Preparation and application of copper porphyrin metal-organic framework encapsulating iron-molybdenum polyacid

Abstract

The present invention relates to the preparation and application of a copper porphyrin metal organic framework encapsulating iron molybdenum polyacid. The composite material obtained by the present invention is used for electrocatalytic nitrate reduction to synthesize ammonia at room temperature and pressure. The present invention designs and prepares a Keggin-type iron molybdenum polyacid (PMo) with a single substitution of an electron-rich transition metal. 11 The copper porphyrin metal organic framework (PMo) encapsulating Fe-molybdenum polyacid was synthesized by a simple one-step solvothermal method using tetra(4-carboxyphenyl)porphyrin (Cu-TCPP) as raw materials. 11 Fe@NU‑902(Cu)). Utilize the periodic pores and regular structure of NU‑902(Cu) to encapsulate PMo 11 Fe, overcomes PMo 11 Fe is easy to agglomerate and dissolve in water. At the same time, the obtained PMo 11 Fe@NU‑902(Cu) material can be combined with PMo 11 The reversible redox activity of Fe polyacid and the large specific surface area, abundant catalytic active sites and stable structure of NU-902(Cu) metal organic framework are the advantages of this invention. The yield of the material prepared by the present invention for electrocatalytic nitrate reduction to ammonia synthesis was 19.38 mg h –1 mg cat. –1 The Faradaic efficiency is 89.44%. The preparation process of the invention is simple, fast and low-cost, and the obtained material has good electrocatalytic ammonia synthesis performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electrocatalytic materials, and in particular to a PMo 11 Fe@NU-902(Cu) composite electrocatalyst and an application thereof. BACKGROUND

[0002] Ammonia (NH3) is one of the world's largest chemical products, widely used in various fields such as dye, medicine and fertilizer production. At the same time, NH3 is also a renewable carbon-free energy carrier with high energy density and hydrogen content. At present, the large-scale synthesis of ammonia is dominated by the energy-consuming and environmentally harmful Haber-Bosch process, which consumes 2% of the world's energy and accounts for 1.4% of global carbon dioxide emissions. Compared with the traditional Haber-Bosch method, the electrocatalytic method can convert renewable energy into ammonia with high energy density and convenient storage and transportation, which can be reacted at room temperature and pressure, reducing equipment cost and energy cost, avoiding CO2 emission problems, and meeting the requirements of green and low-carbon economy. Among them, the electrocatalytic nitrate synthesis of ammonia (NO3RR) not only removes the pollutant nitrate in water, but also produces high-quality and high-value zero-carbon hydrogen-rich fuel ammonia, which not only improves environmental pollution but also relieves energy crisis, and the reasonable design of high-activity and high-selectivity electrocatalyst is the key to realizing high-efficiency NO3RR.

[0003] Metal-organic frameworks (MOFs) are a kind of porous materials with high specific surface area, but the poor chemical stability in water and poor electrical conductivity of most MOFs limit their application. Zirconium-based porphyrin metal-organic framework NU-902(Cu) has excellent chemical stability in aqueous medium, in addition, the introduction of transition metal copper increases the catalytic active site. Polyoxometalate (POM for short), also known as polyacid, is a metal-oxo cluster compound composed of d 0 Transition metal-substituted polyoxometalates are widely used in the field of electrocatalysis due to their reversible redox activity and electron-rich properties. Transition metal-substituted polyoxometalates can be adjusted in composition, charge and structure by changing the type and number of transition metal atoms. However, polyoxometalates have the key problems of easy aggregation and easy dissolution in water.

[0004] In order to overcome these shortcomings and obtain an electrocatalyst with high catalytic performance, the application encapsulates transition metal iron-substituted phosphomolybdic acid H6PMo 11 FeO 40 ·xH2O (referred to as PMo 11 Fe) in zirconium-based porphyrin MOF NU-902(Cu) to form a PMo 11 Fe@NU-902(Cu) composite electrocatalyst with excellent function. SUMMARY

[0005] The purpose of the present application is to solve the problems of easy dissolution in solution and low electron transfer rate of polyacid and metal-organic framework as electrode material for electrocatalytic synthesis of ammonia, in order to improve the performance of the catalyst for electrocatalytic reduction of nitrate to synthesize ammonia, the present application provides a preparation and application of copper porphyrin metal organic framework encapsulating iron molybdenum polyacid.

[0006] In order to solve the above technical problems, the present application is realized by the following technical scheme:

[0007] I. PMo 11 Preparation of Fe: dissolve Na2HPO4·2H2O and FeCl3 in hot water, acidify with 1 mL of concentrated sulfuric acid after cooling, then add an aqueous solution of Na2MoO4·2H2O to the above solution, a large amount of flocculent precipitate appears, slowly add concentrated sulfuric acid until the solution is transparent, extract the heteropoly acid with diethyl ether after cooling, dissolve the extracted heteropoly acid in water, concentrate and crystallize, and dry to obtain iron-substituted phosphorus molybdenum polyacid H6PMo 11 FeO 40 ·xH2O (abbreviated as PMo 11 Fe);

[0008] II. Preparation of composite material: add zirconium oxychloride (ZrOCl2·8H2O) and benzoic acid to N,N-dimethylformamide (abbreviated as DMF), ultrasonic dispersion to dissolve, then add copper-substituted tetra(4-carboxyphenyl) porphyrin (abbreviated as Cu-TCPP) and PMo 11 Fe, ultrasonic to form a clear solution, load into a 50 mL polytetrafluoroethylene lined reaction kettle, heat in an oven for a period of time, cool, centrifuge, wash and dry after the end, to obtain PMo 11 Fe@NU-902(Cu) composite material;

[0009] The mass of Na2HPO4·2H2O in step one is 3.4-3.8 grams, and the mass of FeCl3 is 1.4-1.8 grams;

[0010] The hot water in step one is 20 mL of deionized water with a temperature range of 80-100℃;

[0011] The Na2MoO4·2H2O solution in step one is a solution formed by dissolving 25-27 grams of Na2MoO4·2H2O in 40 mL of deionized water;

[0012] The mass of zirconium oxychloride and benzoic acid in step two is 20-25 mg and 1.4-1.6 grams respectively; the amount of DMF is 15-25 mL;

[0013] The mass of Cu-TCPP in step two is 45-55 mg; PMo 11 The mass of Fe is 80-120 mg;

[0014] The heating temperature in step two is 80-100 DEG C, and the heating time is 10-12 hours;

[0015] The centrifugation and washing in step two are washing with DMF and acetone for 3-5 times respectively;

[0016] The drying in step two is vacuum drying at 50-60 DEG C for 30-60 minutes.

[0017] Compared with the prior art, the present application has the following characteristics:

[0018] The present application first loads PMo 11 Fe polyacid into copper porphyrin metal organic framework NU-902 (Cu) with periodic pores through one-step solvothermal reaction, overcomes the problems of easy agglomeration and easy water solubility of PMo 11 Fe, and the introduction of Fe increases the electronic transmission rate of the material, and the copper in the porphyrin structural unit is more prone to adsorb nitrate to synthesize ammonia, so that the production of hydrogen can be inhibited to some extent, the electron utilization rate is improved, and the performance of electrocatalytic nitrate reduction to synthesize ammonia is improved. 11 PMo 11 Fe@NU-902 (Cu) reaches the best Faraday efficiency of 89.44% at a potential of-1.0 V vs.RHE, and the corresponding ammonia production is 19.38 mg h –1 mg cat. –1 , which is better than most reported MOF catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The powder X-ray diffraction (XRD) pattern of the NU-902 (Cu) and PMo 11 Fe@NU-902 (Cu) composite material.

[0020] Figure 2 The scanning electron microscope (SEM) pattern of the NU-902 (Cu) material.

[0021] Figure 3 The powder X-ray diffraction (XRD) pattern of the PMo 11 Fe@NU-902 (Cu) composite material.

[0022] Figure 4 The powder X-ray diffraction (XRD) pattern of the NU-902 (Cu) and PMo 11The infrared spectrum (FT-IR) comparison chart of Fe@NU-902(Cu) composite material.

[0023] Figure 5 The PMo 11 The linear sweep voltammetry (LSV) curve of Fe@NU-902(Cu) composite material in 0.1M Na2SO4 solution, 0.1M NaNO3 and 0.1M Na2SO4 solution, respectively.

[0024] Figure 6 The PMo 11 The time-current (i-t) chart of Fe@NU-902(Cu) composite material in 0.1M Na2SO4 and 0.1M NaNO3 solution for ammonia synthesis reaction under different voltages.

[0025] Figure 7 The PMo 11 The ultraviolet-visible light absorption spectrum (UV) of Fe@NU-902(Cu) composite material in 0.1M NaNO3 and 0.1M Na2SO4 solution for ammonia synthesis reaction under different voltages.

[0026] Figure 8 The PMo 11 The ammonia yield and Faraday efficiency chart of Fe@NU-902(Cu) composite material in 0.1M NaNO3 and 0.1M Na2SO4 solution for ammonia synthesis reaction under different voltages. DETAILED DESCRIPTION

[0027] The present application will be further described in conjunction with the examples and drawings, but the embodiments of the present application are not limited thereto.

[0028] Example 1

[0029] This example is a preparation case of ellipsoidal NU-902(Cu), which is prepared according to the following method:

[0030] 22mg of zirconium oxychloride (ZrOCl2·8H2O) and 1.5g of benzoic acid were added to 20mL of N,N-dimethylformamide (abbreviated as DMF), and ultrasonic dispersion was performed to dissolve them. Then, 50mg of copper-substituted tetra(4-carboxyphenyl)porphyrin (abbreviated as Cu-TCPP) was added, and a clear solution was formed by ultrasonic treatment. The solution was loaded into a 50mL polytetrafluoroethylene-lined reaction kettle, and heated in an oven at 90℃ for 48h. After cooling, it was washed by centrifugation with DMF and acetone for 4 times, respectively, and then dried in a vacuum drying box at 60℃ for 1h to obtain NU-902(Cu).

[0031] Example 2

[0032] The embodiment provides a PMo 11 Fe@NU-902(Cu) composite catalyst is prepared according to the following method:

[0033] (1) PMo 11 Preparation of Fe: 3.6 g of Na2HPO4·2H2O and 1.6 g of FeCl3 are dissolved in 20 mL of deionized water at 90 DEG C, and after cooling, 1 mL of concentrated sulfuric acid is added for acidification, and then 26 g of Na2MoO4·2H2O is dissolved in 40 mL of water to form a solution, a large amount of flocculent precipitate is generated, concentrated sulfuric acid is slowly added until the solution is transparent, and after cooling, the heteropoly acid is extracted with diethyl ether, the extracted heteropoly acid is redissolved in water, concentrated and crystallized, and dried to obtain iron-substituted phosphorus molybdenum polyacid H6PMo 11 FeO 40 ·xH2O (abbreviated as PMo 11 Fe).

[0034] (2) Preparation of the composite material: 22 mg of zirconium oxychloride (ZrOCl2·8H2O) and 1.5 g of benzoic acid are added to 20 mL of N,N-dimethylformamide (abbreviated as DMF), ultrasonic dispersion is performed to dissolve them, then 50 mg of copper-substituted tetra (4-carboxyphenyl) porphyrin (abbreviated as Cu-TCPP) and 100 mg of PMo 11 Fe are added, a clear solution is formed by ultrasonic treatment, and the solution is loaded into a 50 mL polytetrafluoroethylene-lined reaction kettle, heated in an oven at 90 DEG C for 48 h, and after cooling, the composite material is washed by centrifugation with DMF and acetone for 4 times, and then placed in a vacuum drying box and dried at 60 DEG C for 1 h to obtain PMo 11 Fe@NU-902(Cu) composite material.

[0035] The application is further described below in combination with the drawings and examples:

[0036] Figure 1 The figure shows the PMo 11 Fe@NU-902(Cu) composite material, and the XRD pattern of the PMo 11 Fe@NU-902(Cu) composite material has characteristic peaks at 2θ=18°, 29° and 32°, which are characteristic peaks of PMo 11 Fe, and it is proved that the PMo 11 Fe@NU-902(Cu) composite material is successfully synthesized.

[0037] Figure 2The scanning electron microscope (SEM) image of NU-902(Cu) monomer material is shown. It is observed that the NU-902(Cu) monomer material is micron-sized, presenting an ellipsoidal-like shape.

[0038] Figure 3 The scanning electron microscope (SEM) image of PMo 11 The scanning electron microscope (SEM) image of Fe@NU-902(Cu) composite material is shown. It is observed that the PMo 11 The PMo 11 The Fe@NU-902(Cu) composite material also presents an ellipsoidal-like morphology of micron size, proving that the addition of polyoxometalate does not destroy the original MOF structure.

[0039] Figure 4 The scanning electron microscope (SEM) image of NU-902(Cu) and PMo 11 The infrared spectrum (FT-IR) of Fe@NU-902(Cu) composite material is shown. As shown in the figure, the composite material has both the characteristic peaks of NU-902(Cu), PMo 11 Fe monomer material, only the PMo 11 The peak intensity of Fe is slightly reduced, which may be due to encapsulation in the pore size of NU-902(Cu).

[0040] Figure 5 The scanning electron microscope (SEM) image of PMo 11 The linear sweep voltammetry (LSV) curve of Fe@NU-902(Cu) composite material in 0.1M Na2SO4 solution, 0.1M NaNO3 and 0.1M Na2SO4 solution, respectively, is shown. As shown in the figure, in the same voltage range, the PMo 11 The reduction current density of Fe@NU-902(Cu) is significantly higher than that without nitrate electrolyte, indicating that the PMo 11 The Fe@NU-902(Cu) catalyst has a certain electrocatalytic nitrate reduction ability.

[0041] Figure 6 The scanning electron microscope (SEM) image of PMo 11 The time-current (i-t) diagram of Fe@NU-902(Cu) composite material in 0.1M Na2SO4 and 0.1M NaNO3 solution for ammonia synthesis at different voltages. At different potentials from -0.7V vs. RHE to -1.1V vs. RHE, the PMo 11 The time-current curve (i-t) of Fe@NU-902(Cu) at different potentials for 1 hour of electrocatalytic nitrate reduction for ammonia synthesis shows that the current density remains stable, indicating that the catalyst has good electrochemical stability.

[0042] Figure 7 PMo 11 UV-vis spectra of Fe@NU-902(Cu) composite materials in 0.1M NaNO3 and 0.1M Na2SO4 solution for ammonia synthesis reaction under different voltages, as shown in the figure, with the increase of voltage, the absorbance of the electrolyte after catalytic test and coloration also gradually increased in the absorbance test.

[0043] Figure 8 PMo 11 Ammonia production and Faraday efficiency of Fe@NU-902(Cu) composite materials in 0.1M NaNO3 and 0.1M Na2SO4 solution for ammonia synthesis reaction under different voltages, as shown in the figure, the best Faraday efficiency of 89.44% was reached at-1.0V vs.RHE, and the corresponding ammonia production was 19.38mg h –1 mg cat. –1 , which is much higher than NU-902(Cu) monomer and the same type of material. Therefore PMo 11 Fe@NU-902(Cu) composite material can be used as a high-efficiency catalyst for electrocatalytic reduction of nitrate to ammonia.

[0044] In summary: the copper porphyrin metal-organic framework PMo 11 Fe@NU-902(Cu) is successfully prepared by solvothermal synthesis method, and is successfully used as electrode material for electrocatalytic reduction of nitrate to ammonia, PMo 11 The addition of Fe increases the electron transport rate and the number of active sites of the composite material, the encapsulation of NU-902(Cu) increases the specific surface area of the material, and solves the problem of easy aggregation and easy dissolution of Fe in water. 11 The material has good redox activity, excellent conductivity and stability, and has good potential in the electrocatalytic reduction of nitrate to ammonia.

Claims

1. A method for preparing a copper porphyrin metal-organic framework encapsulating iron-molybdate polyacid, characterized in that: the mass of Na2HPO4·2H2O in step (1) is 3.4-3.8 g; the mass of FeCl3 is 1.4-1.8 g. (1) PMo 11 Preparation of Fe: Na2HPO4.2H2O and FeCl3were dissolved in hot water, after cooling, acidified with 1 mL of concentrated sulfuric acid, then an aqueous solution of Na2MoO4.2H2O was added to the above solution, a large amount of flocculent precipitate appeared, concentrated sulfuric acid was slowly added until the solution was transparent, after cooling, the heteropoly acid was extracted with diethyl ether, the extracted heteropoly acid was redissolved in water, concentrated and crystallized, dried to obtain iron-substituted phosphomolybdic acid H6PMo 11 FeO 40 ·xH2O (abbreviated as PMo 11 Fe); (2) Preparation of composite material: Zirconium oxychloride (ZrOCl2·8H2O), benzoic acid were added into N,N-dimethylformamide (abbreviated as DMF), ultrasonic dispersion to make it dissolve, then copper substituted tetra(4-carboxyphenyl) porphyrin (abbreviated as Cu-TCPP) and PMo 11 Fe, ultrasonic clear solution was formed, was filled into 50 mL polytetrafluoroethylene lined reaction kettle, was heated in oven for a period of time, after the end, centrifugal, washing, drying, PMo 11 Fe@NU-902(Cu) composite material.

2. The method of claim 1, wherein: The hot water in step (1) is 20 mL of deionized water with a temperature range of 80-100 ℃.

3. The production method according to claim 1 or 2, characterized by: The Na2MoO4·2H2O solution in step (1) is a solution formed by dissolving 25-27 g of Na2MoO4·2H2O in 40 mL of deionized water.

4. The production method according to claim 1 or 2, characterized by: The mass of zirconium oxychloride octahydrate and benzoic acid in step (2) is 20-25 mg and 1.4-1.6 g, respectively; the amount of DMF used is 15-25 mL.

5. The method of claim 1, wherein: The heating in step (2) is performed at a temperature of 80-100 ℃ for 10-12 hours.

6. The production method according to claim 1 or 5, characterized by: The mass of Cu-TCPP in step (2) is 45-55 mg; PMo 11 The mass of Fe is 80-120 mg.

7. The method of claim 1, wherein: The washing in step (2) is performed 3-5 times with DMF and acetone, respectively, and the drying is performed under vacuum at 50-60 ℃ for 30-60 minutes.

8. The method of claim 1, wherein: ​ 9. A PMo prepared by the method of any one of claims 1-8 11 Application of Fe@NU-902(Cu) composite in electrocatalytic reduction of nitrate to synthesize ammonia.

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