A method for preparing a janus membrane from polyvinylidene fluoride in a fluorine-containing backsheet, a janus membrane and uses thereof

Abstract

This invention relates to a method for preparing Janus membranes from recycled polyvinylidene fluoride (PVDF) backsheets, the Janus membranes themselves, and their applications. The method includes the following steps: (1) immersing the fluorinated backsheet in an organic solvent, followed by solid-liquid separation to obtain a casting solution; (2) preparing a wet membrane using the casting solution obtained in step (1), immersing the wet membrane in a coagulation bath, and obtaining a Janus membrane through a non-solvent-induced phase separation method. The method provided by this invention enables the preparation of high-value-added, low-cost Janus membranes from waste fluorinated backsheets. These Janus membranes possess hydrophobic / hydrophilic bifacial asymmetric wettability and high water flux, showing broad application prospects in the field of water treatment.

Description

Technical Field

[0001] This invention relates to the field of resource utilization technology for retired photovoltaic modules, specifically to a method for preparing Janus film by recovering polyvinylidene fluoride from fluorinated backsheets, the Janus film and its uses. Background Technology

[0002] The backsheets of crystalline silicon photovoltaic modules are mostly made of fluorinated polymer materials, which possess insulation, water-blocking, and aging-resistant properties to protect and support the cells. KPK (PVDF / PET / PVDF) type backsheets are among the most widely used. Currently, the main disposal methods for waste photovoltaic module fluorinated backsheets include crushing and landfilling, and incineration. However, landfilling causes soil compaction and damages the ecological environment, while incineration produces large amounts of toxic gases, causing air pollution. Therefore, developing recycling and disposal processes for fluorinated backsheets to achieve the recycling and utilization of fluorinated materials is currently a research hotspot.

[0003] CN115338225A discloses a harmless treatment device for fluorine-containing backsheets of waste photovoltaic modules, including a dissolving tank, a crushing box located on one side of the dissolving tank, a mixer and a hot press. The device uses an alkaline alcohol solution to dissolve the PET layer and the fluorine film, and then processes the PET layer and the fluorine film separately, but does not mention the subsequent treatment methods for the PET layer and the fluorine film.

[0004] CN111958352A discloses a photovoltaic module backsheet recycling system, including a feeding mechanism, a grinding mechanism above the feeding mechanism, a cleaning mechanism, and a collection mechanism. The feeding mechanism carries and transports the photovoltaic module in a predetermined direction. The grinding mechanism grinds the backsheet of the photovoltaic module (after the frame has been removed) into powder. The cleaning mechanism cleans the ground parts of the photovoltaic module during the grinding process. The collection mechanism collects the powder and cleaning fluid generated during the grinding of the backsheet. This recycling system only removes the backsheet, which is then landfilled or used as a filler for other materials; it cannot recycle the backsheet as a resource.

[0005] CN109550770A discloses a method and apparatus for the harmless treatment of waste photovoltaic backsheets. This method uses a heating table to soften the fluorinated layer and resin backsheet adhesive of the backsheet, then separates the fluorinated layer and PET layer by manual scraping or milling, and finally processes the fluorinated layer into a fluorinated coating. While this method enables the reuse of the fluorinated layer, its added value is low.

[0006] In nature, lotus leaves, in addition to their superhydrophobic properties—the "lotus effect"—exhibit a unique wetting characteristic known as "Janus," where the surface is superhydrophobic and the bottom hydrophilic. Based on biomimetic strategies, researchers have constructed Janus membrane surfaces with significantly different wetting properties. Currently, Janus membranes are widely used in seawater desalination and oil-water separation. In seawater desalination, Janus membranes are gradually replacing traditional reverse osmosis membranes, offering better separation efficiency and lower operating costs. In oil-water separation, Janus membranes can separate two liquids, reducing environmental pollution. Therefore, if the fluorinated backsheets of waste photovoltaic modules can be harmlessly treated and used as raw materials to prepare high-value-added Janus membranes, it will be of great significance for fluorine resource recovery and environmental protection. Summary of the Invention

[0007] To address the above problems, the present invention aims to provide a method for preparing Janus membranes by recovering polyvinylidene fluoride from fluorinated backsheets, the Janus membranes themselves, and their applications. Compared with the prior art, the method provided by the present invention can prepare high-value-added, low-cost Janus membranes from waste fluorinated backsheets. The Janus membranes have hydrophobic / hydrophilic bifacial asymmetric wettability and high water flux, and have broad application prospects in the field of water treatment.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet, the method comprising the following steps:

[0010] (1) Immerse the fluorine-containing backplate in an organic solvent, and then separate the solid and liquid to obtain the casting solution;

[0011] (2) A wet membrane is prepared using the casting solution obtained in step (1), and the wet membrane is immersed in a coagulation bath to obtain a Janus membrane by a non-solvent phase separation method.

[0012] In this invention, a fluorinated backsheet is first immersed in an organic solvent. During the immersion process, substances such as PVDF (polyvinylidene fluoride), TiO2 (titanium dioxide), and PMMA (polymethyl methacrylate) contained in the fluorinated backsheet enter the casting solution. Then, a wet film is prepared from the casting solution and subjected to a coagulation bath. During the dynamic separation process, the hydrophobic groups contained in PVDF spontaneously migrate to the bottom layer, while the hydrophilic groups contained in TiO2 and PMMA spontaneously migrate to the surface layer, thereby obtaining a Janus film with asymmetric properties on both sides.

[0013] In this invention, the solid-liquid separation method can be a common method in the art, such as filtration or centrifugation.

[0014] Preferably, the fluorinated backsheet in step (1) includes any one of the KPK type backsheet, KPE type backsheet, or KPC type backsheet.

[0015] Preferably, the fluorine-containing backsheet in step (1) is pretreated.

[0016] Preferably, the pretreatment includes: sequentially cleaning and drying the fluorinated backsheet.

[0017] Preferably, the cleaning solution used includes water and / or ethanol.

[0018] In this invention, the pretreatment process may be, for example, wiping the surface of the fluorine-containing backsheet with ethanol, rinsing off surface impurities with pure water, and then drying.

[0019] Preferably, the organic solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide.

[0020] Preferably, the mass ratio of the fluorinated backsheet to the organic solvent is 1:(0.2-0.8), for example, it can be 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7 or 1:0.8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Preferably, the mass concentration of polyvinylidene fluoride in the casting solution is 10-25%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] In this invention, it is preferable to control the concentration of the casting solution within a specific range. On the one hand, this avoids excessively low viscosity leading to excessive fluidity and difficulty in film formation; on the other hand, it avoids excessively high concentration leading to poor fluidity and increased difficulty in pouring the casting solution. Ultimately, this ensures the obtaining of a Janus membrane with asymmetric wettability on both sides and excellent pore structure on the hydrophobic surface.

[0023] Preferably, the immersion time in step (1) is 0.5-6 hours, for example, it can be 0.5 hours, 0.6 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, 5.2 hours, 5.5 hours, 5.8 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, the immersion temperature is 15-35℃, for example, it can be 15℃, 17℃, 19℃, 21℃, 23℃, 25℃, 27℃, 29℃, 31℃, 33℃ or 35℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0025] Preferably, the method for preparing the wet film in step (2) includes: pouring the casting liquid onto a glass plate and then scraping it flat with a scraper to obtain a wet film.

[0026] Preferably, the thickness of the wet film is 150-350 μm, for example, it can be 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, 220 μm, 240 μm, 260 μm, 280 μm, 300 μm, 320 μm, 340 μm or 350 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0027] Preferably, the wet film and the glass plate supporting the wet film are immersed together in a coagulation bath.

[0028] Preferably, the temperature of the coagulation bath in step (2) is 10-60℃, for example, it can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the immersion time in the coagulation bath is 5-30 minutes, for example, it can be 5 minutes, 6 minutes, 8 minutes, 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes, 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes or 30 minutes, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0030] Preferably, the coagulation bath comprises a graphene oxide solution.

[0031] Preferably, the concentration of the graphene oxide solution is 0.1-5 mg / g, for example, it can be 0.1 mg / g, 0.2 mg / g, 0.4 mg / g, 0.5 mg / g, 0.6 mg / g, 0.8 mg / g, 1 mg / g, 1.2 mg / g, 1.5 mg / g, 1.8 mg / g, 2 mg / g, 2.2 mg / g, 2.5 mg / g, 2.8 mg / g, 3 mg / g, 3.2 mg / g, 3.5 mg / g, 3.8 mg / g, 4 mg / g, 4.2 mg / g, 4.5 mg / g, 4.8 mg / g or 5 mg / g, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0032] In this invention, the coagulation bath preferably uses a graphene oxide solution and the concentration of the graphene oxide solution is preferably controlled within a specific range. This allows the layered structure of graphene oxide to be used to adjust the pore structure of the hydrophobic surface, thereby further increasing the pore size and porosity, which is beneficial for improving the pure water flux.

[0033] Preferably, the method further includes step (3): extracting the organic solvent in the coagulation bath after the Janus membrane is prepared.

[0034] Preferably, the extractant used in the extraction includes a chlorine-containing compound extractant.

[0035] Preferably, the extractant comprises dichloromethane and / or trichloromethane.

[0036] In this invention, by preferably extracting the organic solvent in the coagulation bath, the organic solvent can be recycled, thereby further reducing the preparation cost of Janus membrane. Furthermore, Janus membrane has high added value. Therefore, the method provided by this invention is economical and industrially feasible.

[0037] In a second aspect, the present invention provides a Janus membrane, which is obtained by the method for preparing a Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet as described in the first aspect of the present invention.

[0038] The Janus membrane is hydrophilic on one side and hydrophobic on the other side.

[0039] Preferably, the hydrophobic surface of the Janus membrane has a porous structure.

[0040] The Janus membrane provided by this invention has asymmetric wettability on both sides and a regular porous structure on the hydrophobic surface, with a high average pore size and porosity, which is beneficial for improving the pure water flux.

[0041] Preferably, the average pore size of the hydrophobic surface of the Janus membrane is 0.5-2 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Preferably, the porosity of the hydrophobic surface of the Janus membrane is 20-35%, for example, it can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34% or 35%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Thirdly, the present invention provides an application of the Janus membrane as described in the second aspect of the present invention, wherein the Janus membrane is used in the field of water treatment.

[0044] The Janus membrane provided by this invention has asymmetric wettability on both sides and an excellent pore structure with hydrophobic surfaces. The asymmetric wettability on both sides can simultaneously meet the requirements of two contradictory properties in a certain application, while the excellent pore structure can improve flux. It has broad application prospects in water treatment fields such as high-efficiency oil-water separation and seawater desalination.

[0045] As a preferred embodiment of the first aspect of the present invention, the method includes the following steps:

[0046] (1) The fluorinated backsheet is cleaned with water and / or ethanol, then dried, and then immersed in an organic solvent at a temperature of 10-40℃ for 0.5-6h. The fluorinated backsheet includes any one of KPK type backsheet, KPE type backsheet or KPC type backsheet. The organic solvent includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide. The mass ratio of the fluorinated backsheet to the organic solvent is 1:(0.2-0.8). Then, solid-liquid separation is performed to obtain a casting solution. The mass concentration of polyvinylidene fluoride in the casting solution is 10-25%.

[0047] (2) Pour the casting solution obtained in step (1) onto a glass plate, and then scrape it flat with a scraper to obtain a wet film with a thickness of 150-350 μm. Then immerse the wet film and the glass plate supporting the wet film together in a coagulation bath for 5-30 min. The temperature of the coagulation bath is 10-60 °C. The coagulation bath includes a graphene oxide solution with a concentration of 0.1-5 mg / g. Janus membrane is prepared by a non-solvent phase separation method.

[0048] (3) The organic solvent in the coagulation bath after the Janus membrane is prepared is extracted with dichloromethane and / or trichloromethane as extractants to obtain the extract phase with recovered organic solvent.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The method provided by the present invention uses fluorine-containing backsheets from waste photovoltaic modules as raw materials to prepare Janus film, thereby realizing the harmless treatment of fluorine-containing backsheets and the high-value-added resource utilization.

[0051] (2) The method provided by the present invention can achieve hydrophilicity and hydrophobicity control of the membrane in one step, so that one side of the Janus membrane is hydrophilic and the other side is hydrophobic, reducing the additional modification process, reducing the preparation cost of the Janus membrane, and the Janus membrane has high added value, thus improving economic efficiency and industrial feasibility.

[0052] (3) The method provided by the present invention uses graphene oxide solution as a coagulation bath, which can adjust the pore structure of the hydrophobic surface of Janus membrane by utilizing the sheet structure of graphene oxide, increase the average pore size and porosity, and improve the pure water flux, and has broad application prospects in the field of water treatment.

[0053] (4) The Janus membrane obtained by this invention has a pure water contact angle of less than 89.09° on its hydrophilic side and a pure water contact angle of more than 105.41° on its hydrophobic side. The average pore size is greater than 0.67 ± 0.30 μm, the porosity is greater than 7.05%, and the final pure water flux is 10⁶ L / (m²). 2 ·h) or above, under optimal conditions it can reach 210L / (m 2 (h) and above. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating the method described in Embodiment 1 of the present invention;

[0055] Figure 2 The diagram shows the pure water contact angle results of the Janus membranes obtained in Examples 1, 2, 9 and Comparative Example 1 of this invention;

[0056] Figure 3 SEM images of the hydrophilic and hydrophobic surfaces of the Janus membrane obtained in Example 1 of this invention;

[0057] Figure 4 SEM images of the hydrophilic and hydrophobic surfaces of the Janus membrane obtained in Example 2 of this invention;

[0058] Figure 5 SEM images of the hydrophilic and hydrophobic surfaces of the Janus membrane obtained in Example 9 of this invention;

[0059] Figure 6 This is a SEM image of the hydrophilic and hydrophobic surfaces of the Janus membrane obtained in Comparative Example 1 of this invention. Detailed Implementation

[0060] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0061] Example 1

[0062] This embodiment provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet, such as... Figure 1 As shown, the method includes the following steps:

[0063] (1) The retired photovoltaic modules were disassembled to obtain a fluorinated backsheet (KPK type backsheet, model BEF-302, manufacturer: Hangzhou Foster Applied Materials Co., Ltd.). The surface was first wiped with alcohol, then rinsed with water to remove impurities and dried. Then, it was immersed in N,N-dimethylacetamide at a temperature of 25°C for 2 hours. The mass ratio of the fluorinated backsheet to N,N-dimethylacetamide was 1:0.45. Then, it was filtered to obtain a casting solution. The mass concentration of polyvinylidene fluoride in the casting solution was 15%.

[0064] (2) Pour 5 mL of the casting solution obtained in step (1) onto a glass plate, and then scrape it flat with a scraper of a coating machine to obtain a wet film with a thickness of 250 μm. Then immerse the wet film and the glass plate supporting the wet film together in a 0.5 mg / g graphene oxide solution coagulation bath for 5 min. The temperature of the coagulation bath is 25 °C. Janus membrane is prepared by non-solvent phase separation method. The Janus membrane is then soaked in deionized water to remove residual organic solvent.

[0065] (3) The organic solvent in the coagulation bath after the Janus membrane was prepared was extracted with dichloromethane extractant to obtain the extract phase with recovered organic solvent.

[0066] Example 2

[0067] This embodiment provides a method for recovering polyvinylidene fluoride from a fluorinated backsheet to prepare a Janus membrane, the method comprising the following steps:

[0068] (1) The retired photovoltaic modules were disassembled to obtain a fluorinated backsheet (KPK type backsheet, model BEF-302, manufacturer: Hangzhou Foster Applied Materials Co., Ltd.). The surface was first wiped with alcohol, then rinsed with water to remove impurities and dried. Then, it was immersed in N,N-dimethylacetamide at a temperature of 25°C for 2 hours. The mass ratio of the fluorinated backsheet to N,N-dimethylacetamide was 1:0.45. Then, it was filtered to obtain a casting solution. The mass concentration of polyvinylidene fluoride in the casting solution was 15%.

[0069] (2) Pour 5 mL of the casting solution obtained in step (1) onto a glass plate, and then scrape it flat with a scraper of a coating machine to obtain a wet film with a thickness of 250 μm. Then immerse the wet film and the glass plate supporting the wet film together in a 5 mg / g graphene oxide solution coagulation bath for 5 min. The temperature of the coagulation bath is 25 °C. Janus membrane is prepared by non-solvent phase separation method. The Janus membrane is then soaked in deionized water to remove residual organic solvent.

[0070] (3) The organic solvent in the coagulation bath after the Janus membrane was prepared was extracted with dichloromethane extractant to obtain the extract phase with recovered organic solvent.

[0071] Example 3

[0072] This embodiment provides a method for recovering polyvinylidene fluoride from a fluorinated backsheet to prepare a Janus membrane, the method comprising the following steps:

[0073] (1) Disassemble the retired photovoltaic modules to obtain a fluorinated backsheet (KPK type backsheet, model BEF-302, manufacturer: Hangzhou Foster Applied Materials Co., Ltd.). First, wipe the surface with alcohol, then rinse the surface impurities with water and dry it. Then, immerse it in N-methylpyrrolidone at a temperature of 15°C for 0.5h. The mass ratio of the fluorinated backsheet to N-methylpyrrolidone is 1:0.3. Then filter to obtain a casting solution. The mass concentration of polyvinylidene fluoride in the casting solution is 21%.

[0074] (2) Pour 5 mL of the casting solution obtained in step (1) onto a glass plate, and then scrape it flat with a scraper of a coating machine to obtain a wet film with a thickness of 150 μm. Then immerse the wet film and the glass plate supporting the wet film together in a 0.1 mg / g graphene oxide solution coagulation bath for 30 min. The temperature of the coagulation bath is 10 °C. Janus membrane is prepared by non-solvent phase separation method. The Janus membrane is then soaked in deionized water to remove residual organic solvent.

[0075] (3) The organic solvent in the coagulation bath after the Janus membrane was prepared was extracted with dichloromethane extractant to obtain the extract phase with recovered organic solvent.

[0076] Example 4

[0077] This embodiment provides a method for recovering polyvinylidene fluoride from a fluorinated backsheet to prepare a Janus membrane, the method comprising the following steps:

[0078] (1) Disassemble retired photovoltaic modules to obtain fluorinated backsheets (KPK type backsheet, model BEF-302, manufacturer: Hangzhou Foster Applied Materials Co., Ltd.). First, wipe the surface with alcohol, then rinse the surface impurities with water and dry it. Then, immerse it in N,N-dimethylformamide at a temperature of 35°C for 6 hours. The mass ratio of the fluorinated backsheet to N,N-dimethylformamide is 1:0.7. Then filter to obtain casting solution. The mass concentration of polyvinylidene fluoride in the casting solution is 10%.

[0079] (2) Pour 5 mL of the casting solution obtained in step (1) onto a glass plate, and then scrape it flat with a scraper of a coating machine to obtain a wet film with a thickness of 350 μm. Then immerse the wet film and the glass plate supporting the wet film together in a 5 mg / g graphene oxide solution coagulation bath for 5 min. The temperature of the coagulation bath is 40 °C. Janus membrane is prepared by non-solvent phase separation method. The Janus membrane is then soaked in deionized water to remove residual organic solvent.

[0080] (3) The organic solvent in the coagulation bath after the Janus membrane was prepared was extracted with chloroform extractant to obtain the extract phase with recovered organic solvent.

[0081] Example 5

[0082] This embodiment provides a method for recovering polyvinylidene fluoride from a fluorinated backsheet to prepare a Janus membrane. The only difference from Example 1 is that the mass concentration of polyvinylidene fluoride in the casting solution is 5%.

[0083] Example 6

[0084] This embodiment provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet. The only difference from Example 1 is that the mass concentration of polyvinylidene fluoride in the casting solution is 30%.

[0085] Example 7

[0086] This embodiment provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet. The only difference from Example 1 is that the concentration of the graphene oxide solution is 0.05 mg / g.

[0087] Example 8

[0088] This embodiment provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet. The only difference from Example 1 is that the concentration of the graphene oxide solution is 8 mg / g.

[0089] Example 9

[0090] This embodiment provides a method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet. The only difference from Example 1 is that the coagulation bath is water.

[0091] Comparative Example 1

[0092] This comparative example provides a method for preparing Janus membranes. The only difference from Example 1 is that in step (1), the waste fluorinated backsheet is replaced with commercial PVDF (molecular weight of 600,000). That is, step (1) is replaced by: adding PVDF into a beaker containing N,N-dimethylacetamide solution, stirring in a water bath at 70°C for 6 hours, and allowing it to stand and cool to obtain a casting solution. The mass concentration of polyvinylidene fluoride in the casting solution is 15%.

[0093] Taking Examples 1, 2, 9 and Comparative Example 1 as examples, the SEM images of the hydrophilic and hydrophobic surfaces of the obtained Janus membranes are as follows: Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, from Figure 3 and Figure 4 It can be seen that the hydrophobic surfaces of the Janus membranes obtained in Examples 1-2 have a relatively regular pore structure with uniform pore size; from Figure 5-6 It can be seen that the pore size of the hydrophobic surface of the Janus membranes obtained in Example 9 and Comparative Example 1 is uneven and the pore diameter is small.

[0094] The pure water contact angles on both sides of the Janus membranes obtained in Examples 1-9 and Comparative Example 1 were measured using a contact angle meter. The results are shown in Table 1. Taking Examples 1, 2, 9 and Comparative Example 1 as examples, the pure water contact angle results are shown in the figure below. Figure 2 As shown, from Figure 2 As can be seen from the results, the front side of the obtained Janus membrane is hydrophilic, with a pure water contact angle of <90°, while the back side is hydrophobic, with a pure water contact angle of >90°.

[0095] The average pore size and porosity of the hydrophobic surfaces of the Janus membranes obtained in Examples 1-9 and Comparative Example 1 were detected using scanning electron microscopy (SEM) and ImageJ software. The results are shown in Table 1.

[0096] The pure water flux of the Janus membranes obtained in Examples 1-9 and Comparative Example 1 at 0.01 MPa was measured using a filtration device. That is, the volume of water passing through a unit membrane area per unit time under unit pressure. The results are shown in Table 1.

[0097] Table 1

[0098]

[0099] The following points can be observed from Table 1:

[0100] (1) As can be seen from the data in Examples 1-9, the method provided by the present invention can prepare a Janus membrane with asymmetric wetting on both sides by using a fluorine-containing backsheet from a waste photovoltaic module. The pure water contact angle of the hydrophilic side can reach below 89.09°, the pure water contact angle of the hydrophobic side can reach above 105.41°, the average pore size can reach above 0.67±0.30μm, the porosity can reach above 7.05%, and the final pure water flux can reach 106L / (m²). 2 ·h) or above, under optimal conditions it can reach 210L / (m 2 (h) and above.

[0101] (2) A comprehensive comparison of the data from Examples 1 and 5-6 shows that the porosity of the hydrophobic surface in Example 1 is higher and the pure water flux is significantly higher than that in Examples 5-6. Therefore, it can be seen that by optimizing the mass concentration of polyvinylidene fluoride in the casting solution, the present invention can control the fluidity of the casting solution, further improve the porosity of the hydrophobic surface and increase the pure water flux.

[0102] (3) A comprehensive comparison of the data from Example 1 and Examples 7-8 shows that the porosity of the hydrophobic surface in Example 1 is higher and the pure water flux is significantly higher than that in Examples 7-8. It can be seen that by optimizing the concentration of the graphene oxide solution, the present invention can further regulate the pore structure of the hydrophobic surface, thereby improving the porosity of the hydrophobic surface and increasing the pure water flux.

[0103] (4) A comprehensive comparison of the data from Example 1 and Example 9 shows that the Janus membrane obtained in Example 1 has a greater difference in asymmetric wettability on both sides, a higher porosity on the hydrophobic surface, and a higher pure water flux than that in Example 9. Thus, it can be seen that by using graphene oxide solution as a coagulation bath, the present invention can further improve the difference in asymmetric wettability on both sides of the Janus membrane and the porosity on the hydrophobic surface, thereby ultimately improving the pure water flux.

[0104] (5) A comprehensive comparison of the data from Example 1 and Comparative Example 1 shows that the Janus membrane obtained in Example 1 has a greater difference in asymmetric wettability on both sides, a higher porosity on the hydrophobic surface, a larger average pore size, and a higher pure water flux compared to Comparative Example 1. It can be seen that, compared to directly using commercial PVDF, the present invention, by using waste fluorinated backsheets as raw materials, can not only utilize the PVDF in the fluorinated backsheets, but also utilize components such as TiO2 and PMMA to promote the spontaneous migration of hydrophobic groups to the bottom layer and the spontaneous migration of hydrophilic groups to the surface layer, thereby increasing the asymmetric wettability on both sides of the Janus membrane, as well as increasing the average pore size and porosity of the hydrophobic surface, ultimately achieving excellent pure water flux.

[0105] In summary, the method provided by this invention uses fluorinated backsheets from waste photovoltaic modules as raw materials to prepare Janus membranes, achieving harmless treatment of fluorinated backsheets and high-value-added resource utilization. Furthermore, the obtained Janus membranes have broad application prospects in the field of water treatment.

[0106] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing Janus membranes by recovering polyvinylidene fluoride from a fluorinated backsheet, characterized in that, The method includes the following steps: (1) Immerse the fluorine-containing backplate in an organic solvent, and then separate the solid and liquid to obtain the casting solution; (2) A wet membrane is prepared using the casting solution obtained in step (1), and the wet membrane is immersed in a coagulation bath to obtain a Janus membrane by a non-solvent phase separation method. The fluorinated backsheet in step (1) includes any one of the following: KPK type backsheet, KPE type backsheet, or KPC type backsheet; The coagulation bath comprises a graphene oxide solution.

2. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to claim 1, characterized in that, The fluorinated backsheet in step (1) is pretreated; The pretreatment includes: sequentially cleaning and drying the fluorine-containing backsheet; The cleaning solution used includes water and / or ethanol.

3. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to claim 1, characterized in that, The organic solvent in step (1) includes any one or a combination of at least two of N-methylpyrrolidone, N,N-dimethylformamide or N,N-dimethylacetamide; The mass ratio of the fluorinated backplate to the organic solvent is 1:(0.2-0.8); The mass concentration of polyvinylidene fluoride in the casting solution is 10-25%.

4. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to claim 1, characterized in that, The immersion time in step (1) is 0.5-6 hours; The immersion temperature is 15-35℃.

5. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to claim 1, characterized in that, The method for preparing the wet film in step (2) includes: pouring the casting solution onto a glass plate and then scraping it flat with a scraper to obtain a wet film; The thickness of the wet film is 150-350 μm; The wet film and the glass plate supporting the wet film are immersed together in a coagulation bath.

6. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to claim 1, characterized in that, The temperature of the coagulation bath in step (2) is 10-60℃; The immersion time in the coagulation bath is 5-30 minutes; The concentration of the graphene oxide solution is 0.1-5 mg / g.

7. The method for preparing Janus membrane by recovering polyvinylidene fluoride from a fluorinated backsheet according to any one of claims 1-6, characterized in that, The method further includes step (3): extracting the organic solvent in the coagulation bath after the Janus membrane is prepared; The extractant used in the extraction includes a chlorine-containing compound extractant; The extractant includes dichloromethane and / or trichloromethane.

8. A Janus membrane, characterized in that, The Janus membrane is obtained by the method described in any one of claims 1-7 for preparing a Janus membrane by recovering polyvinylidene fluoride from a fluorine-containing backsheet. The Janus membrane is hydrophilic on one side and hydrophobic on the other side.

9. Use of the Janus membrane as described in claim 8, characterized in that, The Janus membrane is used in the field of water treatment.

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