Synthesis method and application of an oxygen-containing alkyl chain functionalized covalent organic framework

Abstract

The invention discloses a synthesis method and application of an oxygen-containing alkyl chain functionalized covalent organic framework, and belongs to the field of environmental protection technology. The present invention synthesizes a covalent organic framework having a triazine structure and a hydroxyl group by a Schiff base reaction of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) triphenylamine and 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-diformaldehyde, and then post-modifies the hydroxyl group to an oxygen-containing alkyl chain by 1-bromo-2(2-methoxyethoxy)ethane to prepare an oxygen-containing alkyl chain functionalized covalent organic framework. The oxygen-containing alkyl chain functionalized covalent organic framework synthesized by the inventive method has the advantages of super hydrophilicity, rich action sites, effective electron-hole separation, efficient electron transfer, etc., has strong photocatalytic reduction ability for U(VI), high efficiency, good selectivity, and has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental protection, and in particular relates to a synthesis method and application of an oxygen-containing alkyl chain functionalized covalent organic framework. Background Art

[0002] Mining, processing, and post-processing in the nuclear industry are often accompanied by the generation of chemically toxic and radioactive uranium-containing wastewater. By studying the existing forms of uranium, the highly mobile and soluble U(VI) in the wastewater can be reduced to the less soluble and low-mobility U(IV), which can effectively remove uranium (T. Chen, K.-F. Yu, C.-X. Dong, X.Yuan, X. Gong, J. Lian, X. Cao, M.-Z. Li, L. Zhou, B.-W. Hu, R. He, W.-K.Zhu, X.-K. Wang, Advanced photocatalysts for uranium extraction: Elaboratedesign and future perspectives, Coord. Chem. Rev. 2022, 467, 214615). Photocatalytic reduction of U(VI) is an attractive strategy due to its broad energy resources, environmental friendliness, and sustainable development. Therefore, the development of novel photocatalysts for the reduction of U(VI) has become a research priority.

[0003] Covalent organic frameworks (COFs) are a class of porous polymers with pre-designed geometric structures, large specific surface areas, and strong stability. They are composed of linkers that can serve as light-absorbing antennas, electron donors, and electron acceptors. Therefore, COFs have excellent potential and good photocatalytic activity in photocatalytic applications, becoming an ideal platform for the conversion of U(VI) (Y.-N. Gong, X.-Y. Guan, H.-L. Jiang, Covalent organic frameworks for photocatalysis: Synthesis, structural features, fundamentals and performance, Coord. Chem. Rev.2023, 475, 214889). However, most traditional COFs photocatalysts have inherent hydrophobicity, which hinders the target species from entering the adsorption sites, leads to low light absorption utilization, rapid recombination of photogenerated electrons and holes, and energy loss during electron excitation and migration, resulting in low efficiency of COFs photocatalysts (Z.-S. Chen, J.-Y.Wang, M.-J. Hao, Y.-H. Xie, X.-L. Liu, H. Yang, Geoffrey IN Waterhouse, X.-K. Wang, S.-Q. Ma, Tuning excited state electronic structure and charge transport in covalent organic frameworks for enhanced photocatalytic performance, Nat. Commun. 2023, 14, 1106). Therefore, it is of great significance to develop new COFs photocatalysts to solve the above problems.

[0004] The photocatalytic reduction process consists of the following steps: (i) the target substance diffuses to the adsorption site of the photocatalyst through mass transfer in water; (ii) the photocatalyst absorbs light and becomes excited, thereby generating photogenerated electrons and holes; (iii) the photogenerated electrons and holes are effectively separated and transferred along the photocatalyst to the active site; and (iv) the target substance is reduced (T. He, W.-L.Zhen, Y.-Z. Chen, Y.-Y. Guo, Z.-E. Li, N. Huang, Z.-P. Li, R.-Y. Liu, Y. Liu,X. Lian, C. Xue, T.-C Sum, W. Chen, D.-L. Jiang, Integrated interfacial design of covalent organic framework photocatalysts to promote hydrogen evolution from water, Nat. Commun.2023, 14, 329). Traditional COFs photocatalytic design often focuses on improving the separation of photogenerated electrons and holes and the efficiency of photogenerated electron transfer, while ignoring the step of transferring the target species to the active site through water mass transfer. This results in a single photocatalytic process controlled by COFs photocatalysts and low photocatalytic efficiency. Therefore, developing COFs-integrated interfacial photocatalysts that can control the entire photocatalytic process, seamlessly connecting each step in the photocatalytic process and resolving the challenges encountered in photocatalysis, is an effective strategy for improving photocatalytic reduction efficiency and has great application potential. Summary of the Invention

[0005] This invention aims to provide a method for synthesizing and applying an oxygenated alkyl chain-functionalized covalent organic framework. The method involves synthesizing a triazine-based covalent organic framework (DHBD-COF) with hydroxyl groups via a Schiff base reaction between 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde. The hydroxyl groups are then post-modified with 1-bromo-2(2-methoxyethoxy)ethane to form an oxygenated alkyl chain-functionalized covalent organic framework (PEO-COF). The superhydrophilic oxygenated alkyl chains facilitate the transfer of U(VI) to the active site. The abundant triazine structure acts as an absorptive antenna, endowing PEO-COF with excellent light absorption. The extended π-conjugation of the linker facilitates the separation of photogenerated electrons and holes. The local charge imbalance created by the oxygenated alkyl chains creates a built-in electric field that enhances the efficiency of photogenerated electron transfer. The oxygen-containing alkyl chain functionalized covalent organic framework synthesized by the method of the present invention can effectively control the entire photocatalytic process, has strong photocatalytic reduction ability for U(VI), high efficiency, good selectivity, and has good application prospects.

[0006] To achieve the above object, the present invention specifically adopts the following technical solutions:

[0007] The present invention provides a method for synthesizing an oxygen-containing alkyl chain functionalized covalent organic framework, comprising the following steps:

[0008] 1) 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde are added to a solvent, degassed by freeze-thaw cycles, flame-sealed, and reacted at 90-150°C to obtain a covalent organic framework;

[0009] 2) The covalent organic framework obtained in step 1) is mixed with 1-bromo-2(2-methoxyethoxy)ethane in a solvent, ultrasonically reacted to obtain a reaction solution, reacted at 70-100°C, cooled and collected the solid, washed and dried to obtain an oxygen-containing alkyl chain functionalized covalent organic framework.

[0010] Furthermore, in step 1), the molar ratio of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine to 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde is 2:(3-6).

[0011] Furthermore, in step 1), the solvent is a mixed solution of mesitylene, 1,4-dioxane and acetic acid, and the volume ratio of mesitylene, 1,4-dioxane and acetic acid is (25.5-50):(4.5-9):1.

[0012] Furthermore, in step 2), the mass ratio of the covalent organic framework to 1-bromo-2(2-methoxyethoxy)ethane is 1:(10-20).

[0013] The present invention also provides the use of the oxygen-containing alkyl chain functionalized covalent organic framework synthesized by the above method in the photocatalytic reduction of U(VI).

[0014] Furthermore, the photocatalytic reduction of U(VI) refers to the photocatalytic reduction of U(VI) to U(IV) by the oxygen-containing alkyl chain functionalized covalent organic framework under ultraviolet / visible light irradiation conditions.

[0015] Furthermore, the oxygen-containing alkyl chain functionalized covalent organic framework can selectively remove U(VI) in the presence of multiple interfering ions; the multiple interfering ions include Na + Mg 2+ 、Al 3+ , K + , Ca 2+ Sc 3+ Cr 3+ 、Ni 3+ 、Zn 2+ 、Y 3+ 、La 3+ 、Ce 3+ 、Pr 3+ 、Pm 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ , Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ He Lu 3+ At least one of .

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The oxygen-containing alkyl chain functionalized covalent organic framework prepared by the present invention can control the entire process of photocatalytic reduction, from superhydrophilicity to promote the transmission of U(VI) to the active site, to the excitation to generate photogenerated electrons-holes after light absorption, and then to the efficient transfer of photogenerated electrons to the active site to reduce U(VI), with ultra-high photocatalytic reduction efficiency.

[0018] (2) The synthesis method of the oxygen-containing alkyl chain functionalized covalent organic framework of the present invention is simple, the product has high purity and good crystallinity.

[0019] (3) The oxygen-containing alkyl chain functionalized covalent organic framework prepared by the present invention overcomes the inherent hydrophobicity of the covalent organic framework, has superhydrophilicity, high water mass transfer efficiency, can quickly transfer more U(VI) to the action site, has a high adsorption capacity for U(VI) and fast removal kinetics.

[0020] (4) The oxygen-containing alkyl chain functionalized covalent organic framework prepared by the present invention has excellent stability under extreme conditions.

[0021] (5) The oxygen-containing alkyl chain functionalized covalent organic framework prepared by the present invention has good selectivity for the photocatalytic reduction of U(VI).

[0022] (6) The oxygen-containing alkyl chain functionalized covalent organic framework prepared by the present invention has strong photocatalytic reduction ability and high efficiency for U(VI) and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the synthesis route of PEO-COF.

[0024] Figure 2 The experimentally measured PXRD pattern and the structurally simulated PXRD pattern of DHBD-COF (a) and the experimentally measured PXRD pattern and the structurally simulated PXRD pattern of PEO-COF (b) are shown.

[0025] Figure 3 Infrared spectra of DHBD-COF (a) and PEO-COF (b).

[0026] Figure 4 Water contact angle diagrams of DHBD-COF (a) and PEO-COF (b).

[0027] Figure 5 PXRD patterns (a) and IR spectra (b) of PEO-COF under different conditions.

[0028] Figure 6UV / visible diffuse reflectance spectra of DHBD-COF and PEO-COF (a), Mott-Schottky plot of PEO-COF (b), and Mott-Schottky plot of DHBD-COF (c).

[0029] Figure 7 Figure 2 is the adsorption isotherm (a) and adsorption kinetics (b) of DHBD-COF and PEO-COF for the photocatalytic reduction of U(VI).

[0030] Figure 8 This is the removal rate of PEO-COF for different metal ions. DETAILED DESCRIPTION

[0031] 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.

[0032] 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.

[0033] Example 1: Synthesis and Characterization of PEO-COF

[0034] 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine (TAPT, 35.4 mg, 0.1 mmol), 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde (DHBD, 36.3 mg, 0.15 mmol), 6 mL of mesitylene, 1 mL of 1,4-dioxane, and 0.2 mL of acetic acid were added to a 20 mL Pyrex quartz tube. The tube was quickly frozen in a liquid nitrogen bath and degassed through three freeze-thaw cycles. The tube was flame-sealed and sonicated to obtain a reaction mixture solution. The reaction mixture solution was placed in an oven at 120 °C for 36 h. After cooling to room temperature, the solid product was collected and washed with tetrahydrofuran, methanol, and acetone, respectively, and then dried in vacuo to obtain an orange-yellow product, the covalent organic framework (DHBD-COF).

[0035] 35.44 mg of DHBD-COF, 1-bromo-2(2-methoxyethoxy)ethane (PEO, 400 μL, density 1.36 mg / μL), 440 mg of potassium carbonate and 16 mL of N,N-dimethylformamide were added to a 25 mL two-necked reaction bottle and ultrasonically mixed to obtain a reaction solution. The reaction solution was stirred at 85 °C for 24 h, cooled and collected, and the solid product was washed with water and tetrahydrofuran, respectively, and then vacuum dried to obtain a yellow oxygen-containing alkyl chain functionalized covalent organic framework (PEO-COF).

[0036] Figure 1 This is a schematic diagram of the synthesis route of PEO-COF.

[0037] Powder X-ray diffraction (PXRD) was used to characterize the crystallinity of PEO-COF functionalized with oxygen-containing alkyl chains. Figure 2 The experimental PXRD pattern and structure simulation PXRD pattern of DHBD-COF (a) and the experimental PXRD pattern and structure simulation PXRD pattern of PEO-COF (b). Figure 2 As can be seen from the experimental PXRD pattern of DHBD-COF, there is a strong diffraction peak at 2θ = 2.38°, indicating that the COF has good crystallinity. By comparing the data of the structure simulation with the experimental data, it can be seen that the experimental PXRD of DHBD-COF matches the simulated structure. Figure 2 b As can be seen from the PXRD pattern of PEO-COF modified with 1-bromo-2(2-methoxyethoxy)ethane, a strong diffraction peak appears at 2θ = 2.38°, which matches the data of structural simulation, indicating that the highly crystalline oxygen-containing alkyl chain functionalized covalent organic framework PEO-COF was successfully synthesized by the method of the present invention.

[0038] Fourier transform infrared spectroscopy (FT-IR) was used to characterize the oxygenated alkyl chain functionalized covalent organic framework PEO-COF. Figure 3 The infrared spectra of DHBD-COF (a) and PEO-COF (b) are shown in Figure 1. Figure 3 a As can be seen from the FT-IR spectra of DHBD-COF, the peak at 1590 cm -1 A new absorption band corresponding to C=N stretching vibration appeared at 3452 cm −1 、3312 cm −1 、3203 cm −1 The absorption peaks at 1667 cm-1 correspond to the amine stretching vibration of TAPT. −1The C=O stretching vibration absorption peak corresponding to DHBD disappears, indicating that an aldol condensation reaction occurs between TAPT and DHBD to prepare DHBD-COF. Figure 3 b As can be seen, compared with DHBD-COF, PEO-COF has a −1 A new absorption band corresponding to COC stretching vibration appeared at , indicating that the hydroxyl groups on the surface of DHBD-COF were successfully modified into oxygen-containing alkyl chains, indicating that the oxygen-containing alkyl chain functionalized covalent organic framework PEO-COF was successfully prepared.

[0039] The water contact angle was used to characterize the hydrophilicity of the oxygen-containing alkyl chain functionalized covalent organic framework PEO-COF. Figure 4 The water contact angle diagrams of DHBD-COF (a) and PEO-COF (b) are shown. Figure 4 It can be seen that the water contact angle of DHBD-COF is 58.9°, and the water contact angle of PEO-COF is 31.9°, indicating that PEO-COF has better hydrophilicity.

[0040] PXRD patterns and FT-IR patterns were used to characterize the stability of PEO-COF under extreme conditions. Figure 5 The PXRD patterns (a) and infrared spectra (b) of PEO-COF under different conditions are shown in Figure 2. Figure 5 a It can be seen that the diffraction peak of PEO-COF at 2θ = 2.38° does not change under different conditions. Figure 5 b It can be seen that PEO-COF has a peak at 1173 cm under different conditions. −1 The absorption band corresponding to COC stretching vibration does not change. The above results indicate that PEO-COF has excellent stability under extreme conditions.

[0041] Since the first step of the photocatalytic reaction is the absorption of photons, the light conversion efficiency can be greatly improved by expanding the light absorption range of the material. Figure 6 The UV / visible diffuse reflectance spectra of DHBD-COF and PEO-COF (a), the Mott-Schottky diagram of PEO-COF (b), and the Mott-Schottky diagram of DHBD-COF (c). Figure 6 It can be seen that the intrinsic absorption edge of PEO-COF is significantly red-shifted compared to DHBD-COF, which may be due to the introduction of oxygen-containing alkyl chains, which reduces the band gap and promotes electron delocalization. The band gaps of DHBD-COF and PEO-COF are calculated to be 2.15 and 2.08 eV respectively based on the Kubelka-Munk function. The performance of the materials and their electronic band positions are determined by Mott-Schottky tests on DHBD-COF and PEO-COF. Figure 6 b and Figure 6As shown in Figure 3, the Mott-Schottky plots of DHBD-COF and PEO-COF at frequencies of 500, 1000, and 1500 Hz all exhibit positive slopes, indicating that they are typical n-type semiconductors, where electrons are the primary charge carriers. The conduction band positions of DHBD-COF and PEO-COF are -1.01 and -1.04 V (vs. NHE), respectively. Combining the band gaps of DHBD-COF and PEO-COF obtained from UV / Vis diffuse reflectance data, the valence band positions are calculated to be 1.34 and 1.24 V (vs. NHE), respectively. Therefore, under photoexcitation, PEO-COF can generate photogenerated electrons to reduce U(VI).

[0042] Example 2: Photocatalytic Reduction of U(VI) by PEO-COF

[0043] 5 mg of oxygen-containing alkyl chain functionalized covalent organic framework PEO-COF was added into 25 mL of methanol (MA) and water (V MA :V H2O =1:49) in a mixed solution and shaken in the dark for 60 minutes to allow U(VI) to reach adsorption-desorption equilibrium on the PEO-COF surface. The suspension was then irradiated with UV / visible light for 2 hours. Afterward, 0.5 mL of the suspension was removed and filtered through a 0.22 μm microporous membrane. The remaining U(VI) concentration in the filtrate was measured using inductively coupled plasma-mass spectrometry. Figure 7 a is the adsorption isotherm of DHBD-COF and PEO-COF for the photocatalytic reduction of U(VI). Figure 7 a It can be seen that the adsorption capacity of U(VI) on PEO-COF after UV / visible light irradiation is as high as 1505.5 mg / g, which is much higher than the adsorption capacity of U(VI) on DHBD-COF.

[0044] 5 mg of oxygen-containing alkyl chain functionalized covalent organic framework PEO-COF was added to 25 mL of methanol and water (V MA :V H2O =1:49) in a mixed solution and shaken in the dark for 60 minutes to allow U(VI) to reach adsorption-desorption equilibrium on the PEO-COF surface. Then, under UV / visible light irradiation, 0.5 mL of the suspension was removed at intervals and filtered through a 0.22 μm microporous membrane. The remaining U(VI) concentration in the filtrate was measured using inductively coupled plasma-mass spectrometry. Figure 7 b is the adsorption kinetics of DHBD-COF and PEO-COF for the photocatalytic reduction of U(VI). Figure 7b As can be seen from the figure, the removal rate of U(VI) by DHBD-COF is low after UV / visible light irradiation; the removal rate of U(VI) by PEO-COF in a dark environment is about 24.3%, while after 20 min of UV / visible light irradiation, the removal rate of U(VI) by PEO-COF is close to 100%, indicating that PEO-COF has strong photocatalytic reduction ability and high efficiency for U(VI).

[0045] Example 3: Study on the selectivity and mechanism of PEO-COF reduction of U(VI)

[0046] Na + Mg 2+ 、Al 3+ , K + , Ca 2+ Sc 3+ Cr 3+ 、Ni 3+ 、Zn 2+ 、Y 3+ 、La 3+ 、Ce 3+ 、Pr 3+ 、Pm 3+ 、Nd 3+ 、Sm 3+ 、Eu 3 + 、Gd 3+ , Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3+ He Lu 3+ The effects of coexisting metal ions in rare earth tailings wastewater on the selectivity of PEO-COF for the reduction of U(VI) were investigated. 5 mg of PEO-COF was added to 50 mL of methanol and water (V) containing 20 mg / L U(VI) and 80 mg / L interfering metal ions. MA :V H2O =1:49) mixed solution was ultrasonicated for 120 min and then irradiated under UV / visible light for 2 h. 0.5 mL of the suspension was taken out and filtered through a 0.22 μm microporous membrane. The concentrations of various metal ions in the filtrate were measured by inductively coupled plasma mass spectrometry. Figure 8 This is the removal rate of different metal ions by PEO-COF. Figure 8It can be seen that even in the presence of multiple interfering ions, the removal efficiency of PEO-COF for U(VI) is still higher than 93%, with good selectivity.

[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 synthesizing an oxygen-containing alkyl chain functionalized covalent organic framework, characterized in that: The steps include: 1) 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine and 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde are added to a solvent, degassed by freeze-thaw cycles, flame-sealed, and reacted at 90-150°C to obtain a covalent organic framework; 2) The covalent organic framework obtained in step 1) is mixed with 1-bromo-2-(2-methoxyethoxy)ethane in a solvent, ultrasonically reacted to obtain a reaction solution, reacted at 70-100°C, cooled and collected the solid, washed and dried to obtain an oxygen-containing alkyl chain functionalized covalent organic framework.

2. The method for synthesizing an oxygen-containing alkyl chain functionalized covalent organic framework according to claim 1, characterized in that: In step 1), the molar ratio of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)triphenylamine to 3,3'-dihydroxy-[1,1'-biphenyl]-4,4'-dicarbaldehyde is 2:(3-6).

3. The method for synthesizing an oxygen-containing alkyl chain functionalized covalent organic framework according to claim 1, characterized in that: Step 1) The solvent is a mixed solution of mesitylene, 1,4-dioxane and acetic acid, and the volume ratio of mesitylene, 1,4-dioxane and acetic acid is (25.5-50):(4.5-9):

1.

4. The method for synthesizing an oxygen-containing alkyl chain functionalized covalent organic framework according to claim 1, wherein: In step 2), the mass ratio of the covalent organic framework to 1-bromo-2-(2-methoxyethoxy)ethane is 1:(10-20).

5. Use of an oxygen-containing alkyl chain functionalized covalent organic framework synthesized by the method according to any one of claims 1 to 4 in the photocatalytic reduction of U(VI).

6. The application according to claim 5, characterized in that The photocatalytic reduction of U(VI) refers to the photocatalytic reduction of U(VI) to U(IV) by an oxygen-containing alkyl chain functionalized covalent organic framework under ultraviolet / visible light irradiation conditions.

7. The use according to claim 5, characterized in that The oxygen-containing alkyl chain functionalized covalent organic framework can selectively remove U(VI) in the presence of multiple interfering ions; the multiple interfering ions include Na + Mg 2+ 、Al 3+ , K + , Ca 2+ Sc 3 + Cr 3+ 、Ni 3+ 、Zn 2+ 、Y 3+ 、La 3+ 、Ce 3+ 、Pr 3+ 、Pm 3+ 、Nd 3+ 、Sm 3+ 、Eu 3+ 、Gd 3+ , Tb 3+ 、Dy 3+ 、Ho 3+ 、Er 3+ 、Tm 3+ 、Yb 3 + He Lu 3+ At least one of .

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