A bimetallic oxide-graphite composite electrode made of iron and nickel, its preparation method and application

Abstract

This invention provides an iron-nickel bimetallic oxide-graphite composite electrode, its preparation method, and its application, belonging to the field of water treatment technology. The iron-nickel bimetallic oxide-graphite composite electrode provided by this invention includes a graphite substrate and an active coating on the surface of the graphite substrate; the active coating includes iron-nickel nanoparticle oxide, a curing agent, and a conductive agent; the mass ratio of the iron-nickel nanoparticle oxide, curing agent, and conductive agent is (1-10):1:1. The iron-nickel bimetallic oxide-graphite composite electrode provided by this invention, when applied to ammonia-nitrogen-containing wastewater, can efficiently and rapidly electrocatalytically oxidize ammonia nitrogen to nitrogen gas, reducing secondary pollution from nitrates, lowering the total nitrogen in the water, and has a wide pH applicability.

Description

Technical Field

[0001] This invention relates to the field of electrochemical water treatment, specifically to an iron-nickel bimetallic oxide-graphite composite electrode, its preparation method, and its application. Background Technology

[0002] Wastewater contains high levels of ammonia nitrogen, which is easily oxidized by microorganisms into nitrates and nitrites. Discharge into natural water bodies harms aquatic life and human health, and is also a major contributor to eutrophication. Biological nitrogen and phosphorus removal, a method utilizing microorganisms to biodegrade, adsorb, and convert organic and some inorganic matter from wastewater into microbial biomass and other internal metabolic products, has been widely used. However, its application is significantly limited under certain conditions, such as high salinity, high ammonia concentration, and low temperature. Electrochemical methods, a novel ammonia nitrogen treatment technology, can rapidly and moderately oxidize ammonia nitrogen in water to nitrogen gas through direct oxidation (electron transfer) or indirect oxidation (such as using chlorine-producing active substances as an oxidation medium) under an applied electric field. This method offers advantages such as fast response, compact operation, good controllability, and high nitrogen generation rate, effectively compensating for the shortcomings of biological activated sludge methods. It holds promise for rapid control and emergency management of ammonia nitrogen in coastal tidal waters or saline wastewater. Chemical oxidation methods include wet oxidation, ozone oxidation, electrochemical treatment, and breakpoint chlorination. Among them, electrochemical treatment technology has the advantages of not producing sludge, high equipment integration, and small footprint, and can achieve better ammonia nitrogen removal effect.

[0003] Although electrochemical methods have shown good results in treating water with high salinity and high chloride ion concentrations, their efficiency depends heavily on the preparation and selection of the anode. Titanium-based metal electrodes are widely used both domestically and internationally for the electrochemical oxidation removal of ammonia nitrogen from water. Commercially available metal electrodes primarily use platinum-group, ruthenium-group, and iridium-group noble metals as active components, such as Ti / RuO2-IrO2, Ti / RuO2-TiO2, and Ti / RuO2-TiO2-IrO2 electrodes. However, these electrode materials often suffer from high cost and poor stability, significantly limiting their large-scale and long-term application. Existing non-noble single-metal anode materials used in electrochemical catalytic oxidation have low ammonia nitrogen removal efficiency and are prone to generating large amounts of nitrates, easily causing secondary pollution. Therefore, to address these issues, developing a low-cost, highly efficient, stable, and long-life anode material is particularly necessary. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide an iron-nickel bimetallic oxide-graphite composite electrode, its preparation method and application. The present invention has a high removal rate of ammonia nitrogen and total nitrogen, and can realize the efficient and rapid conversion of ammonia nitrogen in water into nitrogen gas for removal.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides an iron-nickel bimetallic oxide-graphite composite electrode, which includes a graphite substrate and an active coating coated on the surface of the graphite substrate.

[0007] The active coating comprises an iron-nickel bimetallic oxide, a curing agent, and a conductive agent; and the mass ratio of the iron-nickel bimetallic oxide, the curing agent, and the conductive agent is (1-10):1:1.

[0008] Preferably, the curing agent is polyvinylidene fluoride; the conductive agent is superconducting carbon black.

[0009] This invention also provides a method for preparing the iron-nickel bimetallic oxide-graphite composite electrode as described above, which includes the following steps:

[0010] The active coating solution is obtained by thoroughly mixing iron-nickel bimetallic oxide, curing agent, conductive agent and organic solvent;

[0011] The active coating solution is coated onto the surface of a graphite substrate and then dried to obtain an iron-nickel bimetallic oxide-graphite composite electrode.

[0012] Preferably, the preparation steps of the iron-nickel bimetallic oxide include:

[0013] Iron salts, nickel salts, and urea are added to a mixed solution of water and ethanol, and stirred thoroughly to obtain a mixed ionic metal solution.

[0014] The mixed ionic metal solution was subjected to a hydrothermal reaction, and after washing and drying, an iron-nickel bimetallic oxide was obtained.

[0015] Preferably, the molar ratio of iron salt, nickel salt and urea in the mixed ionic metal solution is (0.5-1):(0.5-1):(6-8).

[0016] Preferably, the amount of the active coating solution applied is 10–30 mg.

[0017] Preferably, it further includes:

[0018] The graphite substrate is pretreated; the pretreatment includes cutting, polishing, ultrasonication, acid etching and washing in sequence.

[0019] This invention also provides an application of the above-described iron-nickel bimetallic oxide-graphite composite electrode in the electrocatalytic oxidation removal of ammonia nitrogen from water.

[0020] Preferably, it includes the following steps:

[0021] An electrocatalytic reaction was carried out by passing a direct current through an iron-nickel bimetallic oxide-graphite composite electrode as the anode, a graphite plate as the cathode, and ammonia nitrogen wastewater as the electrolyte.

[0022] Preferably, the pH of the electrolyte is 4 to 10.

[0023] Preferably, the direct current density of the electrocatalytic reaction is 5–30 mA / cm². 2 The time is 10 to 90 minutes.

[0024] Compared with the prior art, the iron-nickel bimetallic oxide-graphite composite electrode provided by the present invention has the following advantages:

[0025] (1) This invention first prepared an iron-nickel bimetallic oxide-graphite composite electrode, which was applied to water containing ammonia nitrogen and could effectively remove ammonia nitrogen from the water;

[0026] (2) The iron-nickel bimetallic oxide-graphite composite electrode provided by the present invention can more efficiently and quickly electrocatalyze the oxidation of ammonia nitrogen to nitrogen gas than traditional electrocatalytic anode materials, thereby reducing secondary pollution caused by nitrates and reducing the total nitrogen in water bodies.

[0027] (3) The iron-nickel bimetallic oxide-graphite composite electrode provided by the present invention is suitable for different pH conditions and can be directly used for the removal of ammonia nitrogen in natural water bodies and sewage without adjusting the pH value.

[0028] (4) The preparation method provided by the present invention is simple to operate, has a wide range of raw material sources, low production cost, and is suitable for industrial production. Attached Figure Description

[0029] Figure 1 SEM image of iron-nickel bimetallic oxide;

[0030] Figure 2 The image shows the XRD pattern of the iron-nickel bimetallic oxide.

[0031] Figure 3 Diagram of an electrochemical reaction apparatus;

[0032] Figure 4 Degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation of electrodes with different iron-nickel molar ratios for the removal of ammonia nitrogen;

[0033] Figure 5 The graphs show the degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation of ammonia nitrogen using an iron-nickel bimetallic oxide-graphite electrode with different coating amounts.

[0034] Figure 6 The graphs show the degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation of ammonia nitrogen using an iron-nickel bimetallic oxide-graphite electrode at different current densities.

[0035] Figure 7Degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation of ammonia nitrogen using an iron-nickel bimetallic oxide-graphite electrode at different initial pH values;

[0036] Figure 8 The LSV curve of the electrode;

[0037] Figure 9 The selectivity changes of various nitrogen species and gaseous nitrogen during the electrocatalytic oxidation reaction of ammonia nitrogen removal using an iron-nickel bimetallic oxide-graphite electrode. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0039] This invention provides an iron-nickel bimetallic oxide-graphite composite electrode, comprising a graphite substrate and an active coating coated on the surface of the graphite substrate.

[0040] The active coating comprises an iron-nickel bimetallic oxide, a curing agent, and a conductive agent;

[0041] The mass ratio of the iron-nickel bimetallic oxide, curing agent, and conductive agent is (1-10):1:1.

[0042] In this embodiment, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0043] In this embodiment, the active coating is preferably located on one or both sides of the graphite plate, but the present invention does not make a specific limitation.

[0044] In this embodiment, the iron-nickel bimetallic oxide has an iron-nickel nanoparticle structure. The iron-nickel bimetallic oxide can be prepared by the following method:

[0045] First, iron salts, nickel salts, and urea are added to a mixed solution of water and ethanol and stirred thoroughly to obtain a mixed ionic metal solution.

[0046] Preferably, the molar ratio of iron salt, nickel salt, and urea in the mixed ionic metal solution is (0.5–1):(0.5–1):(6–8). The water-soluble iron salt preferably includes one or more of ferric chloride, ferric nitrate, and ferric sulfate. In this embodiment, when the water-soluble iron salt is a mixture of two or more types, there is no particular limitation on the mass ratio of the different water-soluble iron salts; any ratio is acceptable.

[0047] In this embodiment, the water-soluble nickel salt preferably includes one or more of nickel chloride, nickel nitrate, and nickel sulfate. When the water-soluble nickel salt is a mixture of two or more, the present invention does not have a particular limitation on the mass ratio of the different water-soluble nickel salts; any ratio is acceptable.

[0048] In this embodiment, the molar ratio of iron salt, nickel salt, and urea in the mixed ionic metal solution is (0-1):(1-0):(4-8), more preferably (0.5-1):(0.5-1):(6-8), and most preferably 1:1:8. In this invention, the solvent is ethanol, and the volume ratio of ethanol to water in the ethanol solvent is preferably 4:1.

[0049] In this embodiment, the preferred mixing order is to mix water-soluble iron salt with a portion of ethanol solvent to obtain an iron salt solution; mix water-soluble nickel salt with a portion of ethanol solvent to obtain a nickel salt solution; mix urea with the remaining ethanol solvent to obtain a urea solution; and mix the iron salt solution, nickel salt solution, and urea solution to obtain a mixed ionic metal solution.

[0050] In this embodiment, the concentration of the iron salt solution is preferably 0.02–0.04 mol / L, more preferably 0.03 mol / L. The concentration of the nickel salt solution is preferably 0.02–0.04 mol / L, more preferably 0.03 mol / L. The concentration of the urea solution is preferably 0.2–0.3 mol / L, more preferably 0.25 mol / L. This invention does not impose any particular limitation on the mixing method; any mixing method well known to those skilled in the art can be used, such as stirring. This invention does not impose any particular limitation on the speed and time of the stirring mixture, as long as the raw materials are mixed evenly.

[0051] Then, the mixed ionic metal solution is subjected to a hydrothermal reaction, and after washing and drying, an iron-nickel bimetallic oxide is obtained.

[0052] In this embodiment, the hydrothermal reaction temperature is preferably 150-200℃, more preferably 180℃; the time is preferably 6-18h, more preferably 8-15h, and most preferably 12h.

[0053] In this embodiment, the hydrothermal temperature and time affect the structural composition of the iron-nickel bimetallic oxide. If the hydrothermal reaction temperature is too low, the oxide cannot be formed; if the temperature is too high, the oxide particle size distribution becomes wider. If the hydrothermal reaction time is too short, the oxide cannot be formed; if the reaction time is too long, the oxide particle size becomes increasingly larger. This invention, by controlling the hydrothermal reaction temperature and time, can generate iron-nickel bimetallic oxides with high activity and good ammonia nitrogen treatment effect. This invention does not have special limitations on the equipment used for the hydrothermal reaction; any hydrothermal reaction equipment well-known to those skilled in the art can be used. In this embodiment, the hydrothermal reaction is preferably carried out in an oven. In this invention, the solid-liquid separation method is not particularly limited; any solid-liquid separation method well-known to those skilled in the art can be used, such as centrifugal washing. The centrifugal separation speed is preferably 4000–6000 r / min, more preferably 5000 r / min; the centrifugal separation time is preferably 4–6 min, more preferably 5 min. In this invention, the cleaning solvent is preferably deionized water and ethanol, and the number of cleaning cycles is preferably 3 times with deionized water and 3 times with ethanol. The purpose of cleaning is to remove water-soluble impurities from the oxide surface. In this invention, the drying temperature is preferably 60-80°C, more preferably 70°C; the drying time is preferably 2-6 hours, more preferably 3-4 hours.

[0054] In this embodiment, the curing agent is preferably polyvinylidene fluoride.

[0055] In this embodiment, the conductive agent is preferably superconducting carbon black.

[0056] In this embodiment, the mass ratio of the iron-nickel bimetallic oxide, curing agent, and conductive agent is (1-10):1:1, preferably 5:1:1. Insufficient iron-nickel bimetallic oxide will reduce the active sites of the iron-nickel bimetallic oxide-graphite electrode, resulting in a decrease in ammonia nitrogen removal efficiency; excessive iron-nickel bimetallic oxide will reduce the ratio of curing agent and conductive agent, easily causing the active coating of the iron-nickel bimetallic oxide-graphite electrode to peel off and its conductivity to deteriorate.

[0057] This invention also provides a method for preparing the iron-nickel bimetallic oxide-graphite electrode described above, comprising the following steps:

[0058] An active coating solution is obtained by mixing an iron-nickel bimetallic oxide, a curing agent, a conductive agent, and an organic solvent.

[0059] The active coating solution is applied to the surface of a graphite plate and then dried to obtain an iron-nickel bimetallic oxide-graphite electrode.

[0060] In this embodiment, the types and proportions of the iron-nickel bimetallic oxide, curing agent, and conductive agent are consistent with those in the above-mentioned iron-nickel bimetallic oxide-graphite electrode technical solution.

[0061] In this embodiment, the organic solvent preferably includes N,N-dimethylformamide, acetone, or N-methylpyrrolidone.

[0062] In this embodiment, there is no special limitation on the amount of organic solvent used, as long as it is sufficient to allow the active coating liquid to flow.

[0063] In this embodiment, there are no special limitations on the mixing method; any mixing method well known to those skilled in the art can be used, such as stirring. The present invention does not have special limitations on the speed and time of the stirring mixture, as long as it can mix the raw materials evenly.

[0064] In this embodiment, after obtaining the active coating solution, the active coating solution is coated on the surface of a graphite substrate and then dried to obtain an iron-nickel bimetallic oxide-graphite electrode.

[0065] In this embodiment, the graphite substrate needs to be pretreated before use; the pretreatment preferably includes cutting, polishing, ultrasonication, acid etching and water washing to obtain a pretreated graphite substrate.

[0066] in:

[0067] The cutting is preferably mechanical cutting.

[0068] The polishing is preferably done with sandpaper; the sandpaper is preferably 400-1000 grit, more preferably 800 grit.

[0069] The reagent used in the ultrasound is an organic solvent; the organic solvent is preferably acetone; the present invention does not have a special limitation on the ultrasonic power of the ultrasound, as long as it can remove the oil stains on the surface of the graphite plate; the ultrasound time is preferably 5 to 30 minutes, more preferably 10 to 20 minutes; the function of the ultrasound is to remove the oil stains on the surface of the graphite plate.

[0070] The acid used in the acid etching preferably includes hydrochloric acid, oxalic acid, sulfuric acid, nitric acid, or hydrofluoric acid; the concentration of the sulfuric acid is preferably 5-15 wt%, more preferably 10 wt%; the present invention does not have a particular limitation on the concentration of the hydrochloric acid, oxalic acid, sulfuric acid, and nitric acid, and any concentration is acceptable. In the present invention, the purpose of the acid etching is to remove oxides from the surface of the graphite plate. In the present invention, the water washing is preferably deionized water washing, and the present invention does not have a particular limitation on the number of water washings, as long as the acid on the surface of the graphite plate is completely removed.

[0071] In this embodiment, the active coating is preferably applied to one or both sides of the graphite plate. The coating method is preferably repeated coating, and the number of repeated coatings is preferably 2 to 6 times, more preferably 3 to 5 times, and most preferably 5 times. In this invention, the coating is dried after application before the next coating. In this invention, the coating amount of the active coating liquid is preferably 10 to 30 mg, more preferably 15 to 25 mg, and most preferably 25 mg; the coating amount of the active coating liquid is based on the total mass of the iron-nickel bimetallic oxide, curing agent, and conductive agent.

[0072] After coating, the active coating obtained can be dried to obtain an iron-nickel bimetallic oxide-graphite electrode. The drying temperature is preferably 50–80°C, more preferably 60–70°C; the drying time is preferably 5–20 min, more preferably 10–15 min.

[0073] This invention also provides the application of the iron-nickel bimetallic oxide-graphite electrode described in the above technical solution or the iron-nickel bimetallic oxide-graphite electrode prepared by the above technical solution in the electrocatalytic removal of ammonia nitrogen in water.

[0074] In application:

[0075] An electrocatalytic reaction was carried out by passing a direct current through an iron-nickel bimetallic oxide-graphite electrode as the anode, a graphite plate as the cathode, and ammonia-nitrogen-containing wastewater as the electrolyte.

[0076] The distance between the anode and the cathode is preferably 1 to 3 cm, and more preferably 2 cm.

[0077] The preferred current density of the direct current is 5–30 mA / cm². 2 More preferably 10–20 mA / cm 2 .

[0078] The preferred temperature for the electrocatalytic reaction is 10–30°C, more preferably 20–30°C, and most preferably 25°C; the preferred time is 10–90 min, more preferably 30–60 min, and even more preferably 40 min.

[0079] The temperature of the ammonia-nitrogen-containing wastewater is preferably room temperature. In this embodiment, the ammonia nitrogen concentration in the ammonia-nitrogen-containing wastewater is preferably 0–100 mg / L, more preferably 20–50 mg / L, and even more preferably 30–40 mg / L; the pH value of the ammonia-nitrogen-containing water is preferably 4–10, and even more preferably 6–8.

[0080] In embodiments of the present invention, the ammonia-nitrogen-containing wastewater is preferably a simulated wastewater prepared using ammonium chloride and sodium chloride as raw materials.

[0081] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0082] Example 1

[0083] (1) Preparation of iron-nickel bimetallic oxide

[0084] Prepare 60 mL of ethanol solvent, with a volume ratio of ethanol to water of 4:1; dissolve 1.8 mmol of ferric nitrate, 1.8 mmol of nickel nitrate, and 15 mmol of urea in the ethanol solvent, and stir until homogeneous to obtain a mixed metal solution, with a molar ratio of ferric nitrate, nickel nitrate, and urea of ​​1:1:8; subject the mixed metal ion solution to a hydrothermal reaction at 180 °C for 12 h, and allow it to cool naturally after the reaction. Centrifuge the reaction product at 5000 r / min for 5 min, remove the supernatant, wash the obtained solid product three times with deionized water, then three times with ethanol, and dry it at 70 °C for 4 h to obtain iron-nickel bimetallic oxide (FeNiO);

[0085] The SEM image of the FeNiO prepared in this embodiment is shown below. Figure 1 As shown, the XRD pattern is as follows Figure 2 As shown in the image, the SEM image reveals that FeNiO is composed of fine, uniform nanoparticles. The XRD pattern indicates that the main component of FeNiO is an iron-nickel composite oxide.

[0086] Using the aforementioned method for preparing iron-nickel bimetallic oxide, ensuring that the total amounts of ferric nitrate, nickel nitrate, and urea remain constant, iron-nickel material is prepared according to a molar ratio of ferric nitrate, nickel nitrate, and urea of ​​1:0:4, yielding iron oxide (FeO). Its XRD pattern is shown below. Figure 2 As shown in the figure. The XRD pattern indicates that the main component of FeO is iron oxide.

[0087] Using the aforementioned method for preparing the iron-nickel bimetallic oxide, ensuring that the total amounts of ferric nitrate, nickel nitrate, and urea remain constant, and preparing the iron-nickel material according to a molar ratio of ferric nitrate, nickel nitrate, and urea of ​​1:0.5:6, an oxide (Fe1Ni) with an iron-nickel ratio of 1:0.5 is obtained. 0.5 O), its XRD pattern is as follows Figure 2 As shown in the figure. The XRD pattern indicates that Fe1Ni... 0.5 The main component of O is an iron-nickel composite oxide.

[0088] Using the aforementioned method for preparing the iron-nickel bimetallic oxide, while ensuring that the total amounts of ferric nitrate, nickel nitrate, and urea remain constant, an iron-nickel material is prepared according to a molar ratio of ferric nitrate, nickel nitrate, and urea of ​​0.5:1:6, resulting in an oxide (Fe1O2) with an iron-nickel ratio of 0.5:1. 0.5 Ni1O), its XRD pattern is as follows Figure 2 As shown in the XRD pattern, Fe... 0.5 The main component of Ni1O is an iron-nickel composite oxide.

[0089] Using the aforementioned method for preparing the iron-nickel bimetallic oxide, ensuring that the total amounts of ferric nitrate, nickel nitrate, and urea remain constant, an iron-nickel material is prepared according to a molar ratio of ferric nitrate, nickel nitrate, and urea of ​​0:1:4, resulting in an oxide (NiO) with an iron-nickel ratio of 0:1. Its XRD pattern is shown below. Figure 2 As shown in the figure. The XRD pattern shows that the main component of NiO is nickel oxide.

[0090] (2) Pretreatment of graphite substrate

[0091] The graphite substrate was cut into pieces 2.5 cm long and 2 cm wide, polished with 800 grit sandpaper, ultrasonicated in acetone for 15 min, then acid etched in 10 wt% sulfuric acid for 15 min, washed with deionized water, and then dried to obtain the pretreated graphite plate.

[0092] (3) Preparation of iron-nickel bimetallic oxide-graphite electrode

[0093] The iron-nickel bimetallic oxide prepared in step (1) was mixed with polyvinylidene fluoride and superconducting carbon black in a mass ratio of 5:1:1 to obtain 70 mg of the mixture. 1 ml of N-methylpyrrolidone was added and mixed, and the mixture was sonicated for 20 min to obtain a uniform active coating.

[0094] The active coating solution was used to transfer 50 μl of ink twice using a 50 μl pipette and then uniformly coated on both sides of the pretreated graphite plate (GP) obtained in step (2). After each coating, it was dried at 70°C for 10 min. The operation was repeated 5 times to obtain an iron-nickel bimetallic oxide-graphite (FeNiO / GP) electrode. The effective coating area was 2 cm × 2 cm × 2. The content of iron-nickel bimetallic oxide in each 100 μl was 5 mg, so the coating amount of FeNiO / GP was 25 mg.

[0095] Using the aforementioned FeNiO / GP electrode preparation method, FeO and Fe1Ni are respectively used. 0.5 O, Fe 0.5 Electrodes were prepared using four oxides: Ni1O, NiO, and iron oxide-graphite (FeO / GP) electrodes, and oxide-graphite (Fe1Ni) electrodes with an iron-nickel ratio of 1:0.5. 0.5O / GP) electrode, iron-nickel ratio of 0.5:1 oxide-graphite (Fe) 0.5 NiO / GP electrode, nickel oxide-graphite (NiO / GP) electrode.

[0096] Example 2

[0097] Simulated wastewater was prepared under normal temperature and pressure conditions using ammonium chloride and sodium chloride as raw materials. The concentration of ammonia nitrogen in the simulated wastewater was 30 mg / L, the concentration of chloride ions was 1000 mg / L, and the pH was adjusted to 6. 150 mL of the simulated wastewater was placed in a reactor, and the FeNiO / GP electrode, FeO / GP electrode, and Fe1Ni electrode from Example 1 were used respectively. 0.5 O / GP electrode, Fe 0.5 Using Ni1O / GP and NiO / GP electrodes as anodes and a graphite plate as cathode, the rotation speed was set to 500 r / min, and the current density was 10 mA / cm². 2 Electrocatalytic reactions are carried out using direct current, and electrochemical reaction devices such as... Figure 3 As shown. Liquid samples were periodically removed from the reaction apparatus, and the ammonia nitrogen and total nitrogen values ​​in the samples were tested using Nessler's reagent UV spectrophotometry and alkaline potassium persulfate UV spectrophotometry, respectively.

[0098] Figure 4 The graphs show the degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation with different iron-nickel molar ratios. With only Fe and Ni present, after 40 min of electrocatalytic reaction, only 28.06% and 6.93% of ammonia nitrogen, respectively, were removed from the solution, with removal rates of 0.00663 min. -1 (R 2 =0.99893) and 0.00158min -1 (R 2 =0.99988), the total nitrogen removal rates were 18.49% and 4.47%, respectively, and the removal rates were 0.00489 min. -1 (R 2 =0.99953) and 0.00123min -1 (R 2 =0.99998). With the mutual doping between Fe and Ni, the electrocatalytic activity of the electrode is significantly improved. When the molar ratio of iron to nickel is 1:1, the FeNiO / GP electrode exhibits the best electrocatalytic activity, with removal rates of 99.56% and 92.09% for ammonia nitrogen and total nitrogen in the solution, respectively, and removal rates of 0.03310 min. -1 (R 2 =0.99566) and 0.02836min -1 (R 2 =0.99569).

[0099] Example 3

[0100] Following the method for fabricating the FeNiO / GP electrode in Example 1, FeNiO / GP electrodes with coating amounts of 10 mg, 15 mg, 20 mg, 25 mg, and 30 mg were prepared. Simulated wastewater was prepared under ambient temperature and pressure using ammonium chloride and sodium chloride as raw materials. The concentration of ammonia nitrogen in the simulated wastewater was 30 mg / L, the concentration of chloride ions was 1000 mg / L, and the pH was adjusted to 6. 150 mL of the simulated wastewater was placed in a reactor. The FeNiO / GP electrodes with coating amounts of 10 mg, 15 mg, 20 mg, 25 mg, and 30 mg were used as anodes, and a graphite plate was used as the cathode. The rotation speed was set to 500 r / min, and the current density was 10 mA / cm². 2 The electrocatalytic reaction is carried out using direct current. Liquid samples are periodically removed from the reaction apparatus, and the ammonia nitrogen and total nitrogen values ​​in the samples are tested using Nessler's reagent ultraviolet spectrophotometry and alkaline potassium persulfate ultraviolet spectrophotometry, respectively.

[0101] Figure 5 The graphs show the degradation of ammonia nitrogen and total nitrogen (TNO) by electrocatalytic oxidation using a FeNiO / GP electrode with different coating amounts. As the coating amount increases from 10 mg to 30 mg, the electrocatalytic activity of the FeNiO / GP electrode gradually increases, with comparable effects at 25 mg and 30 mg. When the coating amount reaches 30 mg, ammonia nitrogen in the water is almost completely removed within 40 min, and the TNO removal rate is 83.87%, with an ammonia nitrogen removal rate of 0.03367 min. -1 (R 2 =0.99191), the total nitrogen removal rate was 0.0322 min. -1 (R 2 =0.99982). When the Fe-Ni catalyst content was 25 mg, the removal rates of ammonia nitrogen and total nitrogen at 40 min were 99.56% and 92.09%, respectively, with removal rates of 0.03304 min. -1 (R 2 =0.99566) and 0.02836min -1 (R 2 =0.99569), compared to when the FeNiO catalyst content is 30mg, the removal rate is not much different, and both ammonia nitrogen can be basically removed. The 25mg catalyst content is less, therefore, the optimal coating amount is 25mg.

[0102] Example 4

[0103] Simulated wastewater was prepared under normal temperature and pressure conditions using ammonium chloride and sodium chloride as raw materials. The concentration of ammonia nitrogen in the simulated wastewater was 30 mg / L, the concentration of chloride ions was 1000 mg / L, and the pH was adjusted to 6. 150 mL of the simulated wastewater was placed in a reactor, using the FeNiO / GP electrode from Example 1 as the anode and a graphite plate as the cathode. The rotation speed was set to 500 r / min, and a current density of 5 mA / cm² was used. 2 10mA / cm 2 15mA / cm 2 and 20mA / cm 2 The electrocatalytic reaction is carried out using direct current. Liquid samples are periodically removed from the reaction apparatus, and the ammonia nitrogen and total nitrogen values ​​in the samples are tested using Nessler's reagent ultraviolet spectrophotometry and alkaline potassium persulfate ultraviolet spectrophotometry, respectively.

[0104] Figure 6 The graphs show the degradation of ammonia nitrogen and total nitrogen during the electrocatalytic oxidation of ammonia nitrogen using an iron-nickel bimetallic oxide-graphite electrode at different current densities. The degradation occurs when the current density increases from 5 mA / cm². 2 Gradually increase to 20 mA / cm 2 Meanwhile, the removal rates of ammonia nitrogen and total nitrogen gradually increased, with the ammonia nitrogen removal rate increasing from 0.01657 min. -1 (R 2 =0.99626) increased to 0.04634min -1 (R 2 =0.97634), the total nitrogen removal rate decreased from 0.00966 min -1 (R 2 =0.99844) increased to 0.04605min -1 (R 2 =0.99024). Current density is 10 mA / cm². 2 Within 40 minutes, the removal rates of ammonia nitrogen and total nitrogen can reach 99.56% and 92.09%, respectively.

[0105] Example 5

[0106] Simulated wastewater was prepared under normal temperature and pressure conditions using ammonium chloride and sodium chloride as raw materials. The concentration of ammonia nitrogen in the simulated wastewater was 30 mg / L, and the concentration of chloride ions was 1000 mg / L. 150 mL of simulated wastewater with initial pH values ​​of 4, 6, 8, and 10 were placed in a reactor, respectively. The FeNiO / GP electrode from Example 1 was used as the anode, and a graphite plate as the cathode. The rotation speed was set to 500 r / min, and the current density was 10 mA / cm². 2The electrocatalytic reaction is carried out using direct current. Liquid samples are periodically removed from the reaction apparatus, and the ammonia nitrogen and total nitrogen values ​​in the samples are tested using Nessler's reagent ultraviolet spectrophotometry and alkaline potassium persulfate ultraviolet spectrophotometry, respectively.

[0107] Figure 7 The graphs show the degradation of ammonia nitrogen and total nitrogen by electrocatalytic oxidation using a nickel-iron bimetallic oxide-graphite electrode at different initial pH values. With initial pH values ​​of 4, 6, 8, and 10, ammonia nitrogen was essentially removed after 30 min of electrocatalytic reaction. After 40 min, the ammonia nitrogen removal rates were 97.77%, 98.69%, 99.56%, and 96.78%, respectively, while the total nitrogen removal rates were 80.57%, 92.44%, 97.42%, and 77.59%, respectively. This indicates that the nickel-iron bimetallic oxide-graphite electrode exhibits good electrocatalytic oxidation for ammonia nitrogen removal at initial pH values ​​of 4, 6, 8, and 10, and is applicable to a wide range of pH conditions.

[0108] Example 6

[0109] The chloride evolution overpotential (CEP) and oxygen evolution overpotential (OEP) of the electrodes were tested using a three-electrode system in a CHI 660E electrochemical workstation. The working electrodes were the FeO / GP electrode, NiO / GP electrode, FeNiO / GP electrode, and graphite plate (GP) electrode described in Example 1. The reference electrode was a saturated calomel electrode (SCE), and the counter electrode was a platinum wire electrode. Linear sweep voltammetry (LSV) was used for the tests, with a test potential range of 0.5–2.0 V (vs SCE) and a scan rate of 10 mV / s. OEP was tested in 0.5 mol / L Na₂SO₄ solution, and CEP was tested in saturated NaCl solution.

[0110] Figure 8The figure shows the LSV curve of the electrode. It is generally considered that the potential at the intersection of the reverse extension of the current-sharp rise phase and the horizontal axis with the abscissa is the overpotential. The difference between OEP and CEP can represent the selectivity of the electrode for the chlorine evolution reaction. The CEP of the FeO / GP (1.306V) electrode is 0.034V lower than that of the NiO / GP (1.340V) electrode, and the CER activity of the FeO / GP electrode is higher than that of the NiO / GP electrode. This corresponds to the higher ammonia nitrogen removal capacity of the FeO / GP electrode compared to the NiO / GP electrode in Example 2. With the mutual doping of Fe and Ni metals, the OEP of the FeNiO / GP electrode is only 1.364V, and the CER activity is significantly improved. The potential difference between OEP (1.364V) and CEP (1.152V) of the FeNiO / GP electrode is 0.212V. Compared with the potential differences of the FeO / GP (0.200V), NiO / GP (0.148V), and GP (0.192V) electrodes, the FeNiO / GP electrode has the largest potential difference, indicating that the Fe-Ni interaction gives it good selectivity for the chlorine evolution reaction.

[0111] Example 7

[0112] Under normal temperature and pressure conditions, simulated wastewater was prepared using ammonium chloride and sodium chloride as raw materials. The concentration of ammonia nitrogen in the simulated wastewater was 30 mg / L, the concentration of chloride ions was 1000 mg / L, and the pH was adjusted to 6. 150 mL of the simulated wastewater was placed in a reactor. The FeNiO / GP electrode from Example 1 was used as the anode, and a graphite plate as the cathode. The rotation speed was set to 500 r / min, and the current density was 10 mA / cm². 2 The electrocatalytic reaction is carried out using direct current. Liquid samples are periodically removed from the reaction apparatus, and the ammonia nitrogen and total nitrogen values ​​in the samples are tested using Nessler's reagent ultraviolet spectrophotometry and alkaline potassium persulfate ultraviolet spectrophotometry, respectively. The concentrations of nitrate nitrogen and nitrite nitrogen in the samples are detected by ion chromatography.

[0113] Figure 9 The selectivity of various nitrogen species to gaseous nitrogen during the electrocatalytic reaction using a FeNiO / GP electrode is shown. After 20 min of electrocatalytic reaction, the ammonia nitrogen removal rate was 67.60%, and the total nitrogen removal rate was 59.79%; after 40 min of electrocatalytic reaction, the ammonia nitrogen removal rate was 99.56%, and the total nitrogen removal rate was 92.09%. The FeNiO / GP electrode can oxidize ammonia nitrogen to nitrogen gas, with a gas selectivity reaching 96.53% after 40 min, and the nitrate nitrogen concentration remained at around 1 mg / L throughout the reaction.

Claims

1. A nickel-iron bimetallic oxide-graphite composite electrode, characterized in that, Includes a graphite substrate and an active coating applied to the surface of the graphite substrate; The active coating comprises an iron-nickel bimetallic oxide, a curing agent, and a conductive agent; and the mass ratio of the iron-nickel bimetallic oxide, curing agent, and conductive agent is (1~10):1:1; wherein, the preparation steps of the iron-nickel bimetallic oxide include: Iron salts, nickel salts, and urea are added to a mixed solution of water and ethanol, and stirred thoroughly to obtain a mixed ionic metal solution. The mixed ionic metal solution was subjected to a hydrothermal reaction, and after washing and drying, an iron-nickel bimetallic oxide was obtained; the molar ratio of iron salt, nickel salt and urea in the mixed ionic metal solution was (0.5~1):(0.5~1):(6~8).

2. The iron-nickel bimetallic oxide-graphite composite electrode according to claim 1, characterized in that, The curing agent is polyvinylidene fluoride; the conductive agent is superconducting carbon black.

3. The method for preparing the iron-nickel bimetallic oxide-graphite composite electrode as described in claim 1, characterized in that, Includes the following steps: The active coating solution is obtained by thoroughly mixing iron-nickel bimetallic oxide, curing agent, conductive agent and organic solvent; The active coating solution is coated onto the surface of a graphite substrate and then dried to obtain an iron-nickel bimetallic oxide-graphite composite electrode.

4. The preparation method according to claim 3, characterized in that, The amount of the active coating solution applied is 10~30mg.

5. The preparation method according to claim 3, characterized in that, Also includes: The graphite substrate is pretreated; the pretreatment includes cutting, polishing, ultrasonication, acid etching and washing in sequence.

6. The application of the iron-nickel bimetallic oxide-graphite composite electrode as described in claim 1 in the electrocatalytic oxidation removal of ammonia nitrogen from water.

7. The application as described in claim 6, characterized in that, Includes the following steps: An electrocatalytic reaction was carried out by passing a direct current through an iron-nickel bimetallic oxide-graphite composite electrode as the anode, a graphite plate as the cathode, and ammonia nitrogen wastewater as the electrolyte.

8. The application according to claim 7, characterized in that, The electrolyte has a pH of 4-10; the direct current density for the electrocatalytic reaction is 5-30 mA / cm². 2 The time is 10~90 minutes.

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