Flexible silicon dioxide nanofiltration membrane, preparation method, application and filtering device

Abstract

The invention provides a flexible silicon dioxide nanofiltration membrane, a preparation method, application and a filtering device. The preparation method comprises the following steps: S1, providing a clay mineral nanosheet; s2, carrying out acid leaching treatment on the clay mineral nanosheet in an acid solution to obtain a silicon dioxide nanosheet dispersion liquid; s3, performing solid-liquid separation on the silicon dioxide nanosheet dispersion liquid to obtain a solid isolate, and dispersing the solid isolate into a dispersing agent to obtain a loading liquid; s4, enabling the loading liquid to penetrate through the basement membrane to obtain the flexible silicon dioxide nanofiltration membrane loaded with the silicon dioxide nanosheets. According to the method, the membrane flux and the retention rate can be considered, the porous silicon dioxide nanosheets are obtained through acid leaching treatment and accurate etching, the water flux is effectively expanded, and the high retention rate is reserved.

Description

Technical Field

[0001] This invention relates to the field of silica nanofiltration membrane preparation, and more particularly to a flexible silica nanofiltration membrane, its preparation method, its application, and a filtration device. Background Technology

[0002] Nanofiltration membranes are widely used in water treatment. However, for extreme scenarios such as high temperatures, organic solvents, and high levels of organic pollutants, commonly used commercial organic nanofiltration membranes are increasingly unable to meet practical water treatment needs. Two-dimensional laminar flow membranes assembled from two-dimensional materials such as graphene have seen a surge in research in the nanofiltration field in recent years due to their precise sieving, ease of assembly, scalability, and suitability for extreme environments. However, the preparation of these common advanced two-dimensional materials is often complex, using expensive raw materials and toxic reagents, limiting their further development. Layered clay minerals, with their advantages of low cost and large-scale preparation potential, offer a new approach to two-dimensional laminar flow nanofiltration membranes; however, current research on clay mineral nanofiltration membranes generally suffers from low flux and instability under acidic conditions.

[0003] Chinese invention patent application CN112263920A discloses a method for preparing and applying a nanofiltration membrane for macromolecular dyes. It uses natural clay as raw material and obtains a nanofiltration membrane for retaining macromolecular dyes through sodium ion intercalation, liquid-phase exfoliation, centrifugal sieving, and vacuum filtration. However, the nanofiltration membrane prepared from clay mineral nanosheets exhibits poor stability and low flux in nanofiltration tests, and cannot operate for extended periods under acidic conditions, thus failing to meet the needs of practical applications.

[0004] Therefore, it is necessary to provide a flexible silica nanofiltration membrane, its preparation method, its application, and a filtration device to solve or at least alleviate the technical problem of the inability to simultaneously achieve membrane flux and retention rate. Summary of the Invention

[0005] The main objective of this invention is to provide a flexible silica nanofiltration membrane, its preparation method, its application, and a filtration device, aiming to solve the technical problem of the inability to simultaneously achieve membrane flux and retention rate.

[0006] To achieve the above objectives, the present invention provides a method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0007] S1 provides clay mineral nanosheets;

[0008] S2, the clay mineral nanosheets are subjected to acid leaching treatment in an acid solution to obtain a silica nanosheet dispersion; the acid leaching treatment temperature is 40-180℃, the acid leaching treatment time is 0.2-24h, and the concentration of the acid solution is 7-18mol / L;

[0009] S3, the solid separated material obtained after solid-liquid separation of the silica nanosheet dispersion is dispersed in a dispersant to obtain a loaded liquid;

[0010] S4, after the loaded liquid passes through the base membrane, a flexible silica nanofiltration membrane loaded with silica nanosheets is obtained.

[0011] Furthermore, the clay mineral nanosheets are derived from clay minerals; the clay minerals include one or more of talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite; the thickness of the clay mineral nanosheets is 1-12 nm.

[0012] Furthermore, the acid leaching treatment is carried out under stirring conditions; the stirring speed is 200-1000 rpm.

[0013] Furthermore, the acid solution includes one or more of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, and phosphoric acid solution.

[0014] Further, on a dry weight basis, the solid-liquid ratio of the solid separated product and the dispersant is 1 mg:20 mL to 1 mg:700 mL; the dispersant includes ethanol.

[0015] Furthermore, the ratio of the solid isolate to the base membrane, on a dry weight basis, is 1-7 μg / cm³. 2 The process of permeating the loaded liquid through the base membrane is carried out under vacuum filtration conditions; the base membrane includes one of polyethersulfone membrane, polyvinylidene fluoride membrane, polycarbonate membrane, cellulose acetate membrane, and nylon membrane.

[0016] Furthermore, step S4 further includes: after the loading liquid passes through the base membrane, the base membrane is dried; the drying temperature is 25-100℃, and the drying time is 1-24h.

[0017] The present invention also provides a flexible silica nanofiltration membrane, comprising: being prepared by any of the methods described above for preparing flexible silica nanofiltration membranes.

[0018] The present invention also provides an application of the flexible silica nanofiltration membrane as described above in filtering organic solutions.

[0019] The present invention also provides a filtration device comprising a flexible silica nanofiltration membrane as described above.

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

[0021] This invention can balance membrane flux and retention rate. Based on clay mineral nanosheets, it not only obtains porous silica nanosheets through precise etching by acid leaching, effectively increasing water flux, but also retains a high retention rate. In addition, this invention can also increase membrane stability under acidic conditions (pH<2), making it a more promising method for preparing inorganic nanofiltration membranes.

[0022] Specifically, this invention utilizes the rapid etching effect of acid treatment to quickly dissolve highly active metal ions from clay minerals, preserving the layered structure of silica. During the etching process, nanoscale pores are etched onto the surface of the nanosheets, thus reducing the movement distance of solvent molecules during nanofiltration and increasing the nanofiltration flux while maintaining the retention rate. Simultaneously, the nanofiltration membrane assembled from silica nanosheets exhibits strong acid resistance and a certain degree of flexibility, solving the problems of low flux and poor acid and alkali resistance of conventional clay mineral nanofiltration membranes. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 The image shown is the AFM image of the silica nanosheets in Example 3 of this invention.

[0025] Figure 2 This is a TEM image of the silica nanosheets in Example 3 of the present invention;

[0026] Figure 3 This is a pore size distribution diagram of the silica nanosheets in Example 3 of the present invention;

[0027] Figure 4 This is a cross-sectional SEM image of the silica nanofiltration membrane in Example 3 of the present invention;

[0028] Figure 5 The magnesium and aluminum content of the vermiculite membrane obtained in Comparative Example 3 of this invention after filtration in an extremely acidic aqueous solution for different numbers of times;

[0029] Figure 6 The figure shows the nanofiltration performance of the vermiculite membrane obtained in Comparative Example 3 of this invention after filtration in an extremely acidic aqueous solution for different numbers of times using Evans blue aqueous solution; in the figure, red indicates the rejection rate and blue indicates the flux.

[0030] Figure 7The figure shows the nanofiltration performance of the silica nanofiltration membrane obtained in Example 3 of the present invention after filtering in an extremely acidic aqueous solution for different numbers of times with Evans blue aqueous solution; in the figure, red indicates the rejection rate and blue indicates the flux.

[0031] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0034] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0035] The clay minerals used in the embodiments of the present invention are expanded vermiculite particles purchased from China Maclean Company. The main component of the particles is vermiculite (AlFeMgO3Si). The clay mineral nanosheet dispersion is obtained by intercalation and exfoliation using liquid phase ion exchange.

[0036] This invention provides a method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0037] S1 provides clay mineral nanosheets.

[0038] In this invention, the clay mineral nanosheets are derived from clay minerals; the clay minerals include one or more of talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite, and are further preferably vermiculite; in this invention, the thickness of the clay mineral nanosheets is 1-12 nm (further 1-10 nm or 8-12 nm), and the average diameter ranges from 100-3000 nm, mainly concentrated around 500 nm; for example, the average diameter of the clay mineral nanosheets is mainly concentrated in the range of 400-600 nm.

[0039] S2, the clay mineral nanosheets are subjected to acid leaching in an acid solution to obtain a silica nanosheet dispersion.

[0040] In this invention, the acid leaching temperature is 40-180℃, more specifically 90-110℃; the acid leaching duration is 0.2-24h, more specifically 10-20h, and even more specifically 10-14h; the concentration of the acid solution is 7-18mol / L, more specifically 8-16mol / L, and even more specifically 8-12mol / L; and the concentration of the clay mineral nanosheets in the acid solution can be 0.5-1.5g / L.

[0041] In this invention, the clay mineral nanosheets are mixed with an acid solution in the form of a clay mineral nanosheet dispersion, and the clay mineral nanosheets undergo the acid leaching treatment in the acid solution; the volume ratio of the clay mineral nanosheet dispersion to the acid solution is 1:1-1:20, more preferably 1:8-1:20, and even more preferably 1:8-1:12; the concentration of the clay mineral nanosheets in the clay mineral nanosheet dispersion is 1-20 g / L, more preferably 5-15 g / L, and even more preferably 8-12 g / L; the concentration of the acid solution is 7-18 mol / L, more preferably 9-16 mol / L, and even more preferably 9-12 mol / L.

[0042] In this invention, the acid leaching treatment is carried out under stirring conditions; the stirring speed is 200-1000 rpm, and more specifically 300-600 rpm.

[0043] In this invention, the acid solution and the acid liquid each include one or more of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, and phosphoric acid solution; further, the acid solution and the acid liquid are both sulfuric acid solutions.

[0044] As an example, the acid leaching treatment of the present invention includes: mixing the clay mineral nanosheet dispersion and the acid solution evenly and then heating to react.

[0045] S3, the solid separated product obtained after solid-liquid separation of the silica nanosheet dispersion is dispersed in a dispersant to obtain a loaded liquid.

[0046] In this invention, the solid-liquid ratio of the solid isolate to the dispersant, based on dry weight, is 1:20-1:700, further 1:150-1:350, and even further 1:250-1:350, with the unit of solid-liquid ratio being mg / mL. It should be noted that the solid isolate can be dispersed in the dispersant without drying; however, the amount of the solid isolate needs to be determined by converting the dry weight to wet weight ratio. In this invention, the dispersant includes ethanol.

[0047] As an example, the process of dispersing the solid separated product obtained after solid-liquid separation of the silica nanosheet dispersion in a dispersant includes: after centrifuging the silica nanosheet dispersion, discarding the supernatant, and redispersing it with anhydrous ethanol.

[0048] S4, after the loaded liquid passes through the base membrane, a flexible silica nanofiltration membrane loaded with silica nanosheets is obtained.

[0049] In this invention, the ratio of the solid isolate to the base membrane, based on dry weight, is 1-7 μg / cm³. 2 Further, it was 2-4.5 μg / cm 2 Furthermore, it is 2-2.5 μg / cm 2 That is, the mass of the dried solids and the area of ​​the substrate membrane satisfy the above conditions. It should be noted that in the embodiments and comparative examples of the present invention, although the diameter of the PVDF membrane is 90 mm, after installation in the vacuum filtration device, the diameter that can participate in the loading is 75 mm (circular), specifically based on the loading amount in the embodiments and comparative examples; and the membrane area that performs the loading is used as the effective area for subsequent filtration experiments (filtration tests).

[0050] In this invention, the process of permeating the loaded liquid through the base membrane is carried out under vacuum filtration conditions; that is, a flexible silica nanofiltration membrane is assembled on the base membrane under negative pressure by vacuum filtration.

[0051] In this invention, the base membrane includes one of polyethersulfone membrane, polyvinylidene fluoride membrane, polycarbonate membrane, cellulose acetate membrane, and nylon membrane, and is further defined as polyvinylidene fluoride membrane.

[0052] In this invention, after the loading liquid passes through the base membrane, the base membrane is dried; the drying temperature is 25-100℃, and the drying time is 1-24h; further, the drying temperature is 50-70℃, and the drying time is 10-14h.

[0053] In the preparation process of this invention, a porous silica nanosheet dispersion is obtained by reacting and etching a clay mineral nanosheet dispersion with an acid at a high temperature, and then an inorganic nanofiltration membrane is prepared by filtration. The octahedral structure of metal cations is precisely etched on the clay mineral nanosheets by acid treatment, creating nanopores, which greatly increases the water flux. The resulting silica nanofiltration membrane can effectively resist corrosion under acidic conditions and the dissolution effect of organic solvents.

[0054] The present invention also provides a flexible silica nanofiltration membrane, comprising: being prepared by any of the methods described above for preparing flexible silica nanofiltration membranes.

[0055] The present invention also provides an application of the flexible silica nanofiltration membrane as described above in filtering organic solutions.

[0056] Furthermore, the organic solution is an aqueous environment; the filtration is nanofiltration; the filtration pressure can be 0.03-0.07 MPa; the organic solution is an Evans blue aqueous solution; the concentration of Evans blue in the organic solution is 5-15 mg / L; the pH of the organic solution can be less than 2 or less than 0.5; the flexible silica nanofiltration membrane can perform the filtration in an environment with a pH less than 2 or less than 0.5; the flexible silica nanofiltration membrane is tolerant to environments with a pH less than 2 or less than 0.5.

[0057] The present invention also provides a filtration device, wherein the filtration device includes a flexible silica nanofiltration membrane as described above; specifically, the filtration device is a nanofiltration device, and the nanofiltration membrane used in the filtration device is the flexible silica nanofiltration membrane.

[0058] The following are specific examples of the present invention:

[0059] Example 1

[0060] 1. A method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0061] S1 provides a vermiculite nanosheet dispersion; in the vermiculite nanosheet dispersion (vermiculite nanosheets dispersed in water), the concentration of vermiculite nanosheets is 10 g / L; the thickness of the vermiculite nanosheets is about 10 nm, and the average diameter ranges from 100 to 3000 nm, mainly concentrated around 500 nm.

[0062] S2, the vermiculite nanosheet dispersion and sulfuric acid solution were mixed at a volume ratio of 1:10 and reacted at 100℃ for 12h (acid leaching treatment) to obtain a silica nanosheet dispersion; the concentration of the sulfuric acid solution was 10mol / L, and the mixture was continuously stirred at a speed of 400rpm during the reaction.

[0063] S3. Centrifuge the silica nanosheet dispersion at 1000 rpm for 5 min to obtain a solid separator (acid-impregnated silica nanosheets); select the solid separator (corresponding to a dry weight of 0.3 mg) and disperse it in 30 mL of anhydrous ethanol to obtain a loading solution.

[0064] S4. The loaded liquid is filtered under negative pressure using a quartz vacuum filtration device, allowing the loaded liquid to pass through a PVDF membrane (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Industry Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane). This results in silica nanosheets being loaded onto the PVDF membrane at a loading rate of 6.8μg / cm³. 2 Then, the PVDF membrane loaded with silica nanosheets was dried at 60°C for 12 hours to obtain a flexible silica nanofiltration membrane.

[0065] 2. Filtration test of Evans blue aqueous solution:

[0066] The flexible silica nanofiltration membrane in this embodiment was tested for filtration with Evans blue aqueous solution (pressure 0.05 MPa). The concentration of Evans blue solution was 10 mg / L and the volume was 1 L. The test showed that the flux was 15.5 L HMB and the rejection rate was 99.6%.

[0067] Example 2

[0068] 1. A method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0069] S1 provides a vermiculite nanosheet dispersion; in the vermiculite nanosheet dispersion (vermiculite nanosheets dispersed in water), the concentration of vermiculite nanosheets is 10 g / L; the thickness of the vermiculite nanosheets is about 10 nm, and the average diameter ranges from 100 to 3000 nm, mainly concentrated around 500 nm.

[0070] S2, the vermiculite nanosheet dispersion and sulfuric acid solution were mixed at a volume ratio of 1:10 and reacted at 100℃ for 12h (acid leaching treatment) to obtain a silica nanosheet dispersion; the concentration of the sulfuric acid solution was 10mol / L, and the mixture was continuously stirred at a speed of 400rpm during the reaction.

[0071] S3. Centrifuge the silica nanosheet dispersion at 1000 rpm for 5 min to obtain a solid separator (acid-impregnated silica nanosheets); select the solid separator (corresponding dry weight 0.2 mg) and disperse it in 30 mL of anhydrous ethanol to obtain a loading solution.

[0072] S4. The loaded liquid is filtered under negative pressure using a quartz vacuum filtration device, allowing the loaded liquid to pass through a PVDF membrane (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Industry Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane), thereby loading silica nanosheets onto the PVDF membrane at a loading rate of 4.5μg / cm³. 2 Then, the PVDF membrane loaded with silica nanosheets was dried at 60°C for 12 hours to obtain a flexible silica nanofiltration membrane.

[0073] 2. Filtration test of Evans blue aqueous solution:

[0074] The flexible silica nanofiltration membrane in this example was subjected to a filtration test with Evans blue aqueous solution (pressure 0.05 MPa), with a concentration of 10 mg / L and a volume of 1 L, in the same manner as in Example 1. The test showed a flux of 65.4 L HMB and a rejection rate of 99.5%.

[0075] Example 3

[0076] 1. A method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0077] S1 provides a vermiculite nanosheet dispersion; in the vermiculite nanosheet dispersion (vermiculite nanosheets dispersed in water), the concentration of vermiculite nanosheets is 10 g / L; the thickness of the vermiculite nanosheets is about 10 nm, and the average diameter ranges from 100 to 3000 nm, mainly concentrated around 500 nm.

[0078] S2, the vermiculite nanosheet dispersion and sulfuric acid solution were mixed at a volume ratio of 1:10 and reacted at 100℃ for 12h (acid leaching treatment) to obtain a silica nanosheet dispersion; the concentration of the sulfuric acid solution was 10mol / L, and the mixture was continuously stirred at a speed of 400rpm during the reaction.

[0079] S3. Centrifuge the silica nanosheet dispersion at 1000 rpm for 5 min to obtain a solid separator (acid-impregnated silica nanosheets); select the solid separator (corresponding dry weight 0.1 mg) and disperse it in 30 mL of anhydrous ethanol to obtain a loading solution.

[0080] S4. The loaded liquid is filtered under negative pressure using a quartz vacuum filtration device, allowing the loaded liquid to pass through a PVDF membrane (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Industry Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane), thereby loading silica nanosheets onto the PVDF membrane at a loading rate of 2.3μg / cm³. 2 Then, the PVDF membrane loaded with silica nanosheets was dried at 60°C for 12 hours to obtain a flexible silica nanofiltration membrane.

[0081] 2. Filtration test of Evans blue aqueous solution:

[0082] The flexible silica nanofiltration membrane in this example was subjected to a filtration test with Evans blue aqueous solution (pressure 0.05 MPa), with a concentration of 10 mg / L and a volume of 1 L, in the same manner as in Example 1. The test showed a flux of 201.3 L HMB and a rejection rate of 99.7%.

[0083] Example 4

[0084] 1. A method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0085] S1 provides a vermiculite nanosheet dispersion; in the vermiculite nanosheet dispersion (vermiculite nanosheets dispersed in water), the concentration of vermiculite nanosheets is 10 g / L; the thickness of the vermiculite nanosheets is about 10 nm, and the average diameter ranges from 100 to 3000 nm, mainly concentrated around 500 nm.

[0086] S2, the vermiculite nanosheet dispersion and sulfuric acid solution were mixed at a volume ratio of 1:10 and reacted at 100℃ for 12h (acid leaching treatment) to obtain a silica nanosheet dispersion; the concentration of the sulfuric acid solution was 10mol / L, and the mixture was continuously stirred at a speed of 400rpm during the reaction.

[0087] S3. Centrifuge the silica nanosheet dispersion at 1000 rpm for 5 min to obtain a solid separator (acid-impregnated silica nanosheets); select the solid separator (corresponding dry weight 0.05 mg) and disperse it in 30 mL of anhydrous ethanol to obtain a loading solution.

[0088] S4. The loaded liquid is filtered under negative pressure using a quartz vacuum filtration device, allowing the loaded liquid to pass through a PVDF membrane (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Industry Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane), thereby loading silica nanosheets onto the PVDF membrane at a loading rate of 1.1μg / cm³. 2 Then, the PVDF membrane loaded with silica nanosheets was dried at 60°C for 12 hours to obtain a flexible silica nanofiltration membrane.

[0089] 2. Filtration test of Evans blue aqueous solution:

[0090] The flexible silica nanofiltration membrane in this example was subjected to a filtration test with Evans blue aqueous solution (pressure 0.05 MPa), with a concentration of 10 mg / L and a volume of 1 L, in the same manner as in Example 1. The test showed a flux of 251.4 L HMB and a rejection rate of 45.3%.

[0091] Comparative Example 1

[0092] 1. A method for preparing a flexible silica nanofiltration membrane, comprising the following steps:

[0093] S1 provides a vermiculite nanosheet dispersion; in the vermiculite nanosheet dispersion (vermiculite nanosheets dispersed in water), the concentration of vermiculite nanosheets is 10 g / L; the thickness of the vermiculite nanosheets is about 10 nm, and the average diameter ranges from 100 to 3000 nm, mainly concentrated around 500 nm.

[0094] S2, the vermiculite nanosheet dispersion and sulfuric acid solution were mixed at a volume ratio of 1:10 and reacted at 100℃ for 12h (acid leaching treatment) to obtain a silica nanosheet dispersion; the concentration of the sulfuric acid solution was 5mol / L, and the mixture was continuously stirred at a speed of 400rpm during the reaction.

[0095] S3. Centrifuge the silica nanosheet dispersion at 1000 rpm for 5 min to obtain a solid separator (acid-impregnated silica nanosheets); select the solid separator (corresponding dry weight 0.1 mg) and disperse it in 30 mL of anhydrous ethanol to obtain a loading solution.

[0096] S4. The loaded liquid is filtered under negative pressure using a quartz vacuum filtration device, allowing the loaded liquid to pass through a PVDF membrane (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Industry Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane), thereby loading silica nanosheets onto the PVDF membrane at a loading rate of 2.3μg / cm³. 2 Then, the PVDF membrane loaded with silica nanosheets was dried at 60°C for 12 hours to obtain a flexible silica nanofiltration membrane.

[0097] 2. Filtration test of Evans blue aqueous solution:

[0098] The flexible silica nanofiltration membrane in this example was subjected to a filtration test with Evans blue aqueous solution (pressure 0.05 MPa), with a concentration of 10 mg / L and a volume of 1 L, similar to Example 1. The test showed a flux of 57.3 L HMB and a rejection rate of 89.5%.

[0099] Comparative Example 2

[0100] We provide PVDF membranes (90mm in diameter, 0.22μm in pore size, manufactured by Longjin Membrane Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane).

[0101] The PVDF membrane of this comparative example was subjected to filtration test with Evans blue aqueous solution (pressure 0.05 MPa) as in Example 1. The concentration of Evans blue solution was 10 mg / L and the volume was 1 L. The test showed that the flux was 1835.3 LHMB and the rejection rate was 5.3%.

[0102] Comparative Example 3

[0103] 0.1 mg of vermiculite nanosheets (same as in Example 3) were dispersed in 30 mL of anhydrous ethanol to obtain a loading solution. The loading solution was then filtered under negative pressure using a quartz vacuum filtration device, allowing it to pass through a PVDF membrane (90 mm in diameter, 0.22 μm in pore size, manufactured by Longjin Membrane Technology Co., Ltd., model: polyvinylidene fluoride hydrophobic filter membrane), thereby loading the vermiculite nanosheets onto the PVDF membrane at a loading rate of 2.3 μg / cm³. 2 Then, the PVDF film loaded with vermiculite nanosheets was dried at 60°C for 12 hours to obtain the vermiculite film.

[0104] The vermiculite membrane of this comparative example was subjected to filtration test with Evans blue aqueous solution (pressure 0.05 MPa) as in Example 1. The concentration of Evans blue solution was 10 mg / L and the volume was 1 L. The test showed that the flux was 12.7 L HMB and the rejection rate was 99.1%.

[0105] Analysis example 1

[0106] 1. The silica nanosheets obtained by acid treatment of vermiculite nanosheets were filtered into a membrane and tested for dye retention. The retention rate and flux were both at a high level (as in Example 3). The filter membrane without silica nanosheets had almost no retention effect, with a retention rate of only 5.3%. The vermiculite membrane with the same loading had a similar retention effect, but the flux was only 12.7 LHMB.

[0107] Nanofiltration membranes with different loadings of silica nanosheets were tested, and the results are shown in Table 1.

[0108] Table 1. Statistical Table of Dye Retention Performance of Silica Nanofiltration Membranes

[0109] Membrane material categories Flux (LHM) Retention rate (%) Example 1 15.5 99.6 Example 2 65.4 99.5 Example 3 201.3 99.7 Example 4 251.4 45.3 Comparative Example 1 57.3 89.5 Comparative Example 2 1835.3 5.3 Comparative Example 3 12.7 99.1

[0110] 2. The AFM of the silica nanosheet dispersion obtained in Example 3 was measured, such as... Figure 1 As shown, the results yielded nanosheets with a thickness of less than 10 nm and a lateral dimension of approximately 500 nm. The basic structure of the nanosheets was preserved after the acid leaching process, and traces of partial dissolution and reconstruction were visible on the surface.

[0111] TEM measurements were performed on the silica nanosheets obtained in Example 3, such as... Figure 2 As shown, the nanosheets obtained are amorphous silicon dioxide with a large number of micropores smaller than 2 nm.

[0112] The pore size distribution of the silica nanosheets obtained in Example 3 was measured using nitrogen adsorption-desorption method, such as... Figure 3As shown, the results of acid etching show that the nanosheets have a large number of pores with a size of about 0.6 nm.

[0113] The thickness of the loaded membrane was measured on the silica nanofiltration membrane obtained in Example 3, such as... Figure 4 As shown, the results show that the film exhibits a distinct layered structure with a thickness of approximately 32.5 nm.

[0114] 3. The silica nanofiltration membrane obtained in Example 3 and the vermiculite membrane obtained in Comparative Example 3 were subjected to cyclic filtration in an extremely acidic aqueous solution with pH = 0.1 (200 mL of extremely acidic aqueous solution each time). The magnesium and aluminum content in the vermiculite membrane was determined. After filtration of the extremely acidic aqueous solution for the corresponding number of times, its nanofiltration performance in Evans blue aqueous solution was tested (pressure 0.05 MPa). The concentration of Evans blue solution was 10 mg / L and the volume was 1 L.

[0115] like Figure 5-6 As shown, after 5 cycles, the magnesium and aluminum content in the vermiculite film gradually decreased, as determined by energy-dispersive X-ray spectroscopy. Furthermore, the dye rejection rate for Evans blue aqueous solution gradually decreased. Figure 7 As shown, the silica nanofiltration membrane maintains stable dye rejection and flux for Evans blue aqueous solution, indicating that its stability under extremely acidic conditions is far superior to that of vermiculite membrane.

[0116] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a flexible silica nanofiltration membrane, characterized in that, Including the following steps: S1 provides clay mineral nanosheets; S2, the clay mineral nanosheets are subjected to acid leaching treatment in an acid solution to obtain a silica nanosheet dispersion; the acid leaching treatment temperature is 40-180℃, the acid leaching treatment time is 0.2-24h, and the concentration of the acid solution is 7-18mol / L; S3, the solid separated material obtained after solid-liquid separation of the silica nanosheet dispersion is dispersed in a dispersant to obtain a loaded liquid; S4, after the loaded liquid passes through the base membrane, a flexible silica nanofiltration membrane loaded with silica nanosheets is obtained.

2. The method for preparing the flexible silica nanofiltration membrane according to claim 1, characterized in that, The clay mineral nanosheets are derived from clay minerals; the clay minerals include one or more of talc, serpentine, montmorillonite, illite, vermiculite, muscovite, phlogopite, biotite, and sericite; the thickness of the clay mineral nanosheets is 1-12 nm.

3. The method for preparing the flexible silica nanofiltration membrane according to claim 1, characterized in that, The acid leaching treatment is carried out under stirring conditions; the stirring speed is 200-1000 rpm.

4. The method for preparing the flexible silica nanofiltration membrane according to claim 1, characterized in that, The acid solution includes one or more of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, and phosphoric acid solution.

5. The method for preparing a flexible silica nanofiltration membrane according to claim 1, characterized in that, On a dry weight basis, the solid-liquid ratio of the solid separated product and the dispersant is 1 mg:20 mL to 1 mg:700 mL; the dispersant includes ethanol.

6. The method for preparing a flexible silica nanofiltration membrane according to claim 1, characterized in that, The ratio of the solid isolate to the base membrane, on a dry weight basis, is 1-7 μg / cm³. 2 The process of permeating the loaded liquid through the base membrane is carried out under vacuum filtration conditions; the base membrane includes one of polyethersulfone membrane, polyvinylidene fluoride membrane, polycarbonate membrane, cellulose acetate membrane, and nylon membrane.

7. The method for preparing a flexible silica nanofiltration membrane according to claim 1, characterized in that, Step S4 further includes: after the loading liquid passes through the base membrane, the base membrane is dried; the drying temperature is 25-100℃, and the drying time is 1-24h.

8. A flexible silica nanofiltration membrane, characterized in that, include: The flexible silica nanofiltration membrane was prepared using the preparation method described in any one of claims 1-7.

9. The application of the flexible silica nanofiltration membrane as described in claim 8 in filtering organic solutions.

10. A filtration device, characterized in that, The filtration device includes the flexible silica nanofiltration membrane as described in claim 8.

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