Preparation and application of anderson type polyacid modified co-mof nanoflower-like electrocatalyst

Abstract

The present application relates to a kind of Anderson type polyacid modified Co-MOF nanoflower electrocatalyst preparation and application.The purpose of the present application is to solve the problems of poor electrocatalytic ability, easy dissolution and poor conductivity of metal-organic framework as base material caused by polyacid enrichment in existing polyacid-based materials, to improve the electrocatalytic efficiency of ammonia production materials. A kind of Anderson type nickel molybdenum polyacid (referred to as NiMo6) modified cobalt-based metal-organic framework (referred to as Co-MOF) nanoflower electrocatalyst (referred to as Co-MOF / NiMo6) is designed and developed in this patent. Based on the strong acidity of polyacid, it plays an etching role. The composite material has a nanoflower structure. This Anderson type polyacid modified Co-MOF nanoflower electrocatalyst not only has a high specific surface area of layered structure and rich active sites, but also solves the problem of easy dissolution of polyacid in water. The Co-MOF / NiMo6 composite electrocatalytic material obtained by the present application is used for normal temperature and pressure electrocatalytic reduction of nitrate to produce ammonia.

Description

Technical Field

[0001] This invention belongs to the technical field of catalyst materials for electrocatalytic nitrate reduction to ammonia synthesis, specifically relating to the preparation and application of an Anderson-type polyacid modified Co-MOF nanoflower-like electrocatalyst. Background Technology

[0002] Due to the large-scale discharge of domestic sewage and industrial wastewater, as well as the extensive use of agricultural fertilizers, nitrates are accumulating in natural water bodies, becoming a significant pollutant that harms water resources. Therefore, taking effective measures to remove nitrates from water bodies is of paramount importance in water pollution control. The electrocatalytic reduction of nitrates to ammonia can not only effectively remove the pollutant nitrates from water bodies but also produce high-quality, high-value, zero-carbon, hydrogen-rich ammonia fuel, alleviating the energy crisis while improving environmental pollution, and thus has significant application prospects. To improve the yield and efficiency of ammonia synthesis, the catalyst for the electrocatalytic reduction of nitrates needs to be rationally designed; this is the key technological breakthrough in this research direction.

[0003] Polyoxometalates (POMs), also known as polyoxometalates, are nanoscale, electron-rich inorganic metal-oxygen clusters composed of former transition metals (Mo, W, V, Nb, Ta) coordinated with oxygen atoms. POMs exhibit diverse structures and compositions, and their composition, structure, and charge density can be adjusted by changing the types of heteroatoms. Anderson-type POMs, in particular, possess strong redox capabilities, making them suitable for electrocatalytic reactions. However, POMs are highly soluble in water and organic solvents, resulting in poor stability as electrode materials, which limits their further applications. Metal-organic frameworks (MOFs), also known as metal nodes and organic linkers, are porous crystalline materials with unique advantages, such as adjustable metal site composition and ratio, high porosity, and large surface area, which facilitates the adsorption of catalytic precursors. Furthermore, MOFs can form polyoxometalate-based MOFs through electrostatic adsorption, direct bonding, or encapsulation, thereby enhancing electrocatalytic performance through their synergistic effect.

[0004] This patent designs and develops an Anderson-type nickel-molybdenum polyacid (NiMo6) modified cobalt-based metal-organic framework (Co-MOF) nanoflower-like electrocatalyst (Co-MOF / NiMo6). Based on the strong acidity of the polyacid, which acts as an etching agent, the anionic portion of the synthesized NiMo6 replaces the 2-MeIM anions on the Co-MOF surface, leading to framework reconstruction. With the synergistic effect of PVP, Co-MOF / NiMo6 is ultimately formed, and this composite material possesses a nanoflower-like structure. This Anderson-type polyacid modified Co-MOF nanoflower-like electrocatalyst not only possesses a layered structure with a high specific surface area and abundant active sites, but also solves the problem of the polyacid's easy solubility in water. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of easy enrichment and dissolution of polyacids and poor conductivity of metal-organic frameworks, and to improve the electrocatalytic efficiency of electrocatalytic materials for the reduction of nitrate to ammonia.

[0006] I. Preparation of NiMo6 polyacid: (NH4+) 4)6 Mo7O 24 ·4H₂O (5-8 g) was dissolved in 80 mL of deionized water to obtain a solution, which was then heated to boiling. NiSO₄·5H₂O (0.6-1 g) was dissolved in 20 mL of deionized water and poured into the boiling solution. To obtain purer crystals, the solution was recrystallized. The mixed solution was allowed to stand and cool; during the cooling process, NiMo₆ crystals gradually crystallized out of the solution. After the crystallization process was basically complete, a Buchner funnel with a suction flask was used to separate the crystals from the mother liquor by suction filtration, ultimately yielding pale blue crystals.

[0007] II. Preparation of Metal-Organic Frameworks (Co-MOFs): Co(NO3)2·6H2O (0.3-0.4 g) was dissolved in 100 mL of deionized methanol, and 2-methylimidazole (0.3-0.4 g) was dissolved in 100 mL of deionized methanol. The solutions were then mixed, and the mixture was first sonicated in an ultrasonic cleaner for 20 minutes, followed by stirring for 30 minutes, and then allowed to stand for 24 hours. The purple product was collected by centrifugation, washed with deionized methanol, and then vacuum dried at 60 °C for 12-14 hours to obtain the Co-MOF.

[0008] III. Preparation of the composite material: Co-MOF (0.2-0.5 g) was dissolved in 170 mL of deionized methanol, and NiMo6 (0.2-0.5 g) was dissolved in 70 mL of deionized water. The solutions were mixed, and then polyvinylpyrrolidone (0.01-0.05 g) was added. The mixture was stirred for 8 hours and then allowed to stand for 24 hours. The product was collected by centrifugation, and then washed 2-3 times with methanol and water, respectively. The product was then vacuum dried at 60 °C for 12-14 hours to obtain Co-MOF / NiMo6.

[0009] The temperature range for cooling described in step one is 22–25°C.

[0010] The volume of deionized methanol mentioned in step two is 100 mL.

[0011] The mass of Co(NO3)2·6H2O and 2-methylimidazole mentioned in step two is 3-4g and 4-5g, respectively.

[0012] The mass of polyvinylpyrrolidone (PVP) mentioned in step three is 0.01-0.05g.

[0013] The drying temperature in steps two and three is 60°C, and the drying time is 720-840 minutes.

[0014] The drying process described in step three should be carried out under vacuum conditions.

[0015] Compared with the prior art, the present invention has the following characteristics:

[0016] I. This invention is the first to synthesize a Co-MOF / NiMo6 composite electrocatalyst via a static synthesis method. The Co-MOF / NiMo6 composite electrocatalyst exhibits a rose-like structure, with the interlaced nanosheets increasing the specific surface area of ​​the material. The composite of Co-MOF and Anderson-type polyacid enhances the catalyst's electron transport capability and improves the electroresponse rate. The NiMo6 polyacid is uniformly attached to the surface of the Co-MOF sheets, increasing the specific surface area of ​​the composite material, promoting charge separation, and improving the electrocatalytic activity.

[0017] II. This invention utilizes in-situ synthesis to achieve uniform and stable dispersion of NiMo6 polyacids on the surface of Co-MOF. This solves the problem of easy dissolution and aggregation of NiMo6 polyacids during catalytic reactions. This invention is the first application of Co-MOF / NiMo6 polyacid composite electrocatalytic materials in the electrocatalytic reduction of nitrate to ammonia. Attached Figure Description

[0018] Figure 1 This is a scanning electron microscope image of the Co-MOF material.

[0019] Figure 2 This is a scanning electron microscope image of the Co-MOF / NiMo6 material.

[0020] Figure 3 This is a transmission electron microscope (TEM) image of the Co-MOF / NiMo6 composite material.

[0021] Figure 4 The infrared spectra of Co-MOF, NiMo6, and Co-MOF / NiMo6 composite materials are shown.

[0022] Figure 5 The XRD patterns are of Co-MOF and NiMo6 and Co-MOF / NiMo6 composites.

[0023] Figure 6 The graphs show the ammonia production rate and Faraday efficiency of the Co-MOF / NiMo6 composite material in neutral electrolytes (0.1 mol / L NaNO3 and 0.1 mol / L Na2SO4) at room temperature and pressure, under voltages ranging from -0.5 to -0.9 V for 1 hour.

[0024] Figure 7 The image shows the electrochemical linear sweep voltammetry of the Co-MOF / NiMo6 composite material under conditions with and without nitrate. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0026] Implementation Case 1

[0027] This embodiment is a Co-MOF / NiMo6 nanoflower-like catalyst, which is prepared according to the following method:

[0028] (1) Preparation of NiMo6 polyacid: (NH4)6Mo7O 24 ·4H₂O (5-8 g) was dissolved in 80 mL of deionized water to obtain a solution, which was then heated to boiling. NiSO₄·5H₂O (0.6-1 g) was dissolved in 20 mL of deionized water and poured into the boiling solution. To obtain purer crystals, the solution was recrystallized. The mixed solution was allowed to stand and cool; during the cooling process, NiMo₆ crystals gradually crystallized out of the solution. After the crystallization process was basically complete, a Buchner funnel with a suction flask was used to separate the crystals from the mother liquor by suction filtration, ultimately yielding pale blue crystals.

[0029] (2) Preparation of Co-MOF: Co(NO3)2·6H2O (3-4 g) was dissolved in 100 mL of deionized methanol, and 2-methylimidazole (4-5 g) was dissolved in 100 mL of deionized methanol. The solutions were then mixed, and the mixture was placed in an ultrasonic cleaner for 20 minutes, stirred for 30 minutes, and allowed to stand for 24 hours. The purple product was collected by centrifugation, washed with deionized methanol, and dried under vacuum at 60 °C for 12-14 hours to obtain Co-MOF.

[0030] (3) Preparation of Co-MOF / NiMo6 composite material: Co-MOF (0.3-0.4 g) was dissolved in 170 mL of deionized methanol, and NiMo6 (0.3-0.4 g) was dissolved in 70 mL of deionized water. The solutions were mixed, and then polyvinylpyrrolidone (0.012 g) was added. The mixture was stirred for 8 hours and then allowed to stand for 24 hours. The product was collected by centrifugation, and then washed 2-3 times with methanol and water, respectively. The product was then dried under vacuum at 60 °C for 12 hours to obtain Co-MOF / NiMo6.

[0031] Comparison Case 1

[0032] This comparative case provides a Co-MOF electrocatalyst, which differs from Example 1 in that NiMo6 is not added after the solution is mixed in step (3).

[0033] Comparison Case 2

[0034] This comparative case provides a NiMo6 electrocatalyst, which differs from Example 1 in that Co-MOF is not added after the solution is mixed in step (3).

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0036] Figure 1 The image shown is a scanning electron microscope image of the Co-MOF material, which reveals that the Co-MOF material is micrometer-sized and consists of multiple three-dimensional cubic block structures.

[0037] Figure 2 The image shown is a scanning electron microscope image of the Co-MOF / NiMo6 material. It was observed that the prepared Co-MOF / NiMo6 exhibits a rose-like structure with an average size of 2 μm.

[0038] Figure 3 The image shown is a transmission electron microscope (TEM) image of the Co-MOF / NiMo6 composite material. Multiple acid particles are observed to be uniformly distributed on the surface of the Co-MOF layered structure, indicating that NiMo6 is uniformly distributed on the surface of the nanosheets.

[0039] Figure 4The figure shows the infrared spectra of Co-MOF, NiMo6, and Co-MOF / NiMo6 composite materials. As shown, the nanomaterials exhibit infrared spectra in the range of 400–1400 cm⁻¹. -1 Infrared characteristic peaks are present within the range, at 425, 1175, and 1339 cm⁻¹. -1 The three absorption peaks at 650, 900, and 950 cm⁻¹ are attributed to the stretching vibrations of Co-N, CN, and C=N in the Co-MOF structure, respectively. -1 The absorption peak at the point is attributed to the Mo-O-Mo, Mo-O, and Ni-O vibrations in NiMo6, indicating that NiMo6 was successfully loaded onto Co-MOF.

[0040] Figure 5 The XRD patterns of Co-MOF, NiMo6, and Co-MOF / NiMo6 composites are shown. The diffraction peaks at 11°, 26°, 29°, and 32° in the XRD pattern match the diffraction peaks of NiMo6, while the diffraction peaks at 16°, 18°, 22.5°, and 27° belong to Co-MOF. This confirms the successful preparation of the Co-MOF / NiMo6 composite.

[0041] Figure 6 The figure shows the ammonia production rate and Faradaic efficiency of the Co-MOF / NiMo6 composite material in neutral electrolytes (0.1 mol / L NaNO3 and 0.1 mol / L Na2SO4) at room temperature and pressure, under voltages ranging from -0.5 to -0.9 V for 1 hour. The average ammonia production efficiency of the Co-MOF / NiMo6 composite material at a potential of -0.8 V vs. RHE is 11.14 mg / h. -1 mgcat. -1 The Co-MOF / NiMo6 composite material exhibits a Faraday efficiency of 98.2% and good electrocatalytic activity for nitrate reduction to ammonia. Therefore, the preparation of the composite material in this invention improves the electrocatalytic efficiency, and the Co-MOF / NiMo6 composite material can serve as a highly efficient electrocatalytic nitrate reduction catalyst.

[0042] Figure 7 The figure shows the electrochemical linear sweep voltammogram of the Co-MOF / NiMo6 composite material under nitrate-free conditions. As shown, within the voltage range of -0.4V vs. RHE to -1.4V vs. RHE, the reduction current density of the Co-MOF / NiMo6 composite material in the electrolyte containing nitrate ions is significantly higher than that in the electrolyte without nitrate ions, indicating that the Co-MOF / NiMo6 composite material has a certain electrocatalytic ability to reduce nitrate.

[0043] In summary, this invention relates to the preparation and application of an Anderson-type polyacid-modified Co-MOF composite material. A Co-MOF / NiMo6 composite material with a nanoflower-like structure was successfully prepared, increasing the specific surface area and enhancing the electrocatalytic efficiency of nitrate reduction to ammonia. The synthesized Co-MOF / NiMo6 composite material shows great potential in electrocatalytic nitrate reduction to ammonia.

Claims

1. A method for preparing an Anderson-type polyacid-modified Co-MOF nanoflower-like electrocatalyst, characterized in that, Includes the following steps: (1) Preparation of NiMo6 polyacid: (NH4)6Mo7O 24 Dissolve 5-8g of NiSO4·5H2O in 80mL of deionized water to obtain a solution, and heat the solution to boiling; dissolve 0.6-1g of NiSO4·5H2O in 20mL of deionized water to form a NiSO4 solution, and pour the NiSO4 solution into (NH4)6Mo7O 24 In a boiling solution of 4H2O, the resulting mixed solution is recrystallized. The mixed solution is allowed to stand and cool down. During the cooling process, NiMo6 crystals will gradually crystallize out of the solution. After crystallization is complete, a Buchner funnel with a vacuum filtration flask is used to filter the solution, separating the crystals from the mother liquor, and obtaining light blue NiMo6 crystals. (2) Preparation of metal-organic framework Co-MOF: 3-4 g of Co(NO3)2·6H2O was dissolved in 100 mL of deionized methanol, and 4-5 g of 2-methylimidazole was dissolved in 100 mL of deionized methanol; the two solutions were mixed, and the mixture was first placed in an ultrasonic cleaner and sonicated for 20 minutes, then stirred for 30 minutes, and then allowed to stand for 24 hours; the purple product was collected by centrifugation, washed with deionized methanol, and then vacuum dried at 60 °C for 12-14 h to obtain Co-MOF; (3) Preparation of Co-MOF / NiMo6 composite material, namely Anderson-type polyacid modified Co-MOF nanoflower electrocatalyst: 0.2-0.5g of Co-MOF was dissolved in 170mL of deionized methanol, and 0.2-0.5g of NiMo6 was dissolved in 70mL of deionized water; the two solutions were mixed, and 0.01-0.05g of polyvinylpyrrolidone was added. After stirring the mixture for 8 hours, it was allowed to stand for 24 hours; the product was collected by centrifugation, washed 2-3 times with methanol and water respectively, and dried under vacuum at 60℃ for 12-14h to obtain the target electrocatalyst.

2. The preparation method according to claim 1, characterized in that, The temperature range for the static cooling of the mixed solution in step (1) is 22 to 25°C.

3. An application of the Anderson-type polyacid-modified Co-MOF nanoflower-like electrocatalyst prepared by the method described in claim 1 or 2, characterized in that, The electrocatalyst was applied to a neutral electrolyte at room temperature and pressure, specifically a 0.1 mol / L NaNO3 and a 0.1 mol / L Na2SO4 solution, for the electrocatalytic reduction of nitrate to ammonia.

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