A method for preparing composite nanofiltration membranes based on UiO-66 nanoparticles with different degrees of defect.

Abstract

This invention discloses a method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect. The steps are as follows: 1) Terephthalic acid, zirconium chloride, glacial acetic acid, trifluoroacetic acid and N,N-dimethylformamide are mixed and reacted to obtain UiO-66 (UiO-66-X) nanoparticles with different degrees of defect; 2) UiO-66-X nanoparticles are dispersed in an aqueous solution of piperazine and subjected to interfacial polymerization reaction with 1,3,5-benzenetricarboxyl chloride dissolved in n-hexane to obtain a composite nanofiltration membrane with a surface "ridge" structure, which ensures a high rejection rate for Na2SO4 while having a high permeation flux.

Description

Technical Field

[0001] This invention belongs to the field of high-performance nanofiltration membrane materials, specifically, it relates to a method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect. Background Technology

[0002] Nanofiltration (NF) technology plays a significant role in seawater desalination, wastewater treatment, and recycling. Nanofiltration membranes can effectively remove multivalent ions and some small organic molecules, often exhibiting superior permeate flux compared to reverse osmosis (RO) membranes. Thin-film composite (TFC) membranes prepared using interfacial polymerization (IP) dominate the commercial desalination membrane market. However, their inherent permeate selectivity remains a major bottleneck restricting performance improvement. The difficult-to-control diffusion rate of reactants and their rapid polymerization at the immiscible water-organic interface are among the core challenges in enhancing nanofiltration membrane performance.

[0003] The uncontrollability of interfacial polymerization significantly affects the structure of the polyamide separation layer, including its thickness, pore size, and surface morphology. Among these, membrane surface morphology has been shown to significantly influence the separation performance of nanofiltration membranes. Generally, a rougher or more wrinkled membrane surface can provide a larger effective permeation area, thereby improving permeation performance. Previous research has shown that increasing the permeation area of ​​a nanofiltration membrane surface can increase its flux. For example, adding polyvinyl alcohol (PVA) to the aqueous phase can increase the diffusion instability of the reactants during interfacial polymerization, thus preparing a composite nanofiltration membrane with a high-roughness "Turing" structure. Because the polyamide separation layer on its surface exhibits a regular bubble or tubular structure, it optimizes the transport path of water molecules, and the increased surface roughness increases the permeation area, thereby improving the water permeability and water-salt selectivity of the nanofiltration membrane. On the other hand, increasing the hydrophilicity of the membrane surface enhances the affinity of water molecules for the membrane surface, reducing mass transfer resistance and improving membrane permeation performance.

[0004] Metal-organic frameworks (MOFs) are an emerging type of porous crystalline material with high porosity, large surface area, and uniform pore size, making them significant in membrane separation technology. In particular, water-stable MOFs with sub-angstrom-level pore sizes have recently proven promising for water treatment. As a typical MOF material, UiO-66's structural units consist of [Zr6O4(OH)4] metal clusters coordinated to 12 terephthalic acid atoms, possessing the highest coordination number among MOF materials. This high-density structural unit ensures a tight, woven connection within the framework. UiO-66 maintains structural stability in solvents such as water, dimethylformamide, benzene, or acetone, and exhibits strong acid resistance and some alkali resistance. MOF particles with defective properties have proven to be highly efficient molecular and ion adsorbents due to the specific interactions between molecules / ions with specific functional groups and the active sites of the MOF. Therefore, in this invention, UiO-66 nanoparticles with different defects are prepared by in-situ control through the introduction of glacial acetic acid to limit particle size growth, and the addition of trifluoroacetic acid as a capping agent to compete with terephthalic acid for coordination. By dispersing UiO-66 nanoparticles with different defect levels in an aqueous phase and interacting with piperazine monomers, the interfacial polymerization process is influenced, thereby controlling the ridge morphology of the membrane surface and achieving an improvement in membrane permeability. Summary of the Invention

[0005] This invention addresses the high permeability problem of existing nanofiltration membranes by proposing a method for preparing composite nanofiltration membranes based on UiO-66 nanoparticles with varying degrees of defect. In this invention, UiO-66 with different defect degrees is used as a nano-additive, dispersed in an aqueous solution of piperazine, and subjected to interfacial polymerization to prepare composite nanofiltration membranes with different polyamide separation layer structures. A general strategy is proposed to enhance desalination performance by designing nanofiltration membranes with tunable surface nanostructures through MOF particle defect modification. Using UiO-66 with different defect degrees (UiO-66-X) as an aqueous phase additive and dispersing it in the aqueous phase, the surface morphology of the nanofiltration membrane evolves from ridge-like to granular by influencing the diffusion process of the interfacial polymerization reaction. Notably, compared to polyamide separation layers with granular surface morphology, the ridge-like nanostructure of the polyamide separation layer significantly increases the surface permeation area, thus greatly improving the permeability of the nanofiltration membrane.

[0006] This invention is achieved by a method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect, comprising the following steps:

[0007] (1) Using zirconium chloride as the metal source, terephthalic acid as the organic ligand, N,N-dimethylformamide as the solvent, glacial acetic acid as the particle size regulator, and trifluoroacetic acid as the end-capping agent, UiO-66 (UiO-66-X) nanoparticles with different degrees of defect were obtained by mixing and reacting.

[0008] (2) Disperse UiO-66-X nanoparticles in a piperazine / aqueous solution to obtain a UiO-66 / piperazine suspension.

[0009] (3) The suspension from step (2) above is subjected to interfacial polymerization with 1,3,5-benzenetricarboxyl chloride / n-hexane solution on the surface of polysulfone support film.

[0010] (4) The composite membrane prepared in step (3) is rinsed with n-hexane and then placed in an oven at a certain temperature for cross-linking and curing treatment to obtain the composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect.

[0011] In this invention, in order to prepare polyamide separation layer nanostructures with different surface morphologies to improve the permeation performance of nanofiltration membranes, UiO-66 nanoparticles with different defect degrees need to be dispersed in piperazine / aqueous solvent and subjected to interfacial polymerization reaction with 1,3,5-benzenetricarboxyl chloride dissolved in oil solvent to achieve the preparation of composite nanofiltration membranes. The advantages of this invention are: (1) UiO-66 nanoparticles with different defect degrees are used as additives in the preparation of composite nanofiltration membranes, and nanocomposite membranes with different surface morphologies are prepared under the premise of ensuring that their size does not change significantly; (2) When UiO-66-X is used as an aqueous additive, due to the increase in membrane surface roughness and hydrophilicity, the representative nanofiltration membrane with ridged nanostructures has a higher pure water flux and Na2SO4 rejection rate.

[0012] Further, in step (1), the volume ratio of dimethylformamide, glacial acetic acid and trifluoroacetic acid is 40:1:0-1, the concentration of terephthalic acid is 0.048 mol / L, the concentration of zirconium chloride is 0.026 mol / L, and the above raw materials are thoroughly stirred and mixed and placed in a polytetrafluoroethylene reactor for high-temperature synthesis. The preferred reaction temperature is 120-200℃ and the reaction time is 12-24 h.

[0013] Furthermore, the capping agent trifluoroacetic acid can be replaced by one of difluoroacetic acid, formic acid, pyromellitic acid, or benzoic acid.

[0014] Further, in step (2), the UiO-66-X nanoparticles are ultrasonically dispersed in an aqueous solution at a concentration of 0.01–0.3 w / v.%; the aqueous monomer piperazine required for the interfacial polymerization reaction has a concentration of 0.1–3 w / v.% and is in deionized water as the solvent.

[0015] Further, in step (3), the residence time of piperazine / water solution on the polysulfone support layer is 3 to 20 min; the concentration of oil phase monomer 1,3,5-benzenetricarboxyl chloride is 0.05 to 0.5 w / v.%, and the solvent is n-hexane; the interfacial polymerization time is 1 min.

[0016] Furthermore, in step (4), the oven curing crosslinking temperature is 50-100℃ and the curing time is 5-30 min.

[0017] The prepared composite nanofiltration membrane exhibits two different nanostructures on its polyamide layer surface: a "ridge-like" structure and a "granular" structure. Under a pressure of 0.4 MPa, the pure water flux reaches 27.5 L·m³. -2 ·h -1 The retention rate of Na2SO4 remained above 97.8%.

[0018] The advantages and positive effects of this invention are:

[0019] 1. By using UiO-66 nanoparticles with different degrees of defect in the preparation of nanofiltration membranes, nanocomposite membranes with different surface morphologies can be prepared by using UiO-66-X nanoparticles as additives, while ensuring that their crystal size does not change significantly.

[0020] 2. When UiO-66-X is used as an aqueous phase additive, due to the increase in membrane surface roughness and hydrophilicity, the representative nanofiltration membrane with ridged nanostructure has a high pure water flux and Na2SO4 rejection rate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some specific embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a scanning electron microscope image of the nanofiltration membrane prepared according to Comparative Example 5 of the present invention;

[0023] Figure 2 This is a scanning electron microscope image of the nanofiltration membrane prepared according to Example 1 of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This embodiment provides a method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect, characterized by the following steps:

[0026] (1) Using zirconium chloride as the metal source, terephthalic acid as the organic ligand, N,N-dimethylformamide as the solvent, glacial acetic acid as the particle size regulator, and trifluoroacetic acid as the end-capping agent, UiO-66 (UiO-66-X) nanoparticles with different degrees of defect were obtained by mixing and reacting.

[0027] (2) Disperse UiO-66-X nanoparticles in a piperazine / aqueous solution to obtain a UiO-66 / piperazine suspension.

[0028] (3) The suspension from step (2) above is subjected to interfacial polymerization with 1,3,5-benzenetricarboxyl chloride / n-hexane solution on the surface of polysulfone support film.

[0029] (4) The composite membrane prepared in step (3) is rinsed with n-hexane and then placed in an oven at a certain temperature for cross-linking and curing treatment to obtain the composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect.

[0030] In step (1), the capping agent trifluoroacetic acid can be replaced by one of difluoroacetic acid, formic acid, trimesic acid, or benzoic acid, preferably trifluoroacetic acid; the volume ratio of terephthalic acid, zirconium chloride, glacial acetic acid, and trifluoroacetic acid is 40:1:0-1, preferably 40:1:0-0.5; the concentration of terephthalic acid is 0.048 mol / L, and the concentration of zirconium chloride is 0.026 mol / L. After the above raw materials are thoroughly stirred and mixed, they are placed in a polytetrafluoroethylene reactor for high-temperature synthesis. The reaction temperature is 120-200℃, preferably 150℃; the reaction time is 12-24h, preferably 12h.

[0031] In step (2), UiO-66-X nanoparticles are ultrasonically dispersed in an aqueous solution at a concentration of 0.01–0.3 w / v.%, preferably 0.1 w / v.%; the concentration of the aqueous monomer piperazine required for the interfacial polymerization reaction is 0.1–3 w / v.%, preferably 1 w / v.%; and the solvent is deionized water.

[0032] In step (3), the residence time of piperazine / water solution on the polysulfone support layer is 1-20 min, preferably 3 min; the oil phase monomer is 1,3,5-benzenetricarboxyl chloride with a concentration of 0.05-0.5 w / v.%, preferably 0.15 w / v.%; the solvent is n-hexane; the interfacial polymerization time is 10-120 s, preferably 60 s.

[0033] In step (4), the oven curing crosslinking temperature is 50-100℃, preferably 65℃; the curing time is 5-30min, preferably 10min.

[0034] The prepared composite nanofiltration membrane exhibits two different nanostructures on its polyamide layer surface: a "ridge-like" structure and a "granular" structure. Under a pressure of 0.4 MPa, the pure water flux reaches 27.5 L·m³. -2 ·h -1 The retention rate of Na2SO4 remained above 97.8%.

[0035] To better understand the above embodiments of the present invention, further explanation is provided below with reference to specific examples.

[0036] In the following embodiments and comparative examples:

[0037] Terephthalic acid, analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0038] Zirconium chloride, analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] Anhydrous piperazine, analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] 1,3,5-Benzotricarboxylic acid chloride, analytical grade, purchased from Beijing Bailingwei Technology Co., Ltd.;

[0041] n-Hexane, analytical grade, purchased from Tianjin Kemeo Chemical Reagent Co., Ltd.

[0042] Dimethylformamide, analytical grade, purchased from Tianjin Kemeo Chemical Reagent Co., Ltd.

[0043] Glacial acetic acid, analytical grade, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0044] Trifluoroacetic acid, analytical grade, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0045] Example 1

[0046] (1) 0.16 g of zirconium chloride and 0.12 g of terephthalic acid were added to 40 mL of dimethylformamide and stirred with a magnetic stirrer until a clear solution was obtained. Then, a measured amount of 1 mL of glacial acetic acid solution was added and stirred thoroughly. All solutions were transferred to a polytetrafluoroethylene high-pressure reactor and heated at 150 °C for 12 h. After naturally cooling to room temperature, the white precipitate was collected by centrifugation and washed three times with dimethylformamide and glacial acetic acid to remove unreacted terephthalic acid and dimethylformamide molecules trapped in the framework pores. The precipitate was dried at 100 °C for 10 h for later use.

[0047] (2) Piperazine was added to water at a concentration of 1 w / v.% as the aqueous phase, and 1,3,5-benzenetriformyl chloride was added to n-hexane to prepare a solution with a concentration of 0.15 w / v.% as the organic phase. After rinsing the polysulfone support membrane with deionized water, the support membrane was fixed in a custom-made frame with an effective diameter of 7.5 cm. The prepared UiO-66-X nanoparticles were ultrasonically dispersed in the piperazine / aqueous phase solution at a ratio of 0.1 w / v.% for 1 min. The aqueous phase solution (10 mL) was poured into the frame, and the top surface (dense layer) of the base membrane was completely immersed for 3 min. The aqueous phase was then poured out, and excess aqueous phase solution was removed from the membrane surface using a rubber roller. Then, 10 mL of organic phase solution was poured in and left to stand for 1 min, and the excess organic phase was discarded. Subsequently, the membrane was placed in an oven at 65 °C for 10 min to dry and cure, thus preparing the composite nanofiltration membrane.

[0048] Example 2

[0049] (1) 0.16 g of zirconium chloride and 0.12 g of terephthalic acid were added to 40 mL of dimethylformamide and stirred with a magnetic stirrer until a clear solution was obtained. Then, a measured amount of 1 mL of glacial acetic acid solution was added and stirred thoroughly. Finally, 0.25 mL of trifluoroacetic acid was added to the clear solution, and after rapid stirring for 30 min, all solutions were transferred to a polytetrafluoroethylene high-pressure reactor and heated at 150 °C for 12 h. After naturally cooling to room temperature, the white precipitate was collected by centrifugation and washed three times with dimethylformamide and glacial acetic acid to remove unreacted terephthalic acid and dimethylformamide molecules trapped in the framework pores. The precipitate was dried at 100 °C for 10 h for later use.

[0050] (2) Piperazine was added to water at a concentration of 1 w / v.% as the aqueous phase, and 1,3,5-benzenetriformyl chloride was added to n-hexane to prepare a solution with a concentration of 0.15 w / v.% as the organic phase. After rinsing the polysulfone support membrane with deionized water, the support membrane was fixed in a custom-made frame with an effective diameter of 7.5 cm. The prepared UiO-66-X nanoparticles were ultrasonically dispersed in the piperazine / aqueous phase solution at a ratio of 0.1 w / v.% for 1 min. The aqueous phase solution (10 mL) was poured into the frame, and the top surface (dense layer) of the base membrane was completely immersed for 3 min. The aqueous phase was then poured out, and excess aqueous phase solution was removed from the membrane surface using a rubber roller. Then, 10 mL of organic phase solution was poured in and left to stand for 1 min, and the excess organic phase was discarded. Subsequently, the membrane was placed in an oven at 65 °C for 10 min to dry and cure, thus preparing the composite nanofiltration membrane.

[0051] Example 3

[0052] Except that the amount of trifluoroacetic acid added in step (1) of Example 2 was changed to 0.5 mL, the composite nanofiltration membrane was prepared in the same manner as in Example 2.

[0053] Example 4

[0054] Except that the amount of trifluoroacetic acid added in step (1) of Example 2 was changed to 1 mL, the composite nanofiltration membrane was prepared in the same manner as in Example 2.

[0055] Comparative Example 1

[0056] The composite nanofiltration membrane was prepared in the same manner as in Example 1, except that the UiO-66 from step (2) of Example 1 was added to the 1,3,5-benzenetricarboxyl chloride / oil phase solution.

[0057] Comparative Example 2

[0058] The composite nanofiltration membrane was prepared in the same manner as in Example 2, except that the UiO-66 from step (2) of Example 2 was added to the 1,3,5-benzenetricarboxyl chloride / oil phase solution.

[0059] Comparative Example 3

[0060] The composite nanofiltration membrane was prepared in the same manner as in Example 3, except that the UiO-66 from step (2) of Example 3 was added to the 1,3,5-benzenetricarboxyl chloride / oil phase solution.

[0061] Comparative Example 4

[0062] The composite nanofiltration membrane was prepared in the same manner as in Example 4, except that the UiO-66 from step (2) of Example 4 was added to the 1,3,5-benzenetricarboxyl chloride / oil phase solution.

[0063] Comparative Example 5

[0064] Piperazine was added to water at a concentration of 1 w / v.% as the aqueous phase, and 1,3,5-benzenetriformyl chloride was added to n-hexane to prepare a solution at a concentration of 0.15 w / v.% as the organic phase. After rinsing the polysulfone-supported membrane with deionized water, the membrane was fixed in a custom-made frame with an effective diameter of 7.5 cm. 10 mL of the aqueous phase solution was poured into the frame, completely immersing the top surface (dense layer) of the base membrane for 3 min. The aqueous phase was then poured out, and excess aqueous phase solution was removed from the membrane surface using a rubber roller. Then, 10 mL of the organic phase solution was poured in and allowed to stand for 1 min, after which excess organic phase was discarded. Subsequently, the membrane was dried and cured in an oven at 65 °C for 10 min to prepare the composite nanofiltration membrane.

[0065] Performance testing

[0066] In this invention, the membrane flux and salt rejection performance of the composite nanofiltration membranes prepared in Examples 1-4 and Comparative Examples 1-5 were tested using deionized water and Na2SO4 aqueous solution. Specifically, the membrane separation performance was tested using a 1 g / L Na2SO4 solution at 0.4 MPa, and the concentrations of the filtrate and feed solution were measured using a conductivity meter. The results are shown in Table 1 below.

[0067] Table 1. Separation performance and characterization results of the composite nanofiltration membrane

[0068]

[0069] Table 1 shows that the desalination performance of nanofiltration membranes was evaluated by testing the pure water flux and the Na2SO4 rejection rate. A comparison of Examples 1-4 and Comparative Examples 1-4 revealed that, due to the difference in the amount of UiO-66-X nanoparticles added to the aqueous and oil phase solvents, the permeation performance of the membranes prepared with UiO-66-X added to the aqueous phase in Examples 1-4 was significantly greater than that of the membranes in Comparative Examples 1-4 (Example 3: 27.5 L·m⁻¹). -2 ·h -1 Comparative Example 3: 19.7 L·m -2 ·h -1 The permeation performance of the membranes in Comparative Examples 1-4 was only slightly improved compared to the comparative example membranes (17.8–22.3 L·m). -2 ·h -1 The performance improvement of the membranes in Examples 1-4 was more significant (22.2–27.5 L·m⁻¹). -2 ·h -1Furthermore, compared to the membranes of Comparative Examples 1-4, the polyamide layer with a ridged structure in Examples 1-4 has a rougher membrane surface (roughness of Example 3: 86.16 nm), thus possessing a larger effective permeation area. The difference in the surface morphology of the polyamide layer is due to the difference in the influence of UiO-66-X nanoparticles with different defect levels on the interfacial polymerization process. All membranes of the Comparative Examples and Examples exhibit good hydrophilicity. Compared to Comparative Example 5, the addition of UiO-66-X effectively reduced the membrane contact angle. The reduction in the water contact angle of the membranes of Comparative Examples 1-4 is due to the increase in membrane surface roughness. The membranes of Examples 1-4 also have a lower water contact angle because of the ligand defects in UiO-66-X; the exposure of the metal center allows for better affinity between the particles and water. The enhanced membrane surface wettability also contributes to the improvement of membrane permeation performance.

Claims

1. A method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect, characterized in that, Includes the following steps: (1) Using zirconium chloride as the metal source, terephthalic acid as the organic ligand, N,N-dimethylformamide as the solvent, glacial acetic acid as the particle size regulator, and trifluoroacetic acid as the end-capping agent, UiO-66 nanoparticles with different degrees of defect were obtained by mixing and reacting. (2) UiO-66 nanoparticles with different degrees of defect were dispersed in a piperazine / aqueous solution to obtain a suspension; (3) The suspension from step (2) above is subjected to interfacial polymerization with 1,3,5-benzenetricarboxyl chloride / n-hexane solution on the surface of polysulfone supported film; (4) The composite membrane prepared in step (3) is rinsed with n-hexane and then placed in an oven at a certain temperature for cross-linking and curing treatment to obtain the composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect.

2. The method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect according to claim 1, characterized in that, In step (1), the volume ratio of dimethylformamide, glacial acetic acid and trifluoroacetic acid is 40:1:0.25-1, the concentration of terephthalic acid is 0.048 mol / L, and the concentration of zirconium chloride is 0.026 mol / L. The mixture is prepared by hydrothermal reaction.

3. The method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect according to claim 1, characterized in that, In step (2), UiO-66 nanoparticles with different degrees of defect are ultrasonically dispersed in an aqueous solution at a concentration of 0.01–0.3 w / v.%; the concentration of the aqueous monomer piperazine required for the interfacial polymerization reaction is 1 w / v.%, and the solvent is deionized water.

4. The method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect according to claim 1, characterized in that, In step (3), the oil phase monomer is pyromellitic acid chloride with a concentration of 0.15 w / v.% and the solvent is n-hexane; the interfacial polymerization time is 1 min.

5. The method for preparing a composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defect according to claim 1, characterized in that, In step (4), the oven curing crosslinking temperature is 50-100℃ and the curing time is 5-30 min.

6. A composite nanofiltration membrane based on UiO-66 nanoparticles with different degrees of defectification, characterized in that, Composite nanofiltration membranes based on UiO-66 nanoparticles with different degrees of defect were prepared by the preparation method of any one of claims 1-5.

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