Method for judging size of confinement effect between two-dimensional film layers by adopting monomolecular fluorescence

Abstract

The invention discloses a method for judging the size of a confinement effect between two-dimensional film layers by adopting monomolecular fluorescence. A two-dimensional film is a vermiculite two-dimensional film; the method comprises the following steps: providing vermiculite dispersion liquid containing rhodamine 6G; preparing the vermiculite dispersion liquid containing rhodamine 6G into a film; detecting the normalized fluorescence intensity of rhodamine 6G in the membrane; the higher the normalized fluorescence intensity of the rhodamine 6G is, the smaller the interlayer confinement effect of the vermiculite two-dimensional film is; the lower the normalized fluorescence intensity of the rhodamine 6G is, the larger the interlayer confinement effect of the vermiculite two-dimensional film is. According to the method, the size of the confinement force of the confinement space is judged according to the normalized fluorescence intensity of the single-molecule fluorescence probe in the two-dimensional membrane, and the method has great significance in guiding the design of a separation membrane and understanding a separation mechanism.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and more specifically, relates to a method for judging the size of confinement effect between two-dimensional membrane layers by using single-molecule fluorescence. Background Art

[0002] With the increasing demand for environmental protection and energy, the importance of gas and ion separation technology in industrial production, environmental protection and energy utilization has become increasingly prominent. As an efficient and energy-saving separation method, separation membranes have been widely used in many fields such as gas separation, water treatment, and air purification. However, how to accurately evaluate the mass transfer behavior and confinement effect of gases in separation membranes remains an important scientific and technological problem.

[0003] Confinement within subnanometer capillaries enables various anomalous phenomena in ion transport, such as ballistic gas diffusion and frictionless ion and water permeation. In particular, the development of two-dimensional (2D) materials provides the opportunity to fabricate subnanometer capillaries whose width can be tuned by some means, which makes it possible to study the fundamental principles of confined mass transport. The interlayer confinement between 2D materials affects the selectivity and transport rate of molecules in these capillaries. Inspired by these findings, various membranes based on 2D materials have been designed to achieve gas or ion separations beyond the traditional trade-off between permeability and selectivity. However, the current understanding of interlayer confinement as one of the main influencing factors of 2D material selective membranes remains at the level of simulations or assumptions based on performance evaluation. Therefore, the development of a method to study interlayer confinement is urgently needed for the rational design and further optimization of selective membranes with 2D capillaries.

[0004] However, current state-of-the-art characterization techniques, including transmission electron microscopy, scanning probe microscopy, X-ray diffraction, and dielectric spectroscopy, can only provide indirect evidence to prove interlayer confinement, such as the size of capillaries or the filling of percolating media. Some pioneering studies have used the fluorescence signal of reversibly protonated defects to visualize the ion diffusion pathways along the 2D BN surface. Taking advantage of the ability of spatial and temporal resolution, fluorescence microscopy is considered to be an effective technique to track the dynamic processes within capillaries. However, the visualization of interlayer confinement as an invisible interaction remains an unsurmounted challenge. Summary of the invention

[0005] 1. Problem to be solved

[0006] The purpose of the present invention is to provide a new visualization method based on spectral technology, especially fluorescence technology, for accurately evaluating the magnitude of the confinement effect on gas or liquid in a separation membrane.

[0007] On the basis of the above-mentioned purpose of the present invention, in order to solve the problem that the changes of the confinement effects between the layers of existing two-dimensional materials are difficult to directly visualize and monitor, the present invention provides a judgment method based on the rhodamine 6G (R6G) indicator, which uses spectral detection means and fluorescence microscopy and single-molecule fluorescence to directly judge the size of the confinement effects between the layers of two-dimensional materials.

[0008] On the basis of the above-mentioned purpose of the present invention, in order to solve the problem that the changes of interlayer confinement effects of existing two-dimensional materials under different humidity conditions are difficult to be monitored in situ visually, an in-situ visual monitoring method is provided to achieve visual observation of interlayer confinement effects.

[0009] 2. Technical solution

[0010] The present invention finds that the increase of interlayer constraint of the two-dimensional film will reduce the dihedral angle between xanthylium and benzyl in the R6G molecule, thereby causing the attenuation of the R6G fluorescence signal. Based on this, the present invention uses the normalized fluorescence intensity of R6G as a standard for judging the size of the interlayer constraint of the two-dimensional film, and judges the size of the interlayer constraint of the two-dimensional film under different conditions by fluorescence detection, and the above judgment method has been experimentally verified.

[0011] The present invention proposes to use R6G as a single-molecule fluorescent probe, monitor the confinement effect of R6G between two-dimensional membrane layers through single-molecule fluorescence emission spectroscopy and fluorescence microscopy, and realize visual monitoring of the change in the size of the confinement effect. This method provides new direction and technical support for the design and development of efficient gas and ion separation membranes.

[0012] [A method for determining the magnitude of confinement between two-dimensional membrane layers using single-molecule fluorescence]

[0013] The first aspect of the present invention provides a method for determining the size of the confinement effect between two-dimensional film layers using single-molecule fluorescence, comprising:

[0014] providing a dispersion of a two-dimensional material containing fluorescent molecules;

[0015] preparing a film from a two-dimensional material dispersion containing fluorescent molecules;

[0016] detecting the normalized fluorescence intensity of the fluorescent molecules in the membrane;

[0017] The higher the normalized fluorescence intensity of the fluorescent molecule, the smaller the confinement effect between the two-dimensional membrane layers;

[0018] The lower the normalized fluorescence intensity of the fluorescent molecule, the greater the confinement effect between the two-dimensional film layers;

[0019] The normalized fluorescence intensity is the ratio of the fluorescence intensity of the membrane to the ultraviolet absorption intensity.

[0020] According to different fluorescent molecules, the fluorescence intensity is the maximum fluorescence intensity at the optimal excitation wavelength, and the ultraviolet absorption intensity is the maximum ultraviolet absorption intensity.

[0021] The fluorescent molecules should meet the requirement of fluorescence change under the effect of two-dimensional interlayer confinement.

[0022] As a preferred embodiment of any one of the first aspects of the present invention, the two-dimensional membrane may be a two-dimensional gas separation membrane or a two-dimensional ion separation membrane.

[0023] [A method for determining the magnitude of interlayer confinement in vermiculite two-dimensional membranes using single-molecule fluorescence]

[0024] The second aspect of the present invention provides a method for determining the size of the confinement effect between two-dimensional membrane layers by using single-molecule fluorescence, wherein the two-dimensional membrane is a vermiculite two-dimensional membrane;

[0025] Providing a vermiculite dispersion containing rhodamine 6G;

[0026] The vermiculite dispersion containing rhodamine 6G is prepared into a film;

[0027] detecting the normalized fluorescence intensity of rhodamine 6G in the membrane;

[0028] The greater the normalized fluorescence intensity of the rhodamine 6G, the smaller the interlayer confinement effect of the vermiculite two-dimensional film;

[0029] The smaller the normalized fluorescence intensity of the rhodamine 6G, the greater the interlayer confinement effect of the vermiculite two-dimensional film;

[0030] The normalized fluorescence intensity is the ratio of the fluorescence intensity of the membrane to the ultraviolet absorption intensity.

[0031] The fluorescence intensity is the maximum fluorescence intensity of Rhodamine 6G at the optimal excitation wavelength, and the ultraviolet absorption intensity is the maximum ultraviolet absorption intensity of Rhodamine 6G.

[0032] Vermiculite (abbreviated as V) is a natural layered silicate mineral, a type of mica mineral. It has unique expansion properties and good thermal insulation, heat preservation, moisture absorption and adsorption capabilities. V nanosheets have uniform interlayer channels and show good application prospects in membrane separation. They are considered to be an ideal material for preparing high-performance gas separation membranes.

[0033] R6G is an organic fluorescent dye with high fluorescence quantum yield, good photostability and wide spectral characteristics. It shows characteristic absorption and emission changes under external stimuli. In the structure of the fluorescent probe R6G in solution, xanthylium and benzyl present a dihedral angle of 80.4°, which gives it a strong fluorescence emission intensity. However, there are different confinement forces between the layers of two-dimensional materials. When R6G is between the layers of two-dimensional materials in different confinement states, it will feel different constraints, resulting in changes in the dihedral angle between xanthylium and benzyl, which in turn leads to changes in the fluorescence emission intensity.

[0034] The present invention is based on this principle. By changing the fluorescence emission intensity of the fluorescent probe R6G between the two-dimensional vermiculite membrane layers, the change of the interlayer constraint in the two-dimensional capillary is explored, and the size of the confinement effect between the two-dimensional membrane layers is visually determined.

[0035] When the confined space between the two-dimensional material layers decreases, the molecules sandwiched between the two nanosheets tend to be flattened, resulting in a decrease in the dihedral angle and R6G fluorescence quenching. Conversely, when the confined space between the two-dimensional material layers increases, the molecules sandwiched between the two nanosheets tend to be the same as in the solution, resulting in an increase in the dihedral angle and enhanced R6G fluorescence.

[0036] As a preferred embodiment of any one of the second aspects of the present invention, the thickness of the vermiculite two-dimensional film is 1 to 10 μm.

[0037] Preferably, the thickness of the vermiculite two-dimensional film is 3-5 μm. A two-dimensional film with a thickness below 5 μm is nearly transparent, which is convenient for observing the change of fluorescence emission intensity.

[0038] As a preferred embodiment of any one of the second aspects of the present invention, the vermiculite two-dimensional membrane is a vermiculite two-dimensional membrane doped with cellulose nanofibers, and the vermiculite dispersion is a vermiculite dispersion containing cellulose nanofibers.

[0039] As a preferred embodiment of any embodiment of the second aspect of the present invention, the vermiculite two-dimensional membrane is Al 3+ The doped vermiculite two-dimensional membrane is prepared by preparing a membrane with the vermiculite dispersion containing rhodamine 6G and then placing the membrane in a medium containing Al 3+ obtained by soaking in the solution.

[0040] As a preferred embodiment of any embodiment of the second aspect of the present invention, the vermiculite two-dimensional membrane is cellulose nanofibers and Al 3+ The co-doped vermiculite two-dimensional membrane, wherein the vermiculite dispersion is a vermiculite dispersion containing cellulose nanofibers, and the membrane is prepared by the vermiculite dispersion containing rhodamine 6G and then the membrane is placed in a 3+ obtained by soaking in the solution.

[0041] As a preferred embodiment of any one of the second aspects of the present invention, in the vermiculite two-dimensional membrane, the mass percentage of cellulose nanofibers is 0.01 to 33% of the vermiculite.

[0042] As a preferred embodiment of any one of the second aspects of the present invention, the Al 3+ Al in solution 3+ The concentration is 10 -5 ~10 -1 mol / L.

[0043] As a preferred embodiment of any embodiment of the second aspect of the present invention,

[0044] In the vermiculite dispersion containing rhodamine 6G, the concentration of vermiculite is 0.05-10 mg / mL;

[0045] In the vermiculite dispersion containing rhodamine 6G, the concentration of rhodamine 6G is 10 -6 ~10 -5 mol / L.

[0046] As a preferred embodiment of any embodiment of the second aspect of the present invention, the normalized fluorescence intensity is the ratio of the fluorescence emission intensity with a fluorescence emission peak at 560 nm when the fluorescence excitation wavelength is 532 nm to the absorption peak intensity at 532 nm in the ultraviolet-visible spectrum.

[0047] [A method for determining the magnitude of confinement between two-dimensional membrane layers at different relative humidity using single-molecule fluorescence]

[0048] The third aspect of the present invention provides a method for determining the size of the confinement effect between two-dimensional membrane layers at different relative humidities by using single-molecule fluorescence, wherein the two-dimensional membrane is a vermiculite two-dimensional membrane;

[0049] Providing a vermiculite dispersion containing rhodamine 6G;

[0050] The vermiculite dispersion containing rhodamine 6G is prepared into a film;

[0051] detecting the normalized fluorescence intensity of rhodamine 6G in the film at different relative humidity;

[0052] The higher the normalized fluorescence intensity of Rhodamine 6G, the smaller the confinement effect between the two-dimensional membrane layers;

[0053] The lower the normalized fluorescence intensity of Rhodamine 6G, the greater the confinement effect between the two-dimensional membrane layers;

[0054] The normalized fluorescence intensity is the ratio of the fluorescence intensity of the membrane to the ultraviolet absorption intensity.

[0055] It is known in the prior art that the higher the relative humidity, the smaller the confinement effect between the two-dimensional membrane layers and the larger the interlayer spacing. This is consistent with the results of the present invention using the normalized fluorescence intensity of rhodamine 6G to determine the magnitude of the confinement effect between the two-dimensional membrane layers.

[0056] The enhancement and reduction of fluorescence emission can be determined by detecting the fluorescence emission spectrum or observing under a fluorescence microscope, and the normalized fluorescence intensity can be further calculated when necessary. Therefore, the method of the present invention makes it more intuitive to determine the magnitude of the confinement effect between two-dimensional membrane layers at different relative humidities.

[0057] As a preferred embodiment of any embodiment of the third aspect of the present invention, the relative humidity is 0 to 100% RH.

[0058] 3. Beneficial effects

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) In the present invention, it is proposed for the first time to use the normalized fluorescence intensity of a single-molecule fluorescent probe in a two-dimensional membrane to determine the size of the confined space constraint force; specifically, when the constraint force on the R6G fluorescent probe between the two-dimensional material layers increases, the dihedral angle between xanthylium and benzyl in the molecule decreases, and the fluorescence emission intensity increases; conversely, when the two-dimensional confined space increases, the constraint force between the layers decreases, the constraint force on the R6G fluorescent probe between the layers decreases, the dihedral angle between xanthylium and benzyl increases, and the fluorescence emission intensity increases. In this way, the change in the size of the confined space of the two-dimensional separation membrane under different external environmental conditions or under different doping conditions can be accurately determined, which is of great significance for guiding the design of separation membranes and the understanding of separation mechanisms.

[0061] (2) The present invention realizes the visualization of the size changes of the two-dimensional confined channels in the two-dimensional separation membrane through fluorescence microscopy technology.

[0062] (3) The present invention determines the enhancement and weakening of the fluorescence emission of R6G in the two-dimensional film under different relative humidities by detecting the fluorescence emission spectrum or observing under a fluorescence microscope, thereby obtaining the magnitude of the interlayer confinement effect of the two-dimensional film under different humidity conditions, and realizing in-situ real-time observation, making the determination of the magnitude of the interlayer confinement effect of the two-dimensional film under different relative humidities more intuitive. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 Schematic diagram of the mechanism of using R6G to monitor the confined state of a two-dimensional channel;

[0064] Figure 2 (a) cross section and (b) plane of V 2D membrane;

[0065] Figure 3 :

[0066] (a) Visible ultraviolet absorption spectrum and fluorescence emission spectrum of R6G solution (excitation wavelength 532 nm);

[0067] (b) Visible ultraviolet absorption spectrum and fluorescence emission spectrum of V-R6G dispersion (excitation wavelength 532 nm);

[0068] (c) Comparison of fluorescence intensity between R6G solution and V-R6G dispersion at different R6G concentrations;

[0069] (d) Fluorescence intensity ratio of different concentrations of R6G in the absence and presence of vermiculite two-dimensional membrane space confinement I R6G / I R6G / V (excitation wavelength 532nm);

[0070] Figure 4 :

[0071] (a) XRD comparison of V-R6G CNF two-dimensional separation membranes with different CNF addition amounts;

[0072] (b) Comparison of fluorescence emission spectra of V-R6G and V-R6G 2CNF;

[0073] (c) Normalized fluorescence intensity of V-R6G CNF 2D separation membranes with different CNF addition amounts;

[0074] (d) Fluorescence microscopy image of V-R6G 2D membrane;

[0075] (e) Fluorescence microscopy image of V-R6G 2CNF 2D film.

[0076] Figure 5 :

[0077] (a)Al 3+ Linear relationship between ion concentration and normalized fluorescence intensity of R6G;

[0078] (b) Different Al 3+ Ion concentration obtained by V-R6G CNF Al 3+ XRD pattern of 2D film;

[0079] Figure 6 :

[0080] (a) Schematic diagram of the experiment of using humidity to change the size of confined channels in two-dimensional separation membranes;

[0081] (b) Fluorescence microscopy observation of the fluorescence changes of V-R6G two-dimensional film under increasing relative humidity over time. DETAILED DESCRIPTION

[0082] 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 the invention belongs; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0083] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0084] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement or value. The degree of flexibility for a particular variable can be easily determined by one skilled in the art.

[0085] Concentration, amount and other numerical data can be presented in range format herein.It should be understood that such range format is only used for convenience and simplicity, and should be flexibly interpreted as not only including the numerical value clearly described as range limit, but also including all single numerical values ​​or sub-ranges contained in the range, just as each numerical value and sub-range are clearly described.For example, the numerical range of about 1 to about 4.5 should be interpreted as not only including the limit value of 1 to about 4.5 clearly described, but also including single numerals (such as 2,3,4) and sub-ranges (such as 1 to 3,2 to 4, etc.).The same principle is applicable to the scope of only narrating a numerical value, such as "less than about 4.5", which should be interpreted as including all the above-mentioned values ​​and ranges.In addition, no matter how the breadth of the described range or feature is, this explanation should be applicable.

[0086] 1. Materials

[0087] Multilayer vermiculite (V) clay was purchased from Chenxing Company, LiCl, NaCl, and R6G powders were purchased from Heowns, cellulose nanofibers (CNF) were purchased from Xianfeng Nano, and all chemicals were used directly without further purification.

[0088] 2. Preparation of separation membrane

[0089] Based on the principle of this technical solution, this technical solution uses fluorescence spectroscopy to monitor changes in the confined channels of the two-dimensional separation membrane, and is suitable for studying the confinement effect between nanosheet layers in two-dimensional material gas and ion separation membranes.

[0090] The specific two-dimensional material in the embodiment is vermiculite nanosheets (V nanosheets), and the preparation steps are as follows:

[0091] 1. Synthesis of V Nanosheets

[0092] First, V nanosheets were prepared using an ion embedding strategy. Specifically, 0.20 g of thermally expanded V clay was mixed with 200 mL of saturated NaCl intercalation and magnetically stirred at 120 °C for 24 h. After the reaction, the product was filtered using a polyethersulfone (PES) membrane and washed with a large amount of deionized water to remove excess NaCl. Subsequently, the inserted Na + The V was mixed with 200 mL of 2M LiCl solution and stirred under magnetic stirring at 120 °C for 24 h. After this reaction, the same washing process was used and the product was filtered again to remove excess LiCl to obtain Li + Intercalation V. During the ion intercalation process, the intercalation product was dispersed in ultrapure water and ultrasonically treated for 30 minutes to exfoliate it into a few layers of V nanosheets. The dispersion was then centrifuged at 3000 rpm for 30 minutes to remove the unexfoliated V clay at the bottom of the centrifuge tube, and this step was repeated 3 times. Next, the dispersion was centrifuged at 10000 rpm for 30 minutes to remove smaller nanosheets from the supernatant, and this step was also repeated three times. The colloidal suspension at the bottom of the centrifuge tube was resuspended in ultrapure water to obtain a solution containing a few layers of V nanosheets. In order to further determine the concentration of V nanosheets, 10 ml of the few layers of nanosheets obtained by centrifugation were vacuum filtered, and the two-dimensional membrane finally obtained was weighed to determine the concentration of V nanosheets to be 0.3 mg / ml.

[0093] 2. Assembly of V 2D membranes

[0094] The dispersion of the few-layer V nanosheets prepared in the previous step is assembled into a two-dimensional membrane by vacuum filtration.

[0095] 3. V-R6G dispersion, V-R6G two-dimensional membrane, V-R6G CNF two-dimensional membrane, V-R6G CNFAl for monitoring confinement 3+ Preparation of 2D membranes

[0096] Preparation of V-R6G dispersion: 1 ml of V nanosheet dispersion (0.3 mg / ml) and 1 ml of R6G solution (1×10 - 5 mol / L) and mix evenly, and finally add water to make the total volume of the solution 10ml;

[0097] Preparation of V-R6G two-dimensional film: 10 ml of V nanosheet dispersion (0.3 mg / ml) and 2 ml of R6G solution (1×10 - 5 mol / L) and mixed evenly, and water was added to make the total volume of the solution 20 ml, and finally the V-R6G two-dimensional membrane was obtained by suction filtration and then dried;

[0098] Preparation of V-R6G CNF two-dimensional membrane: CNF solution (0.5, 1, 2 ml, 0.5 mg / ml) was added to the V-R6G dispersion, and the mixture was stirred thoroughly to make it uniformly mixed. Finally, water was added to make the total volume of the solution 20 ml. Finally, the V-R6GCNF two-dimensional membrane was obtained by suction filtration and then dried.

[0099] V-R6G CNF Al 3+ Preparation of two-dimensional membrane: The V-R6G 1CNF two-dimensional membrane obtained by filtration was divided into five equal parts and then immersed in different concentrations of Al 3+ 12h in solution (Al 3+ The concentrations of the solutions were 0.00001, 0.001, 0.1, and 1 mol / L) and then dried.

[0100] 3. Characterization of V 2D Films

[0101] 1. Optical microscope image of V 2D film

[0102] like Figure 2 Shown are SEM images of the cross section and plane of the V two-dimensional membrane synthesized in Part 2 of [II. Preparation of separation membrane].

[0103] 4. Spectrum test

[0104] 1. Spectral principle

[0105] The principle of fluorescence spectroscopy is that when a substance absorbs light of a specific wavelength, electrons jump from the ground state to the excited state, then return to a lower excited state through a non-radiative relaxation process, and finally release energy in the form of longer wavelength photons when returning from the excited state to the ground state. This process is called fluorescence emission. Fluorescence spectroscopy provides detailed information about the optical properties and environment of a substance by measuring the fluorescence intensity at different wavelengths.

[0106] The principle of UV-visible spectroscopy is: when a substance absorbs light in the ultraviolet or visible light region, the electrons in its molecules transition from the ground state to the excited state, forming an absorption spectrum; by measuring the absorbance at different wavelengths, the characteristic absorption curve of the substance can be obtained, thereby identifying the type and concentration of the substance.

[0107] In this technical solution, R6G is used as an indicator, and V two-dimensional film is used as a confined channel. 3+ , humidity adjusts the size of the confined space, and uses a UV-visible photometer to detect the concentration of R6G molecules. After the R6G molecules are affected by the size of the confined space between the two-dimensional membrane layers, the molecular structure changes, and these changes are monitored by fluorescence spectroscopy and fluorescence microscopy. These changes in fluorescence efficiency can accurately show the changes in the confined space and confined effect between the two-dimensional material layers, thereby providing guidance for efficient ion and gas separation.

[0108] 2. Spectral measurement

[0109] First, put the V-R6G dispersion prepared in [II. Preparation of separation membrane] into a cuvette, and collect the fluorescence spectrum and UV spectrum signals. The measurement should be carried out in order of concentration from small to large to avoid the test error caused by the residue of high concentration solution. The excitation light source wavelength of the fluorescence emission spectrum is 532nm, and the measurement wavelength range of the UV-visible absorption spectrum is 200-700nm.

[0110] 5. Spectral test of R6G mixed with V at different concentrations in solution

[0111] like Figure 3 As shown in Figures 3a and 3b, the UV absorption peak of R6G is at 532nm, and the emission peak of the fluorescence spectrum is at 560nm. Figure 3 Comparison between a and 3b shows that at the same concentration, the emission peak of the fluorescence spectrum does not move after R6G enters the interlayer, but the intensity is greatly reduced. Figure 3 c is the fluorescence intensity attenuation of R6G solutions with different concentrations added to V solution. In order to maximize the response of the fluorescent molecules to the confinement effect, the R6G concentration was increased from 1×10 -6 Adjust to 1×10 -5 mol / L, the vermiculite concentration was controlled at 0.3 mg / ml, and the fluorescence attenuation (the ratio of the fluorescence intensity at 560 nm to R6G / I R6G+v ) was used to evaluate the sensitivity of the response to the confinement effect. As the concentration of R6G decreased, (I R6G / I R6G+v ) increases to 23.21( Figure 3 d), further decreasing the R6G concentration would cause the fluorescence signal to decrease below the detection limit in subsequent spectroscopy and microscopy studies, so the dye concentration was set to 10 - 6 mol / L to maximize the fluorescence response to confinement.

[0112] 6. Test of the spectrum of CNF-expanded V-R6G two-dimensional membrane confined space

[0113] like Figure 4a, wherein, V-R6G 0.5CNF represents the V-R6G CNF synthesized in Part 3 of [II. Preparation of separation membrane], with a CNF addition amount of 0.5 ml (the mass percentage of CNF to V is about 8.3%), V-R6G 1CNF represents the V-R6G CNF synthesized in Part 3 of [II. Preparation of separation membrane], with a CNF addition amount of 1 ml (the mass percentage of CNF to V is about 16.7%); V-R6G 2CNF represents the V-R6G CNF synthesized in Part 3 of [II. Preparation of separation membrane], with a CNF addition amount of 2 ml (the mass percentage of CNF to V is about 33%); XRD test was performed on the V-R6G CNF two-dimensional membrane obtained in Part [II. Preparation of separation membrane], and the results showed that with the increase of CNF content, the XRD spectrum peak of the 002 crystal plane of V shifted toward the small angle direction, and the peak width also slightly widened. In order to verify the application of R6G in the visualization of confinement in two-dimensional capillaries, the vermiculite (V) film has a UV absorption peak at 532nm, but the fluorescence signal is weak, indicating that the two-dimensional capillary interlayers composed of vermiculite are in a constrained state. However, when cellulose nanofibers (V-R6G CNF) are inserted and the capillaries (interlayer spacing) are expanded, the fluorescence appears ( Figure 4 b). When the CNF mass content increased to 33% of the V content, the normalized fluorescence intensity gradually increased by 9 times compared with that without CNF addition ( Figure 4 c), which is caused by the weakening of the confinement effect in the dilated capillary. In addition, based on the R6G indicator, the confinement effect in the capillary with spatial resolution can be observed by fluorescence microscopy ( Figure 4 de). The VR6G film shows a weak fluorescence signal, indicating the presence of interlayer constraints on the film plane. In contrast, fluorescence appears on the VR6G CNF film, especially in the ripple region, which is mainly due to the decrease in interlayer constraints caused by CNF doping. This experiment embodies the visualization of interlayer constraints based on the R6G indicator.

[0114] VII. Al 3+ Cross-linking and expansion of the spectrum of confined space in V-R6G CNF two-dimensional film

[0115] Ionic crosslinking is another method for regulating interlayer constraints and is widely used in the design of selective membranes. 3 ) 3 9H 2 O aqueous solution, a typical crosslinking agent Al 3+ ( Figure 5 a insert). With Al 3+ As the concentration increased from 0 to 1 mol / L, the normalized fluorescence intensity of the R6G indicator in the vermiculite capillary increased by 201.3%, indicating that the interlayer constraint was weakened ( Figure 5 a). At the same time, XRD results further verified that with the Al 3+ As the concentration increases from 0 to 1 mol / L, the intercapillary space increases from Expand to ( Figure 5 b), namely Al 3+ The cross-linking further weakens the constraints in the capillaries constructed by V, which is consistent with the reduction of the confinement effect shown by the fluorescent indicator.

[0116] 8. In-situ observation of the change of interlayer confinement effect of V-R6G at different humidity by fluorescence microscope

[0117] In order to demonstrate the application value of R6G molecular probe in dynamic process research, the fluorescence intensity of V-R6G membrane under different humidity was monitored by fluorescence microscopy. Water was inserted into the interlayer space of the two-dimensional capillary by humidification. Therefore, a nitrogen gas flow saturated with 100% relative humidity was blown into a chamber under the V-R6G membrane ( Figure 6 a). Then, fluorescence images are captured to track the dynamic changes of interlayer constraints ( Figure 6 b). Under 100% RH humidity input, the dark area (yellow dashed area) gradually brightens, indicating that the interlayer confinement effect weakens after water enters the capillary. Therefore, the confinement effect based on R6G can reveal the dynamic changes of interlayer constraints.

[0118] The method of the present invention demonstrates the use of R6G as a molecular probe to achieve visualization of interlayer confinement. Interlayer confinement reduces the dihedral angle between xanthylium and benzyl in the R6G molecule, resulting in attenuation of the fluorescence signal. Therefore, R6G is used to detect interlayer confinement in a two-dimensional capillary composed of vermiculite and its composite material. The fluorescence signal of R6G is quenched in the original vermiculite channel, while the embedding of cellulose nanofibers reduces the interlayer confinement effect, further resulting in an enhancement of the fluorescence of R6G.

[0119] In addition, the present invention is also suitable for evaluating geometric deformation (such as corrugation) and constraint changes caused by ionic crosslinking by tracking the spatial and spectral signals of R6G. Under the action of the R6G molecular probe, fluorescence microscopy can monitor the dynamic changes of interlayer confinement, providing time and spatial resolution information. Therefore, the strategy of the present invention provides an observation method for directly visualizing interlayer constraints in two-dimensional capillaries, and will be conducive to the design of efficient selective membranes based on two-dimensional materials.

[0120] The above content is a schematic description of the present invention and its implementation methods, which is not restrictive. What is shown in the embodiment is only one of the implementation methods of the present invention, and the actual implementation method is not limited thereto. Therefore, if a person of ordinary skill in the art is inspired by it and designs implementation methods and embodiments similar to the technical solution without creative design without departing from the purpose of the invention, they should all fall within the scope of protection of the present invention.

Claims

1. A method for determining the magnitude of confinement between two-dimensional film layers using single-molecule fluorescence, characterized in that: The two-dimensional membrane is a vermiculite two-dimensional membrane; the method comprises: Providing a vermiculite dispersion containing rhodamine 6G; The vermiculite dispersion containing rhodamine 6G is prepared into a film; detecting the normalized fluorescence intensity of rhodamine 6G in the membrane; The higher the normalized fluorescence intensity of the rhodamine 6G, the smaller the interlayer confinement effect of the vermiculite two-dimensional film is; The lower the normalized fluorescence intensity of the rhodamine 6G, the greater the interlayer confinement effect of the vermiculite two-dimensional film; The normalized fluorescence intensity is the ratio of the fluorescence intensity of the membrane to the ultraviolet absorption intensity.

2. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 1, characterized in that: The thickness of the vermiculite two-dimensional film is 1-10 μm.

3. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 1, characterized in that: The vermiculite two-dimensional membrane is a vermiculite two-dimensional membrane doped with cellulose nanofibers, and the vermiculite dispersion is a vermiculite dispersion containing cellulose nanofibers.

4. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 1, characterized in that: The vermiculite two-dimensional membrane is Al 3+ The doped vermiculite two-dimensional membrane is prepared by preparing a membrane with the vermiculite dispersion containing rhodamine 6G and then placing the membrane in a medium containing Al 3+ obtained by soaking in the solution.

5. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 1, characterized in that: The vermiculite two-dimensional membrane is cellulose nanofibers and Al 3+ The co-doped vermiculite two-dimensional membrane, wherein the vermiculite dispersion is a vermiculite dispersion containing cellulose nanofibers, and the membrane is prepared by the vermiculite dispersion containing rhodamine 6G and then the membrane is placed in a 3+ obtained by soaking in the solution.

6. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 3 or 5, characterized in that: In the vermiculite two-dimensional membrane, the mass percentage of cellulose nanofibers is 0.01-33% of the vermiculite.

7. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to claim 4 or 5, characterized in that: In the vermiculite dispersion, the Al 3+ The concentration is 10 -5 ~10 -1 mol / L.

8. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to any one of claims 1 to 7, characterized in that: In the vermiculite dispersion containing rhodamine 6G, the concentration of vermiculite is 0.05-10 mg / mL; In the vermiculite dispersion containing rhodamine 6G, the concentration of rhodamine 6G is 10 -6 ~10 -5 mol / L.

9. The method for determining the size of the confinement effect between two-dimensional film layers by using single-molecule fluorescence according to any one of claims 1 to 7, characterized in that: The normalized fluorescence intensity is the ratio of the fluorescence emission intensity with a fluorescence emission peak at 560 nm when the fluorescence excitation wavelength is 532 nm to the absorption intensity at 532 nm in the ultraviolet-visible absorption spectrum.

10. A method for determining the magnitude of confinement between two-dimensional film layers at different relative humidities using single-molecule fluorescence, characterized in that: The two-dimensional membrane is a vermiculite two-dimensional membrane; Providing a vermiculite dispersion containing rhodamine 6G; The vermiculite dispersion containing rhodamine 6G is prepared into a film; detecting the normalized fluorescence intensity of rhodamine 6G in the film at different relative humidity; The higher the normalized fluorescence intensity of the rhodamine 6G, the smaller the interlayer confinement effect of the vermiculite two-dimensional film is; The lower the normalized fluorescence intensity of the rhodamine 6G, the greater the interlayer confinement effect of the vermiculite two-dimensional film; The normalized fluorescence intensity is the ratio of the fluorescence intensity of the membrane to the ultraviolet absorption intensity.

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