A kind of covalent organic framework film of staggered stacking and its preparation method and application

Abstract

This invention relates to a staggered covalent organic framework thin film, its preparation method, and its application, belonging to the field of thin film technology. The invention first dissolves an amine monomer in acetic acid solution to obtain an aqueous solution; then dissolves an aldehyde monomer in mesitylene to obtain an organic solution; finally, the aqueous and organic solutions are added to the aqueous and organic phase chambers of a diffusion cell, respectively, for interfacial polymerization. After the reaction, the membrane material is removed, washed, and dried to obtain the staggered covalent organic framework thin film. This film forms a staggered stacked structure and constructs sub-nanometer transport channels with pore sizes of approximately 0.5 nm to 0.7 nm. Through a synergistic mechanism of Donnan repulsion and hydrogen bonding interactions, it maintains structural stability under extreme environments of high acidity, strong corrosion, and high radiation, achieving highly efficient selective permeation of protons and efficient retention of metal ions in high-level radioactive waste liquids.

Description

Technical Field

[0001] This invention belongs to the field of thin film technology, and particularly relates to a staggered stacked covalent organic framework thin film, its preparation method and application. Background Technology

[0002] Nuclear energy, as a highly efficient and low-carbon clean energy source, is playing an increasingly important role in addressing global climate change and optimizing the energy structure. However, the safe treatment and disposal of high-level radioactive waste generated at the end of the nuclear fuel cycle remains a key bottleneck restricting the sustainable development of nuclear energy. This type of waste is characterized by strong acidity, high radioactivity, and complex ionic composition. The nitric acid it contains not only easily causes severe corrosion to treatment equipment but also significantly increases the volume of radioactive waste, thus seriously restricting the sustainable development of the nuclear energy industry. Deacidification of high-level radioactive waste is a crucial preliminary step for its subsequent solidification, safe storage, and geological disposal. An ideal deacidification technology must simultaneously achieve efficient proton permeation and efficient metal ion retention, while maintaining structural stability under extreme environments of strong acid and high radiation. This requirement has become a core technical challenge that urgently needs to be overcome in the fields of nuclear chemical engineering and membrane separation. Current traditional treatment methods, such as calcination denitrification, dilution, or acid-base neutralization, significantly increase the complexity, volume, and cost of waste disposal.

[0003] Membrane separation technology, with its advantages of low energy consumption, continuous operation, and no secondary pollution, has shown broad application prospects in the treatment of radioactive wastewater. It can achieve selective proton transport through defined pores under mild operating conditions. However, traditional polymer and inorganic membranes are prone to structural degradation and performance decline under extreme environments, making them unsuitable for practical applications. Therefore, developing membrane materials with structural stability and chemical adaptability, capable of transporting protons from complex mixed systems, remains a key research focus. Covalent organic framework (COF) films, as a novel crystalline porous material, possess ultra-high specific surface area, highly ordered pore structure, and excellent chemical and thermal stability, demonstrating great application potential in the treatment of radioactive and high-acid wastewater, making them ideal materials for achieving precise ion separation. Their continuous, defect-free active layer structure and controllable stacking mode promise rapid ion transport and efficient sieving, overcoming the inherent limitations of traditional membrane materials. By precisely controlling pore size and functional groups, efficient sieving of protons and metal ions is expected, providing a new technological pathway for the green and efficient deacidification of high-level radioactive wastewater. However, the proton and metal ion selectivity of currently reported two-dimensional COF membranes is still not ideal for practical applications. + Monovalent ions, H + / Divalent ions and H +The selectivity factors for trivalent ions are typically less than 100, 1000, and 2000. This limitation is mainly attributed to the relatively large pore size (approximately 1 nanometer) of most reported COF membranes, which is insufficient for effective proton separation. Therefore, the design of sub-nanochannel COF membranes for proton separation remains an ongoing challenge. Furthermore, existing interfacial polymerization processes cannot precisely control the slip and stacking patterns between COF layers. Although pore sizes can be fine-tuned by adjusting reaction conditions, functionalizing, or constructing composite structures, this often comes at the cost of sacrificing membrane flux, crystallinity, or stability. It is difficult to construct sub-nanochannels between protons and metal ions while maintaining high crystallinity and a stable framework structure. This has become a key technical bottleneck restricting the application of COF membranes in the deacidification of high-level radioactive waste.

[0004] Furthermore, existing research on COF films is limited to simulated feed systems. In real high-level radioactive waste liquid environments with strong acids, high radiation, and complex ion coexistence, their chemical stability, radiation stability, and deacidification efficiency have not been systematically verified or tested in practical applications. The structural stability and separation reliability under extreme environments lack effective data support, which cannot meet the needs of engineering applications.

[0005] Therefore, there is an urgent need to develop a COF thin film material and preparation method that can overcome the above-mentioned bottlenecks. Summary of the Invention

[0006] Therefore, the technical problem to be solved by the present invention is to overcome the problems in the prior art, such as excessively large pore size, insufficient proton selectivity, and the inability of traditional membrane materials to meet the requirements of real high-level radioactive waste liquid treatment due to AA accumulation in COF membranes.

[0007] To address the aforementioned technical problems, this invention provides a staggered covalent organic framework thin film, its preparation method, and its application. This thin film forms a staggered stacked structure and constructs sub-nanometer transport channels with pore sizes of approximately 0.5 nm to 0.7 nm. Through the synergistic mechanism of Donnan repulsion effect and hydrogen bonding interaction, it maintains structural stability under extreme environments of high acidity, strong corrosion, and high radiation, achieving highly efficient selective permeation of protons and efficient retention of metal ions in high-level radioactive waste liquids.

[0008] The first objective of this invention is to provide a method for preparing a staggered covalent organic framework thin film, using a diffusion cell as the reaction apparatus. The diffusion cell consists of two completely symmetrical chambers. In use, a porous base film is vertically fixed between the two chambers, thus separating the diffusion cell into an independent aqueous phase chamber and an organic phase chamber. The preparation method includes the following steps: S1. Dissolve the amine monomer in acetic acid solution to obtain an aqueous solution; S2. Dissolve the aldehyde monomer in mesitylene to obtain an organic phase solution; S3. The aqueous solution described in S1 and the organic solution described in S2 are respectively added to the aqueous phase cavity and the organic phase cavity of the diffusion cell to carry out interfacial polymerization reaction. After the reaction is completed, the membrane material is taken out for washing and drying to obtain the staggered covalent organic framework film.

[0009] In one embodiment of the present invention, the porous base membrane is selected from polyacrylonitrile film, polyethersulfone film or polyamide film.

[0010] In one embodiment of the present invention, the ratio of the effective volume of one side of the diffusion cell to the effective contact area of ​​the membrane is (20-26):(10-15); this ratio can precisely control the diffusion rate of the monomer at the interface, thereby promoting the formation of a staggered stacking structure of the covalent organic framework film.

[0011] In one embodiment of the present invention, in S1, the amine monomer is p-phenylenediamine; And / or, the concentration of the amine monomer in the aqueous solution is 2.8 μmol / mL to 3.2 μmol / mL.

[0012] In one embodiment of the present invention, in S1, the concentration of the acetic acid solution is 8 mol / L-10 mol / L, and the solvent is water.

[0013] In one embodiment of the present invention, in S2, the aldehyde monomer is trialdehyde phloroglucinol; And / or, the concentration of aldehyde monomer in the organic phase solution is 1.8 μmol / mL to 2.2 μmol / mL.

[0014] In one embodiment of the present invention, in S3, the molar ratio of the amine monomer in the aqueous phase solution to the aldehyde monomer in the organic phase solution is (1.4-1.6):1.

[0015] In one embodiment of the present invention, in S3, the temperature of the interfacial polymerization reaction is 60°C-80°C and the time is 36h-60h.

[0016] A second objective of this invention is to provide a staggered covalent organic framework thin film prepared by the method.

[0017] The third objective of this invention is to provide an application of the aforementioned staggered covalent organic framework thin film in the treatment of high-level radioactive waste, proton separation in strong acid systems, and membrane separation in nuclear chemical processes.

[0018] The technical solution of the present invention has the following advantages compared with the prior art: (1) The preparation method described in this invention adopts interfacial polymerization, using amine monomers and aldehyde monomers as raw materials, and grows in situ on the surface of a porous base film to form a Schiff base-connected COF active layer, thereby obtaining a staggered covalent organic framework film. The surface of the film has a uniform and continuous COF active layer, and the pores are at the sub-nanometer level, which can achieve highly selective ion sieving, especially suitable for proton selective transport in acidic systems.

[0019] (2) The preparation method described in this invention uses a double-chamber symmetrical diffusion cell as the reaction device. By adjusting the ratio of the effective volume of one side of the diffusion cell to the effective contact area of ​​the membrane, the monomer concentration, the amount of acetic acid, and the interfacial polymerization reaction conditions, the monomer diffusion rate and reaction kinetics and thermodynamic processes are controlled in a coordinated manner. A quasi-AB staggered stacking structure is precisely constructed, so that the pore size of the film is reduced to the sub-nanometer level. The specific surface area and pore size distribution undergo characteristic changes simultaneously. Moreover, under acidic conditions, the pore size can be dynamically controlled by solvent-induced interlayer slip.

[0020] (3) The covalent organic framework film with staggered stacking described in this invention can achieve efficient proton selective permeation and efficient metal ion retention in high acid systems by means of the synergistic mechanism of Donnan repulsion effect and hydrogen bond interaction during the separation process. It has excellent proton selectivity and deacidification effect. The film preparation process is simple and efficient. It has excellent chemical stability in strong acid environment and good irradiation stability. It can withstand the irradiation conditions required for the treatment of high radioactive waste liquid. It can maintain the stability of structure and separation efficiency in real extreme high acid and high irradiation environment. It is suitable for high radioactive waste liquid treatment, proton separation in strong acid system, nuclear chemical membrane separation and other scenarios. It solves the technical problem that traditional separation materials are difficult to balance high proton flux, high metal ion retention rate and extreme environmental stability. It provides a new technical path for green and efficient deacidification of high radioactive waste liquid. Attached Figure Description

[0021] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein: Figure 1 SEM images of the polyacrylonitrile film and the covalent organic framework film of Example 1 of the present invention are shown below; wherein, (a) is a surface SEM image of the polyacrylonitrile film, (b) is a surface SEM image of the covalent organic framework film, and (c) is a cross-sectional SEM image of the covalent organic framework film. Figure 2 This is a surface SEM image of the covalent organic framework film of Comparative Example 2 of the present invention; Figure 3 This is a cross-sectional SEM image of the covalent organic framework thin film of Comparative Example 5 of the present invention; Figure 4This is an atomic force microscopy image of the covalent organic framework thin film of Example 1 of the present invention; Figure 5 The image shows the FTIR spectrum of the Pa, Tp, and quasi-AB stacked TpPa COF thin film of Example 1 of the present invention. Figure 6 The BET test results are for the covalent organic framework materials of Example 1 and Comparative Example 1 of the present invention; wherein, (a) is the 77K nitrogen adsorption-desorption isotherm of Comparative Example 1, (b) is the pore size distribution curve of Comparative Example 1, (c) is the 77K nitrogen adsorption-desorption isotherm of Example 1, and (d) is the pore size distribution curve of Example 1. Figure 7 The experimental PXRD patterns and simulated AA packing patterns of the covalent organic framework materials of Example 1 and Comparative Example 1 of this invention are shown. Figure 8 The PXRD pattern of the covalent organic framework film of Example 1 of the present invention after Pawley refinement; Figure 9 The PXRD pattern of the covalent organic framework material of Comparative Example 1 of this invention, refined by Pawley. Figure 10 The PXRD pattern of the covalent organic framework thin film of Comparative Example 5 of this invention; Figure 11 The PXRD pattern of the covalent organic framework thin film of Comparative Example 6 of this invention; Figure 12 Thermogravimetric analysis curve of the covalent organic framework thin film of Example 1 of the present invention; Figure 13 The images show the FTIR spectra of the quasi-AB stacked TpPa COF thin film before and after irradiation in Example 1 of this invention. Figure 14 This is a physical image of the quasi-AB stacked TpPa COF film of Embodiment 1 of the present invention, taken during a bending test. Figure 15 The permeation rate of the single-ion system of the covalent organic framework thin film in Example 1 of this invention and H2O + / M n+ Selectivity; Figure 16 This represents the percentage of cesium ion permeation in the covalent organic framework films of Comparative Examples 3-4 of this invention; Figure 17 The percentage of cesium ion permeation in the covalent organic framework films of Examples 1 and Comparative Examples 6-7 of the present invention; Figure 18The permeation flux of the covalent organic framework film of Example 1 of the present invention in nitric acid of different concentrations is 1 mol / L HNO3, (b) corresponds to 3 mol / L HNO3, and (c) corresponds to 5 mol / L HNO3. Figure 19 This demonstrates the proton selectivity of the covalent organic framework film in 3 mol / L HNO3, as described in Comparative Example 7 of this invention. Figure 20 The deacidification performance of the quasi-AB stacked TpPa COF membrane in Example 1 of this invention on real high-level radioactive waste liquid; wherein, (a) is the H on the feed side and the permeate side of the real high-level radioactive waste liquid system. + Concentration versus time curves, (b) show the feed side and permeate side during actual high-level radioactive waste treatment. 137 Comparison of Cs radioactivity. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0023] In this invention, unless otherwise stated, the polyacrylonitrile membrane used in the embodiments of this invention was purchased from Shandong Lanjing Membrane Technology Engineering Co., Ltd., and the molecular weight cutoff is 100,000 Da. Before use, the polyacrylonitrile membrane is washed with anhydrous ethanol and deionized water in sequence to remove surface impurities, and then air-dried for later use. Example 1

[0024] The staggered stacked covalent organic framework thin film and its preparation method in this embodiment specifically include the following steps: S1. Dissolve 0.07 mmol of p-phenylenediamine (Pa) in 23 mL of 9 mol / L aqueous acetic acid solution, and sonicate until completely dissolved to obtain an aqueous solution; S2. Dissolve 0.047 mmol of trialdehyde phloroglucinol (Tp) in 23 mL of mesitylene and sonicate until completely dissolved to obtain an organic phase solution. S3. The aqueous and organic phase solutions were added to the aqueous and organic phase chambers of the diffusion cell, respectively. The diffusion cell was placed in a 70℃ oven for interfacial polymerization for 48 hours, forming a COF active layer on the surface of the polyacrylonitrile membrane. After the reaction, the membrane material was removed and thoroughly washed with ethanol and deionized water, and then naturally dried to obtain a staggered covalent organic framework film, i.e., a quasi-AB stacked TpPa COF film. The diffusion cell consists of two completely symmetrical chambers. During use, the polyacrylonitrile membrane is vertically fixed between the two chambers, thus dividing the diffusion cell into independent aqueous and organic phase chambers. The effective volume of the diffusion cell on one side is 23 mL, and the effective contact area of ​​the membrane is 12.56 cm². 2 (Corresponding to a circle with a diameter of 4cm), the non-woven side of the membrane faces the aqueous phase cavity and the other side faces the organic phase cavity, and the monomers of the two phases undergo a polymerization reaction at the membrane interface. Comparative Example 1

[0025] The comparative example of a staggered stacked covalent organic framework thin film and its preparation method specifically includes the following steps: 63 mg of trialdehyde phloroglucinol (Tp) and 48 mg of p-phenylenediamine (Pa) were weighed and placed in a pressure-resistant tube. A mixed solvent consisting of 1.5 mL of mesitylene and 1.5 mL of dioxane was added, and the mixture was sonicated for 15 min. Then, 0.5 mL of acetic acid solution with a concentration of 3 mol / L was added. The pressure-resistant tube was rapidly frozen in a liquid nitrogen bath at 77 K. After three cycles of evacuation-freezing-thawing to remove oxygen, the pressure-resistant tube was sealed under a nitrogen atmosphere and placed in a 120 °C oven for a constant-temperature interfacial polymerization reaction for 3 days. After the reaction was completed, the solid product was collected by centrifugation and washed repeatedly with anhydrous acetone and ethanol. Finally, it was vacuum dried overnight at 120 °C to obtain AA-stacking covalent organic framework powder, namely AA-stacking TpPa COF powder. Comparative Example 2

[0026] The reaction is basically the same as in Example 1, except that the reaction time is 24 hours. Comparative Example 3

[0027] The process is basically the same as in Example 1, except that the temperature of the interfacial polymerization reaction is adjusted from 70°C to 25°C (RT). Comparative Example 4

[0028] The process is basically the same as in Example 1, except that the temperature of the interfacial polymerization reaction is adjusted from 70°C to 90°C. Comparative Example 5

[0029] The method is basically the same as in Example 1, except that the amount of p-phenylenediamine (Pa) used is 0.14 mmol. Comparative Example 6

[0030] The basic structure is the same as in Example 1, except that p-phenylenediamine (Pa) is replaced with m-phenylenediamine (Ma). Comparative Example 7

[0031] The basic formula is the same as in Example 1, except that p-phenylenediamine (Pa) is replaced with 2,5-aminopyridine (Py). Test Example 1

[0032] The polyacrylonitrile film and the covalent organic framework films prepared in Example 1, Comparative Examples 2 and 5 were characterized using scanning electron microscopy (SEM), and the results are as follows: Figures 1-3 As shown. From Figures 1-3 It can be seen that the surface of the polyacrylonitrile membrane has a disordered and irregular porous structure. After interfacial polymerization in Example 1, the surface of the polyacrylonitrile membrane is completely covered by a uniform, continuous, and dense COF active layer with a thickness of about 170 nm. The structure is regular and without obvious defects, providing an excellent foundation for ion sieving. In Comparative Example 2, due to the short reaction time, the COF active layer on the surface of the obtained film is too thin and has poor continuity, with a large number of irregular pore defects, making it difficult to form a complete and effective separation layer and failing to meet the requirements of ion sieving experiments. In Comparative Example 5, due to the high concentration of amine monomer, the thickness of the COF active layer on the surface of the obtained film is significantly increased. An excessively thick film layer will greatly increase the ion transport resistance, which is not conducive to the efficient transport of protons and metal ions. The above results indicate that the appropriate interfacial polymerization time and monomer ratio are the key to constructing a uniform, continuous, and moderately thick staggered COF film. Test Example 2

[0033] The covalent organic framework thin film prepared in Example 1 was characterized using atomic force microscopy (AFM), and the results are as follows: Figure 4 As shown. From Figure 4 It can be seen that the film surface is generally flat and uniform, without obvious protrusions, holes or cracks, exhibiting continuous and dense surface characteristics. The corresponding surface roughness parameters Ra is 2.82 nm and Rq is 3.68 nm. The low roughness values ​​indicate that the interfacial polymerization process is controllable. The COF active layer grown in situ on the porous base film surface has a regular morphology and good density, without obvious particle agglomeration or local uneven stacking. This further confirms that the preparation method can stably construct COF films with few surface defects and high flatness through staggered stacking, providing an excellent structural basis for efficient proton transport and efficient metal ion retention. Test Example 3

[0034] Fourier transform infrared spectroscopy (FTIR) was used to characterize Pa, Tp, and quasi-AB stacked TpPa COF thin films. The results are as follows: Figure 5 As shown. From Figure 5 It can be seen that the quasi-AB stacked TpPa COF film at 1580 cm⁻¹ -1A characteristic absorption peak for the C=C double bond appears at 1259 cm⁻¹. -1 A characteristic absorption peak for CN single bonds appears at 1637 cm⁻¹, while Tp is at 1637 cm⁻¹. -1 The characteristic absorption peak of the aldehyde group C=O at 3194 cm⁻¹, Pa at 3194 cm⁻¹ -1 -3374cm -1 The characteristic absorption peaks of the amino group NH at the above sites have completely disappeared. The appearance and disappearance of the above characteristic peaks directly confirm that the amine monomer and the aldehyde monomer have successfully condensed through the Schiff base reaction to form a stable β-ketoenamine skeleton structure. Test Example 4

[0035] The nitrogen adsorption-desorption of the covalent organic framework materials prepared in Example 1 and Comparative Example 1 was tested at 77 K using a nitrogen adsorption specific surface area and pore size analyzer (BET). The results are as follows: Figure 6 As shown. From Figure 6 As can be seen, the specific surface area of ​​the covalent organic framework material in Comparative Example 1 is as high as 912.02 m². 2 ・g -1 The pore size distribution is concentrated at 1.6 nm, corresponding to typical large pore size characteristics; while the specific surface area of ​​the covalent organic framework material in Example 1 is reduced to 498.11 m². 2 ・g -1 The pore size distribution is mainly sub-nanopores of 0.6 nm. The above results indicate that the staggered stacking structure can significantly compress the pore size. At the same time, due to the steric hindrance effect of the sub-nano channels on the diffusion of nitrogen molecules, the nitrogen adsorption amount and specific surface area are reduced accordingly. This is highly consistent with the structural characteristics of the quasi-AB layer stacking of the film, providing key pore structure support for efficient and selective proton transport and efficient metal ion retention. Test Example 5

[0036] The covalent organic framework materials prepared in Example 1, Comparative Examples 1, and 5-6 were characterized using powder X-ray diffraction (PXRD), and the results are as follows: Figures 7-11 As shown. From Figures 7-11It can be seen that the quasi-AB stacked TpPaCOF film prepared in Example 1 exhibits strong diffraction peaks at 4.5°, 7.7°, and 12.6°. Materials Studio simulation and Pawley refinement confirmed it to be a quasi-AB staggered stacked structure. The refinement results showed Rwp=6.39% and Rp=4.79%, indicating good fit. The high intensity and regular shape of the diffraction peaks indicate excellent crystallinity and high structural order of the film. Comparative Example 1 prepared an AA stacked TpPaCOF film... The COF powder exhibits a main peak only at 4.5°, with weak reflection peaks at 7.8°, 9.1°, and 12.0°. The characteristic peaks match the AA stacking simulation results, and the refined results show Rwp=7.44% and Rp=5.42%. In Comparative Example 5, the crystallinity of the COF film obtained by increasing the amine monomer concentration decreased and the peak shape broadened, indicating that excessively high monomer concentration would destroy the crystallization order and be detrimental to the formation of a staggered stacking structure. In Comparative Example 6, the TpMa film prepared by replacing p-phenylenediamine with m-phenylenediamine has poor crystallinity and no obvious characteristic diffraction peaks, further demonstrating that the monomer system and process parameters of the examples play a key role in constructing a highly crystallinity staggered stacked COF film. Test Example 6

[0037] The thermal stability of the covalent organic framework thin film prepared in Example 1 was tested using a thermogravimetric analyzer. The test conditions were a nitrogen atmosphere, a heating rate of 10 °C / min, and a temperature range of 30 °C–800 °C. The results are as follows: Figure 12 As shown. By Figure 12 It can be seen that the film exhibits a slight mass loss in the 30℃-120℃ range, mainly due to the evaporation of water molecules adsorbed on the film surface and residual solvent. The film mass remains basically stable in the 120℃-400℃ range, with no significant mass loss, indicating that its framework structure does not undergo thermal decomposition within this temperature range and possesses good medium- and low-temperature thermal stability. When the temperature rises above 400℃, the film begins to show a slow mass loss, and even at 800℃, it still retains a certain mass residue, indicating that its β-ketoenamine covalent framework structure has excellent thermal stability and can withstand conventional heating and high-temperature operating conditions in the treatment of high-level radioactive waste liquid. Combined with its chemical stability and radiation stability, it can meet the thermal stability requirements for membrane separation applications under extreme environments. Test Example 7

[0038] The quasi-AB stacked TpPa COF film prepared in Example 1 was placed at 10 5 Irradiation stability tests were conducted under Gy γ-ray irradiation conditions. After irradiation, the thin film samples before and after irradiation were characterized using Fourier transform infrared spectroscopy. The results are as follows: Figure 13 As shown, from Figure 13It can be seen that the FTIR spectrum of the film after γ-ray irradiation did not show significant changes in the position, intensity, and shape of the characteristic peaks compared to the original film. The characteristic absorption peaks were completely preserved without the generation of new impurity peaks, indicating that the β-keto-enamine covalent framework structure of the film did not break, degrade, or reconstruct under high-dose γ-ray irradiation. The chemical bonds and framework structure remained highly stable, which fully demonstrates that the staggered stacked TpPa COF film prepared by this invention has excellent irradiation stability and can withstand the strong irradiation environment in high-level radioactive waste treatment scenarios. Test Example 8

[0039] The quasi-AB stacked TpPa COF thin film prepared in Example 1 was subjected to manual bending and repeated folding tests. No excessive external force was applied to the film during the tests. After the tests, the changes in the surface and cross-sectional morphology of the film were observed. The results are as follows: Figure 14 As shown. From Figure 14 It can be seen that after bending and folding, the COF active layer on the surface of the film has no cracks, peeling, or wrinkles. The base film and the COF active layer are tightly bonded and remain intact, without structural damage or interlayer separation. This indicates that the staggered COF active layer grown in situ on the surface of the porous base film by the interfacial polymerization method of the present invention is firmly bonded to the base film, and the film has excellent mechanical flexibility and structural stability. Test Example 9

[0040] An H-type diffusion cell was used, with a single metal ion system solution as the feed liquid and deionized water as the permeate. The effective membrane area was 3.46 cm². 2 The experimental conditions were as follows: 30 mL of 0.1 mol / L single metal nitrate solution was added to the feed side, and 30 mL of deionized water was added to the permeate side. The metal ion concentration on the permeate side was determined using ICP-OES and ICP-MS. + The concentration was determined by acid-base titration, and the results are as follows: Figures 15-17 As shown. From Figures 15-17 It can be seen that the H of the thin film in Example 1 + The osmotic flux can reach 77.6 mmol·h⁻¹. -1 ・m -2 The concentration of metal ions in the permeation chamber remained close to the detection limit. + / Na + H + / Sr 2+ H + / Mg 2+ H + / Al 3+ H + / La 3+ With H + / UO2 2+The selectivity factors were 127, 4273, 4738, and 1.3 × 10⁻⁶, respectively. 4 1.36×10 6 The films prepared under the low temperature of 25℃ in Comparative Example 3 showed a significant decrease in crystallinity and irregular interlayer stacking, resulting in obvious leakage of metal ions and a substantial reduction in proton selectivity. In Comparative Example 4, the excessively rapid reaction rate at the higher temperature of 90℃ easily led to increased defects and disordered stacking in the COF active layer, similarly exacerbating metal ion penetration and reducing proton separation selectivity. The films prepared with Ma monomer in Comparative Example 6 exhibited poor crystallinity and no obvious characteristic diffraction peaks; the percentage of cesium ion penetration increased rapidly over time, the metal ion rejection rate was extremely low, and proton selectivity was almost lost. The films prepared with Py monomer in Comparative Example 7 also suffered from disordered framework and channel defects; the cesium ion penetration rate was significantly higher than in Example 1, making efficient proton-metal ion sieving impossible. These results indicate that it is essential to use p-phenylenediamine and trialdehyde-based phloroglucinol as the monomer system, strictly control the interfacial polymerization temperature, and precisely regulate the monomer molar ratio and diffusion cell volume / area ratio to ensure the formation of a highly crystalline quasi-AB misaligned stacking structure, constructing defect-free sub-nanometer channels, and achieving efficient proton selective permeation and efficient metal ion rejection. Test Case 10

[0041] An H-type diffusion cell was used, with a mixed metal ion solution as the feed liquid and deionized water as the permeate. The effective membrane area was 3.46 cm². 2 The experimental conditions were: 30 mL of feed containing Na... + Cs + 、Sr 2+ Ba 2+ Mg 2+ La 3+ Fe 3+ Ce 3 + Al 3+ 、Nd 3+ UO2 2+ Eleven metal cations were prepared in 1 mol / L, 3 mol / L, and 5 mol / L HNO3 solutions, with 30 mL of deionized water on the osmotic side. The experiment lasted for 24 hours. The concentrations of metal ions on the osmotic side were determined by ICP-OES and ICP-MS. + The concentration was determined by acid-base titration, and the results are as follows: Figures 18-19 As shown. From Figures 18-19 It can be seen that the proton permeation flux of the thin film in Example 1 in 1 mol / L, 3 mol / L, and 5 mol / L HNO3 systems reached 867 mol·h⁻¹ in 24 hours. -1 ・m -2 2247 mol·h -1 ・m-2 3945 mol·h -1 ・m -2 Furthermore, the permeation concentrations of all 11 metal cations were below the detection limit, indicating that the membrane still possesses excellent proton transport efficiency and complete metal ion retention in a high-acidity mixed ion system. In contrast, the membrane in Comparative Example 7 showed significant permeation leakage of metal ions and a significant decrease in proton selectivity in a 3 mol / L HNO3 system. These results demonstrate that the membrane in Example 1, with its sub-nanometer transport channels constructed from a highly crystalline quasi-AB misaligned stacking structure, combined with the synergistic mechanism of Donnan repulsion and hydrogen bonding interactions, can accurately sieve protons and metal ions under extreme high-acidity conditions. In contrast, the membrane in Comparative Example 7, due to its disordered framework, channel defects, and large pore size, could not form an effective sieving interface and thus could not achieve efficient separation of protons and metal ions. Test Example 11

[0042] An H-type diffusion cell was used to conduct a real radioactive experiment inside a radioactive glove box. The experimental solution was a 3 mol / L nitric acid system with a radioactivity level of approximately 10. 7 Bq / L (in) 137 (Cs quantification), the system contains multiple radionuclides, with deionized water as the osmotic receiving solution, the experiment lasted 24 hours, and the H on the feed side and osmotic side was determined by acid-base titration. + Concentration was determined using radioactivity analysis to detect radionuclide leakage on the permeation side. The results are as follows: Figure 20 As shown. From Figure 20 As can be seen, in a real spent fuel dissolving liquid diluent system, the quasi-AB stacked TpPa COF membrane of Example 1 can achieve efficient selective proton transmembrane transport. Within 24 hours, the acidity of the feed-side solution decreases by about 50%, while the acidity of the permeate-side increases significantly. At the same time, the radioactivity on the permeate-side remains consistent with the background activity of deionized water. 137 All radionuclides, including Cs, were completely retained without any leakage. Combined with the results of the film's previous irradiation stability, chemical stability, and structural characterization, it is fully demonstrated that the film maintains a high degree of stability in its framework structure and separation performance under real extreme conditions of strong radioactivity, high acidity, and coexistence of multiple ions. It can simultaneously achieve efficient proton transport and efficient retention of radionuclides, and all performance indicators fully meet the practical application requirements for industrial deacidification of high-level radioactive waste.

[0043] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a thin film of a covalent organic framework in a staggered stacking, characterized in that, Using a diffusion cell as the reaction apparatus, the diffusion cell consists of two completely symmetrical chambers. During use, a porous membrane is vertically fixed between the two chambers, thus separating the diffusion cell into an independent aqueous phase chamber and an organic phase chamber. The preparation method includes the following steps: S1. Dissolve the amine monomer in acetic acid solution to obtain an aqueous solution; S2. Dissolve the aldehyde monomer in mesitylene to obtain an organic phase solution; S3. The aqueous solution described in S1 and the organic solution described in S2 are respectively added to the aqueous phase cavity and the organic phase cavity of the diffusion cell to carry out interfacial polymerization reaction. After the reaction is completed, the membrane material is taken out for washing and drying to obtain the staggered covalent organic framework film.

2. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, The porous base membrane is selected from polyacrylonitrile film, polyethersulfone film or polyamide film.

3. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, The ratio of the effective volume on one side of the diffusion cell to the effective contact area of ​​the membrane is (20-26):(10-15).

4. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, In S1, the amine monomer is p-phenylenediamine; And / or, the concentration of the amine monomer in the aqueous solution is 2.8 μmol / mL to 3.2 μmol / mL.

5. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, In S1, the concentration of the acetic acid solution is 8 mol / L-10 mol / L, and the solvent is water.

6. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, In S2, the aldehyde monomer is trialdehyde phloroglucinol; And / or, the concentration of aldehyde monomer in the organic phase solution is 1.8 μmol / mL to 2.2 μmol / mL.

7. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, In S3, the molar ratio of the amine monomer in the aqueous solution to the aldehyde monomer in the organic solution is (1.4-1.6):

1.

8. The method for preparing a staggered covalent organic framework thin film according to claim 1, characterized in that, In S3, the temperature of the interfacial polymerization reaction is 60℃-80℃, and the time is 36h-60h.

9. A staggered covalent organic framework thin film prepared by the method of any one of claims 1-8.

10. The application of the staggered stacked covalent organic framework thin film as described in claim 9 in the treatment of high-level radioactive waste, proton separation in strong acid systems, and membrane separation in nuclear chemical engineering.

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