Composite nanofiltration membrane, preparation method and application thereof

Abstract

This invention discloses a composite nanofiltration membrane, its preparation method, and its application, belonging to the field of membrane material technology. An aqueous solution is prepared using corn stalk extract as the aqueous monomer, and an oil solution is prepared using aromatic sulfonyl chloride compounds as the oil monomer. Interfacial polymerization is carried out on a polyethersulfone supported membrane. The active component, eugenyl-guaiacol fragment, in the corn stalk extract reacts with 1,4-benzenedisulfonyl chloride to form sulfonyl ester bonds. Compared to the amide bonds in traditional polyamide membranes, these bonds are highly inert under acidic conditions and less prone to hydrolysis, thus imparting acid resistance to the membrane material. The phenolic hydroxyl groups impart antifouling properties to the membrane material. Utilizing the synergistic effect of oxidative crosslinking between the eugenyl-guaiacol fragments during interfacial polymerization, combined with the high-density, highly active functional group sulfonyl chloride (-SO2Cl) introduced from the oil solution, a dense three-dimensional polyarylate network structure is ultimately formed on the polyethersulfone supported membrane, endowing the membrane material with high separation performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to a composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology, as an emerging separation method, boasts significant advantages such as simple operation, high separation efficiency, excellent selectivity, and economic efficiency. Nanofiltration membranes, as a separation technology between ultrafiltration and reverse osmosis membranes, have pore sizes ranging from 0.5 to 2 nm. Due to their unique selective separation capabilities, they show broad application prospects in water treatment, environmental protection, and biomedicine, especially in treating high-concentration brine. Nanofiltration membranes typically consist of a porous support (such as polyethersulfone or polysulfone) and an active separation layer. Most nanofiltration membranes use polyamide as the core material of the active separation layer, utilizing the rapid polymerization reaction at the interface between diamine monomers in the aqueous phase and acyl chloride monomers in the organic phase to form a dense polyamide network. Its molecular chain contains numerous amide bonds and aromatic ring structures, where the carbonyl oxygen atom in the amide bond is easily affected by H+. + Attacks disrupt the stability of chemical bonds, leading to molecular chain breakage, which poses numerous challenges to its application in acidic wastewater treatment. Traditional commercial nanofiltration membrane products also largely rely on petrochemical monomers, lacking green and sustainable raw material sources, resulting in high production costs. Furthermore, nanofiltration membranes have limited antifouling capabilities; their surfaces contain hydrophobic regions (hydrophobic groups such as benzene rings aggregate on the membrane surface), allowing organic pollutants in the water to easily adsorb onto the membrane surface through hydrophobic interactions, forming a fouling layer that is difficult to remove, thus leading to a decrease in membrane flux and separation performance.

[0003] Phenolic compounds are rich in hydrophilic hydroxyl groups, making them potential raw materials for preparing antifouling membranes. However, due to the conjugation of hydroxyl groups and aromatic rings in their molecular structure, phenolic compounds are easily oxidized in air, under light, and in high-oxygen environments, which affects their participation in interfacial polymerization reactions and makes it difficult to prepare membranes.

[0004] In my country, agricultural waste (peanut shells, corn stalks, etc.) is a core component of biomass raw materials, with abundant sources, making it one of the most promising raw material types in the current biomass industry. However, its diverse and complex composition has not yet been fully developed and utilized, and it is mostly used as fertilizer, feed, or fuel, resulting in low utilization value. Exploring more potential applications of these agricultural wastes is of great significance for improving resource utilization and expanding low-cost raw materials. Biomass raw materials contain abundant phenolic compounds; however, their actual interfacial reactivity and controllability in interfacial polymerization remain highly uncertain.

[0005] In summary, developing novel nanofiltration membrane materials based on agricultural waste and endowing them with acid resistance, antifouling properties, and high separation performance is of great significance for the high-value application of agricultural waste and for overcoming the problems of insufficient acid resistance and limited antifouling performance of existing nanofiltration membranes. Summary of the Invention

[0006] On the one hand, existing nanofiltration membranes mostly rely on petrochemical-based materials, resulting in high manufacturing costs, and most suffer from insufficient acid resistance and limited antifouling performance. On the other hand, agricultural waste, rich in phenolic compounds, is difficult to fully develop and utilize; it could be a potential raw material for preparing antifouling membranes, but its interfacial reactivity remains unknown. To address one of these issues, this invention, through screening, has for the first time discovered and identified the eugenyl-guaiacol fragment in corn stalk leachate as possessing stable and efficient interfacial reactivity. By interfacially polymerizing this fragment with 1,4-benzenedisulfonyl chloride, an active separation layer with acid resistance and antifouling properties was successfully constructed. This enables the high-value application of corn stalks and provides a novel acid-resistant and antifouling composite nanofiltration membrane.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing a composite nanofiltration membrane, the method comprising: An aqueous solution is prepared using corn stalk extract as the aqueous monomer, and an oil solution is prepared using aromatic sulfonyl chloride compound as the oil monomer. The aqueous solution and the oil solution are subjected to interfacial polymerization on a polyethersulfone support membrane, and a composite nanofiltration membrane is obtained after heat treatment. The corn stalk extract is prepared by mixing corn stalk with phenolic compounds and acid, followed by a hydrothermal reaction. It should be noted that this invention discovered and identified that the eugenyl-guaiacol fragment in corn straw extract possesses stable and efficient interfacial reactivity. It utilizes this fragment to undergo interfacial polymerization (nucleophilic substitution) with aromatic sulfonyl chloride compounds on a polyethersulfone supported membrane to generate sulfonyl ester bonds (-SO-O). Compared to the amide bonds (-CO-NH-) in traditional polyamide membranes, this bond exhibits higher inertness in acidic environments and is less susceptible to proton attack and hydrolysis, thus endowing the membrane material with acid resistance. Simultaneously, corn straw extract is rich in hydrophilic phenolic hydroxyl groups, enhancing the membrane material's antifouling properties. This invention utilizes the synergistic effect of oxidative crosslinking between the eugenyl-guaiacol fragments in the interfacial polymerization reaction, combined with the high-density, highly active functional group sulfonyl chloride (-SO2Cl) introduced from the oil phase solution, to ultimately generate a dense three-dimensional polyarylate network structure on the polyethersulfone supported membrane, endowing the membrane material with highly efficient separation performance.

[0008] Furthermore, the corn stalks were mixed with phenolic compounds and acids in a mass ratio of (0.8~1.2):(1.8~2.2):(0.03~0.05).

[0009] Furthermore, the corn stalks were mixed with phenolic compounds and acids in a mass ratio of 1:2:0.04.

[0010] Furthermore, the above hydrothermal reaction is carried out at 60~100℃ for 1~20 min.

[0011] Furthermore, the phenolic compounds mentioned above are selected from any one or more of phenol, nonylphenol, and bisphenol A.

[0012] Furthermore, the phenolic compounds mentioned above are selected from phenol.

[0013] Furthermore, the aforementioned acids include any one or more of concentrated sulfuric acid, oxalic acid, and maleic acid.

[0014] Furthermore, the aforementioned acid includes concentrated sulfuric acid with a mass fraction of 98%.

[0015] Furthermore, the above-mentioned aromatic sulfonyl chloride compound is 1,4-benzenedisulfonyl chloride. It should be noted that the steric hindrance of the benzene ring structure of 1,4-benzenedisulfonyl chloride can protect its active site sulfonyl chloride functional group (-SO2Cl) from acid damage. At the same time, the sulfonyl chloride functional group is located at the meta position (1,3 position), which reduces the molecular polarity, further reduces the risk of acid corrosion, and enhances the acid resistance of the membrane material.

[0016] Furthermore, the aqueous solution also includes the additive 4-aminozabenzene; it should be noted that 4-aminozabenzene, as an additive, can consume the H generated in the system through a neutralization reaction. + This promotes the forward reaction of interfacial polymerization and prevents the protonation of corn straw leachate groups. By regulating the dissociation state of corn straw leachate, the interfacial polymerization rate is affected to form a dense membrane structure with high cross-linking degree, thereby obtaining a composite nanofiltration membrane with high permeability and high rejection rate.

[0017] Furthermore, the mass ratio of the corn stalk extract to 4-aminoazabenzene in the aqueous solution is (1.5~10):1.

[0018] Furthermore, the mass fraction of the corn stalk extract in the aqueous solution is 1-10%.

[0019] Furthermore, the mass fraction of the above-mentioned 4-aminoazabenzene in the aqueous solution is 0.1~5%.

[0020] Furthermore, the above-mentioned oil phase solution also includes the solvent n-hexane.

[0021] Furthermore, the mass concentration of the above-mentioned 1,4-benzenedisulfonyl chloride in the n-hexane solution is 0.1~5 g / L. It should be noted that the n-hexane solution refers to a homogeneous mixture system in which 1,4-benzenedisulfonyl chloride is dissolved in n-hexane as a solvent.

[0022] Furthermore, the above-mentioned interfacial polymerization reaction includes: at room temperature, first immersing the polyethersulfone support film in an aqueous phase solution for 2-30 minutes, after immersion, pouring out the excess aqueous phase solution and wiping off the water on the film surface, then immersing it in an oil phase solution for 1-30 minutes for interfacial polymerization reaction, and after the reaction is completed, pouring out the excess oil phase solution.

[0023] Furthermore, the volume ratio of the aqueous phase solution to the oil phase solution is 1:1.

[0024] Furthermore, the above heat treatment is carried out in a microwave vacuum dryer at a gauge pressure of -0.1~0 MPa and a temperature of 80~120℃ for 1~3 minutes. It should be noted that by evacuating the microwave vacuum dryer, small molecule byproducts such as HCl generated by the interfacial polymerization reaction can be observed and removed in a timely manner, thereby breaking the reversible equilibrium of the condensation reaction and further ensuring the efficiency of interfacial polymerization.

[0025] Furthermore, the preparation of the above-mentioned polyethersulfone supporting membrane includes: mixing polyethersulfone, polytetrafluoroethylene and an organic solvent, stirring and dissolving to obtain a membrane precursor solution; degassing the membrane precursor solution to obtain a casting solution; and casting the casting solution to obtain a polyethersulfone supporting membrane.

[0026] Furthermore, the mass fraction of the polyethersulfone in the membrane precursor solution is 1-25%.

[0027] Furthermore, the mass fraction of the polytetrafluoroethylene in the membrane precursor solution is 0.1-10%.

[0028] Furthermore, the organic solvents mentioned above include N,N-dimethylacetamide and dichloromethane, wherein the volume ratio of N,N-dimethylacetamide to dichloromethane is 10:1.

[0029] Furthermore, the above stirring is carried out at 60℃~80℃ for 4~10 h.

[0030] Furthermore, the above degassing treatment is carried out in a dryer for 3 to 24 hours.

[0031] Further, the above casting operation includes: uniformly coating the casting solution onto the nonwoven fabric using a doctor blade, with a coating thickness of 100~250 µm; then immediately immersing the nonwoven fabric in water at 25~30℃ for 0.5~1 h, then removing the nonwoven fabric for refrigeration, and finally washing it 2~4 times with deionized water to obtain a polyethersulfone supported film.

[0032] The present invention also provides a composite nanofiltration membrane, which is prepared according to the above method.

[0033] The present invention also provides the application of the above-mentioned composite nanofiltration membrane in the treatment of acidic wastewater.

[0034] Compared with the prior art, the advantages of this invention are as follows: (1) This invention provides a composite nanofiltration membrane, its preparation method, and its application. It is the first time that the eugenyl-guaiacol fragment in corn straw extract has been found to possess stable and highly efficient interfacial reactivity. Based on the above findings and identification results, this invention uses corn straw extract as the aqueous monomer to prepare an aqueous solution and 1,4-benzenedisulfonyl chloride as the oil monomer to prepare an oil solution, successfully preparing a composite nanofiltration membrane via interfacial polymerization. The sulfonyl ester bond (-SO-O-) generated in the reaction exhibits high chemical inertness under acidic conditions, making it difficult to be hydrolyzed by proton attack, thus endowing the membrane material with acid resistance. The corn straw extract is rich in hydrophilic phenolic hydroxyl groups, enhancing the membrane material's antifouling properties. This invention utilizes the synergistic effect of oxidative crosslinking between the eugenyl-guaiacol fragments in the interfacial polymerization reaction, combined with the high-density, highly active functional group sulfonyl chloride (-SO2Cl) introduced from the oil solution, to generate a dense polyarylate three-dimensional network structure on the polyethersulfone supported membrane, endowing the membrane material with highly efficient separation performance.

[0035] (2) The present invention provides a composite nanofiltration membrane and its preparation method and application. 1,4-benzene disulfonyl chloride is selected as the oil phase monomer. The steric hindrance of its benzene ring structure is fully utilized to protect its active site sulfonyl chloride functional group (-SO2Cl) from acid damage. At the same time, the sulfonyl chloride functional group is located in the meta position (1,3 position), which effectively reduces the molecular polarity and can further reduce the risk of acid corrosion and enhance the acid resistance of the membrane material.

[0036] (3) The present invention provides a composite nanofiltration membrane and its preparation method and application, wherein 4-aminoazabenzene is added to the aqueous solution as an additive, which can consume the H generated in the system through a neutralization reaction. + This process promotes the forward propagation of interfacial polymerization and prevents the protonation of groups in corn straw leachate. The interfacial polymerization rate is influenced by regulating the dissociation state of the corn straw leachate. Furthermore, during the heat treatment stage, vacuuming can promptly remove small molecule byproducts such as HCl generated in the interfacial polymerization reaction, thereby disrupting the condensation equilibrium, improving polymerization efficiency, and preparing a composite nanofiltration membrane with high permeability and high rejection rate.

[0037] (4) The present invention provides a composite nanofiltration membrane and its preparation method and application, which uses corn stalks, an agricultural waste with abundant sources, as raw materials to prepare membrane materials. It is green and environmentally friendly, and realizes the high-value application of corn stalks. The prepared composite nanofiltration membrane has excellent acid resistance and anti-fouling properties, providing an economical and sustainable new membrane material for the treatment of acidic wastewater. Attached Figure Description

[0038] Figure 1This is a diagram showing the preliminary experimental results of interfacial polymerization reactions using different biomass raw materials in this invention; where a is sunflower seed shells; b is peanut shells; and c is corn stalks.

[0039] Figure 2 This is an electron microscope scan of the surface of the composite nanofiltration membrane A4 in Embodiment 5 of the present invention.

[0040] Figure 3 This is a scanning electron microscope image of the cross-section of the composite nanofiltration membrane A4 in Embodiment 5 of the present invention.

[0041] Figure 4 These are infrared spectra of corn stalks before and after leaching treatment in this invention.

[0042] Figure 5 It is the solid before and after the interfacial polymerization reaction of corn straw leachate in this invention. 13 1C NMR results.

[0043] Figure 6 These are the infrared spectra of the polyethersulfone supporting membrane, the composite nanofiltration membrane A4, and the composite nanofiltration membrane without corn straw extract in Example 5 of this invention. Detailed Implementation

[0044] The present invention will be further described below with reference to specific embodiments.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0046] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0047] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable. As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof. Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0048] The materials and reagents used in the embodiments of this invention are as follows: Sunflower seed shell powder: Brand - Chacha Food Co., Ltd., sunflower seed shells are ground into powder and then sieved through a 200-mesh sieve; Peanut shell powder: Brand - Su Rui, Item No. hskf, 200 mesh (custom order); Corn stalk powder: Taobao shop - Rural Specialty Industry Base, custom-made 200 mesh; 4-Aminoazabenzene: Purity ≥ 97%; 1,4-Benzenedisulfonyl chloride: Purity ≥98%; n-Hexane: Purity ≥ 99%; N,N-Dimethylacetamide: Purity ≥99%; Dichloromethane: purity ≥ 99.5%.

[0049] Example 1 This embodiment provides a screening method for biomass raw materials.

[0050] Leachates from three agricultural wastes—sunflower seed shells, peanut shells, and corn stalks—were prepared via hydrothermal reaction. Preliminary experiments using interfacial polymerization were conducted to systematically compare the feasibility of preparing biomass-based membranes from these three biomass raw materials. The specific procedures are as follows: (1) Preparation of leachate Sunflower seed shell powder (20 g), peanut shell powder (20 g), and corn stalk powder (20 g) were mixed with phenol (40 g) and concentrated sulfuric acid (98% by mass, 0.8 g) respectively and subjected to hydrothermal reaction at 100℃ for 10 min. After the reaction was completed, the pH of the reaction solution was adjusted to alkaline (around pH 10) with sodium hydroxide solution, filtered, and the filtrate was vacuum dried to obtain the leachate of the corresponding biomass raw materials.

[0051] (2) Preliminary experiment on interfacial polymerization reaction Preparation of aqueous solutions: The above-mentioned leachate was mixed with the additive 4-aminozabenzene and deionized water to obtain aqueous solutions. The mass fraction of the leachate was 1%, and the mass fraction of 4-aminozabenzene was 0.1%. Preparation of the oil phase solution: 1,4-benzenedisulfonyl chloride was mixed with n-hexane as the oil phase monomer to obtain the oil phase solution. The mass concentration of 1,4-benzenedisulfonyl chloride in the n-hexane solution was 0.1 g / L. Interfacial polymerization reaction: Take 2 mL of the above aqueous solution and 2 mL of the above oil solution into sterile centrifuge tubes, respectively, and place them in a well plate shaker (200 rpm) at room temperature for 1 min of contact reaction. Observe with the naked eye whether agglomeration occurs, and then evaluate the interfacial reaction activity of the corresponding leachate.

[0052] (3) Results Analysis The results are as follows Figure 1 As shown, the interfacial reactivity of different biomass raw material leachates exhibits significant differences. When oil phase solutions were added to the three aqueous solutions, the water-oil interface of the sunflower seed shell leachate system showed no significant change, indicating that the reaction degree between its active components and 1,4-benzenedisulfonyl chloride was extremely low, and its interfacial reactivity was weak. The water-oil interface of the peanut shell leachate system showed a very small amount of white precipitate, indicating the presence of a certain amount of active components that can participate in interfacial polymerization, possessing moderate interfacial reactivity. The water-oil interface of the corn straw leachate system, however, generated a large amount of white precipitate, indicating that its active component content was abundant, and its reaction with 1,4-benzenedisulfonyl chloride was vigorous, resulting in significant interfacial reactivity.

[0053] In summary, this study suggests that not all biomass raw materials are suitable for preparing biomass-based membranes. Raw material screening should focus on the content of active ingredients and interfacial reactivity as key evaluation indicators. Corn straw exhibits high interfacial reactivity and is a high-quality candidate raw material for preparing biomass-based membranes.

[0054] Example 2 This embodiment provides a method for preparing a composite nanofiltration membrane using corn straw extract as raw material and the prepared composite nanofiltration membrane A1.

[0055] This method uses corn stalk extract (prepared in the same way as in Example 1) as the aqueous phase monomer to prepare an aqueous phase solution and an aromatic sulfonyl chloride compound as the oil phase monomer to prepare an oil phase solution. The aqueous and oil phase solutions are then subjected to interfacial polymerization on a polyethersulfone supported membrane. After heat treatment, a composite nanofiltration membrane A1 is obtained. The specific preparation process is as follows: S1. Preparation of polyethersulfone support film Polyethersulfone, polytetrafluoroethylene and an organic solvent are mixed and stirred to obtain a membrane precursor solution; the membrane precursor solution is degassed to obtain a casting solution; the casting solution is then subjected to a casting operation to obtain a polyethersulfone supported membrane; S2. Preparation of aqueous and oil phase solutions An aqueous solution was prepared by mixing corn stalk extract as the aqueous phase monomer with additive 4-aminoazinon and deionized water; an oil phase solution was prepared by mixing 1,4-benzenedisulfonyl chloride as the oil phase monomer with solvent n-hexane. S3, interfacial polymerization reaction The aqueous phase solution (100 mL) in S2 was poured into the surface of the polyethersulfone supported membrane in S1 for immersion treatment. After immersion, the excess aqueous phase solution was poured out and the water on the membrane surface was wiped off. Then, the same volume of oil phase solution (100 mL) was poured in to carry out the interfacial polymerization reaction. After the reaction was completed, the excess oil phase solution was poured out. After heat treatment, the composite nanofiltration membrane A1 was obtained.

[0056] In S1: the membrane precursor solution contains 1% polyethersulfone and 0.1% polytetrafluoroethylene, and the organic solvent is N,N-dimethylacetamide and dichloromethane (v:v=10:1). The mixture is stirred at 60°C for 4 h. The degassing treatment is carried out in a desiccator for 3 h. The casting operation is as follows: the casting solution is uniformly coated onto the nonwoven fabric using a doctor blade, with a coating thickness of 100 µm. The nonwoven fabric is then immediately immersed in deionized water at 25°C for 1 h. After that, the nonwoven fabric is removed and refrigerated. Finally, it is washed twice with deionized water to obtain the polyethersulfone supported membrane. In S2: the mass fraction of corn straw extract in the aqueous phase solution is 1%, and the mass fraction of 4-aminoazabenzene is 0.1%; the mass concentration of 1,4-benzenedisulfonyl chloride in the hexane solution in the oil phase solution is 0.1 g / L. In S3: the aqueous solution immersion treatment was carried out at room temperature for 2 min; the interfacial polymerization reaction lasted for 1 min; the heat treatment was carried out in a microwave vacuum dryer (2500 W) at a gauge pressure of -0.1 MPa and 100℃ for 1 min, and then it was taken out and washed with deionized water to obtain the composite nanofiltration membrane A1.

[0057] Example 3 This embodiment provides a method for preparing a composite nanofiltration membrane using corn straw extract as raw material and the prepared composite nanofiltration membrane A2.

[0058] The specific preparation process differs from Example 2, wherein in S1: the mass fraction of polyethersulfone in the membrane precursor solution is adjusted from 1% to 15%, and the mass fraction of polytetrafluoroethylene is adjusted from 0.1% to 5%; the degassing treatment time is adjusted from 3 h to 10 h. In S2: the mass fraction of corn straw extract in the aqueous phase solution was adjusted from 1% to 10%, and the mass fraction of 4-aminoazabenzene was adjusted from 0.1% to 2%; the mass concentration of 1,4-benzenedisulfonyl chloride in the hexane solution in the oil phase solution was adjusted from 0.1 g / L to 2 g / L. In S3: the soaking time in the aqueous solution is adjusted from 2 min to 10 min; the interfacial polymerization reaction time is adjusted from 1 min to 10 min.

[0059] All other operations and conditions were the same as in Example 2, and the composite nanofiltration membrane A2 was finally obtained.

[0060] Example 4 This embodiment provides a method for preparing a composite nanofiltration membrane using corn straw extract as raw material, and the prepared composite nanofiltration membrane A3.

[0061] The specific preparation process differs from Example 2, wherein in S1: the mass fraction of polyethersulfone in the membrane precursor solution is adjusted from 1% to 25%, and the mass fraction of polytetrafluoroethylene is adjusted from 0.1% to 10%; the degassing treatment time is adjusted from 3 h to 24 h. In S2: the mass fraction of corn straw extract in the aqueous phase solution was adjusted from 1% to 8%, and the mass fraction of 4-aminozabenzene was adjusted from 0.1% to 5%; the mass concentration of 1,4-benzenedisulfonyl chloride in the hexane solution in the oil phase solution was adjusted from 0.1 g / L to 5 g / L. In S3: the soaking time in the aqueous solution is adjusted from 2 min to 30 min; the interfacial polymerization reaction time is adjusted from 1 min to 10 min.

[0062] All other operations and conditions were the same as in Example 2, and the composite nanofiltration membrane A3 was finally obtained.

[0063] Example 5 This embodiment provides a method for preparing a composite nanofiltration membrane using corn straw extract as raw material, and observation of the prepared composite nanofiltration membrane A4 and its microstructure.

[0064] The specific preparation process differs from Example 2, wherein in S1: the mass fraction of polyethersulfone in the membrane precursor solution is adjusted from 1% to 23%, and the mass fraction of polytetrafluoroethylene is adjusted from 0.1% to 1%; the coating thickness of the casting solution in the casting operation is adjusted from 100 µm to 150 µm; In S2: the mass fraction of corn straw extract in the aqueous solution was adjusted from 1% to 10%, and the mass fraction of 4-aminozabenzene was adjusted from 0.1% to 2%.

[0065] All other operations and conditions were the same as in Example 2, and the composite nanofiltration membrane A4 was finally obtained.

[0066] The microstructure of the composite nanofiltration membrane A4 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 2 and Figure 3 As shown. Among them, Figure 2 The image shows the surface structure of composite nanofiltration membrane A4. It reveals a typical morphological characteristic of composite membrane materials – a skin layer. This is due to the diffusion of 4-aminoazinon and corn straw extract from the aqueous solution into the hexane system containing 1,4-benzenedisulfonyl chloride in the oil solution during interfacial polymerization. This uneven concentration distribution near the interface triggers Bénard convection, leading to uneven polymer deposition at the interface and thus the formation of the skin layer. Simultaneously, from… Figure 3 The cross-sectional structure diagram of the membrane shown indicates that the composite nanofiltration membrane A4 has an asymmetric membrane structure and a large number of finger-like pores, suggesting that a composite nanofiltration membrane with a porous polyethersulfone support membrane has been successfully prepared.

[0067] Example 6 This embodiment provides a method for preparing a composite nanofiltration membrane using corn stalk extract as raw material, and the prepared composite nanofiltration membrane A5.

[0068] The specific preparation process differs from Example 2, wherein in S1: the mass fraction of polyethersulfone in the membrane precursor solution is adjusted from 1% to 23%, and the mass fraction of polytetrafluoroethylene is adjusted from 0.1% to 1%; the coating thickness of the casting solution in the casting operation is adjusted from 100 µm to 150 µm; In S2: the mass fraction of corn straw extract in the aqueous solution was adjusted from 1% to 5%, and the mass fraction of 4-aminozabenzene was adjusted from 0.1% to 1%.

[0069] All other operations and conditions were the same as in Example 2, and the composite nanofiltration membrane A5 was finally obtained.

[0070] Example 7 This embodiment provides performance tests of the composite nanofiltration membranes A1-A5 in Embodiments 2-6.

[0071] (1) Water permeation flux First, the composite nanofiltration membrane under test was pre-pressurized with deionized water at 4 bar for at least 30 minutes until the permeate flux stabilized. Then, at room temperature, the transmembrane pressure was adjusted and controlled at 10 bar, and the membrane permeate flux was tested using deionized water. The specific calculation formula is as follows: , Where J is the water permeability flux (L / m³) 2 V is the volume of filtrate (L), and A is the effective area of ​​the membrane (m²). 2 T is the filtration time (h), and P is the filtration pressure (bar). (2) Retention rate in acidic environment First, the composite nanofiltration membrane under test was pre-pressurized with deionized water at 4 bar for at least 30 minutes until the permeate flux stabilized. Then, a 1000 ppm magnesium sulfate solution was prepared, and the pH of the solution was adjusted to 2 using glacial acetic acid. Under room temperature conditions, the transmembrane pressure was adjusted and controlled at 10 bar, and the membrane's rejection rate for magnesium sulfate was tested. The specific calculation formula is as follows: , Where R is the retention rate (%), C p C is the permeate concentration (ppm). f The feed concentration is ppm. (3) Pollution resistance The antifouling performance of the composite nanofiltration membrane under test was tested using bovine serum albumin solution to simulate organic pollutants. Specifically, the composite nanofiltration membrane was immersed in 0.1 g / L bovine serum albumin solution for 48 h, and then the water permeation flux of the immersed composite nanofiltration membrane was tested (using the same method as the water permeation flux determination described above).

[0072] The results are shown in Table 1: Table 1. Performance test results of composite nanofiltration membranes A1~A5

[0073] It can be seen that the composite nanofiltration membrane prepared by the present invention using corn stalk extract as raw material has a good rejection rate for magnesium sulfate in an acidic environment (pH=2), indicating that the composite nanofiltration membrane prepared by the present invention has good acid resistance. Simultaneously, the composite nanofiltration membrane exhibits good water permeation flux both before and after contamination with bovine serum albumin, proving that the composite nanofiltration membrane has good antifouling properties. Furthermore, the corn stalk extract used in Example 2 has a relatively low mass fraction of 0.1% in the aqueous solution, resulting in a relatively low rejection rate for magnesium sulfate. In contrast, in other examples, increasing the mass fraction of corn stalk extract resulted in higher magnesium sulfate rejection rates than in Example 2, suggesting that selecting an appropriate amount of corn stalk extract can effectively improve the acid resistance of the nanofiltration membrane.

[0074] Example 8 This embodiment provides the identification of the material composition of corn stalks and corn stalk extracts, as well as the discovery of active components.

[0075] The infrared absorption peaks of the corn stalk powder and corn stalk extract in Example 1 were characterized using an infrared spectrometer to determine their constituent substances.

[0076] The results are as follows Figure 4 As shown, it is located at 1600 cm. -1 and 1508 cm-1 The absorption peaks are due to aromatic skeletal vibrations. Two absorption peaks are significantly enhanced in corn straw extract, indicating that a large amount of benzene-containing compounds are leached, possibly from lignin degradation products. The hydroxyl group is at 3400 cm⁻¹. -1 The significantly enhanced absorption peak at 1230 cm⁻¹ indicates that the corn stalk extract contains a large number of hydroxyl groups. -1 and 1126 cm -1 The absorption peak at the point is related to the stretching vibration of the CO bond, indicating that there are many ether or ester bonds in the corn stalk leachate. In summary, the hydrothermal leaching process may promote the degradation of lignin and cellulose in corn stalks, generating a complex mixture rich in phenols, sugars, and their combinations.

[0077] To further investigate the main material components that play a role in interfacial reactivity, solid-state NMR of carbon was used. 13 The molecular structure of carbon in corn straw extract and the product of the interfacial polymerization reaction between the extract and 1,4-benzenedisulfonyl chloride was characterized by C NMR.

[0078] The results are as follows Figure 5 As shown, before the reaction, 131 ppm and 104 ppm correspond to unoxidized eugenol structural units in corn stalk extract (specifically, aromatic quaternary carbons bonded to methoxy groups and aromatic carbons bonded to oxygen atoms, respectively); 56 ppm corresponds to carbons with methoxy groups; 115 ppm corresponds to guaiac structural units (specifically, unsubstituted aromatic carbons); and 42 ppm corresponds to carbons bonded to sulfonate groups. After the interfacial polymerization reaction, 182 ppm and 175 ppm correspond to oxidized eugenol structural units (specifically, aromatic carbons oxidized to carboxyl groups and aromatic carbons oxidized to ester groups, respectively); 147 ppm corresponds to guaiac structural units (specifically, aromatic quaternary carbons bonded to methoxy and hydroxyl groups); 170 ppm corresponds to carboxyl carbons; 165 ppm corresponds to carbons that form ester groups; and 134 ppm corresponds to carbons on sulfonyl chloride benzene rings. In summary, this indicates that corn straw extract undergoes interfacial polymerization with 1,4-benzene disulfonyl chloride at room temperature, forming ester bonds. The eugenol and guaiac structures in corn straw are the active components that promote the interfacial polymerization of corn straw extract. It is speculated that during the corn straw leaching process, lignin degrades to generate phenolic substances with eugenol and guaiac structures (i.e., the eugenol-guaiacylphenol fragment in this invention). The active hydroxyl groups contained in these substances can undergo nucleophilic substitution reactions with 1,4-benzene disulfonyl chloride to generate sulfonyl ester precipitates insoluble in n-hexane, thereby giving corn straw extract higher interfacial reactivity than other biomass raw materials.

[0079] Finally, to further verify the above speculation, the molecular structure of the polyethersulfone supported membrane, the composite nanofiltration membrane A4 prepared in Example 5, and the composite nanofiltration membrane without corn straw extract (containing only additive 4-aminoazinon and deionized water in the aqueous solution) was characterized by infrared spectroscopy (the other conditions for preparing the composite nanofiltration membrane were the same as in Example 5).

[0080] The results are as follows Figure 6 As shown, compared with the composite nanofiltration membrane without corn stalk extract, the composite nanofiltration membrane A4 with corn stalk extract showed better performance at 1050 cm⁻¹. -1 The appearance of a new peak from the ester group further confirms that 1,4-benzenesulfonyl chloride reacts with the phenolic hydroxyl groups in corn straw extract via interfacial polymerization to form a polyarylate structure.

[0081] Comparative Example 1 This comparative example provides an investigation into the interfacial reactivity of eugenol and guaiacol.

[0082] Specifically, eugenol (CAS: 97-53-0) and guaiacol (CAS: 90-05-1) were used as research objects, and composite nanofiltration membranes were prepared by interfacial polymerization with 1,4-benzenedisulfonyl chloride, and their relevant performance was measured.

[0083] During the interfacial polymerization stage, it was found that eugenol has extremely poor water solubility, making it difficult to form a homogeneous aqueous solution system and thus unable to achieve the interfacial polymerization reaction. In contrast, guaiacol can form a stable homogeneous aqueous solution with 4-aminoazabenzene at 30°C. Therefore, following the methods in Examples 3 and 4, corn straw extract was replaced with guaiacol to prepare composite nanofiltration membranes B1 and B2. The performance of the composite nanofiltration membranes was measured using the same test scheme as in Example 7. The results are shown in Table 2: Table 2. Performance test results of composite nanofiltration membranes A2~A3 and B1~B2

[0084] It can be seen that, under the same preparation conditions as composite nanofiltration membranes A2 and A3, the water flux of the guaiacol-based composite membrane is slightly higher than that of composite nanofiltration membranes A2 and A3, but the rejection rate is significantly lower. This result indicates that the superior performance of the membrane prepared from corn straw extract also stems from its unique cross-linked network structure of eugenol-guaiacol fragments. This invention utilizes the synergistic effect of oxidative cross-linking between eugenol-guaiacol fragments in the interfacial polymerization reaction, combined with the high-density, highly active functional group sulfonyl chloride (-SO2Cl) introduced from the oil phase solution, to generate a denser polyarylate three-dimensional network structure on the polyethersulfone supported membrane, thereby endowing the membrane material with more efficient separation performance. Eugenol or guaiacol alone cannot replace the role of corn straw extract in membrane material preparation.

Claims

1. A method for preparing a composite nanofiltration membrane, characterized in that, The method includes: An aqueous solution was prepared using corn stalk extract as the aqueous monomer; an oil solution was prepared using aromatic sulfonyl chloride compound as the oil monomer; the aqueous solution and the oil solution were subjected to interfacial polymerization on a polyethersulfone support membrane, and a composite nanofiltration membrane was obtained after heat treatment. The corn stalk extract is prepared by mixing corn stalks with phenolic compounds and acids, followed by a hydrothermal reaction. The eugenyl-guaiacol fragment in the corn stalk extract has interfacial reactivity; The eugenyl-guaiacol fragment and the aromatic sulfonyl chloride compound undergo an interfacial polymerization reaction to form a sulfonyl ester bond; The aromatic sulfonyl chloride compound is 1,4-benzenedisulfonyl chloride.

2. The method according to claim 1, characterized in that, The corn stalks are mixed with phenolic compounds and acids in a mass ratio of (0.8~1.2):(1.8~2.2):(0.03~0.05); and / or The hydrothermal reaction is carried out at 60~100℃ for 1~20 min.

3. The method according to claim 2, characterized in that, The phenolic compound is selected from any one or more of phenol, nonylphenol, and bisphenol A; and / or The acid is selected from any one or more of concentrated sulfuric acid, oxalic acid, and maleic acid.

4. The method according to claim 3, characterized in that, The aqueous solution also includes the additive 4-aminozabenzene, and the mass ratio of corn straw extract to 4-aminozabenzene in the aqueous solution is (1.5~10):

1.

5. The method according to claim 4, characterized in that, The oil phase solution also includes the solvent n-hexane, and the mass concentration of 1,4-benzenedisulfonyl chloride in the n-hexane solution is 0.1~5 g / L.

6. The method according to claim 5, characterized in that, The interfacial polymerization reaction includes: at room temperature, first immersing the surface of the polyethersulfone support film in the aqueous phase solution for 2-30 minutes, after immersion, pouring out the excess aqueous phase solution and wiping off the water on the film surface, then immersing in the oil phase solution for 1-30 minutes for interfacial polymerization reaction, and after the reaction, pouring out the excess oil phase solution.

7. The method according to claim 6, characterized in that, The heat treatment is carried out in a microwave vacuum dryer at a gauge pressure of -0.1~0 MPa and a temperature of 80~120℃ for 1~3 min.

8. A composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane is prepared according to any one of claims 1-7.

9. The application of the composite nanofiltration membrane according to claim 8 in the treatment of acidic wastewater.

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