Tempos-cnt composite membrane based on layer-by-layer assembly, preparation method and application

Abstract

This invention discloses a TEMPO-CNT composite membrane based on layer-by-layer assembly, its preparation method, and its application, belonging to the field of electrochemical wastewater treatment material preparation technology. The composite membrane employs a layer-by-layer assembly process, sequentially constructing a carbon-based conductive adsorption layer and a TEMPO catalytic functional layer on a substrate layer to form an ordered layered structure. This structure fully retains the high specific surface area and conductivity of carbon materials while uniformly exposing TEMPO active sites, achieving highly efficient synergistic adsorption and electrocatalytic degradation of pollutants. The composite membrane prepared by this invention is adaptable to various electrochemical systems, including DC and AC (pulse) systems. By applying a corresponding voltage, it can efficiently and with low energy consumption remove trace organic pollutants from wastewater, offering advantages such as flexible operation, wide applicability, and good environmental compatibility.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical wastewater treatment material preparation technology, specifically relating to a TEMPO-CNT composite membrane based on layer-by-layer assembly, its preparation method, and its application. Background Technology

[0002] The continuous development of membrane water treatment technology has always revolved around core requirements such as high-efficiency purification, stable operation, energy consumption optimization, and adaptability to multiple scenarios. In practical applications, this technology needs to precisely target and remove trace organic pollutants in water, such as micrograms / nanograms of endocrine disruptors and other recalcitrant substances. It also needs to maintain a removal rate of no less than 85% under complex substrate conditions, such as tap water and municipal secondary effluent, while possessing strong anti-interference capabilities. Furthermore, the membrane material itself is required to have low pollution and long lifespan, and it is expected to be able to regenerate in situ through green methods such as electrochemistry, achieving a regeneration efficiency of ≥80%, with energy consumption per unit pollutant removal ≤0.5 kWh / mol. In terms of application scenarios, membrane technology needs to be adaptable to diverse scenarios such as drinking water purification, industrial wastewater treatment, and municipal wastewater reuse, balancing convenient small-scale applications with large-scale engineering treatment, using its low-consumption and environmentally friendly characteristics to contribute to water resource recycling and water quality safety.

[0003] Against this backdrop, electrochemical treatment technology has attracted widespread attention due to its clean and efficient characteristics. However, most existing electrode materials are designed for cathode or anodic reactions under direct current conditions, making it difficult to maintain stable and efficient treatment performance in alternating current environments with periodic polarity switching.

[0004] Membrane electrodes composed of TEMPO materials and carbon-based materials (such as carbon nanotubes and graphene) combine the excellent redox reversibility of TEMPO with the high conductivity of carbon-based materials, showing promising application prospects in electrochemical water treatment, especially in alternating current modes. However, the actual performance of this composite material is limited by the shortcomings of existing preparation processes. Common preparation methods, such as spin coating and blending impregnation, often fail to achieve a uniform and stable composite of TEMPO and carbon-based materials in the electrode.

[0005] In the preparation method provided by the invention patent with authorization publication number CN119034507B, due to the intrinsic material properties of TEMPO and carbon nanotubes in the precursor liquid (TEMPO / CNT mixture) such as surface electrical repulsion, the prepared film is prone to detachment or material agglomeration during catalytic application.

[0006] In summary, existing TEMPO-carbon-based composite electrodes still face challenges in terms of fabrication processes, structural stability, and broad applicability to the removal of pollutants across a wide spectrum. Therefore, there is an urgent need to provide an electrode material and its fabrication method that combine high electrocatalytic activity, excellent membrane stability, and good operational adaptability. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a TEMPO-CNT composite membrane based on layer-by-layer assembly, its preparation method, and its application.

[0008] The specific technical solution adopted in this invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a TEMPO-CNT composite membrane based on layer-by-layer assembly, the specific steps of which are as follows: a conductive adsorption layer dispersion containing carbon-based material is uniformly loaded onto the surface of a substrate layer to obtain an intermediate product; subsequently, a catalytic functional layer dispersion containing TEMPO material is uniformly loaded onto the surface of the intermediate product, and after heat treatment, a layer-by-layer assembled TEMPO-CNT composite membrane is obtained.

[0010] Preferably, the carbon-based material in the conductive adsorption layer dispersion is carbon nanotubes or graphene, and the solvent is ethanol.

[0011] Furthermore, the concentration of carbon nanotubes in the conductive adsorption layer dispersion is 5~20 mg / mL; the mass ratio of TEMPO material to carbon nanotubes in the catalytic functional layer dispersion is (1~4):(4~1).

[0012] Preferably, the method for preparing the TEMPO material in the catalytic functional layer dispersion is as follows:

[0013] S1: The TEMPO polymer precursor material is fully dissolved in an organic solvent after nitrogen blowing to remove oxygen. Then, an azobisisobutyronitrile solution is added to the above solution under oxygen-free conditions to carry out a polymerization reaction. The precipitate after the polymerization reaction is dried to obtain the first polymer.

[0014] S2: Dissolve the first polymer in a tetrahydrofuran solution, cool it, add an oxidant, mix well, and carry out an oxidation reaction to obtain the second polymer;

[0015] S3: The second polymer is added dropwise to a sodium hydroxide solution. After removing excess tetrahydrofuran, the product is dried to obtain a partially oxidized TEMPO material.

[0016] Furthermore, the TEMPO polymer precursor material is 2,2,6,6-tetramethylpiperidine-4-methacrylate; the organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide; and the oxidant is m-chloroperoxybenzoic acid.

[0017] Preferably, the substrate layer is a polyethylene terephthalate film or a polyvinylidene fluoride film; the substrate layer is a polyvinylidene fluoride membrane filter with a pore size of 0.1~1 μm, a diameter of 0.5~5 cm, and a thickness of 0.2~3 mm.

[0018] Preferably, the heat treatment process is controlled at a temperature of 60~80℃ for a time of 20~24 h.

[0019] In a second aspect, the present invention provides a TEMPO-CNT composite membrane prepared according to the preparation method described in the first aspect.

[0020] Thirdly, the present invention provides an application of the TEMPO-CNT composite membrane described in the second aspect in water treatment. The TEMPO-CNT composite membrane is placed as the working electrode in a three-electrode reaction system. Wastewater containing trace amounts of organic pollutants is added to the electrolytic reaction tank, allowing the wastewater to flow through the TEMPO-CNT composite membrane. A constant DC potential is applied to the working electrode, causing the trace organic pollutants in the wastewater to be adsorbed and enriched on the surface of the composite membrane, followed by catalytic oxidation and degradation. The wastewater also contains the electrolyte sodium sulfate or sodium chloride. The trace organic pollutants are one or more of sulfamethoxazole, carbamazepine, phenol, or methylene blue.

[0021] Fourthly, the present invention provides an application of the TEMPO-CNT composite membrane described in the second aspect in water treatment. Two TEMPO-CNT composite membranes are placed in an electrolysis reaction system as positive and negative electrodes, respectively. Wastewater containing trace amounts of organic pollutants is added to the electrolysis reaction tank, allowing the wastewater to flow through the TEMPO-CNT composite membrane. Periodically changing asymmetrical voltages are applied to the positive and negative electrodes, causing the trace organic pollutants in the wastewater to be adsorbed and enriched on the surface of the composite membrane and then undergo catalytic oxidation degradation. The pulse period is 1~120 s, and the ratio of positive to negative voltage is (1~7):(7~1).

[0022] The wastewater to be treated also contains the electrolyte sodium sulfate or sodium chloride; the trace organic pollutants are one or more of sulfamethoxazole, carbamazepine, phenol or methylene blue.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention adopts a layer-by-layer assembly process to successfully construct a composite membrane structure with an ordered layer of conductive adsorption layer and catalytic functional layer. This structure not only fully preserves the high specific surface area and conductive network of carbon-based materials, but also makes the TEMPO oxidation active sites uniformly exposed and tightly attached to the surface of carbon-based materials, realizing the efficient synergy between adsorption sites and catalytic sites, and exhibiting the best comprehensive performance.

[0025] (2) The composite membrane prepared by the present invention can be flexibly adapted to both DC and AC electrochemical systems. It can meet different water quality and treatment requirements without replacing the membrane components. It is suitable for a variety of treatment scenarios, from single high-concentration wastewater to complex low-concentration wastewater.

[0026] (3) When using the composite membrane prepared in this invention as the core electrode of the AC electrochemical treatment system, the two membranes can be connected to the positive and negative electrodes of an asymmetric pulsed AC power supply, respectively, so that the solution to be treated flows through the membrane surface or membrane pores. By adjusting the voltage polarity, frequency, duty cycle, and other parameters of the AC power supply, and by utilizing the high adsorption capacity and selective catalytic function of the membrane material, efficient enrichment and synergistic removal of trace organic pollutants by catalytic oxidation can be achieved. This method has the advantages of low energy consumption, good selectivity, simple operation, and strong environmental compatibility. Attached Figure Description

[0027] Figure 1 This is a comparison of the methylene blue removal results of the TEMPO-CNT composite membrane under different voltage conditions in Example 2;

[0028] Figure 2 This is a comparison of the methylene blue removal results of the TEMPO-CNT composite membrane under different pH conditions in Example 3;

[0029] Figure 3 This is a comparison of the methylene blue removal results of the TEMPO-CNT composite membrane under different pulse cycle conditions in Example 4;

[0030] Figure 4 This is a comparison chart of the methylene blue removal results of different composite membranes in Example 5. Detailed Implementation

[0031] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.

[0032] The chemical reagents used in the following examples and their abbreviations are as follows:

[0033] 2,2,6,6-Tetramethylpiperidine-4-methacrylate (TMPMA), N,N-dimethylformamide (DMF), azobisisobutyronitrile (AIBN), tetrahydrofuran (THF), and m-chloroperoxybenzoic acid (mCPBA).

[0034] Example 1

[0035] This embodiment uses a layer-by-layer assembly method to prepare the TEMPO-CNT composite membrane, as detailed below:

[0036] (1) Preparation of polymer PTMPMA

[0037] In a cleanroom fume hood, 25 mL of DMF was added to a reaction flask equipped with a magnetic rotor, and nitrogen gas was continuously purged for 0.5 hours to remove oxygen from the system. Subsequently, 10 g of TMPMA monomer (45.5 mmol) was added, and the temperature of the reaction system was maintained at 30-40°C by heating and continuous stirring to ensure complete dissolution of the TMPMA monomer.

[0038] Subsequently, 75 mg of AIBN initiator (0.0455 mmol) was added slowly to the above solution in multiple portions, and the reaction system was heated to 60°C to initiate the polymerization reaction. The reaction was carried out for 16 hours under continuous nitrogen purging and stirring.

[0039] After the reaction was complete, the polymer was slowly added to 2000 mL of 20% (w / w) methanol solution using a syringe, causing the polymer to precipitate. The precipitate was collected by vacuum filtration and freeze-dried to obtain the white polymer PTMPMA. The calculated yield was 81.03%.

[0040] (2) Partial oxidation of polymer PTMPMA to prepare TMA 51 -co-TMPMA 49

[0041] 10 g of polymer PTMPMA was dissolved in 5 mL of THF to obtain a polymer solution. The polymer solution was cooled in an ice bath. 0.585 g of mCPBA was dissolved in 3.75 mL of THF and then added to the cooled polymer solution. The reaction was stirred continuously for 1 h.

[0042] After the reaction was complete, the colored solution containing the polymer was slowly added dropwise to 50 mL of 0.5 M NaOH solution using a syringe, causing the copolymer to precipitate. The precipitate was collected by filtration and then dissolved in 7.5 mL of THF. This process was repeated to thoroughly wash the mCPBA. The precipitate was then washed sequentially with 125 mL of methanol, 20% methanol-water solution, and deionized water under vacuum filtration to completely remove THF and other water-soluble impurities. Finally, the obtained TEMPO copolymer solid was freeze-dried and stored; the oxidation degree of this polymer was 51%.

[0043] (3) Carbon nanotubes were dispersed in ethanol to prepare a 5 g / L CNT dispersion. A polyvinylidene fluoride (PVDF) microporous filter membrane was placed in a vacuum filtration device as the substrate. 10 mL of the CNT dispersion was poured into the vacuum filtration device (with the substrate placed above the filter membrane) and filtered for 10 min to form a uniform CNT layer on the surface of the PVDF substrate.

[0044] (4) The TEMPO material prepared in step (2) is dispersed in ethanol to prepare a 5 g / L TEMPO dispersion. 10 mL of the TEMPO dispersion is poured into the above apparatus and filtered for 10 min to cover the CNT conductive adsorption layer with a TEMPO catalytic functional layer. After drying, it is heat-treated at 80 °C to obtain a layer-by-layer TEMPO-CNT composite membrane.

[0045] Comparative Example 1

[0046] This comparative example uses a different assembly method to prepare the TEMPO-CNT composite film, as follows:

[0047] (1) Preparation of TEMPO material, the specific preparation method is described in Example 1.

[0048] (2) The prepared TEMPO material was dispersed in ethanol to prepare a 5 g / L TEMPO dispersion. A polyvinylidene fluoride (PVDF) microporous filter membrane was used as the substrate and placed in a vacuum filtration device. 10 mL of TEMPO dispersion was poured into the vacuum filtration device (with the substrate layer placed above the filter membrane) and filtered for 10 min to form a uniform TEMPO catalyst layer on the surface of the PVDF substrate.

[0049] (3) Carbon nanotubes were dispersed in ethanol to prepare a 5 g / L CNT dispersion. 10 mL of the CNT dispersion was poured into the above apparatus and filtered for 10 min to form a uniform CNT conductive adsorption layer on the surface of the TEMPO catalytic functional layer. After drying, the film was heat-treated at 80 °C to obtain a layer-by-layer assembled CNT-TEMPO composite film.

[0050] Comparative Example 2

[0051] This comparative example uses a blending method to prepare TEMPO-CNT composite membranes, as detailed below:

[0052] (1) Preparation of TEMPO material, the specific preparation method is described in Example 1.

[0053] (2) Carbon nanotubes (CNTs) and P(TMA) x -co-TMPMA (1-x) Mix (oxidation degree 51%) at a mass ratio of 1:1 and add ethanol to prepare a 5 g / L co-dispersion.

[0054] (3) A polyvinylidene fluoride (PVDF) microporous filter membrane was used as the substrate and placed in a vacuum filtration device. 20 mL of the blended dispersion prepared in step (1) was poured into the vacuum filtration device and filtered for 10 min to ensure that the solid material was uniformly retained on the surface of the PVDF membrane. After drying, the membrane was heat-treated at 80 °C to obtain the blended TEMPO-CNT composite membrane.

[0055] Example 2

[0056] In this embodiment, the TEMPO-CNT composite film prepared in Example 1 was used as the working electrode, and a removal experiment was conducted using direct current, as detailed below:

[0057] (1) Dissolve methylene blue in a 1 mM NaCl solution, wherein the concentration of methylene blue (as the recalcitrant organic matter to be treated) is 10 μM, and use it as wastewater to be treated.

[0058] (2) The TEMPO-CNT composite film prepared in Example 1 was used as the working electrode, fixed in the electrode slot of the quartz reaction cell and connected to a three-electrode system (Ag / AgCl as the reference electrode and Pt sheet as the counter electrode).

[0059] (3) Add 50 mL of the wastewater to be treated to the electrolytic reaction cell. Using an electrochemical workstation, apply constant DC potentials of +1.0 V, +2.0 V, -0.5 V, and -0.1 V (relative to the Ag / AgCl reference electrode) sequentially to the working electrode. At each potential, start the workstation and begin timing the reaction.

[0060] During the reaction, 2 mL water samples were taken at regular intervals, and their absorbance was measured using a UV-Vis spectrophotometer at the characteristic absorption wavelength of methylene blue. The concentration and removal rate were calculated based on the standard curve. The results are as follows: Figure 1 As shown.

[0061] The results show that under DC conditions, the treatment effect is optimal at a voltage of +2.0 V, with a removal rate of 69.1% after 60 minutes of reaction. The removal rate is lowest at +1.0 V (34.4%), while the removal rates are 48.5% and 42.5% at -0.1 V and -0.5 V, respectively.

[0062] This is mainly because the higher anodic potential provides sufficient oxidative driving force for the TEMPO-CNT composite membrane, which not only enhances the membrane surface's adsorption capacity for pollutants but also fully activates its anodic catalytic oxidation function. At a potential of +2.0 V, the ·N=O active sites of the catalytic functional layer are fully exposed, and through the synergistic effect of enhanced electrostatic adsorption and catalytic oxidation, efficient degradation of cationic methylene blue is achieved.

[0063] Under negative voltage conditions, the membrane surface is in a reducing environment, and the TEMPO groups exist in the form of NH. Their electrostatic adsorption of methylene blue is weaker than that of the oxidized state (·N=O), leading to a decrease in removal rate. Specifically, the removal rate is 48.5% at -0.1 V, decreasing to 42.5% at -0.5 V. While the anode potential of +1.0 V is also a positive voltage, it provides insufficient driving force to fully activate the catalytically active sites on the membrane surface, limiting the synergistic effect of adsorption and electrocatalysis. Therefore, the removal effect is the weakest, with a removal rate of only 34.4% after 60 minutes.

[0064] Example 3

[0065] In this embodiment, the TEMPO-CNT composite film prepared in Example 1 was used as the working electrode, and a pulsed current was used for the removal experiment, as detailed below:

[0066] (1) Dissolve methylene blue in a 1 mM NaCl solution, wherein the concentration of methylene blue (as the recalcitrant organic matter to be treated) is 10 μM, and use it as wastewater to be treated.

[0067] (2) Use two TEMPO-CNT composite films as the positive and negative electrode films respectively, and connect them to the positive and negative electrodes of the pulse AC power supply.

[0068] (3) Add 50 mL of wastewater to be treated to the electrolysis reaction tank and set the initial pH value of the wastewater to 3, 5 or 8. Set the pulse electrical parameters to a positive and negative bias voltage difference of 2.1V (based on the preferred positive bias voltage of 2V and negative bias voltage of -0.1V in Example 2), a duty cycle of 50%, and a pulse period of T=60 s.

[0069] During the reaction, 2 mL water samples were taken at regular intervals, and their absorbance was measured using a UV-Vis spectrophotometer at the characteristic absorption wavelength of methylene blue. The concentration and removal rate were calculated based on the standard curve. The results are as follows: Figure 2 As shown.

[0070] Example 4

[0071] In this embodiment, the TEMPO-CNT composite film prepared in Example 1 was used as the working electrode, and a pulsed current was used for the removal experiment, as detailed below:

[0072] (1) Dissolve methylene blue in a 1 mM NaCl solution, wherein the concentration of methylene blue (as the recalcitrant organic matter to be treated) is 10 μM, and use it as wastewater to be treated.

[0073] (2) Use two TEMPO-CNT composite films as the positive and negative electrode films respectively, and connect them to the positive and negative electrodes of the pulse AC power supply.

[0074] (3) Add 50 mL of wastewater to be treated to the electrolysis reaction tank and set the initial pH value of the wastewater to 5. Set the pulse electrical parameters to a positive and negative bias voltage difference of 2.1V (based on the preferred positive bias voltage of 2V and negative bias voltage of -0.1V in Example 2), a duty cycle of 50%, and set the pulse period T to 1s, 30s, 60s, and 120s respectively.

[0075] During the reaction, 2 mL water samples were taken at regular intervals, and their absorbance was measured using a UV-Vis spectrophotometer at the characteristic absorption wavelength of methylene blue. The concentration and removal rate were calculated based on the standard curve. The results are as follows: Figure 3 As shown.

[0076] Figure 3 The results for different pulse period reaction conditions show that the removal rates of methylene blue under 1s, 30s, 60s, and 120s conditions are 32.4%, 59.4%, 64.2%, and 45.9%, respectively. The results indicate that the removal effect is optimal when the pulse period is 60s. This is because a period that is too short (1s) is prone to aggravated electrode polarization and desorption and re-dissolution of pollutants, while a period that is too long (120s) will weaken the dynamic enrichment effect of the pulse electric field. The 60s period can ensure sufficient adsorption of pollutants and avoid polarization side reactions.

[0077] Figure 2 The results were presented under different pH conditions. The removal rates of methylene blue were 47.4%, 59.4%, and 16.6% under initial solution pH=3, 5, and 8, respectively. The results showed that the removal effect was optimal at pH=5 because methylene blue is in a cationic state in a weakly acidic environment (pH=5), and the electrostatic adsorption with the negatively charged sites of the TEMPO-CNT composite membrane is strongest. At pH=3, the acidity is too strong, which inhibits the oxidation activity of TEMPO. At pH=8, methylene blue is in a neutral molecular state, and the electrostatic adsorption is weakened. Furthermore, the alkaline environment easily leads to the deactivation of active sites on the membrane surface.

[0078] In summary, the optimal parameters for pulsed electroremoval of methylene blue in this experiment are a pulse period of 60 s and pH=5. Under these conditions, the electric field enrichment efficiency can be guaranteed by a suitable pulse period, and the electrostatic adsorption of pollutants on the membrane can be enhanced by the weakly acidic environment, ultimately achieving a highly efficient and stable removal effect.

[0079] Example 5

[0080] In this embodiment, the TEMPO-CNT composite membrane prepared in Example 1, the CNT-TEMPO composite membrane prepared in Comparative Example 1, and the blended TEMPO-CNT composite membrane prepared in Comparative Example 2 were used to conduct methylene blue removal experiments, as detailed below:

[0081] (1) Dissolve methylene blue in a 1 mM NaCl solution, wherein the concentration of methylene blue (as the recalcitrant organic matter to be treated) is 10 μM, and use it as wastewater to be treated.

[0082] (2) The three composite films were used as working electrodes, fixed in the electrode slot of the quartz reaction cell and connected to a three-electrode system (Ag / AgCl as the reference electrode and Pt sheet as the counter electrode).

[0083] (3) Add 50 mL of the wastewater to be treated to the electrolytic reaction tank. Let it stand for 30 minutes, then apply a constant DC potential of +1.0 V (relative to the Ag / AgCl reference electrode) to the working electrode through the electrochemical workstation. Start the workstation and begin timing the reaction. Take 2 mL of water sample at regular intervals, measure its absorbance at the characteristic absorption wavelength of methylene blue using a UV-Vis spectrophotometer, and calculate its concentration and removal rate according to the standard curve.

[0084] (4) Results Analysis

[0085] Comparing the composite membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2, it can be seen that the surface components of the blended TEMPO-CNT composite membrane exhibit significant agglomeration, leading to uneven distribution of the TEMPO catalytic functional layer and insufficient exposure of active sites, which reduces the overall adsorption and catalytic efficiency of the material. In Comparative Example 1, the CNT-TEMPO composite membrane, due to the prior deposition of the TEMPO catalytic functional layer, partially covers the CNT conductive adsorption layer, weakening the synergistic effect of adsorption and electrocatalysis. The layer-by-layer assembly process provided by this invention successfully constructs an ordered layered structure of conductive adsorption layer-catalytic functional layer (TEMPO-CNT composite membrane prepared in Example 1). This structure not only fully preserves the high specific surface area and conductive network of CNTs but also ensures uniform exposure and tight adhesion of TEMPO oxidation active sites to the CNT surface, thereby achieving highly efficient synergy between adsorption and catalytic sites and exhibiting optimal comprehensive performance.

[0086] like Figure 4 As shown, the horizontal axis from -30 to 0 minutes represents the static adsorption stage. The intrinsic adsorption capacity of the three composite membranes for methylene blue showed significant differences: the composite membranes prepared in Comparative Example 1 and Example 1 adsorbed significantly more methylene blue than the composite membrane prepared in Comparative Example 2, with Example 1 exhibiting the strongest adsorption capacity. This indicates that the layer-by-layer assembly process used in this invention endows the composite membrane with superior initial pollutant enrichment performance.

[0087] During the electrocatalytic reaction stage, the removal efficiencies of the three composite membranes for pollutants showed a further widening: the composite membrane prepared in Comparative Example 2 exhibited the lowest methylene blue removal efficiency, removing only 12.5% ​​after 60 minutes; the composite membrane prepared in Example 1 showed the highest methylene blue removal efficiency, with a removal rate of 69.5% after 60 minutes; and the final methylene blue removal rate of the composite membrane prepared in Comparative Example 1 after 60 minutes of electrocatalytic reaction was 56.1%. These results indicate that the composite membrane prepared in Example 1 not only possesses excellent intrinsic adsorption capacity but also exhibits the highest pollutant removal efficiency during electrocatalysis. Its ordered, layered structure enables efficient enrichment of pollutants through the CNT layer and rapid catalytic degradation through uniformly exposed TEMPO active sites on the surface, thereby maximizing the adsorption-catalysis synergy. It is the best performing of the three preparation methods in terms of overall performance. Further optimization of reaction parameters can be implemented to achieve even better electrocatalytic enrichment-catalysis synergy.

[0088] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for preparing a TEMPO-CNT composite membrane based on layer-by-layer assembly, characterized in that, The specific steps are as follows: a conductive adsorption layer dispersion containing carbon-based materials is uniformly loaded onto the surface of a substrate to obtain an intermediate product; then a catalytic functional layer dispersion containing TEMPO materials is uniformly loaded onto the surface of the intermediate product, and after heat treatment, a layer-by-layer assembled TEMPO-CNT composite film is obtained. The carbon-based material in the conductive adsorption layer dispersion is carbon nanotubes or graphene, and the solvent is ethanol. The method for preparing TEMPO material in the catalytic functional layer dispersion is as follows: S1: The TEMPO polymer precursor material is fully dissolved in an organic solvent after nitrogen blowing to remove oxygen. Then, an azobisisobutyronitrile solution is added to the above solution under oxygen-free conditions to carry out a polymerization reaction. The precipitate after the polymerization reaction is dried to obtain the first polymer. S2: Dissolve the first polymer in a tetrahydrofuran solution, cool it, add an oxidant, mix well, and carry out an oxidation reaction to obtain the second polymer; S3: The second polymer is added dropwise to a sodium hydroxide solution to remove excess tetrahydrofuran, and the product is dried to obtain a partially oxidized TEMPO material; The TEMPO polymer precursor material is 2,2,6,6-tetramethylpiperidine-4-methacrylate; the organic solvent is N,N-dimethylformamide or N,N-dimethylacetamide; and the oxidant is m-chloroperoxybenzoic acid. The base layer is made of polyethylene terephthalate film or polyvinylidene fluoride film.

2. The method for preparing the TEMPO-CNT composite membrane based on layer-by-layer assembly according to claim 1, characterized in that, The concentration of carbon nanotubes in the conductive adsorption layer dispersion is 5~20 mg / mL; the mass ratio of TEMPO material to carbon nanotubes in the catalytic functional layer dispersion is (1~4):(4~1).

3. The method for preparing the TEMPO-CNT composite membrane based on layer-by-layer assembly according to claim 1, characterized in that, The substrate layer is a polyvinylidene fluoride membrane filter with a pore size of 0.1~1 μm, a diameter of 0.5~5 cm, and a thickness of 0.2~3 mm.

4. The method for preparing the TEMPO-CNT composite membrane based on layer-by-layer assembly according to claim 1, characterized in that, The heat treatment process is controlled at a temperature of 60~80℃ for a time of 20~24 h.

5. A TEMPO-CNT composite membrane prepared by any one of the preparation methods according to claims 1 to 4.

6. An application of the TEMPO-CNT composite membrane according to claim 5 in water treatment, characterized in that, A TEMPO-CNT composite membrane is placed as the working electrode in a three-electrode reaction system. Wastewater containing trace amounts of organic pollutants is added to the electrolytic reaction cell, allowing the wastewater to flow through the TEMPO-CNT composite membrane. A constant DC potential is applied to the working electrode, causing the trace organic pollutants in the wastewater to be adsorbed and enriched on the surface of the composite membrane, where they undergo catalytic oxidation and degradation. The wastewater also contains sodium sulfate or sodium chloride electrolyte. The trace organic pollutants are one or more of sulfamethoxazole, carbamazepine, phenol, or methylene blue.

7. An application of the TEMPO-CNT composite membrane according to claim 5 in water treatment, characterized in that, Two TEMPO-CNT composite membranes were placed in an electrolysis reaction system as positive and negative electrodes, respectively. Wastewater containing trace organic pollutants was added to the electrolysis reaction tank, allowing the wastewater to flow through the TEMPO-CNT composite membranes. Periodically changing asymmetrical voltages were applied to the positive and negative electrodes, causing the trace organic pollutants in the wastewater to be adsorbed and enriched on the surface of the composite membranes and then undergo catalytic oxidation degradation. The pulse period was 1~120 s, and the ratio of positive to negative voltage was (1~7):(7~1). The wastewater to be treated also contains the electrolyte sodium sulfate or sodium chloride; the trace organic pollutants are one or more of sulfamethoxazole, carbamazepine, phenol or methylene blue.

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