Bio-metal organic framework material for electro-catalysis nitrate reduction and preparation method and application of bio-metal organic framework material

Abstract

The invention discloses a biological metal organic framework material for electrocatalytic nitrate reduction as well as a preparation method and application of the biological metal organic framework material. An SU-102-Fe electrocatalyst is rapidly synthesized on a large scale by utilizing SU-102 through a simple method under a mild condition; the SU-102-Fe not only can realize efficient reduction of nitrate radicals into ammonia (FE gt, 96.5%) in an electrolyte prepared from pure water, but also can normally electrolyze in the environment-polluted industrial wastewater with various impurities and realize good catalytic efficiency (FE gt, 96%), and has huge advantages in practical application.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework functional materials technology, specifically relating to bio-metal-organic framework materials for electrocatalytic nitrate reduction, their preparation methods, and applications. Background Technology

[0002] The global nitrogen cycle is fundamental to ecological stability; however, excessive NO3 in industrial and agricultural wastewater... - Nitrate accumulation threatens the environment and human health. Traditional nitrate removal methods, including biological denitrification and physicochemical treatment, are energy-intensive and have limited potential for recovering valuable products. Electrocatalytic nitrate reduction (eNO3RR), by converting nitrates to ammonia, requires only 6.5 kWh·kg⁻¹ of NH₃, theoretically requiring only 6.5 kWh·kg⁻¹. -1 eNO3RR is higher than that of the Haber-Bosch process (10-13 kWh·kg) -1 It is much more energy efficient and can reduce pollution while producing useful chemicals, providing a promising alternative.

[0003] Although electrocatalytic nitrate reduction has certain advantages, existing eNO3RR catalysts hinder its potential for practical application: most existing eNO3RR electrocatalysts use noble metals (Au, Ag, Pt, Pd, etc.) as the catalytic active center, resulting in high preparation costs; many eNO3RR electrocatalysts using non-noble metals as the active center are inorganic materials, heterojunctions, amorphous materials (including carbon materials), or even mixtures, with highly indeterminate structures, which poses a significant obstacle to studying their catalytic processes and further optimizing their performance; most reported eNO3RR electrocatalysts can only operate at high NO3 levels. - High Faradaic efficiency (FE) and yield can be achieved in pure water electrolytes, but performance deteriorates significantly or becomes extremely poor in real wastewater (containing organic components, insoluble suspended solids, and interference from anions and cations) or simulated industrial wastewater, making practical applications difficult. Currently reported high-performance catalysts require overly demanding synthesis conditions (e.g., strict temperature and humidity control, cumbersome procedures) or require highly sophisticated equipment (carbonization, high-temperature heating), limiting their potential for large-scale production. Therefore, finding non-precious metal electrocatalysts with well-defined structures, low cost, simple operation, and the ability to be mass-produced for practical nitrate wastewater treatment is essential for practical applications.

[0004] Bio-metal-organic frameworks (Bio-MOFs) are an ideal choice for this purpose. They are primarily composed of natural, green components (including plant and animal molecules, plant waste, etc.), avoiding the artificial design and purification of traditional organic ligands and reducing labor and time costs. Furthermore, they possess the advantages of high specific surface area, well-defined and designable crystal structures, abundant active sites, and good dispersibility inherent in MOFs, thus attracting increasing attention. However, there are currently few reports on MOFs used directly or modified from Bio-metal-organic frameworks for electrocatalytic nitrate reduction. This is mainly due to the technical requirements for selecting suitable plant and animal molecules and the synthesis or post-modification of MOFs, which also indicates significant untapped research potential in this area.

[0005] Taking ellagic acid (EA) as an example, MOF materials synthesized from ellagic acid have been reported as follows: SU-101 (J.Am.Chem.Soc.,2020,142,16795−16804); SU-102 (Nature Water, 2023,1,433-442); EA-Pb (Small,2024,2400978); Ca-EA (Inorg. Chem.Front.,2024,11,3056-3062); Fe-EA (ACSAppl.Mater. Interfaces,2018,10,3295-3304); Co-EA, Ni-EA, Cu-EA (Adv.EnergyMater.,2024,2400871). Among them, the central metals of SU-101, EA-Pb, and Ca-EA do not have nitrate reduction activity, and due to the limitation of coordination mode, they also do not have the ability to be modified later. The four materials Fe-EA, Co-EA, Ni-EA and Cu-EA are not suitable for electrocatalytic nitrate reduction due to their poor one-dimensional structural stability. Summary of the Invention

[0006] For the reasons stated above, the first objective of this invention is to provide a bio-metal-organic framework material for electrocatalytic nitrate reduction, using the bio-metal-organic framework SU-102 as the base framework, and loading ferric ions onto SU-102 by coordinating undeprotonated hydroxyl groups on ellagic acid, thereby loading monatomic iron onto SU-102. 3+ Uniformly dispersed inside SU-102 as catalytic sites, forming a highly efficient electrocatalyst for nitrate reduction.

[0007] The second objective of this invention is to provide a method for preparing a bio-metal-organic framework material for electrocatalytic nitrate reduction, wherein the bio-metal-organic framework SU-102 is in an aqueous solution, utilizing the reaction of hydroxyl groups with Fe...3+ It exhibits rapid and strong chelating action to coordinate with ferric precursors; the reaction is mild, the process is simple, and it is suitable for large-scale preparation.

[0008] The third objective of this invention is to provide a bio-metal-organic framework material for electrocatalytic nitrate reduction and its application in ammonia production from electrocatalytic nitrate reduction; the bio-metal-organic framework material has a Faraday efficiency greater than 96.5%; and it possesses both environmental compatibility and green economic characteristics.

[0009] The first objective of this invention can be achieved by adopting the following technical solution:

[0010] A bio-metal-organic framework material for electrocatalytic nitrate reduction, comprising ellagic acid and Zr 4+ The metal-organic framework SU-102 formed by coordination; and the iron ion coordinated with the hydroxyl group on the ellagic acid in SU-102.

[0011] Furthermore, with Zr 4+ The hydroxyl groups of the two ellagic acids are simultaneously coordinated with the iron ion; the hydroxyl group in one ellagic acid is an undeprotonated hydroxyl group, and the hydroxyl group in the other ellagic acid is a deprotonated hydroxyl group.

[0012] The second objective of this invention can be achieved by adopting the following technical solution:

[0013] A method for preparing bio-metal-organic framework materials for electrocatalytic nitrate reduction includes the following steps:

[0014] Ellagic acid and Zr 4+ The coordinated metal-organic framework SU-102 reacts with ferric ions in an aqueous solution to prepare the bio-metal-organic framework material for electrocatalytic nitrate reduction.

[0015] Furthermore, the ferric salt is any one of ferric hydrochloride, sulfate, nitrate, acetate, or hydrate of the other.

[0016] Furthermore, the mass ratio of SU-102 to ferric salt is 1.5:(1-1.5).

[0017] Furthermore, the reaction conditions are: stirring at 20-40℃ for 30-90 minutes.

[0018] Furthermore, SU-102 is prepared by the following method:

[0019] SU-102 was prepared by reacting ellagic acid with zirconium oxychloride octahydrate under solvothermal conditions.

[0020] Furthermore, the mass ratio of ellagic acid to zirconium oxychloride octahydrate is (1.5-2):1.

[0021] Furthermore, the solvent for solvothermal is a mixture of DMF and water, with a volume ratio of DMF to water of 1:(1-2).

[0022] Furthermore, the reaction is carried out in the presence of acetic acid, with the amount of acetic acid being 20%-50% of the solvent volume.

[0023] Furthermore, the conditions for the solvothermal reaction are: 60-80℃ for 2-5 days.

[0024] Furthermore, after the solvothermal reaction, a post-processing procedure is also included: after the reaction solution is cooled, solid and liquid are separated, the solid phase is washed with ethanol and water, and dried in an oven to obtain the SU-102.

[0025] The second objective of this invention can be achieved by adopting the following technical solution:

[0026] Application of bio-metal-organic framework materials for electrocatalytic nitrate reduction in ammonia production.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. A bio-metal-organic framework material for electrocatalytic nitrate reduction according to the present invention, comprising ellagic acid and Zr 4+ The metal-organic framework SU-102 is formed through coordination; and iron ions are coordinated with the hydroxyl groups on ellagic acid in SU-102; the iron ions are loaded within the metal-organic framework through coordination; utilizing the high specific surface area and abundant pore structure of the framework material, Fe... 3+ Uniformly dispersed within the MOF to achieve highly efficient catalytic reduction of nitrate.

[0029] 2. The present invention provides a method for preparing a bio-metal-organic framework material for electrocatalytic nitrate reduction. The hydroxyl groups in the ligand groups of SU-102 material provide coordination sites for iron ions. Metal loading is achieved through a coordination reaction between SU-102 and iron ions. The preparation method is simple, requiring no complex reaction processes or harsh reaction conditions, and can be prepared on a large scale. Furthermore, SU-102 material itself can be prepared via a solvothermal reaction, which also allows for large-scale preparation.

[0030] 3. The bio-metal-organic framework material for electrocatalytic nitrate reduction in this application has a Faraday efficiency greater than 96.5%, which can efficiently reduce nitrate to ammonia; it also has the characteristics of environmental compatibility and green economy; therefore, it has potential applications in electrocatalytic nitrate reduction to ammonia production.

[0031] Attached image description.

[0032] Figure 1 This is a schematic diagram of the synthesis of SU-102-Fe in this application;

[0033] Figure 2 Introducing Fe into SU-102 3+ Optical photographs showing color changes before and after;

[0034] Figure 3 XRD patterns of SU-102 and SU-102-Fe;

[0035] Figure 4 SEM images of SU-102 and SU-102-Fe;

[0036] Figure 5 TEM images of SU-102 and SU-102-Fe;

[0037] Figure 6 EDS plots for SU-102 and SU-102-Fe;

[0038] Figure 7 The N2 adsorption curves for SU-102 and SU-102-Fe are shown.

[0039] Figure 8 XPS plots of SU-102 and SU-102-Fe; where a is the Fe2+ of SU-102-Fe. p Fine spectrum; b represents SU-102 and SU-102-FeO 1 s Fine spectrum;

[0040] Figure 9 The results of synchrotron radiation tests on SU-102-Fe are shown below; where a is the K-side absorption energy diagram of Fe foil, Fe2O3, FeO, and SU-102-Fe; b is the R-space diagram; and c is the coordination model fitting curve of SU-102-Fe.

[0041] Figure 10 The Faraday efficiency of SU-102, SU-102-Fe and Fe2O3 at different voltages;

[0042] Figure 11 The ammonia yields of SU-102, SU-102-Fe, and Fe2O3 at different voltages;

[0043] Figure 12 The graph shows the performance of SU-102-Fe continuous electrolysis for 10 hours; where a represents the current and yield during the SU-102-Fe continuous electrolysis process for 10 hours; and b represents the Faraday efficiency during the SU-102-Fe continuous electrolysis process for 10 hours.

[0044] Figure 13Optical photographs of SU-102-Fe prepared in batches for Example 5;

[0045] Figure 14 Optical photographs of the natural environment of the lake and the samples taken;

[0046] Figure 15 The electrolytic performance of the SU-102-Fe electrocatalyst prepared in Example 5 in simulated industrial nitrate wastewater is shown in Figure a. Figure a represents the Faradaic efficiency of various products of the SU-102-Fe batch at different potentials; Figure b represents the yield of ammonia produced by the SU-102-Fe batch at different potentials; and Figure c represents the current and Faradaic efficiency of the SU-102-Fe batch during a continuous 10-hour electrolysis process.

[0047] Figure 16 The graph shows a comparison between the electrolytic performance of the SU-102-Fe electrocatalyst prepared in Example 5 in simulated industrial nitrate wastewater and the performance of MOF nitrate reduction electrocatalysts reported in the literature. Detailed Implementation

[0048] The technical solution of the present invention will now be clearly and completely described with reference to specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0049] Currently, most reported MOF-based electrocatalysts for nitrate reduction utilize artificially designed synthetic compounds as organic ligands. Their design, synthesis, extraction, separation, identification, and purification require significant manpower, financial resources, and time, under demanding conditions (such as strict temperature and humidity control and high-temperature heating). This results in long synthesis cycles, high costs, and environmentally unfriendly practices for MOF materials, limiting their potential for large-scale production, especially the difficulty in synthesizing highly efficient catalysts at the gram scale in the laboratory. Furthermore, most current eNO3RR electrocatalysts are inorganic, heterojunctions, amorphous materials (including carbon materials), or even mixtures, with highly uncertain structural information. This poses a significant obstacle to studying their catalytic processes and further optimizing their performance. Moreover, most eNO3RR MOF electrocatalysts can only operate under high NO3 conditions. - High Faradaic efficiency (FE) and yield can be achieved in electrolytes prepared with pure water of high concentration. However, real-world wastewater or industrial wastewater contains microorganisms, organic components, chemical oxygen demand (COD), unfilterable suspended solids, and cations and anions, which makes it difficult to apply the reported MOF electrocatalysts in practice.

[0050] SU-102's three-dimensional structure possesses a large porous structure (facilitating mass transfer), an ideal specific surface area (facilitating the exposure of active sites), and the potential for post-modification (with hydroxyl groups for Fe). 3+ Post-modification (as a reactive active site) has the potential to serve as a substrate for the preparation of electrocatalysts for nitrate reduction.

[0051] Materials based on the SU-102 and modified accordingly, such as the SU-102-K, have been reported. + (Chemical Engineering Journal, 2024, 502, 157956); Mg-SU-102 (Nature Communications, 2025, 16, 4297); SU-102-Li + (Small 2024, 2405561); SU-102-Mg (Dalton Trans., 2024, 53, 12043); SU-102@Ti3C2 (Separation and Purification Technology, 2025, 378, 134672); SU-102-Rb + (Ind.Eng.Chem.Res., 2025,64,18268-18276); CaCO3@SU-102 (Journal of Hazardous Materials, 2025,495,139071), etc. are mostly used for gas adsorption separation, pollutant removal and material adsorption, and there are no reports on their use for nitrate reduction.

[0052] Therefore, this application provides a bio-metal-organic framework material for electrocatalytic nitrate reduction, comprising ellagic acid and Zr. 4+ The metal-organic framework SU-102 formed by coordination; and the iron ion coordinated with the hydroxyl group on the ellagic acid in SU-102.

[0053] Ellagic acid and Zr 4+ In the coordination-formed metal-organic framework SU-102, ellagic acid and Zr-O clusters form a hexagonal prism-like three-dimensional MOF, which possesses a large pore structure and an ideal specific surface area. The undeprotonated hydroxyl groups in ellagic acid offer potential for post-modification. It is well known that hydroxyl groups react with Fe... 3+ It exhibits rapid and strong chelating action; therefore, in this application, the undeprotonated hydroxyl group is combined with Fe... 3+ Post-modification of SU-102 with coordination modifiers to make Fe 3+ It is uniformly dispersed inside SU-102-Fe as a catalytic site.

[0054] As one implementation method, with Zr 4+ The hydroxyl groups of the two ellagic acids simultaneously coordinate with the iron ion; one ellagic acid has an undeprotonated hydroxyl group, while the other ellagic acid has a deprotonated hydroxyl group. Fe 3+ With Zr 4 + Simultaneously, it coordinates with two hydroxyl oxygen atoms to form a quadrilateral structure, which is stable.

[0055] This application also provides a method for preparing bio-metal-organic framework materials for electrocatalytic nitrate reduction, including the following steps:

[0056] Ellagic acid and Zr 4+ The coordinated metal-organic framework SU-102 reacts with ferric ions in an aqueous solution to prepare the bio-metal-organic framework material for electrocatalytic nitrate reduction.

[0057] By utilizing natural ellagic acid, a low-cost, highly stable, and structurally well-defined three-dimensional bio-metal-organic framework (MOF) material was obtained. Simple post-modification (with low-temperature stirring) enables the rapid, simplistic, and high-volume (gram-scale) production of electrocatalysts for the reduction of nitrate. Using bio-resources as raw materials overcomes the current widespread problems of difficult MOF ligand supply, long synthesis cycles, and high costs. Using non-precious metals as the catalyst active center reduces production costs and demonstrates great promise for practical applications.

[0058] In one embodiment, the ferric salt is any one of a ferric hydrochloride, sulfate, nitrate, acetate, or hydrate thereof. (The hydroxyl group reacts with Fe...) 3+ It exhibits rapid and strong chelation, enabling good loading. Furthermore, iron, being a non-precious metal, serves as the active center for the catalyst, reducing its manufacturing cost.

[0059] In one embodiment, the mass ratio of SU-102 to ferric salt is 1.5:(1-1.5). The loading of ferric ions in this application can be adjusted according to the amount of ferric salt added. Adding too much ferric salt may clog the pore structure of SU-102, while adding too little will result in insufficient catalytic effect due to low iron content.

[0060] One implementation method involves stirring at 20-40°C for 30-90 minutes. The reaction can proceed with stirring within a relatively low temperature range, requiring no complex processes or stringent conditions.

[0061] In one embodiment, the reaction is carried out in an aqueous solution. SU-102 and the iron precursor can be dispersed or dissolved separately in water, and then the aqueous solutions are mixed for the reaction. Preferably, dispersion or dissolution can be accelerated by ultrasound. More preferably, the concentration of the solution is moderate; the concentration of the SU-102 aqueous solution is 1-20 mg / mL; the iron precursor aqueous solution is sufficient to completely dissolve the iron precursor.

[0062] As one embodiment, SU-102 is prepared by the following method:

[0063] SU-102 was prepared by reacting ellagic acid with zirconium oxychloride octahydrate under solvothermal conditions. The preparation of SU-102 follows existing literature, involving a solvothermal reaction of ellagic acid ligands with zirconium oxychloride octahydrate precursors to obtain SU-102MOF; this method is mature and can be used for mass synthesis.

[0064] In one embodiment, the mass ratio of ellagic acid to zirconium oxychloride octahydrate is (1.5-2):1.

[0065] In one embodiment, the solvent for solvothermal is a mixture of DMF and water, with a volume ratio of DMF to water of 1:(1-2).

[0066] As one implementation method, the reaction is carried out in the presence of acetic acid, with the amount of acetic acid being 20%-50% of the solvent volume.

[0067] As one implementation method, the solvothermal reaction conditions are: 60-80°C for 2-5 days. The reaction conditions for preparing SU-102 are also mild and not harsh.

[0068] In one embodiment, after the solvothermal reaction, a post-processing procedure is also included: after the reaction solution is cooled, solid-liquid separation is performed, the solid phase is washed with ethanol and water, and dried in an oven to obtain SU-102. After the solvothermal reaction synthesis of SU-102, post-processing allows it to be directly used for coordination loading with iron ions.

[0069] The following is a further explanation using specific embodiments.

[0070] Example 1: Preparation of SU-102:

[0071] 900 mg of ellagic acid (EA) and 480 mg of ZrOCl2·8H2O were dissolved in a flask containing 12 mL of DMF and 18 mL of H2O. 12 mL of CH3COOH was added and the mixture was stirred and reacted at 70 °C for 3 days. After the reaction was completed and cooled to room temperature, the precipitate was collected and washed twice with ethanol and water, respectively. Then it was dried overnight in an oven at 70 °C to obtain the metal-organic framework SU-102 sample.

[0072] Example 2: Preparation of SU-102:

[0073] 900 mg of ellagic acid (EA) and 600 mg of ZrOCl2·8H2O were dissolved in a flask containing 25 mL of DMF and 25 mL of H2O. 10 mL of CH3COOH was added and mixed thoroughly. The mixture was reacted at 80 °C for 2 days with stirring. After the reaction was completed and cooled to room temperature, the precipitate was collected and washed twice with ethanol and water, respectively. Then, it was dried overnight in an oven at 70 °C to obtain the metal-organic framework SU-102 sample.

[0074] Example 3: Preparation of SU-102:

[0075] 900 mg of ellagic acid (EA) and 500 mg of ZrOCl2·8H2O were dissolved in a flask containing 6.6 mL of DMF and 13.4 mL of H2O. 10 mL of CH3COOH was added and the mixture was stirred and reacted at 60 °C for 5 days. After the reaction was completed and cooled to room temperature, the precipitate was collected and washed twice with ethanol and water, respectively. Then it was dried overnight in an oven at 70 °C to obtain the metal-organic framework SU-102 sample.

[0076] Example 4 Preparation of SU-102-Fe (small quantity):

[0077] 30 mg of SU-102 prepared in Example 1 was placed in a 25 mL flask, followed by the addition of 15 mL of H2O and sonication for 5 min. Then, 30 mg of Fe(NO3)3·9H2O was dissolved in 10 mL of H2O and poured into the 25 mL flask. The mixture was stirred at room temperature for 45 min, centrifuged at 10,000 rpm, and the precipitate was collected. The precipitate was washed three times with H2O and ethanol, respectively, and dried at room temperature to obtain a bio-metal-organic framework material for electrocatalytic nitrate reduction, named SU-102-Fe (small amount).

[0078] Example 5: Batch preparation (batch synthesis) of SU-102-Fe:

[0079] 900 mg of SU-102 prepared in Example 1 was placed in a 500 mL round-bottom flask, followed by the addition of 200 mL of H2O and sonication for 5 min. Then, 600 mg of Fe(NO3)3·9H2O was dissolved in 100 mL of H2O and poured into the 500 mL round-bottom flask. The mixture was stirred at room temperature for 45 min, centrifuged at 10000 rpm, and the precipitate was collected. The precipitate was washed three times with H2O and ethanol, respectively, and dried at room temperature to obtain a bio-metal-organic framework material for electrocatalytic nitrate reduction, named SU-102-Fe-batch-. The color changes of the reaction solution before and after the reaction are shown in the figure. Figure 2 As shown.

[0080] Material characterization:

[0081] (1) X-ray powder diffraction tests were performed on SU-102 prepared in Example 1, and SU-102-Fe prepared in Examples 4 and 5. The X-ray powder diffraction patterns are shown below. Figure 3 As shown;

[0082] from Figure 3 As can be seen from the XRD, the characteristic peaks of SU-102-Fe prepared after the reaction of SU-102 with the metal precursor did not shift. The basic morphology and structure of the crystal remained unchanged after the introduction of Fe, indicating that the MOF structure maintained the complete crystal form.

[0083] (2) The SU-102 prepared in Example 1 and the SU-102-Fe prepared in Example 4 were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The SEM and TEM images are shown below. Figure 4 and Figure 5 As shown; EDS plot as shown Figure 6 As shown.

[0084] Figure 4 In the study, SU-102-Fe did not undergo a fundamental change in morphology compared to SU-102, indicating that Fe did not form oxides or nanoparticles attached to the SU-102 surface. From... Figure 5 It can be seen that the lattice fringes of SU-102 and SU-102-Fe are the same, indicating that the framework structure was not changed after Fe modification; while from Figure 6 EDS elemental analysis showed that Fe was uniformly distributed within the MOF, further indicating that Fe did not form Fe nanoparticles or Fe clusters, and that Fe existed in the MOF in the form of single atoms.

[0085] (3) The SU-102 prepared in Example 1 and the SU-102-Fe prepared in Example 4 were subjected to N2 adsorption-desorption tests, and the N2 adsorption-desorption curves are shown in Figure 1. Figure 7 As shown.

[0086] N2 adsorption isotherms of SU-102 and SU-102-Fe at 77 K ( Figure 7 This indicates that the specific surface area of ​​SU-102-Fe is smaller than that of SU-102, which indirectly confirms that Fe is fixed in the pores of the space.

[0087] (4) X-ray photoelectron spectroscopy (XPS) was performed on SU-102 prepared in Example 1 and SU-102-Fe prepared in Example 4. The results are as follows: Figure 8 As shown; synchrotron radiation tests were performed on SU-102-Fe, and the results are as follows. Figure 9 As shown.

[0088] Figure 8 Fine spectrum of Fe in SU-102-Fe 2 p 3 / 2 and Fe 2 p 1 / 2 The values ​​at 724.8 eV and 711.1 eV indicate that Fe maintains a +3 valence state. Figure 8 a). Furthermore, the O 1 of SU-102 and SU-102-Fe s The fine spectrum showed significant differences, with a new Fe-O peak appearing at 530.3 eV in SU-102-Fe. Figure 8 (b) also verified the interaction between Fe and the hydroxyl oxygen on SU-102.

[0089] To further clarify the valence state and coordination structure of Fe, synchrotron radiation tests were performed on SU-102-Fe, and K-side XANES reconfirmed that Fe is in the +3 valence state. Figure 9 a); K-edge EXAFS spectroscopy indicates the presence of only Fe-O bonds, with no Fe-Fe or Fe-O-Fe bonds, further demonstrating that Fe is distributed as single atoms in SU-102. Figure 9 b); The EXAFS spectral fit of Fe K-edge of SU-102-Fe matches the simulated Fe coordination structure, indicating that Fe is stably present in the framework by chelating with two hydroxyl oxygens on EA, and is coordinated with four free water molecules to form a 6-coordinate structure ( Figure 9 c).

[0090] Electrocatalytic nitrate reduction performance test:

[0091] Currently, almost none of the synthesized MOF electrocatalysts for nitrate reduction can be directly applied to actual nitrate industrial wastewater or simulated wastewater. Their high FE and yield are limited to laboratory research, which greatly restricts their practical use and commercial production.

[0092] 1. Basic performance test

[0093] The eNO3RR performance was evaluated in a conventional three-electrode configuration of an H-type battery using a neutral electrolyte prepared with pure water and comprising 0.2 M K2SO4 and 2000 ppm KNO3 (nitrate concentration in industrial wastewater is approximately 2000 ppm). The range was from -0.5 to -1.0 V. vs Chronoamperometry and colorimetric analysis were performed within the potential window of the RHE to further evaluate the catalytic performance. Simultaneously, to demonstrate the material advantages, performance was compared using a pristine MOF (SU-102) and commercially available Fe2O3. The Faradaic efficiencies (FE) of SU-102, SU-102-Fe, and Fe2O3 at different voltages were shown in the figure. Figure 10 As shown; ammonia yield under different voltages is as follows: Figure 11 As shown; the current, ammonia yield, and Faraday efficiency during the 10-hour continuous electrolysis of SU-102-Fe are as follows: Figure 12 As shown.

[0094] from Figure 10 It can be seen that the FE of SU-102-Fe is superior to that of SU-102 and Fe2O3 under all applied voltages, with its FE being greater than 96.5% at its highest. Figure 11 In this study, the ammonia yield of SU-102-Fe was 2.2 times and 65 times that of commercial Fe2O3 and SU-102, respectively. This highlights the superiority of the SU-102-Fe catalyst. Furthermore, Figure 12 During continuous electrolysis for up to 10 hours, SU-102-Fe maintained stable current density, yield, and Faradaic efficiency, demonstrating the excellent stability of this electrocatalyst.

[0095] 2. Practical application testing

[0096] For nitrate reduction electrocatalysts, the most important factor is their practical application potential: whether they can be easily mass-produced and whether their performance is suitable for practical wastewater treatment. Therefore, to evaluate the practical application potential of SU-102-Fe, this application conducted a batch synthesis according to Example 5 (preparation of SU-102-Fe - batch product as shown in Example 5). Figure 13 As shown in the figure, it was applied to the testing of actual nitrate-containing wastewater.

[0097] Using natural lake water as the water source Figure 14 And common interfering factors in industrial wastewater (including organic matter, anions and cations) were added to prepare simulated nitrate-rich industrial wastewater (Table 1) for electrolysis testing.

[0098] Table 1. Water quality parameters of simulated industrial wastewater prepared using natural lake water as the water source.

[0099]

[0100] The substances in Table 1 include microorganisms, organic components, chemical oxygen demand (COD), non-filterable suspended solids, and interference from anions and cations in natural water bodies.

[0101] The eNO3RR performance was also evaluated in a conventional three-electrode configuration of H-type cells. The results are as follows: Figure 14 As shown, (a) is the Faraday efficiency diagram of various products at different potentials; (b) is the yield of ammonia at different potentials; and (c) is the current and Faraday efficiency during the continuous 10-hour electrolysis process.

[0102] like Figure 15 As shown, the Faraday efficiency of the SU-102-Fe batch is still -0.7V. vs The RHE efficiency reached its maximum value (>96%), and the ammonia yield was comparable to that of catalysts synthesized in small batches. During long-term stability testing, its current and FE were well maintained. Furthermore, the electrolysis performance of SU-102-Fe in batches under lake water conditions was compared with currently reported MOF electrocatalysts, revealing that even under simulated industrial wastewater conditions, SU-102-Fe represented almost the highest Faraday efficiency. Figure 16 These results indicate that the electrocatalyst SU-102-Fe synthesized by this method can not only be mass-produced but also maintain high catalytic activity when applied to actual wastewater treatment, demonstrating great application potential.

[0103] In summary, this invention utilizes SU-102 to rapidly and in large quantities synthesize SU-102-Fe electrocatalysts at room temperature using a simple method. The synthesized SU-102-Fe can not only achieve efficient reduction of nitrate to ammonia (FE > 96.5%) in electrolytes prepared with pure water, but also achieve good catalytic efficiency in industrial wastewater rich in nitrate and various impurities, demonstrating significant advantages in practical applications.

[0104] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A bio-metal-organic framework material for electrocatalytic nitrate reduction, characterized in that, Including ellagic acid and Zr 4+ The metal-organic framework SU-102 formed by coordination; and the iron ion coordinated with the hydroxyl group on the ellagic acid in SU-102.

2. The bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 1, characterized in that, With Zr 4+ The hydroxyl groups of the two ellagic acids are simultaneously coordinated with the iron ion; the hydroxyl group in one ellagic acid is an undeprotonated hydroxyl group, and the hydroxyl group in the other ellagic acid is a deprotonated hydroxyl group.

3. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction as described in claim 1 or 2, characterized in that, Includes the following steps: Ellagic acid and Zr 4+ The coordinated metal-organic framework SU-102 reacts with ferric ions in an aqueous solution to prepare the bio-metal-organic framework material for electrocatalytic nitrate reduction.

4. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 3, characterized in that, The ferric salt is any one of ferric hydrochloride, sulfate, nitrate, acetate, or hydrate thereof; The mass ratio of SU-102 to ferric salt is 1.5:(1-1.5).

5. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 3, characterized in that, The reaction conditions are: stirring at 20-40℃ for 30-90 minutes.

6. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 3, characterized in that, SU-102 is prepared by the following method: SU-102 was prepared by reacting ellagic acid with zirconium oxychloride octahydrate under solvothermal conditions.

7. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 6, characterized in that, The mass ratio of ellagic acid to zirconium oxychloride octahydrate is (1.5-2):1; The solvent for solvothermal is a mixture of DMF and water, with a volume ratio of DMF to water of 1:(1-2).

8. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 6, characterized in that, The reaction is carried out in the presence of acetic acid, with the amount of acetic acid being 20%-50% of the solvent volume; The conditions for the solvothermal reaction are: 60-80℃ for 2-5 days.

9. The method for preparing the bio-metal-organic framework material for electrocatalytic nitrate reduction according to claim 6, characterized in that, After the solvothermal reaction, a post-processing procedure is also included: after the reaction solution is cooled, the solid and liquid phases are separated, the solid phase is washed with ethanol and water, and dried in an oven to obtain the SU-102.

10. The application of the bio-metal-organic framework material for electrocatalytic nitrate reduction prepared by the method of any one of claims 1 or 2, or the bio-metal-organic framework material for electrocatalytic nitrate reduction prepared by any one of claims 3-9, in the electrocatalytic reduction of nitrate to ammonia.

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