Preparation method, product and application of silicon dioxide nanoparticle modified polyvinylidene fluoride microfiltration membrane

Abstract

The invention relates to the technical field of oil-water separation and microfiltration membrane preparation, in particular to a preparation method, a product and application of a silicon dioxide nanoparticle modified polyvinylidene fluoride microfiltration membrane. The preparation method comprises the following steps: dissolving a silane coupling agent in an organic solvent A to obtain a solution A; a polyvinylidene fluoride membrane is soaked in the solution A, and a PVDF-coated C10H20O5Si membrane is obtained; dispersing nano SiO2 in an organic solvent B to obtain a solution B; uniformly mixing the solution B with the solution A to obtain a mixed solution C; a PVDF-coated C10H20O5Si membrane is soaked in the mixed solution C, and the silicon dioxide nanoparticle modified polyvinylidene fluoride microfiltration membrane is obtained. The raw materials are easy to obtain, the preparation process is simple and environment-friendly, and industrial production is easy to realize. The silicon dioxide nanoparticle modified polyvinylidene fluoride micro-filtration membrane can effectively separate oil / water emulsion, and the separation efficiency of the oil / water emulsion of the transformer is as high as 99.91%.

Description

Technical Field

[0001] The present invention relates to the technical fields of oil-water separation and microfiltration membrane preparation, and particularly to a preparation method, product and application of a silica nanoparticle modified polyvinylidene fluoride microfiltration membrane. Background Art

[0002] Mineral insulating oil is widely used in large power equipment such as transformers and reactors due to its excellent insulation and heat dissipation performance. In order to prevent pollution caused by oil spraying and leakage of large oil-filled electrical equipment such as main transformers and high-reactance reactors, special accident oil pools are set up in substations. The accident oil pools are usually set underground, and the transformer oil can be directly sent to the accident oil pool through the drain pipe.

[0003] While storing the leaked oil of power equipment and the sewage of substations, the accident oil pools also increase the safety hazards of substations and a series of environmental protection problems of sewage leakage; in addition, the traditional management method of accident oil pools is inefficient, and the unreasonable arrangement of human and material resources causes certain economic waste. The harmful characteristics of transformer waste oil include toxicity and flammability. Table 1 is the composition table of transformer waste oil. Among them, polycyclic aromatic hydrocarbons are divided into condensed polycyclic aromatic hydrocarbons and isolated polycyclic aromatic hydrocarbons, such as biphenyl; benzene series include benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene; heavy metals are mainly copper, iron and aluminum. Transformer accidents occur frequently, and the disposal requirements for transformer waste oil are becoming more and more strict. How to adopt scientific and efficient oil-water separation and waste oil and sewage treatment methods, while ensuring the safe and stable operation of substations, strengthening the treatment of oily sewage at the sewage discharge port of the accident oil pool, and making the waste liquid treatment meet the requirements of economic environmental protection and sustainable development has become an important problem faced by the current management of the waste liquid in the accident oil pool of substations.

[0004] Table 1 Composition Table of Transformer Waste Oil

[0005]

[0006] Traditional treatment of oily wastewater is mainly through gravity separation, flotation and filtration, but these technologies still need to be improved in terms of efficiency and operating costs. Due to the strong oil-water interface of oil-water emulsion, traditional technology faces huge challenges in oil-water emulsion separation. Membrane separation technology has the advantages of low energy consumption, high efficiency, strong versatility, no need to add other reagents, easy recovery or treatment of concentrated products, and little influence of oil composition on the separation process, which has great advantages. However, the method of preparing superhydrophilic separation materials on hydrophobic polymers has the disadvantages of complex manufacturing process, expensive experimental raw materials, difficult operation of experimental equipment and harsh preparation conditions. It is limited to laboratory research and does not meet the requirements of industrial production at all. Therefore, it cannot be applied to people's lives. Therefore, it is of great significance to provide a silica nanoparticle modified polyvinylidene fluoride microfiltration membrane with easy raw materials, simple preparation process and easy industrial production for the field of oil-water separation. Summary of the invention

[0007] Based on the above content, the present invention provides a preparation method, product and application of a silicon dioxide nanoparticle modified polyvinylidene fluoride microfiltration membrane.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention is a method for preparing a silicon dioxide nanoparticle-modified polyvinylidene fluoride microfiltration membrane, comprising the following steps:

[0010] Dissolving a silane coupling agent in an organic solvent A to obtain a solution A;

[0011] The polyvinylidene fluoride membrane (PVDF membrane) was immersed in solution A to obtain PVDF@C 10 H 20 O5Si film;

[0012] Dispersing nano-SiO2 in organic solvent B to obtain solution B;

[0013] Mix solution B and solution A to obtain mixed solution C;

[0014] PVDF@C 10 H 20 The O5Si membrane is immersed in the mixed solution C to obtain a silicon dioxide nanoparticle-modified polyvinylidene fluoride microfiltration membrane.

[0015] The second technical solution of the present invention is a silicon dioxide nanoparticle-modified polyvinylidene fluoride microfiltration membrane prepared according to the above-mentioned preparation method.

[0016] The third technical solution of the present invention is the application of the above-mentioned silicon dioxide nanoparticle-modified polyvinylidene fluoride microfiltration membrane in oil / water emulsion separation.

[0017] The present invention discloses the following technical effects:

[0018] The raw materials of the present invention are easily available, the preparation process is simple, it is environmentally friendly, and it is easy to realize industrial production.

[0019] The silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane prepared by the method of the present invention can effectively separate oil / water emulsions, and the separation efficiency for transformer oil / water emulsions is as high as 99.91%.

[0020] The silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane of the present invention is of great significance for treating environmental pollution caused by wastewater and hazardous waste due to oil leakage from accident oil ponds, recycling and regenerating waste oil, and the development of green power grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 Schematic diagram of the synthesis process of the PVDF@C 10 H 20 O5Si@SiO2 membrane in Example 1.

[0023] Figure 2 FESEM images of PVDF membranes (a, b), PVDF@C 10 H 20 O5Si membranes (c, d), PVDF@C 10 H 20 O5Si@SiO2-300 membranes (e, f) in Example 1 and PVDF@SiO2 nanocomposite membranes (g, h) in Comparative Example 1.

[0024] Figure 3 AFM images of PVDF@C 10 H 20 O5Si membranes (a, b) and PVDF@C 10 H 20 O5Si@SiO2-300 membranes (c, d) in Example 1.

[0025] Figure 4 FT-IR spectra of PVDF membranes, PVDF@C 10 H 20 O5Si membranes, PVDF@C 10 H 20 O5Si@SiO2-300 membranes in Example 1.

[0026] Figure 5 For the PVDF membrane, PVDF@C in Example 1 10 H 20 O5Si membrane, PVDF@C 10 H 20 XPS full spectrum of the O5Si@SiO2-300 membrane.

[0027] Figure 6 For the PVDF@C in Example 1 10 H 20 High-resolution O(1s) peak representative spectrum of the O5Si membrane.

[0028] Figure 7 For the PVDF@C in Example 1 10 H 20 High-resolution spectrum of Si(2s) of the O5Si@SiO2-300 membrane.

[0029] Figure 8 For the PVDF@C in Example 1 10 H 20 High-resolution spectrum of Si(2p) of the O5Si@SiO2-300 membrane.

[0030] Figure 9 For the PVDF@C in Example 1 10 H 20 XRD spectrum of the O5Si@SiO2-300 membrane.

[0031] Figure 10 For the PVDF@C in Example 1 10 H 20 Schematic diagram of the oil / water separation process of the O5Si@SiO2 membrane.

[0032] Figure 11 Photographs and optical microscope images of the oil / water emulsion before and after separation by the separation experimental device of the present invention

[0033] Figure 12 For PVDF, PVDF@C in Example 1 10 H 20 O5Si@SiO2-50, PVDF@C 10 H 20 O5Si@SiO2-100, PVDF@C 10 H 20 O5Si@SiO2-200 and PVDF@C 10 H 20 Oil / water emulsion separation efficiency of the O5Si@SiO2-300 membrane.

[0034] Figure 13 For PVDF@C in Example 1 10 H 20 TOC results of the filtrates after O5Si@SiO2-300 membrane separates transformer oil / water emulsion, benzene / water emulsion, toluene / water emulsion and p-xylene / water emulsion Detailed implementation manners

[0035] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics and implementation schemes of the present invention.

[0036] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0038] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0039] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0040] "Normal temperature" as described in the present invention, unless otherwise specified, all represents 20 - 30 °C.

[0041] The first aspect of the present invention provides a preparation method of a silica nanoparticle modified polyvinylidene fluoride microfiltration membrane, comprising the following steps:

[0042] Dissolve a silane coupling agent in organic solvent A to obtain solution A;

[0043] Immerse the polyvinylidene fluoride membrane (PVDF membrane) in Solution A to obtain PVDF@C 10 H 20 O5Si membrane;

[0044] Disperse nano-SiO2 in organic solvent B to obtain Solution B;

[0045] Mix Solution B and Solution A (here Solution A refers to Solution A after immersing the PVDF membrane) to obtain a mixed solution C;

[0046] Immerse the PVDF@C 10 H 20 O5Si membrane in the mixed solution C to obtain a silica nanoparticle modified polyvinylidene fluoride microfiltration membrane.

[0047] In a preferred embodiment of the present invention, the silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane, with the molecular formula C 10 H 20 O5Si, with the English alias KH-570; organic solvent A is ethanol; the volume ratio of the silane coupling agent to organic solvent A is 1:10.

[0048] In some specific embodiments of the present invention, when preparing Solution A, dissolve the silane coupling agent in organic solvent A and stir for 3 h.

[0049] The core purpose of stirring is to accelerate the dissolution and uniform dispersion of the silane coupling agent in the organic solvent through mechanical mixing, avoid agglomeration or side reactions, and provide a stable and uniform solution for the subsequent process. The rotation speed should be moderate to form effective turbulence, ensure the mixing efficiency without destroying the system stability. According to the solvent viscosity, silane structure, and observing the changes in solution transparency or viscosity to verify the stirring effect, ensure that there is no turbidity or stratification. Tests have found that a rotation speed in the range of 200 - 600 r / min is reasonable.

[0050] In a preferred embodiment of the present invention, the conditions for immersing the polyvinylidene fluoride membrane in Solution A are set as follows: the immersion temperature is room temperature; the immersion time is 1 - 3 h.

[0051] The immersion time of the polyvinylidene fluoride (PVDF) membrane in Solution A is set to 1–3 h based on the balance between the modification effect and the membrane structure stability: if the time is too short (<1 h), it will lead to insufficient contact between functional components such as the silane coupling agent and the membrane surface, making it difficult to complete sufficient adsorption or chemical bonding, resulting in an incomplete modified layer, affecting the membrane surface hydrophilicity, interfacial compatibility, and subsequent separation performance; while if the time is too long (>3 h), it will cause over-modification, leading to agglomeration of the coupling agent on the membrane surface or blockage of pores, changing the pore size distribution and increasing the transmembrane resistance, and even causing membrane material swelling and chemical degradation due to the long-term action of the solvent, destroying the mechanical properties and dimensional stability.

[0052] After the polyvinylidene fluoride membrane is soaked in Solution A, it further includes the step of cleaning the membrane with deionized water until it is clean.

[0053] In a preferred embodiment of the present invention, the mass-volume ratio of nano-SiO₂ to organic solvent B is 50 - 400 mg∶200 mL; the organic solvent B is N,N-dimethylformamide (DMF).

[0054] In a preferred embodiment of the present invention, the mass-volume ratio of nano-SiO₂ in Solution B to the silane coupling agent in Solution A is 50 - 400 mg∶5 mL.

[0055] In some specific embodiments of the present invention, when preparing the mixed solution C, Solution B is slowly added to Solution A, and magnetically stirred at room temperature for 1 - 3 h.

[0056] When preparing the mixed solution C, Solution B is slowly added to Solution A and magnetically stirred for 1 - 3 hours. The core purpose is not only to mix the two evenly, but more importantly, to ensure that the two solutions are in full contact and to promote physical or chemical interactions (such as dissolution, dispersion, reaction, etc.) between the components. If the stirring time is too short (e.g., <1 h), due to insufficient contact and mixing between Solution B and Solution A, local concentration unevenness, incomplete reaction or dispersion will occur, affecting the uniformity of the mixed solution C and the subsequent process effects (such as insufficient interfacial bonding force, product performance fluctuations); if the time is too long (e.g., >3 h), although the mixing degree can be further improved, it will increase energy consumption, exacerbate solvent volatilization or cause unnecessary side reactions (such as structural damage of some sensitive components under long-term shearing), and even lead to a decrease in the stability of the system (such as colloid coagulation, emulsion demulsification) due to excessive stirring. The time range of 1 - 3 h can ensure that the two solutions achieve macroscopic uniform mixing and possible interfacial reactions (such as hydrolysis / condensation of silane coupling agent and substrate) through sufficient convection and diffusion, and avoid the insufficient mixing caused by too short time or the system risks caused by too long time, which is a reasonable range that takes into account both efficiency and stability.

[0057] Regarding the stirring speed, it needs to be adjusted according to the solution viscosity, component properties and reaction characteristics. When the speed is too low, the mixing efficiency is insufficient, resulting in local concentration differences or stratification phenomena, and full contact cannot be achieved; when the speed is too high, excessive shear force is introduced (especially for polymer solutions or sensitive systems), damaging the structure or generating bubbles, while increasing energy consumption. It is found that it is reasonable to control the room temperature magnetic stirring speed within 200 - 800 r / min. Within this speed range, moderate turbulence can be formed, ensuring uniform mixing and not damaging the system stability. Optimize by observing the solution state (such as whether there is turbidity, precipitation or bubbles) and experimental objectives (such as reaction rate, product uniformity), and finally achieve a dual balance of mixing and potential reaction through 1 - 3 hours of stirring, avoiding insufficient mixing caused by insufficient time or unnecessary energy consumption caused by too long time.

[0058] In a preferred embodiment of the present invention, PVDF@C 10 H 20 The conditions for impregnating the H

[0059] PVDF@C 10 H 20 O5Si membrane in the mixed solution C are set as follows: the impregnation temperature is room temperature; the impregnation time is 8 - 12 h. 10 H 20 The impregnation time of the O5Si membrane in the mixed solution C is set to 8–12 h based on the comprehensive consideration of the modification layer formation kinetics and the membrane structure stability: when the time is too short (<8 h), the diffusion, adsorption of nano - SiO2 particles on the membrane surface and the interfacial action with the C

[0060] In a preferred embodiment of the present invention, PVDF@C 10 H 20 After the impregnation of the O5Si membrane in the mixed solution C, it also includes the steps of cleaning and drying.

[0061] In a preferred embodiment of the present invention, the drying temperature is 100 °C and the drying time is 20 min.

[0062] The second aspect of the present invention provides a silica nanoparticle - modified polyvinylidene fluoride microfiltration membrane prepared by the above - mentioned preparation method.

[0063] The third aspect of the present invention provides the application of the above - mentioned silica nanoparticle - modified polyvinylidene fluoride microfiltration membrane in oil / water emulsion separation.

[0064] The technical solutions of the present invention, unless otherwise specified, are all conventional solutions in the art. The reagents or raw materials used, unless otherwise specified, are all purchased from commercial channels or have been made public.

[0065] The silane coupling agent used in the examples of the present invention is specifically 3 - (methacryloyloxy) propyltrimethoxysilane, with the molecular formula C 10 H 20 O5Si and the English alias KH - 570.

[0066] In the embodiments of the present invention, the PVDF membrane used is purchased from Wenzhou Maikai Technology Co., Ltd., and the main parameters are: membrane diameter 47mm, pore size 0.22 - 0.45um.

[0067] The ethanol used in the embodiments of the present invention is analytical pure anhydrous ethanol.

[0068] The technical solutions provided by the present invention will be described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0069] Example 1

[0070] Step 1, dissolve the silane coupling agent in ethanol at a volume ratio of 1:10 (take 5 mL of silane coupling agent and 50 mL of ethanol) and stir for 3 h to obtain a hydrolyzed silane coupling agent solution, denoted as solution A; put the PVDF membrane into the above solution A and soak it at room temperature for 2 h, then wash the membrane with deionized water to obtain PVDF@C 10 H 20 O5Si membrane.

[0071] The hydrolysis of the silane coupling agent is not completely anhydrous, but depends on the water naturally present in ethanol and environmental humidity. With the reaction conditions provided by long-term stirring, the Si - O - R’ bond is gradually broken to generate silanol, laying the foundation for the subsequent condensation reaction with the hydroxyl groups on the surface of the substrate (PVDF membrane).

[0072] The analytical pure anhydrous ethanol used in the present invention is not completely water-free, but has a very low water content. According to relevant standards and reference content, the water content of analytical pure anhydrous ethanol ≤ 0.3%. In the national standard for anhydrous ethanol (GB / T678 - 2002), it is clearly stated that the water content of analytical pure anhydrous ethanol ≤ 0.3%. Its "anhydrous" is a relative concept, emphasizing high purity. In fact, it still contains a very small amount of water, but this water content is extremely low and can meet specific requirements for moisture-sensitive experiments, industrial production, etc.

[0073] Step 2, weigh different masses of nano-SiO2 (50 mg, 100 mg, 200 mg, 300 mg, 400 mg) and disperse them in 200 mL of DMF respectively, stir for 30 min to obtain solution B; slowly add solution B into solution A (here solution A refers to the solution A after soaking the PVDF membrane above), stir magnetically at room temperature for 1 - 3 h to obtain a mixed solution C; put the PVDF@C 10 H 20 O5Si membrane into the mixed solution C and soak it at room temperature for 10 h (8 - 12 h is acceptable), then take out the membrane, wash it with deionized water and dry it in an electrothermal constant temperature drying oven (temperature 100 °C, time 20 min) to obtain PVDF@C 10 H 20O5Si@SiO2 film (PVDF@C prepared with different masses of nano - SiO2 10 H 20 The O5Si@SiO2 films are respectively labeled as PVDF@C 10 H 20 O5Si@SiO2 - 50, PVDF@C 10 H 20 O5Si@SiO2 - 100, PVDF@C 10 H 20 O5Si@SiO2 - 200, PVDF@C 10 H 20 O5Si@SiO2 - 300, PVDF@C 10 H 20 O5Si@SiO2 - 400).

[0074] PVDF@C in Example 1 10 H 20 The schematic diagram of the synthesis process of the O5Si@SiO2 film is as Figure 1 shown.

[0075] Comparative Example 1

[0076] Weigh different masses of nano - SiO2 (50 mg, 100 mg, 200 mg, 300 mg, 400 mg) and disperse them in 200 mL of DMF respectively, and stir for 30 min to obtain solution B. Immerse the PVDF film in solution B at room temperature for 10 h, then take out the film, wash it clean with deionized water and dry it in an electro - thermal constant - temperature drying oven (temperature 100 °C, time 20 min) to obtain the PVDF@SiO2 nanocomposite film. To compare with the PVDF@C 10 H 20 O5Si@SiO2 - 300 film, all the PVDF@SiO2 nanocomposite films of the present invention take the PVDF@SiO2 - 300 film as the research object.

[0077] PVDF@C prepared in Example 1 10 H 20 The basic physical and chemical property characterization of the O5Si@SiO2 film is as follows:

[0078] 1. PVDF@C 10 H 20 FESEM characterization of the O5Si@SiO2 film

[0079] Figure 2 For the PVDF film (a, b) in Example 1, PVDF@C 10 H 20 O5Si film (c, d), PVDF@C 10 H20 FESEM characterization results of the O5Si@SiO2-300 film (e, f) and the PVDF@SiO2 nanocomposite film in Comparative Example 1 (g, h). It can be seen from Figure 2 that the PVDF film has a porous structure and a relatively smooth surface (as shown in Figure 2 a, b). 10 H 20 After the surface modification of O5Si, the PVDF@C 10 H 20 O5Si film has a smaller amount of white bright surface compared to the PVDF film because when the original film surface is attached with C 10 H 20 O5Si, the electrons released by the field emission source are not easily aggregated on the film surface. After being modified with C 10 H 20 O5Si, no obvious phase separation occurs between the original film (PVDF film) and the modifier (C 10 H 20 O5Si), indicating good compatibility between the modifier and the original film. Moreover, no obvious particles and cracks appear on the surface of the modified original film, indicating that the modifier is evenly distributed on the original film surface and has good dispersibility (as shown in Figure 2 c, d). A large number of micro-nano hierarchical structures formed by SiO2 nanoparticles are distributed on the surface and pore walls of the PVDF@C 10 H 20 O5Si@SiO2 film (as shown in Figure 2 e, f), which is crucial for achieving efficient oil / water emulsion separation. To study the effect of C 10 H 20 O5Si on the PVDF@C 10 H 20 O5Si@SiO2 film, a PVDF film modified with SiO2 nanoparticles without a C 10 H 20 O5Si layer (i.e., the PVDF@SiO2 nanocomposite film) was prepared. It can be clearly observed from the scanning image of the PVDF@SiO2 film that a large number of SiO2 nanoparticles are agglomerated around the pore walls and not evenly dispersed on the film surface (as shown in Figure 2 g, h). This is because after being treated with C 10 H 20 O5Si, the adhesion to inorganic materials can be improved, enabling SiO2 to better adhere to the PVDF film surface, thereby increasing the permeation flux of the film.

[0080] 2. AFM Characterization of the PVDF@C 10 H 20 O5Si@SiO2 Film

[0081] To prove that SiO2 nanoparticles are uniformly loaded onto the membrane surface, PVDF@C was prepared. 10 H 20 O5Si membrane and PVDF@C 10 H 20 O5Si@SiO2 membrane, and the AFM images with a scanning range of 20μm×20μm were used to further study the surface microstructure and roughness of the membrane. Figure 3 For PVDF@C 10 H 20 O5Si membrane (a, b) and PVDF@C 10 H 20 O5Si@SiO2-300 membrane (c, d) AFM images. As Figure 3 shown, the roughness of the PVDF@C 10 H 20 O5Si membrane and PVDF@C 10 H 20 O5Si@SiO2 membrane are 65nm and 72nm respectively, which proves that SiO2 nanoparticles are uniformly loaded onto the membrane surface and a micro-nano multi-level structure is constructed, while increasing the surface roughness of the membrane, which is beneficial to enhancing the anti-fouling performance of the PVDF@C 10 H 20 O5Si@SiO2 membrane.

[0082] 3. ATR-FITR Characterization of PVDF@C 10 H 20 O5Si@SiO2 Membrane

[0083] Figure 4 FT-IR spectra of PVDF membrane, PVDF@C 10 H 20 O5Si membrane, PVDF@C 10 H 20 O5Si@SiO2-300 membrane. The FT-IR curve of the pure PVDF membrane shows characteristic absorption peaks of PVDF molecules at 1406 cm -1 , 1178 cm -1 , 870 cm -1 and 841 cm -1 . Compared with the PVDF membrane, several new absorption peaks appear in the spectrum of the PVDF@C 10 H 20 O5Si membrane. A stretching vibration peak of Si-O-CH3 appears at a wavenumber of 1083 cm -1 , and a characteristic stretching vibration peak of Si-CH2 appears at a wavenumber of 798 cm -1 . The above phenomena indicate that KH570 molecules have been introduced onto the PVDF membrane. PVDF@C 10 H20 In the FT-IR spectrum of the O5Si@SiO2 film, a typical frequency band appears at 1108 cm -1 wave number, which is attributed to the symmetric stretching mode of Si-O-Si. The peak at 1078 cm -1 wave number clearly corresponds to the stretching vibration of the Si-O-Si bond. The characteristic absorption peak of the intramolecular crystalline water H-O-H bond appears at 1660 cm -1 . The presence of these characteristic peaks indicates that the silanol bonds in the SiO2 structure form intermolecular hydrogen bonds between molecules. The intermolecular hydrogen bonds can enhance the hydrophilicity of the membrane material and thus improve the anti-fouling performance of the membrane. A new absorption peak appears at 1723 cm -1 , which is the absorption peak of the carbonyl group in C 10 H 20 O5Si. The appearance of this peak proves that C 10 H 20 O5Si has been successfully grafted onto the nano-SiO2 particles. The above results indicate that the PVDF@C 10 H 20 O5Si@SiO2 film has been successfully prepared.

[0084] 4. XPS and XRD Characterization of the PVDF@C 10 H 20 O5Si@SiO2 Film

[0085] Figure 5 XPS survey spectra of the PVDF film, the PVDF@C 10 H 20 O5Si film, and the PVDF@C 10 H 20 O5Si@SiO2-300 film are shown. As Figure 5 shown, compared with the PVDF and PVDF@C 10 H 20 O5Si films, an obvious Si element signal is observed in the XPS spectrum of the PVDF@C 10 H 20 O5Si@SiO2 film. Compared with the PVDF film, there is a very weak O(1s) peak at 531.02 eV in the XPS spectrum of the PVDF@C 10 H 20 O5Si film, which is the representative spectrum of the high-resolution O(1s) peak of the PVDF@C Figure 6 H 10 H 20 O5Si film, proving that C 10 H 20 O5Si has been successfully coated on the surface of the PVDF film. Compared with the PVDF@C 10 H 20 O5Si film, the PVDF@C10 H 20 For the SiO2 film, an obvious Si element signal was observed. Figure 7 It is PVDF@C 10 H 20 The high-resolution spectrum of Si(2s) of the O5Si@SiO2-300 film, with a binding energy of 153.26 eV, Figure 8 It is PVDF@C 10 H 20 The high-resolution spectrum of Si(2p) of the O5Si@SiO2-300 film, with a binding energy of 102.33 eV. It proves that PVDF@C 10 H 20 The successful preparation of the O5Si@SiO2-300 film. From Figure 9 It can be seen that a diffraction peak of SiO2 appears at an angle of 25.91°, which also proves that SiO2 is successfully compounded on the PVDF film.

[0086] 5. PVDF@C 10 H 20 The oil-water separation principle of the O5Si@SiO2 film

[0087] The surface characteristics of the film mainly stem from its special micro-nano multi-level structure and the surface chemical composition jointly formed by the hydrophilic silane coupling agent and SiO2. When the oil / water emulsion comes into contact with the PVDF@C 10 H 20 O5Si@SiO2 composite film, due to the super-hydrophilicity of the PVDF@C 10 H 20 O5Si@SiO2 film, water molecules will combine with the oxygen atoms on the film surface as acceptors as hydrogen bond donors, capture water on the film surface of the micro-nano multi-level structure to form a hydration layer, and continuously penetrate downward under the action of gravity or hydrostatic pressure. The hydration layer on the film surface can effectively prevent oil droplets from contaminating the film surface.

[0088] In addition, the separation mechanism of the PVDF@C 10 H 20 O5Si@SiO2 composite film for the emulsion is explained by the capillary force. It is observed from the SEM image that the pore size of the PVDF@C 10 H 20 O5Si@SiO2 composite film is about 0.45 μm. Each pore size on the film surface can be regarded as a capillary, and the thickness of the film is about 0.2 mm. According to the Jurin formula, the calculated Jurin height is about 13 m, which is much larger than the thickness of the composite film. Therefore, water continuously penetrates under the action of capillary force while blocking the passage of oil droplets, achieving the purpose of oil-water separation. The schematic diagram of the oil-water separation process is as Figure 10 shown.

[0089] 6. Oil / Water Emulsion Separation Experiment

[0090] 6.1 Preparation of Oil / Water Emulsion

[0091] Deionized water and organic solvents (V 去离子水 / V 有机溶剂 = 100 / 1) were blended and vibrated for 30 min using an ultrasonic cleaner to obtain an emulsifier-free oil / water emulsion. The organic solvents included benzene, toluene, p-xylene, and transformer oil. The preparation method of the emulsifier-containing emulsion was the same as that of the emulsifier-free oil / water emulsion except that 200 mg of sodium dodecyl sulfate (SDS) was added.

[0092] The membrane was fixed in a fritted filter device with an inner diameter of 4 cm, and the oil / water emulsion was poured into the upper glass tube and filtered under a pressure of 0.07 MPa.

[0093] 6.2 Oil / Water Emulsion Separation

[0094] The separation ability of the membrane was evaluated through the oil / water emulsion separation experiment. Figure 11 For the separation experiment device, photos and optical microscope images of the oil / water emulsion before and after separation. The PVDF@C 10 H 20 O5Si@SiO2 membrane prepared in Example 1 was fixed in a fritted filter device with an effective separation area of 12.56 cm 2 , and the emulsion was poured into the upper glass tube and filtered under a pressure of 0.07 MPa. Among them, the PVDF@C 10 H 20 O5Si@SiO2-400 membrane could not separate the oil / water emulsion under 0.07 MPa, probably because the relatively thick nano-SiO2 layer blocked the pores of the membrane, resulting in the inability of water to penetrate through the membrane. Therefore, photos and optical microscope images of the emulsion after separation by the PVDF@C 10 H 20 O5Si@SiO2-400 membrane were not provided in this experiment. Bottle No. 1 was the original transformer oil / water emulsion, and bottles No. 2, 3, 4, 5, and 6 were PVDF, PVDF@C 10 H 20 O5Si@SiO2-50, PVDF@C 10 H 20 O5Si@SiO2-100, PVDF@C 10 H 20 O5Si@SiO2-200, and PVDF@C 10 H 20The filtrate after the O5Si@SiO2-300 membrane separates the transformer oil / water emulsion shows that the liquid in Bottle No. 1 is uniformly milky white, and a large number of oil droplets are dispersed in the optical microscope image. After separation by the PVDF modified membrane, the filtrate becomes clear, and a small number of oil droplets can be observed in the optical microscope images of Bottles No. 2 and No. 3, indicating incomplete separation. No visible oil droplets are observed in the optical microscope images of Bottles No. 4, 5, and 6. The experimental results show that PVDF@C 10 H 20 O5Si@SiO2-100, PVDF@C 10 H 20 O5Si@SiO2-200 and PVDF@C 10 H 20 The O5Si@SiO2-300 composite membrane can effectively separate the oil / water emulsion.

[0095] 7. PVDF@C 10 H 20 The separation efficiency of the O5Si@SiO2 membrane is affected

[0096] Figure 12 For PVDF, PVDF@C 10 H 20 O5Si@SiO2-50, PVDF@C 10 H 20 O5Si@SiO2-100, PVDF@C 10 H 20 O5Si@SiO2-200 and PVDF@C 10 H 20 The oil / water emulsion separation efficiency of the O5Si@SiO2-300 membrane; as Figure 12 shown, PVDF, PVDF@C 10 H 20 O5Si@SiO2-50, PVDF@C 10 H 20 O5Si@SiO2-100, PVDF@C 10 H 20 O5Si@SiO2-200 and PVDF@C 10 H 20 The O5Si@SiO2-300 membrane, denoted as membranes A, B, C, D, and E in sequence, has separation efficiencies for the transformer oil / water emulsion of 75.33%, 78.88%, 86.31%, 92.55%, and 99.91% respectively. The experimental results show that PVDF@C 10 H 20 The O5Si@SiO2-300 composite membrane is the best choice for oil / water emulsion separation.

[0097] 8, PVDF@C 10 H 20 Effect on the permeation flux of O5Si@SiO2 membrane

[0098] Figure 13 The TOC results of the filtrates after separating surfactant-containing / surfactant-free transformer oil / water emulsion, benzene / water emulsion, toluene / water emulsion, and p-xylene / water emulsion (the preparation methods of the above emulsions are the same as those in "6.1" above) are recorded as filtrates A, B, C, and D. The TOC content of the surfactant-free transformer oil / water filtrate is lower than 8.2 ppm, and the organic carbon (TOC) content in the surfactant-containing transformer oil / water filtrate is lower than 19 ppm. At the same time, the permeation fluxes of the surfactant-free and surfactant-containing transformer oil / water emulsions are 1233 Lm -2 h -1 bar -1 and 572 Lm -2 h -1 bar -1 , and the experimental results show that PVDF@C 10 H 20 O5Si@SiO2-300 membrane can efficiently separate even stable oil / water emulsions. PVDF@C 10 H 20 O5Si@SiO2 composite membrane has the versatility to separate various oil / water emulsions, so it has good application prospects in the field of oil-water separation.

[0099] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of a silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane, characterized in that, It includes the following steps: Dissolve the silane coupling agent in organic solvent A to obtain solution A; Soak the polyvinylidene fluoride membrane in Solution A to obtain PVDF@C 10 H 20 O5Si membrane; Disperse nano-SiO2 in organic solvent B to obtain solution B; Mix solution B and solution A to obtain mixed solution C; Immerse the PVDF@C 10 H 20 O5Si membrane in the mixed solution C to obtain a silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane.

2. The preparation method according to claim 1, characterized in that, The silane coupling agent is 3-(methacryloyloxy)propyltrimethoxysilane; organic solvent A is ethanol; the volume ratio of the silane coupling agent to organic solvent A is 1:

10.

3. The preparation method according to claim 1, wherein The conditions for soaking the polyvinylidene fluoride membrane in solution A are set as follows: the soaking temperature is room temperature; the soaking time is 1-3 h.

4. The preparation method according to claim 1, characterized in that, The mass-volume ratio of nano-SiO2 to organic solvent B is 50-400 mg∶200 mL; organic solvent B is N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, The mass-volume ratio of nano-SiO2 in solution B to the silane coupling agent in solution A is 50-400 mg∶5 mL.

6. The preparation method according to claim 1, wherein PVDF@C 10 H 20 The conditions for immersing the O5Si film in the mixed solution C are set as follows: the immersion temperature is room temperature; the immersion time is 8 - 12 h.

7. The preparation method according to claim 1, wherein, PVDF@C 10 H 20 After the O5Si film is impregnated in the mixed solution C, it also includes the steps of cleaning and drying.

8. The preparation method according to claim 7, wherein The drying temperature is 100 °C and the drying time is 20 min.

9. A silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane prepared by the preparation method according to any one of claims 1-8.

10. Application of the silica nanoparticle-modified polyvinylidene fluoride microfiltration membrane according to claim 1 in oil / water emulsion separation.

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