阅读说明：本技术 一种COFs@HPAN纳滤复合膜的制备方法 (Preparation method of COFs @ HPAN nanofiltration composite membrane ) 是由 韩娜 张雅琪 张兴祥 张总宣 张浩然 于 2020-07-17 设计创作，主要内容包括：本发明公开了一种COFs@HPAN纳滤复合膜的制备方法,通过高速混炼技术将COFs与可熔融PAN基共聚物充分共混制备分布均一的COFs-PAN母粒,然后制备出COFs分布均一的COFs-PAN共混膜,再通过依次进行的三个级别的交联得到COFs@HPAN纳滤复合膜。本方法通过调变水解、辐照、预氧化反应的工艺参数利用依次进行的水解-辐照-预氧化反应对COFs-PAN共混膜进行处理,构筑多层次可调节的网络交联结构,可根据不同用途的需要调控纳滤复合膜的网络交联结构,以达到不同的孔径尺寸,从而实现高效脱色、脱盐和脱除病毒的功能。制得的非对称结构COFs@HPAN纳滤复合膜具有优异的渗透性和选择性、孔隙率高、孔径分布均匀,热力学稳定性、耐化学性、可循环稳定性优异,可应用于苛刻水环境中分离净化。(The invention discloses a preparation method of a COFs @ HPAN nanofiltration composite membrane, which is characterized in that COFs and meltable PAN-based copolymers are fully blended through a high-speed mixing technology to prepare uniformly distributed COFs-PAN master batches, then a COFs-PAN blending membrane with uniformly distributed COFs is prepared, and then the COFs @ HPAN nanofiltration composite membrane is obtained through sequentially carrying out three-level crosslinking. The method processes the COFs-PAN blended membrane by modulating the technological parameters of hydrolysis, irradiation and pre-oxidation reactions and utilizing hydrolysis-irradiation-pre-oxidation reactions which are sequentially carried out, a multi-layer adjustable network cross-linking structure is constructed, and the network cross-linking structure of the nanofiltration composite membrane can be adjusted and controlled according to the requirements of different purposes so as to achieve different pore sizes, thereby realizing the functions of efficient decoloration, desalination and virus removal. The prepared COFs @ HPAN nanofiltration composite membrane with the asymmetric structure has excellent permeability and selectivity, high porosity, uniform pore size distribution, excellent thermodynamic stability, chemical resistance and cycling stability, and can be applied to separation and purification in harsh water environments.)

1. A preparation method of a COFs @ HPAN nanofiltration composite membrane is characterized by comprising the following steps:

1) mixing COFs and meltable PAN-based copolymer to obtain COFs-PAN master batch; the mass of the COFs is 3-95% of the sum of the mass of the COFs and the mass of the meltable PAN-based copolymer;

2) taking the COFs-PAN master batch obtained in the step 1) as a raw material to obtain a COFs-PAN blend membrane;

3) sequentially carrying out primary crosslinking, secondary crosslinking and tertiary crosslinking on the COFs-PAN blended membrane obtained in the step 2) to obtain the COFs @ HPAN nanofiltration composite membrane.

2. The preparation method of the COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein in the step 1), the COFs and the meltable PAN-based copolymer are subjected to high-speed mixing in a double-rotor high-speed mixing mill at a rotation speed of 500-1500 rpm and a temperature of 200-230 ℃ for 5-60 min to obtain the COFs-PAN master batch.

3. The process of claim 1, wherein in step 1), the COFs are selected from the group consisting of COF-1, COF-5, COF-8, COF-10, COF-Dhatab, COF-TpPa-1, COF-TpPa-2, COF-TpBD-Me₂、COF-TpBD-(OMe)₂COF-TpTGcl, COF-SDU1, COF-SDU2 or COF-LZU 10.

4. The process of preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein the mass of the COFs is 60-95% of the sum of the mass of the COFs and the mass of the meltable PAN-based copolymer.

5. The process for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1 or 4, wherein the mass of the COFs is 87-95% of the sum of the mass of the COFs and the mass of the meltable PAN-based copolymer.

6. The process for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein the film forming process in step 2) is:

fully mixing the COFs-PAN master batch obtained in the step 1) and a composite diluent at 130-170 ℃ under the protection of inert gas to obtain a uniform solution, and defoaming to obtain a COFs-PAN casting solution;

the COFs-PAN master batch accounts for 15-35% of the total mass of the COFs-PAN master batch and the composite diluent;

the composite diluent consists of a main diluent and an auxiliary diluent, wherein the main diluent accounts for 40-90% of the mass of the composite diluent; the main diluent is at least one of ethylene carbonate, caprolactam, diphenyl sulfone, benzophenone, diphenyl carbonate, dimethyl sulfoxide, cyclohexyl pyrrolidone or diphenyl ethanone; the auxiliary diluent is at least one of glycerol, glyceryl triacetate, polyvinyl alcohol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, dibutyl sebacate, dimethyl phthalate or acetamide;

preparing a flat membrane: pouring the COFs-PAN membrane casting solution into a mold preheated to 90-150 ℃ for calendering and molding, cooling and solidifying, and removing a composite diluent in an extracting agent to obtain a COFs-PAN blended flat membrane;

preparing a hollow fiber membrane: pouring the COFs-PAN membrane casting solution into a plunger type spinning machine, a single screw or a double screw, extruding at the temperature of 90-230 ℃ under the condition that inert gas or core liquid is introduced into a central tube, cooling and solidifying, and removing a composite diluent in an extracting agent to obtain the COFs-PAN blended hollow fiber membrane;

the cooling and solidifying process conditions are that solidification is carried out for 6-24 hours in an air bath or a water bath at the temperature of 20-50 ℃;

the extractant is water solution or mixed solution of water and ethanol.

7. The process for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein in step 3), the primary cross-linking is hydrolysis, and the hydrolysis process is: hydrolyzing the COFs-PAN blend membrane obtained in the step 2) in an alkali solution with the mass fraction of 1-25 wt% for 0.5-8 h, removing the alkali solution on the surface of the membrane after taking out, and then drying;

the alkaline solution is KOH, NaOH, Mg (OH)₂Or NaHCO₃A solution;

the drying treatment process is carried out for 12-36 hours in a vacuum oven at the temperature of 40-80 ℃.

8. The process for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein in step 3), the secondary crosslinking is irradiation, and the irradiation process is: performing strong light irradiation on the film obtained by the first-stage crosslinking in an ambient gas;

the irradiation light source is ultraviolet light, gamma rays or electron beams; the irradiation time is 1-24 h; the environment gas is nitrogen, oxygen, argon, oxygen/nitrogen mixed gas or oxygen/argon mixed gas; the volume of oxygen in the mixed gas accounts for 10-50% of the total volume of the gas.

9. The method for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 8, wherein when ultraviolet light is used for irradiation, an irradiation source is a mercury arc lamp, and irradiation is performed for 1-24 hours at 80-120 ℃; when gamma-ray irradiation is used, the irradiation source is⁶⁰Co, the radiation dose is 5-560 kGy; when electron beams are used for irradiation, an electron accelerator is used for irradiation, the irradiation energy is 0.5-3 MeV, and the irradiation dose is 20-400 kGy.

10. The process for preparing a COFs @ HPAN nanofiltration composite membrane according to claim 1, wherein in step 3), the tertiary crosslinking is a pre-oxidation reaction, which is: placing the membrane obtained by secondary crosslinking in a tubular furnace, heating to the temperature of 250-350 ℃ in an environment atmosphere, carrying out pre-oxidation treatment for 0.5-12 h, and then cooling to room temperature to obtain the COFs @ HPAN nanofiltration composite membrane;

the environment atmosphere is one of nitrogen, oxygen or argon; the heating rate is 0.5-10 ℃/min; the cooling rate is 5-30 ℃/min.

Technical Field

The invention belongs to the field of COFs nanofiltration membranes, and particularly relates to a preparation method of a COFs @ HPAN nanofiltration composite membrane.

Background

The printing and dyeing wastewater contains complex and difficultly degradable dyes and salt substances, has the characteristics of high chromaticity, high salinity and high toxicity, and causes great harm to the ecological environment and human health. With the continuous improvement of the discharge standard of the printing and dyeing wastewater in China, how to separate and remove the dye and the salt substances in the printing and dyeing wastewater to ensure that the printing and dyeing wastewater reaches the discharge standard is widely concerned.

The membrane separation technology is a process for realizing the classification, separation, purification and enrichment of a multi-component mixture by utilizing the selective permeability of a separation membrane to pollutants with different particle sizes. The method has the advantages of low application cost, simple operation, energy conservation, environmental protection and the like, and is widely applied to the purification treatment of various water bodies such as industrial production sewage, domestic wastewater and the like. Membrane separation techniques include ultrafiltration, microfiltration, electrodialysis, reverse osmosis, nanofiltration, membrane bioreactors, and the like. The pore diameter of the nanofiltration membrane is 1-2 nm, solute components such as dye molecules and high-valence salts can be effectively intercepted, green separation of molecular scale is realized, and the nanofiltration membrane is considered to be one of the best choices for treating printing and dyeing wastewater.

The nanofiltration membrane is the key for treating printing and dyeing wastewater by nanofiltration technology, and is usually formed by crosslinking high molecular materials such as polyimide, polyamide, polyvinylidene fluoride, polyacrylonitrile and the like as a matrix. The traditional nanofiltration membrane has low permeation flux due to compact structure, low porosity and lack of effective and adjustable pore structure. Therefore, substances such as graphene, MOF, COF, nano metal oxide and the like are often used as functional additives to be introduced into a nanofiltration membrane matrix to construct a stable organic micromolecule selective mass transfer channel, so that the permeation flux of the nanofiltration membrane is improved. At present, two methods are mainly used for preparing the COFs composite membrane: firstly, a COFs porous material is used as a filler to be blended with a polymer matrix to prepare a Mixed Matrix Membrane (MMM); secondly, the porous material is grown or spin-coated on the surface of the polymer matrix layer. The COFs nano material can be used as a filler to improve the selectivity and the permeability of the nanofiltration membrane. But the addition amount of COFs is small, and the phenomenon of permeability-selectivity trade-off of the nanofiltration membrane cannot be solved, namely the permeability is improved, and the rejection rate is reduced; on the contrary, the selectivity is increased and the permeability is decreased. With the increase of the content of COFs in the system, the nano filler is agglomerated, the viscosity of the system is increased dramatically, and the problems of difficult processing, increased brittleness of the film, cracks on the surface and the like are brought. Therefore, it is reported that the maximum addition amount of COFs in MMM prepared by a non-solvent induced phase separation (NIPS) method is less than 10%. When the COFs composite membrane is prepared by a surface growth method or a spin-coating method, the crystallization of a nanofiltration separation layer is not perfect enough or the acting force between the nanofiltration separation layer and a base body is weak, the permeability of the COFs composite membrane is remarkably reduced while the selectivity of the COFs composite membrane is increased along with the increase of the number of layers, and the anti-pollution performance and the flux recovery rate are unstable.

The document of application No. 201911048401.3 discloses a method for preparing a covalent organic framework hybrid membrane, which comprises preparing a film forming solution of COFs and polyether copolyamide (PERAX) by ultrasonic stirring, coating the film forming solution on the surface of an inorganic porous membrane by a dip-coating method, and then performing heat treatment to form a membrane by self-crosslinking of the PERAX, thereby obtaining the covalent organic framework hybrid membrane, but the maximum doping amount of the COFs of the hybrid membrane is only 10%, and the COFs are unevenly distributed in the hybrid membrane, so that the obtained hybrid membrane has poor mechanical properties and poor use stability. In the document Shi X.S., Wang R., Xiao.A.K, et al ACS Applied NanoMaterials,2018,1(11): 6320-26, a layer-by-layer growth method is adopted to prepare a COFs composite membrane (TpBD-HPAN) by taking a Hydrolyzed Polyacrylonitrile (HPAN) microfiltration membrane as a matrix, and the experimental result shows that: when the number of COFs is increased from 3 to 11, the pure water flux of the composite membrane is 415 L.m^-2·h^-1·bar^-1Reduced to 2 L.m^-2·h^-1·bar^-1Chemical stability and cycling stability of the composite membrane are not reported.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to solve the technical problem of providing a preparation method of a COFs @ HPAN nanofiltration composite membrane.

The technical scheme for solving the technical problem is to provide a preparation method of a COFs @ HPAN nanofiltration composite membrane, which is characterized by comprising the following steps:

1) mixing COFs and meltable PAN-based copolymer to obtain COFs-PAN master batch; the mass of the COFs is 3-95% of the sum of the mass of the COFs and the mass of the meltable PAN-based copolymer;

2) taking the COFs-PAN master batch obtained in the step 1) as a raw material to obtain a COFs-PAN blend membrane;

3) sequentially carrying out primary crosslinking, secondary crosslinking and tertiary crosslinking on the COFs-PAN blended membrane obtained in the step 2) to obtain the COFs @ HPAN nanofiltration composite membrane.

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the method, COFs and meltable PAN-based copolymer are fully blended through a high-speed mixing technology to prepare COFs-PAN master batches with uniform distribution, a TIPS method is used for preparing a COFs-PAN blending membrane with uniform COFs distribution, and three levels of crosslinking are sequentially carried out to obtain the COFs @ HPAN nanofiltration composite membrane. The method has simple process and clean production, and is suitable for industrial implementation. The prepared COFs @ HPAN nanofiltration composite membrane with the asymmetric structure has excellent permeability and selectivity, high porosity, uniform pore size distribution, excellent thermodynamic stability, chemical resistance and cycling stability, and can be applied to efficient removal, separation and purification of pollutants with different particle sizes in a harsh water environment.

(2) The highest content of COFs in the COFs-PAN blended membrane prepared by combining the TIPS method with the high-speed mixing technology can reach 95%, the COFs blended membrane is uniform in distribution, less in defects, good in repeatability, more excellent in connectivity, uniformity of pore diameter, interception performance and physical and mechanical properties, and high in preparation efficiency.

(3) The TIPS process saves a large amount of solvent recovery and three-waste treatment, and the preparation process is green and environment-friendly.

(4) The method processes the COFs-PAN blended membrane by modulating the technological parameters of hydrolysis, irradiation and pre-oxidation reactions and utilizing hydrolysis-irradiation-pre-oxidation reactions which are sequentially carried out, so that a multi-level adjustable network cross-linking structure is constructed, the network cross-linking structure of the nanofiltration composite membrane can be adjusted and controlled according to the requirements of different purposes (the sizes of dye molecules, salt molecules and the like) so as to reach different aperture sizes, and the nanofiltration composite membrane meeting the application requirements is prepared, so that the functions of efficient decolorization, desalination and virus removal are realized.

(5) In the hydrolysis process, because of the huge density difference between the COFs and the PAN base membrane, part of the COFs is separated from the package of the polymer matrix and migrates to the surface of the membrane, the thickness and the distribution density of the COFs separation layer on the surface of the membrane can be regulated and controlled by regulating and controlling hydrolysis process parameters, and meanwhile, the section of the composite membrane is in an asymmetric structure (as shown in figure 1). OH or NH on the surface of COFs₂And hydrogen bond interaction is generated between the COFs and the substrate, so that the COFs can avoid the shedding of COFs functional nanoparticles in the application process, and the roughness and the hydrophilicity of the surface of the membrane are greatly improved.

(6) Under the action of high-energy irradiation, rays penetrate through the COFs @ HPAN hybrid membrane to bring energy to PAN molecular chains, one atom is ionized and excited to release extra-nuclear electrons to form free radicals, cross-linking reaction (shown in figure 2) occurs between adjacent PAN molecular chains to form a network structure, and the compactness, the physical and mechanical properties and the solvent resistance of the irradiated PAN base membrane are remarkably improved.

(7) And (2) performing high-temperature preoxidation reaction to convert part of-CN groups on the PAN base film into an aromatic ring structure, so as to improve the dimensional stability, the chemical stability, the thermodynamic stability and the physical and mechanical properties of the COFs @ HPAN nanofiltration composite membrane (as shown in figure 3).

Drawings

FIG. 1 is a schematic diagram of the principle of the first-order crosslinking of the present invention;

FIG. 2 is a schematic diagram of the principle of the second-order crosslinking of the present invention;

FIG. 3 is a schematic diagram of the principle of tertiary crosslinking according to the present invention;

Detailed Description

Specific examples of the present invention are given below. The specific examples are only intended to illustrate the invention in further detail and do not limit the scope of protection of the claims of the present application.

The invention provides a preparation method (short for method) of a COFs @ HPAN nanofiltration composite membrane, which is characterized by comprising the following steps:

1) adding the COFs and the meltable PAN-based copolymer into a double-rotor high-speed mixing mill, and mixing at a high speed of 500-1500 rpm and at a temperature of 200-230 ℃ for 5-60 min to obtain COFs-PAN master batches;

in step 1), the meltable PAN-based copolymer may be prepared using materials or methods of preparation disclosed in patents zl201510694690.x or ZL 200810053936.5.

In step 1), the COFs may be, but not limited to, COF-1 (pore size 1.5nm), COF-5 (pore size 2.7nm), COF-8 (pore size 1.64nm), COF-10 (pore size 3.2nm), COF-DhaTab (pore size 3.7nm), COF-TpPa-1 (pore size 1.8nm), COF-TpPa-2 (pore size 1.5nm), COF-TpBD (pore size 2.4nm), COF-TpBD-Me₂(pore size 2.3nm), COF-TpBD- (OMe)₂At least one of (pore diameter: 2.3nm), COF-TpTGcl (pore diameter: 1.3nm), COF-SDU1 (pore diameter: 3.7nm), COF-SDU2 (pore diameter: 3.1nm), and COF-LZU10 (pore diameter: 1.1 nm);

in step 1), the mass of the COFs is 3-95%, preferably 10-95%, more preferably 60-95%, and still more preferably 87-95% of the sum of the mass of the COFs and the mass of the meltable PAN-based copolymer;

2) taking the COFs-PAN master batch obtained in the step 1) as a raw material, and forming a film by a thermally induced phase separation method (TIPS method) to obtain a COFs-PAN blended film; the blended membrane may be a flat sheet membrane or a hollow fiber membrane.

In the step 2), a film forming process adopts a thermally induced phase separation method (TIPS method), and the TIPS method comprises the following steps:

fully mixing the COFs-PAN master batch obtained in the step 1) and a composite diluent at 130-170 ℃ under the protection of inert gas to obtain a uniform solution, and defoaming to obtain a COFs-PAN casting solution;

the COFs-PAN master batch accounts for 15-35% of the total mass of the COFs-PAN master batch and the composite diluent;

the composite diluent consists of a main diluent and an auxiliary diluent, wherein the main diluent accounts for 40-90% of the mass of the composite diluent; the main diluent is at least one of ethylene carbonate, caprolactam, diphenyl sulfone, benzophenone, diphenyl carbonate, dimethyl sulfoxide, cyclohexyl pyrrolidone or diphenyl ethanone; the auxiliary diluent is at least one of glycerol, glyceryl triacetate, polyvinyl alcohol, polyethylene glycol monomethyl ether, polyethylene glycol dimethyl ether, dibutyl sebacate, dimethyl phthalate or acetamide;

preparing a flat membrane: pouring the COFs-PAN membrane casting solution into a mold preheated to 90-150 ℃ for calendering and molding, cooling and solidifying, and removing a composite diluent in an extracting agent to obtain a COFs-PAN blended flat membrane;

preparing a hollow fiber membrane: pouring the COFs-PAN membrane casting solution into a plunger type spinning machine, a single screw or a double screw, extruding at the temperature of 90-230 ℃ under the condition that inert gas or core liquid is introduced into a central tube, cooling and solidifying, and removing a composite diluent in an extracting agent to obtain the COFs-PAN blended hollow fiber membrane.

The cooling and solidifying process conditions are that solidification is carried out for 6-24 hours in an air bath or a water bath at the temperature of 20-50 ℃;

the extracting agent is water solution or mixed solution of water and ethanol;

3) sequentially carrying out primary crosslinking, secondary crosslinking and tertiary crosslinking on the COFs-PAN blended membrane obtained in the step 2) to obtain a COFs @ HPAN nanofiltration composite membrane;

in the step 3), the first-order crosslinking is hydrolysis, and the hydrolysis process comprises the following steps: hydrolyzing the COFs-PAN blend membrane obtained in the step 2) in an alkali solution with the mass fraction of 1-25 wt% for 0.5-8 h, taking out, washing with ethanol and distilled water to remove the alkali solution on the surface of the membrane, and drying to obtain the COFs @ HPAN hybrid membrane. In the hydrolysis process, COFs migrate to the surface of the membrane, and-OH or-NH on the surface of the COFs₂Hydrogen bonding, i.e., primary crosslinking, with the moiety-COOH formed after hydrolysis of PAN. Through primary crosslinking, the COFs-PAN blended membrane is converted into a COFs @ HPAN hybrid membrane, but the physical and mechanical properties, chemical resistance and thermodynamic stability of the membrane are required to be improved;

the alkaline solution is KOH, NaOH, Mg (OH)₂Or NaHCO₃A solution;

the drying treatment process is carried out for 12-36 h in a vacuum oven at the temperature of 40-80 ℃;

in the step 3), the secondary crosslinking is irradiation, and the irradiation process comprises the following steps: performing strong light irradiation on the COFs @ HPAN hybrid membrane obtained by primary crosslinking in the ambient gas; in the irradiation process, partial cross-linking reaction occurs among PAN molecular chains to form a network structure, so that the physical and mechanical properties and solvent resistance of the membrane are obviously improved;

the irradiation light source can be any one of ultraviolet light, gamma rays or electron beams; the irradiation time is 1-24 h; the environment gas is nitrogen, oxygen, argon, oxygen/nitrogen mixed gas or oxygen/argon mixed gas; the volume of oxygen in the oxygen/nitrogen mixed gas and the oxygen/argon mixed gas accounts for 10-50% of the total gas volume;

when ultraviolet light is used for irradiation, the irradiation source is a mercury arc lamp, and irradiation is carried out for 1-24 hours at the temperature of 80-120 ℃; when gamma-ray irradiation is used, the irradiation source is⁶⁰Co is irradiated for 1-24 hours at the irradiation dose rate of 5-24 kGy/h to reach the irradiation dose of 5-560 kGy; when electron beams are used for irradiation, an electron accelerator is used for irradiation, the irradiation energy is 0.5-3 MeV, and the irradiation dose is 20-400 kGy.

In the step 3), the tertiary crosslinking is a pre-oxidation reaction, and the pre-oxidation reaction is as follows: placing the COFs @ HPAN hybrid membrane obtained by secondary crosslinking in a tubular furnace, heating to the temperature of 250-350 ℃ in an environment atmosphere, carrying out pre-oxidation treatment for 0.5-12 h, and then cooling to room temperature to obtain the COFs @ HPAN nanofiltration composite membrane; in the pre-oxidation process, part of CN groups of PAN macromolecular side chains in the membrane network structure are converted into aromatic ring structures, so that the mechanical property, acid and alkali resistance and thermal stability of the membrane are further improved;

the pre-oxidation environment atmosphere is one of nitrogen, oxygen or argon; the heating rate is 0.5-10 ℃/min; the cooling rate is 5-30 ℃/min;