A method for screening clay minerals for preparing two-dimensional channel films

Abstract

A method for screening clay minerals for preparing two-dimensional channel films relates to the field of testing. The method for screening clay minerals for preparing two-dimensional channel films is to separate clay minerals into high-layer charge density minerals, middle-layer charge density minerals, and low-layer charge density minerals according to layer charge density, and then subject them to ultrasonic treatment and peeling to obtain nanosheets. The size and thickness of the nanosheets of the clay minerals are then screened to obtain nanosheets that meet the size of the two-dimensional clay film. Finally, the nanosheets are prepared into films for film flatness testing, and clay materials that can be used to prepare films with highly ordered two-dimensional channels are selected. The method for screening clay minerals for preparing two-dimensional channel films provided in this application can quickly and efficiently screen out clay minerals that are easy to peel and easy to construct into films, filling the gap in the method for screening raw materials for two-dimensional clay channel films.

Description

Technical Field

[0001] The present application relates to the field of testing, and in particular to a method for screening clay minerals for preparing two-dimensional channel films. Background Art

[0002] Membrane separation involves selective separation by placing a barrier of isolating material between two phases or media. This allows one or more components to selectively pass from one medium to another under the presence of an appropriate driving force. The core of membrane separation technology is the membrane material. Traditional membranes are mostly porous organic polymers, but the "trade-off" effect remains a significant challenge: increasing membrane selectivity while reducing flux (Chem. Soc. Rev., 2020, 49, 1071-1089).

[0003] In recent years, two-dimensional nanochannel films with nanometer / subnanometer dimensions, fabricated by layer-by-layer assembly of atomically thin nanosheets, have demonstrated the ability to precisely control the channels within the subnanometer range, enabling highly selective separations of ions with relatively small size differences (Angew. Chem. Int. Ed. 2021, 60, 1-6). Furthermore, the ion transport rate within the channels is thousands of times greater than that in macroscopic fluids, enabling high throughput and demonstrating excellent ion screening potential in various ion separation applications.

[0004] Clay minerals are among the most abundant minerals in the Earth's crust. They are typical aluminosilicate minerals composed of silicon-oxygen tetrahedra and aluminum-oxygen octahedra. They possess a natural nanoscale layered structure and excellent hydration expansion properties. Under external forces, they easily exfoliate into two-dimensional nanosheets. These nanosheets have a two-dimensional structure with an extremely high aspect ratio and retain a naturally negative surface charge and double-layer structure, making them ideal materials for preparing two-dimensional nanochannel membranes (ACS Nano 2022, 16, 4930-4939). The two-dimensional clay films exhibit selective transport of lithium-sodium, lithium-potassium, and lithium-magnesium ions, with a selectivity of up to 380-fold for lithium-magnesium ions. This demonstrates the potential of these films for selective ion transport and holds broad application prospects in salt lake lithium extraction, fuel cells, and seawater desalination. However, clay minerals have family diversity and a wide variety of types. Clay minerals from different origins have different amounts of isomorphic substitution in their lamellar structures due to differences in the mineralization environment, which in turn leads to different layer charge densities in the clay minerals, resulting in differences in the difficulty of exfoliating them to prepare two-dimensional nanosheets. Moreover, there are also differences in clay minerals from different regions of the same origin, and the orderliness of the two-dimensional channel structures of different clay minerals after being cast into membranes is also different, that is, the difficulty of preparing two-dimensional nanochannel films from clay minerals varies.

[0005] Therefore, a method for screening clay minerals for preparing two-dimensional channel thin films is needed to quickly screen out clay mineral raw materials that meet the requirements for preparing two-dimensional channel thin films. Summary of the Invention

[0006] The purpose of this application is to provide a method for screening clay minerals for preparing two-dimensional channel thin films, which can quickly and efficiently screen out clay minerals that are easy to exfoliate and easy to form films, filling the gap in the raw material screening method for two-dimensional clay channel thin films.

[0007] This application is implemented as follows:

[0008] This application provides a method for screening clay minerals for preparing two-dimensional channel thin films, including the following steps:

[0009] Classify clay minerals into high-layer charge density minerals, middle-layer charge density minerals, and low-layer charge density minerals according to the layer charge density;

[0010] Disperse high-layer charge density clay minerals, middle-layer charge density minerals, and low-layer charge density minerals in water and perform ultrasonic exfoliation treatment within the time range of t0 - t n to obtain nanosheets, and detect the average sheet diameter size a and average thickness b of various nanosheets;

[0011] Compare the average sheet diameter size a and average thickness b of various nanosheets with the average sheet diameter size a0 and average thickness b0 of the target nanosheets: If b > b0, the clay mineral corresponding to the nanosheet is not suitable for preparing two-dimensional channel thin films; If b ≤ b0 and a < a0, shorten the ultrasonic time within the corresponding t0 - t n time range for exfoliation and then re-compare the obtained nanosheets. If b ≤ b0 and a ≥ a0 can be satisfied, the nanosheets meet the size requirements; If b ≤ b0 and a ≥ a0 cannot be satisfied, the clay mineral corresponding to the nanosheet is not suitable for preparing two-dimensional channel thin films;

[0012] Disperse the clay mineral nanosheets that meet the size requirements evenly in water to obtain a casting solution, and then filter and dry the film to obtain a待测薄膜 (to-be-tested thin film);

[0013] Test the flatness c of the to-be-tested thin film, and compare the flatness c of the to-be-tested thin film with the flatness c0 of the target thin film. If c < c0, the clay mineral is not suitable for preparing two-dimensional channel thin films; If c ≥ c0, the clay is suitable for preparing two-dimensional channel thin films.

[0014] In some optional embodiments, when classifying clay minerals into high-layer charge density minerals, middle-layer charge density minerals, and low-layer charge density minerals according to the layer charge density, the charge density of high-layer charge density clay minerals is 1, the charge density of middle-layer charge density clay minerals is 0.6 - 0.9, and the charge density of low-layer charge density clay minerals is 0.2 - 0.6.

[0015] In some optional embodiments, the layer charge density is tested by the following method: alkylamine is added to a water suspension of a clay mineral, which is then heated in a water bath with stirring, filtered, and dried to obtain the clay mineral after alkylamine ion exchange, and the clay mineral after alkylamine ion exchange is subjected to XRD testing to obtain the interlayer spacing, and the distribution state of the alkylammonium ions between the clay mineral layers is determined based on the law of interlayer spacing changes, and then the layer charge density of the clay mineral is calculated.

[0016] In some optional embodiments, the carbon chain length of the alkylamine is 8-24, the amount of alkylamine added is 1-5% wt of the clay mineral, the water bath heating temperature is 60-100° C., and the stirring time is 12-24 h.

[0017] In some optional embodiments, the high charge density clay mineral is n When ultrasonic exfoliation is performed to obtain nanosheets, 1-5 g of clay mineral is first dispersed in 100-500 mL of saturated LiCl solution, then stirred in a water bath at 60-100 ° C for 12-24 h, excess LiCl is washed off with deionized water, and then dispersed in 100-500 mL of deionized water, 2.5-5 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100 ° C for 12-36 h, excess octadecyltrimethylammonium chloride is washed off with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 40-50 kHz, an ultrasonic time range of t0 of 22 min, and t n For 30 minutes.

[0018] In some optional embodiments, the middle charge density mineral is n When ultrasonic exfoliation is performed to obtain nanosheets, 1-4 g of clay mineral is first calcined at 750-950° C. in an air atmosphere for 4-10 h, and then the calcined clay mineral is dispersed in 100-800 mL of deionized water, 2-8 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100° C. for 12-30 h, excess octadecyltrimethylammonium chloride is washed with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 30-40 kHz, an ultrasonic time range of t0 of 12 min, and t n For 20 minutes.

[0019] In some optional embodiments, the low-charge density minerals are nWhen ultrasonic exfoliation is performed to obtain nanosheets, 1-3 g of clay mineral is first dispersed in 50-200 mL of saturated NaCl solution, then stirred in a water bath at 50-90 ° C for 12-30 h, excess NaCl is washed off with deionized water, and then dispersed in water to form a 0.5-1% wt clay mineral suspension for ultrasonic treatment. The ultrasonic power is 10-20 kHz, the ultrasonic time range is t0 is 2 min, and t n For 10 minutes.

[0020] In some optional embodiments, the average diameter a and average thickness b of the nanosheets are the arithmetic mean of force microscopy statistical results of n nanosheet atoms, where n≥100.

[0021] In some optional embodiments, the average diameter of the target nanosheets a0 is ≥ 200 nm, and the average thickness b0 is ≤ 5 nm; and / or the thickness of the film to be tested and the target film is 80-200 μm.

[0022] In some optional embodiments, the flatness c is calculated using the following formula: c=1 / sinθ, where θ is the azimuth angle of the film obtained by a small-angle X-ray scattering instrument test, and the flatness of the target film c0≥2.

[0023] The beneficial effects of the present application are as follows: the clay mineral screening method for preparing a two-dimensional channel film provided in the present application is to separate clay minerals into high-layer charge density minerals, middle-layer charge density minerals, and low-layer charge density minerals according to layer charge density, and ultrasonically treat and peel them to obtain nanosheets. The size and thickness of the clay mineral nanosheets are then screened to obtain nanosheets that meet the size of the two-dimensional clay film. The nanosheets are then prepared into a film for film flatness testing to select clay materials that can be used to prepare a highly ordered two-dimensional channel film. The clay mineral screening method for preparing a two-dimensional channel film provided in the present application can quickly and efficiently screen out clay minerals that are easy to peel and easy to construct into films, filling the gap in the screening method for raw materials of two-dimensional clay channel films. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A schematic flow chart of a method for screening clay minerals for preparing two-dimensional channel films provided in an embodiment of the present application;

[0026] Figure 2 This is a small-angle X-ray scattering spectrum of a montmorillonite film screened by the clay mineral screening method for preparing a two-dimensional channel film provided in Example 1 of the present application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0028] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0029] The characteristics and performance of the clay mineral screening method for preparing a two-dimensional channel film of the present application are further described in detail below with reference to the examples.

[0030] like Figure 1 As shown, the embodiment of the present application provides a method for screening clay minerals for preparing a two-dimensional channel film, comprising the following steps:

[0031] S1. Clay minerals are classified into high charge density minerals, medium charge density minerals and low charge density minerals according to layer charge density; optionally, the charge density of high charge density clay minerals is 1, the charge density of medium charge density clay minerals is 0.6-0.9, and the charge density of low charge density clay minerals is 0.2-0.6;

[0032] Optionally, the layer charge density is measured using the following alkylamine ion exchange method: a certain amount of alkylamine is added to an aqueous suspension of a clay mineral, which is then heated in a water bath with stirring, filtered, and dried to obtain the alkylamine ion-exchanged clay mineral. The alkylamine ion-exchanged clay mineral is subjected to XRD analysis to determine the interlayer spacing. Based on the variation in the interlayer spacing, the distribution of alkylammonium ions between the clay mineral layers is determined, and the layer charge density of the clay mineral is then calculated. Optionally, the carbon chain length of the alkylamine is 8-24, the number of alkylamines of different carbon chain lengths added to the aqueous suspension of the clay mineral is 6-10, the amount of alkylamine added is 1-5% by weight of the clay mineral, the water bath heating temperature is 60-100°C, and the stirring time is 12-24 hours.

[0033] S2, disperse high-charge density clay minerals, medium-charge density minerals and low-charge density minerals into water at t0-t nUltrasonic exfoliation is performed within a time range to obtain nanosheets, and the average sheet diameter a and average thickness b of various nanosheets are detected; optionally, the average sheet diameter a and average thickness b of the nanosheets are the arithmetic mean of force microscopy statistical results of n nanosheet atoms, where n≥100.

[0034] Optionally, high charge density clay minerals at t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-5 g of clay mineral is first dispersed in 100-500 mL of saturated LiCl solution, then stirred in a water bath at 60-100 ° C for 12-24 h, excess LiCl is washed off with deionized water, and then dispersed in 100-500 mL of deionized water, 2.5-5 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100 ° C for 12-36 h, excess octadecyltrimethylammonium chloride is washed off with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 40-50 kHz, an ultrasonic time range of t0 of 22 min, and t n For 30 minutes.

[0035] The charge density of the intermediate layer minerals is t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-4 g of clay mineral is first calcined at 750-950° C. in an air atmosphere for 4-10 h, and then the calcined clay mineral is dispersed in 100-800 mL of deionized water, 2-8 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100° C. for 12-30 h, excess octadecyltrimethylammonium chloride is washed with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 30-40 kHz, an ultrasonic time range of t0 of 12 min, and t n For 20 minutes.

[0036] Low charge density minerals at t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-3 g of clay mineral is first dispersed in 50-200 mL of saturated NaCl solution, then stirred in a water bath at 50-90 ° C for 12-30 h, excess NaCl is washed off with deionized water, and then dispersed in water to form a 0.5-1% wt clay mineral suspension for ultrasonic treatment. The ultrasonic power is 10-20 kHz, the ultrasonic time range is t0 is 2 min, and t n For 10 minutes.

[0037] S3. Compare the average sheet diameter size a and the average thickness b of various nanosheets with the average sheet diameter size a0 and the average thickness b0 of the target nanosheets: If b > b0, the clay mineral corresponding to the nanosheet is not suitable for preparing a two-dimensional channel thin film; if b ≤ b0 and a < a0, then shorten the ultrasonic time within the corresponding t0 - t time range for exfoliation and then re-compare the obtained nanosheets. If b ≤ b0 and a ≥ a0 can be satisfied, the nanosheets meet the size requirements; if b ≤ b0 and a ≥ a0 cannot be satisfied, the clay mineral corresponding to the nanosheet is not suitable for preparing a two-dimensional channel thin film. Optionally, the average sheet diameter size a0 of the target nanosheets is ≥ 200 nm, and the average thickness b0 is ≤ 5 nm; n Within the corresponding time range, shorten the ultrasonic time for exfoliation and then re-compare the obtained nanosheets. If b ≤ b0 and a ≥ a0 can be satisfied, the nanosheets meet the size requirements; if b ≤ b0 and a ≥ a0 cannot be satisfied, the clay mineral corresponding to the nanosheet is not suitable for preparing a two-dimensional channel thin film. Optionally, the average sheet diameter size a0 of the target nanosheets is ≥ 200 nm, and the average thickness b0 is ≤ 5 nm;

[0038] S4. Disperse the clay mineral nanosheets that meet the size requirements evenly in water to obtain a casting solution, and then filter and dry the film to obtain the待测薄膜 (to-be-tested thin film);

[0039] S5. Test the flatness c of the to-be-tested thin film, and compare the flatness c of the to-be-tested thin film with the flatness c0 of the target thin film. If c < c0, the clay mineral is not suitable for preparing a two-dimensional channel thin film; if c ≥ c0, the clay is suitable for preparing a two-dimensional channel thin film. Optionally, the thicknesses of the to-be-tested thin film and the target thin film are 80 - 200 μm.

[0040] Optionally, the flatness c is calculated using the following formula: c = 1 / sinθ, where θ is the azimuth angle of the thin film measured by a small-angle X-ray scattering instrument; optionally, the flatness c0 of the target thin film is ≥ 2.

[0041] The method for screening clay minerals for preparing two-dimensional channel thin films provided by the embodiments of the present application summarizes the differences of clay minerals, classifies and summarizes clay minerals according to the layer charge density, the size and thickness of exfoliated nanosheets, and the channel orderliness of two-dimensional clay thin films, and screens different clay minerals through establishing a screening system, so as to quickly and efficiently select clay minerals suitable for preparing two-dimensional channel thin films.

[0042] Among them, by classifying clay minerals according to the magnitude of the layer charge density and setting different exfoliation conditions for clay minerals with different charge densities, it is possible to ensure the stable exfoliation of nanosheets of different types of clay minerals and screen out clay mineral nanosheets with suitable sizes and thicknesses that can be used for preparing thin films. Then, by targeting the assembly of clay mineral nanosheets with qualified sizes and thicknesses into a film and then testing the flatness of the thin film, clay minerals that can prepare highly ordered two-dimensional channel thin films are screened out.

[0043] Example 1

[0044] The present embodiment provides a method for screening clay minerals for preparing a two-dimensional channel film, wherein three montmorillonite clay minerals from different origins are screened and labeled as montmorillonite No. 1, No. 2, and No. 3, respectively;

[0045] S1. Take 1g of each of the three montmorillonite clay minerals and add them to 6 100mL beakers. Add 2%wt of montmorillonite mass of hexaalkyltrimethylammonium chloride, octaalkyltrimethylammonium chloride, decanyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, and hexadecyltrimethylammonium chloride to the 6 100mL beakers of different types of montmorillonite, and then add 60mL of deionized water respectively. After uniform stirring and dispersion, heat in a 100℃ water bath for 12h, and finally centrifuge and dehydrate. After drying the precipitate, it is the alkylammonium intercalated montmorillonite sample. The layer charge density of montmorillonite No. 1, No. 2, and No. 3 is measured to be 0.47, 0.39, and 0.3, respectively.

[0046] S2. According to the layer charge density screening, No. 1, No. 2 and No. 3 montmorillonites are all clay minerals with low layer charge density;

[0047] 1 g of montmorillonite No. 1, No. 2, and No. 3 were dispersed in 100 mL of saturated NaCl solution, then stirred in a 70°C water bath for 24 h. Excess NaCl was washed off with deionized water, and then a 0.5% wt clay mineral suspension was prepared. Nanosheets were exfoliated by ultrasonication at 20 kHz for 10 min.

[0048] S3. Using atomic force microscopy, the average sheet diameter a of the No. 1 montmorillonite nanosheets was 450 nm and the average thickness b was 6 nm. The average sheet diameter a of the No. 2 montmorillonite nanosheets was 150 nm and the average thickness b was 2.5 nm. The average sheet diameter a of the No. 3 montmorillonite nanosheets was 500 nm and the average thickness b was 2 nm.

[0049] By comparing and analyzing the target nanosheets with an average sheet diameter a0 of 200nm and an average thickness b0 of 5nm, it was found that montmorillonite No. 1 was not suitable and was directly eliminated; montmorillonite No. 2 was further exfoliated using an ultrasonic power of 20kHz and an ultrasonic time of 8min, and the prepared nanosheets had an average sheet diameter a of 250nm and an average thickness b of 3nm, which met the requirements and were cast; montmorillonite nanosheets No. 3 met the requirements and were directly cast;

[0050] S4, taking 0.15g of the exfoliated No. 2 and No. 3 montmorillonite nanosheets, respectively, adding deionized water and stirring thoroughly to react to form a casting solution with a mass fraction of 0.5%, and vacuum filtration to prepare a two-dimensional channel film with a membrane thickness of 100μm;

[0051] S5, the flatness of the No. 2 montmorillonite film was calculated by using a small-angle X-ray scattering instrument and was 1.2, which was less than the target flatness of 2 and did not meet the requirements, so it was eliminated; the flatness of the No. 3 montmorillonite film was 2.12 (see Figure 2 ), montmorillonite No. 3 was selected as the raw material for the two-dimensional channel film.

[0052] Figure 2 This is the X-ray small-angle scattering spectrum of the No. 3 montmorillonite film prepared in this example; it can be observed from the figure that the wide angle of the film is 28.1 degrees, and the flatness of the No. 3 montmorillonite film is calculated to be 2.12, indicating that the two-dimensional montmorillonite nanosheets are orderly stacked.

[0053] Example 2

[0054] The embodiment of the present application provides a method for screening clay minerals for preparing a two-dimensional channel film, wherein three clay minerals are screened, and the three clay minerals are mica, vermiculite and montmorillonite;

[0055] S1. Take 3g of three kinds of clay minerals respectively and add them to 6 500mL beakers. Add 5%wt of clay mineral amount of octaalkyltrimethylammonium chloride, decanyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride and octadecyltrimethylammonium chloride to 6 500mL beakers of different kinds of clay minerals respectively. Then add 400mL of deionized water respectively. Stir and disperse them evenly and heat them in a water bath at 80℃ for 24h. Finally, centrifuge and dehydrate the precipitates. After drying, the precipitates are obtained as alkylammonium intercalated clay mineral samples. The layer charge densities of mica, vermiculite and montmorillonite are measured to be 1, 0.7 and 0.33 respectively.

[0056] S2. Based on the layer charge density screening, mica is classified as high layer charge density, vermiculite is classified as medium layer charge density, and montmorillonite is classified as low layer charge density;

[0057] 1 g of high-charge density clay mineral mica was dispersed in 100 mL of saturated LiCl solution, then stirred in a water bath at 100 ° C for 24 h, and the excess LiCl was washed off with deionized water. The washed clay mineral was then dispersed in 100 mL of deionized water, 2.5 g of octadecyltrimethylammonium chloride was added, and then stirred in a water bath at 100 ° C for 24 h. The excess octadecyltrimethylammonium chloride was washed off with deionized water. Then, a 0.5% wt clay mineral suspension was prepared and exfoliated at 50 kHz ultrasonic power for 30 min to obtain nanosheets.

[0058] 1 g of medium-charge density clay mineral vermiculite was calcined at 850°C in air for 6 h, and then the calcined clay mineral was dispersed in 100 mL of deionized water. 2 g of octadecyltrimethylammonium chloride was added, and then stirred in a 100°C water bath for 24 h. The excess octadecyltrimethylammonium chloride was washed with deionized water, and then a 0.5% wt clay mineral suspension was prepared. Nanosheets were exfoliated by ultrasonication at 40 kHz for 20 min.

[0059] 1 g of low-charge-density clay mineral montmorillonite was dispersed in 100 mL of saturated NaCl solution, then stirred in a 70°C water bath for 24 h, the excess NaCl was washed off with deionized water, and then a 0.5% wt clay mineral suspension was prepared. The nanosheets were exfoliated by ultrasonication at 20 kHz for 10 min.

[0060] S3. Using atomic force microscopy, the average diameter a of mica nanosheets was 1000 nm and the average thickness b was 20 nm. The average diameter a of vermiculite nanosheets was 800 nm and the average thickness b was 12 nm. The average diameter a of montmorillonite nanosheets was 620 nm and the average thickness b was 1.85 nm.

[0061] By comparing and analyzing the target nanosheets with an average diameter a0 of 300 nm and an average thickness b0 of 5 nm, it was found that mica and vermiculite were not suitable and were directly eliminated; montmorillonite nanosheets were directly cast into films;

[0062] S4. Take 0.25 g of the exfoliated montmorillonite nanosheets, add deionized water and stir thoroughly to form a casting solution with a mass fraction of 2%, and use vacuum filtration to prepare a two-dimensional nanochannel film with a membrane thickness of 150 μm.

[0063] S5. The flatness of the montmorillonite film is calculated and tested using a small-angle X-ray scattering instrument, and is found to be 3. Montmorillonite is selected as the raw material for the two-dimensional channel film.

[0064] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A method for screening clay minerals for preparing two-dimensional channel films, characterized in that: It includes the following steps: Classify clay minerals into high-layer charge density minerals, medium-layer charge density minerals, and low-layer charge density minerals according to the layer charge density; The high charge density clay minerals, medium charge density minerals and low charge density minerals are dispersed into water at t0-t n time range by ultrasonic exfoliation to obtain nanosheets, and detecting the average sheet diameter a and average thickness b of the various nanosheets; Compare the average sheet diameter size a and the average thickness b of each of the nanosheets with the average sheet diameter size a0 and the average thickness b0 of the target nanosheet: If b > b0, the clay mineral corresponding to the nanosheet is not suitable for preparing a two-dimensional channel film; if b ≤ b0 and a < a0, then within the corresponding time range of t0 - t n Shorten the ultrasonic time within the time range for exfoliation to obtain nanosheets and compare them again. If b ≤ b0 and a ≥ a0 can be satisfied, the nanosheets meet the size requirements; if b ≤ b0 and a ≥ a0 cannot be satisfied, the clay mineral corresponding to the nanosheets is not suitable for preparing a two-dimensional channel film; Disperse the clay mineral nanosheets that meet the size requirements evenly in water to obtain a casting solution, and then perform suction filtration to form a film and dry it to obtain a test film; Test the flatness c of the test film, and compare the flatness c of the test film with the flatness c0 of the target film. If c < c0, the clay mineral is not suitable for preparing a two-dimensional channel film; if c ≥ c0, the clay is suitable for preparing a two-dimensional channel film.

2. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: When classifying clay minerals into high-layer charge density minerals, medium-layer charge density minerals, and low-layer charge density minerals according to the layer charge density, the charge density of the high-layer charge density clay mineral is 1, the charge density of the medium-layer charge density clay mineral is 0.6 - 0.9, and the charge density of the low-layer charge density clay mineral is 0.2 - 0.

6.

3. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: The layer charge density is tested by the following method: Add alkylamine to the aqueous suspension of clay minerals, then heat and stir in a water bath, filter, and dry to obtain the clay minerals after alkylamine ion exchange. Perform XRD testing on the clay minerals after alkylamine ion exchange to obtain the layer spacing, determine the distribution state of alkylammonium ions between the clay mineral layers according to the change law of the layer spacing, and then calculate the layer charge density of the clay minerals.

4. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 3, characterized in that: The carbon chain length of the alkylamine is 8 - 24, the addition amount of the alkylamine is 1 - 5%wt of the mass of the clay minerals, the water bath heating temperature is 60 - 100°C, and the stirring time is 12 - 24h.

5. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: High charge density clay minerals at t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-5 g of clay mineral is first dispersed in 100-500 mL of saturated LiCl solution, then stirred in a water bath at 60-100 ° C for 12-24 h, excess LiCl is washed off with deionized water, and then dispersed in 100-500 mL of deionized water, 2.5-5 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100 ° C for 12-36 h, excess octadecyltrimethylammonium chloride is washed off with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 40-50 kHz, an ultrasonic time range of t0 of 22 min, and t n For 30 minutes.

6. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: The charge density of the intermediate layer minerals is t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-4 g of clay mineral is first calcined at 750-950° C. in an air atmosphere for 4-10 h, and then the calcined clay mineral is dispersed in 100-800 mL of deionized water, 2-8 g of octadecyltrimethylammonium chloride is added, and then stirred in a water bath at 80-100° C. for 12-30 h, excess octadecyltrimethylammonium chloride is washed with deionized water, and then dispersed in water to prepare a 0.5-1% wt clay mineral suspension for ultrasonic treatment, with an ultrasonic power of 30-40 kHz, an ultrasonic time range of t0 of 12 min, and t n For 20 minutes.

7. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: Low charge density minerals at t0-t n When ultrasonic exfoliation is performed to obtain nanosheets, 1-3 g of clay mineral is first dispersed in 50-200 mL of saturated NaCl solution, then stirred in a water bath at 50-90 ° C for 12-30 h, excess NaCl is washed off with deionized water, and then dispersed in water to form a 0.5-1% wt clay mineral suspension for ultrasonic treatment. The ultrasonic power is 10-20 kHz, the ultrasonic time range is t0 is 2 min, and t n For 10 minutes.

8. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: The average sheet diameter size a and the average thickness b of the nanosheets are the arithmetic mean of the statistical results of the atomic force microscopy of n nanosheets, where n ≥ 100.

9. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: [[ID=,8]]The average sheet diameter size a0 of the target nanosheets is ≥ 200nm, and the average thickness b0 is ≤ 5nm; and / or, the thicknesses of the test film and the target film are 80 - 200μm.

10. The method for screening clay minerals for preparing a two-dimensional channel film according to claim 1, characterized in that: The flatness c is calculated by the following formula: c = 1 / sinθ, where θ is the azimuth angle of the film measured by a small-angle X-ray scattering instrument, and the flatness c0 of the target film is ≥ 2.

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