A two-dimensional covalent organic framework with thiophene groups for iodine adsorption, its preparation method and application

Abstract

This invention discloses a two-dimensional covalent organic framework with a thiophene group for iodine adsorption, its preparation method, and its application, belonging to the field of nuclear protection technology. It uses benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde as the aldehyde monomer and 4,4'-diaminoazobenzene as the amino monomer. Utilizing the C3 symmetry of benzotrithiophene and the C2 symmetry of azobenzene, a directional topological assembly is performed. Through Schiff base condensation, a two-dimensional crystalline framework with a highly ordered hcb topology is successfully constructed, achieving molecular-level synergistic integration of sulfur-rich and nitrogen-rich active sites. This results in a uniform 2.7 nm mesoporous channel and a high-density imine bond network within the covalent organic framework, exhibiting high specific surface area and excellent thermal stability. When applied to the adsorption and separation of iodine, it demonstrates an ultra-high saturated adsorption capacity, achieving efficient capture and solidification of radioactive iodine.

Description

Technical Field

[0001] This invention relates to the field of nuclear protection technology, specifically to a two-dimensional covalent organic framework with a thiophene group for iodine adsorption, its preparation method, and its application. Background Technology

[0002] With the rapid development of the nuclear energy industry, radioactive volatile fission products such as iodine isotopes released during nuclear power generation, nuclear fuel reprocessing, nuclear accident emergency response, or nuclear medicine diagnosis and treatment pose a long-term potential threat to the ecological environment and public health due to their high volatility, high chemical toxicity, and long half-life, and are easily dispersed through the atmosphere or water bodies. Therefore, developing efficient, stable, and economical iodine adsorbents to achieve efficient capture and solidification of iodine is a critical problem that urgently needs to be solved in the field of nuclear safety and environmental protection.

[0003] Currently, commonly used iodine adsorbents in industry include silver-based adsorbents, activated carbon, zeolite molecular sieves, and metal-organic frameworks (MOFs), which have attracted much attention in recent years. Among these, silver-based adsorbents are expensive to prepare and prone to aggregation, and AgI may still decompose at high temperatures, leading to the re-release of iodine. Activated carbon and zeolite molecular sieves mainly rely on physical adsorption or weak chemical interactions; although they have high specific surface areas, they lack sufficient binding sites for iodine molecules, resulting in weak binding forces and poor thermal stability. While metal-organic frameworks have high specific surface areas, their frameworks are prone to collapse under humid or acidic conditions.

[0004] Covalent organic frameworks (COFs) are a class of crystalline porous polymers composed of light elements (C, H, N, O, etc.) linked by covalent bonds. They have attracted considerable attention in the field of environmental remediation due to their high specific surface area, low density, designable pore structure, and excellent chemical stability. However, existing COFs still face the following significant bottlenecks: first, low utilization of active sites leads to limited saturation adsorption capacity; second, insufficient pore affinity results in slow adsorption kinetics; and third, structural damage during recycling makes it difficult to balance high adsorption capacity with long lifetime.

[0005] Therefore, developing a novel COF material that combines high iodine adsorption capacity, fast adsorption kinetics, excellent thermal stability, and low cost has significant application value. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a two-dimensional covalent organic framework of thiophene groups for iodine adsorption. This covalent organic framework has a two-dimensional crystalline framework with a highly ordered hcb topology, realizing molecular-level synergistic integration of sulfur-rich active sites and nitrogen-rich active sites, and has ultra-high saturation adsorption capacity and excellent thermal stability.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A two-dimensional covalent organic framework with a thiophene group for iodine adsorption has the structural formula shown in Formula I:

[0009]

[0010] Formula I.

[0011] In a preferred embodiment of the present invention, the structural unit of the two-dimensional covalent organic framework belongs to the trigonal crystal system, space group P3, with cell parameters a=b=43.79197 Å, c=10.00000 Å, α=β=90°, γ=120°.

[0012] In a preferred embodiment of the present invention, the two-dimensional covalent organic framework is formed by the condensation of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene.

[0013] This invention also provides a method for preparing the above-mentioned two-dimensional covalent organic framework with thiophene groups for iodine adsorption, which includes the following steps:

[0014] S1. Mix and grind benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene to make them evenly mixed and obtain a mixed powder.

[0015] S2. Add the mixed solvent and catalyst to the mixed powder in step S1, and after a cycle of freezing, evacuation and thawing to remove oxygen, seal under vacuum and heat to carry out the reaction.

[0016] S3. After the reaction is complete, the product is repeatedly washed to remove unreacted substances and then dried under vacuum to obtain the target product.

[0017] In a preferred embodiment of the present invention, the molar ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde to 4,4'-diaminoazobenzene in step S1 is 1:1 to 2.5; preferably 1:1.5.

[0018] In a preferred embodiment of the present invention, the amount of the mixed solvent used in step S1 is 140 to 170 times the total mass of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene.

[0019] In a preferred embodiment of the present invention, the mixed solvent in step S2 is a solvent composed of mesitylene and dioxane mixed in a volume ratio of 1:3; the catalyst is an aqueous solution of acetic acid with a concentration of 6 mol / L.

[0020] In a preferred embodiment of the present invention, the volume ratio between the catalyst and the mixed solvent in step S2 is 1:8~9.

[0021] In a preferred embodiment of the present invention, the reaction temperature in step S2 is 100~140℃ and the reaction time is 60~200 h.

[0022] The present invention also provides the application of the above-mentioned thiophene group two-dimensional covalent organic framework for iodine adsorption or the material prepared by the above preparation method in iodine adsorption and separation.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] This invention uses benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde as the aldehyde monomer and 4,4'-diaminoazobenzene as the amino monomer. Utilizing the C3 symmetry of benzotrithiophene and the C2 symmetry of azobenzene, a directional topological assembly was performed. A two-dimensional crystalline framework with a highly ordered hcb topology was successfully constructed via Schiff base condensation reaction. This achieved molecular-level synergistic integration of the sulfur-rich active sites of benzotrithiophene and the nitrogen-rich active sites of azobenzene, resulting in a uniform 2.7 nm mesoporous channel and a high-density imine bond network within the prepared covalent organic framework. Furthermore, this covalent organic framework exhibits a high specific surface area and excellent thermal stability. When applied to the adsorption and separation of iodine, this material demonstrates an ultra-high saturated adsorption capacity based on soft acid-soft base interactions and charge transfer mechanisms, achieving efficient capture and solidification of radioactive iodine.

[0025] The preparation method of the present invention achieves solid-phase premixing by introducing grinding before the reaction, which effectively increases the contact area of ​​the reactant monomers and promotes the condensation reaction, enabling the formation of uniform mesoporous channels inside the material and greatly improving the adsorption performance of the material. Attached Figure Description

[0026] Figure 1 This is a powder X-ray diffraction pattern of the thiophene-based two-dimensional covalent organic framework prepared in Example 1 of this invention;

[0027] Figure 2 The Fourier transform infrared spectrum of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of this invention;

[0028] Figure 3 This is a scanning electron microscope image of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of the present invention;

[0029] Figure 4 Thermogravimetric analysis (TGA) curve of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of the present invention;

[0030] Figure 5 This is a nitrogen adsorption-desorption curve of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of the present invention;

[0031] Figure 6 This is a pore size distribution diagram of the thiophene group two-dimensional covalent organic framework obtained in Example 1 of the present invention;

[0032] Figure 7 This is a BET diagram of the two-dimensional covalent organic framework with thiophene groups obtained in Example 1 of this invention;

[0033] Figure 8 This is an iodine vapor adsorption diagram of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of the present invention;

[0034] Figure 9 The diagram shows the iodine vapor desorption process of the thiophene group two-dimensional covalent organic framework prepared in Example 1 of this invention. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] A two-dimensional covalent organic framework with a thiophene group for iodine adsorption has the structural formula shown in Formula I:

[0037]

[0038] Formula I.

[0039] This two-dimensional covalent organic framework is formed by the condensation of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene. The specific synthetic route is as follows:

[0040] .

[0041] Specifically, the preparation method of the above-mentioned thiophene group two-dimensional covalent organic framework for iodine adsorption includes the following steps:

[0042] S1. Benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene are mixed and ground in a mortar at a molar ratio of 1:1 to 2.5 to achieve uniform mixing and solid-phase pretreatment, resulting in a mixed powder.

[0043] S2. Transfer the mixed powder from step S1 to a reaction vessel and add a mixed solvent and catalyst. After cyclic deoxygenation through freezing, evacuation, and thawing, seal under vacuum and heat to 100-140℃ for static reaction for 60-200 h. The amount of mixed solvent is 140-170 times the total mass of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene. The volume ratio between the catalyst and the mixed solvent is 1:8-9. The mixed solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:3, and the catalyst is a 6 mol / L aqueous solution of acetic acid.

[0044] S3. After the reaction is complete, the product is washed repeatedly with acetone 3 to 5 times to remove unreacted substances, and then dried under vacuum to obtain the target product.

[0045] Example 1

[0046] A method for preparing a thiophene-based two-dimensional covalent organic framework for iodine adsorption, comprising the following steps:

[0047] S1. Mix and grind 15.3 mg of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 14.7 mg of 4,4'-diaminoazobenzene in a mortar to achieve uniform mixing and solid-phase pretreatment, and obtain a mixed powder.

[0048] S2. Transfer the mixed powder from step S1 to a reaction vessel and add 1 mL of mixed solvent and 0.1 mL of catalyst. After deoxygenation through freezing, evacuation, and thawing, the mixture is vacuum sealed and heated to 120°C for static reaction for 72 h. The mixed solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:3, and the catalyst is a 6 mol / L aqueous solution of acetic acid.

[0049] S3. After the reaction was completed, the product was washed five times with acetone to remove unreacted material, and then dried under vacuum to obtain 21.6 mg of the target product in the form of yellow powder (named ZCST-105), with a yield of 72%.

[0050] I. Characterization of ZCST-105, a two-dimensional covalent organic framework with a thiophene group

[0051] The thiophene-based two-dimensional covalent organic framework ZCST-105 prepared in Example 1 was characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, morphology characterization, thermogravimetric analysis, and pore structure testing, as detailed below:

[0052] 1. Powder X-ray diffraction analysis

[0053] The crystal structure of ZCST-105 was modeled and refined using powder X-ray diffraction (PXRD) combined with the Reflex module in Material Studio software. The results are as follows: Figure 1 As shown.

[0054] Depend on Figure 1 It can be seen that the simulated spectrum and the experimental spectrum show a high degree of consistency in peak position and intensity. Through Pawley full-spectrum fitting refinement of the experimental data in the 2.0–40.0° range, a satisfactory goodness of fit was obtained (Rwp = 6.32%, Rp = 4.46%). The refined cell parameters are a = b = 43.79197 Å, c = 10.00000 Å, α = β = 90°, γ = 120° (space group P3). This result is in good agreement with the calculated values ​​of the theoretical structural model, strongly confirming that the ZCST-105 material has been successfully constructed and possesses a highly ordered trigonal porous framework structure and excellent crystallinity.

[0055] 2. Fourier transform infrared spectroscopy

[0056] Figure 2 Fourier transform infrared spectra of ZCST-105, a two-dimensional covalent organic framework with a thiophene group, and p-diaminoazobenzene and benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde. Figure 2 Fourier transform infrared (FT-IR) spectroscopy clearly revealed the occurrence of the polymerization reaction and the formation of the target skeleton. Comparison of the monomer and polymer spectra revealed that the characteristic amino (–NH2) peak at approximately 3377 cm⁻¹ of the starting material p-diaminoazobenzene, and the strong carbonyl (C=O) stretching vibration peak at approximately 1668 cm⁻¹ of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde, had essentially disappeared in the ZCST-105 spectrum. Simultaneously, a new strong characteristic absorption band emerged in the product at approximately 1652 cm⁻¹, attributed to the stretching vibration of the newly formed imine bond (C=N).

[0057] The evolution of these characteristic functional group signals strongly confirms that the aldehyde and amino groups between monomers underwent a Schiff base condensation reaction with a high conversion rate, successfully constructing a periodic conjugated framework linked by imine bonds. The weak free end-group signals in the spectrum further demonstrate that this network reaction has extremely high reactivity and excellent structural integrity.

[0058] 3. Morphological characteristics

[0059] Figure 3 This is a scanning electron microscope (SEM) image of the ZCST-105 two-dimensional covalent organic framework with a thiophene group.

[0060] like Figure 3 As shown, ZCST-105 mainly exhibits an irregular, micron-sized blocky morphology. Microscopically, the material is composed of primary blocky particles with sizes ranging from approximately 3 to 10 μm, with the final aggregates having a lateral size distribution between 10 and 40 μm. The particle packing is relatively loose, with fine particles adhering to the surface, and the aggregates naturally contain abundant pores and gaps with widths of 0.1 to 1 μm, forming a macroscopic network of channels conducive to material transport.

[0061] 4. Thermal stability test

[0062] Figure 4 Thermogravimetric analysis (TGA) curve of ZCST-105, a two-dimensional covalent organic framework for thiophene groups.

[0063] Figure 4 The results confirmed that ZCST-105 possesses excellent thermal stability. Before heating to 400℃, the sample mass loss was minimal, mainly attributed to the volatilization of trace solvent molecules adsorbed within the pores; however, the curve showed a sharp decline only after the temperature exceeded 400℃, indicating the onset of pyrolysis and collapse of the framework. This high thermal decomposition temperature of 400℃ demonstrates that the covalent framework structure of ZCST-105 is very robust and can withstand high-temperature operating environments.

[0064] 5. Adsorption-desorption test

[0065] To further investigate the pore characteristics of ZCST-105, adsorption-desorption tests were conducted at 77 K using ultra-high purity nitrogen (>99.9999%). The results... Figure 5 As shown.

[0066] Figure 5 The results show that the isotherms rise sharply in the low-pressure region (P / P0<0.1), revealing abundant micropores; the obvious hysteresis loops in the medium- and high-pressure regions have typical Type IV isotherm characteristics, indicating that there are ordered mesopores inside the material, and the overall adsorption behavior is a combination of Type I and Type IV.

[0067] 6. Pore size distribution test

[0068] Figure 6 This is a pore size distribution diagram of ZCST-105 obtained by BJH method analysis. Figure 6 It can be observed that the most probable pore size of ZCST-105 is precisely distributed at 2.7 nm. This measured pore size data is in high agreement with the pore size derived from the theoretical crystal model, which fully proves that ZCST-105 not only has a huge specific surface area, but also possesses a highly ordered and structurally determined intrinsic microporous-mesoporous structure.

[0069] 7. Specific surface area calculation

[0070] Figure 7 The image shows the BET diagram of the thiophene-based two-dimensional covalent organic framework ZCST-105. The Brunauer-Emmett-Teller (BET) equation yields a specific surface area of ​​938 m²g⁻¹ for ZCST-105, and a total pore volume of approximately 0.79 cm³g⁻¹ at P / P0 = 0.99, demonstrating its well-developed hierarchical pore network.

[0071] In summary, powder X-ray diffraction and refinement confirmed that the thiophene-based two-dimensional covalent organic framework ZCST-105 prepared in Example 1 belongs to the P3 space group and has a highly crystalline hcb topology. The characteristic peak at 1652 cm⁻¹ in infrared spectroscopy confirmed the successful construction of imine bonds. Nitrogen adsorption tests showed that the material has a microporous-mesoporous hierarchical pore structure with a BET specific surface area as high as 938 m² / g. Thermogravimetric analysis confirmed that its framework did not collapse below 400℃, providing a solid material basis for the application of radioactive iodine adsorption.

[0072] Application Example 1

[0073] The thiophene-group two-dimensional covalent organic framework ZCST-105 prepared in Example 1 was applied to the adsorption and separation of radioactive iodine vapor. The specific operation is as follows:

[0074] The vacuum-activated ZCST-105 powder was placed in a sealed environment containing volatile iodine isotopes and subjected to adsorption treatment at atmospheric pressure and 70°C. After adsorption saturation, the material was heated to 80°C for desorption and regeneration, and the released iodine vapor was collected. This adsorption-regeneration cycle was repeated twice. The results are as follows: Figure 8 and Figure 9 As shown.

[0075] Figure 8 and Figure 9The results showed that under an iodine vapor atmosphere at 70℃, ZCST-105 exhibited an iodine adsorption capacity of up to 3.3 g·g⁻¹, significantly superior to traditional activated carbon and most porous materials. Furthermore, after three adsorption-regeneration cycles, its framework structure remained intact, with no significant decrease in adsorption capacity, effectively solving the technical challenge of existing materials achieving both high adsorption capacity and long cycle life. This superior performance is attributed to the material's unique physical-chemical dual adsorption mechanism: at the physical level, the highly ordered hcb topology and approximately 2.7 nm uniform mesopores provide a large storage space for iodine molecules; at the chemical level, the sulfur atoms on the benzotrithiophene units in the framework, acting as soft Lewis bases, interact strongly and specifically with iodine molecules, which act as soft Lewis acids. Simultaneously, the highly reactive nitrogen sites provided by the azo groups and imine bonds induce charge transfer in iodine molecules, transforming them into stable polyiodide anions. This chemical solidification not only enhances the adsorption capacity but also effectively prevents secondary leakage of iodine.

[0076] Example 2

[0077] A method for preparing a thiophene-based two-dimensional covalent organic framework for iodine adsorption, comprising the following steps:

[0078] S1. Mix and grind 18.4 mg of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 17.6 mg of 4,4'-diaminoazobenzene in a mortar to achieve uniform mixing and solid-phase pretreatment, and obtain a mixed powder.

[0079] S2. Transfer the mixed powder from step S1 to a reaction vessel and add 1 mL of mixed solvent and 0.1 mL of catalyst. After deoxygenation through freezing, evacuation, and thawing, the mixture is vacuum sealed and heated to 100°C for static reaction for 96 h. The mixed solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:3, and the catalyst is a 6 mol / L aqueous solution of acetic acid.

[0080] S3. After the reaction was completed, the product was washed twice with acetone to remove unreacted substances, and then dried under vacuum to obtain 23.76 mg of the target product as a yellow powder, with a yield of 66%.

[0081] Example 3

[0082] A method for preparing a thiophene-based two-dimensional covalent organic framework for iodine adsorption, comprising the following steps:

[0083] S1. 19.8 mg of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 19.1 mg of 4,4'-diaminoazobenzene were placed in a mortar, mixed and ground to achieve uniform mixing and solid-phase pretreatment, and a mixed powder was obtained.

[0084] S2. Transfer the mixed powder from step S1 to a reaction vessel and add 1 mL of mixed solvent and 0.1 mL of catalyst. After deoxygenation through freezing, evacuation, and thawing, the mixture is vacuum sealed and heated to 140°C for static reaction for 60 h. The mixed solvent is a mixture of mesitylene and dioxane in a volume ratio of 1:3, and the catalyst is a 6 mol / L aqueous solution of acetic acid.

[0085] S3. After the reaction was completed, the product was washed twice with acetone to remove unreacted substances, and then dried under vacuum to obtain 26.8 mg of the target product in the form of yellow powder, with a yield of 70%.

[0086] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A two-dimensional covalent organic framework with a thiophene group for iodine adsorption, characterized in that: The two-dimensional covalent organic framework has the structural formula shown in Equation I: Formula I.

2. The two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 1, characterized in that: The structural unit of the two-dimensional covalent organic framework belongs to the trigonal crystal system, space group P3, with cell parameters a=b=43.79197 Å, c=10.00000 Å, α=β=90°, and γ=120°.

3. The two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 1, characterized in that: The two-dimensional covalent organic framework is formed by the condensation of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene.

4. A method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption as described in any one of claims 1 to 3, characterized in that: Includes the following steps: S1. Mix and grind benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene to make them evenly mixed and obtain a mixed powder. S2. Add the mixed solvent and catalyst to the mixed powder in step S1, and after a cycle of freezing, evacuation and thawing to remove oxygen, seal under vacuum and heat to carry out the reaction. S3. After the reaction is complete, the product is repeatedly washed to remove unreacted substances and then dried under vacuum to obtain the target product.

5. The method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 4, characterized in that: The molar ratio of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde to 4,4'-diaminoazobenzene in step S1 is 1:1 to 2.

5.

6. The method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 4, characterized in that: The amount of the mixed solvent used in step S1 is 140 to 170 times the total mass of benzo[1,2-b:3,4-b':5,6-b']trithiophene-2,5,8-trialdehyde and 4,4'-diaminoazobenzene.

7. The method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 4, characterized in that: The mixed solvent in step S2 is a solvent composed of mesitylene and dioxane mixed in a volume ratio of 1:3; the catalyst is an aqueous solution of acetic acid with a concentration of 6 mol / L.

8. The method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 4 or 7, characterized in that: The volume ratio between the catalyst and the mixed solvent in step S2 is 1:8~10.

9. The method for preparing a two-dimensional covalent organic framework with a thiophene group for iodine adsorption according to claim 4, characterized in that: The reaction temperature in step S2 is 100~140℃ and the reaction time is 60~200 h.

10. The application of the thiophene-based two-dimensional covalent organic framework for iodine adsorption as described in any one of claims 1 to 3, or the material prepared according to the preparation method described in any one of claims 4 to 9, in iodine adsorption and separation.

Images