A polyamide composite film induced by nano-bubbles for self-assembly of amphiphilic compounds, and a preparation method and application thereof

Abstract

The application discloses a kind of polyamide membranes of nano bubble induced amphiphilic compound self-assembly and its preparation method and application.First, using the nano bubble induced amphiphilic imidazole-urea compound HCx self-assembly at the interface of nano bubble-ethanol / water generated by ethanol and water mixing;Then, the surface of above-mentioned solution is covered with organic phase solution, in the process of nano bubble migration from ethanol / water solution to organic phase solution, using the low solubility characteristics of HCx in organic phase solution, promote HCx precipitation and crystallization on the surface of nano bubble, form armored nano bubble;Finally, using the interface polymerization reaction of organic phase solution containing armored nano bubble and aqueous solution, by armored nano bubble in polyamide separation layer Build nanocavity, and using nano bubble carrier HCx artificial water channel nanoparticle is anchored around nanocavity, to form the polyamide composite membrane rich in nanocavity water channel and HCx artificial water channel nanoparticle, synergistically improve the water flux and salt rejection rate of composite membrane.

Description

Technical Field

[0001] This invention discloses a polyamide composite membrane induced by nanobubbles to self-assemble amphiphilic compounds, its preparation method and application, belonging to the field of separation membrane preparation and application technology. Background Technology

[0002] Self-assembly is one of the effective methods for constructing complex and ordered structures in nature and synthetic systems. Amphiphilic molecules, such as surfactants and block copolymers, are commonly used self-assembly building blocks, typically containing two different functional groups: a hydrophilic head and a hydrophobic alkane chain. Their unique self-assembly characteristics provide a micro-reaction domain for polymerization reactions occurring at the liquid-liquid interface. Interfacial polymerization is a key method for preparing polyamide composite films. During interfacial polymerization, amine monomers and acyl chloride monomers diffuse from the aqueous and organic phase solutions, respectively, to the interface and undergo condensation reactions. This mass transfer process is closely coupled with the reaction kinetics at the phase interface. Therefore, subtle changes at the phase interface or in the bulk phase (such as the aqueous or organic phase) can affect the interfacial polymerization process and lead to changes in the microstructure and macroscopic properties of the polyamide film.

[0003] When amphiphilic molecules encounter interfacial polymerization, their monolayer arrangement at the liquid-liquid interface and the micelle structure formed by their self-assembly in the bulk phase often become the focus of research. Park et al. utilized the monolayer self-assembly arrangement of amphiphilic surfactant molecules at the two-phase interface, and through the strong complexation between surfactant molecules and amine monomers, enhanced the Marangoni instability at the phase interface, constructing a polyamide separation layer with abundant nanocavities and wrinkled structures (NanoLett. 2023, 23, 4822-4829). Patent CN 112755817B, "A high-performance composite nanofiltration membrane, its preparation method and application," introduces a surfactant (phosphodiester compound) into the organic phase, and utilizes the electrostatic interaction between the compound and the organic phase monomers and its self-assembly characteristics at the interface to regulate the structure of the polyamide separation layer by adjusting the interfacial polymerization process. In contrast, patent CN 112892230 B, "A High-Desalination Polyamide Composite Reverse Osmosis Membrane for Seawater Desalination and Its Preparation Method," utilizes the synergistic effect between the surfactant sodium dodecyl sulfate and the triblock ether polymer Pluronic F127 to self-assemble into a three-dimensional network micelle structure in an aqueous solution, effectively controlling the separation layer structure by influencing the diffusion rate of amine monomers. However, the self-assembly behavior of amphiphilic molecules often affects the interfacial stability during the interfacial polymerization process directly or indirectly, potentially damaging the dense structure of the polyamide separation layer. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing a polyamide composite film induced by nanobubbles to self-assemble an amphiphilic compound HCx. First, nanobubbles generated by mixing ethanol and water induce the self-assembly of the amphiphilic compound HCx at the nanobubble-ethanol / water interface to form nanobubbles@HCx. Subsequently, the nanobubbles migrate from the ethanol / water solution to the organic phase solution. Utilizing the low solubility of HCx in the organic phase solution, the precipitation and crystallization of HCx on the surface of the nanobubbles are promoted, forming sub-nanometer artificial water channels of nanobubbles@HCx in the organic phase solution. Nanoparticles (i.e., armored nanobubbles); finally, an interfacial polymerization reaction is carried out between an organic phase solution containing armored nanobubbles and an aqueous phase solution. Nanocavities are constructed in the polyamide separation layer by armored nanobubbles, and HCx artificial water channel nanoparticles are anchored around the nanocavities using nanobubble carriers to form a polyamide composite membrane rich in nanocavity water channels and HCx artificial water channel nanoparticles, which synergistically improves the water flux and salt rejection rate of the composite membrane.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A polyamide composite membrane induced by nanobubbles to self-assemble with amphiphilic compounds includes a support layer and a polyamide separation skin. Nanocavities are distributed within the polyamide separation skin, and HCx artificial water channel nanoparticles are distributed around the nanocavities. The structural formula of HCx is shown below:

[0007]

[0008] Wherein, R represents a straight-chain alkyl group with different numbers of carbon atoms, including but not limited to any one of butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, and octadecyl.

[0009] A method for preparing a polyamide composite membrane induced by nanobubbles and the self-assembly of amphiphilic compounds involves the following steps: First, nanobubbles generated by mixing ethanol and water induce the self-assembly of the amphiphilic compound HCx at the gas-liquid interface, forming a directional arrangement of hydrophilic groups facing the solution and hydrophobic groups facing the interior of the bubbles—nanobubbles@HCx. Subsequently, the nanobubbles@HCx migrate from the ethanol / water solution to the upper organic phase solution. Utilizing the low solubility of HCx in the organic phase solution, HCx precipitation and crystallization on the surface of the nanobubbles@HCx are promoted, forming armored nanobubbles. Finally, the organic phase solution containing armored nanobubbles is coated onto the surface of the aqueous phase solution for interfacial polymerization. The armored nanobubbles construct nanocavities within the polyamide separation layer, and HCx artificial water channel nanoparticles are anchored around the nanocavities using nanobubble carriers, forming a polyamide composite membrane rich in nanocavities and HCx artificial water channel nanoparticles.

[0010] A method for preparing a polyamide composite film induced by nanobubbles and self-assembly of amphiphilic compounds, specifically including the following steps:

[0011] (1) Preloading armored nanobubbles in an organic phase solution: First, amphiphilic compound HCx and water are added sequentially to ethanol; then, an organic phase solution containing polyacrylamide chloride is covered on the surface of the above solution. The rapid mixing of ethanol and aqueous solution is promoted by ultrasound to generate nanobubbles. The gas-liquid interface between the nanobubbles and ethanol / water induces HCx to self-assemble on the surface of the nanobubbles to form nanobubbles @HCx; at the same time, the formed nanobubbles @HCx are promoted to be transported from ethanol / aqueous solution to organic phase solution. The low solubility of HCx in organic phase solution is used to induce HCx on the surface of nanobubbles to precipitate and crystallize in organic phase solution to form armored nanobubbles, thereby realizing the preloading of armored nanobubbles in organic phase solution. The organic phase solution containing armored nanobubbles and polyacrylamide chloride in the upper layer of the ethanol and water mixed solution is taken out for later use.

[0012] (2) Preparation of polyamide composite membrane: A porous support layer is placed in the reaction vessel, and an aqueous phase solution containing polyamine and an organic phase solution containing armored nanobubbles and polyacrylamide chloride are poured in sequentially. After the interfacial polymerization reaction is completed, the solution between the polyamide separation layer and the support layer is filtered out through the support layer through the bottom outlet of the reaction vessel. The polyamide separation layer is loaded on the support layer, and the polyamide composite membrane is obtained after further post-processing.

[0013] The amphiphilic compound HCx in step (1) includes, but is not limited to, any one of HC4, HC5, HC6, HC7, HC8, HC9, HC10, HC11, HC12, HC14, and HC18. The concentration of HCx in the ethanol / water solution is 0.1-2.0 wt.%, or within the range defined by any two values ​​of 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.%, and 2.0 wt.%, preferably 0.2-1.0 wt.%.

[0014] In step (1), the volume ratio of ethanol / water is 20 / 80 to 80 / 20. HCx has good solubility in the ethanol-water solution with the above volume ratio. The number of sonications is 1-4 times, the sonication time is 1-5 seconds, the sonication power is 100-500W, and the sonication frequency is 10-50kHz.

[0015] The porous support layer in step (2) includes, but is not limited to, any one of polysulfone, polyethersulfone, polyethylene, polyvinyl chloride, polyvinylidene fluoride, polyacrylonitrile, polyimide and cellulose acetate.

[0016] In step (2), the polyamine includes, but is not limited to, piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 2,5-dimethylpiperazine, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, polyethyleneimine, divinyltriamine, and N,N-dimethylm-phenylenediamine, with a polyamine concentration of 0.25-2.5 wt%; the polyacrylamide includes, but is not limited to, pyromellitic acid, isophthaloyl chloride, fumarate, malonyl chloride, cyclohexanetrioyl chloride, cyclopentanetetracarboxylate chloride, naphthalenedicarboxylate chloride, chlorosulfonyl phthaloyl chloride, tetrahydrofurandicarboxylate chloride, and 5-(1-pyrrolidinyl)-isophthaloyl chloride, with a polyacrylamide concentration of 0.05-0.25 wt%; and the organic solvent is n-hexane.

[0017] The interfacial polymerization reaction time in step (2) is 40-120s, preferably 45-90s.

[0018] The post-processing in step (2) includes rinsing and heat treatment of the composite membrane, namely rinsing the membrane surface with n-hexane and heat-treating the composite membrane at 30-90℃ for 2-5 minutes.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the traditional strategy of regulating interface polymerization by self-assembly of amphiphilic molecules, the present invention completes the self-assembly of HCx in the pretreatment process, effectively avoiding the influence of self-assembly of amphiphilic molecules on the stability of the interface during the interface polymerization process; (2) It breaks through the limitation of the traditional nanobubble template method which is only used to regulate the structure of nanocavities, and innovatively proposes the "three birds with one stone" strategy of nanobubbles. It not only uses nanobubbles as templates for constructing nanocavities, but also uses nanobubbles to induce the self-assembly of amphiphilic compound HCx, and uses them as carriers to position and load HCx nanoparticles around the nanocavities. Through the multifunctional synergistic effect of nanobubbles, the controllability of the separation layer structure is significantly improved; (3) It cleverly utilizes the low solubility of HCx in organic phase solution to promote the precipitation and crystallization of HCx in organic phase solution, forming HCx sub-nanometer artificial water channel nanoparticles, which further improves the water permeability and selectivity of polyamide composite membranes. Attached Figure Description

[0020] Figure 1 TEM image of HC7 artificial water channel nanoparticles.

[0021] Figure 2 For Comparative Example 1, SEM images of the surface and cross-section of the polyamide layer prepared without the introduction of HCx are shown.

[0022] Figure 3 Example 2 shows SEM images of the surface and cross-section of the separation layer prepared by nanobubbles@HC6 artificial water channel nanoparticles.

[0023] Figure 4 Example 2: TEM image of the cross-section of the separation layer prepared by nanobubbles@HC6 artificial water channel nanoparticles.

[0024] Figure 5 Example 5 shows SEM images of the surface and cross-section of the separation layer prepared by nanobubbles@HC7 artificial water channel nanoparticles.

[0025] Figure 6 Example 6 shows SEM images of the surface and cross-section of the separation layer prepared by nanobubbles@HC8 artificial water channel nanoparticles.

[0026] Figure 7 This is a schematic diagram illustrating the effect of nanobubbles on the self-assembly of HC7 compounds and the influence of armored nanobubbles on the interfacial polymerization process. Detailed Implementation

[0027] The technical solution will be described in detail below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention and do not represent all embodiments.

[0028] Comparative Example 1:

[0029] A method for preparing a polyamide reverse osmosis membrane, specifically comprising:

[0030] First, the bottom outlet of the reaction vessel was connected to a vacuum pump, and a polysulfone support layer was placed inside the vessel (approximately 40 mm in radius). Next, 2.25 mL of water was added to 0.75 mL of ethanol, and a hexane solution containing 0.1 wt% trimesoyl chloride was placed over the ethanol / water solution. The mixture was sonicated three times, for 3 seconds each time, at a power of 300 W and a frequency of 40 kHz, to promote the mixing of ethanol and water to generate nanobubbles and facilitate their migration into the organic phase solution. Subsequently, the organic solution on top of the ethanol / water mixture was aspirated and allowed to stand for 2 minutes. Then, an aqueous phase solution containing 2.0 wt% m-phenylenediamine (approximately 2.4 mm in height) and the stood organic phase solution (approximately 0.6 mm in height) were added sequentially to the vessel. The interfacial polymerization reaction time was 60 seconds. The solution between the polysulfone support layer and the polyamide separation layer was then filtered out using a vacuum pump. Finally, the polyamide separation layer was removed by lifting, the composite membrane surface was rinsed with hexane, and the composite membrane was heat-treated in an 80°C oven for 3 minutes.

[0031] Comparative Example 2:

[0032] A method for preparing a polyamide reverse osmosis membrane based on HC6 powder, specifically:

[0033] First, the bottom outlet of the reaction vessel was connected to a vacuum pump, and a polysulfone support layer was placed inside the vessel (approximately 40 mm in radius). Next, an aqueous solution containing 2.0 wt% m-phenylenediamine (approximately 2.4 mm in height) and an organic solution containing 0.5 wt% HC6 powder + 0.1 wt% trimesoyl chloride (approximately 0.6 mm in height) were added sequentially to the vessel. The interfacial polymerization reaction time was 60 s, and subsequent experimental conditions were the same as in Comparative Example 1.

[0034] The amphiphilic compound HC6 was prepared as follows: 3 mmol of histamine (H) and 3 mmol of hexyl isocyanate (C6) were dissolved in 2.5 mL of ethyl acetate, 5 mL of acetonitrile, and 5 mL of tetrahydrofuran. The mixture was then heated at 80 °C for 3 h, and cooled to room temperature after the reaction was complete. Subsequently, the resulting white product was dissolved in a small amount of ethanol, and excess n-hexane was added. After stirring for 0.5 hours, a white powder of HC6 was obtained.

[0035] Example 1:

[0036] A method for preparing a polyamide reverse osmosis composite membrane induced by nanobubbles and HC6 self-assembly, specifically:

[0037] First, the bottom outlet of the reaction vessel was connected to a vacuum pump, and a polysulfone support layer was placed inside the vessel. Next, 0.3 wt% HC6 powder and 2.25 mL of water were added sequentially to 0.75 mL of ethanol, and a hexane solution containing 0.1 wt% trimesoyl chloride was placed over the ethanol / water solution. The mixture was sonicated three times for 3 seconds each time at a power of 300 W and a frequency of 40 kHz to promote the mixing of ethanol and water and generate nanobubbles. Subsequently, the amphiphilic compound HC6 self-assembled at the gas-liquid interface (nanobubbles-ethanol / water solution). Under ultrasonic assistance, the HC6-modified nanobubbles migrated into the organic phase, forming nanobubbles@HC6 artificial water channel nanoparticles, achieving pre-loading of armored nanobubbles in the organic phase solution. Subsequent experimental steps and conditions were the same as in Comparative Example 1.

[0038] Examples 2-4:

[0039] The HC6 concentrations were 0.5 wt%, 0.7 wt%, and 0.9 wt%, respectively, and the other experimental conditions were the same as in Example 1.

[0040] Example 5:

[0041] A method for preparing a polyamide reverse osmosis composite membrane induced by nanobubbles and HC7 self-assembly, specifically:

[0042] Except for replacing 0.5 wt% HC6 powder with 0.5 wt% HC7 powder, the experimental steps and conditions were the same as in Example 1.

[0043] The amphiphilic compound HC7 was prepared as follows: 3 mmol of histamine (H) and 3 mmol of heptyl isocyanate (C7) were dissolved in 2.5 mL of ethyl acetate, 5 mL of acetonitrile, and 5 mL of tetrahydrofuran. The mixture was then heated at 80 °C for 3 h, and cooled to room temperature after the reaction was complete. Subsequently, the resulting white product was dissolved in a small amount of ethanol, and excess n-hexane was added. After stirring for 0.5 hours, a white powder of HC7 was obtained.

[0044] Example 6:

[0045] A method for preparing a polyamide reverse osmosis composite membrane induced by nanobubbles and HC8 self-assembly, specifically as follows:

[0046] Except for replacing 0.5wt% HC6 powder with 0.5wt% HC8 powder, the experimental steps and conditions were the same as in Example 1.

[0047] The amphiphilic compound HC8 was prepared as follows: 3 mmol of histamine (H) and 3 mmol of octyl isocyanate (C8) were dissolved in 2.5 mL of ethyl acetate, 5 mL of acetonitrile, and 5 mL of tetrahydrofuran. The mixture was then heated at 80 °C for 3 h, and cooled to room temperature after the reaction was complete. Subsequently, the resulting white product was dissolved in a small amount of ethanol, and excess n-hexane was added. After stirring for 0.5 hours, a white powder of HC8 was obtained.

[0048] Test example:

[0049] The testing process for the performance of polyamide reverse osmosis membranes is as follows:

[0050] The reverse osmosis composite membrane was placed in a cross-flow filtration device. The sodium chloride concentration in the feed solution was 2000 ppm, the operating temperature was 25℃, the pressure was 2 MPa, and the effective permeation area of ​​the membrane was 12.56 cm². 2 Run for at least 1 hour to maintain a stable permeation flux.

[0051] Table 1 shows the performance data of reverse osmosis membranes prepared by nanobubble-induced self-assembly of HC6, HC7, and HC8. The water flux of the PA-HC6-0.3% membrane prepared by nanobubble-induced HC6 self-assembly is significantly higher than that of the control membrane. This is mainly attributed to the construction of nanocavity structures by the armored nanobubbles and the provision of additional fluid channels for water molecule transmembrane transport by the HC6 artificial water channel nanoparticles. With increasing HC6 concentration, the number of HC6 sub-nanometer transport channels in the PA-HC6-0.5% membrane increases, and the water flux increases by approximately 110% compared to the control membrane, while maintaining a high salt rejection rate. When the HC6 concentration is further increased, the water flux of the PA-HC6-0.7% and PA-HC6-0.9% membranes gradually decreases. This may be attributed to the excessive accumulation of HC6 artificial water channel nanoparticles in the separation layer, where the severe hydrogen bonding between them and water molecules restricts water transmembrane transport. Furthermore, the sub-nanometer structure of the HC6 artificial water channel nanoparticles... The polyamide separation layer was provided with additional ion sieving capacity, resulting in a slight increase in the salt rejection rate of the PA-HC6 series membranes compared to the control membrane. In contrast, the non-self-assembled HC6 compounds did not show a significant effect on RO membrane performance. The salt rejection rate of Comparative Example 2 was consistent with that of Comparative Example 1, while the water flux was slightly improved. This result further confirms that armored nanobubbles formed by inducing the self-assembly of HCx molecules through nanobubbles can effectively improve RO membrane performance (including water flux and salt rejection rate).

[0052] Table 1 shows the water flux and salt rejection of the reverse osmosis composite membranes prepared in Comparative Example 1 and Examples 1-6.

[0053]

[0054] To analyze the structure of HCx artificial water channel nanoparticles, we conducted a study using the amphiphilic compound HC7 as an example. Figure 1 The results show that the HC7 nanoparticles precipitated in the organic phase solution exhibit a hollow nanosphere structure, indicating the formation of nanobubbles@HC7 artificial water channel nanoparticles, and further demonstrating the formation of nanobubbles@HC7 in the ethanol / water solution. At higher magnification, the edges of the HC7 hollow nanospheres show a short-range ordered periodic arrangement with interplanar spacings of 2.67 and 1.34 nm, corresponding to the (100) and (200) planes of the HCx artificial water channel nanoparticles. Figure 1 b).

[0055] Introducing nanobubbles@HCx artificial water channel nanoparticles into the interfacial polymerization process resulted in a significant change in the separation layer structure. Compared to the control membrane ( Figure 2 PA-HC6-0.5% membrane surface is rougher. Figure 3The PA-HC6-0.5% membrane, rich in highly dispersed nanocavity structures, significantly improves the effective permeation area of ​​the separation layer and reduces its intrinsic thickness from 57 nm in the control membrane to 24 nm, effectively lowering the resistance to water molecule transport across the membrane. To analyze the dispersion state of HC6 nanoparticles within the separation layer, the cross-sectional structure of the PA-HC6-0.5% membrane was observed using TEM. Figure 4 The results show that HC6 nanoparticles are mainly distributed around the nanocavities. This indicates that nanobubbles can not only induce the self-assembly of the amphiphilic compound HCx, but also act as a carrier to directionally load HCx nanoparticles within the separation layer. These HC6 nanoparticles provide additional fluid channels for the transmembrane transport of water molecules, and the synergistic effect of optimized separation layer structure and HC6 nanoparticles significantly enhances the water permeability of the reverse osmosis membrane.

[0056] Subsequently, with the elongation of the hydrophobic alkane chain of HCx, PA-HC7-0.5% ( Figure 5 ) and PA-HC8-0.5% membrane ( Figure 6 The intrinsic thickness of the PA-HC8-0.5% membrane remained almost constant, while the apparent thickness gradually increased, leading to a continuous decrease in the membrane's water flux (Table 1). The significant change in the separation layer thickness may be related to the precipitation process of the amphiphilic compound HCx. In the organic phase solution, HC8, with its long alkyl chain structure, continuously precipitates on the surface of nanobubbles, eventually forming nanoparticles of increased size. These large nanoparticles adsorb onto the nanobubble surface, significantly enhancing the stability of the nanobubbles and increasing the concentration of nanobubbles in the organic phase solution. During interfacial polymerization, the high content of nanobubbles promotes the formation of multilayer nanocavity structures, resulting in an increase in the separation layer thickness of the PA-HC8-0.5% membrane, which in turn affects the membrane's water flux.

[0057] In summary, by adding the amphiphilic compound HCx to an ethanol / water solution, the self-assembly of HCx can be effectively induced by nanobubbles. Figure 7 a. Occurs in ethanol-water); subsequently, the precipitation of HCx in the organic phase solution promotes the formation of nanobubbles@HCx artificial water channel nanoparticles (armored nanobubbles). Figure 7 a, occurring in the organic phase); subsequently, abundant nanocavities are constructed within the separation layer using armored nanobubbles, and HCx nanoparticles are anchored around the nanocavities using nanobubble carriers. Figure 7 b) A polyamide composite membrane rich in nano-cavity water channels and HCx artificial water channel nanoparticles is formed, thereby significantly improving the permeation and separation performance of the polyamide composite membrane.

Claims

1. A polyamide composite film in which nanobubbles induce self-assembly of an amphiphilic compound, characterized by, It includes a support layer and a polyamide separation skin layer. The polyamide separation skin layer contains distributed nanocavities, and HCx artificial water channel nanoparticles are distributed around the nanocavities. The HCx structural formula is shown below: Wherein, R represents a straight-chain alkyl group with different numbers of carbon atoms, including any one of butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, and octadecyl.

2. The method for producing a polyamide composite film in which nano bubbles induce self-assembly of an amphiphilic compound according to claim 1, characterized by, Includes the following steps: (1) Preloading armored nanobubbles in an organic phase solution: First, amphiphilic compound HCx and water are added sequentially to ethanol; then, an organic phase solution containing polyacrylamide chloride is placed on the surface of the above ethanol / water solution. The rapid mixing of ethanol and water is promoted by ultrasound to generate nanobubbles. The gas-liquid interface between the nanobubbles and ethanol / water is used to induce HCx to self-assemble on the surface of the nanobubbles. At the same time, the nanobubbles with surface-modified HCx are transported from the ethanol / water solution to the organic phase solution. The low solubility of HCx in the organic phase solution is used to induce HCx on the surface of the nanobubbles to precipitate and crystallize in the organic phase solution to form armored nanobubbles, thereby achieving preloading of armored nanobubbles in the organic phase solution. The organic phase solution containing armored nanobubbles and polyacrylamide chloride in the upper layer of the ethanol and water mixture is taken out for later use. (2) Preparation of polyamide composite membrane: A porous support layer is placed in the reaction vessel, and an aqueous phase solution containing polyamines and an organic phase solution containing armored nanobubbles and polyacrylamide chlorides are poured in sequentially. After the interfacial polymerization reaction is completed, the solution between the polyamide separation layer and the support layer is filtered out through the support layer, and the prepared polyamide separation layer is retrieved using the support layer. After further post-processing, a polyamide composite membrane is obtained.

3. The method for preparing a polyamide composite film in which nano bubbles induce self-assembly of an amphiphilic compound according to claim 2, characterized by, The amphiphilic compound HCx includes any one of HC4, HC5, HC6, HC7, HC8, HC9, HC10, HC11, HC12, HC14, and HC18, and the concentration of HCx in the ethanol aqueous solution is 0.1-2.0 wt.%.

4. The method for preparing polyamide composite films by nanobubble-induced self-assembly of amphiphilic compounds according to claim 2, characterized in that, In step (1), the volume ratio of ethanol / water is 20 / 80 to 80 / 20, the number of ultrasonic treatments is 1-4, the ultrasonic time is 1-5 seconds, the ultrasonic power is 100-500W, and the ultrasonic frequency is 10-50kHz.

5. The method of claim 2, wherein the method is characterized by, The porous support layer in step (2) includes any one of polysulfone, polyethersulfone, polyethylene, polyvinyl chloride, polyvinylidene fluoride, polyacrylonitrile, polyimide and cellulose acetate.

6. The method of claim 2, wherein the method is characterized by, In step (2), the polyamine includes any one or more of piperazine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 2,5-dimethylpiperazine, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, polyethyleneimine, divinyltriamine, and N,N-dimethylm-phenylenediamine, with a concentration of 0.25-2.5 wt.%; the polyacrylamide includes any one or more of pyromellitic acid, isophthaloyl chloride, fumarate, malonyl chloride, cyclohexanetrioyl chloride, cyclopentanetetracarboxylate chloride, naphthalenedicarboxylate chloride, chlorosulfonyl phthaloyl chloride, tetrahydrofurandicarboxylate chloride, and 5-(1-pyrrolidinyl)-isophthaloyl chloride, with a concentration of 0.05-0.25 wt.%; and the organic solvent is n-hexane.

7. The method of claim 2, wherein the method is characterized by, In step (2), the interfacial polymerization reaction time is 40-120s. The post-processing includes rinsing and heat treatment of the composite membrane, namely, rinsing the membrane surface with n-hexane and heat-treating the composite membrane at 30-90℃ for 2-5min.

8. The application of the polyamide composite membrane according to claim 1, or the polyamide composite membrane prepared by the method according to any one of claims 2-7, in the solution desalination process.

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