Preparation and application of flower-like Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane

Abstract

The invention discloses a preparation method and an application of a flower-like Mg-Al LDH (layered double hydroxide) modified polydimethylsiloxane / polyethersulfone composite membrane. The preparation method comprises the following steps: dissolving polyethersulfone in N, N-dimethylacetamide, scraping a membrane, and soaking the membrane in deionized water; the preparation method comprises the following steps: dissolving PDMS in an isooctane solvent, adding LDH with different concentrations, continuously stirring until LDH is completely dispersed, adding PDMS, a cross-linking agent and a catalyst into the cross-linking agent and the catalyst according to a mass ratio of 10: 2: 1, and preparing the coating by adopting a wet film dip-coating method. And coating to obtain the modified composite membrane. The method is mainly applied to preparation of gas-liquid two-phase gas separation so as to obtain a composite membrane material with high CO2 / O2 selectivity and high gas permeability. Meanwhile, the method is simple in preparation process, the raw materials are cheap and easy to obtain, the LDH modified composite membrane can effectively improve the gas permeability and selectivity of the material, and a new preparation thought is provided for preparing a good CO2 gas separation membrane.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomedical gas-liquid two-phase technology, and relates to the preparation and application of a flower-shaped Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane. Background Art

[0002] Mg-Al layered double hydroxide (LDH) is a hydrotalcite-like compound. The structure of LDH is composed of charged brucite-like layers, and its chemical general formula is [Mg Ⅱ 1-x Al Ⅲ x (OH)] x+ [(X m- ) x / m ·mH2O] x- , the layered structure of LDH consists of a positively charged metal hydroxide main layer and interlayer anions. Therefore, the structure of LDH can be adjusted by the Mg / Al ratio to precisely regulate its physicochemical properties. In addition, the metal-OH on the surface of Mg-Al LDH contains basic sites, which can form metal-HCO3 with CO2, and the interlayer anion CO3 2- of LDH can also act as a mobile carrier for CO2 transmission, which will also promote the transfer of CO2. Therefore, Mg-Al LDH is a good CO2-selective modification filler.

[0003] Polyethersulfone (PES) has become one of the commonly used materials for preparing the support layer of gas separation membranes due to its excellent mechanical stability, chemical stability, and porosity. However, due to the surface microporous structure of the material itself, its gas selectivity in the field of gas separation is relatively low. Polydimethylsiloxane (PDMS) polymer is a silicone rubber material with good CO2 selectivity, and it is dense and has strong film-forming properties. It can be used as a coating to form a defect-free composite membrane on the surface of PES. Bilal Haider et al. mentioned in "Highly permeable innovative PDMS coated polyethersulfone membranes embedded with activated carbon for gas separation" that a separation membrane with PDMS as the functional layer and PES membrane as the support layer was prepared. PES has become a potential support layer due to its comprehensive properties such as high mechanical strength, high heat resistance, and excellent alkali resistance. However, due to the intrinsic properties of PDMS, the upper limit of the CO2 separation performance of the composite membrane is relatively low. Therefore, the unmodified PDMS composite membrane has certain defects. Therefore, in this invention, Mg-Al LDH material with good CO2 selective channels is introduced, and the reaction conditions are explored to synthesize flower-shaped LDH, which is doped into PDMS to form a mixed coating, and the influence of flower-shaped LDH on the CO2 gas permeability and selectivity of the composite membrane is explored. Summary of the Invention

[0004] Regarding the application limitations of the above-mentioned PDMS material, the present invention proposes a simple modification method. Using a hydrothermal synthesis reaction, by adding different concentrations of urea, NH4 + and OH- are used to adjust the pH. Under the synthesis conditions with a relatively high alkalinity, the charge of the edge groups can be reduced and the Coulomb repulsion can be decreased, resulting in edge-edge aggregation rather than substrate-edge growth, which changes the crystal growth path of LDH, thereby synthesizing flower-shaped Mg-Al LDH. Then, using PES, which has stable physical and chemical properties, is non-toxic, and does not change its composition when contacting with gas and liquid phases, as the support material for the composite membrane, and PDMS doped with flower-shaped Mg-Al LDH as the coating to prepare a mixed matrix composite membrane. The method of applying phase inversion and wet coating to prepare the composite membrane in the present invention successfully solves the problem that the PDMS material itself is soft. At the same time, the modified PDMS as the coating has a relatively thin film layer, which can achieve good gas permeability and selectivity.

[0005] Technical solution of the present invention:

[0006] A flower-like Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane, where polyethersulfone is the porous support layer of the composite membrane; PDMS modified with flower-like LDH with different mass parameters is the functional layer; PDMS is dissolved at room temperature, then different concentrations of LDH are added, and then a cross-linking agent is added for cross-linking configuration. The treated modified PDMS coating solution is dip-coated on a pre-prepared polyethersulfone substrate membrane. The modified PDMS serves as the separation coating in the composite membrane, and its thickness can be adjusted by dip-coating. The cross-section of the polyethersulfone serving as the substrate membrane has a loose finger-like pore structure, with a large cavity inside and micropores on its dark surface. The modified PDMS as the functional coating is dense and the LDH is evenly dispersed.

[0007] A preparation method of a flower-like Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane is as follows:

[0008] (1) PES porous support layer: Using the phase inversion method, with N,N-dimethylformamide (DMF) as the solvent, adding 15 wt.% of PES and 5 wt.% of polyethylene glycol (PEG) based on the total solution mass, using PEG as the pore-forming agent, preparing the substrate membrane solution, and ultrasonic standing for 2 h; The film is scraped using a bench-top flat film scraping machine. After scraping, the film is immersed in deionized water for 24 h for phase inversion to obtain the PES porous support layer;

[0009] (2) Preparation of flower-like Mg-Al LDH: Dissolve magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and urea in deionized water according to a molar ratio of 2:1:10 to prepare a solution of Mg 2+ with a concentration of 0.67 mol / L; Put the solution into a reactor and carry out hydrothermal crystallization in an oven at 110 °C for 24 h. During the reaction process, urea hydrolyzes to form a highly alkaline environment, reducing the charge of edge groups and reducing the Coulomb repulsion, changing the crystallization process and causing the crystals to grow in different directions. After the reaction, centrifuge and wash 3 times with deionized water and absolute ethanol, and dry the obtained precipitate in a vacuum oven at 70 °C for 12 h, and grind to obtain flower-like Mg-Al LDH;

[0010] (3) Preparation of PDMS coating composite membrane doped with LDH: Prepare an isooctane solution of PDMS with a concentration of 5 wt.%, add flower-like Mg-Al LDH to the isooctane solution of PDMS and stir until completely dispersed, and control the mass ratio of flower-like Mg-Al LDH to PDMS to be 2%-10%; add a crosslinking agent and a catalyst according to the mass ratio of PDMS, tetraethyl orthosilicate as the crosslinking agent, and dibutyltin dilaurate as the catalyst of 10:2:1, and remove bubbles by ultrasonic treatment to obtain a uniform coating solution; coat the coating solution on the surface of the PES porous support layer by wet coating to form a uniform liquid film on the surface of the PES porous support layer, and dry it at 85 °C for 2 h to obtain a flower-like Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane.

[0011] The above-mentioned flower-like LDH modified polydimethylsiloxane / polyethersulfone composite membrane is applied to the gas-liquid interface and used as a membrane material for gas exchange.

[0012] Advantages of the present invention: The present invention is mainly used to prepare a composite membrane material with high CO2 / O2 selectivity and good gas permeability. First, a polyethersulfone membrane material with certain mechanical strength is prepared by the phase inversion method. As the base membrane of the composite membrane, it can provide certain support for the functional layer membrane material with poor mechanical properties, thus changing the limitations of the functional coating material itself. By blending flower-like LDH with PDMS, a flower-like LDH modified polydimethylsiloxane functional layer is prepared. LDH contains metal-OH basic sites, which can form metal-HCO3 with CO2, improving the adsorption of CO2 by the composite membrane, and the anion CO3 between the LDH layers 2- can also act as a mobile carrier for CO2 transmission and promote the transmission of CO2. The PDMS coating doped with LDH modification, as a dense membrane material, can improve problems such as air plugs and leakage of the feed liquid during the application of the composite membrane. In addition, the raw materials of the present invention are easily available and inexpensive, making the large-scale application of this method possible.

[0013] The present invention mainly tests the CO2 permeability of the morphological characteristics of flower-like LDH. Since flower-like LDH is a 3D morphology, this structure has isotropy in CO2 transmission and adsorption. At the same time, the 3D structure can expose more -OH sites, and the openness of the internal channels of the 3D structure greatly reduces the transmission resistance of CO2, which is beneficial to the adsorption and transmission of CO2. Flower-like LDH can achieve good separation of CO2 and O2 under normal pressure. For the normal pressure environment in organisms, LDH materials are more conducive to the separation of CO2 and O2 gas components in the gas-liquid two-phase medium. Description of the Drawings

[0014] Figure 1SEM spectra, XRD spectra and Fourier transform infrared spectra of two morphologies of LDH. Among them, (A) SEM image of flaky LDH; (B) SEM image of flower-like LDH; (C) Fourier transform infrared (FTIR) spectra of flaky Mg-Al LDH and flower-like Mg-Al LDH; (D) XRD spectra of flaky LDH and flower-like LDH.

[0015] Figure 2 SEM spectra of unmodified and modified PDMS / PES composite membranes with two morphologies of LDH prepared. Among them, (A) Surface image of 5wt.% PDMS / PES composite membrane; (B) Surface image of 5wt.% PDMS / PES composite membrane doped with flaky LDH; (C) Surface image of 5wt.% PDMS / PES composite membrane doped with flower-like LDH; (D) Cross-sectional image of 5wt.% PDMS / PES composite membrane; (E) Cross-sectional image of 5wt.% PDMS / PES composite membrane doped with flaky LDH; (F) Cross-sectional image of 5wt.% PDMS / PES composite membrane doped with flower-like LDH.

[0016] Figure 3 CO2 gas permeability diagrams of flower-like and flaky LDH modified PDMS / PES composite membranes.

[0017] Figure 4 Orbital energy level potential simulation diagrams of PDMS / PES composite membranes modified with flower-like and flaky LDH.

[0018] Figure 5 Molecular dynamics simulation (MD) diagrams of PDMS / PES composite membranes modified with flower-like and flaky LDH. Among them, (A) Mean square displacement (MSD) simulation diagram of CO2 in flower-like LDH and flaky LDH modified composite membranes; (B) Radial distribution function (DFT) simulation diagram of CO2 in PDMS coatings doped with flower-like and flaky LDH. Specific implementation manners

[0019] The following further illustrates the specific implementation manners of the present invention through the attached drawings and technical solutions.

[0020] Example:

[0021] Preparation method of flower-like LDH modified polydimethylsiloxane / polyethersulfone composite membrane, comprising the following steps:

[0022] (1) PES porous support layer: Using the phase inversion method, with N,N-dimethylformamide (DMF) as the solvent and polyethylene glycol (PEG) as the pore former, the total mass of the solution is 60 g, including 9 g of PES, 3 g of PEG, and 48 g of DMF. Prepare the base membrane solution and ultrasonically let it stand for 2 h. Use a bench-top flat film coater for film scraping. After scraping, immerse the film in deionized water for 24 h for phase inversion to obtain the PES porous support layer;

[0023] (2) Preparation of flower-like Mg-Al LDH: Dissolve 10.256 g of magnesium nitrate hexahydrate, 7.5026 g of aluminum nitrate nonahydrate, and 12.012 g of urea in 60 mL of deionized water to prepare a solution with a concentration of 0.67 mol / L. Put the solution into a reactor and carry out hydrothermal crystallization in an oven at 110 °C for 24 h. During the reaction, urea hydrolyzes to form a highly alkaline environment, reducing the charge of edge groups and lowering the Coulomb repulsion, changing the crystallization process and causing the crystals to grow in different directions. After the reaction, centrifuge and wash with deionized water and absolute ethanol 3 times. The obtained precipitate is dried in a vacuum oven at 70 °C for 12 h and ground to obtain flower-like LDH; 2+ Concentration of 0.67 mol / L solution, put the solution into a reactor and carry out hydrothermal crystallization in an oven at 110 °C for 24 h. During the reaction, urea hydrolyzes to form a highly alkaline environment, reducing the charge of edge groups and lowering the Coulomb repulsion, changing the crystallization process and causing the crystals to grow in different directions. After the reaction, centrifuge and wash with deionized water and absolute ethanol 3 times. The obtained precipitate is dried in a vacuum oven at 70 °C for 12 h and ground to obtain flower-like LDH;

[0024] (3) Preparation of PDMS coating composite membrane doped with LDH: Prepare a 5 wt.% PDMS isooctane solution. Dissolve 2 g of PDMS in 38 g of isooctane, and then add 2%, 4%, 6%, 8%, and 10% of LDH relative to the mass of PDMS to the PDMS solution respectively and stir until completely dispersed. Add 400 mg of tetraethyl orthosilicate as the cross-linking agent and 200 mg of dibutyltin dilaurate as the catalyst for 30 min of cross-linking, and ultrasonically remove bubbles to obtain a uniform coating solution; Use the wet coating method to coat the coating solution on the surface of the PES porous support base membrane material to form a uniform liquid film on the surface of the PES porous support base membrane material, and dry it at 85 °C for 2 h to obtain a flower-like LDH-doped PDMS-LDH / PES composite membrane.

[0025] Table 1 Preparation details of 0-10 wt.% flower-like LDH modified PDMS coating solution

[0026]

[0027] The doped flower-like LDH has a good promoting effect on the CO2 transport on the PDMS surface. The flower-like LDH has a 3D morphology, and this structure is isotropic in CO2 transfer and adsorption. At the same time, the 3D structure can expose more -OH sites, and the openness of the internal channels of the 3D structure greatly reduces the resistance to CO2 transfer, which is beneficial to the adsorption and transport of CO2.

[0028] Control example:

[0029] Preparation method of flaky LDH modified polydimethylsiloxane / polyethersulfone composite membrane material, comprising the following steps:

[0030] (1) PES porous support layer: By the phase inversion method, a PES porous base membrane is prepared through a flat film scraping machine.

[0031] (2) Preparation of flaky Mg-Al LDH: Dissolve 1.28 g of magnesium nitrate hexahydrate, 0.94 g of aluminum nitrate nonahydrate, and 1.35 g of urea in 50 mL of deionized water to prepare a solution with a concentration of 0.01 mol / L of Mg 2+ The solution is sealed in a reaction kettle and then placed in an oven at 150 °C, followed by a hydrothermal crystallization reaction for 16 h. In the hydrothermal reaction, the low concentration of urea results in a low hydrolysis pH, causing the crystals to grow along the edges of the substrate. After the reaction, the precipitate is washed three times with deionized water and absolute ethanol, and the obtained precipitate is dried in a vacuum oven at 70 °C for 12 h. After the reaction, the precipitate is centrifugally washed three times with deionized water and absolute ethanol, dried in a vacuum oven at 70 °C for 12 h, and ground to obtain flaky LDH.

[0032] (3) Preparation of PDMS-LDH / PES composite membrane doped with LDH: Prepare a 5 wt.% PDMS isooctane solution. Dissolve 2 g of PDMS in 38 g of isooctane, and then add 2%, 4%, 6%, 8%, and 10% of the mass of flaky LDH compared to PDMS to the PDMS solution and stir until completely dispersed. Add 400 mg of tetraethyl orthosilicate as a crosslinking agent and 200 mg of dibutyltin dilaurate as a catalyst for 30 min of crosslinking, and remove bubbles by ultrasonic treatment to obtain a uniform coating solution; The coating solution is coated on the surface of the PES porous support base membrane material by wet coating to form a uniform liquid film on the surface of the PES porous support base membrane material, and dried at 85 °C for 2 h to obtain a PDMS-LDH / PES composite membrane doped with flaky LDH.

[0033] Characterization and result analysis of the composite membrane material

[0034] 1. The flower-like Mg-Al LDH of the prepared example and the flaky Mg-Al LDH of the comparative example are characterized by field emission scanning electron microscopy, and the crystal structure of the prepared Mg-Al LDH is analyzed by X-ray diffraction analysis (XRD). The characteristic functional groups of the prepared Mg-Al LDH are characterized by Fourier transform infrared spectrometer ATR. The results are as follows Figure 1As shown, Figures (A) and (B) show the scanning electron microscope analysis of the LDH synthesized in the examples and comparative examples. The flower-shaped LDH in the examples and the flake-shaped LDH in the comparative examples were successfully synthesized. Figure (C) shows the FTIR spectra of the flower-shaped LDH in the examples and the flake-shaped LDH in the comparative examples. The characteristic peaks of LDH appear, indicating the synthesis of LDH in the examples and comparative examples. Figure (D) shows the XRD pattern analysis of the flower-shaped LDH in the examples and the flake-shaped LDH in the comparative examples. After comparison with the standard card, there is no obvious difference in the characteristic peaks of the XRD patterns of the examples and comparative examples. However, due to the 3D structure of the flower-shaped LDH, the crystallinity changes. The most obvious is a slight shift at about 33°. Therefore, the flower-shaped and flake-shaped LDH can be distinguished from the XRD patterns.

[0035] 2. Material characterization of the flower-shaped and flake-shaped LDH-doped PDMS-LDH / PES composite membranes prepared in Examples 1-6 and Comparative Examples 1-6 by field emission scanning electron microscopy. First, cryogenic fracture was carried out by liquid nitrogen to observe the cross-sectional morphology of the composite membrane material. The treated composite membrane material was fixed on the sample stage with conductive glue, and gold was sputtered by current to observe the morphology of its surface and cross-section. The characterization results are as Figure 2 shown. (A) and (D) show the surface and cross-sectional views of the PDMS / PES composite membrane prepared in Example 1 and Comparative Example 1. The surface of the dense layer PDMS is smooth and flat, and the thickness of the PDMS coating is about 2.7 μm, forming a uniform and stable functional coating. (B) and (E) show the PDMS-LDH / PES composite membranes prepared in the comparative examples. Obvious flake-shaped LDH morphology can be seen on the surface of the composite membrane. However, due to the large difference in the vertical and horizontal dimensions of the flake-shaped LDH, more flake-shaped LDH is horizontally distributed in the PDMS, which is not conducive to CO2 transmission; (C) and (F) show the PDMS-LDH / PES composite membranes prepared in the examples. Obvious flower-shaped LDH morphology can be seen on the surface of the composite membrane, and the coating thickness of 2.7 μm can just cover the LDH with a size of 2.6 μm. Moreover, due to the 3D morphology of the flower-shaped LDH, there is no problem of uneven arrangement in the PDMS coating, and CO2 transmission can be promoted from each direction.

[0036] 3. Measuring the pure gas permeability of the composite membrane materials of the examples and comparative examples by a gas permeability test device. The composite membrane was placed in the gas test device to keep the test membrane area consistent and control the water bath temperature. Pressure was applied to the coating to maintain the transmembrane pressure at 0.1 MPa. The upper and lower gas paths of the pipeline were purged with pure gas to ensure that the gas in the pipeline was a single flowing gas, and the gas permeation rates of CO2 and O2 were measured separately with a soap bubble flowmeter. J uses GPU (1 GPU = 10 -6 cm 3 / cm 2The permeation rate expressed in (scmHg) is determined by the following equation:

[0037]

[0038] where J is the gas permeability, in GPU; ΔV is the volume of gas passing through the flowmeter, which is 0.1 cm 3 ; T is the room temperature of 25 °C; A is the membrane area, calculated to be 0.785 cm 2 ; t is the time for the gas to pass through the flowmeter, in s; Δp is the test pressure difference, in MPa. Each data was determined in parallel 3 times and the average value was taken. The gas permeability of the examples and comparative examples is as Figure 3 shown. Comparing the flower-like PDMS-LDH / PES composite membrane prepared in the example with the flaky PDMS-LDH / PES composite membrane prepared in the comparative example, the addition of flower-like LDH greatly increased the CO2 permeation rate of the composite membrane, and the CO2 permeability increased with the increase in the doping amount of flower-like LDH, reaching up to about 1700 GPU at most, breaking the upper limit of the intrinsic gas permeability of PDMS. This is because the spatial structure of flower-like LDH is fixed and it has isotropy for the transmission of CO2, and stacking does not affect the transmission efficiency of LDH. The transmission effect of CO2 of the flaky PDMS-LDH / PES composite membrane in the comparative example was greatly reduced because a large amount of flaky LDH accumulated during the doping process, affecting the transmission rate, and the maximum value of the CO2 transmission rate of the composite membrane was only 1100 GPU.

[0039] 4. Using the Dmol3 program in the Materials Studio (MS) software package, the optimization and electronic properties of the PDMS composite membranes doped with LDH in the examples and comparative examples were calculated based on density functional theory (DFT). The generalized gradient approximation and the Perdew-Burke-Ernzerhof (PBE) function were used to describe the electron exchange and correlation effects, and dnd and basfilev4.4 were used as the basis. Molecular dynamics (MD) simulations and geometric optimizations were carried out in the NVT ensemble at 298 K using the Forcite tool of MS and the COMPASS force field, with a total simulation time of 500 ps and a time step of 1 fs to demonstrate the transfer and adsorption of CO2 / O2 two gases in the membrane materials of the examples and comparative examples. The conclusions obtained from the simulations are as Figure 4 and Figure 5 shown, Figure 4 represents the potential energy level orbital diagrams of the examples and comparative examples. There is almost no difference between the two at the high-energy E HOMO orbital, but the example has almost no difference at the low-energy E LUMOLower on the orbit, resulting in ΔE being significantly smaller than that of the comparative example, indicating that less energy is required for the flower-like LDH to transport CO2. The rapid CO2 adsorption ability of the PDMS-LDH / PES composite membrane doped with flower-like LDH is regulated, which is beneficial to the transport of CO2. Figure 5 It shows the molecular dynamics simulation diagrams of the PDMS / PES composite membrane modified with LDH in the example and the comparative example. The results in Figure (A) show that when the PDMS composite membrane is doped with flower-like LDH, the mean square displacement (MSD) of CO2 transport is significantly faster than that of the PDMS composite membrane doped with flaky LDH, indicating that the flower-like LDH has a stronger effect on the transport of CO2. Figure (B) shows that compared with the comparative example, the flower-like LDH in the example can induce CO2 to form a short-range ordered distribution in the membrane material, and this local ordered property can significantly promote the dissolution and diffusion of CO2 in the flower-like LDH-PDMS / PES composite system.

[0040] In the present invention, by adopting the form of a composite membrane, the performance of the dense functional layer is optimized, modified and regulated. The presence of the PES base membrane provides mechanical support for the PDMS layer modified by coating Mg-Al LDH. The prepared flower-like LDH modified PDMS layer provides good CO2 gas permeability for the gas-liquid two-phase separation process after testing. In addition, through molecular dynamics (MSD) simulation, the effective role of flower-like Mg-Al LDH in improving the CO2 gas permeability of the composite membrane is indirectly confirmed theoretically, greatly strengthening the theoretical basis and providing a new idea for the research of gas separation membranes.

Claims

1. A method for preparing a flower-shaped Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane, characterized in that: Changing the reaction temperature and pH value to control the LDH morphology, the steps are as follows: (1) A polyethersulfone porous support layer was prepared by a phase inversion method; (2) Preparation of flower-shaped Mg-Al LDH: Magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and urea were dissolved in deionized water to prepare Mg 2+ A solution with a concentration of 0.67 mol / L; the solution is subjected to hydrothermal crystallization; after the reaction is completed, the solution is centrifuged and washed with deionized water and anhydrous ethanol, and the obtained precipitate is dried and ground to obtain flower-like Mg-Al LDH; (3) Preparation of flower-shaped Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane: prepare a polydimethylsiloxane isooctane solution with a concentration of 5 wt.%, add the flower-shaped Mg-Al LDH into the isooctane solution of PDMS and stir until it is completely dispersed; add the cross-linking agent and the catalyst in a ratio of 10:2:1 by mass of PDMS, cross-linking agent tetraethyl silicate, and catalyst dibutyltin dilaurate, and perform ultrasonic degassing to obtain a uniform coating liquid; apply the coating liquid on the surface of the PES porous support layer by wet coating to form a uniform liquid film on the surface of the PES porous support layer, and dry to obtain a flower-shaped Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane.

2. The preparation method according to claim 1, characterized in that: The molar ratio of magnesium nitrate hexahydrate, aluminum nitrate nonahydrate, and urea is 2:1:

10.

3. The preparation method according to claim 1, characterized in that: The temperature of hydrothermal crystallization is 110℃ and the time is 24h.

4. The preparation method according to claim 1, characterized in that: The drying conditions were: drying at 70°C in vacuum for 12 h.

5. The preparation method according to claim 1, characterized in that: The mass ratio of flower-like Mg-Al LDH to PDMS is 2%-10%.

6. The preparation method according to claim 1, characterized in that: The mass ratio of PDMS, cross-linking agent tetraethyl silicate, and catalyst dibutyltin dilaurate is 10:2:

1.

7. The preparation method according to claim 1, characterized in that: The drying conditions are: drying at 85°C for 2 hours.

8. A flower-shaped Mg-Al LDH modified polydimethylsiloxane / polyethersulfone composite membrane obtained by the preparation method according to claims 1-7 is applied to a gas-liquid interface as a membrane material for gas exchange.

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