A method for inducing the construction of polyamide layer structure in reverse osmosis membranes using low-dose green cosolvents

Abstract

This invention relates to a method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent, belonging to the field of reverse osmosis membrane preparation technology. First, a mixed aqueous solution of m-phenylenediamine, triethylamine, camphor sulfonic acid, and the green co-solvent is poured onto the surface of a polysulfone-based membrane. After removing the aqueous phase solution from the surface, membrane I is obtained. Then, a hexane solution containing trimesoyl chloride is poured onto the surface of membrane I. After removing the organic phase solution from the surface, membrane II is obtained. Finally, after the solution on the surface of membrane II is drained, it is cured and dried in an oven and cooled to room temperature. Finally, it is stored immersed in deionized water to obtain the reverse osmosis membrane. The introduction of the green co-solvent in this invention can increase the diffusion rate of m-phenylenediamine and reduce its interfacial energy barrier, effectively inducing and constructing a polyamide separation layer with a ridge-valley structure. The prepared reverse osmosis membrane not only effectively maintains a high sodium chloride rejection rate but also significantly improves the pure water flux, providing a new method for the design and preparation of high-performance reverse osmosis membrane structures.

Description

Technical Field

[0001] This invention belongs to the field of reverse osmosis membrane preparation technology, and particularly relates to a method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent. Background Technology

[0002] The shortage of freshwater resources is becoming increasingly prominent. As an important way to supplement high-quality freshwater resources, reverse osmosis technology, with polyamide composite reverse osmosis membranes as its core component, has been widely used in unconventional water resource development processes such as seawater desalination and brackish water desalination. Therefore, improving the performance of polyamide membrane composite reverse osmosis membranes is of great significance for promoting the efficient development and recycling of freshwater resources. The polyamide separation layer, generated through interfacial polymerization (IP) using m-phenylenediamine (MPD) as the aqueous phase monomer and trimesoyl chloride (TMC) as the organic phase monomer, plays a decisive role in the separation performance of the reverse osmosis membrane. Due to the extremely fast rate of interfacial polymerization (usually completed within seconds), the reaction process is difficult to control precisely, leading to uncontrolled growth of the polyamide structure. The thickness, morphology, and crosslinking degree of the separation layer structure exhibit non-uniformity and randomness. Therefore, the performance of reverse osmosis membranes suffers from a "permeability-selectivity" trade-off, making it difficult to simultaneously improve water flux and desalination rate, resulting in a technical bottleneck in the development of high-performance reverse osmosis membranes.

[0003] To overcome the trade-off between permeability and selectivity, precise control of the polyamide layer structure is crucial. Adjusting monomer concentration, introducing nanoparticles, adding co-solvents, and constructing intermediate layers can, to some extent, control the polyamide separation layer structure. Among these methods, co-solvent-assisted control is a relatively simple and efficient approach to controlling interfacial polymerization reactions. By adding a co-solvent to the aqueous or organic phase, the reaction microenvironment is adjusted, thereby improving the fine structure of the polyamide layer. However, conventional aqueous co-solvents have the following limitations: First, achieving effective control of the polyamide structure often requires high concentrations (typically exceeding 5-10 wt.%), which not only increases raw material procurement costs but also significantly increases the viscosity of the aqueous solution, inhibiting monomer diffusion and potentially reducing interfacial polymerization efficiency, thus increasing the risk of structural defects in the polyamide layer. Second, many traditional aqueous co-solvents, such as alcohols and ethers, are volatile organic compounds (VOCs), and their large-scale volatilization poses a potential risk to human health, failing to meet the requirements of green environmental protection and sustainable development.

[0004] Therefore, based on a deep understanding of the role of cosolvents in regulating interfacial polymerization reactions, and by screening specific functional group structures and designing the simplest cosolvent structure, a new method can be formed to precisely regulate the interfacial polymerization process and induce the formation of an ideal polyamide layer structure, while meeting the requirements of low dosage, high efficiency and environmental friendliness. This has become the key to breaking through the bottleneck of existing technologies. Summary of the Invention

[0005] This invention aims to solve the problems of excessive addition of aqueous cosolvent and poor environmental performance in the prior art, and to overcome the technical bottleneck of the difficulty in precisely controlling the polyamide layer structure. By screening functional groups, the optimal combination of additive molecular structures is determined, and a method for inducing the construction of a reverse osmosis membrane polyamide layer structure by inducing the construction of an ideal polyamide layer structure with low-dose green cosolvent is provided.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent, comprising the following steps:

[0007] S1. A mixed aqueous solution of m-phenylenediamine, triethylamine, camphor sulfonic acid and green cosolvent is used as the aqueous reaction solution. The aqueous reaction solution is poured onto the surface of the polysulfone-based membrane. After standing, the aqueous solution on the surface is removed to obtain membrane I.

[0008] The green co-solvent is N-butylpyrrolidone; the mass fraction of N-butylpyrrolidone is 0.05~2 wt.%.

[0009] S2. Using a hexane solution containing trimesoyl chloride as the organic phase reaction solution, pour the organic phase reaction solution onto the surface of membrane I obtained in step S1. After standing, remove the organic phase solution from the surface to obtain membrane II.

[0010] S3. Let the membrane II obtained in step S2 stand until the solution on the surface of membrane II is drained, then cure and dry it in an oven and cool it to room temperature. Finally, immerse it in deionized water for storage to obtain a reverse osmosis membrane.

[0011] Further, in step S1, the mass fraction of the N-butylpyrrolidone is 0.05-0.5 wt.%.

[0012] Furthermore, in step S1, the solvent of the aqueous reaction solution is deionized water.

[0013] Further, in step S1, the mass fraction of intermediate-phenylenediamine in the aqueous reaction solution is 1-2 wt.%, the mass fraction of triethylamine is 1.1-2 wt.%, and the mass fraction of camphor sulfonic acid is 1.5-2.6 wt.%.

[0014] Furthermore, in step S1, the amount of the aqueous reaction solution used is 20 mL; the residence time is 30~60 s.

[0015] Further, in step S2, the mass fraction of the pyromellitic trimethylol chloride in the organic phase reaction solution is 0.1~0.15 wt.%.

[0016] Furthermore, in step S2, the amount of the organic phase reaction solution used is 20 mL; the residence time is 10~30 s.

[0017] Furthermore, in step S3, the curing and drying temperature is 100℃ and the time is 3~5 minutes.

[0018] Furthermore, in step S3, the reverse osmosis membrane achieves a pure water flux of 93.11 L·m³ under a pressure of 1.55 MPa. -2 ·h -1 The NaCl retention rate is over 96.95%.

[0019] By employing the above technical solution, it can be seen that this invention, through screening functional groups, forms the optimal combination of additive molecular structures, determining N-butylpyrrolidone as the best aqueous co-solvent. It is not only a green and environmentally friendly solvent, but also, by fully utilizing the advantages of each functional group, it can resolve the contradiction between permeability and selectivity by gently optimizing the interfacial polymerization reaction microenvironment with far lower addition amounts than traditional methods. This provides a novel, practical, and green technical path for preparing next-generation reverse osmosis membranes that combine high performance, high stability, and good economic efficiency.

[0020] The N-butylpyrrolidone molecule has a polar pyrrolidone ring at one end and a nonpolar butyl straight chain at the other. This makes it miscible with both water (through hydrogen bonding and dipole interactions) and n-hexane (through van der Waals forces). This amphiphilic N-butylpyrrolidone molecule can spontaneously and directionally accumulate at the water-organic interface, constructing nanoscale diffusion transport channels. These channels provide a more ordered mass transfer pathway for the diffusion of monomers in the two-phase reaction, thereby effectively improving the monomer mass transfer efficiency and reaction kinetics.

[0021] In interfacial polymerization, the dielectric constant of the aqueous solvent is as high as 80 F / m, while that of the organic phase n-hexane is only 2 F / m. Under traditional interfacial polymerization conditions, a region with a significant difference in polarity is formed between the two. However, N-butylpyrrolidone has a dielectric constant of 25 F / m, approximately one-third that of water. Its addition alters the polarity distribution of the original interfacial region, creating a moderately polar miscible environment between the aqueous and organic phases, with the overall polarity decreasing gradually from the aqueous to the organic phase. Tristyrene chloride, which is originally dissolved in the low-polarity organic phase, must overcome a high polarity barrier to enter the reaction region in traditional interfacial reactions. In the presence of N-butylpyrrolidone, the originally abruptly polar interface transforms into a continuously gradually changing polar gradient region, allowing tristyrene chloride to diffuse more smoothly towards the aqueous phase and approach the reaction interface in a deeper and more controllable manner, thereby promoting the interfacial polymerization reaction. Meanwhile, in a low-polarity reaction environment, the nucleophilic attack ability of the carbon atom of the acyl chloride group is moderately suppressed, while its electrophilicity is enhanced in a polar environment. This characteristic can, to some extent, delay the hydrolysis reaction of trimesoyl chloride, thereby giving m-phenylenediamine more time to undergo an effective polycondensation process, ultimately promoting the interfacial polymerization reaction.

[0022] In the typical Schott-Baumann reaction of interfacial polymerization, the condensation reaction that occurs after the amine monomer contacts the acyl chloride monomer rapidly releases hydrogen ions, leading to a local pH decrease and subsequently protonating the highly reactive m-phenylenediamine. The addition of N-butylpyrrolidone transforms the resulting miscible region into a moderately polar environment, shifting the protonation equilibrium of the m-phenylenediamine towards deprotonation, thereby increasing the effective concentration of m-phenylenediamine participating in the reaction. This change facilitates the formation of an ideal polyamide "ridge-valley" structure with a larger specific surface area, ultimately significantly improving the membrane permeation flux while maintaining a high rejection rate.

[0023] In summary, the beneficial effects of the present invention are as follows:

[0024] (1) Significantly improved reverse osmosis membrane performance: The introduction of N-butylpyrrolidone effectively increases the diffusion rate of the aqueous monomer (m-phenylenediamine) and reduces its energy barrier across the interface, thereby inducing the formation of a polyamide separation layer with a more developed "ridge-valley" structure. The reverse osmosis membrane prepared by this method can achieve a pure water flux of 93.11 L·m at a test pressure of 1.55 MPa. -2 ·h –1 Meanwhile, the retention rate of sodium chloride remains above 96.95%, achieving a synergistic improvement in permeability and selectivity.

[0025] (2) Green and environmentally friendly properties and process friendliness: N-Butylpyrrolidone is a recognized new type of green solvent. Its non-hazardous properties allow it to effectively replace traditional solvents such as N,N-dimethylformamide (DMF), which are environmentally harmful. Its addition amount in the aqueous reaction solution is extremely low (0.05~2 wt.%), significantly reducing chemical consumption and environmental impact. More importantly, N-Butylpyrrolidone itself does not participate in interfacial polymerization reactions and can be completely removed by washing with water after film formation, avoiding the long-term impact of residual solvent on film performance and potential environmental hazards.

[0026] (3) The process is simple and easy to industrialize: This invention only requires adding a trace amount of N-butylpyrrolidone to the aqueous reaction solution, without the need for complex equipment or major modifications to the existing interfacial polymerization process. This simple operation greatly reduces the difficulty and cost of technology promotion, making it have excellent prospects for industrial application.

[0027] (4) Base film friendly and process controllable: N-Butylpyrrolidone, as a mild green solvent, will not erode or damage the surface structure of porous base films such as polysulfone, ensuring that the interfacial polymerization reaction proceeds smoothly on an ideal substrate. At the same time, since N-Butylpyrrolidone does not participate in the chemical reaction, side reactions are avoided, making the interfacial polymerization process more controllable, which is conducive to obtaining a polyamide layer with uniform structure and stable performance.

[0028] (5) Simple and clear structure: N-Butylpyrrolidone is composed of pyrrolidone ring and straight butyl group, without redundant complex groups and branches, which can ensure the predictability and precise control of improving the interface environment, and is conducive to constructing a polyamide separation layer with controllable structure and stable performance.

[0029] As can be seen, this invention achieves precise control of the interfacial polymerization process by introducing a low dose of the green co-solvent N-butylpyrrolidone. Attached Figure Description

[0030] The present invention will be described in detail below with reference to the accompanying drawings and examples. The advantages and implementation methods of the present invention will become more apparent from this description. The accompanying drawings are for illustrative purposes only and do not constitute any limitation on the present invention. In the accompanying drawings:

[0031] Figure 1 This is a mean square displacement curve of m-phenylenediamine in the aqueous reaction solution of the present invention without the addition of N-butylpyrrolidone.

[0032] Figure 2 This is the mean square displacement curve of m-phenylenediamine with N-butylpyrrolidone added to the aqueous reaction solution of the present invention.

[0033] Figure 3These are scanning electron microscope (SEM) images of the surface and cross-section of Embodiment 1 of the present invention.

[0034] Figure 4 These are scanning electron microscope (SEM) images of the surface and cross-section of Embodiment 2 of the present invention.

[0035] Figure 5 These are scanning electron microscope (SEM) images of the surface and cross-section of Embodiment 3 of the present invention.

[0036] Figure 6 These are scanning electron microscope (SEM) images of the surface and cross-section of Embodiment 4 of the present invention.

[0037] Figure 7 These are scanning electron microscope (SEM) images of the surface and cross-section of Comparative Example 1 of this invention.

[0038] Figure 8 These are scanning electron microscope images of the surface and cross-section of Comparative Example 2 of the present invention.

[0039] Figure 9 These are scanning electron microscope images of the surface and cross-section of Comparative Example 3 of the present invention.

[0040] Figure 10 This is a comparison chart showing the performance of the films prepared in the embodiments and comparative examples of the present invention with the performance of films prepared by adding other co-solvents. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the preferred embodiments.

[0042] In the following examples and comparative examples:

[0043] Polysulfone-based membrane, purchased from Shandong Jiuzhang Membrane Technology Co., Ltd., with a pure water flux of 180~240 L·m –2 ·h –1 The retention rate of bovine serum albumin was 95%–98%.

[0044] m-Phenylenediamine (MPD), with a purity of 98%, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0045] Trimethylbenzene chloride (TMC), with a purity of 99%, was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0046] n-Hexane, analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0047] Triethylamine (TEA), analytical grade, purchased from Tianjin Kemeo Co., Ltd.;

[0048] Camphor sulfonic acid was purchased from Shanghai Tixi Chemical Industry Development Co., Ltd.

[0049] N-Butylpyrrolidone (NBP), analytical grade, purchased from Shanghai Aladdin Reagent Co., Ltd.;

[0050] Sodium chloride, analytical grade, purchased from China Maclean Biochemical Co., Ltd.

[0051] Example 1:

[0052] A method for inducing the construction of a polyamide layer structure in a reverse osmosis membrane using a low-dose green co-solvent includes the following steps:

[0053] S1. Pour 20 mL of an aqueous reaction solution containing 2 wt.% m-phenylenediamine, 1.1 wt.% triethylamine, 2.6 wt.% camphor sulfonic acid, and 0.05 wt.% N-butylpyrrolidone onto the surface of the polysulfone membrane. After 30 s, remove the excess aqueous solution from the surface and use a rubber roller to thoroughly remove any remaining aqueous solution, thus obtaining membrane I.

[0054] S2. Pour 20 mL of a 0.1 wt.% hexane solution of pyromellitic chloromethyl chloride as the organic phase reaction solution onto the surface of membrane I obtained in step S1. After 10 s, pour off the excess organic phase solution on the surface to obtain membrane II.

[0055] S3. Let the membrane II obtained in step S2 stand until the solution on the surface of membrane II is drained, then put it into an oven set at 100℃ for curing and drying for 3 minutes, then cool it to room temperature, and finally immerse it in deionized water for storage to obtain a reverse osmosis membrane.

[0056] Example 2:

[0057] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step S1, the mass fraction of N-butylpyrrolidone is 0.1 wt.%, while other conditions are the same as in Example 1.

[0058] Example 3:

[0059] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step S1, the mass fraction of N-butylpyrrolidone is 0.15 wt.%, while other conditions are the same as in Example 1.

[0060] Example 4:

[0061] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step S1, the mass fraction of N-butylpyrrolidone is 0.5 wt.%, while other conditions are the same as in Example 1.

[0062] Comparative Example 1:

[0063] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step S1, the mass fraction of N-butylpyrrolidone is 0 wt.%, while other conditions are the same as in Example 1.

[0064] Comparative Example 2:

[0065] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step S1, the mass fraction of N-butylpyrrolidone is 1 wt.%, while other conditions are the same as in Example 1.

[0066] Comparative Example 3:

[0067] A method for inducing the construction of a polyamide layer structure for a reverse osmosis membrane using a low-dose green co-solvent differs from Example 1 in that, in step (1), the mass fraction of N-butylpyrrolidone is 2 wt.%, while other conditions are the same as in Example 1.

[0068] Performance testing:

[0069] The separation performance of the reverse osmosis membranes prepared in Examples 1-4 and Comparative Examples 1-3 was tested using a medium-pressure membrane performance tester.

[0070] The effective area is 22.06 cm². 2 The reverse osmosis membrane was encapsulated in the membrane tank of a medium-pressure membrane performance tester. Deionized water was used as the feed liquid, the feed temperature was set to 25℃, the cross-flow rate to 40 L / h, and the operating pressure to 1.55 MPa. The reverse osmosis membrane was pre-pressurized for 1 hour to stabilize the flux. Subsequently, the volume of permeate was collected over a certain testing time, and the pure water flux of the reverse osmosis membrane was calculated using the following formula:

[0071]

[0072] In the formula, P is the pure water flux, with units of L·m -2 ·h –1 △V is the permeate volume in L; A is the membrane area in m². 2 △t represents the test time, in hours (h).

[0073] The flux improvement rate is:

[0074]

[0075] In the formula, P t Pure water flux improvement rate, in % (P) 实施例1~4或对比例2~3 The pure water flux is for Examples 1-4 or Comparative Examples 2-3, in L·m -2 ·h –1 ;P 对比例1The pure water flux for Comparative Example 1 is expressed in L·m⁻¹. -2 ·h –1 .

[0076] The reverse osmosis membrane's retention performance was tested using a 2000 mg / L sodium chloride solution as the feed solution. The conductivity of the feed solution and permeate was measured using a conductivity meter, and the desalination rate was calculated using the following formula:

[0077]

[0078] In the formula, R is the sodium chloride rejection rate, in %; C p and C f These are the concentrations of sodium chloride in the permeate and feed solutions, respectively, in mg / L.

[0079] The pure water flux and salt rejection rate of the reverse osmosis membrane are shown in Table 1.

[0080] Table 1. Performance test results of reverse osmosis membranes

[0081]

[0082] According to the performance test data in Table 1, the pure water flux of Comparative Example 1 was 60.02 L·m when N-butylpyrrolidone was not added to the aqueous reaction solution. -2 ·h –1 As the addition of N-butylpyrrolidone gradually increased from 0.05 wt.% to 2 wt.%, the pure water flux of the reverse osmosis membrane showed a significant and continuous upward trend, from 69.90 L·m -2 ·h –1 (Example 1) Increased to 110.70 L·m -2 ·h –1 (Comparative Example 3) The pure water flux increase rate was significantly higher than that of Comparative Example 1, reaching 84.44%. This change indicates that N-butylpyrrolidone effectively promoted the interfacial polymerization reaction, forming a structure more conducive to water transport. When the amount of N-butylpyrrolidone added was in the range of 0.05~0.5 wt.% (Examples 1~4), the sodium chloride rejection rate of the reverse osmosis membrane remained above 96%, meeting the desalination requirements of brackish water and industrial wastewater. This indicates that within this concentration range, N-butylpyrrolidone can still promote the formation of a dense polyamide network structure. However, when the concentration of N-butylpyrrolidone was further increased to 1 wt.% and 2 wt.% (Comparative Examples 2 and 3), although the pure water flux reached 99.09 L·m, the actual increase was not significant. -2 ·h –1 With 110.70 L·m -2 ·h –1 However, the sodium chloride retention rate was below 96%, indicating that excessive N-butylpyrrolidone would cause defects in the polyamide structure.

[0083] In summary, N-butylpyrrolidone, with its amphiphilic properties, has an optimal concentration addition window for regulating interfacial polymerization reactions, ensuring a high salt rejection rate while significantly increasing membrane flux.

[0084] Table 2. Hansen solubility parameters of solvents

[0085]

[0086] As shown in Table 2, by comparing the Hansen solubility parameters of the aqueous reaction solution before and after the addition of N-butylpyrrolidone, it can be observed that the Hansen solubility parameter of the aqueous reaction solution significantly decreases after the addition of N-butylpyrrolidone. This is because the N-butylpyrrolidone molecule possesses both a hydrophobic butyl group and a polar pyrrolidone ring; this simple amphiphilic structure allows it to be efficiently enriched at the water-organic interface. (Solubility parameter distance (R...)) d The R0 value can quantitatively characterize the affinity between two phases; a decrease in the R0 value indicates an increase in affinity. Experiments show that the addition of N-butylpyrrolidone effectively reduces the R0 value at the water-organic interface. d This significantly enhances the affinity and miscibility between the two phases. This increased affinity directly leads to an expansion of the interfacial region and a corresponding increase in the width of the miscible zone. Simultaneously, due to the moderate polarity of N-butylpyrrolidone (dielectric constant approximately 25 F / m), the previously sharply contrasting polarity of the interface can be transformed into a gradient region with a continuous polarity transition. This polar gradient, combined with the broadened miscible zone, provides a milder and more controllable diffusion and reaction environment for pyromellitic tricarboxylate chloride and m-phenylenediamine, thereby significantly optimizing the interfacial polymerization process and achieving precise induced construction of the polyamide layer structure.

[0087] like Figure 1 and Figure 2 As shown, the diffusion coefficient of MPD was significantly improved after the addition of N-butylpyrrolidone, from 0.002 Å. 2 / ps increased to 0.06Å 2The / ps (30-fold increase) indicates that N-butylpyrrolidone effectively promotes the migration of monomers to the reaction interface. This can be attributed to the unique and streamlined amphiphilic structural design of the N-butylpyrrolidone molecule. The carefully selected pyrrolidone ring, as a polar group, exhibits good affinity with water, while the simple butyl alkane chain ensures effective miscibility with n-hexane. This simplified amphiphilic structure allows N-butylpyrrolidone to arrange itself spontaneously and efficiently at the water-organic interface. This not only enhances the affinity between the two phases, thereby optimizing the microenvironment of the interfacial polymerization reaction, but also provides an effective molecular transport channel for the monomers, directly promoting the efficient diffusion of m-phenylenediamine molecules to the interface and effectively regulating the diffusion kinetics of the aqueous monomer m-phenylenediamine (MPD).

[0088] In addition, the present invention also calculated the energy changes of m-phenylenediamine molecules in the aqueous bulk solution, at the reaction interface, and near the organic phase before and after the addition of N-butylpyrrolidone, and further analyzed the changes in the interfacial energy barrier of m-phenylenediamine molecules. The results are shown in Table 3.

[0089] Table 3. Energy of m-phenylenediamine molecule at different positions

[0090]

[0091] Table 3 further demonstrates that N-butylpyrrolidone can significantly reduce the diffusion barrier of MPD across the water-organic interface. This is attributed to the amphiphilic structural design of N-butylpyrrolidone, which effectively reduces the solubility parameter distance (R) between the two phases. d The N-butylpyrrolidone (N-butylpyrrolidone) enhances affinity and, due to its moderate polarity imparted by its polar functional groups, transforms the previously starkly contrasting polarity interface into a gradient region with a continuous polarity transition, while also widening the miscible region. This optimized interfacial environment provides a more thermodynamically compatible and kinetically easier-to-cross pathway for MPD diffusion. Therefore, N-butylpyrrolidone, through its simple and well-defined amphiphilic structure, simultaneously regulates the interfacial polarity distribution and miscible region structure, synergistically reducing the diffusion resistance of MPD, making the interfacial polymerization process more controllable, and thus facilitating the formation of a more ideal polyamide separation layer.

[0092] like Figures 3 to 9As shown, scanning electron microscopy (SEM) analysis of the reverse osmosis membrane surface morphology clearly revealed the regulatory effect of different concentrations of N-butylpyrrolidone (N-butylpyrrolidone) on the microstructure of the polyamide layer. When the N-butylpyrrolidone concentration was 0.05 wt.% (Example 1), the polyamide layer exhibited a preliminary ridge-valley structure. Compared to Comparative Example 1 without N-butylpyrrolidone, the structural change was not significant, which is consistent with the slight increase in flux. As the N-butylpyrrolidone concentration increased to 0.5 wt.% (Examples 2-4), a more developed leaf-like structure and more pronounced ridge-valley morphology formed on the reverse osmosis membrane surface, effectively increasing the membrane's filtration area and thus explaining the continuous increase in flux. However, when the N-butylpyrrolidone concentration was too high (Comparative Examples 2-3, 1-2 wt.%), the polyamide layer exhibited overgrowth and multilayer stacking, leading to a decrease in structural density and the generation of non-selective defects, which well explains the decrease in rejection rate at high concentrations.

[0093] like Figure 10 As shown, the N-butylpyrrolidone used in this invention has significant advantages compared to traditional aqueous cosolvents (such as ethylene glycol and acetone). With a low addition of only 0.5 wt.%, the water flux of the membrane can be significantly increased without sacrificing salt rejection. As a novel green solvent, N-butylpyrrolidone's core advantage lies in its high efficiency with minimal dosage. This characteristic is attributed to its simple and precise molecular structure design. Through optimized functional group combinations, it achieves efficient regulation of the interfacial polymerization process while avoiding the negative effects caused by complex molecular structures.

[0094] In summary, this invention achieves precise control over the polyamide layer structure of reverse osmosis membranes by adjusting the concentration of N-butylpyrrolidone. Within the optimal concentration range (0.05-0.5 wt.%), N-butylpyrrolidone induces the formation of a polyamide separation layer with an ideal ridge-valley structure through the dual effects of promoting m-phenylenediamine diffusion and lowering the interfacial energy barrier. Ultimately, this significantly improves water flux while maintaining a high rejection rate. This research provides important theoretical basis and technical approach for the preparation of high-performance reverse osmosis membranes.

[0095] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A method for inducing the construction of a polyamide layer structure in a reverse osmosis membrane using a low-dose green co-solvent, characterized in that: Includes the following steps: S1. A mixed aqueous solution of m-phenylenediamine, triethylamine, camphor sulfonic acid and green cosolvent is used as the aqueous reaction solution. The aqueous reaction solution is poured onto the surface of the polysulfone-based membrane. After standing, the aqueous solution on the surface is removed to obtain membrane I. The green co-solvent is N-butylpyrrolidone; the mass fraction of N-butylpyrrolidone is 0.05~2 wt.%. S2. Using a hexane solution containing trimesoyl chloride as the organic phase reaction solution, pour the organic phase reaction solution onto the surface of membrane I obtained in step S1. After standing, remove the organic phase solution from the surface to obtain membrane II. S3. Let the membrane II obtained in step S2 stand until the solution on the surface of membrane II is drained, then cure and dry it in an oven and cool it to room temperature. Finally, immerse it in deionized water for storage to obtain a reverse osmosis membrane.

2. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S1, the mass fraction of the N-butylpyrrolidone is 0.05-0.5 wt.%.

3. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S1, the solvent of the aqueous reaction solution is deionized water.

4. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S1, the mass fraction of intermediate phenylenediamine in the aqueous reaction solution is 1~2 wt.%, the mass fraction of triethylamine is 1.1~2 wt.%, and the mass fraction of camphor sulfonic acid is 1.5~2.6 wt.%.

5. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S1, the volume of the aqueous reaction solution used is 20 mL; the residence time is 30-60 s.

6. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S2, the mass fraction of the pyromellitic trimethylol chloride in the organic phase reaction solution is 0.1~0.15 wt.%.

7. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S2, the amount of the organic phase reaction solution used is 20 mL; the residence time is 10~30 s.

8. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S3, the curing and drying temperature is 100℃ and the time is 3~5 minutes.

9. The method for inducing the construction of a reverse osmosis membrane polyamide layer structure using a low-dose green co-solvent according to claim 1, characterized in that: In step S3, the reverse osmosis membrane produced achieves a pure water flux of 93.11 L·m³ at a pressure of 1.55 MPa. -2 ·h -1 The NaCl retention rate is over 96.95%.

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