Bionic strong acid-resistant nanofiltration membrane and preparation method thereof

Abstract

The invention relates to a bionic strong acid-resistant nanofiltration membrane and a preparation method thereof, and the bionic strong acid-resistant nanofiltration membrane comprises a porous support layer and an active separation layer formed on the surface of the porous support layer, the active separation layer is a polymer network layer formed by carrying out interfacial polymerization reaction on a water-phase solution containing polyamine and an oil-phase solution containing polyacyl chloride on the surface of the porous support layer. The water-phase solution and / or the oil-phase solution also contains a bionic amphiphilic phosphate compound, the bionic amphiphilic phosphate compound participates in interfacial polymerization reaction through an active functional group in a molecular structure of the bionic amphiphilic phosphate compound, and the phosphate structure of the bionic amphiphilic phosphate compound is covalently connected into a skeleton of the polymer network layer. The preparation method has the beneficial effects that the bionic amphiphilic phosphate compound with a hydrophilic phosphate head, a hydrophobic alkyl tail and a reaction site is synthesized, so that the bionic amphiphilic phosphate compound is spontaneously and orderly arranged on a water / oil interface and participates in interfacial polymerization, the film forming uniformity is improved, the pore size distribution is narrowed, and the intelligent response characteristic is given to the film.

Description

Technical Field

[0001] This invention relates to the field of high-performance separation membrane technology, and in particular to a biomimetic strong acid resistant nanofiltration membrane and its preparation method. Background Technology

[0002] Nanofiltration membrane separation technology has been widely used in water treatment, food processing, and chemical separation due to its advantages such as low operating pressure, high selectivity, and low energy consumption. Among them, polyamide composite nanofiltration membranes have become the mainstream nanofiltration membranes due to their excellent separation performance. However, the separation layer of traditional polyamide nanofiltration membranes is formed through interfacial polymerization, and its chemical structure contains a large number of amide bonds. In the separation process of strong acid media, traditional polyamide nanofiltration membranes fail rapidly due to the easy hydrolysis of amide bonds. To address this, researchers have turned to developing composite nanofiltration membranes based on polyurea or acid-resistant modified polyamides. In recent years, they have also explored new systems such as polysulfonamide, poly(triazine)amine, and polyurethane by focusing on the polymer backbone structure, in order to fundamentally solve the problem of amide bond hydrolysis.

[0003] Currently, pure isocyanate-amine interfacial polymerization systems are used, such as the invention patent published in CN113509839B, which provides a method to form polyurea with urea bonds as crosslinking units. Although urea bonds are used to improve chemical stability, the reactivity of isocyanates with amines is significantly lower than that of traditional acyl chloride-amine systems. Therefore, it is necessary to increase the monomer concentration or extend the reaction time to obtain sufficient crosslinking degree and retention performance, resulting in a thicker active layer, high mass transfer resistance, and generally low acid permeation flux, making it difficult to meet the requirements of high-efficiency separation. Polysulfonamide nanofiltration membranes are another technical route. These membranes utilize the hydrolytic stability of sulfonamide bonds and can prepare a positively charged separation layer through catalyst-assisted secondary polymerization. Studies have shown that their performance remains stable after being soaked in 25wt% sulfuric acid for 30 days. However, polysulfonamide membranes are sensitive to divalent ions such as Mg2+. 2+ The rejection rate of these membranes is generally below 95%, and the permeation flux often decreases significantly. Polyurethane nanofiltration membranes, on the other hand, utilize the reaction between isocyanate and polyphenols to prepare an ultrathin selective layer with a thickness of only 10 nm through kinetic control, effectively controlling sub-nanopores and exhibiting good acid resistance. However, they are mainly used for sieving large molecular dyes / heavy metal ions, and their efficient rejection capability for small molecular inorganic salt ions has not yet been explored.

[0004] To overcome the performance bottlenecks of separation layer materials, new strategies have emerged in recent years to regulate monomer diffusion and achieve ultrathin separation layers by introducing intermediate layers (such as carbon nanotubes and nanocellulose). In these strategies, the intermediate layer acts as a "reservoir," uniformly adsorbing and storing aqueous amine monomers, promoting the formation of thinner, less defective polyamide separation layers. However, this method requires additional intermediate layer construction steps, increasing process complexity and production costs. The intermediate layer's bonding with the base membrane and separation layer relies primarily on physical adsorption, posing a potential risk of interfacial delamination or performance degradation under long-term operation. Furthermore, the intermediate layer itself does not participate in the chemical structure of the final separation layer, making it impossible to incorporate pH-responsive functions into the membrane's network framework.

[0005] Another strategy involves post-modification or the construction of composite active layer structures. For example, patent publication CN119548987A introduces a polyphenol modification layer after the formation of the polyurea separation layer, while patent publication CN117181027A uses acyl chloride and isocyanate monomers simultaneously in the oil phase to construct a polyamide-polyurea composite network. These methods achieve complementary performance to some extent, but the process steps are complex, increasing the difficulty and cost of production control. More importantly, the introduced additional interfaces or heterogeneous chemical structures may become weak points in performance degradation under long-term erosion by strong acid media due to insufficient interfacial bonding or differences in the expansion coefficients of different materials, affecting the long-term stability of the membrane.

[0006] In addition, some studies have explored the preparation of cross-linked active separation layers with carbon-covalent bonds as the main chain through UV-initiated graft polymerization, utilizing the strong chemical inertness of C-C bonds to achieve extreme acid and alkali resistance. However, the photograft polymerization process has relatively weak control over the formation of highly cross-linked, uniformly pore-sized network structures, and this technical route has poor compatibility with currently mature industrial interfacial polymerization platforms. Other studies have explored improving membrane hydrophilicity and flux by doping the casting solution or aqueous phase with hydrophilic polymers or small molecule wetting agents. However, these physically blended additives are prone to leaching or loss from the polymer network during long-term operation, especially under strong acid conditions, leading to irreversible degradation of membrane performance over time and failing to guarantee long-term operational stability.

[0007] In summary, existing technologies generally face two core contradictions: On a macroscopic level, it is difficult to simultaneously achieve high ion rejection, high acid permeability, and long-term acid resistance; on a technical implementation level, there is a fundamental conflict between chemical methods to improve acid resistance (such as using isocyanates and sulfonyl chlorides) and structural requirements for obtaining excellent separation performance (such as forming a thin and dense active layer). Attempts to compensate for this conflict through process layering or physical modification introduce new interfacial instabilities and functional non-persistence issues. Specifically, existing technologies suffer from three major drawbacks:

[0008] I. Structural defects caused by reaction kinetic bottlenecks: Existing technologies using hydrolysis-resistant monomers such as isocyanates and sulfonyl chlorides have much lower reactivity than traditional acyl chlorides. To achieve sufficient crosslinking degree to retain ions, the monomer concentration must be increased or the reaction time extended, leading to excessive growth and a significant increase in the thickness of the active layer. This structural defect severely limits acid permeation flux, failing to meet the requirements for efficient acid recovery.

[0009] II. Stability defects caused by misaligned modification strategies: Existing methods for constructing composite layers by physically blending hydrophilic additives or post-modification rely solely on physical adsorption or weak interactions between the functional components and the polymer network. Under strong acid environments and long-term osmotic pressure, these additives are prone to dissolution and migration, and the modified layers are easily peeled off, leading to irreversible degradation of the membrane's hydrophilicity and separation performance.

[0010] Third, the performance rigidity caused by the lack of fine-tuning capability: Most existing technical solutions only focus on basic performance such as acid resistance and rejection rate. The chemical composition and microstructure of their separation layer remain fixed after film formation, lacking the ability to respond to external environments (such as pH changes). As a result, the membrane cannot adaptively adjust its separation selectivity when faced with dynamic changes in the ionic composition of complex feed solutions, thus limiting its application scenarios. Summary of the Invention

[0011] (a) Technical problems to be solved

[0012] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a biomimetic strong acid resistant nanofiltration membrane and its preparation method, which solves the technical problem that existing acid resistant nanofiltration membranes are difficult to balance among high ion rejection rate, high acid permeation flux and long-term acid resistance stability.

[0013] (II) Technical Solution

[0014] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0015] In a first aspect, embodiments of the present invention provide a biomimetic strong acid resistant nanofiltration membrane, comprising a porous support layer and an active separation layer formed on the surface of the porous support layer;

[0016] The active separation layer is a polymer network layer formed by interfacial polymerization of an aqueous solution containing polyamines and an oil solution containing polyacryl chlorides on the surface of a porous support layer.

[0017] The aqueous solution and / or the oil solution further contain a biomimetic amphiphilic phosphate compound, which participates in the interfacial polymerization reaction through the active functional groups in its molecular structure, and covalently integrates its phosphate structure into the backbone of the polymer network layer.

[0018] In a preferred embodiment of the present invention, the biomimetic amphiphilic phosphate compound has the general structural formula R1-OP(O)(OH)-O-(CH2). n -X;

[0019] Wherein, R1 is a C8-C18 straight-chain or branched alkyl group; n is an integer from 1 to 6;

[0020] When the biomimetic amphiphilic phosphate compound is added to an aqueous solution, X is an amino, secondary amino, tertiary amino, or ethanolamine residue.

[0021] When the biomimetic amphiphilic phosphate compound is added to the oil phase solution, X is an acyl chloride group, an isocyanate group, or an epoxy group.

[0022] In a preferred embodiment of the present invention, when the biomimetic amphiphilic phosphate compound is added to an aqueous solution, its structure is C0. 12 H 25 -OP(O)(OH)-O-(CH2)2-NH2; When the biomimetic amphiphilic phosphate compound is added to the oil phase solution, the structure is C 12 H 25 -OP(O)(OH)-O-(CH2)2-NCO.

[0023] In a preferred embodiment of the present invention, the active separation layer has a gradient crosslinking structure, wherein the gradient crosslinking structure is a loose inner layer with low crosslinking density and loose structure on the side near the porous support layer, and a dense surface layer with high crosslinking density and dense structure on the side away from the porous support layer.

[0024] In a preferred embodiment of the present invention, the polyamine is selected from at least one of piperazine, piperazine derivatives, m-phenylenediamine, p-phenylenediamine, N-aminoethylpiperazine, and polyethyleneimine;

[0025] The polyacryl chloride is selected from at least one of pyromellitic chloride, phthaloyl chloride, and terephthaloyl chloride.

[0026] In a preferred embodiment of the present invention, the porous support layer is an acid-resistant ultrafiltration membrane, and the material is selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, and polytetrafluoroethylene.

[0027] Secondly, embodiments of the present invention provide a method for preparing a biomimetic strong acid-resistant nanofiltration membrane, comprising the following steps:

[0028] S1. Preparation of biomimetic amphiphilic phosphate compounds: C8-C18 alkyl alcohols are reacted with phosphorus pentoxide, and hydrolysis yields an alkyl phosphate intermediate of R1-OP(O)(OH)-OH; the alkyl phosphate intermediate is reacted with an excess of a compound containing an active functional group in the presence of a condensing agent to obtain a biomimetic amphiphilic phosphate compound R1-OP(O)(OH)-O-(CH2) suitable for aqueous phase. n -X, where R1 is a C8-C18 straight-chain or branched alkyl group, n is an integer from 1 to 6, and X is an amino, secondary amino, tertiary amino, or ethanolamine residue.

[0029] S2. Dissolve the polyamine and the biomimetic amphiphilic phosphate compound suitable for aqueous phase in water to prepare an aqueous solution; use the aqueous solution and an oil solution containing polyacrylamide chloride to carry out an interfacial polymerization reaction to form at least one polymer network layer on the surface of the porous support layer.

[0030] or,

[0031] The biomimetic amphiphilic phosphate compound suitable for the aqueous phase was dissolved in an organic solvent and reacted with a derivatizing reagent to convert its active functional group into an active functional group that can react with polyamines, thus obtaining the biomimetic amphiphilic phosphate compound R1-OP(O)(OH)-O-(CH2) suitable for the oil phase. n -X, where R1 is a C8-C18 straight-chain or branched alkyl group, n is an integer from 1 to 6, and X is an acyl chloride group, isocyanate group, or epoxy group; it is dissolved with a polyacyl chloride in an organic solvent to prepare an oil phase solution; the oil phase solution is used to carry out an interfacial polymerization reaction with an aqueous phase solution containing a polyamine to form at least one polymer network layer on the surface of the porous support layer.

[0032] S3. The membrane after the interfacial polymerization reaction is post-processed to obtain the biomimetic strong acid resistant nanofiltration membrane.

[0033] The compound containing an active functional group refers to a compound that can react with an alkyl phosphate intermediate and introduce its active functional group (such as amino or hydroxyl groups) into the end of the alkyl phosphate intermediate, thereby forming a biomimetic amphiphilic phosphate compound suitable for aqueous phase. By selecting different compounds containing active functional groups, different active functional groups X can be introduced into the end of the biomimetic amphiphilic phosphate compound, thereby controlling its subsequent participation in interfacial polymerization reactions.

[0034] The derivatizing reagent refers to a reagent capable of converting the terminal active functional group of a biomimetic amphiphilic phosphate ester compound suitable for the aqueous phase into the active functional group required for a biomimetic amphiphilic phosphate ester compound suitable for the oil phase. That is, the terminal active functional group (such as an amino group) of the biomimetic amphiphilic phosphate ester compound suitable for the aqueous phase obtained in step S1 is converted into another active functional group (such as an isocyanate group, acyl chloride group, etc.) that can react with polyamines through a derivatization reaction, thereby obtaining a biomimetic amphiphilic phosphate ester compound suitable for the oil phase.

[0035] In a preferred embodiment of the present invention, in step S1, the compound containing an active functional group is selected from at least one of ethylenediamine, propylenediamine, ethanolamine, and hydroxylamine.

[0036] In a preferred embodiment of the present invention, in step S2, the derivatizing reagent is selected from at least one of phosgene, triphosgene, thionyl chloride, and thionyl chloride.

[0037] In a preferred embodiment of the present invention, in step S2, the concentration of the biomimetic amphiphilic phosphate compound suitable for aqueous phase in the aqueous solution is 0.01wt%-1.0wt%;

[0038] The concentration of the biomimetic amphiphilic phosphate compound suitable for the oil phase in the oil phase solution is 0.01wt%-1.0wt%.

[0039] In a preferred embodiment of the present invention, in step S2, the interfacial polymerization reaction adopts a stepwise interfacial polymerization process, including:

[0040] Prepare a first oil phase solution and a second oil phase solution, wherein the concentration of polyacrylamide chloride in the second oil phase solution is higher than that in the first oil phase solution;

[0041] Step 1: Interfacial polymerization: After the aqueous solution comes into contact with the porous support layer, it comes into contact with the first oil phase solution to carry out the first interfacial polymerization reaction and form a loose inner layer.

[0042] The second step is interfacial polymerization: after the first interfacial polymerization reaction, it comes into contact with the second oil phase solution to carry out the second interfacial polymerization reaction, forming a dense surface layer on the loose inner layer.

[0043] In a preferred embodiment of the present invention, the reaction time of the first interface polymerization is 5s-40s; the reaction time of the second interface polymerization is 40s-120s.

[0044] In a preferred embodiment of the present invention, the concentration of the biomimetic amphiphilic phosphate compound suitable for aqueous phase in the aqueous solution is 0.01wt%-1.0wt%.

[0045] In a preferred embodiment of the present invention, the concentration of polyacrylamide chloride in the first oil phase solution is 0.05wt%-0.2wt%, and the concentration of polyacrylamide chloride in the second oil phase solution is 0.2wt%-0.5wt%.

[0046] In a preferred embodiment of the present invention, the concentration of the biomimetic amphiphilic phosphate compound suitable for the oil phase is 0.05wt%-0.2wt% in the first oil phase solution and 0.2wt%-0.5wt% in the second oil phase solution.

[0047] In a preferred embodiment of the present invention, in step S3, the post-treatment is heat treatment, with a heat treatment temperature of 40℃-100℃ and a time of 2min-30min.

[0048] (III) Beneficial Effects

[0049] The beneficial effects of this invention are as follows: A biomimetic strong acid-resistant nanofiltration membrane of this invention successfully constructs an active separation layer formed on the surface of a porous support layer through the synergistic effect of molecular design of biomimetic amphiphilic phosphate ester compounds and a stepwise interfacial polymerization process. The active separation layer of this invention is essentially a cross-linked polymer network formed by the interfacial polymerization of polyamines and polyacrylamide chlorides, with polyamide segments as the main chain backbone and covalently linked to phosphate ester compounds. By synthesizing biomimetic amphiphilic phosphate ester compounds with hydrophilic phosphate ester heads, hydrophobic alkyl tails, and reactive sites, these compounds are spontaneously and orderly arranged at the water / oil interface and participate in interfacial polymerization. This ordered interfacial behavior improves film uniformity and narrows the pore size distribution.

[0050] Among them, the biomimetic amphiphilic phosphate ester compound is permanently anchored in the polyamide network through covalent bonds with its phosphate ester structure, rather than being physically doped. The phosphate ester compound, as a hydrophilic functional group, is covalently locked in the polyamide network, which can improve the hydrophilicity of the membrane and the diffusion path of water molecules while maintaining the degree of crosslinking. Simultaneously, the covalently incorporated phosphate ester compound has two-stage ionization characteristics (pKa1≈2-3, pKa2≈7-12), endowing the strong acid-resistant nanofiltration membrane with pH-responsive intelligent separation function. Under different pH conditions, the phosphate ester compound exhibits different protonation states, thereby reversibly regulating the surface charge and pore size of the active separation layer: in a strong acid environment with pH < 3, the phosphate group is fully protonated, the positive charge of the membrane surface is enhanced, and the hydrogen bonding between molecular chains is strengthened, leading to pore size contraction. Through the synergistic effect of Donnan repulsion and size sieving, high-valence cations (such as Mg) are efficiently retained. 2+ Ni 2+ Cu 2 +(etc.); When the pH rises to the range of 3-8, the phosphate groups gradually ionize (deprotonate), the negative charge on the membrane surface gradually increases, and the pore size slightly expands, allowing for adjustment of the selectivity for ions of different valence states. Under alkaline conditions with pH > 8, the phosphate groups are completely deprotonated, and the membrane surface exhibits a strong negative charge, suitable for the separation of anionic pollutants. This reversible ionization / protonation behavior enables the membrane to sense changes in ambient pH and make adaptive adjustments, achieving selective separation of ions of different valence states, providing a new technical approach for the fractional separation and selective recovery of complex feed solutions.

[0051] The active separation layer is a polyamide layer with a gradient cross-linked structure. This structure is an asymmetric bilayer structure, where the inner layer near the support layer is a loose network with relatively low cross-linking degree, mainly providing high-throughput channels; the outer layer is a dense network with high cross-linking degree, mainly responsible for high-precision ion sieving. This gradient structure synergistic mechanism, with its loose inner layer and dense outer layer, allows the present invention to maintain the separation of Mg... 2+ With a retention rate as high as 99.3%, the water flux reaches 45 LMH. Compared with the existing technology, the retention rate has been increased from 96.5% to 99.3%, the water flux from 22 LMH to 45 LMH, and the acid permeation rate from 75.3% to 95.1%. It successfully solves the technical problem of existing acid-resistant nanofiltration membranes in balancing high retention rate, high flux, and high stability, and endows the membrane with intelligent response characteristics.

[0052] At the structural biomimetic level, this invention can simulate the amphiphilic structure of the hydrophilic head and hydrophobic tail of biological phospholipid molecules. The hydrophilic phosphate head group corresponds to the phosphate group of biological phospholipids, and the hydrophobic C8-C18 alkyl tail chain corresponds to the long chain of fatty acids. At the behavioral biomimetic level, the biomimetic amphiphilic monomers spontaneously and orderly arrange themselves at the oil / water interface to form a highly ordered monolayer, accurately mimicking the ability of biomolecules to form ordered structures at the interface. At the mechanistic biomimetic level, the loose inner layer / dense outer layer gradient structure constructed by stepwise interfacial polymerization simulates the asymmetric flow mosaic characteristics of the inner and outer leaves of the biomembrane. At the same time, the covalently bonded phosphate groups achieve pH responsiveness through reversible protonation / deprotonation, simulating the sensing and response mechanism of the biomembrane ion channel to environmental signals. At the functional biomimetic level, the core functions of the biomembrane are engineered and reproduced, namely, the dense outer layer provides high-precision ion sieving (selective barrier function), the loose inner layer provides low-resistance transport channels (high-throughput transport efficiency), and the pH-responsive adaptive separation capability (dynamic response characteristics). This systematic biomimicry enabled the invention to achieve a synergistic breakthrough in acid flux, ion rejection rate and long-term stability under extremely strong acid conditions, and endowed it with intelligent response functions that are not available in existing technologies.

[0053] The hydrophobic alkyl chain (R1) of biomimetic amphiphilic phosphate compounds can have a carbon chain length selected between C8 and C18. Different chain lengths affect the amphiphilic balance of the monomer, the critical micelle concentration, and its packing density at the interface. Shorter chains (C8-C10) are beneficial for improving molecular flexibility and diffusion rate, and can form a thinner active layer; longer chains (C16-C18) can enhance hydrophobic interactions and promote more ordered interfacial self-assembly. The alkyl chain can also be a branched structure (such as 2-ethylhexyl) or contain unsaturated bonds (such as vinyl) to adjust its packing density and fluidity at the interface and optimize polymerization kinetics. The connecting arm (-(CH2)) links the hydrophilic head group to the reaction site. n - The length n can vary between 1 and 6. Shorter connecting arms (n=1-2) bring reactive functional groups closer to the hydrophilic head group, affecting their orientation and reactivity at the interface; longer connecting arms (n=4-6) increase molecular flexibility, facilitating the contact of reactive functional groups across the interface with polyamines / polyacrylic chlorides. When added to an aqueous solution, X can be a primary amino group, secondary amino group, tertiary amino group, or a group containing both amino and hydroxyl groups (such as ethanolamine residues). Monomers containing tertiary amino groups can impart additional positive charge to the membrane, enhancing Donan repulsion against high-valence cations. When added to an oil solution, X can be an acyl chloride group (-COCl), an isocyanate group (-NCO), or an epoxy group (-CH(O)CH-), allowing it to dissolve in the oil phase and react with the aqueous amine.

[0054] The present invention provides a method for preparing a biomimetic, strong acid-resistant nanofiltration membrane by introducing an amphiphilic phosphate compound as a component of an aqueous or oil-phase solution. This compound directly or partially replaces traditional aqueous or oil-phase formulations and can be continuously produced on a composite membrane production line. The entire preparation process requires no additional intermediate layer coating equipment, post-modification steps, or UV curing devices, and is highly compatible with existing polyamide composite membrane production processes.

[0055] The synthetic route for the amphiphilic phosphate ester compounds designed in this invention uses raw materials (such as alkyl alcohols, phosphorus pentoxide, ethylenediamine, etc.) that are all industrial chemicals with ample market supply and stable prices, eliminating the need for special or scarce fine chemical raw materials. The esterification and amidation reactions involved in the synthesis process do not require harsh conditions such as high temperature and pressure, strong acids and bases, or precious metal catalysts, resulting in low equipment requirements and low energy consumption. The reaction produces few byproducts, and the product separation and purification process is mature, yielding high outputs suitable for large-scale mass production. The biomimetic amphiphilic phosphate ester compounds can exist only in aqueous solution, only in oil solution, or both simultaneously.

[0056] The acid-resistant nanofiltration membrane of this invention can be used in acidic wastewater treatment, acid recovery, or hydrometallurgical liquid separation. The flux of this membrane is more than 100% higher than that of existing pure polyurea membranes. Therefore, when treating the same amount of wastewater, the required membrane area is reduced by more than half, significantly lowering the initial investment cost of membrane elements. Simultaneously, its long-term stability reduces the frequency of membrane element replacement, minimizing long-term operating costs associated with downtime maintenance and consumable replacement. Detailed Implementation These embodiments are provided so that the invention can be understood more clearly and thoroughly, and that the scope of the invention can be fully conveyed to those skilled in the art.

[0057] Example 1:

[0058] This embodiment provides a method for preparing a biomimetic strong acid resistant nanofiltration membrane, including the following steps:

[0059] (1) Preparation of biomimetic amphiphilic phosphate compounds suitable for aqueous phase: 1-dodecyl alcohol (C 12 H 25 OH) and phosphorus pentoxide (P2O5) are mixed in a molar ratio of 2:1 and reacted at 60°C for 4 hours. Hydrolysis yields a dodecyl phosphate intermediate with the structural formula C. 12 H 25 -OP(O)(OH)-OH; The obtained intermediate was dissolved in anhydrous tetrahydrofuran, and excess ethylenediamine and condensing agent N,N'-dicyclohexylcarbodiimide (DCC) were added. The reaction was carried out at room temperature for 12 h. The reaction solution was purified by extraction, washing, and column chromatography to obtain N-(2-aminoethyl)-dodecylphosphonamide (hereinafter referred to as "monomer A"), whose structural formula is C 12 H 25 -OP(O)(OH)-O-(CH2)2-NH2.

[0060] (2) Preparation of aqueous solution: Dissolve 0.2wt% piperazine and 0.05wt% monomer A obtained in step (1) in deionized water and stir evenly to obtain aqueous solution.

[0061] (3) Preparation of oil phase solution: Dissolve 0.15wt% trimesoyl chloride (TMC) in n-hexane and stir until homogeneous to obtain oil phase solution.

[0062] (4) Provide a porous support base membrane: Use a polysulfone ultrafiltration membrane (molecular weight cutoff of 50,000 Da) as the support base membrane, wash it thoroughly with deionized water, and then soak it in deionized water for later use.

[0063] (5) One-step interfacial polymerization: The aqueous solution prepared in step (2) is coated onto the surface of the supporting base membrane and allowed to stand for 2 minutes to fully load the aqueous solution onto the surface and pores of the base membrane. Then, excess aqueous solution droplets are drained from the membrane surface, and the oil solution prepared in step (3) is uniformly coated onto the membrane surface to carry out the interfacial polymerization reaction for 60 seconds.

[0064] (6) Post-treatment: Pour off the excess oil phase solution on the membrane surface, place the membrane in an oven at 75°C for heat treatment for 10 minutes to further crosslink and solidify the active separation layer, and finally thoroughly clean the membrane surface with deionized water to remove the residual solvent, thus obtaining the biomimetic strong acid resistant nanofiltration membrane, denoted as M-1.

[0065] Example 2

[0066] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and embodiment 1 is that: Step (3) prepare oil phase solution: dissolve trimesoyl chloride (TMC) in n-hexane to prepare two oil phase solutions of different concentrations: first oil phase solution: TMC concentration is 0.1wt%; second oil phase solution: TMC concentration is 0.35wt%.

[0067] (5) Step-by-step interface aggregation:

[0068] Step 1: Interfacial polymerization: The aqueous solution prepared in step (2) is coated onto the surface of the supporting base membrane and allowed to stand for 2 minutes to fully load the aqueous solution onto the surface and pores of the base membrane. Then, excess aqueous solution droplets are drained from the membrane surface, and the first oil phase solution prepared in step (3) is uniformly coated onto the membrane surface to carry out the first interfacial polymerization reaction for 20 seconds, forming a loose inner layer with a relatively low crosslinking density on the surface of the supporting base membrane.

[0069] Second step interface polymerization: After completing the first step interface polymerization reaction, without draining the residual oil phase liquid film on the membrane surface, immediately coat the second oil phase solution prepared in step (3) evenly on the membrane surface to carry out the second interface polymerization reaction. The reaction time is 60s, and a dense surface layer with relatively high crosslinking density is constructed on the loose inner layer formed in the first step.

[0070] The remaining steps are the same, denoted as M-2.

[0071] Example 3

[0072] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and embodiment 2 is that: Step (2) prepares an aqueous solution: 0.2wt% piperazine and 0.01wt% monomer A obtained in step (1) are dissolved in deionized water and stirred evenly to obtain an aqueous solution.

[0073] The remaining steps are the same, denoted as M-3.

[0074] Example 4

[0075] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and embodiment 2 is that: Step (2) prepares an aqueous solution: 0.2wt% piperazine and 0.2wt% monomer A obtained in step (1) are dissolved in deionized water and stirred evenly to obtain an aqueous solution.

[0076] The remaining steps are the same, denoted as M-4.

[0077] Example 5

[0078] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and embodiment 2 is that: step (5) stepwise interfacial polymerization: the reaction time of the first interfacial polymerization is 60s.

[0079] The remaining steps are the same, and are denoted as M-5.

[0080] Example 6

[0081] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and Example 2 is that: Step (1) prepares a biomimetic amphiphilic phosphate compound suitable for the oil phase: First, the intermediate N-(2-aminoethyl)-dodecylphosphamide (i.e., monomer A in Example 1) is synthesized according to the method of step (1) in Example 1. Its structural formula is C 12 H 25 -OP(O)(OH)-O-(CH2)2-NH2; The above intermediate was dissolved in anhydrous dichloromethane, and an excess of phosgene in toluene solution was slowly added under ice bath conditions. The mixture was then heated to room temperature and the reaction continued for 4 hours. After the reaction was completed, the solvent and excess phosgene were removed by vacuum distillation to obtain N-(2-ethyl isocyanate)-dodecyl phosphoramide (hereinafter referred to as "monomer B"), whose structural formula is C. 12 H 25 -OP(O)(OH)-O-(CH2)2-NCO.

[0082] The reaction equation is shown below:

[0083] C 12 H 25 -OP(O)(OH)-O-(CH2)2-NH2+COCl2→C 12 H 25 -OP(O)(OH)-O-(CH2)2-NCO+2HCl

[0084] (2) Preparation of aqueous solution: Dissolve 0.25wt% piperazine in deionized water and stir until homogeneous to obtain aqueous solution.

[0085] (3) Preparation of oil phase solutions: Dissolve trimesoyl chloride (TMC) and monomer B obtained in step (1) in n-hexane to prepare two oil phase solutions with different concentrations: First oil phase solution: TMC concentration is 0.1wt%, monomer B concentration is 0.05wt%; Second oil phase solution: TMC concentration is 0.35wt%, monomer B concentration is 0.25wt%.

[0086] The remaining steps are the same, and are denoted as M-6.

[0087] Example 7

[0088] This embodiment provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this embodiment and Example 2 is that: Step (3) prepares the oil phase solution: Trimethylbenzene chloride (TMC) and monomer B obtained in step (1) of Example 6 are dissolved in n-hexane to prepare two oil phase solutions with different concentrations: First oil phase solution: TMC concentration is 0.1wt%, monomer B concentration is 0.05wt%; Second oil phase solution: TMC concentration is 0.35wt%, monomer B concentration is 0.25wt%.

[0089] The remaining steps are the same, and are referred to as M-7.

[0090] Comparative Example 1

[0091] This comparative example provides a biomimetic strong acid resistant nanofiltration membrane. The difference between this comparative example and Example 2 is that monomer A is not added and the aqueous solution contains only polyamine. Specifically, step (2) prepares the aqueous solution: 0.25wt% piperazine is dissolved in deionized water and stirred evenly to obtain the aqueous solution.

[0092] The remaining steps are the same, denoted as C-1.

[0093] Comparative Example 2

[0094] This comparative example follows the method described in the example of prior art patent CN113509839B to prepare a pure polyurea acid-resistant nanofiltration membrane. Isophorone diisocyanate was used as the polyacrylamide chloride, piperazine as the polyamine, the interfacial polymerization reaction time was 120 s, and the post-treatment conditions were the same as in Example 1. The resulting membrane is designated as C-2.

[0095] Verification Example 1

[0096] The biomimetic strong acid resistant nanofiltration membranes prepared in Examples 1-7 and Comparative Examples 1-2 were subjected to systematic performance tests. The specific test methods are as follows:

[0097] (1) Mg 2+ Retention rate: Under conditions of 3.0 MPa and 25 °C, the feed solution containing 2000 ppm MgSO4 was tested. Ion chromatography was used to determine the Mg content in the feed solution and permeate. 2+ Concentration, calculate the rejection rate.

[0098] (2) Acid permeation rate: Under the conditions of 3.0 MPa and 25℃, a cross-flow filtration test was conducted on a mixed feed solution containing 15 wt% H2SO4 and 2000 ppm MgSO4. The H2SO4 content in the feed solution and permeate was determined by acid-base titration. + Concentration, calculate acid permeability.

[0099] (3) Water flux: Record the volume of solution per unit membrane area per unit time under the above test conditions (LMH).

[0100] (4) Long-term stability: The membrane sample was immersed in a 15wt% H2SO4 solution at 50℃, and removed periodically (up to 21 days). The Mg content was tested under standard conditions (1.0MPa, 2000ppm MgSO4, pH 7). 2+ Retention rate is used to assess performance degradation. Based on the time-temperature equivalence principle of polymer materials, increasing temperature and extending time can produce the same effect on material aging or deformation. A commonly used empirical rule is van der Hoff's rule: for every 10°C increase in temperature, the material aging rate increases 2-4 times. A membrane immersed at 50°C for 21 days is equivalent to withstanding more than one year at room temperature.

[0101] The test results of the membranes prepared in Examples 1-7 and Comparative Examples 1-2 are shown in Table 1.

[0102] Table 1

[0103]

[0104] Verification Example 2

[0105] To verify the pH response characteristics of the nanofiltration membrane of the present invention, membrane M-2 obtained in Example 2 was selected, and its response to Mg was tested under different pH conditions. 2+ and Na + The retention performance was assessed. The test pressure was 1.0 MPa, and the feed solution contained 2000 ppm of the corresponding ions. The pH was adjusted using H2SO4 or NaOH. The test results are shown in Table 2.

[0106] Table 2

[0107]

[0108] Based on the performance test results in Table 1, the following analytical conclusions can be drawn:

[0109] A comparison of M-1 and M-2 shows that the membrane prepared by one-step interfacial polymerization, containing the same polyamine, forms a homogeneous and dense active layer. Although it has a certain rejection rate, its flux and acid permeability are lower than those of the membrane prepared by stepwise interfacial polymerization. It is noteworthy that the TMC concentration used in M-1 (0.15 wt%) is lower than the concentration in the second step of M-2 (0.35 wt%), but its flux (28 LMH) and acid permeability (80.2%) are already significantly lower than those of M-2 (45 LMH, 95.1%). Therefore, even if M-1 were to directly use the same high concentration (0.35 wt%) as the second step of M-2 for one-step polymerization, it would only form a thicker and denser homogeneous layer, leading to a further decrease in flux.

[0110] A comparison of M-2 and M-3 with M-4 shows that: decreasing the monomer A concentration slightly increases the membrane flux, but decreases the rejection rate. This is because the ordered arrangement density of monomer A at the interface decreases, leading to a weakening of the surface layer's compactness. Increasing the monomer A concentration slightly increases the rejection rate, but significantly decreases the flux and acid permeability. This is because excessively high monomer A concentrations result in an overly dense interfacial assembly layer, leading to excessively high overall cross-linking and increased thickness of the active layer.

[0111] The comparison between M-5 and M-2 shows that: the first step reaction time is too long, which leads to excessive cross-linking of the initially formed loose inner layer and loss of looseness. In the second step, the high concentration of monomer A is difficult to effectively penetrate and form an ideal gradient structure, resulting in increased overall mass transfer resistance and a significant decrease in flux.

[0112] The performance of M-6 is comparable to that of M-2, indicating that designing monomer B in an oil-soluble form (X being NCO) and applying it to the oil phase can also achieve excellent overall performance. This demonstrates that the structural design of the biomimetic amphiphilic phosphate compound of this invention has high flexibility and adaptability, and its function does not depend on its distribution in a specific phase. As long as it can participate in the interfacial polymerization reaction, it can play a core role in interface guidance and functionalization.

[0113] M-7 maintains high throughput while Mg 2+ The retention rate increased to 99.6%, and long-term stability was also slightly improved. This indicates that when biomimetic amphiphilic phosphate compounds are introduced simultaneously into the aqueous and oil phases, a more ordered and complementary assembly structure can be formed on both sides of the interface. The synergistic effect of monomers on both sides may further optimize the uniformity of the interfacial polymerization reaction and the integrity of the network structure, thereby further improving the separation accuracy and structural stability while keeping the flux essentially unchanged.

[0114] A comparison of C-1 and M-2 shows that the membrane without biomimetic amphiphilic phosphate ester compounds (polyamines / polyacrylic chlorides) exhibits significantly inferior retention performance and long-term stability under strong acid conditions compared to the membrane prepared in this invention. This is due to the lack of covalent anchoring of phosphate ester groups, resulting in insufficient hydrophilicity and hydrolysis resistance of the membrane, as well as the lack of ordered guidance in interfacial polymerization and poor uniformity of the active layer structure.

[0115] A comparison of C-2 and M-2 shows that although existing polyurea technologies have a certain degree of acid resistance, their low reactivity leads to an excessively thick active layer, severely limiting throughput. Furthermore, the lack of covalent anchoring of functional groups results in long-term stability that is still inferior to that of the present invention.

[0116] Based on the performance test results in Table 2, the following analytical conclusions can be drawn:

[0117] The membrane of this invention has significant pH-responsive separation characteristics, and can selectively separate ions of different valence states by adjusting the ambient pH. This intelligent response function is not available in existing acid-resistant membrane technologies.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A biomimetic nanofiltration membrane resistant to strong acids, characterized in that, It includes a porous support layer and an active separation layer formed on the surface of the porous support layer; The active separation layer is a polymer network layer formed by interfacial polymerization of an aqueous solution containing polyamines and an oil solution containing polyacryl chlorides on the surface of a porous support layer. The aqueous solution and / or the oil solution further contain a biomimetic amphiphilic phosphate compound, which participates in the interfacial polymerization reaction through the active functional groups in its molecular structure, and covalently integrates its phosphate structure into the backbone of the polymer network layer.

2. The biomimetic strong acid resistant nanofiltration membrane as described in claim 1, characterized in that, The general structural formula of the biomimetic amphiphilic phosphate compound is R1-OP(O)(OH)-O-(CH2). n -X; Wherein, R1 is a C8-C18 straight-chain or branched alkyl group; n is an integer from 1 to 6; When the biomimetic amphiphilic phosphate compound is added to an aqueous solution, X is an amino, secondary amino, tertiary amino, or ethanolamine residue. When the biomimetic amphiphilic phosphate compound is added to the oil phase solution, X is an acyl chloride group, an isocyanate group, or an epoxy group.

3. The biomimetic strong acid resistant nanofiltration membrane as described in claim 2, characterized in that, When the biomimetic amphiphilic phosphate compound is added to an aqueous solution, its structure is C 12 H 25 -OP(O)(OH)-O-(CH2)2-NH2; When the biomimetic amphiphilic phosphate compound is added to the oil phase solution, the structure is C 12 H 25 -OP(O)(OH)-O-(CH2)2-NCO.

4. The biomimetic strong acid resistant nanofiltration membrane as described in claim 1, characterized in that, The active separation layer has a gradient cross-linking structure, which consists of a loose inner layer with low cross-linking density and loose structure on the side near the porous support layer, and a dense surface layer with high cross-linking density and dense structure on the side away from the porous support layer.

5. The biomimetic strong acid resistant nanofiltration membrane as described in claim 1, characterized in that, The polyamine is selected from at least one of piperazine, piperazine derivatives, m-phenylenediamine, p-phenylenediamine, N-aminoethylpiperazine, and polyethyleneimine; The polyacryl chloride is selected from at least one of pyromellitic chloride, phthaloyl chloride, and terephthaloyl chloride.

6. The biomimetic strong acid resistant nanofiltration membrane as described in claim 1, characterized in that, The porous support layer is an acid-resistant ultrafiltration membrane, and the material is selected from at least one of polysulfone, polyethersulfone, polyvinylidene fluoride, and polytetrafluoroethylene.

7. A method for preparing a biomimetic strong acid resistant nanofiltration membrane, characterized in that, Includes the following steps: S1. Preparation of biomimetic amphiphilic phosphate compounds: C8-C18 alkyl alcohols are reacted with phosphorus pentoxide, and hydrolysis yields an alkyl phosphate intermediate of R1-OP(O)(OH)-OH; the alkyl phosphate intermediate is reacted with an excess of a compound containing an active functional group in the presence of a condensing agent to obtain a biomimetic amphiphilic phosphate compound R1-OP(O)(OH)-O-(CH2) suitable for aqueous phase. n -X, where R1 is a C8-C18 straight-chain or branched alkyl group, n is an integer from 1 to 6, and X is an amino, secondary amino, tertiary amino, or ethanolamine residue. S2. Dissolve the polyamine and the biomimetic amphiphilic phosphate compound suitable for aqueous phase in water to prepare an aqueous solution; use the aqueous solution and an oil solution containing polyacrylamide chloride to carry out an interfacial polymerization reaction to form at least one polymer network layer on the surface of the porous support layer. or, The biomimetic amphiphilic phosphate compound suitable for the aqueous phase was dissolved in an organic solvent and reacted with a derivatizing reagent to convert its active functional group into an active functional group that can react with polyamines, thus obtaining the biomimetic amphiphilic phosphate compound R1-OP(O)(OH)-O-(CH2) suitable for the oil phase. n -X, where R1 is a C8-C18 straight-chain or branched alkyl group, n is an integer from 1 to 6, and X is an acyl chloride group, isocyanate group, or epoxy group; it is dissolved with a polyacyl chloride in an organic solvent to prepare an oil phase solution; the oil phase solution is used to carry out an interfacial polymerization reaction with an aqueous phase solution containing a polyamine to form at least one polymer network layer on the surface of the porous support layer. S3. The membrane after the interfacial polymerization reaction is post-processed to obtain the biomimetic strong acid resistant nanofiltration membrane.

8. The method for preparing the biomimetic strong acid resistant nanofiltration membrane as described in claim 7, characterized in that, In step S2, the concentration of the biomimetic amphiphilic phosphate compound suitable for aqueous phase in the aqueous solution is 0.01wt%-1.0wt%; The concentration of the biomimetic amphiphilic phosphate compound suitable for the oil phase in the oil phase solution is 0.01wt%-1.0wt%.

9. The method for preparing the biomimetic strong acid resistant nanofiltration membrane as described in claim 7, characterized in that, In step S2, the interfacial polymerization reaction adopts a stepwise interfacial polymerization process, including: Prepare a first oil phase solution and a second oil phase solution, wherein the concentration of polyacrylamide chloride in the second oil phase solution is higher than that in the first oil phase solution; Step 1: Interfacial polymerization: After the aqueous solution comes into contact with the porous support layer, it comes into contact with the first oil phase solution to carry out the first interfacial polymerization reaction and form a loose inner layer. The second step is interfacial polymerization: after the first interfacial polymerization reaction, it comes into contact with the second oil phase solution to carry out the second interfacial polymerization reaction, forming a dense surface layer on the loose inner layer.

10. The method for preparing the biomimetic strong acid resistant nanofiltration membrane as described in claim 9, characterized in that, The reaction time for the first interface polymerization is 5s-40s; the reaction time for the second interface polymerization is 40s-120s.

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