Preparation method and application of a coupled micro-nanofiber composite membrane distiller

Abstract

This invention discloses a method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, comprising the following steps: 1. Preparing a hydrophilic PSA / SiO2 fiber membrane substrate; 2. Preparing a hydrophilic-hydrophobic modified composite membrane; 3. Photothermal / magnetic thermal modification: (1) Dissolving PEO powder in a mixed solution of water and alcohol, stirring evenly to obtain a mixed solution for later use; (2) Adding Mxene and CNT to the mixed solution to obtain a photothermal modified solution; (3) Uniformly dispersing Fe3O4 in a PVA solution to obtain a magnetic thermal modified solution; (4) Using an electrostatic spraying process, applying the photothermal modified solution to the surface of the hydrophilic-hydrophobic modified composite membrane, and simultaneously spraying the magnetic thermal modified solution to form a photothermal / magnetic thermal modified mixed layer on the surface of the hydrophilic-hydrophobic modified composite membrane, thereby obtaining a coupled micro / nanofiber composite membrane distillation apparatus. This invention can effectively shorten the water vapor mass transfer path while improving the membrane's permeation flux, anti-wetting performance, and overall separation efficiency, thereby improving distillation efficiency.

Description

Technical Field

[0001] This invention belongs to the field of seawater desalination technology, and particularly relates to a method for preparing and applying a coupled micro / nanofiber composite membrane distillation apparatus. Background Technology

[0002] Abundant seawater is a reliable and sustainable source of freshwater. Membrane distillation (MD) technology is a non-isothermal membrane separation process driven by the vapor pressure gradient between the hot feed side and the cold permeate side. In MD, vapor molecules diffuse from the feed-side solution, pass through a porous hydrophobic membrane, and condense on the permeate side. Compared to other membrane separation processes, membrane distillation technology has become a widely adopted alternative solution for seawater desalination, brine and brackish water treatment, and high-salinity wastewater treatment due to its advantages such as high salt rejection rate, high filtration efficiency, and low membrane fouling. It is also an important method for addressing freshwater scarcity.

[0003] Currently, a typical membrane still typically consists of a photothermal layer and a hydrophobic layer. The photothermal layer absorbs light energy and converts it into heat energy, while the hydrophobic layer is used for water transport and structural support. Membrane distillation can only occur under light conditions, and the transport path is long. Examples include the following patented technologies:

[0004] CN120242769A discloses an optically transparent-light-confined composite nanofiber membrane, its preparation method, and its applications. The optically transparent-light-confined composite nanofiber membrane comprises a PDMS / PS / TPU nanofiber membrane and a photothermal conversion material layer loaded on the PDMS / PS / TPU nanofiber membrane. The PDMS / PS / TPU nanofiber membrane is prepared using PDMS, PS, and TPU as raw materials via electrospinning. The photothermal conversion material layer comprises honeycomb porous carbon nanofibers and PDA. This optically transparent-light-confined composite nanofiber membrane exhibits excellent light transmittance and hydrophobicity in the PDMS / PS / TPU nanofiber membrane, and excellent light absorption and high photothermal conversion capacity in the photothermal membrane distillation desalination application. The optically transparent-light-confined composite nanofiber membrane demonstrates high membrane flux and excellent stability in photothermal membrane distillation performance.

[0005] CN119588173A discloses a method for preparing a double-layer photothermal film distillation material, belonging to the field of membrane distillation technology. The double-layer membrane consists of a polyvinylidene fluoride (PVDF) superhydrophobic membrane as the hydrophobic base layer and a carbon nanotube / nano-semiconductor composite nanofilm as the photothermal layer, with the photothermal layer adhered to the hydrophobic base layer using polyurethane. Its features include: (1) preparation of the electrospun PVDF superhydrophobic membrane; and (2) preparation of the electrospun carbon nanotube / nano-semiconductor composite nanofilm. Simultaneously, a photothermal-driven membrane distillation device is provided. The double-layer photothermal film distillation material prepared using this invention exhibits good photothermal conversion capability, high water vapor flux, and long-term stability, showing broad application prospects in freshwater treatment.

[0006] Although electrospun nanofiber membranes possess high membrane flux, their relatively loose structure results in poor hydrophobicity, leading to a longer water vapor mass transfer path and impacting distillation efficiency. Conventional techniques typically employ hot-pressing post-treatment to balance the loose structure. While this method partially compensates for this deficiency, it sacrifices membrane flux, and the hot-pressed membrane remains susceptible to wetting and fouling during long-term operation. Furthermore, the relatively loose structure of electrospun nanofiber membranes results in poor mechanical properties, making it difficult to form a stable support structure and significantly reducing membrane lifespan. Existing membranes can only operate under sunlight; in cloudy or rainy weather, continuous operation is difficult. Therefore, how to effectively shorten the water vapor mass transfer path while improving membrane permeate flux, anti-wetting properties, and overall separation efficiency, thereby increasing distillation efficiency, and simultaneously maintaining excellent salt resistance, chemical stability, and mechanical tensile strength, while maintaining good stability over long-term operation, to achieve continuous all-weather membrane distillation, has become a pressing challenge for engineers in the seawater desalination field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the technical problem to be solved by this invention is to provide a method for preparing and applying a coupled micro / nanofiber composite membrane still that can effectively shorten the water vapor mass transfer path, improve the membrane's permeation flux, anti-wetting performance, and overall separation efficiency, increase distillation efficiency, and simultaneously maintain excellent mechanical properties, thereby enabling continuous operation of seawater desalination in all weather conditions.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a coupled micro / nanofiber composite membrane distillation device, comprising the following steps:

[0009] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0010] (1) Prepare a PSA solution spinning solution of a certain concentration, add a certain amount of SiO2 nanopowder to the PSA solution spinning solution, and use electrospinning technology to prepare PSA / SiO2 micro / nanofiber membrane under certain spinning conditions to obtain a PSA / SiO2 fiber membrane substrate with hydrophilicity.

[0011] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0012] (2) Prepare a PVDF-HFP solution spinning solution of a certain concentration; add a certain amount of SiO2 nanopowder to the PVDF-HFP solution spinning solution, and use electrospinning technology to cover the surface of the PSA / SiO2 fiber membrane substrate prepared in step (1) under certain spinning conditions to obtain a hydrophilic-hydrophobic modified composite membrane with a hydrophobic surface and a hydrophilic bottom layer.

[0013] III. Photothermal / magnetothermal modification:

[0014] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, stir evenly to obtain a mixed solution, and set aside for later use;

[0015] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain photothermal modified solution;

[0016] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution;

[0017] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using an airbrush during the electrostatic spraying process to form a photothermal / magnetothermal modification mixed layer on the surface of the hydrophilic-hydrophobic modified composite membrane, thus obtaining a coupled micro-nanofiber composite membrane distillation device.

[0018] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, the PSA concentration in the spinning solution of step (1) is 15%, the concentration of SiO2 nanopowder is 0.5-2wt%, and the SiO2 nanopowder is hydrophilic fumed nano silica with a molecular weight (MW) of 60.08.

[0019] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, in step (1), the spinning voltage is 22kV, the surface of the receiving roller is covered with silicone paper, the distance between the syringe and the receiving roller is 15cm, the solution propulsion speed is 0.25ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%.

[0020] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, the concentration of PVDF-HFP in the spinning solution of step (2) is 22%, the concentration of SiO2 nanopowder is 0.5-2wt%, the SiO2 nanopowder is hydrophobic silicon dioxide, and the molecular weight (MW) is 60.08.

[0021] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, in step (2), the spinning voltage is 17kV, the solution propulsion speed is 1ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%.

[0022] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, the concentration of PEO powder in the mixed solution of step (3) is 1-2 wt%, and the mass ratio of water to alcohol is 2:3.

[0023] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, the concentration of Mxene and CNT in the photothermal modification solution of step (4) is 0.25-1.5wt%, and the mass ratio of Mxene to CNT is 1:0.5-2.

[0024] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, the concentration of Fe3O4 in the magnetothermal modification solution in step (5) is 0.34-0.57wt%, and the solvent of the PVA solution is a mixture of water and alcohol with a mass ratio of water to alcohol of 2:3.

[0025] In the above-mentioned method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, in the photothermal / magnetothermal modified mixed layer formed in step (6), the volume ratio of the sprayed amount of the photothermal modified solution to the magnetothermal modified solution is 4-5:5.

[0026] The coupled micro / nanofiber composite membrane distiller prepared by the above method is applied in seawater desalination and high-salt wastewater treatment.

[0027] The advantages of the preparation method and application of the photothermal / magnetothermal coupling effect fiber aerogel of this invention are as follows: This invention prepares a membrane distillation system based on mass-producible electrostatic spinning technology, which has the advantages of simple process, strong controllability and uniform fiber structure. The fiber membrane has a bilayer asymmetry. The middle layer is a hydrophobic PVDF-HFP fiber membrane with abundant pore structure, which prevents liquid water from passing through, optimizes the mass transfer path of water vapor, and facilitates rapid water vapor permeation. The bottom layer of the fiber membrane is a hydrophilic PSA / PAN fiber membrane, which can promote the rapid diffusion of water molecules inside the membrane and significantly enhance the mechanical strength of the membrane. The resulting membrane material usually has high specific surface area, high porosity and good tunability, exhibiting excellent mass transfer performance and antifouling ability in membrane distillation. By introducing functional hydrophilic / hydrophobic nanoparticles SiO2 during the electrospinning process, not only can the mechanical properties and thermal stability of the membrane be enhanced, but its surface wettability can also be controlled. Doping with hydrophilic nanomaterial SiO2 enhances the hydrophilicity of the hydrophilic layer of the fiber membrane, promoting water vapor transport; while introducing hydrophobic SiO2 nanoparticles helps enhance liquid repulsion, thereby improving the anti-wetting performance and overall separation efficiency of the hydrophobic layer of the fiber membrane. During the spraying process, MXene and carbon nanotubes (CNTs) construct a continuous porous network structure on the surface of the PSA@SiO2 / PVDF-HFP@SiO2 nanofiber membrane, providing effective anchoring points for Fe3O4 nanoparticles. The abundant functional groups on the MXene surface can interact with Fe3O4 at the interface, while the bridging effect of CNTs helps improve the structural integrity of the photothermal / magnetothermal modified hybrid layer. Simultaneously, the introduction of trace amounts of PVA as a binder enhances the interfacial bonding between Fe3O4 and the MXene / CNT composite layer and the fiber substrate without significantly affecting the membrane pore structure. This allows the functional layer to be stably attached to the fiber membrane surface through physical intercalation and interfacial bridging, thereby improving its structural stability during membrane distillation. In addition, the fiber membrane exhibits excellent salt resistance, chemical stability, and mechanical tensile strength, and maintains good stability during long-term operation. It provides new solutions and strategies for developing efficient, stable, and all-weather membrane distillation technology, and has broad application prospects in water treatment fields such as seawater desalination and high-salt wastewater treatment. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating the preparation process of the coupled micro / nanofiber composite membrane distillation apparatus of the present invention;

[0029] Figure 2 This is a photograph of a coupled micro / nanofiber composite membrane distillation apparatus.

[0030] Figure 3 An overall structural rendering of a coupled micro / nanofiber composite membrane distillation unit;

[0031] Figure 4 This is a schematic diagram illustrating the working principle of the composite membrane still of the present invention used for seawater desalination;

[0032] Figure 5 This is a diagram illustrating the reaction mechanism of the distillation process in the composite membrane still of the present invention.

[0033] Figure 6 The image shows an electron microscope image of the surface morphology of the composite membrane still prepared in Example 3.

[0034] Figure 7 This is an electron microscope magnified image of the surface morphology of the composite membrane distillation apparatus prepared in Example 3;

[0035] Figure 8 The stress-strain curve of the composite membrane still prepared in Example 3 is shown.

[0036] Figure 9 The image shows the stretch-displacement curve of the composite membrane distillation apparatus prepared in Example 3.

[0037] Figure 10 This is a schematic diagram of the water contact angle of the composite membrane distiller prepared in Example 3;

[0038] Figure 11 This is a schematic diagram showing the permeate flux of the composite membrane distiller prepared in Example 3 under photoheating conditions.

[0039] Figure 12 This is a schematic diagram showing the permeation flux of the composite membrane distiller prepared in Example 3 under magnetic heating conditions.

[0040] Figure 13 Photothermal response test results of composite membrane distillers prepared under different MXene and CNT ratios. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] In this invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish an order. The term "multiple" means "two or more".

[0043] like Figure 1-3 As shown, a method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0044] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0045] (1) Prepare a PSA solution spinning solution of a certain concentration, add a certain amount of SiO2 nanopowder to the PSA solution spinning solution, and use electrospinning technology to prepare PSA / SiO2 micro / nanofiber membrane under certain spinning conditions to obtain a PSA / SiO2 fiber membrane substrate with hydrophilicity.

[0046] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0047] (2) Prepare a PVDF-HFP solution spinning solution of a certain concentration; add a certain amount of SiO2 nanopowder to the PVDF-HFP solution spinning solution, and use electrospinning technology to cover the surface of the PSA / SiO2 fiber membrane substrate prepared in step (1) under certain spinning conditions to obtain a hydrophilic-hydrophobic modified composite membrane with a hydrophobic surface and a hydrophilic bottom layer.

[0048] III. Photothermal / magnetothermal modification:

[0049] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, stir evenly to obtain a mixed solution, and set aside for later use;

[0050] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain photothermal modified solution;

[0051] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution;

[0052] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using an airbrush during the electrostatic spraying process to form a photothermal / magnetothermal modification mixed layer on the surface of the hydrophilic-hydrophobic modified composite membrane, thus obtaining a coupled micro-nanofiber composite membrane distillation device.

[0053] In the additives used in this invention, PSA is polysulfonamide, PVDF-HFP is polyvinylidene fluoride-hexafluoropropylene, PEO is polyethylene oxide, and CNT is carbon nanotubes. PSA can be replaced with PAN, and PVDF-HFP can be replaced with PTFE (polytetrafluoroethylene). In the hydrophilic-hydrophobic modified composite membrane prepared in step (2), the thickness of the PSA / SiO2 micro / nanofiber membrane as the bottom layer is approximately 200 micrometers, and the thickness of the PVDF-HFP / SiO2 micro / nanofiber membrane covering the surface of the PSA / SiO2 micro / nanofiber membrane is approximately 60 micrometers. The thickness of the two fiber membranes can be flexibly adjusted according to the actual needs of membrane distillation. The fiber diameter is 400-600 nm, and the pore size distribution of the PSA@SiO2 membrane is between 1.86-2.79 μm, with 2.30 μm being the dominant pore size, accounting for 95.13%. The pore size distribution of the PSA@SiO2 / PVDF-HFP@SiO2 composite membrane ranges from 1.56 to 2.11 μm, with a dominant pore size of 1.87 μm, accounting for 96.26%. The PPM membrane (coupled micro / nanofiber composite membrane distiller) prepared in Example 3 has a pore size distribution range of 1.12 to 2.03 μm, with 1.12 μm being the dominant pore size, accounting for 97.99%.

[0054] In step (1), the PSA solution spinning solution has a PSA concentration of 15% (mass fraction), a SiO2 nanoparticle concentration of 0.5-2wt%, and the SiO2 nanoparticles are hydrophilic fumed silica nanoparticles with a molecular weight (MW) of 60.08. In step (1), the spinning voltage is 22kV, the receiving roller is covered with silicone paper, the distance between the syringe and the receiving roller is 15cm, the solution propulsion speed is 0.25ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%. In step (2), the PVDF-HFP solution spinning solution has a PVDF-HFP concentration of 22%, a SiO2 nanoparticle concentration of 0.5-2wt%, and the SiO2 nanoparticles are hydrophobic silica with a molecular weight (MW) of 60.08. In step (2), the spinning voltage is 17kV, the solution propulsion speed is 1ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%. In the mixed solution of step (3), the concentration of PEO powder is 1-2 wt%, and the mass ratio of water to alcohol is 2:3. In the photothermal modification solution of step (4), the concentrations of Mxene and CNT are 0.25-1.5 wt%, and the mass ratio of Mxene to CNT is 1:0.5-2. In the magnetothermal modification solution of step (5), the concentration of Fe3O4 is 0.34-0.57 wt%, and the solvent of the PVA solution is a mixture of water and alcohol, with a mass ratio of water to alcohol of 2:3. In the photothermal / magnetothermal modified mixed layer formed in step (6), the volume ratio of the photothermal modification solution to the magnetothermal modification solution is 4-5:5.

[0055] This invention introduces hydrophilic / hydrophobic silica nanoparticles into electrospun fiber membranes, which can regulate the wetting properties of the membrane through surface energy differences and multi-scale structural effects. Hydrophilic SiO2 has high surface energy; its introduction onto the PSA fiber surface enhances the spreading ability of water molecules on the membrane surface and further amplifies hydrophilicity through nanoscale roughening. Hydrophobic SiO2, on the other hand, has low surface energy; constructing a micro-nano dual-scale structure on the PVDF-HFP fiber surface reduces the liquid-solid contact area, thereby significantly enhancing the membrane's hydrophobicity. This differential regulation strengthens the membrane's wettability gradient structure, which is beneficial for water vapor mass transfer and liquid phase permeation suppression during membrane distillation. Simultaneously, adding a certain proportion of alcohol to the photothermal and magnetothermal modification solutions allows for rapid solvent evaporation during spraying, enabling the photothermal / magnetothermal modified hybrid layer to solidify quickly, resulting in a more robust and compact porous network structure.

[0056] Compared to the layer-by-layer deposition immersion method, the electrostatic spraying of this invention can directionally deposit the MXene / CNT photothermal layer onto the surface of the hydrophobic PVDF-HFP@SiO2 membrane, achieving precise coverage of the functional layer, rather than uniform wetting inside or on both sides of the membrane. Simultaneously, the porous network structure formed during the spraying process tightly integrates with the fiber substrate, resulting in stronger adhesion of the photothermal layer and higher structural stability during water flow scouring and long-term membrane distillation operation. Compared to the photothermal and magnetocaloric functional layers constructed through layer-by-layer deposition, the photothermal / magnetothermal modified hybrid layer allows different components to be synergistically distributed within the same layer, avoiding additional heat transfer resistance from interlayer interfaces and facilitating a more uniform and stable membrane surface temperature field. Furthermore, the porous network constructed from the photothermal material serves as an effective loading framework for the magnetocaloric components, improving their adhesion to the fiber surface and thus helping to maintain the structural stability of the functional layer during water flow scouring and thermal cycling.

[0057] like Figure 4-5 As shown, when this composite membrane still is used for seawater desalination in a membrane distillation system, the photothermal material MXene / CNT absorbs photon energy under illumination, exciting its internal electrons to a high-energy state. This excitation energy is then converted into lattice heat through electron-phonon interactions, achieving highly efficient photothermal conversion. After the photothermal layer absorbs light energy, the membrane surface temperature rises, causing liquid water in the seawater to transform into water vapor, which can permeate the hydrophobic membrane. The liquid seawater is isolated on the hydrophobic layer side, and the hydrophobic layer, with a thickness of 60 micrometers, has a short mass transfer path, encouraging more water vapor to migrate from the hydrophobic layer to the hydrophilic layer. Upon entering the hydrophilic layer, the water vapor encounters condensate and transforms into liquid water. Because the hydrophilic layer is located in the liquid phase, the water vapor transport path remains minimal, resulting in high mass transfer efficiency.

[0058] This invention demonstrates the broad application prospects of this innovative, newly developed membrane distillation system, showcasing its all-weather, continuous, and highly efficient permeation capability. The composite nanofiber membrane, as a membrane distillation system, exhibits superior magnetothermal and photothermal responses to non-contact stimuli. It not only excels in photothermal membrane distillation performance but also possesses excellent magnetothermal membrane distillation performance. Furthermore, its bilayer asymmetric structure significantly shortens the mass transfer path, resulting in solar energy utilization efficiency far exceeding that of most previously reported solar-driven and Joule-driven heating evaporators. In addition, as an evaporator, this composite fiber membrane also exhibits outstanding salt resistance, high-temperature resistance, chemical stability, as well as good mechanical properties and long-term operational stability. These characteristics make it highly promising for high-performance water purification and seawater desalination. In summary, this innovation not only provides a highly efficient membrane distillation system but also opens up new avenues for the development of high-performance water purification and seawater desalination technologies, potentially leading to significant breakthroughs in related industries.

[0059] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0060] Example 1:

[0061] A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0062] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0063] (1) Prepare a PSA solution spinning solution with a concentration of 15%, add a certain amount of hydrophilic fumed nano silica to the PSA solution spinning solution to obtain a PSA solution spinning solution with a concentration of 0.5wt% hydrophilic fumed nano silica. Using electrospinning technology, PSA / SiO2 micro / nanofiber membranes are prepared under the spinning conditions of a spinning voltage of 22kV, a silicone paper covering the surface of the receiving roller, a distance of 15cm between the syringe and the receiving roller, a solution propulsion speed of 0.25ml / h, an ambient temperature of 23±3℃, and a humidity of 35±5%. A hydrophilic PSA / SiO2 fiber membrane substrate is obtained.

[0064] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0065] (2) Prepare a PVDF-HFP solution spinning solution with a concentration of 22%; add a certain amount of hydrophobic silica to the PVDF-HFP solution spinning solution to obtain a PVDF-HFP solution spinning solution with a hydrophobic silica concentration of 0.5wt%; use electrospinning technology, under the spinning conditions of spinning voltage of 17kV, solution propulsion speed of 1ml / h, ambient temperature of 23±3℃ and humidity of 35±5%, cover the surface of the prepared PVDF-HFP / SiO2 micro / nanofiber membrane with the surface layer hydrophobic and the bottom layer hydrophilic;

[0066] III. Photothermal / magnetothermal modification:

[0067] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, with a mass ratio of water to alcohol of 2:3, stir evenly to obtain a mixed solution with a PEO powder concentration of 1wt%, and set aside.

[0068] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain a photothermal modification solution with a concentration of 0.25wt% of Mxene and CNT, wherein the mass ratio of Mxene and CNT is 1:0.5;

[0069] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.34wt%. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3.

[0070] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using a spray gun during the electrostatic spraying process. The volume ratio of the photothermal modification solution to the magnetothermal modification solution is 4:5. A photothermal / magnetothermal modification mixed layer is formed on the surface of the hydrophilic-hydrophobic modified composite membrane, and a coupled micro-nanofiber composite membrane distillation device is obtained.

[0071] Example 2:

[0072] A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0073] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0074] (1) Prepare a PSA solution spinning solution with a concentration of 15%, add a certain amount of hydrophilic fumed nano silica to the PSA solution spinning solution to obtain a PSA solution spinning solution with a concentration of 0.5wt% hydrophilic fumed nano silica. Using electrospinning technology, PSA / SiO2 micro / nanofiber membranes are prepared under the spinning conditions of a spinning voltage of 22kV, a silicone paper covering the surface of the receiving roller, a distance of 15cm between the syringe and the receiving roller, a solution propulsion speed of 0.25ml / h, an ambient temperature of 23±3℃, and a humidity of 35±5%. A hydrophilic PSA / SiO2 fiber membrane substrate is obtained.

[0075] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0076] (2) Prepare a PVDF-HFP solution spinning solution with a concentration of 22%; add a certain amount of hydrophobic silica to the PVDF-HFP solution spinning solution to obtain a PVDF-HFP solution spinning solution with a hydrophobic silica concentration of 0.5wt%; use electrospinning technology, under the spinning conditions of spinning voltage of 17kV, solution propulsion speed of 1ml / h, ambient temperature of 23±3℃ and humidity of 35±5%, cover the surface of the prepared PVDF-HFP / SiO2 micro / nanofiber membrane with the surface layer hydrophobic and the bottom layer hydrophilic;

[0077] III. Photothermal / magnetothermal modification:

[0078] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, with a mass ratio of water to alcohol of 2:3, stir evenly to obtain a mixed solution with a PEO powder concentration of 1wt%, and set aside.

[0079] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain a photothermal modification solution with a concentration of 0.5wt% of Mxene and CNT, wherein the mass ratio of Mxene and CNT is 1:0.5;

[0080] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.34wt%. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3.

[0081] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using an airbrush during the electrostatic spraying process. The volume ratio of the photothermal modification solution to the magnetothermal modification solution is 5:5. A photothermal / magnetothermal modification mixed layer is formed on the surface of the hydrophilic-hydrophobic modified composite membrane, and a coupled micro-nanofiber composite membrane distillation device is obtained.

[0082] Example 3:

[0083] A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0084] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0085] (1) Prepare a PSA solution spinning solution with a concentration of 15%, add a certain amount of hydrophilic fumed nano silica to the PSA solution spinning solution to obtain a PSA solution spinning solution with a hydrophilic fumed nano silica concentration of 1wt%, and use electrospinning technology to prepare PSA / SiO2 micro / nanofiber membranes under the spinning conditions of a spinning voltage of 22kV, a silicone oil paper covering the surface of the receiving roller, a distance of 15cm between the syringe and the receiving roller, a solution propulsion speed of 0.25ml / h, an ambient temperature of 23±3℃, and a humidity of 35±5%, to obtain a hydrophilic PSA / SiO2 fiber membrane substrate;

[0086] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0087] (2) Prepare a PVDF-HFP solution spinning solution with a concentration of 22%; add a certain amount of hydrophobic silica to the PVDF-HFP solution spinning solution to obtain a PVDF-HFP solution spinning solution with a hydrophobic silica concentration of 1wt%; use electrospinning technology, under the spinning conditions of spinning voltage of 17kV, solution propulsion speed of 1ml / h, ambient temperature of 23±3℃ and humidity of 35±5%, cover the surface of the prepared PVDF-HFP / SiO2 micro / nanofiber membrane with the surface layer hydrophobic and the bottom layer hydrophilic;

[0088] III. Photothermal / magnetothermal modification:

[0089] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, with a mass ratio of water to alcohol of 2:3, stir evenly to obtain a mixed solution with a PEO powder concentration of 1.5wt%, and set aside for later use;

[0090] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain a photothermal modification solution with a concentration of 1wt% of Mxene and CNT, wherein the mass ratio of Mxene and CNT is 1:1;

[0091] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.46wt%. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3.

[0092] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using an airbrush during the electrostatic spraying process. The volume ratio of the photothermal modification solution to the magnetothermal modification solution is 5:5. A photothermal / magnetothermal modification mixed layer is formed on the surface of the hydrophilic-hydrophobic modified composite membrane, and a coupled micro-nanofiber composite membrane distillation device is obtained.

[0093] Example 4:

[0094] A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0095] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0096] (1) Prepare a PSA solution spinning solution with a concentration of 15%, add a certain amount of hydrophilic fumed nano silica to the PSA solution spinning solution to obtain a PSA solution spinning solution with a concentration of 1.5wt% hydrophilic fumed nano silica. Using electrospinning technology, PSA / SiO2 micro / nanofiber membranes are prepared under the spinning conditions of a spinning voltage of 22kV, a receiving roller surface covered with silicone paper, a distance of 15cm between the syringe and the receiving roller, a solution propulsion speed of 0.25ml / h, an ambient temperature of 23±3℃, and a humidity of 35±5%. A hydrophilic PSA / SiO2 fiber membrane substrate is obtained.

[0097] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0098] (2) Prepare a PVDF-HFP solution spinning solution with a concentration of 22%; add a certain amount of hydrophobic silica to the PVDF-HFP solution spinning solution to obtain a PVDF-HFP solution spinning solution with a hydrophobic silica concentration of 1.5wt%; use electrospinning technology, under the spinning conditions of spinning voltage of 17kV, solution feed speed of 1ml / h, ambient temperature of 23±3℃ and humidity of 35±5%, cover the surface of the prepared PVDF-HFP / SiO2 micro / nanofiber membrane with the surface layer hydrophobic and the bottom layer hydrophilic;

[0099] III. Photothermal / magnetothermal modification:

[0100] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, with a mass ratio of water to alcohol of 2:3, stir evenly to obtain a mixed solution with a PEO powder concentration of 2wt%, and set aside.

[0101] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain a photothermal modification solution with a concentration of 1.25wt% of Mxene and CNT, wherein the mass ratio of Mxene and CNT is 1:1.5;

[0102] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.46wt%. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3.

[0103] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using a spray gun during the electrostatic spraying process. The volume ratio of the photothermal modification solution to the magnetothermal modification solution is 4:5. A photothermal / magnetothermal modification mixed layer is formed on the surface of the hydrophilic-hydrophobic modified composite membrane, and a coupled micro-nanofiber composite membrane distillation device is obtained.

[0104] Example 5:

[0105] A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus includes the following steps:

[0106] I. Preparation of PSA / SiO2 fiber membrane substrate:

[0107] (1) Prepare a PSA solution spinning solution with a concentration of 15%, add a certain amount of hydrophilic fumed nano silica to the PSA solution spinning solution to obtain a PSA solution spinning solution with a concentration of 2wt% hydrophilic fumed nano silica, and use electrospinning technology to prepare PSA / SiO2 micro / nanofiber membranes under the spinning conditions of a spinning voltage of 22kV, a receiving roller surface covered with silicone paper, a distance of 15cm between the syringe and the receiving roller, a solution propulsion speed of 0.25ml / h, an ambient temperature of 23±3℃, and a humidity of 35±5%, to obtain a hydrophilic PSA / SiO2 fiber membrane substrate;

[0108] II. Preparation of hydrophilic-hydrophobic modified composite membranes:

[0109] (2) Prepare a PVDF-HFP solution spinning solution with a concentration of 22%; add a certain amount of hydrophobic silica to the PVDF-HFP solution spinning solution to obtain a PVDF-HFP solution spinning solution with a hydrophobic silica concentration of 2wt%; use electrospinning technology, under the spinning conditions of spinning voltage of 17kV, solution propulsion speed of 1ml / h, ambient temperature of 23±3℃ and humidity of 35±5%, cover the surface of the prepared PVDF-HFP / SiO2 micro / nanofiber membrane with the surface layer hydrophobic and the bottom layer hydrophilic;

[0110] III. Photothermal / magnetothermal modification:

[0111] (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, with a mass ratio of water to alcohol of 2:3, stir evenly to obtain a mixed solution with a PEO powder concentration of 2wt%, and set aside.

[0112] (4) Add Mxene and CNT to the mixed solution prepared in step (3) in a certain proportion, mix evenly, and obtain a photothermal modification solution with a concentration of 1.5wt% of Mxene and CNT, wherein the mass ratio of Mxene and CNT is 1:2;

[0113] (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.57wt%. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3.

[0114] (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using a spray gun during the electrostatic spraying process. The volume ratio of the photothermal modification solution to the magnetothermal modification solution is 4:5. A photothermal / magnetothermal modification mixed layer is formed on the surface of the hydrophilic-hydrophobic modified composite membrane, and a coupled micro-nanofiber composite membrane distillation device is obtained.

[0115] The performance test results of the coupled micro / nanofiber composite membrane distillation apparatus prepared by this invention are as follows:

[0116] 1. Surface morphology

[0117] like Figure 6 , 7 As shown, an electron microscope image and its magnified view of the surface morphology of a bilayer asymmetric fiber membrane are displayed. The addition of functional nanomaterials Fe3O4, MXene, and CNTs results in a distinct protruding structure on the surface of the electrospun fibers, indicating the successful construction of a multifunctional composite layer on the membrane surface. The photothermal materials MXene and CNTs absorb photon energy under illumination, exciting their internal electrons to a high-energy state. This excitation energy is then converted into lattice heat through electron-phonon interactions, achieving efficient photothermal conversion. Meanwhile, the magnetic material Fe3O4, when placed in an alternating magnetic field, exhibits a continuous change in its internal magnetic moment in response to the magnetic field changes, converting electromagnetic energy into heat energy and generating localized temperature rise. This photothermal / magnetocaloric coupling enables all-weather seawater desalination, solving the problem that conventional membrane stills cannot perform membrane distillation at night or under poor sunlight conditions.

[0118] By measuring the permeation flux of MXene / CNT at different concentrations, it was found that in the low concentration range, the permeation flux increased linearly with increasing concentration, reaching a peak of 1.49 kg m³ at 1 wt%. -2 h -1 When the concentration exceeds this critical value, the permeation flux shows a significant downward trend. This is because the formation of van der Waals forces-induced aggregates between MXene / CNT components at high concentrations, as well as the physical blockage of the intramembrane mass transfer channels due to excessive concentration, jointly lead to an increase in mass transfer resistance. Therefore, using 1 wt% yields the best results. At the same time, compared with the control group without illumination, the permeation flux is significantly increased, and the photothermal effect is realized.

[0119] With increasing Fe3O4 content, the surface temperature rises significantly, indicating its excellent magnetocaloric conversion capability, which can effectively drive the membrane distillation process. The permeation fluxes of PPM membranes (0.34 wt%), (0.46 wt%), and (0.57 wt%) under a magnetic field are 2.9, 3.49, and 3.85 kg m³, respectively. -2h -1 Taking into account both the magnetocaloric properties and the uniformity of Fe3O4 dispersion during the spraying process, PPM (0.46wt%) was selected as the representative material for testing.

[0120] 2. Mechanical properties.

[0121] like Figure 8 , 9 As shown in the figure, the tensile strength of the PPM membrane (coupled micro / nanofiber composite membrane distillation apparatus) prepared in Example 3 is 2.71-2.82 MPa, and the maximum bearing capacity is 9.73-11.13 N. The PVDF-HFP / SiO2 fiber membrane, serving as the intermediate layer, has a tensile strength of 1.88 MPa and a maximum bearing capacity of 3.38 N. This demonstrates that the tensile strength of the PPM membrane is 144%-150% higher than that of the PVDF-HFP / SiO2 fiber membrane, and the maximum bearing capacity is 288%-329% higher. Therefore, the hydrophilic PSA / SiO2 fiber membrane matrix, serving as the bottom layer in the composite membrane structure of this invention, provides ideal mechanical properties for the composite membrane distillation apparatus, ensuring stable and long-term membrane distillation operation.

[0122] 3. Permeation flux.

[0123] like Figure 10 As shown, the surface of the coupled micro / nanofiber composite membrane distiller is superhydrophobic, with a hydrophobic angle reaching 150°-154°. The hydrophobic SiO2 nanoparticles play a hydrophobic role in this invention, while simultaneously improving salt resistance. Due to the superhydrophobic effect, salt deposition on the fiber surface is reduced, thus imparting excellent salt resistance, high-temperature resistance, and chemical stability. Furthermore, the pore size distribution of the PPM membrane is between 1.12-2.03 μm, with 1.12 μm being the dominant pore size, accounting for 97.99%. This uniform pore size distribution of the fiber membrane enables efficient water-air transport, thereby facilitating effective seawater desalination. Figure 11 , 12 As shown, the photothermal permeation flux can reach 1.49 kgm³. -2 h -1 The magnetothermal permeation flux can reach 3.49 kgm³. -2 h -1 This demonstrates its high permeation flux. The specific working principle is as follows: Figure 4As shown, all-weather seawater desalination technology can continuously provide a stable supply of fresh water. The unique layered structure and hydrophilic PSA bottom fiber membrane can promote the rapid diffusion of water vapor inside the membrane, optimize the mass transfer path of water vapor, and have a high-efficiency water transport channel. The superhydrophobic surface layer has good anti-saltation performance. In addition, the highly efficient photothermal / magnetothermal modification layer makes it unrestricted by seasons, weather or climate conditions, which helps to ensure the sustainable use of water resources.

[0124] 4. Photothermal response effect

[0125] like Figure 13 As shown, when the CNT content is low (MXene:CNT=1:0.5), although the CNT dispersion is good, its quantity is insufficient to form a complete synergistic network, making it difficult to fully utilize the synergistic photothermal effect of MXene and CNT, with the highest temperature only reaching 58℃. When MXene:CNT=1:1, the sample has the fastest heating rate and the highest steady-state temperature, reaching approximately 63℃, indicating that it has the optimal photothermal conversion capability. At this point, an appropriate amount of CNT can be uniformly dispersed and inserted between MXene nanosheets, effectively suppressing MXene interlayer stacking while constructing a continuous light absorption and heat conduction network, which is beneficial for multiple light reflections and energy capture, and promotes rapid heat transfer to the film surface. When the CNT content is high (MXene:CNT=1:1.5 and 1:2), the limited amount of MXene is insufficient to effectively disperse the excessive CNTs, and CNTs are prone to agglomeration, thereby destroying the original layered structure and heat transfer channels, resulting in a decrease in light absorption efficiency and heat conduction capacity, with the highest temperatures dropping to 59℃ and 53℃, respectively. Therefore, considering light absorption capacity, structural stability, and heat transfer efficiency, MXene:CNT=1:1 is considered the optimal ratio for achieving synergistic effects and optimizing photothermal performance.

[0126] 5. Actual test results.

[0127] When there is sufficient sunlight on a sunny day, the bilayer asymmetric electrostatic nanofiber membrane (MXene and CNT concentrations of 1 wt%, Fe3O4 concentration of 0.46 wt%) prepared in Example 3 can be used in photothermal membrane distillation mode. The coupled photothermal effect of Fe3O4 and MXene gives it excellent photothermal membrane distillation performance, with a permeation flux of such as [missing value] under one day of sunlight. Figure 11 As shown.

[0128] When sunlight is insufficient on cloudy or rainy days, the bilayer asymmetric electrostatic nanofiber membrane (MXene and CNT concentrations of 1 wt%, Fe3O4 concentration of 0.46 wt%) prepared in Example 3 can be processed using either a magnetothermal membrane distillation mode or a photothermal membrane distillation coupled with a magnetothermal membrane distillation mode. In the magnetothermal membrane distillation mode, Fe3O4 imparts excellent magnetothermal membrane distillation performance, with a magnetic field strength of 18.75 kA / m and a permeation flux as shown in the figure. Figure 12 As shown, in the photothermal film distillation coupled with magnetothermal film distillation mode, the MXene photothermal effect coupled with the Fe3O4 magnetothermal effect gives it excellent permeation flux, which remains stable at approximately 3.49 kg·m³. -2 h -1 .

[0129] This invention relates to the preparation of bilayer asymmetric electrostatic nanocomposite fiber membranes by mass-producible electrospinning, and their application in a photo / magnetocalorically driven membrane distillation system. Figure 3 The structure of the electrostatic nanofiber membrane prepared by this invention is shown, indicating that by adding the photothermal material MXene and the magnetothermal material Fe3O4 to the surface, a highly efficient photothermal / magnetothermal layer can be formed, thereby enabling effective seawater desalination. Magnetothermal seawater desalination mainly involves successfully modifying the surface magnetothermally with Fe3O4, followed by magnetic heating of the surface magnetic particles under the action of an external magnetic field (current range 150A-350A, magnetic field strength range 13.75-24.75kA / m; good magnetic heating performance and energy saving; when the current > 350A and the magnetic field strength > 24.75kA / m, the magnetic heating performance hardly increases and energy consumption is high). This solves the problem that conventional membrane distillation cannot be performed at night or when sunlight is insufficient. Photothermal seawater desalination works similarly; the surface material contains MXene, a material with strong solar absorption, which can effectively absorb sunlight to generate heat for seawater desalination. Figure 3 The study also showcased a bilayer asymmetric structure of the fiber membrane. The middle layer is a hydrophobic PVDF-HFP fiber membrane with abundant pores and a thickness of approximately 60 micrometers. This short mass transfer path optimizes the mass transfer path of water molecules, facilitating rapid water vapor permeation while exhibiting excellent anti-saltation properties. The bottom layer is a hydrophilic PSA fiber membrane, which promotes rapid diffusion of water molecules within the membrane. This membrane has a thickness of approximately 200 micrometers and provides efficient water transport channels while enhancing the membrane's mechanical properties.

[0130] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A method for preparing a coupled micro / nanofiber composite membrane distillation apparatus, characterized in that, Includes the following steps: I. Preparation of PSA / SiO2 fiber membrane substrate: (1) Prepare a PSA solution spinning solution of a certain concentration, add a certain amount of SiO2 nanoparticles to the PSA solution spinning solution, and use electrospinning technology to prepare PSA / SiO2 micro / nanofiber membranes under certain spinning conditions to obtain a hydrophilic PSA / SiO2 fiber membrane substrate. II. Preparation of hydrophilic-hydrophobic modified composite membranes: (2) Prepare a PVDF-HFP solution spinning solution of a certain concentration; add a certain amount of SiO2 nanopowder to the PVDF-HFP solution spinning solution, and use electrospinning technology to cover the surface of the PSA / SiO2 fiber membrane substrate prepared in step (1) under certain spinning conditions to obtain a hydrophilic-hydrophobic modified composite membrane with a hydrophobic surface and a hydrophilic bottom layer. III. Photothermal / magnetothermal modification: (3) Dissolve a certain amount of PEO powder in a mixed solution of water and alcohol, stir evenly to obtain a mixed solution, and set aside for later use; (4) Add Mxene and CNT to the mixed solution prepared in step (3) at a mass ratio of 1:1, mix evenly, and obtain a photothermal modification solution with a concentration of Mxene and CNT of 0.25-1.5wt%; (5) A certain amount of Fe3O4 is uniformly dispersed in a PVA solution. The solvent of the PVA solution is a mixture of water and alcohol, and the mass ratio of water to alcohol is 2:3, so as to obtain a magnetothermal modified solution with a Fe3O4 concentration of 0.34-0.57wt%. (6) The photothermal modification solution obtained in step (4) is uniformly sprayed onto the surface of the hydrophilic-hydrophobic modified composite membrane obtained in step (2), i.e. the surface of the PVDF-HFP / SiO2 micro-nanofiber membrane, using an electrostatic spraying process. At the same time, the magnetothermal modification solution obtained in step (5) is sprayed simultaneously using a spray gun during the electrostatic spraying process to form a photothermal / magnetothermal modification mixed layer on the surface of the hydrophilic-hydrophobic modified composite membrane, thus obtaining a coupled micro-nanofiber composite membrane distillation device.

2. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In the PSA solution spinning solution of step (1), the concentration of PSA is 15%, the concentration of SiO2 nanoparticles is 0.5-2wt%, and the SiO2 nanoparticles are hydrophilic fumed nano-silica with a molecular weight of 60.08 (MW).

3. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In step (1), the spinning voltage is 22kV, the surface of the receiving roller is covered with silicone paper, the distance between the syringe and the receiving roller is 15cm, the solution propulsion speed is 0.25ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%.

4. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In the PVDF-HFP solution spinning solution of step (2), the concentration of PVDF-HFP is 22%, the concentration of SiO2 nanoparticles is 0.5-2wt%, and the SiO2 nanoparticles are hydrophobic silicon dioxide with a molecular weight of 60.08 (MW).

5. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In step (2), the spinning voltage is 17kV, the solution propulsion speed is 1ml / h, the ambient temperature is 23±3℃, and the humidity is 35±5%.

6. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In the mixed solution of step (3), the concentration of PEO powder is 1-2 wt%, and the mass ratio of water to alcohol is 2:

3.

7. The method for preparing the coupled micro / nanofiber composite membrane distillation apparatus according to claim 1, characterized in that: In the photothermal / magnetothermal modified hybrid layer formed in step (6), the volume ratio of the photothermal modified solution to the magnetothermal modified solution is 4-5:

5.

8. The application of the coupled micro / nanofiber composite membrane distiller prepared by the preparation method according to any one of claims 1-7 in seawater desalination or high-salt wastewater treatment.

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