Nanoscale zero-valent iron for electro-reduction of nitrate to ammonia and preparation method and application thereof

Abstract

The application discloses a kind of nanometer zero-valent iron for electric reduction of nitrate synthesis ammonia and its preparation method and application.The catalyst is nanometer zero-valent iron material for electric reduction of nitrate synthesis ammonia, using one-step method and by regulating and controlling cobalt reagent dosing amount, nanometer zero-valent iron for electric reduction of nitrate synthesis ammonia with different cobalt content is prepared.The application includes using the catalyst as cathode, in the double-chamber electrolytic cell and direct current power supply double-chamber flow electrolytic cell system equipped with three electrodes, ammonia is prepared by electrocatalytic reduction of nitrate, and ammonia is recovered by acid absorption liquid device.The catalyst delays the problems of easy passivation of nanometer zero-valent iron and serious hydrogen evolution side reaction in the process of electrochemical reduction of nitrate, accelerates the reduction rate of nitrate, improves the ammonia selectivity and faraday efficiency of nitrate, and shows stable application performance in the process of actual wastewater electrocatalytic long-term treatment.

Description

Technical Field

[0001] This invention belongs to the fields of materials engineering and environmental engineering technology, and particularly relates to a nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia, its preparation method and application. Background Technology

[0002] Ammonia is an indispensable raw material in agricultural fertilizers and the chemical industry, with a global annual demand exceeding 150 million tons, playing a vital role in food production and economic growth. It is a mild energy storage medium with high energy density (3 kWh / kg), low transportation and storage costs, and low hazard, and has been proposed as a potential energy carrier for carbon-neutral industries. Currently, the Haber-Bosch process remains the main route for ammonia production, accounting for 1-2% of global energy consumption and 1.44% of global carbon dioxide emissions, posing a challenge to sustainable energy development. On the other hand, excessive fertilization, fuel combustion, and industrial production result in large-scale nitrate emissions into water bodies, threatening the ecological environment and human health. Excessive nitrate in water bodies can cause eutrophication, damage plant and animal health, and, in drinking water, can cause cancer, liver damage, methemoglobinemia, and other health hazards. Electrocatalytic reduction of nitrate to ammonia is widely recognized as a green and economical solution with low chemical input and no secondary pollution. However, the hydrogen evolution side reaction under near-neutral conditions and low ammonia selectivity remain bottlenecks limiting the further development of electrocatalytic reduction of nitrate to ammonia technology.

[0003] Compared to noble metal catalysts, transition metal catalysts with incomplete filling... d The orbital energy level matches the π* orbital energy level of nitrate, effectively injecting electrons as an electron donor, which is beneficial for the adsorption and activation of nitrate and its reduction intermediates. However, the excellent electrochemical reduction performance of traditional iron-based materials (such as iron oxide and single-atom catalysts) relies entirely on an external electron source driven by an electric field and a strongly alkaline environment to suppress the hydrogen evolution reaction. This single driving force often leads to kinetic limitations and cannot fundamentally regulate the local reaction environment to suppress hydrogen evolution.

[0004] Nano-zero valent iron (nFe) 0 Inexpensive, readily available, and environmentally friendly, nFe has strong reducing power and a high specific surface area. 0 It has an inherent thermodynamically driven self-corrosion (Fe 0 -2e − →Fe 2+ This self-corrosion process can provide continuous internal electrons at the catalytic interface, complementing and coordinating with the electrons provided by the external circuit to form a dual-electron drive. Simultaneously, Fe... 0 It loses electrons and corrodes into Fe. 2+ Activating water to generate OH -This creates a localized alkaline environment on the material surface, which can suppress hydrogen evolution side reactions and intermediate N / N coupling, thereby improving ammonia selectivity. However, nFe 0 It is easily passivated, forming a dense surface passivation layer that hinders electron transfer, resulting in a slow increase in interfacial pH and making it difficult to obtain satisfactory ammonia selectivity and Faraday efficiency. nFe is designed by doping with exogenous elements through lattice engineering. 0 Crystal structure and coordination environment are emerging strategies for modulating crystal and electronic structures. Based on p - d and d - d Orbital interactions allow doping elements to modulate the d-band center and Fermi level of Fe, causing electron redistribution, altering the surface microenvironment, changing its interaction with surface active hydrogen, and affecting electron dynamics. Accelerated electron transfer can enhance Fe... 0 Electrons from the nucleus reach the material surface, promoting water activation and dissociation to form active hydrogen and OH groups. - Enhancing the local alkaline environment on the material surface improves its Faraday efficiency and ammonia selectivity for electrocatalytic nitrate ionization. Cobalt (Co), as a siderophile element, has become a promising lattice engineering dopant due to its low Gibbs free energy, high Fermi level, Faraday efficiency, and ammonia selectivity. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia, its preparation method, and its application.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia, comprising the following steps: (1) Weigh 5.8g of ferric chloride and 0.084~1.26g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride; (2) Weigh 6.8g of sodium borohydride and dissolve it in 200mL of deionized water to obtain a sodium borohydride solution; (3) Under a nitrogen atmosphere and with stirring at 100~500 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10~15 mL / min; (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed 3-4 times with oxygen-free deionized water and then dried under vacuum to obtain a dry solid. (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia.

[0007] Furthermore, the ferric chloride is anhydrous ferric chloride.

[0008] Furthermore, the cobalt chloride is cobalt chloride hexahydrate.

[0009] Secondly, the present invention provides nano-zero-valent iron for the electroreduction of nitrate ions to synthesize ammonia.

[0010] Thirdly, this invention provides an application of nano-zero-valent iron for the electro-reduction of nitrate ions to synthesize ammonia in the electrocatalytic reduction of nitrates in water to produce ammonia, specifically including the following steps: The nano-zero-valent iron used for the electroreduction of nitrate to synthesize ammonia was made into ink and coated onto carbon paper as the working electrode in a three-electrode electrochemical system, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. The working and reference electrodes were then placed in the cathode chamber of the three-electrode electrochemical system, and the counter electrode was placed in the anode chamber. The electrolyte solution in the cathode chamber was a mixed solution of nitrate and sodium sulfate, and the electrolyte solution in the anode chamber was a sodium sulfate solution. Ammonia was then produced by electrocatalytic reduction of nitrate in the mixed solution of nitrate and sodium sulfate in the three-electrode electrochemical system. The voltage for the electrocatalytic reduction of nitrate was -1.0 to -1.5 V, and the electrolysis time was 1 to 2 hours. After electrolysis, the generated ammonia was recovered using acid.

[0011] Furthermore, the ink is made of nano-zero-valent iron, isopropanol, and 5wt% Nafion used for the electroreduction of nitrate to synthesize ammonia; the carbon paper is hydrophilic carbon paper; and the cathode chamber and anode chamber are separated by a proton exchange membrane.

[0012] Furthermore, the amount of nano-zero-valent iron used for electroreduction of nitrate to synthesize ammonia in the ink is 20-40 mg, the amount of isopropanol is 720-1440 μL, and the amount of Nafion is 80-160 μL.

[0013] Furthermore, the concentrations of sodium sulfate in the mixed solution of nitrate and sodium sulfate, and in the sodium sulfate solution, are 0.1~0.5 mol / L, respectively.

[0014] Furthermore, the size of the carbon paper is 1~4cm. 2 The size of the counter electrode is 1 cm. 2 The concentration of nitrate-N in the mixed solution of nitrate and sodium sulfate is 100~1000 mg / L.

[0015] Furthermore, the filling solution of the saturated calomel electrode is saturated potassium chloride.

[0016] The beneficial effects of this invention are: 1) By adjusting the amount of cobalt reagent added, nano-zero-valent iron with different cobalt contents for electroreduction of nitrate to synthesize ammonia was prepared, thereby precisely controlling the crystal structure, electron transport capacity and other physicochemical properties of nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia. 2) Using cobalt-doped lattice-doped zero-valent iron nanoparticles as the cathode electrode, rapid nitrate reduction, high ammonia selectivity (90-100%), and Faraday efficiency (over 90%) were achieved, and long-term stable performance was demonstrated in actual nitrate wastewater treatment. 3) Compared with traditional physical and chemical methods for treating nitrates, electrocatalytic reduction of nitrates is more green and economical, and the recovered high-purity ammonium salts can be used as additional chemicals. Attached Figure Description

[0017] Figure 1 The images show the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the concentration change curves of nitrate-N during the reduction of nitrate by nano-zero-valent iron. Figure 2 The images show the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the concentration change curves of ammonia-N during the reduction of nitrate by the nano-zero-valent iron. Figure 3 The diagram shows the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the ammonia selectivity and Faraday efficiency of the nano-zero-valent iron during the reduction of nitrate. Figure 4 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of nano-zero valent iron in the electrocatalytic reduction of nitrate in the potential range of -1.1V to -1.5V vs. SCE. Figure 5 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 1 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 6 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 2 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 7 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 3 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 8The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 4 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 9 The graph shows the ammonia selectivity and Faraday efficiency of the nano-zero-valent iron prepared in Example 3 for electrocatalytic reduction of nitrate in the concentration range of 200~1000 mg / L nitrate-N. Figure 10 The graph shows the nitrate-N removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 3 for electrocatalytic reduction of nitrate to synthesize ammonia during 7 electrocatalytic reduction cycles. Figure 11 The graph shows the nitrate-N removal rate of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia when treating actual nitrate wastewater with a nitrate concentration of approximately 125 mg / L nitrate-N in a two-chamber flow electrolysis cell. Figure 12 The graph shows the ammonia selectivity and recovery of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia when treating actual nitrate wastewater containing about 125 mg / L nitrate-N in a two-chamber flow electrolysis cell. Figure 13 The graph shows the ammonia selectivity and recovery of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia when treating actual nitrate wastewater containing about 3000 mg / L nitrate-N in a two-chamber flow electrolysis cell. Figure 14 The graph shows the relationship between the nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia and the added cobalt-iron molar ratio of nano-zero valent iron, and the measured cobalt-iron molar ratio. Figure 15 The images show the XRD patterns of nano-zero valent iron and nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia. Figure 16 The Tafel slope diagrams of nano-zero valent iron and nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia are shown. Figure 17 The images show the nano-zero-valent iron and charge transfer resistance diagrams of the nano-zero-valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia. Figure 18 The graph shows the surface pH changes of nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia and the reaction of nano-zero valent iron in a two-chamber electrolytic cell. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0019] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0020] In a first aspect, the present invention provides a method for preparing nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia, comprising the following steps: (1) Weigh 5.8g of ferric chloride and 0.084~1.26g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride. The ferric chloride is anhydrous ferric chloride. The cobalt chloride is cobalt chloride hexahydrate.

[0021] (2) Weigh 6.8g of sodium borohydride and add it to 200mL of deionized water to dissolve it and obtain a sodium borohydride solution.

[0022] (3) Under a nitrogen atmosphere and with stirring at 100~500 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10~15 mL / min.

[0023] (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed 3-4 times with oxygen-free deionized water and then dried under vacuum to obtain a dry solid.

[0024] (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

[0025] Secondly, the present invention provides nano-zero-valent iron for the electroreduction of nitrate ions to synthesize ammonia.

[0026] Thirdly, this invention provides an application of nano-zero-valent iron for the electro-reduction of nitrate ions to synthesize ammonia in the electrocatalytic reduction of nitrates in water to produce ammonia, specifically including the following steps: The nano-zero-valent iron used for the electroreduction of nitrate to synthesize ammonia was made into ink and coated onto carbon paper as the working electrode in a three-electrode electrochemical system, with a platinum sheet as the counter electrode and a saturated calomel electrode as the reference electrode. The working and reference electrodes were then placed in the cathode chamber of the three-electrode electrochemical system, and the counter electrode was placed in the anode chamber. The electrolyte solution in the cathode chamber was a mixed solution of nitrate and sodium sulfate, and the electrolyte solution in the anode chamber was a sodium sulfate solution. Ammonia was then produced by electrocatalytic reduction of nitrate in the mixed solution of nitrate and sodium sulfate in the three-electrode electrochemical system. The voltage for the electrocatalytic reduction of nitrate was -1.0 to -1.5 V, and the electrolysis time was 1 to 2 hours. After electrolysis, the generated ammonia was recovered using acid.

[0027] The ink is made of nano-zero-valent iron, isopropanol and 5wt% Nafion used for the electroreduction of nitrate to synthesize ammonia; the carbon paper is hydrophilic carbon paper; the cathode chamber and the anode chamber are separated by a proton exchange membrane.

[0028] The ink contains 20-40 mg of nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia, 720-1440 μL of isopropanol, and 80-160 μL of Nafion.

[0029] The concentrations of sodium sulfate in the mixed solution of nitrate and sodium sulfate, and in the sodium sulfate solution, are 0.1~0.5 mol / L, respectively.

[0030] The carbon paper has a size of 1-4 cm. 2 The size of the counter electrode is 1 cm. 2 The concentration of nitrate-N in the mixed solution of nitrate and sodium sulfate is 100~1000 mg / L.

[0031] The filling solution of the saturated calomel electrode is saturated potassium chloride.

[0032] This invention provides four types of cobalt-content nano-zero-valent iron (Co-nFe) for the electroreduction of nitrate to synthesize ammonia. 0 The method for preparing nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia is characterized by controlling the amount of cobalt reagent added to achieve controllable cobalt content.

[0033] Example 1: A nano-zero-valent iron (1Co-nFe) with a cobalt / iron molar ratio of 1% for the electroreduction of nitrate to synthesize ammonia. 0 Preparation of ) (1) Weigh 5.8g of ferric chloride and 0.084g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride.

[0034] (2) Weigh 6.8g of sodium borohydride and add it to 200mL of deionized water to dissolve it and obtain a sodium borohydride solution.

[0035] (3) Under a nitrogen atmosphere and with stirring at 350 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10 mL / min.

[0036] (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed three times with oxygen-free deionized water and then dried under vacuum at 60°C for 8 hours to obtain a dry solid.

[0037] (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

[0038] The measured cobalt-iron molar ratio of the nano-zero-valent iron prepared in Example 1 for the electroreduction of nitrate to synthesize ammonia was 1.03%, therefore it is denoted as 1Co-nFe. 0 .

[0039] Example 2: A nano-zero-valent iron (5Co-nFe) with a cobalt / iron molar ratio of 5% for the electroreduction of nitrate to synthesize ammonia. 0 Preparation of ) (1) Weigh 5.8g of ferric chloride and 0.42g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride.

[0040] (2) Weigh 6.8g of sodium borohydride and add it to 200mL of deionized water to dissolve it and obtain a sodium borohydride solution.

[0041] (3) Under a nitrogen atmosphere and with stirring at 350 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10 mL / min.

[0042] (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed three times with oxygen-free deionized water and then dried under vacuum at 60°C for 8 hours to obtain a dry solid.

[0043] (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

[0044] The measured cobalt-iron molar ratio of the nano-zero-valent iron prepared in Example 2 for the electroreduction of nitrate to synthesize ammonia was 5.04%, therefore it is denoted as 5Co-nFe. 0 .

[0045] Example 3: A nano-zero-valent iron (10Co-nFe) with a cobalt / iron molar ratio of 10% for the electroreduction of nitrate to synthesize ammonia. 0 Preparation of ) (1) Weigh 5.8g of ferric chloride and 0.84g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride.

[0046] (2) Weigh 6.8g of sodium borohydride and add it to 200mL of deionized water to dissolve it and obtain a sodium borohydride solution.

[0047] (3) Under a nitrogen atmosphere and with stirring at 350 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10 mL / min.

[0048] (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed three times with oxygen-free deionized water and then dried under vacuum at 60°C for 8 hours to obtain a dry solid.

[0049] (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

[0050] The measured cobalt-iron molar ratio of the nano-zero-valent iron prepared in Example 3 for the electroreduction of nitrate to synthesize ammonia was 9.96%, therefore it is denoted as 10Co-nFe. 0 .

[0051] Example 4: A nano-zero-valent iron (15Co-nFe) with a cobalt / iron molar ratio of 15% for the electroreduction of nitrate to synthesize ammonia. 0 Preparation of ) (1) Weigh 5.8g of ferric chloride and 1.26g of cobalt chloride, add them to 200mL of oxygen-free deionized water and dissolve them to obtain a mixed solution of ferric chloride and cobalt chloride.

[0052] (2) Weigh 6.8g of sodium borohydride and add it to 200mL of deionized water to dissolve it and obtain a sodium borohydride solution.

[0053] (3) Under a nitrogen atmosphere and with stirring at 350 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10 mL / min.

[0054] (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed three times with oxygen-free deionized water and then dried under vacuum at 60°C for 8 hours to obtain a dry solid.

[0055] (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

[0056] The measured cobalt-iron molar ratio of the nano-zero-valent iron prepared in Example 4 for the electroreduction of nitrate to synthesize ammonia was 14.97%, therefore it is denoted as 15Co-nFe. 0 .

[0057] Application Example 1: Weigh 20 mg of the nano-zero valent iron and nano-zero valent iron (nFe) prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia. 0 The sample was placed in a 1 mL sample vial containing 720 μL of isopropanol and 80 μL of 5 wt% Nafion solution and sealed. The vial was sonicated for 1 h to obtain a uniformly dispersed ink. Then, the ink from the sample vial was evenly dropped onto a 1×2 cm hydrophilic carbon paper in a glove box. After drying, the paper was clamped and fixed with a platinum electrode clamp and used as a working electrode.

[0058] Deionized water was prepared by argon aeration for 1 hour and used as experimental water. A mixed solution of 100 mg / L nitrate-N and 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the cathode chamber, and another 40 mL solution of 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the anode chamber. The working electrode and reference electrode (i.e., saturated calomel electrode, SCE) were inserted into the cathode chamber, which was then sealed after being filled with argon headspace. A 1×1 cm platinum sheet electrode was inserted into the anode chamber as the counter electrode. Cyclic voltammetry was performed on the three electrodes connected to an electrochemical workstation to activate the working electrode under the following conditions: 10 scans at a scan rate of 0.1 V / s within the range of -0.6 V to -1.8 V vs. SCE. Subsequently, an isoelectric point (it) test was performed under the following conditions: -1.3 V vs. SCE, reaction time 2 hours, and stirring speed of the cathode chamber solution at 700 rpm. At preset time points, 0.5 mL of the reacted liquid was collected in the cathode chamber, and the nitrogen species in the solution were determined by ultraviolet-spectrum spectrophotometry. The curves showing the changes in nitrate removal and ammonia formation during the reaction are shown below. Figure 1 and Figure 2 As shown. Figure 1 The graphs show the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the concentration changes of nitrogen (nitrate-N) in nitrate during the reduction of nitrate by nano-zero-valent iron. Figure 1 It can be seen that, compared with nano-zero-valent iron, the nano-zero-valent iron prepared in Examples 1 to 4 for the electroreduction of nitrate to synthesize ammonia significantly accelerates the removal of nitrate. 10Co-nFe 0 It exhibits the fastest electrocatalytic reduction performance of nitrate, with a removal rate of nFe within 2 hours. 0 The percentage increased from 31% to 99.2%. Figure 2 The figures show the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the concentration change curves of ammonia-N during the reduction of nitrate by the nano-zero-valent iron. Figure 2 It can be seen that, compared to nFe 0 The Co-nFe prepared in Examples 1 to 4 0 Ammonia is generated during the electrocatalytic reduction of nitrate, and the generation of ammonia is significantly accelerated after cobalt lattice doping.

[0059] Figure 3 For different Co-nFe 0 Ammonia selectivity and Faraday efficiency of electrocatalytic reduction of nitrate to ammonia. Figure 3 The figures show the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the ammonia selectivity and Faraday efficiency of the nano-zero-valent iron during the reduction of nitrate. Figure 3 It can be seen that nFe 0 The selectivity and Faradaic efficiency of the electrocatalytic reduction of nitrate to ammonia were 78% and 81%, respectively. In contrast, the Co-nFe prepared in Examples 1-4... 0 The ammonia selectivity and Faraday efficiency were improved, increasing to 85%, 91%, 100%, 95% and 88%, 88%, 96%, 84%, respectively.

[0060] Application Example 2: Weigh 20 mg of the nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia and place them in a 1 mL sample bottle containing 720 μL isopropanol and 80 μL 5wt% Nafion solution. Seal the bottle and sonicate for 1 h to obtain a uniformly dispersed ink. Then, in a glove box, drop the ink from the sample bottle onto a 1×2 cm hydrophilic carbon paper in portions. After drying, clamp and fix it with a platinum electrode clip to use as a working electrode.

[0061] Deionized water was prepared by argon aeration for 1 hour and used as experimental water. A mixed solution of 100 mg / L nitrate-N and 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the cathode chamber, and another 40 mL solution of 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the anode chamber. The working electrode and reference electrode (i.e., saturated calomel electrode, SCE) were inserted into the cathode chamber, which was then headspaced with argon and sealed. A 1×1 cm platinum sheet electrode was inserted into the anode chamber as the counter electrode. Cyclic voltammetry was performed on the three electrodes connected to an electrochemical workstation to activate the working electrode. The test conditions were: 10 scans at a scan rate of 0.05 V / s within the range of -0.6 V to -1.8 V vs. SCE. Subsequently, it tests were performed at different constant potentials: -1.1V, -1.2V, -1.3V, -1.4V, and -1.5V vs. SCE, with a reaction time of 2 hours and a stirring speed of 700 rpm in the cathode chamber. At preset time points, 0.5 mL of the reacted liquid was collected from the cathode chamber, and the nitrogen species in the solution were determined by UV-spectrophotometry. The nitrate removal rate, ammonia selectivity, and Faraday efficiency after the reaction are shown below. Figures 4 to 8 As shown. Figure 4 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of nano-zero valent iron in the electrocatalytic reduction of nitrate in the potential range of -1.1V to -1.5V vs. SCE. Figure 5 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 1 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 6 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 2 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 7 The graph shows the nitrate-N removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero valent iron prepared in Example 3 for electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figure 8 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 4 for the electrocatalytic reduction of nitrate to ammonia in the potential range of -1.1V to -1.5V vs. SCE. Figures 4 to 8It can be seen that within the potential range of -1.1V to -1.5V, the nitrate removal effect first significantly increases and then slightly slows down with increasing negative potential. Ammonia selectivity is optimal at -1.3V, and the Faraday efficiency first significantly increases and then slightly decreases with increasing negative potential. At -1.3V, the electrocatalytic performance of several materials is optimal. Furthermore, within the potential range of -1.1V to -1.5V, the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to ammonia exhibits better electrocatalytic reduction performance than nano-zero-valent iron.

[0062] Application Example 3: Weigh 20 mg of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia and place it in a 1 mL sample bottle containing 720 μL of isopropanol and 80 μL of 5 wt% Nafion solution. Seal the bottle and sonicate for 1 h to obtain a uniformly dispersed ink. Then, in a glove box, drop the ink from the sample bottle onto a 1×2 hydrophilic carbon paper in portions. After drying, clamp and fix it with a platinum electrode clip to use as a working electrode.

[0063] Deionized water was prepared by argon aeration for 1 hour and used as experimental water. 40 mL solutions containing 200–1000 mg / L nitrate-N and 0.1 mol / L sodium sulfate were prepared as electrolyte solutions for the cathode chamber, and 40 mL solutions containing 0.1 mol / L sodium sulfate were prepared as electrolyte solutions for the anode chamber. The working electrode and reference electrode (i.e., saturated calomel electrode, SCE) were inserted into the cathode chamber, which was then sealed after being filled with argon headspace. A 1 × 1 cm platinum sheet electrode was inserted into the anode chamber as the counter electrode. Cyclic voltammetry was performed on the three electrodes connected to an electrochemical workstation to activate the working electrode under the following conditions: 10 scans at a scan rate of 0.05 V / s within the range of -1.3 V vs. SCE. Subsequently, iterative voltammetry (it) was performed at different constant potentials under the following conditions: -1.3 V vs. SCE, reaction time 2 hours, and stirring speed of the cathode chamber solution at 700 rpm. At a preset time point, 0.5 mL of the reacted liquid was taken from the cathode chamber, and the nitrogen species in the solution were determined by ultraviolet-spectrophotometry. Figure 9 The graph shows the ammonia selectivity and Faradaic efficiency of the nano-zero-valent iron prepared in Example 3 for the electrocatalytic reduction of nitrate to ammonia in the concentration range of 200-1000 mg / L nitrate-N. Figure 9 It can be seen that, under -1.3V conditions, the nano-zero-valent iron prepared in Example 3 for the electroreduction of nitrate to synthesize ammonia exhibits ammonia selectivity and Faraday efficiency of over 90% in the nitrate-N concentration range of 200~1000 mg / L.

[0064] Application Example 4: Weigh 20 mg of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia and place it in a 1 mL sample bottle containing 720 μL of isopropanol and 80 μL of 5 wt% Nafion solution. Seal the bottle and sonicate for 1 h to obtain a uniformly dispersed ink. Then, in a glove box, drop the ink from the sample bottle onto a 1×2 cm hydrophilic carbon paper in several portions. After drying, clamp and fix it with a platinum electrode clip to use as a working electrode.

[0065] Deionized water was prepared by argon aeration for 1 hour and used as experimental water. A mixed solution of 100 mg / L nitrate-N and 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the cathode chamber, and another 40 mL solution of 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the anode chamber. The working electrode and reference electrode (i.e., saturated calomel electrode, SCE) were inserted into the cathode chamber, which was then sealed after being filled with argon headspace. A 1×1 cm platinum sheet electrode was inserted into the anode chamber as the counter electrode. Cyclic voltammetry was performed on the three electrodes connected to an electrochemical workstation to activate the working electrode under the following conditions: 10 scans at a scan rate of 0.05 V / s within the range of -1.3 V vs. SCE. Subsequently, iterative voltammetry (it) was performed at different constant potentials under the following conditions: -1.3 V vs. SCE, reaction time 2 hours, and stirring speed of the cathode chamber solution at 700 rpm. At preset time points, 0.5 mL of the reacted liquid was collected from the cathode chamber, and the nitrogen species in the solution were determined by ultraviolet-spectrum spectrophotometry. After one reaction, the solutions in the cathode and anode chambers were replaced, and other experimental conditions remained unchanged, and the second cycle of the experiment was started. The cycle was repeated a total of 7 times. Figure 10 The graph shows the nitrate removal rate, ammonia selectivity, and Faraday efficiency of the nano-zero-valent iron prepared in Example 3 for the electrocatalytic reduction of nitrate to synthesize ammonia during 7 cycles of nitrate reduction. Figure 10 It can be seen that under the conditions of -1.3V vs. SCE, the removal rate of nitrate ions reached more than 95% after 7 cycles, and the ammonia selectivity and Faraday efficiency were both above 90%, indicating that the nano-zero valent iron prepared in Example 3 for the electroreduction of nitrate ions to synthesize ammonia has good application potential.

[0066] Application Example 5: Weigh 40 mg of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia and place it in a 1 mL sample bottle containing 1440 μL of isopropanol and 160 μL of 5 wt% Nafion solution. Seal the bottle and sonicate for 1 h to obtain a uniformly dispersed ink. Then, in a glove box, drop the ink from the sample bottle onto a 1×1 cm hydrophilic carbon paper in portions. After drying, clamp and fix it with a platinum electrode clip to use as a working electrode.

[0067] Construct a practical wastewater electrocatalytic device, comprising a flow electrolytic cell, a DC regulated power supply, an anode electrolyte bottle, a cathode nitrate wastewater bottle, a peristaltic pump, and an acid recovery device (hydrophobic polypropylene hollow fiber degassing membrane, 0.5 mol / L dilute sulfuric acid solution). Insert the working electrode and a 1×1 cm platinum electrode into the cathode and anode chambers respectively, and secure them with copper tape. Assemble the two electrodes into a flow electrolytic cell and connect it to the regulated DC power supply. Prepare 250 mL of a 0.1 mol / L sodium sulfate solution and pump it into the anode chamber using the peristaltic pump (2 mL / min) as the anode electrolyte. The outflowing anode electrolyte is reused. 250 mL of wastewater containing approximately 125 mg / L nitrate-N was filtered through a 0.45 μm aqueous filter membrane and used as the cathode chamber solution. The solution was pumped into the cathode chamber using a peristaltic pump (2 mL / min). After reaction, the effluent entered a hydrophobic polypropylene hollow fiber degassing membrane, which was immersed in a 0.5 mol / L dilute sulfuric acid solution. The effluent from the fiber membrane was then returned to the original nitrate wastewater. The test conditions were: 0.1 A / cm². 2 The current density was measured by taking 0.5 mL of the reacted liquid from the cathode nitrate wastewater bottle and the acid recovery bottle every 24 hours. The nitrogen species in the solution were determined by ultraviolet-spectrophotometry. At the same time, the untreated nitrate wastewater and sodium sulfate solution were replaced and the experiment was continued. Figure 11 The graph shows the nitrate-N removal rate of the nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia when treating actual nitrate wastewater with a concentration of approximately 125 mg / L nitrate-N in a two-chamber flow electrolysis cell. Figure 12 The graph shows the ammonia selectivity and recovery of nano-zero-valent iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia, when used in a two-chamber flow electrolyzer to treat actual nitrate wastewater containing approximately 125 mg / L nitrate-N. Figure 11 and Figure 12 It can be seen that within 336 hours, 10Co-nFe 0 The removal efficiency of nitrate in actual wastewater is over 97%, and the ammonia selectivity is over 98%. Ammonia can be 100% recovered after acid recovery. Figure 13 The graph shows the ammonia selectivity and recovery of nano-zero-valent iron prepared in Example 3 for the electroreduction of nitrate to synthesize ammonia, when used in a two-chamber flow electrolyzer to treat actual nitrate wastewater containing approximately 3000 mg / L nitrate-N. Figure 13 As shown, when treating actual wastewater with approximately 3000 mg / L nitrate in a flowing electrolytic cell, at a current density of 0.5 A / cm²... 2 Under these conditions, nitrate ions can be continuously removed within 120 hours with an ammonia selectivity of over 95%. These results indicate that the nano-zero-valent iron prepared in Example 3 for the electroreduction of nitrate ions to synthesize ammonia has good experimental application capabilities.

[0068] Application Example 6: The relationship between the nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia and the added cobalt-iron molar ratio and the measured cobalt-iron molar ratio is shown in the figure below. Figure 14 As shown. From Figure 14 As can be seen from the examples, the actual cobalt content of the nano-zero-valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia is very close to the amount of cobalt added. This indicates that cobalt has a high affinity for iron, and the actual cobalt doping amount of the nano-zero-valent iron can be precisely controlled by changing the amount of cobalt reagent added.

[0069] Application Example 7: The nano-zero valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia and the XRD characterization results of the nano-zero valent iron are as follows. Figure 15 As shown. From Figure 15 As can be seen from the data, the nano-zero-valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia all exhibited Fe. 0 The diffraction characteristic peaks of the (110), (200) and (211) crystal planes; in addition, after cobalt lattice doping, with the increase of cobalt content, the Fe nano-zero valent iron used for electroreduction of nitrate to synthesize ammonia with different cobalt contents. 0 (110) Crystal plane diffraction characteristic peaks compared to Fe nano-zero valent iron 0 (110) The characteristic peaks of the crystal plane diffraction are slightly shifted to the left, indicating that the lattice constant increases with the increase of cobalt content. This helps the electron transfer between the prepared nano-zero-valent iron and nitrate ions for the electroreduction of nitrate to synthesize ammonia. It also indicates that cobalt doping has entered the Fe. 0 In a body-centered cubic lattice.

[0070] Application Example 8: The Tafel slope and charge transfer resistance of the nano-zero-valent iron and nano-zero-valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia were tested. The test results are as follows: Figure 16 and Figure 17 As shown. Figure 16 The Tafel slope diagrams of nano-zero valent iron and nano-zero valent iron prepared in Examples 1-4 for electroreduction of nitrate to synthesize ammonia are shown. Figure 17 The images show the charge transfer resistance diagrams of nano-zero valent iron and nano-zero valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia. Figure 16 As can be seen, the Tafel slope of the nano-zero-valent iron material decreases after cobalt lattice doping, and further decreases with increasing cobalt content. This indicates that cobalt doping promotes Fe... 0 Nuclear corrosion, and Fe 0 The degree of nuclear corrosion is modulated by the cobalt content. From... Figure 17It can be seen that the charge transfer resistance of the nano-zero-valent iron material decreases after cobalt lattice doping, and this decrease further decreases with increasing cobalt content. This indicates that cobalt doping promotes electron transfer in the material and is modulated by the cobalt content. These results demonstrate that the Fe content of the material can be controlled by adjusting the cobalt content. 0 Nuclear corrosion and nuclear electron transfer promote the electrocatalytic reduction of nitrate to ammonia to varying degrees.

[0071] Application Example 9: 20 mg of nano-zero ferric iron and nano-zero ferric iron prepared in Example 3 for electroreduction of nitrate to synthesize ammonia were weighed and placed in a 1 mL sample bottle containing 720 μL of isopropanol and 80 μL of 5 wt% Nafion. The sample bottle was sealed and sonicated for 1 h to obtain a uniformly dispersed ink. Subsequently, the ink in the sample bottle was evenly dropped onto a 1×2 cm hydrophilic carbon paper in a glove box. After drying, the paper was clamped and fixed with a platinum electrode clamp and used as a working electrode.

[0072] Deionized water was prepared by argon aeration for 1 hour and used as experimental water. A mixed solution of 100 mg / L nitrate-N and 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the cathode chamber, and another 40 mL solution of 0.1 mol / L sodium sulfate was prepared as the electrolyte solution for the anode chamber. The working electrode and reference electrode (i.e., saturated calomel electrode, SCE) were inserted into the cathode chamber, which was then filled with argon headspace and sealed. A 1×1 cm platinum sheet electrode was inserted into the anode chamber as the counter electrode. After connecting the three electrodes to an electrochemical workstation, an it test was performed at -1.3 V vs. SCE potential for 1 hour. The pH was monitored using a pH meter. The test results are as follows: Figure 18 As shown. Figure 18 The graph shows the changes in surface pH of nano-zero valent iron prepared in Examples 1-4 for the electroreduction of nitrate to synthesize ammonia, and the nano-zero valent iron used in the reaction in a two-chamber electrolytic cell; from Figure 18 It can be seen that the pH of the material surface rises rapidly during the reaction, and the rate and extent of pH increase after cobalt doping are significantly higher than those of nano-zero-valent iron. Combined with the higher ammonia selectivity and Faradaic efficiency of nano-zero-valent iron phase nano-zero-valent iron electrocatalytic reduction of nitrate in Application Example 1, this indicates that the enhanced local alkaline environment on the surface after cobalt doping can effectively improve the performance of electrocatalytic reduction of nitrate.

[0073] In summary, this invention achieves the preparation of nano-zero-valent iron with controllable cobalt content for electro-reduction of nitrate to ammonia by adjusting the amount of cobalt reagent added, and its application in the efficient electrocatalytic reduction of nitrate to ammonia.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing nano-zero-valent iron for the electroreduction of nitrate to synthesize ammonia, characterized in that, Includes the following steps: (1) Weigh 5.8g of ferric chloride and 0.084~1.26g of cobalt chloride, add them to 200mL of deionized water to dissolve them and obtain a mixed solution of ferric chloride and cobalt chloride; (2) Weigh 6.8g of sodium borohydride and dissolve it in 200mL of deionized water to obtain a sodium borohydride solution; (3) Under a nitrogen atmosphere and with stirring at 100~500 rpm, the sodium borohydride solution prepared in step (2) is added to the mixed solution of ferric chloride and cobalt chloride prepared in step (1) at a dropping rate of 10~15 mL / min; (4) After the sodium borohydride solution is added dropwise, solid-liquid separation is performed. The solid is washed 3-4 times with oxygen-free deionized water and then dried under vacuum to obtain a dry solid. (5) Grind the dry solid obtained in step (4) into powder to obtain nano-zero valent iron for electroreduction of nitrate to synthesize ammonia.

2. The method for preparing nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia according to claim 1, characterized in that, The ferric chloride is anhydrous ferric chloride.

3. The method for preparing nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia according to claim 1, characterized in that, The cobalt chloride is cobalt chloride hexahydrate.

4. A nano-zero-valent iron prepared by the method according to any one of claims 1-3 for the electroreduction of nitrate to synthesize ammonia.

5. The application of the nano-zero-valent iron as described in claim 4 for the electroreduction of nitrate to ammonia in the electrocatalytic reduction of nitrate in water to produce ammonia, characterized in that, Specifically, the steps include: The nano-zero-valent iron used for electroreduction of nitrate to synthesize ammonia was made into ink and coated on carbon paper as the working electrode in a three-electrode electrochemical system, and a platinum sheet was used as the counter electrode and a saturated calomel electrode was used as the reference electrode. The working electrode and reference electrode are then placed in the cathode chamber of the three-electrode electrochemical system, and the counter electrode is placed in the anode chamber of the three-electrode electrochemical system; the electrolyte solution in the cathode chamber is a mixed solution of nitrate and sodium sulfate, and the electrolyte solution in the anode chamber is a sodium sulfate solution; then, ammonia is produced by electrocatalysis of nitrate in the mixed solution of nitrate and sodium sulfate in the three-electrode electrochemical system. The voltage for the electrocatalytic reduction of nitrate is -1.0 to -1.5V, and the electrolysis time is 1 to 2 hours. After electrolysis, the generated ammonia is recovered using acid solution.

6. The application according to claim 5, characterized in that, The ink is made of nano-zero-valent iron, isopropanol and 5wt% Nafion used for the electroreduction of nitrate to synthesize ammonia; the carbon paper is hydrophilic carbon paper; the cathode chamber and the anode chamber are separated by a proton exchange membrane.

7. The application according to claim 6, characterized in that, The ink contains 20-40 mg of nano-zero-valent iron for electroreduction of nitrate to synthesize ammonia, 720-1440 μL of isopropanol, and 80-160 μL of Nafion.

8. The application according to claim 5, characterized in that, The concentrations of sodium sulfate in the mixed solution of nitrate and sodium sulfate, and in the sodium sulfate solution, are 0.1~0.5 mol / L, respectively.

9. The application according to claim 5, characterized in that, The carbon paper has a size of 1-4 cm. 2 The size of the counter electrode is 1 cm. 2 The concentration of nitrate-N in the mixed solution of nitrate and sodium sulfate is 100~1000 mg / L.

10. The application according to claim 5, characterized in that, The filling solution of the saturated calomel electrode is saturated potassium chloride.

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