Preparation method of hollow fiber nanofiltration membrane based on polytetrafluoroethylene

Abstract

The invention relates to the technical field of preparation of nanofiltration membranes, in particular to a preparation method of a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, which is characterized in that the hydrophilicity of a base membrane is improved through treatment such as polydopamine (PDA) coating and plasma etching; two interfacial polymerization reactions are carried out through amine and acyl chloride substances, so that a compact and defect-free secondary polyamide layer is constructed; a double polymerization reaction is adopted in the interfacial polymerization reaction process. After the first polymerization reaction, the polyamide film layer is easy to have defects, and after the second polymerization reaction, the defects of a surface separation layer of the first polymerization reaction can be made up, so that the polyamide film layer has a better separation effect. And finally, through post-treatment, the crosslinking degree of the composite membrane is enhanced. Meanwhile, through matching of the reaction effect in the secondary polymerization reaction and the etching process, the forming quality of the secondary polyamide layer is guaranteed while reagent waste is avoided, and the prepared nanofiltration membrane can be suitable for separation of strong organic solvents.

Description

Technical Field

[0001] The invention relates to the technical field of nanofiltration membrane preparation, and in particular to a method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene. Background Art

[0002] Due to ecological and environmental requirements, more efficient and environmentally friendly separation technologies are currently needed to replace traditional methods such as distillation and extraction, which are energy-intensive and may produce secondary pollution. In the field of separation, nanofiltration membranes have attracted much attention due to their unique filtration properties. Nanofiltration membranes can screen high and low-valence ions, and at the same time, they have a retention effect on larger organic particles. They can be effectively used to remove organic matter and color, reduce TDS concentration and soften water quality. In the field of drug synthesis, complex organic solutions often need to be treated. Organic solvent nanofiltration can effectively separate target molecules and improve yield and purity. Organic solvent nanofiltration is a membrane process that uses a chemically stable membrane to treat a feed solution containing an organic solvent. The molecular weight cutoff (MWCO) of the nanofiltration membrane is between 200 and 1000 Da. These organic solvent nanofiltration membranes can retain small molecules, while the solvent can permeate through the nanofiltration membrane to achieve effective molecular level separation. Organic solvent nanofiltration processes can be used for product purification, molecular separation, catalyst recovery and solvent recovery, opening up attractive opportunities for process intensification and organic waste management. In the pharmaceutical industry, organic solvent nanofiltration can be used between steps in drug synthesis or in downstream processing to reduce solvent waste, cost and energy consumption. Moreover, organic solvent nanofiltration has great application prospects in green and efficient organic solvent separation and purification.

[0003] However, since most polymers show obvious swelling or dissolution in strong solvents (such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO)), the application of polymer-based organic solvent nanofiltration membranes in strong solvents is severely limited. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene to overcome the above-mentioned shortcomings, using chemically resistant polytetrafluoroethylene (PTFE) as a supporting substrate, and hydrophilicizing the base membrane by polydopamine coating and plasma etching, and then obtaining a hollow fiber nanofiltration membrane that can withstand strong solvents through two interfacial polymerization techniques.

[0005] To this end, on the one hand, the present invention provides a method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, and the method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene comprises: Step S1, placing the hollow fiber membrane support layer in acetone for ultrasonic cleaning, and then placing it in ethanol for ultrasonic cleaning; Step S2, immersing the hollow fiber membrane support layer obtained in step S1 in a Tris-HCl buffer solution containing dopamine hydrochloride for shaking reaction to form a PDA coating on the surface of the hollow fiber membrane support layer; Step S3, using O 2 The surface of the PDA coating is etched by a plasma etching method to obtain a hollow fiber membrane base membrane; Step S4, soaking the hollow fiber membrane base membrane in an amine aqueous solution and an oil phase solution in sequence to perform an interfacial polymerization reaction; Step S5, soaking the hollow fiber membrane base obtained in step S4 in the amine aqueous solution and the oil phase solution with reduced concentrations in turn to perform a secondary interfacial polymerization reaction; Step S6, washing the hollow fiber membrane base membrane obtained in step S5 after the secondary interfacial polymerization reaction with ultrapure water, soaking it in ultrapure water at 60° C. for 5 to 10 minutes, and then soaking it in an aqueous solution containing glycerol for 1 to 2 minutes, and drying it to obtain the hollow fiber nanofiltration membrane; Wherein, the hollow fiber membrane support layer is a polytetrafluoroethylene hollow fiber membrane with an average pore size of 50nm to 200nm and a porosity greater than 70%.

[0006] As a preferred technical solution for the preparation method of a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in the step S4, the amine aqueous phase solution includes, by mass percentage concentration, 2wt% to 3wt% of m-phenylenediamine, 2wt% to 3wt% of polyethyleneimine, 1wt% to 4wt% of dimethyl sulfoxide, 2wt% of piperazine solution, 0.01wt% to 0.03wt% of sodium hydroxide, and the rest is water.

[0007] As a preferred technical solution of the preparation method of the hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in the step S4, the oil phase solution includes 0.1wt% to 0.2wt% of trimesoyl chloride, 0.06wt% to 0.08wt% of p-nitrobenzoyl chloride, and the rest is n-hexane in terms of mass percentage concentration.

[0008] As a preferred technical solution of the method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S5, the mass percentage concentrations of the amine aqueous solution and the oily solution are respectively 30% to 50% of that in S4.

[0009] As a preferred technical solution for the preparation method of hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S3, 2 The duration of etching the PDA coating surface by the plasma etching method is 5 minutes to 10 minutes.

[0010] As a preferred technical solution for the preparation method of hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S3, 2 The following steps are performed before the plasma etching method etches the PDA coating surface: Step S31, plasma etching the surface of the PDA coating using an inert gas for 0.5 min; Step S32, using O 2 The PDA coating surface was plasma etched for 0.5 min; Step S33, respectively detecting the mass change of the hollow fiber membrane support layer in step S31 and step S32, and taking the difference between the mass change of the hollow fiber membrane support layer in step S32 and the mass change of the hollow fiber membrane support layer in step S31 and the mass of the hollow fiber membrane before step S31 as the ratio of 2 Chemical contribution to plasma etching.

[0011] As a preferred technical solution for the preparation method of hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in the step S5, the mass percentage concentration of the amine aqueous phase solution and the oil phase solution is based on the O 2 Selection of chemical contribution for plasma etching; Wherein, the mass percentage concentration of the amine aqueous phase solution and the oil phase solution in step S5 is the same as that of the O 2 The chemical contribution of plasma etching is negatively correlated.

[0012] As a preferred technical solution of the method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S2, the concentration of dopamine hydrochloride is 2 mg / mL to 4 mg / mL, and the pH value of the Tris-HCl buffer is 8.5.

[0013] As a preferred technical solution of the method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S2, the reaction temperature of the oscillation reaction is 25° C., and the duration is 6 h to 12 h.

[0014] As a preferred technical solution for the preparation method of hollow fiber nanofiltration membrane based on polytetrafluoroethylene, in step S4 and step S5, the immersion time of the hollow fiber membrane base membrane in the amine aqueous solution is 1 min, and after draining the water droplets on the membrane surface, the immersion time in the oil phase solution is 0.5 min.

[0015] The beneficial effects of the present invention are: The preparation method of the hollow fiber nanofiltration membrane based on polytetrafluoroethylene of the present invention adopts a double polymerization reaction in the interfacial polymerization reaction process. After the first polymerization reaction, the polyamide film layer is prone to defects. After the second polymerization reaction, the defects of the surface separation layer of the first polymerization reaction can be compensated, so that the polyamide film layer has a better separation effect.

[0016] Furthermore, the effective ratio of m-phenylenediamine, polyethyleneimine, dimethyl sulfoxide in the aqueous phase and trimesoyl chloride and p-nitrobenzoyl chloride in the oil phase makes the surface contact angle of the prepared nanofiltration membrane smaller, thereby increasing the flux of the membrane. At the same time, it is more resistant to inorganic pollution, thereby reducing the flux attenuation problem of the membrane during operation.

[0017] Furthermore, the present invention can reduce the molecular weight cutoff of the prepared separation membrane to below 300 Da by adding small molecule piperazine monomers.

[0018] Furthermore, the present invention combines 2 The dynamic concentration adjustment of the chemical contribution of the plasma etching is used to achieve the matching of the reaction effects during the secondary polymerization reaction and the etching process, thereby avoiding reagent waste and ensuring the molding quality of the secondary polyamide layer.

[0019] Furthermore, the hollow fiber nanofiltration membrane obtained by the present invention uses PTFE as the base membrane, so compared with the traditional nanofiltration, its ability to resist organic solutions is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene in an embodiment of the present invention; Figure 2 A flow chart for determining chemical contribution in an embodiment of the present invention; Figure 3 A bar graph showing the contact angle test results in an embodiment of the present invention; Figure 4 A bar graph showing the permeability test results in an embodiment of the present invention; Figure 5 A bar graph showing the test results of the retention rate in the embodiment of the present invention; Figure 6 It is a bar graph of the retention rate decay test results in the embodiment of the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0023] like Figure 1 As shown, the present invention provides a method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, and the method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene comprises: Pretreatment of hollow fiber membrane support layer: Step S1, placing the hollow fiber membrane support layer in acetone for ultrasonic cleaning, and then placing it in ethanol for ultrasonic cleaning to remove surface impurities; Hydrophilic transformation: Step S2, immersing the hollow fiber membrane support layer obtained in step S1 in a Tris-HCl buffer solution containing dopamine hydrochloride for shaking reaction to form a PDA coating on the surface of the hollow fiber membrane support layer; Step S3, using O 2 The surface of the PDA coating was etched by plasma etching to obtain a hollow fiber membrane base membrane, generating a micro-nano rough structure and introducing oxygen-containing groups to improve the hydrophilicity of the PTFE base membrane. Desalting layer preparation: Step S4, soaking the hollow fiber membrane base film in the amine aqueous solution and the oil phase solution in sequence to perform interfacial polymerization reaction to form a primary polyamide layer; Step S5, soaking the hollow fiber membrane base membrane obtained after step S4 in the amine aqueous solution and the oil phase solution with reduced concentrations in turn to perform a secondary interfacial polymerization reaction to construct a dense secondary polyamide layer with fewer defects; Post-processing: Step S6, washing the hollow fiber membrane base membrane obtained in step S5 after the secondary interfacial polymerization reaction with ultrapure water, soaking it in ultrapure water at 60° C. for 5 to 10 minutes, and then soaking it in an aqueous solution containing glycerol for 1 to 2 minutes, and drying it to obtain a hollow fiber nanofiltration membrane; The hollow fiber membrane support layer is a polytetrafluoroethylene (PTFE) hollow fiber membrane with an average pore size of 50nm to 200nm and a porosity greater than 70%.

[0024] In the above embodiment, due to the use of PTFE as the base membrane, the ability to resist organic solutions is significantly improved compared with the traditional nanofiltration. A double polymerization reaction is used in the interfacial polymerization process. After the first polymerization reaction, the polyamide film layer is prone to defects. After the second polymerization reaction, the defects of the surface separation layer of the first polymerization reaction can be compensated, so that the polyamide film layer has a better separation effect.

[0025] Specifically, in step S4, the amine aqueous phase solution includes 2wt% to 3wt% of m-phenylenediamine, 2wt% to 3wt% of polyethyleneimine, 1wt% to 4wt% of dimethyl sulfoxide, 2wt% of piperazine solution, 0.01wt% to 0.03wt% of sodium hydroxide, and the rest is water. The oil phase solution includes 0.1wt% to 0.2wt% of trimesoyl chloride, 0.06wt% to 0.08wt% of p-nitrobenzoyl chloride, and the rest is n-hexane. The effective proportion of m-phenylenediamine, polyethyleneimine, dimethyl sulfoxide in the aqueous phase and trimesoyl chloride and p-nitrobenzoyl chloride in the oil phase in the above scheme makes the surface contact angle of the prepared nanofiltration membrane smaller, thereby making the flux of the membrane larger, and at the same time, it is more resistant to inorganic pollution, thereby reducing the flux attenuation problem of the membrane during operation. By adding small molecule piperazine monomers, the molecular weight cutoff of the prepared separation membrane can be reduced to below 300Da.

[0026] Specifically, in step S5, the mass percentage concentrations of the amine aqueous solution and the oily solution are both 30% to 50% of that in S4.

[0027] Specifically, in step S3, when using 2 The duration of etching the PDA coating surface by the plasma etching method is 5 minutes to 10 minutes.

[0028] Specifically, in step S2, the concentration of dopamine hydrochloride is 2 mg / mL to 4 mg / mL, and the pH value of the Tris-HCl buffer is 8.5.

[0029] Specifically, in step S2, the reaction temperature of the shaking reaction is 25°C and the duration is 6h to 12h.

[0030] Specifically, in step S4 and step S5, the hollow fiber membrane-based membrane is immersed in the amine aqueous solution for 1 min, and after the water droplets on the membrane surface are drained, the immersion time in the oil phase solution is 0.5 min.

[0031] like Figure 2 As shown, in step S3, using O 2 The following steps are performed before the plasma etching method etches the PDA coating surface: Step S31, plasma etching the surface of the PDA coating using an inert gas for 0.5 min; Step S32, using O 2 The PDA coating surface was plasma etched for 0.5 min; Step S33, respectively detecting the mass change of the hollow fiber membrane support layer in step S31 and step S32, and taking the difference between the mass change of the hollow fiber membrane support layer in step S32 and the mass change of the hollow fiber membrane support layer in step S31 and the mass of the hollow fiber membrane before step S31 as the ratio of 2 Chemical contribution to plasma etching.

[0032] Specifically, in step S5, the mass percentage concentrations of the amine aqueous phase solution and the oil phase solution are based on 2 Selection of chemical contribution for plasma etching; The mass percentage concentration of the amine aqueous solution and the oil phase solution in step S5 is 2 The chemical contribution of plasma etching is negatively correlated.

[0033] In detail, O 2 The plasma etching process is as follows: turn on the power, increase the power of the plasma etcher to the set value (80W in this embodiment), set the processing time, and the active components (O + Free radicals, O - Free radicals) react with the surface of the PDA coating, including: (1) physical sputtering: high-energy ions impact the surface to remove weakly bound impurities; (2) chemical etching: oxygen free radicals react with the CF bonds in PTFE to generate CO, CO 2 Volatile products such as chlorinated hydrocarbons are produced and oxygen-containing groups (-COOH, -OH) are introduced.

[0034] The purpose of determining the chemical contribution is to exclude physical factors and evaluate the 2 The effect of plasma etching on PDA coating at the chemical etching level; in implementation, the theoretical range of chemical contribution can be determined through limited experiments, and the mapping relationship between chemical contribution and 30% to 50% concentration range can be established under the premise of satisfying negative correlation, and selection can be made based on the mapping relationship in implementation. 2 The dynamic concentration adjustment of the chemical contribution of the plasma etching is used to achieve the matching of the reaction effects during the secondary polymerization reaction and the etching process, thereby avoiding reagent waste and ensuring the molding quality of the secondary polyamide layer.

[0035] Example 1: (1) Pretreatment of PTFE hollow fiber membrane support layer: Take a PTFE hollow fiber membrane (average pore size 100 nm, porosity > 70%) and ultrasonically clean it with acetone and ethanol for 30 min in sequence; (2) Hydrophilic modification: The hollow fiber membrane obtained in step (1) was hydrophilic modified by immersing the PTFE membrane in Tris-HCl buffer (pH = 8.5) containing dopamine hydrochloride (2 mg / mL) and shaking at 25°C for 6 h to form a uniform PDA layer; 2 Plasma (power 80W, treatment time 5min) etches the surface of the PDA coating to generate micro-nano rough structures and introduce oxygen-containing groups; (3) Preparation of an amine aqueous solution: Add 2 wt% of m-phenylenediamine, 2 wt% of polyethyleneimine, 1 wt% of dimethyl sulfoxide, 2 wt% of piperazine solution, and 0.01 wt% of sodium hydroxide into ultrapure water, and stir to completely dissolve to obtain an amine aqueous solution.

[0036] (4) Preparation of oil phase solution: Dissolve 0.1 wt% of trimesoyl chloride and 0.06 wt% of p-nitrobenzoyl chloride in n-hexane and stir to obtain an oil phase solution.

[0037] (5) Preparation of desalination layer: The hollow fiber-based membrane prepared in step (2) is immersed in an amine aqueous solution for 1 min, and then the water droplets on the membrane surface are drained; and then it is immersed in an oil phase solution for 0.5 min to carry out interfacial reaction.

[0038] (6) performing a secondary interfacial reaction, but reducing the monomer concentration to 50% of the first addition amount, to construct a secondary polyamide layer; (7) Post-treatment: The nanofiltration membrane prepared in step (4) is taken out and washed with ultrapure water, then immersed in hot water at a temperature of 60°C for heat treatment for 5 min, washed with pure water and then immersed in an aqueous solution containing glycerol for 1 min, and then dried to obtain a nanofiltration membrane that can withstand high concentrations of organic solvents.

[0039] Embodiment 2: (1) Take a PTFE hollow fiber membrane (average pore size 100 nm, porosity > 70%) and ultrasonically clean it with acetone and ethanol for 30 min in sequence; (2) The hollow fiber membrane obtained in step (1) was hydrophilized by immersing the PTFE membrane in Tris-HCl buffer (pH = 8.5) containing dopamine hydrochloride (3 mg / mL) and shaking at 25°C for 8 h; 2 Plasma (power 80W, treatment time 8min) etches the surface of the PDA coating to generate micro-nano rough structures and introduce oxygen-containing groups; (3) Add 2 wt% of m-phenylenediamine, 2 wt% of polyethyleneimine, 1 wt% of dimethyl sulfoxide, 2 wt% of piperazine solution, and 0.01 wt% of sodium hydroxide into ultrapure water, and stir to completely dissolve to obtain an amine aqueous solution.

[0040] (4) Dissolve 0.1 wt% of trimesoyl chloride and 0.06 wt% of p-nitrobenzoyl chloride in n-hexane and stir to obtain an oil phase solution.

[0041] (5) The hollow fiber-based membrane prepared in step (2) is immersed in an amine aqueous solution for 1 min, and then the water droplets on the membrane surface are drained; and then it is immersed in an oil phase solution for 0.5 min to carry out interfacial reaction.

[0042] (6) performing a secondary interfacial reaction, but reducing the monomer concentration to 50% of the first addition amount, to construct a secondary polyamide layer; (7) Post-treatment: The nanofiltration membrane prepared in step (4) was taken out and washed with ultrapure water, then immersed in hot water at a temperature of 60°C for heat treatment for 5 min, washed with pure water, immersed in a glycerol-containing aqueous solution for 1 min, and then dried.

[0043] Embodiment 3: (1) Take a PTFE hollow fiber membrane (average pore size 100 nm, porosity > 70%) and ultrasonically clean it with acetone and ethanol for 30 min in sequence; (2) The hollow fiber membrane obtained in step (1) was hydrophilized by immersing the PTFE membrane in Tris-HCl buffer (pH = 8.5) containing dopamine hydrochloride (4 mg / mL) and shaking at 25°C for 12 h to form a uniform PDA layer; 2 Plasma (power 80W, treatment time 10min) etches the surface of the PDA coating to generate micro-nano rough structures and introduce oxygen-containing groups; (3) Add 2 wt% of m-phenylenediamine, 2 wt% of polyethyleneimine, 1 wt% of dimethyl sulfoxide, 2 wt% of piperazine solution, and 0.01 wt% of sodium hydroxide into ultrapure water, and stir to completely dissolve to obtain an amine aqueous solution.

[0044] (4) Dissolve 0.1 wt% of trimesoyl chloride and 0.06 wt% of p-nitrobenzoyl chloride in n-hexane and stir to obtain an oil phase solution.

[0045] (5) The hollow fiber-based membrane prepared in step (2) is immersed in an amine aqueous solution for 1 min, and then the water droplets on the membrane surface are drained; and then it is immersed in an oil phase solution for 0.5 min to carry out interfacial reaction.

[0046] (6) performing a secondary interfacial reaction, but reducing the monomer concentration to 50% of the first addition amount, to construct a secondary polyamide layer; (7) Post-treatment: The nanofiltration membrane prepared in step (4) was taken out and washed with ultrapure water, then immersed in hot water at a temperature of 60°C for heat treatment for 5 min, washed with pure water, immersed in a glycerol-containing aqueous solution for 1 min, and then dried.

[0047] Embodiment 4: (1) Take a PTFE hollow fiber membrane (average pore size 100 nm, porosity > 70%) and ultrasonically clean it with acetone and ethanol for 30 min in sequence; (2) The hollow fiber membrane obtained in step (1) was hydrophilized by immersing the PTFE membrane in Tris-HCl buffer (pH = 8.5) containing dopamine hydrochloride (4 mg / mL) and shaking at 25°C for 12 h to form a uniform PDA layer; 2 Plasma (power 80W, treatment time 10min) etches the surface of the PDA coating to generate micro-nano rough structures and introduce oxygen-containing groups; (3) Add 3 wt% of m-phenylenediamine, 3 wt% of polyethyleneimine, 4 wt% of dimethyl sulfoxide, 2 wt% of piperazine solution, and 0.03 wt% of sodium hydroxide into ultrapure water, and stir to completely dissolve to obtain an amine aqueous solution.

[0048] (4) Preparation of an oil phase solution: Dissolve 0.2 wt % of trimesoyl chloride and 0.08 wt % of p-nitrobenzoyl chloride in n-hexane and stir to obtain an oil phase solution.

[0049] (5) The hollow fiber-based membrane prepared in step (2) is immersed in an amine aqueous solution for 1 min, and then the water droplets on the membrane surface are drained; and then it is immersed in an oil phase solution for 0.5 min to carry out interfacial reaction.

[0050] (6) performing a secondary interfacial reaction, but reducing the monomer concentration to 50% of the first addition amount, to construct a secondary polyamide layer; (7) Post-treatment: The nanofiltration membrane prepared in step (4) is taken out and washed with ultrapure water, then immersed in hot water at a temperature of 60°C for heat treatment for 5 min, washed with pure water and then immersed in an aqueous solution containing glycerol for 1 min, and then dried to obtain a nanofiltration membrane that can withstand high concentrations of organic solvents.

[0051] For Examples 1-3 in the above embodiments, the changes in their contact angles were measured. The test results are as follows Figure 3 As shown in the figure, after modification, the contact angle of the PTFE-based membrane is significantly reduced, and the modified membrane has good hydrophilicity.

[0052] For Example 4 in the above examples, the permeability of methanol, acetonitrile and dimethylformamide was measured, and at the same time, the retention rate of Congo red (MW = 697Da) was measured. The specific results are as follows Figure 4 and Figure 5 As shown in Figure 2, the synthesized nanofiltration membrane has high methanol, acetonitrile and dimethylformamide permeabilities of 15, 8.2 and 4.1 (in Lm -2 h -1 bar -1 ), and the retention rates of Congo red (MW=697Da) were 95%, 93%, and 92%, respectively, all exceeding 90%.

[0053] Furthermore, the hollow fiber nanofiltration membrane prepared in Example 4 was immersed in a DMF organic solution, and the retention rate of the nanofiltration membrane to Congo red was measured once a day to observe the attenuation of the retention rate. Figure 6 As shown (the horizontal axis is time, the vertical axis is retention rate), after the nanofiltration membrane was immersed in DMF organic solution for 7 days, its retention rate of Congo red decreased from 92% to 85%, and the attenuation rate was 7.6%, which shows that it has a strong resistance to organic solvents.

[0054] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene, characterized in that: include: Step S1, placing the hollow fiber membrane support layer in acetone for ultrasonic cleaning, and then placing it in ethanol for ultrasonic cleaning; Step S2, immersing the hollow fiber membrane support layer obtained in step S1 in a Tris-HCl buffer solution containing dopamine hydrochloride for shaking reaction to form a PDA coating on the surface of the hollow fiber membrane support layer; Step S3, etching the surface of the PDA coating using an O2 plasma etching method to obtain a hollow fiber membrane base membrane; Step S4, soaking the hollow fiber membrane base membrane in an amine aqueous solution and an oil phase solution in sequence to perform an interfacial polymerization reaction; Step S5, soaking the hollow fiber membrane base obtained in step S4 in the amine aqueous solution and the oil phase solution with reduced concentrations in turn to perform a secondary interfacial polymerization reaction; Step S6, washing the hollow fiber membrane base membrane obtained in step S5 after the secondary interfacial polymerization reaction with ultrapure water, soaking it in ultrapure water at 60° C. for 5 to 10 minutes, and then soaking it in an aqueous solution containing glycerol for 1 to 2 minutes, and drying it to obtain the hollow fiber nanofiltration membrane; Wherein, the hollow fiber membrane support layer is a polytetrafluoroethylene hollow fiber membrane with an average pore size of 50nm to 200nm and a porosity greater than 70%.

2. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 1, characterized in that: In step S4, the amine aqueous phase solution includes, by mass percentage, 2wt% to 3wt% of m-phenylenediamine, 2wt% to 3wt% of polyethyleneimine, 1wt% to 4wt% of dimethyl sulfoxide, 2wt% of piperazine solution, 0.01wt% to 0.03wt% of sodium hydroxide, and the rest is water.

3. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 2, characterized in that: In the step S4, the oil phase solution includes, by mass percentage, 0.1 wt% to 0.2 wt% of trimesoyl chloride, 0.06 wt% to 0.08 wt% of p-nitrobenzoyl chloride, and the remainder is n-hexane.

4. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 3, characterized in that: In step S5, the mass percentage concentrations of the amine aqueous solution and the oily solution are both 30% to 50% of that in step S4.

5. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 3, characterized in that: In the step S3, the duration of etching the surface of the PDA coating using the O2 plasma etching method is 5 minutes to 10 minutes.

6. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 5, characterized in that: In step S3, the following steps are performed before etching the surface of the PDA coating using an O2 plasma etching method: Step S31, plasma etching the surface of the PDA coating using an inert gas for 0.5 min; Step S32, plasma etching the surface of the PDA coating using O2 for 0.5 min; In step S33, the mass change of the hollow fiber membrane support layer in step S31 and step S32 is detected respectively, and the difference between the mass change of the hollow fiber membrane support layer in step S32 and the mass change of the hollow fiber membrane support layer in step S31 and the ratio of the mass of the hollow fiber membrane before step S31 are used as the chemical contribution of O2 plasma etching.

7. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 6, characterized in that: In the step S5, the mass percentage concentrations of the amine aqueous solution and the oily solution are selected based on the chemical contribution of the O2 plasma etching; The mass percentage concentration of the amine aqueous solution and the oil phase solution in step S5 is negatively correlated with the chemical contribution of the O2 plasma etching.

8. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 1, characterized in that: In step S2, the concentration of dopamine hydrochloride is 2 mg / mL to 4 mg / mL, and the pH value of the Tris-HCl buffer is 8.

5.

9. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 8, characterized in that: In step S2, the reaction temperature of the shaking reaction is 25° C. and the duration is 6 h to 12 h.

10. The method for preparing a hollow fiber nanofiltration membrane based on polytetrafluoroethylene according to claim 1, characterized in that: In step S4 and step S5, the hollow fiber membrane-based membrane is immersed in the amine aqueous solution for 1 minute, and after the water droplets on the membrane surface are drained, the immersion time in the oil phase solution is 0.5 minutes.

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