Method for the ultrasonic preparation of covalent organic frameworks in a terpene medium

Abstract

The application discloses a method for preparing a covalent organic framework by ultrasonic treatment in a terpene medium. 2-hydroxy-1,3,5-benzene tricarboxaldehyde and p-phenylenediamine are added into a hydrophobic terpene reaction medium selected from limonene, sabinene or beta-pinene in an aldehyde group to amino group equivalent ratio, and 6 mol / L acetic acid aqueous solution is added to form a reaction system with a terpene reaction medium to acetic acid aqueous solution volume ratio of 10:1; a probe type ultrasonic device is used to react for 60 min under the conditions of a set power of 900 W, a frequency of 20 kHz and a pulse opening time of 2 s and a pulse closing time of 1 s. The obtained suspension is subjected to solid-liquid separation, washing, Soxhlet extraction and vacuum drying to obtain a covalent organic framework material. Compared with a comparative example without ultrasonic treatment in the same reaction time, the obtained material has PXRD crystal state characteristics; the separated limonene can be reused in subsequent reactions after being treated by a silica gel column.

Description

Technical Field

[0001] This invention relates to the field of porous crystalline material preparation technology, specifically to a method for preparing covalent organic frameworks using terpene media via ultrasonication, as well as the reuse of the reaction medium and the application of the obtained material for carbon dioxide adsorption. Background Technology

[0002] Covalent organic frameworks (COFs) are porous crystalline materials formed by organic building blocks linked by covalent bonds. They possess characteristics such as tunable pore structure and ease of functionalization, and can be used for adsorption and separation. Imine-linked COFs are typically formed by the condensation of aldehyde-containing building blocks and amino-containing building blocks.

[0003] The preparation of existing imine-type covalent organic frameworks typically requires organic solvents, closed reactions, heating, or long reaction times. Aqueous-phase synthesis, solid-phase synthesis, and microwave or ultrasound-assisted synthesis can shorten reaction time or improve preparation efficiency to varying degrees. However, in specific condensation systems of aldehyde and amino building blocks, the phase state of the reaction medium, the catalytic medium, and the energy input method all affect the dispersion, mass transfer, and product crystallization of the building blocks. Therefore, there is still a need to develop a preparation method that can obtain crystalline products in a shorter time, increase monomer feed rates, and allow for the reuse of the reaction medium.

[0004] Monoethanolamine can reversibly react with carbon dioxide, and when loaded onto porous solids, it can form solid amine adsorbent materials. This invention focuses on the preparation process of covalent organic frameworks and further investigates the carbon dioxide capture performance of the resulting materials after loading with monoethanolamine. Summary of the Invention

[0005] Technical problems to be solved The technical problem to be solved by the present invention is to provide a preparation method that does not require long-term closed heating, can obtain covalent organic framework materials with crystalline characteristics in a short time, and allows the reaction medium to be reused.

[0006] Technical solution To address the aforementioned technical problems, this invention provides a method for preparing covalent organic frameworks using terpene media via ultrasound, comprising the following steps: S1: 2-hydroxy-1,3,5-benzenetrialdehyde and p-phenylenediamine are added to a hydrophobic terpene reaction medium in approximately equal amounts of aldehyde and amino groups and mixed. The hydrophobic terpene reaction medium is selected from one of limonene, juniperene and β-pinene. S2: Add 6 mol / L acetic acid aqueous solution to make the volume ratio of hydrophobic terpene reaction medium to acetic acid aqueous solution 10:1, forming a reaction system containing hydrophobic terpene phase and acetic acid aqueous phase; S3: Using a probe-type ultrasonic device, place the probe in the reaction system and perform ultrasonic reaction for 60 minutes under the conditions of 900 W power, 20 kHz frequency and pulse on 2 s / off 1 s to obtain a suspension; S4: After solid-liquid separation, the solid is sequentially washed with N,N-dimethylformamide, extracted with tetrahydrofuran using a Soxhlet extractor, and dried under vacuum to obtain a covalent organic framework material.

[0007] In one embodiment, the hydrophobic terpene reaction medium is limonene; the amounts of 2-hydroxy-1,3,5-benzenetriformaldehyde, p-phenylenediamine, limonene, and aqueous acetic acid solution are approximately 0.017 kg, 0.016 kg, 0.2 L, and 0.02 L, respectively.

[0008] In one embodiment, the obtained covalent organic framework material is impregnated in an ethanol solution containing monoethanolamine, and then subjected to room temperature shaking, filtration, and vacuum drying to obtain a monoethanolamine-supported covalent organic framework composite adsorbent; carbon dioxide-containing air is then contacted with the composite adsorbent to capture carbon dioxide from the air.

[0009] Under small-scale testing conditions, the ultrasonic response was conducted using a JY92-IIDN type probe-type ultrasonic device with a probe diameter of 3 mm and a nominal maximum power of 900 W; the “900 W” mentioned in this application refers to the set power of the device.

[0010] The hydrophobic terpene reaction media used in this invention include limonene, juniperene, and β-pinene. Examples 1, 8, and 9 show that, under the same acetic acid-water phase ratio and pulsed ultrasound conditions, all three reaction media can yield products with characteristic PXRD diffraction peaks.

[0011] Beneficial effects Compared to Comparative Example 1, which maintained the same building blocks, limonene, and aqueous acetic acid but omitted ultrasound, Example 1 yielded a product with PXRD crystalline characteristics within 60 min, with a yield of 94% and a BET specific surface area of ​​989 m². 2 / g; The solid obtained in Comparative Example 1 at the same reaction time was amorphous. Compared with Comparative Example 2, which was reacted at 120°C in a closed environment for 72 h, Example 1 shortened the reaction time to 60 min and obtained a product yield of 94%, which was higher than 85% in Comparative Example 2.

[0012] In Example 2, the monomer feed amounts were increased to approximately 0.017 kg and approximately 0.016 kg, respectively, and the amount of reaction medium was not increased proportionally to that in Example 1. A dried product of 26.20 g was obtained in 0.2 L of limonene and 0.02 L of acetic acid aqueous solution, with a yield of 92% and a BET specific surface area of ​​764 m². 2 / g indicates that crystalline covalent organic framework materials can still be obtained under conditions of higher feed rates.

[0013] In Example 3, the recovery rates of limonene in the first to fourth cycles were 89%, 86%, 91%, and 89%, respectively. The PXRD patterns of the products from each cycle all retained characteristic diffraction peaks at 2θ=4.78°, indicating that the limonene obtained by silica gel column treatment can be reused in subsequent reactions.

[0014] In Example 7, 0.1 g of monoethanolamine-supported covalent organic framework composite adsorbent reduced the carbon dioxide sensor reading from 390 ppm to approximately 27 ppm within 60 min in a 15 L circulating gas testing apparatus; Comparative Example 3, which did not support monoethanolamine, did not show a significant concentration change. These results only reflect the concentration changes under the stated test conditions and are not equivalent to the equilibrium adsorption capacity. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the COF formed by 2-hydroxy-1,3,5-benzenetrialdehyde and p-phenylenediamine in Example 1; Figure 2 The PXRD pattern, nitrogen adsorption-desorption curve, and pore size distribution of the COF obtained in Example 1 are shown below. Figure 3 The PXRD pattern, nitrogen adsorption-desorption curve, and pore size distribution of the COF obtained in Example 2 are shown below. Figure 4 Here are schematic diagrams and PXRD images of the building blocks used in Example 4 and the resulting COF; Figure 5 Here are schematic diagrams and PXRD images of the building blocks used in Example 5 and the resulting COF; Figure 6 Here are schematic diagrams and PXRD images of the building blocks used in Example 6 and the resulting COF; Figure 7 The images show the limonene recovery process in Example 3 and the PXRD pattern of the recycled COF. Figure 8 The diagram shows the carbon dioxide capture test device and carbon dioxide concentration-time curve in Example 7, where the curve marked "COF capture" corresponds to the monoethanolamine-supported covalent organic framework composite adsorbent. Figure 9 The PXRD pattern of COF obtained in Example 8; Figure 10 The image shows the PXRD pattern of the COF obtained in Example 9. Detailed Implementation

[0016] The following examples are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, the reagents, operating procedures and test conditions used are as described in the following examples.

[0017] Terminology and testing methods "Stoichiometric ratio of the reactive functional groups" refers to the ratio of the amount of aldehyde group to the amount of amino group required to form the corresponding imine bond. For example, in Example 1, 2-hydroxy-1,3,5-benzenetricarboxaldehyde has three aldehyde groups and p-phenylenediamine has two amino groups, and the amounts of both are approximately equivalent to the amounts of aldehyde and amino groups.

[0018] PXRD analysis was performed using a Bruker D8 Advance diffractometer and a Cu target radiation source to determine the crystalline characteristics of the product. Nitrogen adsorption-desorption tests were conducted at 77 K, and the sample was degassed at 120 °C for 8 h, with a relative pressure P / P0 of 10. -6 ~0.99, pore size distribution was calculated using a nonlocal density functional theory model. Yield was calculated as the ratio of the mass of dried product to the mass of the theoretical product calculated based on the limited building blocks; limonene recovery was calculated as the ratio of the volume of recovered limonene to the volume of initial limonene.

[0019] The theoretical product mass, dried product mass, and yield listed in the examples were all calculated using the method described above.

[0020] Preparation and subsequent loading process of covalent organic frameworks S1: Weigh 2-hydroxy-1,3,5-benzenetrialdehyde and p-phenylenediamine in approximately equal amounts of aldehyde and amino groups, add them to a hydrophobic terpene reaction medium selected from limonene, juniperene, or β-pinene, and stir to mix.

[0021] S2: Add 6 mol / L acetic acid aqueous solution to make the volume ratio of hydrophobic terpene reaction medium to acetic acid aqueous solution 10:1, forming a reaction system containing hydrophobic terpene phase and acetic acid aqueous phase; under small-scale test conditions, place a 3 mm diameter probe in the reaction system and react for 60 min under the set power of 900 W, frequency of 20 kHz and pulse on 2s / off 1s conditions of JY92-IIDN type probe ultrasonic equipment.

[0022] S3: After the reaction, the suspension was separated into solid and liquid phases; the obtained solid was washed three times with N,N-dimethylformamide, extracted with tetrahydrofuran by Soxhlet for 24 h, and dried under vacuum at 90 °C for 12 h to obtain COF powder.

[0023] Optionally, in preparing the composite adsorbent, COF powder is impregnated in an ethanol solution containing monoethanolamine, shaken at room temperature for 12 h, filtered, and vacuum dried at 70 °C to obtain a monoethanolamine-supported COF composite adsorbent.

[0024] In this invention, "terpene medium" refers to a hydrophobic terpene reaction medium used in the construction of the elementary reaction stage; subsequent washing, Soxhlet extraction, and monoethanolamine loading steps using other solvents are not part of the terpene medium reaction stage.

[0025] Example 1: Small-scale synthesis

[0026] Weigh 10.68 mg of 2-hydroxy-1,3,5-benzenetrialdehyde and 9.73 mg of p-phenylenediamine, add 2 mL of limonene, and stir to mix. Add 0.2 mL of 6 mol / L acetic acid aqueous solution to make the volume ratio of limonene to acetic acid aqueous solution 10:1. Place the mixture in an ultrasonic reactor and react for 60 min at 900 W, 20 kHz, and a pulse on / off cycle of 2 s to 1 s to obtain a suspension.

[0027] The suspension was subjected to solid-liquid separation; the obtained solid was washed three times with N,N-dimethylformamide, then extracted with tetrahydrofuran by Soxhlet extraction for 24 h, and dried under vacuum at 90 °C for 12 h to obtain a reddish-brown COF powder. The theoretical product mass was 17.17 mg, the dried product mass was 16.14 mg, and the yield was 94%. PXRD showed crystalline diffraction characteristics, with a characteristic diffraction peak at 2θ = 4.78°, and the BET specific surface area was 989 m². 2 / g.

[0028] Example 2: Preparation by increasing the amount of raw materials Approximately 0.017 kg of 2-hydroxy-1,3,5-benzenetrialdehyde and approximately 0.016 kg of p-phenylenediamine were weighed, and 0.2 L of limonene was added with mechanical stirring. 0.02 L of 6 mol / L acetic acid aqueous solution was added, and the mixture was ultrasonically reacted for 60 min using a JY92-IIDN probe-type ultrasonic device at 900 W, 20 kHz, and a pulse on / off cycle of 2 s. After the reaction, solid-liquid separation, washing, Soxhlet extraction, and vacuum drying were performed according to the post-processing method described in Example 1. The theoretical product mass was 28.63 g, the dried product mass was 26.20 g, the yield was 92%, and the BET specific surface area was 764 m². 2 / g.

[0029] Compared with Example 1, Example 2 increased the amount of monomers fed, while the amounts of limonene and aqueous acetic acid were not increased in the same proportion; this example is used to verify the preparation results of the reaction system under the condition of higher monomer feeding, and does not represent a scale-up of the entire reaction system.

[0030] Example 3: Limonene recovery and recycling The liquid phase obtained from the solid-liquid separation in Example 2 was collected and passed directly through a column packed with 300-400 mesh silica gel. The column diameter was 40 mm, and the silica gel packing height was 12 cm. No additional eluent was added, and the effluent containing limonene was collected. The obtained limonene was used in the next batch of reaction, and it was recycled a total of 4 times. The limonene recovery rates of the 1st to 4th cycles were 89%, 86%, 91%, and 89%, respectively. The PXRD patterns of the products from each cycle all retained characteristic diffraction peaks at 2θ = 4.78°, as shown in the figure. Figure 7 As shown.

[0031] Example 4: One of the different combinations of building blocks In Example 1, 2-hydroxy-1,3,5-benzyltricarboxaldehyde and p-phenylenediamine were replaced with pyromellitic tricarboxaldehyde and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, respectively. The reactants were prepared in equimolar amounts according to the functional groups, and the remaining reaction and post-treatment conditions were performed as in Example 1. The theoretical product mass was 27.72 mg, the dried product mass was 18.85 mg, and the yield was 68%. The PXRD pattern of the obtained product is shown below. Figure 4 As shown.

[0032] Example 5: Combination of Different Building Elements (Part 2) The two building blocks in Example 1 were replaced with 2,5-diethoxy-terephthalaldehyde and 1,3,5-tris(4-aminophenyl)benzene, respectively, and the reactants were prepared in equimolar amounts according to the functional groups. The remaining reaction and post-treatment conditions were performed as in Example 1. The theoretical product mass was 25.22 mg, the dried product mass was 18.41 mg, and the yield was 73%. The PXRD pattern of the obtained product is shown below. Figure 5 As shown.

[0033] Example 6: Three Combinations of Different Building Blocks The two building blocks in Example 1 were replaced with 2,5-diethoxyterephthalaldehyde and 1,3,6,8-tetra(4-aminophenyl)pyrene, respectively, and the reactants were prepared in equimolar amounts according to the functional groups. The remaining reaction and post-treatment conditions were performed as in Example 1. The theoretical product mass was 28.22 mg, the dried product mass was 17.21 mg, and the yield was 61%. The PXRD pattern of the obtained product is shown below. Figure 6 As shown.

[0034] Example 7: Preparation of composite adsorbent and testing of carbon dioxide in air 1.0 g of the covalent organic framework material obtained in Example 2 was impregnated in 20 mL of ethanol solution containing 0.8 g of monoethanolamine, shaken at room temperature for 12 h, filtered, and vacuum dried at 70 °C to obtain 1.52 g of monoethanolamine-supported covalent organic framework composite adsorbent. The obtained mass increment is the apparent increment, and the actual loading of monoethanolamine was not calculated based on it.

[0035] Place 0.1 g of the obtained composite adsorbent into Figure 8 The 15 L test system shown uses local air as the initial gas, with a test temperature of 25°C, a relative humidity of 58%, and a gas circulation flow rate of 2 L / min. The carbon dioxide sensor is a GMP252 with a range of 0–5000 ppm, a resolution of 1 ppm, and a sampling interval of 5 s. The carbon dioxide sensor reading gradually decreased from 390 ppm to approximately 27 ppm over 60 minutes. The blank control curve is shown below. Figure 8 As shown; this result is used to characterize the change in carbon dioxide concentration under the closed-loop test conditions and is not used as the equilibrium adsorption capacity.

[0036] Example 8: Different terpene solvents - juniperene The solvent limonene in Example 1 was replaced with juniperene, and the remaining reaction and post-treatment conditions were performed as in Example 1. The theoretical product mass was 17.17 mg, the dried product mass was 14.94 mg, and the yield was 87%. The PXRD pattern of the obtained product is shown below. Figure 9 As shown.

[0037] Example 9: Different terpene solvents - β-pinene In Example 1, limonene was replaced with β-pinene, and the remaining reaction and post-treatment conditions were performed as in Example 1. The theoretical product mass was 17.17 mg, the dried product mass was 14.42 mg, and the yield was 84%. The PXRD pattern of the obtained product is shown below. Figure 10 As shown.

[0038] Comparative Example 1: No ultrasound conditions Keeping the building blocks, limonene, and aqueous acetic acid solution of Example 1 unchanged, but without ultrasound, the reaction was stirred at 60°C for 60 min, yielding a solid mass of 5 mg, which showed an amorphous structure according to PXRD. Extending the reaction time to 24 h, the yield of the product was 40%, but the crystallinity was still lower than that of Example 1.

[0039] Comparative Example 2: Closed Heating Conditions The building blocks from Example 1, along with 2 mL of limonene and 0.2 mL of 6 mol / L acetic acid aqueous solution, were transferred into a 10 mL pressure-resistant tube. After liquid nitrogen freezing, vacuuming, and sealing, the tube was reacted at 120°C for 72 h. The yield of the resulting covalent organic framework was 85%, and its PXRD crystallinity was similar to that of Example 1. This comparative example is only used to compare the reaction time and operating conditions of closed heating versus pulsed ultrasound, and is not intended to demonstrate differences in effectiveness between different reaction media.

[0040] Comparative Example 3: COF without amine loading The un-amine-loaded COF obtained in Example 2 was tested for carbon dioxide in air according to the test method in Example 7. Within 60 minutes, the carbon dioxide sensor reading did not change significantly.

[0041] The above embodiments and comparative examples are used to illustrate the technical solutions and effects of the present invention, and do not constitute a limitation on the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

Claims

1. A method for preparing covalent organic frameworks using terpene media via ultrasound, characterized in that, include: 2-Hydroxy-1,3,5-benzenetrialdehyde and p-phenylenediamine were added to a hydrophobic terpene reaction medium in approximately equal proportions of aldehyde and amino groups and mixed. The hydrophobic terpene reaction medium was selected from limonene, juniperene, and β-pinene. A 6 mol / L aqueous acetic acid solution was added to the hydrophobic terpene reaction medium to make the volume ratio of the two 10:1, forming a reaction system containing a hydrophobic terpene phase and an aqueous acetic acid phase. A probe-type ultrasonic device was used, with the probe placed in the reaction system, and the ultrasonic reaction was carried out for 60 min under the conditions of 900 W power, 20 kHz frequency, and pulse on 2 s / off 1 s to obtain a suspension. The suspension was subjected to solid-liquid separation, and the obtained solid was washed, Soxhlet extracted, and vacuum dried sequentially to obtain a covalent organic framework material.

2. The method according to claim 1, characterized in that, The hydrophobic terpene reaction medium is limonene.

3. The method according to claim 2, characterized in that, Each 10.68 mg of the 2-hydroxy-1,3,5-benzenetrialdehyde corresponds to 9.73 mg of the p-phenylenediamine, 2 mL of limonene, and 0.2 mL of the aqueous acetic acid solution.

4. The method according to claim 2, characterized in that, The amounts of 2-hydroxy-1,3,5-benzenetrialdehyde, p-phenylenediamine, limonene, and aqueous acetic acid solution are approximately 0.017 kg, 0.016 kg, 0.2 L, and 0.02 L, respectively.

5. The method according to any one of claims 1 to 4, characterized in that, The washing was performed three times with N,N-dimethylformamide, the Soxhlet extraction was performed with tetrahydrofuran for 24 h, and the vacuum drying was performed at 90 °C for 12 h.

6. The method according to claim 2 or 4, characterized in that, Also includes: The liquid phase obtained from the solid-liquid separation is passed through a silica gel column, and the effluent containing limonene is collected. The obtained limonene is then reused in subsequent reactions.

7. The method according to claim 6, characterized in that, The silica gel is 300-400 mesh silica gel, the diameter of the silica gel column is 40 mm, the silica gel filling height is 12 cm, and the liquid phase passes directly through the silica gel column without adding any other eluent.

8. The method according to any one of claims 1 to 4, characterized in that, Also includes: The covalent organic framework material was impregnated in an ethanol solution containing monoethanolamine, shaken at room temperature for 12 h, filtered, and vacuum dried at 70 °C to obtain a monoethanolamine-supported covalent organic framework composite adsorbent.

9. The method according to claim 8, characterized in that, Each 1.0 g of the covalent organic framework material corresponds to 0.8 g of monoethanolamine and 20 mL of ethanol.

10. The method according to claim 9, characterized in that, Also includes: 0.1 g of the composite adsorbent was contacted with 15 L of air at 25°C, 58% relative humidity, and a gas circulation flow rate of 2 L / min to capture carbon dioxide from the air.

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