Preparation method of vertical orientation LDH-based composite membrane for H2 purification

Abstract

The invention belongs to the technical field of gas separation membrane materials, and discloses a preparation method of a vertically-oriented LDH-based composite membrane for H2 purification, which adopts a three-step synergistic strategy, and utilizes the principles of constructing a straight-through channel through substrate-induced vertical growth, regulating interlayer spacing by Cl-intercalation to realize molecular sieving, and introducing CO2 adsorption sites by PEI surface grafting to prepare the vertically-oriented LDH-based composite membrane for H2 purification. The preparation method comprises the following steps: by taking a hydrophilic polyacrylonitrile substrate rich in carboxyl as a growth template, growing a vertically arranged NiAl LDH array on the surface of the substrate in situ through a hydrothermal method, further inserting Cl <-> into an interlayer through ion exchange to replace original CO3 < 2->, accurately regulating and controlling the LDH interlayer spacing to 0.306 nm, and finally covalently grafting polyethyleneimine on the surface of LDH by taking epoxy chloropropane as a cross-linking agent. According to the preparation method disclosed by the invention, under the synergistic effect of multiple mechanisms, the obtained composite membrane realizes synchronous improvement of hydrogen permeability and selectivity, has the characteristics of high stability and easiness in large-scale preparation, and is suitable for an industrial H2 purification process.

Description

Technical Field

[0001] This invention belongs to the field of gas separation membrane material technology, and relates to a method for preparing a vertically oriented LDH-based composite membrane for H2 purification. Background Technology

[0002] Hydrogen is a highly efficient and clean energy carrier. However, hydrogen produced as a byproduct in industrial processes such as petroleum refining and chemical synthesis often contains high concentrations of impurities such as carbon dioxide, severely limiting its direct utilization efficiency and subsequent storage and transportation safety. Therefore, developing efficient and low-energy-consumption hydrogen purification technologies to achieve highly selective separation of H2 and CO2 has become one of the core issues urgently needing to be addressed for the development of the hydrogen energy industry.

[0003] Among numerous gas separation technologies, membrane separation is considered one of the most promising hydrogen purification methods due to its advantages such as simple operation, low energy consumption, high modularity, and environmental friendliness. The core of membrane separation technology lies in the membrane material, whose performance directly determines the efficiency and economy of the separation process. In recent years, two-dimensional materials, with their unique layered structure and tunable interlayer nanochannels, have provided a new approach for constructing next-generation high-efficiency separation membranes. Among them, layered bimetallic hydroxides, as anionic two-dimensional layered clay materials, have the general chemical formula [M... 2+ 1-x M 3+ x (OH)2] x+ (A n- ) x / n . LDH (yH₂O) possesses numerous advantages, including tunable composition, exchangeable anions between layers, a surface rich in hydroxyl groups, and mild synthesis conditions. The layers of LDH are composed of divalent and trivalent metal cations linked by edge-sharing hydroxyl octahedra, with charge balance and structural stability maintained between layers through exchangeable anions and water of crystallization. This unique structure allows for precise control of interlayer spacing and interlayer chemical environment by adjusting the metal composition of the layers and the types and quantities of intercalated anions, thus providing an ideal platform for designing membrane materials for the sieving of specific gas molecules.

[0004] However, despite LDH's theoretically excellent gas sieving potential, its practical application in high-performance gas separation membranes still faces a series of key challenges: First, there is a lack of stable and controllable preparation methods to achieve highly vertical and ordered arrangement of LDH nanosheets on a macroscopically flexible substrate to construct low-torsion, straight-through transport channels; second, the interlayer of conventionally hydrothermally synthesized LDH is usually CO3. 2-The interlayer spacing of LDH is relatively narrow (approximately 0.285 nm), smaller than the free volume of H2 (0.289 nm), making it difficult to achieve effective sieving of H2 and CO2. Although this can be adjusted through ion exchange, the process for precisely controlling the exchange degree to obtain the ideal interlayer spacing without compromising membrane integrity remains immature. Furthermore, the interfacial compatibility between the hydrophilic surface of LDH and most polymer substrates is poor, easily leading to non-selective defects at the interface. In the presence of moisture, interlayer swelling is also prone to occur, affecting the long-term separation stability and mechanical strength of the membrane. Existing technologies often struggle to simultaneously address the issues of orientation control, precise interlayer spacing engineering, and interface strengthening, resulting in shortcomings in permeability, selectivity, or stability of the developed LDH membranes, thus limiting their industrial application prospects.

[0005] Therefore, developing a method for preparing LDH composite membranes that can be vertically oriented, with precisely adjustable interlayer spacing, strong interfacial bonding, and excellent gas sieving and permeation performance on large-area flexible substrates is of great significance for promoting the practical application of high-performance hydrogen separation membranes. This invention is proposed against this backdrop. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing a vertically oriented LDH-based composite membrane for H2 purification. Utilizing the mechanism of substrate-induced crystal orientation growth, the polymer substrate is first pretreated with hydrophilicity to provide abundant chemical anchoring sites. Then, LDH nanosheets are induced to grow vertically and orderly on the substrate surface in situ via hydrothermal synthesis, constructing a low-torsion, straight-through mass transfer channel and improving gas permeation performance. This invention employs a step-by-step synergistic strategy, utilizing the principle of anion exchange to regulate interlayer spacing and surface grafting to introduce adsorption sites, through Cl... - Intercalation precisely modulates the free channels between LDH layers to 0.306 nm, achieving molecular-size sieving of H2 and CO2; simultaneously, polyethyleneimine is grafted onto the LDH surface via covalent cross-linking. The construction of the vertically oriented structure significantly reduces the tortuosity of the gas transport path, providing a rapid permeation channel for H2; Cl - Intercalation not only achieves sub-nanometer precision sieving, but its weak hydration also enhances the membrane structure's anti-swelling stability. Surface-grafted PEI further inhibits CO2 transport through reversible chemisorption of CO2 by amino groups. Furthermore, the introduction of PEI segments improves the interfacial compatibility between the inorganic LDH layer and the organic polymer substrate. This multi-faceted coupling of "rapid channel-size sieving-chemisorption-interfacial enhancement" results in a composite membrane that simultaneously possesses high hydrogen permeability, high H2 / CO2 selectivity, and excellent operational stability. The technical solution of the present invention: A method for preparing a vertically oriented LDH-based composite membrane for H2 purification, comprising the following steps: (1) In-situ construction of vertically oriented LDH separation layer; A polyacrylonitrile ultrafiltration membrane was immersed in a 2 mol / L sodium hydroxide aqueous solution and heated at 40–70 °C for 1 hour. It was then thoroughly washed with deionized water until neutral to obtain a hydrolyzed polyacrylonitrile substrate with a carboxyl-rich surface. A hydrothermal growth precursor solution was prepared: Ni… 2+ The concentration is 0.01~0.10 mol / L, Ni 2+ With Al 3+ The molar ratio of urea to total metal ions was 2:1, with urea as a precipitant and a molar ratio of urea to total metal ions of 10:1. Ammonium fluoride was introduced as a crystal growth regulator, with a molar ratio of ammonium fluoride to urea of ​​1:7. The hydrolyzed polyacrylonitrile substrate with a surface rich in carboxyl groups was vertically immersed in the hydrothermal growth precursor solution and sealed in a stainless steel reactor lined with polytetrafluoroethylene. The hydrothermal reaction was carried out at 85 °C for 12-30 hours. After the reaction, the substrate was naturally cooled, the composite membrane was removed, and the surface was rinsed with deionized water and dried at room temperature to obtain a NiAl LDH-HPAN composite membrane with a vertically oriented nanosheet array. (2) Cl - Intercalation adjusts the interlayer spacing; The NiAl LDH-HPAN composite membrane obtained in step (1) was immersed in a sodium chloride aqueous solution with a pH of 4.25-5.00 and a concentration of 1 mol / L, and subjected to ion exchange treatment at 50-80 °C for 24 hours. After the exchange was completed, the composite membrane was removed and washed with deionized water until the washing solution was neutral. After drying, NiAl LDH(Cl) with expanded interlayer spacing was obtained. - )-HPAN composite film; (3) Surface amino functionalization modification; A polyethyleneimine impregnation solution containing 0.5–2.0 wt.% was prepared using water and ethanol at a volume ratio of 1:1 as solvents. Epichlorohydrin was used as a crosslinking agent, with a polyethyleneimine to epichlorohydrin mass ratio of 5:1. The pH of the impregnation solution was adjusted to 6. NiAl LDH(Cl) was then added... - The )-HPAN composite membrane was immersed in the impregnation solution and reacted at 25 ℃ in the dark for 1-3 hours. After the reaction was completed, the composite membrane was removed, thoroughly washed with deionized water and dried to finally obtain the surface-functionalized NiAl LDH(Cl - The PEI-HPAN composite membrane is a vertically oriented LDH-based composite membrane used for H2 purification.

[0007] The Ni 2+ It is nickel nitrate hexahydrate, Al 3+ It is aluminum nitrate nonahydrate.

[0008] Step (1), Ni2+ The concentration was 0.05 mol / L.

[0009] In step (1), the hydrothermal reaction takes 24 hours.

[0010] In step (2), the conditions for ion exchange are pH=4.50 and temperature 60 ℃.

[0011] In step (3), the concentration of polyethyleneimine in the impregnation solution is 1.5 wt.%.

[0012] In step (3), the reaction time under light-protected conditions is 2.5 hours.

[0013] Gas separation performance test: Before conducting the gas permeation performance test, the prepared vertically oriented LDH-based composite membrane was vacuum dried at 50 °C for 12 hours to completely remove residual moisture and solvent; the dried vertically oriented LDH-based composite membrane was then cut into pieces with an effective area of ​​approximately 2.0 cm². 2 The samples were sealed in a self-made flat sheet membrane test cell; the test was conducted using pure gas at 25°C and a transmembrane pressure difference of 0.1 MPa, and the gas flow rate on the permeate side was measured by a soap bubble flow meter; at least three parallel samples were tested for each gas, and the average value was used to calculate the gas permeability and ideal selectivity.

[0014] The gas separation performance test targets include H2 and CO2.

[0015] The beneficial effects of this invention: Addressing the current technical bottleneck of vertically oriented LDH membranes failing to simultaneously achieve high gas permeability and high selectivity, this invention proposes a synergistic construction strategy of "substrate-induced vertical orientation—anion intercalation regulation—surface functionalization modification." Vertically oriented LDH nanosheet arrays construct a through-type mass transfer channel penetrating the membrane layer, significantly reducing the tortuosity and mass transfer resistance of gas permeation; through Cl... - Ion exchange precisely modulated the LDH interlayer spacing to 0.306 nm, achieving a match with the size of H2 molecules' dynamics and endowing the membrane structure with sub-nanometer precision sieving capabilities. Surface-grafted polyethyleneimine not only further enhanced selectivity through the reversible chemisorption of CO2 by amino groups, but its flexible long chains also strengthened the interfacial compatibility and bonding strength between the LDH layer and the polymer substrate. Furthermore, Cl... - As a weakly hydrating intercalating anion, it effectively inhibits interlayer swelling of the membrane in a water-vapor environment, thus improving the long-term stability of the structure. This multi-synergistic mechanism of "rapid mass transfer channel—size sieving—chemisorption—interfacial enhancement" makes the prepared NiAl LDH(Cl) -The PEI-HPAN composite membrane maintains high H2 permeability (≥707 GPU) while achieving excellent H2 / CO2 selectivity (≥78.5). Its overall performance surpasses the 2008 Robeson limit, and its preparation process is mild, has low substrate cost, and is easy to scale up, providing a promising new approach for the industrial preparation of high-efficiency hydrogen separation membranes. Attached Figure Description

[0016] Figure 1 This is a surface SEM image of the NiAl LDH-HPAN composite film prepared in Example 1 of the present invention, showing the morphology of the vertically oriented LDH nanosheet array.

[0017] Figure 2 The NiAl LDH-HPAN and NiAl LDH(Cl) prepared in Example 1 of this invention are - )-HPAN and NiAlLDH(Cl - The comparison chart of H2 permeability and H2 / CO2 selectivity of the three composite membranes (P1, PEI, and HPAN) demonstrates the improved gas separation performance brought about by the synergistic strategy. Detailed Implementation

[0018] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0019] Example 1: This embodiment fully demonstrates the preparation process of the three-step synergistic strategy described in this invention.

[0020] (1) Preparation of vertically oriented NiAl LDH-HPAN composite membrane: First, a polyacrylonitrile (PAN) ultrafiltration membrane was immersed in a 2 mol / L NaOH solution and hydrolyzed at 60 °C for 1 hour. After washing with water until neutral, a hydrolyzed polyacrylonitrile (HPAN) substrate was obtained. 0.582 g of Ni(NO3)2 . 6H2O(Ni) 2+ (Concentration of 0.05 mol / L), 0.375 g Al(NO3)3 . 9H2O(Ni) 2+ :Al 3+A molar ratio of 2:1), 1.501 g CO(NH2)2 (urea, with a molar ratio of 10:1 to total metal ions), and 0.074 g NH4F (urea:NH4F molar ratio = 7:1) were dissolved in 50 mL of deionized water and magnetically stirred for 30 minutes to form a uniform light green precursor solution. The HPAN substrate was vertically immersed in this precursor solution and placed in a high-pressure reactor lined with polytetrafluoroethylene. The reaction was carried out at a constant temperature of 85 °C for 24 hours using hydrothermal reaction. After the reaction, the substrate was allowed to cool naturally to room temperature. The composite membrane was then removed and thoroughly rinsed with deionized water, followed by drying at room temperature to obtain a NiAl LDH-HPAN composite membrane with a vertically oriented nanosheet array. Its surface morphology is as follows: Figure 1 As shown, a vertically arranged array of LDH nanosheets is presented; (2) Cl - Intercalation adjustment of interlayer spacing: Measure 100 mL of deionized water, add 5.844 g of sodium chloride (NaCl) solid, stir to dissolve, and adjust the pH value to 4.50 with 0.1 mol / L dilute hydrochloric acid solution to prepare the intercalation exchange solution. Completely immerse the NiAl LDH-HPAN composite membrane obtained in step (1) in the intercalation exchange solution, and place the container in a constant temperature water bath at 60 ℃ for 24 hours to carry out ion exchange. After the exchange is completed, remove the membrane and wash it with deionized water until neutral, and dry it to obtain NiAl LDH(Cl - )-HPAN composite film.

[0021] (3) Surface amino functionalization modification: 0.75 g of polyethyleneimine (PEI, MW=300) was dissolved in 50 mL of a 1:1 mixture of water and ethanol, and the pH was adjusted to 6 with dilute hydrochloric acid. Then, 0.15 g of epichlorohydrin (ECH) was added, and the mixture was stirred at room temperature for 1 hour for pre-crosslinking. The NiAl LDH(Cl) obtained in step (2) was then... - The )-HPAN composite membrane was immersed in this solution and reacted at 25 °C for 1.5 hours. After the reaction, the membrane was removed and rinsed with plenty of deionized water, and then dried to obtain surface-functionalized NiAl LDH(Cl) - ) / PEI-HPAN composite membrane.

[0022] Gas separation performance test: After vacuum drying the membranes prepared in each of the three steps at 50 °C for 12 hours, their pure H2 and CO2 permeation performance was tested at 25 °C and a pressure difference of 0.1 MPa. The results are as follows. Figure 2 As shown. Surface-functionalized NiAl LDH(Cl) prepared through a three-step synergistic optimization process. - The PEI-HPAN composite membrane has an H2 permeability of 707 GPU and an H2 / CO2 selectivity of 78.5.

[0023] Example 2: This embodiment is basically the same as Embodiment 1, except that the ion exchange temperature in step (2) is adjusted to 80℃. The final product is NiAl LDH(Cl). - ) / PEI-HPAN composite membrane.

[0024] Gas separation performance test: After vacuum drying the prepared composite membrane at 50 °C for 12 hours, its pure H2 and CO2 permeation performance was tested at 25 °C and 0.1 MPa pressure difference. The results showed that its H2 permeability was 962 GPU and its H2 / CO2 selectivity was 46.7.

[0025] Example 3: This embodiment is basically the same as Example 1, except that the concentration of PEI in step (3) is adjusted to 1.0 wt.%. The final product is NiAl LDH(Cl). - ) / PEI-HPAN composite membrane.

[0026] Gas separation performance test: After vacuum drying the prepared composite membrane at 50 °C for 12 hours, its pure H2 and CO2 permeation performance was tested at 25 °C and 0.1 MPa pressure difference. The results showed that its H2 permeability was 760 GPU and its H2 / CO2 selectivity was 73.2.

[0027] Comparative Example 1: No substrate pretreatment was performed during membrane preparation. This comparative example aims to investigate the necessity of substrate hydrolysis pretreatment for the vertical orientation growth of LDH and the final membrane performance. The preparation process is as follows: a raw polyacrylonitrile (PAN) ultrafiltration membrane without any hydrolysis treatment was used directly as the substrate, skipping the substrate hydrolysis process in step (1) of Example 1. Subsequently, NiAl LDH(Cl) was prepared according to the exact same formulation, concentration, temperature, time and operation method as in steps (1), (2) and (3) of Example 1. - ) / PEI-HPAN composite membrane.

[0028] Comparative Example 2: No Cl is present during the membrane preparation process. - Intercalation and PEI modification. This comparative example aims to examine the performance of a pristine LDH membrane with only a vertically oriented structure, without any ion exchange or surface modification. The preparation process is as follows: First, the PAN substrate was hydrolyzed according to the same method as step (1) in Example 1 to obtain an HPAN substrate. Subsequently, a vertically oriented NiAl LDH array was hydrothermally grown on the HPAN substrate according to the same formulation, concentration, temperature, and time as step (1) to obtain a NiAl LDH-HPAN composite membrane. The interlayer anion of this membrane is CO3 introduced during the synthesis process.2- The membrane prepared in this comparative example was not subjected to step (2) Cl in Example 1. - Intercalation and steps (3) PEI modification.

[0029] Comparative Example 3: Cl is present during the membrane preparation process. - Intercalation but without PEI modification. This comparative example aims to evaluate Cl alone. - The contribution of the intercalation step to the membrane gas separation performance was investigated, and the effect of PEI modification on selectivity was revealed as a control. The preparation process is as follows: First, a vertically oriented NiAl LDH-HPAN composite membrane was prepared according to the exact same method as step (1) in Example 1. Then, under the exact same conditions as step (2) in Example 1 (pH=4.50, 60 ℃, 24 h), the LDH composite membrane was immersed in a 1 mol / L NaCl solution for ion exchange, allowing Cl... - Replacement of interlayer CO3 2- NiAl LDH(Cl) was obtained - )-HPAN composite membrane. The membrane prepared in this comparative example was only processed up to Cl. - The intercalation step was not performed in step (3) of Example 1, which involved PEI surface modification.

[0030] Comparative Example 4: The membrane was prepared with PEI modification but without Cl. - Intercalation. This comparative example aims to evaluate the contribution of the PEI surface modification step to the membrane gas separation performance. The preparation process is as follows: First, a vertically oriented NiAl LDH-HPAN composite membrane (with CO3 as the interlayer anion) was prepared according to the exact same method as step (1) in Example 1. 2- Then, the LDH composite membrane was subjected to surface amino functionalization modification under the exact same conditions as step (3) of Example 1 (PEI concentration 1.5 wt.%, pH=6, 25 ℃, 2 h) to obtain NiAl LDH / PEI-HPAN composite membrane. The membrane prepared in this comparative example was not subjected to step (2) of Example 1. - Intercalation.

[0031] The composite membranes prepared in Example 1 and Comparative Examples 1, 2, 3, and 4 were tested for gas separation performance under conditions of 0.1 MPa and 25°C. The results are summarized in Table 1.

[0032] Table 1: Gas separation performance of the LDH composite membrane of Example 1 and the comparative example in pure gas at 0.1 MPa and 25 °C

[0033] The untreated membrane (Comparative Example 1) exhibited selectivity close to the H2 / CO2 Knudsen diffusion coefficient, demonstrating that substrate hydrophilization is a necessary prerequisite for constructing a defect-free vertically oriented separation layer. Compared to the unmodified vertical LDH membrane (Comparative Example 2), the Cl-treated membrane... - The intercalated membrane (Comparative Example 3) showed a significant increase in H2 permeability and H2 / CO2 selectivity of 314% and 59%, respectively, confirming the decisive role of precisely controlling the interlayer spacing to 0.306 nm in improving mass transfer efficiency and size sieving capability. In contrast, the membrane modified only with PEI (Comparative Example 4) showed limited performance improvement, indicating that simply introducing chemisorption sites without interlayer spacing optimization is insufficient to fully realize its sieving potential. - After introducing PEI surface modification on the intercalation basis (Example 1), the membrane maintained high H2 permeability (707.3 GPU) while further improving H2 / CO2 selectivity to 78.5, compared to Cl only. - The intercalated membrane (Comparative Example 3) improved by approximately 80%, highlighting the Cl... - Synergistic effect of intercalation and PEI modification. In summary, "substrate-induced vertical orientation—Cl - The three-step synergistic strategy of "intercalation to regulate interlayer spacing - PEI surface functionalization" enables the composite film to break through the upper limit of Robeson in 2008, demonstrating the advanced nature and inventiveness of this invention.

[0034] Therefore, it can be seen that the "vertical orientation construction - interlayer spacing Cl" adopted in this invention - The three-step synergistic strategy of "intercalation regulation-PEI surface modification" successfully integrates three mechanisms: low tortuosity mass transfer channels, sub-nanometer size sieving, and selective chemical adsorption. This simultaneously achieves a breakthrough improvement in H2 permeability and H2 / CO2 selectivity. Its comprehensive performance exceeds the upper limit of Robeson in 2008 and exhibits good operational stability. It has clear potential for industrial application in the field of high-efficiency hydrogen separation.

[0035] The above embodiments are the concept and description of the technical solution of the present invention, intended to enable more people skilled in the art to understand the main content of the present invention and implement it. However, the implementation of the present invention is not limited to the content of the above embodiments. Any modifications, mergers, simplifications, etc., made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and will be included within the protection scope of the present invention.

Claims

1. A method for preparing a vertically oriented LDH-based composite membrane for H2 purification, characterized in that, The steps are as follows: (1) In-situ construction of vertically oriented LDH separation layer; A polyacrylonitrile ultrafiltration membrane was immersed in a 2 mol / L sodium hydroxide aqueous solution and heated at 40–70 °C for 1 hour. It was then thoroughly washed with deionized water until neutral to obtain a hydrolyzed polyacrylonitrile substrate with a carboxyl-rich surface. A hydrothermal growth precursor solution was prepared: Ni… 2+ The concentration is 0.01~0.10 mol / L, Ni 2+ With Al 3+ The molar ratio of urea to total metal ions was 2:1, with urea as a precipitant and a molar ratio of urea to total metal ions of 10:

1. Ammonium fluoride was introduced as a crystal growth regulator, with a molar ratio of ammonium fluoride to urea of ​​1:

7. The hydrolyzed polyacrylonitrile substrate with a surface rich in carboxyl groups was vertically immersed in the hydrothermal growth precursor solution and sealed in a stainless steel reactor lined with polytetrafluoroethylene. The hydrothermal reaction was carried out at 85 °C for 12-30 hours. After the reaction, the substrate was naturally cooled, the composite membrane was removed, and the surface was rinsed with deionized water and dried at room temperature to obtain a NiAl LDH-HPAN composite membrane with a vertically oriented nanosheet array. (2) Cl - Intercalation adjusts the interlayer spacing; The NiAl LDH-HPAN composite membrane obtained in step (1) was immersed in a sodium chloride aqueous solution with a pH of 4.25-5.00 and a concentration of 1 mol / L, and subjected to ion exchange treatment at 50-80 °C for 24 hours. After the exchange was completed, the composite membrane was removed and washed with deionized water until the washing solution was neutral. After drying, NiAl LDH(Cl) with expanded interlayer spacing was obtained. - )-HPAN composite film; (3) Surface amino functionalization modification; A polyethyleneimine impregnation solution containing 0.5–2.0 wt.% was prepared using water and ethanol at a volume ratio of 1:1 as solvents. Epichlorohydrin was used as a crosslinking agent, with a polyethyleneimine to epichlorohydrin mass ratio of 5:

1. The pH of the impregnation solution was adjusted to 6. NiAl LDH(Cl) was then added... - The )-HPAN composite membrane was immersed in the impregnation solution and reacted at 25 ℃ in the dark for 1-3 hours. After the reaction was completed, the composite membrane was removed, thoroughly washed with deionized water and dried to finally obtain the surface-functionalized NiAl LDH(Cl - The PEI-HPAN composite membrane is a vertically oriented LDH-based composite membrane used for H2 purification.

2. The preparation method according to claim 1, characterized in that, The Ni 2+ It is nickel nitrate hexahydrate, Al 3+ It is aluminum nitrate nonahydrate.

3. The preparation method according to claim 1, characterized in that, Step (1), Ni 2+ The concentration was 0.05 mol / L.

4. The preparation method according to claim 1, characterized in that, In step (1), the hydrothermal reaction takes 24 hours.

5. The preparation method according to claim 1, characterized in that, In step (2), the conditions for ion exchange are pH=4.50 and temperature 60 ℃.

6. The preparation method according to claim 1, characterized in that, In step (3), the concentration of polyethyleneimine in the impregnation solution is 1.5 wt.%.

7. The preparation method according to claim 1, characterized in that, In step (3), the reaction time under light-protected conditions is 2.5 hours.

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