Preparation and application of light-controlled conversion of MOF monolayer film

Abstract

The application discloses a preparation and application of a photo-controlled conversion MOF monolayer film formed by self-assembly of polymer-coated metal organic framework (MOF) nanoparticles. The method comprises the following steps: grafting an ATRP initiator onto the surface of ZIF-8 particles through a post-synthesis exchange reaction; grafting polymers onto the surface of ZIF-8 particles through a surface-initiated ATRP reaction of MMA and AAAB; self-assembling the ZIF-8 particles to form a dense MOF monolayer film at a water-air interface; covering the prepared MOF monolayer film on a large hole side of a polyethylene terephthalate (PET) film with multiple tapered nanochannels to form a hetero film, and detecting photo-controlled ion transmission properties of the hetero film. The application not only provides a new method for preparing a large-area, self-supporting functional MOF monolayer film, but also provides a new idea for preparing a photo-controlled ion channel device.

Description

Technical Field

[0001] This invention relates to the field of materials chemistry. Specifically, it relates to a method for preparing a light-controlled conversion MOF monolayer film by self-assembly of polymer-coated metal-organic framework (MOF) nanoparticles and its application in the field of light-controlled ion channel devices. Background Technology

[0002] In recent years, two-dimensional (2D) monolayers have attracted widespread attention in various applications such as separation, energy storage and conversion, proton conduction, solar cells, and electrochemical devices. Typically, 2D monolayers provide a large number of exposed surface atoms and active sites. Secondly, the edge effects of 2D monolayers can enhance their chemical activity. Furthermore, the very short mass transfer paths in 2D monolayers significantly accelerate molecular motion and improve separation flux. A prime example is graphene, which, after successful preparation using mechanical exfoliation, has achieved a series of unprecedented applications due to its unique properties, including its single-atom thickness, electronic confinement, and lateral crystal structure. In recent years, other monolayers with similar properties to graphene but different compositions, such as transition metal dichalcogenides, hexagonal boron nitride, metal oxides, and graphitic carbonitrides, have also seen rapid development.

[0003] As a new member of the 2D monolayer family, MOF monolayers possess advantages such as high crystallinity, high porosity, tunable pore size, and low mass transfer resistance, making them promising for applications in many different fields. Therefore, some two-dimensional MOF nanosheets have been developed; however, these nanosheets have very small lateral dimensions, preventing the formation of large-area monolayers. Dong and colleagues prepared large-area MOF monolayers, but the formation of such monolayers requires a solid substrate as support, preventing the formation of self-supporting films. Ruoff and colleagues used the Langmuir–Blodgett (L–B) technique to prepare large-area self-supporting MOF monolayers; however, the pressure applied at the water-air interface during film formation requires strict control, increasing the technical complexity and cumbersomeness of the operation. Recently, Cohen and colleagues used liquid-air interface technology to prepare a self-assembled MOF monolayer (SAMM) film. The prepared SAMM membrane is a dense, highly ordered, large-area self-supporting monolayer with an extremely thin thickness (~200 nm) and a high MOF content (87 wt%). This provides an effective method for preparing MOF monolayer membranes with high particle loading without the need for easily modified MOF ligands. However, the fragile nature of this SAMM membrane hinders its further processing, and the lack of functional groups on the film restricts its application in separation and sensing. Summary of the Invention

[0004] This invention aims to design and fabricate a MOF monolayer film with photocontrolled conversion properties. The method utilizes the self-assembly properties of polymer-coated ZIF-8 nanoparticles at the water-air interface to prepare the MOF monolayer film. The MOF monolayer film prepared by this invention can achieve reversible photocontrolled conversion under alternating irradiation with 365nm ultraviolet light and white light, providing a new approach for preparing other functional MOF monolayer films.

[0005] Another objective of this invention is to provide an application scheme for the self-assembly of polymer-coated MOF nanoparticles to form a light-controlled conversion MOF monolayer film. The method involves coating the macropore side of a PET film with a MOF monolayer film to prepare a porous heterostructure. This heterostructure film can achieve reversible switching of light-controlled ion channels, providing a new approach for fabricating novel light-controlled ion channel devices.

[0006] The objective of this invention is achieved through the following approach:

[0007] A method for self-assembling a light-controlled conversion MOF monolayer film from polymer-coated MOF nanoparticles is characterized by utilizing the evaporation-induced self-assembly of core-shell structured MOF particles at the water-air interface. The specific steps are as follows:

[0008] (1) Preparation of monodisperse ZIF-8 nanoparticles: 2-methylimidazole, hexadecyltrimethylammonium bromide (CTAB) and 25 mL of water were mixed in a 100 mL round-bottom flask. Zn(CH3COO)2·2H2O was dissolved in 25 mL of water and added to the round-bottom flask. The molar ratio of the reagents was 2-methylimidazole:Zn(CH3COO)2·2H2O:CTAB = 10:1:0.08. The mixture was gently stirred for 1 min and then allowed to stand at room temperature for 2 h. The crude product was centrifuged (8000 rpm, 10 min). The resulting solid was washed three times with 40 mL of methanol. The washed solid was dried in a vacuum drying oven at 40 °C for 12 h to obtain the product ZIF-8.

[0009] (2) Preparation of his-BiB: Histamine dihydrochloride, triethylamine and 400 mL of chloroform were mixed in a 1 L round-bottom flask; the mixture was stirred in an ice-water bath while bromoisobutyryl bromide was added dropwise to the mixture; the mixture was then reacted overnight at room temperature, with the reagent molar ratio of histamine dihydrochloride:triethylamine:bromoisobutyryl bromide = 1:5:2; after the reaction was completed, the reaction was quenched with 500 mL of 10% KOH aqueous solution, the solution was extracted with dichloromethane, the organic phase was collected and dried with anhydrous magnesium sulfate; the crude product was recrystallized with ethyl acetate to obtain the pure product his-BiB.

[0010] (3) Preparation of ZIF-8-BiB: ZIF-8, his-BiB and 40 mL of n-butanol were mixed in a 100 mL round-bottom flask and heated in an oil bath at a constant temperature of 100 °C for 4 h. The molar ratio of the reagents was ZIF-8:his-BiB = 1:1. After the reaction was completed, the crude product was centrifuged (8000 rpm, 10 min). The obtained solid was washed three times with 40 mL of methanol. The washed solid was dried in a vacuum drying oven at a temperature of 40 °C for 12 h to obtain the product ZIF-8-BiB.

[0011] (4) Preparation of ZIF-8-P(MMA-co-AAAB): ZIF-8-BiB was mixed with 100 mL of methanol in a 250 mL round-bottom flask, and MMA, AAAB, Me6TREN and CuBr were added in sequence. The molar ratio of the reagents was MMA:AAAB:Me6TREN:CuBr:initiator = 1600:100:2:2:1. The mixture was degassed by three cycles of freezing-evacuation-thawing and then reacted at room temperature for 24 h. After the reaction was completed, the crude product was centrifuged (8000 rpm, 10 min). The obtained solid was washed three times with 40 mL of methanol and then once with 40 mL of toluene. The washed solid was dried in a vacuum drying oven at 60 °C for 12 h to obtain the product ZIF-8-P(MMA-co-AAAB).

[0012] (5) Mix 30 mg ZIF-8-P (MMA-co-AAAB) nanoparticles with 1 mL toluene in a small glass bottle, and then sonicate for 40 min; take 10 μL of the above MOF solution and drop it into a culture dish with a diameter of 35 mm and a water depth of 1 cm. After drying at room temperature for 3 min, a SAMM film is formed on the water surface.

[0013] This invention proposes an application scheme for a photocontrolled conversion MOF monolayer film formed by the self-assembly of polymer-coated MOF nanoparticles, including the preparation of a porous heterostructure film and its reversible photocontrolled ion channel switching properties. The specific steps are as follows:

[0014] (1) Preparation of heterogeneous membrane: PET membrane with multiple conical nanochannels was selected as substrate; SAMM membrane was covered on the macropore side of PET membrane.

[0015] (2) Fix the heterogeneous film between two transparent acrylic modules, and then fix the modules on the self-made current testing device.

[0016] (3) Add 0.7 mL of 0.01 M MgCl2 solution to the flow channels on both sides of the acrylic module as electrolytes and record the current.

[0017] (4) Irradiate the heterostructure with 365nm ultraviolet light for 30 minutes and record the current. Then irradiate the heterostructure with white light for 1 hour and record the current.

[0018] The method employed in this invention is as follows: ATRP initiators are grafted onto the surface of ZIF-8 particles via a post-synthetic exchange reaction; polymers are grafted onto the surface of ZIF-8 particles via an ATRP reaction initiated by the surface of methyl methacrylate (MMA) and 4-acrylamidoazobenzene (AAAB); ZIF-8 particles self-assemble at the water-air interface to form a dense MOF monolayer film; the prepared MOF monolayer film is then coated onto the macropore side of a polyethylene terephthalate (PET) film with multiple conical nanochannels to form a heterogeneous film, and its photocontrolled ion transport properties are detected.

[0019] This invention not only provides a new method for preparing large-area, self-supporting functional MOF monolayer films, but also offers new ideas for preparing photocontrolled ion channel devices.

[0020]

[0021] The beneficial effects of this invention are as follows:

[0022] (1) The MOF monolayer film with light-controlled conversion properties prepared by the water-air interface technology in this invention provides a new solution for preparing functional MOF monolayer films;

[0023] (2) This invention combines a MOF monolayer membrane with light-controlled conversion properties with a PET membrane with multiple conical nanochannels to prepare a porous heterostructure membrane with light-controlled ion channel switching properties, providing a new approach for preparing novel light-controlled ion channel devices. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used 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 should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 SEM image of monodisperse ZIF-8 nanoparticles.

[0026] Figure 2 For his-BiB 1 H NMR spectrum.

[0027] Figure 3 The acid hydrolysis product of ZIF-8-BiB 1 H NMR spectrum.

[0028] Figure 4 The acid hydrolysis product of ZIF-8-P(MMA-co-AAAB) 1 H NMR spectrum.

[0029] Figure 5 SEM images (a, b) and energy dispersive spectroscopy (EDS) spectra of the SAMM film (c).

[0030] Figure 6 The UV-vis spectrum of the SAMM film (a) and its photo-induced isomerization cycle (b) are shown.

[0031] Figure 7 SEM images of the porous PET membrane (a) and the heterogeneous membrane (b), IV curves (c), and a schematic diagram of the acrylic module (d) are shown.

[0032] Figure 8 The diagram shows the IV curve of the heterogeneous membrane (a) and the schematic diagram of the photocontrolled ion current switching cycle (b). Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0034] The raw materials and equipment used in the embodiments of this invention are as follows: Histamine dihydrochloride (98%), α-bromoisobutyryl bromide (98%), tris(2-dimethylaminoethyl)amine (Me6TREN, 98%), and copper bromide (CuBr, AR) were purchased from Aladdin Reagent (Shanghai) Co., Ltd. 2-Methylimidazole (97%) and hexadecyltrimethylammonium bromide (CTAB, AR) were purchased from TCI (Shanghai) Chemical Industry Development Co., Ltd. Methyl methacrylate (MMA, 99%) was purchased from Alfaesa (China) Chemical Co., Ltd. 4-Aminoazobenzene (98%) was purchased from Bailingwei Technology Co., Ltd. Acryloyl chloride (98%) was purchased from Adamas Reagent Co., Ltd. PET film (3cm in diameter, 12μm in thickness) was purchased from Beijing Huidexin Technology Co., Ltd. 1H NMR spectroscopy (… 1HNMR was recorded using a BRUKER AVANCE III 400MHz spectrometer. UV-Vis spectra were recorded using a PerkinElmer Lambda 365 spectrophotometer. Scanning electron microscopy (SEM) images were recorded using a Flex SEM 1000Ⅱ scanning electron microscope. Transmission electron microscopy (TEM) images were recorded using a JEOL JEM-2100 transmission electron microscope. I-V curves were recorded using a Keithley 6487 picoammeter. Unless otherwise specified in the examples, conditions were performed under standard conditions or as recommended by the manufacturer. Reagents and instruments not explicitly named were commercially available products.

[0035] Synthesis of AAAB: 1.97 g of 4-aminoazobenzene, 1.23 g of triethylamine, and 50 mL of dichloromethane were mixed in a container. Acryloyl chloride (1.10 g) was then added dropwise with stirring in an ice-water bath. The mixture was stirred overnight at room temperature. After the reaction was complete, the precipitate was removed by filtration. The filtrate was concentrated and purified by column chromatography using a mixed solvent of petroleum ether and ethyl acetate (volume ratio of petroleum ether to ethyl acetate was 3:2). AAAB was obtained.

[0036] Example 1

[0037] Preparation of monodisperse ZIF-8 nanoparticles

[0038] SEM images of monodisperse ZIF-8 nanoparticles are as follows: Figure 1 As shown in the figure, ZIF-8 nanoparticles exist in a single dispersed form with a particle size of 180±20 nm. 2-Methylimidazole (5.3 g), CTAB (196.8 mg), and 25 mL of water were mixed in a 100 mL round-bottom flask. Zn(CH3COO)2·2H2O (1.5 g) was dissolved in 25 mL of water and added to the flask. The mixture was stirred for 1 min and then allowed to stand at room temperature for 2 h. The crude product was centrifuged (8000 rpm, 10 min), and the resulting solid was washed three times with 40 mL of methanol. The washed solid was then dried in a vacuum drying oven at 40 °C for 12 h to obtain the product ZIF-8.

[0039] Example 2

[0040] Preparation of his-BiB

[0041] his-BiB 1 H NMR spectrum as shown Figure 2As shown in the figure, the chemical shift and integral area of ​​the corresponding proton absorption peak in his-BiB can be seen, proving the successful synthesis of his-BiB. Histamine dihydrochloride (5.0 g), triethylamine (12.7 g), and 400 mL of chloroform were mixed in a 1 L round-bottom flask; the mixture was stirred in an ice-water bath, and 12.7 g of bromoisobutyryl bromide was added dropwise to the mixed solution. The mixture was then placed at room temperature for 12 h; after the reaction was completed, the reaction was quenched with 500 mL of 10% KOH aqueous solution, the solution was extracted with dichloromethane, the organic phase was collected, and dried with anhydrous magnesium sulfate; the crude product was recrystallized from ethyl acetate to obtain the pure product his-BiB.

[0042] Example 3

[0043] Preparation of ZIF-8-BiB

[0044] ZIF-8-BiB acid hydrolysis products 1 H NMR spectrum as shown Figure 3 As shown in the figure, the proton peaks corresponding to 2-methylimidazole and his-BiB are present in the same spectrum, proving the successful synthesis of ZIF-8-BiB. The grafting ratio of his-BiB was calculated to be approximately 2.3% by integrating the area. ZIF-8 (200 mg) prepared in Example 1 and his-BiB (455.4 mg) prepared in Example 2 were mixed with 40 mL of n-butanol in a 100 mL round-bottom flask and heated in an oil bath at a constant temperature of 100 °C for 4 h. After the reaction was completed, the crude product was centrifuged (8000 rpm, 10 min), and the resulting solid was washed three times with 40 mL of methanol. The washed solid was then dried in a vacuum drying oven at a temperature of 40 °C for 12 h to obtain the product ZIF-8-BiB. 10.0 mg of dried ZIF-8-BiB particles were immersed in a mixed solvent of 480 μL MeOD and 20 μL L2SO4 (98% by mass), and then the mixture was sonicated until the solution became clear, thus obtaining the acid hydrolysis product of ZIF-8-BiB.

[0045] Example 4

[0046] Preparation of ZIF-8-P(MMA-co-AAAB)

[0047] Acid hydrolysis products of ZIF-8-P(MMA-co-AAAB) 1 H NMR spectrum as shown Figure 4As shown, the content of azophenyl groups in the copolymer was calculated to be approximately 6 mol% based on the integrated area of ​​the proton peak in the figure. ZIF-8-BiB (100 mg) prepared in Example 3 was mixed with 100 mL of methanol in a 250 mL round-bottom flask, and MMA (3.2 g), AAAB (502.6 mg), Me6TREN (9.2 mg), and CuBr (5.7 mg) were added sequentially. The mixture was then frozen with liquid nitrogen for 10 min, evacuated with an oil pump for 1 min, and then thawed naturally at room temperature. This freezing-evacuation-thawing cycle was repeated three times, and the mixture was then reacted at room temperature for 24 h. After the reaction, the crude product was centrifuged (8000 rpm, 10 min), and the resulting solid was washed three times with 40 mL of methanol, and then once with 40 mL of toluene. The washed solid was dried in a vacuum drying oven at 60 °C for 12 h to obtain the product ZIF-8-P (MMA-co-AAAB) (particle size 220 ± 20 nm). 20.0 mg of dried ZIF-8-P (MMA-co-AAAB) particles were immersed in a mixed solvent of 480 μL MeOH and 20 μL H2SO4 (98% by mass), and then the mixture was sonicated for 20 min. The precipitate was collected by centrifugation (8000 rpm, 5 min), and the resulting solid was washed three times with 30 mL MeOH and once with 10 mL toluene. It was then dried in a vacuum dryer at 40 °C for 12 h to obtain the acid hydrolysis product P (MMA-co-AAAB).

[0048] Example 5

[0049] Preparation of SAMM membrane.

[0050] SEM images of SAMM membranes as follows Figure 5 As shown in Figure a, the rolled-up film can be seen; Figure b shows the tight arrangement of nanoparticles on the film surface; and the presence of C, N, O, and Zn elements in Figure c indicates that the SAMM film is formed by the stacking of ZIF-8 particles coated with copolymer. 30 mg of ZIF-8-P (MMA-co-AAAB) nanoparticles prepared in Example 4 were mixed with 1 mL of toluene in a small glass bottle and then sonicated for 40 min. 10 μL of the above MOF solution was dropped into a 35 mm diameter petri dish filled with water to a depth of 1 cm. After drying at room temperature for 3 min, a SAMM film with a diameter of approximately 30 mm formed on the water surface. Its thickness was the same as the particle size, approximately 220 nm, indicating that the SAMM film was formed by the tight stacking of a single layer of ZIF-8 particles.

[0051] Example 6

[0052] UV-vis spectrum and light-controlled conversion properties of SAMM film were tested.

[0053] A schematic diagram of the UV-vis spectrum and photo-induced isomerization cycle of the SAMM film is shown below. Figure 6 As shown in the figure, the SAMM film contains two characteristic peaks. The strong peak at 352 nm is generated by the π–π* transition of trans-azobenzene, while the weak peak at 440 nm is attributed to its n–π* transition. Furthermore, the SAMM film exhibits reversible photoisomerization properties, returning to its initial state after five photoisomerization cycles. Using an opaque white board parallel to the water surface, the SAMM film was lifted from below and removed from the water, then dried at room temperature. The film was then irradiated with 365 nm ultraviolet light (UV lamp, 100W, working distance 3.5cm) for 1 min, and the UV-Vis spectrum was recorded. Finally, the film was irradiated with white light (LED flashlight, maximum power 10W, working distance 3.5cm) for 2 min, and the UV-Vis spectrum was recorded again.

[0054] Example 7

[0055] Preparation of heterogeneous membranes

[0056] SEM images of the surfaces of PET and the heterogeneous film, I-V curves, and schematic diagrams of the acrylic module are shown below. Figure 7 As shown in the figure, the SAMM membrane completely covers the opening of the PET membrane in the heterogeneous membrane, and the current value of the heterogeneous membrane is significantly reduced. After vertically irradiating both sides of the PET membrane with 365nm ultraviolet light for 30 minutes (irradiation distance 5cm), it was clamped into a test mold (e.g., Figure 7As shown in d, the mold consists of two transparent acrylic rectangular blocks. One side surface of each block is placed opposite the other. A transparent acrylic cylindrical protrusion is positioned opposite each other on the opposite surface of each block. The cylindrical protrusions on the two blocks are positioned opposite each other. A circular through-hole with an axis of 5mm in diameter, shaped like an "L," is provided between the end face of the cylindrical protrusion and the upper surface of the block containing the protrusion, serving as a flow channel (volume 0.7mL). The ports of the circular through-holes on the two cylindrical protrusions are positioned opposite each other. Two vertically downward through-holes C are provided on the upper surface of each of the two rectangular blocks, connecting the upper surface and the circular through-hole, serving as pressure balancing channels. The membrane to be treated or tested is clamped between the cylindrical protrusions of the two rectangular blocks, with both sides of the membrane tightly bonded to the surfaces of the cylindrical protrusions of the two rectangular blocks. The ports of the circular through-holes on the cylindrical protrusions are positioned opposite each other on both sides of the membrane. 0.7 mL of NaOH solution (9 M concentration) was added to the left flow channel of the mold as an etching solution, and 0.7 mL of a mixed solution of formic acid (1 M concentration) and potassium chloride (1 M concentration) was added to the right flow channel as a blocking solution. Pt electrodes were placed in the electrolyte solutions in the two flow channels respectively. After etching for 30 min at a constant temperature of 45℃ and a voltage of 1V, the etched PET film was removed from the mold, and the solution on the film surface was rinsed off with deionized water. The film was then immersed in deionized water for later use. The diameter of the large opening (upper base) of the etched frustum-shaped nanochannel was approximately 500 nm, and the diameter of the small opening (lower base) was approximately 40 nm. To prepare a heterogeneous membrane composed of PET and SAMM, the PET membrane was first removed from deionized water and then immersed in water below the SAMM membrane prepared in Example 5, with the surface of the PET membrane facing upward and the surface of the SAMM membrane parallel to the surface of the SAMM membrane. The PET membrane and SAMM membrane were simultaneously lifted out of the water in a direction perpendicular to the water surface and placed in a covered petri dish. The petri dish was then placed in a vacuum drying oven at a constant temperature of 60°C and heated for 30 minutes before being removed to obtain the heterogeneous membrane.

[0057] Example 8

[0058] Photocontrolled ion current switching test of heterogeneous membrane

[0059] The I-V curves of the heterostructure and the schematic diagram of the photocontrolled ion current switching cycle are shown below. Figure 8As shown in the figure, after 30 minutes of UV irradiation, the current value of the heterostructure at -2V increases to 5.3 times the initial current value. After 1 hour of white light irradiation, the current value at -2V returns to the initial current value. Furthermore, the light switching of the ion current can be repeated at least 3 times in the heterostructure without significantly reducing its switching performance. The heterogeneous membrane was fixed between the two cylindrical protrusions of the test mold described in Example 7, and then the test mold was fixed (the test point is the position of the central hole). 0.7 mL of MgCl2 solution (concentration of 0.01 M) was added to the flow channels on both sides of the mold as electrolytes. Pt electrodes were placed in the electrolyte solutions in the two flow channels respectively. A voltage range of -2 V to +2 V was applied to the solution through the Pt electrodes, and the transmembrane current of ions was recorded using a picoammeter. The SAMM side of the heterogeneous membrane was vertically irradiated with 365 nm ultraviolet light (ultraviolet lamp, power of 100 W, working distance of 3.5 cm) for 30 min, and the ion current was recorded. Then, the SAMM side of the heterogeneous membrane was vertically irradiated with white light (LED flashlight, maximum power of 10 W, working distance of 3.5 cm) for 1 h, and the ion current was recorded.

[0060] In summary, this invention designs and prepares a photo-controlled switching MOF monolayer film formed by the self-assembly of polymer-coated MOF nanoparticles. This type of film, formed through evaporation-induced self-assembly of MOF particles at the water-air interface, is a highly dense (MOF particles are closely packed and closely aligned) and extremely thin (~220 nm) film. The SAMM film prepared by this invention can achieve reversible cyclic photo-controlled switching under alternating irradiation with 365 nm ultraviolet and white light, providing a new approach for preparing functionalized MOF monolayer films. Furthermore, by coating the prepared MOF monolayer film onto a PET film with multiple conical nanochannels, a heterostructure film with photo-controlled ion current switching properties can be prepared, providing a new approach for preparing photo-controlled ion channel devices.

Claims

1. A method for preparing a light-controlled conversion MOF monolayer film, characterized in that: This method involves the self-assembly of polymer-coated MOF nanoparticles at the water-air interface. The specific steps are as follows: (1) Mix 28-33 mg of polymer-coated ZIF-8 nanoparticles with 0.7-1.2 mL of toluene in a container, and then sonicate for 30-60 min; (2) Take 10-15 μL of the MOF solution prepared in step (1) and drop it into water in a culture dish with a diameter ≥35 mm and a water depth >300 nm. After drying at room temperature for 1-6 min, a light-controlled conversion MOF monolayer film with a thickness equal to the particle size of the nanoparticles is formed on the water surface. The ZIF-8 polymer-coated in step (1) is ZIF-8-P (MMA- co -AAAB) is a functional polymer grafted onto the surface of ZIF-8 particles via surface atom transfer radical polymerization (ATRP) initiated by methyl methacrylate (MMA) and 4-acrylamidoazobenzene (AAAB).

2. The preparation method according to claim 1, characterized in that: The method involves the self-assembly of polymer-coated MOF nanoparticles at the water-air interface, and the specific steps are as follows: (1) Mix 29-32 mg of polymer-coated ZIF-8 nanoparticles with 0.8-1.1 mL of toluene in a container, and then sonicate for 35-55 min; (2) Take 11-14 μL of the MOF solution prepared in step (1) and drop it into water in a culture dish with a diameter ≥35 mm and a water depth >1 cm. After drying at room temperature for 2-5 min, a light-controlled conversion MOF monolayer film with a thickness equal to the particle size of the nanoparticles is formed on the water surface.

3. The preparation method according to claim 1, characterized in that: The method involves the self-assembly of polymer-coated MOF nanoparticles at the water-air interface, and the specific steps are as follows: (1) Mix 30-31 mg of polymer-coated ZIF-8 nanoparticles with 0.9-1.0 mL of toluene in a container, and then sonicate for 40-50 min; (2) Take 12-13 μL of the MOF solution prepared in step (1) and drop it into water in a culture dish with a diameter ≥35 mm and a water depth >1 cm. After drying at room temperature for 3-4 min, a light-controlled conversion MOF monolayer film with a thickness equal to the particle size of the nanoparticles is formed on the water surface.

4. The preparation method according to any one of claims 1-3, characterized in that: In step (1), ZIF-8-P (MMA- co The specific synthesis steps for -AAAB are as follows: 1) Synthesis of AAAB: 1.90-2.00 g of 4-aminoazobenzene, 1.20-1.30 g of triethylamine, and 50-80 mL of dichloromethane were mixed in a container. Then, 1.10-1.20 g of acryloyl chloride was added dropwise under stirring in an ice-water bath. The mixture was stirred at room temperature for 12-24 h. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was concentrated and purified by column chromatography. 2) Mix 95-105 mg of ZIF-8 modified with ATRP initiator (represented as ZIF-8-BiB) with 95-105 mL of methanol in a container, and then add 3.0-4.0 g of MMA, 500-510 mg of AAAB, 9.0-10.0 mg of tris(2-dimethylaminoethyl)amine Me6TREN, and 5.0-6.0 mg of CuBr in sequence. 3) Freeze the mixture in step 2) with liquid nitrogen for 10-20 min, evacuate the mixture with an oil pump for 1-10 min, and then thaw the mixture naturally at room temperature; repeat the above freezing-evacuation-thawing operation 2-5 times, and then place the mixture at room temperature to react for 18-26 h. 4) After the reaction is complete, centrifuge the crude product at 7000-10000 rpm for 10-20 min. Wash the obtained solid with methanol and then with toluene. 5) The cleaned solid from step 4) is dried in a vacuum drying oven at 50–80°C for 10–15 hours to obtain the product ZIF-8-P (MMA- co -AAAB), with a particle size of 200-240 nm.

5. The preparation method according to any one of claims 1-3, characterized in that, In step (1), ZIF-8-P (MMA- co The specific synthesis steps for -AAAB are as follows: 1) Synthesis of AAAB: 1.92-1.98 g of 4-aminoazobenzene, 1.22-1.28 g of triethylamine, and 60-75 mL of dichloromethane were mixed in a container. Then, 1.12-1.18 g of acryloyl chloride was added dropwise under stirring in an ice-water bath. The mixture was stirred at room temperature for 14-20 h. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was concentrated and purified by column chromatography. 2) ZIF-8 modified with ATRP initiator, denoted as ZIF-8-BiB, was mixed with 97-103 mg of methanol in a container, followed by the sequential addition of MMA 3.2-3.8 g, AAAB 502-508 mg, tris(2-dimethylaminoethyl)amine Me6TREN 9.2-9.8 mg, and CuBr 5.2-5.8 mg. 3) Freeze the mixture in step 2) with liquid nitrogen for 12–18 min, evacuate with an oil pump for 2–8 min, and then thaw the mixture naturally at room temperature; repeat the above freezing-evacuation-thawing operation 2–5 times, and then place the mixture at room temperature to react for 19–25 h. 4) After the reaction is complete, the crude product is centrifuged at 7500–9000 rpm for 12–18 min. The resulting solid is washed with methanol and then with toluene. 5) Place the cleaned solid from step 4) in a vacuum drying oven at 55-70℃ and dry for 11-14 hours to obtain the product ZIF-8-P(MMA- co -AAAB), with a particle size of 200−240 nm.

6. The preparation method according to any one of claims 1-3, characterized in that, In step (1), ZIF-8-P (MMA- co The specific synthesis steps for -AAAB are as follows: 1) Synthesis of AAAB: 1.94-1.96 g of 4-aminoazobenzene, 1.24-1.26 g of triethylamine, and 65-70 mL of dichloromethane were mixed in a container. Then, 1.14-1.16 g of acryloyl chloride was added dropwise under stirring in an ice-water bath. The mixture was stirred at room temperature for 16-18 h. After the reaction was completed, the precipitate was removed by filtration, and the filtrate was concentrated and purified by column chromatography. 2) ZIF-8 modified with ATRP initiator, denoted as ZIF-8-BiB, 99-101 mg was mixed with 99-101 mL of methanol in a container, followed by the sequential addition of MMA 3.4-4.6 g, AAAB 504-506 mg, tris(2-dimethylaminoethyl)amine Me6TREN 9.4-9.6 mg, and CuBr 5.4-5.6 mg; 3) Freeze the mixture in step 2) with liquid nitrogen for 14-16 min, evacuate with an oil pump for 4-6 min, and then thaw the mixture naturally at room temperature; repeat the above freezing-evacuation-thawing operation 2-5 times, and then place the mixture at room temperature to react for 20-24 h. 4) After the reaction is complete, the crude product is centrifuged at 8000–8500 rpm for 14–16 min. The resulting solid is washed with methanol and then with toluene. 5) The cleaned solid from step 4) is dried in a vacuum drying oven at 60-65℃ for 12-13 hours to obtain the product ZIF-8-P(MMA- co -AAAB), with a particle size of 200−240 nm.

7. The preparation method according to claim 4, characterized in that, The ZIF-8-BiB in step 2) is prepared by a post-synthetic exchange reaction of ZIF-8 and the ATRP initiator, represented as his-BiB. The specific steps are as follows: (1) Mix ZIF-8 195-205 mg, his-BiB 450-460 mg and 35-45 mL n-butanol in a container and heat in an oil bath at a constant temperature of 90–110℃ for 3–6 h. (2) After the reaction is complete, the crude product is centrifuged at 6000-10000 rpm for 10-20 min, and the resulting solid is washed with methanol. (3) After cleaning the solid in step (2), place it in a vacuum drying oven with a temperature of 30-60℃ and dry it for 10-15 hours to obtain the product ZIF-8-BiB.

8. The preparation method according to claim 4, characterized in that, The ZIF-8-BiB in step 2) is prepared by a post-synthetic exchange reaction of ZIF-8 and the ATRP initiator, represented as his-BiB. The specific steps are as follows: (1) Mix ZIF-8 197-203 mg, his-BiB 452-458 mg and 37-43 mL n-butanol in a container and heat in an oil bath at a constant temperature of 95-105℃ for 3.5-5 h. (2) After the reaction is complete, the crude product is centrifuged at 7000-9000 rpm for 12-18 min, and the resulting solid is washed with methanol. (3) After cleaning the solid in step (2), place it in a vacuum drying oven with a temperature of 35-50℃ and dry it for 11-14 hours to obtain the product ZIF-8-BiB.

9. The preparation method according to claim 4, characterized in that, The ZIF-8-BiB in step 2) is prepared by a post-synthetic exchange reaction of ZIF-8 and the ATRP initiator, represented as his-BiB. The specific steps are as follows: (1) Mix ZIF-8 199-201 mg, his-BiB 454-456 mg and 39-41 mL n-butanol in a container and heat in an oil bath at a constant temperature of 98-102℃ for 4-4.5 h. (2) After the reaction is complete, the crude product is centrifuged at 8000-8500 rpm for 14-16 min, and the resulting solid is washed with methanol. (3) After cleaning the solid in step (2), place it in a vacuum drying oven with the temperature set at 40-45℃ and dry it for 12-13 hours to obtain the product ZIF-8-BiB.

10. The preparation method according to claim 4, characterized in that, The specific steps for preparing monodisperse ZIF-8 nanoparticles and his-BiB are as follows: (1) Preparation of monodisperse ZIF-8 nanoparticles: 5.0-6.0 g of 2-methylimidazole, 190-200 mg of hexadecyltrimethylammonium bromide (CTAB) and 20-30 mL of water were mixed in a container. 1.4-1.6 g of Zn(CH3COO)2•2H2O was dissolved in 24-26 mL of water and added to the container. The mixture was stirred for 1.4-1.6 min and then allowed to stand at room temperature for 2.0-3.0 h. The crude product was centrifuged at 7000-10000 rpm for 10-20 min, and the resulting solid was washed with methanol. The washed solid was dried in a vacuum drying oven at 30-60℃ for 10-15 h to obtain product ZIF-8 with a particle size of 160-200 nm. (2) Preparation of his-BiB: 4.5-5.5 g of histamine dihydrochloride, 12.0-13.0 g of triethylamine and 350-450 mL of chloroform were mixed in a container; the mixture was stirred in an ice-water bath, and 12.0-13.0 g of α-bromoisobutyryl bromide was added dropwise to the mixed solution. The mixed solution was then placed at room temperature and reacted overnight; after the reaction was completed, the reaction was quenched with 400-600 mL of 10-20% KOH aqueous solution, the solution was extracted with dichloromethane, the organic phase was collected and dried with anhydrous magnesium sulfate; the crude product was recrystallized with ethyl acetate to obtain the pure product his-BiB.

11. The preparation method according to claim 4, characterized in that, The specific steps for preparing monodisperse ZIF-8 nanoparticles and his-BiB are as follows: (1) Preparation of monodisperse ZIF-8 nanoparticles: 5.2-5.8 g of 2-methylimidazole, 192-198 mg of hexadecyltrimethylammonium bromide (CTAB), and 22-28 mL of water were mixed in a container. 1.2-1.8 g of Zn(CH3COO)2•2H2O was dissolved in 22-28 mL of water and added to the container. The mixture was stirred for 1.2-1.8 min and then allowed to stand at room temperature for 2.2-2.8 h. The crude product was centrifuged at 7500-9000 rpm for 12-18 min, and the resulting solid was washed with methanol. The washed solid was dried in a vacuum drying oven at 35-50℃ for 11-14 h to obtain product ZIF-8 with a particle size of 160-200 nm. (2) Preparation of his-BiB: 4.7-5.3 g of histamine dihydrochloride, 12.2-12.8 g of triethylamine and 370-430 mL of chloroform were mixed in a container; the mixture was placed in an ice-water bath and stirred, while 12.2-12.8 g of α-bromoisobutyryl bromide was added dropwise to the mixed solution, and then the mixed solution was placed at room temperature and reacted overnight; after the reaction was completed, the reaction was quenched with 450-550 mL of 12-18% KOH aqueous solution, the solution was extracted with dichloromethane, the organic phase was collected and dried with anhydrous magnesium sulfate; the crude product was recrystallized with ethyl acetate to obtain the pure product his-BiB.

12. The preparation method according to claim 4, characterized in that, The specific steps for preparing monodisperse ZIF-8 nanoparticles and his-BiB are as follows: (1) Preparation of monodisperse ZIF-8 nanoparticles: 5.4-5.6 g of 2-methylimidazole, 192-198 mg of hexadecyltrimethylammonium bromide (CTAB), and 24-26 mL of water were mixed in a container. 1.4-1.6 g of Zn(CH3COO)2•2H2O was dissolved in 24-26 mL of water and added to the container. The mixture was stirred for 1.4-1.6 min and then allowed to stand at room temperature for 2.4-2.6 h. The crude product was centrifuged at 8000-8500 rpm for 14-16 min, and the resulting solid was washed with methanol. The washed solid was dried in a vacuum drying oven at 40-45℃ for 12-13 h to obtain product ZIF-8 with a particle size of 160-200 nm. (2) Preparation of his-BiB: 4.9-5.1 g of histamine dihydrochloride, 12.4-12.6 g of triethylamine and 390-410 mL of chloroform were mixed in a container; the mixture was stirred in an ice-water bath, and 12.4-12.6 g of α-bromoisobutyryl bromide was added dropwise to the mixed solution. The mixed solution was then placed at room temperature and reacted overnight; after the reaction was completed, the reaction was quenched with 480-520 mL of 14-16% KOH aqueous solution, the solution was extracted with dichloromethane, the organic phase was collected and dried with anhydrous magnesium sulfate; the crude product was recrystallized with ethyl acetate to obtain the pure product his-BiB.

13. A light-controlled conversion MOF monolayer film prepared by any one of claims 1-12.

14. An application of the photoconversion MOF monolayer film formed by the self-assembly of polymer-coated MOF nanoparticles as described in claim 13, characterized in that: It is used in photocontrolled ion channel devices.

15. The application according to claim 14, characterized in that: A heterogeneous membrane, constructed by stacking a light-controlled conversion MOF monolayer with a PET membrane, is applied to light-controlled ion channel devices.

16. The application according to claim 15, characterized in that: The ion current was recorded using a picoammeter, and the specific steps are as follows: (1) Preparation of heterogeneous membranes; (2) Fix the heterogeneous membrane between two block-shaped transparent acrylic modules. Set corresponding through holes on the two acrylic modules on both sides of the heterogeneous membrane as flow channels. One port of each flow channel is set on both sides of the heterogeneous membrane. The heterogeneous membrane between the two corresponding flow channel ports is the actual test area. The diameter of the flow channel port is 5 mm. Add 0.7 mL of 0.01 M MgCl2 solution to the flow channels on both sides of the acrylic module as electrolytes. Place Pt electrodes in the electrolyte solutions in the two flow channels. Apply a scanning voltage from -2 V to +2 V through the Pt electrodes as the transmembrane potential. (3) Record the current using a picoammeter: First, irradiate the heterostructure with 365 nm ultraviolet light for 30 min. The ultraviolet lamp power is 100W, and the working distance is 3.5 cm. Record the current value. Then, irradiate the heterostructure with white light for 1 h. The white light is an LED flashlight with a maximum power of 10W and a working distance of 3.5 cm. Record the current value. The preparation of the heterogeneous membrane in step (1) is as follows: 1) Select a PET membrane with multiple frustoconical nanochannels as the substrate; The pore density of the frustum-shaped nanochannels is 1 × 10⁻⁶. 6 -1 × 10 7 pores·cm −2 The average diameter of the macropores is 500-600 nm, the average diameter of the micropores is 40-50 nm, the diameter of the PET membrane is 0.6-3.0 cm, and the thickness is 11-12 μm. 2) The SAMM film is stacked on the large pore side of the PET film to form a heterogeneous film.

17. The application of the photoconversion MOF monolayer film formed by the self-assembly of polymer-coated MOF nanoparticles according to claim 16, In step (1), the diameter of the PET film is 1.0-2.5 cm and the thickness is 11-12 μm.

18. The application of the photoconversion MOF monolayer film formed by the self-assembly of polymer-coated MOF nanoparticles according to claim 17, In step (1), the diameter of the PET film is 1.5-2.0 cm and the thickness is 11-12 μm.

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