Acid-resistant nanofiltration membrane and preparation method thereof

Abstract

The invention discloses an acid-resistant nanofiltration membrane and a preparation method thereof, and belongs to the technical field of membrane separation. The gradient heterojunction active layer is formed on the base film through sequential interfacial polymerization and comprises a polysulfonamide bottom layer adjacent to the base film and a polyamine-metal organic framework composite layer located on the polysulfonamide bottom layer; the gradient heterojunction active layer is coated with the pH response self-repairing layer, and the self-repairing layer comprises pH response type microcapsules dispersed in cross-linked polyvinyl alcohol hydrogel; the membrane has excellent self-repairing capability and maintenance convenience, the repairing efficiency of artificial microcosmic damage in an acid environment within 24 hours can reach 85% or above, tiny scratches and defects generated in the operation or installation process of the membrane can be automatically repaired, the failure of the whole membrane element caused by tiny damage expansion is avoided, and the service life of the membrane element is prolonged. And the unplanned shutdown risk and the special repair and maintenance cost are reduced.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically referring to an acid-resistant nanofiltration membrane and its preparation method. Background Technology

[0002] Nanofiltration membranes, as separation membranes with nanoscale pore sizes, have wide applications in wastewater treatment, material separation, and resource recovery. However, existing polyamide nanofiltration membranes are prone to hydrolysis and structural degradation in strong acid environments, leading to a sharp decline in separation performance. Current methods to improve the acid resistance of nanofiltration membranes mainly include: introducing acid-resistant chemical groups (such as sulfonic acid groups); reinforcing with inorganic nanomaterials (such as TiO2 and SiO2); and surface crosslinking modification.

[0003] However, these methods have limitations: single acid-resistant groups will still degrade under long-term extreme acid conditions; inorganic nanomaterials have poor interfacial compatibility with polymer matrices and are prone to peeling; and the surface modification layer is prone to detachment in acidic environments.

[0004] Therefore, developing a nanofiltration membrane with long-lasting acid resistance and the ability to self-repair after damage is of great practical significance. Summary of the Invention

[0005] In order to overcome some of the problems mentioned in the background above, the present invention provides an acid-resistant nanofiltration membrane and a method for preparing the same, so as to at least partially solve the above problems.

[0006] According to the technical solution of the present invention, an acid-resistant nanofiltration membrane is provided, comprising: Polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer is formed on the base film by sequential interfacial polymerization. The gradient heterojunction active layer includes a polysulfonamide underlayer adjacent to the base film and a polyamine-metal-organic framework composite layer located thereon. A pH-responsive self-healing layer coated on the gradient heterojunction active layer, the self-healing layer comprising pH-responsive microcapsules dispersed in a cross-linked polyvinyl alcohol hydrogel.

[0007] Preferably, the metal-organic framework in the polyamine-metal-organic framework composite layer is a zirconium-based MOF UIO-66-NH2 nanosheet.

[0008] Preferably, the wall material of the pH-responsive microcapsule is polyurea, the core material comprises a mixture of isophorone diisocyanate and hydroxyl-terminated polydimethylsiloxane, and the diameter of the microcapsule is 1-5 μm.

[0009] This invention also provides a method for preparing an acid-resistant nanofiltration membrane, comprising the following steps: Preparation of polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer was constructed on the base film using a sequential interfacial polymerization method. A coating solution loaded with pH-responsive microcapsules is coated onto the gradient heterojunction active layer, and then cross-linked and cured to form a self-healing layer.

[0010] Preferably, the step of preparing the polyetheretherketoneketone ultrafiltration membrane specifically includes: The N-methylpyrrolidone casting solution containing 22 wt% polyether ether ketone ketone and 1 wt% lithium chloride was coated onto a nonwoven fabric using a non-solvent-induced phase separation method. After standing for 10-30 seconds in an environment of 24-26℃ and 55-65% humidity, it was immersed in a 25℃ pure water coagulation bath to complete the phase transformation. After thorough washing with water, the final product was obtained.

[0011] Preferably, the step of constructing the gradient heterojunction active layer includes: Step 1: Interfacial polymerization: Immerse the base film with an aqueous solution of 4,4'-diaminodiphenyl sulfone, remove excess aqueous phase, and then react with an organic solution of trimesoyl chloride for 60-120 seconds to form a polysulfonamide underlayer. The second step is interfacial polymerization: An aqueous solution containing polyethyleneimine and zirconium-amino-1,4-dimethylamine (MOF) nanosheets is impregnated onto the polysulfonamide substrate. After removing the excess aqueous phase, it is reacted with an organic phase solution of terephthaloyl chloride for 60 seconds to form a polyamine-metal-organic framework composite layer. Heat treatment: The obtained composite film is heat-treated at 60-100℃ for 10 min to cross-link the two layers through dynamic covalent bonds and form a gradient heterojunction structure.

[0012] Preferably, in the first step of interface aggregation: The aqueous phase solution was 2.0 wt% of 4,4'-diaminodiphenyl sulfone aqueous solution, and the organic phase solution was 0.15 wt% of pyromellitic sulfonyl chloride in Isopar G solution.

[0013] Preferably, in the second step of interface aggregation: The aqueous phase solution was an aqueous dispersion of 1.5-2.0 wt% polyethyleneimine and 0.05-0.2 wt% aminated UIO-66-NH2 nanosheets, and the organic phase solution was an Isopar G solution of 0.05-0.2 wt% terephthaloyl chloride.

[0014] Preferably, the step of applying the self-healing layer includes: The coating solution comprises 3-8 wt% pH-responsive microcapsules, 2-4 wt% polyvinyl alcohol, 0.4-0.6 wt% glutaraldehyde, and deionized water; The coating liquid was uniformly applied to the gradient heterojunction active layer using a Mayer rod and cured at 25°C for 12 hours to crosslink polyvinyl alcohol and glutaraldehyde to form a hydrogel network, thereby immobilizing the microcapsules within it.

[0015] Furthermore, the present invention also provides an application of an acid-resistant nanofiltration membrane, which is used in the treatment of acidic wastewater with a pH value not greater than 2, acid recovery in hydrometallurgical processes, or concentration and desalination of acidic dye wastewater.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention has excellent self-repair capability and convenient maintenance. For micro-damage caused by human factors, the repair efficiency can reach more than 85% within 24 hours in an acidic environment. Minor scratches and defects generated during membrane operation or installation can be automatically repaired, avoiding failure of the entire membrane element due to the spread of minor damage, reducing the risk of unplanned downtime and the cost of specialized repair and maintenance. Detailed Implementation

[0017] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection.

[0018] This invention provides an acid-resistant nanofiltration membrane, comprising: Polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer is formed on the base film by sequential interfacial polymerization. The gradient heterojunction active layer includes a polysulfonamide (PSA) underlayer adjacent to the base film and a polyamine-metal-organic framework (PA-MOF) composite layer thereon. A pH-responsive self-healing layer coated on the gradient heterojunction active layer, the self-healing layer comprising pH-responsive microcapsules dispersed in a cross-linked polyvinyl alcohol hydrogel.

[0019] In a further embodiment of this example, the metal-organic framework in the polyamine-metal-organic framework composite layer is a zirconium-based MOF UIO-66-NH2 nanosheet.

[0020] In a further embodiment of this example, the wall material of the pH-responsive microcapsule is polyurea, the core material comprises a mixture of isophorone diisocyanate (IPDI) and hydroxyl-terminated polydimethylsiloxane (PHMS), and the diameter of the microcapsule is 1-5 μm.

[0021] This invention also provides a method for preparing an acid-resistant nanofiltration membrane, comprising the following steps: Preparation of polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer was constructed on the base film using a sequential interfacial polymerization method. A coating solution loaded with pH-responsive microcapsules is coated onto the gradient heterojunction active layer, and then cross-linked and cured to form a self-healing layer.

[0022] In a further embodiment of this example, the step of preparing the polyetheretherketoneketone ultrafiltration membrane specifically includes: The N-methylpyrrolidone casting solution containing 22 wt% polyether ether ketone ketone and 1 wt% lithium chloride was coated onto a nonwoven fabric using a non-solvent-induced phase separation method. After standing for 10-30 seconds in an environment of 24-26℃ and 55-65% humidity, it was immersed in a 25℃ pure water coagulation bath to complete the phase transformation. After thorough washing with water, the final product was obtained.

[0023] In a further embodiment of this example, the step of constructing the gradient heterojunction active layer includes: Step 1: Interfacial polymerization: Immerse the base film with an aqueous solution of 4,4'-diaminodiphenyl sulfone, remove excess aqueous phase, and then react with an organic solution of trimesoyl chloride for 60-120 seconds to form a polysulfonamide underlayer. The second step is interfacial polymerization: An aqueous solution containing polyethyleneimine and zirconium-amino-1,4-dimethylamine (MOF) nanosheets is impregnated onto the polysulfonamide substrate. After removing the excess aqueous phase, it is reacted with an organic phase solution of terephthaloyl chloride for 60 seconds to form a polyamine-metal-organic framework composite layer. Heat treatment: The obtained composite film is heat-treated at 60-100℃ for 10 min to cross-link the two layers through dynamic covalent bonds and form a gradient heterojunction structure.

[0024] In a further embodiment of this example, in the first step of interface aggregation: The aqueous phase solution was 2.0 wt% of an aqueous solution of 4,4'-diaminodiphenyl sulfone, and the organic phase solution was 0.15 wt% of an Isopar G solution of trimesoyl chloride (TMC).

[0025] In a further embodiment of this example, in the second step of interface aggregation: The aqueous phase solution was an aqueous dispersion of 1.5-2.0 wt% polyethyleneimine and 0.05-0.2 wt% aminated UIO-66-NH2 nanosheets, and the organic phase solution was an Isopar G solution of 0.1 wt% terephthaloyl chloride (TPC).

[0026] In a further embodiment of this example, the step of applying the self-healing layer includes: The coating solution comprises 3-8 wt% pH-responsive microcapsules, 2-4 wt% polyvinyl alcohol, 0.4-0.6 wt% glutaraldehyde, and deionized water; The coating liquid was uniformly applied to the gradient heterojunction active layer using a Mayer rod and cured at 25°C for 12 hours to crosslink polyvinyl alcohol and glutaraldehyde to form a (PVA) hydrogel network, thereby immobilizing the microcapsules within it.

[0027] A further embodiment of the present invention also provides an application of an acid-resistant nanofiltration membrane, which is used in the treatment of acidic wastewater with a pH value not greater than 2, acid recovery in hydrometallurgical processes, or concentration and desalination of acidic dye wastewater.

[0028] It should be noted that the filter-resistant membrane of the present invention constructs a multi-layered, synergistic protection system that integrates physical barriers, chemical stability, and active repair.

[0029] Firstly, there is the static defense of chemical structure and physical barriers. The main chain of polyetheretherketoneketone (PEEKK) consists of aromatic rings, ketone groups, and ether bonds, forming a highly conjugated rigid structure. This rigid structure makes polymer chain movement difficult, and protons struggle to attack and break the main chain chemical bonds. Compared to traditional polysulfone (PSF) or polyethersulfone (PES) films, the phenylene units of PEEKK are more stable and less prone to ether bond breaking or sulfonation reactions under acid catalysis, thus providing a solid and acid-resistant underlying support for the entire film. Polysulfonamides, on the other hand, have sulfonamide bonds as their key bonds. The sulfur atom is in its highest oxidation state, exhibiting a strong electron-withdrawing effect, which enhances the acidity of the adjacent NH bond. However, the conjugation effect of the aromatic ring stabilizes the entire structure. In an acidic environment, it is far more difficult for protons to attack the sulfonamide bond than to attack the carbonyl carbon of the amide bond, thus providing the first chemical separation barrier to stabilize the PSA layer.

[0030] Zr-MOFs (especially the UIO-66 series) are renowned for their extremely high chemical stability, stemming from the strong coordination bonds formed between their Zr6O4(OH)4 metal cluster and organic ligands (terephthalic acid). The Zr-O bonds have extremely high bond energies, resisting proton attack. Embedding them as nanosheets within polyamine networks serves several purposes: acting as physical crosslinking points to enhance the rigidity of the polymer network and suppressing chain swelling and relaxation under acidic conditions; acting as pre-sieving channels, the regular pores of the MOF itself (approximately 0.6 nm) can perform preliminary sieving of ions and small molecules, reducing the separation burden on the subsequent polymer network and thus lowering the probability of damage; and acting as stress dispersion centers, the rigid MOF nanosheets can effectively disperse and dissipate localized stresses caused by protonation or osmotic pressure, preventing crack initiation and propagation.

[0031] Secondly, there is a dynamic defense against energy dissipation and interface stability. Through sequential interface aggregation, the interface between the PSA layer and the PA-MOF layer is not a sharp interface, but a region with a continuous transition in composition and properties. This is similar to a heterojunction in semiconductors, enabling "bandgap" matching. When acidic stress (which can be regarded as "electron-hole") is generated, the gradient structure can effectively disperse and guide these stresses, preventing them from concentrating at a single interface and causing delamination or cracking.

[0032] Then there's the active repair mechanism. The polyurea wall material in the microcapsules is stable under normal neutral conditions. When the membrane is damaged, acidic media seep in, causing a sharp drop in local pH. Under acidic conditions, the hydrolysis rate of the polyurea wall material accelerates dramatically, leading to rupture. The two repair agents in the core material work synergistically: isophorone diisocyanate, exposed to moisture at the damaged area, rapidly hydrolyzes and polymerizes to form polyurea, physically filling cracks and pores; hydroxyl-terminated polydimethylsiloxane, as a hydrophobic silicone oil, spreads on the repair surface to form a hydrophobic barrier, preventing further penetration of moisture and acid, and assisting in the curing of IPDI; additionally, the cross-linked PVA hydrogel not only firmly fixes the microcapsules to the membrane surface but also possesses hydrophilicity, maintaining the surface hydration layer, providing some degree of anti-fouling, and offering a suitable microenvironment for the repair reaction.

[0033] These three layers of defense do not operate in isolation, but rather form a three-dimensional defense system. The first layer is responsible for resisting routine, uniform acid corrosion; the second layer is responsible for dealing with localized, concentrated stress impacts, preventing the formation of microscopic damage; once the first two lines of defense are breached and microscopic cracks appear, the third layer immediately activates to perform targeted removal and repair, nipping the damage in the bud. Through this synergistic mechanism of "static defense + dynamic buffering + active repair," an exceptionally long acid-resistant lifespan is achieved.

[0034] The following examples and comparative examples were tested respectively, and the experimental materials and testing methods were as follows: Water flux test: 25℃, 0.6 MPa operating pressure, effective membrane area 28.3 cm². 2 ; Retention rate test: 1000 ppm MgSO4 solution; Acid resistance test: The performance is tested after immersion in 20% H2SO4 at 80℃ for the corresponding time; Self-healing test: After creating standard damage (5 μm depth, 100 μm length) on the membrane surface using microneedles, the membrane was repaired for 24 hours in an acidic environment with pH=1, and the repair efficiency was calculated.

[0035] Example 1 Base film preparation: 22 wt% PEEKK and 1 wt% LiCl, with an intrinsic viscosity of 0.9 dL / g, were dissolved in N-methylpyrrolidone and stirred at 80°C for 24 hours to form a homogeneous casting solution. At 25°C and 60% humidity, the solution was coated onto a polyester nonwoven fabric using a doctor blade (200 μm gap). After evaporation in air for 10 seconds, the fabric was immersed in a 25°C pure water coagulation bath. After phase inversion, the fabric was soaked in deionized water for 48 hours.

[0036] Construction of the active layer of the gradient heterojunction: Step 1: Immerse the base film in an aqueous solution of 2.0 wt% 4,4'-diaminodiphenyl sulfone containing 0.1 wt% SDS for 2 min, remove excess aqueous phase by rolling, and react with an Isopar G solution of 0.15 wt% TMC for 120 seconds.

[0037] Step 2: Immerse in 1.8 wt% PEI aqueous solution containing 0.1 wt% UIO-66-NH2 nanosheets for 1 min, roll press and react with Isopar G solution containing 0.1 wt% TPC for 60 seconds, then heat treat at 80℃ for 10 minutes.

[0038] Self-healing layer coating: An aqueous solution of 5 wt% pH-responsive microcapsules (polyurea wall material, IPDI / PHMS core material, diameter 1-5 μm), 3 wt% PVA (99% degree of hydrolysis) and 0.5 wt% glutaraldehyde was coated onto the active layer and cured at 25°C for 12 h.

[0039] The test results are as follows: Initial water flux: 14.2 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 96.3%; After 720 hours of acid resistance testing: Water flux 12.8 L·m -2 ·h -1 ·bar -1 The retention rate was 95.1%; the self-repair efficiency was 87.5%.

[0040] Example 2 The difference from Example 1 is that the content of UIO-66-NH2 nanosheets was modified to 0.05 wt%.

[0041] The test results are as follows: Initial water flux: 15.1 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 94.2%; After 720 hours of acid resistance testing: Water flux 13.2 L·m -2 ·h -1·bar -1 Retention rate: 92.8%; Self-repair efficiency: 86.3%.

[0042] Example 3 The difference from Example 1 is that the content of UIO-66-NH2 nanosheets was modified to 0.2 wt%.

[0043] The test results are as follows: Initial water flux: 13.5 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 97.1%; After 720 hours of acid resistance testing: Water flux 12.3 L·m -2 ·h -1 ·bar -1 Retention rate: 96.3%; Self-repair efficiency: 87.9%.

[0044] Example 4 The difference from Example 1 is that the microcapsule content is modified to 3 wt%.

[0045] The test results are as follows: Initial water flux: 14.5 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 95.8%; After 720 hours of acid resistance testing: Water flux 13.1 L·m -2 ·h -1 ·bar -1 Retention rate: 94.6%; Self-repair efficiency: 82.1%.

[0046] Example 5 The difference from Example 1 is that the microcapsule content was modified to 8 wt%.

[0047] The test results are as follows: Initial water flux: 13.8 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 96.5%; After 720 hours of acid resistance testing: Water flux 12.5 L·m -2 ·h -1 ·bar -1 Retention rate: 95.7%; Self-repair efficiency: 91.4%.

[0048] Example 6 The difference from Example 1 is that the base film was immersed in an aqueous solution of 2.0 wt% 4,4'-diaminodiphenyl sulfone containing 0.1 wt% SDS for 2 min, the excess aqueous phase was removed by roller pressing, and the film was reacted with an Isopar G solution of 0.15 wt% TMC for 60 seconds.

[0049] The test results are as follows: Initial water flux: 14.9 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 94.7%; After 720 hours of acid resistance testing: Water flux 13.4 L·m -2 h -1 ·bar -1 Retention rate: 93.5%; Self-repair efficiency: 86.8%.

[0050] Comparative Example 1 A conventional interfacial polymerization method was used: a polysulfone ultrafiltration membrane was used as the base membrane, m-phenylenediamine (2.0 wt%) as the aqueous phase, and trimesoyl chloride (0.15 wt%) as the n-hexane oil phase. The reaction conditions were the same as in Example 1. No self-healing layer was added.

[0051] The test results are as follows: Initial water flux: 15.3 L·m -2 ·h -1 ·bar -1 Initial MgSO4 rejection rate: 97.2%; After 168 hours of acid resistance testing: water flux dropped sharply to 5.2 L·m -2 ·h -1 ·bar -1 The rejection rate dropped to 68.5%; the membrane structure was completely destroyed, making further testing impossible.

[0052] Application Example 1 The nanofiltration membrane prepared in Example 1 was used to treat a Cu-containing environment at pH 1.5. 2+ 850 mg / L, Fe 3+ 1200 mg / L, SO4 2- Acidic copper mine wastewater with a concentration of 15000 mg / L. After operating for 720 hours at an operating pressure of 0.8 MPa: Cu 2+ The retention rate remained above 98.5%; the water flux increased from the initial 15.2 L·m⁻¹. -2 ·h -1 ·bar -1 Stable at 13.8 L·m -2 ·h -1 ·bar -1 The membrane element exhibits no irreversible fouling, and the chemical cleaning recovery rate is >99%.

[0053] Application Example 2 Treatment of acidic dye wastewater from a printing and dyeing plant, pH=2.0, containing 1500 mg / L Reactive Brilliant Blue KN-R and 20000 mg / L Na₂SO₄. Operating pressure: 1.0 MPa. Dye rejection rate >99.8%; salt rejection rate <15%; no performance degradation after 30 days of continuous operation.

[0054] In summary, this invention successfully fabricates a nanofiltration membrane with excellent acid resistance and self-healing function through a triple synergistic design of a PEEKK base membrane, a gradient heterojunction active layer, and a pH-responsive self-healing layer. The results of the examples demonstrate that this membrane exhibits long-term stability under extreme acidic conditions and can autonomously repair microscopic damage, significantly extending its service life. It shows broad application prospects in fields such as acidic wastewater treatment and hydrometallurgy.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An acid-resistant nanofiltration membrane, characterized in that, include: Polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer is formed on the base film by sequential interfacial polymerization. The gradient heterojunction active layer includes a polysulfonamide underlayer adjacent to the base film and a polyamine-metal-organic framework composite layer located thereon. A pH-responsive self-healing layer coated on the gradient heterojunction active layer, the self-healing layer comprising pH-responsive microcapsules dispersed in a cross-linked polyvinyl alcohol hydrogel.

2. The acid-resistant nanofiltration membrane according to claim 1, characterized in that, The metal-organic framework in the polyamine-metal-organic framework composite layer is a zirconium-based MOF UIO-66-NH2 nanosheet.

3. The acid-resistant nanofiltration membrane according to claim 1, characterized in that, The pH-responsive microcapsules have a wall material of polyurea and a core material comprising a mixture of isophorone diisocyanate and hydroxyl-terminated polydimethylsiloxane. The diameter of the microcapsules is 1-5 μm.

4. The method for preparing the acid-resistant nanofiltration membrane according to any one of claims 1-3, characterized in that, Includes the following steps: Preparation of polyetheretherketoneketone ultrafiltration membrane; A gradient heterojunction active layer was constructed on the base film using a sequential interfacial polymerization method. A coating solution loaded with pH-responsive microcapsules is coated onto the gradient heterojunction active layer, and then cross-linked and cured to form a self-healing layer.

5. The method for preparing the acid-resistant nanofiltration membrane according to claim 4, characterized in that, The specific steps for preparing the polyetheretherketoneketone ultrafiltration membrane are as follows: The N-methylpyrrolidone casting solution containing 22 wt% polyether ether ketone ketone and 1 wt% lithium chloride was coated onto a nonwoven fabric using a non-solvent-induced phase separation method. After standing for 10-30 seconds in an environment of 24-26℃ and 55-65% humidity, it was immersed in a 25℃ pure water coagulation bath to complete the phase transformation. After thorough washing with water, the final product was obtained.

6. The method for preparing the acid-resistant nanofiltration membrane according to claim 4, characterized in that, The step of constructing the gradient heterojunction active layer includes: Step 1: Interfacial polymerization: Immerse the base film with an aqueous solution of 4,4'-diaminodiphenyl sulfone, remove excess aqueous phase, and then react with an organic solution of trimesoyl chloride for 60-120 seconds to form a polysulfonamide underlayer. The second step is interfacial polymerization: An aqueous solution containing polyethyleneimine and zirconium-amino-1,4-dimethylamine (MOF) nanosheets is impregnated onto the polysulfonamide substrate. After removing the excess aqueous phase, it is reacted with an organic phase solution of terephthaloyl chloride for 60 seconds to form a polyamine-metal-organic framework composite layer. Heat treatment: The obtained composite film is heat-treated at 60-100℃ for 10 min to cross-link the two layers through dynamic covalent bonds and form a gradient heterojunction structure.

7. The method for preparing the acid-resistant nanofiltration membrane according to claim 6, characterized in that, In the first step of interface aggregation: The aqueous phase solution was 2.0 wt% of 4,4'-diaminodiphenyl sulfone aqueous solution, and the organic phase solution was 0.15 wt% of pyromellitic sulfonyl chloride in Isopar G solution.

8. The method for preparing the acid-resistant nanofiltration membrane according to claim 6, characterized in that, In the second step of interface aggregation: The aqueous phase solution was an aqueous dispersion of 1.5-2.0 wt% polyethyleneimine and 0.05-0.2 wt% aminated UIO-66-NH2 nanosheets, and the organic phase solution was an Isopar G solution of 0.05-0.2 wt% terephthaloyl chloride.

9. The method for preparing the acid-resistant nanofiltration membrane according to claim 4, characterized in that, The step of applying the self-healing layer includes: The coating solution comprises 3-8 wt% pH-responsive microcapsules, 2-4 wt% polyvinyl alcohol, 0.4-0.6 wt% glutaraldehyde, and deionized water; The coating liquid was uniformly applied to the gradient heterojunction active layer using a Mayer rod and cured at 25°C for 12 hours to crosslink polyvinyl alcohol and glutaraldehyde to form a hydrogel network, thereby immobilizing the microcapsules within it.

10. An application of the acid-resistant nanofiltration membrane according to any one of claims 1-3, characterized in that, The acid-resistant nanofiltration membrane is used in the treatment of acidic wastewater with a pH value not greater than 2, acid recovery in hydrometallurgical processes, or concentration and desalination of acidic dye wastewater.