A nanochannel membrane and a preparation method thereof, and a method for water isotope screening

Abstract

This invention relates to the field of two-dimensional layered membrane water isotope separation technology, and discloses a nanochannel membrane and its preparation method, as well as a method for water isotope sieving. Vermiculite is heated and washed in a sodium chloride solution, then heated in a lithium chloride solution, washed, and centrifuged to obtain a vermiculite nanosheet dispersion. The vermiculite nanosheet dispersion is activated with hydrochloric acid to obtain an activated vermiculite nanosheet dispersion. The activated vermiculite nanosheet dispersion is mixed with an MPTES solution and reacted. After centrifugation, the supernatant is collected to obtain a nanosheet dispersion grafted with functional groups. The nanosheet dispersion grafted with functional groups is vacuum filtered onto a base membrane to prepare a layered membrane. The layered membrane is encapsulated in resin to obtain a vertically aligned nanochannel membrane. The nanochannel membrane prepared by this invention has better nanofiltration performance and operational stability, good anti-swelling properties, and a simple preparation process, exhibiting good water isotope separation effect.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional layered membrane water isotope separation technology, and in particular to a nanochannel membrane and its preparation method, as well as a method for water isotope sieving. Background Technology

[0002] Heavy water (D2O) is a crucial strategic material for defense technology and the nuclear energy industry. It is a primary raw material for fission nuclear weapons production and thermonuclear fusion, and also has wide applications in the biomedical field. Currently, heavy water production is costly, requires stringent separation conditions, involves complex processes, and relies on imported technology. The content of heavy water in natural water is extremely low (~0.015%). Water (H2O) and heavy water, as two typical isotopes, share very similar physicochemical properties. Furthermore, when water and heavy water are mixed, they rapidly generate hemi-heavy water (HDO) through proton exchange chemical equilibrium, resulting in the coexistence of all three. Therefore, water and heavy water are among the most difficult isotope pairs to separate. Currently, physical adsorption and chemical separation methods are commonly used industrially to separate water and heavy water. Physical adsorption utilizes the selective adsorption of water and heavy water by adsorbents (such as zeolites, MOFs, and COFs). However, because heavy water molecules are larger than water molecules, their migration rate in specific adsorbents is slow, making separation difficult. Additionally, porous materials are expensive and prone to adsorption saturation, leading to low separation efficiency. Emerging membrane separation technology has shown great potential in the field of separation due to its advantages such as being green and environmentally friendly, energy-efficient, highly selective, and so on.

[0003] Two-dimensional layered membranes possess unique advantages in rapid molecular transport and precise separation, thus finding wide application in fields such as water treatment. However, traditional two-dimensional layered membranes swell or even chemically degrade in organic solvents, leading to membrane structure collapse or expansion and a sharp decline in separation precision (selectivity). Furthermore, achieving effective separation of water isotopes requires long-range ordered and regularly arranged interlayer channels within the membrane; however, existing membrane separation technologies have limited research in water isotope separation systems. Therefore, developing low-energy, efficient, and environmentally friendly water and heavy water separation technologies is of significant strategic importance. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical problems and provide a nanochannel membrane and its preparation method, as well as a method for water isotope sieving.

[0005] To achieve the above objectives, the present invention is implemented according to the following technical solution: A method for water isotope sieving includes the following steps: using a membrane with confined nanochannel groups, the groups preferentially adsorb heavy water at low temperature, and during the crystallization process, heavy water preferentially binds to heavy water. The two work synergistically to achieve selective crystallization of heavy water, while water remains in flow, thereby achieving the separation of heavy water and water.

[0006] Preferably, the membrane containing the confined nanochannel groups is a nanochannel membrane; the low temperature is 268 K~276 K.

[0007] In this invention, VM-SO3H membrane achieves the best separation effect during heavy water / water separation, with a heavy water concentration of 1 wt% in the heavy water / water system. The separation effect is optimal at a separation temperature of 273 K. This is an advanced separation method for efficient and energy-saving water isotope separation.

[0008] A method for preparing a nanochannel membrane includes the following steps: S1, vermiculite is heated in sodium chloride solution, the product is washed and then heated in lithium chloride solution, the product is washed, and then centrifuged to remove unpeeled vermiculite, and the supernatant is taken to obtain vermiculite nanosheet dispersion. S2, a layered membrane was prepared by vacuum filtration of a vermiculite nanosheet dispersion on a base membrane; S3, the layered membrane obtained in step S2 is encapsulated in resin to obtain a vertically aligned nanochannel membrane.

[0009] Preferably, in step S1, the sodium chloride solution is a saturated sodium chloride solution, and the lithium chloride solution is a saturated lithium chloride solution; the ratio of vermiculite, saturated sodium chloride solution, and saturated lithium chloride solution is 2:100:100, and the comparison unit is g:mL:mL; the centrifugation speed to remove unpeeled vermiculite is 9500 r / min, and the time is 15 min.

[0010] Specifically, step S1 includes the following steps: S1, vermiculite was placed in a saturated sodium chloride solution and heated in an oil bath, then refluxed for 72 h. After reflux, the product was washed three times with deionized water. The washed product was then added to a saturated lithium chloride solution and heated in an oil bath again, then refluxed for 48 h. After reflux, the product was washed three times with deionized water. The unpeeled vermiculite was then removed by centrifugation, and the supernatant was taken to obtain a vermiculite nanosheet dispersion. The oil bath heating temperature was 120℃.

[0011] Preferably, in step S2, the thickness of the prepared layered membrane is 8-12 µm.

[0012] Preferably, in step S2, the vermiculite nanosheet dispersion is mixed with a silane coupling agent solution, and after centrifugation, the supernatant is taken to obtain the nanosheet dispersion with grafted functional groups; the nanosheet dispersion with grafted functional groups is used to prepare a layered membrane on a base membrane by vacuum filtration.

[0013] Preferably, in step S2, the vermiculite nanosheet dispersion is activated with hydrochloric acid to obtain an activated vermiculite nanosheet dispersion; the activated vermiculite nanosheet dispersion is mixed with a silane coupling agent solution and reacted, and the supernatant is taken after centrifugation to obtain a nanosheet dispersion with grafted functional groups; the nanosheet dispersion with grafted functional groups is used to prepare a layered membrane on a base membrane by vacuum filtration. The concentration of the hydrochloric acid is 1 M; the ratio of the vermiculite nanosheet dispersion to the hydrochloric acid is 30:0.1 based on the mass of the vermiculite nanosheets, and the unit of comparison is mg:mL.

[0014] Hydrochloric acid can be used to activate the hydroxyl groups on the surface of vermiculite.

[0015] Preferably, the silane coupling agent solution is an MPTES solution.

[0016] Preferably, the preparation process of the MPTES solution is as follows: MPTES (3-mercaptopropyltriethoxysilane) is added to a mixed solution of ethanol and water and stirred for 6 h to hydrolyze the MPTES and obtain the MPTES solution. The ratio of MPTES, ethanol, and water is 1:90:10, and the unit of comparison is mL:mL:mL; The activated vermiculite nanosheet dispersion, based on the mass of vermiculite nanosheets, had a MPTES ratio of 30:1 in the activated vermiculite nanosheet dispersion to the MPTES solution, with the comparison unit being mg:mL.

[0017] Preferably, in step S2, the reaction process after mixing the activated vermiculite nanosheet dispersion with the MPTES solution is as follows: the activated vermiculite nanosheet dispersion is mixed with the MPTES solution, and a silane reaction is carried out at 40 °C for 8 h. Then, H2O2 solution is added, and the reaction is carried out at 50 °C for 4 h to oxidize the -SH groups on the MPTES to -SO3H groups.

[0018] Preferably, the concentration of the H2O2 solution is 30%; the volume ratio of the H2O2 solution used to the volume of MPTES in the MPTES solution is 3:1, and the comparison unit is mL:mL.

[0019] Specifically, step S2 includes the following steps: 30 mL concentration is 1 mg / mL -1 0.1 mL of 1 M concentrated hydrochloric acid was added to the vermiculite nanosheet dispersion to obtain the activated vermiculite nanosheet dispersion; Add 1 mL of MPTES to a mixed solution of 100 mL of ethanol and water (9:1, v / v) and stir for 6 h to hydrolyze MPTES and obtain an MPTES solution. The activated vermiculite nanosheet dispersion was mixed with the MPTES solution and subjected to a silane reaction at 40 °C for 8 h. Then, 3 mL of H2O2 solution (30% concentration) was added to the solution and reacted at 50 °C for 4 h to oxidize the -SH groups on the MPTES to -SO3H groups. The mixture was sonicated for 4 h and centrifuged at 12000 r / min for 10 min. The supernatant was collected to obtain the nanosheet dispersion with grafted functional groups.

[0020] Preferably, in step S3, the resin is a mixture of epoxy resin and polyamide resin, wherein the mass ratio of epoxy resin to polyamide resin is 3:1.

[0021] More preferably, the resin is epoxy resin E-44 (6101) and polyamide resin low molecular weight-650, purchased from Dingyuan County Danbao Resin Co., Ltd.

[0022] Preferably, step S3 involves embedding a layered membrane in resin and then drying it to obtain a vertically aligned nanochannel membrane.

[0023] Specifically, step S3 includes the following steps: In step S2, a two-dimensional layered membrane with a thickness of 10 μm is obtained. The two-dimensional layered membrane is cut into rectangular strips with a size of 4 mm × 10 mm. The rectangular strips of the layered membrane are placed in a mold, and resin is dripped in so that the rectangular strips of the layered membrane are immersed in the resin. After drying for 6 hours, a dried block is obtained. Excess irregular resin on both sides of the rectangular strips of the layered membrane in the dried block is removed to obtain a smooth and flat vertically arranged nanochannel membrane with a thickness of about 0.5 cm.

[0024] Unlike horizontally arranged channels, molecules are transported in vertically arranged channels along a direction parallel to the interlayer channels, which reduces the influence of interlayer resistance.

[0025] The vertically aligned nanochannel membranes prepared by this invention can achieve a separation factor of up to 2.9 for water isotope separation.

[0026] The present invention also includes nanochannel membranes prepared by the preparation method described above.

[0027] In this invention, the selected Vr nanosheets are rich in hydroxyl functional groups on their surface, enabling them to easily react with silane coupling agents for functionalization modification. The interlayer spacing of the stacked Vr nanosheets is generally around 1.4 nm, and the interlayer spacing changes little after grafting functional groups with different charge intensities.

[0028] Vermiculite membranes are relatively unstable in water and easily swell. This invention uses a resin encapsulation method to prepare vertically aligned nanochannel membranes. Due to the physical confinement of the membrane by the epoxy resin, the stability of the membrane in the solvent is greatly improved.

[0029] This invention employs a membrane with confined nanochannel groups. At low temperatures, these groups preferentially adsorb heavy water, and during crystallization, heavy water preferentially binds to itself. This synergistic effect achieves selective crystallization of heavy water while maintaining water flow, thus separating heavy water from water. The two-dimensional nanosheets, serving as the building blocks of the two-dimensional layered membrane, possess a large aspect ratio, enabling the formation of regular and ordered interlayer channels. Furthermore, the abundant sites on the two-dimensional nanosheets allow for chemical modification, further enhancing the precise separation capability of the two-dimensional layered membrane. Since water molecules and heavy water molecules interact differently with the interface, the effective separation of water isotopes can be achieved by adjusting the forces between the interface and the molecules.

[0030] Furthermore, the abundance of sites on two-dimensional nanosheets allows for chemical modification, further enhancing the precise separation capability of the two-dimensional layered membrane. Due to the differences in hydrogen bond strength and stability between water and heavy water, the effective separation of water isotopes can be achieved by adjusting the interaction forces between the membrane wall and molecules, based on these differences in molecular hydrogen bond strength.

[0031] By preparing Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets and using vacuum filtration to form membranes from solutions of these four nanosheets, four membranes with different charges (VrM membrane, VM-CH3 membrane, VM-SO3H membrane, and VM-F3 membrane) were obtained. These membranes were then embedded in resin to obtain vertically aligned nanochannel membranes (VrM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane, and VM-F3 vertical nanochannel membrane). Using these vertical nanochannel membranes for the separation of heavy water and water systems, a separation factor of up to 2.9 was achieved. The VM-SO3H vertical nanochannel membrane prepared in this invention exhibits good performance in separating water isotopes, good anti-swelling properties, higher nanofiltration performance and operational stability, and the preparation process is simple.

[0032] (1) The Vr nanosheets (vermiculite nanosheets) in this invention are rich in hydroxyl groups, which are easy to react with silane coupling agents, and the top-to-bottom peeling process is relatively simple; (2) Vr nanosheets can be grafted with different functional groups by reacting with different silane coupling agents to prepare nanosheets with different charge intensities (Vr-CH3 nanosheets, Vr-SO3H nanosheets, Vr-F3 nanosheets); the presence of characteristic peaks of different groups in infrared testing proves the successful grafting of different functional groups (CH, O=S=O, CF), and the appearance of characteristic elements (S, F) in XPS testing also proves the successful reaction of silane coupling agents; the different Zeta potentials of the four nanosheets indicate the successful preparation of nanosheets with different charge intensities. (3) Four vermiculite membranes (VM membrane, VM-CH3 membrane, VM-SO3H membrane, VM-F3 membrane) with different charge intensities were prepared by vacuum filtration of the nanosheet solution; the four membranes were then encapsulated with epoxy resin to prepare vertically arranged nanochannel membranes. (4) The prepared VM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane, and VM-F3 vertical nanochannel membrane have stable performance. In the pressure cycling stability test, the permeation flux of the membrane remains basically unchanged with the change of pressure. The long-term stability test shows that, except for a slight decrease in permeability due to membrane compaction in the initial stage, these membranes can maintain a stable permeability within 72 h. XRD test shows that after soaking in various solvents for 6 h, the position and intensity of the characteristic peaks of VM-SO3H remain unchanged, which demonstrates the good stability of the prepared resin-embedded VM-SO3H. (5) When heavy water / water is separated using VM-SO3H vertical nanochannel membrane, the separation factor can reach 2.9 when the heavy water concentration in the system is 1%.

[0033] Beneficial effects: The nanochannel membrane prepared by this invention has better nanofiltration performance and operational stability, good anti-swelling properties, and the preparation process is simple, with good water isotope separation effect. Attached Figure Description

[0034] Figure 1 Infrared images of the nanosheets obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention; Figure 2 XPS spectra of nanosheets obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention; Figure 3 The Zeta potential diagrams of the nanosheets obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention are shown. Figure 4 The images show SEM surface images of the layered films obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention. Figure 5A flowchart illustrating the preparation of vertically aligned nanochannel membranes according to the present invention; Figure 6 The images show SEM cross-sectional views of the layered membranes prepared in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention. Figure 7 The XRD patterns are of the vertically aligned nanochannel membranes prepared in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention. Figure 8 SEM-EDS image of the VM-F3 vertical nanochannel membrane prepared in Comparative Example 2 of this invention; Figure 9 The diagram shows the separation factor of the VM-SO3H vertical nanochannel membrane prepared in Example 2 of this invention for the heavy water / water system. Figure 10 This is a diagram showing the separation factor of the VM vertical nanochannel membrane prepared in Example 1 of the present invention for the heavy water / water system; Figure 11 The pressure cycling performance diagrams of the vertically arranged nanochannel membranes obtained in Example 1, Comparative Example 1, and Example 2 of this invention are shown. Figure 12 This is a diagram showing the long-term operational stability of the vertically aligned nanochannel membranes obtained in Example 1, Comparative Example 1, and Example 2 of the present invention. Figure 13 The image shows the XRD pattern of the vertically aligned nanochannel membrane obtained in Example 2 of this invention after being soaked in solvent. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0036] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0037] There are no particular restrictions on the purity of any of the raw materials used in this invention, but it is preferred to use materials with conventional purity levels used in the field.

[0038] All processes in this invention are referred to by common abbreviations in the field. Each abbreviation is clear and specific in its relevant application, and those skilled in the art can understand the conventional process based on the abbreviation.

[0039] The resin used in the following examples is a mixture of epoxy resin E-44 (6101) and polyamide resin low molecular weight-650, with a mass ratio of epoxy resin E-44 (6101) to polyamide resin low molecular weight-650 of 3:1.

[0040] Epoxy resin E-44 (6101) and polyamide resin low molecular weight-650 were purchased from Dingyuan County Danbao Resin Co., Ltd.

[0041] Example 1 A method for preparing a nanochannel membrane includes the following steps: S1, vermiculite was added to a saturated sodium chloride solution and heated in an oil bath, then refluxed for 72 h, and the product was washed with deionized water; then the washed product was added to a saturated lithium chloride solution and heated in an oil bath, then refluxed for 48 h, and the product was washed with deionized water; then the unpeeled vermiculite was removed by centrifugation, and the supernatant was taken to obtain a vermiculite (Vr) nanosheet dispersion. The product contained 2.0 g of vermiculite and 100 mL of both saturated sodium chloride and saturated lithium chloride solutions. After two reflux condensations, the product was washed three times with deionized water. When centrifuging to remove unseparated vermiculite, the speed was 9500 r / min and the time was 15 min. S2, VM membranes are prepared by vacuum filtration of the above vermiculite nanosheet dispersion on a PVDF substrate membrane, wherein the concentration of the vermiculite nanosheet dispersion is 1 mg / mL. -1 ; S3, the prepared VM membrane has a thickness of about 10 µm. The membrane is cut into rectangular strips with a size of 4 mm × 10 mm and encapsulated in resin to obtain a vertically aligned VM nanochannel membrane. The resin is a mixture of epoxy resin E-44 (6101) and polyamide resin low molecular weight-650 in a ratio of 3:1. The mixture is then dropped into a mold with rectangular strips and dried for 6 hours. After drying, excess resin on both sides of the membrane is removed to obtain a smooth and flat vertically arranged nanochannel membrane with a total thickness of about 0.5 cm, which is named VM vertical nanochannel membrane.

[0042] Comparative Example 1 The only difference from Example 1 is that: In step S2, to a concentration of 1 mg / mL -1 0.1 mL of 1 M concentrated hydrochloric acid was added to 30 mL of vermiculite nanosheet dispersion to activate the hydroxyl groups on the vermiculite surface. Then, 1 mL of N-propyltriethoxysilane was added to 100 mL of an ethanol / water mixture (ethanol:water volume ratio = 9:1), and the mixture was sonicated for 4 h and centrifuged at 12000 r / min for 10 min. The supernatant was collected to obtain the Vr-CH3 nanosheet dispersion. VM-CH3 membranes were prepared on PVDF-based membranes by vacuum filtration. In step S3, the prepared VM-CH3 membrane has a thickness of about 10 µm. The cut VM rectangular strips are changed to VM-CH3 rectangular strips. After resin encapsulation, a smooth and flat vertically arranged nanochannel membrane with a total thickness of about 0.5 cm is obtained, which is named VM-CH3 vertical nanochannel membrane.

[0043] Example 2 The only difference from Example 1 is that step S2 includes the following process: 30 mL concentration is 1 mg / mL -1 0.1 mL of 1 M concentrated hydrochloric acid was added to the vermiculite nanosheet dispersion to obtain the activated vermiculite nanosheet dispersion; Add 1 mL of MPTES to a 100 mL mixture of ethanol and water (9:1, v / v) and stir for 6 h to hydrolyze the MPTES and obtain an MPTES solution. The activated vermiculite nanosheet dispersion was mixed with MPTES solution and subjected to a silane reaction at 40 °C for 8 h. Then, 3 mL of H2O2 solution (30% concentration) was added to the above solution and reacted at 50 °C for 4 h to oxidize the -SH groups on MPTES to -SO3H groups. The mixture was sonicated for 4 h and centrifuged at 12000 r / min for 10 min. The supernatant was collected to obtain the nanosheet dispersion with grafted functional groups.

[0044] VM-SO3H membranes were prepared on PVDF-based membranes by vacuum filtration. In step S3, the prepared VM-SO3H membrane has a thickness of about 10 µm. The cut VM rectangular strips are changed to VM-SO3H rectangular strips. After resin encapsulation, a smooth and flat vertically arranged nanochannel membrane with a total thickness of about 0.5 cm is obtained, which is named VM-SO3H vertical nanochannel membrane.

[0045] Comparative Example 2 The only difference from Comparative Example 1 is: In step S2, 1 mL of N-propyltriethoxysilane was replaced with 1 mL of 3,3,3-trifluoropropylmethyldimethoxysilane; after centrifugation, the supernatant was collected to obtain a Vr-F3 nanosheet dispersion; VM-F3 membranes were prepared on PVDF-based membranes by vacuum filtration. In step S3, the prepared VM-F3 membrane has a thickness of about 10 µm. The cut VM-CH3 rectangular strips are changed to VM-F3 rectangular strips. After resin encapsulation, a smooth and flat vertically arranged nanochannel membrane with a total thickness of about 0.5 cm is obtained, which is named VM-F3 vertical nanochannel membrane.

[0046] The vermiculite nanosheet dispersion, Vr-CH3 nanosheet dispersion, Vr-SO3H nanosheet dispersion, and Vr-F3 nanosheet dispersion prepared in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 were dried to obtain the corresponding Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets.

[0047] The layered membranes prepared from the above-mentioned Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets; the layered membranes prepared from Example 1, Comparative Example 1, Example 2, and Comparative Example 2: VM membrane, VM-CH3 membrane, VM-SO3H membrane, and Vr-F3 membrane; and the vertically aligned nanochannel membranes prepared from them: VM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane, and Vr-F3 vertical nanochannel membrane were compared.

[0048] like Figure 1 The image shown is an infrared spectrum of the nanosheets (Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets) obtained in Examples 1, 1, 2, and 2 of this invention. Figure 1 It can be seen that characteristic peaks of -CH3, O=S=O, and -CF3 appeared after the functional group was grafted, indicating that the functional group was successfully introduced.

[0049] like Figure 2 The image shows the XPS spectra of the nanosheets (Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets) obtained in Examples 1, 1, 2, and 2 of this invention. Figure 2 It can be seen that the corresponding S and F elements appeared after the functional group was grafted, indicating that the functional group was successfully grafted.

[0050] like Figure 3 The figure shows the Zeta potential diagrams of the nanosheets (Vr nanosheets, Vr-CH3 nanosheets, Vr-SO3H nanosheets, and Vr-F3 nanosheets) obtained in Examples 1, 1, 2, and 2 of this invention. The changes in Zeta potential indicate the successful preparation of nanosheets with different charge intensities.

[0051] like Figure 4 The image shown is a SEM surface image of the layered films obtained in Embodiment 1, Comparative Example 1, Embodiment 2, and Comparative Example 2 of the present invention. From... Figure 4 As can be seen from the examples, the laminated membranes VM, VM-CH3, VM-SO3H, and VM-F3 obtained in Examples 1-4 have smooth, intact, and defect-free surfaces.

[0052] like Figure 5The diagram shown is a flowchart of the process for preparing vertically aligned nanochannel membranes according to the present invention.

[0053] like Figure 6 The image shown is a SEM cross-sectional view of the layered membranes (VM membrane, VM-CH3 membrane, VM-SO3H membrane, VM-F3 membrane) obtained in Example 1, Comparative Example 1, Example 2, and Comparative Example 2 of this invention. This shows that the regular stacking of nanosheets is beneficial for constructing regular and flat two-dimensional interlayer channels.

[0054] like Figure 7 The image shows the XRD patterns of the vertically aligned nanochannel membranes (VM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane, and VM-F3 vertical nanochannel membrane) obtained in Examples 1, 1, 2, and 2 of this invention. In the XRD patterns, peaks corresponding to Vr appear in the diffraction angle range of approximately 6.4°. The interlayer spacing was calculated using Bragg's law. The interlayer spacing of the VM nanochannel membrane, VM-CH3 nanochannel membrane, VM-SO3H nanochannel membrane, and VM-F3 nanochannel membrane is approximately 1.4 nm, indicating that the interlayer spacing of these layered membranes is similar after grafting functional groups.

[0055] like Figure 8 The image shown is a SEM-EDS image of the VM-F3 vertical nanochannel membrane obtained in Comparative Example 2 of this invention. The uniform distribution of the amino characteristic element F in the EDS image indicates that the charged groups are uniformly grafted onto the nanochannel walls.

[0056] like Figure 9 The figure shown is a separation factor diagram of the VM-SO3H vertical nanochannel membrane for the heavy water / water system obtained in Example 2 of this invention. The temperature range of the separation process is 268K~276K; from Figure 9 It can be understood that when heavy water / water is separated, the separation factor can reach 2.9 when the heavy water concentration reaches 1 wt% and the temperature is 273 K.

[0057] like Figure 10 The figure shows the separation factor of the VM vertical nanochannel membrane prepared in Example 1 of this invention for the heavy water / water system. The temperature range of the separation process is 268K~276K. This indicates that the separation factor can reach 1.7 when the heavy water concentration reaches 1wt%.

[0058] like Figure 11The figure shows the pressure cycling performance of the vertically aligned nanochannel membranes (VM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane) obtained in Examples 1, 1 Comparative Example, and 2 of this invention. As the pressure changes, the permeation flux of the membrane remains essentially constant, indicating that the vertically aligned nanochannel membranes possess excellent stability.

[0059] like Figure 12 The figure shows the long-term operational stability of the vertically aligned nanochannel membranes (VM vertical nanochannel membrane, VM-CH3 vertical nanochannel membrane, VM-SO3H vertical nanochannel membrane) obtained in Examples 1, 1 Comparative Example, and 2 of this invention. Long-term stability tests show that, except for a slight decrease in permeation flux due to membrane compaction in the initial stage, these membranes can maintain a stable permeability within 72 hours.

[0060] like Figure 13 The image shows the XRD pattern of the vertically aligned nanochannel membrane (VM-SO3H vertical nanochannel membrane) obtained in Example 2 of this invention after solvent immersion. After immersion in various solvents for 6 h, the position and intensity of the characteristic peaks belonging to VM-SO3H remained unchanged, indicating that the prepared vertically aligned nanochannel membrane has good structural and operational stability.

[0061] The technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made in accordance with the technical solutions of the present invention fall within the protection scope of the present invention.

Claims

1. A method for water isotope sieving, characterized in that, Includes the following steps: A membrane with confined nanochannel groups is used to selectively crystallize heavy water by preferentially adsorbing the groups at low temperatures and preferentially binding heavy water during crystallization. The two work synergistically to achieve selective crystallization of heavy water while water remains in flow, thereby achieving the separation of heavy water and water.

2. The method for water isotope sieving according to claim 1, characterized in that: The membrane containing the confined nanochannel groups is a nanochannel membrane; the low temperature is 268 K~276 K.

3. A method for preparing a nanochannel membrane, characterized in that, Includes the following steps S1, vermiculite is heated in sodium chloride solution, the product is washed and then heated in lithium chloride solution, the product is washed, and then centrifuged to remove unpeeled vermiculite, and the supernatant is taken to obtain vermiculite nanosheet dispersion. S2, the vermiculite nanosheet dispersion was activated with hydrochloric acid to obtain the activated vermiculite nanosheet dispersion; the activated vermiculite nanosheet dispersion was mixed with MPTES solution and reacted, and the supernatant was taken after centrifugation to obtain the nanosheet dispersion with grafted functional groups; the nanosheet dispersion with grafted functional groups was used to prepare a layered membrane on the base membrane by vacuum filtration. S3, the layered membrane obtained in step S2 is encapsulated in resin to obtain a vertically aligned nanochannel membrane.

4. The method for preparing a nanochannel membrane according to claim 3, characterized in that: In step S1, the sodium chloride solution is a saturated sodium chloride solution, and the lithium chloride solution is a saturated lithium chloride solution; the ratio of vermiculite, saturated sodium chloride solution, and saturated lithium chloride solution is 2:100:100, and the comparison unit is g:mL:mL; when centrifuging to remove unpeeled vermiculite, the rotation speed is 9500 r / min, and the time is 15 min.

5. A method for preparing a nanochannel membrane according to claim 3, characterized in that: In step S2, the concentration of hydrochloric acid is 1 M; the ratio of vermiculite nanosheet dispersion to hydrochloric acid is 30:0.1 based on the mass of vermiculite nanosheets, and the unit of comparison is mg:mL.

6. A method for preparing a nanochannel membrane according to claim 3, characterized in that: In step S2, the preparation process of the MPTES solution is as follows: MPTES is added to a mixed solution of ethanol and water and stirred for 6 hours to hydrolyze the MPTES and obtain the MPTES solution. The volume ratio of MPTES, ethanol, and water is 1:90:10, and the unit of comparison is mL:mL:mL. The activated vermiculite nanosheet dispersion, based on the mass of vermiculite nanosheets, had a MPTES ratio of 30:1 in the activated vermiculite nanosheet dispersion to the MPTES solution, with the comparison unit being mg:mL.

7. A method for preparing a nanochannel membrane according to claim 6, characterized in that: In step S2, the reaction process after mixing the activated vermiculite nanosheet dispersion with the MPTES solution is as follows: the activated vermiculite nanosheet dispersion is mixed with the MPTES solution and subjected to a silane reaction at 40 °C for 8 h. Then, H2O2 solution is added and the reaction is carried out at 50 °C for 4 h to oxidize the -SH groups on the MPTES to -SO3H groups.

8. The method for preparing a nanochannel membrane according to claim 7, characterized in that: In step S3, the resin is a mixture of epoxy resin and polyamide resin, and the mass ratio of epoxy resin to polyamide resin is 3:

1.

9. The method for preparing a nanochannel membrane according to claim 3, characterized in that: The process of step S3 is to embed the layered membrane in resin and then dry it to obtain a vertically arranged nanochannel membrane.

10. A nanochannel membrane prepared by the preparation method according to any one of claims 3 to 9.

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