Cathode Structure, Its Preparation Method and Application

Abstract

The present invention relates to the field of electrochemical reduction technology, and particularly relates to a cathode structure, a preparation method thereof, and an application. The cathode structure includes a metal substrate and metal-organic framework layers attached to both sides of the metal substrate, and an acidic protective layer is provided on the surface of the metal-organic framework layer. The cathode structure of the present invention can achieve highly stable and efficient electrochemical reduction of iodine, can more efficiently achieve electron transfer, has more stable chemical properties, and is not easily caused by cathode corrosion to result in metal loss or inactivation; at the same time, it has a high selectivity for hydrogen radicals, stably generates a large amount of highly active hydrogen radicals at a lower cathode potential, and can be effectively used for the reduction of iodine in ICMs.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical reduction, and particularly to a cathode structure, a preparation method thereof, and an application thereof. Background Art

[0002] Iodinated X-ray contrast media (ICMs) are one of the most commonly used angiographic agents, which are used to diagnose the internal structure of the human body and assist in visualizing some soft tissues, internal organs, and blood vessels that may not absorb X-rays. Common ICMs include diatrizoic acid, meglumine diatrizoate, iopamidol, etc. The iodine atoms therein have a large electron density and a high efficiency of absorbing X-rays, so that a contrast can be formed between the organ to be measured and the surrounding tissues, thereby achieving clear imaging. ICMs have high stability and are not decomposed and metabolized by the human body. After ingestion, they will be excreted from the body within a very short time and enter the public drainage system. Due to the stable structure of ICMs, they cannot be effectively removed in traditional sewage treatment plants and are thus discharged into the environment. ICMs are generally considered non-toxic to humans and wild animals, but they are polar and persistent, which enables them to exist in the aquatic environment for a long time and penetrate into the groundwater aquifer through the soil. They can be converted into toxic iodinated disinfection by-products during the migration and transformation in the natural water environment or the chlorination disinfection process in water treatment plants, posing a potential risk to the environment and a potential threat to human health.

[0003] Generally, the methods for treating ICMs can be summarized as physical methods, biological methods, chemical methods, and the coupling of several methods. The physical method has a high efficiency in separating ICMs, and physical adsorption or chemical adsorption and their combination can separate multiple ICMs simultaneously. However, this method has a limited adsorption capacity, a cumbersome regeneration process, and only involves a phase transfer of ICMs without reducing their toxicity. Although the biological method for degrading ICMs has a certain effect, it has a long cycle, high requirements for the nutrient ratio of water quality, strict requirements for the dissolved oxygen content at different stages, and most ICMs are difficult to be completely degraded. Chemical methods mainly include incineration, chemical reduction with noble metals having hydrogen storage capacity, advanced oxidation technologies (AOPs), and advanced reduction technologies (ARPs), etc. Incinerating ICMs at high temperatures may produce dioxins / furans, which enhance the toxicity of organic substances. Although decomposing ICMs in a homogeneous phase at high temperature and high pressure can effectively inhibit the formation of dioxins / furans, this technology has a high cost and serious equipment corrosion. The supported catalyst can overcome the above disadvantages by reducing and degrading ICMs at normal temperature and pressure, but it needs to support noble metals and introduce reducing hydrogen, increasing the disposal cost. AOPs that generate strong oxidizing species in-situ (such as ·OH, SO4· - etc.) can rapidly degrade ICMs, but it is difficult to completely mineralize ICMs, and a large amount of iodinated by-products will be generated at the same time. By generating strongly reducing hydrated electrons eaq - The ARPs can selectively degrade low-concentration ICMs, but there are problems such as high energy consumption and low deiodination efficiency. The electrochemical reduction of ARPs technology is the most energy-efficient way, with the advantages of low energy consumption, high reduction rate of ICMs, and no secondary pollution, and it is the mainstream technology for treating ICMs at present. The core problem is how to prepare an efficient, inexpensive, and stable cathode for electrochemical reduction.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a cathode structure, which can achieve more efficient electron transfer, and has stable chemical properties, and can achieve highly stable and efficient electrochemical reduction deiodination.

[0006] The second object of the present invention is to provide a preparation method of the cathode structure, which has simple operation and mild conditions.

[0007] The third object of the present invention is to provide the application of the above cathode structure in electrochemical reduction, specifically, it can be used for electrochemical reduction of iodinated X-ray contrast agents in water.

[0008] The fourth object of the present invention is to provide a system for electrochemical reduction of iodinated X-ray contrast agents.

[0009] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0010] Cathode structure, comprising a metal substrate and a metal-organic framework layer attached to both sides of the metal substrate, and an acidic protective layer is provided on the surface of the metal-organic framework layer.

[0011] The cathode structure of the present invention can achieve highly stable and efficient electrochemical reduction deiodination. Compared with traditional noble metal cathode materials such as gold and platinum, the cathode structure modified with metal-organic frameworks can achieve more efficient electron transfer, and at the same time has more stable chemical properties, and is not easy to cause metal loss or inactivation due to cathode corrosion; compared with other non-noble metal cathode materials, the cathode structure modified with copper metal-organic frameworks has stronger activity, can effectively reduce the activation energy of the reduction reaction, and at the same time has a high hydrogen radical selectivity, and stably generates a large amount of highly active hydrogen radicals at a lower cathode potential, and can be effectively used for the reduction deiodination of ICMs.

[0012] In a specific embodiment of the present invention, the metal substrate includes a titanium-based substrate.

[0013] The titanium-based substrate has low cost and good electrochemical stability.

[0014] In a specific embodiment, the titanium-based substrate layer can directly use a titanium metal layer (such as a titanium plate), or the titanium metal layer can be subjected to conventional surface pretreatment to remove the surface oxide layer and make the surface porous, which can further improve the activity.

[0015] Specifically, the preferred surface pretreatment methods include: sandblasting, alkali washing, and acid corrosion. Among them, the alkali washing includes: soaking in a sodium hydroxide solution with a concentration of 5% - 10% for 15 - 30 min; the acid corrosion includes: continuously soaking in an oxalic acid aqueous solution with a concentration of 8% - 10% at 90 - 95 °C for 2 - 3 h. The treated titanium-based substrate layer is stored for standby under an oxygen-free condition to avoid further oxidation.

[0016] In a specific embodiment of the present invention, the thickness of the titanium-based substrate layer is 1 - 2 mm.

[0017] In a specific embodiment of the present invention, the acidic protective layer includes an alumina layer.

[0018] Using the alumina layer can provide stable acidic protection and prevent metal particles from gradually losing under the anodic potential. At the same time, the alumina layer has good permeability, which can ensure the effective catalytic effect of the active sites of the metal-organic framework layer on ICMs in the aqueous solution.

[0019] In a specific embodiment of the present invention, the thickness of the acidic protective layer is 100 - 1000 nm.

[0020] In a specific embodiment, the acidic protective layer can be directly compounded on the surface of the metal-organic framework layer, or the acidic protective layer can be formed by coating on the metal-organic framework layer through a conventional coating method.

[0021] In a specific embodiment of the present invention, the metal-organic framework layer is mainly made of a metal-organic framework material. In a specific embodiment of the present invention, the thickness of the metal-organic framework layer is 1 - 2 nm.

[0022] In a specific embodiment of the present invention, the metal-organic framework material is a copper-based metal-organic framework material.

[0023] Compared with traditional noble metal cathode materials such as gold and platinum, the cathode structure modified with the metal-organic framework of copper can make the iodine removed after the reduction of ICMs stably exist in the aqueous solution in the form of iodide ions, and can effectively prevent the generation of disinfection by-products such as monoiodoacetic acid, triiodomethane, and iodate.

[0024] In a specific embodiment of the present invention, the copper-based metal-organic framework material can use existing copper-based metal-organic framework materials, such as Cu3(BTC)2, and its preparation method refers to the conventional method.

[0025] In a specific embodiment of the present invention, the copper-based metal-organic framework material can also be a copper-based metal-organic framework material prepared from a copper salt and an acidic ligand. Among them, the copper salt includes copper nitrate; the acidic ligand includes any one of trimesic acid, trimesic acetic acid, and trimesic butyric acid; the preparation method includes preparing by electrochemical deposition under electrochemical oxidation / reduction conditions, and can also be prepared by conventional stirring methods, hydrothermal / solvothermal methods, and so on.

[0026] In a preferred embodiment of the present invention, the metal-organic framework layer is mainly obtained by calcining the metal-organic framework material in a non-oxidizing atmosphere.

[0027] The metal-organic framework layer can also achieve electrochemical reduction deiodination without calcination treatment, but the cathode structure obtained after calcination treatment can further improve the stability and efficiency of the cathode structure.

[0028] Among them, the non-oxidizing atmosphere includes nitrogen and inert gases.

[0029] In a specific embodiment of the present invention, the conditions for the calcination treatment include: the temperature of the calcination treatment is 950-1200 °C, and the time of the calcination treatment is 3-10 h.

[0030] The present invention also provides a method for preparing the above cathode structure, including the following steps:

[0031] The metal-organic framework layer is formed on both sides of the metal substrate, and the acidic protective layer is formed on the surface of the metal-organic framework layer.

[0032] In a specific embodiment of the present invention, it also includes pre-treating the metal substrate, and the pre-treatment includes: sandblasting, alkali washing, and acid corrosion to remove the oxide layer on the surface of the metal substrate such as a titanium plate, and at the same time can also achieve surface porousization.

[0033] Among them, the alkali washing includes: soaking in a sodium hydroxide solution with a concentration of 5%-10% for 15-30 min; the acid corrosion includes: continuously soaking in an oxalic acid aqueous solution with a concentration of 8%-10% at 90-95 °C for 2-3 h. The treated titanium-based substrate layer is stored for standby under an oxygen-free condition to avoid further oxidation.

[0034] In a specific embodiment of the present invention, the method for forming the metal-organic framework layer includes: dispersing the metal-organic framework material in an organic solvent, coating it on both sides of the metal substrate, and drying to form a metal-organic framework layer.

[0035] In another specific embodiment of the present invention, the method for forming the metal-organic framework layer includes: using the metal substrate as an electrode, immersing it in a solution containing an acidic ligand and a copper salt, and forming the metal-organic framework layer under electrochemical oxidation / reduction conditions;

[0036] Wherein, the acidic ligand includes any one of trimesic acid, benzene-1,3,5-tricarboxylic acid, and benzene-1,3,5-trimethylacetic acid.

[0037] In a specific embodiment of the present invention, the conditions of the electrochemical oxidation / reduction include: using the metal substrate as the cathode and a platinum sheet as the anode (counter electrode), with a voltage of 1.5 - 2.0 V and a current of 0.1 - 0.2 A, continuously processing for 25 - 35 min; reversing the anode and cathode, with a voltage of 2.0 - 2.5 V and a current of 0.05 - 0.1 A, continuously processing for 30 - 40 min.

[0038] In a preferred embodiment of the present invention, in the solution, the solvent is water, the concentration of the acidic ligand is 10 - 50 g / L, and the concentration of the copper salt is 0.01 - 0.1 g / L.

[0039] In a preferred embodiment of the present invention, it further includes: after the metal-organic framework layer is formed by compounding, performing a calcination treatment on the metal-organic framework layer under a non-oxidizing atmosphere. Preferably, the conditions of the calcination treatment include: the temperature of the calcination treatment is 950 - 1200 °C, and the time of the calcination treatment is 3 - 10 h.

[0040] By regulating the above calcination conditions, it is possible to form the thinnest single-atom layer of metal carbide material on the surface of the metal substrate.

[0041] In a specific embodiment of the present invention, the method for forming the acidic protective layer includes: coating to form the acidic protective layer.

[0042] Under the above atmosphere, a stable oxygen-deficient environment can be formed to avoid the shrinkage or recrystallization of the metal-organic framework under high-temperature conditions, and ensure the structure of the metal-organic framework material.

[0043] In a specific embodiment of the present invention, the method for forming the acidic protective layer includes: coating to form the acidic protective layer.

[0044] In another specific embodiment of the present invention, the method for forming the acidic protective layer by compounding includes: immersing the metal substrate compounded with the metal-organic framework layer in trimethylaluminum solution for 12 to 24 hours, and calcining in an air atmosphere at 480 to 500 °C; wherein, the solvent of the trimethylaluminum solution is anhydrous methanol or trichloroethane, and the concentration of trimethylaluminum is 5% to 10%. Preferably, the method for forming the acidic protective layer by compounding is repeated 3 to 5 times to make the thickness of the alumina layer 100 to 1000 nm. Through the above treatment method, a stable alumina coating can be formed on the surface of the metal-organic framework layer, and the permeability of alumina is ensured, and the effective catalysis of the active sites of the metal-organic framework layer is guaranteed.

[0045] The present invention also provides an application of the above cathode structure in electrochemically reducing iodinated X-ray contrast agents.

[0046] In the electrochemically reducing technology, through an external power source, the electrons released by the cathode are directly transferred to the target pollutant to achieve reduction and deiodination. In addition, active hydrogen with strong reducing ability is generated by electron excitation at the cathode, and the carried electrons are transferred to the target pollutant to undergo a series of reactions, so as to achieve the purpose of removing the target pollutant.

[0047] The present invention also provides a system for electrochemically reducing iodinated X-ray contrast agents, and the system includes any one of the above-mentioned cathode structures.

[0048] In a specific embodiment of the present invention, the system further includes an electrolytic cell, a power source and an anode, the anode is a graphite electrode, and the power source is a direct current power source.

[0049] In a specific embodiment of the present invention, the plate spacing between the cathode and the anode is 10 to 15 mm.

[0050] In a specific embodiment of the present invention, a gas outlet is provided on the electrolytic cell.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0052] (1) The cathode structure of the present invention can achieve efficient electron transfer and has stable chemical properties, and can stably and efficiently perform electrochemical reduction and deiodination.

[0053] (2) When the cathode structure of the present invention is used in electrochemical reduction, it can be used for the reduction and deiodination of ICMs in aqueous solution, and the removed iodine stably exists in the aqueous solution in the form of iodide ions, which can effectively prevent the generation of disinfection by-products such as monoiodoacetic acid, triiodomethane, and iodate. Description of the Drawings

[0054] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0055] Figure 1 Structural schematic diagram of the cathode structure provided by the embodiment of the present invention;

[0056] Figure 2 Structural schematic diagram of the system for electrochemically reducing iodinated X-ray contrast agents provided by the embodiment of the present invention;

[0057] Figure 3 Variation of the concentration and deiodination rate of meglumine diatrizoate, an iodinated X-ray contrast agent, with time in the experimental example of the present invention;

[0058] Figure 4 Variation of the concentration and deiodination rate of iopamidol, an iodinated X-ray contrast agent, with time in the experimental example of the present invention.

[0059] Reference numerals:

[0060] 1 - Cathode structure; 11 - Metal substrate; 12 - Metal-organic framework layer;

[0061] 13 - Acidic protective layer; 2 - Anode; 3 - Power supply;

[0062] 4 - Electrolytic cell; 5 - Terminal; 41 - Gas outlet. Specific embodiments

[0063] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0064] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0065] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0066] Figure 1 It is a schematic structural diagram of the cathode structure provided by the embodiment of the present invention. As Figure 1 shown, the cathode structure provided by this embodiment includes a metal substrate 11 and a metal-organic framework layer 12 attached to both sides of the metal substrate 11, and an acidic protective layer 13 is provided on the surface of the metal-organic framework layer 12.

[0067] In a specific embodiment of the present invention, the metal substrate is a titanium-based substrate.

[0068] In a specific embodiment, the titanium-based substrate layer can directly adopt a titanium metal layer, such as a titanium plate, or the titanium metal layer can be subjected to conventional surface pretreatment to remove the surface oxide layer and make the surface porous, which can further improve the activity.

[0069] In a specific embodiment of the present invention, the thickness of the titanium-based substrate layer is 1-2 mm.

[0070] In a specific embodiment of the present invention, the acidic protective layer is an alumina layer.

[0071] Using the alumina layer can provide stable acidic protection and prevent the gradual loss of metal particles under the anodic potential. At the same time, the alumina layer has good permeability, which can ensure the effective catalytic effect of the active sites of the metal-organic framework layer on ICMs in the aqueous solution.

[0072] In a specific embodiment of the present invention, the thickness of the alumina layer is 100-1000 nm.

[0073] In a specific embodiment, the acidic protective layer can be directly compounded on the surface of the metal-organic framework layer, or a coating of the acidic protective layer can be formed on the metal-organic framework layer by a conventional coating method.

[0074] In a specific embodiment of the present invention, the metal-organic framework layer is mainly made of a metal-organic framework material.

[0075] In a specific embodiment of the present invention, the thickness of the metal-organic framework layer is 1 to 2 nm.

[0076] In a specific embodiment of the present invention, the metal-organic framework material is a copper-based metal-organic framework material.

[0077] In a specific embodiment of the present invention, the copper-based metal-organic framework material can adopt an existing copper-based metal-organic framework material, such as Cu3(BTC)2 (i.e., HKUST-1), and its preparation method refers to the conventional method.

[0078] In a specific embodiment of the present invention, the copper-based metal-organic framework material can also be a copper-based metal-organic framework material prepared from a copper salt and an acidic ligand. Among them, the copper salt includes copper nitrate; the acidic ligand includes any one of trimesic acid, trimesic acetic acid, and trimesic butyric acid; the preparation method includes preparation under electrochemical oxidation / reduction conditions, and can also adopt conventional stirring methods, hydrothermal / solvothermal methods, etc.

[0079] In a preferred embodiment of the present invention, the metal-organic framework layer is mainly obtained by calcining a metal-organic framework material in a non-oxidizing atmosphere.

[0080] The electrochemical reduction of iodine can also be achieved without calcining the metal-organic framework layer, but the cathode structure obtained after calcining can further improve the stability and efficiency of the cathode structure.

[0081] Among them, the non-oxidizing atmosphere includes nitrogen and inert gases.

[0082] In a specific embodiment of the present invention, the conditions for the calcination treatment include: the temperature of the calcination treatment is 950 to 1200 °C, and the time of the calcination treatment is 3 to 10 h.

[0083] The present invention also provides a preparation method for the above-mentioned cathode structure, including the following steps:

[0084] The metal-organic framework layer is compounded on both sides of the metal substrate, and the acidic protective layer is compounded on the surface of the metal-organic framework layer.

[0085] In a specific embodiment of the present invention, it further includes pre-treating the metal substrate, and the pre-treatment includes: sandblasting, alkali washing, and acid etching to remove the oxide layer on the surface of the metal substrate such as a titanium plate, and at the same time, surface porosification can also be achieved.

[0086] Among them, the alkali washing includes: soaking in a sodium hydroxide solution with a concentration of 5% - 10% for 15 - 30 min; the acid etching includes: continuously soaking in an oxalic acid aqueous solution with a concentration of 8% - 10% at 90 - 95 °C for 2 - 3 h. The treated titanium-based substrate layer is stored for standby under an oxygen-free condition to avoid further oxidation.

[0087] In a specific embodiment of the present invention, the method for forming the metal-organic framework layer by compounding includes: dispersing the metal-organic framework material in an organic solvent, coating it on both sides of the metal substrate, and performing a drying treatment to form a metal-organic framework layer.

[0088] Among them, the drying treatment can adopt a conventional drying method as long as the organic solvent can be removed.

[0089] In another specific embodiment of the present invention, the method for forming the metal-organic framework layer by compounding includes: using the metal substrate as the cathode, immersing it in a solution containing an acidic ligand and a copper salt, and forming a metal-organic framework layer under electrochemical oxidation / reduction conditions;

[0090] Among them, the acidic ligand includes any one of trimesic acid, trimesic acetic acid, and trimesic butyric acid; the copper salt includes copper nitrate.

[0091] In a specific embodiment of the present invention, the conditions of the electrochemical oxidation / reduction include: using the metal substrate as the cathode and a platinum sheet as the anode (counter electrode), with a voltage of 1.5 - 2.0 V and a current of 0.1 - 0.2 A, continuously treating for 25 - 35 min; reversing the anode and cathode, with a voltage of 2.0 - 2.5 V and a current of 0.05 - 0.1 A, continuously treating for 30 - 40 min.

[0092] In a preferred embodiment of the present invention, in the solution, the solvent is water, the concentration of the acidic ligand is 10 - 50 g / L, and the concentration of the copper salt is 0.01 - 0.1 g / L.

[0093] In a preferred embodiment of the present invention, it further includes: after forming the metal-organic framework layer by compounding, performing a calcination treatment on the metal-organic framework layer under a non-oxidizing atmosphere. Preferably, the conditions of the calcination treatment include: the temperature of the calcination treatment is 950 - 1200 °C, and the time of the calcination treatment is 3 - 10 h.

[0094] By regulating the above calcination conditions, it is possible to form the thinnest single-atom layer of metal carbide material on the surface of the metal substrate.

[0095] In a specific embodiment of the present invention, the non-oxidizing atmosphere includes nitrogen and inert gas. Specifically preferably, in the non-oxidizing atmosphere, the volume fraction of nitrogen is 93% - 95%, and the volume fraction of inert gas is 5% - 7%. Among them, the inert gas includes any one or a mixture of two of argon and helium.

[0096] Under the above atmosphere, a stable oxygen-deficient environment can be formed to avoid the shrinkage or recrystallization of the metal-organic framework under high-temperature conditions, and ensure the structure of the metal-organic framework material.

[0097] In a specific embodiment of the present invention, the method for forming the acidic protective layer by compounding includes: coating to form an acidic protective layer.

[0098] In another specific embodiment of the present invention, the method for forming the acidic protective layer by compounding includes: immersing the metal substrate compounded with the metal-organic framework layer in trimethylaluminum solution for 12 - 24 h, and performing calcination in an air atmosphere at 480 - 500 °C, preferably for 20 - 24 h; wherein, the solvent of the trimethylaluminum solution is anhydrous methanol or trichloroethane, and the concentration of trimethylaluminum is 5% - 10%. Preferably, the method for forming the acidic protective layer by compounding is repeated 3 - 5 times to make the thickness of the alumina layer 100 - 1000 nm. Through the above treatment method, a stable alumina coating can be formed on the surface of the metal-organic framework layer, and the permeability of alumina is ensured to guarantee the effective catalysis of the active sites of the metal-organic framework layer.

[0099] The present invention also provides the application of the above cathode structure in the electrochemical reduction of iodinated X-ray contrast agents.

[0100] In different embodiments, the iodinated X-ray contrast agents include, but are not limited to, meglumine diatrizoate and iopamidol.

[0101] In a specific embodiment of the present invention, the method for electrochemically reducing iodinated X-ray contrast agents includes:

[0102] (a) Removing dissolved oxygen from the solution containing iodinated X-ray contrast agents, adding sodium sulfate electrolyte and phosphate to obtain a solution to be treated;

[0103] (b) Using the cathode structure as the cathode and a graphite electrode as the anode, immersing them in the solution to be treated, and performing electrochemical reduction treatment at a current of 0.5 - 1 mA / cm 2 and a voltage of 0.1 - 0.4 V for 10 - 20 min.

[0104] Among them, sodium sulfate electrolyte and phosphate are added so that the concentrations of sodium sulfate electrolyte and phosphate in the solution to be treated are 0.08 - 0.1 mol / L and 0.008 - 0.01 mol / L respectively, preferably 0.1 mol / L and 0.01 mol / L respectively.

[0105] In a specific embodiment of the present invention, the temperature of the electrochemical reduction treatment is 25 ± 2 °C.

[0106] The electrochemical reduction technology realizes reductive deiodination by directly transferring the electrons released by the cathode to the target pollutant through an externally applied power source. In addition, active hydrogen with strong reducing ability is generated by electron excitation at the cathode, and a series of reactions occur by transferring the carried electrons to the target pollutant, thereby achieving the purpose of removing the target pollutant.

[0107] The present invention also provides a system for electrochemically reducing iodinated X-ray contrast agents, as Figure 2 shown, the system includes any one of the above-mentioned cathode structures 1, an anode 2, a power source 3, and an electrolytic cell 4. The cathode structure 1 and the anode 2 are respectively placed in the electrolytic cell 4 and are electrically connected to the negative and positive electrodes of the power source 3 respectively.

[0108] In a specific embodiment of the present invention, the anode 2 is a graphite electrode, and the power source 3 is a DC power source.

[0109] In a specific embodiment of the present invention, a gas outlet 41 is provided on the electrolytic cell 4.

[0110] In a specific embodiment of the present invention, the system further includes a terminal 5, and the power source 3 is electrically connected to the cathode structure 1 and the anode 2 respectively through the terminal 5.

[0111] Example 1

[0112] This example provides a preparation method of a cathode structure, including the following steps:

[0113] (1) Select a titanium plate with a thickness of 2 mm, and perform pretreatment on the titanium plate. The pretreatment method includes: sandblasting, alkali washing, and acid corrosion processes; among them, alkali washing is carried out by soaking in a sodium hydroxide solution with a concentration of 5% - 10% for 30 min, acid corrosion is carried out by continuously soaking in an oxalic acid aqueous solution with a concentration of 10% at 95 °C for 3 h, and then the pretreated titanium plate is stored for standby under an oxygen-free condition.

[0114] (2) Electrochemical oxidation / reduction to prepare a metal-organic framework layer

[0115] Prepare a mixed solution with trimesic acid as the acidic ligand and copper nitrate as the copper salt. The solvent of the mixed solution is water, the concentration of trimesic acid in the mixed solution is 30 g / L, and the concentration of the copper salt in the mixed solution is 0.05 g / L;

[0116] Then, use the pretreated titanium plate in step (1) as the cathode and a platinum sheet as the counter electrode (anode), and immerse them in the mixed solution. Control the cell voltage at 1.5 V and the current at 0.1 A, and continuously process for 25 min; then reverse the cathode and anode, control the cell voltage at 2.0 V and the current at 0.05 A, and continuously process for 30 min to form a copper-based metal-organic framework layer on the surface of the pretreated titanium plate. The thickness of the copper-based metal-organic framework layer is 1.5 nm.

[0117] (3) Place the titanium plate with the metal-organic framework layer attached obtained in step (2) in an atmosphere containing 95% nitrogen and 5% argon for roasting. The roasting temperature is 1050 °C and the roasting time is 5 h; after the roasting is completed, cool down and take out;

[0118] (4) Immerse the structure treated in step (3) in trimethylaluminum solution for 24 h, and then perform roasting at 500 °C in an air atmosphere for 20 h to form a stable alumina coating; repeat this step 4 times to make the thickness of the alumina layer 500 nm; obtain the cathode structure;

[0119] Among them, the solvent of the trimethylaluminum solution is anhydrous methanol, and in the trimethylaluminum solution, the mass concentration of trimethylaluminum is 5%.

[0120] Example 2

[0121] This example refers to the preparation method of the cathode structure in Example 1, and the difference is only that:

[0122] The method for preparing the metal-organic framework layer in step (2) is:

[0123] Use the metal-organic framework material Cu3(BTC)2, disperse it in an organic solvent such as isopropanol, and the dispersion concentration is 1 - 2 g / L; then coat it on both sides of the pretreated titanium plate in step (1), and dry it at room temperature to remove the organic solvent isopropanol to form a metal-organic framework layer. The thickness of the metal-organic framework layer is 1.5 nm.

[0124] Example 3

[0125] This example refers to the preparation method of the cathode structure in Example 1, and the difference is only that:

[0126] The method for preparing the metal-organic framework layer in step (2) is:

[0127] Using the metal-organic framework material Cu3(BTC)2, disperse it in an organic solvent such as isopropanol, and the dispersion concentration is 1-2 g / L; then coat both sides of the titanium plate pretreated in step (1) with it, and dry it at room temperature to remove the organic solvent isopropanol to form a metal-organic framework layer.

[0128] Moreover, without including the calcination in step (3), directly perform the subsequent step (4) on the titanium plate coated with the metal-organic framework layer after the treatment in step (2).

[0129] Example 4

[0130] The preparation method of the cathode structure in this example refers to that of Example 1, and the difference is only that:

[0131] The method for preparing the alumina layer in step (4) is as follows:

[0132] Immerse the structure treated in step (3) in trimethylaluminum solution for 12 h, and then perform calcination at 500 °C for 20 h in an air atmosphere to form a stable alumina coating; repeat this step 3 times to make the thickness of the alumina layer 100 nm.

[0133] Examples 5-8

[0134] This example provides a method for electrochemically reducing iodinated X-ray contrast agents. Refer to Figure 2 the structural schematic diagram for system assembly, including the following steps:

[0135] (1) Take 100 mL of an aqueous solution containing iodinated X-ray contrast agent, and the initial concentration of the iodinated X-ray contrast agent in the aqueous solution is 100 mg / L. Inject it into the electrolytic cell, use a graphite electrode as the anode, and use the cathode structures prepared in Examples 1-4 as the cathode respectively. The area of both electrode plates is 60 cm 2 , adjust the electrode plate spacing to 10 mm, and connect it to a DC power supply;

[0136] (2) Pass nitrogen into the aqueous solution for 10 min to remove dissolved oxygen, and then add sodium sulfate electrolyte and phosphate (such as sodium phosphate) to make the concentrations of sodium sulfate electrolyte and phosphate in the aqueous solution reach 0.1 mol / L and 0.01 mol / L respectively, and the initial pH is 6-7;

[0137] (3) Control the current density to be 0.8 mA / cm 2 , apply an external voltage of 2 V, control the reaction temperature at 25 °C, and continuously process for 10-20 min to achieve the deiodination treatment of the iodinated X-ray contrast agent.

[0138] Examples 5-8 respectively correspond to the implementation manners using the cathode structures prepared in Examples 1-4 as the cathode.

[0139] Experimental Example 1

[0140] The method for electrochemically reducing an iodinated X-ray contrast agent according to Reference Example 5, wherein the iodinated X-ray contrast agent is meglumine diatrizoate. When the electrode is used for the first time, after 20 min of the electrochemically reducing reaction, the meglumine diatrizoate in the aqueous solution is basically removed, and the deiodination rate reaches 98%. The specific changes of the meglumine diatrizoate concentration and the deiodination rate with time are as Figure 3 shown. After repeating the above experiment 10 times, the removal rate of meglumine diatrizoate can still reach 99%, and the deiodination rate can still reach 95%.

[0141] The method for electrochemically reducing an iodinated X-ray contrast agent according to Reference Example 5, wherein the iodinated X-ray contrast agent is iopamidol. When the electrode is used for the first time, after 16 min of the electrochemically reducing reaction, the iopamidol in the aqueous solution is basically removed, and the deiodination rate reaches 97%. The specific changes of the iopamidol concentration and the deiodination rate with time are as Figure 4 shown. After repeating the above experiment 10 times, the removal rate of iopamidol can still reach 99%, and the deiodination rate can still reach 95%.

[0142] Experimental Example 2

[0143] The method for electrochemically reducing an iodinated X-ray contrast agent according to Reference Example 5, wherein the iodinated X-ray contrast agents are meglumine diatrizoate and iopamidol respectively, and the cathodes of Examples 1-4 are used as cathodes respectively. The electrochemically reducing reactions of the iodinated X-ray contrast agents are carried out respectively (the treatment time of meglumine diatrizoate is 20 min, and the treatment time of iopamidol is 16 min), and the deiodination effects of the cathode structures of different examples are compared and analyzed. The specific results are shown in Table 1. When the 4 groups of electrodes are used for the first time, the removal rates of both meglumine diatrizoate and iopamidol can reach 99%, and the deiodination rates are both 96%. After repeating the experiment 10 times, the removal rates of meglumine diatrizoate and iopamidol are 97% and 94% respectively, and the deiodination rates are 90% and 88% respectively.

[0144] Table 1 Test results of deiodination rates after repeating the experiment 10 times for different groups

[0145] Number Meglumine Diatrizoate Iopamidol Example 1 95％ 95％ Example 2 90％ 88％ Example 3 83％ 80％ Example 4 93％ 92％

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cathode structure, characterized in that, It includes a metal substrate and metal-organic framework layers attached to both sides of the metal substrate, and an alumina layer is provided on the surface of the metal-organic framework layers; The metal substrate includes a titanium-based substrate; The thickness of the titanium-based substrate is 1-2 mm; the metal-organic framework layers are mainly obtained by calcining the metal-organic framework material in a non-oxidizing atmosphere, the metal-organic framework material is a copper-based metal-organic framework material; the organic ligand of the metal-organic framework material is an acidic ligand; the acidic ligand includes any one of trimesic acid, trimesic acetic acid and trimesic butyric acid; The conditions of the calcining treatment include: the temperature of the calcining treatment is 950-1200 °C, and the time of the calcining treatment is 3-10 h; The thickness of the metal-organic framework layers is 1-2 nm.

2. The cathode structure according to claim 1, wherein The titanium-based substrate is a titanium metal layer.

3. The cathode structure according to claim 1, wherein The thickness of the alumina layer is 100-1000 nm.

4. The method for preparing the cathode structure according to any one of claims 1-3, characterized in that, It includes the following steps: The metal-organic framework layers are formed by compounding on both sides of the metal substrate, and the alumina layer is formed by compounding on the surface of the metal-organic framework layers.

5. The preparation method of the cathode structure according to claim 4, characterized in that, It also includes pre-treating the metal substrate, and the pre-treatment includes: sandblasting, alkali washing and acid etching; The alkali washing includes: soaking in a sodium hydroxide solution with a concentration of 5%-10% for 15-30 min; The acid etching includes: continuously soaking in an oxalic acid aqueous solution with a concentration of 8%-10% at 90-95 °C for 2-3 h.

6. The preparation method of the cathode structure according to claim 4, wherein, The method for forming the metal-organic framework layers by compounding includes: using the metal substrate as an electrode, immersing it in a solution containing an acidic ligand and a copper salt, forming a metal-organic framework layer under electrochemical oxidation / reduction conditions, and calcining the metal-organic framework layer in a non-oxidizing atmosphere; Among them, the acidic ligand includes any one of trimesic acid, trimesic acetic acid and trimesic butyric acid; the copper salt is copper nitrate.

7. The preparation method of the cathode structure according to claim 6, characterized in that, The conditions of the electrochemical oxidation / reduction include: using the metal substrate as the cathode and a platinum sheet as the anode, with a voltage of 1.5-2.0 V and a current of 0.1-0.2 A, continuously treating for 25-35 min; reversing the anode and cathode, with a voltage of 2.0-2.5 V and a current of 0.05-0.1 A, continuously treating for 30-40 min.

8. The preparation method of the cathode structure according to claim 6, characterized in that, In the solution, the solvent is water, the concentration of the acidic ligand is 10-50 g / L, and the concentration of the copper salt is 0.01-0.1 g / L.

9. The preparation method of the cathode structure according to claim 6, characterized in that, The conditions of the calcining treatment include: the temperature of the calcining treatment is 950-1200 °C, and the time of the calcining treatment is 3-10 h.

10. The preparation method of the cathode structure according to claim 9, characterized in that, The non-oxidizing atmosphere includes nitrogen and inert gas.

11. The method for preparing the cathode structure according to claim 9, characterized in that, In the non-oxidizing atmosphere, the volume fraction of nitrogen is 93%-95%, and the volume fraction of the inert gas is 5%-7%.

12. The preparation method of the cathode structure according to claim 4, characterized in that, The method for forming the alumina layer by compounding includes: soaking the metal substrate compounded with the metal-organic framework layers in trimethylaluminum solution for 12-24 h, and calcining in an air atmosphere at 480-500 °C.

13. Application of the cathode structure according to any one of claims 1-3 in electrochemically reducing an iodinated X-ray contrast agent.

14. Use of the cathode structure according to claim 13 in the electrochemical reduction of iodinated X-ray contrast agents, characterized in that, The method for electrochemically reducing an iodinated X-ray contrast agent includes: (a) Remove the dissolved oxygen from the solution containing the iodinated X-ray contrast agent, add sodium sulfate electrolyte and phosphate to obtain the solution to be treated; (b) Using the cathode structure as the cathode and a graphite electrode as the anode, immerse them in the solution to be treated, and perform electrochemical reduction treatment at a current of 0.5 - 1 mA / cm 2 and a voltage of 0.1 - 0.4 V for 10 - 20 minutes.

15. Use of the cathode structure according to claim 14 in the electrochemical reduction of iodinated X-ray contrast agents, characterized in that, The temperature of the electrochemically reduction treatment is 25 ± 2 °C.

16. A system for electrochemically reducing an iodinated X-ray contrast agent, characterized in that, It includes the cathode structure according to any one of claims 1-3.

17. The system for electrochemically reducing an iodinated X-ray contrast agent according to claim 16, wherein, The system further includes an electrolytic cell, a power source and an anode; the anode and the cathode structure are respectively placed in the electrolytic cell and are respectively electrically connected to the positive and negative electrodes of the power source.

18. The system for electrochemically reducing an iodinated X-ray contrast agent according to claim 17, wherein A gas outlet is provided on the electrolytic cell.

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