An ultra-high-flux covalent organic framework composite nanofiltration membrane and a preparation method thereof

Abstract

The application relates to an ultra-high-flux covalent organic framework composite nanofiltration membrane and a preparation method thereof, belonging to the field of membrane separation technology, and comprising a porous membrane substrate and a selective separation layer of cap-shaped nano-protruding structures grown on the orifice of the porous base membrane through gas-liquid interface polymerization; the covalent organic framework material is an imine two-dimensional layered covalent organic framework material structure. An aqueous phase containing an aldehyde group monomer is used to construct a liquid surface required by an interfacial polymerization reaction on the surface of the porous base membrane, amino monomers under the membrane rapidly sublimate under the condition of heating, the rising amino small-molecule organic matters are subjected to a Schiff base condensation reaction with aldehyde group small-molecule organic matters in the liquid drops on the membrane surface, and the ultra-high-flux covalent organic framework composite membrane is obtained after a period of reaction. The composite membrane prepared by the application has a very high rejection rate for various dye molecules in water, and simultaneously has an ultra-high permeation flux.

Description

Technical Field

[0001] This invention relates to the field of membrane separation and technology, specifically to an ultra-high flux covalent organic framework composite nanofiltration membrane and its preparation method. Background Technology

[0002] Membrane separation technology is considered an important method for solving problems such as water scarcity, environmental pollution, and energy crises. It not only has the functions of separation, concentration, and purification, but also offers advantages such as energy saving, environmental friendliness, high efficiency, scalable manufacturing, and convenient operation and control. Traditional polymer membrane materials have shown advantages such as low cost, good mechanical strength, good flexibility, and ease of processing. However, because their flexible polymer chains cannot support a permanently ordered microporous structure, the separation process is generally based on a dissolution-diffusion mechanism, and their performance is often limited by the trade-off effect, where permeability and selectivity are difficult to balance. How to maximize permeate flux while ensuring retention rate is currently a key research challenge in the field of membrane separation.

[0003] Composite membranes hold great promise for overcoming the defects of traditional polymer membranes, typically consisting of a macroporous support layer and a microporous separation layer. Currently, improvements in the separation performance of composite membranes based on porous polymer layers mainly focus on researching suitable membrane materials and controlling membrane structure. To date, the permeability selectivity of membranes has been continuously improved by controlling membrane thickness or filling with nanomaterials to reduce mass transfer resistance, and by controlling membrane surface roughness to improve the effective mass transfer area. Currently, the selective separation layer is mainly constructed through methods such as in-situ growth, interfacial polymerization, and force-assisted deposition, resulting in continuous membrane layers of varying thicknesses and roughnesses. Further achieving a transformative improvement in the permeability of separation membranes by reducing membrane thickness, filling with nanomaterials, or increasing roughness is extremely difficult. Developing new structures for mass transfer separation layers based on novel materials holds promise for achieving breakthroughs in the permeability selectivity of separation membranes.

[0004] Covalent organic frameworks (COFs), as a new type of porous crystalline organic material, have a pore size ranging from 0.6 to 10 nm. Due to their advantages such as large specific surface area, high porosity, regular structure, uniform pores, good thermochemical stability, and tunable structure, they are ideal materials for constructing high-performance molecular sieve membranes. Currently developed COF composite membranes all achieve a double-layer stacking of the separation layer and the support layer. However, the overlapping area between the separation layer and the support increases the mass transfer resistance during the separation process. Precisely constructing a cap-like structure with selective separation function only outside the pores of the porous support can significantly improve the permeation flux of the composite membrane. This invention grows a strongly stable two-dimensional imine-based layered COF material on the outside of the pores of a porous base membrane to prepare a composite membrane with a cap-like nanoprotrusion structure. This membrane is then used for the removal of small organic molecules (such as dyes) from water, further demonstrating the potential of COF materials in the preparation of ultrafast permeable separation membranes. Summary of the Invention

[0005] The key technical problem to be solved by this invention is to provide a novel composite membrane preparation method with a COF nanocap discrete structure. The prepared composite membrane exhibits excellent removal of water-soluble small organic molecules in water, while also possessing ultra-high permeation flux. The specific technical solution is as follows:

[0006] In a first aspect, the present invention provides an ultra-high flux covalent organic framework composite nanofiltration membrane, comprising a porous base membrane and a selective separation layer composed of multiple discrete COF nanoprotrusion cap structures grown on the surface of the porous base membrane, wherein each discrete COF nanoprotrusion is grown at the pore opening of the porous base membrane by gas-liquid interface polymerization reaction.

[0007] The porous base membrane is selected from organic polymer membranes and inorganic membranes, and has an average pore size of 0.02-1 μm;

[0008] Specifically, the porous base membrane can be in the form of a flat plate, a tubular structure, or a hollow fiber. The COF is an imine-based two-dimensional layered covalent organic framework material obtained by reacting aldehyde small molecules with amine monomers. Further, the aldehyde small molecules are selected from aryl monomers with at least two aldehyde groups, such as preferably one or more of 1,3,5-trialdehyde phloroglucinol, pyromellitic methyl methacrylate, terephthalaldehyde, hexa(4-aldehydephenyl)benzene, tetra(4-benzoyl)methane, and 1,3,5-tris(4-aldehydephenyl)benzene; further, the amine monomers are at least diamine monomers, such as diamines and triamines, such as selected from one or more of hydrazine hydrate, p-phenylenediamine, benzyl diamine, 1,3,5-tris(4-aminophenyl)benzene, 2,5-diaminobenzenesulfonic acid, and tetra(4-aminophenyl)methane. The obtained COF is selected from one of the following: Schiff base (-RC=N- or =CH-N-), hydrazone bond (-NH-N=), or azo bond (=N-N=). Further preferred methods involve gas-liquid interfacial polymerization of p-phenylenediamine with pyromellitic aldehyde and 1,3,5-trialdehyde phloroglucinol on the membrane surface, respectively, to construct COF-LZU1 and TpPa-1 type cap-shaped nanostructure separation layers at the pore openings of the porous membrane.

[0009] The COF nano-protrusion cap structure has an average longitudinal height of 10-50 nm and an average transverse width (radial width) of 50-100 nm.

[0010] Secondly, the present invention provides a method for preparing the above-mentioned composite membrane, wherein the COF nanocap structure separation layer is a nano-confined gas-liquid interface constructed based on the pores of a porous base membrane, and is prepared by polymerization reaction, exhibiting extremely strong stability in water and organic solvents; specifically including the following steps:

[0011] Step a: First, pretreat the base film with organic and / or inorganic solvents, rinse and soak at room temperature for a certain time to remove organic matter and inorganic dust from the surface of the base film;

[0012] Step b: Dissolve the aldehyde small molecule organic compound in an inorganic and / or organic solvent, stir and heat and sonicate to fully dissolve it to obtain an aldehyde small molecule solution;

[0013] Step c: Add the amine monomer block solid to the bottom of the reaction apparatus, wrap it with tin foil, and place it in a sand bath at a certain temperature for a period of time to preheat it, so as to continuously and rapidly supply the gaseous amine monomer for the subsequent reaction.

[0014] Step d: Wipe the moisture off the surface of the pretreated base membrane from step a, place the internally moistened base membrane above the amine monomer in the apparatus of reaction step c, with the front of the base membrane facing the amine monomer below. Quickly pour the aldehyde small molecule solution obtained in step b onto the back of the membrane, while keeping the aldehyde monomer aqueous solution on the back of the membrane. After checking that there is no leakage on the side, place the apparatus in a sand bath at a certain temperature so that the amine monomer continuously sublimates upwards and contacts the aldehyde small molecule droplets penetrating down from the front of the base membrane to form a gas-liquid interface. After reacting for a period of time, a COF nano-protrusion cap structure is formed. After the reaction is completed, the base membrane is removed from the apparatus, and the membrane surface is rinsed with organic and / or inorganic solvents after the reaction to obtain an ultra-high flux covalent organic framework composite membrane.

[0015] Specifically, the organic and / or inorganic solvents mentioned in step a are selected from at least one of ethanol, methanol, toluene, ethyl acetate, acetic acid, and deionized water;

[0016] Specifically, in step b, the concentration of the aldehyde small molecule in the aldehyde small molecule solution is 0.1-1 mg / ml, preferably 0.1-0.5 mg / ml, and more preferably 0.1-0.2 mg / ml. The inorganic and / or organic solvent is selected from one or more of deionized water, toluene, cyclohexane, mesitylene and ethanol. The solution is stirred and heated with sonication to ensure complete dissolution.

[0017] Specifically, the preheating temperature in step c is 110-135℃, and the preheating time is 15 minutes;

[0018] Specifically, the reaction apparatus described in step d consists of three parts ( Figure 1 The two containers are a hemispherical container (1) for holding solid amine monomers, a cylindrical container (2) for holding aldehyde monomer solutions, and a clamp to fix the two parts to prevent leakage at the joint. The porous base membrane is placed between container 1 and container 2, with the front side facing down. Below it is the gaseous amine monomer that sublimates continuously at high temperature, and the liquid droplets of dissolved aldehyde small molecule organic matter that permeate down from the front surface are fixed in the middle with the clamp to prevent leakage. The reaction temperature corresponds to the preheating temperature described in step c. The polymerization reaction at the gas-liquid interface formed on the front side is 1-5 hours, more preferably 2-4 hours. After the reaction is completed, the membrane surface is rinsed with at least one of deionized water, methanol, ethanol, and 1,4-dioxane to remove COF powder deposited on the back of the membrane and unreacted monomers on the membrane. After rinsing, the membrane is soaked in deionized water for later use.

[0019] Preferably, the reaction temperature in step d is 110-135℃, corresponding to a reaction temperature of 40-50℃ on the front side of the membrane. Specifically, for every 5℃ increase in the sand bath temperature, the reaction temperature on the membrane surface increases by 2.5℃.

[0020] Further, depending on the needs of COF preparation, a catalyst can be added to the aldehyde small molecule solution in step b.

[0021] The composite nanofiltration membrane obtained by this invention is used for filtering water-soluble organic molecules in aqueous solutions.

[0022] The beneficial effects of the technical solution provided by this invention are as follows: Unlike traditional bilayer composite membranes with a support layer and a separation layer, this invention utilizes gas-liquid interfacial polymerization to construct COF nanocaps at the pore outlet of a porous base membrane, thus obtaining a cap-like nanoprotrusion structure separation layer composite membrane precisely composited on a porous base membrane. Due to the stable structure of covalent organic framework materials and their inherently ordered pore structure, the cap-like nanoprotrusion structure constructed at the pore opening of the porous support possesses advantages such as ultrathinness and uniform pore size. The novel nanocap structure COF composite membrane, while ensuring the retention of various water-soluble small organic molecules, significantly reduces the mass transfer resistance of water molecules during separation, achieving ultrafast selective separation of dye molecules based on the aqueous phase. Therefore, the prepared novel covalent organic framework composite membrane can stably, rapidly, and efficiently remove dyes from wastewater, with a permeation flux 2-15 times higher than other nanofiltration membranes. Furthermore, the scalability of interfacial polymerization for large-scale production and the ability to obtain a thin selective separation layer to achieve high permeability provide advanced technical support for this invention. This invention is simple and easy to implement. It can uniformly grow a crystalline porous COF nanocap separation layer on a porous support in a short time. Moreover, the preparation process is green and low in energy consumption, laying the foundation for industrial application. Attached Figure Description

[0023] Figure 1 A simplified diagram of the reaction apparatus used in this invention.

[0024] Figure 2 Scanning electron microscope (SEM) images of the surface (2-1) and cross-section (2-2) of the ultra-high flux TpPa-1 nanocap-shaped composite membrane prepared by gas-liquid interfacial polymerization in Example 1 of this invention.

[0025] Figure 3 Example 1 of this invention: Two-dimensional (3-1) and three-dimensional atomic force microscope images of the ultra-high flux TpPa-1 nanocap-shaped composite membrane prepared by gas-liquid interface polymerization.

[0026] Figure 4 Scanning electron microscope (SEM) images of the surface (4-1) and cross-section (4-2) of the ultra-high flux COF-LZU1 nanocap-shaped composite membrane prepared by gas-liquid interfacial polymerization in Example 2 of this invention.

[0027] Figure 5 Example 2 of this invention: Two-dimensional (5-1) and three-dimensional atomic force microscope images of the ultra-high throughput COF-LZU1 nanocap-shaped composite membrane prepared by gas-liquid interface polymerization. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Scanning electron micrographs were observed and measured using a Hitachi S-4300 scanning electron microscope (SEM), and atomic force micrographs were observed and measured using a Bruker Dimension ICON AFM.

[0029] In a first aspect, the present invention provides a novel ultra-high flux COF nanocap structure composite membrane, comprising a porous base membrane and a cap-like nanoprotrusion selective separation layer grown at the pore openings of the base membrane by gas-liquid interface polymerization reaction.

[0030] The aforementioned nanocap structure COF separation layer is a nano-confined gas-liquid interface constructed based on the pores of a porous membrane, and is prepared using a polymerization reaction. It exhibits extremely strong stability in water and organic solvents.

[0031] Preferably, the imine-based two-dimensional layered covalent organic framework materials include one of the following: Schiff bases (-RC=N- or =CH-N-), hydrazone bonds (-NH-N=), or azo bonds (=N-N=); for example, Schiff bases include COF-LZU1, TpPa-1, TpPa-2, TpBD, and BABD-BD; hydrazone bonds include COF-42, COF-43, TFPT-COF, and TpODH; and azo bonds include N3-COF and ACOF-1.

[0032] Specifically, the COF separation layer has a cap-like nano-protrusion structure with an average longitudinal height of 10-50 nm and an average lateral width of 50-100 nm.

[0033] Specifically, the porous base membrane is selected from organic polymer membranes and inorganic membranes, and has an average pore size of 0.02-1 μm. For example, the organic polymer membrane can be a polyacrylonitrile membrane, a polysulfone membrane, a polyethersulfone membrane, a polyvinylidene fluoride membrane, or a polytetrafluoroethylene membrane. The inorganic membrane can be a porous alumina membrane, a zirconium oxide membrane, or a zinc oxide membrane. The porous base membrane can be in the form of a flat sheet, a tubular membrane, or a hollow fiber membrane. Other specifications of ultrafiltration membranes and microfiltration membranes can also be used as the porous base membranes desired in this invention.

[0034] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned composite membrane, comprising:

[0035] Step 101: First, the base film is pretreated with organic and inorganic solvents and soaked at room temperature for a certain period of time to remove organic matter and inorganic dust from the surface of the base film.

[0036] Step 102: Dissolve a certain amount of aldehyde-based small molecule organic compound in deionized water, stir and heat with ultrasonic treatment to ensure complete dissolution;

[0037] Step 103: Add the amine monomer block solid to a hemispherical container, seal it with tin foil, and place it in a sand bath at a certain temperature for a certain period of time to preheat it, so as to continuously and rapidly supply the gaseous amine monomer for the subsequent reaction.

[0038] Step 104: Wipe the moisture off the surface of the pretreated base membrane from Step 101, invert the wet base membrane in the reaction apparatus with the membrane surface facing the amine monomer below, quickly pour the aqueous solution of the aldehyde monomer obtained in Step 102 onto the back of the membrane, check that the apparatus is leak-free, and then place it in a sand bath at a certain temperature for a certain period of time. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface with an organic / inorganic solvent to obtain an ultra-high flux covalent organic framework composite membrane.

[0039] Specifically, the organic / inorganic solvent in step 101 is preferably at least one selected from ethanol, methanol, toluene, ethyl acetate, acetic acid, deionized water, and liquid nitrogen. The concentration of the organic / inorganic solution can be 5 wt%, 10 wt%, 20 wt%, 30 wt%, 50 wt%, or 80 wt%. The treatment time can be 1 h, 2 h, 3 h, 4 h, 6 h, 8 h, or 12 h.

[0040] Specifically, the aldehyde-based small molecule mentioned in step 102 is preferably one or more of 1,3,5-trialdehyde phloroglucinol, pyromellitic methyl methacrylate, terephthalaldehyde, pyromellitic hexa(4-aldehyde phenyl)benzene, tetra(4-benzoyl)methane, and 1,3,5-tris(4-aldehyde phenyl)benzene. The concentration of the aldehyde-based small molecule organic solution is one or more of 0.1 mg / ml, 0.2 mg / ml, 0.3 mg / ml, 0.4 mg / ml, and 0.5 mg / ml. The solvent is selected from deionized water, toluene, cyclohexane, pyromellitic methyl methacrylate, and ethanol. The solution is stirred and heated with ultrasound to ensure complete dissolution.

[0041] Specifically, the amino small molecule organic compound mentioned in step 103 is preferably one or more of hydrazine hydrate, p-phenylenediamine, benzidine, 1,3,5-tris(4-aminophenyl)benzene, 2,5-diaminobenzenesulfonic acid, and tetra(4-benzoyl)methane. The preheating temperature is 110-130℃, specifically one or more of 110℃, 115℃, 120℃, 125℃, and 130℃. The preheating time is uniformly 15 minutes.

[0042] Specifically, the reaction apparatus described in step 104 consists of three parts: a hemispherical container 1 containing solid amine monomers, a cylindrical container 2 containing aldehyde monomer solution, and a clamping device that secures the two parts to prevent leakage at the joint. A porous membrane is placed between containers 1 and 2, facing downwards. Below it is the gaseous amine monomer sublimated at high temperature, and above it is the solution containing dissolved aldehyde small molecule organic compounds. The membrane is secured in the middle with the clamping device to prevent leakage. The reaction temperature corresponds to the preheating temperature described in step 103, and the gas-liquid interface polymerization reaction time is 1-5 hours, specifically 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours. After the reaction, the membrane is rinsed with at least one of deionized water, methanol, ethanol, and 1,4-dioxane to remove COF powder deposited on the back of the membrane and unreacted monomers. After rinsing, the membrane is soaked in deionized water for later use.

[0043] Preferably, the reaction temperature in step 104 is 110-130℃, specifically 110℃, 115℃, 120℃, 125℃, and 130℃, corresponding to reaction temperatures at the membrane surface of 40.0℃, 42.5℃, 45.0℃, 47.5℃, and 50.0℃. For every 5℃ increase in sand bath temperature, the membrane surface temperature increases by 2.5℃. More preferably, p-phenylenediamine undergoes gas-liquid interfacial polymerization with pyromellitic aldehyde and 1,3,5-trialdehyde phloroglucinol at the membrane surface, respectively, to construct a COF-LZU1 and TpPa-1 type cap-shaped nanoprotrusion separation layer at the pore openings of the porous membrane.

[0044] The present invention will be further described below through specific embodiments.

[0045] In the following specific embodiments, operations without specified conditions are performed under standard conditions or conditions recommended by the manufacturer. Raw materials without specified manufacturers and specifications are all commercially available products.

[0046] Example 1

[0047] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and 1,3,5-trialdehyde phloroglucinol were selected as monomers for the synthesis of TpPa-1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0048] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dirt, immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0049] Step b: Dissolve 2 mg of 1,3,5-trialdehyde phloroglucinol in 10 ml of deionized water (corresponding concentration of 0.2 mg / mL), stir to disperse, and then heat at 45°C and sonicate for 1 h to ensure complete dissolution;

[0050] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 120°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0051] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 120°C for 3 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain the ultra-high flux TpPa-1 composite membrane.

[0052] SEM images ( Figure 2 The AFM image shows that the surface of the TpPa-1 composite membrane consists of particles with a diameter of 50-100 nm, and there is no obvious separation layer of thickness in the cross-section. Figure 3 The film surface shows uniform cap-shaped protrusions with a protrusion height of 20-30 nm.

[0053] The prepared composite membrane was placed in a cross-flow circulating filtration dye device for performance testing. The test conditions were as follows: (1) the original solution consisted of 0.1 mg / L Chrome Black T neutral water system, (2) 0.1 mg / L Methyl Blue neutral water system, (3) 0.1 mg / L Congo Red neutral water system, (4) 0.1 mg / L Direct Black neutral water system, (5) 0.1 mg / L Coomassie Brilliant Blue neutral water system, (6) pH=3, 0.1 mg / L Chrome Black T water system, (7) pH=3, 0.1 mg / L Congo Red water system, (8) pH=5, 0.1 mg / L Chrome Black T water system, (9) pH=5, 0.1 mg / L Congo Red water system, (10) pH=9, 0.1 mg / L Chrome Black T water system. (11) pH=9, 0.1 mg / L Congo Red water system, (12) pH=11, 0.1 mg / L Chrome Black T water system, (13) pH=11, 0.1 mg / L Congo Red water system, (14) 0.05 mg / L Chrome Black T neutral water system, (15) 0.05 mg / L Congo Red neutral water system, (16) 0.15 mg / L Chrome Black T neutral water system, (17) 0.15 mg / L Congo Red neutral water system, (18) 0.2 mg / L Chrome Black T neutral water system, (19) 0.2 mg / L Congo Red neutral water system, (20) 0.5 mg / L Chrome Black T neutral water system, (21) 0.5 mg / L Congo Red neutral water system. The above tests were conducted at room temperature. (22) The stock solution consisted of a 0.1 mg / L Chrome Black T neutral water system at a water temperature of 40°C; (23) a 0.1 mg / L Congo Red neutral water system at a water temperature of 40°C; (24) a 0.1 mg / L Chrome Black T neutral water system at a water temperature of 50°C; (25) a 0.1 mg / L Congo Red neutral water system at a water temperature of 50°C; (26) a 0.1 mg / L Chrome Black T neutral water system at a water temperature of 60°C; (27) a 0.1 mg / L Congo Red neutral water system at a water temperature of 60°C. The operating pressure was 0.2 MPa, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0054] The properties of the composite membrane were measured as follows: (1) The chrome black T membrane had a flow rejection rate of 98.7% and a permeation flux of 1476 L / m. 2 ·h·MPa; (2) Methyl blue interception rate was 96.9%, and permeation flux was 1456 L / m 2 ·h·MPa; (3) The Congo red interception rate is 99.1%, and the permeation flux is 1428 L / m 2 ·h·MPa; (4) Direct black interception rate is 99.1%, and permeation flux is 1530L / m 2·h·MPa; (5) Coomassie Brilliant Blue has a flow rejection rate of 99.6% and a permeation flux of 1290 L / m 2 ·h·MPa; (6) Chrome Black T has a flow rejection rate of 99.4% and a permeation flux of 1439 L / m 2 ·h·MPa; (7) The Congo red interception rate was 98.6%, and the permeation flux was 1439 L / m 2 ·h·MPa; (8) Chrome Black T has a flow rejection rate of 98.6% and a permeation flux of 1440 L / m 2 ·h·MPa; (9) The Congo red interception rate is 99.1%, and the permeation flux is 1440L / m 2 ·h·MPa; (10) Chrome Black T has a flow rejection rate of 98.5% and a permeation flux of 1432 L / m 2 ·h·MPa; (11) The Congo red interception rate is 99.1%, and the permeation flux is 1432L / m 2 ·h·MPa; (12) Chrome Black T has a flow rejection rate of 98.9% and a permeation flux of 1442 L / m 2 ·h·MPa; (13) The Congo red interception rate is 99.0%, and the permeation flux is 1442 L / m 2 ·h·MPa; (14) Chrome Black T has a flow rejection rate of 98.5% and a permeation flux of 1597 L / m 2 ·h·MPa; (15) The Congo red interception rate is 99.3%, and the permeation flux is 1649 L / m 2 • h·MPa; (16) Chrome Black T has a flow rejection rate of 99.1% and a permeation flux of 1452 L / m 2 ·h·MPa; (17) Congo red interception rate is 99.3%, and permeation flux is 1500L / m 2 ·h·MPa; (18) Chrome Black T has a flow rejection rate of 99.1% and a permeation flux of 1397 L / m 2 ·h·MPa; (19) Congo red interception rate is 99.4%, and permeation flux is 1492 L / m 2 ·h·MPa; (20) Chrome Black T has a flow rejection rate of 99.2% and a permeation flux of 1298 L / m 2 ·h·MPa; (21) The Congo red interception rate is 99.3%, and the permeation flux is 1363L / m 2 ·h·MPa; (22) Chrome Black T has a flow rejection rate of 97.7% and a permeation flux of 1520 L / m 2 ·h·MPa; (23) Congo red interception rate is 99.1%, and permeation flux is 1650L / m 2 ·h·MPa; (24) Chrome Black T has a flow rejection rate of 97.2% and a permeation flux of 1605 L / m 2·h·MPa; (25) Congo red interception rate is 98.5%, and permeation flux is 1883 L / m 2 • h·MPa; (26) Chrome Black T has a flow rejection rate of 97.3% and a permeation flux of 1676 L / m 2 ·h·MPa; (27) Congo red interception rate is 98.4%, and permeation flux is 2232 L / m 2 ·h·MPa;

[0055] Example 2

[0056] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and trimesoaldehyde were selected as monomers for the synthesis of COF-LZU1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0057] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dust and dirt, and immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0058] Step b: Dissolve 8 mg of pyromellitic aldehyde (corresponding to a concentration of 0.8 mg / mL) and 2 mg of scandium trifluoromethanesulfonate catalyst in 10 mL of deionized water, stir to disperse, and then heat at 45 °C and sonicate for 1 h to ensure complete dissolution;

[0059] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 120°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0060] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 120°C for 2 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain an ultra-high flux COF-LZU1 composite membrane.

[0061] SEM images ( Figure 4 The AFM image shows that the surface of the COF-LZU1 composite membrane consists of particles with a diameter of 50-100 nm, and the cross-section shows no separation layer of significant thickness. Figure 5 The film surface shows uniform cap-like protrusions with a depth of 15-20 nm.

[0062] The prepared composite membrane was placed in a cross-flow circulating filtration dyeing device for performance testing. The test conditions were as follows: (1) the stock solution composition was 0.1 mg / L Chrome Black T aqueous system, (2) 0.1 mg / L Methyl Blue aqueous system, (3) 0.1 mg / L Congo Red aqueous system, (4) 0.1 mg / L Direct Black aqueous system, and (5) 0.1 mg / L Coomassie Brilliant Blue aqueous system. The operating pressure was 0.2 MPa, the operating temperature was room temperature, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0063] The properties of the composite membrane were measured as follows: (1) The chrome black T membrane had a flow rejection rate of 98.2% and a permeation flux of 1062 L / m. 2 ·h·MPa; (2) Methyl blue interception rate was 94.5%, and permeation flux was 1309 L / m 2 ·h·MPa; (3) The Congo red interception rate is 99.6%, and the permeation flux is 1044 L / m 2 ·h·MPa; (4) Direct black interception rate is 98.5%, and permeation flux is 1180L / m 2 ·h·MPa; (5) Coomassie Brilliant Blue has a flow rejection rate of 99.5% and a permeation flux of 849 L / m 2 ·h·MPa;

[0064] Example 3

[0065] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and 1,3,5-trialdehyde phloroglucinol were selected as monomers for the synthesis of TpPa-1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0066] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dirt, immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0067] Step b: Dissolve 4 mg of 1,3,5-trialdehyde phloroglucinol in 10 ml of deionized water (corresponding concentration of 0.4 mg / mL), stir to disperse, and then heat at 45°C and sonicate for 1 h to ensure complete dissolution;

[0068] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 120°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0069] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 120°C for 3 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain the ultra-high flux TpPa-1 composite membrane.

[0070] The prepared composite membrane was placed in a cross-flow circulating filtration dye device for performance testing. The test conditions were as follows: (1) The original solution consisted of a 0.1 mg / L methylene blue neutral water system, the operating pressure was 0.2 MPa, the operating temperature was room temperature, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0071] The properties of the composite membrane were measured as follows: (1) Methylene blue rejection rate was 97.9%, and permeation flux was 610 L / m. 2 ·h·MPa;

[0072] Example 4

[0073] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and 1,3,5-trialdehyde phloroglucinol were selected as monomers for the synthesis of TpPa-1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0074] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dirt, immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0075] Step b: Dissolve 2 mg of 1,3,5-trialdehyde phloroglucinol in 10 ml of deionized water (corresponding concentration of 0.2 mg / mL), stir to disperse, and then heat at 45°C and sonicate for 1 h to ensure complete dissolution;

[0076] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 125°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0077] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 125°C for 3 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain the ultra-high flux TpPa-1 composite membrane.

[0078] The prepared composite membrane was placed in a cross-flow circulating filtration dye device for performance testing. The test conditions were as follows: (1) The original solution consisted of a 0.1 mg / L methylene blue neutral water system, the operating pressure was 0.2 MPa, the operating temperature was room temperature, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0079] The properties of the composite membrane were measured as follows: (1) Methylene blue rejection rate was 93.5%, and permeation flux was 1658 L / m. 2 ·h·MPa;

[0080] Example 5

[0081] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and 1,3,5-trialdehyde phloroglucinol were selected as monomers for the synthesis of TpPa-1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0082] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dirt, immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0083] Step b: Dissolve 2 mg of 1,3,5-trialdehyde phloroglucinol in 10 ml of deionized water (corresponding concentration of 0.2 mg / mL), stir to disperse, and then heat at 45°C and sonicate for 1 h to ensure complete dissolution;

[0084] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 120°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0085] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 120°C for 4 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain the ultra-high flux TpPa-1 composite membrane.

[0086] The prepared composite membrane was placed in a cross-flow circulating filtration dye device for performance testing. The test conditions were as follows: (1) The original solution consisted of a 0.1 mg / L methylene blue neutral water system, the operating pressure was 0.2 MPa, the operating temperature was room temperature, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0087] The properties of the composite membrane were measured as follows: (1) Methyl blue rejection rate was 96.2%, and permeation flux was 1212 L / m. 2 ·h·MPa;

[0088] Example 6

[0089] Polyacrylonitrile (PAN) porous membranes were used, with an average molecular weight cutoff of 50,000 and an average pore size of 0.05 μm. p-Phenylenediamine and 1,3,5-trialdehyde phloroglucinol were selected as monomers for the synthesis of TpPa-1 type covalent organic framework materials, and a gas-liquid interfacial polymerization reaction was employed.

[0090] Step a: Rinse the PAN50 porous base membrane multiple times with a 30wt% ethanol aqueous solution to remove surface dirt, immerse it in the solution for 4 hours to remove surface organic matter, and then immerse it in deionized water to remove the ethanol solvent.

[0091] Step b: Dissolve 2 mg of 1,3,5-trialdehyde phloroglucinol in 10 ml of deionized water (corresponding concentration of 0.2 mg / mL), stir to disperse, and then heat at 45°C and sonicate for 1 h to ensure complete dissolution;

[0092] Step c: Add an appropriate amount of solid p-phenylenediamine to a hemispherical container 1, seal it with tin foil, and place it in a sand bath at 120°C for 15 minutes to provide a continuous and rapid supply of gaseous amine monomers for the subsequent reaction.

[0093] Step d: Wipe the water off the surface of the PAN50 porous membrane pretreated in step a, and place the wetted PAN50 membrane upside down in the reaction apparatus, specifically with the membrane side facing down and the p-phenylenediamine solid facing down. Fix the cylindrical reactor 2 above the back of the membrane, and use clamps to fix the reactor 1, PAN50 membrane, and reactor 2 in place. Quickly pour 10 ml of the aldehyde monomer aqueous solution obtained in step b onto the back of the membrane and check the airtightness of the apparatus. Then place it in a sand bath at 120°C for 5 hours. After the reaction is complete, remove the membrane from the apparatus and rinse the membrane surface multiple times with deionized water to obtain the ultra-high flux TpPa-1 composite membrane.

[0094] The prepared composite membrane was placed in a cross-flow circulating filtration dye device for performance testing. The test conditions were as follows: (1) The original solution consisted of a 0.1 mg / L methylene blue neutral water system, the operating pressure was 0.2 MPa, the operating temperature was room temperature, and the effective test area was 7.065 cm². 2 After filtration and circulation stabilization for 30 minutes, the retentate and the original solution were collected. The permeation flux was calculated based on the volume of solution collected at fixed intervals, and the rejection rate was calculated based on the absorbance values ​​before and after rejection measured by a UV spectrophotometer.

[0095] The properties of the composite membrane were measured as follows: (1) Methyl blue rejection rate was 95.2%, and permeation flux was 1029 L / m. 2 ·h·MPa;

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-flux covalent organic framework composite nanofiltration membrane, characterized in that, It includes a porous base membrane and a selective separation layer composed of multiple discrete COF nanoprotrusion cap structures grown on the surface of the porous base membrane. Each discrete COF nanoprotrusion is grown at the pore opening of the porous base membrane using a gas-liquid interface polymerization reaction.

2. The ultra-high flux covalent organic framework composite nanofiltration membrane according to claim 1, characterized in that, The porous base membrane is selected from organic polymer membranes and inorganic membranes, and has an average pore size of 0.02-1 μm; the porous base membrane is in the shape of a flat plate.

3. The ultra-high flux covalent organic framework composite nanofiltration membrane according to claim 1, characterized in that, The COF is an imine-based two-dimensional layered covalent organic framework material obtained by reacting aldehyde small molecules and amine monomers. The aldehyde small molecules are selected from aryl monomers with at least two aldehyde groups; the amine monomers are at least diamine monomers.

4. The ultra-high flux covalent organic framework composite nanofiltration membrane according to claim 3, characterized in that, The aldehyde molecule is selected from one or more of 1,3,5-trialdehyde phloroglucinol, pyromellitic methyl methacrylate, terephthalaldehyde, pyromellitic hexa(4-aldehyde phenyl)benzene, tetra(4-benzoyl)methane, and 1,3,5-tris(4-aldehyde phenyl)benzene; the amine monomer is selected from one or more of hydrazine hydrate, p-phenylenediamine, benzidine, 1,3,5-tris(4-aminophenyl)benzene, 2,5-diaminobenzenesulfonic acid, and tetra(4-aminophenyl)methane.

5. A high-flux covalent organic framework composite nanofiltration membrane according to claim 3, characterized in that, The obtained COF is selected from one of the following covalent organic framework materials: Schiff base -RC=N- or =CH-N-, hydrazone bond -NH-N= or nitrogen bond =N-N=.

6. The ultra-high flux covalent organic framework composite nanofiltration membrane according to claim 1, characterized in that, The COF nano-protrusion cap structure has an average longitudinal height of 10-50 nm and an average transverse width (radial width) of 50-100 nm.

7. A method for preparing an ultra-high flux covalent organic framework composite nanofiltration membrane according to any one of claims 1-6, characterized in that, The COF nano-protrusion cap-like structure separation layer is a nano-confined gas-liquid interface constructed based on the pores of a porous base membrane. It is prepared by polymerization reaction and has extremely strong stability in water and organic solvents. Specifically, the following steps are included: Step a: First, pretreat the base film with organic and / or inorganic solvents, rinse and soak at room temperature for a certain time to remove organic matter and inorganic dust from the surface of the base film; Step b: Dissolve the aldehyde small molecule organic compound in an inorganic and / or organic solvent, stir and heat and sonicate to fully dissolve it to obtain an aldehyde small molecule solution; Step c: Add the amine monomer block solid to the bottom of the reaction apparatus, wrap it with tin foil, and place it in a sand bath at a certain temperature for a period of time to preheat it, so as to continuously and rapidly supply the gaseous amine monomer for the subsequent reaction. Step d: Wipe the moisture off the surface of the pretreated base membrane from step a, place the internally moistened base membrane above the amine monomer in the apparatus of reaction step c, with the front of the base membrane facing the amine monomer below. Quickly pour the aldehyde small molecule solution obtained in step b onto the back of the membrane, while keeping the aldehyde monomer aqueous solution on the back of the membrane. After checking that there is no leakage on the side, place the apparatus in a sand bath at a certain temperature so that the amine monomer continuously sublimates upwards and contacts the aldehyde small molecule droplets permeating down from the front of the base membrane to form a gas-liquid interface. After reacting for a period of time, a COF nano-protrusion cap structure is formed. After the reaction is completed, remove the base membrane from the apparatus and rinse the membrane surface with organic and / or inorganic solvents to obtain an ultra-high flux covalent organic framework composite membrane.

8. The method according to claim 6, characterized in that, The organic and / or inorganic solvents mentioned in step a are selected from at least one of ethanol, methanol, toluene, ethyl acetate, acetic acid, and deionized water; the inorganic and / or organic solvents in step b are selected from one or more of deionized water, toluene, cyclohexane, mesitylene, and ethanol, and are stirred and heated with ultrasound to fully dissolve them. In step b, the concentration of aldehyde small molecules in the aldehyde small molecule solution is 0.1-1 mg / ml; In step c, the preheating temperature is 110-135℃ and the preheating time is 15 minutes. The reaction temperature corresponds to the preheating temperature described in step c. The gas-liquid interface polymerization reaction formed on the front side takes 1-5 hours. After the reaction is completed, at least one of deionized water, methanol, ethanol, and 1,4-dioxane is selected to rinse the membrane surface to remove the COF powder deposited on the back side of the membrane and the unreacted monomers on the membrane. After rinsing, the membrane is soaked in deionized water for later use. The reaction temperature described in step d is 110-135℃, which corresponds to a reaction temperature of 40-50℃ on the front side of the membrane. Specifically, for every 5℃ increase in the sand bath temperature, the reaction temperature on the membrane surface increases by 2.5℃.

9. The method according to claim 8, characterized in that, In step b, the concentration of aldehyde small molecules in the aldehyde small molecule solution is 0.1-0.5 mg / ml.

10. The method according to claim 8, characterized in that, In step b, the concentration of aldehyde small molecules in the aldehyde small molecule solution is 0.1-0.2 mg / ml.

11. The method according to claim 8, characterized in that, The gas-liquid interface polymerization reaction formed on the front side takes 2-4 hours.

12. The method according to claim 7, characterized in that, According to the requirements of COF preparation, a catalyst is added to the aldehyde small molecule solution in step b.

13. The application of the ultra-high flux covalent organic framework composite nanofiltration membrane according to any one of claims 1-6, for filtering water-soluble organic molecules in aqueous solutions.

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