A method of preparing a sub-nanoporous covalent organic framework membrane

Abstract

The application belongs to the technical field of membrane separation, and particularly relates to a preparation method of a sub-nanopore covalent organic framework membrane. The covalent organic framework membrane has a uniform and regular pore structure, and a pore diameter of only 0.6 nm, and can realize ion separation. When the ratio of aldehyde monomers and 2,4,5-trimethyl-1,3,5-triazine is 3:2, the water flux of the prepared covalent organic framework membrane is 75.3 L / m 2 47.5% for sodium chloride. The preparation method of the sub-nanopore covalent organic framework membrane provided by the application has higher water flux and rejection performance.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and specifically relates to a method for preparing a covalent organic framework membrane with sub-nanopores. Background Technology

[0002] Subnanometer-scale ion / molecular sieving is one of the most challenging problems in the field of membrane technology. Precisely constructing dimensionally stable and uniformly distributed subnanometer channels is a core prerequisite for achieving efficient and selective separation of substances. However, the transport channels of traditional polymer separation membranes mainly rely on the random stacking of polymer chain segments, resulting in a wide pore size distribution. Furthermore, due to the inherent contradiction between the rigidity and flexibility of polymer chains, the selectivity and permeability of the membrane often exhibit a trade-off effect, making it difficult to achieve synergistic enhancement of both. This bottleneck severely restricts the application of traditional membrane materials in higher-precision separation scenarios.

[0003] Covalent organic frameworks (COFs), as an emerging type of crystalline porous material, rely on reversible dynamic chemical bonds to form an ordered network structure. They exhibit uniform pore size, designable structure, and good chemical stability, theoretically capable of overcoming the trade-off limitations of traditional polymer membranes and achieving a balance between high throughput and high separation selectivity. However, existing COFs are constrained by the limited variety of monomers available and low-valent chemical bonding methods. Most COFs have pore sizes greater than 1.4 nm, making them difficult to directly use for precise molecular or ion sieving at the sub-nanometer scale. Therefore, the preparation of COF membranes with sub-nanometer pores remains a significant challenge in this field.

[0004] To address the aforementioned problems, this invention proposes a novel sub-nanoporous covalent organic framework membrane. This invention selects 5-hydroxyisophthalaldehyde as the key building block monomer, enabling it to undergo a reversible dynamic covalent chemical reaction with 1,3,5-trimethyl-2,4,6-triazine to form highly ordered, petal-like sub-nano channels. The median size of these channels is 0.6 nm, falling within the typical kinetic diameter range of hydrated ions and small organic molecules, thus endowing the membrane material with excellent molecular / ion sieving properties. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a covalent organic framework membrane with sub-nanopores. The covalent organic framework membrane has uniform pore size, with a pore size of only 0.6 nm, exhibiting excellent ion sieving characteristics.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for preparing a sub-nanopore covalent organic framework membrane, wherein the pore size of the sub-nanopore covalent organic framework membrane is 0.6 nm. This covalent organic framework membrane is prepared by a reversible dynamic chemical reaction of 5-hydroxyisophthalaldehyde and 1,3,5-trimethyl-2,4,6-triazine. Preferably, the molar ratio of 5-hydroxyisophthalaldehyde and 1,3,5-trimethyl-2,4,6-triazine monomers is 3:2, the solvent is 1,4-dioxane (4 ml), and the solution is 2M NaOH (2 ml).

[0008] This invention also provides a method for preparing a covalent organic framework membrane with sub-nanopores, preferably but not limited to the following method: A membrane solution is prepared by mixing 5-hydroxyisophthalaldehyde (0.3 mmol), 1,3,5-trimethyl-2,4,6-triazine (0.2 mmol), 1,4-dioxane (4 ml), and NaOH solution (2 M, 2 ml). The solution is then ground with a grinding rod and placed in a reaction vessel. After purging with nitrogen, the vessel is sealed and placed in a high-temperature oven at 120°C for 3 days. Subsequently, the membrane is removed, and unreacted monomer molecules are removed by Soxhlet extraction with methanol.

[0009] The sub-nanopore covalent organic framework membrane described in this invention has important applications in the field of membrane separation.

[0010] Taking the optimal covalent organic framework membrane as an example, its pure water flux is 75.3 L / m³. 2 h bar, the Nacl retention rate is 47.5%. Attached Figure Description

[0011] Figure 1 Covalent organic framework membrane molecular structure

[0012] Figure 2 cross-sectional electron micrograph of a covalent organic framework membrane Detailed Implementation

[0013] The technical solution of the present invention is illustrated below with specific examples, but the scope of protection of the present invention is not limited thereto:

[0014] Example 1

[0015] A membrane solution was prepared by mixing 0.3 mmol of 5-hydroxyisophthalaldehyde, 0.2 mmol of 1,3,5-trimethyl-2,4,6-triazine, 2 ml of 1,4-dioxane, and 2 M NaOH solution (2 ml). The solution was ground with a grinding rod and then placed in a reaction vessel. Nitrogen gas was introduced, and the vessel was sealed and placed in a high-temperature oven at 120°C for 3 days. The membrane was then removed, and unreacted monomer molecules were removed by Soxhlet extraction with methanol. The pure water flux was 41.6 L / m³. 2h bar, the Nacl rejection rate is 53.5%.

[0016] Example 2

[0017] A membrane solution was prepared by mixing 0.15 mmol of 5-hydroxyisophthalaldehyde, 0.1 mmol of 1,3,5-trimethyl-2,4,6-triazine, 4 ml of 1,4-dioxane, and 2 ml of 2M NaOH solution. The solution was ground with a grinding rod and then placed in a reaction vessel. Nitrogen gas was introduced, and the vessel was sealed and placed in a high-temperature oven at 120°C for 3 days. The membrane was then removed, and unreacted monomer molecules were removed by Soxhlet extraction with methanol. The pure water flux was 86.2 L / m³. 2 h bar, the Nacl retention rate is 31.6%.

[0018] Example 3

[0019] A membrane solution was prepared using 0.3 mmol of 5-hydroxyisophthalaldehyde, 0.2 mmol of 1,3,5-trimethyl-2,4,6-triazine, 4 ml of 1,4-dioxane, and 2 ml of 2M NaOH solution. The solution was ground with a grinding rod and then placed in a reaction vessel. Nitrogen gas was introduced, and the vessel was sealed and placed in a high-temperature oven at 120°C for one day. The membrane was then removed, and unreacted monomer molecules were removed by Soxhlet extraction with methanol. The pure water flux was 67.4 L / m³. 2 h bar, the Nacl rejection rate is 12.5%.

[0020] Example 4

[0021] A membrane solution was prepared by mixing 0.3 mmol of 5-hydroxyisophthalaldehyde, 0.2 mmol of 1,3,5-trimethyl-2,4,6-triazine, 6 ml of 1,4-dioxane, and 2 ml of 2M NaOH solution. The solution was ground with a grinding rod and then placed in a reaction vessel. Nitrogen gas was introduced, and the vessel was sealed and placed in a high-temperature oven at 120°C for 3 days. The membrane was then removed, and unreacted monomer molecules were removed by Soxhlet extraction with methanol. The pure water flux was 99.1 L / m³. 2 h bar, the Nacl retention rate is 38.2%.

Claims

1. A method for preparing a covalent organic framework membrane with sub-nanopores, characterized in that: It was prepared by a reversible dynamic covalent chemical reaction based on 5-hydroxyisophthalaldehyde and 2,4,6-trimethyl-1,3,5-triazine.

2. The method for preparing a sub-nanoporous covalent organic framework membrane as described in claim 1, characterized in that... 5-hydroxyisophthalaldehyde and 2,4,6-trimethyl-1,3,5-triazine were dispersed in 1,4-dioxane solvent, and then NaOH aqueous solution was added as a catalyst. The solution was spread evenly on the surface of a glass plate, and a covalent organic framework membrane with sub-nanopores was prepared by reversible dynamic covalent chemical reaction under heating conditions.

3. The method for preparing a covalent organic framework membrane with sub-nanopores as described in claim 1, characterized in that... The smallest pore size is 0.6 nm.

4. The method for preparing a covalent organic framework membrane with sub-nanopores as described in claim 2, characterized in that... The membrane was prepared at a temperature of 100-120℃ for 3-5 days.

5. The method for preparing a covalent organic framework membrane with sub-nanopores as described in claim 2, characterized in that... The monomer ratio of 5-hydroxyisophthalaldehyde and 2,4,6-trimethyl-1,3,5-triazine is 0.3-0.6 mmol: 0.2-0.4 mmol, 1,4-dioxane is 2-4 ml, and NaOH is 2 mol / L-4 mol / L, 1-2 ml.

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