Block copolymer, environment-responsive fiber membrane and preparation method and application of environment-responsive fiber membrane

Abstract

The invention provides a block copolymer, an environment-responsive fiber membrane as well as a preparation method and application of the environment-responsive fiber membrane, and belongs to the technical field of wastewater treatment. The segmented copolymer comprises a zwitterionic segment, a fluorine-containing hydrophobic segment and a heavy metal ion chelating group. By designing a segmented copolymer containing a zwitterionic segment, a fluorine-containing hydrophobic segment and a heavy metal ion chelating group, the environmental response type nanofiber membrane capable of dynamically switching the surface wettability according to whether an oil phase exists or not is prepared, and intelligent cooperation of oil absorption and heavy metal adsorption functions is achieved. The environment self-adaptive function switching capacity is achieved, the one-step forming process is adopted, post-modification is not needed, the regeneration condition is mild, a green solvent system is used, and the problems that a traditional material conflicts in function, the process is complex, and regeneration is difficult are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to block copolymers, environmentally responsive fiber membranes, their preparation methods and applications, especially suitable for the treatment of complex polluted wastewater containing emulsified oil and heavy metal ions. Background Technology

[0002] Existing bifunctional adsorbent materials for treating this type of wastewater have the following drawbacks: (1) Serious functional conflict: Traditional blended electrospun membranes wrap hydrophilic heavy metal adsorption sites in a hydrophobic matrix, making it difficult for metal ions to contact effective functional groups and resulting in low adsorption capacity. (2) Harsh regeneration conditions: Existing materials mostly rely on strong acid to remove heavy metals, which easily causes degradation of the polymer skeleton and leaching of fillers, resulting in poor recycling performance; (3) Lack of environmental self-adaptation capability: It cannot dynamically adjust its function according to actual pollutants, resulting in a decrease in efficiency in complex wastewater; (4) Complex preparation process: Most bifunctional membranes require multiple post-modification steps (such as plasma treatment, layer-by-layer self-assembly, hydrothermal growth), which are costly and easy to clog the pores, making it difficult to scale up. Summary of the Invention

[0003] In view of this, to address the aforementioned shortcomings of existing bifunctional adsorbent materials used for treating this type of wastewater, this invention provides block copolymers, environmentally responsive fiber membranes, their preparation methods, and applications. By designing block copolymers containing zwitterionic segments, fluorinated hydrophobic segments, and heavy metal ion chelating groups, an environmentally responsive nanofiber membrane is prepared that can dynamically switch its surface wettability based on the presence or absence of an oil phase, achieving intelligent synergy between oil absorption and heavy metal adsorption functions. It possesses environmentally adaptive functional switching capabilities, employs a one-step molding process without post-modification, and uses mild regeneration conditions and a green solvent system, effectively solving problems such as functional conflicts, complex processes, and difficult regeneration associated with traditional materials.

[0004] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a block copolymer comprising a zwitterionic segment, a fluorinated hydrophobic segment, and a heavy metal ion chelating group.

[0005] Secondly, the present invention provides an environmentally responsive adsorption fiber membrane prepared from the above-mentioned block copolymer. The fiber membrane is hydrophilic in an oil-free aqueous phase to expose heavy metal adsorption sites, and its surface wettability changes to hydrophobicity after contact with an oil phase to preferentially adsorb oil.

[0006] Thirdly, the present invention provides a method for preparing the above-mentioned block copolymer, comprising the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, a fluorinated monomer containing heavy metal ion chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer.

[0007] Fourthly, the present invention provides a method for preparing the above-mentioned environmentally responsive adsorption fiber membrane, comprising the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, the fluorine monomer containing heavy metal chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer. Step (3): Dissolve the block copolymer obtained in step (2) in a polar mixed solvent and stir until completely dissolved to form a spinning solution; Step (4): The spinning solution from step (3) is spun using continuous fiber forming technology to obtain a nonwoven fiber membrane precursor. Step (5): Dry the fiber membrane precursor obtained in step (4) to remove residual solvent and obtain an environmentally responsive nanofiber membrane.

[0008] Fifthly, the present invention provides the application of the above-mentioned environmentally responsive adsorption fiber membrane in the treatment of wastewater containing both oil and heavy metals.

[0009] Compared with the prior art, the present invention has the following beneficial effects: (1) Establishing an "environmentally triggered wettability switching" mechanism: Existing products mostly use physical blending (such as PVDF + chitosan + Fe3O4) or surface grafting (such as PAN-g-PAA), while this invention integrates four major functions—hydrophilicity, hydrophobicity, recognition, and responsiveness—into a single block copolymer backbone through molecular design. Wettability switching is achieved based on the environmentally responsive competition between the hydrophilic effect of the zwitterionic segment and the hydrophobic effect of the fluorinated hydrophobic segment in the block copolymer. No filler or post-modification is required, fundamentally solving the functional conflict problem. Through single-molecule design, the material can autonomously switch functional modes according to the oil / water environment, completely resolving the mutual repulsion between oil absorption and heavy metal adsorption.

[0010] (2) Truly one-step molding, no post-processing required: avoids the complex equipment and multi-step process required by traditional Janus membranes or composite membranes, reduces manufacturing costs and improves pore connectivity.

[0011] (3) Achieve mild, efficient, and reversible regeneration: Utilize biocompatible reducing agents (such as cysteine) to break the chelating groups of heavy metal ions (such as disulfide bonds) to release Hg. 2+ It does not require strong acids or alkalis, thus protecting the structural integrity of the material.

[0012] (4) High selectivity in Hg recognition 2+ Disulfide bonds to soft metal ions (Hg 2+ Pb 2+ It has natural affinity and strong resistance to interference from coexisting ions.

[0013] (5) The use of green solvent system (ethanol / water) conforms to the concept of sustainable development and is easy to promote industrially. Detailed Implementation

[0014] This invention provides a block copolymer comprising a zwitterionic segment, a fluorinated hydrophobic segment, and a heavy metal ion chelating group. This block copolymer integrates the zwitterionic segment (hydrophilic), the fluorinated hydrophobic segment (oleophobic), and the heavy metal chelating group (adsorption function) through molecular design, achieving molecular-level synergy of multifunctional units. It solves the problem of functional site encapsulation and mutual repulsion in traditional blend materials, ensuring effective exposure and synergistic effect of each functional unit at the molecular structure level.

[0015] This invention provides an environmentally responsive adsorption fiber membrane, prepared from the aforementioned block copolymer. The fiber membrane exhibits hydrophilicity in an oil-free aqueous phase to expose heavy metal adsorption sites, and upon contact with an oil phase, its surface wettability changes to hydrophobicity to preferentially adsorb oil. Based on the environmental responsiveness of the block copolymer, this fiber membrane dynamically switches its functional mode, exposing chelating sites to adsorb heavy metals in an oil-free environment and preferentially adsorbing oil upon contact with an oil phase. This enables intelligent synergistic treatment of complex wastewater (oil + heavy metals), overcoming the shortcomings of traditional materials such as lack of self-adaptive ability and low efficiency in treating complex wastewater.

[0016] This invention provides a method for preparing the above-mentioned block copolymer, comprising the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, a fluorinated monomer containing heavy metal ion chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer.

[0017] This preparation method employs RAFT controlled polymerization to synthesize block copolymers in two steps: first, a macromolecular chain transfer agent containing zwitterionic monomers is polymerized, followed by polymerization of fluorinated monomers with chelating groups, allowing for precise control of the molecular structure. This controlled synthesis of block structures avoids the component inhomogeneity and functional conflicts associated with blending or grafting processes, ensuring the stability of the material's properties.

[0018] In this invention, in step (2), the fluorinated monomer is selected from fluorinated methacrylates; the heavy metal ion chelating group is selected from at least one of disulfide bonds (–S–S–), mercapto groups (–SH), or aminothioureas. Fluorinated methacrylate monomers are selected to enhance hydrophobicity, and disulfide bonds, mercapto groups, and aminothiourea chelating groups are used to achieve heavy metal adsorption, thus optimizing the performance of the functional unit. Disulfide bonds and other groups improve the selectivity and regenerability of heavy metal adsorption, while fluorinated monomers enhance the oil phase adsorption capacity, balancing the dual-function efficiency of the material.

[0019] In this invention, the fluorinated methacrylates are 1H,1H-perfluoropropyl methacrylate, hexafluorobutyl methacrylate, or trifluoroethyl methacrylate. Using 1H,1H-perfluoropropyl methacrylate or hexafluorobutyl methacrylate as the fluorinated monomer enhances the oil phase adsorption performance of the hydrophobic segment. These monomers exhibit significant hydrophobic effects, further improving the preferential adsorption capacity of the fiber membrane for the oil phase and optimizing environmental response sensitivity.

[0020] In this invention, in step (1), the zwitterionic monomer is selected from at least one of sulfonated betaine acrylate and carboxylated betaine acrylate. This ensures the hydrophilicity of the hydrophilic segment and the exposure of heavy metal adsorption sites. The zwitterionic monomer has strong hydrophilicity, effectively exposing chelating groups and improving the heavy metal adsorption capacity in an oil-free environment.

[0021] The present invention also provides a method for preparing the above-mentioned environmentally responsive adsorption fiber membrane, comprising the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, the fluorine monomer containing heavy metal chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer. Step (3): Dissolve the block copolymer obtained in step (2) in a polar mixed solvent and stir until completely dissolved to form a spinning solution; Step (4): The spinning solution from step (3) is spun using continuous fiber forming technology to obtain a nonwoven fiber membrane precursor. Step (5): Dry the fiber membrane precursor obtained in step (4) to remove residual solvent and obtain an environmentally responsive nanofiber membrane.

[0022] This method for preparing environmentally responsive adsorption fiber membranes involves a one-step process: "block copolymer synthesis → spinning solution preparation → continuous spinning → drying," eliminating the need for post-processing. This simplifies the preparation process, reduces costs, avoids pore blockage issues caused by post-processing, and improves the pore connectivity and adsorption efficiency of the fiber membrane.

[0023] In this invention, in step (4), the continuous fiber forming technology is selected from one of electrospinning, centrifugal spinning, or air-jet spinning. Fiber membranes are prepared using continuous technologies such as electrospinning / centrifugal / air-jet spinning to achieve large-scale production. Continuous processes are suitable for industrial application, improving production efficiency and ensuring the uniformity and stability of the fiber membranes.

[0024] In this invention, in step (3), the polar mixed solvent is selected from one of an alcohol-water mixed solvent and a ketone-water mixed solvent. This ensures the solubility and spinning performance of the block copolymer. The green solvent system meets environmental protection requirements while ensuring the stability of the spinning solution and improving the quality of fiber membrane formation.

[0025] The present invention relates to the application of the environmentally responsive adsorption fiber membrane in the treatment of wastewater containing both oil and heavy metals. Utilizing the environmental responsiveness and dual-functionality of the fiber membrane, it treats complex wastewater containing both oil and heavy metals. It efficiently and simultaneously removes complex pollutants, solving the problem that traditional materials cannot simultaneously achieve oil phase separation and heavy metal adsorption, making it suitable for complex wastewater scenarios.

[0026] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments.

[0027] Example 1 The fiber membrane was prepared using a one-step electrospinning method. The specific process flow is as follows: Block copolymer synthesis: The reversible addition-fragmentation chain transfer (RAFT) polymerization method was adopted, using 4-cyano-4-(phenylthiocarbamoylthio)valerate as chain transfer agent, to first polymerize sulfonate betaine methacrylate monomer to obtain the macromolecular RAFT reagent PSBMA-CTA. Then, a fluorinated monomer containing terminal disulfide bonds (FMA-SS, where FMA is a fluorinated monomer, specifically trifluoroethyl methacrylate, and SS is a disulfide bond) is added, and polymerization continues to obtain the target block copolymer P (SBMA-b-FMA-SS). A white powder purified by dialysis and freeze-dried.

[0028] Preparation of spinning solution: Weigh 1.0 g of the block copolymer P(SBMA-b-FMA-SS), add 9 mL of anhydrous ethanol and 1 mL of deionized water, and stir magnetically for 12 h until completely dissolved to obtain a 10 wt% transparent spinning solution.

[0029] Electrospinning for film formation: Fill a 10mL syringe with the spinning solution and connect a 21G stainless steel needle. The applied voltage is 14kV, the receiving distance is 15cm, and the propulsion rate is 1.0mL / h. The receiving device is a rotating drum (200 rpm), with an ambient temperature of 25±2℃ and a relative humidity of 50±5%. Spinning continues for 2 hours to obtain a white nonwoven fiber membrane.

[0030] Post-processing: The membrane was dried in a vacuum oven at 60°C for 12 hours to remove residual solvent, thus obtaining the final product.

[0031] Example 2 Same as Example 1, except that the zwitterionic monomer is carboxybetaine methacrylate.

[0032] Example 3 Same as Example 1, except that the fluorinated monomer is selected as 1H,1H-perfluoropropyl methacrylate.

[0033] Example 4 Same as Example 1, except that the fluorinated monomer is hexafluorobutyl methacrylate.

[0034] Example 5 Similar to Example 1, except that the heavy metal ion chelating group is selected as thiol (–SH).

[0035] Example 6 Similar to Example 1, except that the heavy metal ion chelating group is selected as aminothiourea.

[0036] Example 7 Same as Example 1, except that no zwitterionic monomer is added.

[0037] Example 8 Same as Example 1, except that no fluorinated monomer is added.

[0038] Example 9 Same as Example 1, except that no heavy metal ion chelating groups are added.

[0039] Example 10 Same as Example 1, except that no zwitterionic monomers and fluorinated monomers are added.

[0040] Example 11 Same as Example 1, except that no zwitterionic monomers and heavy metal ion chelating groups are added.

[0041] Example 12 Same as Example 1, except that no fluorine-containing monomers and heavy metal ion chelating groups are added.

[0042] Comparative Example 1 Traditional blended adsorption membrane: 5g of PVDF (polyvinylidene fluoride), 2g of chitosan and 1g of Fe3O4 nanoparticles were mixed and dissolved in a mixed solvent of N,N-dimethylformamide and acetone (volume ratio 7:3) to prepare a 15wt% spinning solution. The fiber membrane was prepared using the same electrospinning parameters as in Example 1, without post-modification treatment.

[0043] Examples 1-13 and Comparative Example 1 were tested using the following methods: Contact angle: Using a contact angle measuring instrument (Beijing HARKE-SPCA, China), the membrane was cut into 20×20 mm samples. The contact angle of 3 μL of water or n-dodecane was recorded on the membrane surface when it was stable using a high-speed camera. 3-5 different locations were selected for each sample for testing, and the average value was taken.

[0044] Oil adsorption capacity: Immerse the dry fiber membrane (mass m0) in n-hexane at room temperature. After the adsorption is saturated, take it out, wipe off the surface oil with filter paper, and weigh it m1. Oil adsorption capacity = (m1-m0) / m0 (g / g).

[0045] Hg 2+ Adsorption capacity: The fiber membrane was immersed in Hg(NO3)2 solution (concentration Co) for 5 hours. The remaining concentration Ce was then measured. Adsorption capacity = (Co-Ce)×V / m (mg / g), where V is the solution volume and m is the membrane mass.

[0046] Oil-water mixture removal rate: Preparation containing 50 mg / L crude oil + 50 mg / L Hg 2+ For simulated wastewater, 50 mL of simulated wastewater was added to a fiber membrane, stirred at room temperature for 2 hours, and the oil and water phases were separated. The Hg in the water phase was then measured. 2+ Concentration, removal rate = (Co-Ce) / Co×100%.

[0047]

[0048] In block copolymer molecules, the zwitterionic segments are in an extended state in an oil-free environment, exposing heavy metal chelating groups (such as disulfide bonds), making the fiber membrane surface hydrophilic and facilitating the absorption of Hg. 2+ Chelation; when in contact with the oil phase, the fluorinated hydrophobic segment (such as FMA-SS) migrates to the surface due to hydrophobic interactions, wrapping the disulfide bond inside and covering part of the hydrophilic group, making the surface hydrophobic, preferentially adsorbing the oil phase, and realizing environmentally triggered functional switching.

[0049] As shown in Table 1, the embodiments of the present invention are far superior to Comparative Example 1 in key indicators, proving that the present invention successfully solves the core problem of mutual repulsion between oil absorption and heavy metal adsorption in traditional technologies. The excellent key data of the embodiments of the present invention demonstrate the synergistic effect of complete molecular design. Comparative Example 1 has the worst overall performance, and the comparison highlights the fundamental advantages of the present invention based on molecular design.

[0050] The above description is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A block copolymer, characterized in that, It contains zwitterionic segments, fluorinated hydrophobic segments, and heavy metal ion chelating groups.

2. An environmentally responsive adsorption fiber membrane, characterized in that, Prepared from the block copolymer of claim 1, the fiber membrane is hydrophilic in an oil-free aqueous phase to expose heavy metal adsorption sites, and its surface wettability changes to hydrophobicity after contact with an oil phase to preferentially adsorb oil.

3. The method for preparing a block copolymer according to claim 1, characterized in that, Includes the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, a fluorinated monomer containing heavy metal ion chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer.

4. The method for preparing a block copolymer according to claim 3, characterized in that, In step (2), the fluorinated monomer is selected from fluorinated methacrylates; the heavy metal ion chelating group is selected from at least one of disulfide bonds, mercapto groups or aminothioureas.

5. The method for preparing a block copolymer according to claim 4, characterized in that, Fluorinated methacrylates are 1H,1H-perfluoropropyl methacrylate, hexafluorobutyl methacrylate, or trifluoroethyl methacrylate.

6. A method for preparing a block copolymer according to any one of claims 3-5, characterized in that, In step (1), the zwitterionic monomer is selected from at least one of sulfobetaine methacrylate and carboxybetaine methacrylate.

7. The method for preparing an environmentally responsive adsorption fiber membrane according to claim 2, characterized in that, Includes the following steps: Step (1): The reversible addition-fragmentation chain transfer polymerization method is used to initiate the polymerization reaction of zwitterionic monomers to obtain macromolecular chain transfer agents; Step (2): Using the macromolecular chain transfer agent obtained in step (1) as a regulator, the fluorine monomer containing heavy metal chelating groups is initiated to undergo a polymerization reaction to obtain a block copolymer. Step (3): Dissolve the block copolymer obtained in step (2) in a polar mixed solvent and stir until completely dissolved to form a spinning solution; Step (4): The spinning solution from step (3) is spun using continuous fiber forming technology to obtain a nonwoven fiber membrane precursor. Step (5): Dry the fiber membrane precursor obtained in step (4) to remove residual solvent and obtain an environmentally responsive nanofiber membrane.

8. The method for preparing an environmentally responsive adsorption fiber membrane according to claim 7, characterized in that, In step (4), the continuous fiber forming technology is selected from one of electrospinning, centrifugal spinning or air-jet spinning.

9. A method for preparing an environmentally responsive adsorption fiber membrane according to claim 7 or 8, characterized in that, In step (3), the polar mixed solvent is selected from one of the alcohol-water mixed solvent and the ketone-water mixed solvent.

10. The application of the environmentally responsive adsorption fiber membrane according to claim 2 in the treatment of wastewater containing both oil and heavy metals.

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