A metal hydroxide organic framework composite membrane, a preparation method and application thereof

Abstract

The present application relates to the technical field of composite materials, in particular to a metal hydroxide organic framework composite membrane and a preparation method and application thereof, wherein nickel chloride hexahydrate, terephthalic acid, N, N-dimethylformamide, anhydrous ethanol and deionized water are mixed and dissolved, then poured into a reaction kettle, an AAO membrane with a pore size of 160-200 nm is placed in a mold to make the membrane contact the reaction solution on one side, and the mold is placed in the reaction kettle, and the AAO membrane after reaction in the mold is taken out as the composite membrane. Since the surface of the composite membrane is negatively charged, the composite membrane has good cation selectivity; the MHOF layer with a nanoscale window cavity pore structure can be used as an ion filter and a conductor for enhancing ion selectivity, the passage of ions through the MHOF pore channel can improve the flux of the ions, and the highly ordered AAO nanochannel is an ion storage layer and has the effect of improving ion transmission. The maximum output power density of the composite membrane is higher than that of a commercial application benchmark, and the composite membrane can be applied in salt differential power generation.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, specifically to a metal hydroxide organic framework composite membrane, its preparation method, and its application. Background Technology

[0002] With the growth of the world's population and the development of industry, the demand for energy is constantly increasing, making the search for efficient and environmentally friendly renewable energy sources crucial. Salinity gradient energy, also known as blue energy or osmotic energy, is stored in the salinity gradient between seawater and freshwater or between seawater with different salinity concentrations, containing enormous energy reserves. Compared to other ocean energy sources, it is more stable and has the highest energy density among ocean energy sources. It is a renewable and clean energy source with great development potential, and its potential as a solution to energy problems has attracted widespread attention.

[0003] Porous crystalline materials such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs) have attracted widespread attention in salinity gradient power generation due to their high porosity, unique pore structure, tunable pore size and geometry, and modifiable surfaces. Metal hydroxide organic frameworks (MHOFs) are a novel type of crystalline porous material, generated by the reaction of transition metal oxides and MOFs with layered hydroxides and aromatic carboxylate linkers. Their stability is uniquely enhanced due to strong π-π stacking interactions. These unique properties give them enormous application potential in salinity gradient power generation.

[0004] In recent years, several methods for extracting salinity gradient energy have been proposed, primarily through pressure-delayed osmosis (PRO) and reverse electrodialysis (RED), both based on ion-selective permeation membranes. Previous research indicates that RED, compared to PRO, offers the advantage of directly converting energy from the salinity gradient into electrical energy, resulting in higher energy conversion efficiency. Ion exchange membranes are crucial for extracting salinity gradient energy using RED technology, with ion selectivity and ion flux determining the power density generated during the conversion process. However, commonly used ion exchange membranes for salinity gradient energy extraction in RED technology have several shortcomings that limit their application. These include complex preparation methods, poor mechanical properties, low ion selectivity, excessive internal resistance, low ion flux, and poor stability. These issues lead to lower energy conversion efficiency and power density, failing to meet commercial benchmarks. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a metal hydroxide organic framework composite membrane, its preparation method, and its application.

[0006] The objective of this invention is achieved through the following technical solution: A method for preparing a metal hydroxide organic framework composite membrane, comprising mixing and dissolving nickel chloride hexahydrate, terephthalic acid, N,N-dimethylformamide, anhydrous ethanol and deionized water and pouring the mixture into a reaction vessel, placing an AAO membrane with a pore size of 160-200 nm into a mold in which one side of the membrane is in contact with the reaction solution, and placing the mold containing the AAO membrane into the reaction vessel, reacting at a temperature of 115-130°C for 10-14 h, and removing the AAO membrane after reaction from the mold, which is the metal hydroxide organic framework composite membrane Ni2(OH)2@AAO.

[0007] Furthermore, the weight parts of the reaction raw materials are as follows: nickel chloride hexahydrate: 80-120, terephthalic acid: 80-120, N,N-dimethylformamide: 10-25, anhydrous ethanol: 0.5-1.5, and deionized water: 0.8-1.2.

[0008] Furthermore, the reactor and mold are made of polytetrafluoroethylene.

[0009] Furthermore, the specific operation of placing the AAO membrane into a mold in which one side of the membrane contacts the reaction solution is as follows:

[0010] S1. Mold preparation: Take two PTFE plates of the same size, with a round hole in the middle of one of the PTFE plates; S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front of the film facing the hole, and seal the perimeter of the two plates with PTFE tape.

[0011] Furthermore, the process also includes a post-processing step, specifically: removing the reacted AAO membrane from the mold, rinsing it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immersing the reacted AAO membrane in N,N-dimethylformamide for 1.5–3 hours, then immersing it in an ethanol solution overnight; and finally drying it at a temperature of 45–55°C.

[0012] Furthermore, the reaction solution recovery step is also included, specifically: the reaction solution is poured into a centrifuge tube and centrifuged at 9000-12000 rpm for 4-6 min to collect the light green precipitate. The precipitate is washed with anhydrous ethanol under the same conditions by centrifugation. Finally, the centrifuged and washed precipitate is dried at 60-70℃ for 10-12 h to obtain Ni2(OH)2 powder.

[0013] The metal hydroxide organic framework composite membrane prepared by the above method.

[0014] The above-mentioned metal hydroxide organic framework composite membrane is used in salinity gradient power generation.

[0015] In this invention, salinity gradient energy is obtained by synthesizing a Ni-based MHOF composite film on a porous anodic alumina (AAO) substrate. AAO film fabrication technology is mature, offering a wide range of selectable pore sizes and regularly arranged nanochannels. It serves as a support material for membrane growth while ensuring stable ion transport, and has been widely applied in salinity gradient power generation. Due to the carboxyl groups present on terephthalic acid, the MHOF surface carries a negative charge, resulting in cation selectivity in the Ni2(OH)2@AAO composite film. Furthermore, compared to the original AAO film, the hydrophilicity of the Ni2(OH)2 side of the composite film is significantly improved. The nanoscale windowed pore structure of the MHOF layer can act as an ion filter and a conductor enhancing ion selectivity. Ions passing through the MHOF pore channels have increased flux, and the highly ordered AAO nanochannels serve as an ion storage layer, enhancing ion transport. The prepared Ni2(OH)2@AAO composite membrane, which exhibits asymmetry in structure, pore size, and wettability, achieves a maximum power density of 5.65 W / m³ under a 50-fold KCl concentration gradient (0.5 M / 0.01 M). 2 Above 5.0W / m 2 This is a commercial benchmark. Furthermore, in simulated seawater / river water (0.5M / 0.01M NaCl), the power density can also reach 2.87 W / m³. 2 .

[0016] This invention offers the following advantages: Metal hydroxide organic framework materials (MHOFs) typically exist in powder form, which limits their applications. This invention successfully prepares a Ni-based metal hydroxide organic framework membrane, which, together with an AAO membrane, forms a Ni2(OH)2@AAO composite membrane. This expands the application possibilities of MHOFs in membrane form, and for the first time, it is applied in salinity gradient power generation. Due to its negatively charged surface, it exhibits excellent cation selectivity. The nanoscale windowed pore structure of the MHOF layer can serve as an ion filter and a conductor that enhances ion selectivity. Ions passing through the MHOF pore channels have increased flux, and the highly ordered AAO nanochannels act as an ion storage layer, enhancing ion transport. Under a 50-fold KCl concentration gradient (0.5M / 0.01M), the maximum output power density of the Ni2(OH)2@AAO membrane can reach 5.65 W / m³. 2 Above 5.0W / m 2 The benchmark for commercial applications. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the synthesis of the Ni2(OH)2@AAO composite film prepared by the method of this invention.

[0018] Figure 2 Scanning electron microscope image of the MHOF side of the Ni2(OH)2@AAO composite film prepared in this invention.

[0019] Figure 3 Scanning electron microscope image of the AAO side of the Ni2(OH)2@AAO composite film prepared for this invention.

[0020] Figure 4 This is a scanning electron microscope image of the cross-section of the Ni2(OH)2@AAO composite film prepared in this invention.

[0021] Figure 5 The image shows the EDS energy spectrum of the Ni2(OH)2@AAO composite film prepared in this invention.

[0022] Figure 6 X-ray diffraction patterns of the Ni2(OH)2@AAO composite membrane prepared in this invention, Ni2(OH)2 powder collected in the reactor, and blank AAO membrane.

[0023] Figure 7 Fourier transform infrared spectra of the Ni2(OH)2@AAO composite membrane prepared in this invention, the Ni2(OH)2 powder collected in the reactor, and the blank AAO membrane.

[0024] Figure 8 The contact angles of the Ni2(OH)2@AAO composite film and the blank AAO film prepared in this invention are shown.

[0025] Figure 9 Conductivity diagrams of the Ni2(OH)2@AAO composite membrane prepared in this invention in KCl solutions of different concentrations.

[0026] Figure 10 The graph shows the changes in current density and power density of the Ni2(OH)2@AAO composite film prepared in this invention as a function of external resistance, measured in a 50-fold KCl salinity gradient. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. The scope of protection of the present invention is not limited to the following: Embodiment 1: A method for preparing a metal hydroxide organic framework composite membrane

[0028] (1) Mix and dissolve 80 parts by weight of nickel chloride hexahydrate, 80 parts by weight of terephthalic acid, 10 parts by weight of N,N-dimethylformamide, 0.5 parts by weight of anhydrous ethanol and 0.8 parts by weight of deionized water and pour the mixture into a polytetrafluoroethylene reactor.

[0029] (2) Place an AAO membrane with a pore size of 160-200 nm into a mold in which one side of the membrane is in contact with the reaction solution, and place the mold containing the AAO membrane in a reaction vessel and react at 115°C for 10 h; the specific operation of placing the AAO membrane into the mold in which one side of the membrane is in contact with the reaction solution is as follows:

[0030] S1. Mold preparation: Take two polytetrafluoroethylene (PTFE) sheets of the same size, and make a round hole in the middle of one of the PTFE sheets;

[0031] S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front side of the film facing the opening, and seal the perimeter of the two plates with PTFE tape.

[0032] (3) Take out the AAO membrane after reaction from the mold, rinse it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immerse the AAO membrane in N,N-dimethylformamide for 1.5 h, and then immerse it in ethanol solution overnight; finally dry it at 45 °C to obtain Ni2(OH)2@AAO composite membrane.

[0033] (4) Pour the solution after the reaction into a centrifuge tube, centrifuge at 9000 rpm for 4 min, collect the light green precipitate, wash the precipitate with anhydrous ethanol under the same conditions, and finally dry the precipitate after centrifugation and washing at 60℃ for 10 h to obtain Ni2(OH)2 powder.

[0034] Example 2: A method for preparing a metal hydroxide organic framework composite membrane

[0035] (1) Mix and dissolve 120 parts by weight of nickel chloride hexahydrate, 120 parts by weight of terephthalic acid, 25 parts by weight of N,N-dimethylformamide, 1.5 parts by weight of anhydrous ethanol and 1.2 parts by weight of deionized water and pour the mixture into a polytetrafluoroethylene reactor.

[0036] (2) Place an AAO membrane with a pore size of 160-200 nm into a mold in which one side of the membrane is in contact with the reaction solution, and place the mold containing the AAO membrane in a reaction vessel and react at 130°C for 14 h; the specific operation of placing the AAO membrane into the mold in which one side of the membrane is in contact with the reaction solution is as follows:

[0037] S1. Mold preparation: Take two polytetrafluoroethylene (PTFE) sheets of the same size, and make a round hole in the middle of one of the PTFE sheets;

[0038] S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front side of the film facing the opening, and seal the perimeter of the two plates with PTFE tape.

[0039] (3) Take out the AAO membrane after reaction from the mold, rinse it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immerse the AAO membrane in N,N-dimethylformamide for 3 hours, and then immerse it in ethanol solution overnight; finally dry it at 55°C to obtain Ni2(OH)2@AAO composite membrane.

[0040] (4) Pour the solution after the reaction into a centrifuge tube and centrifuge at 12000 rpm for 6 min to collect the light green precipitate. The precipitate is washed with anhydrous ethanol under the same conditions by centrifugation. Finally, the precipitate after centrifugation and washing is dried at 70℃ for 12 h to obtain Ni2(OH)2 powder.

[0041] Example 3: A method for preparing a metal hydroxide organic framework composite membrane

[0042] (1) Mix and dissolve 95 parts by weight of nickel chloride hexahydrate, 90 parts by weight of terephthalic acid, 15 parts by weight of N,N-dimethylformamide, 0.8 parts by weight of anhydrous ethanol and 1 part by weight of deionized water and pour the mixture into a polytetrafluoroethylene reactor.

[0043] (2) Place an AAO membrane with a pore size of 160-200 nm into a mold in which one side of the membrane is in contact with the reaction solution, and place the mold containing the AAO membrane into a reaction vessel. React at 120°C for 12 hours. The specific operation of placing the AAO membrane into the mold in which one side of the membrane is in contact with the reaction solution is as follows:

[0044] S1. Mold preparation: Take two polytetrafluoroethylene (PTFE) sheets of the same size, and make a round hole in the middle of one of the PTFE sheets;

[0045] S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front side of the film facing the opening, and seal the perimeter of the two plates with PTFE tape.

[0046] (3) Take out the AAO membrane after reaction from the mold, rinse it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immerse the AAO membrane in N,N-dimethylformamide for 2 hours, and then immerse it in ethanol solution overnight; finally dry it at 48°C to obtain Ni2(OH)2@AAO composite membrane.

[0047] (4) Pour the solution after the reaction into a centrifuge tube, centrifuge at 10,000 rpm for 5 min, collect the light green precipitate, wash the precipitate with anhydrous ethanol under the same conditions, and finally dry the precipitate after centrifugation and washing at 65℃ for 11 h to obtain Ni2(OH)2 powder.

[0048] Example 4: A method for preparing a metal hydroxide organic framework composite membrane

[0049] (5) Mix and dissolve 110 parts by weight of nickel chloride hexahydrate, 108 parts by weight of terephthalic acid, 22 parts by weight of N,N-dimethylformamide, 1.2 parts by weight of anhydrous ethanol and 1.1 parts by weight of deionized water and pour the mixture into a polytetrafluoroethylene reactor.

[0050] (6) Place an AAO membrane with a pore size of 160-200 nm into a mold in which one side of the membrane is in contact with the reaction solution, and place the mold containing the AAO membrane in a reaction vessel. React at 125°C for 13.5 h. The specific operation of placing the AAO membrane into the mold in which one side of the membrane is in contact with the reaction solution is as follows:

[0051] S1. Mold preparation: Take two polytetrafluoroethylene (PTFE) sheets of the same size, and make a round hole in the middle of one of the PTFE sheets;

[0052] S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front side of the film facing the opening, and seal the perimeter of the two plates with PTFE tape.

[0053] (7) Take out the AAO membrane after reaction from the mold, rinse it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immerse the AAO membrane in N,N-dimethylformamide for 2.5 h, and then immerse it in ethanol solution overnight; finally dry it at 52 °C to obtain Ni2(OH)2@AAO metal hydroxide organic framework composite membrane.

[0054] (8) Pour the solution after the reaction into a centrifuge tube, centrifuge at 11000 rpm for 5.5 min, collect the light green precipitate, wash the precipitate with anhydrous ethanol under the same conditions, and finally dry the precipitate after centrifugation and washing at 68℃ for 11 h to obtain Ni2(OH)2 powder.

[0055] The following experiments illustrate the beneficial effects of this invention:

[0056] 1. Preparation of Ni2(OH)2@AAO composite film:

[0057] First, a mixture of 0.1 g nickel chloride hexahydrate, 0.1 g terephthalic acid, 16 mL N,N-dimethylformamide, 1 mL anhydrous ethanol, and 1 mL deionized water was ultrasonically dissolved for 30 min. Then, the mixture was poured into a 100 mL polytetrafluoroethylene (PTFE) reactor. An AAO membrane with a pore size of 160-200 nm was ultrasonically cleaned with anhydrous ethanol and deionized water. Two PTFE plates of the same size were taken, one of which had a circular hole in the center. The AAO membrane was cut to the same size as the PTFE plate and cleaned with anhydrous ethanol and deionized water. The AAO membrane was placed between the two PTFE plates, with the front side facing the hole, and sealed with PTFE tape to ensure that only one side of the AAO membrane was in contact with the reaction solution. The reactor was then placed in the reactor and heated at 120 °C for 12 hours. After cooling to room temperature, the composite membrane was removed and repeatedly rinsed with N,N-dimethylformamide and anhydrous ethanol. The membrane was then immersed in N,N-dimethylformamide for 2 hours, followed by immersion in an ethanol solution overnight. Finally, it was dried at 50°C to obtain the Ni2(OH)2@AAO composite membrane. A schematic diagram of the synthesis of the Ni2(OH)2@AAO composite membrane is shown below. Figure 1 As shown.

[0058] The hydrothermal solution after the reaction was poured into a centrifuge tube and centrifuged at 10,000 rpm for 5 min to collect a light green precipitate. The precipitate was then washed three times with anhydrous ethanol under the same conditions. Finally, the precipitate obtained after centrifugation was placed in an oven and dried overnight at 65°C to obtain Ni2(OH)2 powder.

[0059] The Ni2(OH)2@AAO composite film prepared above was subjected to electron microscopy scanning of the MHOF side, as shown below. Figure 2 As shown in the figure, it can be observed that the MHOF side (upper surface) of the composite film is an MHOF layer composed of stacked nanoflower-like structures formed by nanosheets.

[0060] The Ni2(OH)2@AAO composite film prepared above was subjected to electron microscopy scanning of the AAO side, as shown below. Figure 3 As shown, from Figure 3 It can be seen that no MHOF growth is observed on the AAO side (lower surface) of the composite membrane, confirming that MHOF has achieved unilateral growth on the AAO membrane.

[0061] The Ni2(OH)2@AAO composite film prepared above was subjected to brittle fracture in liquid nitrogen, and the cross-section was scanned by electron microscopy, as shown below. Figure 4 As shown, from Figure 4 It can be seen that Ni2(OH)2 grows on the AAO film into a uniform nanosheet structure stacked together, and the AAO pore structure is not destroyed and is arranged in a regular manner.

[0062] The Ni2(OH)2@AAO composite film prepared above was subjected to EDS analysis, as follows: Figure 5 As shown, from Figure 5 It can be seen that Ni, Cl, Al, O and C elements are uniformly distributed on the surface of the composite film.

[0063] The Ni2(OH)2@AAO composite film prepared above, the Ni2(OH)2 powder prepared by recovering the reaction solution, and the blank AAO film were subjected to X-ray diffraction. The results are as follows: Figure 6 As shown. From Figure 6 It can be seen that the synthesized composite film has the characteristic diffraction peaks of both Ni2(OH)2 powder and blank AAO film, which also confirms the successful synthesis of Ni2(OH)2 on the surface of AAO film.

[0064] The Ni2(OH)2@AAO composite film prepared above, the Ni2(OH)2 powder prepared by recovering the reaction solution, and the blank AAO film were subjected to Fourier transform infrared spectroscopy tests, and the results are as follows. Figure 7 As stated. From Figure 7 It can be seen that at 3598 and 3529cm -1 The wavelengths present at these locations correspond to the stretching vibrations of the -OH group. At 1583 and 1363 cm⁻¹... -1 The strong peaks appearing at these locations are attributed to the presence of -COO in terephthalic acid. - Antisymmetric and symmetric stretching vibrations. 1150, 1091, 1022, 815 cm -1 The peak at 2351 cm⁻¹ is related to the vibration of aromatic CH groups. (2351 cm⁻¹ on Ni₂(OH)₂@AAO composite film) -1 The peak at that location corresponds to the AAO film, indicating the successful preparation of the Ni2(OH)2@AAO composite film.

[0065] The contact angles of the Ni2(OH)2@AAO composite film and the blank AAO film prepared above were measured, and the experimental results are as follows: Figure 8 As shown, from Figure 8 As can be seen, the contact angle of the blank AAO membrane is 80.3°, while the contact angle of the Ni2(OH)2@AAO composite membrane is significantly reduced to 12.1°. This greatly improves the hydrophilicity of the membrane, thereby increasing water flux and ion transport.

[0066] 2. Salinity gradient power generation test

[0067] The salinity gradient power generation test of the Ni2(OH)2@AAO composite membrane of this invention was performed using a Keithley 6487 picoammeter. The prepared Ni2(OH)2@AAO composite membrane was installed between electrolytic cells, and Ag / AgCl electrodes were inserted into the cells. Equal volumes of 0.5M and 0.01M KCl solutions were injected into the MHOF and AAO sides, respectively, and an external load resistor was connected for current measurement. The effective test area of ​​the membrane during testing was 0.03 mm². 2 .

[0068] The conductivity of the Ni2(OH)2@AAO composite film in KCl solutions of different concentrations is as follows: Figure 9 As shown in the figure, at high concentrations (>0.1 M), the conductivity fits the volume value well. When the concentration is below 0.1 M, the conductivity value begins to gradually deviate from the volume value (dashed line). At low concentrations, the transmembrane ion transport is higher than the bulk ion conduction, indicating that the transmembrane ion transport behavior in the Ni2(OH)2@AAO membrane is controlled by the surface charge.

[0069] The current density and power density of the Ni2(OH)2@AAO composite membrane as a function of external resistance, measured in a 50-fold KCl salinity gradient, are as follows: Figure 10 As shown in the figure, the current density of the composite membrane measured in a 50-fold KCl salinity gradient decreases continuously with increasing load resistance, while the power density initially increases and then decreases with increasing resistance. The power density reaches its maximum value of 5.65 W / m² when the applied resistance equals the membrane's internal resistance. 2 .

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, are covered within the scope of protection of the present invention.

Claims

1. A method for preparing a metal hydroxide organic framework composite membrane, characterized in that, Nickel chloride hexahydrate, terephthalic acid, N,N-dimethylformamide, anhydrous ethanol, and deionized water are mixed and dissolved, and then poured into a reaction vessel. An AAO membrane with a pore size of 160-200 nm is placed in a mold in which one side of the membrane is in contact with the reaction solution. The mold containing the AAO membrane is then placed in the reaction vessel and reacted at a temperature of 115-130°C for 10-14 hours. The AAO membrane after reaction is removed from the mold, which is the metal hydroxide organic framework composite membrane Ni2(OH)2@AAO.

2. The method for preparing a metal hydroxide organic framework composite membrane according to claim 1, characterized in that, The reactants are in the following weight proportions: nickel chloride hexahydrate: 80-120, terephthalic acid: 80-120, N,N-dimethylformamide: 10-25, anhydrous ethanol: 0.5-1.5, and deionized water: 0.8-1.

2.

3. The method for preparing a metal hydroxide organic framework composite membrane according to claim 1, characterized in that, The reactor and mold are made of polytetrafluoroethylene.

4. The method for preparing a metal hydroxide organic framework composite membrane according to claim 1, characterized in that, The specific operation of placing the AAO membrane into a mold in which one side of the membrane contacts the reaction solution is as follows: S1. Mold preparation: Take two polytetrafluoroethylene (PTFE) sheets of the same size, and make a round hole in the middle of one of the PTFE sheets; S2. Encapsulation: Cut the AAO film to the same size as the PTFE plate, and wash it clean with anhydrous ethanol and deionized water respectively; place the AAO film between the two PTFE plates, with the front side of the film facing the opening, and seal the perimeter of the two plates with PTFE tape.

5. The method for preparing a metal hydroxide organic framework composite membrane according to claim 1, characterized in that, The process also includes a post-processing step, specifically: removing the reacted AAO membrane from the mold, rinsing it repeatedly with N,N-dimethylformamide and anhydrous ethanol, immersing the reacted AAO membrane in N,N-dimethylformamide for 1.5–3 hours, then immersing it in an ethanol solution overnight; and finally drying it at a temperature of 45–55°C.

6. The method for preparing a metal hydroxide organic framework composite membrane according to claim 1, characterized in that, The reaction solution recovery step is also included, specifically: the solution after reaction is poured into a centrifuge tube and centrifuged at 9000-12000 rpm for 4-6 min to collect the light green precipitate. The precipitate is washed with anhydrous ethanol under the same conditions by centrifugation. Finally, the centrifuged and washed precipitate is dried at 60-70℃ for 10-12 h to obtain Ni2(OH)2 powder.

7. The metal hydroxide organic framework composite membrane prepared by the method according to any one of claims 1-6.

8. The application of the metal hydroxide organic framework composite membrane according to claim 7 in salinity gradient power generation.

Images