Preparation method and adsorption application of amidoxime functionalized three-dimensional covalent organic framework

Abstract

The invention discloses a preparation method and adsorption application of amidoxime functionalized three-dimensional covalent organic framework, and belongs to the field of environmental protection technology. The present invention uses tetrakis (4-formylphenyl) methane and 1,4-phenylenediacetonitrile as raw materials to synthesize a three-dimensional covalent organic framework, and then modifies the amidoxime group to prepare the amidoxime functionalized three-dimensional covalent organic framework. The amidoxime functionalized three-dimensional covalent organic framework prepared by the inventive method has regular porous channels and abundant amidoxime functional sites, can achieve selective adsorption of uranyl ions, and has the advantages of high adsorption capacity and rapid adsorption kinetics. The preparation method of the amidoxime functionalized three-dimensional covalent organic framework of the present invention is simple and has a clear structure, can be used for efficient adsorption of uranyl ions, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental protection, and in particular to a preparation method and adsorption application of an amidoxime functionalized three-dimensional covalent organic framework. Background Art

[0002] Nuclear energy, with its low carbon emissions and high efficiency, has long played an irreplaceable role in sustainable energy supply. Uranium, the primary fuel for nuclear power reactors, exists on land, with only 4.5 million tons of uranium in reserve globally, while the total amount of uranium in seawater is estimated to be 4.5 billion tons. Therefore, extracting uranium from seawater has become a key priority for the sustainable development of the nuclear industry (Wang Z, Meng Q, Ma R, Wang Z, Yang Y, Sha H, Ma X, Ruan X, Zou X, Yuan Y, Zhu G. Constructing an ion pathway for uranium extraction from seawater, Chem., 2020, 6, 1683-1691). Therefore, stable and efficient uranium adsorbents are crucial for environmental protection and social development.

[0003] Porous materials, such as porous organic polymers (POPs) (Yan RH, Cui WR, Zhang CR, Li XJ, Huang J, Jiang W, Liang RP, Qiu JD. Bio-inspired hydroxylation imidazole linkedcovalent organic polymers for uranium extraction from aqueous phases, Chem. Eng. J., 2021, 420, 129658) and metal-organic frameworks (MOFs) (Liu W, Dai X, Bai Z, Wang Y, Yang Z, Zhang L, Xu L, Chen L, Li Y, Gui D, Diwu J, Wang J, Zhou R, Chai Z, Wang S, Highly sensitive and selective uranium detection in natural water systems using a luminescent mesoporous metal-organic framework equipped with abundant Lewis basic sites: a combined batch, X-ray absorption spectroscopy, and first principles simulation) Investigation, Environ. Sci. Technol., 2017, 51, 3911) and others have been used as adsorbents for uranium. However, the performance of amorphous POPs is affected by their irregular pores, most of which are buried, hindering their rapid mass transfer. Although MOFs have regular pores and good crystal structures, their stability under extreme conditions (acid, alkali, temperature and radiation) remains a challenge. Highly stable materials are particularly important for uranium extraction. Therefore, it is crucial to develop uranium adsorption materials with high adsorption capacity, good selectivity and stability.

[0004] Due to the low concentration of uranium in seawater, its diffusion process to the adsorbent surface is slow, which greatly affects the extraction efficiency. Recently, electric-driven uranium extraction has been considered as a promising uranium extraction strategy (Wang Z, Meng Q, Ma R, Wang Z, Yang Y, Sha H, Ma X, Ruan X, Zou X, Yuan Y, Zhu G.Constructing an ion pathway for uranium extraction from seawater, Chem, 2020, 6, 1683-1691). The AC electrochemical method using half-wave rectification can electrodeposit uranium compounds into uranium dioxide to increase the adsorption amount (Yang H, Liu X, Hao M, Xie Y, Wang X, Tian H, Waterhouse GIN, Kruger PE, Telfer SG, Ma S. Functionalized iron–nitrogen–carbon electrocatalyst provides a reversible electron transfer platform for efficient uranium extraction from seawater, Adv. Mater, 2021, 33, 2106621). Compared to physical diffusion, electroextraction offers faster migration rates, and the material's electrocatalytic reduction properties can also improve uranium adsorption. One of the challenges in uranium adsorption is designing electroactive materials with a rational structure. Generally speaking, electrode materials used in electrochemical adsorption must meet the following requirements: low equivalent series resistance and charge transfer resistance; abundant active sites for uranium adsorption; and a stable chemical structure to ensure reusability in strong electric fields and radiation environments.

[0005] Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials connected by covalent bonds (PJ Waller, F. Gandara and O.M.Yaghi, Acc, Chemistry of covalent organic frameworks, Chem. Res., 2015, 48, 3053). So far, COFs reported to capture uranium are mainly based on two-dimensional building blocks (Zhang CR, Cui WR, Xu RH, Chen XR, Jiang W, Wu YD, Yan RH, Liang RP, Qiu J-D, Alkynyl-based sp 2carbon-conjugated covalent organic frameworks with enhanced uranium extraction from seawater by photoinduced multiple effects, CCS Chem., 2021, 3, 168-179). Three-dimensional covalent organic frameworks (3D COFs) are an irreplaceable subclass of COFs, with unique characteristics such as extremely high surface area, low mass density and abundant pores, making 3D COFs an excellent material for capturing radioactive elements. However, the 3D COFs reported so far have only limited bonding structures, and most of them are based on BO or C=N connections (Ding H, Li J, Xie G, Lin G, Chen R, Peng Z, Yang C, Wang B, Sun J, Wang C. An AIEgen-based 3D covalent organic framework for white light-emitting diodes, Nat. Commun., 2018, 9, 5234), with relatively poor stability and weak electron delocalization, which hinders the structural diversity and potential applications of 3DCOFs. There is little research on the functionalization of 3D COFs, and the exploration of new functionalized and stable 3D COFs is urgently needed. Currently, there are no reports on the synthesis of functionalized 3D COFs and their use for uranium adsorption / electrosorption. Summary of the Invention

[0006] The present invention aims to provide a preparation method and adsorption application of an amidoxime-functionalized three-dimensional covalent organic framework. The method first uses tetrakis(4-formylphenyl)methane and 1,4-phenylenediacetonitrile as raw materials to synthesize an olefin-linked three-dimensional covalent organic framework, and then modifies the amidoxime groups to prepare the amidoxime-functionalized three-dimensional covalent organic framework. The amidoxime-functionalized three-dimensional covalent organic framework has a unique pore structure that is conducive to size matching of uranyl ions, enabling selective adsorption of uranyl ions and greatly improving the adsorption selectivity of uranyl ions. At the same time, the abundant amidoxime functional groups on the pore walls of the amidoxime-functionalized three-dimensional covalent organic framework also lay the foundation for the specific diffusion of uranyl ions. In addition, by applying alternating voltages of -5V and 0V at the cathode, uranium ions can rapidly migrate and be enriched in the porous structure of the amidoxime-functionalized three-dimensional covalent organic framework, inducing the electrodeposition of uranium compounds to form charge-neutral species, thereby greatly improving the adsorption capacity of uranium. The present invention presents a simple preparation method for amidoxime-functionalized three-dimensional covalent organic frameworks, a well-defined structure, and excellent stability. It can be used for the selective and efficient adsorption of uranyl ions, and has promising application prospects. This invention not only provides new ideas for the design and regulation of the microstructure of adsorption materials, but also offers a new approach for the preparation of highly efficient uranium adsorbents.

[0007] The present invention is achieved through the following technical solutions:

[0008] The present invention provides a method for preparing an amidoxime functionalized three-dimensional covalent organic framework, comprising the following steps:

[0009] 1) Preparation of a three-dimensional covalent organic framework: Tetrakis(4-formylphenyl)methane and 1,4-phenylenediacetonitrile are used as the reaction materials, followed by the addition of a catalyst, sodium ethoxide, and an organic solvent, o-dichlorobenzene, and the mixture is uniformly mixed. The mixture is degassed through a freeze-pump-thaw cycle and flame-sealed, and the mixture is reacted at 80-120°C for 48-96 hours. The precipitate is cooled, collected, washed, and dried to obtain a three-dimensional covalent organic framework.

[0010] 2) Preparation of amidoxime-functionalized three-dimensional covalent organic framework: The three-dimensional covalent organic framework prepared in step 1) is dispersed in a triethylamine and ethanol solution, hydroxylamine hydrochloride is added, and the mixture is stirred at 70-90° C. The product is washed and dried to obtain an amidoxime-functionalized three-dimensional covalent organic framework.

[0011] Preferably, in step 1), the molar ratio of tetrakis(4-formylphenyl)methane to 1,4-phenylenediacetonitrile is 1:(1-3).

[0012] Preferably, in step 2), the mass ratio of the three-dimensional covalent organic framework to hydroxylamine hydrochloride is 1:(1-3).

[0013] Preferably, the volume ratio of the triethylamine and ethanol solution in step 2) is 1:(15-30).

[0014] The present invention also provides the use of the amidoxime functionalized three-dimensional covalent organic framework prepared by the above method in adsorbing uranyl ions.

[0015] The present invention also provides the use of the amidoxime functionalized three-dimensional covalent organic framework prepared by the above method in the electrical adsorption of uranyl ions.

[0016] Preferably, the electroadsorption adopts a two-electrode system, with graphite as the anode and an amidoxime functionalized three-dimensional covalent organic framework modified electrode as the cathode; alternating voltages of 0V and -5V are applied to the cathode.

[0017] Preferably, the amidoxime functionalized three-dimensional covalent organic framework is 2+ It has good electroadsorption selectivity and high adsorption capacity.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The present invention synthesizes a three-dimensional covalent organic framework through a solvent-thermal one-pot method, which has the advantages of simple method, low cost and strong stability.

[0020] (2) The three-dimensional covalent organic framework prepared by the present invention can be modified to introduce amidoxime functional groups to coordinate with uranyl ions, which is beneficial for the selective binding of uranyl ions.

[0021] (3) The olefin-linked three-dimensional covalent organic framework prepared by the present invention has excellent stability and is suitable for uranium removal in seawater environments.

[0022] (4) The unique pore structure of the functionalized three-dimensional covalent organic framework prepared by the present invention is conducive to size matching of uranyl ions, which can achieve selective adsorption of uranyl ions and improve the adsorption selectivity.

[0023] (5) By applying an alternating voltage, the present invention allows uranium ions to rapidly migrate and accumulate in the porous structure of the amidoxime-functionalized three-dimensional covalent organic framework, thereby inducing the electrodeposition of uranium compounds to form charge-neutral species, thereby enhancing the adsorption capacity for uranium.

[0024] (6) The three-dimensional covalent organic framework prepared by the present invention has good stability and regular porous channels and abundant amidoxime functional sites. It can be used as an electro-extraction material for adsorbing uranium from seawater. It has high adsorption capacity and rapid adsorption kinetics and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the synthetic route of TFPM-PDAN-AO.

[0026] Figure 2Fourier transform infrared spectra of TFPM, PDAN, TFPM-PDAN and TFPM-PDAN-AO.

[0027] Figure 3 PXRD patterns of TFPM-PDAN and TFPM-PDAN-AO.

[0028] Figure 4 PXRD patterns of TFPM-PDAN-AO under different conditions.

[0029] Figure 5 This is the adsorption isotherm of TFPM-PDAN-AO for uranyl ions.

[0030] Figure 6 This is the electrical adsorption capacity diagram of TFPM-PDAN-AO for uranyl ions with different concentrations.

[0031] Figure 7 This is the electroadsorption selectivity diagram of TFPM-PDAN-AO for uranyl ions. DETAILED DESCRIPTION

[0032] To make the objects, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be described clearly and completely below in conjunction with the examples. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] Example 1: Preparation and characterization of amidoxime functionalized three-dimensional covalent organic frameworks

[0035] Tetrakis(4-formylphenyl)methane (TFPM) (21.6 mg, 0.05 mmol), 1,4-phenylenediacetonitrile (PDAN) (15.6 mg, 0.1 mmol) and sodium ethoxide (25.52 mg, 0.375 mmol) were added to a Pyrex tube, and o-dichlorobenzene (2.0 mL) was added. The mixture was ultrasonicated for 10 minutes to mix evenly. After three freeze-pump-thaw cycles of degassing, the Pyrex tube was flame-sealed and placed in an oven at 100°C for 72 hours. The reaction product was cooled to room temperature, and the precipitate was separated by vacuum filtration. The precipitate was washed with dichloromethane and tetrahydrofuran in sequence and dried to obtain a solid. The obtained solid was vacuum dried at 80°C for 12 hours to obtain a three-dimensional covalent organic framework (TFPM-PDAN). TFPM-PDAN (375 mg), hydroxylamine hydrochloride (NH2OH·HCl, 700 mg) and triethylamine (4.5 mL) were added to ethanol (100 mL) and stirred at 80°C for 24 h. The mixture was cooled to room temperature, washed three times with ultrapure water and ethanol, and then dried in vacuo at 80°C for 12 h to obtain an amidoxime-functionalized three-dimensional covalent organic framework (TFPM-PDAN-AO).

[0036] Figure 1 This is a schematic diagram of the synthetic route of TFPM-PDAN-AO.

[0037] Figure 2 The Fourier transform infrared (FT-IR) spectra of TFPM, PDAN, TFPM-PDAN and TFPM-PDAN-AO are shown in Figure 2. Compared with the FT-IR spectra of TFPM and PDAN, TFPM-PDAN has a higher peak at 2216 cm -1 A new absorption peak corresponding to the stretching vibration of -CN appeared at the same time, C=O (1697cm -1 ) disappears, indicating that TFPM and PDAN undergo condensation reaction to form TFPM-PDAN. In addition, in the FT-IR spectrum of TFPM-PDAN-AO, the peak at 2216 cm -1 The vibration peaks of -CN at 1660 cm -1 (C=N) and 966cm -1 The vibration peak of the amidoxime group appeared at (NO), indicating that TFPM-PDAN was successfully amidoximated to generate TFPM-PDAN-AO.

[0038] The crystallinity of TFPM-PDAN and TFPM-PDAN-AO was characterized by powder X-ray diffraction (PXRD). Figure 3 is the PXRD pattern of TFPM-PDAN and TFPM-PDAN-AO. Figure 3TFPM-PDAN exhibits a strong diffraction peak at 8.75°, demonstrating the successful synthesis of a highly crystalline three-dimensional covalent organic framework using the method of the present invention. TFPM-PDAN-AO exhibits a similar PXRD pattern to TFPM-PDAN, indicating that the structure of TFPM-PDAN is well preserved during the amidoximation process.

[0039] Figure 4 The PXRD patterns of TFPM-PDAN-AO under different conditions are shown. 2 The porous materials formed by carbon atom hybridization, COFs connected by C=C bonds have better stability than other dynamic covalent bond COFs. Therefore, we immersed TFPM-PDAN-AO in different environmental solutions (6M HCl, 6M NaOH or saturated NaCl solution for 48 hours), or exposed it to γ-rays with a dose of 200kGy for 48 hours at room temperature to study the chemical stability and radiation resistance of TFPM-PDAN-AO. Figure 4 It can be seen that TFPM-PDAN-AO still maintains its good structure after being treated with irradiation, saturated sodium chloride, strong acid or strong base.

[0040] Example 2: Adsorption of uranyl ions by amidoxime-functionalized three-dimensional covalent organic frameworks

[0041] The effect of initial uranyl ion concentration on the adsorption performance of TFPM-PDAN-AO was studied. 5 mg of TFPM-PDAN-AO was added to 25 mL of aqueous solutions containing varying concentrations of uranyl ions (0-500 mg / L). The pH of the aqueous solution was adjusted to 5 with nitric acid or sodium hydroxide solution. The solution was shaken for 12 hours using a thermostatic shaker. The solution was then filtered through a 0.22 μm microporous membrane, and the filtrate was collected. The residual uranyl ion content in the filtrate was measured using inductively coupled plasma-mass spectrometry, and the adsorption capacity of TFPM-PDAN-AO for uranyl ions was calculated. Figure 5 This is the adsorption isotherm of TFPM-PDAN-AO for uranyl ions. Figure 5 As can be seen, due to the strong driving force of the concentration gradient, the adsorption capacity of TFPM-PDAN-AO for uranyl ions increases rapidly with increasing uranyl ion concentration until equilibrium is reached. Fitting revealed that the adsorption isotherm conforms to the Langmuir model, indicating that TFPM-PDAN-AO adsorbs uranyl ions in a monolayer manner, with a maximum adsorption capacity of 472.4 mg / g. TFPM-PDAN-AO has regular porous channels and abundant amidoxime groups on the pore walls, which facilitates the diffusion of uranyl ions.

[0042] Example 3: Application of amidoxime-functionalized three-dimensional covalent organic framework for electrosorption of uranyl ions

[0043] Due to its good stability and adsorption performance for uranyl ions, we studied the use of TFPM-PDAN-AO as an electrosorption material to extract uranium from seawater. The electrosorption experiment was carried out in a standard two-electrode system, using a graphite rod as the anode and a TFPM-PDAN-AO modified graphite felt as the cathode. A function generator (DG1022Z) was used to apply an alternating voltage of -5V and 0V to the cathode for an equal time. The electroextraction experiment was carried out in seawater containing different concentrations (0-1000mg / L) of uranyl ions. After 12 hours, the solution was collected and the remaining uranyl ion content in the solution was measured by inductively coupled plasma mass spectrometry. The uranyl ion content in the solution was measured by q e =(C o -C e )×V / m to calculate the adsorption capacity of TFPM-PDAN-AO for uranyl ions, where q e is the electrosorption capacity, unit is mg / g, V is the solution volume, unit is L, m is the amount of TFPM-PDAN-AO, unit is g, C o is the initial concentration of uranyl ions in mg / L, C e is the equilibrium concentration of uranyl ions, in mg / L. Figure 6 This is the electrosorption capacity diagram of TFPM-PDAN-AO for uranyl ions of different concentrations. Figure 6 As can be seen, the adsorption capacity of TFPM-PDAN-AO increases with increasing uranyl ion concentration, reaching a high of 4685 mg / g at a uranyl ion concentration of 1000 mg / L. During the electrosorption process, pale yellow flocs formed around the electrode, which gradually increased over time. Therefore, the high adsorption capacity of TFPM-PDAN-AO for uranyl ions may be due to the conversion of uranium ions into electrodeposited precipitates, which can be easily collected from the electrode.

[0044] Example 4: Electroadsorption selectivity of amidoxime-functionalized three-dimensional covalent organic frameworks for uranyl ions

[0045] When amidoxime groups are used to adsorb uranium from seawater, vanadium ions are the main competitor to uranyl ions. We investigated the adsorption selectivity of TFPM-PDAN-AO for uranyl ions by electrosorption experiments. Figure 7 The electroadsorption selectivity of TFPM-PDAN-AO to uranyl ions is shown in Figure 2. Figure 7 It can be seen that TFPM-PDAN-AO has a significant effect on the UO2 2+ VO4 3- 、Cu 2+ and Fe 3+The extraction efficiencies of TFPM-PDAN-AO were 99.3%, 19.1%, 18.2% and 15.3% respectively, indicating that TFPM-PDAN-AO has good electrosorption selectivity for uranyl ions. On the one hand, the unique pore structure of TFPM-PDAN-AO is conducive to the size matching of uranyl ions, which can achieve selective adsorption of uranyl ions; on the other hand, the application of 0V and -5V alternating voltages causes the TFPM-PDAN-AO electrode to electrostatically repel the electronegative VO4 3- , improving the adsorption selectivity for uranyl ions.

[0046] The present invention synthesizes olefin-linked TFPM-PDAN via a solvothermal method, resulting in high crystallinity and strong stability. Furthermore, after being functionalized with amidoxime groups, TFPM-PDAN exhibits a high affinity for uranyl ions, facilitating their selective binding. Furthermore, the unique pore structure of TFPM-PDAN-AO, slightly larger than the diameter of hydrated uranyl ions, enables size-matched adsorption of uranyl ions and improves their selective adsorption performance. The excellent stability and abundant amidoxime functional groups of TFPM-PDAN-AO make it suitable as an adsorbent material for extracting uranium from seawater. With its high adsorption capacity and rapid adsorption kinetics, it has promising application prospects.

[0047] The embodiments described above merely represent several preferred embodiments of the present invention. While the descriptions are relatively specific and detailed, they are not intended to limit the present invention. It should be noted that those skilled in the art will readily appreciate that the present invention is susceptible to various variations and modifications. Any modifications, equivalent substitutions, or improvements within the scope of the present invention are intended to be included within the scope of protection of the present invention.

Claims

1. A method for preparing an amidoxime functionalized three-dimensional covalent organic framework, characterized in that: The steps include: 1) Preparation of a three-dimensional covalent organic framework: Tetrakis(4-formylphenyl)methane and 1,4-phenylenediacetonitrile are used as the reaction materials. A catalyst, sodium ethoxide, and an organic solvent, o-dichlorobenzene, are added and mixed evenly. The mixture is degassed through a freeze-pump-thaw cycle and flame-sealed. The mixture is then reacted at 80-120°C for 48-96 hours. The precipitate is cooled, collected, washed, and dried to obtain a three-dimensional covalent organic framework. 2) Preparation of amidoxime-functionalized three-dimensional covalent organic framework: The three-dimensional covalent organic framework prepared in step 1) is dispersed in a triethylamine and ethanol solution, hydroxylamine hydrochloride is added, and the mixture is stirred at 70-90°C. The product is washed and dried to obtain an amidoxime-functionalized three-dimensional covalent organic framework.

2. The method for preparing an amidoxime functionalized three-dimensional covalent organic framework according to claim 1, wherein: In step 1), the molar ratio of tetrakis(4-formylphenyl)methane to 1,4-phenylenediacetonitrile is 1:(1-3).

3. The method for preparing an amidoxime functionalized three-dimensional covalent organic framework according to claim 1, wherein: In step 2), the mass ratio of the three-dimensional covalent organic framework to hydroxylamine hydrochloride is 1:(1-3).

4. The method for preparing an amidoxime functionalized three-dimensional covalent organic framework according to claim 1, wherein: In step 2), the volume ratio of triethylamine to ethanol solution is 1:(15-30).

5. Use of the amidoxime functionalized three-dimensional covalent organic framework prepared by the method according to any one of claims 1 to 4 in the adsorption of uranyl ions.

6. Use of the amidoxime functionalized three-dimensional covalent organic framework prepared by the method according to any one of claims 1 to 4 in the electrosorption of uranyl ions.

7. The use of the amidoxime functionalized three-dimensional covalent organic framework in the electrosorption of uranyl ions according to claim 6, characterized in that: The electroadsorption adopts a two-electrode system, with graphite as the anode and an amidoxime-functionalized three-dimensional covalent organic framework modified electrode as the cathode; alternating voltages of 0 V and -5 V are applied to the cathode.

8. The use of the amidoxime functionalized three-dimensional covalent organic framework in the electrosorption of uranyl ions according to claim 6, characterized in that: The amidoxime functionalized three-dimensional covalent organic framework for UO2 2+ It has electrosorption selectivity for UO2 2+ The adsorption capacity is as high as 4685 mg / g.

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