A positive hetero film and preparation and application thereof

Abstract

The application is a preparation and application of a hetero film composed of a positive metal organic framework (MOF) monolayer film and a porous anodic aluminum oxide (AAO) film. The method adopted is: a macromolecular chain transfer agent is grafted to the surface of MOF particles through post-synthesis modification; a polymer is grafted to the surface of MOF particles through a surface-initiated reversible addition-fragmentation chain transfer polymerization reaction of methyl methacrylate and 1-vinylimidazole; the MOF particles are self-assembled to form a dense MOF monolayer (SAMM) film at a water-air interface; the prepared SAMM film is covered on one side of the AAO film to form a hetero film, and the permeation energy collection performance is detected. The application realizes the first application of the SAMM film in the field of permeation energy collection, and provides a new method for preparing an ion exchange film material with high ion selectivity and permeability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of material chemistry. Specifically, it relates to a method for preparing a hetero film formed by combining a positively charged self-assembled MOF monolayer (SAMM) film self-assembled from functional polymer-coated metal-organic framework (MOF) nanoparticles and a porous anodic aluminum oxide (AAO) film, and the application of the hetero film in the field of osmotic energy harvesting. BACKGROUND

[0002] Under the background of continuous consumption of fossil fuels and increasing demand for energy, developing sustainable and environmentally friendly energy has become a research hotspot. Osmotic energy, also known as salinity gradient energy, is the energy generated by the salinity difference between seawater and river water. It is widely considered as an important blue energy because of its easy accessibility and abundant reserves. Reverse electrodialysis (RED) is a process that directly harvests energy from a salinity gradient through ion-selective membranes, so it has great potential in harvesting osmotic energy. However, the traditional ion exchange membranes used in the RED process have limitations such as poor ion selectivity, insufficient mass transfer, and high membrane resistance, which result in low output power. In order to improve the performance of osmotic energy harvesting, researchers have developed two-dimensional (2D) nanofluidic channels, such as graphene, molybdenum disulfide (MoS2), MXene, boron nitride, and black phosphorus. These nanochannels can promote effective ion transport in the plane direction. However, their poor performance in the transmembrane direction makes this 2D nanofluidic channel impractical for osmotic energy conversion applications. Recently, membranes containing single nanopores, such as single boron nitride nanotubes, single MoS2 nanopores, and single polyethylene terephthalate / polyimide nanopores, have improved the energy density to a new level. However, it is very difficult to prepare such membranes on a macroscopic scale.

[0003] MOFs are a special class of porous crystalline materials with narrow and ordered channel distribution, high specific surface area, and customizable surface properties, which have become promising materials in the fields of energy and environment. The three-dimensionally interconnected sub-nanometer channels endow MOF-based membrane materials with great hope to achieve breakthroughs in both high ion selectivity and permeability. However, despite these advantages, there is still a lack of simple, mild, and flexible methods for preparing dense, crack-free, and ultrathin MOF films.

[0004] SAMM membrane was first proposed by Cohen's group in 2019, which is formed by self-assembly of MOF nanoparticles. It is a dense, highly ordered, large-area, independent monolayer film, and has nanoscale thickness and extremely high MOF loading. This SAMM membrane maintains the characteristics of MOF materials, and due to its ultra-thin thickness, it shows a shorter mass transfer path, so it avoids the trade-off between "permeability-selectivity", and shows broad application potential in the field of osmotic energy harvesting. Although several SAMM membranes have been reported, the fragility of these films prevents further processing, and the lack of functional groups on the films hinders their practical application. In addition, functional modification of SAMM membrane may destroy its dense structure, resulting in larger defects in the film. Therefore, it is still a great challenge to prepare functionalized SAMM membrane and promote its practical application under the premise of ensuring the integrity of SAMM membrane. SUMMARY

[0005] The present application aims to design and prepare a positively charged hetero-membrane. The method adopted is to cover the SAMM membrane formed by self-assembly of functional polymer coated UiO-66-NH2 nanoparticles at the water-air interface on one side of the porous AAO membrane to prepare a positively charged hetero-membrane. The SAMM membrane prepared in the present application is a large-area, dense, extremely thin film, and the hetero-membrane formed by combining with the AAO membrane has high ion selectivity and permeability, providing a new scheme for preparing other functional SAMM membranes.

[0006] Another object of the present application is to provide an application scheme of the above-mentioned positively charged hetero-membrane in the field of osmotic energy harvesting. The method adopted is to fix the hetero-membrane on a self-made electrochemical device, apply voltage through Ag / AgCl electrode, and then use a picoammeter to record the current. This hetero-membrane realizes a maximum output power of 2.99 W / m 2 under a 50-fold NaCl gradient, providing a new idea for preparing new ion exchange membranes with high osmotic energy harvesting performance.

[0007] The object of the present application is achieved by the following scheme:

[0008] A positively charged hetero-membrane, characterized in that the SAMM membrane formed by functional polymer modified MOF particles at the water-air interface is transferred to the surface of the porous AAO membrane to prepare a hetero-membrane. The specific steps are as follows:

[0009] (1) Preparation of monodispersed UiO-66-NH2 nanoparticles: ZrCl4, 2- aminoterephthalic acid and 45 mL of DMF were mixed in a container. The mixture was sonicated for 15 min until the solid was completely dissolved. Then, glacial acetic acid was added to the above mixed solution, where the molar ratio of the reagents was ZrCl4:2-aminoterephthalic acid:glacial acetic acid = 1:1:30. After the mixture was stirred for 15 min, it was transferred to a polytetrafluoroethylene-lined stainless steel autoclave with a capacity of 100 mL and placed in an oven with a constant temperature of 120 °C for 24 h. After the reaction was completed, the reactor was allowed to cool to room temperature naturally, opened, and the product was centrifuged (8000 rpm, 10 min). The obtained solid was washed with DMF and methanol in turn. The washed solid was placed in a vacuum drying oven with a temperature setting of 40 °C for drying for 12 h to obtain the product UiO-66-NH2.

[0010] (2) Preparation of the macro-CTA: 4-cyano-4-[[(dodecylsulfanyl)thiocarbonyl]thio]pentanoic acid, N-hydroxysuccinimide and 40 mL of dry dichloromethane were mixed in a reaction bottle. After stirring in an ice water bath for 60 min, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide was added, where the molar ratio of the reagents was 4-cyano-4-[[(dodecylsulfanyl)thiocarbonyl]thio]pentanoic acid:N-hydroxysuccinimide:1-(3-dimethylaminopropyl)-3-ethylcarbodiimide = 1:1.5:1.6. Then the mixture was stirred at room temperature for 12 h. After the reaction was completed, the product was washed with dilute hydrochloric acid, saturated NaHCO3 and deionized water in turn, and the product in the aqueous solution was extracted with dichloromethane. Then the dichloromethane solution was dried with anhydrous MgSO4 for 20 min. The dried solution was filtered and concentrated, and the crude product was purified by a silica gel column with a mixture of petroleum ether and ethyl acetate (2:1 by volume) as the eluent.

[0011] The above purified product (NSH-CTA), dopamine hydrochloride and 40 mL of dry tetrahydrofuran were mixed in a reaction bottle. After stirring in an ice water bath for 60 min, triethylamine was added, where the molar ratio of the reagents was NSH-CTA:dopamine hydrochloride:triethylamine = 1:1.1:1.1. Then the mixture was stirred at room temperature for 12 h. After the reaction was completed, the solvent was rotary evaporated, and the crude product was dissolved in dichloromethane. The product was washed with dilute hydrochloric acid and deionized water in turn, and the product in the aqueous solution was extracted with dichloromethane. Then the dichloromethane solution was dried with anhydrous MgSO4 for 20 min. The dried solution was filtered and concentrated, and the crude product was purified by a silica gel column with a mixture of petroleum ether and ethyl acetate (1:1 by volume) as the eluent. The purified product was placed in a vacuum drying oven with a temperature setting of 40 °C for drying for 12 h to obtain the product cat-CTA.

[0012] (3) Preparation of macromolecular chain transfer agent modified UiO-66-NH2(UiO-66-NH2-CTA): UiO-66-NH2, cat-CTA and DMF were mixed in a reaction bottle, and the molar ratio of reagents was UiO-66-NH2: cat-CTA = 1:6. The mixture was ultrasonicated for 30 min until the solid was completely dispersed. Then the reaction bottle was placed in an oil bath pot with a constant temperature of 100°C for 4h. After the reaction was completed, the product was cooled to room temperature, centrifuged (8000 rpm, 10 min), and the obtained solid was sequentially washed with DMF and methanol, and then placed in a vacuum drying box with a temperature setting of 40°C for drying for 12h to obtain the product UiO-66-NH2-CTA.

[0013] (4) Preparation of polymer coated UiO-66-NH2(UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ): UiO-66-NH2-CTA was mixed with DMF in a container, and then methyl methacrylate (MMA), 1-vinylimidazole (VIM) and 2,2'-azobisisobutyronitrile (AIBN) were sequentially added, and the molar ratio of reagents was CTA: MMA: VIM: AIBN = 1:40000:400:1. The mixture was frozen with liquid nitrogen for 15 min, pumped with an oil pump for 5 min, and then naturally thawed at room temperature. After 3 cycles of freezing-pumping-thawing, the mixture was placed in an oil bath pot with a constant temperature of 70°C for 24h. After the reaction was completed, the crude product was centrifuged (8000 rpm, 10 min), and the obtained solid was washed with DMF and then toluene. The product was placed in a vacuum drying box with a temperature setting of 60°C for drying for 12h to obtain the product UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ).

[0014] (5) 50mg of UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ) nanoparticles were mixed with 1mL of toluene in a small glass bottle, and then ultrasonicated for 40min. 10μL of the above MOF solution was taken and dropped into a petri dish with a diameter of 35mm and a water depth of 1cm. After being placed at room temperature for 3min, the toluene was completely volatilized, and a SAMM film was formed on the water surface. A porous AAO membrane (pore size range 20-30nm, pore density about 1.0×10 12 pores / cm 2) Immersed the water under the SAMM membrane, slowly moved to the water surface in the direction of AAO side parallel to the water surface until the SAMM completely covered on the AAO membrane, that is, formed a composite membrane. The composite membrane was placed in a culture dish with a cover, dried at room temperature for 24 h to form a hetero membrane.

[0015] The application provides an application scheme of a positive hetero membrane in the field of osmotic energy collection, and specific steps are as follows:

[0016] The hetero membrane and a silicon wafer with a central hole with an area of 0.004mm 2 were fixed between two modules of a self-made electrochemical device, 1mL of 500mM NaCl solution was added into a flow-through groove on the SAMM side, 1mL of 10mM NaCl solution was added into a flow-through groove on the silicon wafer side, an Ag / AgCl electrode was inserted into each electrolyte solution, a voltage was applied through the electrode, and a picoammeter was used to record the current.

[0017] The method adopted in the application is: cat-CTA is grafted to the surface of UiO-66-NH2 particles through post-synthesis modification; functional polymers are grafted to the surface of UiO-66-NH2 particles through surface-initiated reversible addition-fragmentation chain transfer reaction of MMA and VIM; the functional polymer-coated MOF particles are self-assembled into a dense SAMM membrane at a water-air interface; the prepared SAMM membrane is covered on one side of a porous AAO membrane to form a hetero membrane, and the osmotic energy collection performance of the hetero membrane is detected.

[0018] The application not only provides a new method for preparing a large-area, dense and extremely thin functionalized MOF single-layer membrane, but also provides a new idea for preparing an ion exchange membrane material with high osmotic energy collection efficiency.

[0019] The application realizes the first application of the SAMM membrane in the field of osmotic energy collection, and provides a new method for preparing an ion exchange membrane material with high ion selectivity and permeability.

[0020] The application has the following beneficial effects:

[0021] (1) The positive MOF single-layer membrane prepared by the water-air interface technology provides a new scheme for preparing a functionalized MOF single-layer membrane;

[0022] (2) The positive hetero membrane prepared by combining the prepared positive MOF single-layer membrane with a porous AAO membrane provides a new idea for preparing a new type of ion exchange membrane material with high osmotic energy collection efficiency. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. Other related drawings can also be obtained by those of ordinary skill in the art without creative labor on the basis of these drawings.

[0024] Figure 1 SEM image of monodisperse UiO-66-NH2nanoparticles;

[0025] Figure 2 SEM image of cat-CTA 1 HNMR spectrum;

[0026] Figure 3 HNMR spectrum of UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 acidolysis product; 1 HNMR spectrum;

[0027] Figure 4 Cross-sectional SEM image of SAMM membrane;

[0028] Figure 5 SEM images of AAO substrate (a) and hetero-membrane (b, c);

[0029] Figure 6 Current density (open symbols) and power density (closed symbols) collected for hetero-membranes under 50-fold NaCl gradient;

[0030] Figure 7 Schematic of the current test device module.

[0031] Figure 8 Schematic of the film fabrication and testing process of the present application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely as follows.

[0033] 4-Cyano-4-[[(dodecylthio)thiocarbonyl]thio]pentanoic acid (97%) was purchased from Shanghai Myrel Biochemical Technology Co., Ltd. N-hydroxysuccinimide (98%), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, ZrCl4 (98%), dopamine hydrochloride (98%), 2-aminoterephthalic acid (98%), VIM (99%), and AIBN (98%) were purchased from Aladdin Reagent (Shanghai) Co., Ltd. MMA (99%) was purchased from Alfa Aesar (China) Chemical Co., Ltd. Porous AAO membrane was purchased from Hefei Jinghui Nanotechnology Co., Ltd. H NMR spectrum ( 1 H NMR spectra were recorded using a Bruker Avance III 400 MHz spectrometer. Scanning electron microscopy (SEM) images were recorded using a Flex SEM 1000 II scanning electron microscope. I–V curves were recorded using a Keithley 6487 picoammeter. Unless otherwise specified in the examples, conventional conditions or manufacturer recommendations were followed. All reagents and instruments used, unless the manufacturer is specified, are commercially available.

[0034] Example 1

[0035] Preparation of monodispersed UiO-66-NH2 nanoparticles

[0036] SEM images of monodispersed UiO-66-NH2 nanoparticles are shown in Figure 2. Figure 1 As shown in the figure, it can be seen that UiO-66-NH2 nanoparticles exist in a single dispersed form, and their particle size is 130±30nm.

[0037] Specific process: ZrCl4 (183 mg), 2-aminoterephthalic acid (143 mg) and 45 mL N, N-dimethylformamide (DMF) were mixed in a container. After the mixture was ultrasonicated for 15 minutes until the solid was completely dissolved, glacial acetic acid (1.36 mL) was added to the above mixed solution. After the mixture was stirred for 15 minutes, it was transferred to a polytetrafluoroethylene-lined stainless steel autoclave with a capacity of 100 mL and placed in an oven with a constant temperature of 120 ° C for 24 hours. After the reaction was completed, the reactor was allowed to cool naturally to room temperature and then opened. The product was centrifuged (8000 rpm, 10 min), and the obtained solid was washed with DMF and methanol in turn. The washed solid was placed in a vacuum drying oven set at a temperature of 40 ° C and dried for 12 hours to obtain the product UiO-66-NH2, whose pore size is The total pore volume is 0.2-0.3cm 3 / g.

[0038] Example 2

[0039] Preparation of cat-CTA

[0040] cat-CTA 1 H NMR spectra are shown in Figure 2, from which the chemical shifts and integral areas of the corresponding proton absorption peaks in cat-CTA can be seen, proving the successful synthesis of cat-CTA. Figure 2

[0041] Specific process: 4-cyano-4-[[(dodecylsulfanyl)thiocarbonyl]thio]pentanoic acid (1.0 g), N-hydroxysuccinimide (428 mg) and 40 mL of dry dichloromethane were mixed in a reaction bottle. After stirring in an ice water bath for 60 min, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (760 mg) was added, and then the mixture was stirred at room temperature for 12 h. After the reaction was completed, the product was sequentially washed with dilute hydrochloric acid (1 M), saturated NaHC03 and deionized water, and the product in the aqueous solution was extracted with dichloromethane, followed by drying the dichloromethane solution with anhydrous MgS04 for 20 min. The dried solution was filtered, concentrated to a solution volume of 0.5 mL, and the crude product was purified by a silica gel column (silica gel particle size 200-300 mesh) with an eluent of a mixture of petroleum ether and ethyl acetate at a volume ratio of 2:1 to obtain the product NHS-CTA.

[0042] NSH-CTA (1.0 g), dopamine hydrochloride (417 mg) and 40 mL of dry tetrahydrofuran were mixed in a reaction bottle. After stirring in an ice water bath for 60 min, triethylamine (306 μL) was added, and then the mixture was stirred at room temperature for 12 h. After the reaction was completed, the solvent was evaporated by a rotary evaporator, and the crude product was dissolved in dichloromethane and sequentially washed with dilute hydrochloric acid (1 M) and deionized water, and the product in the aqueous solution was extracted with dichloromethane, followed by drying the dichloromethane solution with anhydrous MgS04 for 20 min. The dried solution was filtered, concentrated to a solution volume of 0.5 mL, and the crude product was purified by a silica gel column (silica gel particle size 200-300 mesh) with an eluent of a mixture of petroleum ether and ethyl acetate at a volume ratio of 1:1. The purified product was dried in a vacuum drying oven with a temperature setting of 40°C for 12 h to obtain the product cat-CTA.

[0043] Example 3

[0044] Preparation of UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 )

[0045] Acidolysis product of UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ) 1 H NMR spectra are shown in Figure 2, from which the chemical shifts and integral areas of the corresponding proton absorption peaks in cat-CTA can be seen, proving the successful synthesis of cat-CTA. Figure 3 ​The content of imidazole groups in the copolymer was calculated to be about 1 mol% from the integral area of the proton peaks in the figure.

[0046] Specific process: 1) UiO-66-NH2(100 mg) obtained in Example 1, cat-CTA (144 mg) obtained in Example 2 and 40 mL DMF were mixed in a reaction bottle, and the mixture was ultrasonicated for 30 min until the solid was completely dispersed. Then the reaction bottle was placed in an oil bath pot with a constant temperature of 100°C for reaction for 4 h. After the reaction was completed, the product was cooled to room temperature, and then centrifuged (8000 rpm, 10 min). The obtained solid was washed with DMF and methanol successively, and then placed in a vacuum drying box with a temperature setting of 40°C for drying for 12 h to obtain the product UiO-66-NH2-CTA.

[0047] 2) UiO-66-NH2-CTA (100 mg) was mixed with 100 mL DMF in a container, and ultrasonicated for 30 min until the solid was completely dispersed. Then MMA (20 mL), VIM (174 μL) and AIBN (10 mg·mL -1 , 76 μL) were added successively. The mixture was frozen with liquid nitrogen for 15 min, and then pumped with an oil pump (pressure range of 3-5 Mpa) for 5 min, and then naturally thawed at room temperature. After the above freezing-pumping-thawing operation was repeated for 3 times, the mixture was placed in an oil bath pot with a constant temperature of 70°C for reaction for 24 h. After the reaction was completed, the crude product was centrifuged (8000 rpm, 10 min), and the obtained solid was washed with DMF and then toluene. The product was placed in a vacuum drying box with a temperature setting of 60°C for drying for 12 h to obtain the product UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ) (particle size of 160±30 nm).

[0048] 3) 20.0 mg of dried UiO-66-NH2-P(MMA 0.99 -co-VIM 0.01 ) particles were immersed in a mixed solvent of 500 μL of methanol and 6 μL of HF solution (48% by mass aqueous solution), and then the mixture was ultrasonicated for 20 min. The obtained precipitate was collected by centrifugation (8000 rpm, 5 min), and the obtained solid was washed with 30 mL of methanol for 3 times and then with 10 mL of toluene for 1 time, and then placed in a vacuum drying box with a temperature setting of 60°C for drying for 12 h to obtain the acidolysis product P(MMA-co-VIM).

[0049] Example 4

[0050] Preparation of SAMM membrane

[0051] The SEM image of the SAMM membrane is as follows:Figure 4 As shown in Figure a, the curled film can be seen, and the dense arrangement of nanoparticles on the surface of the film can be seen from Figure b. The calculated film thickness is about 160nm, indicating that the SAMM film is a dense film formed by the dense stacking of single-layer MOF nanoparticles.

[0052] Specific process: 50 mg of UiO-66-NH2-P(MMA prepared in Example 3 0.99 -co-VIM 0.01 ) nanoparticles were mixed with 1 mL of toluene in a small glass bottle and then ultrasonicated for 40 min to obtain MOF dispersion.

[0053] Take 10 μL of the above MOF dispersion and drop it into a culture dish filled with water with a diameter of 35 mm and a water depth of 1 cm. After leaving it at room temperature for 3 minutes, a SAMM film with a diameter of about 30 mm is formed on the water surface.

[0054] Example 5

[0055] Preparation of heterogeneous membranes

[0056] SEM images of AAO and heterogeneous membranes are shown in Figure 2. Figure 5 As shown in the figure, it can be seen that the SAMM membrane in the heterogeneous membrane completely covers the opening of the AAO membrane. The thickness of the upper SAMM membrane is calculated from the cross-sectional SEM image to be about 160nm, which is consistent with the thickness of the single-layer SAMM, indicating that only one layer of SAMM membrane is covered on the AAO substrate. Due to the positive charge of the AAO membrane itself, it has weak osmotic energy conversion performance, so we choose porous AAO as the substrate of the heterogeneous membrane. At the same time, we compared the output power of AAO membranes with different pore sizes under simulated seawater and river water salinity gradients. The specific process is: four porous AAO membranes with different pore sizes (pore size range of 20-30nm (pore density of 1.0×10 12 pores / cm 2 , membrane thickness is 60 μm), 40-70 nm (pore density is 8.0×10 11 pores / cm 2 , membrane thickness is 100 μm), 80-100 nm (pore density is 5.0×10 11 pores / cm 2 , membrane thickness is 100 μm), 110-150 nm (pore density is 1.0×10 11 pores / cm 2 , the membrane thickness is 120μm)) and the central hole area is 0.004mm 2The silicon wafer layers are fixed together between two modules of the current test device (the actual test area is the hole area on the silicon wafer), and the two modules on both sides of the membrane are provided with corresponding through holes as flow channels, and the ports of the two flow channels are arranged on the opposite sides of the membrane. Add 1 mL of 500 mM NaCl solution to the flow channel on one side of the AAO membrane, and add 1 mL of 10 mM NaCl solution to the flow channel on the other side of the silicon wafer. Put Ag / AgCl electrodes into the electrolyte solution in the two flow channels, apply a scanning voltage of -0.2V to +0.2V as the transmembrane potential through the electrodes, and record the ionic current generated by the solution in the two flow channels using a picoammeter. We found that the output power densities of the four AAO membranes were 0.37 W / m 2 (20-30 nm in diameter), 0.12 W / m 2 (40-70 nm in diameter), 0.10 W / m 2 (80-100 nm in diameter), and 0.09 W / m 2 (110-150 nm in diameter), so we chose the relatively better AAO membrane (20-30 nm in diameter, 1.0×10 12 pores / cm 2 , and 60 μm in thickness) as the substrate to prepare a hetero membrane by combining with the SAMM membrane.

[0057] Specific process: After the SAMM membrane of Example 4 is formed on the water surface, immerse the AAO membrane in the water under the SAMM, and slowly move it towards the water surface in a manner that the side of the AAO is parallel to the water surface until the SAMM completely covers the AAO. Place the composite membrane in a culture dish with a cover, and dry it at room temperature for 24 h to form a hetero membrane.

[0058] Example 6

[0059] Permeation energy collection performance test of the hetero membrane

[0060] The current density and power density curves of the hetero membrane obtained in Example 5 under a 50-fold NaCl gradient and the schematic diagram of the modules in the current test device are shown in Figure 6 , Figure 7 As can be seen from the figures, the hetero membrane can produce a maximum current density of 215 A / m 2 and a maximum power density of 2.99 W / m 2 under the salinity gradient of simulated seawater and river water, which proves that the hetero membrane has a broad application prospect in the field of permeation energy collection. In addition, we conducted two control experiments to test the permeation energy conversion performance of the AAO substrate and the hetero membrane without imidazole groups, respectively, and the output powers were 0.37 W / m 2 and 1.59 W / m 2By comparison, it was found that compared with the AAO substrate, the output power of both heterogeneous membranes under a 50-fold NaCl gradient increased, and the power increase of the heterogeneous membrane containing imidazole groups was greater, indicating that the introduction of imidazole groups into the SAMM membrane can further enhance the osmotic energy conversion performance of the heterogeneous membrane.

[0061] Specific process: Polymethyl methacrylate (PMMA) was grafted onto the surface of UiO-66-NH2 particles by the method described in Example 3 to prepare UiO-66-NH2-PMMA particles (particle size was 160±30 nm, and the difference from Example 3 was that VIM was not added in step (2), and only MMA (20 mL) was added as a monomer for polymerization reaction). UiO-66-NH2-P(MMA) was grafted onto the surface of UiO-66-NH2 particles by the method described in Example 4 (the difference from Example 4 was that UiO-66-NH2-PMMA was grafted onto the surface of UiO-66-NH2 particles to prepare UiO-66-NH2-PMMA particles (particle size was 160±30 nm, and the difference from Example 3 was that VIM was not added in step (2), and only MMA (20 mL) was added as a monomer for polymerization reaction). 0.99 -co-VIM 0.01 ) nanoparticles are replaced by UiO-66-NH2-PMMA particles of equal mass), UiO-66-NH2-PMMA particles are used to form a SAMM film (with a thickness of about 160nm) at the water-air interface, and the SAMM film is further covered on the AAO substrate by the method described in Example 5 to form a heterogeneous membrane (the difference from Example 5 is that the SAMM membrane used is UiO-66-NH2-PMMA particles forming a SAMM film at the water-air interface). Compared with the heterogeneous membrane obtained in Example 5 (SAMM containing imidazole groups), this SAMM does not contain imidazole groups and is tested as a control group. The AAO substrate and the two heterogeneous membranes are respectively connected to a central pore area of ​​0.004mm 2 The silicon wafers were stacked together and fixed between the two modules of the current test device (the actual test area was the hole area on the silicon wafer, and the silicon wafer was attached to the AAO membrane side of the heterogeneous membrane). Corresponding through holes were set as flow channels on the two modules on both sides of the membrane, and one port of each flow channel was set correspondingly on both sides of the membrane. In order to simulate the osmotic energy collection of actual seawater and river water, the salt gradient in the flow channels on both sides was set to 50 times that of NaCl solution. For the AAO substrate test, 1mL of 500mM NaCl solution was added to the flow channel on the AAO membrane side, and 1mL of 10mM NaCl solution was added to the flow channel on the silicon wafer side. For the heterogeneous membrane test, 1mL of 500mM NaCl solution was added to the flow channel on the SAMM side, and 1mL of 10mM NaCl solution was added to the flow channel on the silicon wafer side. Ag / AgCl electrodes were placed in the electrolyte solutions in the two flow channels, respectively. A scanning voltage varying from -0.2 V to +0.2 V was applied through the electrodes as the transmembrane potential. A picoammeter was used to record the ionic current generated by the solutions in the two flow channels. The short-circuit currents obtained were 0.27 μA (AAO substrate), 0.49 μA (heterogeneous membrane without imidazole), and 0.86 μA (heterogeneous membrane obtained in Example 5).

[0062] The area of ​​​​the silicon wafer is 0.004mm 2 The through-holes serve as the effective test area.

[0063] The current test device is composed of two polytetrafluoroethylene rectangular blocks, one side of which is placed opposite to the other, and a polytetrafluoroethylene cylindrical protrusion (such as Figure 7 The cylindrical protrusions on the two rectangular blocks are arranged relative to each other, and a circular through hole with an L-shaped axis and a diameter of 5 mm is provided between the end face of the cylindrical protrusion and the upper surface of the rectangular block where the cylindrical protrusion is located, which serves as a flow channel (volume is 1.2 mL). The circular through hole ports on the two cylindrical protrusions are arranged relative to each other, and two vertically downward through holes C connecting the upper surface and the circular through holes are provided on the upper surfaces of the two rectangular blocks, which serve as pressure balance grooves. The membrane to be treated or tested is clamped between the cylindrical protrusions of the two rectangular blocks, and both sides of the membrane are sealed and attached to the surfaces of the cylindrical protrusions of the two rectangular blocks, and the circular through hole ports on the cylindrical protrusions are arranged relative to each other on both sides of the membrane.

[0064] In summary, the present invention designed and prepared a positively charged MOF monolayer membrane formed by self-assembly of functional polymer-coated MOF nanoparticles. This type of membrane, formed by evaporation-induced self-assembly of MOF particles at the water-air interface, is very dense (MOF particles are closely packed and arranged) and extremely thin (~160 nm). The prepared SAMM membrane was combined with a porous AAO membrane to produce a positively charged heterogeneous membrane that exhibited efficient osmotic energy harvesting. This invention not only provides a new method for preparing functionalized SAMM membranes but also offers new insights into the preparation of ion exchange membrane materials with efficient osmotic energy harvesting.

[0065] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A method of preparing a positive hetero film, characterized by: The method is formed by combining a self-assembled metal organic framework (MOF) monolayer (SAMM) film with positive electricity and a porous anodic aluminum oxide (AAO) film, and the specific steps are as follows: After the SAMM film is formed at the water-air interface, the AAO film is immersed in water under the SAMM film, and then the AAO film is moved towards the water surface with one side surface of the AAO film facing the water surface until the SAMM film covers one side surface of the AAO to form a composite film; The SAMM film is formed by self-assembly of MOF nanoparticles coated with a functional polymer at a water-air interface, and the specific steps are as follows: (1) 30-100 mg of functional polymer-coated UiO-66-NH2, denoted as UiO-66-NH2-P(MMA 0.99 - co -VIM 0.01 ) nanoparticles were mixed in a container with 0.7-1.2 mL of toluene, followed by sonication for 30-60 min to obtain a MOF dispersion; (2) 10-15 μL of the MOF dispersion prepared in step (1) is dropped into water in a culture dish with an internal cavity diameter of ≥30 mm and a water depth of >300 nm, and after being placed at room temperature for 1-6 min, toluene is completely volatilized, and a SAMM film formed by a monolayer of nanoparticles is formed on the water surface, with a thickness of the size of the nanoparticle diameter, The functional polymer is grafted onto the surface of UiO-66-NH2 particles by methyl methacrylate (MMA) and 1-vinylimidazole (VIM) initiated surface reversible addition−fragmentation chain transfer (RAFT) polymerization in step (1). 0.99 - co -VIM 0.01 The functional polymer is grafted onto the surface of UiO-66-NH2 particles by methyl methacrylate (MMA) and 1-vinylimidazole (VIM) initiated surface reversible addition−fragmentation chain transfer (RAFT) polymerization in step (1).

2. The preparation method according to claim 1, characterized in that, The composite film is placed in a culture dish with a cover and dried at room temperature for 12-24 h to obtain a positive hetero film; The AAO membrane has a pore size of 20-70 nm and a pore density of 0.1 x 10 12 -1.5 x 10 12 pores / cm 2 .

3. The preparation method according to claim 1, characterized in that The UiO-66-NH2-P(MMA of step (1) above 0.99 - co -VIM 0.01 ) is prepared according to the following specific steps: (1) The macromolecular chain transfer agent-modified UiO-66-NH2 is denoted as UiO-66-NH2-CTA, 95-105 mg, mixed with 95-105 mL of DMF in a vessel, followed by the sequential addition of MMA, VIM, and 50-100 μL of 2,2'-azobisisobutyronitrile AIBN with a concentration of 10 mg-mL -1 -1. (2) The mixture in step (1) is frozen with liquid nitrogen for 10-20 min, pumped with an oil pump with a pressure range of 1-10 Mpa for 1-10 min, and then the mixture is naturally thawed at room temperature; after 2-5 cycles of the above freezing-pumping-thawing operation, the mixture is placed in an oil bath pot with a constant temperature of 60-100℃ for 18-26 h; (3) After the reaction is completed, the crude product is centrifuged at 7000-10000 rpm for 10-20 min, and the obtained solid is washed with DMF and then with toluene; (4) The product UiO-66-NH2-P(MMA was obtained after drying the solid washed in step (3) at 50-80 °C for 10-15 h 0.99 - UiO-66-NH2-CTA is prepared by post-synthesis modification of UiO-66-NH2 and macromolecular chain transfer agent cat-CTA, and the specific steps are as follows: -VIM 0.01 ) with a particle size of 160 ± 30 nm.

4. The production method according to claim 3, characterized by, 95-105 mg of UiO-66-NH2, 100-180 mg of cat-CTA and 30-60 mL of DMF are mixed in a reaction bottle, and the mixture is ultrasonically treated for 20-60 min until the solid is completely dispersed; then the reaction bottle is reacted at a constant temperature of 90-120℃ for 3-6 h; after the reaction is completed, the product is cooled to room temperature, and the product is centrifuged at 7000-10000 rpm for 10-20 min, and the obtained solid is washed with DMF and then with methanol, and then placed in a vacuum drying box with a temperature setting of 30-60℃ for drying for 10-15 h to obtain the product UiO-66-NH2-CTA. The preparation of monodisperse UiO-66-NH2 nanoparticles and cat-CTA, and the specific steps are as follows:

5. The preparation method according to claim 4, characterized in that ​ Preparation of monodispersed UiO-66-NH2 nanoparticles: 160-210 mg of ZrCl4, 120-170 mg of 2-amino terephthalic acid and 30-60 mL of DMF were mixed in a container; the mixture was ultrasonicated for 5-30 min until the solid was completely dissolved; then, 1.0-2.0 mL of glacial acetic acid was added to the above mixed solution, stirred for 5-30 min; the mixture was transferred to an autoclave and placed in an oven with a constant temperature of 100-140 °C for 20-30 h; after the reaction was completed, the reactor was naturally cooled to room temperature and opened, and the product was centrifuged at 7000-10000 rpm for 10-20 min, and the obtained solid was washed with DMF and methanol in turn; the washed solid was placed in a vacuum drying oven with a temperature setting of 30-60 °C for drying for 10-15 h to obtain the product UiO-66-NH2, and the particle size was 130 ± 30 nm.

6. The preparation method according to claim 4, characterized in that Preparation of cat-CTA, the specific steps are as follows: Preparation of cat-CTA: 0.8-1.2 g of 4-cyano-4-[[(dodecylsulfanyl)thiocarbonyl]thio]pentanoic acid, 400-440 mg of N-hydroxysuccinimide and 30-60 mL of dry dichloromethane were mixed in a reaction bottle; the reaction bottle was placed in an ice water bath and stirred for 30-60 min, then 700-800 mg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide was added; the mixture was stirred at room temperature for 10-15 h; after the reaction was completed, the product was washed with 0.5-2.0 M dilute hydrochloric acid, saturated NaHCO3 and deionized water in turn, and the product in the aqueous solution was extracted with dichloromethane, then the dichloromethane solution was dried with anhydrous MgSO4 for 10-40 min; the dried solution was filtered and concentrated, and the crude product was purified by a silica gel column, and the eluent was a mixed solution of petroleum ether and ethyl acetate with a volume ratio of 1:1-5:1; 0.8-1.2 g of the above purified product, 400-430 mg of dopamine hydrochloride and 30-60 mL of dry tetrahydrofuran were mixed in a reaction bottle; the reaction bottle was placed in an ice water bath and stirred for 30-60 min, then 280-320 μL of triethylamine was added; the mixture was stirred at room temperature for 10-15 h; after the reaction was completed, the solvent was rotary evaporated, the crude product was dissolved in dichloromethane, then washed with 0.5-2.0 M dilute hydrochloric acid and deionized water in turn, and the product in the aqueous solution was extracted with dichloromethane, then the dichloromethane solution was dried with anhydrous MgSO4 for 10-40 min; the dried solution was filtered and concentrated, and the crude product was purified by a silica gel column, and the eluent was a mixed solution of petroleum ether and ethyl acetate with a volume ratio of 1:1-4:1; the purified product was placed in a vacuum drying oven with a temperature setting of 30-60 °C for drying for 10-15 h to obtain the product cat-CTA.

7. The positive hetero-membrane prepared by the method of any one of claims 1-6.

8. Use of the hetero film according to claim 7, characterized in that, The osmotic energy between salt water and water can be collected.

9. The production method according to claim 8, characterized by, The osmotic energy is collected by using an electrochemical device, and the ionic current of the solution in the two flow channels is recorded by using a picoammeter. The specific steps are as follows: The hetero-membrane and the silicon wafer are fixed between two modules of the electrochemical device, and corresponding through holes are arranged on the two modules on the two sides of the hetero-membrane as flow channels. One port of the two flow channels is arranged on the corresponding side of the hetero-membrane, and the through hole on the silicon wafer between the two corresponding flow channel ports is the actual test area. 300-800 mM NaCl solution is added to the flow channel on the SAMM side, and 8-13 mM NaCl solution is added to the flow channel on the AAO side. Ag / AgCl electrodes are placed in the electrolyte solutions in the two flow channels, a scanning voltage of-0.4 V to +0.4 V is applied to the electrodes as a transmembrane potential, and the current value is recorded by using a picoammeter.

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