Iron monatomic catalyst modified composite membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of composite membrane materials and environmental pollution treatment, and particularly relates to an iron monatomic catalyst modified composite membrane as well as a preparation method and application thereof. The iron monatomic modified carbon-doped graphite-like carbon nitride catalyst is obtained by forming a precursor through supramolecular self-assembly of citric acid complexed with iron ions and melamine and then performing pyrolysis, and highly dispersed iron monatomic greatly improves the atom utilization rate and reduces the metal dosage. The composite membrane effectively solves the problems that a powder catalyst is difficult to recycle and secondary pollution is easily caused, the prepared composite membrane has self-cleaning regeneration characteristics, and the problem that a traditional filter membrane is easily polluted is solved. The preparation method of the composite membrane is simple in process, low in equipment requirement and suitable for industrial production. The composite membrane disclosed by the invention has wide and efficient removal performance on various organic pollutants in water, is universal in applicability and has great application potential.

Description

Technical Field

[0001] This invention belongs to the field of composite membrane materials and environmental pollution control technology, specifically relating to a composite membrane modified with an iron single-atom catalyst, its preparation method, and its application. Background Technology

[0002] With the rapid development of human society and the continuous advancement of industrialization, water pollution has become increasingly serious. Currently, residual organic pollutants such as dyes and antibiotics in water bodies pose a serious threat to the ecological environment and human health. Common wastewater treatment technologies include Fenton technology, membrane filtration technology, and photocatalysis technology. Among these, photocatalysis technology is an advanced oxidation process that uses light energy to drive a catalyst to degrade organic pollutants. It has advantages such as being green, mild, and environmentally friendly, but it generally suffers from low catalytic efficiency and low solar energy utilization, limiting its practical application. Fenton technology degrades pollutants by generating highly oxidizing free radicals through Fenton or Fenton-like reactions. It is characterized by simple operation and high degradation efficiency, but this process is often accompanied by the formation of iron sludge, and the powdered catalyst is difficult to recover, easily causing secondary pollution.

[0003] Membrane filtration technology relies on membrane materials with specific pore sizes to remove pollutants through filtration and adsorption. It has advantages such as low energy consumption and high filtration efficiency and has been widely used in the field of wastewater treatment. However, its membrane pores are easily fouled and clogged, which leads to a shortened membrane lifespan.

[0004] In response to the limitations of existing photocatalytic technologies in utilizing sunlight and their low catalytic efficiency, the problems of Fenton technology in generating iron sludge and having difficulty in catalyst recovery, as well as the problems of membrane materials being easily contaminated and having a short service life, there is an urgent need to develop new wastewater treatment materials and technologies that are green and environmentally friendly, have high water purification capabilities, and are recyclable. Summary of the Invention

[0005] This invention aims to overcome the problems of low photocatalytic efficiency, iron sludge formation and difficult catalyst recovery in Fenton reactions, and easy fouling and short lifespan of membrane filtration in existing technologies. By integrating photocatalysis and Fenton technology, a highly efficient and green photo-Fenton system is constructed. Furthermore, metal single-atom preparation technology is used to improve the utilization rate of metal atoms and its catalytic efficiency. Finally, this catalytic system is combined with membrane filtration technology to successfully develop a composite membrane that combines photo-Fenton catalysis and filtration separation characteristics. This invention immobilizes powdered catalysts in a polymer membrane, effectively solving the problems of difficult recovery and easy secondary pollution of powdered catalysts. Simultaneously, it endows the composite membrane with photo-Fenton catalytic properties, giving it self-cleaning ability, significantly reducing membrane fouling, and extending its service life.

[0006] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution:

[0007] This invention provides a method for preparing a composite membrane, comprising the following steps:

[0008] 1) Dissolve citric acid in water and stir at room temperature until dissolved. Then add soluble iron salt and stir at room temperature to obtain solution A.

[0009] 2) Disperse melamine in water and stir to dissolve it at 65-90℃ to obtain solution B;

[0010] 3) Slowly add solution A to solution B to carry out supramolecular self-assembly to obtain suspension C; continuously stir and evaporate suspension C at 65-90℃ to obtain solid powder D;

[0011] 4) After grinding solid powder D, place it in a covered crucible and calcine it in air at 500-600℃ for 2-5 hours. Cool it to room temperature to obtain iron single-atom modified carbon doped graphite phase carbon nitride catalyst, i.e. iron single-atom catalyst, denoted as Fe-C-CN.

[0012] 5) Disperse the Fe-C-CN catalyst and activated carbon (AC) in N,N-dimethylformamide (DMF) and ultrasonically disperse them evenly to obtain suspension E; add polyvinylidene fluoride (PVDF) and polyvinylpyrrolidone (PVP, K88-96) to suspension E and stir at 55-85℃ for 2-8 hours to obtain casting solution;

[0013] 6) The casting solution was coated onto a glass plate and evenly coated. The Fe-C-CN / AC / PVDF composite membrane was obtained by solvent-inducing phase separation method.

[0014] Further, in step 1), the mass ratio of citric acid to water is 1 to 10:800.

[0015] Further, in step 1), the concentration of iron in solution A is 0.472–4.729 g·L⁻¹. -1 .

[0016] Further, in step 2), the mass ratio of melamine to water is 1.2 to 6.3:200.

[0017] Further, in step 5), the mass ratio of polyvinylidene fluoride, polyvinylpyrrolidone, N,N-dimethylformamide, Fe-C-CN catalyst and activated carbon is 34:10:189.6~303.4:2~12:1~6.

[0018] Further, in step 6), a non-solvent-induced phase separation method is used to form a film with a thickness of 100–400 µm, and the film is formed in a deionized water coagulation bath.

[0019] The present invention also provides a composite membrane modified with an iron single-atom catalyst, which is prepared by the above-described preparation method.

[0020] This invention also provides an application of a composite membrane in the removal of pollutants from water. It can be used to remove various organic pollutants from water, including dyes, antibiotics, and phenolic compounds. By adding persulfate as an oxidant to the wastewater solution, and allowing the wastewater solution to pass through the membrane by gravity under photo-assisted conditions, efficient purification of the wastewater can be achieved.

[0021] The beneficial effects of this invention are:

[0022] 1. The iron single-atom catalyst used in this invention is prepared by citric acid complexing iron ions with melamine through supramolecular self-assembly and pyrolysis. It has low raw material cost, very little iron content and high dispersion, simple synthesis process, environmentally friendly, and has the potential for large-scale production.

[0023] 2. The composite membrane prepared by the present invention through blending and non-solvent-induced phase separation method allows Fe-C-CN catalyst and activated carbon to be uniformly distributed in PVDF matrix, which has both excellent pollutant adsorption capacity and photo-Fenton regeneration performance. The composite membrane preparation method is simple, requires low equipment, and is suitable for industrial production.

[0024] 3. The composite membrane of this invention exhibits highly efficient photo-Fenton degradation performance even under low concentration persulfate (1 mM) conditions. Compared to pure PVDF membranes (removal rate 12.5%) and C-CN / PVDF membranes without Fe single-atom modification and activated carbon addition (removal rate 43.0%), the Fe-C-CN / AC / PVDF composite membrane shows better removal of tetracycline hydrochloride (50 mL, 20 mg·L⁻¹) in water. -1 The single-pass filtration removal rate can reach 92.5%.

[0025] 4. The composite membrane of this invention is effective over a wide pH range (2-11), with different water qualities (deionized water, tap water, lake water), and in the presence of various interfering anions (SO4). 2- Cl - HCO3 - Under these conditions, it can still maintain a high pollution purification efficiency, demonstrating good environmental adaptability and anti-interference ability.

[0026] 5. The composite membrane of this invention has broad and efficient removal performance for various organic pollutants in water (such as dyes, antibiotics, phenolic compounds, etc.), and is widely applicable.

[0027] Of course, any product implementing this invention does not necessarily need to achieve all of the above advantages at the same time. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 These are scanning electron microscope (SEM) images of the different films prepared in Example 1 and Comparative Examples 1-3, and their surface pore size distribution diagrams.

[0030] Among them, (a) pure PVDF membrane, (b) C-CN / PVDF composite membrane without Fe single-atom modification and without activated carbon, (c) Fe-C-CN / PVDF composite membrane without activated carbon, and (d) Fe-C-CN / AC / PVDF composite membrane;

[0031] Figure 2 These are X-ray diffraction (XRD) patterns of the different films prepared in Example 1 and Comparative Examples 1-3;

[0032] Among them, the membranes include pure PVDF membranes, C-CN / PVDF composite membranes, Fe-C-CN / PVDF composite membranes, and Fe-C-CN / AC / PVDF composite membranes;

[0033] Figure 3 These are Fourier transform infrared (FT-IR) spectra of the different films prepared in Example 1 and Comparative Examples 1-3;

[0034] Among them, the membranes include pure PVDF membranes, C-CN / PVDF composite membranes, Fe-C-CN / PVDF composite membranes, and Fe-C-CN / AC / PVDF composite membranes;

[0035] Figure 4 These are stress-strain diagrams of different films prepared in Example 1 and Comparative Examples 1-3;

[0036] Among them, the membranes include pure PVDF membranes, C-CN / PVDF composite membranes, Fe-C-CN / PVDF composite membranes, and Fe-C-CN / AC / PVDF composite membranes;

[0037] Figure 5 These are water contact angle diagrams of different membranes prepared in Example 1 and Comparative Examples 1-3;

[0038] Among them, the membranes include pure PVDF membranes, C-CN / PVDF composite membranes, Fe-C-CN / PVDF composite membranes, and Fe-C-CN / AC / PVDF composite membranes;

[0039] Figure 6The graphs show the performance of different membranes prepared in Example 1 and Comparative Examples 1-3 in removing tetracycline hydrochloride (TC) from water under two different conditions (no light and no persulfate: Dark, with light and persulfate: Light + PDS).

[0040] Figure 7 The graphs show the performance of Fe-C-CN / AC / PVDF composite membranes with different activated carbon contents prepared in Examples 1-4 in removing tetracycline hydrochloride (TC) from water under Light + PDS conditions.

[0041] Figure 8 This is a graph showing the performance of the Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 in removing tetracycline hydrochloride (TC) from water at different pH values ​​under Light + PDS conditions;

[0042] Figure 9 The Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 was used to remove different interfering anions (SO4) under Light + PDS conditions. 2- Cl - HCO3 - Performance diagram of tetracycline hydrochloride (TC) in water;

[0043] Figure 10 This is a graph showing the removal performance of the Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 for various organic pollutants in water under Light + PDS conditions;

[0044] Figure 11 This is a graph showing the multiple-cycle performance of the Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 in removing tetracycline hydrochloride (TC) from water under Dark and Light + PDS conditions, as well as the Fe leaching rate in each cycle. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] This invention provides a composite membrane modified with an iron single-atom catalyst, its preparation method, and its application. The iron single-atom modified carbon-doped graphitic carbon nitride catalyst (Fe-C-CN) is obtained by supramolecular self-assembly of citric acid with complexed iron ions and melamine to form a precursor, followed by pyrolysis. The mass fraction of iron in the catalyst is 0.5–3.0 wt.%, and the highly dispersed iron single atoms greatly improve atom utilization and reduce metal usage. The Fe-C-CN / AC / PVDF composite membrane is prepared using a blending-nonsolvent-induced phase separation method, in which the Fe-C-CN catalyst and activated carbon are uniformly distributed in the PVDF matrix, giving the composite membrane excellent pollutant adsorption performance and photo-Fenton regeneration performance. This invention effectively solves the problems of difficult recovery and secondary pollution caused by powdered catalysts. The prepared composite membrane has self-cleaning and regeneration characteristics, overcoming the problem of easy contamination of traditional filter membranes. The preparation method of this composite membrane is simple, requires low equipment, and is suitable for industrial production. The composite membrane of this invention has broad and efficient removal performance for various organic pollutants in water (such as dyes, antibiotics, phenolic compounds, etc.), and has wide applicability and great application potential.

[0047] The specific embodiments of the present invention are as follows:

[0048] Example 1

[0049] A composite membrane modified with an iron single-atom catalyst and its preparation method:

[0050] 1) Weigh 63.1 mg of citric acid and dissolve it in 8 mL of deionized water, then add 91.3 mg of ferric chloride hexahydrate and stir at room temperature to obtain solution A;

[0051] 2) Weigh 756.7 mg of melamine and disperse it in 30 mL of deionized water. Stir at 80 °C to dissolve it, and obtain solution B;

[0052] 3) Solution A is slowly added to solution B to carry out supramolecular self-assembly to obtain suspension C. The solvent is evaporated by continuous stirring at 80 °C to obtain solid powder D.

[0053] 4) Grind solid powder D thoroughly, place it in a covered crucible, calcine it at 550 °C in air atmosphere for 2 h, and after cooling to room temperature, grind it thoroughly again to obtain iron single-atom modified carbon doped graphitic carbon nitride Fe-C-CN (2.5%Fe), denoted as Fe-C-CN.

[0054] 5) Disperse 200 mg Fe-C-CN and 125 mg activated carbon (AC) in 5 mL N,N-dimethylformamide and sonicate to ensure uniform dispersion; then add 850 mg PVDF and 250 mg PVP (K88-96) and stir at 65 °C for 5 h to obtain casting solution;

[0055] 6) The casting solution was coated onto a glass plate and evenly coated with a doctor blade. After standing at room temperature for 12 min, it was placed in deionized water. The composite membrane Fe-C-CN / AC (11 wt.%) / PVDF was prepared by a solvent-inducible phase separation method, denoted as Fe-C-CN / AC / PVDF. The membrane thickness was 200 μm, and the effective membrane area was 12.56 cm². 2 .

[0056] Example 2

[0057] The difference between this embodiment and Embodiment 1 is that the amount of activated carbon in step 5) is changed to 75 mg, and the resulting composite membrane is denoted as Fe-C-CN / AC(11 wt.%) / PVDF.

[0058] Example 3

[0059] The difference between this embodiment and Example 1 is that the amount of activated carbon in step 5) is changed to 100 mg, and the resulting composite membrane is denoted as Fe-C-CN / AC(11 wt.%) / PVDF.

[0060] Example 4

[0061] The difference between this embodiment and Example 1 is that the amount of activated carbon in step 5) is changed to 150 mg, and the resulting composite membrane is denoted as Fe-C-CN / AC(11 wt.%) / PVDF.

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 1 is that the amount of Fe-C-CN catalyst and activated carbon added in step 5) is 0 mg, and the resulting membrane is labeled as PVDF.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that the amount of ferric chloride hexahydrate in step 1) is changed to 0 mg, and the amount of activated carbon added in step 5) is changed to 0 mg. The resulting composite membrane is labeled as C-CN / PVDF.

[0066] Comparative Example 3

[0067] The difference between this comparative example and Example 1 is that the amount of activated carbon in step 5) is changed to 0 mg, and the resulting composite membrane is labeled as Fe-C-CN / PVDF.

[0068] from Figure 1 As can be seen from the SEM images of the different films prepared in Example 1 and Comparative Examples 1-3, Figure 1 (a) The surface of the pure PVDF membrane exhibits a macroporous structure with an average pore size of 2.40 μm; Figure 1 (b) As shown in the figure, the pore size of the C-CN / PVDF composite membrane is slightly reduced due to the addition of C-CN powder, with an average pore size of 1.47 μm; Figure 1 (c) As shown in the figure, the Fe-C-CN / PVDF composite membrane has a smaller pore size than pure PVDF due to the addition of Fe-C-CN catalyst, with an average pore size of 1.32 μm. Figure 1 (d) Due to the addition of activated carbon, the pore size of the Fe-C-CN / AC-PVDF composite membrane is further reduced, with an average pore size of 0.52 μm.

[0069] according to Figure 2 The XRD patterns of the different films prepared in Example 1 and Comparative Examples 1-3 show that all film samples exhibit a diffraction peak of β-phase PVDF at 20.7°; and the films prepared in Example 1 and Comparative Examples 2-3 exhibit a diffraction peak of graphite-like carbon nitride at 27.8°. No diffraction peaks of Fe species were observed in the XRD patterns of the Fe-C-CN / PVDF and Fe-C-CN / AC-PVDF composite films, indicating that Fe is highly dispersed in the samples.

[0070] from Figure 3 The FT-IR spectra of the different films prepared in Example 1 and Comparative Examples 1-3 shown can be seen that the various film samples exhibit different wavelengths at 837 cm⁻¹. -1 and 1278 cm -1 The signal peaks of the coupling of the -CH2 and -CF2 stretching vibrations of the β-phase PVDF were all observed at 1072 cm⁻¹. -1 The signal peak of the CF bond was observed at 809 cm⁻¹; in addition, the different films prepared in Example 1 and Comparative Examples 2-3 showed a signal peak at 809 cm⁻¹. -1 The characteristic peak of CN=C in the triazine ring structure of carbon nitride is shown at the position.

[0071] from Figure 4The stress-strain diagrams of the different membranes prepared in Example 1 and Comparative Examples 1-3 show that the addition of Fe-C-CN and activated carbon effectively improves the mechanical properties of the Fe-C-CN / AC-PVDF composite membrane. Compared to the pure PVDF membrane, the maximum tensile stress of the Fe-C-CN / AC-PVDF composite membrane increases from 7.1 MPa to 16.6 MPa, and the maximum tensile strain increases from 4.3% to 9.2%. This enhanced mechanical property significantly improves the long-term durability of the Fe-C-CN / AC-PVDF composite membrane in wastewater treatment processes.

[0072] from Figure 5 The water contact angle diagrams of the different membranes prepared in Example 1 and Comparative Examples 1-3 show that the pure PVDF membrane exhibits hydrophobicity with a water contact angle of 100.8°; while the water contact angles of the C-CN / PVDF and Fe-C-CN / PVDF composite membranes decrease to 68.5° and 65.1°, respectively, indicating that the introduction of C-CN or Fe-C-CN makes the composite membrane hydrophilic. Since activated carbon is hydrophobic, the water contact angle of the Fe-C-CN / AC-PVDF composite membrane increases to 114.4°.

[0073] Specific applications of this invention are as follows:

[0074] Application Example 1

[0075] The experimental procedures for removing pollutants from water using the various membranes prepared in this invention are as follows:

[0076] 1) Prepare a solution with a concentration of 40 mg·L -1 The absorbance of the tetracycline hydrochloride (TC) aqueous solution at a wavelength of 357 nm was measured using a UV-Vis spectrophotometer.

[0077] 2) Load the prepared membrane into a wastewater treatment filtration device, and then measure 50 mL of a membrane with a concentration of 40 mg·L⁻¹. -1 The TC aqueous solution was poured into the filtration device, and the filtration was carried out spontaneously by the weight of the solution. The filtered solution was collected and its absorbance at a wavelength of 357 nm was measured using a UV spectrophotometer. The TC removal rate was calculated, and the performance of the membrane for TC interception and adsorption under Dark conditions was obtained.

[0078] 3) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 A TC aqueous solution was prepared, and potassium persulfate was added to the solution to achieve a concentration of 1 mM. After stirring thoroughly, the solution was poured into a filter device equipped with the prepared membrane, and a xenon lamp was turned on to provide simulated sunlight irradiation conditions (light power density of 200 mW / cm²). 2The TC aqueous solution was filtered under Light + PDS conditions. The filtered solution was collected and its absorbance at a wavelength of 357 nm was measured using a UV spectrophotometer. The TC removal rate was calculated to obtain the wastewater treatment performance of the membrane under Light + PDS conditions.

[0079] Depend on Figure 6 The removal rates of TC in water by the different membranes prepared in Example 1 and Comparative Examples 1-3 show that: under Dark conditions, the Fe-C-CN / AC / PVDF composite membrane exhibits a higher TC removal capacity, with a TC removal rate of 62.4% after a single filtration, which is significantly higher than that of the pure PVDF membrane (7.9%), the C-CN / PVDF composite membrane (21.4%), and the Fe-C-CN / PVDF composite membrane (30.5%). Under Light + PDS conditions, the Fe-C-CN / AC-PVDF composite membrane also shows a superior TC removal capacity compared to other membranes. Moreover, due to its efficient interception and adsorption capacity and photo-Fenton degradation performance, the composite membrane achieves a TC removal rate of 92.5% in water, far exceeding that of the pure PVDF membrane (12.5%), the C-CN / PVDF composite membrane (43.0%), and the Fe-C-CN / PVDF composite membrane (63.5%).

[0080] Depend on Figure 7 The results of TC removal in water by the composite membranes prepared in Examples 1-4 and Comparative Example 3 under Light + PDS conditions show that when the mass fraction of activated carbon in the composite membrane is 11 wt.%, the membrane exhibits the best wastewater purification effect. This is a comprehensive reflection of the activated carbon's adsorption capacity for pollutants and its influence on photo-Fenton interaction.

[0081] Application Example 2

[0082] The performance of the composite membrane prepared in Example 1 in removing TC from water under different pH conditions was tested. The experimental steps are as follows:

[0083] 1) Prepare a solution with a concentration of 40 mg·L -1 The absorbance of the TC aqueous solution at a wavelength of 357 nm was measured using a UV-Vis spectrophotometer.

[0084] 2) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 The pH values ​​of the solutions were adjusted to 2, 5, 6.37, 9, and 11 using TC aqueous solutions.

[0085] 3) Add potassium persulfate to the above solution to a concentration of 1 mM, stir well, pour the solution into a filter device equipped with the prepared membrane, and turn on the xenon lamp to provide simulated sunlight irradiation conditions (light power density of 200 mW / cm²).2 The TC aqueous solution was filtered under Light + PDS conditions, the filtered solution was collected, and its absorbance at a wavelength of 357 nm was measured using a UV spectrophotometer to calculate the TC removal rate.

[0086] Depend on Figure 8 The results of treating TC solutions with different pH values ​​using the Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 show that the Fe-C-CN / AC / PVDF composite membrane has excellent TC removal ability in a wide pH range (2-11), indicating that the composite membrane has broad applicability.

[0087] Application Example 3

[0088] The performance of the composite membrane prepared in Example 1 in removing total chloride (TC) from water under various interfering anions was tested. The experimental steps are as follows:

[0089] 1) Prepare a solution with a concentration of 40 mg·L -1 The absorbance of the TC aqueous solution at a wavelength of 357 nm was measured using a UV-Vis spectrophotometer.

[0090] 2) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 TC aqueous solution, different anions (SO4) were added to the solution respectively. 2− Cl − HCO3 − This ensures that the anion concentration is 5 mM.

[0091] 3) Add potassium persulfate to the above solution to a concentration of 1 mM, stir well, pour the solution into a filter device equipped with the prepared membrane, and turn on the xenon lamp to provide simulated sunlight irradiation conditions (light power density of 200 mW / cm²). 2 The TC aqueous solution was filtered under Light + PDS conditions, the filtered solution was collected, and its absorbance at a wavelength of 357 nm was measured using a UV spectrophotometer to calculate the TC removal rate.

[0092] Depend on Figure 9 The Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 shown in the figure is effective against various interfering anions (SO4). 2− Cl − HCO3 − The composite membrane still exhibits excellent TC removal capability even under the presence of certain conditions, demonstrating its superior anti-interference ability.

[0093] Application Example 4

[0094] The performance test of the composite membrane prepared in Example 1 in removing other recalcitrant organic pollutants from water was conducted as follows:

[0095] 1) Prepare solutions with a concentration of 40 mg·L⁻¹. -1 Aqueous solutions of oxytetracycline hydrochloride (OTC), ciprofloxacin (CIP), thionine (TH), rhodamine B (RhB), methylene blue (MB), methyl orange (MO), resorcinol (RES), p-nitrophenol (PNP), and o-nitrophenol (ONP) were used, and the absorbance of each solution at its maximum absorption wavelength was measured using a UV-Vis spectrophotometer.

[0096] 2) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 Various organic pollutants in aqueous solution were treated with potassium persulfate to a concentration of 1 mM.

[0097] 3) Pour the above-mentioned aqueous solution of organic pollutants into a filter device equipped with the prepared membrane, and turn on the xenon lamp to provide simulated sunlight irradiation conditions (light power density of 200 mW / cm²). 2 The solutions were filtered under Light + PDS conditions, and the filtered solutions were collected. The absorbance of each solution at its maximum absorption wavelength was measured using a UV spectrophotometer, and the organic pollutant removal rate was calculated.

[0098] Depend on Figure 10 The Fe-C-CN / AC / PVDF composite membrane prepared in Example 1 shows excellent removal effects on various dyes, antibiotics, and phenolic compounds, proving that the composite membrane has universal applicability for the removal of organic pollutants and indicating that the composite membrane has excellent application potential.

[0099] Application Example 5

[0100] The composite membrane prepared in Example 1 was tested for its recycling performance in removing total chloride (TC) from water under conditions of no light and no persulfate (Dark). The experimental steps are as follows:

[0101] 1) Prepare a solution with a concentration of 40 mg·L -1 The absorbance of the tetracycline hydrochloride (TC) aqueous solution at a wavelength of 357 nm was measured using a UV-Vis spectrophotometer.

[0102] 2) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 The TC aqueous solution was poured into a filter device equipped with the prepared membrane. The filtration was carried out spontaneously by the weight of the solution. The filtered solution was collected and its absorbance at a wavelength of 357 nm was measured using a UV spectrophotometer. The TC removal rate was calculated to obtain the TC interception and adsorption performance of the membrane in the first cycle under Dark conditions.

[0103] 3) Without any treatment of the membrane, the membrane is used ten times in step (2) to obtain the membrane's TC removal performance in water after ten cycles under Dark conditions.

[0104] Application Example 6

[0105] The composite membrane prepared in Example 1 was tested for its recycling performance in removing total chloride (TC) from water under light irradiation and with the addition of persulfate (Light + PDS). The experimental steps are as follows:

[0106] 1) Measure 50 mL of a solution with a concentration of 40 mg·L⁻¹ -1 Add potassium persulfate to the TC aqueous solution to make the concentration 1 mM, and stir until homogeneous;

[0107] 2) Pour the above solution into a filter device equipped with the prepared membrane, and turn on the xenon lamp to provide simulated sunlight irradiation conditions (light power density of 200 mW / cm²). 2 The TC aqueous solution was filtered under Light + PDS conditions, the filtered solution was collected and its absorbance at 357 nm wavelength was measured using a UV spectrophotometer, the TC removal rate was calculated, and the TC removal performance of the membrane under the first cycle under Light + PDS conditions was obtained.

[0108] 3) Without any treatment of the membrane, the membrane is used ten times in step (2) to obtain the membrane's TC removal performance in water after ten cycles under Light + PDS conditions.

[0109] Depend on Figure 11 The Fe-C-CN / AC / PVDF composite membrane prepared in Example 1, under Dark conditions, exhibited a significant decrease in TC removal rate after multiple cycles due to TC interception and adsorption; after ten cycles, the TC removal rate was only 4.2%. However, under Light + PDS conditions, the composite membrane could degrade adsorbed organic pollutants in situ through photo-Fenton degradation, and after ten cycles, the TC removal rate could still reach nearly 80%. During ten cycles, the leaching rate of Fe was negligible (<0.15 mg / L), far below the value stipulated in the Drinking Water Hygiene Standard (GB5749-2006). This demonstrates that the Fe-C-CN / AC / PVDF composite membrane possesses excellent stability and can be continuously used in wastewater purification processes over a long period.

[0110] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a composite film, characterized by, Includes the following steps: 1) Dissolve citric acid in water and stir at room temperature until dissolved. Then add soluble iron salt and stir at room temperature to obtain solution A. 2) Disperse melamine in water and stir to dissolve it at 65-90℃ to obtain solution B; 3) Slowly add solution A to solution B to carry out supramolecular self-assembly to obtain suspension C; continuously stir and evaporate suspension C at 65-90℃ to obtain solid powder D; 4) After grinding solid powder D, place it in a covered crucible and calcine it in air at 500-600℃ for 2-5 hours. Cool it to room temperature to obtain iron single-atom modified carbon doped graphite phase carbon nitride catalyst, i.e. iron single-atom catalyst, denoted as Fe-C-CN. 5) Disperse the Fe-C-CN catalyst and activated carbon in N,N-dimethylformamide and ultrasonically disperse them evenly to obtain suspension E; add polyvinylidene fluoride and polyvinylpyrrolidone to suspension E and stir at 55-85℃ for 2-8 hours to obtain casting solution. 6) The casting solution was coated onto a glass plate and evenly coated. The Fe-C-CN / AC / PVDF composite membrane was obtained by solvent-inducing phase separation method.

2. The production method according to claim 1, characterized by, In step 1), the mass ratio of citric acid to water is 1 to 10:

800.

3. The preparation method according to claim 1, characterized in that, In step 1), the concentration of iron element in the solution A is 0.472-4.729 g·L -1 .

4. The preparation method according to claim 1, characterized in that, In step 2), the mass ratio of melamine to water is 1.2 to 6.3:

200.

5. The preparation method according to claim 1, characterized in that, In step 5), the mass ratio of polyvinylidene fluoride, polyvinylpyrrolidone, N,N-dimethylformamide, Fe-C-CN catalyst and activated carbon is 34:10:189.6~303.4:2~12:1~6.

6. The preparation method according to claim 1, characterized in that, In step 6), a non-solvent-induced phase separation method is used to form a film with a thickness of 100–400 µm, and the film is formed in a deionized water coagulation bath.

7. A composite membrane modified with an iron single-atom catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the composite membrane according to claim 7 in the removal of pollutants from water bodies.

Images