Methoxy-type covalent organic framework composite membrane, preparation method and application thereof

Abstract

The application discloses a methoxy type covalent organic framework composite film and a preparation method and application thereof. The preparation method of the methoxy type covalent organic framework composite film comprises the following steps: (1) preparing an oil phase: weighing aldehyde monomers and amine monomers, adding the aldehyde monomers and the amine monomers into an organic solvent, and making the aldehyde monomers and the amine monomers completely dissolved to obtain the oil phase; (2) preparing a water phase: the water phase is an acetic acid aqueous solution; and (3) obtaining the methoxy type covalent organic framework composite film through an interfacial polymerization method. The application provides application of the methoxy type covalent organic framework composite film in organic matter filtration and organic matter selective screening, and the methoxy type covalent organic framework composite film has low cost, small energy consumption and high separation efficiency.

Description

Technical Field

[0001] This invention belongs to the field of pressure-driven membrane separation, specifically relating to covalent organic framework composite membranes, their preparation methods, and applications. Technical Background

[0002] Chemical separation is a crucial aspect of the chemical industry, with some energy consumption in industrial separation processes relying on heating procedures involving chemical phase changes, such as distillation or evaporation. Notably, nanofiltration membrane separation technology is increasingly becoming an advanced separation method worthy of extensive research due to its high separation efficiency and environmental sustainability. Traditional polymer nanofiltration (NF) membranes are primarily characterized by a non-porous, amorphous network with a theoretical pore size of less than 2 nm. The filtration process within these membranes involves the slow movement of water molecules through a disordered network driven by a concentration gradient. This leads to a trade-off between low permeability and high solute repulsion in NF membranes.

[0003] Furthermore, the amorphous network structure of traditional nanofiltration membranes complicates their separation mechanism, resulting in separation efficiencies lower than theoretically expected. This presents a challenge for traditional polymer nanofiltration membranes in achieving effective molecular separation. Therefore, researchers have proposed a strategic approach to design ordered nanoporous membranes at the molecular level. The emergence of nanoporous molecular sieve membranes, represented by graphene, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs), has provided new directions for membrane technology development. Among them, COFs, as crystalline polymers with inherent porosity, stand out, offering customizable molecular-level structures and functional properties. This unique property not only creates higher separation performance but also introduces innovative pathways for molecular sieving. Typically, COF molecular sieving relies on mixing two or more substances with significantly different molecular weights, structures, and other physicochemical properties; sieving two substances with similar molecular weights or other similar physicochemical properties is nearly impossible. This invention facilitates the further development of COF composite membranes for the selective sieving of near-molecular-weight organic compounds. Summary of the Invention

[0004] The purpose of this invention is to provide a methoxy-based covalent organic framework composite membrane, its preparation method, and its application in filtering organic matter and selectively sieving organic matter.

[0005] The present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a methoxy-based covalent organic framework composite membrane, the method comprising the following steps:

[0007] (1) Preparation of oil phase: Weigh the aldehyde monomer and amine monomer and add them to an organic solvent to dissolve them completely to obtain the oil phase; the aldehyde monomer is 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl (TFB-OMe), the amine monomer is tris(4-aminophenyl)amine (TAPA), and the molar ratio of the aldehyde monomer and the amine monomer is between 1:1 and 1:3;

[0008] (2) Preparation of aqueous phase: The aqueous phase is an aqueous solution of acetic acid, and the acetic acid is used as a catalyst;

[0009] (3) First, fix the ultrafiltration base membrane onto the interfacial polymerization framework. Then, pour the aqueous phase onto the front side of the ultrafiltration base membrane and time it for 5–90 seconds. Pour off the aqueous phase from the membrane surface and allow it to air dry naturally until there are no water stains. Next, pour the oil phase onto the front side of the membrane and time it for 5–90 seconds. Pour off the oil phase from the membrane surface and allow it to air dry naturally. Place the membrane after interfacial polymerization in a vacuum drying oven at 40–120°C for 1–8 minutes to obtain a methoxy-type covalent organic framework composite membrane. Then, store the composite membrane in deionized water for further use.

[0010] In this invention, the ultrafiltration base membrane is preferably a polyacrylonitrile (PAN) ultrafiltration membrane.

[0011] Furthermore, in step (1), the molar ratio of the aldehyde monomer and the amine monomer is 1:1.

[0012] Furthermore, in step (1), the organic solvent is selected from at least one of n-hexane, mesitylene, and dichloromethane (DCM), more preferably dichloromethane.

[0013] Furthermore, in step (2), the aqueous phase is a 0.005-0.1M aqueous solution of acetic acid, more preferably a 0.015-0.055M aqueous solution of acetic acid.

[0014] Furthermore, in step (3), the contact time between the aqueous phase and the ultrafiltration membrane is 10-60s, most preferably 30s; the contact time between the oil phase and the membrane is 10-60s, more preferably 10-30s, and most preferably 10s.

[0015] Furthermore, in step (3), the membrane after interfacial polymerization is placed in a vacuum drying oven at 50-90°C, more preferably 60°C; and heat-treated for 3-8 minutes, most preferably 5 minutes.

[0016] In a second aspect, the present invention provides a methoxyl-containing covalent organic framework composite membrane prepared according to the preparation method described in the first aspect.

[0017] Thirdly, the present invention provides the application of the methoxy-containing covalent organic framework composite membrane in filtering organic matter, wherein the organic matter is a negatively charged organic matter with a molecular weight Mw ≥ 450 g / mol or a positively charged organic matter with a molecular weight Mw ≥ 1000 g / mol.

[0018] Preferably, the organic compound is a negatively charged organic compound with a molecular weight Mw ≥ 461 g / mol or a positively charged organic compound with a molecular weight Mw ≥ 1298 g / mol. For example, it has excellent retention effects on organic compounds such as Eriochrome Black T (EBT, Mw = 461 g / mol, negatively charged), Congo Red (CR, Mw = 696 g / mol, negatively charged), Coomassie Brilliant Blue G250 (G250, Mw = 854 g / mol, negatively charged), and Alsin Blue (AB, Mw = 1298 g / mol, positively charged).

[0019] Fourthly, the present invention provides the application of the methoxy-type covalent organic framework composite membrane in the selective sieving of organic matter, wherein one of the organic matter to be sieved is a negatively charged organic matter with a molecular weight Mw ≥ 450 g / mol or a positively charged organic matter with a molecular weight Mw ≥ 1000 g / mol, and the other is a negatively charged organic matter with a molecular weight Mw < 450 g / mol or a positively charged organic matter with a molecular weight Mw < 500 g / mol.

[0020] Preferably, among the organic compounds to be screened, one type is a negatively charged organic compound with a molecular weight Mw ≥ 461 g / mol or a positively charged organic compound with a molecular weight Mw ≥ 1298 g / mol, and the other type is a negatively charged organic compound with a molecular weight Mw ≤ 327 g / mol or a positively charged organic compound with a molecular weight Mw ≤ 479 g / mol.

[0021] This invention provides a methoxy-based covalent organic framework composite membrane prepared by interfacial polymerization of triphenylaminoamine as an amine monomer and an aldehyde monomer with a methoxy side chain. The small pore size of the methoxy-containing and negatively charged COF allows negatively charged organic compounds with a molecular weight less than 450 g / mol to pass through, while retaining large organic molecules (Eriochrome Black T, Congo Red, Coomassie Brilliant Blue G250). It also achieves selective sieving of two organic compounds with very similar molecular weights, ultimately resulting in a composite nanofiltration membrane with a high retention rate for large organic molecules and the ability to selectively sieve near-molecular-weight organic compounds.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] (1) The methoxy-type covalent organic framework composite membrane prepared by the present invention can achieve efficient separation of organic macromolecules, and can operate stably for a long time under a low operating pressure of 0.1 MPa. It has low cost, low energy consumption and high separation efficiency.

[0024] (2) The methoxy-type covalent organic framework composite membrane prepared by the present invention has a more compact COF layer formed by interfacial polymerization compared with PAN-based membrane, which in turn reduces the membrane's permeability.

[0025] (3) The methoxy-based covalent organic framework composite membrane prepared in this invention exhibits high rejection rates for four organic compounds: Eriochrome Black T (EBT, Mw = 461 g / mol, negatively charged), Congo Red (CR, Mw = 696 g / mol, negatively charged), Coomassie Brilliant Blue G250 (G250, Mw = 854 g / mol, negatively charged), and Alsin Blue (AB, Mw = 1298 g / mol, positively charged). Furthermore, the separation performance of the COF composite membrane is related to the charge and molecular weight of the organic compounds. When the molecular weights are similar, the rejection rate for negatively charged organic compounds is higher; however, as the molecular weight increases, the rejection rate shows a significant increase.

[0026] (4) The methoxy-type covalent organic framework composite membrane prepared by the present invention has a large difference in the retention of two organic compounds with similar molecular weights, which enables it to be used in the sieving system of organic compounds with similar molecular weights.

[0027] (5) The methoxy-type covalent organic framework composite membrane prepared by the present invention has an increased water contact angle due to the presence of methoxy groups in the aldehyde monomer. Attached Figure Description

[0028] Figure 1 A schematic diagram of the chemical synthesis and theoretical simulation pore size of the methoxy-based covalent organic framework TFB-OMe-TAPACOF;

[0029] Figure 2 The infrared spectra of the amine monomer, aldehyde monomer, PAN base film, and prepared M1 film used in Example 1 of the present invention are shown.

[0030] Figure 3 The images show scanning electron microscope (SEM) images of the surface and cross-section of the polyacrylonitrile-based membrane and the prepared M1 membrane used in Example 1 of this invention; in the images: a1) is the surface of the polyacrylonitrile-based membrane; a2) is the surface of the M1 membrane; b1) is the cross-section of the membrane (PAN surface); b2) is the cross-section of the M1 membrane;

[0031] Figure 4 The permeation coefficients of the methoxy-based COF composite membrane and the PAN-based membrane prepared in the embodiments of the present invention for deionized water;

[0032] Figure 5-1 and 5-2The images show the retention effects of the M1 membrane prepared in Example 1 of this invention on negatively charged organic compounds of different molecular weights (methyl orange (MO, Mw = 327 g / mol), chrome black T (EBT, Mw = 461 g / mol), Congo red (CR, Mw = 696 g / mol), Coomassie brilliant blue G250 (G250, Mw = 854 g / mol)) and positively charged organic compounds of different molecular weights (rhodamine B (RhB, Mw = 479 g / mol) and alsine blue (AB, Mw = 1298 g / mol)).

[0033] Figure 6 The sieving effect of the M1 membrane prepared in Example 1 of the present invention on a mixed solution of 0.05 g / L methyl orange and 0.05 g / L chrome black T;

[0034] Figure 7 The sieving effect of the M1 membrane prepared in Example 1 of the present invention on a mixed solution of 0.05 g / L Chrome Black T and 0.05 g / L Rhodamine B;

[0035] Figure 8 The contact angle (in aqueous solution) of the M1 film and the PAN base film prepared in Example 1 of the present invention.

[0036] Figure 9 This study demonstrates the retention effect of the M1 membrane prepared in Example 1 of this invention on a long-term test of an organic compound, Congo red (CR, Mw = 696 g / mol). Detailed Implementation

[0037] The following examples further illustrate the content of the present invention, but the content of the present invention is not limited to the following examples. The following examples describe in more detail the covalent organic framework composite membrane for selective sieving of near-molecular-weight organic compounds and its preparation method, and these examples are given by way of illustration, but these examples do not limit the scope of the present invention. Unless otherwise specified, the experimental methods used in the present invention are conventional methods, and the experimental equipment, materials, reagents, etc. used can be purchased from chemical companies.

[0038] The PAN (GC-UF0503) used in this embodiment of the invention was purchased from Guochu Technology (Xiamen) Co., Ltd.

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0040] Example 1:

[0041] (1) Preparation of TAPA / TFB COF composite membrane: At room temperature, 12.0 mg of 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl (TFB-OMe) and 13.8 mg of tris(4-aminophenyl)amine (TAPA) were weighed into 20.0 ml of dichloromethane and mixed and ultrasonically stirred until completely dissolved, which served as the organic phase. The aqueous phase consisted of 20.0 ml of deionized water with 240 μl of 3M acetic acid aqueous solution added. A 9 cm × 9 cm PAN ultrafiltration membrane was fixed on the interfacial polymerization frame, and then the aqueous phase was poured onto the front side of the membrane. After 30 seconds, the aqueous phase on the membrane surface was poured off and allowed to air dry naturally until no water stains remained. Then the oil phase was poured onto the front side of the membrane, and after 10 seconds, the oil phase on the membrane surface was poured off and allowed to air dry naturally. The membrane after interfacial polymerization was dried in a vacuum drying oven at 60°C for 5 minutes to obtain the TFB-OMe-TAPA / PAN COF composite membrane, named M1 membrane. The composite membrane was then stored in deionized water for further use.

[0042] (2) Evaluation of nanofiltration membrane separation performance: Using the M1 membrane prepared by the method described in this invention as the filter membrane, it was placed in a filtration device and subjected to cross-flow filtration at 25°C and 0.1 MPa. The test area was 22.05 cm². 2 The permeability coefficient and rejection rate of the membrane were determined by detecting the solvent concentration in the filtrate. The solvent was a 0.05 g / L aqueous solution of organic matter. The permeability coefficient of the M1 membrane to a negatively charged methyl orange (MO, Mw = 327 g / mol, negatively charged) solution was measured to be 148.70 ± 9.20 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate of methyl orange (MO, Mw = 327 g / mol, negatively charged) was 2.72% ± 0.77%; the permeability of the chrome black T (EBT, Mw = 461 g / mol, negatively charged) solution was 100.80 ± 1.65 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate of Eriochrome Black T (EBT, Mw = 461 g / mol, negatively charged) was 95.88% ± 0.24%; the permeability coefficient of Congo Red (CR, Mw = 696 g / mol, negatively charged) solution was 60.55 ± 1.16 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate of Congo Red (CR, Mw = 696 g / mol, negatively charged) was 98.09% ± 0.16%; the permeability coefficient of Coomassie Brilliant Blue G250 (G250, Mw = 854 g / mol, negatively charged) solution was 47.96 ± 0.07 L·m⁻¹. -2 ·h -1 ·bar-1 The retention rate of Coomassie Brilliant Blue G250 (G250, Mw = 854 g / mol, negatively charged) was 99.08% ± 0.03%. See appendix for details. Figure 5-1 The permeability of the M1 membrane to a positively charged Rhodamine B (RhB, Mw = 479 g / mol, positively charged) solution is 82.56 ± 1.25 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate of Rhodamine B (RhB, Mw = 479 g / mol, positively charged) was 2.86% ± 0.52%; the permeability coefficient of Alsin Blue (AB, Mw = 1298 g / mol, positively charged) solution was 29.58 ± 0.06 L·m⁻¹. -2 ·h -1 ·bar -1 The rejection rate of Alsin Blue (AB, Mw = 1298 g / mol, positively charged) was 99.35% ± 0.21%. See appendix for details. Figure 5-2 .

[0043] Example 2:

[0044] The M1 membrane prepared by the method described in this invention was used as a filter membrane and placed in a filtration device. Cross-flow filtration was performed at 25°C and 0.1 MPa, and the tested area was 22.05 cm². 2 The solvent was a mixed solution of 0.05 g / L methyl orange and chrome black T. After three consecutive sieve filtrations, the separation factor of the MO / EBT mixed system was calculated to be 7.8. See attached diagram for details. Figure 6 .

[0045] Example 3:

[0046] The M1 membrane prepared by the method described in this invention was used as a filter membrane and placed in a filtration device. Cross-flow filtration was performed at 25°C and 0.1 MPa, and the tested area was 22.05 cm². 2 The solvent was a mixed solution of two organic compounds, 0.05 g / L Chrome Black T and Rhodamine B. After three consecutive sieve filtrations, the separation factor of the MO / EBT mixed system was calculated to be 26.7. See attached document for details. Figure 7 .

[0047] In this invention, tris(4-aminophenyl)amine (TAPA) and 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl (TFB-OMe) are selected as the amine monomer and aldehyde monomer, respectively, and they undergo a Schiff base condensation reaction to generate a COF structure. See appendix for details. Figure 1 .

[0048] The M1 and PAN base films prepared according to the method in Example 1 were subjected to Fourier transform infrared spectroscopy. Analysis showed that the amine NH stretch band was 3200 cm⁻¹. -1 The disappearance of [something], while the newly appearing [something] is located at 1232cm. -1 The C=N ratio indicates the successful formation of a Schiff base structure in the resulting COF membrane, demonstrating the successful formation of a COF membrane on a PAN-based substrate. See appendix for details. Figure 2 .

[0049] M1 and PAN-based membranes prepared according to the method in Example 1 were selected for scanning electron microscopy (SEM) testing. Analysis of the surface SEM images showed that the growth of the COF membrane layer partially masked the pores in the PAN-based membrane, and the composite membrane surface was relatively smooth. This is consistent with experimental data showing that the COF composite membrane has a lower permeability coefficient for deionized water than the PAN-based membrane. Analysis of the cross-sectional SEM images revealed that the thickness of the M1 membrane was approximately 119–124 nm. See attached image for details. Figure 3 .

[0050] Example 4:

[0051] M1 and PAN-based membranes prepared according to the method in Example 1 were selected, and their permeation coefficients for deionized water were tested. Test conditions: cross-flow filtration at 25°C and 0.1 MPa; test area: 22.05 cm². 2 The permeability coefficient of the PAN-based membrane to deionized water is 126.07 ± 6.99 L·m. -2 ·h -1 ·bar -1 The permeability coefficient of the M1 membrane for deionized water is 90.10 ± 1.34 L·m. -2 ·h -1 ·bar -1 See appendix for details. Figure 4 .

[0052] Example 5:

[0053] M1 and PAN base films prepared according to the method in Example 1 were selected, and their deionized water contact angles were tested to evaluate their hydrophilicity and hydrophobicity properties. The water contact angle of PAN was 66.9 ± 4.3°; the water contact angle of M1 was 79.0 ± 8.6°. This result is consistent with the hydrophilicity / hydrophobicity principle caused by the presence of methoxy groups in aldehyde monomers. See Appendix for details. Figure 8 .

[0054] Example 6:

[0055] M1, prepared according to the method in Example 1, was used to determine its long-term rejection rate and flux for a mixed solution of Congo red and sodium chloride. The concentration of Congo red (CR, Mw = 696 g / mol) was 0.05 g / L, the test pressure was 0.1 MPa, the test temperature was 25°C, cross-flow filtration was used, and the test area was 22.05 cm². 2 The test duration was 40 hours. The M1 membrane showed a rejection rate of over 98.00% for Congo red (CR, Mw = 696 g / mol), with a flux of approximately 65 L·m⁻¹. -2 ·h -1 ·bar -1 Left and right. See appendix for details. Figure 9 .

Claims

1. The application of a methoxyl-containing covalent organic framework composite membrane in the selective sieving of organic matter, characterized in that: Among the organic compounds to be screened, one type is a negatively charged organic compound with a molecular weight Mw ≥ 461 g / mol or a positively charged organic compound with a molecular weight Mw ≥ 1298 g / mol, and the other type is a negatively charged organic compound with a molecular weight Mw ≤ 327 g / mol or a positively charged organic compound with a molecular weight Mw ≤ 479 g / mol. The preparation method of the methoxyl-containing covalent organic framework composite membrane includes the following steps: (1) Preparation of oil phase: Weigh the aldehyde monomer and amine monomer and add them to an organic solvent to dissolve them completely to obtain the oil phase; the aldehyde monomer is 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl, the amine monomer is tris(4-aminophenyl)amine, and the molar ratio of the aldehyde monomer and the amine monomer is 1:1; (2) Preparation of the aqueous phase: The aqueous phase is a 0.015-0.055 M aqueous solution of acetic acid; (3) First, fix the ultrafiltration base membrane on the interfacial polymerization framework, then pour the aqueous phase onto the front side of the ultrafiltration base membrane, time for 30 s, pour off the aqueous phase on the membrane surface, and let it air dry naturally until there are no water stains; then pour the oil phase onto the front side of the membrane, time for 10 s, pour off the oil phase on the membrane surface, and wait for it to air dry naturally; place the membrane after interfacial polymerization in a vacuum drying oven at 60 ℃ for 1~8 min to obtain a covalent organic framework composite membrane with methoxy groups.

2. The application as described in claim 1, characterized in that: The ultrafiltration base membrane is a polyacrylonitrile ultrafiltration membrane.

3. The application as described in claim 1, characterized in that: In step (1), the organic solvent is selected from at least one of n-hexane, mesitylene, and dichloromethane.

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