A membrane electrocatalytic system, a dual oxidation synergistic membrane electrocatalytic system, and a water treatment method based thereon

Abstract

The present invention relates to a membrane electrocatalytic system, a dual-oxidation synergistic membrane electrocatalytic system and a water treatment method based thereon. The anode of the membrane electrocatalytic system of the present invention is a carbon fiber membrane loaded with tin dioxide, which is prepared by using a tin-containing metal organic framework compound as a tin source, introducing a carbon source, and forming or forming-heat treatment. The specific anode membrane adopted in the present invention has good mass transfer efficiency and stability, and the active oxygen species mainly produced in the electrochemical oxidation process is singlet oxygen, which exhibits strong anti-interference performance to impurities in water such as anions, has high selectivity for electron-rich substances such as drugs, and has potential advantages in removing drugs and personal care products in sewage. Furthermore, the present invention also proposes a dual-oxidation synergistic membrane electrocatalytic system, which can greatly increase the singlet oxygen production by utilizing the synergistic reaction of anode and cathode, has high energy efficiency, and provides a high-efficiency and simple system and method for deep treatment of sewage.

Description

Technical Field

[0001] The present invention relates to the fields of electrochemistry and water treatment, and in particular to a membrane electrocatalytic system, a dual-oxidation synergistic membrane electrocatalytic system, and a water treatment method based thereon. Background Art

[0002] As water scarcity has become a global issue, clean drinking water has been listed as one of the United Nations' 17 Sustainable Development Goals. Effective wastewater treatment and reuse can reduce pollution to the aquatic environment and alleviate the pressure of water shortages. In recent years, pharmaceuticals and personal care products have been widely used and continuously enter the aquatic environment through sewage discharge and other channels, posing a significant threat to human health and ecological safety. Emerging technologies such as electrochemical advanced oxidation technology (AEOT) are very promising for treating these pollutants. AEOT uses catalytically active electrode materials and, through the action of an electric field, utilizes the catalytic activity to directly induce electrochemical reactions on the electrodes or to generate strong oxidizing active substances on the electrode surface to oxidize and remove difficult-to-degrade organic pollutants from wastewater.

[0003] The electrochemical advanced oxidation process has simple equipment, flexible control, and high processing efficiency. However, due to the limitations of electrode materials and configurations, the electrochemical process for degrading refractory organic matter has long suffered from low current efficiency and high energy consumption, which has limited the industrialization of the application of electrochemical technology. In addition, the electrochemical advanced oxidation process is basically a traditional hydroxyl radical reaction process. For example, the three-dimensional electrode electrochemical system disclosed in Patent Document 1 (CN106966465A) uses divalent iron (Fe) as the electrode. 2+ ) and H₂O₂ catalyze the chain reaction to generate ·OH, which is then used to oxidize and decompose pollutants in the water. However, given that complex wastewater often has a high salt content, anions with low redox potentials, such as chloride ions, easily quench hydroxyl radicals. Therefore, the construction of an electrochemical system suitable for advanced wastewater treatment with high energy efficiency and strong anion interference resistance is of practical research significance. Summary of the Invention

[0004] Problems to be solved by the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a membrane electrocatalytic system, which has good mass transfer efficiency. At the same time, the non-radical process based on singlet oxygen shows strong anti-interference performance for impurities in water, such as anions, and has high selectivity for electron-rich substances such as drugs, and has potential advantages in removing drugs and personal care products from wastewater.

[0006] Another object of the present invention is to provide a dual-oxidation cooperative membrane electrocatalytic system, which utilizes the coordinated reaction of anode and cathode to not only further improve energy efficiency but also significantly increase singlet oxygen production.

[0007] Furthermore, another object of the present invention is to provide a water treatment method based on the aforementioned membrane electrocatalytic system or the dual oxidation synergistic membrane electrocatalytic system.

[0008] Solutions for solving problems

[0009] Through long-term research, the inventors found that the above technical problems can be solved by implementing the following technical solutions:

[0010] [1] A membrane electrocatalytic system, wherein the anode of the membrane electrocatalytic system is a carbon fiber membrane loaded with tin dioxide, and the carbon fiber membrane loaded with tin dioxide is prepared by molding or molding-heat treatment using a tin-containing metal organic framework compound as a tin source and introducing a carbon source.

[0011] [2] The membrane electrocatalytic system according to [1], wherein the carbon source is selected from at least one of a polymer, a polymer precursor, a sugar and an inorganic carbon source, further the polymer is selected from one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyester, polyamide, etc., and the inorganic carbon source is selected from one or more of graphite felt, carbon felt, graphite paper, carbon paper, carbon cloth and graphite cloth.

[0012] [3] The membrane electrocatalytic system according to [1] or [2], wherein the mass ratio of the tin source to the carbon source is (0.1 to 10):1.

[0013] [4] The membrane electrocatalytic system according to any one of the technical solutions [1] to [3], wherein the forming is selected from one of electrospinning, air spinning, coating film forming, sheeting method, and sol-gel method.

[0014] [5] The membrane electrocatalytic system according to any one of the technical solutions [1] to [4], wherein, further, the heat treatment includes pre-oxidation and carbonization steps.

[0015] [6] The membrane electrocatalytic system according to [5] is characterized in that the carbonization temperature of the carbonization step is 300 to 1300°C.

[0016] [7] The membrane electrocatalytic system according to any one of the technical solutions [1] to [6] is characterized in that the cathode of the membrane electrocatalytic system is selected from one of a carbon fiber membrane doped with a transition metal, a stainless steel mesh, a titanium mesh, a carbon felt, and a graphite felt.

[0017] [8] A dual-oxidation synergistic membrane electrocatalytic system, comprising an anode and a cathode, wherein the anode is a carbon fiber membrane loaded with tin dioxide, wherein the carbon fiber membrane loaded with tin dioxide is prepared by molding or molding-heat treatment using a tin-containing metal organic framework compound as a tin source and introducing a carbon source, and the cathode is an iron-doped carbon fiber membrane.

[0018] [9] The dual-oxidation synergistic membrane electrocatalytic system according to [8], wherein the iron-doped carbon fiber membrane is prepared by using iron salt as the iron source and introducing a carbon source through molding or molding-heat treatment.

[0019]

[10] A water treatment method, wherein the water treatment method adopts the membrane electrocatalytic system described in any one of the technical solutions [1] to [7] or the dual oxidation synergistic membrane electrocatalytic system described in any one of the technical solutions [8] or [9].

[0020]

[11] The water treatment method according to

[10] , wherein the active oxygen species generated by electrochemical oxidation are mainly singlet oxygen.

[0021] Effects of the Invention

[0022] The membrane electrocatalytic system provided by the present invention uses a carbon fiber membrane loaded with tin dioxide as the anode. The anode membrane has good mass transfer efficiency and stability, and the main active oxygen species produced during the electrochemical oxidation process is singlet oxygen. It exhibits strong anti-interference performance against impurities in water such as anions, and has high selectivity for electron-rich substances such as drugs, and has potential advantages in removing drugs and personal care products from sewage. In some preferred embodiments of the present invention, the dual oxidation synergistic membrane electrocatalytic system provided by the present invention has a synergistic effect between the cathode and the anode. The synergistic oxidation of the cathode and the anode can make full use of the half-reactions on the two electrodes, which can greatly increase the singlet oxygen production and has high energy efficiency, thereby significantly improving the treatment efficiency and energy utilization of the system, and has potential advantages in removing difficult-to-degrade organic matter in sewage. The present invention provides an efficient and simple system and method for deep treatment of sewage. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 : Scanning electron micrographs before heat treatment ((a)(b) Tin-containing metal organic framework compound particles; (c)(d) Pure carbon fiber membrane; (e)(f) Tin dioxide-doped carbon fiber membrane; (g)(h) Iron-doped carbon fiber membrane)

[0024] Figure 2 Schematic diagram of the preparation process and system construction ((a) Schematic diagram of the carbon fiber membrane preparation process; (b) Schematic diagram of the dual-oxidation synergistic membrane electrocatalytic system construction; (c) Schematic diagram of different operation modes)

[0025] Figure 3: Scanning electron microscope images and X-ray photoelectron spectroscopy spectra of MOF-SnO2@CF and Fe@CF of Example 1 of the present invention ((a) Scanning electron microscope image of MOF-SnO2@CF; (b) Scanning electron microscope image of Fe@CF; (c)

[0026] X-ray photoelectron spectroscopy of MOF-SnO2@CF; (d) X-ray photoelectron spectroscopy of Fe@CF)

[0027] Figure 4 : X-ray diffraction pattern of Fe@CF of Example 1 of the present invention

[0028] Figure 5 :Effects of tin dioxide precursor type and content and carbonization temperature on degradation ((a) Effects of tin dioxide precursor type and content on degradation; (b) Effect of carbonization temperature on degradation; (c) X-ray diffraction patterns of MOF-SnO2@CF at different carbonization temperatures; (d) Raman spectra of MOF-SnO2@CF at different carbonization temperatures)

[0029] Figure 6 :Degradation curves of semi-batch experiments in different modes and degradation curves of one-shot membrane degradation ((a) Degradation curves of semi-batch experiments in different modes; (b) Degradation curves of one-shot membrane degradation in different modes)

[0030] Figure 7 : Ion spectra of three peaks with residence times of (a) 2.24, (b) 10.34 and (c) 21.95 min in the total ion current.

[0031] Figure 8 :Pro standard sample (a) and fragment ion spectrum of detected PRO (b)

[0032] Figure 9 :Fragment ion spectra of three products with mass-to-charge ratios of (a) 134, (b) 118, and (c) 100

[0033] Figure 10 : Scanning electron micrographs of (a) MOF-SnO2@CF and (b) Fe@CF fiber membranes used in a single membrane pass experiment; X-ray photoelectron spectra of (c) MOF-SnO2@CF and (d) Fe@CF fiber membranes that were not used and used in a single membrane pass experiment; X-ray photoelectron spectra of (e) MOF-SnO2@CF and (f) Fe@CF fiber membranes used in a single membrane pass experiment (peak separation)

[0034] Figure 11:Effects of quenchers on propranolol degradation under (a) cathode-dominated, (b) anode-dominated, and (c) synergistic modes; (d) Electron paramagnetic resonance signals of singlet oxygen under different modes; (e) Degradation curves of furfuryl alcohol in aqueous solution and 50% deuterated water solution; (f) Fluorescence intensity of singlet oxygen adducts; (g) Schematic diagram of the cathodic synergistic mechanism

[0035] Figure 12 :Electron paramagnetic resonance signals of singlet oxygen and hydroxyl radicals in (a)(b) cooperative mode, (c)(d) anodic dominant mode and (e)(f) cathodic dominant mode

[0036] Figure 13 :Effects of different water qualities on PRO degradation DETAILED DESCRIPTION

[0037] The following describes embodiments of the present invention, but the present invention is not limited thereto. The present invention is not limited to the various configurations described below; various modifications may be made within the scope of the invention. Embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included within the technical scope of the present invention. In addition, all documents listed in this specification are cited as references in this specification.

[0038] Unless defined otherwise, technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0039] In the context of describing this specification (especially in the context of the following claims), the terms "a," "an," and "the" and similar language are to be construed to cover both the singular and the plural, unless the context indicates otherwise or clearly contradicted by context. The term "plurality" includes two or more.

[0040] In this specification, a numerical range expressed using "numerical value A to numerical value B" or "numerical value A - numerical value B" means a range including the endpoints numerical values ​​A and B.

[0041] In this specification, the use of "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process. In this specification, "optional" or "optionally" means that the event or situation described below may or may not occur, and the description includes both cases where the event occurs and cases where the event does not occur.

[0042] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "some specific / preferred technical solutions," "other specific / preferred technical solutions," etc., mean that the specific elements (e.g., features, structures, properties, and / or characteristics) described in connection with the embodiment are included in at least one embodiment described herein and may or may not be present in other embodiments. Furthermore, it should be understood that the elements may be combined in various embodiments in any appropriate manner.

[0043] The term "comprises" and any variations thereof in the description and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements, but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0044] The membrane electrocatalytic system of the present invention utilizes porous membrane materials as electrodes to construct an electrochemical reaction system. The anode of the present invention is a tin dioxide-loaded carbon fiber membrane. This tin dioxide-loaded carbon fiber membrane is produced by using a tin-containing metal organic framework compound as a tin source, introducing a carbon source, and then forming or forming and heat treating the membrane.

[0045] <Anode: Tin dioxide-loaded carbon fiber membrane>

[0046] Metal-Organic Frameworks (MOFs) refer to crystalline porous materials with a periodic network structure formed by self-assembly of transition metal ions and organic ligands, that is, MOFs are a framework structure composed of organic ligands (connecting bridges) with different connection numbers and transition metal ion nodes. It has the advantages of high porosity, low density, large specific surface area, regular pores, adjustable pore size, topological structure diversity and tailorability, which can greatly improve the electrochemical performance of the battery. The tin-containing metal organic framework compound (Sn-MOF for short) of the present invention refers to a central metal ion mainly including tin. In some preferred embodiments of the present invention, the tin-containing metal organic framework compound refers to a transition metal ion that is tin, and can also be called a tin-based metal organic framework compound. Taking into account that tin dioxide has good electrocatalytic properties, the present invention chooses to derive tin dioxide by Sn-MOF. The types of organic ligands of the tin-containing metal organic framework compound of the present invention are not limited, for example, they can be common nitrogen-containing heterocyclic organic ligands, carboxyl-containing organic ligands, nitrogen-containing heterocyclic and carboxylic acid mixed ligands, phosphine-containing ligands, etc. Preferably, organic carboxylic acids such as 1,4-benzenedicarboxylic acid, 2,6-naphthalene dicarboxylic acid, etc. are used as ligands. The preparation method of the tin-containing metal organic framework compound of the present invention is not limited, and conventional hydrothermal / solvothermal synthesis, ultrasonic method, microwave heating method, electrochemical method and mechanochemical synthesis method can be used. In some specific embodiments of the present invention, the organic carboxylic acid and the base can be dispersed in a solvent at a ratio of hydrogen ions to hydroxide ions of 1:1, and a stannous ion Sn is added. 2+ The tin salt is reacted at a temperature of 20 to 100° C. for 2 to 6 hours, filtered, washed, and dried at 60 to 80° C. to obtain a tin-containing metal organic framework compound; further, the organic carboxylic acid is selected from one or more of aromatic carboxylic acids, aliphatic carboxylic acids, or nitrogen heterocyclic carboxylic acids; the Sn-containing 2+ The stannous salt is selected from one or more of stannous chloride, stannous sulfate or stannous citrate; the solvent can be selected from methanol, water or N,N-dimethylformamide (DMF) or a mixture thereof (such as a mixture of water and DMF); in some specific embodiments of the present invention, the stannous ion Sn 2+The molar ratio of the tin salt to the organic carboxylic acid is 1:1.5 to 3.5. The tin source of the present invention is a precursor to tin dioxide obtained after heat treatment. The present invention uses Sn-MOF as a tin source, which not only promotes the exposure of catalytic sites but also increases the amount of catalyst in the membrane electrode. Compared with the use of tin tetrachloride as a tin source, Sn-MOF can achieve a higher doping amount. Because SnCl4 is an inorganic salt with very limited solubility in organic solvents, when the amount of SnCl4 added is large, it and the carbon source such as polyacrylonitrile may not be able to form a uniform spinning solution; in addition, in some specific embodiments of the present invention, when SnCl4 and Sn-MOF with the same Sn content are doped, the first-order reaction kinetic constant of the Sn-MOF-derived membrane anode for the degradation of propranolol (abbreviated as PRO) is at least 15% higher than that of the SnCl4-derived membrane anode. This may be because the particle diameter of MOFs is larger than the fiber diameter, which can expose more SnO2 and increase the chance of contact with the pollutant solution, while when SnCl4 is used as a precursor, a lot of SnO2 will be wrapped inside the fiber.

[0047] The carbon source of the present invention refers to a material capable of providing carbon fibers, including precursors capable of producing carbon fiber materials or graphitization. In some embodiments of the present invention, the carbon source comprises at least one of a polymer, a polymer precursor, a carbohydrate, and an inorganic carbon source, wherein a polymer precursor in the present invention refers to a substance that can self-polymerize to form a polymer. Preferably, the polymer is selected from high molecular polymers with good spinnability, such as one or more of polyacrylonitrile (PAN), polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyester, polyamide, etc.; the polymer precursor mainly includes polyphenols, and the structure of the polyphenols contains two or more phenolic hydroxyl structures, such as dopamine, dopa, catechol, resorcinol, tannic acid, gallic acid, catechin, anthocyanin, pyrogallol and its salts, hydrates, etc. In addition to polyphenols, the polymer precursor also includes small molecule organic compounds such as formaldehyde; sugars include one or more monosaccharides such as glucose and fructose, oligosaccharides such as sucrose, and polysaccharides; the inorganic carbon source is selected from one or more of graphite felt, carbon felt, graphite paper, carbon paper, carbon cloth and graphite cloth. The difference from the aforementioned organic carbon source is that when the inorganic carbon source is selected, no subsequent heat treatment step is required. In some preferred embodiments of the present invention, the carbon source includes one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, glucose, dopamine, dopamine hydrochloride, dopa, dopa hydrochloride, catechol, resorcinol and formaldehyde. More preferably, the carbon source of the present invention is selected from one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyester and polyamide. In some preferred embodiments of the present invention, the mass ratio of the tin source to the carbon source of the present invention is (0.1-10):1. In order to obtain better electrochemical performance, the mass ratio of the tin source to the carbon source is (0.5-5):1, and more preferably (0.7-1.5):1.

[0048] The forming of the present invention mainly refers to the process of preparing a porous membrane from a tin source and a carbon source. The porous structure can not only provide abundant sites for electrochemical reactions, but also effectively enhance mass transfer during the transmembrane flow of the pollutant solution. The forming method is not particularly limited. In some specific embodiments of the present invention, the forming is selected from one of electrostatic spinning, air spinning, coating film forming, tableting, and sol-gel methods. For example, when an inorganic carbon source is selected, a carbon fiber membrane loaded with tin dioxide can be obtained by coating film forming. In some specific embodiments of the present invention, the forming is selected from electrostatic spinning, which has simple manufacturing equipment, low spinning cost, many types of spinnable materials, and controllable process. Electrostatic spinning refers to the process of jet spinning a polymer solution or melt in a strong electric field. Under the action of the electric field, the droplet at the needle tip will change from a spherical shape to a conical shape, and extend from the tip of the cone to obtain fiber filaments. This method can produce filaments with a nanometer diameter. In some specific embodiments of the present invention, Sn-MOF is added to a solvent as a tin source, stirred or ultrasonically dispersed, and then a high molecular weight polymer with good spinnability such as polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyester, and polyamide is added. After stirring evenly, it is used for electrospinning. The liquid injection rate is 1 to 3 mL / h, the time is 6 to 12 hours, the relative humidity is controlled at 20 to 40%, the positive and negative voltages of the electrospinning are + (12.00 to 16.00) kV and - (6.00 to 8.00) kV, respectively, and the distance from the needle to the rotating shaft is 12 to 18 cm. Furthermore, the aforementioned solvent is selected from an aprotic polar solvent, such as N,N-dimethylformamide. In some specific embodiments of the present invention, the fibers obtained by electrospinning are mainly composed of continuous and uniform carbon fibers with a diameter of about 150 to 400 nm. The incorporation of the catalyst does not have a significant effect on the morphology of the carbon fibers. The Sn-MOF particles are basically embedded in the carbon fibers and have a relatively good connection with the carbon fibers. At the same time, a large area is exposed to the outside, which can effectively contact with pollutants.

[0049] In some embodiments of the present invention, if an organic carbon source is used, the resulting membrane needs to be heat treated after the forming step. This is primarily to graphitize the carbon source. Increasing the degree of graphitization can significantly improve electron transfer efficiency. In some embodiments of the present invention, the heat treatment includes pre-oxidation and carbonization steps. Pre-oxidation ensures toughness during subsequent spinning, and tension is applied during the pre-oxidation process. In some embodiments of the present invention, the electrospun fiber membrane is pre-oxidized in a muffle furnace. The pre-oxidation temperature is increased from room temperature to 260-300°C and maintained for 0.5-3 hours, followed by natural cooling. The carbonization step primarily involves graphitizing the carbon source through oxygen-free calcination. In some embodiments of the present invention, the pre-oxidized spun membrane is placed in a tubular furnace and calcined at high temperature under the protection of an inert gas, such as argon, without oxygen. The carbonization temperature is preferably increased by 0.5-10°C / min, and more preferably by 2-6°C / min. The inventors have discovered that carbonization temperature affects the degree of graphitization of the carbon fibers and the SnO2 content in the membrane anode, thereby affecting its performance. However, catalytic performance and carbonization temperature are not simply positively or negatively correlated. In some embodiments of the present invention, the carbonization temperature is preferably 300-1300°C, preferably 500-1000°C. The inventors have found that carbonization temperature affects the anode in two ways: On the one hand, increasing the carbonization temperature promotes graphitization and improves electron transfer efficiency; on the other hand, high temperatures cause SnO2 to be thermally reduced by carbon, reducing the content of effective catalyst in the tin dioxide anode. The degradation effect shows that of these two factors, the degree of graphitization has a more dominant impact on performance. Therefore, the carbonization temperature of the present invention is more preferably 850-950°C, with 900°C being the optimal carbonization temperature. In some embodiments of the present invention, the carbonization time is 0.5-6 hours, preferably 1-4 hours. The temperature can then be naturally cooled or at a rate of 0.5-10°C / min. After carbonization treatment, the tin dioxide-loaded carbon fiber membrane of the present invention (abbreviated as MOF-SnO2@CF) is obtained. In some specific embodiments of the present invention, the morphology of the Sn-MOF particles loaded on the carbon fiber does not change significantly after heat treatment, except that a few holes appear on the surface of the particles. This is caused by certain changes in the carbon skeleton of Sn-MOF after heat treatment. The inventors found that although MOF-SnO2@CF contains a large amount of elemental Sn, the X-ray photoelectron spectroscopy spectrum can prove the presence of the active component SnO2. In other specific embodiments of the present invention, the MOF-SnO2@CF prepared according to the above method of the present invention has hydrophobic surface properties with a contact angle of 130 to 140°.

[0050] <Cathode>

[0051] In some embodiments of the present invention, the cathode of the membrane electrocatalytic system is selected from one of a transition metal-doped carbon fiber membrane, a stainless steel mesh, a titanium mesh, a carbon felt, and a graphite felt. In some embodiments of the present invention, the transition metal is selected from one or more of manganese, iron, cobalt, nickel, copper, and cerium. Preferably, the transition metal is iron.

[0052] In some specific embodiments of the present invention, a transition metal-doped carbon fiber membrane can be obtained by introducing a transition metal salt as a transition metal source, introducing a carbon source, and forming or forming-heat treatment. The type of the above-mentioned transition metal salt is not particularly limited, for example, it can be selected from one or more of nitrates, halogen salts, acetates, acetylacetonates, sulfates or their hydrates. Furthermore, an iron salt can be used as an iron source, a carbon source is introduced, and an iron-doped carbon fiber membrane is obtained by forming or forming-heat treatment. For the carbon source, reference can be made to the description of the carbon source in the aforementioned anode preparation process. In some specific embodiments of the present invention, the mass ratio of the iron source to the carbon source is (0.1-0.8):1. In order to obtain better electrochemical performance, the mass ratio of the iron source to the carbon source is (0.2-0.6):1, and more preferably (0.3-0.5):1. There is no particular restriction on the forming method. In some specific embodiments of the present invention, the forming is selected from one of electrostatic spinning, air spinning, coating film forming, sheeting method, and sol-gel method. For example, when an inorganic carbon source is selected, a transition metal-doped carbon fiber film can be obtained by coating film forming. In some specific embodiments of the present invention, the forming is selected from electrostatic spinning. More specifically, the iron salt is added to the solvent, stirred or ultrasonically dispersed, and then one or more high molecular polymers with good spinnability such as polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyester, and polyamide are added. After stirring evenly, it is used for electrostatic spinning. The liquid injection speed is 1 to 3 mL / h, the time is 6 to 12 hours, the relative humidity is controlled to 20 to 40%, the positive and negative voltages of the electrostatic spinning are + (5.00 to 9.00) kV and - (8.00 to 12.00) kV, respectively, and the distance from the needle to the rotating shaft is 10 to 14 cm. Furthermore, the aforementioned solvent is selected from aprotic polar solvents, such as N, N-dimethylformamide. In some embodiments of the present invention, the fibers obtained by electrospinning are primarily composed of continuous, uniform carbon fibers with a diameter of approximately 150 to 400 nm, with ferrous acetylacetonate uniformly distributed throughout the fibers. Following the forming step, the resulting membrane undergoes heat treatment, primarily to graphitize the carbon source. Increased graphitization significantly improves electron transfer efficiency. In some embodiments of the present invention, the heat treatment includes pre-oxidation and carbonization steps. Pre-oxidation ensures toughness during subsequent spinning, and tension is applied during the pre-oxidation process. In some embodiments of the present invention, the electrospun fiber membrane is pre-oxidized in a muffle furnace at a heating rate of 1 to 4°C / min, from room temperature to 260 to 300°C, maintained at this temperature for 0.5 to 3 hours, and then allowed to cool naturally. The carbonization step primarily involves graphitizing the carbon source through oxygen-free calcination. In some embodiments of the present invention, the pre-oxidized spun membrane is placed in a tube furnace and calcined at high temperature under an inert gas, such as argon, without oxygen. The carbonization heating rate is preferably 0.5 to 10° C. / min, more preferably 2 to 6° C. / min.In some specific embodiments of the present invention, the carbonization temperature is preferably 300-1300°C, further 500-1000°C, more preferably 850-950°C, and further 900°C is the optimal carbonization temperature. In some specific embodiments of the present invention, the carbonization time is 0.5-6h, further 1-4h. Afterwards, the temperature can be naturally lowered or the cooling rate can be 0.5-10°C / min. After the carbonization treatment, the iron-doped carbon fiber membrane (abbreviated as Fe@CF) of the present invention is obtained. In some specific embodiments of the present invention, after carbonization, the shrinkage of the carbon fiber exposes some small catalyst particles, which are relatively evenly distributed on the fiber surface. It can be seen from the X-ray diffraction pattern that Fe mainly exists in the form of carburized iron. In other specific embodiments of the present invention, the Fe@CF prepared according to the above method of the present invention has hydrophobic surface properties and a contact angle of 130-140°.

[0053] <Membrane Electrocatalytic System>

[0054] Membrane electrocatalytic systems can be divided into three modes according to the difference between the anode and the cathode: anode-dominant mode, cathode-dominant mode and synergistic mode. The membrane electrocatalytic system of the present invention mainly includes anode-dominant mode and synergistic mode. Specifically, in some specific embodiments of the present invention, the anode-dominant mode refers to a carbon fiber membrane loaded with tin dioxide as the anode, and other conventional porous membranes as cathodes and collector layers. The cathode-dominant mode refers to a carbon fiber membrane doped with transition metals such as iron as the cathode, and other conventional porous membranes as cathodes and collector layers. The synergistic mode refers to a carbon fiber membrane loaded with tin dioxide as the anode, a carbon fiber membrane doped with iron as the cathode, and other conventional porous membranes as collector layers. The membrane electrocatalytic system corresponding to this synergistic mode is called a dual-oxidation synergistic membrane electrocatalytic system in the present invention. Conventional porous membranes are not particularly significant, such as stainless steel mesh or titanium mesh. In some preferred embodiments of the present invention, the anode-dominant mode refers to using a carbon fiber membrane loaded with tin dioxide as the anode, and a stainless steel mesh as both the cathode and the collector layer; the cathode-dominant mode refers to using an iron-doped carbon fiber membrane as the cathode, and a stainless steel mesh as both the anode and the collector layer; the synergistic mode refers to using a carbon fiber membrane loaded with tin dioxide as the anode, an iron-doped carbon fiber membrane as the cathode, and a stainless steel mesh as the collector layer. In some specific embodiments of the present invention, the collector layer is connected to the power supply through an annular titanium sheet, and the anode and cathode are separated by a plastic separator and / or a rubber gasket to avoid short circuits. Furthermore, the voltage between the anode and cathode of the dual-oxidation synergistic membrane electrocatalytic system of the present invention is 2 to 5 V, further 3 V, and the membrane flux is 600 to 800 L m -2 h -1 , further 680L m -2 h -1 .

[0055] In some specific embodiments of the present invention, the inventors found that the degradation effect of the anode-dominant mode was significantly greater than that of the cathode-dominant mode, and the degradation effect of the synergistic mode was not only greater than that of the cathode-dominant mode and the anode-dominant mode, but also greater than the sum of the cathode-dominant and anode-dominant modes, achieving a degradation effect of "1+1>2", indicating that the membrane electrocatalytic system not only has the process of pollutant degradation by the anode and cathode, but also has synergy between the anode and cathode. In some specific embodiments of the present invention, the dual-oxidation synergistic membrane electrocatalytic system has a high apparent rate constant for the removal of difficult-to-degrade organic matter such as drugs without the use of aeration and chemicals, and can greatly reduce the toxicity of difficult-to-degrade organic matter, reduce its threat to human health and ecological safety, and has good prospects for removing pollutants. The experimental results of the present invention show that whether it is a semi-batch experiment or a one-time membrane experiment, the dual-oxidation synergistic membrane electrocatalytic system exhibits very excellent degradation performance. In addition, the energy efficiency of the dual-oxidation synergistic membrane electrocatalytic system is significantly improved compared with the single catalytic electrode mode (anode-dominant mode or cathode-dominant mode). The electrical energy required to degrade propranolol per logarithmic concentration pollutant removed in the synergistic mode does not exceed 0.02kWh / m 3 -log, the entire redox process of the electrode is fully utilized.

[0056] Through further research on quenching experiments, the inventors found that the active oxygen species generated by the MOF-SnO2@CF anode during electrochemical oxidation are mainly singlet oxygen. Singlet oxygen is molecular oxygen in an excited electronic state (i.e. 1 O2). It is speculated that the MOF-SnO2@CF anode produces 1 There are two main pathways for O2: (1) Water in the solution is oxidized to hydroxyl radicals on the anode surface, and the main hydroxyl radicals are adsorbed hydroxyl radicals, namely M(·OH) (Equation 1). M(·OH) reacts with superoxide anions (·O2 - ) and electron transfer occurs between them, generating singlet oxygen ( 1 O2)(Equation 2).

[0057] M+H2O→M(·OH)+H + +e - (1)

[0058] M(·OH)+·O2 - → 1 O2+OH - (2)

[0059] The active oxygen species generated at the Fe@CF cathode are mainly superoxide radicals. It is speculated that O2 undergoes a one-electron reduction process at the Fe@CF cathode to produce superoxide radicals (Equation 3).

[0060] O2+e - → O2- (3)

[0061] This also explains why the anode-dominated mode has a significantly better degradation effect on difficult-to-degrade organic matter such as propranolol than the cathode-dominated mode.

[0062] For the cooperative mode, the quenching experiment can show that singlet oxygen is the main active oxygen species in the double-oxidation cooperative film electrocatalytic system, and superoxide radicals will first be converted into 1 O2 then reacts with pollutants. The synergy between the cathode and anode can greatly improve 1 The production of O2 can achieve more efficient degradation of refractory organic matter such as propranolol. The inventors speculate that 1 The increase in O2 production may be mainly due to the O2 generated at the Fe@CF cathode. - Recombination occurs at the MOF-SnO2@CF anode. Specifically, the Fe@CF cathode produces more superoxide anions than the stainless steel mesh cathode, allowing more adsorbed hydroxyl radicals to be converted to singlet oxygen. Because singlet oxygen has high selectivity for drugs like propranolol, and because the energy input is nearly identical to that of the two-half-electrode mode, the entire redox process utilizing the electrodes is highly energy efficient.

[0063] <Water Treatment Method>

[0064] The present invention also provides a water treatment method, which utilizes the aforementioned membrane electrocatalytic system of the present invention. Furthermore, the membrane electrocatalytic system includes an anode-dominant mode or a synergistic mode. In some preferred embodiments of the present invention, considering that the synergistic mode has significantly better degradation effects, the aforementioned dual-oxidation synergistic membrane electrocatalytic system of the present invention is preferably used. The water to be treated in the present invention includes domestic or industrial organic wastewater or drinking water. Furthermore, the organic wastewater includes one or more of coal chemical wastewater, petrochemical wastewater, pharmaceutical wastewater, landfill leachate, printing and dyeing wastewater, and papermaking wastewater. Because the active oxygen species generated by electrochemical oxidation in the present invention are mainly singlet oxygen, the present invention can effectively degrade and remove refractory organic matter in the water to be treated. The membrane electrocatalytic system of the present invention can be used for deep treatment of wastewater. By utilizing the synergistic reaction of the anode and cathode to significantly increase the singlet oxygen yield, the present invention has potential advantages in the selective removal of electron-rich refractory organic matter such as pharmaceuticals from wastewater. In addition, because the present invention is a non-free radical pathway, the present invention has excellent deep treatment effects on tap water, lake water, and even high-salt wastewater (wastewater with a total salt content of at least 1% by mass, calculated as NaCl).

[0065] Example

[0066] The present invention will be further described below through specific embodiments:

[0067] Example 1

[0068] Preparation of tin-containing metal organic framework compound (Sn-MOF): Add 12mmol of terephthalic acid (C8H6O4) and 24mmol of lithium hydroxide (LiOH) to a 100mL mixed solution of deionized water and N,N-dimethylformamide (DMF) in a ratio of 1:1. After the solid is completely dissolved, add 20mL of 0.25M stannous sulfate (SnSO4) solution dropwise, stir at 150rpm for 2h at 25℃, and then separate with a centrifuge (7000rpm, 5min). Wash with DMF (25mL each time) and deionized water (50mL each time) three times each. Finally, put it in an oven to dry (60℃, 12h) to produce a Sn-containing metal organic framework compound, which is recorded as Sn-MOF. The morphology of the obtained product was observed using a scanning electron microscope (see Figure 1 (a) and Figure 1 (b)).

[0069] Preparation of tin dioxide loaded carbon fiber membrane: 2g of the tin-containing metal organic framework compound (Sn-MOF) prepared by the above method was added to 20mL N,N-dimethylformamide and ultrasonicated for 30min to fully disperse it. Then 2g of polyacrylonitrile (Mw=150000) was slowly added and stirred at a speed of 400rpm for 12h. The stirred solution was used for electrospinning, the liquid injection rate was 1.5mL / h, the time was 10h, the relative humidity was controlled at 30%, the positive and negative voltages of electrospinning were +15.00 and -7.50kV respectively, and the distance from the needle (No. 21) to the rotating shaft was 15cm. The morphology of the obtained membrane was observed by scanning electron microscopy (see Figure 1 (e) and Figure 1 (f)). The electrospun membrane was pre-oxidized in a muffle furnace, heated at a rate of 2°C / min, heated to 280°C, held for 2 hours, and then cooled naturally; then carbonized in an argon atmosphere at a rate of 5°C / min, heated to a carbonization temperature of 900°C, held for 1 hour, and then cooled at a rate of 5°C / min to obtain a tin dioxide-loaded carbon fiber membrane (MOF-SnO2@CF). The process flow diagram can be found in Figure 2 (a) The morphology of the product was observed using a scanning electron microscope (see Figure 3 (a)), X-ray photoelectron spectroscopy analysis (see Figure 3 (c)).

[0070] Preparation of iron-loaded carbon fiber membrane: Add 0.98g of ferrous acetylacetonate to 20mL of N,N-dimethylformamide and ultrasonicate for 30min to fully disperse it. Then slowly add 2g of polyacrylonitrile (Mw=150000) and stir at 400rpm for 12h. The stirred solution was used for electrospinning with a liquid injection rate of 1.5mL / h for 10h. The relative humidity was controlled at 30%. The positive and negative voltages of electrospinning were +7.50 and -10.00kV respectively. The distance from the needle (No. 21) to the rotating shaft was 12cm. The morphology of the obtained membrane was observed by scanning electron microscopy (see Figure 1 (g) and Figure 1 (h)). The electrospun membrane was pre-oxidized in a muffle furnace, heated at a rate of 2°C / min, heated to 280°C, held for 2 hours, and then cooled naturally; then carbonized in an argon atmosphere at a rate of 5°C / min, heated to 900°C, held for 1 hour, and then cooled at a rate of 5°C / min to obtain an iron-loaded carbon fiber membrane. The process flow diagram can be found in Figure 2 (a). The morphology of the product was observed using a scanning electron microscope ( Figure 3 (b)), X-ray photoelectron spectroscopy analysis (see Figure 3 (d)) and X-ray diffraction pattern analysis (see Figure 4 ), it can be concluded that the atomic contents of C, N, O, and Fe in Fe@CF are 87.2%, 5.5%, 5.9%, and 1.4%, respectively. From the X-ray diffraction pattern, it can be seen that Fe mainly exists in the form of carburized iron.

[0071] Constructing a synergistic model: using a carbon fiber membrane loaded with tin dioxide as the anode and a carbon fiber membrane loaded with iron as the cathode, with an effective filtration area of ​​7 cm 2 , using stainless steel mesh as the current collecting layer, connected to the power supply through a ring-shaped titanium sheet. The cathode and anode are separated by a 0.3mm thick plastic separator and a 0.5mm thick O-shaped rubber gasket to prevent short circuit. Figure 2 (b) and Figure 2 (c).

[0072] Constructing the anode-dominant mode: using the carbon fiber membrane loaded with tin dioxide as the anode, not using the carbon fiber membrane loaded with iron as the cathode, and using the stainless steel mesh as both the cathode and the current collector. Figure 2 (c).

[0073] Construct cathode dominant mode: use iron-loaded carbon fiber membrane as cathode, do not use tin dioxide-loaded carbon fiber membrane, and stainless steel mesh as anode and collector layer. Figure 2 (c).

[0074] Semi-batch experiment: The feed solution was circulated between the reactor and the reservoir, and the solution in the reservoir was sampled and analyzed.

[0075] One-pass membrane experiment: After the feed solution passes through the reactor, the effluent water is no longer circulated, and the reactor effluent water solution is directly sampled and analyzed.

[0076] Propranolol (PRO) degradation rate test method: The PRO concentration in the solution was determined by high-performance liquid chromatography, and the degradation rate was calculated based on the sample concentration and the starting concentration. The HPLC instrument used was an Agilent 1200LC equipped with a UV detector (λ = 218 nm) and a C-18 column (XDB-C18 Eclipse, Agilent). The mobile phase consisted of a mixture of 70% by volume phosphoric acid (0.1% by volume) and 30% by volume acetonitrile (80%:20% for samples quenched with furfuryl alcohol (FFA) and p-benzoquinone (pBQ). HPLC experimental conditions were: a flow rate of 1 mL / min, a residence time of 7 min, an injection volume of 20 μL, and a column temperature of 30°C.

[0077] <Investigating the performance of different types of carbon fiber membranes>

[0078] Different types of carbon fiber membranes were used as anodes in semi-batch experiments in anode-dominated mode to evaluate their performance.

[0079] Preparation method of pure carbon fiber membrane (CF): Add 2g polyacrylonitrile (Mw=150000) and stir at a speed of 400rpm for 12h. The uniformly stirred solution is used for electrospinning, the liquid injection rate is 1.5mL / h, the time is 10h, the relative humidity is controlled at 30%, the positive and negative voltages of electrospinning are +15.00 and -7.50kV respectively, and the distance from the needle (No. 21) to the rotating shaft is 15cm. The membrane produced by electrospinning is pre-oxidized in a muffle furnace, heated at a rate of 2℃ / min, heated to 280℃ and maintained for 2h, and then cooled naturally; then carbonized in an argon atmosphere, the heating rate is 5℃ / min, heated to the carbonization temperature of 900℃ and maintained for 1h, and then cooled at a rate of 5℃ / min to obtain a pure carbon fiber membrane (CF). The morphology of the obtained pure carbon fiber membrane was observed using a scanning electron microscope (see Figure 1 (c) and Figure 1 (d))

[0080] Preparation method of tin dioxide carbon fiber membrane (SnCl4-SnO2@CF) with tin tetrachloride as precursor: Similar to the preparation method of the tin dioxide-loaded carbon fiber membrane in Example 1, except that Sn-MOF is replaced with tin tetrachloride pentahydrate (SnCl4·5H2O) with the same Sn content. The amount of SnCl4·5H2O with the same Sn content as 0.5g Sn-MOF is 0.368g, and the rest are the same.

[0081] The preparation methods of the tin dioxide carbon fiber film (1 / 4MOF-SnO2@CF) with 0.5g Sn-MOF as a precursor, the tin dioxide carbon fiber film (1 / 2MOF-SnO2@CF) with 1g Sn-MOF as a precursor, and the tin dioxide carbon fiber film (MOF-SnO2@CF) with 2g Sn-MOF as a precursor used in Example 1 are similar, with the only difference being the amount of Sn-MOF used.

[0082] After testing, the degradation rates of propranolol (PRO) using CF, SnCl4-SnO2@CF, 1 / 4MOF-SnO2@CF, 1 / 2MOF-SnO2@CF and MOF-SnO2@CF as anodes were 81.2±0.5, 97.6±0.6, 96.9±1.2, 98.0±0.1 and 97.8±0.1%, respectively (see Figure 5 (a)). It can be seen that no matter which precursor-derived SnO2 catalyst is used, the degradation effect of PRO is significantly better than that of pure carbon fiber membrane (CF), indicating that SnO2 plays a key role in electrochemical oxidation. When doped with SnCl4 and Sn-MOF with the same Sn content, the Sn-MOF-derived membrane anode (0.202±0.017min -1 ) degradation of PRO by the first-order reaction kinetic constant (0.176 ± 0.004 min) than that of the SnCl4-derived membrane anode. -1 ) is 15% higher. This is likely because the MOF particle diameter is larger than the fiber diameter, which allows for greater SnO2 exposure and increases contact with the pollutant solution. When SnCl4 is used as a precursor, much of the SnO2 is encapsulated within the fiber. As the MOF doping level increases, the rate constant for PRO degradation at the membrane anode increases. Therefore, subsequent experiments used MOF-SnO2@CF as the catalytic membrane anode.

[0083] X-ray photoelectron spectroscopy and X-ray diffraction analysis were performed on 1 / 4MOF-SnO2@CF, 1 / 2MOF-SnO2@CF, MOF-SnO2@CF and Sn-MOF to determine their chemical composition and content. With the increase of Sn-MOF doping amount, the atomic content percentage of Sn and O in MOF-SnO2@C fiber membrane also increased (Table 1), while the atomic content percentage of C and N decreased. Although MOF-SnO2@CF contains a large amount of elemental Sn, the Sn 3d 3 / 2 and Sn 3d 5 / 2 The peak proves the existence of the active component SnO2 ( Figure 3 (c)), the characteristic diffraction peak (110) of SnO2 in the X-ray diffraction pattern ( Figure 5 (c)) also proves this point.

[0084] Table 1 Atomic content percentage of each element in SnO2 carbon fiber film and Sn-MOF particles

[0085]

[0086] <Influence of Carbonization Temperature>

[0087] Based on Example 1, the carbonization temperature during the preparation of the tin dioxide-loaded carbon fiber membrane was changed, and the prepared different tin dioxide-loaded carbon fiber membranes were used as the anode of a semi-batch experiment in the anode-dominated mode to perform a propranolol (PRO) degradation rate test, thereby investigating the effect of the carbonization temperature on the performance.

[0088] Figure 5 (b) shows the effect of carbonization temperature on the degradation of propranolol. The performance of MOF-SnO2@CF at different carbonization temperatures was analyzed from the first-order reaction kinetic constants. The order of performance is as follows: 900℃ (0.307±0.015min -1 )>500℃(0.298±0.015min -1 )>800℃(0.247±0.025min -1 )>600℃(0.215±0.028min -1 )>700℃(0.196±0.029min -1 ), that is, there is no simple positive or negative correlation between the anode catalytic performance and the carbonization temperature. In Raman spectroscopy ( Figure 5 (d)), the D peak and G peak of MOF-SnO2@CF appeared at 1355 cm -1 and 1577cm -1The D peak represents the carbon defect and the G peak represents the ordered graphite carbon. As the carbonization temperature increases, the degree of graphitization of the carbon fiber increases. The X-ray spectrum shows that ( Figure 5 (c) After carbonization at 500°C, characteristic peaks of SnO and SnO2 appear in the anode, the components that play a major role in anodic oxidation. Starting at 600°C, characteristic peaks of elemental Sn appear, due to the gradual carbothermal reduction of tin oxide at high temperatures. After carbonization at temperatures above 700°C, the anode is primarily composed of elemental Sn. The degradation effect indicates that 900°C is the optimal carbonization temperature.

[0089] <Effects of different modes on degradation rate>

[0090] In the semi-intermittent experiment ( Figure 6 (a)), the degradation rate of propranolol in the synergistic mode of Example 1 (98.0±2.0%) was increased by 34% compared with the cathode-dominated mode of Example 1 (72.9±1.5%). Although the degradation effect was very similar to that of the anodic mode of Example 1 in the later stage of the reaction, the degradation rate of the synergistic mode was significantly faster than that of the anode-dominated mode in the early stage. Further analysis of the first-order reaction kinetic constants showed that the first-order reaction kinetic constant of the synergistic mode (0.415±0.028min -1 ) is not only greater than the cathode-dominated mode (0.086±0.015min -1 ) and anode-dominated mode (0.307±0.015min -1 ), and is greater than the sum of the cathode-dominated and anode-dominated modes, achieving a degradation effect of "1+1>2", indicating that the membrane electrocatalytic system not only has the process of pollutant degradation by the anode and cathode respectively, but also a synergistic process between the anode and cathode.

[0091] Compared with previous studies (Table 2), the dual-oxidation synergistic membrane electrocatalytic system showed the highest apparent rate constant for PRO removal without the use of aeration and chemicals. At low current densities, the normalized apparent rate constant significantly exceeded the value calculated from data in previous studies, indicating that the dual-oxidation synergistic membrane electrocatalytic system has good prospects for pollutant removal.

[0092] Table 2 Comparison of propranolol degradation effects in different studies

[0093]

[0094]

[0095]

[0096] *: Estimated from figures in the corresponding literature.

[0097] The degradation rate calculation formula is as follows: Where V is the volume of the solution (L), C0 is the initial concentration of propranolol (mg / L), R is the degradation rate (%), and A is the active area of ​​the electrode (m 2 ), t is the reaction time (min).

[0098] The normalized apparent reaction rate constant is calculated as follows: Where k is the apparent rate constant (min -1 ), I is the current used (A).

[0099] Analysis of the oxidation products of PRO in synergistic mode revealed that ( Figures 7 to 9 ), 3-isopropylamino-1,2-propanediol and its two decomposition products were detected, while other compounds were largely undetectable, indicating that no detectable concentrations of benzenes, phenols, and cyclic compounds were produced. These results demonstrate that the dual-oxidation synergistic membrane electrocatalytic system can significantly reduce the toxicity of PRO, thereby alleviating its threat to human health and ecological safety.

[0100] Although semi-batch experiments are beneficial for the analysis of reaction kinetics, the degradation effect of a one-pass membrane experiment is often more meaningful for practical applications. Figure 6 (b)), the synergistic mode showed very excellent degradation performance. The degradation rate of PRO reached 97.5±1.7% within a residence time of about 2.9s, and the degradation effect remained stable in the later period, with no trend of decreasing degradation effect. It can be clearly seen that the degradation effect of the synergistic mode on PRO is much better than the other two modes. Compared with the cathode-dominated (24.2±7.3%) and anode-dominated modes (68.8±3.3%), the degradation rates increased by approximately 303% and 41%, respectively. Compared with the sum of the degradation rates of the cathode-dominated and anode-dominated modes, there is also an increase of more than 4%, which further verifies the synergistic effect between the anode and cathode. The membrane used in the single filtration experiment was characterized to evaluate its stability. From Figure 10 It can be seen that compared with the original membrane, the morphology and chemical composition of MOF-SnO2@CF and Fe@CF membranes do not change much, indicating that the fiber membrane has high stability.

[0101] <Effects of different modes on energy efficiency>

[0102] The electrical energy per order (Electrical energy per order, E EO ) is a very useful indicator for evaluating the energy efficiency of the system. EO is the electrical energy required to remove each level of pollutant concentration, and is calculated as follows:

[0103]

[0104] Where U, I, and Q are the voltage (V), current (A), and flow rate (m 3 / h), C f and C p are the pollutant concentrations in the inlet and outlet water (mg / L), respectively.

[0105] According to the data from the one-pass membrane experiment, the E of PRO degradation in the synergistic mode was calculated. EO (0.02kWh / m 3 -log) compared to cathode-dominated mode (0.03 kWh / m 3 -log), anode dominant mode (0.05kWh / m 3 -log) decreased by 33% and 60%, respectively, indicating that the synergy between the cathode and anode can greatly improve the energy efficiency of the electrochemical oxidation process, because the entire redox process of the electrode is fully utilized.

[0106] <Analysis of Reactive Oxygen Species>

[0107] The main reactive oxygen species produced by Fe@CF were analyzed by quenching experiments in the cathode-dominated mode. Figure 11 (a) can be seen ( Figure 11 The control in the experiment refers to the degradation experiment without adding any quencher, and the adsorption refers to the degradation experiment conducted at open circuit voltage without adding any quencher). After adding p-benzoquinone to quench superoxide radicals, the degradation rate decreased significantly. However, after adding furfuryl alcohol and tert-butanol to quench singlet oxygen and hydroxyl radicals respectively, the degradation effect did not change much, indicating that singlet oxygen and hydroxyl radicals were basically not generated. The electron paramagnetic resonance spectrum ( Figure 12 (e) and Figure 12 (f)) There is almost no 2,2,6,6-tetramethyl-4-piperidone-singlet oxygen conjugate (TEMP- 1 This is also confirmed by the signals of the superoxide radicals and the combination of 5,5-dimethyl-1-pyrroline-N-oxide and hydroxyl radicals (DMPO-·OH). Therefore, the active oxygen species generated by the Fe@CF cathode are mainly superoxide radicals.

[0108] The active oxygen species ( Figure 11(b)). When tert-butanol and p-benzoquinone were used as quenchers, the degradation effect of the anode on PRO decreased slightly, indicating that a small amount of hydroxyl radicals and superoxide radicals were generated in the system. When methanol was used as a quencher, the degradation effect decreased significantly. Since methanol can not only quench hydroxyl radicals in the solution, but also quench adsorbed hydroxyl radicals, it can be inferred that the MOF-SnO2@CF anode can produce more adsorbed hydroxyl radicals and a small amount of free hydroxyl radicals. After the addition of furfuryl alcohol, the degradation curve changed very significantly, and the PRO concentration showed a trend of first decreasing and then increasing, and finally basically remained the same as the adsorption curve. This shows that after the addition of furfuryl alcohol, the SnO2 anode basically did not degrade PRO, and the main adsorption process occurred, proving that singlet oxygen is the most important active oxygen species in anodic oxidation, and the large amount of adsorbed hydroxyl radicals, a small amount of free hydroxyl radicals and superoxide anions mentioned above are almost all first converted into singlet oxygen and then react with pollutants. It can be seen from the electron sequential resonance spectrum ( Figure 12 (c) and Figure 12 (d)), after adding 2,2,6,6-tetramethyl-4-piperidone, TEMP- 1 The characteristic triplet peak of O2 was detected, while when 5-dimethyl-1-pyrroline-N-oxide was used to capture free hydroxyl radicals, there was basically no DMPO-·OH signal, which further verified that the active oxygen species generated by the MOF-SnO2@CF anode during the electrochemical oxidation process were mainly singlet oxygen, which also explained that the anode-dominated mode had a better degradation effect on PRO.

[0109] The active oxygen species ( Figure 11 (c)). After adding tert-butyl alcohol, the degradation curve changed very little, indicating that the free ·OH contributed little to the process; after adding p-benzoquinone, the degradation effect decreased to a certain extent; and after adding furfuryl alcohol, a trend similar to the furfuryl alcohol quenching experiment in the anode-dominated mode first decreased and then increased, and finally reached the same level as the adsorption curve. This shows that singlet oxygen is the main active oxygen species in the electrocatalytic membrane system, and superoxide radicals will first be converted into 1 O2 then reacts with the pollutants. The electron paramagnetic resonance spectrum shows obvious TEMP- 1 O2 signal, but no DMPO-·OH signal was detected ( Figure 12 (a) and Figure 12 (b)) further verifies the above conclusion.

[0110] Since the lifetime of singlet oxygen in heavy water (D2O) is much longer (up to 60μs) than in water (3-4μs), a 50% heavy water solution was used for probe degradation experiments and fluorescence emission spectroscopy tests. The removal efficiency of the singlet oxygen probe furfuryl alcohol by the synergistic dual oxidation synergistic membrane electrocatalytic system was 96.1±0.9% in 50% D2O solution and 86.2±4.7% in water solution. Figure 11 (e)), the first-order reaction kinetic constant of 50% D2O solution (0.134±0.005min -1 ) than aqueous solution (0.080±0.009min -1 ) is 66% higher. The concentration of singlet oxygen is measured by fluorescence emission spectroscopy by measuring the fluorescence intensity of the probe and the singlet oxygen adduct. The fluorescence intensity of the adduct in 50% D2O is 21.4% higher than that in aqueous solution ( Figure 11 (f)). When the furfuryl alcohol concentration is 100 mM, the aqueous solution exhibits the lowest intensity, as furfuryl alcohol has already quenched most of the singlet oxygen. The improved performance in a 50% D2O solution further confirms the dual-oxidation synergistic membrane electrocatalytic system for singlet oxygen generation.

[0111] The three different modes of TEMP- 1 O2 signal comparison ( Figure 11 (d)), it was found that the signal intensity generated by the cooperative mode was significantly stronger than that of the other two modes. 1 The ratio of O2 peak area to Mn standard peak area (I sig / I Mn ), which can be used to relatively quantitatively analyze the 1 O2 concentration. Synergistic mode I sig / I Mn (5.04) is much larger than the sum of modes 1 (0.22) and 2 (1.51), and is about 3.3 times that of the anode-dominated mode, indicating that the synergy between the cathode and anode can greatly improve the 1 The production of O2 can achieve efficient degradation of PRO. Based on the analysis of reactive oxygen species produced in various modes, it can be inferred that 1 The increase in O2 production may be mainly due to the O2 generated at the Fe@CF cathode. - Recombination occurs at the MOF-SnO2@CF anode ( Figure 11 (g)).

[0112] <Effects of different water qualities on propranolol degradation>

[0113] Using the collaborative mode of Example 1, 5 mg / L propranolol (PRO) solution was prepared with deionized water, tap water and lake water as solvents to conduct degradation experiments in semi-batch mode. The results are shown in Figure 13 .Depend on Figure 13 It can be seen that although tap water and lake water contain a variety of anions, cations and other impurities, the degradation curve has no obvious difference from that when deionized water is used as the solvent, indicating that the process of PRO degradation by this system has excellent anti-interference ability and can still efficiently degrade PRO in complex water quality.

[0114] Industrial applicability

[0115] The technical solution disclosed in the present invention can be applied in industry.

Claims

1. A membrane electrocatalytic system, characterized in that: The anode of the membrane electrocatalytic system is a carbon fiber membrane loaded with tin dioxide. The carbon fiber membrane loaded with tin dioxide uses a tin-containing metal organic framework compound as a tin source, introduces a carbon source, and is prepared by molding or molding-heat treatment.

2. The membrane electrocatalytic system according to claim 1, characterized in that The carbon source is selected from at least one of a polymer, a polymer precursor, a sugar and an inorganic carbon source.

3. The membrane electrocatalytic system according to claim 2, characterized in that: The polymer is selected from one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, polyester, and polyamide, and the inorganic carbon source is selected from one or more of graphite felt, carbon felt, graphite paper, carbon paper, carbon cloth, and graphite cloth.

4. The membrane electrocatalytic system according to any one of claims 1 to 3, characterized in that: The mass ratio of the tin source to the carbon source is (0.1-10):

1.

5. The membrane electrocatalytic system according to any one of claims 1 to 3, characterized in that: The forming is selected from one of electrostatic spinning, air spinning, coating film forming, tableting method and sol-gel method.

6. The membrane electrocatalytic system according to claim 5, characterized in that: The heat treatment includes pre-oxidation and carbonization steps.

7. The membrane electrocatalytic system according to claim 6, characterized in that: The carbonization temperature of the carbonization step is 300-1300°C.

8. The membrane electrocatalytic system according to any one of claims 1 to 3, characterized in that: The cathode of the membrane electrocatalytic system is selected from one of a carbon fiber membrane doped with a transition metal, a stainless steel mesh, a titanium mesh, a carbon felt, and a graphite felt.

9. A dual-oxidation synergistic membrane electrocatalytic system, characterized in that: The invention comprises an anode and a cathode. The anode is a carbon fiber membrane loaded with tin dioxide. The carbon fiber membrane loaded with tin dioxide is prepared by using a tin-containing metal organic framework compound as a tin source, introducing a carbon source, and forming or forming-heat treatment. The cathode is an iron-doped carbon fiber membrane.

10. The dual-oxidation synergistic membrane electrocatalytic system according to claim 9, characterized in that: The iron-doped carbon fiber membrane is prepared by using iron salt as an iron source, introducing a carbon source, and forming or forming-heat treatment.

11. A water treatment method, characterized in that: The water treatment method adopts the membrane electrocatalytic system according to any one of claims 1 to 8 or the dual-oxidation synergistic membrane electrocatalytic system according to any one of claims 9 or 10.

12. The water treatment method according to claim 11, characterized in that: The active oxygen species generated by the electrochemical oxidation method are mainly singlet oxygen.

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