Method for preparing polyamide / sulfonated COFs reverse osmosis membrane through in-situ copolymerization

Abstract

According to the method for preparing the polyamide / sulfonated COFs reverse osmosis membrane through in-situ copolymerization, a polysulfone ultrafiltration membrane is used as a supporting layer, a water-phase monomer solution and an organic-phase monomer solution are subjected to a one-step in-situ copolymerization reaction on a water-phase / organic interface on the supporting layer, and the polyamide / sulfonated COFs reverse osmosis membrane is prepared. The preparation method is simple in technological process and low in cost, the sulfonated COFs material is introduced into a polyamide layer through one-step interface in-situ copolymerization, the dispersity and compatibility of the sulfonated COFs can be well enhanced, the interface polymerization process is regulated and controlled by fully utilizing a porous structure, hydrophilicity and indirect control of monomer diffusion, and the like, and the preparation method is suitable for large-scale industrial production. The trade-off effect of a traditional polyamide reverse osmosis membrane is broken through, the salt rejection rate is increased while high water flux is guaranteed, and the polyamide reverse osmosis membrane has very high practical application value.

Description

Technical Field

[0001] The invention relates to a method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization, and specifically belongs to the technical field of reverse osmosis membranes. Background Art

[0002] Reverse osmosis (RO) technology is widely used in seawater desalination, brackish water desalination and water purification production. Reverse osmosis technology involves material science, polymer materials, system optimization, polymer membrane synthesis methods and modification, etc. Ultra-thin composite polyamide RO membrane is still the main membrane material for RO process.

[0003] Nowadays, research on reverse osmosis composite membranes is very extensive at home and abroad, among which the most widely used membrane is polyamide composite membrane. The microstructure of polyamide composite membrane is composed of a porous support layer and a polyamide ultra-thin separation layer (about 100 nm thick) for separation. Its significant advantage is that the support layer and separation layer of TFC membrane can be optimized according to different needs. However, traditional polyamide has the common problem of low permeation flux. Domestic and foreign scholars have tried to shift the research focus to the modification of polyamide membranes to improve the permeation performance (water flux and salt retention rate) of composite membranes.

[0004] However, the "trade-off effect" between water flux and salt retention rate in the preparation process of reverse osmosis membranes has always troubled researchers from various countries. Specifically, when the water flux of the membrane is increased, some salt retention rate will always be lost. So how to coordinate the contradictions between RO membrane water flux and salt retention rate, and achieve a significant increase in reverse osmosis membrane water flux while still having a high salt retention rate, has become an extremely attractive research direction.

[0005] The process of doping composite membranes with nanomaterials is very mature, among which MOFs nanomaterials and COFs nanomaterials are the most representative. Both types of nanomaterials have highly adjustable pore structures, high specific surface areas, customizable chemical functions, and good polymer compatibility, and have attracted much attention in the development and application of modified polyamide composite membranes. Zhao et al. (Zhao DL, Yeung WS, Zhao Q, et al. Thin-film nanocomposite membranes incorporated with UiO-66-NH2 nanoparticles for brackish water and seawater desalination [J]. Journal of Membrane Science, 2020, 604: 118039.) introduced amino-modified UiO-66 (UiO-66-NH2) particles into the membrane by pre-deposition, which improved the water flux and salt retention rate of the membrane. Li et al. (C. Li, S. Li, L. Tian, ​​et al. Covalent organic frameworks (COFs)-incorporated thin film nanocomposite (TFN) membranes for high-flux organic solvent nanofiltration (OSN)[J]. Journal of Membrane Science, 2019, 572: 520–531.) used SNW-1 COFs as an additive to the aqueous solution, and the prepared COFs-doped OSN membrane had an ethanol permeability increase of 46.7% and excellent solvent resistance. However, the above-mentioned studies all used a two-step method to blend with pre-synthesized nanomaterials to prepare TFN membranes. This two-step preparation process is complicated and time-consuming. The key is that MOFs and COFs nanoparticles are easy to agglomerate, resulting in uneven composite membranes and affecting the overall performance of the membrane. To this end, the present invention proposes a one-step copolymerization method with a relatively simple process flow and low cost: by using a one-step in-situ copolymerization method, a sulfonated COFs material is introduced into a polyamide layer, which can not only greatly enhance the dispersibility and compatibility of the sulfonated COFs in the interfacial polymerization monomer solution, but also indirectly control the monomer diffusion rate during interfacial polymerization by utilizing the porous structure and hydrophilicity of the sulfonated COFs material, thereby achieving the regulation of the reaction rate of the interfacial polymerization process. However, according to current literature reports, there has been no report on introducing sulfonated organic framework materials (sulfonated COFs) into a polyamide layer by in-situ copolymerization to prepare a reverse osmosis membrane. Summary of the invention

[0006] The present invention provides a method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization. Starting from solving the "trade-off" effect of the existing traditional polyamide membrane, COFs nanomaterials are introduced into the polyamide layer, and high water flux and high salt retention rate are successfully achieved at the same time, thereby effectively improving the performance of the reverse osmosis membrane.

[0007] The present invention discloses a method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization. The polysulfone (PSF) ultrafiltration membrane is used as a support layer. An aqueous monomer solution and an organic monomer solution are subjected to a one-step in-situ copolymerization reaction at the aqueous / organic interface of the support layer to prepare a polyamide / sulfonated COFs reverse osmosis membrane. The specific process is as follows: Step 1: Immerse the polysulfone (PSF) ultrafiltration membrane in a deionized water solution to remove the surface protective agent and use it as a support layer for later use; Step 2: Add 2,5-diaminobenzenesulfonic acid (Pa-SO3H) to the metaphenylenediamine (MPD) monomer solution, and then add sodium dodecyl sulfate (SDS) as an interfacial stabilizer, and disperse them evenly to form an aqueous phase solution; disperse 1,3,5-trialdehyde phloroglucinol (Tp) in the trimesoyl chloride monomer solution to form an organic phase solution; Step 3: Pour the aqueous monomer solution onto the surface of the polysulfone ultrafiltration membrane, remove the excess aqueous monomer solution on the surface after 1 to 10 minutes of infiltration, then pour the organic monomer solution of the same volume as the aqueous monomer solution onto the surface of the polysulfone ultrafiltration membrane, after 2 to 300 seconds of in-situ copolymerization, remove the remaining organic solution on the surface, and then wash the surface of the polysulfone ultrafiltration membrane with n-hexane, followed by heat treatment to obtain a polyamide / sulfonated COFs reverse osmosis membrane.

[0008] In the step 2, the MPD content in the aqueous monomer solution is 1.0 wt%~4.0wt%, and the Pa-SO3H content is 0 wt%~2.0 wt%; the TMC content in the organic monomer solution is 0.01 wt%-0.3wt%, and the Tp content is 20 mg / L~500 mg / L; and the content of the interfacial stabilizer SDS is 0.01 wt%~0.2 wt%.

[0009] The in-situ copolymerization reaction time is 2 to 300 s.

[0010] The heat treatment temperature is 40-80°C and the time is 15-40 min.

[0011] The beneficial effects of the present invention are as follows: the preparation method of the present invention has a simple process flow and low cost. The sulfonated COFs material is introduced into the polyamide layer through a one-step interfacial in-situ copolymerization, which can not only well enhance the dispersibility and compatibility of the sulfonated COFs, but also make full use of its porous structure and strong hydrophilicity, indirectly control the monomer diffusion rate, thereby achieving the purpose of regulating the interfacial polymerization process, breaking the "trade-off" effect existing in traditional polyamide reverse osmosis membranes, while ensuring a high water flux while still having a high salt retention rate, and has a high practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 : Physical picture of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 1 of the present invention; Figure 2 : Physical picture of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 2 of the present invention; Figure 3 : Physical picture of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 3 of the present invention; Figure 4 : Field emission scanning electron microscopy image of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 1 of the present invention; Figure 5 : Field emission scanning electron microscopy image of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 2 of the present invention; Figure 6 : Field emission scanning electron microscopy image of the polyamide / sulfonated COFs reverse osmosis membrane prepared in Example 2 of the present invention; Figure 7 : Conceptual diagram of the method for preparing polyamide / sulfonated COFs reverse osmosis membrane by in situ copolymerization of the present invention. DETAILED DESCRIPTION

[0013] Example 1 The PSF ultrafiltration membrane was immersed in a deionized water solution to remove the surface protective agent and used as a support layer; the PSF ultrafiltration membrane was fixed, and 1.5 wt% MPD, 0.5 wt% Pa-SO3H and 0.05 wt% SDS were dissolved in deionized water to prepare an aqueous monomer solution; 0.2 wt% TMC and 50 mg / L Tp were dissolved in n-hexane to prepare an organic monomer solution; 10 mL of the aqueous monomer solution was poured on the PSF ultrafiltration membrane, and after 5 minutes, the excess aqueous monomer solution was rolled off with a glass rod, and then 10 mL of the organic monomer solution was poured on the membrane surface to start the interfacial in situ copolymerization reaction. After the reaction, the excess organic phase solution was poured off, and the surface of the PSF ultrafiltration membrane was cleaned with n-hexane, and after being placed in an oven for heat treatment at 60°C for 30 minutes, a polyamide / sulfonated COFs reverse osmosis membrane was obtained, which was stored in deionized water for later use.

[0014] Example 2 The PSF ultrafiltration membrane was immersed in a deionized water solution to remove the surface protective agent and used as a support layer; the PSF ultrafiltration membrane was fixed, and 2.5 wt% MPD, 1.0 wt% Pa-SO3H and 0.10 wt% SDS were dissolved in deionized water to obtain an aqueous monomer solution; 0.2 wt% TMC and 200 mg / L Tp were dissolved in n-hexane to obtain an organic monomer solution; 5 mL of the aqueous monomer solution was poured on the PSF ultrafiltration membrane, and after 5 minutes, the excess aqueous monomer solution was rolled off with a glass rod, and then 5 mL of the organic monomer solution was poured on the surface of the PSF ultrafiltration membrane to start the interfacial in-situ copolymerization reaction. After the reaction, the excess organic monomer solution was poured off, and the surface of the PSF ultrafiltration membrane was cleaned with n-hexane, and after heat treatment at 60°C in an oven for 30 minutes, a polyamide / sulfonated COFs reverse osmosis membrane was obtained, which was stored in deionized water for later use.

[0015] Example 3 The PSF ultrafiltration membrane was immersed in a deionized water solution to remove the surface protective agent and used as a support layer; the PSF ultrafiltration membrane was fixed, and 3 wt% MPD, 0.5 wt% Pa-SO3H and 0.15 wt% SDS were dissolved in deionized water to prepare an aqueous monomer solution; 0.3wt% TMC and 400 mg / L Tp were dissolved in n-hexane to prepare an organic monomer solution; 8 mL of the aqueous monomer solution was poured on the PSF ultrafiltration membrane, and after 5 minutes, the excess aqueous monomer solution was rolled off with a glass rod, and then 8 mL of the organic monomer solution was poured on the surface of the PSF ultrafiltration membrane to start the interfacial in-situ copolymerization reaction. After the reaction, the excess organic monomer solution was poured off, and the membrane surface was cleaned with n-hexane. After heat treatment in an oven at 60°C for 30 minutes, a polyamide / sulfonated COFs reverse osmosis membrane was obtained, which was stored in deionized water for later use.

[0016] Results of Example 1 The performance of the reverse osmosis membrane is evaluated by the permeation flux and salt rejection rate. After the performance of the polyamide / sulfonated COFs reverse osmosis membrane was evaluated with pure water and 2000 ppm NaCl brine solution at 15.5 bar, its pure water flux can reach , the permeate flux and salt rejection are and 98.88%.

[0017] Results of Example 2 The performance of the reverse osmosis membrane is evaluated by the permeation flux and salt rejection rate. After the performance of the polyamide / sulfonated COFs reverse osmosis membrane was evaluated with pure water and 2000 ppm NaCl brine solution at 15.5 bar, its pure water flux can reach , the permeate flux and salt rejection are and 98.69%.

[0018] Results of Example 3 The performance of the reverse osmosis membrane is evaluated by the permeation flux and salt rejection rate. After the performance of the polyamide / sulfonated COFs reverse osmosis membrane was evaluated with pure water and 2000 ppm NaCl brine solution at 15.5 bar, its pure water flux can reach , the permeate flux and salt rejection are and 98.59%.

[0019] Results Analysis according to Figure 1-3 The actual picture shows that the surface of the polyamide / sulfonated COFs reverse osmosis membrane is smooth and the surface color is yellow-green; Figure 4-6 Field emission scanning electron microscopy (FESEM) characterization showed that an uneven continuous dense layer appeared on the surface of the polyamide / sulfonated COFs reverse osmosis membrane, and the number of pores also increased to a certain extent, but a raised nodular structure appeared on the surface, which was an aggregate in the interface process, indirectly increasing the effective filtration area of ​​the membrane, reducing mass transfer limitations, and thus improving the separation performance.

[0020] The prepared polyamide / sulfonated COFs reverse osmosis membrane was compared through separation performance evaluation. The polyamide / sulfonated COFs reverse osmosis membrane was superior to the traditional polyamide membrane reverse osmosis membrane (pure water flux and rejection rate were and 97.92%) breaks the "trade-off" effect of traditional polyamide reverse osmosis membranes, and its pure water flux and salt retention rate have been greatly improved. By introducing sulfonated covalent organic framework nanomaterials into the polyamide layer and making full use of their porous structure and hydrophilicity, the prepared polyamide / sulfonated COFs reverse osmosis membrane has high flux and high salt retention rate.

Claims

1. A method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization, characterized in that: The method uses a polysulfone ultrafiltration membrane as a support layer, and an aqueous monomer solution and an organic monomer solution are subjected to a one-step in-situ copolymerization reaction at the aqueous phase / organic phase interface on the support layer to prepare a polyamide / sulfonated COFs reverse osmosis membrane. The specific process is as follows: Step 1: immerse the polysulfone ultrafiltration membrane in a deionized water solution to remove the surface protective agent and use it as a support layer for standby use; Step 2: Add 2,5-diaminobenzenesulfonic acid to the metaphenylenediamine monomer solution, and then add sodium dodecyl sulfate as an interfacial stabilizer, and disperse them evenly to form an aqueous phase solution; disperse 1,3,5-trialdehyde phloroglucinol in the trimesoyl chloride monomer solution to form an organic phase solution; Step 3: Pour the aqueous monomer solution onto the surface of the polysulfone ultrafiltration membrane, remove the excess aqueous monomer solution on the surface after 1 to 10 minutes of infiltration, then pour the organic monomer solution of the same volume as the aqueous monomer solution onto the surface of the polysulfone ultrafiltration membrane, after 2 to 300 seconds of in-situ copolymerization, remove the remaining organic solution on the surface, and then wash the surface of the polysulfone ultrafiltration membrane with n-hexane, followed by heat treatment to obtain a polyamide / sulfonated COFs reverse osmosis membrane.

2. The method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization according to claim 1, characterized in that: In the step 2, the MPD content in the aqueous monomer solution is 1.0 wt%~4.0 wt%, and the Pa-SO3H content is 0 wt%~2.0 wt%; the TMC content in the organic monomer solution is 0.01 wt%-0.3wt%, and the Tp content is 20 mg / L~500 mg / L; and the content of the interfacial stabilizer SDS is 0.01 wt%~0.2 wt%.

3. The method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization according to claim 1, characterized in that: The in-situ copolymerization reaction time is 2 to 300 s.

4. The method for preparing a polyamide / sulfonated COFs reverse osmosis membrane by in-situ copolymerization according to claim 1, characterized in that: The heat treatment temperature is 40-80°C and the time is 15-40 min.

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