Preparation method and application of covalent organic framework film with amphiphilic cavity cyclodextrin

Abstract

This invention belongs to the field of covalent organic framework membranes, and discloses a covalent organic framework membrane with amphiphilic cleft cyclodextrin, its preparation method, and its application. The preparation method includes the following steps: Step 1: Synthesis of COF nanosheets; Step 2: Preparation of the amphiphilic cleft cyclodextrin COF membrane. The application of the amphiphilic cleft cyclodextrin COF membrane prepared by the above method in dye and / or salt separation solutions is also disclosed. This invention achieves efficient molecular / ion separation by embedding cyclodextrin (CD) with a hydrophilic outer cavity and a hydrophobic inner cavity into adjacent COF nanosheets through a vacuum-assisted self-assembly process, and obtains an amphiphilic cleft cyclodextrin COF membrane with adjustable mass transfer channels. The embedding of CD can adjust the interlayer spacing between COF nanosheets, forming continuous mass transfer channels, thereby improving membrane permeability.

Description

Technical Field

[0001] This invention belongs to the field of covalent organic framework membranes, specifically a covalent organic framework membrane with amphiphilic cyclodextrin, its preparation method, and its application. Background Technology

[0002] Covalent organic framework (COF) membranes have broad application prospects, with known applications including water treatment, gas separation, energy storage, and conversion. COF membranes hold great potential in water treatment, particularly in the separation of salts and dyes. For dye separation, COF membranes show significant application potential. The tunable pore structure and chemical environment of COF membranes enable the selective separation of dye molecules. By adjusting the pore size, surface properties, and hydrophilic / hydrophobic characteristics of COF membranes, efficient separation of dyes of different types and sizes can be achieved. COF membranes also show potential in the separation of salt and dye mixtures. In the separation of salt and dye mixtures, COF membranes can achieve selective separation by adjusting their pore structure and surface properties. COF membranes with specific pore sizes can be designed to selectively block one component based on the different properties of salts and dyes. For example, COF membranes can be designed with smaller pore sizes to allow salt ions to pass through while blocking dye molecules. Thus, when the mixture passes through the COF membrane, salt ions can be effectively separated, while dye molecules are trapped within the membrane. Furthermore, the charge-selective properties of COF membranes can also be utilized. By modifying the surface of COF membranes or controlling their charge properties, salt ions or dye molecules with specific charges can be selectively retained, leading to their selective separation on the COF membrane. This is significant for addressing environmentally and economically important issues such as dye wastewater treatment and dye recovery. In summary, COF membranes possess unique advantages and potential for salt and dye separation in water treatment. By adjusting the pore size, chemical properties, and surface characteristics of COF membranes, highly efficient salt and dye separation can be achieved, providing a sustainable, efficient, and environmentally friendly solution for water resource development and protection.

[0003] Currently, various methods for preparing COF films have been explored, including in-situ growth and self-assembly. In-situ grown COF films are formed by direct crystallization at interfaces or on substrates, and have the potential for large-area preparation. However, defects such as lattice defects and incomplete crystal interfaces may exist between crystals, which adversely affect the retention of small molecules. In contrast, two-dimensional (2D) COF nanosheets with good processability can be prepared into self-assembled COF films through methods such as pressure, vacuum-assisted filtration, or coating, ensuring the integrity and continuity of the film. In addition, a series of liquid-liquid interface synthesis methods have been developed to prepare highly crystallinity, high quality, and high yield 2D COF nanosheets, and their morphology and size can be effectively controlled by adjusting the concentration, pH, and temperature. Whether in single-phase, two-phase, or multi-solution systems, organic / aqueous phase synthesis methods have proven to be an effective route for synthesizing highly crystallinity COF nanosheets.

[0004] For self-assembled COF membranes, the stacking behavior of COF nanosheets significantly affects membrane performance. This can be achieved by modulating the interlayer interactions between COF nanosheets. Ideally, COF nanosheets self-assemble into COF membranes via AA stacking, forming ultrashort and vertical mass transfer channels to achieve high membrane permeability. However, in self-assembled COF membranes, COF nanosheets are not entirely stacked in an AA stacking pattern, but rather in other stacking patterns such as AB or ABC stacking. Incomplete AA stacking leads to increased mass transfer resistance, thereby reducing the permeability of the COF membrane. Therefore, it is necessary to explore ways to optimize the stacking behavior of COF nanosheets and fully utilize the porosity of the COF nanosheets to maximize the separation performance of the COF membrane. Summary of the Invention

[0005] To improve the permeability of COF membranes and address the increased mass transfer resistance caused by incomplete AA stacking during COF nanosheet self-assembly, this invention provides a method for preparing a covalent organic framework membrane with amphiphilic cyclodextrin and its application. The specific technical solution is as follows:

[0006] A method for preparing an amphiphilic cyclodextrin COF membrane includes the following steps:

[0007] Step 1: Synthesis of COF nanosheets

[0008] COF nanosheets were synthesized using a liquid-liquid interface synthesis method. The specific steps were as follows: 0.1 mmol of trimethylolpropane (Tp) and 0.15 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO3H) were dissolved in 20 mL of octanoic acid and 30 mL of deionized water, respectively. The resulting solutions were sonicated for 0.5 h. The octanoic acid solution containing Tp was then added dropwise to the top layer of the aqueous solution containing Pa-SO3H, and the reaction was carried out at 20 °C for 7 days. After the reaction was completed, the bottom aqueous phase was collected and transferred to a dialysis tube for dialyzing for 3 days. Finally, the concentration was determined to be 1 mg / mL using a dry weighing method.

[0009] Step 2: Preparation of amphiphilic cyclodextrin COF membrane

[0010] A COF membrane with amphiphilic cavity cyclodextrin was prepared by vacuum-assisted self-assembly. The specific steps were as follows: a certain amount of COF nanosheets and CD prepared in step one were thoroughly mixed to obtain a uniform dispersion; the mixture was filtered through a vacuum filter onto a PAN membrane and then dried at 60°C for 0.25 h to finally prepare a CD / COF-x membrane, where x represents the amount of CD assembled.

[0011] Furthermore, the MWCO of the dialysis tube described in step one is 30,000 Da.

[0012] Furthermore, in step two, the CD assembly amount x corresponding to 1 mg COF nanosheets is 1 mg, 5 mg, or 10 mg.

[0013] Furthermore, the CD is one or more of γ-CD, α-CD, and β-CD.

[0014] Application of the amphiphilic cyclodextrin COF membrane prepared by the above method in dye and / or salt separation solutions.

[0015] This invention utilizes a vacuum-assisted self-assembly process to embed cyclodextrin (CD) with a hydrophilic outer cavity and a hydrophobic inner cavity into adjacent COF nanosheets, achieving highly efficient molecular / ion separation and obtaining an amphiphilic cavity cyclodextrin COF membrane with tunable mass transfer channels. The embedding of CD can adjust the interlayer spacing between COF nanosheets, forming continuous mass transfer channels, thereby improving membrane permeability. The separation capability of molecules and ions in the CD / COF membrane is evaluated by testing the retention effect of the mixed solution on dye molecules and salt ions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the relationship between CD assembly quantity and CD / COF film thickness;

[0017] Figure 2 This is a schematic diagram showing the relationship between CD assembly quantity and the surface roughness of the CD / COF film. Detailed Implementation

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] The method for preparing the amphiphilic cyclodextrin COF membrane of the present invention includes the following steps:

[0020] Step 1: Synthesis of COF nanosheets

[0021] COF nanosheets were synthesized using a liquid-liquid interface synthesis method. The specific steps were as follows: 0.1 mmol of trimethylolpropane (Tp) and 0.15 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO3H) were dissolved in 20 mL of octanoic acid and 30 mL of deionized water, respectively. The resulting solutions were sonicated for 0.5 h to ensure proper dispersion. The octanoic acid solution containing Tp was carefully added dropwise to the top layer of the aqueous solution containing Pa-SO3H, and the reaction was carried out at 20 °C for 7 days. After the reaction was complete, the bottom aqueous phase was collected and transferred to a dialysis tube (MWCO = 30,000 Da) for dialyzing for 3 days. Finally, the concentration was determined to be 1 mg / mL using the dry weighing method.

[0022] Step 2: Preparation of amphiphilic cyclodextrin COF membrane

[0023] A vacuum-assisted self-assembly method was used to prepare amphiphilic cyclodextrin COF membranes. The specific steps were as follows: a certain amount of COF nanosheets obtained in step one and γ-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was vacuum filtered onto a PAN membrane and then dried at 60°C for 0.25 h to finally prepare a CD / COF-x membrane (where x represents the amount of CD assembled, which can be selected from 1 mg, 5 mg, or 10 mg). Furthermore, using 1 mg of COF nanosheets and 10 mg of different types of cyclodextrins (α-CD and β-CD), an α / β-CD / COF-10 membrane was prepared using the same method.

[0024] Preparation of COF membranes

[0025] COF membranes were prepared using a vacuum-assisted self-assembly method. The specific steps were as follows: a certain amount of COF nanosheets obtained in step one were vacuum filtered onto a PAN membrane and then dried at 60°C for 0.25 h. During this process, a series of COF-x membranes (where x included 0.5 mg, 0.8 mg, and 1.0 mg) were prepared by changing the assembly amount of COF nanosheets.

[0026] The mass transfer channels within the COF membrane were controlled by adjusting the amount of CD assembly. SEM cross-sectional images revealed that the thickness of the COF membrane without CD (COF-1.0) was 0.25 ± 0.02 μm. Figure 1As shown, with the increase of CD assembly amount, from 1 mg to 10 mg, the film thickness gradually increased from 0.40 ± 0.02 μm to 0.93 ± 0.01 μm. This is because the introduction of CD increases the interlayer spacing between adjacent COF nanosheets, thereby increasing the film thickness. Figure 2 As shown, AFM images revealed a slight increase in the surface roughness of the CD / COF film with increasing CD assembly amount. This slight increase in surface roughness indicates that CDs are primarily enriched between adjacent COF nanosheets to increase the interlayer spacing.

[0027] COF membrane testing

[0028] Test Example 1

[0029] 1.0 mg of COF nanosheets were vacuum filtered onto a PAN membrane and then dried at 60 °C for 0.25 h, resulting in the COF-1.0 membrane. Water flux permeability tests were conducted on the COF-1.0 membrane in dead-end filtration, and selectivity tests were performed on organic dyes such as methyl orange (MO), methylene blue (MEB), chrome black T (EBT), and alexandrite blue (AB). The results showed that the COF-1.0 membrane exhibited a pure water flux of 42 L / m³ at an operating pressure of 2 bar. -2 h -1 The retention rates for the four dyes were 88.3% (MO), 96.5% (MEB), 97.9% (EBT), and 98.3% (AB), respectively.

[0030] Test Example 2

[0031] 0.5 mg of COF nanosheets were vacuum filtered onto a PAN membrane and then dried at 60 °C for 0.25 h, resulting in a COF-0.5 membrane. Water flux permeability tests were conducted on the COF-0.5 membrane in dead-end filtration, and selectivity tests were performed on the retention of organic dyes such as MO, MEB, EBT, and AB. The results showed that the COF-0.5 membrane exhibited a pure water flux of 73.7 L / m³ at an operating pressure of 2 bar. -2 h -1 The rejection rates for the four dyes were 86.6% (MO), 95.5% (MEB), 96.8% (EBT), and 97.2% (AB), respectively.

[0032] Test Example 3

[0033] COF nanosheets with a concentration of 0.8 mg were vacuum filtered onto a PAN membrane and then dried at 60 °C for 0.25 h, resulting in a membrane designated COF-0.8. Water flux permeability tests were conducted on the COF-0.8 membrane in dead-end filtration, and selectivity tests were performed on the retention of organic dyes such as MO, MEB, EBT, and AB. The results showed that the COF-0.8 membrane exhibited a pure water flux of 58 Lm³ at an operating pressure of 2 bar. -2 h -1 The rejection rates for the four dyes were 87.1% (MO), 95.8% (MEB), 97.2% (EBT), and 97.4% (AB), respectively.

[0034] Table 1 shows that the nanofiltration performance of COF membranes was evaluated by varying the assembly amounts of COF nanosheets. The results indicate that as the assembly amount of COF nanosheets increased from 0.5 mg to 1.0 mg, the water flux increased from 74 L / m³ to [missing value]. - 2h -1 (COF-0.5) reduced to 42 L m - 2 h -1 (COF-1.0). This change can be explained by the inverse relationship between membrane permeability and membrane thickness, where increasing the assembly amount leads to an increase in membrane thickness, thereby reducing membrane permeability. Meanwhile, COF membranes with different assembly amounts of COF nanosheets exhibit a retention rate exceeding 96% for large-sized dye molecules, primarily attributed to the size sieving effect. This effect occurs when the pore or channel size on the membrane is smaller than the size of the dye molecule, thus hindering the passage of dye molecules and enhancing the selectivity of the COF membrane.

[0035] Example 1

[0036] 1.0 mg of COF nanosheets and 10 mg of γ-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was then vacuum filtered onto a PAN membrane and dried at 60 °C for 0.25 h to prepare a CD / COF-10 membrane. Water flux permeability tests were conducted on the CD / COF-10 membrane in dead-end filtration, and selectivity tests were performed for the retention of organic dyes such as MO, MEB, EBT, and AB. The results showed that the CD / COF-10 membrane exhibited a pure water flux of 160 μm³ at an operating pressure of 2 bar. -2 h -1 The retention rates for the four dyes were 95.9% (MO), 97.1% (MEB), 99.4% (EBT), and 99.6% (AB), respectively.

[0037] Test Example 1 was used as a comparative example of Example 1.

[0038] As shown in Table 1, the mass transport channels of the COF membrane were modulated using CDs, which have external hydrophilic properties and internal hydrophobic cavities. The incorporation of CDs significantly enhanced the permeability of the amphiphilic cavity cyclodextrin COF membrane with tunable mass transfer channels, resulting in a 4-fold increase in water flux compared to the COF membrane without CDs (COF-1.0). This is because during the assembly of COF nanosheets into the COF membrane, the COF nanosheets tend to overlap, leading to coiled and discontinuous mass transfer channels. However, with the introduction of CDs, adjacent COF nanosheets form continuous channels both in-plane and between layers, thereby increasing the membrane permeability.

[0039] Example 2

[0040] 1.0 mg of COF nanosheets and 1 mg of γ-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was then vacuum filtered onto a PAN membrane and dried at 60 °C for 0.25 h to prepare the CD / COF-1 membrane. Water flux permeability tests were conducted on the CD / COF-1 membrane in dead-end filtration, and selectivity tests were performed for organic dyes such as MO, MEB, EBT, and AB. The results showed that the CD / COF-1 membrane exhibited a pure water flux of 93 L / m³ at an operating pressure of 2 bar. -2 h -1 The retention rates for the four dyes were 94.8% (MO), 96.6% (MEB), 98.1% (EBT), and 99.1% (AB), respectively.

[0041] Example 3

[0042] 1.0 mg of COF nanosheets and 5 mg of γ-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was then vacuum filtered onto a PAN membrane and dried at 60 °C for 0.25 h to prepare the CD / COF-5 membrane. Water flux permeability tests were conducted on the CD / COF-5 membrane in dead-end filtration, and selectivity tests were performed for organic dyes such as MO, MEB, EBT, and AB. The results showed that the CD / COF-5 membrane achieved a pure water flux of 129 L / m³ at an operating pressure of 2 bar. -2 h -1 The rejection rates for the four dyes were 95.2% (MO), 97.1% (MEB), 98.8% (EBT), and 99.5% (AB), respectively.

[0043] As shown in Table 1, a comparison of Examples 1-3 shows that when the amount of CD assembled increases from 1 mg (CD / COF-1) to 10 mg (CD / COF-10), the water flux increases from 93 L / m³. -2 h -1 Increased to 160L m -2h -1 The introduction of CD improves the mass transfer channels within the COF membrane, explaining the significant enhancement in membrane permeability. Simultaneously, in amphiphilic cavity cyclodextrin COF membranes with tunable mass transfer channels, the rejection rate for macromolecular dyes exceeds 97%. This is because the inherent pore size of the amphiphilic cavity cyclodextrin COF membrane with tunable mass transfer channels is smaller than that of the COF nanosheets, and the rejection rate is affected by the size sieving effect, allowing larger AB molecules to pass through. The retention rate was significantly higher than 99%. Furthermore, the Donnan effect also played a role; the amphiphilic cavity cyclodextrin COF membrane with tunable mass transfer channels exhibited higher repulsion for negatively charged EBTs and slightly lower repulsion for positively charged MEBs, despite their similar dimensions.

[0044] Example 4

[0045] 1.0 mg of COF nanosheets and 10 mg of α-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was then vacuum filtered onto a PAN membrane and dried at 60 °C for 0.25 h to prepare the α-CD / COF-10 membrane. Water flux permeability tests were conducted on the α-CD / COF-10 membrane in dead-end filtration, and selectivity tests were performed for organic dyes such as MO, MEB, EBT, and AB. The results showed that the α-CD / COF-10 membrane exhibited a pure water flux of 110 L / m³ at an operating pressure of 2 bar. -2 h -1 The rejection rates for the four dyes were 91.0% (MO), 96.4% (MEB), 97.8% (EBT), and 98.2% (AB), respectively.

[0046] Example 5

[0047] 1.0 mg of COF nanosheets and 10 mg of β-CD were thoroughly mixed to obtain a uniform dispersion. The resulting mixture was then vacuum filtered onto a PAN membrane and dried at 60 °C for 0.25 h to prepare the β-CD / COF-10 membrane. Water flux permeability tests were conducted on the β-CD / COF-10 membrane in dead-end filtration, and selectivity tests were performed for organic dyes such as MO, MEB, EBT, and AB. The results showed that the β-CD / COF-10 membrane exhibited a pure water flux of 147 L / m³ at an operating pressure of 2 bar. -2 h -1 The retention rates for the four dyes were 91.8% (MO), 96.8% (MEB), 98.3% (EBT), and 98.8% (AB), respectively.

[0048] Table 1 shows the nanofiltration performance of CD / COF membranes with different sizes. The study found that the water flux of the CD / COF-10 membrane reached 160 L / m³. -2 h -1 It is significantly higher than α-CD / COF-10 (water flux 110 L m). -2 h -1 ) and β-CD / COF-10 (water flux 147 L m -2 h -1 The CD / COF-10 membrane exhibits better permeability than the α-CD / COF-10 and β-CD / COF-10 membranes. This is because the hydroxyl groups introduced by γ-CD are evenly distributed, enhancing the membrane's hydrophilicity and improving its permeability.

[0049] Example 6

[0050] The CD / COF-10 membrane obtained in Example 1 was used to test the dye / salt separation performance in a mixed solution of dye and salt. The CD / COF-10 membrane maintained a consistently high rejection rate for dye molecules, exceeding 99%. However, the rejection rate for salt ions showed less variation. In the AB / NaCl, AB / Na2SO4, EBT / NaCl, and EBT / Na2SO4 systems, the salt removal rates of the CD / COF-10 membrane were 11%, 11%, 28%, and 30%, respectively. The corresponding dye and salt selectivities were 304 (AB / NaCl), 252 (AB / Na2SO4), 163 (EBT / NaCl), and 95 (EBT / Na2SO4), respectively.

[0051] Example 7

[0052] The CD / COF-10 membrane obtained in Example 1 was used to test the dye / salt separation performance in separate solutions of dye and salt. The CD / COF-10 membrane showed retention rates of 99.6% (AB), 99.4% (EBT), 8.5% (NaCl), and 28.4% (Na2SO4) for dye and salt in separate solutions, respectively. The corresponding selectivities for dye and salt were 252 (AB / NaCl), 197 (AB / Na2SO4), 149 (EBT / NaCl), and 116 (EBT / Na2SO4), respectively.

[0053] As shown in Table 2, the CD / COF-10 membrane exhibits high selectivity in the dye-salt mixed solution, maintaining a rejection rate for dye molecules consistently above 99%, while the rejection rate for salt ions shows little variation. However, in separate dye and salt solutions, the membrane's rejection rates for dye and salt differ significantly. This indicates that the presence of salt may affect the membrane's selectivity for dye. Furthermore, the selectivity values ​​for dye and salt also vary between the mixed solution and the individual solutions, which may be related to the solution composition and ionic properties. Overall, the CD / COF-10 membrane demonstrates excellent performance in dye / salt separation.

[0054]

[0055]

[0056] Table 1. Nanofiltration performance of COF membranes and COF membranes with amphiphilic cavity cyclodextrin.

[0057]

[0058] Table 2. Dye / salt separation performance of amphiphilic cyclodextrin COF membranes.

Claims

1. A method for preparing a COF membrane with amphiphilic cyclodextrin, characterized in that... Includes the following steps: Step 1: Synthesis of COF nanosheets COF nanosheets were synthesized using a liquid-liquid interface synthesis method. The specific steps were as follows: 0.1 mmol of trimethylolpropionate (Tp) and 0.15 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO3H) were dissolved in 20 mL of octanoic acid and 30 mL of deionized water, respectively. The resulting solutions were sonicated for 0.5 h. The octanoic acid solution containing Tp was then added dropwise to the top layer of the aqueous solution containing Pa-SO3H, and the reaction was carried out at 20 °C for 7 days. After the reaction was completed, the bottom aqueous phase was collected and transferred to a dialysis tube for dialyzing for 3 days. Finally, the concentration was determined to be 1 mg / mL using a dry weighing method. Step 2: Preparation of amphiphilic cyclodextrin COF membrane A COF membrane with amphiphilic cavity cyclodextrin was prepared by vacuum-assisted self-assembly. The specific steps were as follows: a certain amount of COF nanosheets and CD prepared in step one were thoroughly mixed to obtain a uniform dispersion; the mixture was filtered through a vacuum filter onto a PAN membrane and then dried at 60 °C for 0.25 h to finally prepare a CD / COF-x membrane, where x represents the amount of CD assembled. In step two, the assembly amount x corresponding to 1 mg COF nanosheet CD is 1 mg, 5 mg, or 10 mg; The CD is one or more of γ-CD, α-CD, and β-CD.

2. The method for preparing an amphiphilic cyclodextrin COF membrane as described in claim 1, characterized in that: The MWCO of the dialysis tube mentioned in step 1 is 30,000 Da.

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