Two-dimensional layered kaolinite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention provides a two-dimensional layered kaolinite nanofiltration membrane, and a preparation method and application thereof, and the preparation method comprises the following steps: mixing kaolinite powder and an intercalator according to a first solid-to-liquid ratio, heating, stirring, carrying out intercalation reaction completely, and carrying out solid-liquid separation to obtain a solid kaolinite intercalation compound; mixing the kaolinite intercalation compound with water according to a second solid-to-liquid ratio, adjusting the pH value of the mixed solution to 9-13, and carrying out dispersion treatment to obtain a kaolinite nanosheet dispersion liquid; enabling the kaolinite nanosheet dispersion liquid to penetrate through the porous basement membrane, and depositing kaolinite nanosheets in the kaolinite nanosheet dispersion liquid on the porous basement membrane to obtain the two-dimensional layered kaolinite nanofiltration membrane; the operation steps are simple, no complex equipment or a large amount of organic solvent is used, and the method conforms to the concept of green chemistry. The prepared two-dimensional layered kaolinite nanofiltration membrane can be used in various fields of water treatment, organic solvent separation and the like, and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of dyeing and printing wastewater treatment technology, and particularly relates to two-dimensional layered kaolinite nanofiltration membrane, its preparation method and application. Background Technology

[0002] Dyeing and printing wastewater is a typical type of difficult-to-treat industrial wastewater, characterized by its large volume and high content of small-molecule organic pollutants. Traditional treatment methods for dyeing and printing wastewater mainly include physical, chemical, and biological methods. However, these methods have many limitations in practical applications and fail to meet the water quality requirements for dyeing and printing wastewater. Membrane separation technology, as an advanced water treatment technology, has shown great application potential in the field of dyeing and printing wastewater treatment due to its advantages such as low energy consumption, no secondary pollution, and high separation efficiency, and can retain dyes. However, the current preparation process of nanofiltration membranes is complex, the raw materials are expensive, and the yield is low, which limits its widespread application in large-scale dyeing and printing wastewater treatment. In addition, the size of the currently prepared two-dimensional nanosheets is relatively large, which seriously affects the optimization of water flux, thus restricting further improvement of nanofiltration membrane performance.

[0003] Kaolinite is a natural layered clay mineral with abundant and inexpensive reserves. Its main structure consists of silicon-oxygen tetrahedra and aluminum-oxygen octahedra, with relatively small single-layer nanosheets. However, current applications of kaolinite are mainly concentrated in traditional fields such as ceramics and packing materials, and it has not yet been fully developed and applied in the field of nanofiltration membrane separation technology.

[0004] Based on this, the present invention provides a two-dimensional layered kaolinite nanofiltration membrane, its preparation method and application, to solve the technical problem of how to obtain a nanofiltration membrane based on kaolinite that takes into account both water flux and retention rate. Summary of the Invention

[0005] The main objective of this invention is to provide a two-dimensional layered kaolinite nanofiltration membrane, its preparation method, and its application, aiming to solve the technical problem of how to obtain a nanofiltration membrane based on kaolinite that balances water flux and retention rate.

[0006] To achieve the above objectives, the present invention provides a method for preparing a two-dimensional layered kaolinite nanofiltration membrane, comprising the following steps: Kaolinite powder and intercalating agent were mixed at the first solid-liquid ratio. After heating and stirring until the intercalation reaction was complete, solid-liquid separation was performed to obtain the solid, which was the kaolinite intercalation complex.

[0007] After mixing the kaolinite intercalation complex with water at a second solid-liquid ratio, the pH of the mixed solution was adjusted to 9-13, and after dispersion treatment, a kaolinite nanosheet dispersion was obtained.

[0008] The kaolinite nanosheet dispersion is permeated through a porous substrate membrane, and the kaolinite nanosheets in the kaolinite nanosheet dispersion are deposited on the porous substrate membrane to obtain the two-dimensional layered kaolinite nanofiltration membrane.

[0009] According to an embodiment of this application, the first solid-liquid ratio is 1 mg: (5~15) mL.

[0010] The second solid-liquid ratio is 1 mg: (60~100) mL.

[0011] According to embodiments of this application, the intercalating agent includes one or more of dimethyl sulfoxide and saturated urea solution.

[0012] The molar concentration of the saturated urea solution is 17-18 mol / L.

[0013] According to the embodiments of this application, the heating and stirring temperature is 60~100℃, and the heating and stirring time is 6~10h.

[0014] According to an embodiment of this application, the dispersion processing step includes: After the mixed solution was subjected to homogenization, ultrasonication and centrifugation in sequence, the upper centrifuged liquid was collected to obtain the kaolinite nanosheet dispersion.

[0015] The mass concentration of the kaolinite nanosheet dispersion is 2~6 g / L.

[0016] The homogenization process is performed at a speed of 8000~12000 rpm for 15~25 minutes.

[0017] The ultrasonic treatment power is 300~500W, and the ultrasonic treatment duration is 15~25min.

[0018] The centrifugation speed is 1800~2200 rpm, and the centrifugation time is 5~15 min.

[0019] According to embodiments of this application, the porous substrate membrane includes one of polyvinylidene fluoride membrane, polyethersulfone membrane, and nylon membrane.

[0020] The porous base membrane has a pore size of 0.22~0.45μm.

[0021] According to an embodiment of this application, the solid-liquid separation is performed by centrifugation, and the solid obtained from the solid-liquid separation is washed to remove residual intercalating agent from the surface of the kaolinite intercalation composite.

[0022] The solid-liquid separation is performed by centrifuging at a speed of 3800~4200 rpm for a duration of 8~12 min.

[0023] The present invention also provides a two-dimensional layered kaolinite nanofiltration membrane, which is prepared by the above-described preparation method.

[0024] The thickness of the two-dimensional layered kaolinite nanofiltration membrane is 270~280 nm.

[0025] According to an embodiment of this application, the kaolinite nanosheets deposited on the two-dimensional layered kaolinite nanofiltration membrane are formed by stacking single-layer kaolinite nanosheets.

[0026] The loading of the deposited kaolinite nanosheets is 3.0~4.5 mg / g.

[0027] The thickness of the monolayer kaolinite nanosheets is 4~8 nm and the diameter is 0.6~0.9 μm.

[0028] The present invention also provides an application of the above-mentioned two-dimensional layered kaolinite nanofiltration membrane in filtering dyes.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, mixing kaolinite powder and an intercalating agent at a first solid-liquid ratio, followed by heating and stirring, accelerates the intercalation reaction, allowing the intercalating agent to be uniformly inserted between the kaolinite layers, thus improving the efficiency and uniformity of the reaction. This step effectively increases the spacing between the kaolinite layers, providing space for subsequent nanosheet exfoliation and facilitating the formation of kaolinite nanosheets.

[0030] This invention involves mixing the kaolinite intercalation complex with water at a second solid-liquid ratio, and then adjusting the pH of the mixed solution to alkaline. This not only facilitates the removal of hydrated hydrogen ions between the kaolinite layers and enhances the interlayer electrostatic repulsion, but also promotes further exfoliation of the kaolinite intercalation complex, improving the stability of the kaolinite nanosheet dispersion and ensuring efficient and uniform dispersion of the kaolinite nanosheets. The intercalation rate is 73.17–93.48%.

[0031] This invention permeates a kaolinite nanosheet dispersion through a porous substrate membrane. The kaolinite nanosheets in the dispersion are uniformly deposited on the porous substrate membrane, forming a dense and uniform two-dimensional layered structure, thus improving the separation performance of the two-dimensional layered kaolinite nanofiltration membrane. The retention rate is 96-98%, and the water flux of the two-dimensional layered kaolinite nanofiltration membrane is 42-63 LMH / bar. The thickness of the obtained two-dimensional layered kaolinite nanofiltration membrane is 270-280 nm. The kaolinite nanosheets deposited on the two-dimensional layered kaolinite nanofiltration membrane are formed by stacking multiple layers of monolithic kaolinite nanosheets. The thickness of each monolithic kaolinite nanosheet is 4-8 nm, and the diameter is 0.6-0.9 μm.

[0032] This invention utilizes the synergistic interaction of the above steps to produce a two-dimensional layered kaolinite nanofiltration membrane that balances water flux and retention rate using readily available and inexpensive raw materials. This results in good economic efficiency and ease of large-scale production and application. Furthermore, the operation is simple, requiring no complex equipment or large amounts of organic solvents, aligning with the principles of green chemistry. The prepared two-dimensional layered kaolinite nanofiltration membrane can be used in various fields such as water treatment and organic solvent separation, demonstrating broad application prospects. Attached Figure Description

[0033] 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.

[0034] Figure 1 The X-ray diffraction pattern of the kaolinite intercalation complex in Example 1 of this invention; Figure 2 These are atomic force microscopy images and particle size distributions of kaolinite nanosheets from Example 1 of this invention; wherein, Figure 2 (a) is an atomic force microscope image of kaolinite nanosheets. Figure 2 (b) shows the thickness of a single layer of kaolinite nanosheets; Figure 3 Diagram showing the diameter of a single-layer kaolinite nanosheet; Figure 4 This is a scanning electron microscope image of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 of the present invention; Figure 5 The graph shows the membrane flux and rejection rate of Evans blue dye molecules for the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 of the present invention. Figure 6 The graph shows the membrane flux and rejection rate of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 of this invention for different dye molecules. Figure 7 The X-ray diffraction pattern of the kaolinite intercalation complex in Example 3 of this invention; Figure 8 The X-ray diffraction pattern of the kaolinite intercalation complex in Example 4 of this invention; Figure 9 The graphs show the membrane flux and rejection rate of two-dimensional layered kaolinite nanofiltration membranes prepared from different porous substrate membranes in Examples 5-6 of this invention. Figure 10 The graph shows the loading of kaolinite nanosheets with respect to membrane flux and rejection rate in Examples 1-3 of this invention.

[0035] 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

[0036] 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.

[0037] 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.

[0038] To achieve the above objectives, the present invention provides a method for preparing a two-dimensional layered kaolinite nanofiltration membrane, comprising the following steps: S1: Kaolinite powder and intercalating agent are mixed according to the first solid-liquid ratio. After heating and stirring until the intercalation reaction is complete, solid-liquid separation is performed to obtain the solid as kaolinite intercalation complex.

[0039] In some embodiments, the insertion of an intercalating agent alters the interlayer structure of kaolinite, increasing the interlayer spacing and making the active sites of kaolinite more easily exposed. Kaolinite is a typical 1:1 layered silicate mineral, its crystal structure consisting of alternating layers of silicon-oxygen tetrahedra (SiO4) and aluminum-oxygen octahedra (Al(OH)4). The interlayers of kaolinite are primarily bound together by hydrogen bonds and van der Waals forces. These forces are relatively weak, and the weak interlayer bonding makes the kaolinite interlayers easily penetrated by external forces (such as the molecular forces of the intercalating agent), thereby disrupting the original interlayer structure. On the other hand, the interlayers of kaolinite typically contain a small amount of water molecules, which are bonded to the oxygen atoms of kaolinite through hydrogen bonds. The presence of water molecules weakens the interlayer bonding forces, making the interlayer structure more easily disrupted. Intercalating agent molecules can enter the interlayers through interaction with water molecules or by directly replacing water molecules, making the kaolinite layers easier to disperse. Combined with heating and stirring, the thermal motion of the intercalating agent molecules can be increased, making it easier for them to overcome the interlayer bonding forces and enter the interlayers, thus improving the insertion efficiency. After intercalation, the dispersibility of kaolinite is significantly improved, making it easier to prepare kaolinite nanosheet dispersions. High-temperature calcination leads to dehydroxylation of kaolinite, causing the hydroxyl groups to be removed, forming and releasing water molecules. After dehydroxylation, the structure of kaolinite changes from a layered structure to an amorphous or semi-crystalline structure. Due to the disappearance of hydroxyl groups, the hydrogen bonding sites between urea and dimethyl sulfoxide and the kaolinite layers decrease or completely disappear. This prevents the intercalating agent from effectively binding to kaolinite, and the intercalation process cannot continue. Therefore, this application requires controlling the heating and stirring of the mixture after mixing the kaolinite powder and the intercalating agent.

[0040] In some embodiments, the first solid-liquid ratio is 1 mg:(5~15) mL. Insufficient intercalating agent can lead to incomplete reaction between kaolinite powder and the intercalating agent, preventing the intercalating agent from fully inserting into the kaolinite interlayers. This results in some kaolinite interlayers remaining unmodified, uneven intercalation, and ultimately, unstable performance of the resulting kaolinite intercalation composite. Excessive intercalating agent increases production costs, reduces reaction efficiency, and makes the subsequent removal of excess intercalating agent lengthy. Therefore, selecting a suitable first solid-liquid ratio ensures uniform insertion of the intercalating agent into the kaolinite interlayers, improves reaction efficiency, reduces costs, simplifies subsequent processing, and ultimately yields a stable and well-dispersed kaolinite intercalation composite.

[0041] In some embodiments, the first solid-liquid ratio is 1 mg: (5~10) mL.

[0042] In some embodiments, the first solid-liquid ratio is 1 mg:(8~12) mL.

[0043] In some embodiments, the first solid-liquid ratio is 1 mg:(10~15) mL.

[0044] S2: After mixing the kaolinite intercalation complex with water according to the second solid-liquid ratio, the pH of the mixed solution is adjusted to 9-13, and after dispersion treatment, a kaolinite nanosheet dispersion is obtained.

[0045] In some embodiments, the second solid-liquid ratio is 1 mg:(60~100) mL. A suitable second solid-liquid ratio ensures that the kaolinite intercalation complex is fully dispersed in water, forming a uniform nanosheet dispersion. If the second solid-liquid ratio is too high, there will be too much kaolinite intercalation complex, making it difficult to disperse the kaolinite nanosheets uniformly and causing them to easily aggregate, resulting in poor uniformity and stability of the kaolinite nanosheet dispersion. It may also cause some intercalation complex to fail to be fully exfoliated into nanosheets, affecting the performance of the final product.

[0046] In some embodiments, the second solid-liquid ratio is 1 mg:(60~80) mL.

[0047] In some embodiments, the second solid-liquid ratio is 1 mg:(80~100) mL.

[0048] In some embodiments, the second solid-liquid ratio is 1 mg:(70~90) mL.

[0049] In some embodiments, the second solid-liquid ratio is 1 mg:(75~85) mL.

[0050] In some embodiments, the pH of the mixed solution is adjusted to 9-13. Under alkaline conditions, hydroxide ions (OH-) - It will react with hydrated hydrogen ions (H3O) between the kaolinite layers. + A neutralization reaction occurs, weakening the electrostatic attraction between layers. Simultaneously, hydroxyl ions are adsorbed on the kaolinite surface, carrying a negative charge and increasing the electrostatic repulsion between layers. This makes it easier for the kaolinite layers to be exfoliated into kaolinite nanosheets, and the kaolinite nanosheets can be uniformly dispersed in solution, preventing re-aggregation and thus improving the uniformity and stability of the kaolinite nanosheet dispersion.

[0051] In some embodiments, the pH of the mixed solution is adjusted using a 1-3 mol / L sodium hydroxide solution, potassium hydroxide solution, or ammonia solution.

[0052] In some embodiments, the pH of the mixed solution is adjusted using a 1.5-2.5 mol / L sodium hydroxide solution.

[0053] In some embodiments, the pH of the mixed solution is adjusted to 10-12. Excessively high pH leads to an excessively high concentration of hydroxide ions in the solution, resulting in excessive byproducts and affecting reaction efficiency. Furthermore, excessively high pH leads to excessive surface charge on the kaolinite nanosheets, generating excessive electrostatic repulsion and causing nanosheet aggregation. Therefore, strictly controlling the pH within the range of 9-13 is crucial to ensuring the successful preparation of the kaolinite nanosheet dispersion.

[0054] S3: The kaolinite nanosheet dispersion is passed through a porous base membrane, and the kaolinite nanosheets in the kaolinite nanosheet dispersion are deposited on the porous base membrane to obtain the two-dimensional layered kaolinite nanofiltration membrane.

[0055] In some embodiments, a vacuum filtration device is used to permeate the kaolinite nanosheet dispersion through a porous substrate membrane, whereby the kaolinite nanosheets in the dispersion are deposited on the porous substrate membrane. Kaolinite nanosheets possess a layered structure and uniform nanoscale pores, enabling the formation of a dense filtration layer on the porous substrate membrane. This effectively intercepts target precipitates (such as salts, organic matter, etc.), improving the selectivity and separation efficiency of the two-dimensional layered kaolinite nanofiltration membrane. Simultaneously, after deposition on the porous substrate membrane, the kaolinite nanosheets form a stable two-dimensional layered structure, enhancing the mechanical strength and chemical stability of the two-dimensional layered kaolinite nanofiltration membrane and extending its service life.

[0056] The above-described method for preparing a two-dimensional layered kaolinite nanofiltration membrane accelerates the intercalation reaction by mixing kaolinite powder with an intercalating agent at a first solid-liquid ratio and then heating and stirring. This allows the intercalating agent to be uniformly inserted into the interlayers of kaolinite, improving the efficiency and uniformity of the reaction. This step effectively increases the spacing between the kaolinite layers, providing space for subsequent nanosheet exfoliation and facilitating the formation of kaolinite nanosheets. After mixing the kaolinite intercalation complex with water at a second solid-liquid ratio, adjusting the pH of the mixed solution to alkaline not only helps remove hydrated hydrogen ions from the kaolinite layers and enhances the interlayer electrostatic repulsion, but also promotes further exfoliation of the kaolinite intercalation complex, improving the stability of the kaolinite nanosheet dispersion and ensuring efficient and uniform dispersion of the kaolinite nanosheets. Under negative pressure, when a kaolinite nanosheet dispersion is passed through a porous substrate membrane, the kaolinite nanosheets in the dispersion can be uniformly deposited on the porous substrate membrane to form a dense and uniform two-dimensional layered structure, thereby improving the separation performance of the two-dimensional layered kaolinite nanofiltration membrane.

[0057] Through the coordinated processes described above, a two-dimensional layered kaolinite nanofiltration membrane can be prepared using readily available and inexpensive raw materials, offering good economic efficiency and facilitating large-scale production and application. Furthermore, the operation is simple, requiring no complex equipment or large amounts of organic solvents, aligning with the principles of green chemistry. The prepared two-dimensional layered kaolinite nanofiltration membrane can be used in various fields such as water treatment and organic solvent separation, demonstrating broad application prospects.

[0058] In some embodiments, the intercalating agent includes one or more of dimethyl sulfoxide and saturated urea solution.

[0059] The molar concentration of the saturated urea solution is 17.0~18.0 mol / L.

[0060] In some embodiments, the intercalating agent is dimethyl sulfoxide (DMSO). DMSO is of analytical grade. DMSO is a polar solvent capable of forming hydrogen bonds with oxygen atoms on the kaolinite surface, enhancing the intercalation effect. Furthermore, under heating conditions, DMSO exhibits good thermal stability, enabling it to efficiently intercalate between kaolinite layers at high temperatures, significantly improving intercalation efficiency and making the kaolinite layers easier to exfoliate.

[0061] In some embodiments, the intercalating agent is a saturated urea solution, and the solvent is water. The molar concentration of the saturated urea solution is 17.9~18.0 mol / L. The amino (-NH2) and carbonyl (-CO-) groups in the urea molecule can form hydrogen bonds with oxygen atoms on the surface of kaolinite, enhancing the intercalation effect. Moreover, urea decomposes under heating conditions, generating ammonia and carbon dioxide, which can further expand the interlayer space of kaolinite, promoting intercalation. Urea can efficiently insert into the interlayer space of kaolinite, significantly improving the intercalation efficiency and making the kaolinite layers easier to peel off. The intercalated kaolinite has better dispersibility and can be more uniformly dispersed in subsequent processing.

[0062] In some embodiments, the heating and stirring temperature is 60~100℃, and the heating and stirring time is 6~10h.

[0063] In some embodiments, the heating and stirring temperature is 60~80℃, and the heating and stirring time is 6~8h.

[0064] In some embodiments, the heating and stirring temperature is 70~90℃, and the heating and stirring time is 6~8h.

[0065] In some embodiments, the heating and stirring temperature is 75~85°C, and the heating and stirring time is 6~7 hours.

[0066] In some embodiments, the dispersion processing step includes: After the mixed solution was subjected to homogenization, ultrasonication and centrifugation in sequence, the upper centrifuged liquid was collected to obtain the kaolinite nanosheet dispersion.

[0067] The mass concentration of the kaolinite nanosheet dispersion is 2~6 g / L.

[0068] The homogenization process is performed at a speed of 8000~12000 rpm for 15~25 minutes.

[0069] The ultrasonic treatment power is 300~500W, and the ultrasonic treatment duration is 15~25min.

[0070] The centrifugation speed is 1800~2200 rpm, and the centrifugation time is 5~15 min.

[0071] In some embodiments, the rotation speed of the homogenization process is 9000~11000 rpm, and the homogenization time is 15~25 min.

[0072] The ultrasonic treatment power is 350~450W, and the ultrasonic treatment duration is 15~25min.

[0073] The centrifugation speed is 1900~2100 rpm, and the centrifugation time is 5~15 min.

[0074] In some embodiments, the mass concentration of the kaolinite nanosheet dispersion is 3~5 g / L.

[0075] In some embodiments, after dispersion treatment, a drying treatment is performed for 6 to 24 hours to obtain a dried two-dimensional layered kaolinite film.

[0076] In some embodiments, the porous substrate membrane is one of polyvinylidene fluoride membrane, polyethersulfone membrane, and nylon membrane.

[0077] The porous base membrane has a pore size of 0.22~0.45μm.

[0078] In some embodiments, the porous base membrane is a polyvinylidene fluoride (PVDF) membrane. The pore size of the porous base membrane is 0.22 μm, or the pore size of the porous base membrane is 0.45 μm.

[0079] In some embodiments, the diameter of the porous base membrane is 70-80 mm.

[0080] In some embodiments, the solid-liquid separation is performed by centrifugation, and the solid obtained from the solid-liquid separation is washed to remove residual intercalating agent from the surface of the kaolinite intercalation composite.

[0081] The solid-liquid separation is performed by centrifuging at a speed of 3800~4200 rpm for a duration of 8~12 min.

[0082] In some embodiments, the kaolinite intercalation complex rapidly settles under centrifugal force, forming a solid precipitate. This allows for efficient separation of the kaolinite intercalation complex from the liquid, and the resulting solid can be washed to effectively remove residual intercalating agent from the surface, thereby improving the purity and stability of the product.

[0083] In some embodiments, the solid-liquid separation is performed by centrifugation at a speed of 3900~4100 rpm for a duration of 8~10 min.

[0084] The present invention also provides a two-dimensional layered kaolinite nanofiltration membrane, which is prepared by the above-described preparation method.

[0085] The thickness of the two-dimensional layered kaolinite nanofiltration membrane is 270–280 nm. Adjusting the thickness of the two-dimensional layered kaolinite nanofiltration membrane to a suitable thickness can provide appropriate resistance and selectivity, thereby achieving efficient separation during nanofiltration. This helps to improve water resource recovery rates and reduce pollutant emissions.

[0086] In some embodiments, the thickness of the two-dimensional layered kaolinite nanofiltration membrane is 274~278 nm.

[0087] In some embodiments, the kaolinite nanosheets deposited on the two-dimensional layered kaolinite nanofiltration membrane are formed by stacking single-layer kaolinite nanosheets.

[0088] The loading of the deposited kaolinite nanosheets is 3.0~4.5 mg / g.

[0089] The single-layer kaolinite nanosheets have a thickness of 4–8 nm and a diameter of 0.6–0.9 μm. This thickness and diameter ensure that the two-dimensional layered kaolinite nanofiltration membrane has a high rejection rate for dye molecules while also exhibiting excellent water permeability.

[0090] In some embodiments, the thickness of the monolayer kaolinite nanosheets is 5–7 nm. This ultrathin structure allows for the formation of very narrow channels between the kaolinite nanosheets, thereby achieving high selectivity. These channels can effectively intercept molecules or ions of a specific size, while allowing smaller molecules (such as water molecules) to pass through quickly, resulting in efficient filtration. The larger diameter provides a higher specific surface area, enabling the kaolinite nanosheets to more effectively intercept target substances and improve separation efficiency.

[0091] In some embodiments, the loading of the deposited kaolinite nanosheets is 3.5~4.5 mg / g. For example, if the loading of the deposited kaolinite nanosheets is 3.77 mg / g, then 3.77 mg of kaolinite nanosheets are loaded per gram of porous substrate membrane.

[0092] In some embodiments, the loading of the deposited kaolinite nanosheets is 3.5~4.0 mg / g.

[0093] The present invention also provides an application of the above-mentioned two-dimensional layered kaolinite nanofiltration membrane in filtering dyes.

[0094] In some embodiments, the dye is present in water, and the dye includes one or more of Evans Blue, Methyl Blue, Congo Red, and Chrome Black T.

[0095] In some embodiments, the deposited kaolinite nanosheets possess a layered structure and nanoscale pores, enabling effective interception of dye molecules. The two-dimensional layered kaolinite nanofiltration membrane formed by its multi-layered stacking further enhances the filtration effect. It can efficiently remove dyes from water, significantly reducing the color of the water and achieving higher water quality standards. While maintaining high dye removal efficiency, the two-dimensional layered kaolinite nanofiltration membrane has a high water flux, reducing energy consumption during the filtration process. The two-dimensional layered kaolinite nanofiltration membrane is not only suitable for treating water containing common dyes such as Evans Blue, Methylene Blue, Congo Red, and Chrome Black T, but can also treat other types of dye-contaminated water, demonstrating broad applicability.

[0096] To further illustrate the present invention, the following examples are provided: Example 1 A method for preparing a two-dimensional layered kaolinite nanofiltration membrane, comprising the following steps: S1: Kaolinite powder and an intercalating agent were mixed at a first solid-liquid ratio. After heating and stirring until the intercalation reaction was complete, solid-liquid separation was performed to obtain a solid kaolinite intercalation complex. The first solid-liquid ratio was 1 mg: 10 mL, the intercalating agent was dimethyl sulfoxide, the heating and stirring temperature was 80℃, and the heating and stirring time was 6 h. Solid-liquid separation was performed by centrifugation at a speed of 4000 rpm for 10 min.

[0097] S2: The kaolinite intercalation complex was mixed with water at a second solid-liquid ratio. The pH of the mixed solution was adjusted to 11 using a 2 mol / L sodium hydroxide solution. After dispersion treatment, a kaolinite nanosheet dispersion was obtained. The second solid-liquid ratio was 1 mg:80 mL. The mass concentration of the kaolinite nanosheet dispersion was 4 g / L. The dispersion treatment steps were as follows: the mixed solution was subjected to homogenization, ultrasonication, and centrifugation sequentially. The supernatant was collected to obtain the kaolinite nanosheet dispersion. The homogenization speed was 10,000 rpm, and the homogenization time was 20 min; the ultrasonication power was 400 W, and the ultrasonication time was 20 min; the centrifugation speed was 2,000 rpm, and the centrifugation time was 10 min.

[0098] S3: The kaolinite nanosheet dispersion was permeated through a porous substrate membrane, which was a polyvinylidene fluoride membrane with a pore size of 0.22 μm and a diameter of 75 mm. Kaolinite nanosheets in the dispersion were deposited on the porous substrate membrane to obtain a two-dimensional layered kaolinite nanofiltration membrane. The loading of the deposited kaolinite nanosheets was 3.77 mg / g.

[0099] Structural verification of the kaolinite intercalation complex and the two-dimensional layered kaolinite nanofiltration membrane: X-ray diffraction (XRD) was used to test kaolinite raw materials, kaolinite intercalation complexes, and two-dimensional layered kaolinite nanofiltration membranes, such as... Figure 1 As shown. It should be noted that, Figure 1 The kaolinite membrane in the image is the two-dimensional layered kaolinite nanofiltration membrane prepared in this invention. From... Figure 1 It can be observed that the characteristic peak of kaolinite after intercalation shifted from the original 12.48° to 8.04°, indicating a significant increase in interlayer spacing, and an intercalation rate of 93.48%, demonstrating successful kaolinite intercalation. The two-dimensional layered kaolinite nanofiltration membrane prepared according to the method in Example 1 showed only one characteristic peak, corresponding to a position of 12.36°, proving that the two-dimensional layered kaolinite nanofiltration membrane is composed of single-layer kaolinite nanosheets stacked layer by layer.

[0100] Verification of the thickness and diameter of monolayer kaolinite nanosheets: The thickness and diameter of monolayer kaolinite nanosheets were measured using atomic force microscopy (AFM) and a particle size analyzer (DLS), such as... Figure 2 and Figure 3 As shown, the thickness of a single-layer kaolinite nanosheet is only 6 nm, the diameter of the raw kaolinite is 5.77 μm, and the diameter of the single-layer kaolinite nanosheet after processing by this process is 0.894 μm.

[0101] Verification of the structure and thickness of the two-dimensional layered kaolinite nanofiltration membrane: The two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was examined by scanning electron microscopy, as follows: Figure 4 As shown, the cross-section of the kaolinite membrane was observed by using liquid nitrogen to embrittle it. It can be observed that the two-dimensional layered kaolinite nanofiltration membrane is composed of stacked single-layer kaolinite nanosheets without obvious gaps. The thickness of the two-dimensional layered kaolinite nanofiltration membrane is 276 nm, which is beneficial for the separation of dye molecules.

[0102] Selectivity of two-dimensional layered kaolinite nanofiltration membranes for dye molecules: The two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was placed in a cross-flow filtration device for filtration of an aqueous solution containing 20 mg / L Evans blue dye molecules. The filtration pressure was set to 1 bar, and the filtration area was 8 cm². 2 The filtration time was 60 minutes. Specific data on membrane flux and retention rate were obtained by detecting the Evans blue concentration in the collected permeate and calculating the rejection rate, as follows: Figure 5 As shown, the two-dimensional layered kaolinite nanofiltration membrane exhibits a 96% rejection rate for Evans blue. Furthermore, by weighing the permeate, the water flux of the two-dimensional layered kaolinite nanofiltration membrane was calculated to be 55 LMH / bar, enabling highly efficient dye separation.

[0103] See Figure 6 The figure shows the membrane flux and rejection rate of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 of the present invention for different dye molecules.

[0104] The two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was placed in a cross-flow filtration device for filtration of an aqueous solution containing 20 mg / L Congo red dye molecules. The filtration pressure was set to 1 bar, and the filtration area was 8 cm². 2 The filtration time was 60 minutes. By detecting the concentration of Congo red in the collected permeate and calculating the rejection rate, it was found that the two-dimensional layered kaolinite nanofiltration membrane had a rejection rate of 98% for Congo red. Furthermore, by weighing the permeate, the water flux of the two-dimensional layered kaolinite nanofiltration membrane was calculated to be 57 LMH / bar.

[0105] The two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was placed in a cross-flow filtration device for filtration of an aqueous solution containing 20 mg / L Chrome Black T dye molecules. The filtration pressure was set to 1 bar, and the filtration area was 8 cm². 2 The filtration time was 60 minutes. By detecting the concentration of Eriochrome Black (T) in the collected permeate and calculating the rejection rate, it was found that the two-dimensional layered kaolinite nanofiltration membrane had a rejection rate of 97% for Eriochrome Black (T). Furthermore, by weighing the permeate, the water flux of the two-dimensional layered kaolinite nanofiltration membrane was calculated to be 63 LMH / bar.

[0106] The two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was placed in a cross-flow filtration device for filtration of an aqueous solution containing 20 mg / L methylene blue dye molecules. The filtration pressure was set to 1 bar, and the filtration area was 8 cm². 2 The filtration time was 60 minutes. By detecting the concentration of methylene blue in the collected permeate and calculating the rejection rate, it was found that the two-dimensional layered kaolinite nanofiltration membrane had a methylene blue rejection rate of 97%. Furthermore, by weighing the permeate, the water flux of the two-dimensional layered kaolinite nanofiltration membrane was calculated to be 58 LMH / bar.

[0107] Example 2 Compared to Example 1, the intercalating agent was changed.

[0108] The intercalating agent was a saturated urea solution with a molar concentration of 17.98 mol / L. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane.

[0109] The intercalation rate of the kaolinite intercalation composite prepared in Example 2 was tested to be 73.17%.

[0110] Example 3 Compared to Example 1, the heating and stirring temperature was changed.

[0111] The heating and stirring temperature was 60°C. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane. (See also...) Figure 7 , Figure 7 The X-ray diffraction pattern of the kaolinite intercalation complex in Example 3 of the present invention is shown.

[0112] The intercalation rate of the kaolinite intercalation composite prepared in Example 3 was tested to be 89.52%.

[0113] Example 4 Compared to Example 1, the heating and stirring temperature was changed.

[0114] The heating and stirring temperature was 100°C. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane. See [link to example]. Figure 8 , Figure 8 The X-ray diffraction pattern of the kaolinite intercalation complex in Example 4 of this invention is shown.

[0115] The intercalation rate of the kaolinite intercalation composite prepared in Example 4 was tested to be 87.98%.

[0116] Example 5 Compared to Example 1, the porous basement membrane was modified.

[0117] The porous substrate membrane was a polyethersulfone membrane. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane. See also... Figure 9 , Figure 9 The graphs show the membrane flux and rejection rate of two-dimensional layered kaolinite nanofiltration membranes prepared from different porous substrate membranes in Examples 5-6 of this invention.

[0118] Tests showed that the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 5 had a 96% rejection rate for Evans blue and a water flux of 42 LMH / bar.

[0119] Example 6 Compared to Example 1, the porous basement membrane was modified.

[0120] The porous base membrane was a nylon membrane. The other steps were the same as in Example 1, and a two-dimensional layered kaolinite nanofiltration membrane was obtained.

[0121] Tests showed that the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 6 had a 96% rejection rate for Evans blue and a water flux of 43 LMH / bar.

[0122] Analysis example 1 Compared to Example 1, the loading of kaolinite nanosheets was changed.

[0123] The loading of kaolinite nanosheets was 1.88 mg / g. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane.

[0124] Tests showed that the water flux of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 1 was 90 LMH / bar, but the rejection rate of Evans blue was 75%, which could not meet the water quality requirements.

[0125] Analysis example 2 Compared to Example 1, the loading of kaolinite nanosheets was changed.

[0126] The loading of kaolinite nanosheets was 2.83 mg / g. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane.

[0127] Tests showed that the water flux of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 2 was 81 LMH / bar, but the rejection rate of Evans blue was 85%, which could not meet the water quality requirements.

[0128] Analysis example 3 Compared to Example 1, the loading of kaolinite nanosheets was changed.

[0129] The loading of kaolinite nanosheets was 4.72 mg / g. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane.

[0130] Testing revealed that the water flux of the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 3 was 45 LMH / bar. This was attributed to the increased loading of kaolinite nanosheets, which led to an increase in the thickness of the membrane and a longer water transport path. However, the Evans blue rejection rate was 96%.

[0131] See Figure 10 , Figure 10 The graph shows the loading of kaolinite nanosheets with respect to membrane flux and rejection rate in Examples 1-3 of this invention.

[0132] Analysis example 4 Compared to Example 1, the loading of kaolinite nanosheets was changed.

[0133] The loading of kaolinite nanosheets was 5.65 mg / g. Other steps were the same as in Example 1, resulting in a two-dimensional layered kaolinite nanofiltration membrane.

[0134] Tests showed that the two-dimensional layered kaolinite nanofiltration membrane prepared in Example 4 had a 97% rejection rate for Evans blue, but its water flux was 35 LMH / bar, which was not conducive to water flux optimization.

[0135] This invention accelerates the intercalation reaction by mixing kaolinite powder and an intercalating agent at a first solid-liquid ratio, followed by heating and stirring. This allows the intercalating agent to be uniformly inserted into the interlayers of kaolinite, improving the efficiency and uniformity of the reaction. This step effectively increases the spacing between the kaolinite layers, providing space for subsequent nanosheet exfoliation and promoting the formation of kaolinite nanosheets. After mixing the kaolinite intercalation complex with water at a second solid-liquid ratio, adjusting the pH of the mixed solution to alkaline not only helps remove hydrated hydrogen ions from the kaolinite layers and enhances the interlayer electrostatic repulsion, but also promotes further exfoliation of the kaolinite intercalation complex, improving the stability of the kaolinite nanosheet dispersion and ensuring efficient and uniform dispersion of the kaolinite nanosheets. Under negative pressure, the kaolinite nanosheet dispersion is permeated through a porous substrate membrane. The kaolinite nanosheets in the dispersion are uniformly deposited on the porous substrate membrane, forming a dense and uniform two-dimensional layered structure, thus improving the separation performance of the two-dimensional layered kaolinite nanofiltration membrane.

[0136] Through the synergistic process of the above steps, a two-dimensional layered kaolinite nanofiltration membrane can be prepared using readily available and inexpensive raw materials, offering good economic efficiency and ease of large-scale production and application. Furthermore, the operation is simple, requiring no complex equipment or large amounts of organic solvents, aligning with the principles of green chemistry. The prepared two-dimensional layered kaolinite nanofiltration membrane can be used in various fields such as water treatment and organic solvent separation, and is particularly suitable for treating water containing common dyes such as Evans Blue, Methylene Blue, Congo Red, and Chrome Black T, demonstrating broad application prospects.

[0137] In summary, the above-described 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 using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a two-dimensional layered kaolinite nanofiltration membrane, characterized in that, Includes the following steps: S1: Kaolinite powder and intercalating agent are mixed according to the first solid-liquid ratio. After the intercalation reaction is complete by heating and stirring, solid-liquid separation is performed to obtain the solid as kaolinite intercalation complex. S2: After mixing the kaolinite intercalation complex with water according to the second solid-liquid ratio, the pH of the mixed solution is adjusted to 9-13, and after dispersion treatment, a kaolinite nanosheet dispersion is obtained. S3: The kaolinite nanosheet dispersion is passed through a porous base membrane, and the kaolinite nanosheets in the kaolinite nanosheet dispersion are deposited on the porous base membrane to obtain the two-dimensional layered kaolinite nanofiltration membrane.

2. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, The first solid-liquid ratio is 1 mg: (5~15) mL; The second solid-liquid ratio is 1 mg: (60~100) mL.

3. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, Intercalating agents include one or more of dimethyl sulfoxide and saturated urea solution; The molar concentration of the saturated urea solution is 17-18 mol / L.

4. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, The heating and stirring temperature is 60~100℃, and the heating and stirring time is 6~10h.

5. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, The dispersion processing steps include: After the mixed solution was subjected to homogenization, ultrasonication and centrifugation in sequence, the supernatant was collected to obtain the kaolinite nanosheet dispersion. The mass concentration of the kaolinite nanosheet dispersion is 2~6 g / L; The homogenization process is performed at a speed of 8000~12000 rpm for 15~25 min. The power of the ultrasonic treatment is 300~500W, and the duration of the ultrasonic treatment is 15~25min; The centrifugation speed is 1800~2200 rpm, and the centrifugation time is 5~15 min.

6. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, The porous substrate membrane includes one of polyvinylidene fluoride membrane, polyethersulfone membrane, and nylon membrane; The porous base membrane has a pore size of 0.22~0.45μm.

7. The method for preparing a two-dimensional layered kaolinite nanofiltration membrane according to claim 1, characterized in that, The solid-liquid separation is performed by centrifugation, and the solid obtained from the solid-liquid separation is washed to remove residual intercalating agent from the surface of the kaolinite intercalation composite. The solid-liquid separation is performed by centrifuging at a speed of 3800~4200 rpm for a duration of 8~12 min.

8. A two-dimensional layered kaolinite nanofiltration membrane, characterized in that, It was prepared by the preparation method according to any one of claims 1 to 6; The thickness of the two-dimensional layered kaolinite nanofiltration membrane is 270~280 nm.

9. The two-dimensional layered kaolinite nanofiltration membrane according to claim 8, characterized in that, The kaolinite nanosheets deposited on the two-dimensional layered kaolinite nanofiltration membrane are formed by stacking single-layer kaolinite nanosheets. The loading of the deposited kaolinite nanosheets is 3.0~4.5 mg / g; The thickness of the monolayer kaolinite nanosheets is 4~8 nm and the diameter is 0.6~0.9 μm.

10. The application of a two-dimensional layered kaolinite nanofiltration membrane as described in any one of claims 8 to 9 in filtering dyes.

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