A multi-level asymmetric covalent organic framework membrane, its preparation method and application

Abstract

This invention discloses a multi-level asymmetric covalent organic framework membrane, its preparation method, and its applications. The multi-level asymmetric covalent organic framework membrane comprises a three-layer structure: a positively charged COF-QA membrane at the top, a macroporous AAO membrane in the middle, and a negatively charged COF-SO3H membrane at the bottom. Some pores in the COF membranes on both sides are connected to some macropores in the AAO membrane. The membrane is prepared by in-situ growth of COF-DT membranes on both sides of the AAO membrane and grafting groups with different charges onto both sides. The membrane exhibits high porosity and ordered channels, ensuring high ion flux. The multi-level asymmetric structure provides high rectification response, reduces ion back diffusion, and the opposite charge promotes ion movement along the electric field direction, providing a driving force for ion separation. The output power density is 74.5 W / m³ under a 500-fold salinity gradient. ‑2 It has broad application prospects for permeation energy conversion.

Description

Technical Field

[0001] This invention relates to a multi-level asymmetric covalent organic framework membrane, its preparation method and application, and particularly to a multi-level asymmetric COF membrane, its preparation method and its application in permeation energy conversion, belonging to the field of permeation energy conversion technology. Background Technology

[0002] With the growth of global energy demand, the development of efficient, renewable, and environmentally friendly energy sources is imperative. Among the clean energy sources already developed, the chemical energy existing in the salinity gradient has attracted much attention in recent years due to the extremely high theoretical energy capacity generated between high-salinity seawater and low-salinity river water. This enormous chemical potential energy can be obtained through reverse electrodialysis (RED) technology, in which ions are driven through an ion-exchange membrane under a salinity gradient, generating a net current. Therefore, the Gibbs free energy generated by solution mixing can be directly converted into electrical energy. In the past decade, with the development of materials science and the enrichment of mass transport theory, various materials have been successfully used to harvest permeate energy. Selective permeate membranes based on graphene oxide, molybdenum disulfide, metal-organic frameworks, etc., have shown great potential in permeate energy harvesting. However, in practical applications, due to the reduced spatial range of the electric double layer (EDL) electrostatic effect and the charge screening effect caused by high concentrations of counterions, the membranes often exhibit decreased selectivity and poor energy harvesting performance. Therefore, new nanostructure design concepts are urgently needed to promote the further development of high-performance membranes. When an electric field exists within the membrane, it promotes the movement of cations in the direction of the electric field, providing an additional driving force for ion separation and remaining effective over a wide range of salt concentrations. Therefore, we designed a multi-level asymmetric membrane with an inherent field effect to introduce an additional driving force for ion separation, thus solving the problem of reduced selectivity in permeation energy collection and enabling the efficient development of salinity resources. Summary of the Invention

[0003] Objectives of this invention: The first objective is to provide a multilevel asymmetric covalent organic framework membrane based on a covalent organic framework. The second objective is to provide a method for preparing this multilevel asymmetric covalent organic framework membrane, which is simple to operate and readily achievable. The third objective is to provide an application of this multilevel asymmetric covalent organic framework membrane in salinity gradient energy conversion. This membrane can be used for salinity gradient energy conversion to extract permeation energy from a salinity gradient, and it exhibits stable performance, high conversion power, and excellent output even under a wide salinity gradient.

[0004] Technical solution: The present invention discloses a multi-level asymmetric covalent organic framework membrane, which comprises a three-layer structure, wherein the top layer is a positively charged COF-QA membrane, the middle layer is an anodic aluminum oxide film material (AAO) with a macroporous structure, and the bottom layer is a negatively charged COF-SO3H membrane. Some pores of the COF-QA membrane and some pores of the COF-SO3H membrane are connected to some macropores in the anodic aluminum oxide film material with a macroporous structure.

[0005] Furthermore, the thickness of the positively charged COF-QA film is 100-110 nm, preferably 106 nm, and the pore size of the positively charged COF-QA film is 2-2.4 nm, preferably 2.3 nm.

[0006] Furthermore, the thickness of the negatively charged COF-SO3H film is 102-107 nm, preferably 100 nm, and the pore size of the negatively charged COF-SO3H film is 1.7-1.9 nm, preferably 1.8 nm.

[0007] Furthermore, the pore diameter of the macroporous anodic aluminum oxide film material is 50–80 nm, preferably 70 nm.

[0008] Furthermore, the zeta potential of the positively charged COF-QA film is 16–19 mV, preferably 18 mV.

[0009] Furthermore, the zeta potential of the negatively charged COF-SO3H membrane is -36 to -39 mV, preferably -38 mV.

[0010] The method for preparing the multi-level asymmetric covalent organic framework membrane of the present invention includes the following steps:

[0011] (1) Aluminum oxide is sandwiched in an H-type electrolytic cell. 1,3,5-triaminophenylbenzene (TAPB) solution and 2,5-dihydroxy-1,4-benzaldehyde (DHBDA) solution are added to both chambers of the electrolytic cell. A catalyst is added and the mixture undergoes a Schiff base reaction to obtain a DT / AAO / DT membrane.

[0012] (2) 3-bromopropyltrimethylammonium bromide solution and 3-bromopropylalkyl sulfonate sodium solution were added to both sides of the H-type electrolytic cell, and the QA / AAO / SO3H membrane was obtained by the Schiller Williamson ether reaction.

[0013] (3) Take out the QA / AAO / SO3H membrane, wash it with solvent, and dry it under vacuum to obtain a multi-level asymmetric covalent organic framework membrane.

[0014] Furthermore, in step (1), the solvent used to prepare the TAPB solution and DHBDA solution is a mixed solution of 1,4-dioxane and mesitylene in a volume ratio of 4:1.

[0015] Furthermore, in step (2), the solvent used to prepare the 3-bromopropyltrimethylammonium bromide solution and the 3-bromopropylalkyl sulfonate sodium solution is N,N-dimethylformamide.

[0016] Further, in step (1), the concentration of the TAPB solution is 0.02 to 0.02 mmol / mL, preferably 0.02 mmol / mL, and the concentration of the DHBDA solution is 0.015 to 0.03 mmol / mL, preferably 0.03 mmol / mL.

[0017] Furthermore, in step (1), the catalyst is glacial acetic acid.

[0018] Furthermore, in step (1), the temperature of the Schiff base reaction is 50-70°C, preferably 70°C, and the reaction time is 48-60h, preferably 48h.

[0019] Furthermore, in step (2), the concentrations of the 3-bromopropyltrimethylammonium bromide solution and the sodium 3-bromopropyl sulfonate solution are both 0.8–1 mol / L, preferably 1 mol / L.

[0020] Furthermore, in step (2), the temperature of the Schering Williamson ether reaction is 80-100°C, preferably 100°C, and the reaction time is 12-30h, preferably 24h.

[0021] Furthermore, in step (3), the solvent is tetrahydrofuran.

[0022] Furthermore, in step (3), the vacuum drying temperature is 80-100°C, preferably 80°C, and the vacuum drying time is 12-24 hours, preferably 12 hours.

[0023] The application of the multi-level asymmetric covalent organic framework membrane described in this invention in the salinity gradient energy conversion process.

[0024] Furthermore, during application, the concentrated salt solution and the dilute salt solution form a salinity difference, which converts the salinity difference energy into electrical energy.

[0025] Furthermore, the molar concentration ratio of the concentrated salt solution to the dilute salt solution is (0.5–5):0.01.

[0026] Furthermore, the molar concentration of the concentrated salt solution is 0.5–5 mol / L.

[0027] Furthermore, the molar concentration of the dilute salt solution is 0.01 mol / L.

[0028] Furthermore, the concentrated salt solution and the dilute salt solution contain the same types of salts.

[0029] Furthermore, both the concentrated salt solution and the dilute salt solution are sodium chloride solutions.

[0030] This invention first grows COF-DT membranes on both sides of the AAO layer using an in-situ growth method, and then grafts sulfonate and quaternary ammonium salt groups with different charges onto both sides. The COF layers on both sides have high porosity and a regular, ordered pore arrangement. The high porosity and ordered pore arrangement of COF ensure high ion flux in permeation energy collection. Due to the advantages of the multi-level asymmetric structure, it exhibits a high rectification response, thereby reducing Joule thermally induced energy dissipation and ion concentration polarization (ICP) effects in unfavorable diffusion directions. In addition, the COF membrane materials on both sides carry opposite charges, and an electric field exists within the membrane pointing from the COF-QA side to the COF-SO3H side. This electric field promotes the movement of cations along the direction of the electric field, providing additional driving force for ion separation and remaining effective over a wide range of salt concentrations. The multi-level asymmetric membrane output power density can reach 74.5 W / m² under a 500-fold salinity gradient. -2 In summary, multi-stage asymmetric membranes constructed from COF can achieve excellent output power through permeation energy conversion, and have broad application prospects.

[0031] The multi-level asymmetric covalent organic framework membrane designed in this invention achieves high selectivity and rapid ion transport. Compared with traditional heterogeneous membranes, the multi-level asymmetric structure has a stronger rectification ratio, reducing energy dissipation in unfavorable diffusion directions caused by Joule heating and the ion concentration polarization (ICP) effect. Furthermore, in neutral solutions, the surfaces of the COF-QA membrane and the COF-SO3H membrane are positively and negatively charged, respectively, creating a potential difference within the membranes. This promotes the migration of cations towards the COF-SO3H direction while hindering the migration of anions towards the COF-SO3H direction. The asymmetric structure and asymmetric surface charge distribution of the multi-level asymmetric membrane enhance ion charge separation, accelerate cation transport, and remain effective over a wide salinity range, thus improving energy harvesting performance.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0033] (1) The multi-level asymmetric covalent organic framework membrane of the present invention includes a COF-QA membrane with a positive charge at the top, an anodic aluminum oxide membrane material (AAO) with a macroporous structure in the middle, and a COF-SO3H membrane with a negative charge at the bottom. The preparation method is simple and convenient, and the reaction conditions are easy to achieve.

[0034] (2) The multi-level asymmetric covalent organic framework membrane of the present invention has significant advantages in the application of salinity gradient osmosis energy conversion:

[0035] First, COF materials possess ordered nanochannels, ultra-high porosity, and tunable surface properties. The ordered nanochannels and high porosity lay the foundation for rapid ion transport and high ion flux. The tunable surface properties allow for the direct integration of different functional groups along the pore walls, providing feasibility for preparing permeation energy harvesting materials with varying properties.

[0036] Secondly, the inherent structural asymmetry of multilevel asymmetric covalent organic framework membranes, compared to traditional heterostructure membranes, combines the strong confinement effect of the cavity, significantly improving the ion current rectification characteristics. This reduces energy dissipation in unfavorable diffusion directions and the ion concentration polarization (ICP) effect caused by Joule heating.

[0037] Meanwhile, due to the asymmetric charge distribution of the multi-level asymmetric covalent organic framework membrane, the surfaces of COF-QA and COF-SO3H are positively and negatively charged, respectively, in neutral solution, forming a potential difference within the membrane. The asymmetric surface charge distribution enhances ion charge separation, accelerates cation transport, and improves energy harvesting performance.

[0038] Furthermore, the multi-level asymmetric covalent organic framework membrane of this invention successfully converts salinity gradient energy into electrical energy in salinity gradient osmosis energy conversion. Under simulated salinity gradient conditions utilizing seawater (0.5 mol / L NaCl) and river water (0.01 mol / L NaCl), the maximum output power density reached 9.5 W / m³. -2 This is at the commercial standard 5W m -2 Furthermore, by increasing the salinity gradient (5 mol / L NaCl / 0.01 mol / L NaCl), the maximum output power density can be increased to 74.5 W / m³. -2 .

[0039] Finally, the invention was able to support the normal operation of the timer under the condition of ten 50-fold NaCl salinity gradient electrolyzers connected in series, which proves the excellent application potential of multi-level asymmetric covalent organic framework membranes. Attached Figure Description

[0040] Figure 1 A schematic diagram of the preparation process of the multi-level asymmetric covalent organic framework membrane prepared in Example 1;

[0041] Figure 2 This is a schematic diagram of the preparation process of the AAO membrane in Example 1;

[0042] Figure 3 A scanning electron microscope image of the AAO membrane prepared in Example 1;

[0043] Figure 4 Scanning electron microscope image of the multi-level asymmetric covalent organic framework membrane prepared in Example 1;

[0044] Figure 5 This is a schematic diagram of the salinity gradient osmosis energy conversion device in Example 2;

[0045] Figure 6 The graphs show the relationship between current density and external resistance, and the relationship between power density and external resistance, obtained during the energy conversion of the multi-level asymmetric covalent organic framework membrane under different salinity gradients in Example 2.

[0046] Figure 7 The permeation energy conversion efficiency of the multi-level asymmetric covalent organic framework membrane prepared in Example 1 under different salinity gradients;

[0047] Figure 8 The graph shows the relationship between power density and external resistance of the multi-level asymmetric membranes prepared in Example 2 with different grafting times under a NaCl gradient of 0.01 mol / L: 5 mol / L.

[0048] Figure 9 A comparison of the output power density of the multi-level asymmetric covalent organic framework membrane prepared in Example 1 with that of QA / AAO and SO3H / AAO prepared in Comparative Examples 1-2 under a NaCl gradient of 0.01 mol / L: 5 mol / L;

[0049] Figure 10 This is a comparison graph of the permeation energy harvesting power density in Example 1 and Comparative Example 3;

[0050] Figure 11 The following are the salinity gradient permeation energy conversion test results of the covalent organic framework multilevel asymmetric membrane in Example 3 over 8 days: (A) Current density versus external resistance, (B) Power density versus external resistance.

[0051] Figure 12 The diagram shows the covalent organic framework multilevel asymmetric membrane used as a timer in Example 1. Detailed Implementation

[0052] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0053] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Example 1: Preparation of Multilevel Asymmetric Covalent Organic Framework Membranes

[0054] (1) Preparation of anodic aluminum oxide (AAO) film:

[0055] First, the aluminum foil is ultrasonically cleaned for 15 minutes each with anhydrous ethanol and 1 mol / L KOH solution, followed by thorough rinsing with deionized water to remove any residual liquid. The initial anodizing process uses 0.3 mol / L oxalic acid as the electrolyte and is carried out at a constant voltage of 40V and 25°C for 30 minutes. Next, the oxide layer formed on the surface of the aluminum foil after the initial anodizing is cleaned for 40 minutes at 60°C using an acidic solution composed of 5 wt% phosphoric acid and 1.5 wt% oxalic acid. A second anodizing process is then performed for 6 hours, with all other conditions remaining the same as the initial anodizing. Subsequently, a saturated SnCl2 solution is used to remove the aluminum substrate. Finally, the AAO film is treated with a 5 wt% phosphoric acid solution for 60 minutes to remove the barrier layer on top of the anodized aluminum film. The entire preparation process is as follows: Figure 2 As shown.

[0056] Next, the prepared AAO membrane was immersed in a 30% hydrogen peroxide solution and boiled at 95°C for 30 minutes to modify the channel surface with abundant hydroxyl groups. Finally, the AAO membrane was soaked in deionized water overnight and then dried. By adjusting the voltage during the anodizing process, the pore size of the anodic aluminum oxide membrane nanochannels can be effectively controlled. Scanning electron microscopy analysis of the AAO membrane showed that its pore size was 70 nm, and the pores were uniformly distributed. Figure 3 As shown.

[0057] (2) Preparation of multi-level asymmetric membranes of covalent organic frameworks:

[0058] First, a mixed solution of anhydrous 1,4-dioxane and mesitylene (v:v = 4:1) was prepared. Then, this mixed solution was used to prepare TAPB and DHBDA solutions with concentrations of 0.02 mmol / L and 0.03 mmol / L, respectively. The AAO prepared in Example 1 (1) was placed in an H-type electrolytic cell. 5 mL of TAPB and DHBDA solutions were added to both chambers, and 200 μL of anhydrous acetic acid was added as a catalyst. The reaction was carried out at 70 °C for 48 h. A DT / AAO / DT membrane was obtained. A 1 mol / L solution of 3-bromopropyltrimethylammonium bromide and a 1 mol / L solution of sodium 3-bromopropanesulfonate were prepared using N,N-dimethylformamide as a solvent. 10 mL of 3-bromopropyltrimethylammonium bromide and 1 mol / L of sodium 3-bromopropanesulfonate were added to both sides of the DT / AAO / DT membrane, respectively. The reaction was carried out at 100 °C for 24 h to obtain a QA / AAO / SO3H membrane. The obtained QA / AAO / SO3H membrane material was taken out, washed with tetrahydrofuran solvent, and vacuum dried at 80°C for 12 hours to obtain a multi-level asymmetric covalent organic framework membrane. The preparation process is as follows: Figure 1 As shown.

[0059] Scanning electron microscopy analysis was performed on the multi-level asymmetric covalent organic framework membrane prepared in this embodiment. The results are as follows: Figure 4 As shown. Figure 4 Scanning electron microscope (SEM) images of the hierarchical asymmetric covalent organic framework membrane prepared in Example 1 are shown. (A) is a cross-sectional image of the hierarchical asymmetric covalent organic framework membrane. (B) is a side cross-sectional image of the COF-SO3H hierarchical asymmetric covalent organic framework membrane. (C) is a side cross-sectional image of the COF-QA hierarchical asymmetric covalent organic framework membrane. (D) is a side planar image of the COF-SO3H hierarchical asymmetric covalent organic framework membrane. (E) is a side planar image of the COF-QA hierarchical asymmetric covalent organic framework membrane. Figure 4 As can be seen, both sides of the film have dense and defect-free COF films with a thickness of approximately 100 nanometers. These results confirm the formation of a double-sided asymmetric structure on the AAO substrate.

[0060] Example 2: Preparation of multi-level asymmetric membranes with different grafting times

[0061] The preparation process is the same as in Example 1, except that the reaction time after adding 10 mL of 3-bromopropyltrimethylammonium bromide and sodium 3-bromopropanesulfonate to both sides of the DT / AAO / DT membrane in step (2) of Example 1 is changed to 12 h, 18 h and 30 h respectively.

[0062] Example 3: Application of Salinity Gradient Osmosis Energy Conversion in Multi-Level Asymmetric Covalent Organic Framework Membranes

[0063] 1. Salinity gradient osmosis energy conversion device, such as Figure 5 As shown, the salinity gradient osmosis energy conversion device is a two-chamber electrochemical electrolytic cell (H-C). The multi-stage asymmetric covalent organic framework membrane prepared in Example 1 is fixed between the two cells. A concentrated salt solution (0.5–5 mol / L NaCl electrolyte solution) is loaded on the COF-QA side, and a dilute salt solution (0.01 mol / L NaCl electrolyte solution) is loaded on the COF-SO3H side. The two salt solutions are connected to the circuit via an external electrochemical workstation and a load resistor. By adjusting the external resistance value, the relationship curves between current density, power density, and external resistance are measured. The results are as follows: Figure 6 As shown.

[0064] Figure 6 The graphs shown in Example 3 depict the relationship between current density, power density, and external resistance obtained during the energy conversion of different salinity gradients in the multi-level asymmetric covalent organic framework membrane. (A) shows the relationship between current density and external resistance, and (B) shows the relationship between power density and external resistance. Figure 6 It can be seen that under a NaCl gradient of 0.01 mol / L: 0.5 mol / L, the corresponding external circuit power density is 9.5 W / m². -25W m meets commercial standards -2 The power density reaches 74.5 W / m³ at a concentration of 0.01 mol / L: 5 mol / L NaCl. -2 .like Figure 7 As shown, the multi-level asymmetric covalent organic framework membrane in Example 1 achieved an energy conversion efficiency of 34% at high salt concentrations, demonstrating the superior permeation energy collection performance of the multi-level asymmetric covalent organic framework membrane at high salt concentrations.

[0065] 2. Permeation energy collection of multi-stage asymmetrical covalent organic framework membranes with different grafting times

[0066] Using the salinity gradient permeation energy conversion device from step 1, the multi-level asymmetric covalent organic framework membrane prepared in Example 2 was used to replace the composite membrane in the salinity gradient permeation energy conversion device, with other conditions remaining unchanged. The effect of changing the grafting time on the salinity gradient permeation energy conversion performance was investigated, and the results are as follows: Figure 8 As shown.

[0067] Figure 8 The graphs showing the power density versus external resistance obtained from the energy conversion of multi-stage asymmetrical covalent organic framework membranes with different grafting times in Examples 1 and 2 are derived from... Figure 7 It can be observed that when the grafting time is 12h, 18h, 24h, and 30h, the corresponding external circuit power density under a 0.01mol / L:5mol / L NaCl gradient is 39.3Wm. -2 58.4W m -2 74.5W m -2 and 42.1W m -2 Furthermore, the salinity gradient osmotic energy conversion output power is highest when the grafting time is 24 hours.

[0068] Comparative Example 1

[0069] Preparation of QA / AAO membrane: The preparation process is the same as in Example 1, except that the AAO membranes from Example 1 are placed parallel to each other in a standard reaction flask, and the COF membrane is grown only on one side of the AAO membrane. After obtaining DT / AAO, 10 mL of a 1 mol / L 3-bromopropyltrimethylammonium bromide solution prepared with N,N-dimethylformamide as solvent is added, and the reaction is carried out at 100°C for 24 h. The above composite membrane material is then removed, washed with tetrahydrofuran solvent, and vacuum dried at 80°C for 12 h to obtain the QA / AAO membrane.

[0070] Comparative Example 2

[0071] Preparation of SO3H / AAO membrane: Similar to the preparation of QA / AAO membrane, except that 1 mol / L 3-bromopropyltrimethylammonium bromide solution is replaced with 1 mol / L 3-bromopropane sulfonate sodium solution to obtain SO3H / AAO membrane.

[0072] The QA / AAO membrane and SO3H / AAO membrane prepared in Comparative Examples 1 and 2 were subjected to salinity gradient osmosis energy conversion. The experimental procedure was the same as in Example 2, and the results are as follows. Figure 8 As shown.

[0073] Depend on Figure 9 Experimental results showed that, under a NaCl concentration gradient of 0.01 mol / L: 5 mol / L, the output power density of the multi-level asymmetric membrane QA / AAO / SO3H prepared in Example 1 was significantly higher than that of QA / AAO prepared in Comparative Example 1 and SO3H / AAO prepared in Comparative Example 2. The external circuit power density of QA / AAO and SO3H / AAO under a 0.01 mol / L: 5 mol / L NaCl gradient was 28.8 W / m². -2 and 34.6W m -2 The power density of the external circuit of the multi-level asymmetric membrane QA / AAO / SO3H is far lower than that of the present invention. The asymmetric structure and asymmetric surface charge distribution of the multi-level asymmetric membrane enhance ion charge separation, accelerate cation transport, and are effective over a wide salinity range, thereby improving energy harvesting performance.

[0074] Comparative Example 3

[0075] We will compare our existing publicly reported asymmetric films with similar structures, such as ZIF-8-AAO-WO3 (see Fu, Y. Wang, J. Jiang, B. Lu, J. Zhai, ACS Applied Materials & Interfaces 2021, 13, 35197-35206), J-MOF (see Z.-Q. Li, G.-L. Zhu, R.-J. Mo, M.-Y. Wu, X.-L. Ding, L.-Q. Huang, Z.-Q. Wu, X.-H. Xia, ACS Applied Materials & Interfaces 2023, 15, 23922-23930) and MC / AAO / MS (see S. Zhou, L. Xie, X. Zhang, M. Yan, H. Zeng, K. Liang, L. Jiang, B. Kong, Advanced... The output power density of the salinity gradient infiltration energy conversion (Materials 2022, 35.) is compared with the salinity gradient infiltration energy harvesting performance of the multi-stage asymmetric membrane in Example 1. The results are as follows: Figure 10 As shown. Figure 10This is a comparison chart showing the maximum output power density obtained by the multi-stage asymmetric membrane in Example 1 and the existing membrane material in Comparative Example 3 during the energy conversion of 0.01 mol / L:0.5 mol / L NaCl salinity gradient permeation. Figure 10 The comparative results showed that the permeation energy collection performance of the multi-level asymmetric covalent organic framework membrane prepared in Example 1 was much higher than that of other membranes.

[0076] Example 3: Stability test of salinity gradient permeation energy conversion of multi-stage asymmetric membranes

[0077] The multi-level asymmetric covalent organic framework membrane from Example 1 was subjected to salinity gradient permeation energy conversion tests after being placed for 0, 2, 4, 6, and 8 days, respectively. The results are as follows: Figure 11 As shown. The multi-level asymmetric covalent organic framework membrane prepared in Example 1 exhibited good stability in the application of salinity gradient permeation energy conversion. After 8 consecutive days of testing, the output power density decreased by less than 5%, laying a reliable foundation for subsequent practical applications.

[0078] Example 4: Practical Application of Multilevel Asymmetric Covalent Organic Framework Membranes

[0079] A tandem generator was constructed using the multi-level asymmetric covalent organic framework membrane from Example 1. With ten electrolytic cells connected in series in a 0.01 mol / L: 0.5 mol / L NaCl configuration, as shown... Figure 12 The output voltage reached 1.43V, which is sufficient to support the normal operation of the timer, further demonstrating the excellent application potential of the multi-stage asymmetric membrane.

Claims

1. A multi-level asymmetric covalent organic framework membrane, characterized in that, The multi-level asymmetric covalent organic framework membrane comprises a three-layer structure, wherein the top layer is a positively charged COF-QA membrane, the middle layer is an anodic aluminum oxide membrane material with a macroporous structure, and the bottom layer is a negatively charged COF-SO3H membrane. Some pores of the COF-QA membrane and some pores of the COF-SO3H membrane are connected to some macropores in the anodic aluminum oxide membrane material with a macroporous structure.

2. The multi-level asymmetric covalent organic framework membrane according to claim 1, characterized in that, The COF-QA membrane has a thickness of 100–110 nm and a pore size of 2–2.4 nm. The COF-SO3H membrane has a thickness of 102–107 nm and a pore size of 1.7–1.9 nm. The pore diameter of the macroporous anodic aluminum oxide membrane material is 50–80 nm.

3. The method for preparing the multi-level asymmetric covalent organic framework membrane according to claim 1 or 2, characterized in that, Includes the following steps: (1) Aluminum oxide is sandwiched in an H-type electrolytic cell. 1,3,5-triaminophenylbenzene solution and 2,5-dihydroxy-1,4-benzaldehyde solution are added to both chambers of the electrolytic cell. A catalyst is added and the mixture undergoes a Schiff base reaction to obtain a DT / AAO / DT membrane. (2) 3-bromopropyltrimethylammonium bromide solution and 3-bromopropylalkyl sulfonate sodium solution were added to both sides of the H-type electrolytic cell, and the QA / AAO / SO3H membrane was obtained by the Schiller Williamson ether reaction. (3) Take out the QA / AAO / SO3H membrane, wash it with solvent, and dry it under vacuum to obtain a multi-level asymmetric covalent organic framework membrane.

4. The preparation method according to claim 3, characterized in that, In step (1), the solvent used to prepare the 1,3,5-triaminophenylbenzene solution and the 2,5-dihydroxy-1,4-benzaldehyde solution is a mixed solution of 1,4-dioxane and mesitylene in a volume ratio of 4:

1. In step (2), the solvent used to prepare the 3-bromopropyltrimethylammonium bromide solution and the 3-bromopropane sulfonate sodium solution is N,N-dimethylformamide.

5. The preparation method according to claim 3, characterized in that, In step (1), the concentration of the 1,3,5-triaminophenylbenzene solution is 0.02-0.02 mmol / mL, and the concentration of the 2,5-dihydroxy-1,4-benzaldehyde solution is 0.015-0.03 mmol / mL.

6. The preparation method according to claim 3, characterized in that, In step (1), the catalyst is glacial acetic acid, the Schiff base reaction temperature is 50-70℃, and the Schiff base reaction time is 48-60h.

7. The preparation method according to claim 3, characterized in that, In step (2), the concentrations of the 3-bromopropyltrimethylammonium bromide solution and the 3-bromopropylalkyl sulfonate sodium solution are both 0.8–1 mol / L, the reaction temperature of the Schillerson ether is 80–100 °C, and the reaction time of the Schillerson ether is 12–30 h.

8. The preparation method according to claim 3, characterized in that, In step (3), the solvent is tetrahydrofuran, the vacuum drying temperature is 80-100℃, and the vacuum drying time is 12-24h.

9. The application of the multi-level asymmetric covalent organic framework membrane as described in claim 1 or 2 in the process of salinity gradient energy conversion.

10. The application according to claim 9, characterized in that, During application, a salinity difference is formed between the concentrated salt solution and the dilute salt solution, converting the salinity gradient energy into electrical energy. The molar concentration ratio of the concentrated salt solution to the dilute salt solution is (0.5–5). 0.01, where both the concentrated salt solution and the dilute salt solution are sodium chloride solutions.

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