COFs-based hollow imprinted microcapsule adsorbent and preparation method thereof

Abstract

The invention belongs to the technical field of environment-friendly functional materials and adsorption materials, and particularly relates to a COFs-based hollow imprinted microcapsule adsorbent and a preparation method thereof. The preparation method comprises the following steps: carrying out amine-aldehyde condensation reaction on 1, 3, 5-tri (4-aminophenyl) benzene, 2, 5-dimethoxy phthalaldehyde and 2, 5-divinyl benzaldehyde to synthesize a vinyl functionalized covalent organic framework; the preparation method comprises the following steps: firstly, preparing a COFs-DVA skeleton, then carrying out sulfydryl modification by virtue of a two-step thiol-ene click reaction, and grafting imprinted boric acid molecules (3-acrylamido phenylboronic acid) onto the COFs-DVA skeleton, so as to obtain the phenylboronic acid functionalized hollow imprinted microcapsule adsorbent COFs-DVA-SH-BA MIPMCs, and the adsorbent is applied to adsorption separation of a compound containing a cis-dihydroxyl structure. According to the invention, the defects of poor selectivity, difficult regeneration and insufficient stability of the traditional adsorbent are overcome, and a solution is provided for efficient separation and resource recovery of the cis-dihydroxy compound.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly functional materials and adsorption materials, and particularly relates to a COFs-based hollow imprinted microcapsule adsorbent and a preparation method thereof. Background Art

[0002] Traditional adsorption technology relies on activated carbon or resin, and generally faces bottleneck problems such as low selectivity, difficult regeneration and poor structural stability: physical adsorption is easily affected by environmental interference, desorption requires high temperature or strong acid and alkali conditions, and the microporous structure is prone to collapse, making it difficult to meet the needs of efficient removal of cis-dihydroxy compounds.

[0003] In response to the above problems, boron affinity technology provides a new highly selective adsorption pathway by dynamically covalently bonding phenylboronic acid groups with cis-dihydroxyl groups. To date, a variety of borate affinity functionalized materials have been synthesized and applied to the extraction of cis-diol flavonoids, such as molecular imprinting-based, magnetic nanoparticle-based, and carbon nanotube-based materials. However, the complex synthesis process of these adsorbents, low phenylboronic acid concentration, slow adsorption rate, low specific surface area and porosity, hinder their application in the purification of cis-diol flavonoid compounds.

[0004] At the same time, covalent organic frameworks (COFs) materials have become ideal adsorption substrates due to their regular pores, high specific surface area and functional properties. Introducing boronic acid groups into COFs pores through monomer pre-design can give the material specific recognition ability; for example: 2 The COF layer was grown on the surface of a metal organic framework (MOF) and phenylboronic acid was introduced into the COF pores by post-modification, but there were problems with the complex hybrid structure and large mass transfer resistance. 2+ In the coordinated COF channel, the phenylboronic acid molecules are fixed by the metal-ligand interaction, and there is a coordination bond that is easy to dissociate (the target molecule and Zn 2+ Competitive coordination leads to the shedding of the boronic acid group) and problems such as single function and poor universality. Summary of the invention

[0005] The mass production of cis-dihydroxy compounds may cause occupational health, ecological safety, water safety and other problems. Therefore, it is urgent to find an effective method to achieve the selective separation of cis-dihydroxy compounds such as luteolin and catechol. Among them, the adsorption separation method has the advantages of simple operation, low cost and good stability. In particular, it is more important to explore new methods for the development of adsorbents that can achieve selective separation.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present invention is: a new type of functionalized hollow microcapsule based on boron affinity technology and molecular imprinting technology is prepared by adopting a post-modification strategy for the efficient adsorption of cis-dihydroxy compounds. First, 1,3,5-tris(4-aminophenyl)benzene TAPB, 2,5-dimethoxybenzenedicarboxylic acid DMTP and 2,5-divinylbenzaldehyde DVA are used as raw materials, and vinyl functionalized COFs-DVA is synthesized by amine aldehyde condensation reaction by emulsion polymerization, and then it is thiol-modified by a two-step thiol-ene "click" reaction and the imprinted boric acid molecule (3-acrylamidophenylboronic acid) is grafted onto the COFs skeleton to obtain phenylboronic acid functionalized imprinted microcapsules COFs-DVA-SH-BAMIPMCs.

[0007] Furthermore, the method for preparing the COFs-based hollow imprinted microcapsule adsorbent comprises the following steps:

[0008] (1) Preparation of COFs-DVA

[0009] First, an oil phase (solution A) was prepared by dissolving 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,5-dimethoxyphthalaldehyde (DMTP), and 2,5-divinylbenzaldehyde (DVA) in n-butanol.

[0010] Then, an aqueous phase (solution B) was prepared by dissolving a certain amount of dodecyltrimethylammonium bromide (DTAB) in ultrapure water.

[0011] Solution B was added to solution A at 9000 rpm to obtain a stable emulsion. Then, scandium trifluoromethanesulfonate (Sc(OTf) 3 ) as a catalyst to initiate the interfacial reaction and gently shake for 3 minutes. The emulsion was then heated at 70°C for 30 minutes to promote further growth of the polymer to obtain a suspension. After the reaction was cooled to room temperature, the suspension was centrifuged and the solid product was washed three times with ethanol.

[0012] Finally, the product was transferred to a high temperature and pressure resistant reaction bottle containing a mixed solution of 1,4-dioxane and mesitylene (volume ratio 4:1-2:1). Ultrapure water and acetic acid were added to the solution in sequence, and the suspension was heated at 70°C for 6-12h. After the reaction was completed, the yellow solid product was washed three times with tetrahydrofuran (THF) and dried in a vacuum oven overnight to obtain COFs-DVA.

[0013] The molar volume ratio of 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,5-dimethoxybenzaldehyde (DMTP), 2,5-divinylbenzaldehyde (DVA) and n-butanol is 4:3:3:600; the concentration of solution B is 200 mg / L; the stirring speed of the obtained stable emulsion is 9000 rpm; Sc(OTf) 3 The concentration of the catalyst solution was 1.0 mmol / L; ultrapure water and CH 3 The volume ratio of COOH is 1:1.5.

[0014] (2) Preparation of COFs-DVA-SH

[0015] COFs-DVA and azobisisobutyronitrile (AIBN) were added to a thick-walled pressure bottle, nitrogen was passed for 15 minutes to remove oxygen, and then 1,2-ethanedithiol was added. The reaction system was stirred at 90°C for 72 hours. After the reaction, the product was repeatedly washed with acetone at 9000 rpm and collected by centrifugation, and finally dried in a vacuum drying oven for 12 hours to obtain the thiol functionalized material COFs-DVA-SH;

[0016] The mass volume ratio of COFs-DVA, azobisisobutyronitrile and 1,2-ethanedithiol is: 40-20:2:4-5. (The mass ratio of COFs-DVA to AIBN is (40-20):2, and the solid-liquid ratio of COFs-DVA to 1,2-ethanedithiol is (40-20mg):4-5mL.

[0017] (3) Preparation of COFs-DVA-SH-BA MIPMCs

[0018] The target (luteolin) and 3-acrylamidophenylboronic acid were magnetically stirred and dispersed in deionized water for 12 hours for pre-assembly, and then COF-DVA-SH was added to the above solution and nitrogen was passed for 15 minutes, and then azobisisobutyronitrile (AIBN) was added, and nitrogen was continued for 15 minutes to ensure that the system was in an oxygen-free environment. Subsequently, the system was reacted at 80°C for 72 hours. After the reaction was completed, the product was washed three times with methanol / acetic acid (9:1, volume ratio) solution, and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs.

[0019] The mass ratio of the target product to 3-acrylamide phenylboronic acid and COFs-DVA-SH is 70-150:20-30:20-30, and the amount of the initiator is 5% of the mass of 3-acrylamide phenylboronic acid; the system reacts at 80° C. for 72 minutes.

[0020] The COFs-based hollow microcapsule adsorption material prepared by the above method is used for the selective adsorption and separation of cis-dihydroxy compounds.

[0021] The specific method for selective adsorption and separation of cis-dihydroxy compounds is as follows: the adsorbent and the solution containing the cis-dihydroxy compound are mixed and added to a centrifuge tube, and the centrifuge tube is placed in an oscillator at different temperatures for adsorption. After a period of reaction, the supernatant is collected, and the absorbance of the supernatant at λ=350nm is measured by a UV-visible spectrophotometer to obtain the adsorption capacity of the adsorbent. The selective adsorption and separation effect of the COFs-based hollow imprinted microcapsule adsorbent on cis-dihydroxy compounds is investigated at different pH, different temperatures, different initial concentrations, and different adsorption times.

[0022] Technical advantages of the present invention:

[0023] The invention realizes the efficient selective adsorption and controllable regeneration of cis-dihydroxy compounds through the synergistic effect of boron affinity technology and molecular imprinting technology.

[0024] On the one hand, the phenylboronic acid groups modified on the surface of the material specifically bind to the cis-dihydroxy structure through dynamic covalent bonds, combined with the spatial matching effect of molecular imprinting, to form a dual action mechanism of "chemical recognition-spatial locking". This design significantly improves the selectivity of the target molecules, can effectively distinguish between structural analogs and non-analogs, and avoid competitive adsorption interference. On the other hand, the high porosity of the regular pores of COFs further provides abundant adsorption sites, significantly improving the adsorption capacity.

[0025] The covalent bond between the phenylboronic acid group and the cis-dihydroxyl group has pH-responsive properties, which enables lossless desorption of the target under mild conditions. The synergistic effect of the COFs rigid skeleton and hollow microcapsules avoids structural collapse or loss of active sites during recycling, ensuring the long-term stability of the material. In addition, the material exhibits strong tolerance to complex water quality environments and a wide range of pH / temperature conditions, and can be used in a variety of scenarios such as industrial wastewater treatment and biomedical separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 a, b, and c are scanning electron microscope images of COFs-DVA obtained in Example 1, Example 2, and Example 3, respectively; d is a scanning electron microscope image of COFs-DVA in Example 1 magnified to 200 nm; e and f are scanning electron microscope images of COFs-DVA-SH in Example 1 and Example 2, respectively; g and h are scanning electron microscope images of COFs-DVA-SH in Examples 4 and 5, respectively.

[0027] Figure 2 This is the thermogravimetric analysis curve of COFs-DVA, COFs-DVA-SH, and COFs-DVA-SH MIPMCs in Example 1.

[0028] Figure 3The infrared spectra of COFs-DVA and COFs-DVA-SH of Example 1 are shown.

[0029] Figure 4 2. XRD diagram of COFs-DVA and COFs-DVA-SH in Example 1.

[0030] Figure 5 This is the effect of pH (5.0-9.0) on the adsorption capacity of COFs-DVA-SH-BAMIPMCs and COFs-DVA-SH-BA NIPMCs under Example 1.

[0031] Figure 6 The adsorption capacity of COFs-DVA-SH-BA MIPMCs and COFs-DVA-SH-BA NIPMCs for LTL in Example 1, Example 6, and Example 7 at pH = 8.

[0032] Figure 7 (a) is the chemical structure diagram of the template molecule and template molecule analogs, Figure 7 (b) is the adsorption capacity of COFs-DVA-SH-BA MIPMCs and COFs-DVA-SH-BA NIPMCs in Example 1 for luteolin (LTL), catechol (CT), rutin (RT), phenol (Phenol), and tetranitrophenol (4-Nitrophenol).

[0033] Figure 8 This is the adsorption kinetic model of COFs-DVA-SH-BA MIPMCs and COFs-DVA-SH-BA NIPMCs in Example 1.

[0034] Fig. 9 This is the adsorption isotherm of COFs-DVA-SH-BA MIPMCs in Example 1.

[0035] Fig.10 Regeneration diagram of COFs-SH-BA MIPMCs in Example 1 through five consecutive adsorption-desorption cycles.

[0036] Fig.11 (a) Diagram of the preparation process of COFs-DVA-SH-BA MIPMCs and (b) diagram of the preparation principle. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific embodiments.

[0038] Example 1

[0039] (1) Preparation of COFs-DVA

[0040] First, the oil phase (solution A) was prepared by dissolving TAPB (0.04 mmol, 14.1 mg), DMTP (0.03 mmol, 5.8 mg) and DVA (0.03 mmol, 5.6 mg) in 6 mL of n-butanol. Then, the aqueous phase (solution B) was prepared by dissolving DTAB in ultrapure water (16 mL, 200 mg / L). Solution B was added to solution A at 9000 rpm to obtain a stable emulsion. Next, 16 mL of 7.9 mg of Sc(OTf) was added. 3 Sc(OTf) 3 The aqueous solution (concentration of 1 mmol / L) was used as a catalyst to initiate the interfacial reaction and was gently shaken for 3 min. The emulsion was heated at 70 °C for 30 min to promote further growth of the polymer. After the reaction was cooled to room temperature, the suspension was centrifuged and washed 3 times with ethanol. Finally, the product was transferred to a high temperature and pressure resistant reaction bottle containing 5 mL of a mixed solution of 1,4-dioxane and mesitylene (volume ratio 4:1). Ultrapure water (1 mL) and acetic acid (1.5 mL) were added to this solution in sequence, and the suspension was heated at 70 °C for 12 h. After the reaction was completed, the yellow solid product was washed 3 times with tetrahydrofuran (THF) and dried in a vacuum oven overnight to obtain COFs-DVA.

[0041] (2) Preparation of COFs-DVA-SH

[0042] 40 mg COFs-DVA and 2 mg AIBN were added to a 40 mL thick-walled pressure bottle, nitrogen was passed for 15 min to remove oxygen, and then 4.0 mL 1,2-ethanedithiol was added. The reaction system was stirred at 90 ° C for 72 h. After the reaction, the product was washed with acetone at 9000 rpm for 3 times and centrifuged, and finally dried in a vacuum drying oven for 12 h to obtain the thiol functionalized material COFs-DVA-SH;

[0043] (3) Preparation of COFs-DVA-SH-BA MIPMCs

[0044] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 150 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of methanol / acetic acid (9:1, volume ratio) mixed solution, and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BA NIPMCs were prepared according to the same steps without the target.

[0045] Example 2

[0046] (1) Preparation of COFs-DVA

[0047] A stable emulsion was obtained as in Example 1. Then, 16 mL of 7.9 mg Sc(OTf) was added. 3 Sc(OTf) 3 The aqueous solution (concentration of 1 mmol / L) was used as a catalyst to initiate the interfacial reaction and was gently shaken for 3 min. The emulsion was heated at 70 °C for 30 min to promote further growth of the polymer. After the reaction was cooled to room temperature, the suspension was centrifuged and the solid product was washed three times with ethanol. Finally, the product was transferred to a high temperature and pressure resistant reaction bottle containing a mixed solution of 5 mL of 1,4-dioxane and mesitylene (volume ratio 3:1). Ultrapure water (1 mL) and acetic acid (1.5 mL) were added to this solution in sequence, and the suspension was heated at 70 °C for 9 h. After the reaction was completed, the yellow solid product was washed three times with tetrahydrofuran (THF) and dried in a vacuum oven overnight to obtain COFs-DVA.

[0048] (2) Preparation of COFs-DVA-SH

[0049] 30 mg COFs-DVA and 2 mg AIBN were added to a 40 mL thick-walled pressure bottle, nitrogen was passed for 15 min to remove oxygen, and then 4.0 mL 1,2-ethanedithiol was added. The reaction system was stirred at 90 ° C for 72 h. After the reaction, the product was washed with acetone at 9000 rpm for 3 times and centrifuged, and finally dried in a vacuum drying oven for 12 h to obtain the thiol functionalized material COFs-DVA-SH;

[0050] (3) Preparation of COFs-DVA-SH-BA MIPMCs

[0051] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 110 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of a mixed solution of methanol / acetic acid (9:1, volume ratio), and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BA NIPMCs were prepared according to the same steps without the target.

[0052] Example 3

[0053] (1) Preparation of COFs-DVA

[0054] A stable emulsion was obtained as in Example 1. Then, 16 mL of 7.9 mg Sc(OTf) was added. 3 Sc(OTf) 3 The aqueous solution (concentration of 1 mmol / L) was used as a catalyst to initiate the interfacial reaction and was gently shaken for 3 min. The emulsion was heated at 70 °C for 30 min to promote further growth of the polymer. After the reaction was cooled to room temperature, the suspension was centrifuged and the solid product was washed three times with ethanol. Finally, the product was transferred to a high temperature and pressure resistant reaction bottle containing a mixed solution of 5 mL of 1,4-dioxane and mesitylene (volume ratio 2:1). Ultrapure water (1 mL) and acetic acid (1.5 mL) were added to this solution in sequence, and the suspension was heated at 70 °C for 6 h. After the reaction was completed, the yellow solid product was washed three times with tetrahydrofuran (THF) and dried in a vacuum oven overnight to obtain COFs-DVA.

[0055] (2) Preparation of COFs-DVA-SH

[0056] 20 mg COFs-DVA and 2 mg AIBN were added to a 40 mL thick-walled pressure bottle, nitrogen was passed for 15 min to remove oxygen, and then 4.0 mL 1,2-ethanedithiol was added. The reaction system was stirred at 90 ° C for 72 h. After the reaction, the product was washed with acetone at 9000 rpm for 3 times and centrifuged, and finally dried in a vacuum drying oven for 12 h to obtain the thiol functionalized material COFs-DVA-SH;

[0057] (3) Preparation of COFs-DVA-SH-BA MIPMCs

[0058] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 70 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of a mixed solution of methanol / acetic acid (9:1, volume ratio), and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BA NIPMCs were prepared according to the same steps without the target.

[0059] Example 4

[0060] (1) Obtain COFs-DVA in the same manner as in Example 1.

[0061] (2) Preparation of COFs-DVA-SH

[0062] 40 mg COFs-DVA and 3 mg AIBN were added to a 40 mL thick-walled pressure bottle, nitrogen was passed for 15 min to remove oxygen, and then 4.0 mL 1,2-ethanedithiol was added. The reaction system was stirred at 90 ° C for 72 h. After the reaction, the product was washed with acetone at 9000 rpm for 3 times and centrifuged, and finally dried in a vacuum drying oven for 12 h to obtain the thiol functionalized material COFs-DVA-SH;

[0063] (3) Preparation of COFs-DVA-SH-BAMIPMCs

[0064] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 150 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of a mixed solution of methanol / acetic acid (9:1, volume ratio), and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BANIPMCs were prepared according to the same steps without the target.

[0065] Example 5

[0066] (1) Obtain COFs-DVA in the same manner as in Example 1.

[0067] (2) Preparation of COFs-DVA-SH

[0068] 40 mg COFs-DVA and 2 mg AIBN were added to a 40 mL thick-walled pressure bottle, nitrogen was passed through for 15 min to remove oxygen, and then 5.0 mL 1,2-ethanedithiol was added. The reaction system was stirred at 90 ° C for 72 h. After the reaction, the product was washed with acetone at 9000 rpm for 3 times and centrifuged, and finally dried in a vacuum drying oven for 12 h to obtain the thiol functionalized material COFs-DVA-SH;

[0069] (3) Preparation of COFs-DVA-SH-BAMIPMCs

[0070] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 150 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of a mixed solution of methanol / acetic acid (9:1, volume ratio), and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BANIPMCs were prepared according to the same steps without the target.

[0071] Example 6

[0072] (1) Obtain COFs-DVA in the same manner as in Example 1.

[0073] (2) Obtaining the thiol functionalized material COFs-DVA-SH in the same manner as in Example 1;

[0074] (3) Preparation of COFs-DVA-SH-BAMIPMCs

[0075] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 150 mg:30 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 20 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of methanol / acetic acid (9:1, volume ratio) solution, and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BA NIPMCs were prepared according to the same steps without the target.

[0076] Example 7

[0077] (1) Obtain COFs-DVA in the same manner as in Example 1.

[0078] (2) Obtaining the thiol functionalized material COFs-DVA-SH in the same manner as in Example 1;

[0079] (3) Preparation of COFs-DVA-SH-BAMIPMCs

[0080] The target LTL and 3-acrylamidophenylboronic acid were pre-assembled in a ratio of 150 mg:20 mg by magnetic stirring in 10 mL of deionized water for 12 h, and then 30 mg of COF-DVA-SH was added to the above solution and nitrogen was passed for 15 min, and then 1 mg of AIBN was added and nitrogen was continued for 15 min to ensure an oxygen-free environment for the system. Subsequently, the system was reacted at 80 ° C for 72 h. After the reaction was completed, the product was washed three times with 10 mL of methanol / acetic acid (9:1, volume ratio) solution, and finally the product was vacuum dried to obtain COFs-DVA-SH-BA MIPMCs. As a control, COFs-DVA-SH-BA NIPMCs were prepared according to the same steps without the target.

[0081] Analysis of attached pictures

[0082] Figure 1a, b, c are scanning electron microscope images of COFs-DVA obtained in Example 1, Example 2 and Example 3, respectively, d is a scanning electron microscope image of COFs-DVA of Example 1 magnified to 200nm, and e and f are scanning electron microscope images of COFs-DVA-SH of Example 1 and Example 2, respectively. It can be seen from the figure that when the reaction is 6h, irregular spherical particles are present, and there is considerable agglomeration. The surface with a reaction time of 12h is smoother, and the number of spherical structures increases significantly. As the polymerization reaction time increases, the diameter of the spherical structure increases accordingly. As the volume ratio of the incubation solvent (1,4-dioxane and mesitylene) increases, the overall polarity of the mixed solvent decreases, resulting in changes in the solubility of the reaction system, thereby affecting the diffusion rate and interfacial polymerization of the COF precursor, making the agglomeration more obvious. At 200nm, it can be seen that there are obvious and uniform wrinkles on the surface of the material, which also provides more binding sites for the boronic acid functional group. By comparing the microscopic morphology of COFs-DVA-SH prepared in Example 1 (COFs-DVA dosage 40 mg) and Example 3 (COFs-DVA dosage 20 mg), it is found that when the amount of COFs-DVA added is reduced, the degree of collapse of the microcapsule structure increases significantly. This shows that COFs-DVA itself has a stable hollow microcapsule configuration, and its skeleton integrity depends on sufficient monomer cross-linking support; azobisisobutyronitrile (AIBN) needs to reach the minimum threshold concentration (2 mg / 40 mgCOFs-DVA) to fully induce the thiol-ene click reaction, ensuring that the thiol is uniformly grafted to the surface of the hollow structure, thereby maintaining the mechanical strength of the microcapsule. g is a SEM image of COFs-DVA-SH prepared in Example 4. It can be seen that a more obvious agglomeration phenomenon is produced compared to Example 1. It may be that when the initiator is excessive, the thiol-ene click reaction rate will be accelerated, resulting in more free radicals generated per unit time, and promoting the formation of a denser cross-linked network. h is the SEM image of COFs-DVA-SH prepared in Example 5. It can be seen that after increasing the amount of thiol, the microcapsules collapsed more obviously. The mechanical strength of the collapsed microcapsules decreased, and they were easily broken during centrifugation, washing or practical applications.

[0083] Figure 2The thermogravimetric analysis curves of COFs-DVA, COFs-DVA-SH, and COFs-DVA-SH MIPMCs in Example 1. It can be seen that the three materials lost 25.93%, 38.74%, and 45.64% of their weight respectively after complete decomposition at 800°C. The weight loss of the three materials gradually increased, and the COFs-DVA-SH modified with thiol groups began to significantly accelerate the weight loss process at 150°C compared to COFs-DVA, which may be due to the grafting of thiol groups on the COFs surface through a "click" reaction. The weight loss of COFs-DVA-SHMIPMCs increased further compared to COFs-DVA-SH, and it could only maintain 54.46% of the initial mass, which indicates the success of imprinting polymerization. In addition, the maximum weight loss of the three materials at 250°C is only about 7.6%, indicating that the materials have good thermal stability at this temperature.

[0084] Figure 3 The infrared spectra of COFs-DVA and COFs-DVA-SH in Example 1 are shown in Figure 1. -1 The absorption peak at 1701cm corresponds to the stretching vibration of C=N, which provides strong evidence for the covalent bonding between TAPB and DMTP. -1 The absorption peak at 3500cm is attributed to the C=O stretching vibration in DMTP and DVA, which further verifies the existence of carbonyl in the structure. -1 The NH stretching vibration peak was observed near 2500 cm, indicating that the amino group was successfully introduced into the COFs structure. -1 There is no obvious -SH characteristic peak at the site, which may be due to the limitation of FT-IR spectrum sensitivity, making the -SH absorption peak weak.

[0085] Figure 4 The XRD diagrams of COFs-DVA and COFs-DVA-SH in Example 1 are shown in Figure 1. It can be observed that the synthesized COFs-DVA has obvious diffraction peaks at 2.80°(100), 4.85°(110), 5.60°(200), 7.42°(210) and 9.70°(220). The intensity and position of these diffraction peaks are highly consistent with the data reported in the literature, indicating that the COFs-DVA material has a similar crystal structure. Further analysis shows that the diffraction peak intensity of the modified COFs-DVA-SH at the 100, 110, and 200 crystal planes is reduced. This reduction in crystallinity may be attributed to the introduction of thiol functional groups.

[0086] Adsorption performance analysis test

[0087] The specific method is as follows:

[0088] The adsorbent (5 mg) was added to a centrifuge tube and mixed with a cis-dihydroxy compound solution (LTL solution, CT solution, RT solution, Phenol solution, 4-Nitrophenol solution) (10 mL), wherein the cis-dihydroxy compound solution was dissolved in a methanol / water mixed solution (3:7, volume ratio) to prepare an initial concentration of 25 mg / L. In the experiment of investigating the effect of pH in the range of 5.0-9.0, the pH value of the solution was adjusted with hydrochloric acid or sodium hydroxide, and then the centrifuge tube was placed in an oscillator at different temperatures for adsorption. After a period of reaction, the supernatant was collected and the absorbance of the supernatant was measured at λ = 350 nm using a UV-visible spectrophotometer.

[0089] Each group of experiments was performed three times and the average value was taken. t , mg / g) is calculated by formula (1).

[0090]

[0091] Among them, C 0 (mg / L) and Ct (mg / L) are the concentrations of the target in the solution before and after adsorption at adsorption time t, m (mg) is the mass of the adsorbent, and V (mL) is the volume of the test solution.

[0092] In addition, the adsorption kinetics of the adsorbent were evaluated using pseudo-first-order (2) and pseudo-second-order kinetic models (3).

[0093] ln(Q e -Q t )=lnQ e -k 1 t (2)

[0094]

[0095] Where Qt (mg / g) and Qe (mg / g) are the amount of target adsorbed per gram of adsorbent at time t (min) and at equilibrium, respectively. 1 (min -1 ) represents the pseudo-first-order reaction rate constant, k 2 (g / mg·min) represents the pseudo-second-order reaction rate constant.

[0096] The adsorption isotherm was studied by adding the adsorbent (5 mg) to 10 mL of target solution with different initial concentrations (20-120 mg / L). The adsorption equilibrium was reached after 1 h of oscillation adsorption. The experimental data were fitted with the Langmuir and Freundlich models, and the equations were (4) and (5) respectively.

[0097]

[0098] Where Ce (mg / L) is the concentration of the target in the solution at equilibrium, Qm (mg / g) is the maximum adsorption capacity of the adsorbent for the target, and K L (L / mg) is the Langmuir adsorption constant, K F (mg / g)·(L / mg) 1 / n is the Freundlich adsorption constant, and 1 / n is the adsorption intensity constant.

[0099] Specific recognition ability is an important indicator for evaluating the availability of adsorbents in the selective separation of target molecules. In order to measure the specificity of COFs-DVA-SH-BA MIPMCs, the recognition of LTL was compared with that of structural analogs CT, RT and non-structural analogs Phenol and 4-Nitrophenol. The distribution coefficient (Kd) and selectivity coefficient (k) can be calculated according to formulas (6)-(7).

[0100]

[0101] Where K d (L / g) represents the distribution coefficient, Q e (mg / g) is the equilibrium adsorption capacity. e (mg / L) is the equilibrium concentration. The selectivity coefficient (k) of the adsorbent for LTL relative to the competitive substance can be obtained according to the following formula:

[0102]

[0103] Where x represents a competitor.

[0104] Effect example 1:

[0105] In order to optimize the recovery effect, the adsorption behavior of the cis-dihydroxy compound solution (taking LTL as an example) on COFs-DVA-SH-BAMIPMCs and COFs-DVA-SH-BA NIPMCs under different pH conditions was investigated in Example 1. In order to optimize the recovery effect, the adsorption behavior of the cis-dihydroxy compound solution (taking LTL as an example) on COFs-DVA-SH-BA MIPMCs and COFs-DVA-SH-BANIPMCs prepared in Example 1 under different pH conditions was investigated. When the solution is an alkaline environment and the pH is higher than the pKa value of the boric acid group, the boric acid group B atom in the hollow microcapsule adsorbent is sp 3 The hybrid tetraborate anion exists in the form of a cis-diol structure, which easily forms a stable five-membered or six-membered cyclic ester, thereby enhancing the adsorption of LTL. When the pH is lower than the pKa, the B atom is sp2 The presence of the triangular structure causes the boric acid-cis-diol complex to dissociate, thus weakening the adsorption effect. Figure 5 It can be seen that when the pH increases from 5.0 to 8.0, the adsorption capacity of both adsorbents increases. Among them, the adsorption capacity of the hollow imprinted microcapsule adsorbent COFs-DVA-SH-BAMIPMCs at pH 8 reaches 34.49 mg / g, while the adsorption capacity of the hollow non-imprinted microcapsule adsorbent COFs-DVA-SH-BANIPMCs is 12.38 mg / g, indicating that the imprinting process effectively enhances the recognition of LTL. At pH 5.0, the adsorption capacity of the two microcapsules is the lowest, which is attributed to the weakened dissociation of the boric acid group when the pH is lower than the pKa value. When the pH value increases from 8.0 to 9.0, the adsorption performance of the two microcapsules decreases, which may be attributed to the deprotonation and protonation process of the boric acid functional group.

[0106] At the same pH, the adsorption capacities of Example 1, Example 6 and Example 7 are compared. Figure 6 As shown, the adsorption amount of Example 6 is slightly increased compared with that of Example 1, which may be because the 3-acrylamide group is used as a functional monomer, and the increase in its addition can form more phenylboronic acid ester bond sites that specifically bind to LTL, thereby improving the imprinting efficiency. However, the adsorption amount of Example 7 is significantly decreased compared with that of Example 1, which may be attributed to the increase in the amount of carrier material (COFs-DVA-SH) used to provide more surface loading sites, but the imprinting process did not fully cover all carriers, resulting in a decrease in the adsorption amount per unit mass.

[0107] Effect Example 2:

[0108] Specific recognition ability is an important indicator for evaluating the availability of adsorbents in the selective separation of target molecules. In order to analyze the specific adsorption and separation performance of COFs-DVA-SH-BAMIPMCs, the recognition of LTL was compared with that of structural analogs CT, RT and non-structural analogs Phenol and 4-Nitrophenol (the structures of the test compounds are as follows Figure 7 a) were compared.

[0109] The adsorption results of COFs-DVA-SH-BAMIPMCs and COFs-DVA-SH-BANIPMCs on five target substances in Example 1 are as follows: Figure 7As shown in b, the adsorption capacities of COFs-DVA-SH-BAMIPMCs for LTL, CT, RT, Phenol, and 4-Nitrophenol are 6.82 mg / g, 7.64 mg / g, 20.54 mg / g, 30.07 mg / g, and 35.25 mg / g, respectively. In contrast, the adsorption capacities of COFs-DVA-SH-BANIPMC for the targets are significantly lower than those of COFs-DVA-SH-BAMIPMCs. It is worth noting that compared with LTL, CT and RT have similar cis-diol structures, indicating that borate affinity plays a vital role in the selective recognition of LTL. This indicates that the adsorbent has good selective adsorption capacity for LTL and has abundant boronic acid recognition sites.

[0110] Effect example 3:

[0111] The distribution coefficients and selectivity coefficients of COFs-DVA-SH-BA MIPMCs for the five targets in Example 1 and Example 6 are shown in Table 1. d It can be seen from the values ​​that COFs-DVA-BAMIPMCs has the strongest adsorption capacity for the template molecule LTL, indicating that molecular imprinting has successfully formed a cavity matching LTL, and the imprinting technology has greatly improved the specific adsorption. From the selectivity coefficient k, it can be seen that the selectivity of COFs-DVA-BA MIPMCs for the other four test compounds is 4-Nitrophenol>Phenol>RT>CT, and the selectivity for CT is the lowest, which may be due to the similar structure of CT and LTL, resulting in competitive adsorption. The k value of COFs-DVA-BANIPMCs is generally low, indicating that the non-imprinted adsorbent has poor selectivity and only relies on surface physical adsorption or weak chemical action. The K of Example 6 d and k values ​​are smaller than those in Example 1, where K of LTL d The K values ​​of competitors 4-Nitrophenol, Phenol, and RT decreased to 3.06, reflecting the weakening of specific adsorption. d Both increased, indicating that nonspecific adsorption was enhanced. In addition, the selectivity coefficient of LTL relative to the competitor in Example 6 decreased, which directly proved that the excess boronic acid monomer damaged the molecular imprinting effect.

[0112] Table 1 Distribution coefficient and selectivity coefficient data of COFs-DVA-BA MIPMCs

[0113]

[0114] Effect example 4:

[0115] The adsorption rate control process of COFs-DVA-SH-BAMIPMCs and COFs-DVA-SH-BA NIPMCs on the target was studied and analyzed, and the fitting curve of the relevant kinetic model was drawn. Take 10mL of the target solution with a pH of 8.5, add 5mg of adsorbent, measure the concentration of organic matter in the adsorbed solution after different adsorption times, and calculate the adsorption capacity based on the results. The test results are as follows: Figure 8 As shown in the figure, at 30 °C, the adsorption capacity of COFs-DVA-SH-BA MIPMCs and COFs-DVA-SH-BANIPMCs for LTL increased rapidly within the first 60 min, which was mainly attributed to the high concentration of LTL, abundant boronic acid binding sites and the porous structure of the adsorbent. The results showed that COFs-DVA-SH-BA MIPMCs reached 93.08% of the maximum adsorption capacity at 180 min and tended to saturation around 270 min. In contrast, COFs-DVA-SH-BA NIPMCs had a slower adsorption rate and lower adsorption capacity, mainly due to the lack of boronic acid binding sites.

[0116] The adsorption capacity of COFs-DVA-SH-BA MIPMCs was almost 2.5 times that of NIPMCs, further indicating that the imprinting process significantly enhanced the recognition and adsorption kinetics of LTL.

[0117] In order to further explore the rate control mechanism of LTL adsorption by microcapsules, a kinetic model was fitted. The correlation coefficient (R 2 =0.998 and 0.989) are both higher than the correlation coefficient of the pseudo-first-order model (R 2 = 0.944 and 0.960). In addition, the calculated equilibrium adsorption capacity (Q b e ) are 36.98 mg / g and 12.36 mg / g, which is consistent with the experimental value (Q a e )35.25mg / g and 12.18mg / g are closer. The results show that the pseudo-second-order kinetic model can more accurately describe the adsorption behavior of microcapsules on LTL, and the adsorption mechanism is mainly controlled by chemical adsorption involving borate.

[0118] Effect Example 5:

[0119] The adsorbent (5 mg) was added to 10 mL of LTL solution with different initial concentrations (20-120 mg / L), and the solution was shaken in a shaker at 25°C, 30°C and 35°C for 1 h. The adsorbent material was taken out and the concentration of organic matter in the solution after adsorption was measured. The adsorption capacity was calculated based on the results and the adsorption isotherm was drawn. Fig. 9It is an adsorption isotherm model. The results show that the removal of the target by the material increases with the increase of initial concentration and gradually tends to equilibrium. As the temperature increases, the adsorption amount of LTL by the material increases accordingly.

[0120] The Freundlich and Langmuir isotherm models were used to describe the isothermal adsorption process of COFs-DVA-SH-BA MIPMCs at different temperatures. The results showed that the Langmuir model was more suitable for fitting the adsorption experimental results of LTL than the Freundlich model, indicating that the adsorption process of COFs-DVA-SH-BA MIPMCs on LTL was more consistent with the monolayer adsorption characteristics. In addition, the Q calculated by the two models at different temperatures m , K L , K F The values ​​gradually increase with the increase of temperature, which shows that the affinity of COFs-DVA-SH-BA MIPMCs to LTL gradually increases with the increase of temperature. It shows that appropriate temperature increase is conducive to the adsorption of LTL, and COFs-DVA-SH-BA MIPMCs has good affinity for LTL.

[0121] Effect Example 6:

[0122] Excellent adsorbents must not only have good adsorption capacity, but also good regeneration performance, and continuous adsorption-desorption experiments are often used to evaluate the regeneration ability of samples. The regeneration performance of COFs-DVA-SH-BAMIPMCs prepared in Example 1 was investigated by comparing the adsorption capacity of COFs-DVA-SH-BAMIPMCs in 5 adsorption-desorption cycles at 30°C and pH 8.5. The relevant data are shown in Figure 2. Fig.10 As shown in the figure, after 5 adsorption-desorption cycles, the adsorption capacity of COFs-SH-BAMIPMCs for LTL decreased from 34.99 mg / g to 32.79 mg / g, and the desorption efficiency remained at around 93.74%. The trend of decreasing adsorption capacity may be attributed to the incomplete desorption or decomposition of a small number of recognition sites during the elution process.

[0123] In summary, COFs-SH-BA MIPMCs have good adsorption stability and reusability, and have good application potential in the field of selective adsorption and separation of cis-dihydroxy compounds.

Claims

1. A method for preparing a COFs-based hollow imprinted microcapsule adsorbent, characterized in that: The preparation method steps are as follows: (1) Preparation of COFs particles containing double bonds: Using 1,3,5-tris(4-aminophenyl)benzene TAPB, 2,5-dimethoxyphthalaldehyde DMTP and 2,5-divinylbenzaldehyde DVA as raw materials, vinyl-functionalized COFs-DVA were synthesized by amine-aldehyde condensation reaction via emulsion polymerization; (2) Preparation of porous imprinted COFs microcapsules: COFs-DVA was modified with thiol groups through a two-step thiol-ene "click" reaction and the imprinted boronic acid molecule 3-acrylamidophenylboronic acid was grafted onto the COFs skeleton to obtain phenylboronic acid functionalized imprinted microcapsule adsorbent COFs-DVA-SH-BA MIPMCs.

2. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 1, characterized in that: The preparation steps of vinyl functionalized COFs-DVA are as follows: 1) dissolving 1,3,5-tris(4-aminophenyl)benzene TAPB, 2,5-dimethoxyphthalaldehyde DMTP and 2,5-divinylbenzaldehyde DVA in n-butanol to prepare an oil phase-solution A; 2) dissolving dodecyltrimethylammonium bromide (DTAB) in ultrapure water to prepare an aqueous phase (solution B); 3) adding solution B to solution A under high-speed stirring to obtain a stable emulsion; 4) adding the Sc(OTf)3 catalyst solution to the emulsion in step 3) to initiate an interfacial reaction; then heating the emulsion at 70°C for 30 minutes to induce further growth to obtain a suspension; 5) After cooling the suspension obtained in step 4) to room temperature, the solid product is washed with methanol, then centrifuged, and marked as H-Amor-OMe; H-Amor-OMe is incubated in a bottle containing 1,4-dioxane / mesitylene solution; 6) Ultrapure water and CH3COOH were added to the solution in step 5) in sequence, and the resulting suspension was heated at 70°C for reaction. The yellow solid was washed with tetrahydrofuran and dried in vacuo overnight, which was recorded as COFs-DVA.

3. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 2, characterized in that: The molar volume ratio of 1,3,5-tri(4-aminophenyl)benzene, 2,5-dimethoxybenzenedicarbaldehyde and 2,5-divinylbenzaldehyde to n-butanol is 4:3:3:600; the concentration of solution B is 200 mg / L; the stirring speed for obtaining a stable emulsion is 9000 rpm; the concentration of Sc(OTf)3 catalyst solution is 1.0 mmol / L; the volume ratio of 1,4-dioxane to mesitylene is 4-2:1; the volume ratio of ultrapure water to CH3COOH is 1:1.

5.

4. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 1, characterized in that: In step (2), the method for modifying COFs-DVA with thiol groups is as follows: COFs-DVA and azobisisobutyronitrile are mixed in a thick-walled pressure bottle, nitrogen is introduced to exhaust oxygen, and 1,2-ethanedithiol is injected into the pressure bottle, followed by reaction at high temperature, the product is collected by centrifugation, washed with acetone, and vacuum dried to obtain COFs-DVA-SH.

5. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 4, characterized in that: The mass volume ratio of COFs-DVA, azobisisobutyronitrile and 1,2-ethanedithiol is 40-20:2:4-5; the reaction at high temperature is carried out at 90°C for 72 hours.

6. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 1, characterized in that: In step (2), the preparation method of the phenylboronic acid functionalized imprinted microcapsule adsorbent is as follows: the target substance and 3-acrylamide phenylboronic acid are stirred and dispersed in deionized water for pre-assembly, and then COF-DVA-SH is added to the pre-assembly solution and nitrogen is passed through it, and then azobisisobutyronitrile is added and nitrogen is passed through it again. After the reaction, it is eluted with a methanol:acetic acid mixed solution, and vacuum dried to obtain COFs-DVA-SH-BA MIPMCs.

7. The method for preparing the COFs-based hollow imprinted microcapsule adsorbent according to claim 6, characterized in that: The mass ratio of the target product to 3-acrylamidophenylboronic acid and COFs-DVA-SH is 70-150:20-30:20-30, and the amount of azobisisobutyronitrile is 5% of the mass of 3-acrylamidophenylboronic acid; the system is reacted at 80° C. for 72 minutes.

8. A COFs-based hollow imprinted microcapsule adsorbent prepared according to the method according to any one of claims 1 to 7.

9. An application of a COFs-based hollow imprinted microcapsule adsorbent prepared by the method according to any one of claims 1 to 7, characterized in that: The COFs-based hollow imprinted microcapsule adsorbent is used for selective adsorption and separation of cis-dihydroxy compounds.

10. The use of the COFs-based hollow imprinted microcapsule adsorbent according to claim 9, characterized in that: The cis-dihydroxy compounds are: luteolin and catechol.

Images