Self-locking interlayer forward osmosis membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane separation, and relates to a forward osmosis membrane with a self-locking intermediate layer and a preparation method thereof.The ZIF-8 / NVP self-locking intermediate layer is constructed, the strong interaction force of ZIF-8 and NVP materials on a water-phase monomer is utilized, the water-phase monomer is promoted to be attached to the intermediate layer, the reaction concentration of the water-phase monomer in the subsequent interfacial polymerization reaction process is increased, and the forward osmosis membrane with the self-locking intermediate layer is obtained. Defects of a polyamide separation layer are avoided, the density of the separation layer is improved, and the reverse solute interception capacity of the forward osmosis membrane is improved. By utilizing the chemical characteristic that NVP can be converted into PVP with a net structure after being irradiated by ultraviolet light, ZIF-8 monomers are connected in series, so that the stability of a middle layer is improved, the diffusion rate of a water-phase monomer is slowed down, the thickness of a separation layer is reduced, and the water permeability of the forward osmosis membrane is improved. The technical problems of poor water permeability, poor reverse solute interception and the like caused by the defects of too thick separation layer, non-selective defect holes and the like of the traditional forward osmosis membrane are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and relates to a self-locking intermediate layer forward osmosis membrane and a preparation method thereof. Background Art

[0002] Forward osmosis (FO) membrane technology utilizes the osmotic pressure difference (Δπ) formed by the concentration difference on both sides of the membrane, enabling water molecules to spontaneously diffuse from the low-osmotic feed solution side (FS) through the semi-permeable membrane to the high-osmotic draw solution side (DS) without an external pressure, achieving the purpose of separation and enrichment. Due to the fact that forward osmosis membrane technology requires no external pressure, has low membrane fouling, and high rejection rate, it shows great application potential in fields such as seawater desalination, water treatment, and food processing.

[0003] Thin-film composite forward osmosis membrane is the most widely used type of forward osmosis membrane, which consists of a support layer and a separation layer. Although thin-film composite membranes are widely used, they often have a low permeation rate and poor reverse solute rejection. This is related to the structural problems of the thick and defect-rich pores in the separation layer of traditional thin-film composite membranes. This structural problem is related to the diffusion and attachment behavior of the aqueous monomer in interfacial polymerization. The excessive thickness of the separation layer is due to the diffusion of the aqueous monomer; the defects in the separation layer are due to the loss of the aqueous monomer caused by the large pores in the support layer.

[0004] With the rapid development of nanotechnology, researchers have found that constructing a nanomaterial intermediate layer in the support layer and the separation layer can effectively improve the water flux and separation performance of forward osmosis membranes. Metal-organic framework materials are a class of crystalline materials composed of metal ions connected by bridging organic ligands. Their flexible and adjustable microporous structure and simple preparation characteristics make them advantageous intermediate layer materials. By using metal-organic framework materials to construct an intermediate layer, on the one hand, the tiny pores in the metal-organic framework material intermediate layer can increase the diffusion resistance of the aqueous monomer, slow down the diffusion rate, and reduce the thickness of the separation layer; on the other hand, the metal-organic framework material intermediate layer can also prevent the loss of the aqueous monomer and avoid the formation of defect pores in the separation layer.

[0005] Previously, metal-organic framework intermediate layers mostly increased the diffusion resistance of aqueous monomers by simply increasing the loading amount, which led to the metal-organic framework materials being more likely to carry the separation layer and exfoliate together under hydraulic action, resulting in a decline in membrane performance. Based on this, it is necessary to further explore the preparation method of high-performance forward osmosis membranes to simultaneously achieve the regulation of the diffusion and attachment behavior of aqueous monomers and the improvement of the stability of the intermediate layer, thereby improving the water permeability and reverse solute rejection performance of forward osmosis membranes.

[0006] Synthesizing a separation layer with a thin thickness, high density, uniform texture and no defects is a key factor in improving the water permeability and reverse solute rejection performance of forward osmosis membranes. To achieve this goal, the selection and optimization of the intermediate layer material are crucial. Among many nanomaterials, metal-organic framework nanomaterials, ZIF-8 has a high specific surface area and abundant micropores, which can effectively prevent the loss of aqueous monomers and increase their diffusion rate into the organic phase. However, there are obvious limitations in solely relying on increasing the loading amount of ZIF-8 to regulate the attachment and diffusion behavior of aqueous monomers. With the increase in the ZIF-8 loading amount, although the initial storage amount of amine monomers can be increased to a certain extent and the diffusion rate can be slowed down, an excessive loading amount will increase the thickness and complexity of the intermediate layer, and also make the intermediate layer more vulnerable to external factors and become unstable. For example, it may fall off under pressure or water flow impact. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention provides a self-locking intermediate layer forward osmosis membrane and its preparation method, which solves the technical problems such as poor water permeability and reverse solute rejection caused by the disadvantages of the existing forward osmosis membranes, such as too thick separation layer and non-selective defect holes.

[0008] The present invention is realized through the following technical solutions: A self-locking intermediate layer forward osmosis membrane and its preparation method, comprising the following steps: Disperse ZIF-8 nanomaterials and NVP in methanol, stir in the dark and then ultrasonically disperse to obtain a ZIF-8 nanomaterial dispersion containing NVP; Disperse the aqueous solution and the photoinitiator in deionized water to obtain an aqueous solution containing the photoinitiator; disperse trimesoyl chloride in n-hexane to obtain an organic phase solution; The ZIF-8 nanomaterial dispersion containing NVP is loaded on the surface of the nylon support layer by vacuum filtration to form a ZIF-8 / NVP intermediate layer; Load the aqueous solution containing the photoinitiator on the ZIF-8 / NVP intermediate layer, and irradiate with ultraviolet light of different intensities to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer; Add the organic phase solution to the ZIF-8 / PVP intermediate layer, carry out an interfacial polymerization reaction, and then carry out a thermal curing treatment to form a polyamide separation layer, and obtain a ZIF-8 / NVP self-locking intermediate layer forward osmosis membrane.

[0009] Preferably, in the ZIF-8 nanomaterial dispersion containing NVP, for every 100 mL of methanol, the mass of ZIF-8 is 0.002 g - 0.006 g, and the mass of NVP is 0.1 g - 0.8 g.

[0010] Preferably, the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.1 wt% - 0.5 wt%; the photoinitiator is 2-hydroxy-4'(2-hydroxyethoxy)-2-methylpropiophenone.

[0011] Preferably, the aqueous solution is prepared by dissolving an amine monomer in deionized water, and the mass percentage concentration of the amine monomer is 1.5 wt% - 3 wt%. The types of amine monomers include one of m-phenylenediamine (MPD), piperazine (PIP), polyethyleneimine (PEI), and dopamine (DA).

[0012] Preferably, the mass percentage concentration of trimellitic acid chloride in the organic phase solution is 0.1 wt% - 0.5 wt%.

[0013] Preferably, the power density range of the ultraviolet light is 100 mW / cm 2 -170 mW / cm 2 , and the ultraviolet irradiation time is 20 s - 35 s.

[0014] Preferably, the thermal curing treatment conditions are thermal curing at a temperature of 50 °C - 80 °C for 2 min - 5 min.

[0015] Preferably, the specific preparation process of the ZIF-8 nanomaterial is as follows: 2-methylimidazole and zinc nitrate are respectively dissolved in methanol, stirred at room temperature, the zinc nitrate solution is added to the 2-methylimidazole solution, the synthesized mixed solution is stirred and reacted, the product is collected by centrifugation, washed and dried to obtain the ZIF-8 nanomaterial.

[0016] Preferably, the power of the ultrasonic dispersion is 160 W - 180 W, and the time is 30 min - 40 min.

[0017] A self-locking intermediate layer forward osmosis membrane is prepared by the method for preparing the self-locking intermediate layer forward osmosis membrane described above.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a self-locking intermediate layer forward osmosis membrane and a preparation method thereof. NVP is pre-embedded in ZIF-8. After depositing the aqueous phase, NVP is photo-stimulated to self-polymerize into a network-like PVP structure. PVP interpenetrates and blocks ZIF-8 and semi-crosslinks with the subsequent formed polyamide separation layer. Based on the interpenetration and blockage of ZIF-8 by PVP, the stability of the intermediate layer can be improved; at the same time, this structure can further increase the diffusion resistance of the aqueous phase monomers, reduce the thickness of the separation layer, and is beneficial to improving the water permeability performance; in addition, the crosslinking of PVP and the polyamide separation layer also helps to improve the density of the separation layer and improve the reverse solute rejection performance. The present invention optimizes the structure of the separation layer by constructing a ZIF-8 / NVP self-locking intermediate layer, and successfully prepares a new type of self-locking intermediate layer forward osmosis membrane with excellent advantages such as water permeability, salt rejection performance, and stability. First, the Zn ions and imidazole rings of ZIF-8 can generate coordination and hydrogen bond interactions with the aqueous phase monomers. The strong interaction forces enable the intermediate layer to adsorb more aqueous phase monomers, increase the concentration of the aqueous phase monomers at the reaction interface of interfacial polymerization, and thus improve the density of the polyamide separation layer, avoid non-selective defects in the separation layer, and enhance the salt rejection performance of the forward osmosis membrane. Secondly, after ultraviolet light irradiation, NVP monomers are connected in series with each other to form a PVP with a network structure, which interpenetrates and blocks the ZIF-8 material, and the ZIF-8 / NVP intermediate layer is transformed into a ZIF-8 / PVP intermediate layer. The formation of the PVP network increases the steric hindrance effect on the transport of aqueous phase monomers during the interfacial polymerization process. Cooperating with the strong interaction forces, they jointly act to slow down the diffusion rate of the aqueous phase monomers into the organic phase, greatly reducing the thickness of the polyamide separation layer and improving the water permeability of the forward osmosis membrane. Finally, the PVP with a network structure connects the ZIF-8 monomers in series with each other, making the intermediate layer more stable and ensuring that the performance of the forward osmosis membrane can be maintained stable during long-term operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0020] Figure 1 is a schematic flow chart of the preparation method of the new type of self-locking intermediate layer forward osmosis membrane provided by the present invention; Figure 2 is a surface morphology diagram of a traditional polyamide forward osmosis membrane in the prior art of forward osmosis membrane preparation technology (Comparative Example 1); Figure 3 is a cross-sectional morphology diagram of a traditional polyamide forward osmosis membrane in the prior art of forward osmosis membrane preparation technology (Comparative Example 1); Figure 4It is the surface morphology diagram of the novel self-locking intermediate layer forward osmosis membrane in the embodiment of the present invention (Embodiment 2); Figure 5 It is the cross-sectional morphology diagram of the novel self-locking intermediate layer forward osmosis membrane in the embodiment of the present invention (Embodiment 2). Detailed implementation manners

[0021] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0022] To enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts should belong to the protection scope of the present invention.

[0023] It should be noted that the process equipment or devices not specifically noted in the following embodiments are all conventional equipment or devices in the art, unless otherwise specified.

[0024] Please refer to Figure 1 , a preparation method of a novel self-locking intermediate layer forward osmosis membrane provided by the present invention, specifically a preparation method of a ZIF-8 / NVP novel self-locking intermediate layer forward osmosis membrane, includes the following steps: Step 1, the preparation method of ZIF-8 nanomaterials is as follows: Dissolve 10 g - 30 g of 2-methylimidazole (2-Hmim) and 1 g - 2 g of zinc nitrate (Zn(NO3)2·H2O) in 60 g - 80 g and 5 g - 8 g of methanol respectively. While vigorously stirring at a speed of 600 rpm / min - 800 rpm / min at room temperature, slowly add the zinc nitrate solution to the 2-methylimidazole solution to synthesize a mixed solution. After stirring for 12 - 24 hours, centrifuge at a high speed of 5000 rpm / min - 10000 rpm / min for 20 - 40 minutes to collect the product. Wash the product several times with methanol, and then place the product in a vacuum dryer at 80°C - 100°C for 12 - 24 hours to obtain ZIF-8 nanomaterials.

[0025] Step 2, Disperse 0.004 g - 0.006 g of 2-methylimidazole zinc salt (ZIF-8) nanomaterials and 0.1 g - 0.8 g of NVP into methanol, stir in the dark and then ultrasonically disperse to obtain a uniform ZIF-8 nanomaterial dispersion containing N-vinylpyrrolidone (NVP). Among them, the power of ultrasonic dispersion is 160 - 180 W and the time is 30 - 40 min; Step 3, Dissolve the amine monomer in deionized water to obtain an aqueous solution, and add a photoinitiator to the aqueous solution to obtain an aqueous solution containing the photoinitiator; Among them, the types of amine monomers include: m-phenylenediamine (MPD), piperazine (PIP), polyethyleneimine (PEI), dopamine (DA), and the mass percentage concentration of the amine monomer in the aqueous solution is 1.5 wt% - 3 wt%; The photoinitiator is 2-hydroxy-4'(2-hydroxyethoxy)-2-methylpropiophenone, and the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.1 wt% - 0.5 wt%.

[0026] Dissolve trimesoyl chloride (TMC) in n-hexane to prepare an organic phase solution; The mass percentage concentration of trimesoyl chloride in the organic phase solution is 0.1 wt% - 0.5 wt%.

[0027] Step 4, Load the ZIF-8 nanomaterial dispersion containing NVP prepared in Step 2 onto the surface of the nylon support layer in the form of vacuum filtration (the pressure of vacuum filtration is 0.07 - 0.09 MPa; the time is 30 - 50 s) to form a ZIF-8 / NVP intermediate layer. Then load the aqueous solution containing the photoinitiator prepared in Step 2 onto the ZIF-8 / NVP intermediate layer, soak for 2 - 3 min and then remove the excess solution, and then irradiate with ultraviolet light of different intensities (the power density range is 100 mW / cm 2 -170 mW / cm 2 , The irradiation time is 20 s - 35 s) to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer. Subsequently, add the organic phase solution prepared in Step 2, remove the excess solution after the reaction, and place it in a vacuum oven, and carry out thermal curing at 40 ºC - 80 ºC for 2 min - 5 min to complete the interfacial polymerization reaction; In this preparation method, the effective area of the nylon support layer is 15 cm 2 -20 cm 2 , and the pore size is 0.1 - 0.25 μm.

[0028] On the surface of the nylon support layer, a ZIF-8 / nanomaterial dispersion containing NVP is loaded onto the surface of the nylon support layer in the form of vacuum filtration to form a ZIF-8 / polyvinylpyrrolidone (PVP) intermediate layer. Then, an aqueous solution containing a photoinitiator is loaded. After ultraviolet light irradiation, ZIF-8 / NVP is promoted to transform into a ZIF-8 / PVP intermediate layer, and an interfacial polymerization is carried out on the ZIF-8 / PVP intermediate layer to obtain a separation layer. Compared with traditional nanomaterial membranes, the nanomaterial intermediate layer of this ZIF-8 / NVP self-locking intermediate layer forward osmosis membrane reduces the loss of nanomaterials and optimizes the membrane structure. At the same time, the strong interaction between the intermediate layer and the aqueous monomer promotes the attachment of the aqueous monomer to the intermediate layer, greatly reducing the loss of the aqueous monomer, avoiding the formation of non-selective defects in the polyamide separation layer, improving the density of the separation layer, and enhancing the reverse solute rejection performance of the membrane. Moreover, after ultraviolet light irradiation, NVP is photopolymerized into a PVP network, which interpenetrates and blocks ZIF-8, enhancing the steric hindrance effect of the diffusion of the aqueous monomer, increasing the diffusion resistance of the aqueous monomer, slowing down the diffusion rate of the aqueous monomer, reducing the thickness of the polyamide separation layer, and further improving the water permeability of the membrane. In addition, the PVP network connects ZIF-8 nanoparticles in series with each other, further improving the stability of the intermediate layer. A novel self-locking intermediate layer forward osmosis membrane with high separation performance is prepared.

[0029] The test conditions for the membrane prepared in the present invention are as follows: deionized water is used as the feed solution, and 1 mol / L NaCl solution is used as the draw solution. At room temperature, the rotation speed of the peristaltic pump is controlled at 350 r / min, and the flow rates of the feed solution and the draw solution should be kept consistent to test the performance of the prepared forward osmosis membrane, and the water flux J V and the reverse solute flux J S are calculated according to the following formulas respectively:

[0030]

[0031] In the formula, △V represents the permeation volume (L), Aeff represents the effective membrane area (m 2 ), Ct represents the salt concentration (g / L) on the feed side at time t, Vt represents the volume (L) on the feed side at time t, and △t represents the permeation time (h).

[0032] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention.

[0033] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the 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. 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.

[0034] In the following examples, unless otherwise specified, all raw materials are commercially available or prepared by conventional methods in the art.

[0035] In the following, m-phenylenediamine: with a purity of 99.5%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; zinc nitrate hexahydrate: with a purity of 98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 2-methylimidazole: with a purity of 98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; 2-hydroxy-4’(2-hydroxyethoxy)-2-methylpropiophenone: with a purity of 98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; trimesoyl chloride: with a purity of 98%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; n-hexane: with an analytical purity, purchased from Guangdong Guanghua Sci-Tech Co., Ltd.; N,N-dimethylformamide: with an analytical purity, purchased from Guangdong Guanghua Sci-Tech Co., Ltd.; methanol: with an analytical purity, purchased from Tianjin Tianli Chemical Reagent Co., Ltd.; N-vinylpyrrolidone: with an analytical purity, purchased from Guangdong Guanghua Sci-Tech Co., Ltd.

[0036] It should be noted that the process equipment or devices not specifically specified in the following examples are all conventional equipment or devices in the art, unless otherwise stated.

[0037] Example 1 A preparation method of a novel self-locking intermediate layer forward osmosis membrane provided by the present invention, specifically a preparation method of a ZIF-8 / NVP novel self-locking intermediate layer forward osmosis membrane, includes the following steps: Step 1, the preparation method of ZIF-8 nanomaterials is as follows: Dissolve 20 g of 2-methylimidazole (2-Hmim) and 1.5 g of zinc nitrate (Zn(NO3)2·H2O) in 70 g and 6 g of methanol respectively. While vigorously stirring at a speed of 650 rpm / min at room temperature, slowly add the zinc nitrate solution to the 2-methylimidazole solution to synthesize a mixed solution. After stirring for 15 hours, centrifuge at a high speed of 8000 rpm / min for 30 minutes to collect the product. Wash the product with methanol several times, and then place the product in a vacuum dryer at 90 °C for 16 hours to obtain ZIF-8 nanomaterials.

[0038] Step 2: Disperse 0.006 g of 2-methylimidazole zinc salt (ZIF-8) nanomaterials and 0.5 g of NVP into 100 mL of methanol, stir in the dark and then ultrasonically disperse to obtain a uniform ZIF-8 nanomaterial dispersion containing N-vinylpyrrolidone (NVP). Among them, the power of ultrasonic dispersion is 170 W and the time is 35 min; Step 3: Dissolve the amine monomer in deionized water to obtain an aqueous solution, and add a photoinitiator to the aqueous solution to obtain an aqueous solution containing the photoinitiator; among them, the amine monomer is m-phenylenediamine (MPD), and the mass percentage concentration of the amine monomer in the aqueous solution is 2 wt%; the photoinitiator is 2-hydroxy-4’(2-hydroxyethoxy)-2-methylpropiophenone, and the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.3 wt%.

[0039] Dissolve trimesoyl chloride (TMC) in n-hexane to prepare an organic phase solution; the mass percentage concentration of trimesoyl chloride in the organic phase solution is 0.3 wt%.

[0040] Step 4: Load the ZIF-8 nanomaterial dispersion containing NVP prepared in Step 2 onto the surface of the nylon support layer in the form of vacuum filtration (the pressure of vacuum filtration is 0.08 MPa; the time is 40 s) to form a ZIF-8 / NVP intermediate layer. Then load the aqueous solution containing the photoinitiator prepared in Step 2 onto the ZIF-8 / NVP intermediate layer, soak for 2 min and then remove the excess solution, and then irradiate with ultraviolet light of different intensities (the power density range is 120 mW / cm 2 , the irradiation time is 20 s) to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer. Subsequently, add the organic phase solution prepared in Step 2, remove the excess solution after the reaction, and place it in a vacuum oven for 3 min of thermal curing at 60 °C to complete the interfacial polymerization reaction; In this preparation method, the effective area of the nylon support layer is 16 cm 2， The pore size of the nylon support layer is 0.22 μm.

[0041] Test the prepared forward osmosis membrane. The average water flux of the forward osmosis membrane is 23.98 LMH, and the reverse salt flux is 0.57 gMH.

[0042] Comparative Example 1: Without adding the ZIF-8 nanomaterial dispersion containing NVP, photoinitiator, and without irradiating with ultraviolet light, using a support layer of nylon membrane with a pore size of 0.22 μm, at room temperature, immerse the support layer in an aqueous solution with a mass percentage concentration of 2 wt% for 2 min, then pour the organic phase solution with a mass percentage concentration of 0.5 wt% onto the surface of the support layer, pour off the excess organic phase solution after 1 min, and finally cure thermally at 60 °C for 2 min. The remaining preparation method is the same as that of Example 1; Evaluate the prepared forward osmosis membrane. The feed solution is deionized water, and the draw solution is 1 mol / L sodium chloride solution. Test at room temperature for 30 min; the water flux of the prepared forward osmosis membrane is 11.85 (LMH), and the reverse salt flux is 1.15 (gMH).

[0043] Comparative Example 2: Compared with Comparative Example 1, the difference in the preparation method of the forward osmosis membrane in this Comparative Example 2 is only that the ZIF-8 nanomaterial is dispersed in 100 mL of methanol and loaded on the surface of the nylon support layer to form a ZIF-8 intermediate layer, and then the aqueous phase solution and the organic phase solution are loaded in sequence for interfacial polymerization reaction. The mass of the ZIF-8 nanomaterial is 0.006 g, and it is uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment. Similarly, the prepared forward osmosis membrane is tested. The average water flux of the forward osmosis membrane is 21.13 LMH, and the reverse salt flux is 0.45 gMH.

[0044] Comparative Example 3: Compared with Comparative Example 1, the difference in the preparation method of the forward osmosis membrane in this Comparative Example 3 is only that the ZIF-8 nanomaterial is dispersed in 100 mL of methanol and loaded on the surface of the nylon support layer to form a ZIF-8 intermediate layer, and then the aqueous phase solution and the organic phase solution are loaded in sequence for interfacial polymerization reaction. The mass of the ZIF-8 nanomaterial is 0.004 g, and it is uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment. Similarly, the prepared forward osmosis membrane is tested. The average water flux of the forward osmosis membrane is 19.23 LMH, and the reverse salt flux is 0.49 gMH.

[0045] Example 2: In Example 2 of the present invention, compared with Example 1, the difference is only that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.5 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.3 wt%; the power density of the ultraviolet light is 140 mV / cm 2; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 26.85 LMH, and the reverse salt flux was 0.21 gMH.

[0046] Example 3: In Example 3 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.5 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.3 wt%; the power density of the ultraviolet light is 160 mV / cm 2 ; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 22.44 LMH, and the reverse salt flux was 0.32 gMH.

[0047] Example 4: In Example 4 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.5 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.3 wt%; the power density of the ultraviolet light is 140 mV / cm 2 ; The ultraviolet light irradiation time is 35 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 23.15 LMH, and the reverse salt flux was 0.50 gMH.

[0048] Example 5: In Example 5 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.5 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.1 wt%; the power density of the ultraviolet light is 140 mV / cm 2 ; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 21.25 LMH, and the reverse salt flux was 0.47 gMH.

[0049] Example 6: In Example 6 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.5 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.5 wt%; the power density of the ultraviolet light is 140 mV / cm 2; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 22.86 LMH, and the reverse salt flux was 0.31 gMH.

[0050] Example 7: In Example 7 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.1 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.3 wt%; the power density of the ultraviolet light is 140 mV / cm 2 ; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 23.02 LMH, and the reverse salt flux was 0.51 gMH.

[0051] Example 8: In Example 8 of the present invention, compared with Example 1, the preparation method is only different in that the masses of the ZIF-8 nanomaterial and NVP are 0.006 g and 0.8 g respectively, and they are uniformly dispersed in methanol by vigorous stirring and ultrasonic treatment; the mass percentage concentration of the photoinitiator is 0.3 wt%; the power density of the ultraviolet light is 140 mV / cm 2 ; The ultraviolet light irradiation time is 20 s. Similarly, the prepared forward osmosis membrane was tested, and the average water flux of the forward osmosis membrane was 20.09 LMH, and the reverse salt flux was 0.24 gMH.

[0052] Example 9 Step 1, the preparation method of the ZIF-8 nanomaterial is as follows: Dissolve 10 g of 2-methylimidazole (2-Hmim) and 1 g of zinc nitrate (Zn(NO3)2·H2O) in 60 g and 5 g of methanol respectively. While vigorously stirring at a speed of 600 rpm / min at room temperature, slowly add the zinc nitrate solution to the 2-methylimidazole solution to synthesize a mixed solution. After stirring for 12 hours, centrifuge at a high speed of 5000 rpm / min for 20 minutes to collect the product. Wash the product several times with methanol, and then place the product in a vacuum dryer at 80 °C for 12 hours to obtain the ZIF-8 nanomaterial.

[0053] Step 2, disperse 0.002 g of zinc 2-methylimidazole (ZIF-8) nanomaterial and 0.2 g of NVP in 100 mL of methanol, stir in the dark and then disperse by ultrasonic treatment to obtain a uniform ZIF-8 nanomaterial dispersion containing N-vinylpyrrolidone (NVP), wherein the power of the ultrasonic dispersion is 160 W and the time is 30 min; Step 3: Aqueous solution is obtained by dissolving amine monomer in deionized water. A photoinitiator is added to the aqueous solution to obtain an aqueous solution containing the photoinitiator. Herein, the amine monomer is polyethyleneimine (PEI), and the mass percentage concentration of the amine monomer in the aqueous solution is 1.5 wt%. The photoinitiator is 2-hydroxy-4’(2-hydroxyethoxy)-2-methylpropiophenone, and the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.1 wt%.

[0054] Trimellitic acid chloride (TMC) is dissolved in n-hexane to prepare an organic phase solution. The mass percentage concentration of trimellitic acid chloride in the organic phase solution is 0.1 wt%.

[0055] Step 4: The ZIF-8 nanomaterial dispersion containing NVP prepared in Step 2 is loaded on the surface of the nylon support layer in the form of vacuum filtration (the pressure of vacuum filtration is 0.07 MPa; the time is 30 s) to form a ZIF-8 / NVP intermediate layer. Then, the aqueous solution containing the photoinitiator prepared in Step 2 is loaded on the ZIF-8 / NVP intermediate layer and soaked for 3 min, and then the excess solution is removed. Then, it is irradiated with ultraviolet light of different intensities (the power density range is 100 mW / cm 2 , and the irradiation time is 20 s) to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer. Subsequently, the organic phase solution prepared in Step 2 is added, and after the reaction, the excess solution is removed, and it is placed in a vacuum oven and thermally cured at 40 ºC for 2 min to complete the interfacial polymerization reaction; In this preparation method, the effective area of the nylon support layer is 15 cm 2 , and the pore size of the nylon support layer is 0.1 μm.

[0056] Example 10 Step 1: The preparation method of ZIF-8 nanomaterials is as follows: 15 g of 2-methylimidazole (2-Hmim) and 1.5 g of zinc nitrate (Zn(NO3)2·H2O) are respectively dissolved in 65 g and 5 g of methanol. While vigorously stirring at a rotation speed of 600 rpm / min at room temperature, the zinc nitrate solution is slowly added to the 2-methylimidazole solution to synthesize a mixed solution. After stirring for 20 hours, the product is collected by high-speed centrifugation at a rotation speed of 6000 rpm / min for 25 minutes. The product is washed with methanol several times, and then the product is placed in a vacuum dryer at 90 ºC for 12 hours to obtain ZIF-8 nanomaterials.

[0057] Step 2: Disperse 0.003 g of 2-methylimidazole zinc salt (ZIF-8) nanomaterial and 0.3 g of NVP into 100 mL of methanol, stir in the dark and then ultrasonically disperse to obtain a uniform ZIF-8 nanomaterial dispersion containing N-vinylpyrrolidone (NVP). Among them, the power of ultrasonic dispersion is 160 W and the time is 30 min. Step 3: Dissolve the amine monomer in deionized water to obtain an aqueous solution, and add a photoinitiator to the aqueous solution to obtain an aqueous solution containing the photoinitiator. Among them, the amine monomer is piperazine (PIP), and the mass percentage concentration of the amine monomer in the aqueous solution is 2.0 wt%. The photoinitiator is 2-hydroxy-4'(2-hydroxyethoxy)-2-methylpropiophenone, and the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.2 wt%.

[0058] Dissolve trimesoyl chloride (TMC) in n-hexane to prepare an organic phase solution. The mass percentage concentration of trimesoyl chloride in the organic phase solution is 0.2 wt%.

[0059] Step 4: Load the ZIF-8 nanomaterial dispersion containing NVP prepared in Step 2 on the surface of the nylon support layer in the form of vacuum filtration (the pressure of filtration is 0.07 MPa; the time is 30 s) to form a ZIF-8 / NVP intermediate layer. Then load the aqueous solution containing the photoinitiator prepared in Step 2 on the ZIF-8 / NVP intermediate layer, soak for 3 min and then remove the excess solution, and then irradiate with ultraviolet light of different intensities (the power density range is 100 mW / cm 2 , and the irradiation time is 20 s) to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer. Subsequently, add the organic phase solution prepared in Step 2, remove the excess solution after the reaction, and place it in a vacuum oven for 3 min of thermal curing at 50 ºC to complete the interfacial polymerization reaction; In this preparation method, the effective area of the nylon support layer is 18 cm 2 , and the pore diameter of the nylon support layer is 0.15 μm.

[0060] Example 11 Step 1: The preparation method of the ZIF-8 nanomaterial is as follows: Dissolve 30 g of 2-methylimidazole (2-Hmim) and 2 g of zinc nitrate (Zn(NO3)2·H2O) in 80 g and 8 g of methanol respectively. While stirring vigorously at a speed of 800 rpm / min at room temperature, slowly add the zinc nitrate solution to the 2-methylimidazole solution to synthesize a mixed solution. After stirring for 24 hours, centrifuge at a speed of 10,000 rpm / min for 40 minutes to collect the product. Wash the product several times with methanol, and then place the product in a vacuum dryer at 100 ºC for 24 hours to obtain the ZIF-8 nanomaterial.

[0061] Step 2: Disperse 0.005 g of 2-methylimidazole zinc salt (ZIF-8) nanomaterial and 0.6 g of NVP into 100 mL of methanol, stir in the dark and then ultrasonically disperse to obtain a uniform ZIF-8 nanomaterial dispersion containing N-vinylpyrrolidone (NVP). Among them, the power of ultrasonic dispersion is 180 W and the time is 40 min; Step 3: Dissolve the amine monomer in deionized water to obtain an aqueous solution, and add a photoinitiator to the aqueous solution to obtain an aqueous solution containing the photoinitiator; among them, the types of amine monomers include dopamine (DA), and the mass percentage concentration of the amine monomer in the aqueous solution is 3 wt%; the photoinitiator is 2-hydroxy-4'(2-hydroxyethoxy)-2-methylpropiophenone, and the mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.5 wt%.

[0062] Dissolve trimesoyl chloride (TMC) in n-hexane to prepare an organic phase solution; the mass percentage concentration of trimesoyl chloride in the organic phase solution is 0.5 wt%.

[0063] Step 4: Load the ZIF-8 nanomaterial dispersion containing NVP prepared in Step 2 on the surface of the nylon support layer in the form of vacuum filtration (the pressure of vacuum filtration is 0.09 MPa; the time is 50 s) to form a ZIF-8 / NVP intermediate layer. Then load the aqueous solution containing the photoinitiator prepared in Step 2 on the ZIF-8 / NVP intermediate layer and soak for 3 min, then remove the excess solution. Load the aqueous solution containing the photoinitiator prepared in Step 2 on the intermediate layer and soak, remove the excess solution after soaking, and then irradiate with ultraviolet light of different intensities (the power density range is 170 mW / cm 2 , and the irradiation time is 35 s) to promote the self-crosslinking of NVP to form a ZIF-8 / PVP intermediate layer. Subsequently, add the organic phase solution prepared in Step 2, remove the excess solution after the reaction, and place it in a vacuum oven for 5 min of heat curing at 80 °C to complete the interfacial polymerization reaction; In this preparation method, the effective area of the nylon support layer is 20 cm 2 , and the pore size of the nylon support layer is 0.25 μm.

[0064] The detailed comparison of the test data of the forward osmosis membranes in Comparative Examples 1-3 and Examples 1-8 is shown in Table 1.

[0065] Table 1. Comparison of test data of the forward osmosis membranes in the examples of the present invention

[0066] As can be seen from Table 1, constructing a ZIF-8 / NVP self-locking intermediate layer can effectively improve the water permeability and reverse solute rejection ability of the forward osmosis membrane. ComparisonFigure 2 and Figure 4 It is found that the defective holes on the surface of the forward osmosis membrane obtained by constructing the ZIF-8 / NVP self-locking intermediate layer disappear; compared with Figure 3 and Figure 5 it is found that the thickness of the separation layer of the forward osmosis membrane obtained by the ZIF-8 / NVP self-locking intermediate layer is reduced.

[0067] In summary, the present invention provides a preparation scheme for a novel self-locking intermediate layer forward osmosis membrane. By constructing the ZIF-8 / NVP self-locking intermediate layer, the attachment and diffusion behaviors of aqueous monomers are regulated to improve the performance of the forward osmosis membrane. While increasing the water flux of the forward osmosis membrane, the reverse salt flux of the membrane is reduced. Specifically, in the technical solution of the embodiment of the present invention, by constructing the ZIF-8 / NVP self-locking intermediate layer, the strong interaction force of the ZIF-8 and NVP materials on the aqueous monomers is utilized to promote the attachment of the aqueous monomers on the intermediate layer, so as to increase the reaction concentration of the aqueous monomers in the subsequent interfacial polymerization reaction process, avoid the formation of defects in the polyamide separation layer, improve the density of the separation layer, improve the reverse solute rejection ability of the forward osmosis membrane, and reduce the reverse solute flux. Utilizing the chemical property that NVP will be converted into a network structure of PVP after ultraviolet light irradiation, the ZIF-8 monomers are interconnected to improve the stability of the intermediate layer and produce a steric hindrance effect on the aqueous monomers, inhibit the diffusion of the aqueous monomers, reduce the thickness of the polyamide separation layer, enhance the water permeability of the forward osmosis membrane, and increase the water flux. A forward osmosis membrane with high water permeability and strong reverse solute rejection performance is prepared.

[0068] In the present invention, if there is no special description, all the embodiments and preferred implementation methods mentioned in this article can be combined with each other to form a new technical solution.

[0069] In the present invention, if there is no special description, all the technical features and preferred features mentioned in this article can be combined with each other to form a new technical solution.

[0070] In the present invention, if there is no special description, the percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0071] In the present invention, if there is no special description, the various components or their preferred components involved can be combined with each other to form a new technical solution.

[0072] In the present invention, unless otherwise stated, the numerical range "a~b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been fully listed in this article, and "6~22" is only an abbreviated representation of these numerical combinations.

[0073] The "scope" disclosed by the present invention can be in the form of one or more lower limits and one or more upper limits respectively.

[0074] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0075] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in order. Preferably, the reaction method herein is carried out sequentially.

[0076] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods or materials similar to or equivalent to the described content can also be applied to the present invention.

[0077] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof, characterized in that, It includes the following steps: Disperse ZIF-8 nanomaterials and NVP into methanol, stir in the dark and then ultrasonically disperse to obtain a ZIF-8 nanomaterial dispersion containing NVP; Disperse the aqueous solution and the photoinitiator into deionized water to obtain an aqueous solution containing the photoinitiator; disperse trimesoyl chloride into n-hexane to obtain an organic phase solution; The ZIF-8 nanomaterial dispersion containing NVP is loaded on the surface of the nylon support layer by vacuum filtration to form a ZIF-8 / NVP intermediate layer; Then, an aqueous solution containing the photoinitiator is loaded on the ZIF-8 / NVP intermediate layer, and NVP is induced to self-crosslink by ultraviolet light irradiation of different intensities to form a ZIF-8 / PVP intermediate layer; Add the organic phase solution to the ZIF-8 / PVP intermediate layer, carry out an interfacial polymerization reaction, and then carry out a thermal curing treatment to form a polyamide separation layer, and obtain a ZIF-8 / NVP self-locking intermediate layer forward osmosis membrane.

2. The self-locking intermediate layer forward osmosis membrane according to claim 1 and its preparation method are characterized in that, In the ZIF-8 nanomaterial dispersion containing NVP, for every 100 mL of methanol, the mass of ZIF-8 is 0.002 g - 0.006 g, and the mass of NVP is 0.1 g - 0.8 g.

3. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof according to claim 1, wherein The mass percentage concentration of the photoinitiator in the aqueous solution containing the photoinitiator is 0.1 wt% - 0.5 wt%; the photoinitiator is 2-hydroxy-4’(2-hydroxyethoxy)-2-methylpropiophenone.

4. The self-locking intermediate layer forward osmosis membrane according to claim 3 and the preparation method thereof are characterized in that, The aqueous solution is prepared by dissolving an amine monomer in deionized water, and the mass percentage concentration of the amine monomer is 1.5 wt% - 3 wt%; The types of the amine monomer include one of m-phenylenediamine, piperazine, polyethyleneimine, and dopamine.

5. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof according to claim 1, characterized in that, The mass percentage concentration of trimesoyl chloride in the organic phase solution is 0.1 wt% - 0.5 wt%.

6. The self-locking intermediate layer forward osmosis membrane according to claim 1 and its preparation method, characterized in that, The power density range of the ultraviolet light is 100 mV / cm 2 -170 mV / cm 2 , and the ultraviolet irradiation time is 20 s - 35 s.

7. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof according to claim 1, characterized in that, The thermal curing treatment conditions are thermal curing at a temperature of 50 °C - 80 °C for 2 min - 5 min.

8. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof according to claim 1, characterized in that, The specific preparation process of the ZIF-8 nanomaterials is as follows: Dissolve 2-methylimidazole and zinc nitrate in methanol respectively, stir at room temperature, add the zinc nitrate solution to the 2-methylimidazole solution, synthesize the mixed solution, stir and react, then centrifuge to collect the product, wash and dry to obtain ZIF-8 nanomaterials.

9. A self-locking intermediate layer forward osmosis membrane and a preparation method thereof according to claim 1, characterized in that, The power of the ultrasonic dispersion is 160 W - 180 W, and the time is 30 min - 40 min.

10. A self-locking intermediate layer forward osmosis membrane, characterized in that, Prepared by the method for preparing a self-locking intermediate layer forward osmosis membrane according to any one of claims 1 to 9.

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