MOF (Metal Organic Framework) membrane material with dynamic photoresponsiveness, separation membrane and preparation method

Abstract

The invention belongs to the technical field of stimuli-responsive materials and dye separation, and relates to an MOF (Metal Organic Framework) membrane material with dynamic photoresponsiveness, a separation membrane and a preparation method, the membrane material is prepared by modifying photoresponsive azobenzene-4-benzoic acid molecules between layers of two-dimensional NUS-8 nanosheets, and by virtue of the specific photoresponse behavior of azobenzene molecules, the dynamic photoresponsiveness of the two-dimensional NUS-8 nanosheets is improved, so that the dynamic photoresponsiveness of the two-dimensional NUS-8 nanosheets is improved. And the material is endowed with an adjustable dynamic light response function. Under the irradiation of ultraviolet light, azobenzene molecules are subjected to trans-cis conformation transformation, and the interlayer spacing of the two-dimensional NUS-8 nanosheets is reversibly switched, so that the pore structure and molecular screening performance of the membrane material are regulated and controlled. When azobenzene molecules are converted from trans form to cis form, the interlayer spacing of the material is reduced, so that the size of pores is remarkably reduced, dye molecules are effectively prevented from passing through, and the interception capacity of the membrane material is remarkably improved. And after the ultraviolet irradiation is relieved, the azobenzene molecules are recovered to the original trans-structure, the interlayer spacing is recovered, and the permeability of the membrane is recovered. And the light responsiveness and the stability are improved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of stimulus-responsive materials and dye separation, and relates to a MOF membrane material, a separation membrane with dynamic light responsiveness and a preparation method thereof. Background Art

[0002] With the increasing environmental pollution problems, especially water pollution, traditional water treatment methods are facing a series of challenges such as low efficiency and high energy consumption. Therefore, membrane separation technology has gradually gained wide application in the fields of water treatment, gas separation, catalytic reaction, etc. due to its advantages of high efficiency and energy conservation. The performance of membrane materials directly affects the efficiency of membrane separation technology, and how to optimize the selectivity, permeability and adjustability of the membrane has become the research focus in the field of membrane separation.

[0003] Metal-organic framework (MOF) materials have become a research hotspot in the field of membrane separation due to their large specific surface area, rich pore structure and highly adjustable chemical functionality. However, once the inherent pore structure of existing MOF membrane materials is formed, it lacks flexibility and adjustability, resulting in relatively fixed separation performance under different separation requirements. Therefore, how to achieve dynamic regulation of the pore structure of MOF membranes and further optimize the separation performance of the membranes has become a key topic in current research.

[0004] To overcome these limitations, in recent years, researchers have proposed MOF materials introducing a stimulus-responsive mechanism to dynamically regulate the pore structure and separation performance of MOFs through changes in the external environment (such as temperature, light, pH value, etc.). The preparation strategies of stimulus-responsive MOF materials mainly focus on the following several approaches: (1) introducing freely rotating dynamic molecules into the material framework to achieve MOFs with enhanced operability and flexibility; (2) incorporating guest molecules into MOFs that can respond to environmental stimuli, such as spiropyran, azobenzene, stilbene; (3) reasonably selecting stimulus-responsive ligands or non-coordinating side chain groups as framework building units to endow stimulus-responsive functions. Although substantial progress has been made, there are still challenges in the rational design of the structure and framework construction. For example, the structural changes of some photo-responsive MOF materials are not significant enough, or the response time is long, making it difficult to meet the rapid regulation requirements in practical applications. In addition, existing stimulus-responsive MOF membrane materials often lack strong light responsiveness and stability, which limits their wide application in complex environments. Summary of the Invention

[0005] The purpose of the present invention is to provide a MOF membrane material, a separation membrane with dynamic light responsiveness and a preparation method thereof, so as to solve the technical problem that existing stimulus-responsive MOF membrane materials often lack strong light responsiveness and stability.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions: In the first aspect, the present application discloses a preparation method of a MOF membrane material with dynamic light responsiveness, including: S1: Add ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene to DMF to obtain a mixed solution A. Add ultrapure water and formic acid to the mixed solution A, mix evenly and then heat and react to obtain a milky white suspension. Centrifuge and wash the milky white suspension to obtain a NUS-8 nanosheet suspension; S2: After mixing the NUS-8 nanosheet suspension with hydrochloric acid, successively carry out heating reaction, centrifugation and washing to obtain a uniformly dispersed suspension; S3: Dissolve azobenzene-4-benzoic acid in DMF to obtain a mixed solution B. After mixing the mixed solution B with the suspension, heat and react to obtain an orange suspension. Centrifuge and wash the orange suspension to obtain a NUS-8-Azobenzene nanosheet suspension. Preferably, the molar ratio of ZrCl4 to 1,3,5-tris(4-carboxyphenyl)benzene is (1.9~2.1):1; the dosage ratio of ZrCl4 to DMF is 30-32 mg: 15 ml.

[0007] Preferably, 4.0-4.2 ml of ultrapure water and 4.0-4.2 ml of formic acid are added to the mixed solution A. Preferably, in S2, the concentration of the NUS-8 nanosheet suspension is 2.0-2.2 g·L -1 , the addition amount is 15-17 ml, and the concentration of the hydrochloric acid solution is 1 mol·L -1 , the addition amount is 15 mL. Preferably, in S3, the dosage ratio of azobenzene-4-benzoic acid to DMF is 58-60 mg: 30 ml. Preferably, the temperature of the heating reaction is 120 °C - 150 °C. In the second aspect, the present application discloses a MOF membrane material with dynamic light responsiveness, which is prepared by using the preparation method described in any one of the above.

[0008] In the third aspect, the present application discloses a preparation method of a separation membrane with dynamic light responsiveness, which is prepared by using the above-mentioned MOF membrane material with dynamic light responsiveness, including: Prepare an ethanol dispersion of NUS-8-Azobenzene nanosheets. Through a negative pressure sand core suction filtration device for the ethanol dispersion, transfer the NUS-8-Azobenzene nanosheets onto PAN-400 to obtain a NUS-8-Azobenzene nanosheet separation membrane.

[0009] Preferably, the concentration of the ethanol dispersion is 0.1 - 0.3 mg·ml -1 , and the negative pressure during the transfer of NUS-8-Azobenzene nanosheets is 0.9 - 1.2 bar.

[0010] Fourthly, the present application discloses a separation membrane with dynamic light responsiveness, which is prepared by using the preparation method described in any one of the above, and the thickness of the separation membrane is 330 - 400 nm.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1) The present invention utilizes the unique light-responsive characteristics of azobenzene molecules, enabling the pore structure and permeability of the membrane material to be adjusted by light. This light-responsive reversibility allows the molecular sieving ability and permeability of the membrane material to be dynamically adjusted to meet the requirements of different application scenarios. In contrast, traditional membrane materials usually operate under fixed pore sizes and screening performances, lacking flexibility and adjustment capabilities.

[0012] 2) When the azobenzene molecules transform from the trans conformation to the cis conformation, the interlayer spacing between NUS-8-Azobenzene nanosheets decreases, effectively preventing the passage of larger molecules (such as congo red and acid fuchsin), and enhancing the rejection performance of the membrane material. This adjustment method is simpler and more accurate compared to the fixed pore size or the screening mechanism relying on external chemical modification of traditional membrane materials, and can efficiently filter and separate target molecules.

[0013] 3) The membrane material in the present invention exhibits good reversible light-responsive characteristics. Under ultraviolet light irradiation, the pore structure of the membrane can be controllably adjusted, and after the removal of ultraviolet light irradiation, the permeability of the membrane can be restored. This characteristic enables the membrane material to be repeatedly adjusted during multiple uses, avoiding the problem of performance degradation of traditional membrane materials during long-term use, and improving the durability and adaptability of the membrane. Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0015] Figure 1 It is a scanning electron microscope image of the NUS-8-Azobenzene nanosheets prepared in Example 2; among them, (a) is the 300nm view; (b) is the 400nm view; Figure 2It is the atomic force microscopy image of the NUS-8-Azobenzene nanosheets prepared in Example 2; among them, (a) is the microscopic picture; (b) is the diagram showing the thickness of the nanosheets. Figure 3 It is the transmission electron microscopy image of the NUS-8-Azobenzene nanosheets prepared in Example 2; among them, (a) and (b) are the partial views of different regions respectively. Figure 4 It is the XRD pattern of the nanosheets; among them, (a) is the XRD comparison pattern of NUS-8 and NUS-8-Azobenzene nanosheets; (b) is the partial enlarged view of the (001) peak of the XRD of NUS-8 and NUS-8-Azobenzene nanosheets. Figure 5 It is the nuclear magnetic spectrum of the NUS-8-Azobenzene sample prepared in Example 2. Figure 6 It is the Fourier transform infrared spectrum of the nanosheets; among them, (a) is the Fourier transform infrared spectrum of NUS-8 nanosheets; (b) is the Fourier transform infrared spectrum of NUS-8-Azobenzene nanosheets. Figure 7 It is the ultraviolet-visible absorption spectra of the NUS-8-Azobenzene suspension and film prepared in Example 2 under different light illumination times; among them, (a) is the spectrum of the NUS-8-Azobenzene suspension; (b) is the spectrum of the NUS-8-Azobenzene film. Figure 8 It is the separation situation of the NUS-8-Azobenzene film prepared in Example 2 of the present invention for six organic dyes with different molecular weights before and after ultraviolet light illumination. Detailed implementation manners

[0016] To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0017] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not limit the scope of the present invention in any way, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0018] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values within the ranges (including integers and fractions).

[0019] In this text, unless otherwise specified, the terms "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0020] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings: The present application discloses a preparation method of a MOF membrane material with dynamic light responsiveness, including: S1: ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene are added to DMF to obtain a mixed solution A. Ultra-pure water and formic acid are added to the mixed solution A, and after mixing evenly, the mixture is heated and reacted to obtain a milky white suspension. The milky white suspension is centrifuged and washed to obtain a NUS-8 nanosheet suspension; S2: The NUS-8 nanosheet suspension is mixed with hydrochloric acid, and after heating and reacting, centrifuging and washing in sequence, a uniformly dispersed suspension is obtained; S3: Azobenzene-4-benzoic acid is dissolved in DMF to obtain a mixed solution B. The mixed solution B is mixed with the suspension, and after heating and reacting, an orange suspension is obtained. The orange suspension is centrifuged and washed to obtain a NUS-8-Azobenzene nanosheet suspension.

[0022] The present invention proposes an innovative preparation method. By modifying azobenzene molecules into the interlayer of two-dimensional nanosheets, the MOF membrane material is given significant light-responsive characteristics. Azobenzene molecules can be converted from the trans isomer to the cis isomer under light irradiation, resulting in a significant change in the layer spacing of the material. Through this method, not only can the pore structure of the MOF membrane material be adjusted under light irradiation, but it can also quickly restore its original structure after removing the light irradiation, showing reversible light-responsive characteristics. This azobenzene molecule-based light-responsive MOF membrane material has high adjustability and reversibility, significantly enhancing the adaptability of the membrane material, and providing new solutions for fields such as dye separation and water treatment.

[0023] In some embodiments, the molar ratio of ZrCl4, 1,3,5-tris(4-carboxyphenyl)benzene, and DMF is (1.9~2.1):1.

[0024] In some embodiments, the amounts of ZrCl4 and DMF used are 30 - 32 mg: 15 ml.

[0025] In some embodiments, 4.0 - 4.2 ml of ultrapure water and 4.0 - 4.2 ml of formic acid are added to the mixed solution A.

[0026] In some embodiments, in S2, the concentration of the NUS-8 nanosheet suspension is 2.0 - 2.2 g·L -1 , the addition amount is 15 - 17 ml, and the concentration of the hydrochloric acid solution is 1 mol·L -1 , and the addition amount is 15 mL.

[0027] In some embodiments, in S3, the dosage ratio of azobenzene-4-benzoic acid to DMF is 58 - 60 mg: 30 ml.

[0028] In some embodiments, the temperature of the heating reaction is 120 °C - 150 °C.

[0029] In some embodiments, a method for preparing a MOF membrane material with dynamic light responsiveness includes: S1. Add ZrCl4 (0.128 - 0.132 mmol) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB, 0.067 - 0.071 mmol) to 15 ml of DMF to obtain a mixed solution. Add ultrapure water (4.0 - 4.2 ml) and formic acid (4.0 - 4.2 ml) to the mixed solution, and perform ultrasonic treatment on the above mixed solution (15 - 20 minutes). After the ultrasonic treatment, place the mixed solution in a reaction kettle and heat it (120 °C). After reacting for 24 h, obtain a milky white suspension, and perform centrifugal washing multiple times to finally obtain a uniformly dispersed NUS-8 nanosheet suspension.

[0030] S2. Take the NUS-8 suspension prepared in step S1 and hydrochloric acid (15 mL; 1 1 mol·L -1 ) and mix them in a heat-resistant glass bottle, perform ultrasonic treatment for 10 - 15 minutes, and heat at 80 °C for 12 hours. After the reaction, perform centrifugal washing on the obtained suspension multiple times to obtain a uniformly dispersed clean suspension.

[0031] S3. Dissolve azobenzene-4-benzoic acid (58 - 60 mg) in DMF (30 ml), mix it with the suspension obtained in step S2, then place the mixture in a reaction kettle and heat it (120 °C). After reacting for 12 h, centrifuge and wash the resulting orange suspension multiple times to finally obtain a uniformly dispersed suspension of NUS-8-Azobenzene nanosheets.

[0032] In some embodiments, the power of the ultrasonic treatment is 200 - 300 W, and the cumulative ultrasonic time is 15 - 20 min.

[0033] In some embodiments, the centrifugation speed is 8000 - 10000 r / min, the centrifugation time is 5 - 7 min, and the centrifugation and washing operation is not less than 5 times.

[0034] This application discloses a MOF membrane material with dynamic light responsiveness, which is prepared by using the preparation method described in any one of the above. This membrane material endows the material with an adjustable dynamic light response function by modifying the light-responsive azobenzene-4-benzoic acid molecules between the layers of two-dimensional NUS-8 nanosheets and relying on the unique light response behavior of azobenzene molecules. Under ultraviolet light irradiation, the azobenzene molecules undergo a "trans-cis" conformational transformation, resulting in a reversible switch in the interlayer spacing of the two-dimensional NUS-8 nanosheets, thereby regulating the pore structure and molecular sieving performance of the membrane material. When the azobenzene molecules change from the trans form to the cis form, the interlayer spacing of the material shrinks, thus significantly reducing the pore size, effectively preventing dye molecules from passing through, and significantly improving the rejection ability of the membrane material. Conversely, after the ultraviolet light irradiation is removed, the azobenzene molecules can return to the original trans structure, the interlayer spacing is restored, and the permeability of the membrane is restored. The present invention provides an innovative idea for the design of intelligent separation technology and provides important theoretical basis and technical support for the development of new and efficient separation materials.

[0035] This application also discloses a preparation method of a separation membrane with dynamic light responsiveness, which is prepared by using the above-mentioned MOF membrane material with dynamic light responsiveness, and includes: Prepare an ethanol dispersion of NUS-8-Azobenzene nanosheets, and transfer the NUS-8-Azobenzene nanosheets onto PAN-400 through a negative pressure sand core suction filtration device for the ethanol dispersion to obtain a NUS-8-Azobenzene nanosheet separation membrane.

[0036] In some embodiments, the concentration of the ethanol dispersion is 0.1 - 0.3 mg·ml -1 , and the negative pressure during the transfer of NUS-8-Azobenzene nanosheets is 0.9 - 1.2 bar.

[0037] The present application also discloses a separation membrane with dynamic light responsiveness, and the thickness of the separation membrane is 330 - 400 nm. Utilizing the unique light-responsive property of azobenzene molecules, when azobenzene molecules transform from the trans conformation to the cis conformation, the layer spacing between NUS-8-Azobenzene nanosheets shrinks, thereby enhancing the molecular sieving ability of the membrane, effectively preventing larger dye molecules from passing through, and significantly enhancing the rejection performance of the membrane. When the ultraviolet light irradiation is removed, the azobenzene molecules revert to the trans conformation, resulting in the layer spacing between NUS-8-Azobenzene nanosheets returning to its original state, and further restoring the permeability of the membrane. This process exhibits excellent reversible light-responsive characteristics and can achieve the adjustable and repeatable regulation of membrane performance.

[0038] Further preferably, the membrane separation performance of the NUS-8-Azobenzene nanosheet separation membrane is verified by a dead-end separation device. All measurements are carried out at room temperature and under the condition of a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane is obtained by collecting the filtrate over a certain period of time and averaging it, and each data point is obtained from three consecutive tests.

[0039] In the separation of organic dyes, the separation membrane with dynamic light responsiveness can effectively regulate the reversible switching of the layer spacing of two-dimensional NUS-8 nanosheets by utilizing the property of reversible conformational transformation of azobenzene molecules under light irradiation. NUS-8-Azobenzene not only has excellent separation performance, but also its molecular sieving ability can be dynamically regulated by changes in light irradiation, achieving the efficient separation of target substances such as dye molecules. At the same time, the pore structure and permeability of this material have the characteristics of reversible regulation, can respond to external light changes, and meet different application requirements.

[0040] <Example 1> The following takes the preparation method of the NUS-8 membrane as an example for illustration, and its preparation method includes the following steps: (1) Preparation of the mixed solution: ZrCl4 (0.128 - 0.132 mmol) and H3BTB (0.067 - 0.071 mmol) are added to 15 ml of DMF, and ultrapure water (4.0 - 4.2 ml) and formic acid (4.0 - 4.2 ml) are added to the resulting solution to obtain a mixed solution.

[0041] (2) Preparation of NUS-8 The mixed solution obtained in step (1) is ultrasonically treated (for 15 - 20 minutes). After the ultrasonication, the mixed solution is heated in a reaction kettle (at 120 °C). Among them, the oven heating temperature is 120 °C and the heating time is 24 h. After the reaction, the obtained milky white suspension is centrifuged and washed. Among them, the centrifugation speed is 8000 - 10000 r / min, the centrifugation time is about 5 - 7 min, and the centrifugation and washing operation is not less than 5 times. Subsequently, the washed black suspension is dried under vacuum at 150 °C to obtain NUS-8, or the washed milky white suspension is dropped with ethanol to prepare a NUS-8 dispersion with a certain concentration.

[0042] (3)Preparation of NUS-8 separation membrane The NUS-8 nanosheets are configured into an ethanol dispersion with a concentration of 0.1 mg·ml -1 −1. Take 10 ml of this dispersion and transfer the NUS-8 nanosheets to PAN-400 through a negative pressure sand core filtration device with a negative pressure of 0.9 bar to obtain a NUS-8 nanosheet separation membrane.

[0043] (4)Organic dye separation test The membrane separation performance of the NUS-8 nanosheet separation membrane is verified by a dead-end separation device. All measurements are carried out at room temperature and under the condition of a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane is obtained by collecting the filtrate within a certain time and averaging it, and each data point is obtained from three consecutive tests.

[0044] <Example 2> On the basis of the foregoing use of the NUS-8 nanosheet separation membrane for organic dye separation in the present invention, taking the method of further modifying the interlayer of the NUS-8 nanosheets with azobenzene-4-benzoic acid to finally form a NUS-8-Azobenzene nanosheet separation membrane with dynamic light response as an example, its preparation method includes the following steps: (1)Preparation of NUS-8 suspension: 0.128 mmol of ZrCl4 and 0.067 mmol of H3BTB are added to 15 ml of DMF to obtain a mixed solution. 4.0 ml of ultrapure water and 4.0 ml of formic acid are added to the mixed solution to obtain a mixed liquid. The above mixed liquid is ultrasonically treated for 15 minutes. After the ultrasonication, the mixed liquid is heated in a reaction kettle at 120 °C. After reacting for 24 h, the obtained milky white suspension is centrifuged and washed multiple times to finally obtain a uniformly dispersed NUS-8 nanosheet suspension.

[0045] (2)HCl treatment of NUS-8 suspension Take the above NUS-8 suspension and hydrochloric acid (15 mL; 11 mol·L-1) and mix them in a heat-resistant glass bottle. Sonicate for 10 minutes and heat at 80 °C for 12 hours. After the reaction, centrifuge and wash the resulting suspension multiple times to obtain a clean suspension with uniform dispersion.

[0046] (3) Preparation of NUS-8-Azobenzene Dissolve 58 mg of azobenzene-4-carboxylic acid in DMF (30 ml), mix it with the suspension obtained in step S2, and then heat the mixture in a reaction kettle (120 °C). After reacting for 12 h, centrifuge and wash the resulting orange suspension multiple times to finally obtain a suspension of NUS-8-Azobenzene nanosheets with uniform dispersion. Then dry the washed orange suspension under vacuum at 150 °C to obtain NUS-8-Azobenzene nanosheets, or drop the washed orange suspension into ethanol to prepare a dispersion of NUS-8-Azobenzene nanosheets.

[0047] (4)Preparation of NUS-8-Azobenzene Separation Membrane Prepare an ethanol dispersion of NUS-8-Azobenzene nanosheets with a concentration of 0.1 mg·ml -1 Take 10 ml of this dispersion and transfer NUS-8-Azobenzene nanosheets to PAN-400 through a negative pressure sand core filtration device with a negative pressure of 0.9 bar to obtain a NUS-8-Azobenzene nanosheet separation membrane.

[0048] (5)Organic Dye Separation Test The membrane separation performance of the NUS-8-Azobenzene nanosheet separation membrane was verified by a dead-end separation device. All measurements were carried out at room temperature and under a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane was obtained by collecting the filtrate over a certain period of time and averaging it. Each data point was obtained from three consecutive tests.

[0049] <Example 3> Based on the use of the NUS-8 nanosheet separation membrane for organic dye separation in the foregoing of the present invention, taking the method of further modifying the interlayer of NUS-8 nanosheets with azobenzene-4-carboxylic acid to finally form a NUS-8-Azobenzene nanosheet separation membrane with dynamic light response as an example, its preparation method includes the following steps: (1)Preparation of NUS-8 Suspension: 0.132 mmol of ZrCl4 and 0.071 mmol of H3BTB were added to 15 ml of DMF to obtain a mixed solution. 4.2 ml of ultrapure water and 4.2 ml of formic acid were added to the mixed solution, and the above mixed solution was ultrasonically treated for 20 minutes. After the ultrasonic treatment, the mixed solution was heated in a reaction kettle (130 °C). After reacting for 24 h, a milky white suspension was obtained, which was centrifuged and washed repeatedly, and finally a uniformly dispersed suspension of NUS-8 nanosheets was obtained.

[0050] (2)HCl treatment of the NUS-8 suspension The above NUS-8 suspension and hydrochloric acid (15 mL; 11 mol·L-1) were mixed in a heat-resistant glass bottle, ultrasonically treated for 10 - 15 minutes, and heated at 80 °C for 12 hours. After the reaction, the obtained suspension was centrifuged and washed repeatedly to obtain a uniformly dispersed clean suspension.

[0051] (3)Preparation of NUS-8-Azobenzene 60 mg of azobenzene-4-benzoic acid was dissolved in DMF (30 ml) and mixed with the suspension obtained in step S2. Subsequently, the mixed solution was heated in a reaction kettle at 130 °C. After reacting for 12 h, the obtained orange suspension was centrifuged and washed repeatedly, and finally a uniformly dispersed suspension of NUS-8-Azobenzene nanosheets was obtained. Subsequently, the washed orange suspension was dried under vacuum at 150 °C to obtain NUS-8-Azobenzene nanosheets, or the washed orange suspension was dropped into ethanol to prepare a dispersion of NUS-8-Azobenzene nanosheets.

[0052] (4)Preparation of the NUS-8-Azobenzene separation membrane The NUS-8-Azobenzene nanosheets were configured into an ethanol dispersion with a concentration of 0.2 mg·ml -1 . 10 ml of this dispersion was taken, and the NUS-8-Azobenzene nanosheets were transferred to PAN-400 through a negative pressure sand core filtration device under a negative pressure of 1.0 bar to obtain a NUS-8-Azobenzene nanosheet separation membrane.

[0053] (5)Separation test of organic dyes The membrane separation performance of the NUS-8-Azobenzene nanosheet separation membrane was verified through a dead-end separation device. All measurements were carried out at room temperature and under a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane was obtained by collecting the filtrate within a certain time and averaging it, and each data point was obtained from three consecutive tests.

[0054] <Example 4> Based on the above-mentioned use of the NUS-8 nanosheet separation membrane for the separation of organic dyes in the present invention, taking the method of further modifying the interlayer of NUS-8 nanosheets with azobenzene-4-benzoic acid to finally form a NUS-8-Azobenzene nanosheet separation membrane with dynamic light response as an example, its preparation method includes the following steps: (1) Preparation of NUS-8 suspension: Add 0.130 mmol of ZrCl4 and 0.069 mmol of H3BTB to 15 ml of DMF to obtain a mixed solution. Add 4.1 ml of ultrapure water and 4.1 ml of formic acid to the mixed solution, and ultrasonically treat the above mixed solution (15 - 20 minutes). After the ultrasonic treatment, place the mixed solution in a reaction kettle and heat it (150 °C). After reacting for 24 h, a milky white suspension will be obtained. Centrifuge and wash it multiple times to finally obtain a uniformly dispersed NUS-8 nanosheet suspension.

[0055] (2) Treatment of NUS-8 suspension with HCl Take the above NUS-8 suspension and hydrochloric acid (15 mL; 11 mol·L-1) and mix them in a heat-resistant glass bottle. Ultrasonically treat for 13 minutes and heat at 80 °C for 12 hours. After the reaction, centrifuge and wash the obtained suspension multiple times to obtain a uniformly dispersed clean suspension.

[0056] (3) Preparation of NUS-8-Azobenzene Dissolve 59 mg of azobenzene-4-benzoic acid in DMF (30 ml), and mix it with the suspension obtained in step S2. Subsequently, place the mixed solution in a reaction kettle and heat it (110 °C). After reacting for 12 h, centrifuge and wash the obtained orange suspension multiple times to finally obtain a uniformly dispersed NUS-8-Azobenzene nanosheet suspension. Subsequently, dry the washed orange suspension under vacuum at 150 °C to obtain NUS-8-Azobenzene nanosheets, or drop the washed orange suspension into ethanol to prepare a NUS-8-Azobenzene nanosheet dispersion.

[0057] (4) Preparation of NUS-8-Azobenzene separation membrane Prepare an ethanol dispersion of NUS-8-Azobenzene nanosheets with a concentration of 0.3 mg·ml -1 Take 10 ml of this dispersion and transfer NUS-8-Azobenzene nanosheets to PAN-400 through a negative pressure sand core suction filtration device with a negative pressure of 1.2 bar to obtain a NUS-8-Azobenzene nanosheet separation membrane.

[0058] (5)Separation Test of Organic Dyes The membrane separation performance of the NUS-8-Azobenzene nanosheet separation membrane was verified by a dead-end separation device. All measurements were carried out at room temperature and under a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane was obtained by collecting the filtrate over a certain period of time and averaging it. Each data point was obtained from three consecutive tests.

[0059] <Morphology and Structure Characterization of NUS-8-Azobenzene> Take 1 mL of the dispersion of the NUS-8-Azobenzene nanomaterial prepared in Example 2 and add it to centrifuge tubes respectively. Add 5 mL of ethanol for dilution. Take 6 microliters from each and drop it onto silicon wafers, and observe under a scanning electron microscope. Then, take another 1 mL of the dispersion of the NUS-8-Azobenzene nanomaterial prepared in Example 2 and add it to centrifuge tubes respectively. Add 10 mL of ethanol for dilution. Then take 10 microliters from each and drop it onto silicon wafers and copper grids, and observe under an atomic force microscope and a transmission electron microscope.

[0060] As Figure 1 shown in Figure 1 Figures (a) and (b), it can be seen from the scanning electron microscope (SEM) photos that the NUS-8-Azobenzene nanosheets stack to form a uniform and dense thin film, and the surface shows good flatness and uniformity.

[0061] As Figure 2 shown, it can be seen from the atomic force microscope (AFM) photos that the thickness of the NUS-8-Azobenzene nanosheets is about 4 nm.

[0062] As Figure 3 shown in Figure 3 Figures (a) and (b), it can be seen from the transmission electron microscope (TEM) photos the nanosheet structure of NUS-8-Azobenzene. Through its high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, it can be seen that in the NUS-8-Azobenzene nanosheets, the Zr6 clusters show obvious misalignments between adjacent layers, forming different Moiré patterns. This phenomenon may be related to the role of monodentate carboxylic acid molecules between layers, and these groups may cause this misalignment by changing the interlayer interaction forces.

[0063] 30 mg each of the NUS-8 and NUS-8-Azobenzene nanomaterials prepared in Examples 1 and 2 were respectively subjected to XRD tests. Then, 3 mg of the NUS-8 and NUS-8-Azobenzene nanomaterials prepared in Examples 1 and 2 were dissolved in a solution of D2O containing saturated K3PO4, and 0.5 ml of DMSO-d6 was added for 1H-NMR characterization. Another 5 mg each of the NUS-8 and NUS-8-Azobenzene nanomaterials prepared in Examples 1 and 2 were respectively subjected to Fourier transform infrared spectroscopy tests.

[0064] As Figure 4 shown, both NUS-8 and NUS-8-Azobenzene nanosheets exhibit similar characteristic peaks in the XRD pattern, indicating that after the azobenzene molecule modifies NUS-8, it still maintains good crystallinity. At the same time, the appearance of the multi-level diffraction peaks (100) / (010) proves good long-range order in the ab plane, and the weaker peak at (001) indicates poor long-range order along the c direction, which also conforms to the structural expectation of two-dimensional materials. At the same time, the corresponding (001) peak of the material shifts from 18.54° to 18.29° after modification. According to the Bragg equation calculation, the interplanar spacing of the (100) crystal plane increases from 6.87 Å to 7.57 Å, indicating that the monodentate carboxylic acid has successfully inserted into the interlayer of the NUS-8 nanosheets.

[0065] As Figure 5 shown, the characteristic signals of H3BTB were detected in NUS-8. For the digested NUS-8-Azobenzene sample, in addition to the characteristic peaks related to the H3BTB ligand that can be clearly identified, the representative ¹H NMR peaks of the monodentate azobenzene molecule also appear in the spectrum. These results further confirm the success of the modification process and confirm the effective binding between the monodentate carboxylic acid molecule and the surface of NUS-8.

[0066] As Figure 6 shown, there is an additional peak near 1653 cm -1 , which is attributed to the stretching vibration of the C=O bond formed by the coordination of the carboxyl group on the monodentate carboxylic acid with the metal center Zr + , proving the successful coordination of Zr ions with the monodentate azobenzene.

[0067] <Photoresponsiveness of NUS-8-Azobenzene> A. Verification of Photoresponsiveness As Figure 7As shown in Figure 7 (a), the original trans - conformation NUS - 8 - Azobenzene suspension exhibits a significant absorption peak at 350 nm, attributed to the π - π* transition of the azobenzene trans - structure; a weaker absorption peak is observed in the range of 400 - 500 nm, which belongs to the n - π* transition of the azobenzene cis - structure. Under 365 nm ultraviolet light irradiation, the intensity of the π - π* absorption band at 350 nm of the NUS - 8 - Azobenzene film decreases significantly; meanwhile, the intensity of the weak absorption band related to the n - π* transition increases. After 15 minutes of ultraviolet light irradiation, the system tends to a photo - stable state, and the maximum conformational conversion rate is observed to be 35%, indicating that the conformational transformation of azobenzene molecules in the NUS - 8 matrix is subject to certain structural constraints and this constraint is more significant in the film state( Figure 7 (b)). Through 10 minutes of visible light irradiation, the cis - to - trans conformational conversion can be fully achieved, further indicating that the NUS - 8 - Azobenzene film has reversible photo - responsiveness and can achieve switchable regulation of cis - trans conformations.

[0068] The NUS - 8 - Azobenzene nanosheets were configured into an ethanol dispersion with a concentration of 0.1 mg·ml -1 . Take 10 ml of this dispersion and transfer the NUS - 8 - Azobenzene nanosheets to PAN - 400 through a negative - pressure sand - core filtration device with a negative pressure of 0.9 bar to obtain the NUS - 8 - Azobenzene nanosheet separation membrane. The NUS - 8 - Azobenzene nanosheet separation membrane was installed in a dead - end separation device. All measurements were carried out at room temperature and under a transmembrane pressure of 5.0 bar. The solvent permeability of each membrane was obtained by collecting the filtrate over a certain period of time and averaging, and each data point was obtained from three consecutive tests.

[0069] As Figure 8 shown, when irradiated with 365 nm light for 10 min, the rejection rates of NUS - 8 - Azobenzene for six dyes (Congo Red, Rose Bengal, Acid Fuchsin, Methylene Blue, Rhodamine B, Acid Blue 25) all increase while the fluxes decrease. Among them, the flux of Congo Red increases significantly from 0.8 L·m⁻²·h⁻¹·bar⁻¹ to 15.9 L·m⁻²·h⁻¹·bar⁻¹, while maintaining a high rejection rate (>95%). This is evidence of the "trans - cis" conformational conversion of membrane azobenzene molecules in MOF. Due to the bending of azobenzene molecules, the interlayer distance decreases, and dye molecules are more likely to be blocked in the channels, resulting in an increase in the rejection rate.

[0070] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a MOF film material with dynamic light responsiveness, characterized in that: include: S1: adding ZrCl4 and 1,3,5-tri(4-carboxyphenyl)benzene to DMF to obtain a mixed solution A, adding ultrapure water and formic acid to the mixed solution A, mixing well and then heating to react to obtain a milky white suspension, centrifuging and washing the milky white suspension to obtain a NUS-8 nanosheet suspension; S2: After the NUS-8 nanosheet suspension is mixed with hydrochloric acid, it is subjected to heating reaction and centrifugal washing in sequence to obtain a uniformly dispersed suspension; S3: Azobenzene-4-benzoic acid is dissolved in DMF to obtain a mixed solution B. The mixed solution B is mixed with the suspension, and then heated to react to obtain an orange suspension. The orange suspension is centrifuged and washed to obtain a NUS-8-Azobenzene nanosheet suspension.

2. The method for preparing a MOF film material with dynamic light responsiveness according to claim 1, characterized in that: The molar ratio of ZrCl4 to 1,3,5-tri(4-carboxyphenyl)benzene is (1.9-2.1):1; the dosage ratio of ZrCl4 to DMF is 30-32 mg: 15 ml.

3. The method for preparing a MOF film material with dynamic light responsiveness according to claim 1, characterized in that: To the mixed solution A, 4.0-4.2 ml of ultrapure water and 4.0-4.2 ml of formic acid were added.

4. The method for preparing a MOF film material with dynamic light responsiveness according to claim 1, characterized in that: In S2, the concentration of the NUS-8 nanosheet suspension is 2.0-2.2 g·L -1 , the amount added is 15-17 ml, the concentration of hydrochloric acid solution is 1 mol·L -1 , the amount added is 15 mL.

5. The method for preparing a MOF film material with dynamic light responsiveness according to claim 1, characterized in that: In the S3, the usage ratio of azobenzene-4-benzoic acid to DMF is 58-60 mg: 30 ml.

6. The method for preparing a MOF film material with dynamic light responsiveness according to claim 1, characterized in that: The temperature of the heating reaction is 120°C-150°C.

7. A MOF film material with dynamic light responsiveness, characterized in that: The method is prepared by any one of claims 1 to 6.

8. A method for preparing a separation membrane with dynamic light responsiveness, characterized in that: The method is prepared by using the MOF film material with dynamic light responsiveness as claimed in claim 7, comprising: The NUS-8-Azobenzene nanosheets were prepared into an ethanol dispersion, and the ethanol dispersion was filtered through a negative pressure sand core filtration device to transfer the NUS-8-Azobenzene nanosheets onto PAN-400 to obtain a NUS-8-Azobenzene nanosheet separation membrane.

9. The method for preparing a separation membrane with dynamic light responsiveness according to claim 8, characterized in that: The concentration of the ethanol dispersion is 0.1-0.3 mg ml -1 , the negative pressure during the transfer of NUS-8-Azobenzene nanosheets was 0.9-1.2 bar.

10. A separation membrane with dynamic light responsiveness, characterized in that: The separation membrane is prepared by the preparation method according to any one of claims 8 or 9, and the thickness of the separation membrane is 330 to 400 nm.

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