A polyvinylidene fluoride-based composite film and its preparation method and application

Abstract

The present invention provides a polyvinylidene fluoride based composite membrane and its preparation method and application. The polyvinylidene fluoride based composite membrane is prepared by extruding and spreading a polyvinylidene fluoride based composite dispersion on the surface of a coagulation bath solution, solidifying it into a film, and drying it to obtain a polyvinylidene fluoride based composite membrane; the polyvinylidene fluoride based composite dispersion is formed by dissolving and dispersing polyvinylidene fluoride and fluorinated nano-silicon dioxide in a solvent, and the mass percentage concentration of the polyvinylidene fluoride is 10-13.5wt%; the coagulation bath solution is formed by dissolving a solvent in water, and the mass ratio of the solvent to the water is 50-70:50-30 by mass. The present invention improves the anti-infiltration property of the pores in the membrane by improving the hydrophobicity of the polymer skeleton surface in the membrane, significantly improving the salt rejection rate, and preventing salt scale from contaminating the pores in the membrane, thereby achieving long-term stable operation during the seawater desalination process.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane distillation seawater desalination, in particular to a polyvinylidene fluoride composite membrane and a preparation method and application thereof. Background Art

[0002] With the rapid growth of the global population and the continued development of industry, the shortage of freshwater resources has become an imminent and critical issue, and seawater desalination has become one of the most effective solutions. Conventional commercial reverse osmosis, multi-effect distillation, and multi-stage flash evaporation all require large equipment space and a continuous supply of electricity and heat, which has certain limitations. Therefore, membrane distillation (MD) technology, which can efficiently utilize low-quality thermal energy (including renewable energy such as solar energy and geothermal energy), has great application prospects in seawater desalination. Membrane distillation desalination is based on the vapor pressure difference across the membrane. Low temperature drives water vapor through the hydrophobic porous membrane, leaving non-volatile salts in the feed solution, achieving efficient desalination. It is insensitive to salt concentration and requires simple equipment. Therefore, hydrophobic porous membranes are the key to membrane distillation technology, maintaining the liquid-gas interface on the membrane surface, making the process of vaporizing seawater stable and efficient. However, traditional polymer hydrophobic porous membranes suffer from low flux and membrane pore wetting in seawater desalination, leading to membrane fouling and scaling, which affect the stability of seawater desalination and make it difficult for membrane distillation technology to achieve a synergistic improvement in flux and stability. Therefore, improving the hydrophobicity of hydrophobic porous membranes is an effective way to prevent the porous membrane from being wetting and achieve improved desalination stability.

[0003] To enhance the hydrophobicity of hydrophobic porous membranes, superhydrophobic surface modification is commonly used. This technique utilizes lotus leaf-like micro-nanostructures to create an air layer between the rough surface and the water, thereby stabilizing the liquid-gas interface. However, even superhydrophobic surfaces experience depletion of this air layer over extended membrane distillation processes, leading to wetting of the membrane pores and an inability to effectively inhibit the passage of brine, resulting in a loss of desalination stability. Therefore, the use of composite nanofillers can simultaneously enhance the surface roughness and manipulate the pore structure to mitigate pore wetting and improve membrane distillation stability. Blending nanofillers with polymers can increase membrane surface roughness, creating a micro-nanostructure while also imparting a certain degree of roughness to the inner pore walls. This creates an air layer between the membrane surface and the water, supporting the liquid-gas interface on the hydrophobic membrane surface. Commonly used nanofillers include carbon nanotubes and hydrophobically modified fillers (silica, titanium dioxide, calcium carbonate, and MXene). For example, electrospun composite membranes utilize micro-nanostructures on the fiber surface to achieve high porosity and anti-wetting properties despite large pores, effectively mitigating flux degradation. Professor Lan of the University of Ottawa in Canada used a polyvinylidene fluoride composite porous membrane containing hydrophobic silica nanoparticles. Using a non-solvent-induced phase separation process, the hydrophobic silica particles were embedded within the membrane surface and matrix. This modulated the surface microstructure, forming an air layer on the membrane surface that effectively resisted water infiltration into the membrane pores (Effects of superhydrophobicSiO2 nanoparticles on the performance of PVDF flat sheet membranes for vacuum membrane distillation, Desalination 2015, 373, 47, https: / / doi.org / 10.1016 / j.desal.2015.07.002). Furthermore, the presence of the air layer increased the liquid-gas interface area, thereby increasing the vaporization area and thus improving the membrane distillation flux. Therefore, the hydrophobic silica particles composite polyvinylidene fluoride porous membrane with a thickness of 100 μm was used for membrane distillation desalination of 35 g / L sodium chloride solution at 27 °C, and the desalination efficiency was 2.9 kg / m 2 The flux of ·h is 4 times higher than that of pure polyvinylidene fluoride porous membrane, and the salt rejection rate is as high as 99.98%.

[0004] Based on this strategy, Professor Kwon of the Ulsan Institute of Science and Technology in South Korea proposed a holistic approach for fabrication of superhydrophobic MXene-based membranes for enhanced membrane distillation (Desalination 2024, 580,117536, https: / / doi.org / 10.1016 / j.desal.2024.117536). Through nonsolvent-induced phase separation, MXene nanosheets were concentrated on the porous membrane surface and within the matrix, resulting in a 289 μm thick composite membrane. The MXene nanosheets primarily formed a hierarchical micro-nanostructure on the surface of the PVDF membrane. Their rough surface promoted the formation of an air layer, enhancing hydrophobicity and achieving a water contact angle exceeding 143°. Furthermore, the membrane exhibited self-cleaning properties. Therefore, the presence of the surface air layer effectively inhibits the infiltration of water into the membrane pores and increases the effective volatile interface area. In the membrane distillation desalination of 35 g / L sodium chloride solution at 70 °C, the water flux reaches 8 kg / m 2 ·h.

[0005] However, although hydrophobic composite porous membranes can use the surface micro-nanostructure formed by nanofillers to inhibit membrane pore infiltration, they still face the problem of low flux due to the extra water vapor transmission resistance provided by the air layer on the membrane surface. In addition, the hydrophobic properties brought by the surface micro-nanostructure are still faced with the depletion of the air layer, so that the membrane distillation hydrophobic porous membrane requires a certain thickness to ensure that the air layer is not broken through by long-term membrane distillation. The thickness of the membrane is also related to the water vapor transmission distance and has the potential to increase the flux. Therefore, the traditionally prepared hydrophobic porous membranes are mostly between 50 and 400 μm, which makes it difficult to reduce the membrane thickness while ensuring hydrophobicity, so as to break through the limitations of the hydrophobic porous membrane's membrane pore anti-infiltration and increase the membrane distillation flux. Summary of the Invention

[0006] In view of this, the present invention proposes a polyvinylidene fluoride-based composite membrane and its preparation method and application to solve the problems of insufficient hydrophobicity of existing membrane materials and poor anti-infiltration property of the internal structure of the membrane, resulting in low salt rejection rate and poor stability of membrane distillation seawater desalination, while reducing the membrane thickness to improve its water flux.

[0007] In a first aspect, the present invention provides a method for preparing a polyvinylidene fluoride-based composite membrane, comprising: extruding and spreading a polyvinylidene fluoride-based composite dispersion on the surface of a coagulation bath solution, solidifying the dispersion into a membrane, and drying the membrane to obtain a polyvinylidene fluoride-based composite membrane;

[0008] The polyvinylidene fluoride-based composite dispersion is formed by dissolving and dispersing polyvinylidene fluoride and fluorinated nano-silica in a solvent, wherein the mass percentage concentration of the polyvinylidene fluoride is 10-13.5 wt %;

[0009] The coagulation bath solution is formed by dissolving a solvent in water, and the mass ratio of the solvent to the water is 50-70:50-30 by mass.

[0010] On the basis of the above technical solution, preferably, the fluorinated nano-silica accounts for 5 to 13 wt % of the mass of the polyvinylidene fluoride; and the fluorinated nano-silica is selected from hydrophobic fluorinated nano-silica with a particle size of 7 to 40 nm.

[0011] On the basis of the above technical solution, preferably, the solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone and tetrahydrofuran.

[0012] In a second aspect, the present invention relates to a polyvinylidene fluoride-based composite membrane prepared by the above method, wherein the polyvinylidene fluoride-based composite membrane has a thickness of 6.6~22.1 μm, a porosity of 59.7~69.8%, a pore size of 175~204 nm, a water contact angle of 116~132°, and a water liquid osmotic pressure of 1.39~1.94 bar.

[0013] In a third aspect, the present invention also relates to the application of polyvinylidene fluoride-based composite membrane in seawater desalination.

[0014] In a fourth aspect, the present invention provides a seawater desalination system, including a membrane distillation seawater desalination device and the above-mentioned polyvinylidene fluoride-based composite membrane.

[0015] On the basis of the above technical solution, preferably, the membrane distillation seawater desalination device includes a membrane module, and the membrane module is used to be equipped with a polyvinylidene fluoride-based composite membrane.

[0016] In a fifth aspect, the present invention provides a method for desalination of seawater based on the above system, the method comprising: circulating heated seawater in the system, condensing the heated seawater, and obtaining desalinated seawater.

[0017] In a sixth aspect, the present invention further relates to a method for evaluating the stability of a seawater desalination system, the method comprising:

[0018] evaluating the stability of the seawater desalination system according to the salt rejection rate and water flux of the polyvinylidene fluoride-based composite membrane;

[0019] The salt rejection rate of the polyvinylidene fluoride-based composite membrane is calculated by the salt content of the initial seawater and the salt content of the water collected after condensation, and the calculation formula is shown in formula (I):

[0020] R = (1 - C P / C F ) × 100% (Ⅰ),

[0021] In formula (I), R is the salt rejection rate, C F is the initial seawater salinity, C P is the salt content of the water collected after condensation;

[0022] The water flux of the polyvinylidene fluoride-based composite membrane is the mass of water collected after condensation.

[0023] On the basis of the above technical solution, preferably, in the process of desalination of seawater, the salt rejection rate of the polyvinylidene fluoride composite membrane is 89.6~99.9%, and the water flux is 10.06~22.58 kg / m 2 ·h.

[0024] The polyvinylidene fluoride-based composite film provided by the present invention, and its preparation method and application have the following beneficial effects compared with the prior art:

[0025] (1) In order to improve the performance of membrane distillation desalination, the existing technology usually requires complex and unstable hydrophobic modification of the membrane surface. The present invention focuses on improving the hydrophobicity of the polymer skeleton surface in the membrane, greatly improving the anti-infiltration property of the pores in the membrane, significantly improving the salt rejection rate, and blocking the pollution of the pores in the membrane by salt scale, thereby achieving long-term stable operation during the seawater desalination process.

[0026] (2) The present invention can achieve the improvement of the stable anti-wetting performance of the PVDF / F-SiO2 composite membrane without complicated post-processing. By adjusting the concentration of polyvinylidene fluoride (PVDF), the amount of hydrophobic fluorinated nano-silica (F-SiO2) nanoparticles added and the composition of the coagulation bath, the thickness, pore size and anti-wetting performance of the PVDF / F-SiO2 composite membrane can be controlled.

[0027] (3) The existing technology modification requires a thicker membrane to solve the problem of structural instability caused by the modification. Too high a thickness will lead to a decrease in water flux. The present invention prepares an ultra-thin PVDF / F-SiO2 composite membrane, which solves the problem of flux decrease usually caused by traditional modification and achieves a synergistic improvement in water flux and stability performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 A schematic diagram of a membrane distillation seawater desalination device provided by the present invention;

[0030] Figure 2 This is a cross-sectional scanning electron microscope (SEM) in-hole scanning magnification image of Example 2 provided by the present invention;

[0031] Figure 3 This is a cross-sectional scanning electron microscope (SEM) in-hole scanning magnification image of Comparative Example 1 provided by the present invention;

[0032] Figure 4 This is a cross-sectional scanning electron microscope (SEM) in-hole scanning magnification image of Comparative Example 2 provided by the present invention;

[0033] Figure 5 A schematic diagram of the principle of membrane distillation seawater desalination using the polyvinylidene fluoride based composite membrane prepared by the present invention;

[0034] Figure 6 This is a stability test chart of different membrane materials provided by the present invention under the same conditions. DETAILED DESCRIPTION

[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0036] The present invention adopts the preparation method of the polymer membrane with a published invention patent (authorization announcement number: CN116751382B), which realizes the uniform and stable attachment of F-SiO2 nanoparticles on the surface of the PVDF skeleton, greatly improving the hydrophobicity of the internal skeleton of the PVDF / F-SiO2 composite membrane. The basic principles for the uniform and stable attachment of F-SiO2 nanoparticles to the surface of the PVDF skeleton are as follows: 1) The surface of F-SiO2 nanoparticles is hydrophobic, but they can be fully infiltrated and stably dispersed in the solvent; 2) During the process of PVDF / F-SiO2 composite dispersion spreading to form a film on the surface of the coagulation bath solution, the water in the coagulation bath will gradually replace the solvent in the PVDF / F-SiO2 composite dispersion, prompting PVDF to precipitate and solidify to form a porous network skeleton structure; 3) During the process of water in the coagulation bath gradually replacing the solvent in the PVDF / F-SiO2 composite dispersion, the hydrophobic F-SiO2 nanoparticles will gradually become unstable and precipitate; 4) The fluorinated surface of F-SiO2 nanoparticles has similar properties to the fluorinated molecular chain of PVDF, and has high interfacial compatibility, so it can be firmly attached to the surface of the PVDF skeleton.

[0037] Membrane technology plays a vital role in the desalination process, but currently used membrane materials face two major challenges. On the one hand, the membrane's insufficient hydrophobicity and weak internal structure resistance to wettability directly lead to low salt retention efficiency, resulting in a low salt rejection rate. Furthermore, such membranes are susceptible to salt scale contamination, which gradually fills the pores within the membrane, further reducing the salt rejection efficiency and seriously affecting the stability of the membrane distillation process, making it difficult to maintain consistent performance during long-term operation. On the other hand, thicker membrane materials are sometimes selected to enhance the membrane's mechanical strength or improve its anti-fouling capabilities, but this creates another problem: low water flux. Increased membrane thickness hinders the passage of water molecules, thereby reducing the freshwater output efficiency of the entire system. These two factors work together to limit the widespread application and effectiveness of membrane distillation technology in the desalination field.

[0038] Since the membrane materials provided by the prior art and the membrane distillation technology used in the field of seawater desalination have not achieved the desired results, the inventors have made the present invention through further research.

[0039] The present invention selects appropriate amounts of hydrophobic fluorinated nanosilica (F-SiO2) and polyvinylidene fluoride (PVDF) and adds them to N,N-dimethylformamide (DMF). The mixture is stirred at 20-25°C to form a PVDF / F-SiO2 composite solution containing 4-14 wt% F-SiO2. The PVDF / F-SiO2 composite solution is then extruded and spread on the surface of a coagulation bath solution, cured, and dried to obtain a PVDF / F-SiO2 composite membrane. The PVDF / F-SiO2 composite membrane prepared by the present invention has a controllable thickness between 7.5 and 21.4 μm and a controllable porosity between 61.1 and 68.6%.

[0040] The inventors further applied the PVDF / F-SiO2 composite membrane prepared by the present invention to the performance characterization of membrane distillation (MD) seawater desalination. The prepared PVDF / F-SiO2 composite membrane was assembled into a membrane distillation device to study the seawater desalination performance. The Bohai seawater was heated to 60°C and circulated in the membrane module at a flow rate of 300 mL / min. The cycle diagram is shown in FIG. Figure 1 As shown (this figure is cited from Tailored PVDF membrane with coordinated interfacial nano / micro-structure for enhanced membrane distillation, Desalination 2024, 573, 117177, https: / / doi.org / 10.1016 / j.desal.2023.117177). Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The stability of the seawater desalination system was evaluated based on the salt rejection and water flux of the polyvinylidene fluoride-based composite membrane. The salt rejection and water flux of the polyvinylidene fluoride-based composite membrane were calculated from the mass and salinity of the initial seawater and the salinity and mass of the water collected after condensation.

[0041] The following are specific examples of the present invention. The sources of materials involved in the examples and comparative examples are as follows. Unless otherwise specified, the rest are commercially available conventional products.

[0042] Fluorinated nano-silica with a particle size of 7-40 nm, CAS number: 112945-52-5, Shanghai Aladdin Technology Co., Ltd.

[0043] Example 1

[0044] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.39 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 5 wt%.

[0045] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 70:30; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0046] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0047] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 1 showed a thickness of 9.7 μm, a porosity of 68.1%, a pore size of 193 nm, a liquid osmotic pressure (LEPw) of 1.46 bar, and a water contact angle (WCA) of 119°.

[0048] The PVDF / F-SiO2 composite membrane prepared in Example 1 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 16.43 kg / m 2 ·h, and the salt retention rate was 90.1%.

[0049] Example 2

[0050] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.70 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 9 wt%.

[0051] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 9 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0052] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0053] The PVDF / F-SiO2 composite membrane with a F-SiO2 content of 9 wt% prepared in Example 2 was observed using a field emission scanning electron microscope (FESEM) of Hitachi, Japan, Regulus SU8230. The cross-sectional microporous structure was sponge-like, and the F-SiO2 content in the pores was appropriate and evenly distributed in the pores without a large amount of agglomeration. Figure 2 As shown, the PVDF / F-SiO2 composite membrane was measured by scanning to have a thickness of 10.4 μm, a porosity of 65.6%, a pore size of 190 nm, a water liquid osmotic pressure (LEPw) of 1.52 bar, and a water contact angle (WCA) of 125°.

[0054] The PVDF / F-SiO2 composite membrane prepared in Example 2 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 22 kg / m 2 ·h, the salt retention rate is 99.9%.

[0055] The reason may be that the PVDF / F-SiO2 composite membrane prepared in Example 2 has sponge-like pores and is composed of Figure 2 It can be seen that the F-SiO2 nanoparticles are densely attached to the surface of the PVDF skeleton and do not block the pores, which can greatly improve the hydrophobicity of the pores inside the membrane, thereby effectively improving the membrane's anti-infiltration properties, helping to improve the salt rejection rate and maintain high water flux.

[0056] Example 3

[0057] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.01 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 13 wt%.

[0058] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 13 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0059] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0060] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 3 showed a thickness of 11.3 μm, a porosity of 61.8%, a pore size of 186 nm, a liquid osmotic pressure (LEPw) of 1.50 bar, and a water contact angle (WCA) of 126°.

[0061] The PVDF / F-SiO2 composite membrane prepared in Example 3 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 18.84 kg / m 2 ·h, and the salt retention rate was 98.3%.

[0062] Comparative Example 1

[0063] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.31 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 4 wt%.

[0064] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 4 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0065] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0066] The PVDF / F-SiO2 composite membrane with a F-SiO2 content of 9 wt% prepared in Comparative Example 1 was observed using a field emission scanning electron microscope (FESEM) of Regulus SU8230 produced by Hitachi, Japan. The cross-sectional microporous structure of the membrane was sponge-like, and the F-SiO2 in the pores was evenly distributed but the content was too low. Figure 3 As shown. Figure 2 It can be seen that the thickness of the PVDF / F-SiO2 composite membrane measured by scanning is 8.8 μm, the porosity is 69.7%, the pore size is 194 nm, the water liquid osmotic pressure (LEPw) is 1.44 bar, and the water contact angle (WCA) is 116°.

[0067] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 1 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 15.92 kg / m 2 ·h, and the salt retention rate was 90.4%.

[0068] Analysis shows that the reason may be: although the composite membrane prepared in comparative example 1 exhibits sponge-like pores, there are very few F-SiO2 nanoparticles on the PVDF skeleton in this "sponge", which is insufficient to form a nanoscale rough morphology on the skeleton surface. The improvement in the hydrophobicity of the internal skeleton of the PVDF / F-SiO2 composite membrane is not obvious, and the anti-infiltration property of the pore channels inside the membrane cannot be significantly improved, resulting in a low salt rejection rate.

[0069] Comparative Example 2

[0070] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.09 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 14 wt%.

[0071] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0072] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0073] The PVDF / F-SiO2 composite membrane with a F-SiO2 content of 9 wt% prepared in Comparative Example 2 was observed using a field emission scanning electron microscope (FESEM) of Regulus SU8230 produced by Hitachi, Japan. The cross-sectional microporous structure was sponge-like. The F-SiO2 content in the pores was too high, resulting in a large number of agglomerates in the pores. Figure 4 As shown, the PVDF / F-SiO2 composite membrane was measured by scanning to have a thickness of 11.9 μm, a porosity of 60.6%, a pore size of 184 nm, a water liquid osmotic pressure (LEPw) of 1.49 bar, and a water contact angle (WCA) of 130°.

[0074] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 2 was assembled into a membrane distillation device to study its desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 17.64 kg / m 2 ·h, and the salt rejection rate was 97.9%.

[0075] The reason for this may be that the PVDF / F-SiO2 composite membrane prepared in Comparative Example 2 exhibits sponge-like pores, but Figure 4 It can be seen that although too many F-SiO2 nanoparticles are densely distributed on the surface of the PVDF skeleton, they also form large agglomerates in the pores, resulting in a significant decrease in the water flux of the membrane.

[0076] Example 4

[0077] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.39 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDFF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 5 wt%.

[0078] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0079] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0080] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 4 showed a thickness of 19.2 μm, a porosity of 67.5%, a pore size of 185 nm, a liquid osmotic pressure (LEPw) of 1.86 bar, and a water contact angle (WCA) of 118°.

[0081] The PVDF / F-SiO2 composite membrane prepared in Example 4 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 11.97 kg / m 2 ·h, and the salt retention rate was 91.2%.

[0082] Example 5

[0083] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.70 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 9 wt%.

[0084] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 50:50. A PVDF / F-SiO2 composite solution containing 9 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0085] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0086] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 5 showed a thickness of 20.5 μm, a porosity of 64.9%, a pore size of 181 nm, a liquid osmotic pressure (LEPw) of 1.94 bar, and a water contact angle (WCA) of 122°.

[0087] The PVDF / F-SiO2 composite membrane prepared in Example 5 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 16.25 kg / m 2 ·h, the salt retention rate is 99.9%.

[0088] Example 6

[0089] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.01 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 13 wt%.

[0090] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. The PVDF / F-SiO2 composite solution prepared above with a 13 wt% F-SiO2 content was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0091] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0092] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 6 showed a thickness of 21.4 μm, a porosity of 61.1%, a pore size of 178 nm, a liquid osmotic pressure (LEPw) of 1.91 bar, and a water contact angle (WCA) of 124°.

[0093] The PVDF / F-SiO2 composite membrane prepared in Example 6 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 14.01 kg / m 2 ·h, and the salt retention rate is 99.3%.

[0094] Comparative Example 3

[0095] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.31 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 4 wt%.

[0096] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 4 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0097] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0098] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 3 showed a thickness of 18.7 μm, a porosity of 69.2%, a pore size of 187 nm, a liquid osmotic pressure (LEPw) of 1.85 bar, and a water contact angle (WCA) of 115°.

[0099] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 3 was assembled into a membrane distillation device to study its desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 10.06 kg / m 2 ·h, and the salt retention rate was 90.8%.

[0100] Comparative Example 4

[0101] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.09 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 14 wt%.

[0102] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0103] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0104] Scanning measurements showed that the thickness of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 4 was 22.1 μm, the porosity was 59.8%, the pore size was 175 nm, the liquid osmotic pressure (LEPw) of water was 1.89 bar, and the water contact angle (WCA) was 130°.

[0105] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 4 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 13.13 kg / m 2 ·h, and the salt retention rate was 98.7%.

[0106] Example 7

[0107] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.39 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 5 wt%.

[0108] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 60:40; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0109] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0110] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 7 showed a thickness of 16.9 μm, a porosity of 68.3%, a pore size of 188 nm, a liquid osmotic pressure (LEPw) of 1.69 bar, and a water contact angle (WCA) of 121°.

[0111] The PVDF / F-SiO2 composite membrane prepared in Example 7 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 13.88 kg / m 2 ·h, and the salt retention rate was 90.8%.

[0112] Example 8

[0113] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.70 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 9 wt%.

[0114] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40; a PVDF / F-SiO2 composite solution having a 9 wt% F-SiO2 content prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0115] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0116] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 8 showed a thickness of 17.5 μm, a porosity of 65.7%, a pore size of 186 nm, a liquid osmotic pressure (LEPw) of 1.76 bar, and a water contact angle (WCA) of 127°.

[0117] The PVDF / F-SiO2 composite membrane prepared in Example 8 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 18.6 kg / m 2 ·h, the salt retention rate is 99.9%.

[0118] Example 9

[0119] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.01 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 13 wt%.

[0120] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 13 wt% F-SiO2 prepared in the above-mentioned preparation was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0121] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0122] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 9 showed a thickness of 18.0 μm, a porosity of 61.4%, a pore size of 183 nm, a liquid osmotic pressure (LEPw) of 1.74 bar, and a water contact angle (WCA) of 132°.

[0123] The PVDF / F-SiO2 composite membrane prepared in Example 9 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 14.01 kg / m 2 ·h, and the salt retention rate is 99.3%.

[0124] Comparative Example 5

[0125] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.31 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 4 wt%.

[0126] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. At room temperature, a PVDF / F-SiO2 composite solution containing 4 wt% F-SiO2 prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0127] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0128] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 5 showed a thickness of 16.1 μm, a porosity of 69.4%, a pore size of 192 nm, a liquid osmotic pressure (LEPw) of 1.66 bar, and a water contact angle (WCA) of 120°.

[0129] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 5 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 13.05 kg / m 2 ·h, and the salt retention rate was 90.5%.

[0130] Comparative Example 6

[0131] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 1.09 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 7.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 13.5 wt% and a F-SiO2 content of 14 wt%.

[0132] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0133] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0134] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 6 showed a thickness of 18.6 μm, a porosity of 60.3%, a pore size of 180 nm, a water liquid osmotic pressure (LEPw) of 1.72 bar, and a water contact angle (WCA) of 130°.

[0135] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 6 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 15.5 kg / m 2 ·h, and the salt retention rate was 98.2%.

[0136] Example 10

[0137] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.28 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 5 wt%.

[0138] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 70:30; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0139] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0140] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 10 showed a thickness of 7.5 μm, a porosity of 68.6%, a pore size of 201 nm, a liquid osmotic pressure (LEPw) of 1.41 bar, and a water contact angle (WCA) of 121°.

[0141] The PVDF / F-SiO2 composite membrane prepared in Example 10 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 17.41 kg / m 2 ·h, and the salt retention rate was 90.2%.

[0142] Example 11

[0143] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.50 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 9 wt%.

[0144] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 9 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0145] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0146] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 11 showed a thickness of 8.3 μm, a porosity of 65.5%, a pore size of 198 nm, a liquid osmotic pressure (LEPw) of 1.48 bar, and a water contact angle (WCA) of 129°.

[0147] The PVDF / F-SiO2 composite membrane prepared in Example 11 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 22.58 kg / m 2 ·h, and the salt retention rate is 99.4%.

[0148] Example 12

[0149] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.73 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 13 wt%.

[0150] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 13 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0151] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0152] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 12 showed a thickness of 8.9 μm, a porosity of 62.1%, a pore size of 194 nm, a liquid osmotic pressure (LEPw) of 1.45 bar, and a water contact angle (WCA) of 128°.

[0153] The PVDF / F-SiO2 composite membrane prepared in Example 12 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 20.67 kg / m 2 ·h, and the salt rejection rate is 98.5%.

[0154] Comparative Example 7

[0155] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.22 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 4 wt%.

[0156] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 4 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0157] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0158] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 7 showed a thickness of 6.6 μm, a porosity of 69.8%, a pore size of 204 nm, a water liquid osmotic pressure (LEPw) of 1.39 bar, and a water contact angle (WCA) of 118°.

[0159] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 7 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 16.37 kg / m 2 ·h, and the salt retention rate was 89.6%.

[0160] Comparative Example 8

[0161] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.78 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 14 wt%.

[0162] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0163] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0164] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 8 showed a thickness of 9.6 μm, a porosity of 60.9%, a pore size of 191 nm, a water liquid osmotic pressure (LEPw) of 1.42 bar, and a water contact angle (WCA) of 132°.

[0165] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 8 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 19.67 kg / m 2 ·h, and the salt retention rate was 97.6%.

[0166] Example 13

[0167] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.28 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 5 wt%.

[0168] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0169] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0170] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 13 showed a thickness of 14.7 μm, a porosity of 67.9%, a pore size of 196 nm, a liquid osmotic pressure (LEPw) of 1.56 bar, and a water contact angle (WCA) of 123°.

[0171] The PVDF / F-SiO2 composite membrane prepared in Example 13 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 14.2 kg / m 2 ·h, and the salt retention rate was 90.9%.

[0172] Example 14

[0173] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.50 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 9 wt%.

[0174] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 50:50. A PVDF / F-SiO2 composite solution containing 9 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0175] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0176] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 14 showed a thickness of 15.4 μm, a porosity of 64.8%, a pore size of 193 nm, a liquid osmotic pressure (LEPw) of 1.61 bar, and a water contact angle (WCA) of 126°.

[0177] The PVDF / F-SiO2 composite membrane prepared in Example 14 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 19.97 kg / m 2 ·h, the salt retention rate is 99.9%.

[0178] Example 15

[0179] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.73 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 13 wt%.

[0180] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. The PVDF / F-SiO2 composite solution prepared above with a 13 wt% F-SiO2 content was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0181] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0182] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 6 showed a thickness of 15.9 μm, a porosity of 61.4%, a pore size of 191 nm, a liquid osmotic pressure (LEPw) of 1.60 bar, and a water contact angle (WCA) of 129°.

[0183] The PVDF / F-SiO2 composite membrane prepared in Example 6 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 18.31 kg / m 2 ·h, the salt retention rate is 99.1%.

[0184] Comparative Example 9

[0185] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.22 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 4 wt%.

[0186] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 4 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0187] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0188] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 9 showed a thickness of 13.8 μm, a porosity of 69.3%, a pore size of 198 nm, a water liquid osmotic pressure (LEPw) of 1.54 bar, and a water contact angle (WCA) of 117°.

[0189] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 9 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 13.69 kg / m 2 ·h, and the salt retention rate was 90.4%.

[0190] Comparative Example 10

[0191] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.78 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 14 wt%.

[0192] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0193] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0194] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 10 showed a thickness of 16.4 μm, a porosity of 60.1%, a pore size of 188 nm, a water liquid osmotic pressure (LEPw) of 1.58 bar, and a water contact angle (WCA) of 131°.

[0195] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 10 was assembled into a membrane distillation device to study its desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 16.75 kg / m 2 ·h, and the salt retention rate was 98.7%.

[0196] Example 16

[0197] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.28 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 5 wt%.

[0198] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 60:40; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0199] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0200] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 16 showed a thickness of 12.7 μm, a porosity of 68.1%, a pore size of 198 nm, a liquid osmotic pressure (LEPw) of 1.48 bar, and a water contact angle (WCA) of 118°.

[0201] The PVDF / F-SiO2 composite membrane prepared in Example 16 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 15.36 kg / m 2 ·h, and the salt rejection rate was 91.4%.

[0202] Example 17

[0203] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.50 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 9 wt%.

[0204] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40; a PVDF / F-SiO2 composite solution having a 9 wt% F-SiO2 content prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0205] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0206] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 17 showed a thickness of 13.5 μm, a porosity of 65.7%, a pore size of 195 nm, a liquid osmotic pressure (LEPw) of 1.55 bar, and a water contact angle (WCA) of 121°.

[0207] The PVDF / F-SiO2 composite membrane prepared in Example 17 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 20.89 kg / m 2 ·h, the salt retention rate is 99.9%.

[0208] Example 18

[0209] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.73 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 13 wt%.

[0210] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 13 wt% F-SiO2 prepared in the above-mentioned preparation was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0211] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0212] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 18 showed a thickness of 14.1 μm, a porosity of 61.7%, a pore size of 193 nm, a liquid osmotic pressure (LEPw) of 1.52 bar, and a water contact angle (WCA) of 126°.

[0213] The PVDF / F-SiO2 composite membrane prepared in Example 18 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 18.62 kg / m 2 ·h, and the salt retention rate is 99.3%.

[0214] Comparative Example 11

[0215] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.22 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 4 wt%.

[0216] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. At room temperature, a PVDF / F-SiO2 composite solution containing 4 wt% F-SiO2 prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0217] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0218] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 5 showed a thickness of 11.8 μm, a porosity of 69.5%, a pore size of 201 nm, a liquid osmotic pressure (LEPw) of 1.46 bar, and a water contact angle (WCA) of 119°.

[0219] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 5 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 14.08 kg / m 2 ·h, and the salt retention rate was 90.6%.

[0220] Comparative Example 12

[0221] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.78 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 5.6 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 10 wt% and a F-SiO2 content of 14 wt%.

[0222] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0223] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0224] Scanning measurements showed that the thickness of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 12 was 14.9 μm, the porosity was 60.5%, the pore size was 190 nm, the liquid osmotic pressure (LEPw) of water was 1.50 bar, and the water contact angle (WCA) was 127°.

[0225] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 12 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 17.14 kg / m 2 ·h, the salt retention rate is 99.1%.

[0226] Example 19

[0227] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.34 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 5 wt%.

[0228] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 70:30; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0229] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0230] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 19 showed a thickness of 8.7 μm, a porosity of 68.4%, a pore size of 198 nm, a liquid osmotic pressure (LEPw) of 1.45 bar, and a water contact angle (WCA) of 121°.

[0231] The PVDF / F-SiO2 composite membrane prepared in Example 19 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 17.13 kg / m 2 ·h, and the salt retention rate was 90.7%.

[0232] Example 20

[0233] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.61 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 9 wt%.

[0234] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 9 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0235] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0236] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 20 showed a thickness of 9.5 μm, a porosity of 65.6%, a pore size of 194 nm, a liquid osmotic pressure (LEPw) of 1.51 bar, and a water contact angle (WCA) of 125°.

[0237] The PVDF / F-SiO2 composite membrane prepared in Example 20 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 22.23 kg / m 2 ·h, the salt retention rate is 99.8%.

[0238] Example 21

[0239] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.88 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 13 wt%.

[0240] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 13 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0241] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0242] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 21 showed a thickness of 9.9 μm, a porosity of 62.2%, a pore size of 192 nm, a liquid osmotic pressure (LEPw) of 1.49 bar, and a water contact angle (WCA) of 123°.

[0243] The PVDF / F-SiO2 composite membrane prepared in Example 21 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 20.13 kg / m 2 ·h, and the salt retention rate is 98.9%.

[0244] Comparative Example 13

[0245] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.27 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 4 wt%.

[0246] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30; a PVDF / F-SiO2 composite solution having a F-SiO2 content of 4 wt% prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0247] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0248] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 13 showed that the thickness was 8.0 μm, the porosity was 69.7%, the pore size was 200 nm, the liquid osmotic pressure (LEPw) of water was 1.42 bar, and the water contact angle (WCA) was 116°.

[0249] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 13 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 16.05 kg / m 2 ·h, and the salt retention rate was 90.2%.

[0250] Comparative Example 14

[0251] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.95 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 14 wt%.

[0252] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 70:30. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0253] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0254] Scanning measurements showed that the PVDF / F-SiO2 composite membrane prepared in Comparative Example 14 had a thickness of 10.8 μm, a porosity of 60.8%, a pore size of 188 nm, a water liquid osmotic pressure (LEPw) of 1.46 bar, and a water contact angle (WCA) of 126°.

[0255] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 14 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 18.96 kg / m 2 ·h, and the salt retention rate was 98.1%.

[0256] Example 22

[0257] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.34 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 5 wt%.

[0258] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath at room temperature; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0259] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0260] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 22 showed a thickness of 18.3 μm, a porosity of 67.7%, a pore size of 193 nm, a liquid osmotic pressure (LEPw) of 1.83 bar, and a water contact angle (WCA) of 124°.

[0261] The PVDF / F-SiO2 composite membrane prepared in Example 22 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 13.56 kg / m 2 ·h, and the salt rejection rate was 91.4%.

[0262] Example 23

[0263] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.61 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 9 wt%.

[0264] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 50:50. A PVDF / F-SiO2 composite solution containing 9 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0265] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0266] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 23 showed a thickness of 19.1 μm, a porosity of 65.1%, a pore size of 189 nm, a water liquid osmotic pressure (LEPw) of 1.89 bar, and a water contact angle (WCA) of 127°.

[0267] The PVDF / F-SiO2 composite membrane prepared in Example 23 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 17 kg / m 2 ·h, the salt retention rate is 99.9%.

[0268] Example 24

[0269] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.88 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 13 wt%.

[0270] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. The PVDF / F-SiO2 composite solution prepared above with a 13 wt% F-SiO2 content was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0271] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0272] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 24 showed a thickness of 19.9 μm, a porosity of 61.6%, a pore size of 187 nm, a liquid osmotic pressure (LEPw) of 1.86 bar, and a water contact angle (WCA) of 128°.

[0273] The PVDF / F-SiO2 composite membrane prepared in Example 24 was assembled into a membrane distillation device to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 15.8 kg / m 2 ·h, the salt retention rate is 99.5%.

[0274] Comparative Example 15

[0275] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.27 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 4 wt%.

[0276] 2) Prepare a coagulation bath by mixing DMF and pure water in a 50:50 mass ratio; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 4 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0277] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0278] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 15 showed a thickness of 17.5 μm, a porosity of 69.3%, a pore size of 195 nm, a liquid osmotic pressure (LEPw) of 1.80 bar, and a water contact angle (WCA) of 120°.

[0279] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 15 was assembled into a membrane distillation device to study its desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 11.78 kg / m 2 ·h, and the salt retention rate was 90.8%.

[0280] Comparative Example 16

[0281] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.95 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 14 wt%.

[0282] 2) A coagulation bath was prepared by mixing DMF and pure water in a 50:50 mass ratio. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0283] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0284] Scanning measurements showed that the PVDF / F-SiO2 composite membrane prepared in Comparative Example 16 had a thickness of 20.6 μm, a porosity of 59.7%, a pore size of 183 nm, a water liquid osmotic pressure (LEPw) of 1.84 bar, and a water contact angle (WCA) of 131°.

[0285] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 16 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 14.26 kg / m 2 ·h, and the salt retention rate was 98.8%.

[0286] Example 25

[0287] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.34 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 5 wt%.

[0288] 2) Prepare a coagulation bath by mixing DMF and pure water in a mass ratio of 60:40; at room temperature, use a rubber-tipped dropper to slowly pipette the PVDF / F-SiO2 composite solution prepared above with a 5 wt% F-SiO2 content onto the surface of the coagulation bath; the PVDF / F-SiO2 composite solution rapidly spreads on the surface of the coagulation bath and solidifies into a film.

[0289] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) was dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0290] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 25 showed a thickness of 15.5 μm, a porosity of 68.2%, a pore size of 197 nm, a liquid osmotic pressure (LEPw) of 1.64 bar, and a water contact angle (WCA) of 123°.

[0291] The PVDF / F-SiO2 composite membrane prepared in Example 25 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 14.73 kg / m 2 ·h, and the salt retention rate was 91.1%.

[0292] Example 26

[0293] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.61 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 9 wt%.

[0294] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40; a PVDF / F-SiO2 composite solution having a 9 wt% F-SiO2 content prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper; the PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0295] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0296] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 26 showed a thickness of 16.3 μm, a porosity of 65.2%, a pore size of 192 nm, a liquid osmotic pressure (LEPw) of 1.72 bar, and a water contact angle (WCA) of 124°.

[0297] The PVDF / F-SiO2 composite membrane prepared in Example 26 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a water flux of 19.39 kg / m 2 ·h, the salt retention rate is 99.9%.

[0298] Example 27

[0299] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.88 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 13 wt%.

[0300] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 13 wt% F-SiO2 prepared in the above-mentioned preparation was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0301] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0302] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Example 27 showed a thickness of 17.1 μm, a porosity of 61.8%, a pore size of 189 nm, a liquid osmotic pressure (LEPw) of 1.69 bar, and a water contact angle (WCA) of 127°.

[0303] The PVDF / F-SiO2 composite membrane prepared in Example 27 was assembled into a membrane distillation apparatus to study its desalination performance. Bohai Sea water was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed at a vacuum pressure of 0.9 bar through a 5°C condenser. The collected water was analyzed to determine the stability of the membrane distillation desalination process. The test results showed a flux of 18.04 kg / m 2 ·h, and the salt retention rate is 99.2%.

[0304] Comparative Example 17

[0305] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.27 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 4 wt%.

[0306] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. At room temperature, a PVDF / F-SiO2 composite solution containing 4 wt% F-SiO2 prepared in the above preparation was slowly pipetted onto the surface of the coagulation bath using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0307] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0308] Scanning measurements of the PVDF / F-SiO2 composite membrane prepared in Comparative Example 17 showed a thickness of 14.6 μm, a porosity of 69.4%, a pore size of 199 nm, a liquid osmotic pressure (LEPw) of 1.63 bar, and a water contact angle (WCA) of 121°.

[0309] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 17 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 13.65 kg / m 2 ·h, and the salt retention rate was 90.5%.

[0310] Comparative Example 18

[0311] 1) Weigh 50 g of DMF and add it to a beaker. Weigh 0.95 g of F-SiO2 and add it to the beaker and stir for 1 hour to disperse it. After it is evenly dispersed, add 6.8 g of PVDF and stir for 24 hours to dissolve it into a homogeneous mixed solution to obtain a PVDF / F-SiO2 composite solution with a PVDF content of 12 wt% and a F-SiO2 content of 14 wt%.

[0312] 2) A coagulation bath was prepared by mixing DMF and pure water in a mass ratio of 60:40. A PVDF / F-SiO2 composite solution containing 14 wt% F-SiO2 prepared above was slowly pipetted onto the surface of the coagulation bath at room temperature using a rubber-tipped dropper. The PVDF / F-SiO2 composite solution rapidly spread on the surface of the coagulation bath and solidified into a film.

[0313] 3) The PVDF / F-SiO2 composite membrane prepared in step 2) is dried at room temperature for 24 h to obtain a PVDF / F-SiO2 composite membrane with controllable thickness and pore size.

[0314] Scanning measurements showed that the PVDF / F-SiO2 composite membrane prepared in Comparative Example 18 had a thickness of 17.8 μm, a porosity of 60.4%, a pore size of 186 nm, a water liquid osmotic pressure (LEPw) of 1.68 bar, and a water contact angle (WCA) of 130°.

[0315] The PVDF / F-SiO2 composite membrane prepared in Comparative Example 18 was assembled into a membrane distillation device to study its seawater desalination performance. Bohai seawater was heated to 60°C and circulated through the membrane module at a flow rate of 300 mL / min. Water vapor was condensed through a 5°C condenser under a vacuum pressure of 0.9 bar. The collected water was analyzed to determine the stability of the membrane distillation process during seawater desalination. The test results showed a water flux of 16.22 kg / m 2 ·h, and the salt retention rate was 98.3%.

[0316] By analyzing Examples 1 to 27 of the present invention and Comparative Examples 1 to 18, it can be seen that the process of membrane distillation seawater desalination and the reasons and mechanisms for improving the anti-wetting performance of the hydrophobic fluorinated nano-silica used in the present invention during the membrane distillation process are shown in Figure 5. Figure 5 It can be seen that hydrophobic fluorinated nano-silica is densely distributed on the surface of the PVDF skeleton. It enhances the hydrophobicity of the skeleton surface and improves the anti-infiltration property of the pores inside the membrane, thereby hindering the movement of the gas-liquid interface into the membrane and preventing salt scale from contaminating the pore structure inside the membrane, thereby improving the stability of membrane distillation seawater desalination.

[0317] By comparing and analyzing Examples 1 to 27 of the present invention and Comparative Examples 1 to 18, Figure 5 It can be seen that:

[0318] When the F-SiO2 content increases, the water contact angle of the PVDF / F-SiO2 composite membrane does not change much, but the LEPw increases accordingly, which increases the mass transfer resistance of water and reduces the possibility of water entering the membrane, thereby improving the stability performance during the seawater desalination process. This is attributed to the hydrophobic F-SiO2 particles forming a superhydrophobic structure in the pores of the PVDF / F-SiO2 composite membrane, which hinders the movement of the gas-liquid interface while increasing the effective gas-liquid evaporation area and improving the water flux.

[0319] As the F-SiO2 content increases, the LEPw, water flux and salt retention performance of the PVDF / F-SiO2 composite membrane first increase and then decrease. The thickness of the PVDF / F-SiO2 composite membrane does not increase much. Compared with the membrane with a thickness of at least 200 μm in other technologies, the PVDF / F-SiO2 composite membrane of the present invention is maintained at an ultra-thin thickness as a whole, and the PVDF / F-SiO2 composite membrane with an F-SiO2 content of 9 wt% prepared in Example 2 of the present invention achieves the highest flux and salt retention rate. Even under other conditions, the composite membrane has the relatively optimal performance when the F-SiO2 content is 9 wt%. This is because when the F-SiO2 content is too little, the hydrophobic structure in the composite membrane pores cannot be formed, and the gas-liquid interface can easily pass directly through the ultra-thin film. However, when the F-SiO2 content is too high, large agglomerates will be generated, resulting in a decrease in porosity, and the agglomerates formed by agglomeration will produce defects due to pressure during the membrane distillation desalination process, thereby reducing the salt retention rate.

[0320] In summary, the appropriate F-SiO2 content can obtain a super-hydrophobic structure in the pores of the PVDF / F-SiO2 composite membrane without changing the surface structure. The PVDF / F-SiO2 composite membrane of the present invention can maintain a high hydrophobicity of 22 kg / m while maintaining an ultra-thin thickness of 10 μm. 2h flux and 99.9% salt rejection rate, compared with the traditional commercial membrane produced by Merck Millipore under the same conditions of membrane distillation seawater desalination test, it shows higher flux and long-term stability. Figure 6 As shown. Figure 6 It can be seen that the PVDF / F-SiO2 composite membrane of the present invention solves the problem of poor stability of membrane distillation seawater desalination due to insufficient hydrophobicity of traditional membrane materials, and the problem of low water flux due to excessive thickness of other technical membranes.

[0321] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride-based composite film, characterized in that: include: Extruding and spreading the polyvinyl difluoride based composite dispersion on the surface of a coagulation bath solution, solidifying it into a film, and drying it to obtain a polyvinyl difluoride based composite film; The polyvinylidene fluoride-based composite dispersion is formed by dissolving and dispersing polyvinylidene fluoride and fluorinated nano-silica in a solvent, wherein the mass percentage concentration of the polyvinylidene fluoride is 10-13.5 wt %; The coagulation bath solution is formed by dissolving a solvent in water, and the mass ratio of the solvent to the water is 50-70:50-30 by mass; The fluorinated nano-silica accounts for 5 to 13 wt % of the mass of the polyvinylidene fluoride; the fluorinated nano-silica is selected from hydrophobic fluorinated nano-silica with a particle size of 7 to 40 nm.

2. The method for preparing a polyvinylidene fluoride-based composite film according to claim 1, wherein: The solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone and tetrahydrofuran.

3. A polyvinylidene fluoride-based composite film, characterized in that The polyvinylidene fluoride composite film is prepared by the preparation method according to any one of claims 1 to 2; The polyvinylidene fluoride-based composite membrane has a thickness of 6.6-22.1 μm, a porosity of 59.7-69.8%, and a water contact angle of 116-132°.

4. The polyvinylidene fluoride-based composite film according to claim 3, wherein The polyvinylidene fluoride composite membrane has a salt rejection rate of 89.6-99.9% and a water flux of 10.06-22.58 kg / m 2 ·h.

5. Use of the polyvinylidene fluoride-based composite membrane according to claim 4 in seawater desalination.

6. A seawater desalination system, comprising a membrane distillation seawater desalination device, characterized in that: It also includes the polyvinylidene fluoride-based composite film as claimed in claim 4.

7. The seawater desalination system according to claim 6, characterized in that: The membrane distillation seawater desalination device comprises a membrane assembly, and the membrane assembly is used to be equipped with a polyvinylidene fluoride-based composite membrane.

8. A method for desalination of seawater, characterized in that: The method comprises: placing the heated seawater in the system according to claim 6 or 7 for circulation, condensing, and obtaining desalinated seawater.

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