CN117946355A - Preparation method and application of asymmetric self-supporting covalent organic framework film - Google Patents

Abstract

The invention discloses a method for preparing an asymmetric self-supporting covalent organic framework film and its application. By a water-organic phase two-phase interface method, a water phase containing amine monomers and an organic phase containing aldehyde monomers undergo polycondensation reaction at the interface to obtain an asymmetric self-supporting covalent organic framework film; an inorganic salt is added to the water phase system, and the reaction of the amine monomers with the aldehyde monomers in the organic phase is accelerated by accelerating the mass transfer of the amine monomers in the water phase and the synergistic effect of the coordinated pre-assembly. The scheme of the present invention enables the polymerization reaction that cannot be carried out at room temperature and pressure to be carried out through the driving effect of the inorganic salt, with a fast reaction rate and high yield. In addition, the covalent organic framework film prepared by the present invention has the characteristics of good crystallinity, high porosity, good mechanical properties and chemical stability, and excellent molecular sieving ability.

Description

Preparation method and application of asymmetric self-supporting covalent organic framework film

Technical Field

The invention belongs to the technical field of new material films, and in particular relates to a preparation method of an asymmetric self-supporting covalent organic framework film and an application thereof.

Background technique

Covalent organic framework polymer materials (COFs) are a new generation of crystalline framework polymer materials and are considered to be one of the most advanced materials in the 21st century. They have ultra-high specific surface area, regular and periodic pore structure, narrow pore size distribution, good chemical stability and excellent designability. The diversity of the basic chemical structure gives COF a variety of topological structures. The pore size can be precisely controlled at the sub-nanometer scale. At the same time, it is easy to functionalize and give COFs new functions. COFs polymer materials are widely used in adsorption, separation, catalysis, proton conduction and other aspects.

There is great concern about the increasing impacts of organic pollutants such as organic dyes and emerging trace organic contaminants (TrOCs) on natural waterways and aquatic ecosystems, posing potential threats to human health and the health of the aquatic environment. Of particular concern are TrOCs, a class of pollutants that currently lacks relevant environmental management policies or emission standards. These pollutants include steroid hormones, phytoestrogens, endocrine disrupting chemicals, pharmaceuticals and personal care products, industrial chemicals, disinfection by-products, and pesticides. Due to their small molecular weight, high toxicity, and high durability, TrOCs are difficult to remove from aquatic environments.

Membrane technology offers a promising and sustainable approach to remove these pollutants from aqueous environments. However, the pore size of most commercial membranes is larger than the molecular size of most trace organic pollutants, making effective interception challenging. Current COFs membranes have demonstrated excellent capabilities in removing pollutants such as dyes, drugs, and hydrated ions from water and organic solvents. However, the COFs backbone is composed of building blocks that are typically 0.8 to 5 nanometers, and their inherent pore size poses a challenge to the recognition of smaller TrOCs through COFs channels.

Most COFs reactions need to be carried out under high temperature and high pressure conditions, and the powder materials obtained are difficult to reuse multiple times. As an emerging membrane material, COFs membrane can be reused multiple times and is recyclable, with great application prospects. COFs membrane types are mainly divided into imines, triazines, ^SP2 , hydrazones, borate esters, etc. according to different bonding types. These types of COFs membranes often require high temperature and high pressure and the presence of catalysts to react, which brings great difficulties to the preparation of COFs. Among them, the difficulty of preparing ionic COFs membranes is much greater than that of non-ionic COFs membranes. Generally speaking, the interfacial polymerization technology used to manufacture non-ionic COFs membranes is difficult to directly migrate to the manufacture of ionic COFs membranes. According to literature reports, the preparation of ionic COFs membranes by interfacial polymerization strategies takes at least 15 days, and the crystallinity of the obtained ionic COFs membranes is very poor. What's more, ionic COFs membranes cannot be obtained at all. The strong electron-withdrawing action and steric hindrance effect of the ionic groups carried by the monomers greatly reduce the reaction activity of the monomers, making it impossible to prepare COFs membranes by interfacial reactions. In addition, the COFs film obtained by conventional methods is symmetrical, which is not conducive to molecular separation.

The above information disclosed in this background technology section is only intended to increase the understanding of the overall background of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to ordinary technicians in this field.

Summary of the invention

In view of the deficiencies of the above-mentioned prior art, the present invention provides a method for preparing an asymmetric self-supporting covalent organic framework film and its application. The method for preparing an asymmetric COFs membrane of the present invention is simple and controllable, with high efficiency and excellent product quality. The prepared COFs membrane has high crystallinity, excellent stability and film-forming properties. At the same time, the COFs membrane has a special asymmetric structure, which increases the pore size gradient difference between the upper and lower surfaces, which is beneficial to increase the flux when strengthening molecular separation, and at the same time has excellent molecular screening ability.

The preparation method of the asymmetric self-supporting covalent organic framework film of the present invention is obtained by a water-organic phase two-phase interface method, wherein a water phase containing amine monomers and an organic phase containing aldehyde monomers undergo condensation polymerization at the interface; an inorganic salt is added to the water phase system, and the reaction of the amine monomers with the aldehyde monomers in the organic phase is accelerated by accelerating the mass transfer of the amine monomers in the water phase and the synergistic effect of coordination preassembly.

The amine monomer is an amine monomer having an anionic group (including anionic groups such as -SO ₃ H), a cationic group (such as -N ⁺ ) or a neutral group.

Further, the amine monomer is selected from 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid, 4,4'-diaminobiphenyl-2,2'-disulfonic acid, 4,4'-diamino-1,1'-biphenyl-3,3'-dicarboxylic acid, p-phenylenediamine, 4,4'-biphenylenediamine, 3,5-diamino-1,2,4-triazole, 9H-carbazole-3,6-diamine, 4,4'- One of azodiphenylamine, 1,3,5-tri(4-aminophenyl)benzene, 5,10,15,20-tetrakis(4-aminophenyl)porphyrin, tri(4-aminophenyl)amine, trans-1,4-cyclohexanediamine, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, ethidium bromide, triaminoguanidine hydrochloride, hydrazine hydrate, and tri(2-aminoethyl)amine.

Furthermore, the amine monomer is 2,5-diaminobenzenesulfonic acid, 2,4-diaminobenzenesulfonic acid, 4,4'-diaminobiphenyl-2,2'-disulfonic acid, p-phenylenediamine, 4,4'-biphenylenediamine, ethidium bromide or triaminoguanidine hydrochloride.

The aldehyde monomer is selected from the group consisting of trialdehyde phloroglucinol, trimesic acid, thieno[3,2-b]thiophene-2,5-dicarboxaldehyde, 2-hydroxy-1,3,5-benzenetricarboxaldehyde, 2-hydroxybenzene-1,4-dicarboxaldehyde, 2,5-difluoroterephthalaldehyde, 2,5-dimethoxybenzene-1,4-dicarboxaldehyde, 2,5-dichloroterephthalaldehyde, 2,5-dibromobenzene-1,4-dicarboxaldehyde, 2,5-dimethylterephthalaldehyde, tetrafluoroterephthalaldehyde, One of dicarboxaldehyde, 5,10,15,20-tetrakis(4-formylphenyl)-21H,23H-porphyrin, 4,4'-biphenyldicarboxaldehyde, 2,5-dihydroxy-1,4-benzenedicarboxylic acid aldehyde, 2,2-bipyridine-4,4-dicarboxaldehyde, 1,2,4,5-tetrakis(4-formylphenyl)benzene, and 4,4'-(2,2-bis((4-formylphenoxy)methyl)propane-1,3-diyl)bis(oxy))dibenzaldehyde.

Furthermore, the aldehyde monomer is trialdehyde phloroglucinol or trimesaldehyde.

The solvent of the organic phase is dichloromethane.

The inorganic salt is easily soluble in water.

The method for preparing the asymmetric self-supporting covalent organic framework film of the present invention comprises the following steps:

Step 1: dissolving the amine monomer and the inorganic salt in an aqueous solution respectively, and then mixing the two to obtain an aqueous phase solution, wherein the inorganic salt provides a driving force to promote the amine monomer to accelerate mass transfer; dissolving the polyaldehyde in dichloromethane to obtain an organic phase solution;

Step 2: Add the organic phase solution to the reactor, then slowly add the aqueous phase solution along the edge of the reactor to the top of the organic phase solution, and let it stand at room temperature for 0.5-12 hours;

Step 3: Aspirate the water and dichloromethane solution in the reaction system to obtain a covalent organic framework polymer film at the interface, add dichloromethane, ethanol and aqueous solution respectively to wash away excess monomers, salts and solvents, and then place the film in water to obtain an ionic or neutral covalent organic framework polymer film.

In step 1, the molar concentration of the inorganic salt in the aqueous phase solution is 1-10 mmol/L, the molar concentration of the amine monomer is 0.1-9 mmol/L, and the molar concentration of the polyaldehyde monomer in the organic phase solution is 0.1-9 mmol/L.

Furthermore, the molar ratio of the amine monomer to the aldehyde monomer is preferably 3:2.

In step 1, the inorganic salt is a strong acid-strong base salt or a strong acid-weak base salt, the strong acid-strong base salt is selected from one or more of Na ₂ SO ₄ , NaCl, and NaNO ₃ , and the strong acid-weak base salt is selected from one or more of (NH ₄ ) ₂ SO ₄ , NH ₄ NO ₃ , and NH ₄ Cl.

In step 1, the ratio of the inorganic salt to water is limited, and is preferably (1 mmol: 80 mL) to (10 mmol: 40 mL).

In step 1, the molar ratio of the inorganic salt to the amine monomer is preferably (1-5):1.

In step 2, the ratio of the volume of the aqueous phase to the volume of the organic phase is 40-50 mL:30-45 mL, for example, 40 mL:30 mL, 40 mL:35 mL, 40 mL:40 mL, 50 mL:45 mL, 50 mL:40 mL.

The invention discloses an application of the asymmetric self-supporting covalent organic framework film prepared by the invention in pollutant separation.

Furthermore, the pollutant separation includes separation of organic dyes, drug molecules, etc.

Furthermore, the organic dye includes one or more of reactive green, rose bengal, brilliant blue, reactive black, Congo red, indigo, methyl orange, etc.; the drug molecule includes one or more of tetracycline, ciprofloxacin, vitamin B12, etc.

Compared with the prior art, the beneficial effects of the present invention are as follows:

The present invention adopts the electrostatic effect of monomers and salts to accelerate monomer mass transfer and interface pre-assembly strategy interfacial polymerization method, dissolves amine monomers in the aqueous phase, then adds strong acid and strong base salt or strong acid and weak base salt to strengthen mass transfer; dissolves aldehyde monomers in the organic phase; then mixes the two-phase solution, and the two monomers react rapidly at the interface to grow into anionic, cationic, and neutral asymmetric covalent organic polymer membranes. Compared with the prior art, the interfacial reaction is accelerated, and anionic, cationic, and neutral covalent organic polymer membranes can be synthesized within 0.5-12 hours. For specific amine monomers and aldehyde monomers, when preparing membrane materials, the separation ability obtained mainly depends on: the film-forming property of the membrane, the crystallinity of the membrane, the pore size of the membrane, and the thickness of the membrane.

The COFs obtained by the method of the present invention have an asymmetric structure, which can increase the gradient difference of the COFs pore size and strengthen the transmission of the fluid in the membrane. The membrane preparation method is simple and controllable, and the prepared covalent organic polymer membrane has high crystallinity and film-forming properties, and exhibits excellent molecular separation ability.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the characterization of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer membrane. (a) SEM image of the rough upper surface of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (b) SEM image of the smooth lower surface of TpDa-SO ₃ H anion covalent organic framework polymer membrane; (c) SEM image of the junction between the upper and lower surfaces of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (d) Digital photo of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (e) Schematic diagram of the chemical structure of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer; (f) XRD diffraction curve of TpDa-SO ₃ H anion asymmetric covalent organic framework polymer membrane.

Figure 2 is a molecular separation picture of TpDa-SO ₃ H anionic covalent organic framework polymer membrane, where the molecules include: (a) reactive green [RG]; (b) rose red [RB]; (c) brilliant blue [BBR]; (d) reactive black [RB5]; (e) Congo red [CR]; (f) methyl orange [MO]. The test conditions are room temperature and pressure of 0.5MPa.

Figure 3 is the characterization of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane. (a) SEM image of the rough upper surface of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (b) SEM image of the smooth lower surface of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (c) SEM image of the junction between the upper and lower surfaces of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (d) Digital photo of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (e) Schematic diagram of the chemical structure of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer; (f) XRD diffraction curve of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane.

Figure 4 is a molecular separation picture of TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane, where the molecules include: (a) reactive green [RG]; (b) rose red [RB]; (c) brilliant blue [BBR]; (d) reactive black [RB5]; (e) Congo red [CR]; (f) indigo [IC]; (g) methyl orange [MO]. The test conditions are room temperature and pressure of 0.5MPa.

Figure 5 is the characterization of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane. (a) SEM image of the rough upper surface of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (b) SEM image of the smooth lower surface of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (c) SEM image of the junction between the upper and lower surfaces of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (d) Digital photo of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane; (e) Schematic diagram of the chemical structure of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer; (f) High-magnification transmission electron microscope image of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane.

Figure 6 is a molecular separation picture of TpBa-SO ₃ H anion asymmetric covalent organic framework polymer membrane, where the molecules include: (a) reactive green [RG]; (b) rose red [RB]; (c) brilliant blue [BBR]; (d) reactive black [RB5]. The test conditions are room temperature and pressure of 0.5MPa.

Figure 7 is a molecular separation picture of the TpHZ cationic covalent organic framework polymer membrane, where the molecules include: (a) reactive green [RG]; (b) rose red [RB]; (c) brilliant blue [BBR]; (d) reactive black [RB5]; (e) Congo red [CR]; (f) indigo [IC]; (g) methyl orange [MO]. The test conditions are room temperature and pressure of 0.5 MPa.

Figure 8 is a molecular separation picture of TpPa neutral covalent organic framework polymer membrane, where the molecules include: (a) reactive green [RG]; (b) rose red [RB]; (c) brilliant blue [BBR]; (d) reactive black [RB5]; (e) Congo red [CR]; (f) indigo [IC]; (g) methyl orange [MO]. The test conditions are room temperature and pressure of 0.5 MPa.

Figure 9 is a picture of drug molecule separation of TpDa-SO ₃ H anionic covalent organic framework polymer membrane, where the molecules include: (a) vitamin B12 [VB12]; (b) rifampicin [RF]; (c) tetracycline [TC]; (d) ciprofloxacin [CF]. The test conditions are room temperature and pressure of 0.5 MPa.

Figure 10 shows the growth of TpPa neutral covalent organic framework polymer membrane at different times. (a) Digital image of TpPa neutral covalent organic framework polymer membrane changing with time; (b) Digital image of TpPa (10 mmol Na ₂ SO ₄ ) neutral covalent organic framework polymer membrane changing with time.

Figure 11 shows the growth of TpDt cationic covalent organic framework polymer membrane at different times. (a) Digital image of TpDt cationic covalent organic framework polymer membrane changing with time; (b) Digital image of TpDt (10 mmol Na ₂ SO ₄ ) cationic covalent organic framework polymer membrane changing with time.

Figure 12 shows the mass transfer in the TpPa-SO ₃ H anion asymmetric covalent organic framework polymer membrane system. (a) Changes in absorbance of Pa-SO ₃ H during interface transfer when there is/is not Na ₂ SO ₄ in the system; (b) Changes in absorbance at different times when there is Na ₂ SO ₄ in the system, and the transfer rate k=0.06075 A/min; (c) Changes in absorbance at different times when there is no Na ₂ SO ₄ in the system, and the transfer rate k=0.01075 A/min; When there is Na ₂ SO ₄ in the system, the transfer rate of Pa-SO ₃ H is 5.7 times that of the transfer rate without Na ₂ SO ₄ .

Detailed ways

The technical solution of the present invention is exemplarily described in detail below in conjunction with specific implementation modes of the present invention, but it should be understood that the protection scope of the present invention is not limited by the specific implementation modes.

Unless explicitly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising" etc., will be understood to include the stated components but not to exclude other components.

Example 1: Preparation of a high-crystallinity TpDa-SO ₃ H anionic asymmetric covalent organic framework polymer membrane.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 2,4-diaminobenzenesulfonic acid (Da-SO ₃ H) and 10 mmol of sodium sulfate (strong acid and strong base salt) were added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was allowed to stand at room temperature for 12 h to obtain the TpDa-SO ₃ H membrane. Then, the water and organic solvent in the upper and lower layers were sucked out with a rubber-tipped dropper, and 60 mL of dichloromethane, ethanol and water were added to the culture dish for washing for 6 h to remove the unreacted monomers and organic solvents. Finally, the membrane was placed in a deionized water phase environment for subsequent molecular separation.

The performance test of the samples in this embodiment is shown in Figures 1-2. The SEM images of the upper and lower surfaces of the membrane in Figure 1 are shown in (a)-(c), (d) the digital photo of the membrane shows the excellent film-forming property of TpDa-SO ₃ H, (e) shows the chemical structure of TpDa-SO ₃ H, and (f) XRD proves that the prepared TpDa-SO ₃ H ionic covalent organic polymer membrane has high crystallinity. Its molecular separation is shown in Figure 2, and it can be seen that the prepared TpDa-SO ₃ H membrane has excellent molecular separation ability.

Example 2: Preparation of a high crystallinity TpPa-SO ₃ H anionic asymmetric covalent organic framework membrane.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H) and 10 mmol of sodium sulfate (strong acid and strong base salt) were added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was allowed to stand at room temperature for 0.5 h to obtain the TpPa-SO ₃ H membrane. Then, the water and organic solvent of the upper and lower layers were sucked out with a rubber-tipped dropper, and 60 mL of dichloromethane, ethanol and water were added to the culture dish for washing for 6 h to remove the unreacted monomers and organic solvents. Finally, the membrane was placed in a deionized water phase environment for subsequent molecular separation.

The performance test of the samples in this embodiment is shown in Figures 3-4, where the SEM images of the upper and lower surfaces of the membrane in Figure 3 are shown in (a)-(c), (d) the digital photo of the membrane shows the excellent film-forming property of TpPa-SO ₃ H, (e) shows the chemical structure of TpPa-SO ₃ H, and (f) XRD proves that the prepared TpPa-SO ₃ H ionic covalent organic polymer membrane has high crystallinity. Its molecular separation is shown in Figure 4, and it can be seen that the prepared TpPa-SO ₃ H membrane has excellent molecular separation ability.

Example 3: Preparation of TpBa-SO ₃ H anionic asymmetric covalent organic framework membrane with high crystallinity.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 4,4'-diaminobiphenyl-2,2'-disulfonic acid (Ba-SO ₃ H) and 10 mmol of sodium sulfate (strong acid and strong base salt) were added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was allowed to stand at room temperature for 12 hours to obtain TpBa-SO ₃ H. Then, the water and organic solvent in the upper and lower layers were sucked out with a rubber-tipped dropper, and 60 mL of dichloromethane, ethanol and water were added to the culture dish for washing for 6 hours to remove the unreacted monomers and organic solvents. Finally, the membrane was placed in a deionized water phase environment for subsequent molecular separation.

The performance test of the samples in this embodiment is shown in Figures 5-6, where the SEM images of the upper and lower surfaces of the membrane in Figure 5 are shown in (a)-(c), (d) the digital photo of the membrane shows the excellent film-forming property of TpBa-SO ₃ H, (e) shows the chemical structure of TpBa-SO ₃ H, and (f) HR-TEM proves that the prepared TpBa-SO ₃ H ionic covalent organic polymer membrane has high crystallinity. Its molecular separation is shown in Figure 6, and it can be seen that the prepared TpBa-SO ₃ H has good molecular separation ability.

Example 4: Comparison of film formation rates of TpPa neutral covalent organic framework polymer films prepared in the presence of Na ₂ SO ₄ (strong acid and strong base salt).

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of p-phenylenediamine (Pa) and 10 mmol of sodium sulfate (strong acid and strong base salt, Figure 10 (a) without sodium sulfate, Figure 10 (b) with sodium sulfate) were added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous phase solution was slowly added to the organic phase solution along the periphery of the culture dish. The film formation conditions at different times were observed, and the comparison showed that the addition of sodium sulfate could accelerate the film formation of TpPa neutral covalent organic framework polymer.

Example 5: Comparison of film formation rates of TpDt cationic covalent organic framework polymer films prepared in the presence of Na ₂ SO ₄ (strong acid and strong base salt).

2 mmol of trialdehyde pyrogallol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of triaminoguanidine hydrochloride (Dt) and 10 mmol of sodium sulfate (strong acid and strong base salt, Figure 11 (a) without sodium sulfate, Figure 11 (b) with sodium sulfate) were added to 40 mL of deionized water, and an aqueous phase mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous phase solution was slowly added to the aqueous phase solution along the periphery of the culture dish. The film formation conditions at different times were observed, and the comparison showed that the addition of sodium sulfate could accelerate the film formation of the TpDt cationic covalent organic framework polymer.

To test the mass transfer rate of Pa-SO ₃ H monomer, 1 mL of pure DCM solvent was added to the lower layer of the culture dish, and 3 mL of aqueous solution containing or not containing Na ₂ SO ₄ was added to the upper layer. The mass transfer rate was tested using a UV spectrophotometer. Figures 12 (a) and (b) show that in the presence of strong acid and strong base salts (strong acid and strong base salts), a fast mass transfer rate (k = 0.06075 A/min) was exhibited, resulting in rapid film formation. Figure 9 (c) shows a slow mass transfer rate (k = 0.01075 A/min) in the absence of strong acid and strong base salts (strong acid and strong base salts), resulting in slow film formation or no film formation (Table 1).

In summary, the present invention provides a method for rapidly preparing cationic, anionic and neutral covalent organic polymer membranes by accelerating monomer mass transfer and interfacial preassembly strategy polymerization provided by inorganic salts. The method has certain universality, and the prepared COFs membrane has the characteristics of good film-forming property and high crystallinity. Among them, the TpPa-SO ₃ H anionic covalent organic framework membrane has very excellent molecular separation ability.

Comparative Example 1: Attempt to prepare TpDa-SO ₃ H anionic covalent organic framework membrane without adding strong acid or strong base salt.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 2,4-diaminobenzenesulfonic acid (Da-SO ₃ H) was added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was left at room temperature for 48 h, but no film was obtained. In this case, no film could be obtained without the addition of strong acid or strong base salt.

Comparative Example 2: An attempt was made to prepare a TpPa-SO ₃ H anionic covalent organic framework membrane without adding strong acid or strong base salt.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H) was added to 40 mL of deionized water, and an aqueous phase mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous phase mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was left to stand at room temperature for 1 h without a film. In this case, no film could be obtained without the addition of strong acid or strong base salt. When the reaction time was 4 h, a film was obtained, but this film was very fragile and could not be used for separation.

Comparative Example 3: An attempt was made to prepare a TpBa-SO ₃ H anionic covalent organic framework membrane without adding strong acid or strong base salt.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonication; 3 mmol of 4,4'-diaminobiphenyl-2,2'-disulfonic acid (Ba-SO ₃ H) was added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonication. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was left at room temperature for 3 months without a film. No film could be obtained when no strong acid or strong base salt was added.

Comparative Example 4: When weak acid and strong base salts (such as sodium bicarbonate, sodium phosphate, etc.) are added, an attempt is made to prepare a TpPa-SO ₃ H anionic covalent organic framework membrane.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonication. 3 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H) and 10 mmol of weak acid and strong base salt (such as sodium bicarbonate, sodium phosphate, etc.) were added to 40 mL of deionized water, and an aqueous phase mixed solution was obtained by ultrasonication. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous phase mixed solution was slowly added to the organic phase solution along the periphery of the culture dish. The culture dish was left at room temperature for 30 days without a film. No film was obtained when this weak acid and strong base salt was added.

Comparative Example 5: When adding different metal cation sulfates (such as magnesium sulfate, iron sulfate, etc.), an attempt was made to prepare a TpPa-SO ₃ H anion covalent organic framework membrane.

2 mmol of trialdehyde phloroglucinol was added to the dichloromethane organic phase solution, and a clear solution was obtained by ultrasonic treatment. 3 mmol of 2,5-diaminobenzenesulfonic acid (Pa-SO ₃ H) and 10 mmol of magnesium sulfate or ferric sulfate were added to 40 mL of deionized water, and an aqueous mixed solution was obtained by ultrasonic treatment. The dichloromethane solution was added to an 80 mL culture dish, and then the aqueous mixed solution was slowly added to the organic phase solution along the periphery of the culture dish, and the culture dish was left to stand at room temperature for 5 days. In this case, the TpPa-SO ₃ H anionic covalent organic framework membrane could not be obtained.

The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims (8)

1. The preparation method of the asymmetric self-supporting covalent organic framework film is characterized by comprising the following steps of:

Step 1: respectively dissolving an amine monomer and inorganic salt in an aqueous solution, and then mixing the two to obtain an aqueous solution, wherein the inorganic salt provides a driving force to promote the amine monomer to accelerate mass transfer; dissolving polybasic aldehyde in a solvent dichloromethane to obtain an organic phase solution;

step 2: adding an organic phase solution into the reactor, slowly adding the aqueous phase solution above the organic phase solution along the edge of the reactor, and standing at room temperature for reaction for 0.5-12 hours;

Step 3: sucking water and dichloromethane solution in the reaction system, sequentially adding dichloromethane, ethanol and water solution to wash out excessive monomer and salt, and then placing the membrane in water to obtain the ionic or neutral covalent organic framework polymer membrane.

2. The method of manufacturing according to claim 1, characterized in that:

The amine monomer is an amine monomer with an anionic group, a cationic group or a neutral group.

3. The preparation method according to claim 2, characterized in that:

The amine monomer is selected from the group consisting of 2, 5-diaminobenzenesulfonic acid, 2, 4-diaminobenzenesulfonic acid, 4' -diaminobiphenyl-2, 2' -dicarboxylic acid, 4' -diaminobiphenyl-2, 2' -disulfonic acid, 4' -diamino-1, 1' -biphenyl-3, 3' -dicarboxylic acid, p-phenylenediamine, 4' -biphenyldiamine, 3, 5-diamino-1, 2, 4-triazole, 9H-carbazole-3, 6-diamine, 4' -azobis-aniline one of 1,3, 5-tris (4-aminophenyl) benzene, 5,10,15, 20-tetrakis (4-aminophenyl) porphyrin, tris (4-aminophenyl) amine, trans-1, 4-cyclohexanediamine, 2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane, 9-bis (4-aminophenyl) fluorene, ethidium bromide, tris aminoguanidine hydrochloride, hydrazine hydrate, tris (2-aminoethyl) amine.

4. The method of manufacturing according to claim 1, characterized in that:

The aldehyde monomer is selected from the group consisting of triallylmethanol, trimellitic aldehyde, thieno [3,2-b ] thiophene-2, 5-dicarboxaldehyde, 2-hydroxy-1, 3, 5-benzene tricaldehyde, 2-hydroxybenzene-1, 4-dicarboxaldehyde, 2, 5-difluoro-terephthalaldehyde, 2, 5-dimethoxy benzene-1, 4-dicarboxaldehyde, 2, 5-dichloro-terephthalaldehyde, 2, 5-dibromobenzene-1, 4-dicarboxaldehyde, 2, 5-dimethyl-terephthalaldehyde, tetrafluoroterephthalaldehyde, 5,10,15, 20-tetrakis (4-aldyl benzene) -21H, 23H-porphyrin, 4 '-biphenyl-dicarboxaldehyde, 2, 5-dihydroxy-1, 4-benzene dicarboxaldehyde, 2-bipyridine-4, 4-dicarboxaldehyde, 1,2,4, 5-tetrakis (4-formylphenyl) benzene, 4' - (2, 2-bis 4-formylphenoxy) methyl) propane-1, 3-diyl) bis (oxy)) of the bis (oxy) benzene.

5. The method of manufacturing according to claim 1, characterized in that:

In the step 1, the inorganic salt is a strong acid and strong alkali salt or a strong acid and weak alkali salt, the strong acid and strong alkali salt is one or more selected from Na ₂SO₄、NaCl、NaNO₃ , and the strong acid and weak alkali salt is one or more selected from (NH ₄)₂SO₄、NH₄NO₃、NH₄ Cl).

6. The method of manufacturing according to claim 1, characterized in that:

in the step 1, the molar concentration of inorganic salt in the aqueous phase solution is 1-10mmol/L, and the molar concentration of amine monomer is 0.1-9 mmol/L; the molar concentration of the polyaldehyde monomer in the organic phase solution is 0.1-9 mmol/L.

7. Use of an asymmetric self-supporting covalent organic framework film prepared according to the method of any one of claims 1-6 for contaminant separation.

8. The use according to claim 7, characterized in that:

the pollutant separation comprises separation of organic dye and drug molecules;

The organic dye comprises one or more of active green, rose bengal, brilliant blue, active black, congo red, indigo and methyl orange; the drug molecules include one or more of tetracycline, ciprofloxacin and vitamin B12.