Preparation method of self-driven-salt separation-photo-thermal hollow fiber composite membrane

Abstract

The invention discloses a preparation method of a self-driven-salt separation-photo-thermal hollow fiber composite membrane, according to the method, photo-thermal conversion and salt separation functions are achieved through in-situ oxidation of a photo-thermal functional layer and interfacial polymerization of a salt separation selection layer, and the membrane is characterized in that (1) a porous hollow fiber membrane is adopted as a supporting layer of the composite membrane; mechanical strength and a seawater transmission channel are provided; (2) a hydrophilic inner core is inserted into the hollow fiber membrane, seawater is driven to flow through capillary action, and a self-driving effect is achieved; (3) a cross-linked polyamide network composite layer is formed on the inner wall of the hollow fiber membrane by adopting an interfacial polymerization process inside the hollow fiber membrane, so that the salt separation effect of the hollow fiber membrane is enhanced; and (4) tannic acid (TA)-pyrrole (Py) in-situ modification and Fe < 3 + > oxidation reaction are adopted outside the hollow fiber membrane to generate Fe < 3 + >-tannic acid (TA)-pyrrole (Py) which is compounded on the outer surface of the hollow fiber membrane, so that membrane surface blackening is realized, and a photo-thermal conversion function is integrated.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and particularly relates to a preparation method of a self-driven-salt separation-photothermal hollow fiber composite membrane. Background Art

[0002] In many fields such as chemical engineering, energy, and environment, mixed salt systems widely exist and have an important impact. In the development of salt lake resources, salt lake brines contain a variety of mixed salts such as rich sodium chloride, potassium chloride, magnesium chloride, etc. Effectively separating and extracting these mixed salts can obtain high-purity potassium salts for agricultural potassium fertilizer production, improving the yield and quality of crops; the extracted magnesium salts are important industrial raw materials, widely used in industries such as metal smelting and building materials. In the treatment of industrial wastewater, many industrial production processes generate wastewater containing a mixed system of heavy metal salts and conventional salts, such as the mixed salts of copper salts, nickel salts, and sodium chloride in electroplating wastewater. Separating and extracting the target salt from such wastewater can not only realize the recycling of heavy metal resources, reduce production costs, but also reduce the environmental pollution caused by heavy metals, protect the ecological balance, and meet the strategic needs of sustainable development.

[0003] The traditional crystallization method uses the differences in the solubility of different salts in a solvent with the change of temperature or solvent composition to achieve separation. However, this method is difficult to efficiently separate salts with similar solubility curves, and co-crystallization is likely to occur, resulting in low purity of the target salt. For example, when separating sodium sulfate and sodium chloride, it is difficult to completely separate the two by the conventional crystallization method. The precipitation method separates by adding a precipitant to form a precipitate of specific ions. However, the selection and dosage control of the precipitant are relatively difficult. An excessive amount of precipitant may introduce new impurities, and part of the target salt may be entrained during the precipitation process, causing losses. The ion exchange method uses the difference in the affinity of ion exchange resins for different ions for separation. However, the resin is easily contaminated, the regeneration process is complex and costly, and the exchange capacity is limited, making it difficult to meet the requirements of large-scale industrial production.

[0004] As a new type of membrane separation technology, nanofiltration technology has the characteristic of selective retention of different valence ions. Chinese Patent CN108722343A proposes to utilize the characteristics of high retention rate of divalent ions and high transmittance of monovalent ions by nanofiltration membranes to achieve the separation of a mixed salt solution of sodium sulfate and sodium chloride. However, the cost of nanofiltration membranes is relatively high, and they are easily contaminated by organic substances, colloids, etc. during the actual operation process, resulting in a decrease in membrane flux. Frequent membrane cleaning and replacement increase the operating cost. Electrodialysis technology realizes separation by the directional migration of anions and cations in ion exchange membranes under the action of an electric field. For example, Patent CN202010728488.8 uses electrodialysis to treat mixed salt wastewater containing multiple ions. However, the electrodialysis process has high energy consumption, high equipment investment, strict requirements for the performance and stability of ion exchange membranes, and problems such as concentration polarization when treating high-concentration mixed salt solutions, which limit its application range.

[0005] The preparation method of a self-driven desalination-photothermal hollow fiber composite membrane proposed by the present invention has significant innovation and advantages. This composite membrane innovatively combines photothermal conversion and self-driven desalination functions. It uses photothermal materials to absorb light energy and convert it into heat energy, promoting the mass transfer process of salt solutions and achieving self-driven desalination without additional power equipment, greatly reducing energy consumption. In terms of separation performance, by optimizing the structure and surface properties of the hollow fiber membrane, it shows high separation selectivity for different valence ions, can effectively overcome problems such as co-crystallization and impurity introduction in traditional methods, and significantly improve the purity and recovery rate of target salts. At the same time, this preparation method is simple and controllable, with relatively low costs, and is expected to achieve large-scale industrial production, bringing new technological changes to the field of mixed salt separation and extraction, and promoting the green and efficient development of related industries. Summary of the Invention

[0006] An object of the present invention is to propose a preparation method of a self-driven desalination-photothermal hollow fiber composite membrane. This preparation method uses a hollow fiber membrane as the support layer, forms a cross-linked polyamide network on the inner wall of the membrane through an interfacial polymerization process to integrate the desalination function for the hollow fiber membrane, and through the in-situ modification of tannic acid (TA)-pyrrole (Py) and the oxidation reaction of Fe 3+ to generate Fe 3 + -tannic acid (TA)-pyrrole (Py) is adsorbed on the outer surface of the hollow fiber membrane to provide the hollow fiber with photothermal conversion function, and a hydrophilic core is inserted to provide the hollow fiber with a capillary spontaneous water absorption driving force to achieve a self-driven effect.

[0007] To achieve the above object, the technical solution of the present invention is realized in the following manner:

[0008] A preparation method of a self-driven desalination-photothermal hollow fiber composite membrane includes the following steps:

[0009] (1) Preparation of the hollow fiber membrane: Dissolve a polymer and a pore former in an organic solvent to form a spinning solution, extrude the spinning solution through a spinneret to form hollow fibers, and through solvent-nonsolvent double diffusion rapid phase separation in a coagulation bath, solidify into a microporous membrane, and finally wash and dry to remove the solvent to form a mold.

[0010] (2) Preparation of the interfacial polymerization layer: First, prepare aqueous and oil-phase monomer solutions respectively, then immerse the hollow fiber membrane in the aqueous solution to fully wet its inner wall and quickly transfer it to the oil-phase solution, so that the aqueous and oil-phase monomers polymerize on the inner wall of the membrane to form a cross-linked network, and finally take out the reacted membrane and treat it at a specific temperature for a period of time to enhance the stability of the cross-linked network and separation performance.

[0011] (3) Preparation of the photothermal layer: First, prepare a tannic acid (TA)-pyrrole (Py) solution, adjust the pH with Tris-HCl solution, and add an appropriate amount of ethanol to optimize the properties; then immerse the hollow fiber membrane filaments with both ends sealed in this solution to modify its outer surface in-situ; next, prepare an FeCl3 solution, put the modified membrane into the mixture and perform ultrasonic treatment; finally, soak the membrane filaments at an appropriate temperature for a period of time to allow Fe 3+ to fully react with tannic acid (TA)-pyrrole (Py) and adsorb on the outer surface of the membrane, realizing the blackening of the membrane body and photothermal conversion.

[0012] (4) Insertion of the hydrophilic inner core: Remove the sealed part and insert the hydrophilic inner core to form a capillary driving structure.

[0013] Furthermore, the material of the hollow fiber membrane described in step (1) includes one of polyethersulfone (PES), polyvinylidene fluoride (PVDF), polysulfone (PSF), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), and polybenzimidazole (PBI).

[0014] Furthermore, the aqueous monomer used in the interfacial polymerization described in step (2) includes one of piperazine (PIP), metaphenylenediamine (MPD), ethylenediamine (EDA), and hexamethylenediamine (HMD), and the oil-phase monomer is trimesoyl chloride (TMC).

[0015] Among them, the mass fraction of the aqueous monomer is 0.5 wt% - 2 wt%, and the mass fraction of the oil-phase monomer is 0.1 wt% - 0.3 wt%.

[0016] Furthermore, in the tannic acid (TA)-pyrrole (Py) solution used for the preparation of the photothermal layer described in step (3), the concentration of tannic acid (TA) is 0.5 wt% - 2 wt%, the concentration of pyrrole (Py) is 1 wt% - 3 wt%, and the pH of the Tris-HCl solution is 8.0 - 9.0.

[0017] Furthermore, the Fe 3+ oxidation conditions are that the concentration of the FeCl3 solution is 0.1 wt% - 0.5 wt%, the mixture of tannic acid (TA)-pyrrole (Py) and the FeCl3 solution is ultrasonically treated for 15 min - 45 min, the soaking time of the membrane filaments is 2 h - 4 h, and the reaction temperature is 25°C - 40°C.

[0018] Furthermore, the hydrophilic inner core described in step (4) includes one of cotton thread, hemp thread, bamboo fiber filament, seaweed fiber thread, and wood pulp composite fiber filament.

[0019] The present invention adopts a composite hollow fiber membrane, forms a cross-linked polyamide network on the inner wall of the membrane by using an interfacial polymerization process to achieve the function of salt separation, and uses Fe on the outer surface of the membrane 3+The oxidation reaction and complexation reaction are respectively carried out on pyrrole and tannic acid to generate Fe 3+ -Tannic acid (TA)-pyrrole (Py) realizes the blackening of the outer surface of the membrane, provides the function of photothermal conversion for the outer surface of the membrane, inserts a hydrophilic inner core into the hollow fiber membrane to provide driving force for the hollow fiber membrane filaments to achieve the self-driving effect. The membrane filaments prepared by this method have the effects of self-driving, salt separation and photothermal at the same time, and are suitable for fields such as seawater desalination treatment and low-energy consumption salt separation.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1. Functional synergy: It integrates self-driving seawater transportation, efficient salt separation and photothermal conversion, and does not require external power support.

[0022] 2. Energy-saving characteristics: Through capillary driving and solar photothermal conversion, the system energy consumption is significantly reduced, which is suitable for low-grade energy utilization scenarios.

[0023] 3. Structural optimization: The hollow fiber design improves the processing efficiency per unit volume, the blackening layer on the outer surface enhances the light absorption capacity, and the internal salt separation layer realizes precise salt retention.

[0024] 4. Environmental adaptability: It is resistant to high pressure and pollution, can treat high-salt wastewater, and is suitable for remote areas and complex water quality conditions.

[0025] 5. Wide application: It is suitable for fields such as seawater desalination and wastewater resource utilization, and can expand the energy recovery function when combined with solar energy equipment. Description of the Drawings

[0026] Figure 1 is the process schematic diagram of the present invention;

[0027] Figure 2 is the structural design schematic diagram of the hollow fiber composite membrane of the present invention;

[0028] Figures 3 to 5 is the cross-sectional scanning electron micrograph of the hollow fiber base membrane of the present invention;

[0029] Figures 6 to 8 is the cross-sectional scanning electron micrograph of the hollow fiber composite membrane of the present invention;

[0030] Figure 9 is the preparation flow chart of the self-driving-salt separation-photothermal hollow fiber composite membrane of the present invention. Detailed Embodiments

[0031] The present invention will be further described below with reference to the drawings.

[0032] To enable relevant personnel in the field to understand the present invention more clearly, the present invention will be further described in detail below in conjunction with examples. The following selected examples are the preferred embodiments of the present invention, and the scope of protection required by the present invention is not limited thereto.

[0033] As Figure 1 and 2 shown, an embodiment of the present invention provides a preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane, including the following steps: (1) The interior of the hollow fiber membrane is treated by an interfacial polymerization process to form a cross-linked polyamide network on its inner wall; (2) After sealing both ends of the hollow fiber membrane, the outer surface is successively subjected to in-situ modification of tannic acid (TA) - pyrrole (Py) and Fe 3+ oxidation reaction to cover the outer surface of the membrane with a photothermal coating layer; (3) Remove the sealed part and insert a hydrophilic inner core to form a capillary driving structure. The specific preparation process is as Figure 9 shown.

[0034] Example 1

[0035] Construction of the mechanical support layer: An 18 wt% polyethersulfone hollow fiber membrane is used as the support layer of the composite membrane;

[0036] Construction of the separation layer inside the membrane: Aqueous monomer: 0.5 wt% piperazine;

[0037] Oil-phase monomer: 0.15 wt% trimesoyl chloride;

[0038] Prepare a polyamide layer inside the membrane by interfacial polymerization;

[0039] Modification of the photothermal functional layer: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0040] Oxidative polymerization: 0.1 wt% ferric chloride solution and precursor solution:

[0041] Prepare the photothermal layer of the hollow fiber membrane by soaking the outer surface of the membrane; Preparation of the self-driven system: Select a cotton core as the hydrophilic inner core to achieve the self-driven effect.

[0042] Example 2

[0043] Construction of the mechanical support layer: An 18 wt% polyethersulfone hollow fiber membrane is used as the support layer of the composite membrane; Construction of the separation layer inside the membrane: Aqueous monomer: 1.0 wt% piperazine;

[0044] Oil-phase monomer: 0.15 wt% trimesoyl chloride;

[0045] Prepare a polyamide layer inside the membrane by interfacial polymerization;

[0046] Modification of the photothermal functional layer: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0047] Oxidative polymerization: 0.1 wt% ferric chloride solution and precursor solution:

[0048] Prepare the photothermal layer of the hollow fiber membrane by the method of external membrane soaking; Self-driving system preparation: Select a cotton core as the hydrophilic inner core to achieve the self-driving effect.

[0049] Example 3

[0050] Mechanical support layer construction: 18 wt% polyethersulfone hollow fiber membrane as the support layer of the composite membrane; Membrane inner separation layer construction: Aqueous monomer: 2.0 wt% piperazine;

[0051] Oil phase monomer: 0.15 wt% trimesoyl chloride;

[0052] Prepare the polyamide layer in the membrane by interfacial polymerization; Photothermal functional layer modification: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0053] Oxidative polymerization: 0.1 wt% ferric chloride solution and precursor solution:

[0054] Prepare the photothermal layer of the hollow fiber membrane by the method of external membrane soaking; Self-driving system preparation: Select a cotton core as the hydrophilic inner core to achieve the self-driving effect.

[0055] Example 4

[0056] Mechanical support layer construction: 18 wt% polyethersulfone hollow fiber membrane as the support layer of the composite membrane; Membrane inner separation layer construction: Aqueous monomer: 2 wt% piperazine;

[0057] Oil phase monomer: 0.15 wt% trimesoyl chloride;

[0058] Prepare the polyamide layer in the membrane by interfacial polymerization; Photothermal functional layer modification: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0059] Oxidative polymerization: 0.2 wt% ferric chloride solution and precursor solution:

[0060] Prepare the photothermal layer of the hollow fiber membrane by the method of external membrane soaking;

[0061] Self-driving system preparation: Select a cotton core as the hydrophilic inner core to achieve the self-driving effect.

[0062] Example 5

[0063] Mechanical support layer construction: 18 wt% polyethersulfone hollow fiber membrane as the support layer of the composite membrane;

[0064] Membrane inner separation layer construction: Aqueous monomer: 2.0 wt% piperazine;

[0065] Oil phase monomer: 0.15 wt% trimellitic acid chloride;

[0066] Prepare a polyamide layer in the membrane by interfacial polymerization;

[0067] Photothermal functional layer modification: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0068] Oxidative polymerization: 0.3 wt% ferric chloride solution and precursor solution:

[0069] Prepare the photothermal layer of the hollow fiber membrane by soaking outside the membrane;

[0070] Self-driving system preparation: Select a cotton core as the hydrophilic inner core to achieve the self-driving effect.

[0071] Example 6

[0072] Mechanical support layer construction: 18 wt% polyethersulfone hollow fiber membrane as the support layer of the composite membrane;

[0073] Membrane inner separation layer construction: Aqueous phase monomer: 2.0 wt% piperazine;

[0074] Oil phase monomer: 0.15 wt% trimellitic acid chloride;

[0075] Prepare a polyamide layer in the membrane by interfacial polymerization;

[0076] Photothermal functional layer modification: Precursor solution: 1 wt% tannic acid and 2 wt% pyrrole;

[0077] Oxidative polymerization: 0.4 wt% ferric chloride solution and precursor solution:

[0078] Prepare the photothermal layer of the hollow fiber membrane by soaking outside the membrane;

[0079] Self-driving system preparation: Select a cotton core as the hydrophilic inner core to achieve the self-driving effect.

[0080] The performance of a self-driving-salt separation-photothermal hollow fiber composite membrane prepared is shown in the table:

[0081] Photothermal conversion rate (%) Desalination rate (%) Sodium-magnesium separation ratio Example 1 65.3 91.2％ 1.28 Example 2 64.8 90.7％ 1.73 Example 3 66.7 89.6％ 1.86 Example 4 68.6 93.7％ 1.21 Example 5 70.7 95.4％ 1.18 Example 6 72.4 98.6％ 1.15

[0082] In the studies of Examples 1 to 3, the gradient regulation of the piperazine mass fraction had a significant impact on the interfacial polymerization behavior. With the orderly increase in the piperazine concentration, the degree of interfacial polymerization reaction in the membrane gradually deepened, and the microstructure of the polyamide separation layer showed a regular evolution from loose to dense, and its three-dimensional network cross-linking density was systematically optimized. This precise regulation at the structural level effectively enhanced the selective sieving ability of the membrane body for different valence ions - the retention performance for magnesium chloride and sodium chloride showed a synergistic improvement trend with the cross-linking densification process, and the separation selectivity of sodium and magnesium ions was substantially improved.

[0083] This design strategy achieved a functional leap of the polyamide separation layer from "basic retention" to "efficient sieving" through the precise control of the piperazine concentration, providing an innovative solution for the efficient separation of sodium and magnesium ions in seawater desalination and the directional removal of heavy metal ions in industrial wastewater. Its core advantage lies in constructing a positive correlation between the degree of interfacial polymerization and ion selectivity through the refined regulation of a single variable, laying a solid theoretical and practical foundation for the engineering preparation of high-performance nanofiltration membrane materials.

[0084] In Examples 4 to 6, the gradient regulation of the ferric ion concentration had a significant impact on the coordination complex structure of the photothermal membrane. With the orderly increase in the Fe 3+ concentration, the in-situ polymerization reaction of tannic acid (TA) and pyrrole (Py) showed a differential evolution, and the formed Fe 3+ -TA-Py ternary composite layer gradually transformed from a loose linear coordination to a dense network chelation structure, and the delocalization degree of the intermolecular conjugated Π bond and the nanoparticle dispersion uniformity were systematically optimized.

[0085] This design strategy achieved a functional upgrade of the photothermal membrane from "single light absorption" to "light-thermal-adsorption coupling" through the precise control of the Fe 3+ concentration, providing an innovative technical path for fields such as the resource utilization of high-salt wastewater and the remediation of heavy metal-polluted water bodies. Its core advantage lies in constructing a positive correlation between the component concentration and the multifunctionality of the membrane body by means of the refined regulation of metal ion coordination chemistry, laying a solid theoretical and practical foundation for the cross-scale design of environmental functional materials.

[0086] The above are the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane, characterized in that It includes the following steps: (1) Preparation of the hollow fiber membrane: Dissolve the polymer and the pore-forming agent in an organic solvent to form a spinning solution, extrude it through a spinneret to form hollow fibers, and through solvent-nonsolvent double diffusion rapid phase separation in a coagulation bath, solidify it into a microporous membrane, and finally wash and remove the solvent and then dry and form it; (2) Preparation of the interfacial polymerization layer: First, prepare the aqueous and oil-phase monomer solutions separately, then immerse the hollow fiber membrane in the aqueous solution to fully wet its inner wall and quickly transfer it to the oil-phase solution, so that the aqueous and oil-phase monomers polymerize on the inner wall of the membrane to form a crosslinked network, and finally take out the reacted membrane and treat it at a specific temperature for a period of time to enhance the stability of the crosslinked network and the separation performance; (3) Preparation of the photothermal layer: First, prepare a tannic acid (TA)-pyrrole (Py) solution, adjust the pH with Tris-HCl solution, and add an appropriate amount of ethanol to optimize the properties. Then, immerse the hollow fiber membrane filaments with both ends sealed in this solution to in-situ modify its outer surface. Next, prepare an FeCl3 solution, put the modified membrane into the mixed solution and perform ultrasonic treatment. Finally, soak the membrane filaments at an appropriate temperature for a period of time to allow Fe 3+ to fully react with tannic acid (TA)-pyrrole (Py) and adsorb on the outer surface of the membrane, realizing the blackening of the membrane body and photothermal conversion; (4) Insertion of the hydrophilic inner core: Remove the sealed part and insert the hydrophilic inner core to form a capillary driving structure.

2. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1 is characterized in that: The hollow fiber membrane constitutes a porous support layer with a three-dimensional through-hole structure, allowing seawater to freely transmit; the hydrophilic inner core forms a capillary driving force through the water absorption of the material; the crosslinked network is a selective salt-separating polymer network formed based on interfacial polymerization; the photothermal layer is a photothermal conjugated polymer network constructed through an in-situ oxidation reaction.

3. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1, characterized in that: In step (1), the material of the hollow fiber membrane is selected from one of polyethersulfone (PES), polyvinylidene fluoride (PVDF), polysulfone (PSF), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), and polybenzimidazole (PBI).

4. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1, characterized in that: In step (2), the hydrophilic inner core is selected from one of cotton thread, linen thread, bamboo fiber filament, seaweed fiber thread, and wood pulp composite fiber filament.

5. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1, characterized in that: In step (2), the interfacial polymerization process parameters are: the aqueous-phase monomer is one of piperazine (PIP), m-phenylenediamine (MPD), ethylenediamine (EDA), and hexamethylenediamine (HMD), and its concentration is 0.5 wt% - 2 wt%, the oil-phase monomer is trimesoyl chloride (TMC), and its concentration is 0.1 wt% - 0.3 wt%, the solvent is n-hexane; the coating time is 30 s - 60 s, the heat treatment temperature is 60 °C - 80 °C, and the time is 10 min - 30 min.

6. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1, characterized in that: In step (3), the ratio of the tannic acid (TA)-pyrrole (Py) solution is: the concentration of tannic acid (TA) is 0.5 wt% - 2 wt%, the concentration of pyrrole (Py) is 1 wt% - 3 wt%, the pH of the Tris-HCl solution is 8.0 - 9.0, and the volume ratio of ethanol is 40% - 60%.

7. The preparation method of a self-driven - salt separation - photothermal hollow fiber composite membrane according to claim 1, characterized in that: The Fe described in step (4) 3+ The oxidation conditions are as follows: the concentration of the FeCl3 solution is 0.1 wt% to 0.5 wt%, the tannic acid (TA)-pyrrole (Py) is mixed with the FeCl3 solution and ultrasonically treated for 15 min to 45 min, the soaking time of the membrane filaments is 2 h to 4 h, and the reaction temperature is 25 °C to 40 °C.

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