradiimide, the material being represented by the formula M(NDI)₂(Cl)₂, where M = Co and Ni; the material is a single crystal material with a two-dimensional layered structure, belonging to the monoclinic crystal system, p21 / c space group, with an M-N₄ structure, one M(II) ion coordinated to two chloride ions and pyridine groups in four ligands, the two-dimensional layered structure being a 3D M-cMOF single crystal structure formed by stacking AB layers, with interlayer spacing of...

[0007] The second aspect of this invention provides a method for preparing the above-mentioned metal-organic framework semiconductor material, using N,N'-di(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide as a bridging ligand and divalent metal M ions as metal nodes, to synthesize a metal-organic framework semiconductor material with M-N4 via solvent diffusion; the synthetic route is as follows:

[0008] MCl2·6H2O+3-NDI-Py→M(NDI)2(Cl)2.

[0009] Preferably, the method includes the following steps:

[0010] (1) N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide was added to chloroform to prepare the bottom layer solution, and the salt of the divalent M metal was added to methanol to prepare the upper layer solution. The middle layer was a methanol solution.

[0011] (2) Place the reaction solution obtained in step (1) in a test tube and react at room temperature for at least two weeks until crystals precipitate.

[0012] (3) Wash with chloroform three times, filter, and then calcine at 300-400℃ for 1-10 hours under nitrogen protection to obtain metal-organic framework semiconductor material.

[0013] Preferably, the concentration of N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide in the bottom layer solution is 1-100 mg / mL, the concentration of the divalent M metal salt in the upper layer solution is 2-200 mg / mL, the molar ratio of N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide to M metal is 2:1, and the intermediate layer is pure methanol.

[0014] Preferably, the salt of the divalent M metal is CoCl2·6H2O or NiCl2·6H2O.

[0015] Preferably, the preparation method of N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide includes the following steps:

[0016] a. Place 1,4,5,8-naphthalenetetracarboxylic anhydride and 3-(aminomethyl)pyridine in a molar ratio of 1:2 into a round-bottom beaker containing 15 ml of DMF, and heat the mixture under reflux and stir for 12 h;

[0017] b. After cooling, the black solution was filtered off, and a brownish-yellow crude solid was obtained. The solid was washed three times with acetone to obtain N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimine.

[0018] The third aspect of the present invention provides a method for preparing a gas diffusion electrode, wherein the metal-organic framework semiconductor material is ground, ultrasonically dispersed in an ethanol solution of Nafion, and then loaded onto a carbon material to obtain a gas diffusion electrode.

[0019] Preferably, the metal-organic framework semiconductor material has a concentration of 5 mg / ml in ethanol; the carbon support includes one of glassy carbon, carbon paper, and carbon cloth; and the loading of the metal-organic framework material in the gas diffusion electrode is 0.1 mg / cm³. 2 The electrode area is 1 cm². 2 .

[0020] The fourth aspect of the present invention provides an application of the above-described gas diffusion electrode in the electrocatalytic oxygen reduction preparation of hydrogen peroxide.

[0021] The MOF electrode is used as the cathode, and the nickel foam, Pt-Ti, or Pt electrode is used as the anode. The anode and cathode are separated by anion exchange membrane or cation exchange membrane, and a 0.1M potassium hydroxide aqueous solution is used as the electrolyte.

[0022] The present invention has the following beneficial effects:

[0023] 1. This invention integrates a soft base containing a pyridine group and a soft acid metal center into a catalytic center of M-N4. Based on the principle of soft and hard acid-base theory, this can endow the framework with strong base stability and thermal stability. The two-dimensional coordination structure can endow this metal-organic framework semiconductor material with strong conductivity at room temperature through strong interlayer π-π interactions and the redox properties of 1,4,5,8-naphthalenetetracarboxylic diimide itself. This metal-organic framework semiconductor material contains strong metal / ligand chelating interactions and strong interlayer π-π stacking, which can effectively confine the M-N4 center and improve its charge transport, thus helping to improve chemical and electrochemical stability.

[0024] 2. The synthesis steps of this invention are simple and the required conditions are mild. After simple grinding, the MOF single crystal is loaded onto a gas diffusion electrode. The excellent conductivity of MOF is conducive to charge conduction, contributing to the high activity and electrochemical stability of the catalyst.

[0025] 3. The semiconductor metal-organic framework material catalyst of the present invention has strong coordination bonds and high conductivity, which ensures its high chemical stability and electrocatalytic stability. The uniformly dispersed M-N4 catalytic centers ensure its high selectivity for electrocatalytic oxygen reduction to generate hydrogen peroxide. Attached Figure Description

[0026] Figure 1 This is a two-dimensional layered structure diagram of the metal-organic framework semiconductor material in Example 1;

[0027] Figure 2The image shows the XRD pattern of the metal-organic framework semiconductor material in Example 1, and the comparison between the simulated PXRD pattern and the measured powder XRD pattern.

[0028] Figure 3 Thermogravimetric analysis (TGA) of the metal-organic framework semiconductor material in Example 2;

[0029] Figure 4 This is a linear sweep voltammetry curve of the gas diffusion electrode of the metal-organic framework semiconductor material in Example 5. Detailed Implementation

[0030] The present invention will now be described in detail with reference to examples and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0031] Example 1

[0032] 40.0 mg (0.1 mmol) of N,N'-bis(3-pyridyl)-1,4,5,8-naphthotetramethyldiimide, a ligand derived from 1,4,5,8-naphthotetramethyldiimide, was dissolved in 10 mL of chloroform and added to the bottom of a 25 mL test tube as the lower layer. 2 mL of methanol was slowly added dropwise to the surface of the liquid as an intermediate buffer layer. Subsequently, 3 mL of a methanol solution containing 29.7 mg (0.125 mmol) of CoCl2·6H2O or NiCl2·6H2O was slowly added to the methanol buffer layer. After the addition was complete, the tube was carefully sealed and left to stand at room temperature for two weeks to obtain needle-like crystals.

[0033] like Figure 1 As shown, this conductive MOF single crystal exists in monoclinic space group p21 / c. The asymmetric unit consists of a ligand, an independent divalent metal ion, a Cl- anion, and a free water molecule. Based on the asymmetric unit, a two-dimensional structure is formed through coordination bonds, which possesses… The pores. Through strong π-π stacking interactions of the naphthalenediimide motif, adjacent layers further stack into an alternating AB stacking model, forming a three-dimensional framework. The distance between two layers is calculated as... Strong hydrogen bonds were observed between the lattice water and the framework.

[0034] The XRD results of this MOF single crystal are in Figure 2 As can be seen from the figure, the XRD of the experimentally synthesized single crystal material matches the curve of the simulated X-ray single crystal diffraction, indicating that the synthesized single crystal material has good crystallinity and purity.

[0035] Example 2

[0036] The thermal stability of the metal-organic framework semiconductor single crystal material prepared in Example 1 was characterized by thermogravimetric analysis (TGA). The TGA was conducted under a nitrogen atmosphere at a heating rate of 5 °C / min. Thermogravimetric analysis is as follows: Figure 3As shown, the results indicate a two-step weight loss. The first step, approximately 10% weight loss, occurs below 200℃, attributed to surface adsorption and the removal of solvent molecules from the pores within the single crystal. The second step involves the decomposition of the single crystal ligands at around 400℃, demonstrating the material's good thermal stability. Furthermore, 50mg of the single crystal from the urban area was heated to 350℃ in a tube furnace with nitrogen purging at a rate of 5℃ / min and maintained for two hours, followed by natural cooling to room temperature. The structure remained unchanged compared to the sample before heat treatment.

[0037] Single-crystal stability test of metal-organic framework materials: 50 mg of single crystal was weighed and immersed in 10 mL of aqueous solution for 24 h, followed by centrifugation and drying. The structure of the sample remained unchanged after immersion.

[0038] Example 3

[0039] Weigh 50 mg of the metal-organic framework material single crystal prepared in Example 1 and grind it into powder in an agate mortar. Add the powder to a 0.25 wt% Nafion ethanol solution and disperse it with ultrasonic assistance to prepare a 5 mg / mL suspension. Drop it onto a carbon support and let it dry naturally to serve as the working electrode.

[0040] Example 4

[0041] The electrode obtained in Example 3 was installed in an H-type cell or a flow cell, and the electrochemical stability of the catalyst was tested using a 1M potassium hydroxide solution as the electrolyte solution.

[0042] Comparison of experimental data between the catalyst obtained after the electrocatalytic oxygen reduction reaction and the metal-organic framework material before the reaction revealed no significant changes, indicating that the MOF exhibits high electrochemical stability during the electrocatalytic oxygen reduction process. Furthermore, the electrode maintained a constant current of 400 mA / cm². 2 and 200mA / cm 2 The ability to stably catalyze the reduction of oxygen to produce hydrogen peroxide with a selectivity of over 90% for 40 hours and 130 hours respectively demonstrates the electrocatalytic stability of this gas diffusion electrode.

[0043] Example 5

[0044] The gas diffusion electrode prepared in Example 3 was installed in a flow cell. Linear sweep voltammetry (LSV) tests were performed on the catalyst using 1.0 M and 0.1 M potassium hydroxide solutions as electrolytes, respectively, yielding high current densities of 200 mA and 1000 mA. Figure 4 This demonstrates that the electrode possesses high electrocatalytic oxygen reduction activity. Furthermore, measurements were performed at 10, 35, 75, 100, 200, 300, 754, and 800 mA / cm². 2 The selectivity of hydrogen peroxide under electric current, except for 800 mA / cm2 Except for a selectivity of 84% for hydrogen peroxide, the selectivity is 100% at all other current densities.

[0045] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for producing a gas diffusion electrode, characterized by, Metal-organic framework semiconductor materials are milled, ultrasonically dispersed in Nafion's ethanol solution, and then loaded onto carbon materials to obtain a gas diffusion electrode. The metal-organic framework semiconductor material is represented by the formula M(NDI)2(Cl)2, where M = Co and Ni; the material is a single crystal material with a two-dimensional layered structure, belonging to the monoclinic crystal system, p21 / c space group, with M-N4 nodes, one M(II) coordinated to two chloride ions and pyridine groups in four ligands, the two-dimensional layered structure is formed by stacking AB to form a 3D M-cMOF single crystal structure with an interlayer spacing of 3.35 Å; The metal-organic framework semiconductor material is prepared by using N,N'-di(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide as a bridging ligand and divalent metal M ions as metal nodes, via solvent diffusion to synthesize a metal-organic framework semiconductor material with M-N4; the synthetic route is as follows: MCl2·6H2O+ 3-NDI-Py → M(NDI)2(Cl)2.

2. The method for producing a gas diffusion electrode according to claim 1, characterized by, The preparation method of the metal-organic framework semiconductor material includes the following steps: (1) N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide was added to chloroform to prepare the bottom layer solution, and the salt of the divalent M metal was added to methanol to prepare the upper layer solution. The middle layer was a methanol solution. (2) Place the reaction solution obtained in step (1) in a test tube and react at room temperature for at least two weeks until crystals precipitate; (3) Wash with chloroform three times, filter, and then calcine at 300-400℃ for 1-10 hours under nitrogen protection to obtain metal-organic framework semiconductor material.

3. The production method of a gas diffusion electrode according to claim 2, characterized by, The concentration of N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide in the bottom layer solution is 1-100 mg / mL, the concentration of the divalent M metal salt in the upper layer solution is 2-200 mg / mL, the molar ratio of N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimide to M metal is 2:1, and the intermediate layer is pure methanol.

4. The method for producing a gas diffusion electrode according to claim 2, characterized by, The preparation method of the N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthalenetetramethyldiimide includes the following steps: a. Place 1,4,5,8-naphthalenetetracarboxylic anhydride and 3-(aminomethyl)pyridine in a molar ratio of 1:2 into a round-bottom beaker containing 15 ml of DMF, and heat the mixture under reflux with stirring for 12 h; b. After cooling, filter off the black solution to obtain a brownish-yellow crude solid substance, and wash it three times with acetone to obtain N,N'-bis(3-methylpyridinyl)-1,4,5,8-naphthyltetramethyldiimine.

5. The method for producing a gas diffusion electrode according to claim 1, characterized by, The metal-organic framework semiconductor material has a concentration of 5 mg / ml in ethanol; the carbon material includes one of glassy carbon, carbon paper, and carbon cloth; the loading of the metal-organic framework material in the gas diffusion electrode is 0.1 mg / cm³. 2 The electrode area is 1 cm². 2 .

6. The application of a gas diffusion electrode prepared by the method according to any one of claims 1-5 in the electrocatalytic oxygen reduction to prepare hydrogen peroxide.

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