An electrode containing a MOF-derived carbon material and a preparation method and application thereof

Abstract

The application discloses an electrode containing MOF-derived carbon material and a preparation method and application thereof, the electrode is mainly catalyzed by a bimetallic MOF-derived carbon material, and the electrode is mainly reduced to ammonia nitrogen, by using a ruthenium oxide electrode as an anode, and adding a proper amount of chloride ions, ammonia nitrogen as a product can be converted into nitrogen, so that efficient denitrification is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nitrate reduction, more particularly, it relates to an electrode containing MOF-derived carbon material, and simultaneously provides a preparation method and application of the electrode. BACKGROUND

[0002] Water is the source of life, and the uncontrolled discharge of various organic and inorganic pollutants has led to water pollution. In the past few decades, due to overuse of fertilizers, burning of fossil fuels and discharge of industrial wastewater containing NO3 – , the concentration of nitrate in surface water and groundwater has increased dramatically. Nitrate is the highest valence nitrogen oxide, which is stable in nature and has high solubility in water, and is easy to diffuse in groundwater. These properties make nitrate easy to migrate and ultimately result in a wide range of pollution. The nitrogen element contained in nitrate is a nutrient for plant growth, and the presence of a large amount of nitrate nitrogen in water bodies can lead to eutrophication of water bodies. At the same time, NO3 – enters the human body through drinking water and is converted to NO2 – in the human body, which can cause methemoglobinemia and even cancer, seriously threatening human health.

[0003] The main nitrate removal technology at present is biological denitrification method. This method has good applicability in the field of nitrate removal after years of practice. However, when the carbon-nitrogen ratio of the wastewater to be treated is low, external addition of organic carbon source is usually required to completely reduce nitrate. The additional organic carbon source increases the treatment cost, and the added carbon source can increase the COD of the discharged wastewater, resulting in non-compliance of the effluent. Various problems limit its further application in the removal of nitrate nitrogen. In recent years, electrochemical reduction of nitrate has become a green treatment technology. This method does not require additional chemicals and will not cause secondary pollution. By providing electrons, nitrate reduction reaction occurs in the catalytic layer of the cathode, and nitrate can be reduced. However, the main reduction products are nitrite, ammonia nitrogen and nitrogen gas, among which nitrite and ammonia nitrogen can also cause water pollution.

[0004] It is well known that electrode material is the key in the process of electrochemical nitrate reduction. Researchers have been working hard to develop efficient electrode materials in the past few decades. The main electrode materials currently studied include non-metallic electrode materials, noble metal electrode materials, transition metal electrode materials, and metal oxide materials. However, the current non-metallic electrode materials have unsatisfactory treatment effect; the noble metal electrode materials are expensive and have poor economic efficiency; the transition metal is easy to oxidize and corrode during use; and the overall nitrate reduction capacity of the metal oxide electrode is weak, resulting in poor use effect.

[0005] Therefore, there is a need to develop new electrode materials. SUMMARY

[0006] 1. Problem to be solved

[0007] One of the objects of the present application is to provide an electrode containing MOF-derived carbon material, which has a large specific surface area, high porosity, and superior nitrate reduction performance.

[0008] Meanwhile, the present application provides a method for preparing an electrode containing MOF-derived carbon material.

[0009] Another object of the present application is to provide a method for reducing nitrate, in which electrochemical treatment of nitrate is performed using an electrode containing MOF-derived carbon material, and the method has high efficiency in removing nitrate nitrogen and the final product contains less than 1% of nitrite nitrogen, which is harmful to the human body.

[0010] 2. Technical solution

[0011] To solve the above problems, the technical solution adopted by the present application is as follows:

[0012] According to one of the objects of the present application, the present application provides a method for preparing an electrode containing MOF-derived carbon material, which comprises the following steps:

[0013] S1. preparing a mixed solution containing MOF-derived carbon material, conductive agent, and binder;

[0014] S2. applying the mixed solution to a base material;

[0015] S3. performing drying treatment to obtain the electrode;

[0016] wherein,

[0017] The mass ratio of the MOF-derived carbon material, conductive agent, and binder is (6-8):1:1.

[0018] The MOF-derived carbon material is prepared by the following method:

[0019] A1. preparing MOF material, which contains at least one metal;

[0020] A2. performing high-temperature treatment on the MOF material at 600-800°C to obtain MOF-derived carbon material;

[0021] According to the method for preparing an electrode containing MOF-derived carbon material according to any one of the first aspect of the first object of the present application, the conductive agent includes, but is not limited to, any one of acetylene black, carbon black, carbon nanotube, and the like.

[0022] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the binder includes but is not limited to any one of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), naphthol (nafion).

[0023] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the solvent of the mixed solution includes one or more of pure water, ethanol, N-methyl pyrrolidone.

[0024] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the MOF material includes but is not limited to any one or more of ZIF-8, ZIF-l, ZIF-L, ZIF-67, MOF-5, MOF-74, MIL-53, MIL-100, MIL-101 and HKUST-1, preferably ZIF-L.

[0025] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, in S2, the base material is pretreated by:

[0026] sequentially contacting the base material with a solution containing a ketone organic matter;

[0027] pretreating the base material;

[0028] The base material is pretreated by:

[0029] First step: contacting and soaking the base material with a solution containing a ketone organic matter;

[0030] Second step: contacting and soaking the base material with an acid solution;

[0031] Third step: contacting and soaking the base material with pure water.

[0032] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the organic solvent includes but is not limited to any one or more of acetone or ethanol.

[0033] The method for preparing the electrode containing MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the base material includes but is not limited to any one or more of foamed nickel, foamed copper, foamed titanium.

[0034] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the acid solution includes, but is not limited to, any one or several of sulfuric acid solution, hydrochloric acid solution.

[0035] Further, the concentration of the acid solution is not particularly limited, but is preferably 1-3 mol / L.

[0036] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, in S2, the loading of the MOF-derived carbon material per unit area of the base material is 1-10 mg / cm 2 .

[0037] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, in S3, the conditions of the drying treatment include: under vacuum conditions, at a temperature of 60-80°C, drying for 12-24 h.

[0038] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, in the preparation step A1 of the MOF-derived carbon material:

[0039] The MOF material includes metal cobalt; or,

[0040] The MOF material includes metal copper; or,

[0041] The MOF material includes metal cobalt and copper, and the molar ratio of the cobalt to the copper is (1-2):(1-2);

[0042] Preferably, the molar ratio of the cobalt to the copper is 1:(1-4), more preferably, the molar ratio of the cobalt to the copper is 1:(2-4); most preferably, the molar ratio of the cobalt to the copper is 1:1.

[0043] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the embodiments of the first aspect of the first object of the present application, the MOF material is prepared by a hydrothermal method:

[0044] Prepare a solution A containing dimethyl imidazole;

[0045] Prepare a solution B containing metal ions;

[0046] Mix solution A and solution B, and perform hydrothermal treatment;

[0047] The molar ratio of the dimethyl imidazole to the metal ions is 8:(1-3).

[0048] Further, the metal includes cobalt and copper, and the molar ratio of the cobalt and copper is (1-2) : (1-2).

[0049] The method for preparing the electrode containing the MOF-derived carbon material according to any one of the first aspect of the first aspect of the first object of the present application in the preparation step A2 of the MOF-derived carbon material includes:

[0050] The conditions of the high-temperature treatment include: treating at a temperature of 600-800℃ for 1-5h, preferably 1-3h, in an inert gas atmosphere.

[0051] Based on the technical solution of any one of the first object and the above of the present application, the second object of the present application is to provide an electrode containing a MOF-derived carbon material.

[0052] The electrode includes:

[0053] The substrate material,

[0054] The MOF-derived carbon material present on the substrate material;

[0055] The MOF-derived carbon material includes a metal element and / or a metal oxide.

[0056] The MOF-derived carbon material includes a metal element and / or a metal oxide.

[0057] Based on the technical solution of any one of the first object and / or the second object of the present application, the third object of the present application is to provide a method for reducing nitrate.

[0058] The nitrate is subjected to electrochemical treatment by using a three-electrode system.

[0059] The concentration of nitrogen in the nitrate is 50-500mg / L.

[0060] The three-electrode system includes a working electrode, a counter electrode and a reference electrode.

[0061] The working electrode is the electrode containing the MOF-derived carbon material prepared by the method of any one of the above.

[0062] The voltage of the electrochemical treatment is -1.9-1.1V, and the reaction time is 1-10h.

[0063] The method for reducing nitrate according to any one of the first aspect of the third object of the present application,

[0064] The method for reducing nitrate according to any one of the first aspect of the third object of the present application,

[0065] After the electrochemical treatment of the nitrate;

[0066] Chloride ions are added again.

[0067] The method for reducing nitrate according to any one of the first aspect of the third object of the present application,

[0068] The chloride ion dosage is 1000 mg / L-3000 mg / L.

[0069] Beneficial effects

[0070] The electrode containing the MOF-derived carbon material provided by the application has a large specific surface area, high porosity and excellent nitrate reduction performance.

[0071] It should be noted that when the molar ratio of cobalt to copper is less than 1 (especially 0.3-0.6), the best nitrate reduction treatment effect is achieved.

[0072] The method for reducing nitrate provided by the application uses an electrode containing a MOF-derived carbon material to perform electrochemical treatment of nitrate, and the method has high efficiency in removing nitrate nitrogen, and the final product mainly contains ammonia nitrogen, and the content of harmful nitrite nitrogen is less than 1%. BRIEF DESCRIPTION OF DRAWINGS

[0073] Figure 1 Scanning electron micrographs of different metal ratio MOF and MOF-derived carbon prepared in the examples (a) Co-MOF, (b) Co2Cu1-MOF, (c) Co1Cu1-MOF, (d) Co1Cu2-MOF, (e) Cu-MOF, (f) Co / NC, (g) Co2Cu1 / NC, (h) Co1Cu1 / NC, (i) Co1Cu2 / NC, (j) Cu / NC;

[0074] Figure 2 XRD patterns of different metal ratio MOF-derived carbon materials;

[0075] Figure 3 XRD pattern of Co1Cu2-MOF material;

[0076] Figure 4 Signal peaks of hydrogen radicals in different electrodes;

[0077] Figure 5 Schematic diagram of a reaction device;

[0078] Figure 6 Nitrogen species ratio distribution graph at 90 min under different cycle numbers;

[0079] Figure 7 Nitrogen species ratio distribution graph at 90 min under different cycle numbers. DETAILED DESCRIPTION

[0080] The present disclosure can be more readily understood by reference to the following description, taken in conjunction with the accompanying drawings and examples, which constitute a part of this disclosure. It is understood that the present disclosure is not limited to the particular products, methods, conditions or parameters described and / or shown herein, as these can vary. Furthermore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, unless otherwise specified.

[0081] It should also be understood that, for clarity, certain features of the disclosure can be described in the context of separate embodiments, but can also be provided in combination in a single embodiment. That is, unless explicitly stated otherwise, each separate embodiment is considered to be combinable with any other embodiment, and such combinations are considered to represent a different embodiment. Conversely, various features of the disclosure described in the context of a single embodiment can also be provided separately or in any sub-combination, for the sake of simplicity. Finally, while a particular embodiment can be described as part of a series of steps or part of a more general structure, each step or sub-structure can itself be considered an independent embodiment.

[0082] Unless otherwise stated, it is to be understood that each individual element of a list and each combination of individual elements of that list are to be construed as a separate embodiment. For example, a list of embodiments recited as“A, B, or C” is to be construed as including the embodiments of“A,”“B,”“C,”“A or B,”“A or C,”“B or C,” or“A, B, or C.”

[0083] In this disclosure, the singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to“a substance” is a reference to at least one of such a substance and equivalents thereof.

[0084] Terms including ordinal numbers such as“first” and“second” can be used to explain various components or fluids, but the components, fluids are not limited by the terms. Thus, the terms are used only to distinguish the component / fluid from another component / fluid without departing from the teaching of the disclosure.

[0085] When describing items by using conjunctive terms such as“… and / or …” and the like, the description should be understood to include any one of the associated listed items and all combinations of one or more of them.

[0086] Generally, the use of the term“about” indicates an approximation that can vary depending on the desired properties to be obtained by the disclosed subject matter and will be interpreted in a functionally dependent manner based on the context in which the term is used. Thus, a person of ordinary skill in the art will be able to interpret the degree of deviation on a case-by-case basis. In some cases, the number of significant digits used in expressing a particular value can be representative of the degree of precision intended for the term“about.” In other cases, a range of values can be used to determine the range of deviation permitted by the term“about.” Further, all ranges in the present disclosure are inclusive and combinable, and a reference to a value includes each value within the range.

[0087] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the terminology used herein and / or any and all combinations of the listed items are intended to be interpreted in an inclusive and non-limiting sense.

[0088] In order to make the technical solutions and advantages of the present application, the technical solutions in the embodiments of the present application will be described in detail below.

[0089] [1] Preparation method of MOF-derived carbon material electrode

[0090] The preparation method of the MOF-derived carbon material electrode of the present application comprises the following steps:

[0091] S1. Prepare a mixed solution containing MOF-derived carbon material, conductive agent, and binder;

[0092] S2. Apply the mixed solution to a base material;

[0093] S3. Perform drying treatment to obtain the electrode;

[0094] In S1, the MOF-derived carbon material is prepared by the following method:

[0095] A1. Prepare a MOF material, which includes at least one metal;

[0096] A2. Perform high-temperature treatment on the MOF material at a temperature of 600-800℃ to obtain a MOF-derived carbon material;

[0097] The metal included in the MOF material is at least one type, more preferably two or more types, for example, the metal can be any one or several of cobalt, copper. However, it should be noted that, from the perspective of efficient removal of nitrate nitrogen and nitrite nitrogen, and avoiding the accumulation of nitrite nitrogen, it is preferred that the MOF material includes metallic cobalt and copper, the presence of metallic cobalt can promote the conversion of nitrite nitrogen to ammonia nitrogen, but part of the nitrate nitrogen is still generated during the reaction and cannot be quickly removed, and the MOF-derived carbon material containing bimetallic copper and cobalt exhibits faster conversion of nitrite during the reaction. The ability to produce less nitrate nitrogen, and the bimetallic copper and cobalt MOF-derived carbon material can more efficiently convert nitrite nitrogen to ammonia nitrogen, and has faster removal performance for the generated nitrate.

[0098] From a microscopic point of view, the MOF material is connected by metal elements, so the metal is part of the MOF material, and the MOF-derived carbon material is prepared by high-temperature carbonization of the MOF material. At high temperatures, the connected metal is converted from an ionic state to an elemental substance, and the organic matter is converted into a porous carbon.

[0099] The source of the "MOF material including at least one metal" has no special requirements and can be prepared by existing known methods, such as hydrothermal method, but needs to meet the process parameters required by the present application as follows:

[0100] Prepare solution A containing dimethyl imidazole, the concentration of dimethyl imidazole is 8mmol / L-32mmol / L;

[0101] Prepare solution B containing metal ions, the concentration of metal ions is 1mmol / L-12mmol / L;

[0102] Mix solution A and solution B and perform hydrothermal treatment;

[0103] Ensure that the molar ratio of dimethyl imidazole to metal ions is 8:(1-3).

[0104] Further, the metal includes cobalt and copper, and the molar ratio of cobalt to copper is (1-2):(1-2).

[0105] For A2, the "MOF material is subjected to high temperature treatment" can be prepared by the known method; for example, using a high temperature calcination method of tube furnace, taking a certain amount of MOF material, after grinding, placing in a porcelain boat, and then putting into a tube furnace, high temperature carbonization treatment is carried out under the condition of inert gas. But need to meet the process parameters required by the present application as follows: the carbonization step uses tube furnace as heating device, the gas flow is controlled at 0.1-0.3L / min, the temperature is raised at a rate of 2-5℃ / min under nitrogen atmosphere, when the treatment temperature is reached, the treatment time (i.e. the constant temperature pyrolysis time) is carried out, and after natural cooling to room temperature, the required MOF derived carbon material is obtained. Among them, the material is recorded as Co x Cu y / NC.

[0106] Further, for the treatment temperature of the high temperature treatment, it is required to reach 350℃, and the MOF material is sufficient to carbonize, preferably 600-800℃, and the treatment time is 1-3h. For example:

[0107] The treatment temperature is 600℃, and the treatment time is 2-3h;

[0108] The temperature of the environment is 650℃, and the treatment time is 2-3h;

[0109] The temperature of the environment is 700℃, and the treatment time is 2-3h;

[0110] The temperature of the environment is 750℃, and the treatment time is 1-2h;

[0111] The temperature of the environment is 800℃, and the treatment time is 1-2h;

[0112] In S1, the ratio of MOF derived carbon material, conductive agent and binder contained in the "mixed solution" is preferably 8:1:1, and is dispersed in an appropriate amount of alcohol to form; the alcohol can be listed for example ethanol, isopropanol, etc.

[0113] In S1, there is no special requirement for the type of "conductive agent", which can be listed for example any one or several of acetylene black, carbon black, carbon nanotube; its core function is to increase the conductive contact between active substances and improve the electronic conductivity, that is, to collect micro-current between active substances and between active substances and current collector, so as to reduce the contact resistance of electrode and accelerate the moving speed of electrons.

[0114] In S1, there is no special requirement for the type of "binder", which can be listed for example any one or several of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), naphthol (nafion); its core function is to load the catalyst and conductive agent on the surface of the aggregate.

[0115] In S2, the "base material" can be exemplified by, for example, foamed nickel, foamed copper, and foamed titanium.

[0116] Further, the "base material" needs to be pretreated before use to remove grease and / or oxidation layer possibly present on the surface of the "base material"; for example, a solution containing ketone organic matter can be used to remove the grease present on the surface of the "base material"; a solution containing acid can be used to remove the oxidation layer present on the surface of the "base material". Taking the pretreatment of foamed nickel as an example, the specific pretreatment mode can be exemplified as follows: the foamed nickel is washed with deionized water, and then immersed in an acetone solution for ultrasonic treatment for 15-30 min to remove the surface grease; the foamed nickel after the degreasing treatment in acetone is immersed in 1 mol / L sulfuric acid for ultrasonic treatment for 15-30 min to remove the surface oxidation layer of the foamed nickel; the foamed nickel after acid treatment is immersed in anhydrous ethanol for ultrasonic treatment for 15-30 min for further cleaning.

[0117] In S2, before the "mixed solution" is applied to the "base material", the mixed solution is preferably subjected to mixing treatment, and the specific pretreatment mode can be exemplified as follows: ultrasonic treatment for 60-120 min to make the mixture uniformly dispersed, and then oscillation for 15 min-30 min by a vortex mixer to make the mixture further uniformly dispersed.

[0118] In S3, after the "base material" coated with the mixed solution is subjected to alcohol volatilization, drying treatment is performed; the specific pretreatment mode can be exemplified as follows: after the "base material" coated with the mixed solution is subjected to alcohol volatilization, the "base material" is placed in a vacuum oven for drying under the condition of vacuum and 60-80 ℃ for 12-24 h to finally obtain a working electrode. The name of different working electrodes is recorded as CoxCuy / NC / Ni.

[0119] [2] Electrode containing MOF-derived carbon material

[0120] Based on the preparation method provided by the present application, the present application can also provide an electrode containing a MOF-derived carbon material.

[0121] The electrode comprises:

[0122] a base material,

[0123] a MOF-derived carbon material present on the base material.

[0124] The MOF-derived carbon material comprises a metal element and / or a metal oxide.

[0125] [3] Method for reducing nitrate

[0126] A third object of the present application is to provide a method for reducing nitrate, which comprises electrochemically treating the nitrate in a three-electrode system, wherein the concentration of the nitrate is 50-500 mg / L.

[0127] As shown in Figure 5 For the electrochemical treatment of the nitrate, the required reaction device mainly comprises an electrochemical workstation, a magnetic stirrer and an electrolytic cell of a three-electrode system, wherein the three-electrode system comprises a working electrode, a counter electrode and a reference electrode.

[0128] The type of the counter electrode is not particularly limited, and examples of the counter electrode include commonly used anodes such as a pt electrode or a RuO2 electrode.

[0129] The magnetic stirrer promotes the uniformity of the solution and enhances the mass transfer through the stirring of the magnetic particles. The three-electrode electrolytic cell comprises a working electrode, a reference electrode and a counter electrode, and is the main reaction device for the electrochemical reduction of nitrate. The electrolytic cell is prepared from organic glass and has a volume of 100 ml. The reference electrode is an Ag / AgCl electrode, the working electrode is the CoxCuy / NC / Ni electrode prepared in the present application, and the counter electrode is a commonly used anode such as a pt electrode or a RuO2 electrode. All experiments are carried out at normal temperature and pressure.

[0130] The electrochemical workstation controls a constant voltage. The voltage for the electrochemical treatment is 1.1-1.9 V, and the reaction time is 1-10 h.

[0131] After the electrochemical treatment of the nitrate, the nitrate nitrogen is converted into ammonia nitrogen, and then the ammonia nitrogen is converted into hypochlorous acid by adding an appropriate amount of chloride ions. The ammonia nitrogen is efficiently removed by using the hypochlorous acid. The addition amount of the chloride ions is 1000 mg / L-3000 mg / L.

[0132] Example 1

[0133] Take a 100ml beaker, add 30ml deionized water, and then use an electronic balance to weigh 24mmol dimethylimidazole, which is dissolved in 30ml deionized water, and stir until uniform, and record as solution A; take another 100ml beaker, add 30ml deionized water, and then use an electronic balance to weigh 3mmol Cu(NO3)2·3H2O and Co(NO3)2·6H2O according to different metal ratios, which are dissolved in 30ml deionized water, and stir until uniform, and record as solution B; pour solution A into solution B quickly, stir until uniform, and then transfer to a 100ml hydrothermal kettle, and perform hydrothermal reaction in a constant-temperature 70℃ oven for 8h; after the reaction is complete, take the hydrothermal kettle out of the oven and cool to room temperature; the obtained MOF material is washed with ethanol multiple times, and after each washing, continue to collect by centrifugation using a centrifuge. The final MOF material (ZIF-L) is first air-dried indoors, and then placed in a vacuum oven for drying at 80℃ under vacuum for 12h; the obtained MOF material is subjected to carbonization treatment in a tube furnace, with the carbonization parameters controlled as follows: nitrogen flow rate is 0.1L / min, heating rate is 2℃ / min, carbonization temperature is 600℃, and carbonization time is 3h. After carbonization treatment, the desired MOF-derived carbon material is obtained, and is recorded as Co1Cu2 / NC; the prepared MOF-derived carbon material, acetylene black, and PTFE electrode are mixed in ethanol according to a mass ratio of 8:1:1, ultrasonic treatment is performed for 1h to make them uniformly dispersed, and then they are coated onto a pretreated nickel foam substrate.

[0134] wherein the cobalt-copper metal ratio is 1:2, the desired MOF-derived carbon material is obtained, and is recorded as Co1Cu2 / NC, and the electrode is recorded as Co1Cu2 / NC / Ni;

[0135] wherein the cobalt-copper metal ratio is 1:1, the desired MOF-derived carbon material is obtained, and is recorded as Co1Cu1 / NC, and the electrode is recorded as Co1Cu1 / NC / Ni;

[0136] wherein the cobalt-copper metal ratio is 2:1, the desired MOF-derived carbon material is obtained, and is recorded as Co2Cu1 / NC, and the electrode is recorded as Co2Cu1 / NC / Ni.

[0137] Comparative Example 1

[0138] The procedure is basically the same as in Example 1, except that only Cu(NO3)2·3H2O is added when preparing the MOF material, and the rest of the conditions are not changed, and the obtained material is recorded as Cu / NC, and the obtained electrode is a Cu / NC / Ni electrode.

[0139] Comparative Example 2

[0140] The MOF material was prepared by the method of Example 1, except that only Co(NO3)2·6H2O was added, and the obtained material was recorded as Co / NC, and the obtained electrode was a Co / NC / Ni electrode.

[0141] Comparative Example 3

[0142] The MOF material was prepared by the method of Example 1, except that after the obtained MOF material was prepared by the hydrothermal method, the MOF material was directly used for subsequent electrode preparation.

[0143] The obtained MOF material was not subjected to carbonization treatment in a tube furnace.

[0144] The obtained MOF material was directly used for subsequent electrode preparation.

[0145] The obtained material was recorded as Co1Cu2-MOF, and the obtained electrode was a Co1Cu2-MOF / Ni electrode.

[0146] Example 2

[0147] As shown in Figure 1 are scanning electron microscope images of the MOF materials and MOF-derived carbon materials prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. The Co1Cu2-MOF material prepared in Comparative Example 3 is the MOF material corresponding to the preparation of the Co1Cu2 / NC material in Example 1. Co-MOF is a MOF material similar to a "leaf shape", Cu-MOF is a MOF material similar to a "round sheet shape", and the MOF material containing copper and cobalt bimetal is a MOF material similar to a "flower shape". By comparing the MOF materials before and after carbonization, it can be found that the bimetallic MOF-derived carbon material has stable structural properties, while the monometallic MOF material has severe deformation.

[0148] Comparative Example 4

[0149] As shown in Figure 2XRD patterns of the MOF-derived carbon materials prepared in Example 1, Comparative Example 1, Comparative Example 2. It can be seen that the XRD pattern of the single-metal MOF-derived carbon Co / NC shows diffraction peaks at 2 theta angles of 44.2°, 51.5° and 75.8°, which correspond to the (111), (200) and (220) crystal planes of metallic Co (JCPDS 15-0806), respectively, and the diffraction peaks at 36.5° and 42.4° can be attributed to the (111) and (200) crystal planes of CoO (JCPDS 43-1004), indicating that for the single-metal Co-MOF, after carbonization, Co and CoO were mainly generated; the XRD pattern of the single-metal MOF-derived carbon Cu / C shows three diffraction peaks at 2 theta angles of 43.3°, 50.4° and 74.1°, which can be attributed to the (111), (200), (220) and (311) crystal planes of metallic Cu (JCPDS 04-0836), respectively, and a weak peak at 36.4° can be attributed to the (111) crystal plane of CuO (JCPDS 05-0667), indicating that for the single-metal Cu-MOF, elemental Cu was mainly formed during carbonization, and a small amount of Cu was oxidized. For the dual-metal MOF-derived carbon, all the MOF-derived carbon materials of different ratios showed obvious diffraction peaks of metallic Cu and metallic Co, indicating that metallic copper and metallic cobalt were the main catalyst components, and part of the metals were oxidized to form metal oxides; 2+1 O(JCPDS 05-0667), indicating that high-temperature carbonization can indeed reduce the high-valence metals in the MOF material.

[0150] As shown in Figure 3 the XRD pattern of the MOF material Co1Cu2-MOF in Comparative Example 3 does not show diffraction peaks corresponding to metallic Cu and metallic Co, indicating that high-temperature carbonization can indeed reduce the high-valence metals in the MOF material.

[0151] Comparative Example 5

[0152] As shown in Figure 4 ESR tests of the MOF-derived carbon materials prepared in Example 1 and Comparative Example 2, through ESR tests, the atomic hydrogen peak intensity generated by different electrodes can be obtained, and the atomic hydrogen yield can be preliminarily compared, and atomic hydrogen can participate in the reduction of nitrate, through Figure 4 it can be seen that the electrodes prepared from the dual-metal MOF-derived carbon have stronger ability to generate atomic hydrogen;

[0153] The BET test results of the MOF-derived carbon materials prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown in Table 1. The distribution of the adsorption isotherm curve shows that the specific surface areas of the MOF-derived carbon materials prepared with different metal ratios are quite different. According to Table 1, the specific surface areas are in the order of Co1Cu1 / NC > Co1Cu2 / NC > Co / NC > Cu / NC. The specific surface areas of Co / NC and Cu / NC are relatively small, while the specific surface areas of the bimetallic materials are relatively large. The pores in the bimetallic MOF-derived carbon are mainly mesopores. The formation of mesoporous structures may be beneficial to exposing active sites and promoting electrolyte transport, thereby enhancing the electrocatalytic activity of the material.

[0154] The Co1Cu2-MOF material prepared in Comparative Example 3 has a larger specific surface area, indicating that the material structure will collapse to some extent during the carbonization process.

[0155] Table 1 Specific surface areas and average pore diameters of different electrodes

[0156]

[0157] Example 3

[0158] The wastewater treatment device of the present embodiment is shown in Figure 4 The wastewater treatment device of the present embodiment is shown in

[0159] In the present example, the nitrate reduction experiments of Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were carried out, and the specific steps are as follows: (1) 50 mL of 100 mg N / L nitrate nitrogen solution prepared was taken with a graduated cylinder and poured into a customized electrolytic cell;

[0160] (2) A platinum electrode was used as the counter electrode, and the electrode prepared in the present patent was used as the working electrode. The electrodes were immersed in the prepared solution;

[0161] (3) The reaction conditions were controlled at a voltage of -1.5 V, and the reaction time was 90 min. After appropriate dilution of the final reaction solution, the absorbance of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen was measured using a UV spectrophotometer, and the corresponding concentrations were calculated according to the standard curve. The removal rates of nitrogen species are shown in Table 2.

[0162] Table 2 Removal rates of different nitrogen species

[0163]

[0164]

[0165] According to the experimental results, it can be seen that the electrode synthesized by the bimetallic MOF derived carbon has better treatment effect, among which Co1Cu2 / NC / Ni obtains the best treatment effect, and 94.27% of nitrate nitrogen is removed within two hours, which is much higher than that of other electrodes. The main product of nitrate nitrogen reduction of all electrodes is ammonia nitrogen, and the accumulation of nitrite nitrogen is less in the material containing cobalt, while the accumulation of nitrite nitrogen is more in the electrode containing only single metal copper. Therefore, further treatment is needed to remove the generated ammonia nitrogen in the wastewater.

[0166] Example 4

[0167] In this example, efficient denitrification is achieved by adding chloride ions, and the specific steps are as follows:

[0168] (1) Take 50 mL of prepared 100 mg N / L nitrate nitrogen solution with a measuring cylinder and pour it into a customized electrolytic cell; take 1000 mg / l Cl as the source of chloride ions, and add NaCl as the source of chloride ions. - ,

[0169] (2) Take platinum electrode as the counter electrode, and the electrode prepared in this patent as the working electrode, immerse the electrode in the prepared solution;

[0170] (3) Control the reaction conditions as voltage-1.5V, and the reaction time is 90min. After appropriate dilution of the final reaction solution, measure the absorbance of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen with ultraviolet spectrophotometer, and calculate the corresponding concentration according to the standard curve, as shown in Table 3. Finally, the removal rate of nitrogen species is obtained.

[0171] Table 3 Removal rate of nitrogen species

[0172] Electrode Nitrate nitrogen removal rate Ammonia nitrogen generation rate Nitrite nitrogen generation rate Total nitrogen removal rate Co1Cu2 / NC / Ni 70.60％ 0％ 0％ 70.60％ Co1Cu2 / MOF / Ni 6.15％ 0％ 0％ 6.15％

[0173] As compared with Example 3, the addition of chloride ions effectively increases the removal rate of total nitrogen, but to some extent, it inhibits the reduction of nitrate. The addition of chloride ions needs to be reasonably controlled.

[0174] Example 5

[0175] In this example, the stability of the materials Co1Cu2 / NC / Ni and Co1Cu2-MOF / Ni is verified by a cycle experiment, and the specific steps are as follows:

[0176] (1) Take 50 mL of prepared 100 mg N / L nitrate nitrogen solution with a measuring cylinder and pour it into a customized electrolytic cell;

[0177] (2) Using a platinum electrode as the counter electrode and the electrode prepared in this patent as the working electrode, the electrode is immersed in the prepared solution;

[0178] (3) The reaction conditions were controlled at voltage -1.5V and reaction time of 90min. After the final reaction solution was appropriately diluted, the absorbance of nitrate nitrogen, ammonia nitrogen and nitrite nitrogen was measured using a UV spectrophotometer, and the corresponding concentrations were calculated according to the standard curve. Finally, the removal rate of nitrogen species was obtained.

[0179] (4) Repeat steps (1), (2), and (3) of this embodiment five times.

[0180] Depend on Figure 6 It can be seen that the nitrate removal rate is stable after 90 minutes. This indicates that the Co1Cu2 / NC / Ni electrode prepared from Co1Cu2 / NC material has good stability in the nitrate reduction field.

[0181] Depend on Figure 7 It can be seen that the nitrate removal rate is low and unstable after 90 minutes. This indicates that the Co1Cu2 / MOF / Ni electrode prepared from Co1Cu2 / N material has poor stability in the nitrate reduction field.

Claims

1. A method for reducing nitrates, characterized in that, The nitrate was electrochemically treated using a three-electrode system; The concentration of nitrate nitrogen is 50–500 mg / L; in, The three-electrode system includes a working electrode, a counter electrode, and a reference electrode; The working electrode is an electrode containing MOF-derived carbon material, and its preparation includes the following steps: S1. Prepare a mixture containing MOF-derived carbon material, conductive agent, and binder; S2. Apply the mixture onto the substrate material; S3. Perform a drying process to obtain the electrode; in, The mass ratio of the MOF-derived carbon material, conductive agent, and binder is (6~8):1:1; The MOF-derived carbon material was prepared by the following method: A1. Prepare MOF materials, which are obtained by a hydrothermal method: Prepare solution A containing dimethylimidazole; Prepare solution B containing metal ions; Mix solutions A and B, and then perform hydrothermal treatment. Wherein, the molar ratio of the dimethylimidazole to the metal ion is 8:(1~3). The MOF material includes cobalt and copper, and the molar ratio of cobalt to copper is (1~2):(1~2). A2. The MOF material is subjected to high-temperature treatment at 600~800℃ to obtain MOF-derived carbon material; The voltage for the electrochemical treatment is -1.9 to 1.1 V, and the reaction time is 1 to 10 h.

2. The method for reducing nitrate according to claim 1, characterized in that, After electrochemical treatment of the nitrate, Add chloride ions again; in, The chloride ion dosage is between 1000 mg / L and 3000 mg / L.

3. The method for reducing nitrate according to claim 1 or 2, characterized in that, In S2, the substrate material undergoes pretreatment through the following process: Step 1: Contact and soak the substrate material in the organic solvent; Step 2: Contact and immerse the substrate material in the acid solution; Step 3: Contact and immerse the substrate material in pure water.

4. The method for reducing nitrate according to claim 1 or 2, characterized in that, In S2, the loading of MOF-derived carbon material per unit area of ​​the substrate material is 1–10 mg / cm². 2 .

5. The method for reducing nitrate according to claim 1 or 2, characterized in that, In S3, the drying conditions include: drying at 60–80 °C for 12–24 h under vacuum conditions.

6. The method for reducing nitrate according to claim 5, characterized in that, In step A2 of the preparation of the MOF-derived carbon material: The conditions for the high-temperature treatment include: treatment at a temperature of 600–800°C for 1–3 hours in an inert gas atmosphere.

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