Double-template molecularly imprinted composite magnetic covalent organic framework material as well as preparation method and application thereof

Abstract

The invention discloses a double-template molecularly imprinted composite magnetic covalent organic framework material and a preparation method and application thereof.A layer-by-layer assembly method is adopted, a covalent organic framework is assembled on the surface of aminated ferroferric oxide nanoparticles at the room temperature, then an imprinted layer is formed on the surface of the covalent organic framework through a surface molecular imprinting method, and the double-template molecularly imprinted composite magnetic covalent organic framework material is obtained. And the double-template molecularly imprinted composite magnetic covalent organic framework material MCOF (at) MIP is prepared. The MCOFF-MIP prepared by the preparation method disclosed by the invention has excellent magnetic responsiveness. Experiments show that the MCOFF-MIP has a good adsorption effect and selectivity on four kinds of bisphenol, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of magnetic adsorbent and environmental detection, and in particular to the preparation of a double-template molecular imprinting composite magnetic covalent organic framework material and the enrichment and extraction of bisphenol by the material. Background Art

[0002] Bisphenol compounds (BPs) are a class of compounds in which two hydroxyphenyl groups are connected by carbon atoms or sulfur atoms. Common bisphenol compounds include bisphenol A (BPA), bisphenol B (BPB), bisphenol F (BPF), bisphenol AF (BPAF), etc. Bisphenol compounds are important raw materials for the production of various polymer materials such as polycarbonate and epoxy resin, and are also used in the production of fine chemical products such as plasticizers, flame retardants, and coatings. Bisphenol compounds are a class of environmental endocrine disruptors that are bioaccumulative and difficult to degrade. Long-term exposure to bisphenols can cause obesity, diabetes, hypertension, cardiovascular disease, cancer, and other diseases, and can also cause reproductive development abnormalities. Therefore, in order to reduce the risks of bisphenol pollutants to human health, it is of great significance to detect bisphenol pollutants in food and water. The ban on bisphenols has gradually become a global consensus, and countries and regions have successively issued strict limit regulations on bisphenol A and its analogues in food contact materials and packaging containers. On July 18, 2023, the European Commission's Directorate-General for Health and Food Safety announced a ban on the intentional addition of bisphenol A and other bisphenol substances with similar structures to food contact materials. my country allows bisphenol A to be used in the production of plastic resins, paints and coatings and their additives, as well as adhesive additives, with a specific migration limit (SML) of 0.6 mg / kg, and requires that it should not be used in the production of food contact materials and products for infants and young children. A variety of technologies have been developed, among which chromatography, including gas chromatography (GC) and high performance liquid chromatography (HPLC), is a fast, simple, low detection limit, and high sensitivity method for detecting bisphenols. It is widely used because it can quickly detect multiple bisphenol compounds at the same time. However, due to the low content of bisphenol compounds in food and beverages and the existence of complex matrix effects, a fast, simple and effective chromatographic analysis sample pretreatment technology is required before chromatographic analysis. Summary of the invention

[0003] One of the purposes of the present invention is to synthesize a magnetic adsorbent MCOF@MIP with good magnetic responsiveness and large specific surface area; the second purpose is to provide a detection method for selectively extracting bisphenol with a wide linear range and good sensitivity.

[0004] In order to achieve the above purpose, the present invention adopts the following scheme

[0005] A method for preparing a dual-template molecular imprinting composite magnetic covalent organic framework material comprises the following steps:

[0006] (1) Preparation of magnetic covalent organic frameworks

[0007] NH 2 -Fe 3 O 4 @SiO 2 , 2,5-dihydroxyterephthalaldehyde, and 1,3,5-tri(4-aminophenyl)benzene were mixed in anhydrous ethanol, acetic acid solution was used as a reaction catalyst, and mechanical stirring was performed at room temperature. The aldehyde group in 2,5-dihydroxyterephthalaldehyde reacted with NH 2 -Fe 3 O 4 @SiO 2 The amino groups in 2,5-dihydroxyterephthalaldehyde and 1,3,5-tri(4-aminophenyl)benzene react at room temperature to form a covalent organic framework COF, synthesizing the magnetic covalent organic framework MCOF, SiO 2 Coated in Fe 3 O 4 The surface of the nanoparticles was then modified by amino to obtain NH 2 -Fe 3 O 4 @SiO 2 ;

[0008] (2) Preparation of dual-template molecularly imprinted composite magnetic covalent organic framework materials

[0009] The template molecule and the functional monomer 3-aminopropyltriethoxysilane are added to ethanol and magnetically stirred to form a template-monomer mixture. The magnetic covalent organic framework MCOF is evenly dispersed in ethanol and added to the template-monomer mixture. The mixture is mechanically stirred, and a crosslinking agent tetraethyl orthosilicate TEOS and a catalyst ammonia water are added dropwise while stirring. The mixture is reacted at room temperature. After the reaction is completed, magnetic separation, washing and drying are performed. Finally, the template molecule is eluted to remove the template molecule to obtain a molecular imprinting polymer MCOF@MIP. The template molecules are two of bisphenol A, bisphenol B, bisphenol F and bisphenol AF.

[0010] Specifically, the molar ratio of 2,5-dihydroxyterephthalaldehyde to 1,3,5-tris(4-aminophenyl)benzene is 3:2. 2 -Fe 3 O 4 @SiO 2 The mass ratio of 2,5-dihydroxyterephthalaldehyde to 5:1.

[0011] Specifically, the molar ratio of the magnetic covalent organic framework MCOF, the template molecule, the functional monomer 3-aminopropyltriethoxysilane, and tetraethyl orthosilicate TEOS is 1:1:4:8.

[0012] Specifically, the elution in step (2) is as follows: performing Soxhlet extraction on the solid matter dried in step (2) with a mixed solution of methanol and acetic acid in a volume ratio of 9:1 to remove the template molecules, then washing with methanol until neutral, and drying to obtain the molecularly imprinted polymer MCOF@MIP.

[0013] Specifically, the NH 2 -Fe 3 O 4 @SiO 2 Preparation, specifically: using the solvothermal method to synthesize ferroferric oxide Fe 3 O 4 , using tetraethyl orthosilicate in Fe 3 O 4 The surface is coated with a layer of silicon shell to obtain Fe 3 O 4 @SiO 2 , the silicon shell can protect Fe 3 O 4 To avoid corrosion under acidic conditions, Fe 3 O 4 @SiO 2 With 3-aminopropyltriethoxysilane in a mixed solution of ethanol and water (100:5, v:v), mechanically stirred at 80 °C, amino-functionalized ferrosoferric oxide NH 2 -Fe 3 O 4 @SiO 2 .

[0014] Application of dual-template molecularly imprinted composite magnetic covalent organic framework materials in the enrichment of bisphenol

[0015] The MCOF@MIP prepared by the present invention has excellent magnetic responsiveness. Experiments show that the MCOF@MIP of the present invention has good adsorption effect and selectivity for four bisphenols and has good application prospects.

[0016] The present invention uses the detection target bisphenol as a template molecule, the hydroxyl group in the bisphenol is connected to the amino group in the functional monomer 3-aminopropyltriethoxysilane through hydrogen bonding, and the functional monomer is polymerized with tetraethyl orthosilicate under the action of a catalyst, and after the reaction is completed, the template molecule is eluted to form a molecular imprinted polymer with specific adsorption pore sites and specific adsorption to the template molecule. The present invention uses two bisphenols as template molecules, and can not only adsorb the template molecule itself, but also adsorb structures similar to the template molecule. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart for preparing the dual-template molecular imprinting composite magnetic covalent organic framework material.

[0018] Figure 2 FT-IR graphs of MCOF@MIP and MCOF@NIP of the present invention.

[0019] Figure 3 This is the hysteresis loop of MCOF@MIP of the present invention.

[0020] Figure 4 SEM and TEM of MCOF@MIP of the present invention.

[0021] Figure 5 This is a comparison chart of the adsorption amounts of four bisphenols (BPF, BPA, BPB, BPAF) and two competitive adsorption molecules (DEP, HQ) by MCOF@MIP and MCOF of the present invention.

[0022] Figure 6 This is a comparison chart of the adsorption amounts of four bisphenols (BPF, BPA, BPB, BPAF) and two competitive adsorption molecules (DEP, HQ) by MCOF@MIP and MCOF@NIP of the present invention.

[0023] Figure 7 This is a chromatogram of the spiked recovery experiment of bisphenol in the Yellow River water sample using the MCOF@MIP of the present invention. Implementation

[0025] The present invention is described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0026] Example 1: Preparation of amino-functionalized ferrosoferric oxide

[0027] 2.60 g FeCl 3 6H 2 O, 5.75g NaAc and 1.0g polyethylene glycol were dissolved in 50mL ethylene glycol solution, and the mixture was magnetically stirred for 30min, then transferred into a 50mL stainless steel reactor lined with polytetrafluoroethylene, heated to 200°C in a constant temperature blast drying oven, reacted for 8h and then naturally cooled to room temperature, washed with ethanol three times and dried to obtain Fe 3 O 4 Nanoparticles.

[0028] 0.150 g Fe 3 O 4 The nanoparticles and 100 mL of ethanol were evenly dispersed in a three-necked flask. Under mechanical stirring, 1.2 mL of ammonia solution, 25 mL of deionized water and 100 μL of tetraethyl orthosilicate (TEOS) were added dropwise to the mixture. After stirring for 9 h, Fe 3 O 4 The surface of the nanoparticles is covered with a layer of SiO2 , use a magnet to collect Fe 3 O 4 @SiO 2 The samples were washed three times with ethanol and then dried.

[0029] Fe 3 O 4 @SiO 2 Dispersed in a mixed solution of 5 mL of deionized water and 100 mL of anhydrous ethanol, 2 mL of 3-aminopropyltriethoxysilane APTES was then added to the solution while stirring. Stirring was continued at 80 °C for 24 h. After cooling to room temperature, the amino-functionalized Fe 3 O 4 @SiO 2 (NH 2 -Fe 3 O 4 @SiO 2 The final product was then washed with ethanol and dried in a vacuum oven at 60°C overnight.

[0030] Example 2: Preparation of magnetic covalent organic framework

[0031] (1) 0.125 g NH 2 -Fe 3 O 4 @SiO 2 Ultrasonic dispersion in 50 mL of anhydrous ethanol, accurately weigh 0.0293 g, 0.0150 mmol of 2,5-dihydroxyterephthalaldehyde DHTA and 0.0402 g, 0.100 mmol of 1,3,5-tris(4-aminophenyl)benzene TAPB, and dissolve them in 30 mL and 60 mL of anhydrous ethanol respectively under ultrasonic action;

[0032] (2) Then, NH 2 -Fe 3 O 4 @SiO 2 , DHTA and TAPB ethanol solution was added into a 500mL three-necked flask, 1.33mL 6.0mol / L acetic acid solution was added thereto as a reaction catalyst, and mechanical stirring was carried out at room temperature (about 20°C, 1atm) for 3 days to obtain a magnetic covalent organic framework MCOF. The magnetic covalent organic framework MCOF was washed with anhydrous ethanol and vacuum dried at 50°C overnight for use.

[0033] Example 3: Preparation of MCOF@MIP and MCOF@NIP

[0034] (1) Weigh 1 mmol, 0.2282 g of bisphenol A BPA and 1 mmol, 0.2508 g of bisphenol B BPB and dissolve them in 50 mL of ethanol, accurately weigh 4 mmol of 3-aminopropyltriethoxysilane APTES and add them to the above solution, and stir magnetically for 2 hours to form a template-monomer mixture;

[0035] (2) Weigh 250 mg of magnetic covalent organic framework MCOF into a 250 mL three-necked flask, add 10 mL of ethanol, and disperse it evenly by ultrasound. Then pour the template-monomer mixture into the three-necked flask and stir it mechanically for 30 min. While stirring, add 8 mmol of tetraethyl orthosilicate TEOS and 0.5 mL of ammonia water dropwise. React at room temperature for 4 h. After the reaction is completed, separate the polymer product with a magnet, wash off the unreacted raw materials with anhydrous ethanol, and dry it in vacuum at 60 ° C overnight;

[0036] (3) The solid product obtained in step (2) was subjected to Soxhlet extraction with a mixed solution of methanol-acetic acid (9:1, V / V) to remove the template molecules, and a UV-visible spectrophotometer was used to confirm whether the template molecules were completely eluted. Finally, the solid product was washed with methanol until neutral, and dried to obtain the molecularly imprinted polymer MCOF@MIP.

[0037] Without adding template molecules and keeping other conditions the same, MCOF@NIP was obtained.

[0038] Figure 2 FT-IR graph of MCOF@MIP and MCOF@NIP of the present invention. -1 Fe 3 O 4 The stretching vibration peak of Fe-O in -1 The absorption peak at 1435cm belongs to the stretching vibration of Si-O-Si. -1 and 1622cm -1 The peaks between them can be attributed to the benzene skeleton and C=N vibration, demonstrating the successful synthesis of MCOF@MIP and MCOF@NIP.

[0039] Figure 3 This is the hysteresis loop of the MCOF@MIP of the present invention. As can be seen from the figure, the saturation magnetization intensity of MCOF@MIP is 5.21emu / g. This shows that MCOF@MIP has good magnetic properties and can be used for magnetic solid phase extraction of bisphenol in samples.

[0040] Figure 4 The SEM and TEM images of the MCOF@MIP of the present invention are shown in Figure 1. The surface morphology of the MCOF@MIP was characterized by SEM and TEM electron microscopes, and it can be seen that the MIP layer is spherical and coated on the surface of the MCOF, showing an obvious core-shell structure.

[0041] Experimental Example 5:

[0042] Bisphenol mixed standard solution preparation

[0043] 100 mg of each of the four standard substances, BPA, BPB, BPF, and BPAF, were weighed respectively, dissolved in methanol and prepared into a 1 g / L mixed bisphenol standard stock solution. By stepwise dilution, 50 mg / L, 1 mg / L, 10 μg / L, 100 μg / L, and 1000 μg / L BPs bisphenol mixed standard solutions were obtained. All solutions were stored in a refrigerator at 4°C to prevent volatilization.

[0044] Magnetic solid phase extraction process

[0045] Take 50 μg / L of bisphenol mixed standard solution, add sodium chloride to adjust the ionic strength to 40 mmol / L and pH to 6, weigh 20 mg of MCOF@MIP and put it into 10 mL of the adjusted 50 μg / L bisphenol mixed standard solution, place it in a shaker for 30 minutes, add a magnet to collect the MCOF@MIP adsorbed with bisphenol, add 1 mL of ethanol desorption solvent to the collected MCOF@MIP adsorbed with bisphenol and ultrasonicate for 3 minutes, then add a magnet to separate the adsorbent MCOF@MIP, place the supernatant in a centrifuge tube, repeat the desorption 4 times, blow the solvent dry with nitrogen, use 200 μL of methanol to re-dissolve, filter with a 0.22 μm filter membrane, and refrigerate in a refrigerator at 4°C for high performance liquid chromatography detection.

[0046] Optimization of magnetic solid phase extraction conditions

[0047] In order to obtain the best magnetic solid phase extraction efficiency, the main parameters affecting magnetic solid phase extraction were optimized. Optimized parameters: the dosage of adsorbent MCOF@MIP was 2, 5, 10, 15, 20 and 30 mg respectively; the number of desorptions was 1, 2, 3, 4 and 5 times respectively; the desorption solvents were methanol MeOH, ethanol EtOH and acetonitrile ACN respectively; the ionic strength was 0, 20, 40, 60, 80 and 100 mmol / L respectively; the pH was 4, 5, 6, 7, 8 and 9 respectively. The optimization experiment was analyzed by preparing a 50 μg / L mixed standard solution of bisphenol, and all experiments were repeated three times.

[0048] The optimal conditions were finally determined to be: desorption solvent: ethanol; elution volume: 4 mL, elution times: 4 times, adsorbent dosage: 20 mg; pH: 6; ionic strength: 40 mmol / L.

[0049] Under the above optimal experimental conditions, the adsorbent MCOF@MIP was used to perform magnetic solid phase extraction on the mixed standard solution of bisphenols, and then combined with HPLC for detection. The linear ranges (LRs) and correlation coefficients (R 2 ) and limits of detection (LODs) are shown in the following table:

[0050] Under the above optimal experimental conditions, the MCOF and MCOF@MIP prepared in Examples 3 and 4 were used to perform magnetic solid phase extraction on the bisphenol mixed standard solution, and then tested by HPLC. The results are as follows: Figure 5 The results show that the molecular imprinting layer can improve the enrichment of bisphenol.

[0051] Experimental Example 6:

[0052] Preparation of 50mg / L diethyl phthalate DEP standard solution:

[0053]

[0054] Weigh 5 mg of DEP, dissolve it in methanol to prepare a 500 mg / L DEP standard stock solution, and dilute it to obtain a 50 mg / L DEP standard solution.

[0055] Preparation of 50mg / L hydroquinone HQ standard solution:

[0056] Weigh 5 mg HQ, dissolve it in methanol to prepare a 500 mg / L HQ standard stock solution, and dilute it to obtain a 50 mg / L HQ standard solution.

[0057] Weigh 10 mg of MCOF@MIP and place them in 10 mL of 50 mg / L bisphenol standard solution, 10 mL of 50 mg / L DEP standard solution, and 10 mL of 50 mg / L HQ standard solution, respectively, and place them in a shaker for 30 min. Remove the supernatant and filter it through a 0.22 μm filter membrane, then refrigerate it at 4 °C for high performance liquid chromatography detection. All experiments were repeated three times.

[0058] Figure 6 The adsorption capacity of four bisphenols (BPF, BPA, BPB, BPAF) and two competitive adsorption molecules (DEP, HQ) by MCOF@MIP and MCOF@NIP of the present invention was compared. The high adsorption capacity and selective adsorption capacity prove that MCOF@MIP can be used for the selective adsorption of bisphenol pollutants in the environment.

[0059] Experimental Example 7: Detection of Bisphenol in Yellow River Water

[0060] Under the optimal extraction conditions of Example 5, MCOF@MIP was used to perform magnetic solid phase extraction of bisphenol in the Yellow River water, and then detected in combination with HPLC.

[0061] Take 1 mg / L bisphenol mixed standard solution, add sodium chloride to adjust the ionic strength to 40 mmol / L and pH to 6, then add Yellow River water filtered by 0.22 μm filter membrane, adjust the bisphenol concentration in the solution to 10 μg / L, 100 μg / L and 1000 μg / L respectively, weigh 20 mg of MCOF@MIP in 10 mL of the adjusted bisphenol mixed standard solution, place it in a shaker for 30 minutes, and make MCOF@MIP evenly dispersed in the water sample. Separate the adsorbent with a magnet, discard the supernatant, add 1 mL of ethanol desorption solvent, sonicate for 3 minutes, separate the adsorbent with a magnet, place the supernatant in a centrifuge tube, repeat desorption 4 times, blow the solvent dry with nitrogen, re-dissolve with 200 μL of methanol, filter with 0.22 μm filter membrane, and refrigerate at 4 ° C for high performance liquid chromatography detection.

[0062] HPLC conditions: mobile phase: methanol: ultrapure water = 60:40 (v:v); flow rate: 1 mL / min; UV wavelength: 227 nm; column temperature: 35°C.

[0063] Figure 7 The chromatogram of the MCOF@MIP of the present invention applied to the spike recovery experiment of bisphenol in the Yellow River water sample. The blank sample of the Yellow River water (black); spiked with 10 μg / L (red); spiked with 100 μg / L (blue); spiked with 1000 μg / L (purple). (Peak 1 is BPF, peak 2 is BPA, peak 3 is BPB, and peak 4 is BPAF). The good recovery rate shows that this method can be used for the detection of actual samples.

[0064] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a dual-template molecularly imprinted composite magnetic covalent organic framework material, characterized in that: The following steps are involved: (1) Preparation of magnetic covalent organic frameworks NH2-Fe3O4@SiO2, 2,5-dihydroxyterephthalaldehyde, and 1,3,5-tri(4-aminophenyl)benzene are mixed in anhydrous ethanol, acetic acid solution is used as a reaction catalyst, and mechanical stirring is performed at room temperature. The aldehyde group in 2,5-dihydroxyterephthalaldehyde combines with the amino group in NH2-Fe3O4@SiO2, and 2,5-dihydroxyterephthalaldehyde and 1,3,5-tri(4-aminophenyl)benzene react at room temperature to form a covalent organic framework COF, thereby synthesizing a magnetic covalent organic framework MCOF. SiO2 is coated on the surface of Fe3O4 nanoparticles and then modified by amino group to obtain NH2-Fe3O4@SiO2. (2) Preparation of dual-template molecular imprinting composite magnetic covalent organic framework materials The template molecule and the functional monomer 3-aminopropyltriethoxysilane are added to ethanol and magnetically stirred to form a template-monomer mixture. The magnetic covalent organic framework MCOF is evenly dispersed in ethanol and added to the template-monomer mixture. The mixture is mechanically stirred, and a crosslinking agent tetraethyl orthosilicate TEOS and a catalyst ammonia water are added dropwise while stirring. The mixture is reacted at room temperature. After the reaction is completed, magnetic separation, washing and drying are performed. Finally, the template molecule is eluted to remove the template molecule to obtain a molecular imprinting polymer MCOF@MIP. The template molecules are two of bisphenol A, bisphenol B, bisphenol F and bisphenol AF.

2. The method for preparing a dual-template molecularly imprinted composite magnetic covalent organic framework material according to claim 1, characterized in that: The molar ratio of the 2,5-dihydroxyterephthalaldehyde to 1,3,5-tri(4-aminophenyl)benzene is 3:2, and the mass ratio of NH2-Fe3O4@SiO2 to 2,5-dihydroxyterephthalaldehyde is 5:

1.

3. The method for preparing a dual-template molecularly imprinted composite magnetic covalent organic framework material according to claim 1, characterized in that: The molar ratio of the magnetic covalent organic framework MCOF, the template molecule, the functional monomer 3-aminopropyltriethoxysilane and tetraethyl orthosilicate TEOS is 1:1:4:

8.

4. The method for preparing a dual-template molecularly imprinted composite magnetic covalent organic framework material according to claim 1, characterized in that: The elution in step (2) is specifically as follows: Soxhlet extraction is performed on the solid matter dried in step (2) using a mixed solution of methanol and acetic acid in a volume ratio of 9:1 to remove the template molecules, and then washed with methanol until neutral, and dried to obtain the molecularly imprinted polymer MCOF@MIP.

5. A dual-template molecularly imprinted composite magnetic covalent organic framework material prepared by the method according to any one of claims 1 to 4.

6. Use of the dual-template molecular imprinting composite magnetic covalent organic framework material according to claim 5 in bisphenol enrichment.

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