PI / COF-316 composite aerogel as well as preparation method and application thereof

Abstract

The invention relates to the technical field of functional materials, in particular to PI / COF-316 composite aerogel as well as a preparation method and application thereof. The PI / COF-316 composite aerogel is prepared through an electrostatic spinning method and a freeze-drying method, and the adsorption capacity of the PI composite aerogel loaded with 35 wt% of COF-316 to iodine can reach 376 mg / g. After five times of adsorption-desorption cycles, the adsorption capacity of the adsorbent still can be kept 90% or above of the initial value, and excellent regeneration performance is shown. The prepared aerogel is excellent in iodine adsorption capacity and large in specific surface area, and efficient treatment of iodine is facilitated; the preparation method disclosed by the invention is simple, high in operability, environment-friendly and low in cost, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a PI / COF-316 composite aerogel, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Radioactive iodine, due to its volatility, biocompatibility, and high mobility, is a crucial contaminant in gaseous radioactive waste, posing a significant threat should it leak into the environment. Therefore, the research and development of highly efficient iodine adsorbents is of paramount importance.

[0004] Solid-phase adsorption is the most commonly used method for enriching and storing radioactive iodine, and it has been widely studied and applied. Activated carbon's adsorption performance decreases under extreme high-temperature and high-humidity environments, and its selective adsorption capacity for iodine is limited. MOF materials have poor hydrothermal stability, and structural collapse easily occurs when adsorbing gaseous radioactive iodine in real nuclear waste gas treatment environments. Zeolite molecular sieves have narrow pore size distributions and low iodine molecule capture efficiency. Covalent organic frameworks (COFs) possess highly flexible molecular designability and tunable pore structure, making them of great research value and application prospects in the design and preparation of gaseous iodine adsorbent materials. However, existing research on using COF materials for gaseous iodine uptake faces several challenges, including: difficult synthesis of the monomers used; the need for a harsh inert atmosphere and high reaction temperature in the preparation of the target COF material; and slow iodine adsorption kinetics, which hinders large-scale preparation and practical applications.

[0005] Polyimide (PI) aerogels, as a novel porous functional material, exhibit significant comprehensive performance advantages by combining the excellent properties of polyimide with the unique structure of aerogels. This material possesses a three-dimensionally interconnected hierarchical pore structure (including micropores, mesopores, and macropores), providing ample adsorption sites and efficient mass transfer channels for iodine molecules. PI not only retains the inherent chemical resistance, excellent mechanical strength, and outstanding thermal stability of the polyimide matrix, but also possesses the typical characteristics of aerogel materials, such as low density, high specific surface area, and low thermal conductivity. However, existing research indicates that there is still considerable room for improvement in the application of pure polyimide aerogels for iodine adsorption: firstly, the wide pore size distribution of the material leads to a relatively low utilization rate of effective adsorption sites; secondly, its surface chemical properties are relatively simple, limiting its selective adsorption capacity in complex gas environments. Summary of the Invention

[0006] In view of this, the present invention provides a PI / COF-316 composite aerogel, its preparation method, and its application. By combining COF-316 with PI aerogel, the present invention can synergistically leverage the advantages of both to achieve highly efficient capture of gaseous iodine.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing PI / COF-316 composite aerogel, comprising the following steps: S1: Tetrafluoroterephthalonitrile (TFPN), 2,3,6,7,10,11-hexahydroxybenzophenanthrene (HHTP), triethylamine (TEA) and 1,4-dioxane were mixed and sonicated, then degassed by freezing, and then heated to react. After the reaction was completed, the mixture was filtered, washed and dried to obtain COF-316 particles. S2: Dissolve 4,4'-diaminodiphenyl ether (ODA) in dimethylacetamide (DMAc) solvent, then add 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), stir the reaction to obtain PAA precursor solution; S3: PAA nanofiber membranes were prepared by electrospinning; the spun PAA nanofiber membranes were dispersed in water and homogenized to prepare PAA nanofiber dispersions; then, the COF-316 particles prepared in step S1 were added to the PAA nanofiber dispersions and subjected to continuous ultrasonic treatment for 2-6 h to obtain a mixed dispersion. S4: Pour the mixed dispersion into a mold and freeze for a period of time, then freeze-dry under vacuum to obtain PAA / COF-316 composite aerogel; S5: PAA / COF-316 composite aerogel is subjected to programmed temperature heating and imidization treatment to obtain PI / COF-316 composite aerogel.

[0008] Preferably, the diameter of the nano-COF-316 in S1 is 20~200 nm.

[0009] Preferably, the ultrasound time in S1 is 10-30 min.

[0010] Preferably, the mass ratio of TFPN, HHTP and TEA in S1 is 1:1-1.2:2.7-3, more preferably 1:1.11:2.89.

[0011] Preferably, the mass-to-volume ratio of TFPN to 1,4-dioxane in S1 is 1:70-75 g / mL.

[0012] Preferably, the washing in S1 is performed using dimethylformamide, water, and tetrahydrofuran, respectively.

[0013] Preferably, the drying in S1 is performed by heating at 55-65°C for 4-8 hours, followed by vacuum drying at 150-165°C for 12-18 hours.

[0014] Preferably, the concentration of the PAA precursor solution in S2 is 10~14 wt%.

[0015] Preferably, the BPDA monomer in S2 is added in 6 to 8 portions after the ODA monomer has been completely dissolved in DMAc.

[0016] Preferably, the ODA:BPDA molar ratio in S2 is 1:1 to 1.02.

[0017] Preferably, the mass-to-volume ratio of ODA to DMAc in S2 is 1:15-20 g / mL.

[0018] Preferably, the electrospinning process described in S3 is as follows: a cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm is used to collect nanofibers, and a silicone paper receiving substrate is placed on the receiving device; the parameters are adjusted as follows: the distance from the spinneret to the roller receiving surface is 15 cm to 20 cm, the high voltage power supply voltage is 18 kV to 22 kV, the feeding speed is 0.0008 mm / s to 0.001 mm / s, the rotation speed is 100 r / min to 200 r / min, and the spinneret swings laterally from the center position with an amplitude of 50 cm and a swing speed of 5 mm / s; Preferably, the concentration of COF-316 particles in the dispersion in S3 is 10-40 wt%; more preferably, it is 15-35 wt%.

[0019] Preferably, the freezing temperature in S4 is -70~-80℃, and the freezing time is 10-20 h.

[0020] Preferably, in step S5, the PAA / COF-316 composite aerogel is placed in a muffle furnace; the programmed heating program is as follows: heating from room temperature to 180°C at a rate of 5~15°C / min, heating from 180°C to 250°C at a rate of 5~10°C / min, heating from 250°C to 300°C at a rate of 5~10°C / min, holding each temperature stage for 1 hour, and then naturally cooling to room temperature.

[0021] In a second aspect, the present invention provides a PI / COF-316 composite aerogel prepared by the preparation method described in the first aspect.

[0022] COF-316 has the following outstanding characteristics: (1) a highly ordered microporous structure with pore sizes ranging from 0.6 to 1.2 nm, which is highly matched with the size of iodine molecules and can significantly improve the utilization rate of adsorption sites; (2) excellent chemical and thermal stability, which is fully adaptable to the high-temperature environment of nuclear waste gas treatment; (3) high specific surface area (>300 m² / m³). 2 The presence of COF-316 covalent organic framework material provides ample active sites for physical adsorption. Introducing COF-316 as a functional modifier for PI aerogel allows for the synergistic effect of both materials, achieving highly efficient capture of gaseous iodine.

[0023] Preferably, the specific surface area of ​​the PI / COF-316 composite aerogel is 20~80 m². 2 / g.

[0024] Preferably, the diameter of the PI fiber is 50~350 nm.

[0025] Preferably, the COF-316 nanoparticles have a particle size of 20~200 nm.

[0026] Thirdly, the present invention provides the application of PI / COF-316 composite aerogel as described in the second aspect in the adsorption of gaseous iodine.

[0027] Preferably, the PI / COF-316 composite aerogel can be applied to the treatment of nuclear power plant exhaust gas and the adsorption of gaseous iodine in nuclear accident emergency response scenarios.

[0028] This invention prepares PI / COF-316 composite aerogel via electrospinning and freeze-drying. Under iodine vapor conditions at 75°C, the PI composite aerogel loaded with 35 wt% COF exhibits an iodine adsorption capacity of 376 mg / g. After five adsorption-desorption cycles, its adsorption capacity remains above 90% of its initial value, demonstrating excellent regeneration performance. These properties make it promising for applications in nuclear power plant exhaust gas treatment and nuclear accident emergency response.

[0029] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The present invention uses PAA / COF-316 aerogel with uncrosslinked fibers obtained by electrospinning and freeze-drying, and then thermal imidizes it to obtain PI / COF-316 aerogel with chemically crosslinked fibers and COF-316 particles. The physically encapsulated COF-316 nanoparticles can enhance the adsorption performance of the aerogel for I2, which is beneficial to improving the application efficiency of the aerogel in environmental remediation and pollutant removal.

[0030] (2) The preparation method used in this invention is simple, highly operable, low in cost, environmentally friendly, and has strong universality. The preparation method is easy to industrialize and can produce PI / COF-316 aerogel on a large scale.

[0031] (3) The preparation method in this invention can be further extended to the effective regulation and synthesis of nanofiber / COF composite aerogels, and the performance of nanofiber aerogels can be adjusted by changing the type of COF material. During the electrospinning process, the morphology of nanofibers can be adjusted by adjusting the electrospinning parameters (voltage, feed rate, temperature, humidity, receiver rotation speed, etc.). By adjusting the hydrothermal time, PI nanofiber aerogels modified with COF material with different diameter distributions can be grown. In the PI / COF aerogel of this invention, in addition to the high specific surface area and high porosity of the aerogel itself, the high specific surface area and porous structure of COF particles provide a large number of adsorption sites, enabling the aerogel to effectively adsorb I2 molecules. Attached Figure Description

[0032] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0033] Figure 1 SEM images and particle size distribution diagrams of the prepared COF-316 particles are shown, with the SEM images magnified by 35,000 times. Figure 2 A schematic diagram illustrating the fabrication of nanofiber membranes using electrospinning technology; wherein: 1. syringe; 2. nanofibers; 3. receiving substrate; Figure 3 The SEM image of the prepared PI / COF composite aerogel is shown at a magnification of 300x. Figure 4 SEM images of the prepared PI composite aerogel and its fiber diameter distribution are shown, with the SEM images magnified 180 times. Figure 5 Nitrogen adsorption-desorption curves of the prepared COF-316, PI aerogel, and PI / COF-316 composite aerogel; Figure 6 The adsorption capacity of the prepared PI and PI / COF composite aerogels at different times and their adsorption models were determined. Detailed Implementation

[0034] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0036] Example 1: Synthesis of COF-316 See Figure 1 Weigh 0.54 g TFPN, 0.6 g HHTP, 1.56 g TEA, and 40 mL 1,4-dioxane and place them in a dry Schlenk flask. Sonicate the mixture for 20 min, then freeze it in a liquid nitrogen bath. After degassing through three freeze-pump-thaw cycles, heat at 120 °C for 72 h. The resulting product is a yellow precipitate, which is collected by filtration and further washed with DMF, H2O, and THF. Finally, heat the yellow powder at 60 °C for 6 h, followed by vacuum drying at 160 °C for 15 h to obtain the covalent organic framework COF-316.

[0037] Example 2: Synthesis of PAA nanofiber membranes See Figure 2 Weigh 22 mL of dimethylacetamide (DMAc) into a flask. Weigh 1.2077 g of 4,4'-diaminodiphenyl ether (ODA) and 1.7923 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and place the ODA into a three-necked flask. Fix the flask containing the dissolved ODA and mechanically stir for 15 min to ensure complete dissolution of the monomer. Add BPDA in six equal portions, each containing 1 / 6 of the total mass. After each addition of BPDA has completely dissolved, add the next portion approximately 20 min apart. After all additions are complete, rapidly mechanically stir for 1 hour to allow the monomer to react fully, producing a 12 wt% PAA precursor solution.

[0038] PAA nanofiber membranes were prepared by electrospinning. The electrospinning parameters were set as follows: voltage 20 kV, rotation speed 150 r / min, temperature 30℃, humidity 65%, feed speed 0.0010 mm / s, needle tip distance 20 cm from the grid receiving base, oscillation at the center position with an amplitude of 50 cm and an oscillation speed of 5 mm / s, and electrospinning time 120 min. After taking the samples, they were dried in an oven at 60℃ for 12 h.

[0039] Example 3: Synthesis of PI / COF-316 Aerogel See Figure 3Electrospun PAA nanofiber membranes were cut into 0.5 × 0.5 mm pieces. 0.3 g of the PAA nanofiber membrane was then immersed in 50 g of aqueous solvent and homogenized at 160,000 rpm for 15 min to obtain a fiber dispersion with a fiber solids content of 0.6 wt%. Subsequently, 0.045 g of COF-316 particles were added to the fiber dispersion and sonicated continuously for 4 h to obtain a dispersion with a COF-316 solids content of 15 wt%. The dispersion was then poured into a cylindrical mold and frozen at -78℃ for 12 h, followed by vacuum freeze-drying to prepare PAA / COF-316 aerogel. Finally, the aerogel was placed in a muffle furnace and heated to 180℃, 250℃, and 300℃ for 1 h each to complete thermal imidization, yielding PI / COF-316 aerogel.

[0040] Example 4 Compared with Example 3, the difference is that 0.075 g of COF-316 particles were weighed and added to the fiber dispersion, and sonicated continuously for 4 h to obtain a dispersion with a COF-316 solid content of 25 wt%.

[0041] Example 5 Compared with Example 3, the difference is that 0.105 g of COF-316 particles were weighed and added to the fiber dispersion, and sonicated continuously for 4 h to obtain a dispersion with a COF-316 solid content of 35 wt%.

[0042] Example 6 Compared to Example 3, the difference lies in that 0.135 g of COF-316 particles were weighed and added to the fiber dispersion, and the mixture was continuously sonicated for 4 h to obtain a dispersion with a COF-316 solid content of 45 wt%. Example 6 shows that when the COF-316 loading increased to 45 wt%, the aerogel exhibited structural collapse.

[0043] Example 7: Synthesis of PI Aerogel See Figure 4 Electrospun PAA nanofiber membranes were cut into 0.5 × 0.5 mm pieces. 0.3 g of the PAA nanofiber membrane was then immersed in 50 g of aqueous solvent and homogenized at 160,000 rpm for 15 min to obtain a fiber dispersion with a fiber solids content of 0.6 wt%. The dispersion was then poured into a cylindrical mold and frozen at -78°C for 12 h. Following vacuum freeze-drying, PI aerogel was obtained. Finally, the aerogel was placed in a muffle furnace and heated to 180°C, 250°C, and 300°C for 1 h each to complete thermal imidization, yielding the PI aerogel.

[0044] Example 8: Nitrogen adsorption-desorption of COF-316, PI aerogel, and PI / COF-316 composite aerogel See Figure 5 Nitrogen adsorption-desorption tests were performed on the COF-316 nanoparticles prepared in Example 1 and the aerogels prepared in Examples 3-6. The test method is as follows: 0.1 g of each sample was weighed and placed in a BET sample tube, and vacuum degassing was performed at 120 °C for 3 hours to remove surface adsorbates. Subsequently, the nitrogen adsorption-desorption isotherm was measured in a liquid nitrogen environment, and the specific surface area was calculated using the BET (Brunauer-Emmett-Teller) model.

[0045] Example 9: Adsorption performance of PI / COF-316 aerogel for iodine vapor See Figure 6 As per Table 1, iodine vapor adsorption tests were performed on the aerogels prepared in Examples 3-6. 56 mg (denoted as m0) of aerogel sample was accurately weighed and placed in a sealed glass vial containing 0.23 g of solid iodine. The sealed system was allowed to stand at a constant temperature (e.g., 75 °C), and the mass of the aerogel after adsorption (denoted as m0) was recorded at 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 12 h, 14 h, and 19 h. t ).

[0046] Adsorption capacity calculation: according to formula Q t =(m t Calculate the adsorption capacity Q at different time points using (-m0) / m0. t , where m0 = 56 mg is the initial mass.

[0047] Table 1. Correlation coefficients (R²) of the Pseudo-first-order or Pseudo-second-order models 2 )

[0048] This invention prepares PI / COF-316 composite aerogel via electrospinning and freeze-drying. Under iodine vapor conditions at 75°C, the PI composite aerogel loaded with 35 wt% COF achieves an iodine adsorption capacity of 376 mg / g. After five adsorption-desorption cycles, its adsorption capacity remains above 90% of its initial value, demonstrating excellent regeneration performance. These properties make it promising for applications in nuclear power plant exhaust gas treatment and nuclear accident emergency response.

[0049] The PI / COF-316 composite aerogels prepared by this invention using electrospinning and freeze-drying techniques exhibit high temperature resistance and chemical corrosion resistance, while also possessing a high iodine adsorption capacity. This invention has low production costs and wide applications, enabling the adsorption of iodine particles at the source of high-temperature gas emissions, thus achieving air purification.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing PI / COF-316 composite aerogel, characterized in that, Includes the following steps: S1: TFPN, HHTP, TEA and 1,4-dioxane were mixed and sonicated, then degassed by freezing and heated to react. After the reaction was completed, COF-316 particles were obtained by filtration, washing and drying. S2: Dissolve ODA in DMAc solvent, then add BPDA, stir the reaction to obtain PAA precursor solution; S3: Preparation of PAA nanofiber membrane by electrospinning: The spun PAA nanofiber membrane was dispersed in water and homogenized to prepare PAA nanofiber dispersion; Subsequently, the COF-316 particles prepared by S1 were added to the PAA nanofiber dispersion and subjected to continuous ultrasonic treatment for 2-6 h to obtain a mixed dispersion. S4: Pour the mixed dispersion into a mold and freeze for a period of time, then freeze-dry under vacuum to obtain PAA / COF-316 composite aerogel; S5: PAA / COF-316 composite aerogel is subjected to programmed temperature heating and imidization treatment to obtain PI / COF-316 composite aerogel.

2. The preparation method according to claim 1, characterized in that, The diameter of the nano-COF-316 described in S1 is 20~200nm; or, the ultrasonic time in S1 is 10-30 min; or, the mass ratio of TFPN, HHTP, and TEA in S1 is 1:1-1.2:2.7-3, preferably 1:1.11:2.89; or, the mass-volume ratio of TFPN to 1,4-dioxane in S1 is 1:70-75g / mL; or, the washing in S1 is performed with dimethylformamide, water, and tetrahydrofuran respectively; or, the drying in S1 is performed by heating at 55-65℃ for 4-8 h, followed by vacuum drying at 150-165℃ for 12-18 h.

3. The preparation method according to claim 1, characterized in that, The concentration of the PAA precursor solution in S2 is 10~14wt%; or, the BPDA monomer in S2 is added in 6~8 portions after the ODA monomer is completely dissolved in DMAc; or, the molar ratio of ODA:BPDA in S2 is 1:1~1.02; or, the mass-volume ratio of ODA to DMAc in S2 is 1:15-20g / mL.

4. The preparation method according to claim 1, characterized in that, The electrospinning process described in S3 is as follows: a cylindrical roller receiver with a diameter of 12 cm and a length of 30 cm is used to collect nanofibers, and a silicone paper receiving substrate is placed on the receiving device; the parameters are adjusted as follows: the distance from the spinneret to the roller receiving surface is 15 cm to 20 cm, the high voltage power supply voltage is 18 kV to 22 kV, the feeding speed is 0.0008 mm / s to 0.001 mm / s, the rotation speed is 100 r / min to 200 r / min, and the spinneret swings laterally from the center position with an amplitude of 50 cm and a swing speed of 5 mm / s.

5. The preparation method according to claim 1, characterized in that, The concentration of COF-316 particles in the dispersion in S3 is 10-40 wt%; preferably 15-35 wt%.

6. The preparation method according to claim 1, characterized in that, The freezing temperature in S4 is -70~-80℃, and the freezing time is 10-20h.

7. The preparation method according to claim 1, characterized in that, The programmed temperature rise procedure described in S5 is as follows: the temperature rises from room temperature to 180℃ at a rate of 5~15℃ / min, from 180℃ to 250℃ at a rate of 5~10℃ / min, and from 250℃ to 300℃ at a rate of 5~10℃ / min. Each temperature stage is held for 1 hour, and then the temperature is naturally cooled to room temperature.

8. The PI / COF-316 composite aerogel prepared by the preparation method according to any one of claims 1-7.

9. The PI / COF-316 composite aerogel as described in claim 8, characterized in that, The specific surface area of ​​the PI / COF-316 composite aerogel is 20-80 m². 2 / g; or, the diameter of the PI fiber is 50~350 nm; or, the particle size of the COF-316 nanoparticles is 20~200 nm.

10. The application of the PI / COF-316 composite aerogel as described in claim 8 or 9 in the adsorption of gaseous iodine; preferably, its application in the adsorption of gaseous iodine in nuclear power plant exhaust gas treatment and nuclear accident emergency response scenarios.

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