A method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration
By introducing polyethyleneimine-modified carbon nanotubes and monomers such as bipyridine into covalent organic framework membranes, highly crystalline COF membranes were synthesized in situ, solving the crystallinity problem of covalent organic framework membranes and achieving efficient organic solvent separation and low-energy processing.
Patent Information
- Application Number
- CN202410456466.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-16
- Publication Date
- 2025-12-02
- Estimated Expiration
- 2044-04-16
AI Technical Summary
Existing technologies make it difficult to prepare highly crystalline covalent organic framework membranes, resulting in poor processability and film-forming properties. Furthermore, traditional organic solvent treatment methods suffer from high energy consumption and environmental pollution.
Polyethyleneimine-modified carbon nanotubes (PEI@CNTs) were used as the base film. 2,4-Diaminoresorcinol was combined as the aldehyde monomer and 5,5'-diamino-2,2'-bipyridine (Bpy) as the amine monomer. Highly crystalline COFs films were synthesized in situ. Hexagonal β-ketoenamine linkages were formed by reversible enol-ketone tautomerism and dynamic imine bonds. The macrocyclic structure provided high crystallinity.
It achieves high efficiency in organic solvent separation, including high throughput and high rejection rate, reducing energy consumption and environmental pollution.
Smart Images
Figure BDA0004794386070000061
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing a covalent organic framework membrane resistant to organic solvents, belonging to the field of organic solvent nanofiltration membrane preparation technology. Background Technology
[0002] Organic solvents are a class of organic compounds widely used in daily life and production. They have relatively small molecular weights and are liquid at room temperature. Since the Second Industrial Revolution, the use of organic solvents in various industries has increased year by year, inevitably generating a large amount of organic solvent waste. Improper treatment and indiscriminate discharge of organic solvent waste have caused serious environmental pollution problems. Therefore, the treatment and recycling of organic solvents have gradually become a focus of attention. Currently, common methods for treating organic solvents include distillation, absorption, and extraction. Distillation generally operates at high temperatures, making it difficult to treat temperature-sensitive small organic molecules; it is only suitable for the separation of common industrial compounds. Extraction requires high-quality containers, and for some organic solvents with unclear extraction mechanisms, new solvents need to be introduced as extractants. Furthermore, the subsequent mixture requires secondary separation, increasing separation costs. Absorption utilizes the volatility of organic solvents, achieving separation and recovery by mixing organic waste gas with an absorbent through miscibility or reaction. However, absorbents are usually organic solvents, which can cause secondary environmental pollution and does not meet the requirements of green and sustainable development. Organic solvent nanofiltration technology, as an emerging organic solvent treatment technology, has attracted widespread attention due to its advantages such as low energy consumption, small footprint, no phase change or chemical reaction during separation, and high separation efficiency. As the core of organic solvent nanofiltration technology, the permeability selectivity of the organic solvent nanofiltration membrane determines the separation efficiency of the organic solvent nanofiltration process.
[0003] In recent years, covalent organic frameworks (COFs), as highly ordered framework polymers, have been recognized as promising high-performance membrane materials. COFs are expected to exhibit the following advantages as membrane materials: (1) COFs have a periodic framework pore structure with high porosity, which can overcome the trade-off effect between permeability and selectivity; (2) Compared with the disordered and tortuous polyamide network pores, the long-range ordered structure of the framework pores can reduce mass transfer resistance, enabling rapid water molecule transfer within the membrane and achieving high permeability; (3) COFs walls contain high-density, uniformly distributed cuttable sites, offering strong design flexibility and facilitating the simultaneous coupling of size sieving and electrostatic repulsion mechanisms to achieve high selectivity; (4) The rigid framework pores and π-π stacking effect theoretically make COFs resistant to acids and alkalis and have strong antioxidant properties. Therefore, COFs materials are expected to become a new generation of membrane materials in the field of organic solvent nanofiltration.
[0004] One of the major challenges in the preparation of COFs is the issue of crystallinity. Using strong covalent bonds to connect COF building blocks often results in low-crystallinity or amorphous materials. Theoretically, the connection of COF building blocks to form amorphous materials is a thermodynamically favorable process. Most polymers can be linked by strong covalent bonds between building blocks; however, these polymers are often disordered, making it difficult to obtain crystalline materials. To obtain crystalline polymers, the covalent bonds between building blocks need to be reversible, and the reaction rate needs to be controlled within a manageable range, allowing the building blocks in the polymer to self-correct and rectify defects, ultimately forming a crystalline polymer. Under mild conditions, the covalent bonds between building blocks usually tend towards irreversible covalent connections, making the formation of crystalline polymers through covalent bonding a significant challenge. Therefore, finding building block types that can form reversible covalent bonds and suitable reaction conditions is crucial for the synthesis of crystalline polymers. Dynamic covalent chemistry (DCC) involves a series of reversible equilibrium covalent chemical reactions based on thermodynamic equilibrium. The introduction of dynamic covalent chemistry provides a strong guarantee for the synthesis of crystalline materials and is widely used in the synthesis of crystalline COFs. Since COFs typically exist in the form of solid powders and are almost insoluble in any solvent, their processability and film-forming properties are poor. Furthermore, the preparation of COF films involves both polymerization and crystallization. Therefore, preparing highly crystalline COF films with a certain mechanical strength remains a significant challenge. Summary of the Invention
[0005] To address the aforementioned technical problems in the prior art, this invention provides a method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration, the specific technical solution of which is as follows:
[0006] A method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration specifically includes the following steps:
[0007] Step 1: Preparation of PEI@CNTs base film: Polyethyleneimine was dissolved in ethanol, and carbon nanotubes were added after complete dissolution. After sonication for a period of time, the mixture was allowed to stand for several hours. After centrifugation for a period of time, the supernatant was collected to obtain PEI@CNTs, and the concentration was measured by UV-vis. The PEI@CNTs were diluted and dispersed in deionized water and vacuum-coated into a mixed cellulose membrane (MCE). After drying at room temperature, the membrane was placed in N,N-dimethylacetamide (DMAC) to dissolve the MCE, thus obtaining the PEI@CNTs base film.
[0008] Step 2: In-situ synthesis of nanofiltration membranes:
[0009] 5,5'-Diamino-2,2'-bipyridine (Bpy) and 2,4,6-tricarboxymethylresorcinol (TFR) powders were dissolved in deionized (DI) water and 1,4-dioxane, respectively. Scandium trifluoromethanesulfonate catalyst was then added to the Bpy solution and dissolved completely by sonication. The prepared PEI@CNTs membrane was placed in a beaker, and the above Bpy and TFR solutions were added. The beaker was then sealed and allowed to stand at room temperature for reaction. The resulting membrane material was named TFR-Bpy1 / CNTs nanofiltration membrane. It was washed multiple times with 1,4-dioxane, ethanol, and DI water in sequence.
[0010] Furthermore, in step one, the mass ratio of polyethyleneimine to carbon nanotubes is 100 / 7 to 15.
[0011] Furthermore, in step one, the ultrasound time is 30-40 minutes.
[0012] Furthermore, in step one, the concentration of PEI@CNTs after dilution is 1-1.5 mg / L.
[0013] Furthermore, the mass ratio of Bpy to TFR was 8.4 / 6.3-5.6 / 3.9.
[0014] Furthermore, in step two, the ultrasound time is 15-25 minutes.
[0015] Furthermore, in step two, the reaction time is 48-72 hours.
[0016] The nanofiltration membrane prepared by this invention is used for the separation of organic solvents and dyes, and its separation performance is as follows: pure water flux is 200 Lm. -2 h - 1 bar -1 The ethanol flux was 48 Lm. -2 h -1 bar -1 The n-hexane flux is 128 Lm. -2 h -1 bar -1 The flux of ethyl acetate was 203 Lm. -2 h -1 bar -1 The retention rates were 98% for Congo Red, 99% for Methyl Blue, 93% for Tiger Red, and 99% for Alcian Blue.
[0017] The preparation method of this invention uses polyethyleneimine-modified carbon nanotubes (PEI@CNTs) as the base membrane, 2,4,6-tricarboxymethylresorcinol (TFR) as the aldehyde monomer, and 5,5'-diamino-2,2'-bipyridine (Bpy) as the amine monomer to synthesize highly crystalline COF membranes in situ for organic solvent nanofiltration. The PEI-modified CNTs substrate provides mechanical strength to the nanofiltration membrane. TFR, as an asymmetric aldehyde monomer, can achieve a balance between irreversible enol-keto tautomerism and dynamic imine bonds, thereby generating a hexagonal β-keto-enamine linked macrocycle. Through reversible imine exchange, a macrocycle containing imine bonds is formed, which can provide highly crystalline COFs. Detailed Implementation
[0018] The present invention will be further described below with reference to the embodiments.
[0019] Example 1
[0020] The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration in this embodiment includes the following steps:
[0021] Step 1: Preparation of PEI@CNTs base membrane: Weigh 600 mg of polyethyleneimine and dissolve it in 40 mL of ethanol. After complete dissolution, add 40 mg of carbon nanotubes, sonicate for 30 min, let stand for 12 h, centrifuge at 8000 rpm for 20 min, and collect the supernatant to obtain PEI@CNTs. The concentration is measured by UV-vis. Dilute PEI@CNTs to 1 mg / L, disperse in deionized water, and vacuum-film the membrane into a mixed cellulose membrane (MCE). After drying at room temperature, place the membrane in N,N-dimethylacetamide (DMAC) to dissolve the MCE, obtaining the PEI@CNTs base membrane.
[0022] Step 2: 16.75 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 11.64 mg of 2,4,6-tricarboxymethylresorcinol (TFR) powder were dissolved in 20 mL of deionized (DI) water and 20 mL of 1,4-dioxane, respectively. Then, 3.9 mg of scandium trifluoromethanesulfonate catalyst was added to the Bpy solution, and the mixture was sonicated for 15 min until fully dissolved. The prepared PEI@CNTs membrane was then placed in a beaker, and the aforementioned Bpy and TFR solutions were added. The beaker was then sealed and allowed to stand at room temperature for 72 hours. The resulting membrane material was named TFR-Bpy3 / CNTs nanofiltration membrane; it was then washed repeatedly with 1,4-dioxane, ethanol, and DI water.
[0023] The nanofiltration membrane from Example 1 was used for the separation of organic solvent dyes, and the separation performance was: pure water flux of 200 Lm. -2 h -1 bar -1The ethanol flux was 48 Lm. -2 h -1 bar -1 The n-hexane flux is 128 Lm. -2 h -1 bar -1 The flux of ethyl acetate was 203 Lm. -2 h - 1 bar -1 The retention rates were 98% for Congo Red, 99% for Methyl Blue, 93% for Tiger Red, and 99% for Alcian Blue.
[0024] Example 2
[0025] The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration in this embodiment includes the following steps:
[0026] Step 1: Preparation of PEI@CNTs base membrane: Weigh 500 mg of polyethyleneimine and dissolve it in 50 mL of ethanol. After complete dissolution, add 35 mg of carbon nanotubes, sonicate for 40 min, let stand for 24 h, centrifuge at 7000 rpm for 15 min, and collect the supernatant to obtain PEI@CNTs. The concentration is measured by UV-vis. Dilute PEI@CNTs to 1.5 mg / L, disperse in deionized water, and vacuum-cast into a mixed cellulose membrane (MCE). After drying at room temperature, place the membrane in N,N-dimethylacetamide (DMAC) to dissolve the MCE, obtaining the PEI@CNTs base membrane.
[0027] Step 2: 5.6 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 3.9 mg of 2,4,6-tricarboxymethylresorcinol (TFR) powder were dissolved in 20 mL of deionized (DI) water and 20 mL of 1,4-dioxane, respectively. Then, 1.3 mg of scandium trifluoromethanesulfonate catalyst was added to the Bpy solution, and the mixture was sonicated for 25 min until fully dissolved. The prepared PEI@CNTs substrate membrane was then placed in a beaker, and the aforementioned Bpy and TFR solutions were added. The beaker was then sealed and allowed to stand at room temperature for 48 hours. The resulting membrane material was named TFR-Bpy1 / CNTs nanofiltration membrane; it was then washed repeatedly with 1,4-dioxane, ethanol, and DI water.
[0028] The nanofiltration membrane from Example 2 was used for the separation of organic solvent dyes, and the separation performance was: pure water flux of 236 Lm. -2 h -1 bar -1 The ethanol flux is 50 Lm -2 h -1 bar -1 The hexane flux was 194 Lm. -2h -1 bar -1 The ethyl acetate flux was 261 Lm. -2 h - 1 bar -1 The rejection rates were 96% for Congo Red, 85% for Methyl Blue, 80% for Tiger Red, and 99% for Alcian Blue.
[0029] Comparative Example 1
[0030] The preparation process is as follows:
[0031] Step 1: Preparation of PEI@CNTs base membrane: Weigh 600 mg of polyethyleneimine and dissolve it in 40 mL of ethanol. After complete dissolution, add 40 mg of carbon nanotubes, sonicate for 30 min, let stand for 12 h, centrifuge at 8000 rpm for 20 min, and collect the supernatant to obtain PEI@CNTs. The concentration is measured by UV-vis. Dilute PEI@CNTs to 1 mg / L, disperse in deionized water, and vacuum-film the membrane into a mixed cellulose membrane (MCE). After drying at room temperature, place the membrane in N,N-dimethylacetamide (DMAC) to dissolve the MCE, obtaining the PEI@CNTs base membrane.
[0032] Step 2: 8.4 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 6.3 mg of trialdehyde phloroglucinol (Tp) powder were dissolved in 20 mL of deionized (DI) water and 20 mL of 1,4-dioxane, respectively. Then, 0.7 mg of scandium trifluoromethanesulfonate catalyst was added to the Bpy solution, and the mixture was sonicated for 15 min until fully dissolved. Afterward, the prepared PEI@CNTs substrate membrane was placed in a beaker, and the above Bpy and TFR solutions were added. The beaker was then sealed and allowed to stand at room temperature for 72 hours. The resulting membrane material was named Tp-Bpy. 0.5 / CNTs nanofiltration membrane. It was then washed multiple times sequentially with 1,4-dioxane, ethanol, and DI water.
[0033] Comparative Example 1 nanofiltration membrane was used for the separation of organic solvent dyes. The separation performance was: pure water flux of 258 Lm. -2 h -1 bar -1 The ethanol flux was 9.5 Lm. -2 h -1 bar -1 The hexane flux was 41 Lm. -2 h -1 bar -1 The rejection rates were as follows: Congo Red 64%, Methyl Blue 83%, Tiger Red 30%, and Alcian Blue 99%.
[0034] Comparative Example 2
[0035] The preparation process is as follows:
[0036] Step 1: Preparation of PEI@CNTs base membrane: Weigh 600 mg of polyethyleneimine and dissolve it in 40 mL of ethanol. After complete dissolution, add 40 mg of carbon nanotubes, sonicate for 30 min, let stand for 12 h, centrifuge at 8000 rpm for 20 min, and collect the supernatant to obtain PEI@CNTs. The concentration is measured by UV-vis. Dilute PEI@CNTs to 1 mg / L, disperse in deionized water, and vacuum-film the membrane into a mixed cellulose membrane (MCE). After drying at room temperature, place the membrane in N,N-dimethylacetamide (DMAC) to dissolve the MCE, obtaining the PEI@CNTs membrane.
[0037] Step 2: 16.9 mg of Pa-SO3 (2,5-diaminobenzenesulfonic acid) and 11.64 mg of 2,4,6-tricarboxymethylresorcinol (TFR) powder were dissolved in 20 mL of deionized (DI) water and 20 mL of 1,4-dioxane, respectively. Then, 3.9 mg of scandium trifluoromethanesulfonate catalyst was added to the Pa-SO3 solution, and the mixture was sonicated for 15 min until fully dissolved. Afterward, the prepared PEI@CNTs substrate membrane was placed in a beaker, and the above Pa-SO3 and TFR solutions were added. The beaker was then sealed and allowed to stand at room temperature for 72 hours. The resulting membrane material was named TFR-Pa-SO3. 3 / 3 / CNTs nanofiltration membrane. It was then washed multiple times sequentially with 1,4-dioxane, ethanol, and DI water.
[0038] Comparative Example 2 nanofiltration membrane was used for the separation of organic solvent dyes. The separation performance was: pure water flux of 93.8 Lm. -2 h - 1 bar -1 The ethanol flux is 23 Lm -2 h -1 bar -1 The hexane flux is 75 Lm -2 h -1 bar -1 The rejection rates were as follows: Congo Red 89%, Methyl Blue 75%, Chrome Black T 98%, and Alsin Blue 99%.
[0039]
[0040] Table 1 shows the organic solvent rejection performance of the prepared nanofiltration membranes.
Claims
1. A method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration, specifically comprising the following steps: Step 1: Preparation of PEI@CNTs base film: Polyethyleneimine was dissolved in ethanol, and carbon nanotubes were added after complete dissolution. The mixture was sonicated for a period of time and then allowed to stand for several hours. After centrifugation for a period of time, the supernatant was collected to obtain PEI@CNTs, and the concentration was measured by UV-vis. The PEI@CNTs were diluted and dispersed in deionized water and vacuum-coated into a mixed cellulose membrane. After drying at room temperature, the membrane was placed in N,N-dimethylacetamide to dissolve the mixed cellulose membrane, thus obtaining the PEI@CNTs base film. Step 2: In-situ synthesis of nanofiltration membranes: 5,5'-diamino-2,2'-bipyridine and 2,4,6-tricarboxymethylresorcinol powders were dissolved in deionized water and 1,4-dioxane, respectively. 5,5'-diamino-2,2'-bipyridine and 2,4,6-tricarboxymethylresorcinol will be referred to as Bpy and TFR, respectively. Scandium trifluoromethanesulfonate catalyst was then added to the Bpy solution and dissolved completely by sonication. The prepared PEI@CNTs base membrane was placed in a beaker, and the above-mentioned Bpy and TFR solutions were added respectively. Then, the beaker was sealed and allowed to stand at room temperature for reaction. The resulting membrane material was named TFR-Bpy / CNTs nanofiltration membrane. It was washed multiple times with 1,4-dioxane, ethanol and deionized water in sequence.
2. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: In step one, the mass ratio of polyethyleneimine to carbon nanotubes is 100 / 7~15.
3. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: In step one, the ultrasound time is 30-40 minutes.
4. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: In step one, the concentration of PEI@CNTs after dilution is 1-1.5 mg / L.
5. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: The mass ratio of Bpy to TFR is 8.4 / 6.3-5.6 / 3.
9.
6. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: In step two, the ultrasound session lasts 15-25 minutes.
7. The method for preparing a highly crystalline covalent organic framework membrane for organic solvent nanofiltration according to claim 1, characterized in that: In step two, the reaction time is 48-72 hours.