Preparation method and application of heteroporous metal covalent organic framework

Abstract

The present invention discloses a preparation method and application of a heteroporous metal covalent organic framework, belonging to the field of environmental protection technology. The present invention first co-cultivates 2,2'-bipyridine-5,5'-diamine with CuCl2·2H2O to obtain a copper metal single crystal, and then reacts the copper metal single crystal, [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde and p-diaminobenzene through a Schiff base reaction to prepare a heteroporous metal covalent organic framework. The hierarchical pore structure of the heteroporous metal covalent organic framework of the present invention can accelerate ion transport, and the introduction of metal sites can improve the photoelectrocatalytic performance, so that it has excellent photocatalytic uranium reduction characteristics. The heteroporous metal covalent organic framework of the present invention has good crystallinity, high stability, and a simple preparation method. It can be used for efficient photocatalytic reduction of uranium 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 preparation method and application of a heteroporous metal covalent organic framework. Background Art

[0002] Covalent organic frameworks (COFs) are a class of porous crystalline materials connected by stable covalent bonds, allowing the targeted integration of various functional units into highly ordered periodic arrays (Lohse, MS; Bein, T., Covalentorganic frameworks: structures, synthesis, and applications, Adv. Funct. Mater., 2018, 28, 1705553). Because COFs are composed of light elements (typically H, B, C, N, O, and Si), their physical and chemical properties are inherently limited, including high hydrophobicity and poor photoelectron transport and catalytic properties (Dong, JQ; Han, XY; Liu, H.; Li, Y.; Cui, Y., Metal-covalent organic frameworks (MCOFs): a bridge between metal-organic frameworks and covalent organic frameworks, Angew. Chem. Int. Ed., 2020, 59, 13722). Metal-organic frameworks (MOFs) combine a variety of metal ions and organic linkers to achieve complex pore structures and synergistic functions. However, the relative strength of ligand bonds can easily limit their practical applications, especially in harsh environments (Feng, L.; Wang, KY; Day, GS; Ryder, MR; Zhou, HC, Destruction of metal-organic frameworks: positive and negative aspects of stability and lability, Chem. Rev., 2020, 120, 13087). Therefore, the targeted introduction of metal ions into COFs to form metal COFs (MCOFs) can combine the properties of COFs and MOFs, thereby achieving a balance in crystallinity, porosity, stability, and tunability.

[0003] 2,2′-Bipyridine is a C2-symmetric planar molecule, and its derivatives have been widely used as common building blocks for developing two-dimensional MCOFs through post-synthesis metallation. For example, 2,2′-bipyridine COF was post-metallated with Re(CO)5Cl to prepare Re-COF with AA stacking, which achieved visible light-driven CO2 reduction (Yang, S.; Hu, W.; Zhang, X.; He, P.; Pattengale, B.; Liu, C.; Cendejas, M.; Hermans, I.; Zhang, X.; Zhang, J.; Huang, J., 2D covalent organic frameworks as intrinsic photocatalysts forvisible light-driven CO2 reduction, J. Am. Chem. Soc., 2018, 140, 14614). IICobalt-modified covalent organic framework as a robust water oxidation electrocatalyst (Aiyappa, HB; Thote, J.; Shinde, DB; Banerjee, R.; Kurungot, S., Cobalt-modified covalent organic framework as a robust water oxidation electrocatalyst, Chem. Mater. 2016, 28, 4375). However, this common post-loading method usually places the metal sites on the mesoporous walls of COFs, resulting in a decrease in the crystallinity of MCOFs and difficulty in controlling the actual metal loading (Kaczmarek, AM; Liu, YY; Kaczmarek, MK; Liu, H.; Artizzu, F.; Carlos, LD; Voort, P. Van Der., Developing luminescent ratiometric thermometers based on a covalent organic framework (COF), Angew. Chem. Int. Ed., 2020, 59, 1932). Furthermore, the design of MCOFs has primarily focused on building blocks with matching symmetries. Currently, a variety of MCOFs with square, hexagonal, or triangular pores have been designed and prepared. While well-defined pores provide nanoscale channels for selective ion transport and conversion, loading metal complexes on the long channel walls often increases the resistance to reactant transport to the active sites, hindering adsorption and catalytic applications (Yin, ZJ; Xu, SQ; Zhan, TG; Qi, QY; Wu, ZQ; Zhao, X., Ultrahigh volatile iodine uptake by hollow microspheres formed from aheteropore covalent organic framework. Chem. Commun., 2017, 53, 7266). Heteroporous MCOFs offer the potential to address these challenges by providing metal catalytic sites with pores of varying sizes that enable cooperative hierarchical transport. However, their complex structure poses significant challenges to their design and synthesis.

[0004] This study prepares a heteroporous metal covalent organic framework (MCOF) (Bpy-COF-Cu) by directly incorporating copper single crystals into a covalent organic framework (COF) via a three-component, one-pot method. Bpy-COF-Cu avoids the drawbacks of post-modification and achieves more controllable metal loading. Furthermore, the smaller mesopores primarily interconnect with the micropores, facilitating ion access to the active sites, while the larger mesopores reduce diffusion barriers, thereby improving ion transport efficiency. Furthermore, the regular distribution of metal sites confined within the micropores significantly enhances the photoelectric performance of Bpy-COF-Cu, enabling cyclic, confined catalysis of uranium under illumination. Consequently, Bpy-COF-Cu enables ultrafast photocatalytic reduction of uranium without the use of sacrificial reagents. Due to the synergistic effect of the metal catalytic sites and the framework structure, Bpy-COF-Cu achieves an extremely high removal efficiency (>99%) in uranium mine wastewater. Currently, there are no reports of synthesizing heteroporous metal covalent organic frameworks using a three-component, one-pot method for photocatalytic reduction of uranium. Summary of the Invention

[0005] To address the limitations of current metal covalent organic framework (MCOF) synthesis methods, the difficulty in controlling metal loading, and the need for sacrificial agents during uranium reduction, the present invention provides a method for preparing and applying a heteroporous MCOF. Using presynthesized copper single crystals, [1,1′:3′,1″-terphenyl]-3,3″,5,5″-tetracarboxaldehyde, and benzidine as raw materials, the heteroporous MCOF (Bpy-COF-Cu) was prepared via a Schiff base reaction. Bpy-COF-Cu possesses three pore sizes, two of which are primarily interconnected with micropores, facilitating ion access to active sites while reducing diffusion barriers and improving transport efficiency. The uniform distribution of metal sites within the micropores significantly enhances the photoelectric performance of Bpy-COF-Cu. The heteroporous MCOF synthesized by this method exhibits both ultrahigh and ultrafast uranium removal rates under illumination, demonstrating promising application prospects.

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

[0007] The present invention provides a method for preparing a heteroporous metal covalent organic framework, comprising the following steps:

[0008] 1) Mixing 2,2'-bipyridine-5,5'-diamine and copper salt as reaction raw materials, adding them to a solvent, and reacting at 90-120°C to obtain a copper metal single crystal;

[0009] 2) mixing the copper metal single crystal obtained in step 1), [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde and p-diaminobenzidine as reaction raw materials, adding a solvent, and sonicating to obtain a reaction mixture;

[0010] 3) The reaction mixture obtained in step 2) is subjected to freeze-thaw cycle degassing and flame sealing, reacted at 100-140° C., filtered, washed, and dried to obtain a heteroporous metal covalent organic framework.

[0011] Furthermore, in step 1), the copper salt is CuCl2·2H2O, and the molar ratio of 2,2'-bipyridine-5,5'-diamine to CuCl2·2H2O is 1:(1-2).

[0012] Furthermore, in step 1), the solvent is a mixed solution of N,N-dimethylformamide, ethanol and water, and the volume ratio thereof is 1:(2-4):(2-4).

[0013] Furthermore, in step 2), the molar ratio of the copper metal single crystal, [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde and p-diaminobenzidine is (1-3):2:(1-3).

[0014] Furthermore, in step 2), the solvent is a mixed solution of o-dichlorobenzene, n-butanol and acetic acid solution in a volume ratio of (4-6):(4-6):1; the concentration of the acetic acid solution is 2-4 mol / L.

[0015] The present invention also provides the use of the heteroporous metal covalent organic framework obtained by the preparation method in photocatalytic removal of uranium.

[0016] Furthermore, the photocatalytic removal of uranium refers to the conversion of soluble U VI Photocatalytic reduction to insoluble U IV .

[0017] The present invention also provides a heteroporous metal covalent organic framework obtained by the above preparation method for selectively removing UO2 from uranium mine wastewater containing competitive ions. 2+ The competitive ions include Na + 、Ni + 、Zn 2+ , Ca 2+ Mg 2+ 、Cu 2+ 、Cd 2+ 、Mn 2+ , Pb 2+ 、Al 3+ 、Fe 3+ Cr 3+ 、As 3+ 、Dy 3+ 、Nd 3+ 、La 3+ 、Tm 3+ Th 4+ , VO2 + .

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

[0019] (1) The present invention introduces copper metal single crystals into a three-component one-pot method to prepare a heteroporous metallic covalent organic framework, which has the advantages of simple preparation method, good crystallinity and high stability.

[0020] (2) The heteroporous covalent organic framework prepared by the present invention has a heteroporous structure and a metal single crystal that can achieve good ion transport and light absorption, and has significant photocatalytic properties, which can convert soluble U VI Photocatalytic reduction to insoluble U IV , improves the U VI removal effect.

[0021] (3) The present invention reveals the photocatalytic mechanism of the prepared heteroporous metal covalent organic framework for uranyl ions.

[0022] (4) The heteroporous metal covalent organic framework prepared by the present invention has the characteristics of fast ion transport, high site recycling rate, and good removal effect, which is conducive to cost reduction and sustainable development and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the synthetic route of Bpy-COF-Cu.

[0024] Figure 2 PXRD patterns of experimentally measured and simulated AA stacking structures of Bpy-COF-Cu (a) and 13 C cross-polarization / magic angle spinning solid-state NMR spectrum (b).

[0025] Figure 3 This is the photocurrent diagram of Bpy-COF-Cu.

[0026] Figure 4 Bpy-COF-Cu to UO2 2+ Removal kinetics (a) and reduction rate constants (b).

[0027] Figure 5 Bpy-COF-Cu in UO2 2+ XPS spectra of the solution before and after visible light irradiation (a) and the corresponding U 4 f High-resolution spectrum (b).

[0028] Figure 6 Bpy-COF-Cu for the treatment of UO2 in uranium mine wastewater 2+ Removal efficiency and anti-interference diagram. DETAILED DESCRIPTION

[0029] 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.

[0030] 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.

[0031] Example 1: Preparation and characterization of heteroporous metal covalent organic frameworks

[0032] 2,2'-Bipyridine-5,5'-diamine (Bpy, 9.3 mg, 0.05 mmol) and CuCl2·2H2O (8.5 mg, 0.05 mmol) were added as reaction materials to a mixture of N,N-dimethylformamide (DMF, 0.25 mL), water (H2O, 0.5 mL), and ethanol (EtOH, 0.75 mL) in a 5 mL glass vial. The reaction was incubated at 100°C for 3 days and then cooled to room temperature at a rate of 5°C / h. Dark green crystals were collected and dried in air to obtain copper single crystals (Bpy-Cu).

[0033] Copper single crystal (Bpy-Cu, 6.4 mg, 0.02 mmol), [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde (TPTCA, 13.7 mg, 0.04 mmol) and p-diaminobenzidine (BZ, 10.9 mg, 0.06 mmol) were added to a 10 mL Pyrex tube, and then o-dichlorobenzene (o-DCB, 0.50 mL), n-butanol (n-BuOH, 0.50 mL) and acetic acid aqueous solution (HOAc, 0.10 mL, 3 M) were added. After ultrasonic treatment for 10 min, a reaction mixture solution was obtained. The reaction mixture solution was degassed by three freeze-thaw cycles, and the Pyrex tube was sealed with a flame and heated at 120 The product was heated in an oven at 400 °C for 3 days, cooled, and separated by filtration. The filtered yellow solid product was washed with H2O, tetrahydrofuran (THF), and DMF, respectively, and Soxhlet extracted with THF overnight. It was then dried in a vacuum at 80 °C for 12 h to obtain a heteroporous metal covalent organic framework (Bpy-COF-Cu) with a yield of approximately 87%.

[0034] Figure 1 This is the synthetic route of Bpy-COF-Cu.

[0035] Figure 2 PXRD patterns of experimentally measured and simulated AA stacking structures of Bpy-COF-Cu (a) and 13 C cross-polarization / magic angle spinning solid-state NMR spectrum (b). Figure 2 It can be seen from a that the experimentally measured 2θ angle of PXRD of Bpy-COF-Cu shows a strong diffraction peak at 2.8°, and three relatively weak diffraction peaks at 5.6°, 9.4° and 22.5°, which correspond to the (110), (310), (600) and (001) crystal planes, respectively. The experimentally measured PXRD pattern of the heteroporous metal covalent organic framework Bpy-COF-Cu matches the PXRD pattern of the simulated AA stacking structure, indicating that the metal heteroporous covalent organic framework Bpy-COF-Cu prepared by the method of the present invention has high crystallinity. Figure 2 b As can be seen, Bpy-COF-Cu 13 C cross-polarization / magic angle spinning solid-state nuclear magnetic resonance (NMR) spectroscopy revealed a peak belonging to -C=N at 158 ​​ppm, indicating that the aldehyde group of TPTCA condensed with the amino group of Bpy-Cu.

[0036] Figure 3 The photocurrent diagram of Bpy-COF-Cu is shown in Figure 2. Figure 3 It can be seen that the heteroporous metal covalent organic framework Bpy-COF-Cu can generate a strong current under light conditions, while the current is significantly weakened under dark conditions, indicating that Bpy-COF-Cu has excellent photoelectric activity and can be used as a good photocatalytic material.

[0037] The above results show that the method of the present invention was successfully used to synthesize a highly crystalline metal heteroporous covalent organic framework Bpy-COF-Cu, which has good photoelectric properties.

[0038] Example 2: Application of Bpy-COF-Cu in Photocatalytic Removal of Uranyl Ions

[0039] 5 mg of Bpy-COF-Cu was added to a solution containing 50 ppm uranyl ions (UO2 2+ ) solution, samples (1 mL suspension) were taken for different illumination times, filtered with a 0.22 μm microporous filter membrane, and the filtrate was collected. The residual UO2 in the filtrate was measured by inductively coupled plasma mass spectrometry. 2+ Content, calculation of heteroporous metal covalent organic framework Bpy-COF-Cu to UO2 2+ The removal rate is calculated as follows: q =( C 0- C e ) / C 0×100%. Among them, q is the removal rate; C 0 is UO2 2+ Initial concentration, in mg / L; C e It is UO2 2+ The equilibrium concentration of , in mg / L.

[0040] Figure 4 Bpy-COF-Cu to UO2 2+ The removal kinetics (a) and reduction rate constant (b) of Figure 4 a It can be seen that under light conditions, Bpy-COF-Cu reacts with UO2 2+ The removal rate quickly reached equilibrium (97.7%) within 1 hour. Figure 4 b As can be seen from the pseudo first-order kinetic model, the corresponding reduction rate constant (k) is calculated to be 0.063 min -1 The Bpy-COF-Cu synthesized by the method of the present invention reacts with UO2 under light conditions. 2+ The removal effect of the conjugated microporous polymer material is better than that of most existing materials. For example, the removal rate of 50 ppm of U(VI) by the conjugated microporous polymer material is 86% in 2 h, k = 0.015 min -1 (Yu, F.; Zhu, Z.; Li, C.; Li, W.; Liang, R.; Yu, S.; Xu, Z.; Song, F.; Ren, Q.; Zhang, Z., A redox-active perylene-anthraquinone donor-acceptor conjugated microporous polymer with an unusual electron delocalization channel for photocatalytic reduction of uranium (VI) in strongly acidic solution. Appl. Catal. B-Environ., 2022, 314, 121467); Halogen hydrogen-bonded covalent organic framework material showed an 85% removal efficiency for 50 ppm of U(VI) in 50 min, k = 0.014 min -1(Feng, L.; Yuan, Y.; Yan, B.; Feng, T.; Jian, Y.; Zhang, J.; Sun, W.; Lin, K.; Luo, G.; Wang, N., Halogen hydrogen-bonded organic framework (XHOF) constructed by singlet open-shell diradical for efficient photoreduction of U(VI), Nat. Comm., 2022, 13, 1389). Bpy-COF-Cu versus UO2 2+ The high removal efficiency and fast removal rate of Bpy-COF-Cu can be attributed to: on the one hand, the smaller mesopores of Bpy-COF-Cu are directly connected to the microporous catalytic sites to promote the entry of ions into the active sites, while the larger mesopores can further reduce the diffusion barrier, thereby improving the transmission efficiency; on the other hand, the regular distribution of metal sites confined in the micropores greatly improves the photoelectric performance of Bpy-COF-Cu and realizes the catalytic conversion of UO2 under light. 2+ Therefore, Bpy-COF-Cu can convert soluble U into VI Rapidly reduced to insoluble U IV , achieving ultra-high efficiency UO2 2+ Remove.

[0041] In addition, Bpy-COF-Cu was added to the UO2 2+ After shaking under light conditions, the suspension was filtered through a 0.22 μm microporous filter membrane to collect the solid and measure the X-ray photoelectron spectroscopy (XPS). Figure 5 Bpy-COF-Cu in UO2 2+ XPS spectra of the solution before and after visible light irradiation (a) and the corresponding U 4 f High-resolution spectrum (b). Figure 5 a It can be seen that Bpy-COF-Cu has a strong U4 f Signal. In U 4 f In the high-resolution XPS spectrum, U 4 f The signal is divided into two peaks, U 4 f 5 / 2 (394.7 eV and 392.8 eV) and U 4 f 7 / 2 (385.1 eV and 382.3 eV), corresponding to U VI and U IV status, indicating that most UVI Restored to U IV And coexist on the surface of photocatalyst. The above results show that Bpy-COF-Cu has a great 2+ It has excellent photocatalytic reduction performance.

[0042] Example 3: Bpy-COF-Cu in UO2 2+ Anti-interference in removal

[0043] Bpy-COF-Cu was added to aqueous solutions containing different ions (UO2 2+ The initial concentration of Bpy-COF-Cu was 50 ppm and the other competing ions were 500 ppm), and the effect of Bpy-COF-Cu on UO2 2+ removal efficiency and anti-interference ability. Figure 6 Bpy-COF-Cu for the treatment of UO2 in uranium mine wastewater 2+ Removal efficiency and anti-interference diagram. Figure 6 It can be seen that under visible light irradiation, Bpy-COF-Cu has a strong effect on UO2 2 + The removal efficiency is very high, and common competitive cations (Na + 、Ni + 、Zn 2+ , Ca 2+ Mg 2+ 、Cu 2+ 、Cd 2+ 、Mn 2+ , Pb 2+ 、Al 3+ 、Fe 3+ Cr 3+ 、As 3+ 、Dy 3+ 、Nd 3+ 、La 3+ 、Tm 3+ Th 4+ , VO2 + ) has little interference with the Bpy-COF-Cu reaction on UO2 2+ Even in mixed ions, Bpy-COF-Cu has a significant effect on the removal of UO2. 2+ The removal rate of Bpy-COF-Cu to UO2 2+ The removal rate of UO2 is as high as 99%, indicating that the Bpy-COF-Cu prepared by the method of the present invention has a good effect on the removal of UO2 2+ The removal has good anti-interference ability and application potential.

[0044] 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 a heteroporous metal covalent organic framework, characterized in that: The steps include: 1) Mixing 2,2'-bipyridine-5,5'-diamine and a copper salt as reaction raw materials, adding them to a solvent, and reacting at 90-120°C to obtain a copper metal single crystal; 2) mixing the copper metal single crystal obtained in step 1), [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde and p-diaminobenzidine as reaction raw materials, adding a solvent, and sonicating to obtain a reaction mixture; 3) The reaction mixture obtained in step 2) is subjected to freeze-thaw cycle degassing and flame sealing, reacted at 100-140° C., filtered, washed, and dried to obtain a heteroporous metal covalent organic framework.

2. The method for preparing a heteroporous metal covalent organic framework according to claim 1, wherein: Step 1) The copper salt is CuCl2·2H2O, and the molar ratio of 2,2'-bipyridine-5,5'-diamine to CuCl2·2H2O is 1:(1-2).

3. The method for preparing a heteroporous metal covalent organic framework according to claim 1, wherein: In step 1), the solvent is a mixed solution of N,N-dimethylformamide, ethanol and water in a volume ratio of 1:(2-4):(2-4).

4. The method for preparing a heteroporous metal covalent organic framework according to claim 1, wherein: In step 2), the molar ratio of the copper metal single crystal, [1,1':3',1''-terphenyl]-3,3'',5,5''-tetraaldehyde and p-diaminobenzidine is (1-3):2:(1-3).

5. The method for preparing a heteroporous metal covalent organic framework according to claim 1, wherein: In step 2), the solvent is a mixed solution of o-dichlorobenzene, n-butanol and acetic acid solution in a volume ratio of (4-6):(4-6):1; the concentration of the acetic acid solution is 2-4 mol / L.

6. Use of the heteroporous metal covalent organic framework obtained by the preparation method according to any one of claims 1 to 5 in photocatalytic removal of uranium.

7. The application according to claim 6, characterized in that The photocatalytic removal of uranium refers to the conversion of soluble U VI Photocatalytic reduction to insoluble U IV .

8. The heteroporous metal covalent organic framework prepared by the method according to any one of claims 1 to 5 is used for selectively removing UO2 from uranium mine wastewater containing competing ions 2+ The application is characterized in that The competing ions include Na + 、Ni + 、Zn 2+ , Ca 2+ Mg 2 + 、Cu 2+ 、Cd 2+ 、Mn 2+ , Pb 2+ 、Al 3+ 、Fe 3+ Cr 3+ 、As 3+ 、Dy 3+ 、Nd 3+ 、La 3+ 、Tm 3+ Th 4+ , VO2 + .

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