Covalent organic framework with redox activity and bionic nano-channel structure as well as preparation method and application of covalent organic framework

Abstract

The invention discloses a covalent organic framework with oxidation-reduction activity and a bionic nano-channel structure as well as a preparation method and application of the covalent organic framework, and belongs to the technical field of environmental protection. According to the preparation method, 2, 4-dihydroxybenzene-1, 3, 5-tricarboxaldehyde and 2, 5-bis (allyloxy) terephthaloyl hydrazine are taken as raw materials, a two-dimensional covalent organic framework with oxidation-reduction activity is synthesized, and then a sulfonic acid group with negative charges is covalently grafted, so that a functional material with a bionic nano-channel structure is formed. The material has regular porous channels and rich functional sites, the porous channels provide efficient mass transfer paths and adsorption spaces for uranyl ions, and the functional sites realize specific recognition of the uranyl ions through oxidation-reduction reaction and electrostatic interaction, so that the material shows synergistic advantages of strong selectivity, high adsorption capacity and rapid adsorption kinetics on uranium. The method is simple and low in cost, and the prepared material is clear in structure, good in hydrophilicity, capable of efficiently adsorbing uranyl ions and good in application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental protection, and particularly relates to a covalent organic framework with redox activity and biomimetic nanochannel structure, and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of nuclear power, spent fuel produced by nuclear power plants is continuously accumulated, and the spent fuel contains a large amount of fissile nuclides (235U and 239Pu, etc.) and transmutable nuclides (mainly 238U), which are valuable nuclear energy resources. Uranium is a key element in nuclear fuel, but it is also a highly toxic and radioactive environmental pollutant. Due to the widespread use of nuclear power, large-scale uranium mining, nuclear accidents and improper disposal of nuclear waste, a large amount of radioactive uranium mainly in the form of uranyl ions penetrates into the environment (Wang, X.; Li, G.; Huang, H.; Jin, H.; Liu, Y.; Yang, F.; He, R.; Zhu, W. Implanting open active pairs into open flower-structured Cu-S-O nanosheets for electrochemical uranium extraction in radioactive wastewater. Appl. Catal. B-Environ. 2025, 367, 125081). Therefore, stable and efficient uranium adsorbents are crucial for environmental protection and social development.

[0003] Porous materials, such as porous organic polymers (POPs) and metal-organic frameworks (MOFs), have been used as adsorbents for uranium. However, the performance of amorphous POPs is affected by irregular pores, and most of the pores are buried, hindering fast mass transfer. Although MOFs have regular pores and good crystal structure, stability under extreme conditions (acid, base, temperature and radiation) is still a challenge. High stability is particularly important for the extraction of uranyl ions, and therefore, it is crucial to develop uranium adsorbent materials with high adsorption capacity, good selectivity and stability.

[0004] Covalent organic framework materials (COFs) are a new class of porous crystalline materials connected by covalent bonds. Due to their regular porosity, large specific surface area and excellent stability, COFs are considered to be excellent candidate materials for adsorbing uranium. Although good progress has been made in the study of adsorbents based on amidoxime COFs, the limited adsorption sites and poor selectivity are still problems to be solved for current COF-based materials. SUMMARY

[0005] The present application aims to provide a covalent organic framework (COF) with redox activity and biomimetic nanochannel structure, and a preparation method and application thereof. The method uses 2,4-dihydroxybenzene-1,3,5-triformaldehyde and 2,5-bis(allyloxy)terephthalic dihydrazide as building units, and synthesizes a two-dimensional COF containing a hydroxyl structure through a solvothermal method. The intramolecular hydroxyl group can form a reduction site with electron transfer capability through enol tautomerism. Then, a negatively charged sulfonate group is introduced through covalent grafting to construct a biomimetic nanochannel structure on the inner wall of the framework channel. The high-density sulfonate groups on the regular nanochannel form an electrostatic enrichment environment, providing a linear mass transfer path for uranium. Further, the enol tautomerism drives the transformation of U(VI) to U(IV), promoting the solid-phase capture of uranium. Thus, a synergistic mechanism of valence transformation, directional attraction and efficient capture of uranyl ions is realized. The preparation method of the covalent organic framework with redox activity and biomimetic nanochannel structure developed in the present application is simple, has a clear structure and good stability. Through the mechanism of "hydroxyl tautomerism reduction + electrostatic targeted capture", the limitations of limited adsorption sites and low adsorption efficiency of traditional materials are broken through, and the covalent organic framework has good application prospects. The present application not only provides a new idea for the design and regulation of the microstructure of adsorption materials, but also provides a new way for preparing efficient uranium adsorbents.

[0006] The present application is realized by the following technical solutions: The present application provides a covalent organic framework with redox activity and biomimetic nanochannel structure, which has a structure as shown in formula (I).

[0007] The hydroxyl group contained in the framework channel can form a reduction site with electron transfer capability through enol tautomerism. High-density sulfonate groups on the regular nanochannel form an electrostatic enrichment environment, providing a linear mass transfer path for uranium, thereby constructing a biomimetic nanochannel structure on the inner wall of the framework channel.

[0008] The present application provides a preparation method of a covalent organic framework with redox activity and biomimetic nanochannel structure, which comprises the following steps: 1) Preparation of a redox-type covalent organic framework: 2,4-dihydroxybenzene-1,3,5-triformaldehyde and 2,5-bis(allyloxy)terephthalic dihydrazide are used as reaction raw materials, acetic acid is added as a catalyst, and an organic solvent o-dichlorobenzene and n-butanol are mixed uniformly. After degassing through freeze-pump-thaw cycle and flame sealing, the mixture is placed at 80-120 ℃ for 12-48 hours. After cooling and collecting the precipitate, washing and drying, a redox-type covalent organic framework is obtained. 2) Covalent organic framework with biomimetic nanochannel structure: the redox-type covalent organic framework prepared in step 1) is uniformly dispersed in a tetrahydrofuran solution, and 2-mercaptoethanesulfonic acid sodium and azobisisobutyronitrile are sequentially added. Under the protection of a nitrogen atmosphere, constant temperature stirring is carried out at 45-80 ℃ for 12-24 hours; after the reaction is completed, purification steps such as washing and drying are carried out, and finally a covalent organic framework material with both redox activity and biomimetic nanochannel structure is obtained.

[0009] As a preferred, the molar ratio of 2,4-dihydroxybenzene-1,3,5-tricarboxaldehyde and 2,5-bis(allyloxy)terephthalohydrazide in step 1) is 1:(1-2).

[0010] As a preferred, the volume ratio of o-dichlorobenzene, n-butanol and acetic acid in step 1) is 1:(0.5-1.5):(0.03-0.09). As a preferred, the mass ratio of the redox-type covalent organic framework, 2-mercaptoethanesulfonic acid sodium and azobisisobutyronitrile in step 2) is 1:(1-3):(0.5-1.5).

[0011] The application also provides the use of the covalent organic framework with both redox activity and biomimetic nanochannel structure prepared by the above method in adsorbing uranyl ions. The covalent organic framework is added to an aqueous solution containing different concentrations of uranyl ions, a constant temperature oscillator is used for oscillation for 12 hours, a 0.22 μm microporous filter is used for filtration, the filtrate is collected, inductively coupled plasma mass spectrometry is used to measure the content of residual uranyl ions in the filtrate, and the adsorption capacity of the covalent organic framework for uranyl ions is calculated.

[0012] As a preferred, the concentration of the aqueous solution containing different concentrations of uranyl ions is in the range of 0-500 mg / L.

[0013] As a preferred, before the aqueous solution containing different concentrations of uranyl ions is mixed with the covalent organic framework material, the pH of the solution needs to be adjusted to 2.0-6.0, more preferably 5.0, by using nitric acid or sodium hydroxide solution.

[0014] As a preferred, the adsorption capacity is calculated by the following formula: q t =( C 0 - C t ) / m × V ; wherein V is the volume of the solution, unit L, m is the amount of covalent organic framework used, unit g, C 0 is the initial concentration of uranyl ions, unit mg / L,C t is the equilibrium concentration of uranyl ion, unit mg / L.

[0015] "Like charges repel, unlike charges attract" is a basic law of ion transport in nature, which also applies to biological systems. In biological transport / extraction systems, charged residues act as selective filters for ion channels, allowing specific recognition and ultra-fast transport of target ions. Therefore, proteins in biological ion transport systems act as charged microchannels, providing a medium for ions to enter and exit the cell membrane. Inspired by the principle of charge interaction observed in biological ion channels, we propose that by introducing redox functional COFs materials as a simulated cell membrane, the current problem of limited adsorption sites can be solved, and negatively charged functional groups are introduced as simulated transporters to change the pore environment inside the COFs, thereby creating a biomimetic nanotransport system that can effectively capture uranium.

[0016] Compared with the prior art, the beneficial effects of the present application are: (1) The present application synthesizes redox-active covalent organic frameworks by solvothermal one-pot method, which has the advantages of simple method, low cost and strong stability.

[0017] (2) The redox-active covalent organic framework prepared by the present application can reduce soluble U(VI) to insoluble U(IV) through its enol tautomerism, promoting the solid-phase capture of uranium and overcoming the current problem of limited adsorption sites of adsorbents.

[0018] (3) The present application constructs a biomimetic nanochannel in the COF pore wall by covalently grafting negatively charged sulfonic acid groups, simulating the charge selective recognition mechanism of biological ion channels and providing a dedicated high-speed transport path for uranyl ions.

[0019] (4) The present application uses the electrostatic attraction of the negative charge microenvironment in the pore to directionally capture uranyl ions, significantly improving the selective adsorption capacity of uranium in complex systems and breaking through the selectivity bottleneck caused by competitive ion interference of traditional materials.

[0020] (5) Based on the enol tautomerism property of the hydroxyl structure in the framework, the present application reduces soluble U(VI) to insoluble U(IV) in situ, realizes the valence state conversion and solid-phase capture of uranyl ions through the three-level synergistic effect of "adsorption-reduction-fixation", and breaks through the site capacity limitation of traditional adsorbents relying only on physical adsorption.

[0021] (6) The present application synchronously realizes the efficient enrichment of uranyl ions by fusing the dual mechanisms of "hydroxyl tautomerism reduction" and "electrostatic target capture", solving the problem of low adsorption efficiency and poor selectivity of existing materials. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Synthetic scheme for Bd-Th-SO3Na.

[0023] Figure 2 FT-IR spectra of Bd, Th, Bd-Th and Bd-Th-SO3Na.

[0024] Figure 3 PXRD patterns of Bd-Th and Bd-Th-SO3Na.

[0025] Figure 4 Zeta potential plots of Bd-Th and Bd-Th-SO3Na.

[0026] Figure 5 CV plots of Bd-Th and Bd-Th-SO3Na.

[0027] Figure 6 Adsorption isotherm plots of Bd-Th and Bd-Th-SO3Na for uranyl ions.

[0028] Figure 7 Adsorption kinetics plots of Bd-Th and Bd-Th-SO3Na for uranyl ions.

[0029] Figure 8 Selectivity plots of Bd-Th and Bd-Th-SO3Na for uranyl ions. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with embodiments. Unless otherwise specified, the specific conditions in the embodiments are carried out according to conventional conditions or the conditions suggested by the manufacturers. The reagents or instruments used are not specified by the manufacturers, and are all conventional products that can be purchased on the market.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0032] Bd-Th-SO3Na. Bd-Th (60 mg), sodium 2-mercaptoethanesulfonate (128.05 mg) and azobisisobutyronitrile (36 mg) were added to tetrahydrofuran (30 mL), the mixture was sonicated for 10 min and then heated at 65 °C under N2atmosphere for 24 h. The precipitate was collected by centrifugation, washed with tetrahydrofuran and acetone, and dried at 50 °C under vacuum for 24 h to give an orange solid.

[0033] Figure 1 is a schematic diagram of the synthesis route of Bd-Th-SO3Na.

[0034] Figure 2 is the Fourier transform infrared spectrogram of Bd, Th, Bd-Th and Bd-Th-SO3Na. Compared with the FT-IR of Bd and Th, Bd-Th has a new absorption peak at 1624 cm -1 , which corresponds to the C=N stretching vibration, indicating that Bd and Th have undergone condensation to form Bd-Th. In addition, the S=O stretching vibration peak at 1048 cm -1 in the FT-IR spectrum of Bd-Th-SO3Na indicates that the sulfonate group has been successfully introduced into the Bd-Th skeleton.

[0035] X-ray powder diffraction (PXRD) technology was used to characterize the crystallinity of Bd-Th and Bd-Th-SO3Na. Figure 3 is the PXRD pattern of Bd-Th and Bd-Th-SO3Na. As can be seen from Figure 3 , Bd-Th has a strong diffraction peak at 3.3°, indicating that the covalent organic framework with high crystallinity is successfully synthesized by the method of the present application, and is well fitted with the AA stacking model. Bd-Th-SO3Na has a similar PXRD pattern to Bd-Th, indicating that the crystal structure of Bd-Th is well preserved during the covalent grafting of sulfonate.

[0036] Figure 4is the Zeta potential plot of Bd-Th and Bd-Th-SO3Na. Zeta potential analysis further indicates that Bd-Th-SO3Na has a negative surface charge, which is attributed to the presence of sulfonate (-SO3 - ) groups. The negative charge distribution makes UO2 2+ has a strong electrostatic attraction, providing evidence for the construction of "biomimetic nanochannel construction".

[0037] Figure 5 is the cyclic voltammetry (CV) plot of Bd-Th and Bd-Th-SO3Na. The initial reduction potential of Bd-Th and Bd-Th-SO3Na was determined by cyclic voltammetry. The results show that the initial reduction potential of Bd-Th and Bd-Th-SO3Na against the standard hydrogen electrode (SHE) is about -0.59 V and -0.45 V, respectively, which is much lower than U(VI) / U(IV) (0.411 V). This result indicates that the reduction of UO2 2+ by Bd-Th and Bd-Th-SO3Na is thermodynamically feasible.

[0038] The effect of initial concentration of uranyl ions on the adsorption performance of Bd-Th and Bd-Th-SO3Na was studied. 5 mg of Bd-Th and Bd-Th-SO3Na was added to 25 mL of aqueous solution containing different concentrations (0-500 mg / L) of uranyl ions, and the pH value of the aqueous solution was adjusted to 5 using nitric acid or sodium hydroxide solution. A constant temperature shaker was used for shaking for 12 hours, and a 0.22 μm microporous filter membrane was used for filtration. The filtrate was collected, and the content of residual uranyl ions in the filtrate was measured by inductively coupled plasma mass spectrometry. The adsorption capacity of Bd-Th and Bd-Th-SO3Na for uranyl ions was calculated. Figure 6 is the adsorption isotherm plot of Bd-Th and Bd-Th-SO3Na for uranyl ions. As can be seen from Figure 6 , due to the driving force of concentration gradient, the adsorption capacity of Bd-Th and Bd-Th-SO3Na for uranyl ions increases rapidly with the increase of uranyl ion concentration until reaching an equilibrium state. It is found by fitting that the isothermal adsorption process conforms to the Langmuir model, indicating that the adsorption of Bd-Th and Bd-Th-SO3Na for uranyl ions is monolayer adsorption, and the maximum adsorption capacity is 696 mg / g and 1576 mg / g, respectively.

[0039] Figure 7This is the adsorption kinetic diagram of Bd-Th and Bd-Th-SO3Na on uranyl ions. In the adsorption kinetic study, 20 mg of Bd-Th and Bd-Th-SO3Na were added to 35 mL of an aqueous solution containing 50 mg / L uranyl ions. The pH of the aqueous solution was adjusted to 5 with nitric acid or sodium hydroxide solution, and the mixture was stirred for the required time (5 min, 10 min, 20 min, 30 min, 40 min, 60 min, 80 min, 100 min). 0.5 mL of the sample was then filtered through a 0.22 μm microporous membrane, and the filtrate was collected. The uranium content in the filtrate was measured using inductively coupled plasma mass spectrometry (ICP-MS), and the adsorption kinetics of the material on UO2 was calculated. 2+ The adsorption capacity of the material under different contact times was plotted to determine the adsorption capacity of UO2. 2+ The removal efficiency graph shows that Bd-Th-SO3Na reaches adsorption equilibrium within 5 minutes, a stark contrast to Bd-Th which takes 20 minutes. This phenomenon can be attributed to the strong electrostatic attraction between sulfonate and uranyl ions in the nanochannels.

[0040] When a metallo-oxime group is used to adsorb uranium from seawater, vanadium ions are the main competitors for uranyl ions. To test the effect of competing ions, 10 mg / L of NaCl, CaCl2, MgCl2, ZnCl2, CuCl2, and NaVO3 were added to a uranium solution for capture studies. In selective adsorption experiments, the adsorbent was 5 mg, the volume of the uranium-containing aqueous solution was 10 mL, the initial concentration was 10 ppm, and the contact time was 2 hours. After 2 hours, the filtrate was collected through a 0.2 μm syringe filter, and the concentration was measured by ICP-MS. Figure 8 This is a graph showing the adsorption selectivity of Bd-Th and Bd-Th-SO3Na for uranyl ions. (From...) Figure 8 It can be seen that Bd-Th-SO3Na has an effect on 10 mg / L UO2 2+ Na + Mg 2+ Ca 2+ Zn 2+ Cu 2+ and VO4 3- The extraction efficiencies were 95.6%, 1%, 0.3%, 2.9%, 0%, 11.5%, and 1.8%, respectively, indicating that Bd-Th-SO3Na exhibits good adsorption selectivity for uranyl ions. From the perspective of the mechanism of action, on the one hand, the unique redox active sites of Bd-Th-SO3Na can promote the selective reduction and adsorption of uranyl ions; on the other hand, the negatively charged sulfonate groups on its surface can effectively inhibit the negatively charged VO4³⁺ ions through electrostatic repulsion. - The proximity of ions to the adsorption site significantly enhances the adsorption selectivity for uranyl ions.

[0041] The present application synthesizes a BD-TH-SO3Na covalent organic framework by a solvothermal method, which has both redox active sites and biomimetic nanochannel structures. The former provides specific binding sites for uranyl ions and promotes their valence state conversion, and the latter realizes rapid mass transfer of uranyl ions through the confinement space effect, both of which synergistically endow the material with excellent uranium adsorption performance.

[0042] The above-described embodiments only express several preferred embodiments of the present application, which are described in a more specific and detailed manner, but are not used to limit the present application. It should be noted that the present application can also have various changes and modifications for those skilled in the art, and any modification, equivalent replacement, improvement, etc. made within the concept and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A covalent organic framework possessing both redox activity and a biomimetic nanochannel structure, characterized in that, The covalent organic framework has a structure as shown in formula (I); The hydroxyl groups within the framework channels can form reduction sites with electron transfer capabilities through enol tautomerism. The high-density sulfonate groups on the regular nanopores create an electrostatic enrichment environment, providing a linear mass transfer path for uranium, thereby constructing a biomimetic nanochannel structure on the inner wall of the framework channels.

2. A method for preparing a covalent organic framework with both redox activity and biomimetic nanochannel structure as described in claim 1, characterized in that, Includes the following steps: 1) Preparation of redox covalent organic framework: 2,4-dihydroxybenzene-1,3,5-tricarboxaldehyde and 2,5-bis(allyloxy)terephthalohydrazide were used as reactants, and acetic acid was added as a catalyst and o-dichlorobenzene and n-butanol were added as organic solvents. The mixture was degassed by a freeze-pump-thaw cycle and sealed with a flame. The mixture was placed at 80-140 °C for 12-48 hours. The precipitate was collected after cooling, washed and dried to obtain the redox covalent organic framework. 2) Covalent organic framework with biomimetic nanochannel structure: The redox covalent organic framework obtained in step 1) was uniformly dispersed in tetrahydrofuran solution, and sodium 2-mercaptoethanesulfonate and azobisisobutyronitrile were added sequentially; under nitrogen atmosphere protection, the reaction was carried out at a constant temperature of 45-80 °C for 12-24 hours with stirring; after the reaction was completed, the covalent organic framework material with both redox activity and biomimetic nanochannel structure was finally obtained through purification steps such as washing and drying.

3. The method according to claim 2, characterized in that, In step 1), the molar ratio of 2,4-dihydroxybenzene-1,3,5-tricarboxaldehyde and 2,5-bis(allyloxy)terephthalohydrazide is 1:(1-2).

4. The method according to claim 2, characterized in that, In step 1), the volume ratio of o-dichlorobenzene, n-butanol, and acetic acid is 1:(0.5-1.5):(0.03-0.09).

5. The method according to claim 2, characterized in that, In step 2), the mass ratio of the redox covalent organic framework, sodium 2-mercaptoethanesulfonate, and azobisisobutyronitrile is 1:(1-3):(0.5-1.5).

6. The application of the covalent organic framework with both redox activity and biomimetic nanochannel structure as described in claim 1 in the adsorption of uranyl ions.

7. The application of the covalent organic framework with both redox activity and biomimetic nanochannel structure as described in claim 6 in the adsorption of uranyl ions, characterized in that, The obtained covalent organic framework material was added to aqueous solutions containing different concentrations of uranyl ions, shaken for 12 hours using a constant temperature shaker, filtered through a 0.22 μm microporous membrane, and the filtrate was collected. The remaining uranium concentration in the filtrate was measured using inductively coupled plasma mass spectrometry, and the adsorption capacity of the covalent organic framework for uranyl ions was calculated.

8. The application of the covalent organic framework with both redox activity and biomimetic nanochannel structure as described in claim 7 in the adsorption of uranyl ions, characterized in that, The concentration range of the aqueous solutions containing uranyl ions is 0-500 mg / L.

9. The application of the covalent organic framework with both redox activity and biomimetic nanochannel structure as described in claim 8 in the adsorption of uranyl ions, characterized in that, Before mixing the aqueous solution containing different concentrations of uranyl ions with the covalent organic framework, the pH of the solution needs to be adjusted to 2.0-6.0, more preferably 5.0, using nitric acid or sodium hydroxide solution.

10. The application of the covalent organic framework with both redox activity and biomimetic nanochannel structure according to claim 7 in the adsorption of uranyl ions, characterized in that, The adsorption capacity is calculated using the following formula: q t =( C o - C t ) / m × V ;in V It refers to the volume of the solution, in liters (L). m This refers to the amount of covalent organic framework used, in grams. C o This refers to the initial concentration of uranyl ions, in mg / L. C t It is the equilibrium concentration of uranyl ions, in mg / L.

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