Method for predicting mass transfer efficiency of two-dimensional separation membrane by dielectric spectroscopy

Abstract

The application discloses a method for predicting the limited mass transfer efficiency of a two-dimensional separation membrane by using dielectric spectrum, comprising the following steps: S1, respectively measuring the dielectric spectrum of water in the two-dimensional separation membrane and a reference membrane in the range of 10 ‑3 ~ 10 3 Hz, calculating the dielectric relaxation time after obtaining the dielectric relaxation frequency; S2, judging the limited mass transfer efficiency of water in the two-dimensional separation membrane according to the dielectric relaxation time ratio τ / τ0 of the dielectric relaxation time τ of water in the two-dimensional separation membrane and the dielectric relaxation time τ0 of the reference membrane; when the τ / τ0 is less than 1, it is judged that the limited mass transfer efficiency of water in the two-dimensional separation membrane is higher than that of the reference membrane; when the τ / τ0 is greater than 1, it is judged that the limited mass transfer efficiency of water in the two-dimensional separation membrane is lower than that of the reference membrane. The method can accurately predict the limited mass transfer efficiency of different types of two-dimensional separation membranes, effectively reflect the state and relative transmission rate of water in the interlayer of the two-dimensional separation membrane, and provide technical support for the research on the high-efficiency separation two-dimensional membrane.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and more specifically, relates to a method for predicting the confined mass transfer efficiency of a two-dimensional separation membrane using dielectric spectroscopy. Background Technology

[0002] Membrane separation technology, as a highly efficient, energy-saving, and environmentally friendly technology, has attracted increasing attention in fields such as gas purification, seawater desalination, biomass production, and wastewater treatment. Separation techniques utilizing polymer, inorganic, or composite membranes, based on differences in molecular size or dissolution-diffusion processes, can achieve selective permeation of molecules. However, membrane design and separation efficiency are hampered by adhesion or polymer chain movement within porous structures, as well as the trade-off effect between permeability and selectivity. Recent studies have shown that separation membranes based on two-dimensional materials maintain excellent selectivity while exhibiting high permeation rates, closely related to exceptionally high water transport characteristics and highly smooth sub-nanometer channels. Numerous studies have reported on graphene oxide-based membranes that utilize pervaporation for efficient dehydration, successfully achieving the effective separation of alcohol-water mixtures in biomass products. Furthermore, researchers have used metal-organic framework (MOF) nanosheet membranes with honeycomb structures and aluminum-free zeolite membranes based on stabilized zirconia for ethanol recovery. Researchers synthesized a (SiO2) / (silicalite-1) / (SiO2) sandwich membrane using space-constrained technology and achieved the separation of n-butanol / water through pervaporation. In existing techniques, researchers have introduced cellulose nanofibers into covalent organic framework (COF) membranes to improve membrane stability and achieve efficient butanol dehydration. Therefore, utilizing two-dimensional layered materials, based on the aforementioned advantages, holds promise for breaking trade-off limitations in biomass dehydration applications and demonstrates great potential as a highly efficient separation membrane.

[0003] Existing technologies report that some two-dimensional membranes can achieve better mass transfer efficiency after cationic or anionic modification (crosslinking). However, the mass transfer efficiency of two-dimensional membranes is affected by many factors such as interlayer spacing, intercalation ion radius, valence state, and temperature. Before actually separating the analytes using two-dimensional membranes, it is impossible to accurately predict or characterize whether the mass transfer efficiency of the modified two-dimensional membrane will be improved. This requires researchers to spend a lot of time and effort screening conditions before confirming whether the modified two-dimensional membrane has improved mass transfer efficiency. These conditions include the type of modified ions in the membrane, the interaction between permeating molecules and channels, interfacial interactions (conjugation and hydrophilicity / hydrophobicity), mass transfer structure, and temperature. Even after screening for optimal conditions, if the mass transfer efficiency of the modified membrane does not show a substantial improvement compared to the unmodified membrane, all the aforementioned screening work becomes ineffective, wasting the time, effort, and economic costs invested by researchers in this project.

[0004] To reduce the waste of time, effort, and economic costs, researchers explored methods for predicting the mass transfer efficiency of two-dimensional (2D) membranes. Unlike traditional polymer or nanoporous membranes, the size sieving effect and the abundance of hydrophilic groups in 2D membranes are insufficient to achieve efficient separation of alcohol-water mixtures. Therefore, the mass transfer efficiency of 2D membranes cannot be simply predicted by measuring the film XRD or contact angle. However, subsequent studies have shown that the behavior and physical properties of confined water in 2D membranes, such as strong hydrogen bond networks and the potential formation of monolayers, affect the rapid permeation of water while simultaneously blocking the permeation of alcohol. This indicates that the mass transfer efficiency of 2D membrane separation (especially alcohol-water separation) is related to the state of confined water in the 2D membrane. However, confined water includes both capillary water and water adsorbed on the surface; only the state of capillary water is related to the mass transfer efficiency of 2D membrane separation. Current research on the mass transfer efficiency of confined water separated from two-dimensional membranes only characterizes the confined water (capillary water and water adsorbed on the surface) from the perspective of its mass. For example, a quartz crystal microbalance (QCM) is first used to measure the adsorption curve of the confined water, and then the mass of the capillary water is determined by different ranges of the slope of the adsorption curve, thereby establishing an indirect relationship between the mass of the capillary water and the permeation rate of the two-dimensional membrane. However, the determination of the slope in this method is somewhat subjective and does not reflect the viscosity and other states of the capillary water in the two-dimensional membrane, resulting in limitations in the predicted mass transfer efficiency.

[0005] Therefore, there is an urgent need in this field for an effective technique to characterize the state of confined water in membranes, which can accurately and objectively determine the mass transfer efficiency of two-dimensional membranes for water, saving research time and costs. Summary of the Invention

[0006] 1. The problem to be solved

[0007] To address the inaccuracies and subjectivity inherent in existing methods for predicting the confinement mass transfer efficiency of two-dimensional separation membranes, this invention provides a method for predicting the confinement mass transfer efficiency of two-dimensional separation membranes using dielectric spectroscopy. This method can accurately and objectively predict the confinement mass transfer efficiency of the same or different types of two-dimensional separation membranes, effectively reflecting the state and relative transport rate of water between the membrane layers, thus providing technical support for research on efficient two-dimensional separation membranes.

[0008] 2. Technical Solution

[0009] The technical solution adopted in this invention is as follows:

[0010] The first aspect of this invention provides a method for predicting the confinement mass transfer efficiency of a two-dimensional separation membrane using dielectric spectroscopy.

[0011] The confined mass transfer efficiency includes the permeation rate;

[0012] The methods include:

[0013] S1 measures the dielectric spectra of specific components in the two-dimensional separation membrane and the reference membrane, respectively, and calculates the dielectric relaxation frequency and then the dielectric relaxation time. The dielectric relaxation frequency is obtained by fitting the dielectric spectrum curve with the Havriliak-Negami equation. The Havriliak-Negami equation is as follows:

[0014]

[0015] Where ε' and ε” represent the real and imaginary parts of the dielectric constant, respectively; ε ∞ It is the value of ε' at infinitely high frequencies, where Δε represents the relaxation strength, i.e., the value of ε' at zero frequency and infinitely high frequencies (ε ∞ The difference between ); τ is the characteristic dielectric relaxation time, ω represents the angular frequency; parameters α and β are used to describe the skewness and broadening of the dielectric function, and their values ​​range from 0 to 1; j represents different Havriliak-Negami terms in multiple relaxation processes;

[0016] S2 determines the confined mass transfer efficiency of the specific component in the two-dimensional separation membrane based on the ratio of the dielectric relaxation time τ of the specific component in the two-dimensional separation membrane to the dielectric relaxation time τ0 of the reference membrane (this ratio can also be called the relative relaxation time) τ / τ0:

[0017] When τ / τ0 is less than 1, it is determined that the confinement mass transfer efficiency of the two-dimensional separation membrane for this specific component is higher than that of the reference membrane.

[0018] When τ / τ0 is greater than 1, it is determined that the confinement mass transfer efficiency of the two-dimensional separation membrane for this specific component is lower than that of the reference membrane.

[0019] The two-dimensional separation membrane and the reference membrane are non-conductive two-dimensional separation membranes.

[0020] According to the Debye model, the dielectric relaxation time τ in a confined space can be expressed as:

[0021]

[0022] Where k and T are the Boltzmann constant and temperature, respectively; a R The radius of the dipole molecular cluster is represented by η; η is used to describe the viscosity of the fluid (e.g., amino, organic solvents, and ionic liquids). Therefore, τ represents the increased viscosity. Furthermore, increased local viscosity generally leads to a slower rate of molecular permeation, consistent with predictions from the Hagen-Poiseuille equation. Therefore, studying dielectric relaxation processes allows for the assessment of the viscosity of confined fluids and its impact on molecular transport.

[0023] Unlike the relaxation process of bulk water in the 6-80 GHz range, the low-frequency region (e.g., 10 GHz) exhibits different relaxation processes.-3 ~10 3 The characteristic dielectric peak (Hz) can be used to characterize confined water in 2D nanocapillaries without the need for additional removal of surface liquid effects, as is required by other techniques such as electrochemical quartz crystal microbalance (EQCM), infrared spectroscopy, neutron scattering, positron annihilation, and nuclear magnetic resonance (NMR).

[0024] Theoretically, the method of this invention is applicable to the prediction of confined mass transfer efficiency of water or other non-aqueous solvents with dielectric peaks observable on dielectric spectra in two-dimensional separation membranes. However, due to the limitation of the instrument frequency range, this invention only performs dielectric spectrum experiments to predict the confined mass transfer efficiency of water in two-dimensional separation membranes, and verifies the accuracy of the prediction through actual measurements. However, the principle is also applicable to the prediction of confined mass transfer efficiency of other non-aqueous solvents with dielectric peaks observable on dielectric spectra in two-dimensional separation membranes.

[0025] A second aspect of the present invention provides a method for predicting the confinement mass transfer efficiency of a two-dimensional separation membrane using dielectric spectroscopy.

[0026] The confined mass transfer efficiency includes the permeation rate;

[0027] The methods include:

[0028] S1 measured water levels at 10°C on both the two-dimensional separation membrane and the reference membrane. -3 ~10 3 After obtaining the dielectric relaxation frequency from the dielectric spectrum in the Hz range, the dielectric relaxation time is calculated. The dielectric relaxation frequency is obtained by fitting the dielectric spectrum curve with the Havriliak-Negami equation. The Havriliak-Negami equation is as follows:

[0029]

[0030] Where ε' and ε” represent the real and imaginary parts of the dielectric constant, respectively; ε ∞ It is the value of ε' at infinitely high frequencies, where Δε represents the relaxation strength, i.e., the value of ε' at zero frequency and infinitely high frequencies (ε ∞ The difference between ); τ is the characteristic dielectric relaxation time, ω represents the angular frequency; parameters α and β are used to describe the skewness and broadening of the dielectric function, and their values ​​range from 0 to 1; j represents different Havriliak-Negami terms in multiple relaxation processes;

[0031] The water here refers to pure water or water in an aqueous system;

[0032] S2 determines the confined mass transfer efficiency of water in the two-dimensional separation membrane based on the ratio of the dielectric relaxation time τ of water in the two-dimensional separation membrane to the dielectric relaxation time τ0 of the reference membrane (this ratio can also be called the relative relaxation time) τ / τ0:

[0033] When τ / τ0 is less than 1, it is determined that the confined mass transfer efficiency of the two-dimensional separation membrane for water is higher than that of the reference membrane.

[0034] When τ / τ0 is greater than 1, it is determined that the confined mass transfer efficiency of the two-dimensional separation membrane for water is lower than that of the reference membrane.

[0035] The two-dimensional separation membrane and the reference membrane are non-conductive two-dimensional separation membranes.

[0036] In this invention, the permeation rate refers to the ability of a membrane to allow fluid to pass through a unit area of ​​the membrane per unit time without damaging its dielectric structure.

[0037] In this invention, dielectric relaxation is measured using a dielectric spectrometer. Dielectric relaxation represents the process by which microscopic particles in a system, polarized by an external electric field (i.e., a non-thermal equilibrium state), return to thermal equilibrium after the external electric field is removed. The greater the degree of confinement of water between the two-dimensional material layers, the higher the viscosity of the confined water and the longer the dielectric relaxation time. Under the same conditions, a shorter dielectric relaxation time of water in a two-dimensional separation membrane indicates a lower viscosity and a less confined state of the water, thus resulting in a faster water permeation rate. Conversely, a longer dielectric relaxation time of water in a two-dimensional separation membrane indicates a higher viscosity and a greater degree of confinement of the water, thus resulting in a slower water permeation rate.

[0038] The Eyring model (Equation 3) can be used to understand the thermodynamic properties of confined water in two-dimensional interlayers:

[0039]

[0040] Where h and k B ΔS and ΔH represent Planck's constant and Boltzmann's constant, respectively; ΔS and ΔH represent the entropy change and enthalpy change during polarization, respectively. In a confined space, a higher ΔH indicates that more hydrogen bonds need to be broken during relaxation to form larger molecular clusters, while a lower ΔS indicates that the molecular clusters become more ordered under the influence of an external field.

[0041] As a preferred embodiment of the second aspect of the present invention, when τ / τ0 equals 1, it is determined that the confined mass transfer efficiency of the two-dimensional separation membrane for water is basically the same as that of the reference membrane.

[0042] As a preferred embodiment of any technical solution in the second aspect of the present invention, the two-dimensional separation membrane comprises a two-dimensional membrane of the same or different type as the reference membrane. For example, the two-dimensional separation membrane may be a vermiculite two-dimensional membrane and the reference membrane may be a graphene oxide two-dimensional membrane, or the two-dimensional separation membrane may be a graphene oxide two-dimensional membrane and the reference membrane may be a vermiculite two-dimensional membrane.

[0043] As a preferred embodiment of any technical solution in the second aspect of the present invention, the two-dimensional separation membrane comprises a membrane obtained by cationic modification or anionic modification based on a reference membrane. These are two-dimensional membranes of the same type; for example, for materials with negative surface charges, cationic modification can be used, and the modifying cation can be a metal ion, ammonium ion, quaternary ammonium salt, etc.; for materials with positive surface charges, anionic modification can be used, and the modifying anion can be oxalic acid, carbonic acid, etc.

[0044] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane or the two-dimensional separation membrane is independently selected from graphene oxide two-dimensional membrane or cation-modified graphene oxide two-dimensional membrane.

[0045] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane is a two-dimensional graphene oxide membrane, and the two-dimensional separation membrane is a cation-modified two-dimensional graphene oxide membrane; the surface of the two-dimensional graphene oxide membrane is negatively charged, and it is generally modified with cations.

[0046] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane is a mica two-dimensional membrane, and the two-dimensional separation membrane is a cation-modified mica two-dimensional membrane; or the reference membrane is a cation-modified mica two-dimensional membrane, and the two-dimensional separation membrane is a mica two-dimensional membrane; the surface of the mica two-dimensional membrane is negatively charged, and it is generally modified with cations.

[0047] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane is a COF two-dimensional membrane, and the two-dimensional separation membrane is a cation-modified COF two-dimensional membrane or anion-modified COF two-dimensional membrane; or the reference membrane is a cation-modified COF two-dimensional membrane or anion-modified COF two-dimensional membrane, and the two-dimensional separation membrane is a COF two-dimensional membrane; the surface charge of the COF two-dimensional membrane is determined by the functional groups. When the surface functional groups are negatively charged, cation modification is generally used; when the surface functional groups are positively charged, anion modification is generally used.

[0048] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane is a MOF two-dimensional membrane, and the two-dimensional separation membrane is a cation-modified MOF two-dimensional membrane or anion-modified MOF two-dimensional membrane; or the reference membrane is a cation-modified MOF two-dimensional membrane or anion-modified MOF two-dimensional membrane, and the two-dimensional separation membrane is a MOF two-dimensional membrane. The surface charge of the MOF two-dimensional membrane is determined by the functional groups. When the surface functional groups are negatively charged, cation modification is generally used; when the surface functional groups are positively charged, anion modification is generally used.

[0049] As a preferred embodiment of any technical solution in the second aspect of the present invention, when the reference membrane is a two-dimensional graphene oxide membrane and the two-dimensional separation membrane is a cation-modified two-dimensional graphene oxide membrane, the cation-modified two-dimensional graphene oxide membrane comprises Al 3+Modified graphene oxide two-dimensional film, Mn 2+ Modified graphene oxide two-dimensional film, La 3+ Modified graphene oxide two-dimensional film or Ba 2+ One or more of the modified graphene oxide two-dimensional films.

[0050] As a preferred embodiment of any technical solution in the second aspect of the present invention, the reference membrane or the two-dimensional separation membrane is independently selected from graphene oxide two-dimensional membrane and vermiculite two-dimensional membrane. For example, the reference membrane can be a graphene oxide two-dimensional membrane, and the two-dimensional separation membrane can be a vermiculite two-dimensional membrane, or vice versa.

[0051] As a preferred embodiment of any technical solution in the second aspect of the present invention, the water is pure water or water in an aqueous system. When it is pure water, the confined mass transfer efficiency is mainly reflected in the permeation rate of water in the two-dimensional membrane. When it is water in an aqueous system, it means that the system also contains other solvents besides water, and the confined mass transfer efficiency is mainly reflected in the permeation rate of water in the two-dimensional membrane and the selectivity of the two-dimensional membrane for water. For example, in an embodiment of the present invention, the selectivity is obtained by first measuring the permeation rate of the substance in a unit system, i.e., 100% water or 100% alcohol; then the ratio of the water permeation rate to the alcohol permeation rate is considered as the selectivity. The selectivity can also be obtained by directly using a water and alcohol mixture for dielectric spectroscopy testing.

[0052] As a preferred embodiment of any technical solution in the second aspect of the present invention, the aqueous system is an alcohol-water system. An alcohol-water system refers to any system in which alcohols and water are miscible in any proportion, such as ethanol / water, propanol / water, isopropanol / water, isobutanol / water, or n-butanol / water, where water exists in a proportion ranging from 0.1% to 99.9%. For example, the proportion of water can be 10%, 20%, 30%, 50%, or 80%.

[0053] As a preferred embodiment of any technical solution in the second aspect of the present invention, the applicable temperature is 0 to 35°C.

[0054] 3. Beneficial effects

[0055] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0056] (1) This invention is the first to discover the correlation between the state of water in the two-dimensional separation membrane and the relative transport rate (permeation rate) and dielectric relaxation. The method of this invention measures dielectric relaxation by dielectric spectroscopy, and accurately predicts whether the confinement mass transfer efficiency of the same type of two-dimensional separation membrane, such as modified two-dimensional separation membrane, is improved compared with unmodified two-dimensional separation membrane by the change of dielectric relaxation (relative dielectric relaxation time). It also verifies the difference in the confinement mass transfer efficiency of different types of two-dimensional separation membranes, such as graphene oxide two-dimensional membrane and vermiculite two-dimensional membrane, for water, providing technical support for the research of efficient two-dimensional separation membranes. Compared with traditional methods for characterizing two-dimensional membranes to predict mass transfer efficiency, such as contact angle and XRD, the dielectric spectroscopy method of this invention is simpler, more efficient, more accurate and objective in reflecting the mass transfer efficiency of water in two-dimensional separation membranes.

[0057] (2) Taking graphene oxide two-dimensional membrane, vermiculite two-dimensional membrane, etc. as examples, the present invention uses dielectric spectroscopy to predict the confined mass transfer efficiency of water in two-dimensional membrane and conducts experimental verification. The verification results show that the dielectric spectroscopy prediction is consistent with the experimental results. Attached Figure Description

[0058] Figure 1 (a,b) Top and side SEM images of a self-supporting graphene oxide (GO) two-dimensional film; (c,d) Top and side SEM images of a vermiculite two-dimensional film.

[0059] Figure 2 (a,c) AFM images of knocking mode of GO and vermiculite nanosheets deposited on Si wafer substrates; (b,d) corresponding height profiles of GO and vermiculite nanosheets.

[0060] Figure 3 XPS spectra of (a) GO two-dimensional films, (b) GO-Al films, (d) GO-Mn films, (f) GO-La films, and (h) GO-Ba films. (c) XPS Al 2p peak of GO-Al film; (e) XPS Mn 2p peak of GO-Mn film; (g) XPS La 3d peak of GO-La film; (i) XPS Ba 3d peak of GO-Ba film.

[0061] Figure 4 (a) Top view of the dielectric testing apparatus; (b) Side view of the dielectric testing apparatus.

[0062] Figure 5 Dielectric study of two-dimensional graphene oxide (GO) films:

[0063] (a) Schematic diagram of dielectric spectrum measurement of a gold electrode / two-dimensional film / gold electrode sandwich structure device.

[0064] (b) Imaginary part ε” of dielectric constant of GO two-dimensional film at 25°C with different humidity. The curve is fitted by the Havriliak-Negami equation (Equation 2), and the shaded peaks are attributed to confined water.

[0065] (c) The imaginary part ε" of the dielectric constant of the GO two-dimensional film in an ethanol environment at 25 °C.

[0066] (d) The changes in relaxation time τ (left y-axis: red dot plot) and water content (right y-axis: blue bar plot) of GO two-dimensional film at 25°C under different relative humidities (RH), ranging from 40% to 90%.

[0067] Figure 6 (a) Variation of the imaginary part ε" of the dielectric constant of the GO two-dimensional film at different temperatures under 90% relative humidity. The curves are fitted by the Havriliak-Negami formula, and the peaks filled by shades are attributed to confined water molecules.

[0068] (b) The dependence of the dielectric relaxation time τ (obtained experimentally) of the original GO film on temperature, fitted by the Eyring model, within the temperature range (10℃ to 30℃). The red line represents the fitted line of the Eyring model.

[0069] Figure 7 Dielectric relaxation and mass transfer behavior of ionically crosslinked (modified) graphene oxide two-dimensional films. (a) At different humidity levels at 25℃, Al 3+ The imaginary part ε" of the dielectric constant of the cross-linked GO two-dimensional film varies with frequency.

[0070] (b) La at different humidity levels at 25°C 3+ The imaginary part ε" of the dielectric constant of the cross-linked GO two-dimensional film varies with frequency.

[0071] (c) At different humidity levels at 25°C, Mn 2+ The imaginary part ε" of the dielectric constant of the cross-linked GO two-dimensional film varies with frequency.

[0072] (d) Ba at different humidity levels at 25℃ 2+ The imaginary part ε" of the dielectric constant of the cross-linked GO two-dimensional film varies with frequency.

[0073] The curve was fitted by the Havriliak-Negami formula, and the peak filled with shaded areas was attributed to restricted water.

[0074] Figure 8 :(a)Al 3+ Mn 2+ La 3+ Ba 2+The imaginary part ε" of the dielectric constant of the crosslinked GO two-dimensional film at 90% RH and 25℃ varies with frequency. The above-mentioned ion-modified crosslinked two-dimensional films (GO-X) are named GO-Al / Mn / La / Ba, respectively. (b) The ratio of the relaxation time of GO-Al and GO-La films to the dielectric relaxation time of GO two-dimensional films at different relative humidities.

[0075] (c) Relationship between water permeation (left y-axis) and the ratio of water to isopropanol permeation rates (right y-axis) of the ion-crosslinked two-dimensional membrane at 90% RH and 25°C, and the corresponding relaxation time τ (upper x-axis). The red curves are visual aids. Left y-axis: dot plot; right y-axis: blue bar chart.

[0076] Figure 9 Contact angle characterization method for predicting water permeation rate in two-dimensional membranes: (a) Contact angle photographs of GO two-dimensional membranes with different ion crosslinking. (b) Contact angle trends (left y-axis) and pure water permeation rate (right y-axis) of GO two-dimensional membranes with different ion crosslinking. Figure 10 XRD characterization for predicting water permeation rates in two-dimensional membranes: (a) XRD patterns of GO two-dimensional membranes with different ion crosslinking at 25 °C and 100% RH. (b) Interlayer spacing trends (left y-axis) and experimentally verified pure water permeation rates (right y-axis) of GO two-dimensional membranes with different ion crosslinking.

[0077] Figure 11 (a) Imaginary part ε" of dielectric constant of GO 2D membrane (GO) and vermiculite 2D membrane (V) at 90% RH and 25°C. The curves are fitted using the Havriliak-Negami formula, and the peaks filled with shade represent confined water. (b) Bar chart of water to isopropanol permeation rates (left y-axis) and the ratio of water to isopropanol permeation rates (★, right y-axis) of GO 2D membrane and vermiculite 2D membrane. Detailed Implementation

[0078] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0079] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0080] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0081] Experimental Section

[0082] Materials: Expanded vermiculite was purchased from Shijiazhuang Chenxing Industrial Co., Ltd. Freeze-dried graphene oxide (GO) nanosheets with a size greater than 500 nm were purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. (XFNANO). Chemical reagents such as sodium chloride (NaCl), lithium chloride (LiCl), aluminum trichloride hexahydrate (AlCl3·6H2O), manganese chloride tetrahydrate (MnCl2·4H2O), lanthanum chloride (LaCl3), and barium chloride dihydrate (BaCl2·2H2O) were purchased from Tianjin Xiens Opd Technology Co., Ltd. In all synthesis and analysis in the examples, deionized water purified using an (18.2 MΩ) Millipore Milli-Q system was used.

[0083] The present invention will be further described below with reference to specific embodiments.

[0084] I. Graphene oxide film (GO film or GO two-dimensional film), Al 3+ Modified graphene oxide two-dimensional film (GO-Al film), Mn 2+ Modified graphene oxide two-dimensional film (GO-Mn film), La 3+ Modified graphene oxide two-dimensional film (GO-La film) or Ba 2+ Preparation of modified graphene oxide two-dimensional films (GO-Ba films)

[0085] Freeze-dried graphene oxide (GO) nanosheets were dispersed in ultrapure water and stirred overnight, followed by sonication for 15 min. The GO nanosheet dispersion was then centrifuged at low speed (3000 rpm / min, supernatant retained) to remove undispersed multilayer GO nanosheets. Next, centrifugation at high speed was performed to remove smaller nanosheets (8000 rpm / min, bottom colloid retained). After high-speed centrifugation, the colloid was dispersed in ultrapure water to obtain a monolayer GO nanosheet colloidal solution.

[0086] Single-layer GO nanosheets are assembled into two-dimensional nanosheet films (GO films) through vacuum filtration.

[0087] At room temperature, GO membranes were immersed in 1M solutions of AlCl3, MnCl2, LaCl3, and BaCl2 for 12 hours to prepare GO-Al, GO-Mn, GO-La, and GO-Ba membranes, respectively. After crosslinking, the membranes were rinsed with deionized water to remove residual ions from the membrane surface and then air-dried to obtain the GO-Al, GO-Mn, GO-La, and GO-Ba membranes.

[0088] II. Preparation of Vermiculite Film (Vermiculite Two-Dimensional Film)

[0089] Vermiculite was exfoliated into nanosheets via ion intercalation. First, 0.20 g of vermiculite was mixed with 200 mL of saturated NaCl solution and refluxed at 120 °C with magnetic stirring for 24 h to obtain intercalated NaCl nanosheets. + Vermiculite. After the reaction, the product was filtered through a polyethersulfone (PES) membrane and washed with plenty of deionized water to remove excess salt. Subsequently, Na... + The exchanged vermiculite was mixed with 200 mL of 2 M LiCl solution and refluxed at 120 °C with magnetic stirring for 24 h. The product was then filtered through the same washing process as before to obtain Li. + Exchanged vermiculite. After ion intercalation, Li... + The exchanged vermiculite was dispersed in ultrapure water and sonicated for 30 min to exfoliate it into monolayer nanosheets. The resulting colloidal solution was then centrifuged multiple times at 3000 rpm / min to remove unexfoliated vermiculite, followed by centrifugation at 10000 rpm / min to remove smaller nanosheets. Finally, the nanosheets were reassembled into a self-supporting membrane (vermiculite membrane or vermiculite two-dimensional membrane) by vacuum filtration.

[0090] III. Characterization

[0091] The surface morphology of the two-dimensional nanosheets and films, as well as the film thicknesses (GO film and vermiculite film), were observed using a Carl Zeiss Merlin high-resolution field emission scanning electron microscope (FE-SEM) at an operating voltage of 5.0 kV. Figure 1 ).

[0092] X-ray diffraction (XRD) data acquisition was performed using a Rigaku benchtop X-ray diffractometer equipped with a HyPix-400MF 2D hybrid pixel array detector (HPAD) and Cu Kα radiation (λ = 0.15405 nm), operating in Bragg-Brentano mode at 40 kV and 15 mA. Interlayer distances of the films were tested under different humidity conditions: saturated salt solutions were prepared by dissolving different amounts of salt in deionized water to obtain different relative humidities (RH): LiCl (12% RH), MgCl2 (33% RH), NaCl (75% RH), and KCl (84% RH). The films were placed above an XRD testing apparatus containing the different saturated salt solutions. Prior to measurement, the apparatus was placed in a sealed container containing the same saturated salt solution for 4 hours.

[0093] The thickness of the nanosheets was measured in vibration mode using atomic force microscopy (AFM) with a Dimension ICON-PT (Bruker). Figure 2 ).

[0094] X-ray photoelectron spectroscopy (XPS, Thermo Kalpha) was used to study the chemical composition of GO and GO films crosslinked with different ions (cationically modified GO films). Figure 3 ).

[0095] IV. Preparation of Dielectric Testing Device

[0096] To manufacture flexible dielectric testing devices (see schematic diagram for details) Figure 4 A PET / GO / PET sandwich structure was formed by encapsulating a two-dimensional film and two porous PET sheets with epoxy resin. Before gold sputtering, masking tape was used to cover the edges of the PET to avoid covering areas where gold was not needed. Then, gold was sputtered onto both sides of the device separately at 10 mA for 90 seconds using an ion sputtering instrument to fabricate metal electrodes. Copper foil with soldered copper wires was adhered to the edges of the PET holes and the two-dimensional film using carbon tape, and silver paste was applied at the junction to enhance conductivity. The other end of the copper wires was soldered to a copper sheet, which was then connected to a fixture for dielectric spectrum testing.

[0097] V. Dielectric relaxation spectrum test

[0098] All dielectric spectroscopy measurements in this invention were obtained using an MFIA impedance analyzer in Zurich, controlled by LabOne software. When an alternating electric field is applied to the two-dimensional film sample, water molecules polarize and cause dipole rotation, allowing the collection of impedance information with respect to frequency (Z* = Z' + jZ”), where Z' and Z” are the real and imaginary parts of the impedance obtained from electrochemical impedance spectroscopy (EIS), respectively. This information is then converted into the frequency dependence of the complex permittivity (ε*) using equations (1), (2), and (3).

[0099]

[0100]

[0101]

[0102] Where ε' (dielectric constant) and ε' (dielectric loss factor) are the real and imaginary parts of the dielectric constant, respectively; ω is the angular frequency (ω = 2πf), f is the frequency, C0 (ε0A / d) is the capacitance of the film, and ε0 is the vacuum dielectric constant (8.854 × 10⁻⁶). -14 F cm –1 ).

[0103] VI. Membrane water content test

[0104] Before measurement, the membrane sample was placed in a glove box overnight to remove water absorbed by the membrane outdoors, and then the weight (m³) of the membrane at 0% RH was measured using a quasi-micro balance. 0％ RH The membrane was then removed from the glove box for testing. The dried membrane was placed in a balance within a constant temperature and humidity chamber, initially set to 25°C and 30% RH. At this point, the real-time weight of the membrane was recorded using the Launch SPDC Data Collection V 2.03 software included with the microbalance. This condition was maintained for 4 hours to ensure membrane stability. When the membrane weight hardly changed over time, the weight of the membrane at this point was recorded as (m). 30％ RH Under these conditions, the humidity in the constant temperature and humidity chamber was then increased by a 10% RH gradient while maintaining a constant temperature for 4 hours. The formula for moisture content at x% RH is:

[0105] (m x％RH -m 0％ RH ) / m 0％ RH ×100% Formula 4.

[0106] VII. Permeability Test of Water / Isopropanol System

[0107] The sample membrane was encapsulated in a test apparatus filled with either alcohol or water. To measure the membrane's water permeation rate, the apparatus was placed in a test chamber equipped with a quasi-micro balance, with test conditions of 25°C and 30% relative humidity. However, for alcohol permeation rate testing, since the membrane may absorb moisture from the air, the permeation test apparatus needed to be placed in a quasi-micro balance inside a glove box. The weight change of the permeation apparatus over time, i.e., the weight loss curve, was recorded using the software integrated with the quasi-micro balance.

[0108] 8. Dielectric relaxation of GO film under different relative humidity and temperature

[0109] (1) Dielectric relaxation of two-dimensional films (taking GO film as an example) under different relative humidity

[0110] First, see the schematic diagram of the dielectric testing device. Figure 4 Double-sided gold-sprayed GO films (the GO films prepared in Part 1) were prepared according to the method in Part 4 for dielectric spectroscopy testing. Figure 5 a) To obtain τ, the complex permittivity ε(ω) can be described using the semi-empirical Havriliak-Negami equation, which incorporates several dipole dynamic parameters:

[0111]

[0112] Where ε' and ε” represent the real and imaginary parts of the dielectric constant, respectively; ε ∞ It is the value of ε' at infinitely high frequencies, where Δε represents the relaxation strength, i.e., the value of ε' at zero frequency and infinitely high frequencies (ε ∞ The difference between ) ; τ is the characteristic dielectric relaxation time, ω represents the angular frequency; parameters α and β are used to describe the skewness and broadening of the dielectric function, and their values ​​range from 0 to 1; j represents different Havriliak-Negami terms in multiple relaxation processes.

[0113] Based on Equation 2, the dielectric spectrum of the imaginary part ε" of the dielectric constant of GO films placed in environments with different relative humidityes (30%RH, 50%RH, 70%RH, 90%RH) at 25℃ is fitted, as follows: Figure 5 As shown in b, the Havriliak-Negami peak was observed at 10. -3 Up to 10 3 In the Hz range. In contrast, when the GO film is exposed to anhydrous ethanol vapor, the dielectric peak disappears ( Figure 5 c). The above results indicate that from 10 -3 Up to 10 3The dielectric relaxation process in the Hz range is attributed to confined water in a two-dimensional membrane (2D nanocapillary).

[0114] The dielectric relaxation time of GO films was studied under different relative humidities (RH) at a temperature of 25℃. The dielectric relaxation time decreased exponentially with a linear increase in RH from 40% to 90%. Figure 5 d) At this point, the water content inside the membrane increases from 10.3% to 63.9%.

[0115] (2) Dielectric relaxation of two-dimensional films (taking GO film as an example) at different temperatures

[0116] In addition, we also tested the dielectric relaxation of the GO film at different temperatures (10 to 35 °C). Figure 6 The results showed that, under the same conditions, the higher the temperature, the shorter the dielectric relaxation time of water in the GO membrane. This is because the higher the temperature, the more intense the molecular thermal motion and the stronger the molecular dipole rotation.

[0117] IX. Relationship between dielectric relaxation and water permeability of cationic cross-linked GO membranes

[0118] Based on the above findings, dielectric spectroscopy can reveal the internal molecular state during mass transport in modified GO membranes. Ionic crosslinking, as a common modification method, can improve membrane selectivity and stability and has been widely applied in gas separation, seawater desalination, and nanofiltration. However, apart from adjusting channel size, the effects of charged ions on confined water are rarely reported. In this section, we use different cations (Al... 3+ Mn 2+ La 3+ Ba 2+ Taking a cross-linked GO two-dimensional membrane (preparation method is described in Part 1) as an example, the applicability of dielectric spectroscopy in predicting water permeation rate in two-dimensional separation membranes is demonstrated.

[0119] Figure 7 Showing Al 3+ Ba 2+ La 3+ Mn 2+ The imaginary part ε" of the dielectric constant of the crosslinked GO film varies with frequency at 25℃ and different humidity levels (30%RH, 50%RH, 70%RH, 90%RH). The figure shows that the dielectric relaxation peaks of the four cationic crosslinked films are all located at 10. -3 Hz to 10 3 Within the Hz range, as humidity increases, the dielectric relaxation peaks of the four cationic crosslinked films shift to higher frequencies, which is consistent with the original GO film ( Figure 5b) Similarly. However, at the same humidity (90%) and temperature (25°C), the dielectric relaxation peak frequencies of GO films with different cationic crosslinks showed significant differences (Table 1).

[0120] Table 1. Relative permittivity relaxation time τ / τ0 of confined water in cationic modified graphene oxide films at RH 90%.

[0121] GO membrane GO-Al membrane GO-Mn membrane GO-La membrane GO-Ba membrane Dielectric relaxation frequency (Hz) 54.50 128.00 14.90 10.28 0.48 Dielectric relaxation time τ(s) <![CDATA[0.0029(τ0)]]> 0.00124 0.01068 0.01548 0.3316 <![CDATA[Relative dielectric relaxation time τ / τ0]]> 1 0.4287 3.6832 5.3386 114.3354

[0122] For example, such as Figure 7 a. At 90% RH, the dielectric relaxation peak of the GO-Al film is located at 128 Hz, which is higher than the dielectric relaxation frequency of the original GO film (54.5 Hz). Figure 6 (a)). In contrast, another trivalent cation, La 3+ The dielectric relaxation peak of the crosslinked GO film is located at a lower frequency compared to the original GO film. The dielectric relaxation time of the original GO film is τ0 under different humidity conditions, while the relaxation times τ0 of the GO-La and GO-Al films show opposite trends relative to the original GO film under all humidity conditions. Figure 7 (a and 7b). The relative relaxation time of the GO-Al membrane (i.e., the ratio of the dielectric relaxation time τ of the two-dimensional separation membrane to the dielectric relaxation time τ0 of the reference membrane) τ / τ0 is less than 1, indicating that the state of the confined water is more "relaxed" compared to the original GO membrane, while the slower relaxation process of the GO-La membrane (τ / τ0 is greater than 1) indicates that the confined water molecules are more "confined". Figure 7 c and 7d are respectively in the divalent cation Ba 2+ and Mn 2+ The frequency dependence of the imaginary part of the dielectric relaxation peak of the cross-linked GO film under different humidity conditions. Figure 8 It can be seen that the dielectric relaxation processes of the two (GO-Ba and GO-Mn) at 90% RH are extremely different. The dielectric peak frequency of the GO-Mn film (14.9 Hz) is much higher than that of the GO-Ba film (0.48 Hz). This indicates that at 90% RH, the water in the GO-Ba film is more confined and has a higher viscosity. Therefore, we speculate that the GO-Mn film has a higher water permeation rate than the GO-Ba film.

[0123] Based on the aforementioned relative permittivity relaxation time τ / τ0, the predicted order of the permeation rate of confined water in the cation-modified graphene oxide membrane is GO-Al > GO-Mn > GO-La > GO-Ba.

[0124] 10. Measured water permeability of cationic cross-linked GO membrane

[0125] According to the water permeability of the GO membranes crosslinked by cations with measured water / isopropanol in Part VII and the original GO membranes (prepared in Part I), the test conditions are as follows: the temperature is 25 °C and the relative humidity is 30%. The water permeation rates measured in the experiment show the following trend: GO-Al > GO-Mn > GO-La > GO-Ba( Figure 8 c).

[0126] The selectivity is obtained as follows: First, measure the permeation rates of substances in the unit systems of 100% water or 100% isopropanol respectively; then regard the ratio of the water permeation rate to the isopropanol permeation rate as the selectivity. The results show that the relationship between the ratio of the isopropanol and water permeation rates and the corresponding relative relaxation time τ / τ0 also conforms to the predicted trend.

[0127] XI. Prediction of the water permeability of cation-crosslinked GO membranes using contact angle and XRD

[0128] In the prior art, other characterization methods are used to explain the selective transport of 2D layered materials, such as contact angle measurement and XRD characterization. To compare the prediction accuracy, we also used other characterization methods to explore the water mass transfer efficiency of cation-crosslinked GO membranes( Figure 9 and Figure 10 ).

[0129] (1) Contact angle

[0130] Contact angle measurement is a commonly used method for characterizing surface properties and can be used to evaluate the wettability on the membrane surface, thereby predicting the interaction between water and the interlayer transport channels. As Figure 9 a, in the cation-crosslinked GO membranes, the increasing order of the contact angle is: GO-Al < GO-Mn < GO-Ba < GO-La, indicating that the interlayer hydrophilicity weakens compared with the original GO membrane (contact angle of 43°). According to previous studies, enhanced surface hydrophilicity will lead to increased water permeation. However, the water permeation predicted by contact angle measurement does not match the experimental results( Figure 9 b).

[0131] Contact angle measurement, as a surface chemistry characterization method, its test results are usually affected by surface roughness in addition to being affected by the inherent properties of substances. Different preparation methods, such as vacuum-assisted filtration, gas-liquid self-assembly, spin coating or blade coating, will result in membranes with different surface properties (such as surface energy, roughness, surface charge), thus causing misunderstandings about interlayer transport.

[0132] (2) XRD

[0133] In-situ XRD is also a method used in the prior art to evaluate the channel size effect. Therefore, this invention measured the XRD pattern of a cationicly crosslinked GO film at 100% relative humidity and discussed the effect of interlayer channel size on interlayer mass transfer. Figure 10 The results show that the changes in interlayer space are inconsistent with the changes in water permeability.

[0134] In contrast, the state of confined water within 2D nanocapillaries was directly monitored using the dielectric relaxation method, providing a reliable approach to promote the rational design of separation membranes based on 2D materials.

[0135] 12. Predicting the water permeability of vermiculite two-dimensional membranes using the dielectric relaxation method.

[0136] This dielectric study is also applicable to evaluating other 2D material-based films. For example, the dielectric relaxation peak of water in a vermiculite film (prepared according to the method in Part II) is located at a lower frequency (τ / τ0 > 1) than in a GO film (prepared according to the method in Part I), exhibiting a slower dielectric relaxation process. Figure 11 a) This leads to a decrease in water permeation rate and a reduction in the separation factor (selectivity) (as verified by experiments). Figure 11 b).

[0137] This invention investigates the dielectric properties of an alcohol-water separation membrane based on graphene oxide (GO). By analyzing the dielectric relaxation process, the additional viscosity caused by confinement in the low-frequency region of the dielectric spectrum can be assessed. The results show that cation intercalation (crosslinking) can modulate the viscosity of confined water, thereby increasing or decreasing the water permeation rate and thus regulating the selectivity of alcohol-water separation. Compared with evaluation methods such as XRD or contact angle measurement, the dielectric study of this invention more accurately and comprehensively reflects the mass transfer efficiency of water transport in two-dimensional membranes. Therefore, dielectric spectroscopy can promote the development of highly efficient two-dimensional separation membrane materials by providing deeper insights into the nanofluidics of 2D nanochannels.

[0138] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. A method for predicting the confined mass transfer efficiency of a two-dimensional separation membrane using dielectric spectroscopy, characterized in that, The applicable temperature range is 0~35℃; The confined mass transfer efficiency includes the permeation rate; The methods include: S1 measured water levels at 10°C on both the two-dimensional separation membrane and the reference membrane. -3 ~10 3 After obtaining the dielectric relaxation frequency from the dielectric spectrum in the Hz range, the dielectric relaxation time is calculated. The dielectric relaxation frequency is obtained by fitting the dielectric spectrum curve with the Havriliak-Negami equation. The Havriliak-Negami equation is as follows: Where ε' and ε'' represent the real and imaginary parts of the dielectric constant, respectively; ε ∞ It is the value of ε' at infinitely high frequencies, where Δε represents the relaxation strength, i.e., the difference between ε' at zero frequency and infinitely high frequencies. ∞ The difference between them; τ It is the characteristic dielectric relaxation time. ω Represents angular frequency; parameters α and β Used to describe the skewness and broadening of the dielectric function, with values ​​ranging from 0 to 1; j Represents different Havriliak-Negami terms in multiple relaxation processes; S2 is based on the dielectric relaxation time of water in the two-dimensional separation membrane. τ The ratio of the dielectric relaxation time to the reference film dielectric relaxation time τ0 τ / τ 0. Determine the confined mass transfer efficiency of water in a two-dimensional separation membrane: when τ / τ When 0 is less than 1, it is determined that the confined mass transfer efficiency of the two-dimensional separation membrane for water is higher than that of the reference membrane. when τ / τ When 0 is greater than 1, it is determined that the confined mass transfer efficiency of the two-dimensional separation membrane for water is lower than that of the reference membrane. The two-dimensional separation membrane and the reference membrane are non-conductive two-dimensional separation membranes; The reference membrane is a two-dimensional graphene oxide membrane, and the two-dimensional separation membrane is a cation-modified two-dimensional graphene oxide membrane; or The reference membrane is a mica two-dimensional membrane, and the two-dimensional separation membrane is a cation-modified mica two-dimensional membrane; or The reference membrane is a COF two-dimensional membrane, and the two-dimensional separation membrane is a cation-modified COF two-dimensional membrane; or The reference membrane is a two-dimensional MOF membrane, and the two-dimensional separation membrane is a cation-modified two-dimensional MOF membrane; The water in the alcohol-water system is water.

2. The method for predicting the confined mass transfer efficiency of a two-dimensional separation membrane using dielectric spectroscopy according to claim 1, characterized in that, When the reference membrane is a two-dimensional graphene oxide membrane and the two-dimensional separation membrane is a cation-modified two-dimensional graphene oxide membrane, the cation-modified two-dimensional graphene oxide membrane includes Al. 3+ Modified graphene oxide two-dimensional film, Mn 2+ Modified graphene oxide two-dimensional film, La 3+ Modified graphene oxide two-dimensional film or Ba 2+ One or more of the modified graphene oxide two-dimensional films.

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