High-flux, high-selective screening uiO-66-based composite nanofiltration membrane, and preparation method and application thereof

Abstract

The application discloses a kind of high-flux, high selective screening UiO-66-based composite nanofiltration membrane and preparation method thereof.The UiO-66-based composite nanofiltration membrane includes substrate layer-UiO-66-based MOF transition layer-polyamide skin layer from bottom to top in sequence;The UiO-66-based MOF transition layer is coated on the surface of the substrate layer by in-situ growth, activation;The polyamide skin layer is generated on the surface of UiO-66-based MOF transition layer;Its preparation steps include: S1.washing and drying of substrate layer;S2.preparation of precursor solution;S3.in-situ growth of UiO-66 on substrate layer;S4.activation;S5.forming polyamide skin layer on the surface of UiO-66-based MOF transition layer;The membrane can be used in domestic water purification, industrial wastewater recovery, seawater desalination and the like.Under the synergistic effect of the three-layer structure of the membrane, the nanofiltration performance of flexible polymer porous membrane is significantly improved, with high flux and high selective screening, efficient water purification can be realized, and the preparation method provided by the application is low in cost, simple and easy to popularize.

Description

Technical Field

[0001] This invention belongs to the field of water purification membrane separation, specifically relating to a high-flux, high-selectivity UiO-66-based composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Water treatment membranes offer advantages such as reusability, high separation efficiency, low carbon emissions, and small footprint in wastewater reuse and seawater desalination, and also have the potential for sustainable production of clean drinking water. Various membrane materials are available in the water purification field, including forward osmosis (FO) membranes, nanofiltration (NF) membranes, and reverse osmosis (RO) membranes. Nanofiltration membranes, with their high flux at relatively low operating pressures, are widely used in water purification. However, due to limitations in current technology and processes, commercial NF membranes still face the challenge of balancing water flux and retention rate—a "trade-off" phenomenon where increasing the membrane's water flux generally reduces its solute retention rate. Therefore, researchers have extensively incorporated high specific surface area porous materials into nanofiltration membranes to achieve a balance in membrane permeability selectivity.

[0003] Metal-organic frameworks (MOFs) are porous materials with a fixed framework structure, composed of metals or metal clusters linked by organic ligands. They possess both a fixed framework structure and good compatibility with organic matter. Due to their high porosity and high specific surface area, MOFs can optimize the separation and permeation capabilities of nanofiltration membranes, thereby improving their seawater desalination capacity. UiO-66, as a MOF with excellent water resistance, is widely used in water treatment. However, as a porous powder material, UiO-66 often suffers from problems such as difficulty in self-forming membranes, particle agglomeration and poor dispersion, and poor compatibility with substrates, resulting in numerous defects and reducing the nanofiltration performance of the membrane.

[0004] To improve the nanofiltration performance of membranes, researchers are constantly exploring new methods. A study (Nature Communications, 2019, 10(1): 1-9.) reported a hybrid matrix membrane prepared by blending UiO-66 and ultra-high molecular weight polyethylene, exhibiting a dye rejection rate of 99%. To address the aggregation problem of UiO-66 in the membrane layer, a study (Journal of Membrane Science, 2022, 654.) reported introducing dopamine (DA) into the aqueous phase of interfacial polymerization. The polydopamine (PDA) formed by the self-polymerization of DA acts as a connecting bridge between the PA layer and nanoparticles, enabling cross-linking between the nanoparticles, PA layer, and matrix, thus increasing the compatibility between the PA layer and nanoparticles. However, the modification of the polymer molecules has a certain impact on the pore size of UiO-66 itself. Chinese invention patent CN110075804A discloses a metal-organic framework material UiO-66 coated with γ-Al2O3 particles and its preparation method. The method uses spherical γ-Al2O3 as a matrix to grow the metal-organic framework material UiO-66 on the surface of γ-Al2O3 through in-situ growth. However, this method requires the prior preparation of γ-Al2O3 particles, and the preparation process is relatively complicated.

[0005] Clearly, these existing technologies are limited by the special properties of the materials, the complexity of the preparation methods, and the special requirements of the equipment. There are still many technical and operational difficulties in promoting their use, resulting in high costs, low efficiency, and difficulty in achieving industrialization and large-scale promotion. Summary of the Invention

[0006] To address the problems in related technologies, such as the difficulty in dispersing UiO-66 particles during nanofiltration membrane preparation, poor compatibility with the substrate, resulting in low nanofiltration membrane performance, high cost of high-performance nanofiltration membrane preparation, and difficulty in large-scale promotion, this invention provides the following technical solution:

[0007] This invention provides a high-throughput, high-selectivity UiO-66-based composite nanofiltration membrane, which comprises, from bottom to top, a substrate layer, a UiO-66-based MOF transition layer, and a polyamide skin layer; the UiO-66-based MOF transition layer is coated on the surface of the substrate layer after in-situ growth and activation; the polyamide skin layer is formed on the surface of the UiO-66-based MOF transition layer.

[0008] Furthermore, the UiO-66-based MOF transition layer is uniformly loaded on the surface of the substrate layer, providing active sites for the bonding of the polyamide skin layer to the substrate.

[0009] Furthermore, chemical bonds are formed between the base layer and the polyamide skin layer through the active sites.

[0010] Furthermore, the substrate is a flexible polymer porous membrane, including any one of nylon membrane, polyethersulfone (PES) membrane, polysulfone (PSF) membrane, polyacrylonitrile (PAN) membrane, and fabric membrane.

[0011] This invention also provides a method for preparing the above-mentioned high-flux, high-selectivity UiO-66-based composite nanofiltration membrane, comprising the following steps:

[0012] S1. Cleaning and drying of the base layer;

[0013] S2. Preparation of precursor solution: UiO-66 precursor solution was prepared using zirconium chloride, terephthalic acid-based organic ligand, and a first polar solvent;

[0014] S3. In-situ growth of UiO-66 on the substrate layer: The substrate layer described in S1 is immersed in the precursor solution described in S2 and then subjected to a hydrothermal reaction to obtain a membrane in-situ grown with UiO-66.

[0015] S4. Activation to obtain UiO-66-based MOF transition layer: The UiO-66 film grown in situ as described in S3 is washed in a second polar solvent, activated, and vacuum dried to obtain the UiO-66-based MOF transition layer.

[0016] S5. Forming a polyamide skin on the surface of the UiO-66-based MOF transition layer: The same surface of the UiO-66-based MOF transition layer described in S4 is successively contacted with the aqueous phase of piperazine and the oil phase of trimesoyl chloride. Through interfacial polymerization, a dense polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0017] Further, the zirconium chloride, terephthalic acid-based organic ligand, and polar solvent 1 are prepared into the UiO-66 precursor solution in a molar ratio of 1 to 5: 1 to 5: 500.

[0018] Furthermore, the terephthalic acid-based organic ligand is one of terephthalic acid, 2-aminoterephthalic acid, 1,2,4-benzenetricarboxylic acid, or pyromellitic acid.

[0019] Furthermore, the first polar solvent is either N,N-dimethylformamide or water.

[0020] Furthermore, the substrate layer is immersed in the precursor solution for 0.5 to 1 hour, and the hydrothermal reaction time is 6 to 48 hours.

[0021] Furthermore, the second polar solvent is any one of methanol, ethanol, acetone, chloroform, or water, and the vacuum drying temperature is 60°C to 80°C, and the time is 12 to 48 hours.

[0022] Furthermore, the piperazine aqueous phase is an aqueous solution with a piperazine content of 1-4% and a triethylamine content of 2-6%, and the contact time between the surface of the UiO-66-based MOF transition layer and the piperazine aqueous phase is 3-10 minutes.

[0023] Furthermore, the trimesoyl chloride oil phase is a hexane solution with a trimesoyl chloride content of 0.1-3%; the interfacial polymerization reaction time is 0.2-1 minute.

[0024] The high-flux, high-selectivity UiO-66-based composite nanofiltration membrane provided by this invention, or the UiO-66-based composite nanofiltration membrane prepared by the method of this invention, is used in domestic water purification, industrial wastewater recycling, and seawater desalination.

[0025] In this invention, the substrate layer is a flexible polymer porous membrane. Flexible polymer porous membranes have high porosity, large pore size, and excellent hydrophilicity, resulting in a fast water molecule permeation rate. They also possess excellent mechanical stability, ensuring the support performance of the substrate material under certain pressure. The in-situ grown UiO-66-based MOF nanolayer exhibits uniform loading, is defect-free, and free from aggregation, increasing the specific surface area of ​​the membrane material and providing numerous active sites for the bonding between the skin layer and the substrate layer. The dense polyamide skin layer can intercept ions under certain external pressure, extending the membrane's lifespan. The synergistic effect of this three-layer membrane structure significantly enhances the nanofiltration performance of the UiO-66-based composite nanofiltration membrane, achieving high flux and high selectivity for water purification. Furthermore, the preparation method of this invention is low-cost, simple to operate, and easy to promote. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a SEM image of the UiO-66-based composite nanofiltration membrane prepared in Example 1 of this invention, showing the loading of UiO-66 on the surface of a nylon membrane.

[0028] Figure 2 a is a bar chart of the pure water flux of the composite nanofiltration membranes in Examples 1-6 of this invention.

[0029] Figure 2 b is a bar chart of the pure water flux of the composite nanofiltration membranes of Embodiment 2 and Comparative Examples 1-3 of the present invention.

[0030] Figure 3a is a comparison chart of the ion rejection rates of the composite nanofiltration membranes in Examples 1-6 of this invention.

[0031] Figure 3 b is a comparison chart of the ion rejection rates of the composite nanofiltration membranes of Example 2 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0032] The invention will be more fully understood through the following detailed description, which should be read in conjunction with the accompanying drawings. Detailed embodiments of the invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0033] Example 1

[0034] This embodiment provides a method for preparing a NU@PA composite nanofiltration membrane, the specific steps of which include:

[0035] (1) Base layer is ready

[0036] In this embodiment, the flexible polymer porous membrane substrate is made of nylon. The nylon membrane is cleaned with ethanol and water, and then dried for later use.

[0037] (2) Preparation of precursor solution

[0038] Dissolve 0.7g zirconium chloride and 0.8g terephthalic acid in 150mL of N,N-dimethylformamide, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66 precursor solution.

[0039] (3) In-situ growth of UiO-66 on the basal layer

[0040] After soaking the nylon membrane from step (1) in the UiO-66 precursor solution prepared in step (2) for 1 hour, the UiO-66 precursor solution soaked with the nylon membrane was transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. The reactor was then placed in an oven and heated to 120°C for 48 hours for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature to obtain Nylon-UiO-66-NH2 with in-situ grown UiO-66.

[0041] (4) Activation to obtain UiO-66-based MOF transition layer

[0042] Nylon-UiO-66-NH2 was washed three times with N,N-dimethylformamide and then three times with methanol to remove unreacted reagents and macromolecular organic solvents from the micropores of UiO-66.

[0043] To further obtain the microporous structure of UiO-66, Nylon-UiO-66-NH2 was dried in a vacuum drying oven at 60°C for 12 hours to obtain a UiO-66-based MOF transition layer, Nylon-UiO-66 film.

[0044] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0045] Piperazine (PIP, 3 w / v%) and triethylamine (TEA, 3 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and pyromellitic trimethylol chloride (TMC, 0.1 w / v%) was dissolved in n-hexane to prepare the TMC oil phase.

[0046] One side of the UiO-66-based MOF transition layer Nylon-UiO-66 membrane was exposed in the PIP aqueous phase for 5 minutes, and then the same side was exposed in the TMC oil phase to carry out interfacial polymerization. After 30 seconds, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer Nylon-UiO-66 membrane, thus obtaining the NU@PA composite nanofiltration membrane.

[0047] Performance Characterization

[0048] The NU@PA composite nanofiltration membrane obtained in step (5) was observed under a scanning electron microscope, as follows: Figure 1 As shown, the UiO-66 in the UiO-66-based composite nanofiltration membrane exhibits uniform, defect-free, and agglomerated loading on the surface of the nylon membrane, increasing the specific surface area of ​​the membrane material. Simultaneously, it provides numerous active sites for the bonding between the polyamide skin and the nylon membrane. These active sites are lattice defects formed during the synthesis of the UiO-66-based MOF transition layer, the Nylon-UiO-66 membrane. Chemical bonds are formed between the polyamide skin and the nylon membrane through these active sites.

[0049] The pure water flux of the NU@PA composite nanofiltration membrane obtained in step (5) was tested at a pressure of 5 bar, and the pure water flux was 65 L / m³. -2 h -1 .like Figure 2 As shown in a.

[0050] Figure 3a represents the rejection rate of the NU@PA composite nanofiltration membrane, measured with 1000 ppm Na₂SO₄ and NaCl as feed solutions, respectively. The membrane has a rejection rate of 98.2% for Na₂SO₄ and 7.1% for NaCl. - and SO4 2- The ion selectivity is 51.6, enabling efficient separation of monovalent and divalent anions.

[0051] Example 2

[0052] This embodiment provides a method for preparing an N-UN@PA composite nanofiltration membrane, the specific steps of which include:

[0053] (1) Base layer is ready

[0054] In this embodiment, the flexible polymer porous membrane substrate is made of nylon. The nylon membrane is cleaned with ethanol and water, and then dried for later use.

[0055] (2) Preparation of precursor solution

[0056] Dissolve 0.6g of zirconium chloride and 0.75g of 2-aminoterephthalic acid in 200mL of N,N-dimethylformamide, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66 precursor solution.

[0057] (3) In-situ growth of UiO-66 on the basal layer

[0058] After soaking the nylon membrane prepared in step (1) in the UiO-66 precursor solution prepared in step (2) for 1 hour, the UiO-66 precursor solution soaked with the nylon membrane was transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. The reactor was then placed in an oven and heated to 150°C for 24 hours for hydrothermal reaction. After the reaction was completed, the reactor was cooled to room temperature to obtain the in-situ grown UiO-66 Nylon-UiO-66-NH2 membrane.

[0059] (4) Activation to obtain UiO-66-based MOF transition layer

[0060] The Nylon-UiO-66-NH2 membrane was washed three times with N,N-dimethylformamide and then activated three times with methanol to remove unreacted reagents and macromolecular organic solvents from the micropores of the Nylon-UiO-66-NH2 membrane.

[0061] To further activate UiO-66, the Nylon-UiO-66-NH2 membrane was dried in a vacuum drying oven at 60°C for 12 hours to obtain the UiO-66-based MOF transition layer Nylon-UiO-66-NH2 membrane.

[0062] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0063] Piperazine (PIP, 2 w / v%) and triethylamine (TEA, 3 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and trimesoyl chloride (TMC, 0.12 w / v%) was dissolved in n-hexane to prepare the TMC oil phase. One side of the Nylon-UiO-66-NH2 membrane was exposed to the PIP aqueous phase for 5 minutes, and then the same side was exposed to the TMC oil phase. After interfacial polymerization for 45 seconds, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer Nylon-UiO-66-NH2 membrane, resulting in the N-UN@PA composite nanofiltration membrane.

[0064] Performance Characterization

[0065] The nanofiltration performance of the N-UN@PA composite nanofiltration membrane obtained in step (5) was tested at a pressure of 4 bar. The pure water flux of the N-UN@PA composite nanofiltration membrane in this embodiment was 56 L / m³. -2 h -1 ,like Figure 2 As shown in a.

[0066] Figure 3 a represents the rejection rate of the N-UN@PA composite nanofiltration membrane, measured with 1000 ppm Na₂SO₄ and NaCl as feed solutions, respectively. The membrane has a rejection rate of 98.7% for Na₂SO₄ and 9.5% for NaCl. - and SO4 2- The ion selectivity was 69.62, achieving efficient separation of monovalent and divalent anions.

[0067] Example 3

[0068] This embodiment provides a method for preparing a PES-UC1@PA composite nanofiltration membrane, the specific steps of which include:

[0069] (1) Base layer is ready

[0070] In this embodiment, the flexible polymer porous membrane substrate is a polyethersulfone (PES) membrane. The PES membrane is cleaned with ethanol and water, and then dried for later use.

[0071] (2) Preparation of UiO-66 precursor solution

[0072] Dissolve 0.9 g of zirconium chloride and 0.85 g of 1,2,4-benzenetricarboxylic acid in 180 mL of water, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66 precursor solution.

[0073] (3) In-situ growth of UiO-66 on the basal layer

[0074] After soaking the polyethersulfone (PES) membrane prepared in step (1) in the UiO-66 precursor solution prepared in step (2) for 1 hour, the UiO-66 precursor solution soaked with the polyethersulfone (PES) membrane was transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. The reactor was then placed in an oven and heated to 100°C for hydrothermal reaction for 36 hours. After the reaction was completed, the reactor was cooled to room temperature to obtain the in-situ grown UiO-66 PES-UiO-66-COOH membrane.

[0075] (4) Activation to obtain UiO-66-based MOF transition layer

[0076] The PES-UiO-66-COOH membrane was washed three times with water and then activated three times with ethanol to remove unreacted reagents and macromolecular organic solvents from the micropores of the PES-UiO-66-COOH membrane. To further activate UiO-66, the PES-UiO-66-COOH membrane was dried in a vacuum drying oven at 60℃ for 48 h to obtain the UiO-66-based MOF transition layer PES-UiO-66-COOH membrane.

[0077] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0078] Piperazine (PIP, 4 w / v%) and triethylamine (TEA, 4 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and trimesoyl chloride (TMC, 0.15 w / v%) was dissolved in n-hexane to prepare the TMC oil phase. One side of the UiO-66-based MOF transition layer PES-UiO-66-COOH membrane was exposed to the PIP aqueous phase for 5 minutes, and then the same side was exposed to the TMC oil phase. After interfacial polymerization for 0.5 minutes, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer PES-UiO-66-COOH membrane, resulting in the PES-UC1@PA composite nanofiltration membrane.

[0079] Performance Characterization

[0080] The nanofiltration performance of the PES-UC1@PA composite nanofiltration membrane obtained in step (5) was tested at a pressure of 6 bar. The pure water flux of the PES-UC1@PA composite nanofiltration membrane was 65 L / m³. -2 h -1 ,like Figure 2 As shown in a.

[0081] Figure 3a represents the rejection rate of the PES-UC1@PA composite nanofiltration membrane, measured with 1000 ppm Na2SO4 and NaCl as feed solutions, respectively. The membrane's rejection rate for Na2SO4 was 97.7%, and for NaCl it was 17.3%. - and SO4 2- The ion selectivity is 36.00, achieving efficient separation of monovalent and divalent anions, such as... Figure 3 As shown in b.

[0082] Example 4

[0083] This embodiment provides a method for preparing a PSF-UC2@PA composite nanofiltration membrane, the specific steps of which include:

[0084] (1) Base layer is ready

[0085] In this embodiment, the flexible polymer porous membrane substrate is a polysulfone (PSF) membrane. The polysulfone (PSF) membrane is cleaned with ethanol and water, and then dried for later use.

[0086] (2) Preparation of precursor solution

[0087] Dissolve 1.5g zirconium chloride and 1.25g pyromellitic acid in 150mL of water, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66 precursor solution.

[0088] (3) In-situ growth of UiO-66 on the basal layer

[0089] After soaking the polysulfone (PSF) membrane prepared in step (1) in the UiO-66 precursor solution prepared in step (2) for 1 hour, the UiO-66 precursor solution soaked with the polysulfone (PSF) membrane was transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. The reactor was then placed in an oven and heated to 120°C for 24 hours for hydrothermal reaction. After the reaction was completed, the mixture was cooled to room temperature to obtain the in-situ grown UiO-66 PSF-UiO-66-(COOH)2 membrane.

[0090] (4) Activation to obtain UiO-66-based MOF transition layer

[0091] The PSF-UiO-66-(COOH)2 membrane was washed three times with water and then activated three times with ethanol to remove unreacted reagents and macromolecular organic solvents from the micropores of the PSF-UiO-66-(COOH)2 membrane. To further activate UiO-66, the membrane was dried in a vacuum drying oven at 60°C for 24 hours to obtain the UiO-66-based MOF transition layer PSF-UiO-66-(COOH)2 membrane.

[0092] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0093] Piperazine (PIP, 4 w / v%) and triethylamine (TEA, 3 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and trimesoyl chloride (TMC, 0.2 w / v%) was dissolved in n-hexane to prepare the TMC oil phase. One side of the UiO-66-based MOF transition layer PSF-UiO-66-(COOH)2 membrane was exposed to the PIP aqueous phase for 5 minutes, and then the same side was exposed to the TMC oil phase. After interfacial polymerization for 1 minute, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer PSF-UiO-66-(COOH)2 membrane, resulting in the PSF-UC2@PA composite nanofiltration membrane.

[0094] Performance Characterization

[0095] The nanofiltration performance of the PSF-UC2@PA composite nanofiltration membrane was tested at a pressure of 5 bar. The pure water flux of the PSF-UC2@PA composite nanofiltration membrane was 57 L / m³. -2 h -1 ,like Figure 2 As shown in a.

[0096] The rejection rates of the PSF-UC2@PA composite nanofiltration membrane were measured using 1000 ppm Na2SO4 and NaCl as feed solutions, respectively. The membrane had a rejection rate of 98.1% for Na2SO4 and 13.5% for NaCl. - and SO4 2- The ion selectivity is 45.53, achieving efficient separation of monovalent and divalent anions, such as... Figure 3 As shown in a.

[0097] Example 5

[0098] This embodiment provides a method for preparing a PAN-UN6@PA composite nanofiltration membrane, the specific steps of which include:

[0099] (1) Base layer is ready

[0100] In this embodiment, the flexible polymer porous membrane substrate is a polyacrylonitrile (PAN) membrane. The PAN membrane is cleaned with ethanol and water, and then dried for later use.

[0101] (2) Preparation of precursor solution

[0102] Dissolve 1.2g of zirconium chloride and 1.35g of 2-aminoterephthalic acid in 150mL of N,N-dimethylformamide, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66-NH2 precursor solution.

[0103] (3) In-situ growth of UiO-66-NH2 on the basal layer

[0104] After soaking the PAN membrane prepared in step (1) in the UiO-66-NH2 precursor solution prepared in step (2) for 0.5 hours, the precursor solution soaked with the PAN membrane is transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. After sealing the reactor, it is placed in an oven, heated to 120°C, and kept at that temperature for 6 hours. After the reaction is completed, it is cooled to room temperature to obtain the PAN-UiO-66-NH2 membrane with in-situ grown UiO-66-NH2.

[0105] (4) Activation to obtain UiO-66-based MOF transition layer

[0106] The PAN-UiO-66-NH2 membrane was washed three times with water and then three times with acetone to remove unreacted reagents and macromolecular organic solvents from the micropores of the PAN-UiO-66-NH2 membrane. To further activate UiO-66, the membrane was dried in a vacuum drying oven at 80°C for 24 hours to obtain the UiO-66-based MOF transition layer PAN-UiO-66-NH2 membrane.

[0107] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0108] Piperazine (PIP, 1 w / v%) and triethylamine (TEA, 6 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and trimesoyl chloride (TMC, 3 w / v%) was dissolved in n-hexane to prepare the TMC oil phase. One side of the UiO-66-based MOF transition layer PAN-UiO-66-NH2 membrane was exposed to the PIP aqueous phase for 3 minutes, and then the same side was exposed to the TMC oil phase. After interfacial polymerization for 0.2 minutes, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer PAN-UiO-66-NH2 membrane, resulting in the PAN-UN6@PA composite nanofiltration membrane.

[0109] Performance Characterization

[0110] The nanofiltration performance of the PAN-UN6@PA composite nanofiltration membrane was tested at a pressure of 6 bar. The pure water flux of the PAN-UN6@PA composite nanofiltration membrane was 67 L / m³. -2 h -1 ,like Figure 2 As shown in a.

[0111] The rejection rates of the PAN-UN6@PA composite nanofiltration membrane were measured using 1000 ppm Na₂SO₄ and NaCl as feed solutions, respectively. The membrane had a rejection rate of 98.5% for Na₂SO₄ and 5.7% for NaCl. - and SO4 2-The ion selectivity is 62.87, achieving highly efficient separation of monovalent and divalent anions, such as... Figure 3 As shown in a.

[0112] Example 6

[0113] This embodiment provides a method for preparing a PET-U@PA composite nanofiltration membrane, the specific steps of which include:

[0114] (1) Base layer is ready

[0115] In this embodiment, the flexible polymer porous membrane substrate is made of polyester fiber (PET) fabric. The PET is cleaned with ethanol and water, and then dried for later use.

[0116] (2) Preparation of precursor solution

[0117] Dissolve 2.3g of zirconium chloride and 2.5g of terephthalic acid in 100mL of N,N-dimethylformamide, and sonicate the solution until the solutes are completely dissolved to prepare a UiO-66 precursor solution.

[0118] (3) In-situ growth of UiO-66 on the basal layer

[0119] After soaking the PAN film prepared in step (1) in the UiO-66 precursor solution prepared in step (2) for 1 hour, the PET-lined precursor solution was transferred to a polytetrafluoroethylene-lined container and sealed in a stainless steel reactor. The reactor was then placed in an oven, heated to 130°C, and kept at that temperature for 24 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain the PET-UiO-66 film with in-situ grown UiO-66.

[0120] (4) Activation to obtain UiO-66-based MOF transition layer

[0121] The PET-UiO-66 membrane was washed three times with water and then three times with chloroform to remove unreacted reagents and macromolecular organic solvents from the micropores of the PET-UiO-66 membrane. To further activate UiO-66, the membrane was dried in a vacuum drying oven at 80°C for 48 hours to obtain the UiO-66-based MOF transition layer PET-UiO-66 membrane.

[0122] (5) A polyamide skin is formed on the surface of the UiO-66-based MOF transition layer.

[0123] Piperazine (PIP, 4 w / v%) and triethylamine (TEA, 2 w / v%) were dissolved in deionized water to prepare the PIP aqueous phase, and trimesoyl chloride (TMC, 2 w / v%) was dissolved in n-hexane to prepare the TMC oil phase. One side of the UiO-66-based MOF transition layer PET-UiO-66 membrane was exposed to the PIP aqueous phase for 10 minutes, and then the same side was exposed to the TMC oil phase. After interfacial polymerization for 0.2 minutes, a dense polyamide skin was formed on the surface of the UiO-66-based MOF transition layer PET-UiO-66 membrane, resulting in a PET-U@PA composite nanofiltration membrane.

[0124] Performance Characterization

[0125] The nanofiltration performance of the PET-U@PA composite nanofiltration membrane was tested at a pressure of 5 bar. The pure water flux of the PET-U@PA composite nanofiltration membrane was 56 L / m³. -2 h -1 ,like Figure 2 As shown in a.

[0126] The rejection rates of the PET-U@PA composite nanofiltration membrane were measured using 1000 ppm Na₂SO₄ and NaCl as feed solutions, respectively. The membrane had a rejection rate of 97.9% for Na₂SO₄ and 4.5% for NaCl. - and SO4 2- The ion selectivity is 45.48, achieving highly efficient separation of monovalent and divalent anions, such as... Figure 3 As shown in a.

[0127] Compare with Example 1

[0128] This embodiment is basically the same as Embodiment 2, except that UiO-66-NH2 is not grown in situ on the surface of the nylon membrane. Instead, a dense polyamide skin is formed by direct polymerization at the surface interface of the nylon membrane to synthesize the Nylon@PA membrane. The specific steps are as follows:

[0129] (1) Base layer is ready

[0130] Clean the nylon membrane with ethanol and water, then dry it for later use.

[0131] (2) A dense polyamide layer is formed on the surface of the nylon film.

[0132] Aqueous phase was prepared by dissolving piperazine (PIP, 2 w / v%) and triethylamine (TEA, 3 w / v%) in deionized water, and oil phase was prepared by dissolving trimesoyl chloride (TMC, 0.12 w / v%) in n-hexane.

[0133] One side of a nylon membrane was exposed to the PIP aqueous phase for 5 minutes, and then the same side was exposed to the TMC oil phase. After the interfacial polymerization reaction lasted for 45 seconds, a dense polyamide skin was formed on the surface of the nylon membrane, resulting in a Nylon@PA membrane.

[0134] The nanofiltration performance of the Nylon@PA membrane was tested at a pressure of 5 bar. The pure water flux of the Nylon@PA nanofiltration membrane was 37 L / m³. - 2 h -1 ,like Figure 2 As shown in b.

[0135] The rejection rates of the Nylon@PA membrane were measured using 1000 ppm Na₂SO₄ and NaCl as feed solutions. The membrane had a rejection rate of 75.6% for Na₂SO₄ and 11.5% for NaCl. - and SO4 2- The ion selectivity is 3.63, such as Figure 3 As shown in b.

[0136] Compare with Example 2

[0137] This comparative example is basically the same as Example 2, except that: UiO-66-NH2 is not grown in situ on the surface of the nylon membrane, but the particles of UiO-66-NH2 are directly mixed in the aqueous monomer of the interfacial polymerization and then formed into N@UN-PA-W composite nanofiltration membrane through interfacial polymerization.

[0138] The nanofiltration performance of the composite membrane was tested at a pressure of 5 bar. The pure water flux of the N@UN-PA-W composite nanofiltration membrane was 45 Lm. -2 h -1 .like Figure 2 As shown in b.

[0139] The rejection rates of the N@UN-PA-W composite nanofiltration membrane were measured using 1000 ppm Na₂SO₄ and NaCl as feed solutions. The rejection rate for Na₂SO₄ was 85.2%, the rejection rate for NaCl was 12.9%, and the rejection rate for Cl₂SO₄ was [not specified]. - and SO4 2- The ion selectivity is 5.89. For example... Figure 3 As shown in b.

[0140] Compare with Example 3

[0141] This comparative example is basically the same as Example 2, except that: UiO-66-NH2 is not grown in situ on the surface of the nylon membrane, but the particles of UiO-66-NH2 are directly mixed in the oil phase monomer of the interfacial polymerization and then formed into N@UN-PA-O composite nanofiltration membrane through interfacial polymerization.

[0142] The nanofiltration performance of the composite membrane was tested at a pressure of 5 bar. The pure water flux of the N@UN-PA-W composite nanofiltration membrane was 47 Lm. -2 h -1 .like Figure 2 As shown in b.

[0143] The rejection rates of the N@UN-PA-O composite nanofiltration membrane were measured using 1000 ppm Na₂SO₄ and NaCl as feed solutions. The rejection rate for Na₂SO₄ was 87.3%, the rejection rate for NaCl was 8.9%, and the rejection rate for Cl₂SO₄ was [not specified]. - and SO4 2- The ion selectivity is 7.17. For example... Figure 3 As shown in b.

[0144] Examples 1-6 all used the method of the present invention to prepare UiO-66-based composite nanofiltration membranes, see reference. Figure 1 The UiO-66-based composite nanofiltration membrane prepared by the method of the present invention has a uniform load, no defects, and no agglomeration on the surface of the transition layer, which increases the specific surface area of ​​the membrane material and provides a large number of active sites for the bonding between the skin layer and the substrate layer.

[0145] Comparing the pure water flux of the composite nanofiltration membranes prepared in Examples 1-6 and Comparative Examples 1-3, the pure water flux of the UiO-66-based composite nanofiltration membranes prepared in Examples 1-6 is significantly higher than that of the composite nanofiltration membranes prepared in Comparative Examples 1-3 without in-situ growth of UiO-66-NH2 on the substrate surface. (See reference...) Figure 2 The bar charts show the pure water flux of the composite nanofiltration membranes in Examples 1-6 and Comparative Examples 1-3 of this invention. Among them, the N-UN@PA composite nanofiltration membrane in Example 2 has the highest pure water flux, which is 56 L / m³ at a pressure of 4 bar. -2 h -1Examples 1-6 describe the UiO-66-based composite nanofiltration membranes prepared in which the substrate layer is a flexible polymer porous membrane. This flexible polymer porous membrane exhibits high porosity, large pore size, and excellent hydrophilicity, resulting in a fast water molecule permeation rate. It also possesses excellent mechanical stability, ensuring the support performance of the substrate material under certain pressure. The in-situ grown UiO-66-based MOF transition layer is uniformly loaded on the substrate surface, free from defects and agglomeration, increasing the specific surface area of ​​the membrane material and providing numerous active sites for the bonding between the polyamide skin and the substrate layer. The polyamide skin layer is formed through interfacial polymerization on the surface of the UiO-66-based MOF transition layer. This dense polyamide skin layer can intercept ions under certain external pressure, extending the membrane's lifespan. The synergistic effect of this three-layer membrane structure significantly enhances the nanofiltration performance of the UiO-66-based composite nanofiltration membrane, resulting in high flux and high selectivity, achieving highly efficient water purification.

[0146] Figure 3 This is a comparison chart of the ion rejection rates of the composite nanofiltration membranes of Examples 1-6 and Comparative Examples 1-3 of the present invention (using 1000 ppm Na2SO4 and NaCl as feed solutions, respectively). The composite nanofiltration membranes prepared in Examples 1-6 show the ion rejection rates of the membranes for Cl... - and SO4 2- The ion selectivity was significantly higher than that of the Nylon@PA membranes prepared in Control Examples 1-3 for Cl. - and SO4 2- The selectivity for ions was highest for the N-UN@PA composite nanofiltration membrane prepared in Example 2, particularly for Cl. - and SO4 2- The ion selectivity reached 69.62%.

[0147] In summary, the present invention provides a UiO-66-based composite nanofiltration membrane, which comprises, from bottom to top, a substrate layer, a UiO-66-based MOF transition layer, and a polyamide skin layer. The UiO-66-based MOF transition layer is grown and activated in situ and then coated on the surface of the substrate layer. The UiO-66-based MOF transition layer is uniformly loaded on the surface of the substrate layer without agglomeration, providing active sites for the bonding between the polyamide skin layer and the substrate layer. The polyamide skin layer is formed on the surface of the UiO-66-based MOF transition layer, forming a UiO-66-based composite nanofiltration membrane comprising the substrate layer, the UiO-66-based MOF transition layer, and the polyamide skin layer. The UiO-66-based composite nanofiltration membrane can be used in domestic water purification, industrial wastewater recycling, and seawater desalination. The synergistic effect of the three-layer structure of the UiO-66-based composite nanofiltration membrane significantly improves the nanofiltration performance of the composite nanofiltration membrane, resulting in high flux and high selectivity, thus achieving efficient water purification. The method provided by this invention for preparing the UiO-66-based composite nanofiltration membrane is low-cost, simple, and easy to promote.

Claims

1. A high-flux, high-selectivity UiO-66-based composite nanofiltration membrane, characterized in that: The UiO-66-based composite The nanofiltration membrane consists of, from bottom to top, a base layer, a UiO-66-based MOF transition layer, and a polyamide skin layer; The UiO-66-based MOF transition layer is uniformly coated on the surface of the substrate layer after in-situ growth and activation via hydrothermal reaction, providing active sites for the bonding of the polyamide skin layer and the substrate layer; The polyamide skin is formed on the surface of the UiO-66-based MOF transition layer, and chemical bonds are formed between the base layer and the polyamide skin through the active sites.

2. The high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 1, characterized in that: The base layer is a flexible polymer porous membrane, including any one of nylon membrane, polyethersulfone membrane, polysulfone membrane, polyacrylonitrile membrane, and fabric membrane.

3. A method for preparing a high-flux, high-selectivity UiO-66-based composite nanofiltration membrane as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Cleaning and drying of the base layer; S2. Preparation of precursor solution: UiO-66 precursor solution was prepared using zirconium chloride, terephthalic acid-based organic ligand, and a first polar solvent; S3. In-situ growth of UiO-66 on the substrate: The substrate described in S1 is immersed in the UiO-66 precursor solution described in S2 and then subjected to a hydrothermal reaction to obtain a membrane in-situ grown with UiO-66. S4. Activation to obtain UiO-66-based MOF transition layer: The UiO-66 film grown in situ as described in S3 is washed and activated in a second polar solvent, and then vacuum dried to obtain the UiO-66-based MOF transition layer; S5. Formation of a polyamide skin on the surface of the UiO-66-based MOF transition layer: The same surface of the UiO-66-based MOF transition layer described in S4 is successively contacted with the aqueous phase of piperazine and the oil phase of trimesoyl chloride, and a polyamide skin is formed on the surface of the UiO-66-based MOF transition layer through interfacial polymerization reaction.

4. The method for preparing the high-throughput, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The zirconium chloride, terephthalic acid-based organic ligand, and a first polar solvent were prepared into the UiO-66 precursor solution in a molar ratio of 1–5:1–5:

500.

5. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The terephthalic acid-based organic ligand is any one of terephthalic acid, 2-aminoterephthalic acid, 1,2,4-benzenetricarboxylic acid, or pyromellitic acid.

6. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The first polar solvent is either N,N-dimethylformamide or water.

7. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The substrate layer is immersed in the UiO-66 precursor solution for 0.5 to 1 hour.

8. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The hydrothermal reaction time is 6 to 48 hours.

9. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The second polar solvent is any one of N,N-dimethylformamide, methanol, ethanol, acetone, chloroform, or water.

10. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The vacuum drying temperature described in S4 is 60℃~80℃, and the time is 12~48 hours.

11. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: In S5, the piperazine aqueous phase is an aqueous solution with a piperazine content of 1-4% and a triethylamine content of 2-6%, and the contact time between the surface of the UiO-66-based MOF transition layer and the piperazine aqueous phase is 3-10 minutes.

12. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The organic phase of the pyromellitic chloride is a hexane solution with a pyromellitic chloride content of 0.1-3%.

13. The method for preparing the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane according to claim 3, characterized in that: The interfacial polymerization reaction time is 0.2 to 1 minute.

14. The application of the high-flux, high-selectivity UiO-66-based composite nanofiltration membrane as described in any one of claims 1-2, or the UiO-66-based composite nanofiltration membrane prepared by the preparation method as described in any one of claims 3-13, in domestic water purification, industrial wastewater recovery, or seawater desalination.

Images