Two-dimensional MOF membrane preparation method based on electrophoretic deposition method

Abstract

The invention discloses a preparation method of a two-dimensional MOF (Metal Organic Framework) membrane based on an electrophoretic deposition method, which comprises the following steps: synthesizing a two-dimensional Cu-TCPP nanosheet with a flat structure by taking meso-tetra (4-carboxyphenyl) porphin (TCPP) as a ligand; the obtained two-dimensional Cu-TCPP nanosheet is dissolved in a solvent, and an F nanosheet solution is obtained; and inputting the F nanosheet solution serving as a deposition solution into electrophoretic deposition equipment, and depositing the F nanosheets on a substrate AAO in an electrophoretic deposition manner to form a film, thereby finally obtaining the two-dimensional MOF film. According to the preparation method disclosed by the invention, the meso-tetra (4-carboxyphenyl) porphin (TCPP) is taken as the ligand, and the two-dimensional Cu-TCPP nanosheet with a flat structure is taken as an electrophoretic deposition object, so that the performance of the prepared two-dimensional MOF membrane is obviously improved, and the preparation efficiency is improved.

Description

Technical Field

[0001] The invention relates to a two-dimensional MOF film preparation technology, and in particular to a two-dimensional MOF film preparation method based on an electrophoretic deposition method. Background Art

[0002] Membrane separation is a separation technology that does not require phase change. It has the advantages of low energy consumption, high separation efficiency, small footprint and continuous operation. In recent years, emerging two-dimensional material membranes not only have these advantages, but also can show high selectivity and high permeability separation performance that surpass traditional material membranes by precisely controlling surface properties and interlayer structures. However, the research on two-dimensional MOF membranes is still in its infancy and faces many challenges. On the one hand, some types of MOF nanosheets present a rich morphology, including relatively flat or nanoscale and subnanometer curled structures. However, there is a relative lack of research on the construction of two-dimensional MOF membranes and their effects on separation performance. On the other hand, the current methods for preparing two-dimensional MOF membranes are relatively limited. The traditional vacuum filtration method is time-consuming, while the repeatability and controllability of the hot drop coating method are relatively poor. Therefore, there is an urgent need to develop a preparation method that is simple to operate, highly controllable and can achieve rapid membrane formation. Summary of the invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the prior art, a method for preparing a two-dimensional MOF membrane based on electrophoretic deposition is provided. By using tetrakis(4-carboxyphenyl)porphine (TCPP) as a ligand and a two-dimensional Cu-TCPP nanosheet with a flat structure as an electrophoretic deposition object, not only the performance of the prepared two-dimensional MOF membrane is significantly improved, but also the preparation efficiency is improved.

[0004] Technical solution: To achieve the above object, the present invention provides a method for preparing a two-dimensional MOF film based on electrophoretic deposition, comprising the following steps:

[0005] S1: Using meso-tetrakis(4-carboxyphenyl)porphine (TCPP) as a ligand, a two-dimensional Cu-TCPP nanosheet with a flat structure was synthesized;

[0006] S2: dissolving the two-dimensional Cu-TCPP nanosheets obtained in step S1 into a solvent to obtain a F nanosheet solution;

[0007] S3: The F nanosheet solution is used as a deposition liquid and input into an electrophoretic deposition device. The F nanosheets are deposited into a film on the substrate AAO by electrophoretic deposition. The film completely covers the substrate AAO, and finally a two-dimensional MOF film is obtained.

[0008] Furthermore, in step S1, a two-dimensional Cu-TCPP nanosheet having a flat structure is synthesized by using a method of assisting a bottom-up surfactant PVP in combination with the selection of a structure regulator.

[0009] Furthermore, in step S1, the surfactant is polyvinyl pyrrolidone.

[0010] Furthermore, in step S1, the structure regulators are trifluoroacetic acid and formic acid.

[0011] Furthermore, in step S3, a two-dimensional MOF film of a specified thickness is obtained by controlling the time of electrophoretic deposition.

[0012] Furthermore, in step S3, the thickness of the two-dimensional MOF film ranges from 60 to 450 nm.

[0013] Furthermore, the concentration of the F nanosheet solution in step S2 is calculated as follows: weigh the mass of two dried nylon substrates as m1 and m2, then take 2 ml of the nanosheet dispersion and load it on the two substrates, and weigh them again as M1 and M2 after they are completely dried, and calculate the concentration of the F nanosheet solution C = (M1-m1+M2-m2) / 4, in mg·mL-1. The purpose of this step is to ensure that the F nanosheet solution has a consistent concentration.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0015] 1. By using tetrakis(4-carboxyphenyl)porphine (TCPP) as a ligand and taking the two-dimensional Cu-TCPP nanosheets with a flat structure as the object of electrophoretic deposition, not only the performance of the prepared two-dimensional MOF membrane is significantly improved, such as nanofiltration performance, water permeability and retention rate, but also the preparation efficiency is improved.

[0016] 2. The electrophoretic deposition method is introduced into the preparation process of the two-dimensional MOF membrane. The thickness of the two-dimensional MOF membrane can be controlled by controlling the time of electrophoretic deposition. The thickness of the two-dimensional MOF membrane corresponds to different membrane properties. Therefore, the performance control of the two-dimensional MOF membrane is achieved. Without changing the process steps and procedures, it can adapt to the preparation requirements of two-dimensional MOF membranes with different performances, achieving a technical breakthrough in the preparation process of the two-dimensional MOF membrane. DETAILED DESCRIPTION

[0017] The present invention is further explained below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0018] Embodiment 1:

[0019] This embodiment provides a method for preparing a two-dimensional MOF film based on electrophoretic deposition, comprising the following steps:

[0020] S1: Using meso-tetrakis (4-carboxyphenyl) porphine (TCPP) as a ligand, a two-dimensional Cu-TCPP nanosheet with a flat structure was synthesized by a bottom-up method assisted by a surfactant polyvinyl pyrrolidone, combined with the selection of structure modifiers trifluoroacetic acid and formic acid;

[0021] S2: dissolving the two-dimensional Cu-TCPP nanosheets obtained in step S1 into a solvent to obtain a F nanosheet solution;

[0022] The concentration of the F nanosheet solution is calculated as follows: weigh the mass of two dry nylon substrates as m1 and m2, then take 2 ml of the nanosheet dispersion and load it on the two substrates respectively, and weigh them again as M1 and M2 after they are completely dried, and calculate the concentration of the F nanosheet solution C = (M1-m1+M2-m2) / 4, in mg·mL-1. The purpose of this step is to ensure that the F nanosheet solution has a consistent concentration;

[0023] S3: The F nanosheet solution is used as a deposition liquid and input into an electrophoretic deposition device. The F nanosheets are deposited on the substrate AAO to form a film, which completely covers the substrate AAO. By controlling the time of electrophoretic deposition, a uniformly covered ultra-thin two-dimensional MOF film with a thickness ranging from 60 to 450 nm is obtained.

[0024] The thickness of the two-dimensional MOF film prepared in this example is 200 nm.

[0025] Embodiment 2:

[0026] This embodiment adopts the existing vacuum filtration method to prepare the two-dimensional MOF membrane, and the specific preparation process is as follows:

[0027] The filtration device used includes a filter cup, a filtration head, a filtration bottle and a joint clamp. The selected two-dimensional Cu-TCPP membrane is supported on an organic nylon substrate with a diameter of 50 mm and a pore size of 200 nm.

[0028] First, fix the nylon substrate between the suction head and the filter cup, and fix the upper and lower ends with a joint metal clip. To ensure sealing, add a small amount of ethanol to the filter cup to wet the substrate. Next, inject a certain concentration and volume of Cu-TCPP nanosheet solution with a wrinkled or flat morphology into the suction cup, and then turn on the switch of the circulating vacuum water pump to extract the membrane. Wait for the dispersion to be completely drained, make sure there is no excess dispersion on the surface of the membrane, then use curved handle pointed tweezers to remove the membrane from the device and transfer it to a watch glass. After drying at room temperature for at least 12 hours, a two-dimensional MOF membrane with a flat morphology (Flat) was obtained.

[0029] Embodiment 3:

[0030] In this example, the performance of the two-dimensional MOF membranes obtained in Examples 1 and 2 is compared as follows:

[0031] Nanofiltration performance test: The nanofiltration performance of two-dimensional MOF membranes of different thicknesses was tested in detail. Compared with the two-dimensional MOF membrane with a thickness of 530nm prepared by vacuum filtration in Example 2, the two-dimensional MOF membrane obtained in Example 1 can increase the retention rate of dye molecule EB to 99.0% with a membrane thickness of only 200nm. Its membrane permeability reaches 9.40L·m-2·h-1·bar-1, which is 2.3 times that of Example 2, and has excellent acid and alkali chemical stability, pressure resistance and long-term stability.

[0032] Performance test of water permeability and rejection rate: Compared with the two-dimensional MOF membrane of Example 2, the two-dimensional MOF membrane obtained in Example 1 exhibited excellent water permeability and similar high rejection rate. This is mainly attributed to the thinner film thickness of the two-dimensional MOF membrane, which leads to a shorter transmission path, while its better hydrophilicity promotes the rapid transmission of water molecules.

[0033] Therefore, after testing, it was found that the two-dimensional MOF membrane of Example 1 was superior to that of Example 2 in terms of coverage, hydrophilicity, water permeability, stability, pressure resistance, and retention rate.

[0034] In addition, the preparation time of Example 1 is significantly lower than that of Example 2, which means that the preparation efficiency is improved.

[0035] Therefore, the effectiveness and practical effect of the method of the present invention are fully verified.

Claims

1. A method for preparing a two-dimensional MOF film based on electrophoretic deposition, characterized in that: The steps include: S1: Using meso-tetrakis(4-carboxyphenyl)porphine (TCPP) as a ligand, a two-dimensional Cu-TCPP nanosheet with a flat structure was synthesized; S2: dissolving the two-dimensional Cu-TCPP nanosheets obtained in step S1 into a solvent to obtain a F nanosheet solution; S3: The F nanosheet solution is used as a deposition liquid and input into an electrophoretic deposition device, and the F nanosheets are deposited into a film on the substrate AAO by electrophoretic deposition, and finally a two-dimensional MOF film is obtained.

2. A method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 1, characterized in that: In the step S1, a two-dimensional Cu-TCPP nanosheet having a flat structure is synthesized by using a method of assisting a bottom-up surfactant PVP and combining the selection of a structure regulator.

3. A method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 2, characterized in that: The surfactant in step S1 is polyvinyl pyrrolidone.

4. The method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 2, characterized in that: In step S1, the structure regulators are trifluoroacetic acid and formic acid.

5. The method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 1, characterized in that: In the step S3, a two-dimensional MOF film of a specified thickness is obtained by controlling the time of electrophoretic deposition.

6. The method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 5, characterized in that: The thickness of the two-dimensional MOF film in step S3 is in the range of 60 to 450 nm.

7. The method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 1, characterized in that: The concentration of the F nanosheet solution in step S2 is calculated as follows: weigh the masses of two dry nylon substrates as m1 and m2, then take 2 ml of the nanosheet dispersion and load it on the two substrates respectively, and weigh them again as M1 and M2 after they are completely dried, and calculate the concentration of the F nanosheet solution C = (M1-m1+M2-m2) / 4.

8. The method for preparing a two-dimensional MOF film based on electrophoretic deposition according to claim 1, characterized in that: In the step S3, the F nanosheets are deposited on the substrate AAO to form a film, and the film completely covers the substrate AAO.