Forward osmosis membrane with temperature response composite nano material middle layer and preparation method of forward osmosis membrane

Abstract

The invention relates to a temperature response composite nanomaterial interlayer forward osmosis membrane and a preparation method thereof, and belongs to the technical field of membrane separation. The forward osmosis membrane sequentially comprises a supporting layer, a middle layer and a separation layer from bottom to top, wherein the middle layer comprises an N-isopropylacrylamide modified metal organic framework nano material; the separation layer is a polyamide film and has a ridge-valley structure formed by temperature regulation interface polymerization. The water permeability and reverse solute interception performance of the forward osmosis membrane are improved.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane and its preparation method. Background Technology

[0002] Forward osmosis (FO) membrane technology, as an emerging membrane separation process, utilizes the osmotic pressure difference created by the concentration difference across the membrane. This allows water molecules to spontaneously diffuse from the low-osmotic-pressure feed liquid side (FS) to the high-osmotic-pressure draw liquid side (DS) without external force, achieving separation and enrichment. Because FO membrane technology requires no external pressure, has low membrane fouling, and high rejection rates, it shows great application potential in seawater desalination, water treatment, and food processing.

[0003] Most forward osmosis membranes currently studied are thin-layer composite forward osmosis membranes (TFC), which consist of a support layer and a separation layer. While TFC membranes are widely used, the rapid diffusion of amine monomers on the support layer surface often results in an excessively thick separation layer, leading to a lower permeation rate. Furthermore, the resulting separation layer tends to create large pores in the support layer, forming non-selective defects. These structural characteristics negatively impact the application of forward osmosis membranes. Optimizing the structure of forward osmosis membranes is crucial for improving their performance.

[0004] Studies have shown that the separation layer structure is directly affected by the release characteristics of aqueous monomers, and constructing an intermediate layer can effectively regulate the release behavior of amine monomers. By constructing an intermediate layer with strong interactions with aqueous monomers, the diffusion rate of aqueous monomers can be reduced. Based on the reduction in the aqueous monomer rate, the thickness of the synthesized separation layer is reduced. For example, Chinese Patent Publication No. CN119186292A discloses a photoisomeric metal-organic framework intermediate layer forward osmosis membrane and its preparation method. The method involves loading UiO-67-SP nanomaterials onto the surface of a nylon support layer and performing interfacial polymerization of amine monomers and acyl chlorides under light irradiation or dark conditions to form a spiropyran / zirconium-based photoisomeric metal-organic framework intermediate layer, thereby optimizing the separation layer structure to improve water flux and salt ion retention performance. However, an excessively low aqueous monomer diffusion rate may lead to insufficient cross-linking of the separation layer, affecting the membrane's separation performance. Conversely, if the aqueous monomer diffusion rate is too fast, the monomer supply continues, and interfacial polymerization continues, increasing the separation layer thickness and cross-linking degree, which adversely affects the membrane's water permeability. Therefore, dynamic control of aqueous monomer diffusion is crucial for constructing a separation layer with appropriate thickness and cross-linking degree. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane and its preparation method, so as to solve the technical problem of how to dynamically control the interfacial polymerization process to overcome the drawbacks of excessively thick separation layer, non-selective defect pores and insufficient cross-linking degree of forward osmosis membrane, thereby simultaneously improving water permeability and reverse solute retention.

[0006] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which includes, from bottom to top, a support layer, an intermediate layer, and a separation layer. The intermediate layer contains N-isopropylacrylamide-modified metal-organic framework nanomaterials. The separation layer is a polyamide film with a ridge-valley structure formed by temperature-controlled interfacial polymerization, wherein the interfacial polymerization reaction is carried out at an organic phase solution temperature of 20~70°C.

[0007] Preferably, the support layer is a nylon ultrafiltration membrane with an average pore size of 0.1 μm to 0.25 μm, and the effective area of ​​the nylon ultrafiltration membrane is 20 cm². 2 .

[0008] This invention also provides a method for preparing the above-mentioned temperature-responsive composite nanomaterial intermediate forward osmosis membrane, comprising the following steps: 1) Provide a nylon ultrafiltration membrane with an average pore size of 0.1μm~0.25μm as a support layer; 2) An N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion is loaded onto the surface of the support layer to form an intermediate layer; 3) An interfacial polymerization reaction is carried out on the surface of the intermediate layer, wherein the temperature of the organic phase solution used for interfacial polymerization is 20℃~70℃, thereby forming a polyamide film separation layer with a ridge-valley structure on the surface of the intermediate layer, thus obtaining a forward osmosis membrane composed of a support layer, an intermediate layer and a separation layer.

[0009] Preferably, in step 2), the intermediate layer is formed by the following method: dispersing N-isopropylacrylamide-modified metal-organic framework nanomaterials in deionized water, ultrasonically treating the dispersion, and then loading the dispersion onto the surface of the support layer by vacuum filtration; the ratio of the N-isopropylacrylamide-modified metal-organic framework nanomaterials to deionized water is (0.002-0.009) g: (50-150) mL. Preferably, the ultrasonic treatment conditions include ultrasonic treatment at 20℃-30℃ for 30 min-60 min.

[0010] Preferably, in step 2), the preparation method of the N-isopropylacrylamide modified metal-organic framework nanomaterial includes: First, metal-organic framework nanomaterials were degassed under vacuum at 150℃-180℃ for 12-24 h to obtain pretreated metal-organic framework nanomaterials. Then, N-isopropylacrylamide was dissolved in diethyl ether to form a solution, and the solution was mixed with the pretreated metal-organic framework nanomaterials. After stirring, the diethyl ether was removed by vacuum evaporation, so that N-isopropylacrylamide was uniformly loaded on the surface of the metal-organic framework nanomaterials. Subsequently, tetrahydrofuran and azobisisobutyronitrile were added, and the reaction was carried out at 50℃-60℃ for 48-54 h to obtain a crude product. Finally, the crude product was washed sequentially with methanol, acetone, and dichloromethane, and then degassed at 80℃-100℃ for 12-24 h before grinding to obtain N-isopropylacrylamide modified metal-organic framework materials. The ratio of the metal-organic framework nanomaterial, N-isopropylacrylamide, diethyl ether, tetrahydrofuran, and azobisisobutyronitrile is (0.2-0.5) g: (0.2-0.4) g: (10-15) mL: (10-15) mL: (0.05-0.1) g.

[0011] Preferably, the preparation method of the metal-organic framework nanomaterial includes: dispersing zirconium tetrachloride and 4,4'-biphenyl dicarboxylic acid in a mixed solution of N,N-dimethylformamide and deionized water at room temperature and sonicating to obtain a first mixture; reacting the first mixture at 120℃-140℃ for 24h-30h and then cooling to room temperature, filtering to obtain a precipitate; washing the precipitate alternately with N,N-dimethylformamide and ethanol three to five times, filtering and drying to obtain the metal-organic framework nanomaterial; the ratio of zirconium tetrachloride, 4,4'-biphenyl dicarboxylic acid, N,N-dimethylformamide and deionized water is (0.1-0.2) g : (0.1-0.2) g : (8-10) mL : (0.005-0.01) mL.

[0012] Preferably, in step 3), the polyamide film separation layer is formed by the following method: the intermediate layer is placed in an aqueous solution and soaked for 1 min to 3 min, the aqueous solution containing amine monomers; then, at 20°C to 70°C, the intermediate layer after soaking in the aqueous solution is placed in an organic solution and soaked for 1 min to 3 min, the organic solution containing acyl chloride monomers; the amine monomers and the acyl chloride monomers undergo an interfacial polymerization reaction to form the polyamide film separation layer.

[0013] Preferably, the aqueous phase solution is a m-phenylenediamine aqueous phase solution with a mass percentage concentration of 1 wt%-3 wt%; the organic phase solution is a trimesoyl chloride organic phase solution with a mass percentage concentration of 0.3 wt%-0.7 wt%.

[0014] More preferably, the aqueous phase solution of m-phenylenediamine is obtained by dissolving m-phenylenediamine in deionized water; and the organic phase solution of trimesoyl chloride is obtained by dissolving trimesoyl chloride in n-hexane.

[0015] Preferably, after the interfacial polymerization reaction, the process further includes thermal stabilization and curing at 20°C to 70°C for 2 to 5 minutes.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a temperature-responsive composite nanomaterial intermediate forward osmosis membrane. The metal-organic framework material itself provides a high specific surface area, promoting the adhesion and storage of aqueous monomers, laying the foundation for the formation of a dense, defect-free polyamide film separation layer. The molecular chains of the temperature-responsive polymer N-isopropylacrylamide undergo conformational changes at different temperatures. At lower temperatures, the molecular chains extend, increasing hydrophilicity; at higher temperatures, the molecular chains collapse, increasing hydrophobicity. This characteristic is beneficial for dynamically controlling the microenvironment of the interfacial polymerization reaction. Temperature-controlled polymerization, by setting the organic phase solution temperature to 20-70℃, achieves active control of the reaction rate and monomer diffusion behavior. Ultimately, this synergistic effect results in a highly dense separation layer, improving salt rejection, while rapid self-polymerization reduces the separation layer thickness and forms an ideal ridge-valley structure, increasing water flux, thereby simultaneously improving the membrane's water permeability and reverse solute rejection. Therefore, the temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane of the present invention significantly improves water flux and reduces reverse salt ion flux, which can solve the problems of poor water permeability and salt rejection caused by the excessively thick separation layer and the presence of non-selective pores in existing forward osmosis membranes.

[0017] Furthermore, the nylon membrane with an average pore size of 0.1μm to 0.25μm serves as a support layer, providing a stable substrate. This pore size range can provide sufficient mechanical support for the upper intermediate layer and separation layer, while effectively preventing excessive penetration of aqueous monomers into the support layer and causing losses, thus helping to form a complete and uniform separation layer on the surface.

[0018] This invention also provides a method for preparing the aforementioned temperature-responsive composite nanomaterial interlayer forward osmosis membrane. The preparation process is simple and low-cost. This method modifies the metal-organic framework material (UiO-67) by introducing N-isopropylacrylamide (NIPAM) and uses this composite material as the interlayer. Due to the temperature-responsive characteristics of NIPAM and the temperature control of the organic phase solution during interfacial polymerization (20℃~70℃), the UiO-67-NIPAM interlayer exhibits temperature zoning from top to bottom due to the non-uniformity of heat transfer. This temperature zoning results in a high-temperature region at the top and a low-temperature region at the bottom of the interlayer. In the upper layer of the interlayer, the amide functional groups of NIPAM are coiled up, resulting in poor accessibility and weak interaction with the aqueous monomers, exhibiting a hydrophobic state. This allows for the rapid release of amine monomers from the upper interlayer, leading to initial cross-linking with the organic phase at the upper interlayer interface. In the lower interlayer, the amide functional groups of NIPAM are fully exposed, resulting in stronger interaction with the aqueous monomers, exhibiting a hydrophilic state. This prevents further transport of the aqueous monomers to the lower interlayer interface. Under the synergistic effect of the hydrophobic upper layer and the hydrophilic lower layer, the interfacial polymerization of the interlayer accelerates and self-terminates, forming a thin and dense polyamide film separation layer. Optimizing the separation layer structure can simultaneously improve the water permeability of the forward osmosis membrane and the solute retention performance of the reverse osmosis membrane. Furthermore, increasing the interfacial polymerization temperature promotes the escape of dissolved gases from the aqueous phase, causing the separation layer to bulge and form a ridge-valley structure, increasing the water permeation contact area, increasing water storage space, and further improving water flux. The forward osmosis membrane prepared by this invention significantly improves water flux and salt ion retention, thereby reducing reverse salt flux. It can solve the problems of poor water permeability and ion recovery caused by the excessively thick separation layer and non-selective pores in existing forward osmosis membranes.

[0019] Furthermore, dispersing 0.003g-0.009g of N-isopropylacrylamide-modified metal-organic framework nanomaterials in 50-150mL of deionized water optimized the dynamic regulation of the interlayer's adhesion to aqueous monomers and its sustained-release performance, thus improving the performance of the forward osmosis membrane. The dispersion loading and corresponding dispersion treatment conditions ensured that the interlayer could uniformly and stably cover the support layer surface, forming a defect-free interlayer and avoiding localized weakness or defects in the separation layer caused by the unevenness of the interlayer.

[0020] Furthermore, the preparation method of N-isopropylacrylamide-modified metal-organic framework materials ensures the preparation of composite nanomaterials with well-defined structures and controllable grafting rates. Vacuum degassing of the metal-organic framework material removes impurities within the pores, ensuring effective grafting of N-isopropylacrylamide. The solvents diethyl ether and tetrahydrofuran, along with the corresponding reaction conditions (the ratio of metal-organic framework nanomaterials, N-isopropylacrylamide, diethyl ether, tetrahydrofuran, and azobisisobutyronitrile), ensure the smooth progress of the polymerization reaction on the surface of the metal-organic framework material, resulting in a material basis with a desired temperature-responsive intermediate layer.

[0021] Furthermore, MOF nanomaterials were synthesized using zirconium tetrachloride and 4,4'-biphenyl dicarboxylic acid as raw materials under specific solvent systems (N,N-dimethylformamide and deionized water) and reaction conditions (120℃-140℃ for 24-30 hours). This method enabled the preparation of MOF materials with regular pore structures and high specific surface areas. The high specific surface area provides a large adhesion area for subsequent grafting of temperature-responsive polymers (NIPAM), thereby ensuring effective storage of aqueous monomers and preventing excessive loss, thus enabling the effective formation of a defect-free, highly cross-linked polyamide separation layer.

[0022] Alternating washing with DMF (N,N-dimethylformamide) and ethanol, followed by vacuum filtration and drying, ensured that the final MOF nanomaterials possessed high purity and good dispersibility. Residual impurities or material agglomeration would severely affect the uniformity and stability of the intermediate layer, leading to defects in the separation layer.

[0023] Furthermore, soaking in the aqueous solution for 1-3 minutes and in the organic solution for 1-3 minutes is crucial for forming an ideal separation layer. This ensures the reaction proceeds fully, resulting in a separation layer with moderate cross-linking and a complete structure. If the time is too short, the reaction will be insufficient, potentially leading to inadequate cross-linking and the formation of defects and pores; if the time is too long, an excessively thick polyamide layer may form, reducing water permeability.

[0024] By explicitly setting the organic phase solution temperature for interfacial polymerization within a wide range of 20°C to 70°C, two key advantages are achieved: firstly, it provides an optimal temperature range for conventional interfacial polymerization; more importantly, this temperature range covers the lowest critical dissolution temperature (LCST, typically around 32°C) of the N-isopropylacrylamide (NIPAM) polymer in the temperature-responsive interlayer. This means that operators can actively utilize the thermosensitive properties (hydrophilic / hydrophobic transition) of the interlayer to control the diffusion rate of aqueous amine monomers (such as m-phenylenediamine) and the interfacial reaction microenvironment by selecting whether the reaction occurs above or below the LCST. This allows for dynamic control over the morphology (such as ridge-valley structure) and density of the polyamide layer.

[0025] Furthermore, an aqueous solution of m-phenylenediamine with a mass percentage concentration of 1 wt%-3 wt% further enhances the retention effect of the intermediate layer on the m-phenylenediamine monomer, reduces the diffusion rate of the m-phenylenediamine monomer, and facilitates the formation of an ultrathin separation layer; an organic solution of trimesoyl chloride with a mass percentage concentration of 0.3 wt%-0.7 wt% further promotes the interfacial polymerization reaction between the m-phenylenediamine monomer and trimesoyl chloride to form a separation layer.

[0026] Furthermore, thermosetting conditions help improve the crosslinking degree and stability of the release layer. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the temperature difference between the surface and bottom of the intermediate layer of the temperature-responsive composite nanomaterial prepared in Example 3 of the present invention. Detailed Implementation

[0028] To enable those skilled in the art to understand the features and effects of the present invention, the following descriptions and definitions are only general descriptions of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in the event of any conflict, the definitions in this specification shall prevail.

[0029] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0030] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0031] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0032] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0033] This invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane, comprising the following steps: Step 1) Provide a nylon ultrafiltration membrane with an average pore size of 0.1μm~0.25μm as a support layer; Step 2) At room temperature, 0.1 g-0.2 g of zirconium tetrachloride and 0.1 g-0.2 g of 4,4'-biphenyl dicarboxylic acid are dispersed in a mixed solution of 8 mL-10 mL of N,N-dimethylformamide and 0.005 mL-0.010 mL of deionized water and sonicated to obtain a first mixture. The first mixture is placed in a stainless steel autoclave lined with tetrafluoroethylene and reacted continuously at 120℃-140℃ for 24 h-30 h. After the reaction, the mixture is cooled to room temperature and filtered to obtain a precipitate. The precipitate is washed three to five times alternately with N,N-dimethylformamide and ethanol, filtered and dried to obtain metal-organic framework nanomaterials. Step 3) The preparation method of N-isopropylacrylamide modified metal-organic framework nanomaterials is as follows: 0.2g-0.5g of metal-organic framework nanomaterials are degassed under vacuum at 150℃-180℃ for 12-24h to obtain pretreated metal-organic framework nanomaterials; then 0.2g-0.4g of N-isopropylacrylamide (NIPAM) is dissolved in 10mL-15mL of diethyl ether to form a solution, and the solution is mixed with the pretreated metal-organic framework nanomaterials and stirred. After removing diethyl ether by vacuum evaporation, N-isopropylacrylamide was uniformly loaded onto the surface of the metal-organic framework nanomaterial. Subsequently, 10 mL-15 mL of tetrahydrofuran and 0.05 g-0.10 g of azobisisobutyronitrile were added, and the reaction was carried out at 50 °C-60 °C for 48-54 h to obtain a crude product. Finally, the crude product was washed sequentially with methanol, acetone, and dichloromethane, and then degassed at 80-100 °C for 12-24 h before grinding to obtain N-isopropylacrylamide modified metal-organic framework nanomaterials. Step 4) Disperse 0.002g-0.009g of N-isopropylacrylamide-modified metal-organic framework nanomaterials uniformly in (50-150)mL of deionized water, stir in the dark, and then sonicate at 20-30℃ for 30min-90min to obtain an N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion. The ultrasonic dispersion power is 160W-180W. Subsequently, the N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion is loaded onto the surface of the support layer by vacuum filtration to form an N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer. Step 5) The N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer is immersed in a 1 wt%-3 wt% m-phenylenediamine aqueous solution for 1 min-3 min, and the excess solution is removed. Then, the N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer after immersion in the m-phenylenediamine aqueous solution is immersed in a 0.3 wt%-0.7 wt% pyromellitic acid chloride organic solution at 20℃-70℃ for 1 min-3 min, and the excess solution is discarded. Then, it is heat-stabilized and cured in an oven at 20℃-70℃ for 2 min-5 min to complete the interfacial polymerization reaction and form a polyamide film separation layer. Thus, a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane composed of a support layer, an intermediate layer and a separation layer is obtained.

[0034] The test conditions for the temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane prepared in this invention are as follows: using deionized water as the feed solution and 1 mol / L NaCl solution as the draw solution, the peristaltic pump speed is controlled at 350 r / min at room temperature, and the flow rates of the feed solution and draw solution should be kept consistent. The performance of the prepared forward osmosis membrane is tested under these conditions. Permeability performance is a key indicator for evaluating the effectiveness of the forward osmosis membrane. Water flux (Jv) reflects the membrane's ability to permeate water molecules, and reverse salt flux (Js) is an indicator of the membrane's salt rejection capacity. These are calculated using the following formulas:

[0035]

[0036] In the formula, ΔV represents the permeation volume (L), and Aeff represents the effective membrane area (m²). 2 Ct represents the salt concentration (g / L) at time t on the raw water side, Vt represents the volume (L) of the raw water side at time t, and Δt represents the infiltration time (h).

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents parts by weight, and "ratio" represents weight proportion.

[0039] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0040] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] Unless otherwise specified in the following examples, all raw materials are commercially available or prepared by conventional methods in the art.

[0042] In the following examples and comparative examples, the average pore size of the nylon support layer used was 0.1–0.25 μm, and the effective area of ​​the nylon support layer was 20 cm². 2 All other raw materials used are common commercially available products that can be purchased directly or can be prepared using conventional techniques in this field.

[0043] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art, unless otherwise stated.

[0044] Example 1 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, comprising the following steps: Step 1) Provide a nylon ultrafiltration membrane with an average pore size of 0.2 μm as a support layer; Step 2) At room temperature, 0.117 g of zirconium tetrachloride and 0.121 g of 4,4'-biphenyl dicarboxylic acid were dispersed in a mixed solution of 10 mL of N,N-dimethylformamide and 0.01 mL of deionized water and sonicated to obtain a first mixture. The first mixture was placed in a stainless steel autoclave lined with tetrafluoroethylene and reacted continuously at 120°C for 24 h. After the reaction, the mixture was cooled to room temperature and filtered to obtain a precipitate. The precipitate was washed alternately with N,N-dimethylformamide and ethanol three to five times, filtered and dried to obtain metal-organic framework nanomaterials. Step 3) 0.3 g of metal-organic framework nanomaterials were degassed under vacuum at 150 °C for 12 h to obtain pretreated metal-organic framework nanomaterials; then 0.25 g of N-isopropylacrylamide (NIPAM) was dissolved in 10 mL of diethyl ether to form a solution, and the solution was mixed with the pretreated metal-organic framework nanomaterials. After stirring, the diethyl ether was removed by vacuum evaporation, so that N-isopropylacrylamide was uniformly loaded on the surface of the metal-organic framework nanomaterials; then 10 mL of tetrahydrofuran was added to neutralize 0.075 g of azobisisobutyronitrile, and the reaction was carried out at 60 °C for 48 h to obtain a crude product. After the reaction was completed, the crude product was washed with methanol, acetone and dichloromethane in sequence, and then degassed at 80 °C for 12 h and ground to obtain N-isopropylacrylamide modified metal-organic framework nanomaterials; Step 4) 0.006 g of N-isopropylacrylamide-modified metal-organic framework nanomaterials were uniformly dispersed in 100 mL of deionized water. After stirring in the dark and ultrasonic treatment at 25 °C for 90 min, an N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion was obtained. The ultrasonic dispersion power was 170 W. Subsequently, the N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion was loaded onto the surface of the support layer by vacuum filtration to form an N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer. Step 5) The N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer is immersed in a 2.5 wt% m-phenylenediamine aqueous solution for 3 min, and the excess solution is removed. Then, the N-isopropylacrylamide-modified metal-organic framework nanomaterial intermediate layer after immersion in the m-phenylenediamine aqueous solution is immersed in a 0.5 wt% trimesoyl chloride organic solution at 25°C for 1 min, and the excess solution is discarded. Then, it is heat-stabilized and cured in an oven at 60°C for 2 min to complete the interfacial polymerization reaction and form a polyamide film separation layer. Thus, a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane composed of a support layer, an intermediate layer and a separation layer is obtained.

[0045] The prepared membrane was tested, and the average water flux of the forward osmosis membrane was 18.92 L·m. -2 ·h -1 (LMH), reverse salt flux is 2.33 g·m -2 ·h -1 (gMH).

[0046] Example 2 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that the temperature of the organic phase solution is 40°C, while the remaining steps are the same as in Example 1.

[0047] The prepared forward osmosis membrane was tested, and the average water flux was 21.76 LMH, while the reverse salt flux was 1.52 gMH.

[0048] Example 3 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that the temperature of the organic phase solution is 60°C, while the remaining steps are the same as in Example 1.

[0049] The prepared forward osmosis membrane was tested, and the average water flux was 28.60 LMH, while the reverse salt flux was 1.44 gMH.

[0050] like Figure 1 As shown, the highest temperature on the surface of the intermediate layer of the N-isopropylacrylamide-modified metal-organic framework nanomaterial (the side in contact with the thermal organic phase) reaches 59.7°C, while the highest temperature on the bottom surface of the intermediate layer of the N-isopropylacrylamide-modified metal-organic framework nanomaterial (the side near the support layer) is only 32.4°C, with a significant temperature difference of about 27.3°C between the two.

[0051] This temperature gradient directly confirms that the N-isopropylacrylamide-modified metal-organic framework nanomaterial interlayer possesses excellent temperature responsiveness and thermal conductivity asymmetry. The underlying mechanism is as follows: when heated above the lowest critical dissolution temperature (LCST, approximately 32°C) of NIPAM, the PNIPAM molecular chains in the upper part of the interlayer near the heat source undergo a hydrophilic-hydrophobic transition and collapse, thereby weakening the adsorption and interaction with aqueous monomers (such as m-phenylenediamine). Meanwhile, in the lower part of the interlayer away from the heat source, where the temperature remains below the LCST, the PNIPAM molecular chains maintain an extended hydrophilic state, strongly binding the m-phenylenediamine monomer.

[0052] This "hot at the top, cold at the bottom" temperature field distribution leads to a "promoted at the top, suppressed at the bottom" diffusion kinetics difference in the m-phenylenediamine monomer within the interlayer: the upper portion of m-phenylenediamine is released rapidly, preferentially reacting with the organic phase monomer to form a dense cross-linked network; the lower portion of m-phenylenediamine diffuses slowly, delaying the polymerization reaction. This difference in diffusion rate is key to achieving the "self-termination" of the interfacial polymerization reaction, ultimately leading to the formation of an ultrathin polyamide separation layer with a distinct "ridge-valley" structure on the surface of the interlayer of the N-isopropylacrylamide-modified metal-organic framework nanomaterial.

[0053] therefore, Figure 1 This study demonstrates that by controlling the temperature of the organic phase, the interfacial polymerization process can be precisely controlled at the molecular scale by utilizing the temperature response characteristics of the intermediate layer, thereby obtaining a forward osmosis membrane that combines high water flux (such as 28.60 LMH in Example 3) with low reverse salt flux (1.44 gMH).

[0054] Example 4 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 3 in that the mass of N-isopropylacrylamide modified metal-organic framework nanomaterial in the dispersion is 0.002 g, while the remaining steps are the same as in Example 3.

[0055] The prepared forward osmosis membrane was tested, and the average water flux was 22.32 LMH, while the reverse salt flux was 1.62 gMH.

[0056] Example 5 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 3 in that: the mass of N-isopropylacrylamide added in the method for preparing N-isopropylacrylamide modified metal-organic framework nanomaterials is 0.1 g, and the remaining steps are the same as in Example 3.

[0057] The prepared forward osmosis membrane was tested, and the average water flux was 19.38 LMH, while the reverse salt flux was 1.68 gMH.

[0058] Example 6 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 3 in that: the membrane is thermally stabilized and cured in an oven at 25°C for 2 minutes, while the remaining steps are the same as in Example 3.

[0059] The prepared forward osmosis membrane was tested, and the average water flux was 26.32 LMH, while the reverse salt flux was 2.52 gMH.

[0060] Example 7 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that the mass percentage concentration of the aqueous solution is 2wt%.

[0061] The prepared forward osmosis membrane was tested, and the average water flux was 19.68 LMH, while the reverse salt flux was 2.92 gMH.

[0062] Comparative Example 1: The preparation method of the forward osmosis membrane in Comparative Example 1 differs from that in Example 1 in that it does not use N-isopropylacrylamide-modified metal-organic framework nanomaterials. The method includes the following steps: The support layer of a nylon ultrafiltration membrane with an average pore size of 0.2 μm is immersed in a 2.5 wt% aqueous solution of m-phenylenediamine for 3 minutes, and excess solution is removed. Then, the support layer of the nylon ultrafiltration membrane after immersion in the m-phenylenediamine aqueous solution is immersed in a 0.5 wt% organic solution of trimesoyl chloride at 25°C for 1 minute, and excess solution is discarded. Finally, it is placed in an oven at 60°C for heat stabilization and curing for 2 minutes to complete the interfacial polymerization reaction, thereby forming a separation layer on the surface of the support layer of the nylon ultrafiltration membrane, thus obtaining a forward osmosis membrane composed of a support layer and a separation layer.

[0063] The prepared forward osmosis membrane was tested, and the average water flux was 14.75 LMH, while the reverse salt flux was 3.86 gMH.

[0064] Table 1. Comparison of various test data for the forward osmosis membranes of the comparative examples and embodiments of the present invention.

[0065] As shown in Table 1, the average water flux of the forward osmosis membranes prepared in Examples 1-7 of this application is above 18.92 LMH, with a maximum of 28.60 LMH; the reverse salt flux is below 2.92 gMH, with a minimum of 1.44 gMH. The water flux of the forward osmosis membrane prepared in Comparative Example 1 is 14.75 LMH, and the reverse salt flux is 3.86 gMH. This demonstrates that constructing an N-isopropylacrylamide-modified metal-organic framework nanomaterial interlayer can effectively improve the water permeability of the forward osmosis membrane and its reverse solute retention capacity. Figure 1 The figure shows the real-time temperatures of the surface and bottom of the intermediate layer when the organic phase temperature is adjusted to 60°C. As can be seen from the figure, due to its temperature-dependent characteristics, the surface and bottom temperatures of the intermediate layer are inconsistent during interfacial polymerization. When the organic phase solution is heated above the LCST of NIPAM, under thermal conductivity, the NIPAM on the surface of the intermediate layer in contact with the organic phase undergoes a collapse effect, weakening its interaction with the aqueous monomer m-phenylenediamine (m-phenylenediamine). This promotes the rapid release of m-phenylenediamine stored on the surface of the intermediate layer and preferentially forms a dense cross-linked network. Meanwhile, the NIPAM on the bottom of the intermediate layer remains in an extended molecular chain state, exhibiting a stronger interaction with m-phenylenediamine, thus delaying the diffusion of m-phenylenediamine stored on the bottom of the intermediate layer. This further forms a "top-promoting, bottom-suppressing" structure, leading to the self-termination of interfacial polymerization, resulting in a thin and dense polyamide film separation layer.

[0066] Example 8 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 3 in that: in step 4), the mass of the N-isopropylacrylamide modified metal-organic framework nanomaterial used is 0.009 g, and the remaining steps are the same as in Example 3.

[0067] The prepared forward osmosis membrane was tested, and the average water flux was 26.95 LMH, while the reverse salt flux was 1.49 gMH.

[0068] Example 9 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 4), the ultrasonic treatment time of the N-isopropylacrylamide modified metal-organic framework nanomaterial dispersion is 30 min, and the remaining steps are the same as in Example 1.

[0069] The prepared forward osmosis membrane was tested, and the average water flux was 17.85 LMH, while the reverse salt flux was 2.65 gMH.

[0070] Example 10 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 4), the ultrasonic treatment time of the N-isopropylacrylamide modified metal-organic framework nanomaterial dispersion is 60 min, and the remaining steps are the same as in Example 1.

[0071] The prepared forward osmosis membrane was tested, and the average water flux was 19.10 LMH, while the reverse salt flux was 2.40 gMH.

[0072] Example 11 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane, which differs from Example 1 in that: in step 5), the aqueous solution is a 1 wt% m-phenylenediamine aqueous solution, and the remaining steps are the same as in Example 1.

[0073] The prepared forward osmosis membrane was tested, and the average water flux was 16.53 LMH, while the reverse salt flux was 3.25 gMH.

[0074] Example 12 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane, which differs from Example 1 in that: in step 5), the aqueous solution is a 3wt% m-phenylenediamine aqueous solution, and the remaining steps are the same as in Example 1.

[0075] The prepared forward osmosis membrane was tested, and the average water flux was 15.40 LMH, while the reverse salt flux was 2.15 gMH.

[0076] Example 13 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 5), the organic phase solution is a 0.3 wt% solution of trimesoyl chloride n-hexane, and the remaining steps are the same as in Example 1.

[0077] The prepared forward osmosis membrane was tested, and the average water flux was 16.80 LMH, while the reverse salt flux was 3.10 gMH.

[0078] Example 14 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 5), the organic phase solution is a 0.7 wt% pyromellitic acid chloride n-hexane solution, and the remaining steps are the same as in Example 1.

[0079] The prepared forward osmosis membrane was tested, and the average water flux was 13.55 LMH, while the reverse salt flux was 2.05 gMH.

[0080] Example 15 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 5), after interfacial polymerization, it is thermally stabilized and cured at 20°C for 5 minutes, while the remaining steps are the same as in Example 1.

[0081] The prepared forward osmosis membrane was tested, and the average water flux was 17.20 LMH, while the reverse salt flux was 3.02 gMH.

[0082] Example 16 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, which differs from Example 1 in that: in step 5), after interfacial polymerization, it is thermally stabilized and cured at 70°C for 5 minutes, while the remaining steps are the same as in Example 1.

[0083] The prepared forward osmosis membrane was tested, and the average water flux was 18.10 LMH, while the reverse salt flux was 1.95 gMH.

[0084] Example 17 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane. The difference between this method and Example 1 is that in step 5), the temperature of the organic phase solution used for interfacial polymerization is 20°C, while the remaining steps are the same as in Example 1.

[0085] The prepared forward osmosis membrane was tested, and the average water flux was 16.45 LMH, while the reverse salt flux was 3.30 gMH.

[0086] Example 18 The present invention provides a method for preparing a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane. The difference between this method and Example 1 is that in step 5), the temperature of the organic phase solution used for interfacial polymerization is 70°C, while the remaining steps are the same as in Example 1.

[0087] The prepared forward osmosis membrane was tested, and the average water flux was 20.15 LMH, while the reverse salt flux was 1.85 gMH.

[0088] The above embodiments 1-7 are preferred embodiments of the present invention and are not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

[0089] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane, characterized in that, The structure comprises, from bottom to top, a support layer, an intermediate layer, and a separation layer. The intermediate layer contains N-isopropylacrylamide-modified metal-organic framework nanomaterials. The separation layer is a polyamide film with a ridge-valve structure formed by a temperature-controlled interfacial polymerization reaction, wherein the interfacial polymerization reaction is carried out at an organic phase solution temperature of 20-70°C.

2. The temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane according to claim 1, characterized in that, The support layer is a nylon ultrafiltration membrane with an average pore size of 0.1 μm to 0.25 μm, and the effective area of ​​the nylon ultrafiltration membrane is 20 cm². 2 .

3. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 1 or 2, characterized in that, Includes the following steps: 1) Provide a support layer; 2) An N-isopropylacrylamide-modified metal-organic framework nanomaterial dispersion is loaded onto the surface of the support layer to form an intermediate layer; 3) An interfacial polymerization reaction is carried out on the surface of the intermediate layer, wherein the temperature of the organic phase solution used for interfacial polymerization is 20℃~70℃, thereby forming a polyamide film separation layer with a ridge-valley structure on the surface of the intermediate layer, thus obtaining a temperature-responsive composite nanomaterial intermediate layer forward osmosis membrane composed of a support layer, an intermediate layer and a separation layer.

4. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 3, characterized in that, In step 2), the intermediate layer is formed by the following method: dispersing N-isopropylacrylamide-modified metal-organic framework nanomaterials in deionized water, ultrasonically treating the dispersion, and then loading the dispersion onto the surface of the support layer by vacuum filtration; the ratio of N-isopropylacrylamide-modified metal-organic framework nanomaterials to deionized water is (0.002-0.009) g: (50-150) mL.

5. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 4, characterized in that, The conditions for ultrasonic treatment include ultrasonic treatment at 20℃-30℃ for 30min-90min.

6. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 3, characterized in that, In step 2), the preparation method of the N-isopropylacrylamide modified metal-organic framework nanomaterial includes: First, the metal-organic framework nanomaterials were degassed under vacuum at 150℃-180℃ for 12-24 h to obtain pretreated metal-organic framework nanomaterials. Then, N-isopropylacrylamide was dissolved in diethyl ether to form a solution, and the solution was mixed with the pretreated metal-organic framework nanomaterials. After stirring, the diethyl ether was removed by vacuum evaporation, so that N-isopropylacrylamide was uniformly loaded on the surface of the metal-organic framework nanomaterials. Subsequently, tetrahydrofuran and azobisisobutyronitrile were added, and the reaction was carried out at 50℃-60℃ for 48-54 h to obtain a crude product. Finally, the crude product was washed sequentially with methanol, acetone, and dichloromethane, and then degassed at 80℃-100℃ for 12-24 h before grinding to obtain N-isopropylacrylamide modified metal-organic framework nanomaterials. The ratio of the metal-organic framework nanomaterial, N-isopropylacrylamide, diethyl ether, tetrahydrofuran, and azobisisobutyronitrile is (0.2-0.5) g: (0.2-0.4) g: (10-15) mL: (10-15) mL: (0.05-0.1) g.

7. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 6, characterized in that, The preparation method of the metal-organic framework nanomaterial includes: dispersing zirconium tetrachloride and 4,4'-biphenyl dicarboxylic acid in a mixed solution of N,N-dimethylformamide and deionized water at room temperature and sonicating to obtain a first mixture; reacting the first mixture at 120℃-140℃ for 24h-30h and then cooling to room temperature, filtering to obtain a precipitate; washing the precipitate alternately with N,N-dimethylformamide and ethanol three to five times, filtering and drying to obtain the metal-organic framework nanomaterial; the ratio of zirconium tetrachloride, 4,4'-biphenyl dicarboxylic acid, N,N-dimethylformamide and deionized water is (0.1-0.2) g : (0.1-0.2) g : (8-10) mL : (0.005-0.01) mL.

8. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 3, characterized in that, In step 3), the polyamide film separation layer is formed by the following method: the intermediate layer is placed in an aqueous solution and soaked for 1 min to 3 min, the aqueous solution containing amine monomers, and then the intermediate layer after soaking in the aqueous solution is placed in an organic solution at 20℃ to 70℃ and soaked for 1 min to 3 min, the organic solution containing acyl chloride monomers, and the amine monomers and the acyl chloride monomers undergo an interfacial polymerization reaction to form the polyamide film separation layer.

9. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 8, characterized in that, The aqueous phase solution is a m-phenylenediamine aqueous phase solution with a mass percentage concentration of 1 wt%-3 wt%; the organic phase solution is a trimesoyl chloride organic phase solution with a mass percentage concentration of 0.3 wt%-0.7 wt%.

10. The method for preparing a temperature-responsive composite nanomaterial intermediate forward osmosis membrane according to claim 8, characterized in that, Following the interfacial polymerization reaction, the process further includes thermal stabilization and curing at 20°C to 70°C for 2 to 5 minutes.

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