A ptfeg-based composite membrane material with directional pores and a preparation method thereof

Abstract

This invention provides a PTFE-based composite membrane with oriented channels and its preparation method. It employs an inverted process route: high-temperature matrix shaping precedes low-temperature growth of functional materials. First, the PTFE membrane undergoes high-temperature sintering and rapid quenching to ensure the mechanical strength and pore structure stability of the PTFE matrix. Then, ZIF-8 is grown in situ in a mild methanol system, ensuring that ZIF-8 is never exposed to temperatures above 250°C, thus eliminating the risk of thermal decomposition and framework collapse. Simultaneously, pre-dispersed nano-ZnO is used as the zinc source, reacting with 2-methylimidazole in step 2. The conversion rate of ZnO to ZIF-8 is close to 100%. The resulting ZIF-8 exhibits high crystallinity, a complete structure, and a stable specific surface area of ​​1500 m². 2 / g or more, fully retaining its inherent advantage of high specific surface area.

Description

Technical Field

[0001] This invention relates to the field of water treatment separation materials technology, and in particular to a PTFE-based composite membrane material with directional channels and its preparation method. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is widely used in water treatment, gas separation, and biomedicine due to its excellent chemical stability, thermal stability, and low surface energy. Currently, the mainstream industrial process for large-scale preparation of PTFE microporous membranes is the mechanical stretching method. The main steps involve blending PTFE dispersion resin with a lubricant, extruding the paste, calendering it into sheets, biaxially stretching it, and high-temperature sintering to obtain a PTFE porous membrane with a "fiber-node" structure. To improve the removal capacity of PTFE membranes for heavy metals, antibiotics, and other micropollutants in water, functional modification is often achieved by introducing zeolite imidazole ester framework material-8 (ZIF-8), which has a high specific surface area and a regular pore structure.

[0003] Conventional modification schemes are mainly divided into two categories: The first step is to blend ZIF-8 with PTFE resin, and then prepare a composite film by extrusion, stretching, and high-temperature sintering above the melting point (usually above 330°C). Secondly, the entire process of stretching and sintering the PTFE membrane is completed first, and then ZIF-8 is loaded onto the surface of the finished membrane through a post-impregnation method.

[0004] In addition, some studies have used polyethylene oxide (PEO) as a sacrificial template to be introduced into PTFE processing to assist in pore formation. However, existing solutions are mostly based on intermittent processes such as electrospinning, and PEO is usually removed by high-temperature sintering.

[0005] Therefore, developing a preparation method that can simultaneously achieve the mechanical properties of PTFE microporous membranes, introduce and functionalize ZIF-8, and coordinate the thermal compatibility between various processes has significant technical value and promising industrial application prospects. Summary of the Invention

[0006] The purpose of this invention is to provide a PTFE-based composite membrane material with directional channels and its preparation method. The process route of matrix pre-shaping, low-temperature functionalization and precise modification not only solves the main contradiction of thermal compatibility between PTFE and ZIF-8, but also improves the adsorption capacity of heavy metal ions and antibiotics in water.

[0007] To achieve the above objectives, this technical solution provides a method for preparing a PTFE-based composite membrane with oriented channels, comprising the following steps: S1: Mixed granulation: Mixed masterbatch is obtained by mixing polytetrafluoroethylene dispersion resin, polyethylene oxide and nano zinc oxide, wherein the amount of polyethylene oxide added is 15%~25% of the mass of polytetrafluoroethylene dispersion resin, and the amount of nano zinc oxide added is 8%~15% of the mass of polytetrafluoroethylene dispersion resin; S2: Paste extrusion: The mixed masterbatch is extruded through a paste extruder at a temperature lower than the melting point of the polytetrafluoroethylene dispersion resin to obtain the extrudate; S3: Calendering into sheets: The extrudate is placed in a calender and pressed into sheets to obtain thin sheets; S4: Low-temperature bidirectional porosity stretching: a thin film is bidirectionally stretched at a temperature below 150°C to obtain a stretched film with a predetermined porosity structure. S5: High-temperature sintering and shaping: The stretched film with a predetermined oriented hole structure is sintered at high temperature. After sintering, it is quenched and cooled to room temperature at a cooling rate of more than 10℃ / s to obtain a PTFE / PEO / ZnO composite base film. S6: Methanol integrated treatment: The PTFE / PEO / ZnO composite membrane is placed in a methanol solution containing 2-methylimidazole for reaction. After the reaction is completed, it is washed and dried to obtain a PTFE / ZIF-8 composite porous membrane. S7: 5-Aminotetrazole modification: The PTFE / ZIF-8 composite porous membrane was placed in a methanol-water-alcohol ternary solvent system containing 5-aminotetrazole and reacted. After the reaction was completed, it was washed and dried to obtain a PTFE-based composite membrane with oriented channels.

[0008] The main process of this method for preparing PTFE-based composite membranes with oriented channels is as follows: First, a stretched membrane with a predetermined oriented pore structure is prepared by low-temperature stretching. Then, high-temperature sintering is performed to enhance the mechanical properties of the PTFE matrix in the stretched membrane with the predetermined oriented pore structure and to form a stable microporous structure. Next, PEO is removed by methanol integrated treatment and ZIF-8 is grown in situ. Finally, 5-AT is selected for post-synthetic ligand exchange modification to achieve precise delivery of 5-AT from the solution to the framework coordination sites. The effective window pore size and cage size of the ZIF-8 framework on the PTFE surface are further controlled to obtain a PTFE-based composite membrane with oriented channels.

[0009] In step S1 of the mixed granulation process: In some embodiments, the nano-zinc oxide has a particle size of 20~100nm, which can ensure that it is uniformly dispersed in the PTFE matrix and rapidly and completely converted into crystalline ZIF-8 in the methanol system, while not clogging the directional channels and ensuring the mechanical stability of the membrane, thus providing sufficient and stable active sites for the efficient adsorption and removal of heavy metals and antibiotics.

[0010] In some embodiments, the number average molecular weight of the polytetrafluoroethylene dispersion resin is ≥5×10⁻⁶.6 The standard specific gravity is 2.14~2.16 g / cm³. 3 This ensures that the membrane possesses excellent mechanical strength, stable oriented pore structure, and high chemical corrosion resistance under high stretching and high-temperature sintering.

[0011] In some embodiments, the molecular weight of polyethylene oxide is 3 × 10⁻⁶. 5 Up to 4×10 6 It can achieve good extrusion effect and efficient sacrificial pore formation, so that the membrane material's formability, pore structure uniformity and functional compatibility are optimized.

[0012] In step S2, where the paste is extruded: This scheme controls the mixing masterbatch to be extruded as a paste at a temperature lower than the melting point of the polytetrafluoroethylene dispersion resin. The advantage of this design is that it can keep the mixing masterbatch in a suitable paste state of fluidity, ensure that the extruded green body is dense, uniform and dimensionally stable, and at the same time avoid thermal decomposition or agglomeration of PEO and nano ZnO, providing structural protection for subsequent low-temperature stretching, high-temperature sintering and in-situ growth of ZIF-8.

[0013] In some embodiments, the extrusion temperature is 35~55℃ and the extrusion pressure is 5~20MPa.

[0014] In step S3 of calendering: Pressing the extrudate into a uniformly thick sheet using a calender ensures uniform stress and regular pore structure during subsequent biaxial stretching, resulting in stable and consistent overall membrane performance. It also provides a uniform reaction carrier for in-situ growth of ZIF-8 and modification of 5-AT, thereby improving the yield of industrial production.

[0015] In some embodiments, the thickness of the sheet is 0.1~2 mm.

[0016] In some embodiments, the calendering temperature of the calender is controlled at 20~60°C.

[0017] In step S4 of low-temperature bidirectional porosimetry stretching: This method involves biaxially stretching thin sheets at temperatures below 150°C to obtain stretched films with predetermined directional pore structures. The aim is to construct a regular and interconnected directional pore structure while protecting polyethylene oxide and nano-zinc oxide from thermal damage, thus laying a structural foundation for subsequent high-temperature sintering, in-situ growth of ZIF-8, and efficient adsorption and separation.

[0018] In some embodiments, the sheet is first stretched longitudinally at a temperature below 150°C and then stretched laterally. The first stretching is high in the longitudinal direction to allow the PTFE molecular chains, PEO template, and ZnO particles to be uniformly arranged along the flow direction, forming a straight longitudinal fiber skeleton, which provides the main direction for subsequent pore orientation. Finally, the lateral stretching gently opens the gaps between the oriented longitudinal fibers to form oriented nanopores that are arranged along the stretching direction and penetrate the film thickness.

[0019] In some embodiments, the stretching temperature is 140~150°C.

[0020] In some embodiments, the longitudinal stretching ratio is 10 to 50 times, the transverse stretching ratio is 10 to 30 times, and the total stretching ratio is 36 to 48 times.

[0021] In step S5, which involves high-temperature sintering and shaping: In some embodiments, the stretched membrane with a predetermined oriented hole structure is sintered at a high temperature, wherein the sintering temperature is 350~380°C. The high temperature allows the PTFE molecular chains to melt and bond together, forming a stable and strong fiber-node skeleton structure, making the membrane less prone to damage, resistant to high pressure and erosion during use. Furthermore, sintering permanently shapes the predetermined oriented hole structure formed by low-temperature stretching, ensuring that the final pores are aligned along the stretching direction, are uniformly connected, and have stable pore size.

[0022] Furthermore, the sintering time is 1 to 10 minutes, and the sintering atmosphere is air or an inert atmosphere.

[0023] In some embodiments, after sintering, the material is quenched and cooled to room temperature at a cooling rate greater than 10°C / s. This instantly freezes the crystal structure and pore structure of PTFE, preventing pore shrinkage, decreased porosity, and reduced flux caused by slow cooling, thus obtaining a PTFE / PEO / ZnO composite base film. In some embodiments, the sintered stretched film is directly immersed in a quenching cooling medium to quench and cool the stretched film to room temperature at a cooling rate of ≥10℃ / s.

[0024] In some embodiments, the quenching cooling medium is a mixture of water at 10~25°C and ice water at 0°C.

[0025] Specifically, the sintered stretched film is first immersed in water at 10~25℃ and then immersed in a mixture of ice and water at 0℃ to cool it.

[0026] In step S6 of the integrated methanol treatment: The PTFE / PEO / ZnO composite membrane was placed in a methanol solution containing 2-methylimidazole and reacted at 30~60℃ for 4~24 hours. After the reaction, it was washed 2~5 times with fresh methanol and dried under vacuum to obtain the PTFE / ZIF-8 composite porous membrane.

[0027] It should be noted that the integrated methanol treatment can simultaneously achieve the dissolution and removal of PEO and the in-situ conversion of ZnO to ZIF-8 under mild conditions of 30~60℃. While clearing the directional channels, ZIF-8 crystals with complete crystallization and strong bonding are grown in situ on the pore walls. This not only solves the problem of thermal incompatibility between PTFE and ZIF-8, but also provides sufficient active sites for subsequent 5-AT modification and efficient adsorption of heavy metals and antibiotics.

[0028] In some embodiments, the concentration of 2-methylimidazole is 0.1~0.3 mol / L.

[0029] In some embodiments, the molar amount of 2-methylimidazole is 1 to 5 times the molar amount of ZnO in the PTFE / PEO / ZnO composite base film.

[0030] In some embodiments, the drying temperature is 40~80℃ and the drying time is 6~24 hours.

[0031] In step S7 regarding the modification of 5-aminotetrazole: In some embodiments, the volume ratio of methanol, water and amine in the methanol-water-alkanolamine ternary solvent system is (40~80%):(15~55%):(4~6%).

[0032] In some embodiments, the alcoholamine is one of ethanolamine, diethanolamine, or 2-methylaminoethanol.

[0033] In some embodiments, the concentration of 5-aminotetrazole is 0.05~0.1 mol / L.

[0034] In some embodiments, the PTFE / ZIF-8 composite porous membrane is placed in a methanol-water-alcohol ternary solvent system containing 5-aminotetrazole and reacted at room temperature to 60°C for 10 to 24 hours. After the reaction is completed, the membrane is washed and dried to obtain a PTFE-based composite membrane with oriented channels.

[0035] Secondly, this solution provides a PTFE-based composite membrane with oriented channels, which is prepared according to the above-mentioned method for preparing PTFE-based composite membrane with oriented channels. The PTFE-based composite membrane has oriented nanopores arranged along the stretching direction, wherein the pore size of the nanopores is 5-25 nm, the inner wall of the pores is loaded with ZIF-8 crystals, and the effective window pore size of ZIF-8 after 5-AT modification is 3.4-5.5 Å.

[0036] In some embodiments, the specific surface area of ​​the ZIF-8 crystals in the oriented PTFE-based composite membrane is maintained at 1500 m². 2 / g or more.

[0037] In some embodiments, the PTFE-based composite membrane with oriented channels is effective against heavy metal ions (Pb). 2+ Cd 2+ Cu 2+ Cr 6+ The adsorption capacity of ) and antibiotics (tetracycline, etc.) is increased by more than 10 times compared with the unmodified form.

[0038] Compared with existing technologies, this technical solution has the following characteristics and beneficial effects: 1. Resolving the major contradiction between high-temperature sintering of PTFE and thermal incompatibility with ZIF-8, ensuring the integrity of the ZIF-8 crystal structure: This application adopts an inverted process route, prioritizing high-temperature matrix shaping followed by low-temperature growth of functional materials. First, high-temperature sintering and rapid quenching at ≥10℃ / s of the PTFE film are completed, fully ensuring the mechanical strength and pore structure stability of the PTFE matrix. Then, ZIF-8 is grown in situ in a mild methanol system at 30-60℃, ensuring that ZIF-8 never comes into contact with temperatures above 250℃, thus eliminating the risk of thermal decomposition and framework collapse at its source. Simultaneously, using pre-dispersed nano-ZnO as the zinc source, combined with 2-methylimidazole in the reaction steps, the conversion rate of ZnO to ZIF-8 is close to 100%. The resulting ZIF-8 has high crystallinity, a complete structure, and a specific surface area consistently maintained above 1500 m² / g, fully retaining its inherent advantage of high specific surface area.

[0039] 2. The synergistic effect of low-temperature stretching and PEO sacrificial template forms highly oriented nanopores, significantly improving filtration accuracy and adsorption efficiency: This application utilizes a low-temperature biaxial stretching process, combined with a step-by-step stretching method of first longitudinal stretching and then transverse stretching, to highly oriented PTFE molecular chains along the stretching direction, forming a continuous "fiber-node" framework, while avoiding thermal damage to PEO and nano-ZnO. Using PEO as a sacrificial template, it forms a continuous polymer phase synchronously with the PTFE molecular chains during stretching. After subsequent methanol dissolution and removal, the space occupied by PEO is directly transformed into interconnected nanopores arranged along the stretching direction. Combined with a rapid quenching and cooling step, the crystallization and pore structure of PTFE are instantly frozen, preventing pore shrinkage and collapse. Ultimately, the membrane pore size is precisely controlled within the 5-25nm range, with a narrow pore size distribution and straight, interconnected pores, ensuring high-purity water throughput while significantly improving the retention accuracy and adsorption contact area for micro-pollutants.

[0040] 3. Integrated methanol treatment process achieves synergistic effect between PEO removal and in-situ ZIF-8 growth, avoiding additional high-temperature steps: This application uses a methanol solution containing 2-methylimidazole as a single reaction system. Leveraging methanol's properties as both a good solvent for PEO and a reaction medium for in-situ ZIF-8 growth, two main processes are completed simultaneously: first, methanol fully dissolves and washes away PEO within the membrane, clearing the oriented pores; second, the 2-methylimidazole in the solution undergoes a coordination reaction with the pre-dispersed nano-ZnO within the membrane, generating ZIF-8 crystals in situ. This process completely eliminates the high-temperature sintering removal step required by the traditional PEO sacrificial template method, avoiding damage to functional materials from additional high temperatures. Simultaneously, the in-situ grown ZIF-8 crystals are directly anchored to the inner wall of the pores, tightly bonded to the PTFE matrix, solving the problems of uneven ZIF-8 loading, easy detachment, and easy pore blockage in the traditional post-impregnation method.

[0041] 4.5-AT ternary solvent system modification achieves precise pore size control and active site enrichment, resulting in improved adsorption capacity compared to unmodified systems: A methanol-water-alkanolamine ternary solvent system was constructed, in which methanol activates the ZIF-8 pores, promoting ligand diffusion into the cage cavity; water regulates the ligand exchange reaction kinetics, preventing excessively rapid reactions that could lead to framework collapse; the alkanolamine solvent precisely anchors the 5-AT ligand through hydrogen bonding, achieving efficient delivery from solution to the coordination sites in the ZIF-8 framework. 5-AT is then synthesized to replace part of the 2-methylimidazole on the ZIF-8 surface through ligand exchange, precisely controlling the effective window pore size to 3.4-5.5 Å without disrupting the ZIF-8 framework structure, highly matching the molecular size of heavy metal ions and antibiotics such as tetracycline. Simultaneously, the multiple N-atom coordination sites in the 5-AT molecule can form stable chelates with heavy metal ions, enhancing the adsorption capacity for antibiotics through hydrogen bonding and π-π stacking interactions, ultimately improving the membrane material's adsorption capacity for Pb. 2+ Cd 2+ Cu 2+ Cr 6+ The adsorption capacity of heavy metal ions and antibiotics such as tetracycline is more than 10 times higher than that of the unmodified membrane. Attached Figure Description

[0042] Figure 1 This is a morphological image of the sample from Example 1.

[0043] Figure 2 This is a morphological image of the sample from Example 2.

[0044] Figure 3 This is a morphological image of the sample from Example 3.

[0045] Figure 4 This is a morphology diagram of sample 1 (Comparative Example 1).

[0046] Figure 5This is a morphology diagram of sample 2 in Comparative Example 2.

[0047] Figure 6 This is a morphology image of sample 3 in Comparative Example.

[0048] Figure 7 This is a morphology image of sample 4 in Comparative Example.

[0049] Figure 8 These are adsorption capacity diagrams of the samples from Examples 1-3 and Comparative Examples 1-4.

[0050] Figure 9 These are the XRD patterns of the samples from Example 1 and Comparative Example 1.

[0051] Figure 10 It is an adsorption kinetic curve. Detailed Implementation

[0052] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0053] Example: Example 1: (a) Mixing and granulation: Take PTFE dispersion resin (molecular weight 6×10) 6 100g of PEO (standard specific gravity 2.15) and PEO (molecular weight 1×10⁻⁶) 6 20g of nano ZnO (50nm particle size) and 12g of nano ZnO were mixed evenly at high speed.

[0054] (b) Paste extrusion: Extruded into rods at 45°C and 10 MPa.

[0055] (c) Calendering: Calendering at 40°C into a sheet with a thickness of 0.5 mm.

[0056] (d) Low temperature stretching: first stretch longitudinally by 30 times at 145℃, then stretch transversely by 20 times.

[0057] (e) Sintering: Sinter at 360°C for 5 minutes, then quench in water at 25°C.

[0058] (f) Integrated methanol treatment: Prepare a 0.2 mol / L 2-methylimidazolium methanol solution. The molar amount of ZnO is approximately 0.147 mol (12 g ZnO). The molar amount of 2-methylimidazolium is twice that of ZnO (0.294 mol / L, volume adjusted according to membrane size). Immerse the membrane at 50°C for 12 hours, wash three times with methanol, and vacuum dry at 60°C for 12 hours.

[0059] (g) 5-AT modification: Prepare a mixed solvent of methanol:water:ethanolamine = 70:25:5 (volume ratio), add 5-AT to a concentration of 0.08 mol / L, react at 40°C for 16 hours, wash with methanol, and dry at 60°C to obtain the sample of Example 1.

[0060] Performance: Pure water flux 450L / (m²) 2 ·h·bar); for Pb 2+ The adsorption capacity was 285 mg / g (28 mg / g for the unmodified control); the adsorption capacity for tetracycline was 210 mg / g (20 mg / g for the control); XRD showed that the ZIF-8 characteristic peak was consistent with the simulation.

[0061] Example 2 (a) Mixed granulation: 100g of PTFE, 15g of PEO, and 8g of nano ZnO (particle size 20nm).

[0062] (b) Paste extrusion: 35℃, 5MPa.

[0063] (c) Calendering into sheets: 20℃, thickness 0.2mm.

[0064] (d) Low temperature stretching: 140℃, 10 times in the longitudinal direction and 10 times in the transverse direction.

[0065] (e) Sintering: 330℃, 10 minutes, ice water quenching.

[0066] (f) Integrated methanol treatment: 0.1 mol / L 2-methylimidazole, 30°C, 24 hours, washing and drying as in Example 1.

[0067] (g) 5-AT modification: methanol:water:diethanolamine = 80:15:5, 5-AT concentration 0.05mol / L, room temperature for 24 hours.

[0068] Performance: Pure water flux 520L / (m²) 2 ·h·bar); Pb 2+ Adsorption of 260 mg / g; adsorption of tetracycline of 195 mg / g.

[0069] Example 3 (a) Mixed granulation: 100g of PTFE, 25g of PEO, and 15g of nano ZnO (particle size 100nm).

[0070] (b) Paste extrusion: 55℃, 20MPa.

[0071] (c) Calendering into sheets: 60℃, thickness 1.5mm.

[0072] (d) Low temperature stretching: 150℃, 50 times in the longitudinal direction and 30 times in the transverse direction.

[0073] (e) Sintering: 400℃, 1 minute, water quenching.

[0074] (f) Integrated methanol treatment: 0.3 mol / L 2-methylimidazole, 60℃, 4 hours.

[0075] (g) 5-AT modification: methanol:water:ethanolamine = 40:55:5, 5-AT concentration 0.1mol / L, 60℃, 10 hours.

[0076] Performance: Pure water flux 380L / (m²) 2 ·h·bar); Pb 2+ Adsorption of 270 mg / g; adsorption of tetracycline of 205 mg / g.

[0077] Comparative example: Comparative Example 1: The remaining steps were the same as in Example 1, except for step (g). The resulting PTFE / ZIF-8 membrane was effective against Pb. 2+ The adsorption capacity is only 28 mg / g, and the adsorption of tetracycline is 20 mg / g.

[0078] Comparative Example 2: The remaining steps were the same as in Example 1, except that step (d) was changed to stretching at 180°C. Results: The membrane mechanical properties decreased, the ZIF-8 loading became uneven, and Pb... 2+ The adsorption capacity is 45 mg / g, the adsorption of tetracycline is 35 mg / g, and XRD shows partial decomposition of ZIF-8.

[0079] Comparative Example 3: The remaining steps were the same as in Example 1, but PEO was not added in step (a). Results: No oriented channels, low ZIF-8 loading (only 50% of that in Example 1), poor adsorption performance, Pb 2+ Adsorption of 150 mg / g; adsorption of tetracycline of 103 mg / g.

[0080] Comparative Example 4: The remaining steps are the same as in Example 1, but in step (g), the ratio of methanol:water:ethanolamine is 65:25:10. Results: Over-etching of ZIF-8 on the PTEF membrane surface resulted in smaller particle size and weakened adsorption performance after modification, leading to Pb... 2+ Adsorption: 208 mg / g; Tetracycline adsorption: 146 mg / g.

[0081] Performance testing: Analysis of experimental results: Morphology testing: Morphology images of samples from various embodiments and comparative examples are shown below. Figures 1 to 7 As shown, where Figure 1 This is a morphological image of the sample from Example 1. Figure 2 This is a morphological image of the sample from Example 2. Figure 3 This is a morphological image of the sample from Example 3. Figure 4 This is a morphology diagram of sample 1 in Comparative Example 1. Figure 5 This is a morphology image of sample 2 in Comparative Example 2. Figure 6 This is a morphology image of sample 3 in Comparative Example 3. Figure 7 This is a morphology diagram of Comparative Example 4. It can be seen that the samples of Examples 1 to 3 all have rough surfaces, while Comparative Examples 1 to 4 all have smooth surfaces.

[0082] Figure 8 These are adsorption capacity graphs for Examples 1-3 and Comparative Examples 1-4. The adsorption capacity curves show that the adsorption capacity of the Example groups is higher than that of the Comparative Examples. Examples 1-3 used PTFE, PEO, and nano-ZnO blending and granulation, low-temperature moderate stretching, temperature-controlled sintering and quenching, in-situ growth of ZIF-8, and 5-AT amine modification to prepare porous composite membranes. The process parameters of each example were reasonably matched, the membrane pore structure was regular, the ZIF-8 loading was uniform and the crystal structure was complete, and the adsorption capacity of Pb²⁺ was high. + The adsorption capacity reaches 260–285 mg / g, the adsorption capacity for tetracycline reaches 195–210 mg / g, and the pure water flux can reach 380–520 L / (m²). h Among them, Example 1 showed the best overall adsorption performance (bar).

[0083] Comparative Example 1 was not modified with 5-AT and lacked adsorption active functional groups. It relied solely on ZIF-8 physical adsorption for Pb²⁺. + The adsorption capacities of tetracycline in Comparative Example 1 and Comparative Example 2 were only 28 mg / g and 20 mg / g, respectively, indicating a significant deterioration in adsorption performance. The excessively high stretching temperature in Comparative Example 2 resulted in a decrease in the mechanical properties of the membrane, partial decomposition of ZIF-8 crystals, and uneven loading, leading to a significant reduction in adsorption capacity. Comparative Example 3 did not add PEO pore-forming agent, resulting in the absence of directional interconnected pores in the membrane, a significant reduction in ZIF-8 loading, insufficient pollutant mass transfer and adsorption sites, and a significant decrease in adsorption performance. The improper ratio of 5-AT modified solvent in Comparative Example 4 caused excessive etching of ZIF-8, a reduction in active sites, and a significant weakening of adsorption performance.

[0084] XRD tests were performed on Example 1 and Comparative Example 1, and the XRD test images are shown below. Figure 9 As shown, the X-ray diffraction (XRD) patterns are as follows: Curve a represents the PTFE / ZIF-8 composite film (before 5-AT modification), with characteristic ZIF-8 peaks appearing at 2θ = 7.3°, 10.4°, and 12.7°; Curve b represents the 5-AT modified film, where the characteristic peak positions are slightly shifted and the intensity is weakened, indicating that the ZIF-8 framework structure is intact, but some 2-methylimidazolium ligands are replaced by 5-AT, thus the characteristic peak intensity is weakened, further confirming the successful exchange of organic ligands.

[0085] The adsorption kinetics curve of tetracycline on the sample of Example 1 is as follows: Figure 10As shown, Figure 10 In the middle (a), the quasi-first-order dynamics fit is shown. Figure 10 In Figure (b), the pseudo-second-order kinetics are fitted. The results show that the adsorption rate of the membrane after 5-AT modification is significantly improved, and the pseudo-second-order kinetic correlation coefficient R²>0.99 indicates that chemisorption is dominant.

[0086] Those skilled in the art should understand that the technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] The above embodiments are merely illustrative of several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for producing a PTFE-based composite membrane material having oriented pores, characterized by, Includes the following steps: S1: Mixed granulation: Mixed masterbatch is obtained by mixing polytetrafluoroethylene dispersion resin, polyethylene oxide and nano zinc oxide, wherein the amount of polyethylene oxide added is 15%~25% of the mass of polytetrafluoroethylene dispersion resin, and the amount of nano zinc oxide added is 8%~15% of the mass of polytetrafluoroethylene dispersion resin; S2: Paste extrusion: The mixed masterbatch is extruded through a paste extruder at a temperature lower than the melting point of the polytetrafluoroethylene dispersion resin to obtain the extrudate; S3: Calendering into sheets: The extrudate is placed in a calender and pressed into sheets to obtain thin sheets; S4: Low-temperature bidirectional porosity stretching: a thin film is bidirectionally stretched at a temperature below 150°C to obtain a stretched film with a predetermined porosity structure. S5: High-temperature sintering and shaping: The stretched film with a predetermined oriented hole structure is sintered at high temperature. After sintering, it is quenched and cooled to room temperature at a cooling rate of more than 10℃ / s to obtain a PTFE / PEO / ZnO composite base film. S6: Methanol integrated treatment: The PTFE / PEO / ZnO composite membrane is placed in a methanol solution containing 2-methylimidazole for reaction. After the reaction is completed, it is washed and dried to obtain a PTFE / ZIF-8 composite porous membrane. S7: 5-Aminotetrazole modification: PTFE / ZIF-8 composite porous membrane is placed in a methanol-water-alcohol ternary solvent system containing 5-aminotetrazole for reaction. After the reaction is completed, it is washed and dried to obtain a PTFE-based composite membrane with oriented channels.

2. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The particle size of nano zinc oxide is 20-100 nm.

3. The method for preparing the PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The extrusion temperature is 35~55℃ and the extrusion pressure is 5~20 MPa.

4. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The calendering temperature is controlled between 20 and 60°C, and the thickness of the sheet is 0.1 to 2 mm.

5. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The sheet is first stretched longitudinally at a temperature below 150°C, and then stretched laterally. The longitudinal stretching ratio is 10 to 50 times, the transverse stretching ratio is 10 to 30 times, and the total stretching ratio is 36 to 48 times.

6. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The concentration of 2-methylimidazole is 0.1~0.3 mol / L, and the molar amount of 2-methylimidazole is 1~5 times the molar amount of ZnO in the PTFE / PEO / ZnO composite base film.

7. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 1, characterized in that, The volume ratio of methanol, water and amine in the methanol-water-alkanolamine ternary solvent system is (40~80%):(15~55%):(4~6%).

8. The method for preparing a PTFE-based composite membrane with oriented channels according to claim 7, characterized in that, The concentration of 5-aminotetrazole is 0.05~0.1 mol / L.

9. A PTFE-based composite membrane material with oriented channels, characterized in that, The PTFE-based composite membrane with oriented channels is prepared according to any one of claims 1 to 8. The PTFE-based composite membrane has oriented nanopores arranged along the stretching direction, wherein the pore size of the nanopores is 5-25 nm, the inner wall of the pores is loaded with ZIF-8 crystals, and the effective window pore size of ZIF-8 after 5-AT modification is 3.4-5.5 Å.

10. The PTFE-based composite membrane with oriented channels according to claim 9, characterized in that, It is used to adsorb heavy metal ions and antibiotics.

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