Functionalized nanoporous graphene membrane for mixed ion separation and preparation method thereof
Functionalized nanoporous graphene membranes were prepared by a one-step CVD method, combined with plasma etching and chemical modification, which solved the problem of balancing high selectivity and high flux in traditional membrane materials. This method achieves efficient mixed ion separation and is suitable for applications such as seawater desalination, lithium extraction from salt lakes, and fuel cells.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PEKING UNIV
- Filing Date
- 2023-09-21
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies struggle to efficiently separate mixed ions, especially monovalent metal ions and anions. Furthermore, traditional polymer membranes cannot achieve both high selectivity and high flux, and are prone to aging and plasticization, failing to meet the demands of lithium extraction from salt lakes, seawater desalination, and fuel cells.
Functionalized nanoporous graphene films were prepared in one step using CVD technology. Nanopores were introduced by plasma etching, and specific functional groups were introduced at the edges of the nanopores using non-covalent and covalent modification methods to achieve high-density, narrow-distribution nanopore structures and functionalization. This was combined with heteroatom doping and precise control of the type and number of functional groups.
It achieves highly selective and high-throughput mixed ion separation, overcomes the "trade-off" effect of traditional separation membranes, is suitable for large-area samples, has good stability and mechanical strength, and is applicable to seawater desalination, lithium extraction from salt lakes, and fuel cells.
Smart Images
Figure CN117282278B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of membrane separation technology, specifically to a functionalized nanoporous graphene membrane for mixed ion separation and its preparation method. Background Technology
[0002] Mixed ion separation plays a crucial role in lithium extraction from salt lakes, brine refining, and zero-discharge of high-salinity wastewater. Especially with the widespread application of monovalent metal ions in energy storage, metallurgy, and agriculture, the efficient separation of cation mixtures has become a significant demand. It is projected that by 2025, the global demand for monovalent cations will reach millions of tons, with extraction from salt lakes, seawater, and brackish water being the primary sources. However, salt lake brines mainly contain Li. + Na + K + Ca 2+ Mg 2+ isocations and SO4 2- Cl - CO3 2- Anions are similar, with some ions showing small differences, and sub-nanometer ion sizes (such as bare ions). Hydrated ions ), angstrom-scale ion size difference The presence of identical charge valence states between mixtures makes ion separation one of the most challenging separation tasks. Furthermore, to address water scarcity, seawater desalination technology has been widely adopted in some coastal areas. Seawater desalination technology involves Na+... + K + Ca 2+ Mg 2+ SO4 2- Cl - Separation of mixed ions is crucial. However, large-scale, sustainable, and low-cost seawater desalination remains a challenge. Fuel cells are power generation devices that directly convert the chemical energy of fuel into electrical energy, representing an ideal power generation technology with high energy efficiency and no environmental pollution. However, currently used proton exchange membranes generally suffer from fuel permeation problems, becoming a bottleneck restricting the further promotion and application of fuel cell technology.
[0003] Membrane separation is a simple, efficient, and safe separation technology widely used in chemical engineering, biomedicine, energy, and other fields. Due to its non-thermal, low-carbon, and green characteristics, it has significant advantages and great potential in the separation of mixed ions. The performance of the separation membrane determines the efficiency of the separation process. Membrane performance is mainly measured by two important parameters: permeability—the rate at which target molecules pass through the membrane—and selectivity—the retention capacity for non-target molecules. Generally speaking, membrane flux is inversely correlated with membrane thickness. Therefore, to achieve both high flux and high selectivity, an ideal separation membrane should have an extremely thin thickness and a highly ordered nanoporous structure. Currently, the separation membrane materials widely used in industry are traditional organic polymers, mainly including cellulose, polyamides, polysulfones, and organosilicon polymers. For traditional polymer separation membranes, the thinnest separation layer is on the scale of tens to hundreds of nanometers. Below this scale, the polymer chains usually loosen, leading to a decrease in separation selectivity. Furthermore, it is difficult to ensure defect-free and complete coverage during the preparation of even smaller separation layers, making it difficult to further improve the performance of polymer membranes and overcome the "trade-off" effect. Furthermore, although polymer membranes are low in cost and easy to mass-produce, they are prone to aging and plasticization during operation. Therefore, developing novel membrane materials and membrane preparation technologies for the development of high-performance separation membrane products is crucial to overcoming existing limitations in applications such as lithium extraction from salt lakes, seawater desalination, and fuel cell membranes.
[0004] Separation membranes fabricated using inorganic two-dimensional (2D) materials possess ultra-thin thicknesses and can incorporate high-density ordered nanopores, achieving both extremely high permeability and selectivity. Utilizing molecular sieving principles, they hold promise for overcoming the "trade-off" effect inherent in traditional polymer membranes. Furthermore, inorganic 2D material separation membranes typically exhibit high-temperature resistance and chemical corrosion resistance, ensuring reliability for long-term use. Currently, the most widely researched inorganic 2D material separation membrane is the graphene membrane, including graphene oxide membranes and monolayer graphene membranes. Monolayer graphene is a single-atom-layer two-dimensional nanomaterial composed solely of carbon atoms, possessing high Young's modulus and stable physicochemical properties, making it a potential next-generation separation membrane. Moreover, the highly smooth surface of graphene, coupled with a hydrophobic substrate, helps mitigate membrane fouling and scaling issues during separation, simplifying membrane management and potentially reducing maintenance costs, making it an ideal membrane material. Thin, efficient, and stable monolayer nanoporous graphene membranes can provide a new pathway for seawater desalination. Using graphene single-atom-layer two-dimensional material as a proton conduction membrane can make modern fuel cells lighter, thinner, and more efficient.
[0005] However, perfect graphene is impermeable to almost all molecules and ions except hydrogen and protons. To achieve better ion separation performance, high-performance nanopores must first be introduced into graphene to construct nano-scale ion channels, enabling initial ion separation at the dimensional level. Furthermore, functionalization of the pore edges is crucial for ion sieving. By introducing appropriate functional groups, the channel surface can be functionalized, and further ion sieving can be achieved by utilizing the difference in the interaction forces between ions and functional groups. Therefore, the ion selectivity and permeation rate of the separation membrane can be optimized by controlling the size and shape of the nanopores and the structure and number of functional groups grafted onto the nanopore edges. Research results show that functionalized nanopores on graphene provide extremely low transfer barriers and excellent proton selectivity for proton transfer. However, due to the similar valence states and ionic radii of lithium, sodium, and potassium ions, effective mixed ion sieving remains a significant challenge. Therefore, the design and fabrication of functionalized nanoporous graphene is imperative to meet the application requirements of monolayer graphene in mixed ion separation membranes.
[0006] The functionalization of graphene surfaces typically employs covalent grafting and non-covalent composite methods, or a combination of both. Non-covalent functionalization combines modifying molecules with graphene through electrostatic interactions, π-π interactions, ionic bonds, and hydrogen bonds, enhancing graphene's properties. Covalent functionalization utilizes graphene's active double bonds and electron-rich benzene rings, chemically reacting other reactants to form stable covalent bonds with graphene, thus endowing graphene with specific superior properties. Due to its versatility, reliability, and stability, this method has attracted considerable attention from researchers. Based on the functionalizing reagents used, covalent functionalization can be categorized into organic small molecule covalent functionalization, polymer covalent functionalization, and inorganic metal covalent functionalization. Commonly used covalent functionalization pathways include solution chemical reactions, photocatalytic reactions, plasma etching, and free radical addition reactions. Current research focuses primarily on the functionalization of graphene surfaces, lacking exploration and study on the functionalization of nanoporous graphene. Precisely modifying functional groups to the edges of nanopores remains a significant challenge in this field. Furthermore, the covalent bonding reaction inevitably damages the original graphene structure, causing irreversible changes to its inherent physicochemical properties. The functionalization of monolayer or few-layer graphene requires precise control of chemical reaction conditions. Additionally, given the stable structure of graphene composed of hexagonal benzene rings, increasing the number of functional group grafts is a major challenge in graphene functionalization.
[0007] Currently, research on functionalized nanoporous graphene separation membranes mainly focuses on theoretical simulations. Many researchers simulate the effects of different functional groups and pore sizes on ion separation performance by applying pressure and potential differences. For example, researchers used classical molecular dynamics simulations to predict the application potential of nanoporous graphene with hydroxyl-rich pore edges in seawater desalination; and they were the first to use molecular dynamics simulations to demonstrate the potential of membranes modified with negatively charged fluorine and nitrogen atoms. Sub-nanoporous monolayer graphene can separate cations and anions. D. Konatham et al. elucidated through molecular dynamics simulations that carboxyl functional groups can enhance the ion repulsion of nanopores. S. Zhao et al. confirmed through theoretical simulations that the negative charge at the edge of graphene sub-nanopores significantly hinders the separation of cations and anions through electrostatic interactions. - Promotes K through transmembrane transport + The via, and its radius is The nanopores still exhibit excellent ion selectivity. However, this phenomenon was not observed in neutrally charged graphene nanopores. Simulation results show that sub-nanopore graphene with charged pore edges is expected to become an ideal membrane material for next-generation desalination and lithium extraction from salt lakes, effectively improving the efficiency of existing processes.
[0008] Regarding experimental research on functionalized nanoporous graphene, current experimental data is relatively scarce, and in-depth exploration of ion transport mechanisms is urgently needed. Researchers have introduced nanopores and functional groups into graphene using techniques such as electro-pulse, plasma bombardment, and heavy ion bombardment coupled with chemical solution etching. However, due to limitations in reaction conditions, various functional groups (carbonyl, carboxyl, epoxy, and hydroxyl, etc.) have been grafted onto the graphene film, and the types of functional groups are limited (mostly oxygen-containing functional groups). The controllability of the type, amount, and location of grafted functional groups is poor. The ion selectivity of nanoporous graphene separation membranes obtained by the above methods needs improvement, especially the separation effect between monovalent metal ions and monovalent anions and cations, which has not been reported in detail. Although single-pore graphene separation membranes have good K... + / Cl - While offering selective separation, the process is complex due to limitations in instruments and technology, and it is suitable for small sample sizes, resulting in high costs and hindering scale-up and practical application. Existing literature does not provide data on the ion separation performance of porous separation membranes. Therefore, obtaining a functionalized nanoporous graphene membrane for efficient mixed ion separation is urgently needed. Summary of the Invention
[0009] The purpose of this invention is to provide a high-performance functionalized nanoporous graphene membrane for mixed ion separation that is easy to operate, suitable for large-area sample preparation, and has a pore size distribution mainly at the nanometer level, and a method for preparing the same, so as to solve at least one of the technical problems existing in the background art.
[0010] To achieve the above objectives, the present invention adopts the following technical solution:
[0011] This invention provides a functionalized nanoporous graphene membrane for mixed ion separation and its preparation method, comprising:
[0012] Functionalized nanoporous graphene membranes were prepared in one step using CVD technology.
[0013] Using graphene on a metal substrate as raw material, it is transferred to a non-metallic substrate;
[0014] Vacancy defects are introduced into graphene on a non-metallic substrate using plasma etching.
[0015] Two-step plasma etching protected by a Faraday cage selectively expands vacancy defects into nanopores of a specified size.
[0016] Based on the structural characteristics and differentiated requirements of nanoporous graphene, specific functional groups are chemically modified onto the nanopores of graphene. By modifying the reaction type and reaction conditions, the physical confinement and chemical binding of specific ions by the functionalized nanopores are achieved, thus preparing nanoporous graphene films.
[0017] Optionally, the one-step preparation of functionalized nanoporous graphene using CVD technology uses one or more of ammonia, pyrrole, pyridine, or melamine as a nitrogen source, one or more of boron trichloride, boric acid, or borane as a boron source, and thiourea and / or sulfur powder as a sulfur source; the metal in the graphene raw material on the metal substrate is copper, nickel, platinum, or a copper-nickel alloy; the non-metal in the non-metal substrate is a silicon wafer, silicon dioxide, polycarbonate track etching film, polytetrafluoroethylene, or polyethersulfone polymer film.
[0018] Optionally, vacancy defects can be introduced into graphene on a non-metallic substrate using a plasma method; wherein the plasma type is hydrogen plasma, helium plasma, argon plasma, or nitrogen plasma, etc.
[0019] Optionally, in the plasma method, the gas pressure is 10-300 Pa, the ignition power is 0-100 W, and the time is 0-300 s.
[0020] Optionally, two-step plasma etching protected by a Faraday cage can selectively expand vacancy defects into nanopores of a specified size. The plasma gas used can be oxygen, hydrogen, ozone, chlorine, water vapor, carbon tetrafluoride, or sulfur hexafluoride, etc.
[0021] Optionally, two-step plasma etching with Faraday cage protection is used, with a gas pressure of 10–200 Pa, an ignition power of 1–50 W, and a processing time of 10–180 s.
[0022] Optionally, the pore shape, pore density, and pore size distribution of nanoporous graphene can be adjusted by synergistically controlling the gas pressure, power, and etching time in the two-step plasma etching process.
[0023] Optionally, symmetrical and asymmetric modification processes of nanoporous graphene membranes can be achieved through a self-built reaction vessel.
[0024] Optionally, by modifying different types of functional groups, the type and amount of charge on the surface of nanoporous graphene membranes can be precisely controlled.
[0025] Optionally, a phenyl-containing solution is chemically modified with graphene having nanopores of a specified size, and non-covalent bonds of molecules containing specific functional groups are modified onto the graphene through π-π interactions to obtain functionalized nanoporous graphene.
[0026] Optionally, a polymer solution containing amine, carboxyl, or hydroxyl groups is spin-coated onto graphene with nanopores of a specified size. Molecules containing specific functional groups are then composited onto the graphene through π-π interactions and electrostatic interactions to obtain functionalized nanoporous graphene. Alternatively, a solution containing a halogen reagent is chemically reacted with graphene with nanopores of a specified size, and specific functional groups are covalently grafted onto the nanopores to obtain halogenated nanoporous graphene. By controlling the halogenation reaction temperature, reaction time, and reactant concentration, the grafting rate and amount of functional groups grafted onto the nanoporous graphene can be adjusted, while maintaining the structural stability of the nanoporous graphene.
[0027] or;
[0028] A solution containing an aryl diazonium salt was chemically reacted with graphene containing nanopores of a specified size, resulting in the covalent grafting of specific functional groups into the nanopores, thus yielding diazonium-modified nanoporous graphene. The grafting rate and amount of functional groups in the nanoporous graphene were adjusted by controlling the reaction temperature, reaction time, and reactant concentration, while simultaneously maintaining the structural stability of the nanoporous graphene.
[0029] Optionally, a solution containing aryl carboxylates or aromatic amines is electrochemically reacted with graphene having nanopores of a specified size, thereby covalently grafting specific functional groups onto the nanopores to obtain carboxyl or amine-modified nanoporous graphene. By controlling the reaction time and reactant concentration, the grafting rate and the amount of functional groups grafted into the nanoporous graphene can be adjusted, while maintaining the structural stability of the nanoporous graphene.
[0030] Optionally, a solution containing halide ions and / or halide complex ions is subjected to a photochemical halogenation reaction with graphene having nanopores of a specified size to obtain halogen-modified nanoporous graphene. By controlling the light intensity, reaction time, and reactant concentration, the grafting rate and functional group grafting amount of the nanoporous graphene can be adjusted, while maintaining the structural stability of the nanoporous graphene.
[0031] Optionally, a photocatalyst can be used to catalyze the redox reaction of molecules such as oxygen, generating active oxygen-containing free radicals which are then grafted onto nanopores of graphene of a specified size to achieve photocatalytic oxidation modification, resulting in nanoporous graphene modified with oxygen-containing functional groups. By controlling the reaction time and reactant concentration, the grafting rate and the amount of functional groups grafted into the nanoporous graphene can be adjusted, while maintaining the structural stability of the nanoporous graphene.
[0032] or;
[0033] Photocatalytic oxidation modification of nanoporous graphene is achieved by photo-initiated reaction between nanoporous graphene of a specified size and benzoyl peroxide. By controlling the light intensity, reaction time, and reactant concentration, the grafting rate and functional group grafting amount of nanoporous graphene can be adjusted, while maintaining the structural stability of the nanoporous graphene.
[0034] or;
[0035] In the process of CVD growth of graphene, heteroatoms such as nitrogen, sulfur, and boron are introduced into the gas source to achieve the preparation of heteroatom-doped functionalized nanoporous graphene in one step.
[0036] The beneficial effects of this invention are as follows: A non-covalent modification method is used to rapidly and efficiently prepare various functionalized nanoporous graphenes while maintaining the stability of the nanopores, resulting in a separation membrane with high mechanical strength. A heteroatom doping method is employed to precisely control the graphene growth process, enabling one-step preparation of functionalized nanoporous graphenes and avoiding the introduction of secondary defects and surface contaminants. A covalent grafting method is used, offering high grafting efficiency, controllable grafting functional group types and grafting sites, and a wide range of grafting reaction selection. Simultaneously, reaction conditions can be precisely controlled to avoid significant damage to the nanoporous graphene, making it suitable for the preparation of nano-scale functionalized nanoporous graphenes with narrow pore sizes. By separating the pore-forming process from the chemical modification process, specific functional groups can be directionally introduced onto the nanoporous graphene according to differentiated needs. This functionalized nanoporous graphene not only overcomes the challenge of simultaneously achieving ion selectivity and flux in traditional separation membranes but also exhibits strong scalability and excellent stability. The prepared functionalized nanoporous graphene separation membrane demonstrates high separation efficiency for mixed ions.
[0037] The advantages of additional aspects of the invention will be set forth more clearly in the following description or will be learned by practice of the invention. Attached Figure Description
[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0039] Figure 1 This is a flowchart illustrating the preparation and performance testing of the separation membrane according to an embodiment of the present invention.
[0040] Figure 2 This is a flowchart illustrating the preparation method of functionalized nanoporous graphene according to an embodiment of the present invention.
[0041] Figure 3 This is a schematic diagram of the XPS characterization results of the functionalized nanoporous graphene described in an embodiment of the present invention.
[0042] Among them, (a) is the XPS full spectrum of nanoporous graphene modified with functional groups; (b) is the XPS C1s spectrum of nanoporous graphene modified with fluorine functional groups.
[0043] Figure 4 This image shows the ion separation performance of the functionalized nanoporous graphene described in this invention and a comparison with reported results in the literature. Specifically, (a) shows the IV curves of the functionalized nanoporous graphene separation membrane in KCl and LiCl electrolyte solutions with concentration gradients of 10; (b) shows the KCl and LiCl electrolyte solutions prepared using conventional methods and the functionalized nanoporous graphene separation membrane prepared in this invention. + / Li + Separation performance comparison; (c) IV curve of the functionalized nanoporous graphene separation membrane in HCl electrolyte solution with a concentration gradient of 10; (d) H2O curve of the separation membrane prepared by conventional method and the functionalized nanoporous graphene separation membrane prepared in the embodiments of the present invention. + / Cl - Comparison of separation performance.
[0044] Figure 5 This is a structural diagram of the reaction vessel used to prepare asymmetric functionalized nanoporous graphene membranes according to an embodiment of the present invention. Detailed Implementation
[0045] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.
[0046] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0047] It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as here.
[0048] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.
[0049] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.
[0050] To facilitate understanding of the present invention, the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.
[0051] Those skilled in the art should understand that the accompanying drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily essential for implementing the present invention.
[0052] This embodiment provides a preparation scheme for functionalized nanoporous graphene membranes applied to mixed ion separation, which synergistically regulates pore structure and surface chemical properties to improve mixed ion separation performance. Specifically, it includes a one-step preparation of heteroatom-doped functionalized nanoporous graphene, the introduction of decoupled nanopores, and the chemical modification of the graphene nanopores.
[0053] First, heteroatom-doped functionalized nanoporous graphene was prepared by a one-step CVD method.
[0054] Secondly, by employing two independent etching techniques, high-density, narrow-distribution nanopores were introduced into two-dimensional materials such as graphene. The formation of nanopores on graphene consists of two stages: nanopore formation and nanopore expansion. Using this controllable method, nanopores with controllable density and pore size were obtained. Based on obtaining high-density nanoporous graphene with extremely narrow pore size distribution, non-covalent and covalent functionalization (composite structure, halogenation, oxidation, hydrogenation, amination, etc.) of nanoporous graphene was completed using solution chemical reactions, electrocatalysis, photocatalysis, and plasma modification. This resulted in the preparation of functionalized graphene nanopores with both symmetrical and asymmetrical structures, and the surface charge of the functionalized nanoporous graphene was tunable. Based on the separation membrane obtained by the above method, efficient separation of mixed ions was successfully achieved. The separation membrane exhibits both high selectivity and high throughput, overcoming the challenge of the incompatibility between separation selectivity and permeability in traditional separation membranes. Furthermore, the separation membrane has good cycling stability and is expected to be applied in fields such as seawater desalination, lithium extraction from salt lakes, and salinity gradient energy conversion.
[0055] 1. Transfer of graphene on a metal substrate
[0056] Graphene is used as a raw material on a metal substrate, including copper, nickel, platinum, copper-nickel alloys, etc.; it is then transferred to other substrates, including silicon wafers, silicon dioxide, PCTE (polycarbonate track etching film), PTFE (polytetrafluoroethylene), PES (polyethersulfone), etc.
[0057] 2. Introducing nanopores into graphene
[0058] First, vacancy defects are introduced into graphene using plasma etching methods (hydrogen plasma, helium plasma, argon plasma, nitrogen plasma, etc., with pressures ranging from 10 to 300 Pa, ignition power from 0 to 100 W, and processing times from 0 to 300 s). Second, a two-step plasma etching process protected by a Faraday cage selectively expands these high-density vacancy defects into nanopores of a specified size. The plasma gases used are hydrogen, ozone, chlorine, water vapor, carbon tetrafluoride, and sulfur hexafluoride, with pressures around 10 to 200 Pa, ignition power from 1 to 50 W, and processing times from 10 to 180 s. The density, pore shape, and pore size of the nanopores on the graphene are adjusted by synergistically controlling the gas pressure, etching time, and etching intensity during the two-step plasma etching process.
[0059] 3. Preparation of functionalized nanoporous graphene
[0060] Based on π-π interactions and electrostatic interactions, and according to the structural characteristics and differentiated requirements of nanoporous graphene, specific molecules or polymers are non-covalently modified onto graphene through liquid-phase composite or spin-coating methods. By using various characterization techniques to modulate the type of molecules or polymers and reaction conditions, the physical confinement and chemical binding of specific ions by functionalized nanopores can be achieved, thereby improving separation performance and preparing novel ion "one-way valves".
[0061] π-π action: Functionalization reaction of phenyl-containing solutions (aniline, aminopyrene, p-phenylenediamine, etc.) (25-50℃);
[0062] Electrostatic effect: Spin coating of solutions containing polymers such as polyethyleneimine, polyacrylonitrile, and polyvinyl alcohol (500-4000 rpm / 25℃);
[0063] Based on methods such as solution chemistry, electrocatalysis, photochemistry, and plasma modification, and according to the structural characteristics and differentiated requirements of nanoporous graphene, specific functional groups are covalently grafted onto graphene nanopores. By using various characterization methods to modulate the covalent reaction type and reaction conditions, the functionalized nanopores can achieve physical confinement and chemical binding of specific ions, thereby improving separation performance and preparing novel ion "one-way valves".
[0064] like Figure 5 As shown, in this embodiment, the symmetrical and asymmetric modification process of nanoporous graphene membranes is achieved through a self-built reaction vessel. By modifying different types of functional groups, the type and amount of charge on the surface of the nanoporous graphene membrane can be precisely controlled. The reaction vessel consists of two cylinders, open at the top and sealable during the reaction, with their central axes connected to facilitate chemical reactions. For asymmetric modification, the chemically modified sample is transferred to a substrate with a central circular hole (materials include quartz, glass, polytetrafluoroethylene, silicon nitride, silicon, etc., with the appropriate substrate selected according to the reaction type). Based on the chemical reaction principle, different types of chemical reagents are added to the two cylinders respectively. Under certain temperature, pressure, and stirring conditions, the asymmetric functionalized nanoporous graphene membrane is prepared.
[0065] Halogenated nanoporous graphene: chemical reaction in solutions containing halogen reagents (HCl, HBr, HF, and AgF, etc.) (25–100℃);
[0066] Plasma-modified nanoporous graphene: Plasma modification with gases such as XF2, F2, Cl2, and N2 (gas pressure 10–300 Pa, ignition power 0–20 W, time 0–300 s);
[0067] Diazonium salt modified nanoporous graphene: solution chemical reaction of aryl diazonium salt (25-50℃);
[0068] Electrocatalytic modification of nanoporous graphene: electrochemical reaction of solution containing aryl carboxylates or aromatic amines (5–25 °C);
[0069] Photohalogenation-modified nanoporous graphene: Photohalogenation-modified nanoporous graphene refers to nanoporous graphene modified with halide ions and / or halide-containing complex ions. A solution containing halide ions and / or halide-containing complex ions (one or more of fluoride, chloride, bromide, and iodide ions) is used. The reaction system is illuminated, with a xenon lamp (200–1100 nm) as the light source. For example, halogen gases generate free radicals under photoexcitation, which attack the nanoporous graphene and add to the pore edges. The addition of halogen free radicals to nanoporous graphene hardly destroys the graphene structure.
[0070] Photo-oxidative modification of nanoporous graphene: One approach utilizes photocatalysts such as TiO2 to catalyze redox reactions of oxygen molecules, generating active oxygen-containing free radicals that attack the nanoporous graphene, thus achieving photocatalytic oxidation modification. Another approach involves photo-initiated reactions between nanoporous graphene and benzoyl peroxide, achieving photocatalytic oxidation modification of the nanoporous graphene.
[0071] A one-step CVD growth method for preparing heteroatom-doped functionalized nanoporous graphene: Graphene on a metal substrate is used as the raw material. The metals include copper, nickel, platinum, copper-nickel alloys, etc. Nitrogen, boron and other atoms are similar in size to carbon atoms and are easy to dopant. During the graphite growth process, gases or reagents containing nitrogen, boron and sulfur are introduced into / injected into the reactor. Experimental conditions such as temperature, heating program and pressure are controlled to adjust the nanopore density, pore size and heteroatom doping amount on the graphene.
[0072] Ion transport performance tests show that this type of separation membrane can achieve unidirectional transport of mixed ions and exhibits a negative differential resistance effect, providing experimental support for the development of ion circuits. Furthermore, further ion separation performance tests indicate that the functionalized nanoporous graphene separation membrane prepared using this method performs better than separation membranes prepared using traditional methods, achieving higher ion permeability at K0. + / Li + K + / Cl - and H + / Cl - The selectivity was 48.6, 76, and 59.3, respectively; the separation performance of the KCl and LiCl mixed salt was 264.1; and the separation performance of the LiCl and MgCl2 mixed salt was 23. Meanwhile, the separation membrane exhibited good cycling stability and acid and alkali resistance.
[0073] In summary, this invention provides a method for preparing a functionalized nanoporous graphene separation membrane with synergistic regulation of pore structure and surface chemical properties. This method can be used to prepare mixed-ion separation membranes exhibiting high selectivity, high flux, and good stability. Traditional preparation techniques cannot controllably and directionally introduce specific functional groups onto nanoporous graphene. This method, through a one-step CVD process to prepare heteroatom-doped nanoporous graphene or by decoupling the pore-forming process from the chemical modification process, achieves controllable functionalization of nanoporous graphene. Based on differentiated requirements and the structural characteristics of nanoporous graphene, the preparation of functionalized nanoporous graphene separation membranes can be directionally achieved, with highly tunable properties such as the type, number, composite or grafting position, spatial configuration, charge, and polarity of the modifying molecules or functional groups. The functionalized nanoporous graphene separation membrane exhibits high mixed-ion selectivity, ion flux, and excellent cycling stability and acid / alkali resistance.
[0074] A non-covalent modification method was employed to rapidly and efficiently prepare various functionalized nanoporous graphenes while maintaining the stability of the nanopores, resulting in separation membranes with high mechanical strength. A heteroatom doping method was used to precisely control the graphene growth process, enabling one-step preparation of functionalized nanoporous graphenes and avoiding the introduction of secondary defects and surface contaminants. A covalent grafting method was employed, offering high grafting efficiency, controllable grafted functional group types, and a wide range of grafting reactions. Simultaneously, precise control of reaction conditions prevented significant damage to the nanoporous graphene, making it suitable for preparing nano-scale functionalized nanoporous graphenes with narrow pore sizes. By separating the pore-forming process from the chemical modification process, specific functional groups were directionally introduced onto the nanoporous graphene according to differentiated needs. This functionalized nanoporous graphene not only overcomes the challenge of simultaneously achieving ion selectivity and flux in traditional separation membranes but also exhibits strong scalability and excellent stability. Ion transport performance tests showed that the nanoporous graphene separation membrane prepared using this method has high separation efficiency for mixed ions, with some results significantly exceeding the performance of separation membranes prepared by traditional methods reported in the literature. This method utilizes heteroatom doping or plasma etching to couple non-covalent or covalent functionalization. The related equipment is simple to operate and highly scalable, making it suitable for processing large-area samples and thus having broad application prospects.
[0075] This invention provides a one-step heteroatom doping and plasma etching method to introduce high-quality nanopores coupled with non-covalent modification or covalent grafting strategies to prepare functionalized nanoporous graphene separation membranes for mixed ion separation. There are no special requirements for the graphene. CVD-grown monolayer graphene is preferred, but multilayer graphene or other two-dimensional materials can also be used. There are no limitations on the plasma etching equipment. For the first step of introducing defects, in addition to plasma, wet etching (acidic potassium permanganate solution, hydrogen peroxide solution, sulfuric acid solution, etc.), vapor phase etching (oxygen, hydrogen, carbon dioxide, water vapor, etc.), and ultraviolet ozone oxidation can also be used. For the second step of functionalization, in addition to covalent modification and covalent grafting, self-assembly and doping methods can also be used. In terms of applications, besides mixed ion separation, functionalized nanoporous graphene membranes can also be applied to concentration power generation, ion enrichment, gas separation, ion or gas detection, and many other fields.
[0076] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that, based on the technical solutions disclosed in the present invention, various modifications or variations that can be made by those skilled in the art without creative effort should be included within the scope of protection of the present invention.
Claims
1. A method for preparing functionalized nanoporous graphene membranes for mixed ion separation, characterized in that, include: Graphene is grown on a metal substrate using a CVD method; nitrogen, sulfur, or boron heteroatoms are introduced into the gas source during the graphene growth process. Transferring graphene from a metal substrate to a non-metallic substrate; Vacancy defects were introduced into graphene on a non-metallic substrate using a plasma method. Two-step plasma etching protected by a Faraday cage selectively expands vacancy defects into nanopores of a specified size. Symmetric and asymmetric modification processes of nanoporous graphene membranes were achieved through a self-built reaction vessel. The self-built reaction vessel consisted of two cylinders with open tops that could be sealed during the reaction, and their central axes were connected to facilitate chemical reactions. For asymmetric modification, the chemically modified sample was transferred to a substrate with a central hole. Based on the principles of chemical reactions, different types of chemical reagents were added to the two cylinders respectively. Under certain temperature, pressure, and stirring conditions, asymmetric functionalized nanoporous graphene membranes were prepared. The modification process includes: chemically modifying graphene with nanopores of a specified size using a phenyl-containing solution, and non-covalently modifying the graphene with functional group molecules through π-π interactions to obtain a functionalized nanoporous graphene film; or spin-coating a polymer solution containing amine, carboxyl, or hydroxyl groups onto graphene with nanopores of a specified size, and composite the functional group molecules onto the graphene through π-π interactions or electrostatic interactions to obtain a functionalized nanoporous graphene film; or chemically reacting a solution containing a halogen reagent with graphene with nanopores of a specified size, and covalently grafting the functional groups onto the nanopores to obtain a halogen-modified nanoporous graphene film; or chemically reacting a solution containing an aryl diazonium salt with graphene with nanopores of a specified size, and covalently grafting the functional groups onto the nanopores to obtain a diazonium salt-modified nanoporous graphene film.
2. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 1, characterized in that, The metal on the metal substrate is copper, nickel, platinum, or a copper-nickel alloy; the non-metal in the non-metal substrate is a silicon wafer, silicon dioxide, polycarbonate track etching film, polytetrafluoroethylene, or polyethersulfone.
3. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 1, characterized in that, The method involves introducing vacancy defects into graphene on a non-metallic substrate using a plasma method. The plasma can be hydrogen plasma, helium plasma, argon plasma, or nitrogen plasma.
4. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 3, characterized in that, In the plasma method, the gas pressure is 10~300 Pa, the ignition power is 0~100 W, and the time is 0~300 s.
5. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 4, characterized in that, The two-step plasma etching protected by the Faraday cage selectively expands vacancy defects into nanopores of a specified size. The plasma gas used is oxygen, hydrogen, ozone, chlorine, water vapor, carbon tetrafluoride, or sulfur hexafluoride.
6. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 5, characterized in that, Two-step plasma etching protected by a Faraday cage is performed at a pressure of 10–200 Pa, an ignition power of 1–50 W, and a processing time of 10–180 s.
7. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 1, characterized in that, The modification process also includes: electrochemically reacting a solution containing aryl carboxylates or aromatic amines with graphene having nanopores of a specified size, and covalently grafting functional groups into the nanopores to obtain a nanoporous graphene film modified with carboxyl or amine groups.
8. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 1, characterized in that, The chemical reaction of a solution containing a halogen reagent with graphene having nanopores of a specified size includes: photochemical halogenation of a solution containing halogen ions and / or halogen complex ions with graphene having nanopores of a specified size to obtain a halogen-modified nanoporous graphene film.
9. The method for preparing functionalized nanoporous graphene membranes for mixed ion separation according to claim 1, characterized in that, The modification process also includes: using a photocatalyst to catalyze the oxidation-reduction reaction of oxygen molecules, generating active oxygen-containing free radicals which are grafted onto the nanopores of graphene of a specified size to achieve photocatalytic oxidation modification and obtain nanoporous graphene films modified with oxygen-containing functional groups. or; Photocatalytic oxidation modification of nanoporous graphene is achieved by photo-initiated reaction between nanoporous graphene of a specified size and benzoyl peroxide.