Water isotope pervaporation separation method and system based on two-dimensional material film

Abstract

This invention relates to a method and system for water isotope pervaporation separation based on a two-dimensional material membrane, belonging to the field of membrane separation technology. The method combines pervaporation with a two-dimensional material membrane, which is either a two-dimensional nanoporous membrane or a mixed matrix membrane. It utilizes the sub-nanometer interlayer channels of the nanoporous membrane or the kinetic quantum sieving effect of the polymer chain micropores in the mixed matrix membrane, as well as the chemical affinity quantum sieving effect of the binding sites on the surface of the two-dimensional material, coupled with pervaporation to achieve water isotope separation. Under the action of quantum sieving, lighter isotopes transport faster than heavier isotopes; particles are in a vibrating state within the pores; lighter isotopes have higher zero-point energies and more intense vibrations, making them easier to break free from adsorption sites; heavier isotopes have lower zero-point energies and are more easily adsorbed, thus achieving separation. This scheme, by leveraging intramembrane quantum sieving, synergistically combining the phase transition of pervaporation with the transmembrane chemical potential gradient, can achieve low-energy and high-efficiency separation of water isotopes, promoting applications in membrane separation and the field of two-dimensional materials.

Description

Technical Field

[0001] This invention belongs to the field of two-dimensional material membrane and water isotope separation technology, specifically relating to a water isotope pervaporation separation method and system based on two-dimensional material membrane. Background Technology

[0002] Hydrogen isotopes deuterium (D) and tritium (T) hold irreplaceable strategic positions in national defense and future energy fields. Deuterium oxide, heavy water (D₂O), with its extremely low neutron absorption cross section and excellent moderation properties, is an indispensable neutron moderator and coolant in heavy water reactor nuclear power plants; while tritium, as a radioactive isotope of hydrogen, is a key fuel in magnetic confinement fusion reactors (such as ITER). Furthermore, the oxygen isotope oxygen-18 (… 18 Oxygen (H2O) is also highly valuable in biomedicine and environmental science. High-abundance deoxygenated water (H2O) 18 O) is not only an ideal material for environmental isotope tracing, but also for the production of the radionuclide fluorine-18 (fluorine-18) in positron emission tomography (PET). 18 Tritium (F) is a core precursor and is of great significance for the early diagnosis of cancer and cardiovascular diseases. However, the acquisition of these isotope resources currently faces severe challenges: tritium is usually present as a radioactive byproduct in nuclear wastewater and urgently needs to be rendered harmless or recycled; while in nature... 18 O2 abundance is extremely low, resulting in extremely high extraction costs. Existing water isotope separation technologies mainly include membrane distillation, adsorption, chemical exchange, water electrolysis, and cryogenic distillation. Due to the extremely small differences in the physicochemical properties between water isotope molecules (e.g., similar mass and saturated vapor pressure), the above methods are generally limited by thermodynamic equilibrium, resulting in bottlenecks such as high energy consumption, complex equipment, and low separation coefficients. Taking the hydrogen sulfide-water dual-temperature exchange method (GS method), which is relied upon for industrial-grade heavy water production, as an example, its process is lengthy and involves toxic media, leading to extremely high operation and maintenance costs. Therefore, there is an urgent need to develop a new water isotope separation technology with lower energy consumption, simpler process, and higher efficiency to overcome the limitations of existing methods.

[0003] In recent years, membrane separation technology has been increasingly applied to isotope separation due to its advantages such as low energy consumption and simple operation. Membrane distillation, in particular, has been widely used for water isotope separation. However, in membrane distillation, the separation process based on porous hydrophobic membranes is difficult to surpass that of simple distillation, and membrane pore wetting during long-term operation can lead to separation failure. Pervaporation (PV) shares many similarities with membrane distillation; both utilize vapor pressure differences to allow water molecules to permeate through a separation membrane. The dissolution-diffusion separation principle of pervaporation membranes allows them to exhibit high selectivity based on differences in the solubility and diffusion rates of different components, almost completely blocking the passage of solute ions or macromolecules in ion removal. The vapor pressure difference in the pervaporation process is generally provided by a vacuum pump, typically requiring about 0.1 MPa to ensure water molecule passage, which is relatively low compared to other methods. These characteristics make its application in water isotope separation possible.

[0004] Although pervaporation technology has demonstrated excellent performance in organic solvent dehydration and volatile organic compound recovery through long-term development, existing traditional polymer membranes and conventional inorganic membranes are still constrained by the classic "permeation flux-selectivity" trade-off effect. Especially when dealing with water isotope systems with extremely similar physicochemical properties, traditional membrane materials struggle to achieve efficient separation due to the lack of sub-nanometer precision sieving channels and specific recognition sites. In contrast, two-dimensional materials, as an emerging membrane building block, have proven their potential to break through traditional performance limits in fields such as gas separation and reverse osmosis. Two-dimensional nanosheets, represented by graphene oxide (GO) and MXene, not only possess ultra-high specific surface area and abundant surface functional groups but also unique layered stacked structures. This structure allows for the construction of mass transfer channels that can utilize minute differences in isotope size and the quantum sieving effect through precise angstrom-level control of interlayer spacing; simultaneously, their abundant surface functional groups provide specific binding / adsorption sites for isotope molecules. This allows the two-dimensional membrane to couple the transmembrane chemical potential gradient of quantum sieving and perevaporation during the pervaporation process, amplifying the differences in water isotope diffusion rates and thus significantly improving the separation performance of water isotopes. The quantum sieving effect achieved by the tunable interlayer nanochannels of the two-dimensional material, combined with the specific adsorption effect brought by its surface functional groups, provides an ideal solution for overcoming the performance bottlenecks of traditional membrane materials and achieving efficient and low-energy separation of water isotopes during perevaporation. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a water isotope pervaporation separation method and system based on a two-dimensional material membrane, establishing a pervaporation isotope separation system to obtain a water isotope separation method with low energy consumption and high selectivity.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a water isotope pervaporation separation method based on a two-dimensional material membrane, which combines pervaporation with a two-dimensional material membrane. The two-dimensional material membrane is a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane. The two-dimensional material nanoporous membrane and its sub-nanometer interlayer channels or the polymer chains of the two-dimensional material mixed matrix membrane with micropores of different sizes generate a kinetic quantum sieving effect, and the chemical affinity quantum sieving effect provided by the binding sites on the surface of the two-dimensional material provides a chemical affinity quantum sieving effect. Pervaporation and quantum sieving effects are coupled to separate water isotopes. Under the action of quantum sieving, the transport rate of lighter water isotopes is greater than that of heavier isotopes; the particles are in a state of vibration at the pore size position, the lighter isotopes vibrate more violently and have higher zero-point energy, making it easier to break free from the adsorption site; while the heavier isotopes have lower zero-point energy and are more likely to be adsorbed on the adsorption site of the two-dimensional material, thus achieving separation from the lighter isotopes.

[0007] Furthermore, the phase transition generated during the desorption process of pervaporation and the transmembrane chemical potential gradient of the pervaporation process are coupled with quantum sieving, allowing water isotope molecules to flow through the pores at a faster rate, with the transmembrane chemical potential gradient being either a concentration difference or a pressure difference.

[0008] Furthermore, the two-dimensional material nanoporous membrane is a GO membrane, MXene membrane, TMDs membrane, or LDHs membrane; two-dimensional materials refer to nanomaterials that exhibit a sheet-like structure under an electron microscope, with a thickness at the atomic or sub-nanometer scale and a lateral dimension greater than the thickness. The two-dimensional material is selected from one or more of the following combinations: graphene materials, transition metal carbon / nitrides, transition metal chalcogenides, single-element alkenes, and hexagonal boron nitride. Alternatively, two-dimensional materials may be derivatives of two-dimensional materials that have been doped with N, P, and B elements, or derivatives that have undergone surface functionalization modification by grafting amino, carboxyl, or sulfonic acid groups.

[0009] Furthermore, a two-dimensional material hybrid matrix membrane refers to a composite membrane formed by using a continuous phase polymer matrix or inorganic matrix as a carrier and a dispersed phase two-dimensional material as a filler; the polymer matrix includes one or more blends of the following materials: Polyamides, polysulfones / polyethersulfones, fluoropolymers, polyimides, hydrophilic polymers, polyacrylonitrile, polyurethanes, polyetheretherketones, and polymers with inherent micropores.

[0010] Furthermore, two-dimensional material mixed matrix membranes are prepared by interfacial polymerization, casting or phase inversion; two-dimensional material nanoporous membranes are prepared by vacuum filtration, blade coating or spraying.

[0011] Furthermore, the interlayer spacing can be controlled by physical intercalation, chemical cross-linking, or heat treatment methods, and the control of the interlayer spacing is based on the isotope separation requirements.

[0012] Secondly, the present invention provides a water isotope pervaporation separation system based on a two-dimensional material membrane, used to realize the water isotope pervaporation separation method based on a two-dimensional material membrane as described above. The system includes a feeding device, a delivery pump, and a two-dimensional material membrane assembly connected along the medium flow direction. The two-dimensional material membrane assembly includes a two-dimensional material membrane, a support, a first chamber, and a second chamber. The two-dimensional material membrane is located between the first and second chambers. The first chamber has a mixed solution inlet, and the second chamber has a circulating liquid outlet. The mixed solution inlet is connected to the feeding device, and the circulating liquid outlet has two parallel pipelines. Each of the two pipelines has a collection unit, and the outlets of the two collection units are connected to a vacuum pump. The support is located in the second chamber, and the second chamber is connected to a vacuum pipeline. The two-dimensional material membrane is a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane.

[0013] Furthermore, a buffer bottle is installed on the pipeline from the outlet of the collection unit to the vacuum pump; valves are installed at both the inlet and the outlet of the two-dimensional material membrane module; valves are installed at both the inlet and outlet of the collection unit on both pipelines; a pressure gauge is also installed at the outlet of the collection unit; and a temperature sensor is installed at the inlet of the two-dimensional material membrane module; the collection unit is a cold trap, and a peristaltic pump is used for the transfer pump.

[0014] Thirdly, the present invention provides a testing method for a water isotope pervaporation separation system based on a two-dimensional material membrane, comprising the following steps: (1) Construct the water isotope pervaporation separation system based on two-dimensional material membrane as described above; (2) Prepare a mixed solution containing the target isotope, with the concentration of the target isotope in the mixed solution ranging from 1 ppm to 50 wt%. Before and / or during the contact with the pervaporation membrane, heat the mixed solution to 25-80°C using a heating unit and stir at a constant temperature to eliminate the concentration gradient. (3) Place the hose connected to the membrane module into the delivery pump and set the parameters of the delivery pump; place both ends of the hose into the feeding device and turn on the delivery pump to circulate the water isotope mixed feed liquid. (4) Place different two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes into the membrane module of the pervaporation system and connect them to the steam pipe to achieve the separation of water isotopes; (5) Record the water isotope separation results, complete the test and clean.

[0015] Furthermore, the heating method includes preheating of the feed liquid and heating of the membrane itself. The preheating methods of the feed liquid include water bath, oil bath, solar thermal and / or geothermal, and the heating methods of the membrane itself include Joule heating, photothermal heating or embedded electric heating element.

[0016] Fourthly, the present invention provides an application method for the water isotope pervaporation separation system based on the two-dimensional material membrane as described above, by replacing the two-dimensional material membrane with different parameters and changing the system pressure and temperature to perform water isotope pervaporation separation or test the performance of the two-dimensional material membrane.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: Water isotopes have significant strategic value, necessitating an effective separation method. Two-dimensional materials, due to their sub-nanometer interlayer spacing and abundant surface functional groups, possess the ability to sieve water isotopes. Pervaporation, driven by both heat and chemical potential gradients, and aided by dissolution-diffusion mechanisms, effectively separates near-boiling mixtures. Furthermore, two-dimensional materials meet the membrane density requirements of pervaporation membranes, making them highly suitable for water isotope separation. This invention provides a water isotope pervaporation separation system based on a two-dimensional material membrane, leveraging the quantum sieving effect of the two-dimensional material within the membrane and the synergistic effect of phase transition and transmembrane chemical potential gradient during pervaporation. It also involves preparing two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes to effectively separate water isotopes with low energy consumption, thus promoting the application of membrane separation methods and two-dimensional materials in water isotope separation. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the principle of water isotope separation in this invention; Figure 2 This is a schematic diagram of a two-dimensional material hybrid matrix membrane; Figure 3 This is a schematic diagram of a two-dimensional nanoporous membrane. Figure 4 This is a diagram illustrating the water isotope separation mechanism of a two-dimensional material hybrid matrix membrane. Figure 5 This is a diagram illustrating the water isotope separation mechanism of a two-dimensional nanoporous membrane. Figure 6 This is a system diagram of a pervaporation unit. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention proposes a water isotope pervaporation separation method and system based on two-dimensional material membranes. It applies two-dimensional material nanoporous membranes and two-dimensional material hybrid matrix membranes to the pervaporation method, utilizing the confinement effect generated by the sub-nanometer interlayer channels of the two-dimensional materials, kinetic quantum sieving, and chemical affinity quantum sieving provided by the surface binding sites of the two-dimensional materials. These are coupled with the pervaporation process (synergistic permeate-side phase transition and transmembrane chemical potential gradient) to separate water isotopes. (Reference) Figure 1 The extremely small pore size of two-dimensional materials constitutes a physical energy barrier, and the transport rate of lighter water isotopes is greater than that of heavier isotopes due to kinetic quantum sieving. Particles are in a vibrating state at the pore locations; lighter isotopes vibrate more violently, possessing higher zero-point energies and easily escaping adsorption sites, while heavier isotopes, with their lower zero-point energies, are more easily adsorbed onto the adsorption sites of the two-dimensional material, achieving separation from the lighter isotopes. Furthermore, the phase transition generated during desorption in pervaporation and the transmembrane chemical potential gradient, such as the concentration or pressure difference, coupled with quantum sieving, allow water isotope molecules to flow through the pores at ultrafast speeds, amplifying the sieving effect and making the entire separation process more efficient. Pervaporation using a two-dimensional material mixed matrix membrane can separate water isotopes, similar to pervaporation using two-dimensional material nanoporous membranes. Simultaneously, the different sizes of micropores in the polymer chains of the mixed matrix membrane can also achieve the same effect as interlayer sieving in two-dimensional materials.

[0022] Example 1: This invention provides a water isotope pervaporation separation system based on a two-dimensional material membrane, comprising a feeding device, a delivery pump, and a two-dimensional material membrane module connected along the medium flow direction. The mixed solution inlet of the two-dimensional material membrane module is connected to the feeding device. The circulating liquid outlet of the two-dimensional material membrane module is divided into two pipelines, each with a collection unit. The outlets of the two collection units are connected to a vacuum pump. The two-dimensional material membrane module includes a two-dimensional material membrane, a support, a first chamber, and a second chamber. The chamber containing the support is connected to a vacuum pipeline. The two-dimensional material membrane is a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane. A buffer bottle is installed on the pipeline from the outlet of the collection unit to the vacuum pump. Valves are installed at the inlet and the outlet of the two-dimensional material membrane module. Valves are also installed at the inlet and outlet of the collection units on both pipelines. A pressure gauge is also installed at the outlet of the collection unit. A temperature sensor is installed at the inlet of the two-dimensional material membrane module. The collection unit is a cold trap.

[0023] Example 2: This invention provides a testing method for a water isotope pervaporation separation system based on a two-dimensional material membrane, comprising the following steps: (1) Construct a pervaporation system; (2) Prepare a mixed solution containing the target isotope (including H2O / D2O mixture, H2O / T2O mixture, D2O / T2O mixture), wherein the concentration of the target isotope in the mixed solution ranges from 1 ppm to 50 wt%, and the mixed solution is heated to a preset temperature by a heating unit before and / or during contact with the pervaporation membrane, the solution temperature is adjusted to 25–80°, preferably 40±0.5°C, and stirred at a constant temperature for 1–2 h to eliminate the concentration gradient; (3) Before separation, put the rubber hose connected to the membrane module into the peristaltic pump and set the peristaltic pump speed; put both ends of the rubber hose into the storage device for raw material liquid, fix the pipe with clamps, and turn on the peristaltic pump to circulate the water isotope mixed raw material liquid.

[0024] (4) Place the two-dimensional material nanoporous membrane or the two-dimensional material mixed matrix membrane into the membrane module of the pervaporation system and connect it to the steam pipe. Based on the combination of the pervaporation system and the two-dimensional material nanoporous membrane / two-dimensional material mixed matrix membrane, the separation of water isotopes is achieved. (5) Record the water isotope separation results and complete the cleaning of the test system.

[0025] The pervaporation system described in step (1) employs the water isotope pervaporation separation system based on a two-dimensional material membrane as described in Example 1. This pervaporation system utilizes a two-dimensional material membrane to separate water isotopes in the membrane module section, including the use of a quantum sieving mechanism and the coupling of quantum sieving with the pervaporation system to separate water isotopes.

[0026] The pervaporation system described in step (1) is driven by chemical potential, and its driving mode adopts vacuum driving mode and purge gas mode.

[0027] (a) The vacuum-driven mode separates water isotopes and brings them into the collection unit through a coordinated strategy of upstream heat source and downstream vacuum. (b) In the purge gas mode, a dry, inert gas is introduced into the permeate side of the membrane to purge the vapor into the collection unit; The isotope mixture in step (2) includes H2O / D2O mixture, H2O / T2O mixture, and D2O / T2O mixture. 16 O / H2 18 O mixture. Adjust the solution temperature near the membrane to 25–80°C and stir at this temperature for 1–2 hours to eliminate the concentration gradient; the concentration range of the mixture is 1 ppm to 50 wt%. The preferred solution temperature is 40 ± 0.5°C; The heating method described in step (2) is the preheating of the feed liquid and the heating of the membrane itself.

[0028] (a) A preheating device located upstream of the membrane module for preheating the feed liquid; (b) A membrane heating device thermally coupled to the pervaporation membrane for directly heating the pervaporation membrane so that heat is transferred to the feed liquid through the membrane.

[0029] In step (2), the heating method for preheating the mixed solution is a water bath, oil bath, solar heat or geothermal heat.

[0030] In the heating method described in step (2), the film heating device includes Joule heating, photothermal heating or embedded electric heating element.

[0031] Example 3: Based on the method steps of Example 2 above, in step (4), two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes with different process parameters are used to test the performance of two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes.

[0032] Example 4, a testing method for a water isotope pervaporation separation system based on a two-dimensional material membrane according to the present invention, includes the following steps: (1) Construct the above-mentioned pervaporation system; (2) Prepare a mixed solution containing the target isotope (including H2O / D2O mixture, H2O / T2O mixture, D2O / T2O mixture), wherein the concentration of the target isotope in the mixed solution ranges from 1 ppm to 50 wt%. For example, place the mixed solution in an oil bath for preheating, adjust the solution temperature to 25–80°C, preferably 40±0.5°C, and stir at a constant temperature for 1–2 hours to eliminate the concentration gradient. (3) Before separation, put the rubber hose connected to the membrane module into the peristaltic pump and set the peristaltic pump speed; put both ends of the rubber hose into the storage device for raw material liquid, fix the pipe with clamps, and turn on the peristaltic pump to circulate the water isotope mixed raw material liquid.

[0033] (4) Prepare a two-dimensional material dispersion, adjust the interlayer spacing according to different isotope separation requirements, and use membrane preparation methods such as vacuum filtration and interfacial polymerization to prepare a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane. (5) Place a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane into the membrane module of the pervaporation system and connect it to the steam pipe. Based on the combination of the pervaporation system and the two-dimensional material nanoporous membrane / two-dimensional material mixed matrix membrane, the separation of water isotopes is achieved. (6) Record the water isotope separation results and complete the cleaning of the test bench.

[0034] The preparation before separation in step (3) includes cleaning some experimental equipment and preparing experimental materials. The equipment to be cleaned and prepared is as follows: (a) Clean all cold traps before the experiment. First, rinse the cold traps with tap water and repeat several times. Then rinse with deionized water to ensure that no other substances affect the measurement results. After rinsing, put the cold traps into the oven to dry. (b) Before the experiment, clean the sand core with deionized water and measure the conductivity of the cleaning water. If it is below 50 μs / cm, the cleaning can be stopped and the core can be placed in an ultrasonic cleaner for ultrasonic treatment for 5-15 minutes.

[0035] As an optional embodiment, based on Embodiment 4, the two-dimensional material described in step (4) refers to a nanomaterial that exhibits a layered structure under an electron microscope, with a thickness at the atomic or sub-nanometer scale (e.g., 0.3 nm to 5 nm), and a lateral dimension greater than its thickness. Specifically, the two-dimensional material is selected from one or more of the following combinations: (a) Graphene materials: graphene oxide, graphene, reduced graphene oxide; (b) Transition metal carbides / nitrides (MXenes): such as Ti3C3T x Ti2CT x Nb2CT x V2CT x ; (c) Transition metal chalcogenides (TMDs): such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), and tungsten diselenide (WSe2); (d) Single-element alkenes (Xenes): such as phosphorene, borophene, and silicene; (e) Hexagonal boron nitride (h-BN).

[0036] And derivatives of the above two-dimensional materials after elemental doping (such as N, P, B doping) and surface functionalization modification (such as grafting amino, carboxyl, sulfonic acid groups).

[0037] Based on the above optional embodiment, the two-dimensional material dispersion preparation method in step (4) is as follows: (a) Providing a precursor: Providing the layered bulk material or multilayer two-dimensional material powder to be processed; (b) Constructing a dispersion system: The layered bulk material or multilayer two-dimensional material powder is added to a solvent to form a premixed liquid; (c) Peeling and dispersion: Apply an external force field (such as ultrasound and vibration) to the premixed liquid to peel the layered bulk material or multilayer two-dimensional material powder into few-layer or single-layer nanosheets; (d) Screening and collection: Remove large particles of impurities that have not been peeled off, collect the supernatant, and obtain the two-dimensional material dispersion.

[0038] Furthermore, based on Example 4, the interlayer spacing control method described in step (4) employs physical intercalation, chemical crosslinking, or heat treatment.

[0039] As an example, the vacuum filtration method described in step (4) is operated as follows: (a) When using the vacuum filtration method, select a filtration device that is compatible with the substrate and place the substrate on the sand core of the vacuum filtration device. (b) Pour the required two-dimensional material dispersion into a vacuum filtration flask with a set volume. In this application, the two-dimensional material dispersion is GO dispersion. First, calculate the GO content required for film formation. According to the calculated content, add GO to deionized water, pour it into multiple centrifuge tubes and put them into a centrifuge for centrifugation. Take the supernatant after centrifugation, clean it with ultrasonication, and use it as the raw material liquid for vacuum filtration. (c) Start the vacuum pump to form a negative pressure. Driven by the pressure, the aqueous phase passes through the substrate and the sand core. The material nanosheets in the dispersion are uniformly stacked on the substrate to form a thin film. Filter until the surface of the film is dry and free of moisture.

[0040] As an example, based on Embodiment 4, the specific operation of interface aggregation in step (4) is as follows: (a) Select a suitable porous support layer, such as polysulfone (PSF), polyethersulfone (PES) or polyacrylonitrile (PAN), and pretreat the porous support layer by immersing it in deionized water. (b) Immerse the porous support layer in the aqueous phase for 1-5 minutes, remove the aqueous phase from the surface of the porous support layer, and then pour in the organic phase to react for 10-60 seconds to obtain a thin film.

[0041] (c) Place the prepared film in an oven for curing at a temperature of 60-100℃ for 3-10 minutes. (d) After cooling, store the film in deionized water or 0.5% sodium bisulfite (SBS) solution.

[0042] Optionally, the two-dimensional material nanoporous membrane described in step (4) is a GO membrane, a two-dimensional transition metal carbide (MXene) membrane, a transition metal sulfide (TMDs) membrane, or a layered bimetallic hydroxide (LDHs) membrane.

[0043] The two-dimensional material mixed matrix membrane mentioned in step (4) refers to a composite membrane formed by using a continuous phase polymer matrix or inorganic matrix as a carrier and the above-mentioned two-dimensional material as a dispersed phase filler.

[0044] As an example, the polymer matrix is ​​a blend of one or more of the following materials: (a) Polyamides: including fully aromatic polyamides, semi-aromatic polyamides, and aliphatic polyamides; especially cross-linked polyamide networks formed by interfacial polymerization of m-phenylenediamine (MPD) or piperazine (PIP) with trimesoyl chloride (TMC); (b) Polysulfone / polyethersulfone (PSf / PES): commonly used in ultrafiltration membranes or as a support layer for composite membranes; (c) Fluoropolymers: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE); (d) Polyimide: including polyimide (PI), polyetherimide (PEI), and polybenzimidazole (PBI), suitable for solvent-resistant or high-temperature applications; (e) Hydrophilic polymers: polyvinyl alcohol (PVA), chitosan (CS), sodium alginate (SA), cellulose and its derivatives (such as cellulose acetate CA); (f) Others: Polyacrylonitrile (PAN), polyurethane (PU), polyether ether ketone (PEEK), and polymers with inherent micropores (PIMs).

[0045] As an example, the two-dimensional material described in step (4) is added to the polyamide membrane as a filler to form a hybrid matrix membrane, including the following steps: (a) Prepare a sufficient mass of GO for dilution according to the required GO content in the aqueous phase; (b) Add the modified material in a set proportion and perform corresponding ultrasonic, heating and stirring treatments; (c) Add the amine monomer to the aqueous phase, add deionized water to the target mass, and use the resulting solution as the aqueous phase for the next step of interfacial polymerization.

[0046] Furthermore, based on Example 4, the specific steps for connecting the steam pipe in step (5) are as follows: (a) Close the valves in the pipeline; (b) Connect the hose to the cold trap, open the upstream and downstream valves of the cold trap, turn on the vacuum pump to evacuate or turn on the purge gas device to push the vapor flow into the cold trap, and then close the downstream valve of the cold trap and the vacuum pump.

[0047] (c) Place the cold hydrazine in the liquid nitrogen bottle and start timing after the reading stabilizes.

[0048] Based on Example 4, the experimental steps described in step (5) are as follows: (a) After timing, wait 20 minutes and record the required conditions for the experiment, such as temperature, pressure, start time, and end time. (b) After 20 minutes, remove the cold trap and place it in a fixture to wait for the condensate to freeze and melt. (c) Close the experimental side pipe and open the other side pipe to repeat the above steps and the steam pipe connection steps for the next experiment.

[0049] Based on Example 4, the result processing procedure in step (6) is as follows: (a) Record the net weight of the cold trap before the experiment. After the experiment, wipe the condensate off the surface of the cold trap, weigh the total weight of the cold trap, and record the weight of the condensate inside the cold trap. (b) Pour the condensate into a test tube and analyze the proportion of isotopes by methods such as ¹H NMR (hydrogen nuclear magnetic resonance), infrared or Raman spectroscopy, liquid scintillation counting, isotope ratio mass spectrometry, and optical cavity ring-down spectroscopy, and calculate the selectivity.

[0050] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0051] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0052] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0053] Example 5, refer to Figure 2 The hybrid matrix membrane described in this application uses a two-dimensional material as a filler. In practice, a hybrid matrix membrane with modified GO as a filler was fabricated. The preparation process is as follows: (1) Dilute 5 mg / mL of GO dispersion to a final GO concentration of 0.008 wt%, weigh sodium lignosulfonate with a mass ratio of 10:1 to GO, add it to the GO dispersion, and sonicate for 1 h. (2) Add glucose and ammonia water with a mass ratio of 6:1 and stir with a rotor magnetically for 3 hours in a water bath at 95°C. (3) After the water bath is completed, add 2wt% m-phenylenediamine and 2.2wt% camphor sulfonic acid to the obtained solution, add water to 27.5g, and finally add 3.5wt% triethylamine to prepare an aqueous phase; (4) Prepare 20g of 0.15wt% pyrithione tricarboxylic acid chloride solution as the organic phase; (5) Dissolve the undissolved solute in the centrifuge tube using a vortex stirrer and sonicate at 80 Hz for 1 h. (6) Cut the polysulfone substrate and soak it in deionized water for 1 hour; (7) Before film formation, use a roller to remove water from the substrate surface, immerse the substrate in the aqueous phase for 2 minutes, pour off the aqueous phase, and use a roller to remove the residual aqueous phase on the surface. (8) Pour in the organic phase to carry out the reaction, and react for 60 seconds; (9) Place in an oven to cure for 5 minutes, take it out and cut it into a circle, store it in deionized water and place it in a refrigerator.

[0054] Example 6, a method for preparing a PVA / SPCN film, comprising the following steps: (1) Add 50 mg of polyvinyl alcohol (PVA) to 100 mL of deionized water and heat at 90 °C for 6 h until completely dissolved to obtain a PVA solution with a concentration of 0.5 mg / mL. (2) Take a set volume of the PVA solution and add it to the SPCN nanosheet dispersion, and stir at 800 rpm for 1 h to obtain a PVA / SPCN mixture; (3) Film formation is carried out by vacuum filtration: the PVA / SPCN mixture is filtered onto the surface of the PC / AAO substrate to form a film layer; (4) After filtration, the obtained membrane is placed in a vacuum oven at 60°C and dried for 12 hours to obtain a PVA / SPCN membrane.

[0055] In some embodiments, to study the effect of PVA content on membrane performance, the initial mass of SPCN in each membrane can be fixed at 5 mg, and the mass fraction of PVA in the PVA / SPCN membrane can be controlled by adjusting the volume of the added PVA solution. The PVA mass fraction is the ratio of PVA mass to the sum of the masses of PVA and SPCN, and the PVA mass fraction is 0.5%-10%.

[0056] Furthermore, to investigate the effect of SPCN content on membrane performance, the amount of SPCN added was adjusted while maintaining a constant PVA mass fraction, and the absolute amount of PVA added was adjusted accordingly. The mass fraction of SPCN ranged from 0.05% to 1%. Example 7, referring to Figure 3 Example 2: The two-dimensional material nanoporous membrane described in this application was actually fabricated into a GO membrane. The preparation process and parameters are as follows: (1) Take 5 mg / mL GO dispersion and dilute it with deionized water to 0.2 mg / mL; (2) The diluted GO dispersion was placed in an ultrasonic cleaner and ultrasonically treated for 1 hour; (3) Place the ultrasonically treated dispersion into 6 centrifuge tubes evenly, centrifuge for 30 minutes, and then pour the supernatant into a beaker for later use. (4) Prepare graduated cylinders of different volumes, place the polyvinylidene fluoride (PVDF) substrate on the vacuum filtration device, install the filtration flask, add the dispersion to the filtration flask according to the volume (e.g., 5 mL of 0.2 mg / mL dispersion is needed for 1 mg GO membrane), perform filtration, prepare the GO membrane with the required content, and wait for the membrane surface to dry and be free of water before taking it out. (5) Place the membrane after filtration into a drying oven and dry for 12 hours.

[0057] This application also prepares different GO membranes by changing the GO membrane preparation parameters based on Example 7. The specific parameters are shown in Table 1.

[0058] Table 1

[0059] Example 8, a method for preparing an MXene-PCN nanosheet film, comprising the following steps: (1) Dilute the MXene dispersion with a concentration of 5 mg / mL to 0.02 mg / mL with deionized water and sonicate it for 10 min under nitrogen protection at a temperature below 5°C. (2) According to the set ratio, different volumes of the MXene dispersion (0.02 mg / mL) were added to the PCN nanosheet dispersion with a concentration of 0.02 mg / mL, and ultrasonically treated for 10 min under nitrogen protection and at a temperature higher than 5°C to obtain MXene-PCN mixed dispersions with different concentrations, the concentration of MXene being 0%-40% (vol). (3) Take a predetermined volume of the MXene-PCN mixed dispersion and filter it onto a porous α-Al2O3 / PES substrate by vacuum filtration to obtain an MXene / PCN nanosheet film. (4) Without adding MXene dispersion, the pure PCN nanosheet film was prepared by vacuum filtration onto a porous α-Al2O3 / PES substrate. (5) The obtained pure PCN nanosheet film and MXene / PCN nanosheet film were dried in a vacuum oven at room temperature for at least 12 hours.

[0060] Example 9, a method for preparing a pure SPCN membrane, comprising the following steps: (1) Take a certain amount of SPCN nanosheet dispersion for later use; (2) A certain volume of SPCN nanosheet dispersion was filtered onto the surface of the PC / AAO substrate to form a film layer by vacuum filtration. (3) After filtration, the obtained membrane was placed in a vacuum oven at 60°C and dried for 12 hours to obtain a pure SPCN membrane.

[0061] In some embodiments, to ensure comparability between different membrane samples, the initial mass fraction of SPCN in each membrane is 0.05%-1%.

[0062] Reference Figure 4 In the pervaporation process of the two-dimensional material mixed matrix membrane, the feed side is the surface of the separation layer. The water isotope mixture to be separated flows over the surface of the separation layer, and the separated molecules dissolve and permeate into the membrane. Through the free volume and gaps between polymer chains and the nanoscale channels formed by the two-dimensional material, diffusion is driven by the chemical potential gradient. During the diffusion process, the diffusion rate of isotopes is changed by the effect of the transmembrane chemical potential gradient (concentration, pressure) during pervaporation, in conjunction with the quantum sieving effect of polymer chains and two-dimensional materials, amplifying the difference in diffusion rate, thereby achieving the separation effect of water isotopes. The water isotopes overflow into the membrane in the form of vapor through the pressure difference of the substrate surface and reach the permeate side, completing the pervaporation process in the membrane.

[0063] refer to Figure 5 The pervaporation process of two-dimensional material nanoporous membranes is similar to that of mixed matrix membranes. The difference is that the sieving of two-dimensional material nanoporous membranes amplifies the sieving effect of the two-dimensional material itself. In order to adjust the sieving effect of two-dimensional materials, the interlayer spacing and surface functional groups of two-dimensional material membranes can be changed by modification. The modification method is described in Example 3.

[0064] Example 10: By crosslinking with a crosslinking agent and physical intercalation of graphitic carbon nitride (g-C3N4), the interlayer spacing of the GO film is reduced, making the GO film more effective at distinguishing isotope molecules. The crosslinking agent used is a crosslinking agent containing amino and thiocarbonyl groups, such as thiourea (TU). The modification process is as follows: (1) Add a set proportion of TU to the prepared GO dispersion, heat and stir at 80°C for 1 h to obtain GO-TU dispersion; the mass ratio of GO to TU is 1:1-1:10. (2) Take g-C3N4 dispersion and add it to GO-TU dispersion in proportion. Stir magnetically for 1 hour and wait for g-C3N4 to be completely and evenly dispersed. Use vacuum filtration to prepare the modified two-dimensional material membrane. The details are not repeated here.

[0065] refer to Figure 6Example 11: The system of the pervaporation method comprises a feed liquid circulation system in the upper half of a two-dimensional material membrane module, a vacuum pipeline in the lower half, and the membrane module itself. The two-dimensional material membrane module includes a two-dimensional material membrane, a support, a first chamber, and a second chamber. The first chamber has a mixed solution inlet, and the second chamber has a circulating liquid outlet. The mixed solution inlet of the two-dimensional material membrane module is connected to a feeding device. The feed liquid is located in a feed bottle placed in an oil bath, and a peristaltic pump provides the power required for the feed liquid circulation. The feed liquid flows through the upper chamber of the two-dimensional material membrane module in the pipeline, contacting the feed side of the membrane during this process. (Refer to...) Figure 4 , Figure 5 Temperature sensors are installed on the pipeline to monitor the real-time temperature inside the pipeline. At the same time, the pipeline is covered with an insulation layer to reduce convective heat exchange between the feed pipeline and the outside.

[0066] The first and second chambers are connected by bolts arranged in a circumferential direction. To prevent leakage of the feed liquid, grooves are made on the contact surfaces of the first and second chambers to place sealing rings. The permeate side of the membrane module first places the sand core, and the chamber below the sand core is connected to the vacuum pipe. The surface of the two-dimensional material membrane module is covered with heat insulation cotton to reduce heat loss of the feed liquid in the two-dimensional material membrane module area.

[0067] The second chamber has a circulating liquid outlet connected to two pipes, and the opening and closing of the pipes are controlled by valves. While one pipe is connected to a cold trap to collect condensate, the cold trap in the other pipe can be thawed at room temperature to ensure the continuity of condensate collection. Pressure gauges are installed on both pipes to measure the vacuum level. The pipes are connected in front of a buffer bottle, which is connected to a vacuum pump. By opening and closing different valves on both sides, the pressure on one side of the pipe can be released from the other side, which is beneficial for controlling the vacuum level.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A water isotope pervaporation separation method based on a two-dimensional material film, characterized by, The pervaporation method is combined with two-dimensional material membranes, which are either two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes. The kinetic quantum sieving effect generated by the polymer chains of the two-dimensional material nanoporous membrane and its sub-nanometer interlayer channels or the two-dimensional material mixed matrix membrane, as well as the chemical affinity quantum sieving effect provided by the binding sites on the surface of the two-dimensional material, are used to couple pervaporation and quantum sieving effects to separate water isotopes. Under the action of quantum sieving, the transport rate of lighter water isotopes is greater than that of heavier isotopes; the particles are in a state of vibration at the pore size position, the lighter isotopes vibrate more violently and have higher zero-point energy, making it easier to break free from the adsorption site; while the heavier isotopes have lower zero-point energy and are more likely to be adsorbed on the adsorption site of the two-dimensional material, thus achieving separation from the lighter isotopes.

2. The water isotope pervaporation separation method based on a two-dimensional material film according to claim 1, characterized by, The phase transition generated during the desorption process of pervaporation and the transmembrane chemical potential gradient of the pervaporation process are coupled with quantum sieving. Water isotope molecules flow through the pores at a faster speed, and the transmembrane chemical potential gradient is the concentration difference or pressure difference.

3. The water isotope pervaporation separation method based on a two-dimensional material film according to claim 1, characterized by, Two-dimensional material films are GO films, MXene films, TMDs films, or LDHs films; two-dimensional materials refer to nanomaterials that exhibit a sheet-like structure under an electron microscope, with a thickness at the atomic or sub-nanometer scale and a lateral dimension greater than the thickness. The two-dimensional materials are selected from one or more of the following combinations: graphene materials, transition metal carbon / nitrides, transition metal chalcogenides, single-element alkenes, and hexagonal boron nitride. Alternatively, two-dimensional materials may be derivatives of two-dimensional materials that have been doped with N, P, and B elements, or derivatives that have undergone surface functionalization modification by grafting amino, carboxyl, or sulfonic acid groups.

4. The water isotope pervaporation separation method based on a two-dimensional material film according to claim 1, characterized by, Two-dimensional material hybrid matrix membranes refer to composite membranes formed by using a continuous phase polymer matrix or inorganic matrix as a carrier and a dispersed phase two-dimensional material as a filler; the polymer matrix includes one or more blends of the following materials: Polyamides, polysulfones / polyethersulfones, fluoropolymers, polyimides, hydrophilic polymers, polyacrylonitrile, polyurethanes, polyetheretherketones, and polymers with inherent micropores.

5. The water isotope pervaporation separation method based on a two-dimensional material film according to claim 1, characterized by, The interlayer spacing is controlled by physical intercalation, chemical cross-linking or heat treatment methods, and the control of the interlayer spacing is based on the requirements of isotope separation.

6. A water isotope pervaporation separation system based on a two-dimensional material film, characterized in that, The method for water isotope pervaporation separation based on a two-dimensional material membrane according to any one of claims 1-5 includes a feeding device (1), a delivery pump (2), and a two-dimensional material membrane assembly connected along the medium flow direction. The two-dimensional material membrane assembly includes a two-dimensional material membrane (3), a support, a first chamber (4), and a second chamber (5). The two-dimensional material membrane (3) is located between the first chamber (4) and the second chamber (5). The first chamber (4) has a mixed solution inlet, and the second chamber (5) has a circulating liquid outlet. The mixed solution inlet is connected to the feeding device (1), and the circulating liquid outlet has two parallel pipelines. Each pipeline has a collection unit (7), and the outlets of the two collection units are connected to a vacuum pump (6). The support is located in the second chamber (5), and the second chamber (5) is connected to a vacuum pipeline. The two-dimensional material membrane is a two-dimensional material nanoporous membrane or a two-dimensional material mixed matrix membrane.

7. The two-dimensional material film-based water isotope pervaporation separation system according to claim 7, characterized in that, A buffer bottle (8) is installed on the pipeline from the outlet of the collection unit (7) to the vacuum pump (6); valves are installed at the inlet of the two-dimensional material membrane module and the outlet of the separation liquid of the two-dimensional material membrane module. Valves are installed at the inlet and outlet of the collection unit on both pipelines. A pressure gauge is also installed at the outlet of the collection unit, and a temperature sensor is installed at the inlet of the two-dimensional material membrane module. The collection unit (7) is a cold trap, and the delivery pump (2) is a peristaltic pump.

8. A method for testing a water isotope pervaporation separation system based on a two-dimensional material film, characterized in that, Includes the following steps: (1) Construct a water isotope pervaporation separation system based on a two-dimensional material membrane as described in claim 6 or 7; (2) Prepare a mixed solution containing the target isotope, with the concentration of the target isotope in the mixed solution ranging from 1 ppm to 50 wt%. Before and / or during the contact with the pervaporation membrane, heat the mixed solution to 25-80°C using a heating unit and stir at a constant temperature to eliminate the concentration gradient. (3) Place the hose connected to the membrane module into the delivery pump (2) and set the parameters of the delivery pump (2); place both ends of the hose into the feed device (1) and turn on the delivery pump (2) to circulate the water isotope mixing raw material liquid. (4) Place different two-dimensional material nanoporous membranes or two-dimensional material mixed matrix membranes into the membrane module of the pervaporation system and connect them to the steam pipe to achieve the separation of water isotopes; (5) Record the water isotope separation results, complete the test and clean.

9. The test method of claim 8, wherein, The heating method includes preheating of the feed liquid and heating of the membrane itself. The preheating methods of the feed liquid include water bath, oil bath, solar thermal and / or geothermal, and the heating methods of the membrane itself include Joule heating, photothermal heating or embedded electric heating element.

10. The method of using the water isotope pervaporation separation system based on a two-dimensional material film according to claim 6 or 7, characterized in that, By changing the two-dimensional material membrane with different parameters and varying the system pressure and temperature, water isotope pervaporation separation or the performance of the two-dimensional material membrane can be tested.

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