An ultrathin composite membrane with an interpenetrating network skeleton structure and a preparation method and application thereof

Abstract

This invention belongs to the field of membrane separation technology and discloses an ultrathin composite membrane with an interpenetrating network framework structure, its preparation method, and its application. The preparation method includes: pouring a zirconium metal solution onto the surface of a PSf base membrane, allowing metal ions to adsorb onto the PSf membrane surface; then immersing the other side of the PSf membrane in a ligand solution of 2-aminoterephthalic acid and triethylamine for a coordination reaction; after the reaction is complete, removing the membrane and placing it under suitable temperature and humidity conditions; as the organic solvent and triethylamine molecules on the membrane surface volatilize, the metal ions and organic ligands on the membrane surface complete heterogeneous nucleation and growth, forming a pure MOF membrane; finally, based on the amino group carried by the selected UiO-66-NH2, immersing an organic monomer solution onto the surface of the prepared MOF membrane, allowing interfacial polymerization reactions to occur on the MOF membrane surface and within the crystallites, thereby obtaining an ultrathin composite membrane with an interpenetrating network framework structure, which can be applied in the fields of CH4 / N2 separation and dye / salt separation.

Description

Technical Field

[0001] This application belongs to the field of membrane separation technology, and relates to an ultrathin composite membrane with an interpenetrating network skeleton structure, its preparation method and application. Background Technology

[0002] Membrane separation technology, as a highly efficient, energy-saving, and environmentally friendly physical separation method, has shown great application potential in gas separation (such as CO2 capture and natural gas purification) and water treatment (such as dye wastewater desalination and dye / salt separation). Methane (kinetic diameter 0.38 nm) and nitrogen (0.364 nm) have extremely similar sizes and physical properties. Traditional polymer membranes exhibit small differences in solubility and diffusion rates for CH4 and N2, making it difficult to achieve a breakthrough in separation factor. Furthermore, controlling defects in ultrathin separation layers remains a technological challenge. In addition, for the treatment of textile dyeing and printing wastewater, the separation membrane not only needs to intercept organic dye molecules but also must possess high salt permeability (to achieve dye / salt separation) and excellent antifouling capabilities, rendering traditional polymer membranes ineffective for the efficient treatment of dyeing and printing wastewater.

[0003] To address the aforementioned bottlenecks, researchers have attempted to introduce porous crystalline materials—metal-organic frameworks (MOFs)—into the preparation process of separation membranes. MOFs are self-assembled from metal ions or clusters with organic ligands, possessing tunable pore size (3-20 Å) and large specific surface area (>1000 m²). 2 g -1 MOF nanoparticles offer advantages such as abundant functional groups. However, based on interfacial polymerization strategies, ultrathin and highly hydrophilic polyamide layers (PA layers) are constructed by polycondensation reactions of aqueous and organic monomers on the surface of porous supports. Theoretically, the introduction of MOF nanoparticles can allow for molecular-level control of the PA layer without significantly increasing mass transfer resistance. Reported strategies often involve directly incorporating pre-synthesized MOF nanoparticles (such as ZIF-8, UiO-66-NH2, and MIL-101) into the aqueous or organic phase, preparing mixed matrix membranes (MMMs) via blend-interfacial polymerization. The results show that this type of membrane improves CH4 permeability. However, since the particle size of 3D-MOF is usually between 50-200 nm, it is easy to aggregate or deposit in the PA layer, causing interface defects, non-selective porosity, and even reducing mechanical strength. At the same time, the weak interfacial compatibility between the particles and the polymer matrix is ​​prone to detachment under long-term operation or high-pressure CH4 conditions, resulting in selective degradation. In addition, most MOF-based membrane materials are difficult to be suitable for both improving gas separation performance and for dye / salt separation research.

[0004] Therefore, how to achieve uniform and continuous growth of MOFs on the substrate surface at room temperature, and further construct a dense and defect-free polymer functional layer through interfacial polymerization, while maintaining the advantages of rapid CH4 molecule transfer through MOF channels and a high degree of improvement in dye / salt separation performance, remains a key problem that urgently needs to be solved in the field of separation membranes. Summary of the Invention

[0005] In order to achieve uniform growth of MOFs on the substrate surface under room temperature conditions and obtain a uniform and defect-free ultrathin composite film, this application provides a method for preparing an ultrathin MOF composite film. This method is simple in process and significantly overcomes the problems of uneven growth of MOFs, interface defects and flux-selectivity contradictions in the prior art.

[0006] In a first aspect, the present invention provides a method for preparing an ultrathin composite film having an interpenetrating network framework structure, the method comprising the following steps:

[0007] S1. Add ZrCl4 to methanol and disperse it evenly to obtain a metal precursor solution; disperse 2-aminoterephthalic acid in methanol, and after thorough dispersion, add triethylamine to obtain a ligand solution;

[0008] S2. Pour the metal precursor solution into the first side of the PSf membrane, which has been soaked in deionized water beforehand, so that the metal ions are anchored on the surface of the first side of the PSf membrane.

[0009] S3. The second side of the PSf membrane treated in step S2 is immersed in a ligand solution. The ligand solution diffuses upward under polarity, allowing the metal ions to grow in situ with the ligands in the ligand solution, forming a uniform and dense MOF layer on the surface of the first side of the PSf membrane through heterogeneous nucleation.

[0010] S4. Dry the PSf film obtained in step S3, and then pour a hexane solution of trimesoyl chloride into the first side of the PSf film to carry out interfacial polymerization through immersion treatment;

[0011] S5. The PSf membrane obtained in step S4 is dried to obtain an ultrathin composite membrane with an interpenetrating network skeleton structure.

[0012] Specifically, after pouring a zirconium metal solution onto the surface of a PSf substrate membrane, metal ions are adsorbed onto the PSf membrane surface based on hydrogen bonding and electrostatic interactions. The other side of the PSf membrane is then immersed in a solution of 2-aminoterephthalic acid (BDC-NH2) and triethylamine ligands. Under the polarity of the solvent, the triethylamine small molecules and organic ligands migrate towards the zirconium metal solution side. Under the influence of the triethylamine small molecules, which inhibit the initial nucleation and growth of MOFs, the coordination reaction between the metal ions and organic ligands on the membrane surface is restricted at the membrane-liquid interface. After the reaction is complete, the membrane is removed... After the membrane is placed under suitable temperature and humidity conditions, as the organic solvent and triethylamine molecules on the membrane surface volatilize, the metal ions and organic ligands on the membrane surface complete heterogeneous nucleation and growth, forming a pure MOF membrane. Finally, based on the effect of the amino groups carried by the selected UiO-66-NH2, the organic phase monomer solution is immersed in the surface of the MOF membrane prepared above, and interfacial polymerization reaction can occur on the surface of the MOF membrane and in the intergranular space, thereby obtaining an ultrathin composite membrane with an interpenetrating network framework structure, which is then applied in the fields of CH4 / N2 separation and dye / salt separation.

[0013] In some embodiments of the present invention, the concentration of ZrCl4 in the metal precursor solution is 0.227-0.327 wt%; the concentration of 2-aminoterephthalic acid in the ligand solution is 2.26-2.36 wt%, and the concentration of triethylamine is 2.4-3.77 wt%.

[0014] In some embodiments of the present invention, the time interval between step S2 and step S3 is 10-15 s.

[0015] In some embodiments of the present invention, in step S3, the in-situ growth time is 4-5 hours.

[0016] In some embodiments of the present invention, the drying process in step S4 is: drying at 25-40°C for 10-15 minutes.

[0017] In some embodiments of the present invention, in step S4, the concentration of trimesoyl chloride in the hexane solution is 0.1-0.4 wt%.

[0018] In some embodiments of the present invention, the soaking time in step S4 is 5-10 minutes.

[0019] In some embodiments of the present invention, the drying process in step S5 is: drying at 55-65°C for 10-15 min.

[0020] In a third aspect, the present invention provides an ultrathin composite membrane with an interpenetrating network skeleton structure prepared by the above-described preparation method.

[0021] A third aspect of the present invention provides an application of the above-described ultrathin composite membrane with an interpenetrating network skeleton structure in gas separation and / or dyeing and printing wastewater separation.

[0022] Compared with existing technologies, this invention is based on a reverse diffusion in-situ growth strategy. By controlling the mass fraction of the polymerization inhibitor molecules and the volatilization film-forming conditions, a MOF layer composed of highly crystalline and continuously dense MOF nanoparticles is formed on the PSf interface. Then, interfacial polymerization is completed using an organic phase solution to construct an ultrathin PA layer coating the MOF nanoparticles and form an interpenetrating network framework structure to repair intergranular defects in the MOF layer. The ultrathin PA layer also maintains the unobstructed pores of the MOF nanoparticles. The membrane prepared by this invention exhibits excellent gas separation and dye / salt separation characteristics. At a test pressure of 2 bar, the pure CH4 flux reaches 4096.16 GPU, the pure N2 flux reaches 401.51 GPU, and the CH4 / N2 selectivity reaches 10.20. It also demonstrates excellent long-term operational stability. Furthermore, the UiO-66-NH2 / PA-2-9 membrane achieves a water flux of 81.25 Lm for dye / salt separation at a test pressure of 1 bar. -2 h -1 bar -1 The dye / salt selectivity can reach 19.96%. Attached Figure Description

[0023] Figure 1 The images are of the UiO-66-NH2-1 film prepared in Example 1; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications;

[0024] Figure 2 The images are of the UiO-66-NH2-2 film prepared in Example 2; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications;

[0025] Figure 3 The images are of the UiO-66-NH2-3 film prepared in Example 3; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications;

[0026] Figure 4 The images are of the UiO-66-NH2 / PA-1 membrane prepared in Example 4; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications, and Figure (3) is a cross-sectional SEM morphology image;

[0027] Figure 5 The images are of the UiO-66-NH2 / PA-2 membrane prepared in Example 5; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications, and Figure (3) is a cross-sectional SEM morphology image;

[0028] Figure 6 The images are of the UiO-66-NH2 / PA-3 membrane prepared in Example 6; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications, and Figure (3) is a cross-sectional SEM morphology image;

[0029] Figure 7 The images are of the UiO-66-NH2 / PA-2-1 membrane prepared in Example 7; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications, and Figure (3) is a cross-sectional SEM morphology image;

[0030] Figure 8 The images are of the UiO-66-NH2 / PA-2-17 film prepared in Example 8; wherein, Figure (1) and Figure (2) are surface SEM images at different magnifications, and Figure (3) is a cross-sectional SEM image;

[0031] Figure 9 The graph shows the test results of gas separation performance in Test Example 1;

[0032] Figure 10 The graph shows the test results of the separation performance of the four reactive dyes in Test Example 2;

[0033] Figure 11 The figure shows the test results of salt separation performance in Test Example 2. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments, but this does not limit the present application.

[0035] The model and manufacturer information of the instruments used for measurement in the various embodiments of this application are as follows:

[0036] Field emission scanning electron microscope (SEM), model Drop Shape Analyzer 100, manufactured by Bruker GmbH, Germany;

[0037] Atomic force microscope (AFM), model: Tensor II, manufactured by Hitachi, Japan;

[0038] Specific surface area and porosity analyzer (BET), model: Micromeritics, ASAP 2020 PlusHD88, manufactured by Micromeritics, Inc., USA;

[0039] X-ray diffraction (XRD), model: D2 Discover diffractometer, manufactured by Bruker GmbH, Germany;

[0040] Fourier transform infrared spectrometer (FTIR), model: ALPHAII, manufactured by Bruker GmbH, Germany;

[0041] Constant temperature and humidity chamber, model: PCTHI-150T, manufactured by Stuka Instrument Equipment Co., Ltd.

[0042] Unless otherwise specified below, the specifications and manufacturer information of all raw materials used in the various embodiments of this application are commercially available:

[0043] Methanol, purchased from Shanghai Runjie Technology Development Co., Ltd.

[0044] Triethylamine (TEA), purchased from Maclean Biochemical Technology Co., Ltd.

[0045] n-Hexane, 99% purity, purchased from Aladdin Reagent Co., Ltd.

[0046] The specifications for pyromellitic trimethylol chloride were all 98%, purchased from Saen Chemical Technology Co., Ltd.

[0047] Zirconium chloride: 98% purity, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0048] 2-Aminoterephthalic acid: ≥99%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0049] Polysulfone (PSF) ultrafiltration membrane: average pore size 20-30 nm, provided by Zhongyi Filter Material Store in Zhouwangmiao Town, Haining City. Soak in deionized water for 2-3 hours before use.

[0050] Example 1

[0051] (1) Preparation of metal precursor solution

[0052] A 0.2 wt% ZrCl4 solution was completely dissolved in methanol to obtain a metal precursor solution of UiO-66-NH2.

[0053] (2) Preparation of ligand solution

[0054] 1.9 wt% of 2-amino-terephthalic acid was completely dissolved in methanol solution. After complete dissolution, 2.4 wt% of TEA was added to obtain a ligand solution of UiO-66-NH2.

[0055] (3) Preparation of UiO-66-NH2-1 membrane

[0056] A pre-wetted PSf membrane, soaked in deionized water, was fixed onto a polytetrafluoroethylene (PTFE) frame with the smooth side of the membrane facing upwards. A metal solution was then poured into the frame. Zirconium ions rapidly adsorbed onto the polar sites (carboxyl and hydroxyl groups) on the PSf membrane surface within 10–15 seconds via hydrogen bonding and electrostatic interactions, forming a positively charged metal transition layer. The other side of the membrane was then immersed in a ligand solution containing 2-aminoterephthalic acid (BDC-NH2) and TEA. Due to the adsorption of metal ions on the upper side of the membrane, TEA and ligand molecules migrated to the upper side. TEA, with its advantages of inhibiting early MOF nucleation and growth and its ability to coordinate with metal ions, suppressed the coordination reaction between metal ions and organic ligands at the membrane-liquid interface. After 4 hours of reaction, the membrane was removed and dried in a 30°C oven for 9 minutes. As the organic solvent and TEA on the membrane surface evaporate, the metal ions and organic ligands on the membrane surface complete heterogeneous nucleation and growth, thus preparing an ultrathin and dense uniform UiO-66-NH2 / PA-1 membrane. Electron microscopy images of the membrane surface at 100 nm and 1 µm are shown below. Figure 1 As shown.

[0057] Example 2

[0058] (3) The TEA mass fraction was changed to 3.16 wt%, and the rest of the method was the same as in Example 1 to prepare the UiO-66-NH2-2 film. The electron microscope images of the film surface at 100 nm and 1 µm are shown below. Figure 2 As shown.

[0059] Example 3

[0060] The TEA mass fraction was changed to 3.77 wt%, and the rest of the method was the same as in Example 1 to prepare the UiO-66-NH2-3 film. The electron microscope images of the film surface at 100 nm and 1 µm are shown below. Figure 3 As shown.

[0061] from Figure 1-3 As can be seen, as the amount of TEA added gradually increases, the pore size on the membrane surface gradually disappears. This is because TEA has the function of inhibiting the nucleation and growth of MOF in the early stage. However, as the concentration of TEA increases, the degree of inhibition of MOF nucleation and growth is greater, which is conducive to the uniform distribution of metal ions and the formation of a denser membrane. However, when the concentration of TEA is too high, there are too many metal ions coordinated by TEA. As TEA volatilizes, the effective selective layer of the formed membrane is thicker, which leads to a decrease in its separation selectivity.

[0062] Example 4

[0063] (1) Preparation of metal precursor solution

[0064] A 0.2 wt% ZrCl4 solution was completely dissolved in methanol to obtain a metal precursor solution of UiO-66-NH2.

[0065] (2) Preparation of ligand solution

[0066] 1.9 wt% of 2-amino-terephthalic acid was completely dissolved in methanol solution. After complete dissolution, 2.4 wt% of TEA was added to obtain a ligand solution of UiO-66-NH2.

[0067] (3) Preparation of organic phase monomer solution

[0068] Add 0.2 g of TMC to 100 mL of pure n-hexane reagent and stir thoroughly at room temperature for 3 h to obtain an organic monomer solution.

[0069] (4) Preparation of UiO-66-NH2-1 membrane

[0070] A pre-wetted PSf membrane, soaked in deionized water, was fixed onto a polytetrafluoroethylene (PTFE) frame with the smooth side of the membrane facing upwards. A metal solution was then poured into the frame. Zirconium ions rapidly adsorbed onto the polar sites (carboxyl and hydroxyl groups) on the PSf membrane surface within 10–15 seconds via hydrogen bonding and electrostatic interactions, forming a positively charged metal transition layer. The other side of the membrane was then immersed in a ligand solution containing 2-aminoterephthalic acid (BDC-NH2) and TEA. Due to the adsorption of metal ions on the upper side of the membrane, TEA and ligand molecules migrate to the upper side. TEA, with its advantages of inhibiting early nucleation and growth of MOFs and its ability to coordinate with metal ions, inhibits the coordination reaction between metal ions and organic ligands at the membrane-liquid interface. After 4 hours of reaction, the membrane was removed and dried in a constant temperature and humidity chamber at 30°C and 40% humidity for 9 minutes. As the organic solvent and TEA on the membrane surface evaporate, the metal ions and organic ligands on the membrane surface complete heterogeneous nucleation and growth.

[0071] (5) Preparation of UiO-66-NH2 / PA-1 membrane

[0072] A 0.2 wt% TMC solution in n-hexane was poured onto the membrane surface obtained in step (4), and the membrane was soaked for 2 min. Then, it was dried in a 60℃ oven for 10 min to obtain the UiO-66-NH2 / PA-1 membrane. SEM images of the membrane surface at 100 nm and 1 µm and the cross-sectional SEM image of the membrane at 200 nm are shown below. Figure 4 As shown.

[0073] Example 5

[0074] The TEA mass fraction was changed to 3.16 wt%, and the remaining steps were the same as in Example 4, to prepare the UiO-66-NH2 / PA-2 film. Electron micrographs of the PSf film and the UiO-66-NH2 / PA-2 film are shown below. Figure 5 As shown; Figure (1) is the SEM image of the PSf film on the substrate at 100 nm; Figure (2) is the SEM image of the UiO-66-NH2 / PA-2 film at 100 nm; Figure (3) is the SEM image of the surface of the UiO-66-NH2 / PA-2 film at 1 µm; Figure (4) is the SEM image of the cross section of the UiO-66-NH2 / PA-2 film at 200 nm.

[0075] from Figure 5 As can be seen, compared with the original PSf membrane used as the substrate, the UiO-66-NH2 / PA-2 membrane surface has uniform and dense MOF nanoparticles. The added TEA inhibits the nucleation and growth of MOFs. After the TEA volatilizes, metal ions are uniformly distributed on the PSf interface layer, forming a denser membrane with a thickness of 146.4 nm, which further enhances the separation selectivity of the composite membrane.

[0076] Example 6

[0077] The TEA mass fraction was changed to 3.77 wt%, and the remaining steps were the same as in Example 4, to prepare the UiO-66-NH2 / PA-3 membrane. The surface SEM images at 100 nm and 1 µm and the cross-sectional SEM image at 200 nm are shown below. Figure 6 As shown.

[0078] See Figure 4-6 As can be seen from the SEM images of the membrane surface, when the amount of TEA doped gradually increases, obvious MOF nanoparticles appear on the membrane surface. With the increase of TEA concentration, the inhibition of MOF nucleation and growth is greater, which is conducive to the uniform distribution of metal ions and the formation of a denser membrane. However, the SEM images of the membrane cross section show that when the TEA concentration is too high, there are too many metal ions coordinated by TEA. As TEA volatilizes, the effective selective layer of the formed membrane is thicker, reaching 183.5 nm, which leads to a decrease in its separation selectivity.

[0079] Example 7

[0080] The drying time of the membrane in a constant temperature and humidity chamber at 30°C and 40% was changed to 1 min, and the remaining steps were the same as in Example 5, resulting in a UiO-66-NH2 / PA-2-1 membrane. SEM images of the membrane surface at 100 nm and 1 µm and a cross-sectional SEM image at 400 nm are shown below. Figure 7 As shown.

[0081] Example 8

[0082] The drying time of the membrane in a constant temperature and humidity chamber at 30°C and 40% was changed to 17 min, while the remaining steps were the same as in Example 5, resulting in a UiO-66-NH2 / PA-2-17 membrane. SEM images of the membrane surface at 100 nm and 1 µm and a cross-sectional SEM image of the membrane at 400 nm are shown below. Figure 8 As shown.

[0083] from Figure 7 It can be seen that when the drying time of TEA is 1 min, the surface of the UiO-66-NH2 / PA-2-1 membrane has no obvious pores or particles, but some tiny cracks appear, and the membrane thickness is approximately 72.97 nm; from Figure 5 It can be seen that when the TEA drying time is 9 min, obvious and uniform particles appear on the surface of the UiO-66-NH2 / PA-2 membrane, and the membrane thickness is approximately 146.4 nm; from Figure 8 As can be seen, when the drying time of TEA is 17 min, obvious and uniform particles appear on the surface of the UiO-66-NH2 / PA-2-17 membrane, and the thickness of the membrane is approximately 192.1 nm.

[0084] Test Example 1

[0085] The gas permeation performance and selectivity of the membranes were evaluated at room temperature using a self-made gas permeation testing system. Various parameters of the membranes were characterized at three different locations, and the performance of each membrane was described using the mean and standard deviation.

[0086] Performance testing methods

[0087] For the determination of single-gas permeation, see the literature Q. Ma, K. Mo, S. Gao, Y. Xie, J. Wang, H. Jin, A. Feldhoff, S. Xu, JYS Lin, Y. Li, Ultrafast Semi‐Solid Processing of Highly Durable ZIF‐8 Membranes for Propylene / Propane Separation. Angew. Chem. Int. Ed. 59 (2020) 21909-21914. The sample was placed and fixed in a circular stainless steel tank with a sealing ring, and dry He was used as the permeate-side purge gas. The composition of the permeate gas was analyzed by gas chromatography (GC) and a thermal conductivity detector (HP7890, Porapak N). The permeate-side pressure was maintained at the normal atmospheric pressure in the apparatus. Permeation experiments were performed at room temperature using feed pressures ranging from 1 to 3.0 bar. The CH4 / N2 separation performance (permeability and selectivity) of the membrane was measured using a dry CH4 / N2 (50 / 50 v / v) gas mixture.

[0088] For a single gas permeation measurement, all feed flow rates were set to 10 mL / min. -1 The transmembrane pressure was maintained between 1 and 3.0 bar and controlled using a precision pressure gauge. The permeation flux of the target gas was measured using a soap bubble flow meter (HY-5020, Qingdao Hengyuan Instrument Co., Ltd., China). The tail gas was directly vented from the intercept side. The gas permeability P (mol / m³) was measured. -2 s -1 Pa -1 ) can be derived from the formula The result is calculated. Where P... i (mol·s) -1 A(m) is the molar flow rate of permeate component i. 2 ) is the effective membrane area, and ∆Pi (Pa) is the transmembrane pressure difference.

[0089] The CH4 flux, N2 flux, and CH4 / N2 selectivity of the UiO-66-NH2 / PA-1, UiO-66-NH2 / PA-2, and UiO-66-NH2 / PA-3 membranes obtained in Examples 4, 5, and 6, and the UiO-66-NH2 / PA-2-1 and UiO-66-NH2 / PA-2-17 membranes obtained in Examples 7 and 8, respectively, were measured. The measurement data are shown in Table 1 and... Figure 9 As shown:

[0090] Table 1. Test results of gas separation performance of samples in Examples 4-8

[0091]

[0092] Figure 9 Figure (a) shows the methane permeation flux of the membranes of Examples 4, 5, and 6 under mixed gas conditions and different pressures, tested using the method of Test Example 1. Figure (b) shows the nitrogen permeation flux of the membranes of Examples 4, 5, and 6 under mixed gas conditions and different pressures, tested using the method of Test Example 1. Figure (c) shows the methane / nitrogen separation selectivity of the membranes of Examples 4, 5, and 6 under mixed gas conditions and different pressures, tested using the method of Test Example 1. It can be seen that at the same pressure, as the TEA content in the membrane increases, the membrane's CH4 / N2 separation selectivity decreases; at the same TEA content, as the pressure increases, the membrane's CH4 / N2 separation selectivity increases.

[0093] Figure 9 Figure (d) shows the methane permeation flux of the membranes in Examples 5, 7, and 8 under pure gas conditions and different pressures, tested using the method of Test Example 1. Figure (e) shows the nitrogen permeation flux of the membranes in Examples 5, 7, and 8 under pure gas conditions and different pressures, tested using the method of Test Example 1. Figure (f) shows the methane / nitrogen separation selectivity of the membranes in Examples 5, 7, and 8 under pure gas conditions and different pressures, tested using the method of Test Example 1. It can be seen that when the TEA doping content is intermediate (Example 5), with the test pressure unchanged, the membrane's CH4 / N2 separation selectivity increases with the increase of the first-step drying time (aimed at removing TEA). With the drying time unchanged, the membrane's CH4 / N2 separation selectivity increases with the increase of pressure. However, considering both gas permeation flux and separation selectivity, the UiO-66-NH2 / PA-2 membrane balances gas permeability / selectivity. This demonstrates that the CH4 / N2 separation performance of the MOF membrane obtained by the method described in this application can be improved by adjusting the TEA concentration and drying time.

[0094] Test Example 2

[0095] Different types of membranes were cut to the same size as the test membrane cell area and placed in the membrane cell. The samples were pre-pressed at 1 bar for 2 hours to achieve stability. Then, the permeation rate and rejection rate of the membrane to different dyes and salt solutions were recorded at equal time intervals, and the average value was taken. The performance stability of the membrane was tested over a longer period of time.

[0096] Performance testing methods

[0097] For the determination method of dye / salt separation selectivity, please refer to the literature Liu Y, Wang XP, Zong ZA, et al. Thin film nanocomposite membrane incorporated with 2D-MOF nanosheets for highly efficient reverse osmosis desalination[J]. Journal of MembraneScience, 2022, 653(5): 120520. The flux and rejection rate of the prepared nanofiltration membrane were tested using a crossflow filtration device. The effective area of ​​the test membrane cell was 7.06 cm². 2 The concentrations of dye and salt were both 100 ppm. The sample was pre-compressed at 1 bar for 2 hours to achieve stable conditions. The membrane permeability and retention were measured within 20 minutes.

[0098] The membrane permeability (P) can be expressed by the formula Calculation results:

[0099] Where V(L) is the volume of permeate through the membrane, and A(m 2 ) represents the effective area of ​​the membrane under test, t (h) represents the test time, Δp (bar) represents the transmembrane pressure during the test, and the unit of P is (L m). -2 h -1 bar -1 ).

[0100] The concentrations of dye in the feed inlet and permeate were determined using UV / Vis spectroscopy (Shimadzu), and the concentrations of salt were determined using an FE38 conductivity meter (Mettler Toledo). The concentrations were calculated based on the standard curves of dye and salt, and then determined using the formula... Calculate the retention rates (R%) of dyes and salts:

[0101] Wherein, CP is the permeation solution and Cf is the feed solution.

[0102] The flux cutoff and retention rate of Reactive Red 24 and MgCl2 of the UiO-66-NH2-1 membrane, UiO-66-NH2-2 membrane, UiO-66-NH2-3 membrane, UiO-66-NH2 / PA-1, UiO-66-NH2 / PA-2, and UiO-66-NH2 / PA-3 obtained in Examples 1-6 were measured respectively. The measurement data are shown in Table 2.

[0103] Table 2. Test results of flux cutoff and retention rate of Reactive Red 24 and MgCl2 in the samples obtained in Examples 1-6.

[0104]

[0105] As shown in Table 2, with the increase of the TEA mass fraction, the rejection flux of Reactive Red 24 and MgCl2 in the samples of Examples 1-3 showed a clear trend of first increasing and then decreasing. The selectivity for Reactive Red 24 tended to be stable, while the rejection rate for MgCl2 was relatively low. This indicates that the increase of TEA mass fraction significantly restricted the coordination of metal ions and ligands. Under the same drying conditions, the higher the TEA mass fraction, the smaller the MOF particle size on the membrane surface, the stronger the membrane compactness, which is not conducive to water passage and thus reduces the rejection flux of dyes. Examples 4-6 also showed the same trend after the addition of organic phase, indicating that the addition of organic phase did not have a significant negative impact on the separation performance of the membrane. Moreover, the formed membrane surface had a significant adsorption effect on dyes, and most salts could preferentially pass through the membrane, ultimately achieving a highly efficient separation effect of dyes / salts.

[0106] Figure 10 Figures show the results of the separation performance tests for four reactive dyes. Figure (a) is a bar chart showing the separation flux of the sample membranes from Examples 4, 5, and 6 for the four reactive dyes; Figure (b) is a graph showing the retention rate of the sample membranes from Examples 4, 5, and 6 for the four reactive dyes. Figure 10 It can be seen that as the mass fraction of TEA introduced increases, the water flux of Reactive Red 24 shows a clear trend of first increasing and then decreasing, while the selectivity tends to stabilize. With the separation selectivity all greater than 98%, the UiO-66-NH2 / PA-2 membrane in Example 5 has the highest dye permeation flux.

[0107] Figure 11 Figure 1 shows the salt separation performance test results. Figure 2 shows the salt separation flux test results of the membranes in Examples 4, 5, and 6, and Figure 3 shows the salt rejection rate test results of the membranes in Examples 4, 5, and 6. As can be seen from the figures, the water flux of MgCl2 rejection also shows a clear trend of first increasing and then decreasing, and the rejection rate is relatively low. This indicates that with the increase of TEA content, the membrane surface formed has a significant adsorption effect on dyes, and most of the salt can preferentially pass through the membrane, ultimately achieving a highly efficient separation effect of dyes / salts.

[0108] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing an ultrathin composite membrane with an interpenetrating network framework structure, the method comprising the following steps: S1. Add ZrCl4 to methanol and disperse it evenly to obtain a metal precursor solution; disperse 2-aminoterephthalic acid in methanol, and after thorough dispersion, add triethylamine to obtain a ligand solution; S2. Pour the metal precursor solution into the first side of the PSf membrane, which has been soaked in deionized water beforehand, so that the metal ions are anchored on the surface of the first side of the PSf membrane. S3. The second side of the PSf membrane treated in step S2 is immersed in a ligand solution. The ligand solution diffuses upward under polarity, allowing the metal ions to grow in situ with the ligands in the ligand solution, forming a uniform and dense MOF layer on the surface of the first side of the PSf membrane through heterogeneous nucleation. S4. Dry the PSf film obtained in step S3, and then pour a hexane solution of trimesoyl chloride into the first side of the PSf film to carry out interfacial polymerization through immersion treatment; S5. The PSf membrane obtained in step S4 is dried to obtain an ultrathin composite membrane with an interpenetrating network skeleton structure.

2. The preparation method according to claim 1, characterized in that, In the metal precursor solution, the concentration of ZrCl4 was 0.227-0.327 wt%; in the ligand solution, the concentration of 2-aminoterephthalic acid was 2.26-2.36 wt%, and the concentration of triethylamine was 2.4-3.77 wt%.

3. The preparation method according to claim 1, characterized in that, The time interval between steps S2 and S3 is 10-15 seconds.

4. The preparation method according to claim 1, characterized in that, In step S3, the in-situ growth time is 4-5 hours.

5. The preparation method according to claim 1, characterized in that, The drying process in step S4 is as follows: dry at 25-40℃ for 10-15 minutes.

6. The preparation method according to claim 1, characterized in that, In step S4, the concentration of trimesoyl chloride in the hexane solution is 0.1-0.4 wt%.

7. The preparation method according to claim 1, characterized in that, In step S4, the soaking time is 5-10 minutes.

8. The preparation method according to claim 1, characterized in that, The drying process in step S5 is as follows: drying at 55-65℃ for 10-15 minutes.

9. The ultrathin composite membrane with an interpenetrating network skeleton structure prepared by the preparation method according to any one of claims 1-8.

10. The application of the ultrathin composite membrane with an interpenetrating network skeleton structure as described in claim 9 in gas separation and / or dyeing and printing wastewater separation.

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