A catalyst gradient distribution monatomic nanofiber catalytic membrane, a preparation method and application thereof

Abstract

The present application relates to a kind of catalyst gradient distribution single-atom nanofiber catalytic membrane, its preparation method and application, belong to membrane separation-catalysis coupling and sewage treatment technical field.The technical problems that catalytic membrane in prior art cannot effectively treat high-salinity wastewater, catalyst and active oxygen utilization rate are low.The single-atom nanofiber catalytic membrane of the present application includes nanofiber base membrane and metal-C3N4 single-atom catalyst gradient distribution on the surface of nanofiber base membrane.The preparation method of the present application first synthesizes metal-C3N4 single-atom catalyst;Then configure different concentration metal-C3N4 single-atom catalyst spinning solution;Finally, gradient spinning, pore making, drying are carried out, obtain single-atom nanofiber catalytic membrane, realize the stable load of single-atom catalyst in catalytic membrane, and realize the gradient distribution of hole channel singlet oxygen concentration, greatly improve the catalytic degradation efficiency of nanofiber catalytic membrane to organic pollutant molecule.

Description

Technical Field

[0001] This invention relates to a single-atom nanofiber catalytic membrane for generating singlet oxygen, and more particularly to a highly active metal-C3N4 single-atom catalyst gradient distribution nanofiber catalytic membrane, its preparation method, and its application in degrading high-salt, high-concentration organic pollutant wastewater. It belongs to the field of membrane separation-catalysis coupling and wastewater treatment technology. Background Technology

[0002] Advanced oxidation technologies (AORs) are widely used in wastewater treatment processes due to their high mineralization efficiency for organic pollutants. For example, AOR processes such as ozone oxidation, Fenton / Fenton-like reactions, UV radiation, and electrochemical oxidation can all generate reactive oxygen species, thereby degrading recalcitrant organic matter. Commonly used heterogeneous catalytic ozone oxidation and Fenton reactions convert toxic pollutants into less toxic molecules or short-chain compounds by generating hydroxyl radicals (·OH). However, inorganic ions (such as Cl-) in actual wastewater... - HCO3 - NO3 - (etc.) and natural organic matter (NOM) quench ·OH, leading to a decrease in the decomposition rate of pollutants; in contrast, non-free radicals such as singlet oxygen (etc.) 1 O2 (oxygen ions) is a molecular oxygen in an excited paramagnetic state. It possesses both strong oxidizing properties and resistance to anion interference, making it particularly suitable for catalytic oxidation reactions in high-salt, high-concentration organic environments. How to achieve advanced oxidation processes... 1 The specific generation of O2 is key to the efficient treatment of high-salinity wastewater.

[0003] Current research reports on the catalytic activation of potassium permonosulfate (PMS) to form potassium permonosulfate using materials such as transition metal oxides and carbon-based metal catalysts derived from metal-organic frameworks (MOFs). 1 O2, however, its catalytic activity and selectivity are suppressed due to the unavoidable aggregation of active sites. Single-atom catalysts, with their atomically dispersed metal active sites, unique electronic structure, and maximized atom utilization, exhibit excellent oxidation activation ability and high selectivity in catalytic reactions, making them ideal for activating PMS and selectively generating O2. 1 Highly efficient catalysts for O2. In traditional batch advanced oxidation processes, catalyst powder is suspended in solution, and catalyst nanoparticles are prone to agglomeration, resulting in low exposure of catalytic active sites; nanoparticles are difficult to recover, leading to catalyst loss; reactive oxygen species and contaminants rely on diffusion for mass transfer, but due to the limited diffusion distance of reactive oxygen species, most contaminants in the bulk solution cannot come into contact with reactive oxygen species, resulting in low utilization of reactive oxygen species and low degradation rate of contaminants. Anchoring nanocatalytic particles on porous or large-particle supports is an effective method to improve their dispersibility, stability, and recyclability.

[0004] Membrane catalysis is a novel membrane process that combines membrane separation with catalysis. Catalytic membranes possess micron- and nano-scale pores, allowing nanocatalysts to be loaded into confined channels. This confines catalytic active sites, oxidants, and contaminants within a limited space, shortening the diffusion distance of oxidants and contaminants to the active surface and maximizing reactant contact. Simultaneously, the catalytic interface within the pores adsorbs reactants, generating concentration polarization that facilitates effective collisions between reactive oxygen species and contaminants. Therefore, the contaminant degradation efficiency of catalytic membranes is significantly higher than that of catalyst powders. In particular, the coupling of nanofiber membranes with catalysts overcomes the poor permeability of traditional nanocatalytic membranes. Chinese patent (CN117299206A) discloses a simple method for preparing an iron oxide / polyetherimide nanofiber catalytic membrane. The method involves preparing a polyetherimide nanofiber membrane using electrospinning, followed by immersion in a catalyst precursor solution, where iron oxide grows in situ on the fiber surface. This catalytic membrane activates hydrogen peroxide to generate free radicals for efficient pollutant degradation, but its effectiveness in treating high-salinity wastewater is limited. Furthermore, the catalyst is uniformly distributed within the membrane, resulting in high reactive oxygen species concentrations even at the downstream end of channels with lower pollutant concentrations, leading to decreased catalyst and reactive oxygen species utilization. How to prepare activated PMS to generate free radicals... 1 The development of single-atom nanofiber catalytic membranes for O2, and the achievement of gradient distribution of the catalyst to improve reactive oxygen species and catalyst utilization, remains an unsolved technical challenge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a single-atom nanofiber catalytic membrane with a gradient catalyst distribution, its preparation method, and its applications. The single-atom catalyst inside the nanofiber catalytic membrane of this invention exhibits a gradient distribution of mass fraction, resulting in high utilization of catalytic active sites and a high proportion of dominant generation of highly active singlet oxygen, making it particularly suitable for the treatment of high-salt, high-concentration wastewater.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0007] The first aspect of the present invention provides a single-atom nanofiber catalytic membrane with a catalyst gradient distribution, comprising a nanofiber substrate membrane and a metal-C3N4 single-atom catalyst gradient distributed on the surface of the nanofiber substrate membrane.

[0008] Preferably, the nanofiber base film has a thickness of 100-300 micrometers, an average pore size of 0.1-1.0 micrometers, and is made of one of polyacrylonitrile, polyvinylidene fluoride, and polyethersulfone.

[0009] Preferably, the particle size of the metal-C3N4 single-atom catalyst is no greater than 1 micrometer; more preferably, the particle size of the metal-C3N4 single-atom catalyst is 40 to 400 nanometers.

[0010] Preferably, the content of the metal-C3N4 single-atom catalyst in the single-atom nanofiber catalytic membrane is 1wt% to 10wt%; more preferably, the mass ratio of the metal-C3N4 single-atom catalyst in the single-atom nanofiber catalytic membrane is 3wt% to 6wt%.

[0011] Preferably, the single-atom nanofiber catalytic membrane activates potassium hydrogen sulfate to generate singlet oxygen, and the generated singlet oxygen accounts for 70-100 mol% of the total active oxygen.

[0012] A second aspect of this invention provides a method for preparing a single-atom nanofiber catalytic membrane with a catalyst gradient distribution, comprising the following steps:

[0013] S1. Prepare precursor A solution, precursor B solution and precursor C solution respectively;

[0014] The precursor A solution is an aqueous solution containing a metal salt and an acid; the precursor B solution is an aqueous solution containing cyanuric acid and / or ammonium sulfate; the precursor C solution is an aqueous solution containing melamine and / or urea.

[0015] S2. Mix and stir the precursor A solution obtained in step S1 with the precursor B solution to obtain the precursor D solution;

[0016] S3. Mix and stir the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 to obtain complex solution E, and then filter to obtain the complex.

[0017] S4. The complex obtained in step S3 is dried and ground, and then calcined at 400-600℃ to obtain a metal-C3N4 single-atom catalyst.

[0018] S5. Add the dried polymer particles, the metal-C3N4 single-atom catalyst obtained in step S4, and the pore-forming agent to the solvent and heat and stir to uniformly disperse the metal-C3N4 single-atom catalyst, and adjust the mass fraction of the metal-C3N4 single-atom catalyst to obtain spinning solutions with different metal-C3N4 single-atom catalyst concentrations.

[0019] S6. The spinning solution obtained in step S5 is placed in an electrospinning machine for spinning. During the process, spinning solutions with different concentrations of single-atom catalysts are replaced to obtain a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction.

[0020] S7. The nanofiber catalytic membrane obtained in step S6 is immersed in a solution to form pores, and then dried to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution.

[0021] Preferably, in step S1, the metal salt is at least one of cobalt salt, iron salt, nickel salt, and manganese salt; and the acid is at least one of oxalic acid and citric acid.

[0022] Preferably, in step S1, the concentration of the metal salt in solution A is 1–10 mmol / L, and the concentration of the acid is 10–35 mmol / L; the concentration of solution B is 10–40 mmol / L; and the concentration of solution C is 10–90 mmol / L.

[0023] More preferably, in solution A, the concentration of the metal salt is 2–10 mmol / L and the concentration of the acid is 10–30 mmol / L; the concentration of solution B is 10–20 mmol / L; and the concentration of solution C is 10–30 mmol / L.

[0024] Preferably, in step S2, the mixing and stirring time is 0.5 to 2 hours.

[0025] Preferably, in step S3, the mixing and stirring time is 4 to 8 hours; and the filtration method is vacuum filtration.

[0026] Preferably, step S4 is as follows: the complex is placed in a vacuum oven and dried at 60-80°C overnight, then ground to obtain a powdered complex. The powdered complex is then placed in a tube furnace and heated to 400-600°C at a rate of 2-5°C / min in an inert atmosphere. The temperature is maintained for 4-6 hours, and then naturally cooled to room temperature to obtain a metal-C3N4 single-atom catalyst.

[0027] Preferably, in step S5, the polymer is one of polyacrylonitrile, polyvinylidene fluoride, and polyethersulfone.

[0028] The pore-forming agent is one of polyvinylpyrrolidone and polyethylene glycol;

[0029] The solvent is one of N-methylpyrrolidone, dimethylamide, and acetone;

[0030] In the spinning solution, the mass percentages of the dried polymer particles, the pore-forming agent, and the metal-C3N4 single-atom catalyst obtained in step S4 are 6-18 wt%, 2-12 wt%, and 1-10 wt%, respectively.

[0031] The heating and stirring temperature is 60-80℃, and the stirring time is 6-12 hours.

[0032] Preferably, step S6 is as follows: spinning with a spinning solution containing 7wt% to 10wt% of metal-C3N4 single-atom catalyst for 3 to 6 hours, then replacing the spinning solution with a concentration of 4wt% to 6wt% of metal-C3N4 single-atom catalyst and continuing spinning for 3 to 6 hours, then replacing the spinning solution with a concentration of 1wt% to 3wt% of metal-C3N4 single-atom catalyst and continuing spinning for 3 to 6 hours, to obtain a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction;

[0033] The spinning conditions are: ambient humidity 25-65%RH, spinning distance 5-20cm, spinning voltage 5-25kV, and feed rate 0.1-0.5mm / min.

[0034] Preferably, step S7 is as follows: immerse the nanofiber catalytic membrane in deionized water, sonicate it in a water bath for 0.5 to 1.5 hours, and place it at 50°C to 70°C for 24 to 48 hours to wash away the pore-forming agent, and then dry it to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution.

[0035] A third aspect of the present invention provides the application of the above-mentioned catalyst gradient-distributed single-atom nanofiber catalytic membrane in wastewater treatment, wherein the catalyst gradient-distributed single-atom nanofiber catalytic membrane activates persulfate to generate singlet oxygen, thereby oxidizing and degrading pollutants in wastewater.

[0036] Preferably, the conditions for the oxidative degradation of pollutants in wastewater by the single-atom nanofiber catalytic membrane with gradient catalyst distribution are: reaction temperature 20-40℃, reaction pH 2-10, salt content 0-20000ppm, and persulfate addition amount 0.5-4mM.

[0037] More preferably, the salt content is 5000 to 20000 ppm.

[0038] Preferably, the contaminant is at least one of antibiotics, endocrine disruptors, and dyes.

[0039] More preferably, the antibiotic is at least one of tetracycline, sulfonylurea, and penicillin; the endocrine infectious agent is at least one of bisphenol A, phthalate, and alkylphenol; and the dye is at least one of methylene blue, rhodamine B, orange yellow G, and Gangu red.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] 1) This invention uses a blending-electrospinning method to load and interweave single-atom catalysts on and inside the membrane fiber surface. Compared with existing processes such as vacuum filtration, impregnation-calcination, etc., this improves the stability of single-atom catalysts loaded in the membrane. At the same time, the single-atom nanofiber catalytic membrane has a crisscross fiber structure with high porosity and good pore connectivity, which improves the membrane permeability of the catalytic membrane.

[0042] 2) This invention achieves a gradient distribution of single-atom catalysts inside the nanofiber membrane, thereby achieving a gradient distribution of active oxygen concentration within the membrane pores, matching it with the gradually decreasing pollutant concentration within the pores. Compared to current catalytic membranes where the catalyst is uniformly distributed inside the membrane, this invention significantly improves the utilization rate of both the catalyst and active oxygen, while reducing the amount of catalyst added while ensuring excellent catalytic degradation effects.

[0043] 3) This invention greatly improves the catalytic degradation efficiency of nanofiber membranes for organic pollutants, enabling the immediate filtration and catalytic degradation of small organic molecules in wastewater; the membrane efficiently activates persulfate and selectively generates singlet oxygen, achieving a mineralization rate of over 60% for high-salt, high-concentration refining wastewater; at the same time, the membrane has good reusability, providing a new and effective method for wastewater treatment. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are only some specific embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of step S6 of the preparation method of the present invention, which involves preparing a nanofiber catalytic membrane with a gradient distribution of the mass fraction of a single-atom catalyst.

[0046] Figure 2 The single-atom nanofiber catalytic membrane prepared in Example 1 of this invention activates PMS to generate singlet oxygen. 1 Image showing the detection results for O2. Detailed Implementation

[0047] To further understand the present invention, preferred embodiments of the present invention are described below. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0048] The catalyst gradient distribution single-atom nanofiber catalytic membrane of the present invention includes a nanofiber base membrane and a metal-C3N4 single-atom catalyst gradient distributed on the surface of the nanofiber base membrane.

[0049] In this invention, the preferred thickness of the nanofiber substrate membrane is 100–300 micrometers, with an average pore size of 0.1–1.0 micrometers. The material includes, but is not limited to, polyacrylonitrile, polyvinylidene fluoride, and polyethersulfone. The particle size of the metal-C3N4 single-atom catalyst is no greater than 1 micrometer. The content of the metal-C3N4 single-atom catalyst in the single-atom nanofiber catalytic membrane with a catalyst gradient distribution is 1–10 wt%. It is understood that when the metal-C3N4 single-atom catalyst is mixed into the spinning solution for spinning, smaller catalyst particles are easily buried in the membrane matrix, thus affecting the exposure rate of catalytic active sites; while larger catalyst particles have a greater impact on the porosity and stability of the single-atom nanofiber catalytic membrane. Simultaneously, it is understood that a lower catalyst loading will reduce the single-cycle catalytic degradation efficiency of the single-atom nanofiber catalytic membrane; while a higher catalyst loading will have a greater impact on the pore size and porosity of the single-atom nanofiber catalytic membrane, leading to a decrease in membrane permeability. Based on comprehensive experimental verification and membrane system operating cost estimation, this invention preferably uses a metal-C3N4 single-atom catalyst with a particle size of 40-400 nanometers and a metal-C3N4 single-atom catalyst content of 3wt%-6wt% in the single-atom nanofiber catalytic membrane.

[0050] In this invention, it is preferred that a single-atom nanofiber catalytic membrane is used to activate potassium persulfate to generate singlet oxygen, with the generated singlet oxygen accounting for 70-100 mol% of the total active oxygen.

[0051] The method for preparing a single-atom nanofiber catalytic membrane with a catalyst gradient distribution according to the present invention includes the following steps:

[0052] S1. Prepare precursor A solution, precursor B solution and precursor C solution respectively;

[0053] The precursor A solution is an aqueous solution composed of a metal salt such as cobalt, iron, nickel, or manganese, an acid such as oxalic acid or citric acid, and water in any proportion; the concentration of the metal salt in solution A is 1–10 mmol / L, and the concentration of the acid is 10–35 mmol / L; the precursor B solution is an aqueous solution composed of a monomer such as cyanuric acid or ammonium sulfate and water in any proportion; the concentration of solution B is 10–40 mmol / L; the precursor C solution is an aqueous solution composed of a monomer such as melamine or urea and water in any proportion; the concentration of solution C is 10–90 mmol / L.

[0054] S2. Mix the precursor A solution obtained in step S1 with the precursor B solution and stir for 0.5 to 2 hours to obtain the precursor D solution.

[0055] S3. Mix the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 and stir for 4-8 hours to obtain complex solution E, and then filter to obtain the complex.

[0056] S4. The complex obtained in step S3 is placed in a vacuum oven and dried at 60-80°C overnight. Then, it is ground to obtain a powdered complex. The powdered complex is then placed in a tube furnace and heated to 400-600°C at a rate of 2-5°C / min in an inert atmosphere (such as nitrogen). The temperature is maintained for 4-6 hours and then naturally cooled to room temperature to obtain a metal-C3N4 single-atom catalyst.

[0057] S5. Add the dried polymer particles, the metal-C3N4 single-atom catalyst obtained in step S4, and the pore-forming agent to the solvent and heat and stir at 60℃~80℃ for 6~12h to uniformly disperse the metal-C3N4 single-atom catalyst. Adjust the mass fraction of the metal-C3N4 single-atom catalyst to obtain spinning solutions with different metal-C3N4 single-atom catalyst concentrations.

[0058] The polymer is one of polyacrylonitrile, polyvinylidene fluoride, polyethersulfone, etc., the pore-forming agent is one of polyvinylpyrrolidone, polyethylene glycol, etc., the solvent is one of N-methylpyrrolidone, dimethylamide, acetone, etc., and the contents of polymer, pore-forming agent and metal-C3N4 single-atom catalyst in the spinning solution are 6wt%~18wt%, 2wt%~12wt%, and 1wt%~10wt%, respectively.

[0059] S6. Spinning with a spinning solution containing 7wt%–10wt% metal-C3N4 single-atom catalyst for 3–6 hours, then replacing the spinning solution with a concentration of 4wt%–6wt% metal-C3N4 single-atom catalyst and continuing spinning for 3–6 hours, then replacing the spinning solution with a concentration of 1wt%–3wt% metal-C3N4 single-atom catalyst and continuing spinning for 3–6 hours, finally obtaining a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction; the process parameters for the spinning process are: ambient humidity 25–65%RH, spinning distance 5–20cm, spinning voltage 5–25kV, and feed rate 0.1–0.5mm / min;

[0060] S7. Immerse the nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction obtained in step S6 into deionized water, sonicate it in a water bath for 0.5 to 1.5 hours, and place it at 50°C to 70°C for 24 to 48 hours to wash away the pore-forming agent. Then dry it to obtain the single-atom nanofiber catalytic membrane with a gradient distribution of catalyst.

[0061] The single-atom nanofiber catalytic membrane with gradient catalyst distribution of the present invention can be used in wastewater treatment. Under certain temperature, pH and salt content, the single-atom nanofiber catalytic membrane with gradient catalyst distribution activates persulfate to generate active oxygen mainly in the singlet state, thereby oxidizing and degrading pollutants in wastewater.

[0062] In this invention, the pollutant can be at least one of antibiotics, endocrine disruptors, and dyes. Specifically, the antibiotic is at least one of tetracycline, sulfonylurea, and penicillin; the endocrine disruptor is at least one of bisphenol A, phthalates, and alkylphenols; and the dye is at least one of methylene blue, rhodamine B, orange yellow G, and Congo red.

[0063] In this invention, the preferred conditions for the oxidative degradation of pollutants in wastewater using a single-atom nanofiber catalytic membrane with a gradient catalyst distribution are: reaction temperature of 20–40°C, reaction pH of 2–10, salt content of 5000–20000 ppm, and persulfate addition of 0.5–4 mM. Testing showed that the single-atom nanofiber catalytic membrane with a gradient catalyst distribution can achieve a pollutant mineralization rate of over 60% in the degradation of high-salt refining wastewater with a salt content greater than 5000 ppm. It is understood that the single-atom nanofiber catalytic membrane with a gradient catalyst distribution of this invention exhibits equivalent catalytic degradation performance in the treatment of low-salt or salt-free wastewater environments.

[0064] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to embodiments.

[0065] In the following embodiments, various processes and methods not described in detail are conventional methods known in the art. Unless otherwise specified, the materials, reagents, apparatus, instruments, equipment, etc., used in the following embodiments are commercially available.

[0066] Example 1

[0067] S1. Add 0.15 g of ferric nitrate nonahydrate and 0.15 g of oxalic acid to 100 g of water to obtain precursor A solution; add 0.6 g of cyanuric acid to 125 g of water to obtain precursor B solution; add 0.8 g of melamine to 160 g of water to obtain precursor C solution.

[0068] S2. Mix the precursor A solution obtained in step S1 with the precursor B solution and stir for 0.5 h to obtain the precursor D solution;

[0069] S3. Mix the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 and stir for 4 hours to obtain complex solution E, and then filter to obtain the complex.

[0070] S4. The complex obtained in step S3 is placed in a vacuum oven and dried at 60°C overnight. Then, it is ground to obtain a powdered complex. The powdered complex is then placed in a tube furnace and heated to 600°C at a rate of 4°C / min in an inert gas environment. The temperature is maintained for 4 hours and then naturally cooled to room temperature to obtain the Fe-C3N4 single-atom catalyst.

[0071] S5. Add dried polyacrylonitrile particles, polyvinylpyrrolidone, and Fe-C3N4 single-atom catalyst to N-methylpyrrolidone, and heat and stir at 60℃~80℃ for 12h to obtain spinning solution. Prepare three spinning solutions with different concentrations of Fe-C3N4 single-atom catalyst, with the contents of polyacrylonitrile (wt%): polyvinylpyrrolidone (wt%): Fe-C3N4 single-atom catalyst (wt%) being 12wt%: 6wt%: 8wt%, 12wt%: 6wt%: 5wt%, and 12wt%: 6wt%: 2wt%, respectively, and denoted as spinning solution 1, spinning solution 2, and spinning solution 3.

[0072] S6, such as Figure 1 As shown, spinning solution 1 was loaded into a syringe, and spinning was carried out for 4 hours using a No. 22 single-nozzle needle. Then, the spinning solution in the syringe was replaced with spinning solution 2, and spinning continued for 4 hours. Finally, the spinning solution in the syringe was replaced with spinning solution 3, and spinning was carried out for 4 hours, ultimately obtaining a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction. During the spinning process, the ambient humidity was controlled at 30% RH, the spinning distance was 10 cm, the spinning voltage was 10 kV, and the feed rate was 0.15 mm / min.

[0073] S7. Immerse the nanofiber catalytic membrane obtained in step S6 in deionized water, sonicate it in a water bath for 0.5 h, and place it at 60°C for 24 h to wash away the pore-forming agent. Then dry it to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution, denoted as Fe-C3N4 single-atom nanofiber catalytic membrane.

[0074] PMS was activated using the Fe-C3N4 single-atom nanofiber catalytic membrane prepared in Example 1, and the detection results were analyzed. Figure 2 The presence of the characteristic triplet of singlet oxygen detected by paramagnetic resonance indicates that the Fe-C3N4 single-atom nanofiber catalytic membrane activates PMS to generate singlet oxygen, which is beneficial for the Fe-C3N4 single-atom nanofiber catalytic membrane to oxidize and degrade small organic molecules under high-salt conditions.

[0075] The performance of the Fe-C3N4 single-atom nanofiber catalytic membrane prepared in Example 1 was tested. The catalytic membrane was used to catalytically degrade a single pollutant solution. Tetracycline was selected as the pollutant, with a concentration of 30 ppm. NaCl was added to the solution to a concentration of Cl. - With a content of 10,000 ppm, a persulfate addition of 1 mM, an initial pH of 7, and a reaction temperature of 25°C, the pollutant solution can achieve a tetracycline removal rate of 98% and a mineralization rate of 65% after a single membrane pass.

[0076] Example 2

[0077] S1. Add 0.025 g of cobalt acetate tetrahydrate and 0.6 g of citric acid to 100 g of water to obtain precursor A solution; add 0.6 g of ammonium sulfate to 125 g of water to obtain precursor B solution; add 0.8 g of urea to 160 g of water to obtain precursor C solution.

[0078] S2. Mix the precursor A solution obtained in step S1 with the precursor B solution and stir for 0.5 h to obtain the precursor D solution;

[0079] S3. Mix the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 and stir for 4 hours to obtain complex solution E, and then filter to obtain the complex.

[0080] S4. The complex obtained in step S3 is placed in a vacuum oven and dried at 60°C overnight. Then, it is ground to obtain a powdered complex. The powdered complex is then placed in a tube furnace and heated to 550°C at a rate of 2°C / min in an inert gas environment. The temperature is maintained for 4 hours and then naturally cooled to room temperature to obtain a Co-C3N4 single-atom catalyst.

[0081] S5. Add dried polyvinylidene fluoride particles, polyethylene glycol, and Co-C3N4 single-atom catalyst to N-methylpyrrolidone, and heat and stir at 60℃~80℃ for 12h to obtain spinning solution. Prepare three spinning solutions with different concentrations of Co-C3N4 single-atom catalyst, with polyvinylidene fluoride (wt%): polyethylene glycol (wt%): Co-C3N4 single-atom catalyst (wt%) contents of 9wt%: 9wt%: 8wt%, 9wt%: 9wt%: 5wt%, and 9wt%: 9wt%: 2wt%, respectively, and designate them as spinning solution 1, spinning solution 2, and spinning solution 3.

[0082] S6. Take spinning solution 1 and load it into a syringe. Using a No. 22 single-nozzle needle, spin for 4 hours (spinning stage 1). Then, replace the spinning solution in the syringe with spinning solution 2 and continue spinning for 4 hours (spinning stage 2). Finally, replace the spinning solution in the syringe with spinning solution 3 and spin for 4 hours (spinning stage 3), ultimately obtaining a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction. During the spinning process, the ambient humidity is controlled at 30% RH, the spinning distance is 10 cm, the spinning voltage is 10 kV, and the feed rate is 0.15 mm / min.

[0083] S7. Immerse the nanofiber catalytic membrane obtained in step S6 in deionized water, sonicate it in a water bath for 0.5 h, and place it at 60°C for 24 h to wash away the pore-forming agent. Then dry it to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution, denoted as Co-C3N4 single-atom nanofiber catalytic membrane.

[0084] The performance of the Co-C3N4 single-atom nanofiber catalytic membrane prepared in Example 2 was tested. The catalytic membrane was used to catalytically degrade high-salt refining wastewater with a salinity of approximately 20,000 ppm and a COD content of approximately 1,000 ppm. The amount of persulfate added was 4 mM, the initial pH was adjusted to 7, and the reaction temperature was 25°C. After two passes through the membrane, the COD removal rate reached 62%.

[0085] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0086] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

Claims

1. A single-atom nanofiber catalytic membrane with a catalyst gradient distribution, characterized in that, This includes a nanofiber-based membrane and a metal-C3N4 single-atom catalyst with a gradient distribution on the surface of the nanofiber-based membrane; The metal-C3N4 single-atom catalyst has a particle size of 40–400 nanometers; and / or, the content of the metal-C3N4 single-atom catalyst in the single-atom nanofiber catalytic membrane is 3 wt%–6 wt%. The method for preparing the single-atom nanofiber catalytic membrane with catalyst gradient distribution includes the following steps: S1. Prepare precursor A solution, precursor B solution and precursor C solution respectively; The precursor A solution is an aqueous solution containing a metal salt and an acid; the precursor B solution is an aqueous solution containing cyanuric acid and / or ammonium sulfate; the precursor C solution is an aqueous solution containing melamine and / or urea. S2. Mix and stir the precursor A solution obtained in step S1 with the precursor B solution to obtain the precursor D solution; S3. Mix and stir the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 to obtain complex solution E, and then filter to obtain the complex. S4. The complex obtained in step S3 is dried and ground, and then subjected to 400-600 rpm. o Calcination with C yields a metal-C3N4 single-atom catalyst. S5. Add the dried polymer particles, the metal-C3N4 single-atom catalyst obtained in step S4, and the pore-forming agent to the solvent and heat and stir to uniformly disperse the metal-C3N4 single-atom catalyst, and adjust the mass fraction of the metal-C3N4 single-atom catalyst to obtain spinning solutions with different metal-C3N4 single-atom catalyst concentrations. S6. The spinning solution obtained in step S5 is placed in an electrospinning machine for spinning. During the process, spinning solutions with different concentrations of single-atom catalysts are replaced to obtain a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction. S7. The nanofiber catalytic membrane obtained in step S6 is immersed in a solution to form pores, and then dried to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution. The process in step S6 is as follows: spinning solution with a concentration of 7wt% to 10wt% of metal-C3N4 single-atom catalyst is used for spinning for 3 to 6 hours, then the spinning solution with a concentration of 4wt% to 6wt% of metal-C3N4 single-atom catalyst is used for spinning for another 3 to 6 hours, then the spinning solution with a concentration of 1wt% to 3wt% of metal-C3N4 single-atom catalyst is used for spinning for another 3 to 6 hours, thus obtaining a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction; the spinning conditions are: ambient humidity 25 to 65%RH, spinning distance 5 to 20 cm, spinning voltage 5 to 25 kV, and feed rate 0.1 to 0.5 mm / min.

2. The single-atom nanofiber catalytic membrane with catalyst gradient distribution according to claim 1, characterized in that, The nanofiber-based membrane has a thickness of 100–300 micrometers and an average pore size of 0.1–1.0 micrometers. And / or, the nanofiber-based membrane is made of one of polyacrylonitrile, polyvinylidene fluoride, and polyethersulfone; And / or, the particle size of the metal-C3N4 single-atom catalyst is no greater than 1 micrometer; And / or, the metal includes one of cobalt, iron, nickel, and manganese; And / or, the content of the metal-C3N4 single-atom catalyst in the single-atom nanofiber catalytic membrane is 1wt% to 10wt%.

3. The single-atom nanofiber catalytic membrane with catalyst gradient distribution according to claim 1, characterized in that, The single-atom nanofiber catalytic membrane activates potassium hydrogen sulfate to produce singlet oxygen, which accounts for 70-100 mol of the total active oxygen.

4. The method for preparing a single-atom nanofiber catalytic membrane with a catalyst gradient distribution according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Prepare precursor A solution, precursor B solution and precursor C solution respectively; The precursor A solution is an aqueous solution containing a metal salt and an acid; the precursor B solution is an aqueous solution containing cyanuric acid and / or ammonium sulfate; the precursor C solution is an aqueous solution containing melamine and / or urea. S2. Mix and stir the precursor A solution obtained in step S1 with the precursor B solution to obtain the precursor D solution; S3. Mix and stir the precursor D solution obtained in step S2 with the precursor C solution obtained in step S1 to obtain complex solution E, and then filter to obtain the complex. S4. The complex obtained in step S3 is dried and ground, and then subjected to 400-600 rpm. o Calcination with C yields a metal-C3N4 single-atom catalyst. S5. Add the dried polymer particles, the metal-C3N4 single-atom catalyst obtained in step S4, and the pore-forming agent to the solvent and heat and stir to uniformly disperse the metal-C3N4 single-atom catalyst, and adjust the mass fraction of the metal-C3N4 single-atom catalyst to obtain spinning solutions with different metal-C3N4 single-atom catalyst concentrations. S6. The spinning solution obtained in step S5 is placed in an electrospinning machine for spinning. During the process, spinning solutions with different concentrations of single-atom catalysts are replaced to obtain a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction. S7. The nanofiber catalytic membrane obtained in step S6 is immersed in a solution to form pores, and then dried to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution. The process in step S6 is as follows: spinning solution with a concentration of 7wt% to 10wt% of metal-C3N4 single-atom catalyst is used for spinning for 3 to 6 hours, then the spinning solution with a concentration of 4wt% to 6wt% of metal-C3N4 single-atom catalyst is used for spinning for another 3 to 6 hours, then the spinning solution with a concentration of 1wt% to 3wt% of metal-C3N4 single-atom catalyst is used for spinning for another 3 to 6 hours, thus obtaining a nanofiber catalytic membrane with a gradient distribution of single-atom catalyst mass fraction; the spinning conditions are: ambient humidity 25 to 65%RH, spinning distance 5 to 20 cm, spinning voltage 5 to 25 kV, and feed rate 0.1 to 0.5 mm / min.

5. The method for preparing a single-atom nanofiber catalytic membrane with a catalyst gradient distribution according to claim 4, characterized in that, In step S1, the metal salt is at least one of cobalt salt, iron salt, nickel salt, and manganese salt; the acid is at least one of oxalic acid and citric acid. In solution A, the concentration of the metal salt is 1–10 mmol / L and the concentration of the acid is 10–35 mmol / L; in solution B, the concentration is 10–40 mmol / L; and in solution C, the concentration is 10–90 mmol / L. And / or, in step S2, the mixing and stirring time is 0.5 to 2 hours; And / or, in step S3, the mixing and stirring time is 4 to 8 hours, and the filtration method is vacuum filtration; And / or, step S4 involves placing the complex in a vacuum oven at 60–80°C. o Dry at C overnight, then grind to obtain a powdered complex. The powdered complex is then placed in a tube furnace and heated in an inert atmosphere at 2–5 °C. o Heating rate increased to 400-600 °C / min o C, heat treatment for 4-6 hours, and then naturally cooled to room temperature to obtain metal-C3N4 single-atom catalyst; And / or, in step S5, the polymer is one of polyacrylonitrile, polyvinylidene fluoride, and polyethersulfone; The pore-forming agent is one of polyvinylpyrrolidone and polyethylene glycol; The solvent is one of N-methylpyrrolidone, dimethylamide, and acetone; In the spinning solution, the mass percentages of the dried polymer particles, the pore-forming agent, and the metal-C3N4 single-atom catalyst obtained in step S4 are 6–18 wt%, 2–12 wt%, and 1–10 wt%, respectively. The heating and stirring temperature is 60-80°C. o C, the stirring time is 6-12 hours; And / or, step S7 is as follows: immerse the nanofiber catalytic membrane in deionized water, sonicate in a water bath for 0.5–1.5 h, and then... o C~70 o The film was placed at C for 24–48 h to wash away the pore-forming agent, and then dried to obtain a single-atom nanofiber catalytic membrane with a catalyst gradient distribution.

6. The application of the single-atom nanofiber catalytic membrane with catalyst gradient distribution according to any one of claims 1 to 3 in wastewater treatment, characterized in that, The catalyst, with its gradient distribution of single-atom nanofibers, activates persulfate to generate singlet oxygen, thereby oxidizing and degrading pollutants in wastewater.

7. The application of the single-atom nanofiber catalytic membrane with catalyst gradient distribution according to claim 6 in wastewater treatment, characterized in that, The conditions for the oxidative degradation of pollutants in wastewater by the single-atom nanofiber catalytic membrane with a catalyst gradient distribution are: reaction temperature 20–40 °C. o C, reaction pH 2–10, salt content 0–20000 ppm, persulfate addition 0.5–4 mM; And / or, the contaminant is at least one of antibiotics, endocrine disruptors, and dyes.

8. The application of the single-atom nanofiber catalytic membrane with catalyst gradient distribution according to claim 7 in wastewater treatment, characterized in that, The salt content is 5000–20000 ppm.

9. The application of the single-atom nanofiber catalytic membrane with catalyst gradient distribution according to claim 7 in wastewater treatment, characterized in that, The antibiotic is at least one of tetracycline, sulfonylurea, and penicillin; the endocrine infectious agent is at least one of bisphenol A, phthalate, and alkylphenol; and the dye is at least one of methylene blue, rhodamine B, orange yellow G, and Congo red.

Images