Magnetic covalent organic framework material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of organic framework materials, and particularly relates to a magnetic covalent organic framework material as well as a preparation method and application thereof. The magnetic covalent organic framework material is spherical particles and comprises Fe3O4 and COF, the COF wraps the Fe3O4 nanoparticles to form a shell layer, and the shell layer formed by the COF is obtained by connecting a first construction monomer and a second construction monomer through a covalent bond. The magnetic covalent organic framework material has strong adsorption capacity on ester compounds such as ethyl benzoate, ethyl phenylacetate, phenethyl acetate or ethyl phenylpropionate, and the maximum adsorption capacity can be 55.56 mg / g, 52.63 mg / g, 56.18 mg / g and 58.82 mg / g respectively.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of covalent organic framework materials, and particularly relates to a magnetic covalent organic framework material, a preparation method thereof, and an application thereof. Background Art

[0002] Magnetic solid-phase extraction (MSPE) is a potential candidate method for the accurate detection of important or harmful compounds in complex food matrices, and has comprehensive advantages such as rapidity, greenness, simplicity, etc. The magnetic extraction material is the core of the MSPE technology and is the key factor determining the extraction and separation efficiency.

[0003] Covalent organic frameworks (COFs) are a new type of porous crystalline material, which are formed by the bonding of light elements (C, B, O, Si, N) through strong covalent bonds. Due to the advantages of COFs materials such as periodic structure, permanent porosity, large surface area, low density, adjustable porosity, excellent chemical stability, controllable structure, and easy functionalization, they have received considerable attention in the fields of gas separation and storage, catalysis, drug delivery, and optoelectronics. In addition, these characteristics also make them attractive candidates for adsorption materials. Their chemical properties are caused by the presence of many hydrophobic groups and benzene rings, enabling them to be used as reversed-phase materials to effectively adsorb various analytes through π-π stacking interactions.

[0004] Therefore, it is of great significance to develop COFs composite materials with characteristics such as high extraction efficiency and easy separation. At present, combining COF materials and magnetic nanoparticles (MNPs) to construct a new type of magnetic covalent organic framework (MCOFs) material is an effective method. This effective cooperation solves the disadvantages of easy oxidation and aggregation of MNPs and overcomes the difficulty of separating COFs materials. However, currently, the synthesis of COFs mainly relies on traditional methods such as solvothermal synthesis, which has high energy consumption, harsh conditions, high risks, and poor adsorption performance, restricting its practical application. Summary of the Invention

[0005] In the present invention, through a physical coating method, the COFs material is coated on the surface of Fe 3 O 4 nanoparticles, and the MCOFs material Fe 3 O 4 @TPB-Dha with a magnetic core is synthesized at room temperature; the synthesized Fe 3 O 4 @TPB-Dha has a π-conjugated system and rich hydroxyl or imine structures. These unique structures and specific functional groups (such as the carbonyl group in aromatic esters) promote their interaction, making the prepared Fe 3 O4 @TPB - Dha shows great potential in detecting trace aromatic ester compounds in complex matrices and exhibits excellent adsorption performance.

[0006] To achieve the above object, the present invention can adopt the following technical solutions:

[0007] On the one hand, the present invention provides a magnetic covalent organic framework material, which is spherical particles and includes Fe 3 O 4 and COF. The COF wraps around the Fe 3 O 4 nanoparticles to form a shell layer. The shell layer formed by COF is obtained by covalently bonding a first building monomer and a second building monomer. Among them, the first building monomer is selected from 1,3,5 - tris(4 - aminophenyl)benzene or tris(4 - aminophenyl)amine, and the second building monomer is selected from 2,3 - dihydroxyterephthalaldehyde or 2,5 - dihydroxyterephthalaldehyde.

[0008] Preferably, the structure of the above COF is as follows:

[0009] Preferably, the diameter of the above spherical particles is 100 nm - 200 nm.

[0010] More preferably, the diameter of the above spherical particles is 140 nm - 150 nm.

[0011] Preferably, the thickness of the shell layer formed by the above COF is 20 nm - 30 nm.

[0012] More preferably, the thickness of the shell layer formed by the above COF is 24 nm - 26 nm.

[0013] On the other hand, the present invention provides a preparation method of the magnetic covalent organic framework material in the present invention, including: dispersing 1,3,5 - tris(4 - aminophenyl)benzene, 2,3 - dihydroxyterephthalaldehyde and Fe 3 O 4 (Na 3 Cit) after mixing, and reacting to obtain the magnetic covalent organic framework material.

[0014] Preferably, the above preparation method satisfies one or more of the following conditions: (i) The preparation method of Fe 3 O 4 (Na 3 Cit) includes: mixing FeCl 3 ·6H 2 O, sodium citrate and sodium acetate in an ethanol environment; then carrying out a hydrothermal reaction to obtain Fe3 O 4 (Na 3 Cit); (ii) The mass ratio of the first building monomer, the second building monomer and Fe 3 O 4 (Na 3 Cit) is (1.5 - 2.5):(1 - 2):(30 - 70); (iii) Mix and disperse the first building monomer, the second building monomer and Fe 3 O 4 (Na 3 Cit) in a weak base solution environment; then add an acid to react to obtain a magnetic covalent organic framework material; (iv) Use ultrasonic waves for dispersion treatment, and the power of the ultrasonic waves is 500W - 1000W; (v) The way of adding the acid includes: dropping at a rate of 0.1mL / min - 0.2mL / min; (vi) The volume ratio of the added acid to the volume of the weak base solution is 0.05 - 0.2; (vii) The reaction time ≥ 10min.

[0015] More preferably, the above preparation method satisfies one or more of the following conditions: (a) The mass ratio of FeCl 3 ·6H 2 O, sodium citrate and sodium acetate is 5:1:10; (b) The hydrothermal reaction temperature is 180°C - 250°C; (c) The acid is acetic acid; (d) The weak base solution is a dimethyl sulfoxide (DMSO) solution, and the molar concentration of the weak base is 0.2mol / L - 0.7mol / L; (e) The concentration of the acid is 15mol / L - 20mol / L.

[0016] On the other hand, the present invention provides an application of the magnetic covalent organic framework material in the present invention in adsorbing aromatic ester compounds; the aromatic ester compounds include one or more of ethyl benzoate, ethyl phenylacetate, phenethyl acetate and ethyl phenylpropionate.

[0017] The beneficial effects of the present invention include:

[0018] (1) The Fe 3 O 4 @TPB - Dha provided by the present invention has a strong adsorption capacity for ester compounds such as ethyl benzoate, ethyl phenylacetate, phenethyl acetate or ethyl phenylpropionate, and the maximum adsorption amounts can be 55.56mg / g, 52.63mg / g, 56.18mg / g and 58.82mg / g respectively.

[0019] (2) The Fe 3 O 4The preparation method of @TPB-Dha successfully solves the problem that COFs have a low weight density and are difficult to separate from complex food matrices. Moreover, compared with the solvothermal synthesis method, the present invention establishes a more energy-saving, safe, and green room-temperature synthesis method for COFs. Description of the Drawings

[0020] Figure 1 is Fe 3 O 4 Schematic diagram of the synthesis route of @TPB-Dha;

[0021] Figure 2 is Fe 3 O 4 SEM image of @TPB-Dha;

[0022] Figure 3 is Fe 3 O 4 TEM image of @TPB-Dha;

[0023] Figure 4a is Fe 3 O 4 Full-scan XPS spectrum of @TPB-Dha;

[0024] Figure 4b is Fe 3 O 4 N1s fine spectrum of the full-scan XPS spectrum of @TPB-Dha;

[0025] Figure 4c is Fe 3 O 4 Fe 2p fine spectrum of the full-scan XPS spectrum of @TPB-Dha;

[0026] Figure 5 is Fe 3 O 4 Infrared spectrum of @TPB-Dha;

[0027] Figure 6 is Fe 3 O 4 XRD full-scan spectrum of @TPB-Dha;

[0028] Figure 7 is Fe 3 O 4 Hysteresis loop of @TPB-Dha;

[0029] Figure 8 is Fe 3 O 4 @TPB-Dha's 2 N adsorption-desorption curve;

[0030] Figure 9a The linear correlation coefficients in the pseudo-first-order kinetic model of ethyl benzoate, ethyl phenylacetate, phenethyl acetate and ethyl phenylpropionate on Fe 3 O 4 @TPB-Dha;

[0031] Figure 9b The linear correlation coefficients in the pseudo-second-order kinetic model of ethyl benzoate, ethyl phenylacetate, phenethyl acetate and ethyl phenylpropionate on Fe 3 O 4 @TPB-Dha;

[0032] Figure 9c The linear correlation coefficients in the Langmuir isothermal adsorption model of ethyl benzoate, ethyl phenylacetate, phenethyl acetate and ethyl phenylpropionate on Fe 3 O 4 @TPB-Dha;

[0033] Figure 9d The linear correlation coefficients in the Freundlich isothermal adsorption model of ethyl benzoate, ethyl phenylacetate, phenethyl acetate and ethyl phenylpropionate on Fe 3 O 4 @TPB-Dha. Detailed implementation manners

[0034] The examples given are for better illustration of the present invention, but the content of the present invention is not limited only to the given examples. Therefore, those skilled in the art who make non-essential improvements and adjustments to the implementation manners according to the above-mentioned invention content still fall within the protection scope of the present invention.

[0035] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. Unless having an apparently different meaning in the context, the expressions in the singular form include the plural form. As used herein, it should be understood that terms such as "including", "having", "containing" are intended to indicate the existence of features, numbers, operations, components, parts, elements, materials or combinations. The terms of the present invention are disclosed in the description, and are not intended to exclude the possibility of the existence or addition of one or more other features, numbers, operations, components, parts, elements, materials or their combinations. As used herein, depending on the context, " / " can be interpreted as "and" or "or".

[0036] An embodiment of the present invention provides a magnetic covalent organic framework material. The magnetic covalent organic framework material is spherical particles, which include Fe 3 O 4 and COF, and the COF wraps Fe 3 O 4A shell layer is formed on the nanoparticles. The shell layer formed by the COF is obtained by covalently bonding a first building monomer and a second building monomer. Among them, the first building monomer is selected from 1,3,5-tris(4-aminophenyl)benzene or tris(4-aminophenyl)amine, and the second building monomer is selected from 2,3-dihydroxyterephthalaldehyde or 2,5-dihydroxyterephthalaldehyde.

[0037] It should be noted that the present invention uses Fe 3 O 4 nanoparticles as the core, 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,3-dihydroxyterephthalaldehyde (Dha) as building monomers, and a novel MCOF material Fe 3 O 4 @TPB-Dha, that is, a magnetic covalent organic framework material, is simply prepared by a room temperature synthesis method.

[0038] In some specific examples, the structure of the above COF is as follows:

[0039] It should be noted that the structural formula of the COF obtained by covalently bonding the above first building monomer and the second building monomer can be as shown above.

[0040] In some specific examples, the diameter of the above spherical particles is 100 nm - 200 nm, such as 120 nm - 180 nm, 130 nm - 170 nm or 140 nm - 150 nm, etc., and further such as 115 nm, 135 nm, 150 nm, 170 nm or 190 nm, etc.

[0041] In some specific examples, the thickness of the shell layer formed by the above COF is 20 nm - 30 nm, such as 22 nm - 28 nm, 23 nm - 27 nm or 24 nm - 26 nm, etc., and further such as 21 nm, 23 nm, 25 nm, 27 nm or 29 nm, etc.

[0042] The embodiment of the present invention also provides a preparation method of the magnetic covalent organic framework material in the present invention, including: mixing and dispersing a first building monomer, a second building monomer and Fe 3 O 4 (Na 3 Cit), and reacting to obtain a magnetic covalent organic framework material.

[0043] It should be noted that the preparation method in the present invention aims to solve several key problems existing in the preparation process of current covalent organic framework materials, including the low weight density of COFs and the difficulty in separating them from complex food matrices, as well as the large energy consumption, harsh conditions and high risks of the solvothermal synthesis method, and the poor adsorption performance. For this reason, the present invention proposes a brand-new preparation method, which has low energy consumption for synthesis, mild and easy-to-control conditions, and can synthesize magnetic covalent organic framework materials that are easy to separate from complex food matrices and have high adsorption performance.

[0044] In some specific examples, the above preparation method satisfies one or more of the following conditions:

[0045] (i) The preparation method of Fe 3 O 4 (Na 3 Cit) includes: mixing FeCl 3 ·6H 2 O, sodium citrate and sodium acetate in an ethanol environment; then carrying out a hydrothermal reaction to obtain Fe 3 O 4 (Na 3 Cit); specifically, Fe 3 O 4 (Na 3 Cit) in the present invention can be prepared according to the methods well-known to those skilled in the art, such as "Yonghui Deng, Yue Cai, Zhenkun Sun, Jia Liu, Chong Liu, Jing Wei, Wei Li, Chang Liu, Yao Wang, Dongyuan Zhao, Multifunctional Mesoporous Composite Microspheres with Well-Designed Nanostructure: A Highly Integrated Catalyst System, Journal of the American Chemical Society: 132 (2010) 8466 - 8473"; it can also be purchased; in addition, the Fe 3 O 4 nanoparticles (Fe 3 O 4 (Na 3 Cit)) prepared in the present invention are small, with a spherical crystal microstructure, and have abundant carboxylate groups (ROO-) on the surface that can serve as adsorption sites and have good chemical stability;

[0046] (ii) The first building monomer, the second building monomer and Fe3 O 4 (Na 3 The mass ratio of Cit) is (2 - 4):(1 - 3):(3 - 5);

[0047] (iii) Mix and disperse the first building monomer, the second building monomer and Fe 3 O 4 (Na 3 Cit) in a weak base solution environment; then add an acid to react to obtain a magnetic covalent organic framework material;

[0048] (iv) Use ultrasonic waves for dispersion treatment, and the power of the ultrasonic waves is 500W - 1000W, such as 600W, 700W, 800W or 900W, etc.;

[0049] (v) The method of adding the acid includes: dropping at a rate of 0.1mL / min - 0.2mL / min; such as 0.12mL / min, 0.15mL / min or 0.18mL / min, etc.;

[0050] (vi) The volume ratio of the added acid to the volume of the weak base solution is 0.05 - 0.2, such as 0.08, 0.1, 0.13, 0.15 or 0.17, etc.;

[0051] (vii) The reaction time ≥ 10min.

[0052] In some specific examples, the above preparation method satisfies one or more of the following conditions:

[0053] (a) The mass ratio of FeCl 3 ·6H 2 O, sodium citrate and sodium acetate is 5:1:10;

[0054] (b) The hydrothermal reaction temperature is 180°C - 250°C; such as 200°C, 220°C or 240°C, etc.;

[0055] (c) The acid is acetic acid; specifically, the acid in the present invention can be well - known in the art, such as acetic acid;

[0056] (d) The weak base solution is a dimethyl sulfoxide (DMSO) solution, and the molar concentration of the weak base is 0.2mol / L - 0.7mol / L, such as 0.4mol / L, 0.5mol / L or 0.6mol / L, etc.;

[0057] (e) The concentration of the acid is 15mol / L - 20mol / L, such as 17mol / L, 18mol / L or 19mol / L, etc.

[0058] The embodiments of the present invention also provide an application of the magnetic covalent organic framework material in the present invention in adsorbing aromatic ester compounds; the aromatic ester compounds include one or more of ethyl benzoate, ethyl phenylacetate, phenethyl acetate, and ethyl phenylpropionate.

[0059] It should be noted that the magnetic covalent organic framework material in the present invention has a strong adsorption capacity for ethyl benzoate, ethyl phenylacetate, phenethyl acetate, or ethyl phenylpropionate, and can be applied to adsorb the above-mentioned aromatic ester compounds.

[0060] To better understand the present invention, the content of the present invention will be further clarified below with specific examples, but the content of the present invention is not limited to the following examples.

[0061] I. Preparation and characterization of functionalized magnetic covalent organic framework material (Fe 3 O 4 @TPB-Dha)

[0062] Example 1

[0063] As Figure 1 shown, the synthesis route of Fe 3 O 4 @TPB-Dha mainly includes the preparation of Fe 3 O 4 nanoparticles and the coating of two building monomers, 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,3-dihydroxyterephthalaldehyde (Dha). The specific steps are as follows:

[0064] (1) Prepare Fe 3 O 4 (Na 3 Cit) nanoparticles by hydrothermal synthesis method. The specific steps are as follows: Measure 40 mL of ethylene glycol into a 250 mL three-necked flask, add 54 mg / mL (concentration in 40 mL of ethylene glycol) FeCl 3 ·6H 2 O particles and dissolve; wait for FeCl 3 ·6H 2After sufficient dissolution of O, add a 11 mg / mL sodium citrate anhydrous solution (concentration in 40 mL ethylene glycol), stir in a water bath at a constant temperature of 80 °C for 2 h to fully dissolve sodium citrate and uniformly disperse it in ethylene glycol; continue to add 49.25 mg / mL sodium acetate anhydrous (concentration in 40 mL ethylene glycol) to the above system, stir thoroughly for 30 min to fully dissolve and disperse, obtain a homogeneous system, and transfer it to a 100 mL polytetrafluoroethylene stainless steel high-temperature and high-pressure reactor. React fully at 200 °C for 10 h; after the reaction is completed, wait for the reactor to cool to room temperature, measure the pH of the supernatant, collect the black product at the bottom of the reactor, wash it 6 times with ethanol and ultrapure water respectively (until neutral), and vacuum dry it at -50 °C for 24 h to prepare Fe 3 O 4 nanoparticles (Fe 3 O 4 (Na 3 Cit) powder), grind it with a grinder and set aside.

[0065] (2) Two kinds of building monomers were used to coat the surface of Fe 3 O 4 nanoparticles, dry and wash to obtain Fe 3 O 4 @TPB-Dha nanomaterials. The specific steps are as follows: Weigh 50 mg of Fe 3 O 4 (Na 3 Cit) powder, 1.8 mg / mL 1,3,5-tris(4-aminophenyl)benzene (TPB) powder (concentration in 20 ml dimethyl sulfoxide) and 1.28 mg / mL 2,3-dihydroxyterephthalaldehyde (Dha) powder (concentration in 20 ml dimethyl sulfoxide) into an 80 ml beaker, add 20 ml dimethyl sulfoxide (DMSO), disperse fully, and dropwise add (5 s / drop) 0.6 ml acetic acid (99%, 17.5 mol / L) under ultrasonic conditions. The whole process lasts for 10 min, then incubate at room temperature for 10 min, separate the solid product with the assistance of a magnet, wash it with tetrahydrofuran, methanol and ultrapure water respectively until neutral, and vacuum freeze-dry it at -50 °C for 24 h to obtain Fe 3 O 4 @TPB-Dha nanomaterials.

[0066] SEM and TEM were respectively used to characterize the morphology of Fe 3 O 4 @TPB-Dha, and the results are as Figure 2 and Figure 3 shown. The results show that the prepared magnetic nanomaterials present spherical particles with uniform particle size and good dispersibility; Fe 3 O 4The average particle size of the @TPB-Dha nanomaterial is about 145.46 nm, and Fe 3 O 4 All @TPB-Dha nanoparticles exhibit an obvious core-shell structure, and the shell thickness is about 25 nm ( Figure 2 ); The above results indicate that the above preparation method successfully coated the COF layer on Fe 3 O 4 to obtain Fe 3 O 4 @TPB-Dha.

[0067] X-ray photoelectron spectroscopy (XPS) characterization was used to analyze the elements of the prepared Fe 3 O 4 @TPB-Dha magnetic nanomaterial; Among them, the full XPS spectrum of Fe 3 O 4 @TPB-Dha shows that at 711 eV, 532 eV, 400 eV and 285 eV, they correspond to Fe 2p, O 1s, N 1s and C1s respectively ( Figure 4a ); It can be seen from the N 1s fine spectrum that the diffraction peak at a binding energy of 399.2 eV can be attributed to C=N, indicating the formation of an imine bond ( Figure 4b ); The Fe 2p fine spectrum shows that the signal peaks of Fe 2p 3 / 2 and Fe 2p 1 / 2 are located at 710.78 eV and 723.78 eV respectively, while 714.58 eV belongs to Fe 3+ , indicating the existence of Fe 3 O 4 ( Figure 4c ); In addition, it can be seen from Table 1 that after wrapping Fe 3 O 4 with COFs materials, the C content increases significantly, and at the same time, nitrogen elements of C-N and C=N appear; The above XPS results indicate the successful preparation of the Fe 3 O 4 @TPB-Dha material.

[0068] Table 1 Element change of Fe 3 O 4 after being wrapped with COFs materials

[0069]

[0070] In addition, in order to verify Fe 3 O 4The successful synthesis of @TPB-Dha was characterized by Fourier transform infrared spectroscopy for its characteristic functional groups, and the results are as Figure 5 shown. The stretching vibration of Fe-O-Fe appears as a peak at 578 cm -1 , indicating the successful magnetization of TPB-Dha. Meanwhile, the C=O signal of the aldehyde unit in Dha at 2868 cm -1 and the stretching vibrations of -NH -1 in TPB at 3436, 3355, and 3212 cm 2 are strongly attenuated, which confirms the high degree of co-condensation of the two starting materials. In addition, a new C=N characteristic peak appears at 1619 cm 3 O 4 in Fe -1 @TPB-Dha, indicating the formation of an imine bond between TPB and Dha. The above FT-IR results indicate the successful preparation of the MCOF material.

[0071] In addition, the crystal structure of the prepared Fe 3 O 4 @TPB-Dha was characterized by XRD. The wide-angle XRD results of the synthesized Fe 3 O 4 @TPB-Dha magnetic nanomaterials are as Figure 6 shown. The diffraction peaks at 2θ of 30.31°, 35.61°, 43.31°, 53.23°, 57.43°, and 62.72° correspond to the typical crystal plane diffractions of Fe 3 O 4 (220), (311), (400), (422), (511), and (440), proving the successful magnetization and crystallization of the Fe 3 O 4 @TPB-Dha magnetic nanomaterials.

[0072] In addition, the magnetic properties of the prepared nanomaterials were characterized by a vibrating sample magnetometer (VSM). The results Figure 7 are as 3 O 4 shown. The saturation magnetization value of Fe 3 O 4 @TPB-Dha is 26.19 emu / g. Therefore, the prepared Fe

[0073] @TPB-Dha can respond quickly to an external magnetic field, has a high saturation magnetization value, and meets the requirements for effective sample separation. 2 In addition, the pore size distribution and specific surface area were measured using the NFigure 8 As shown, Fe 3 O 4 The adsorption curve of FeO@TPB-Dha shows the characteristics of a typical Type IV adsorption isotherm, confirming its mesoporous structure with the pore diameter mainly distributed around 3.41 nm. After calculation, the Brunauer-Emmett-Teller (BET) surface area and pore volume of FeO@TPB-Dha are 180.66 m 3 O 4 / g and 0.37 cm 2 / g respectively, which helps to improve its adsorption capacity and makes it an ideal adsorbent for extracting esters. 3

[0074] In summary, these results indicate the successful synthesis of FeO@TPB-Dha, which has an obvious core-shell structure, good dispersibility, good crystallinity of the material, and superparamagnetism and other advantages. 3 O 4

[0075] Example 2

[0076] Replace 1,3,5-tris(4-aminophenyl)benzene in Example 1 with tris(4-aminophenyl)amine and replace 2,3-dihydroxyterephthalaldehyde with 2,5-dihydroxyterephthalaldehyde to prepare FeO@TPB-Dha, and the preparation method is the same as that in Example 1. 3 O 4

[0077] II. Adsorption Kinetics Experiment of Functionalized Magnetic Covalent Organic Framework Material (FeO@TPB-Dha) 3 O 4

[0078] In the following experiments, the preparation of the simulated wine sample is as follows: Accurately pipette 15 mL of anhydrous ethanol (chromatographically pure) into a 100 mL volumetric flask, dilute to volume with ultrapure water and shake well to prepare an ethanol-aqueous solution with a volume fraction of 15% as the simulated wine sample, and adjust the pH of the simulated wine sample with 0.2 mol / L dilute hydrochloric acid solution and 1 mol / L ammonia water solution, and store it in a refrigerator at -4°C for later use.

[0079] ​​​​In the following experiments, in the GC-MS analysis, the gas chromatography conditions were as follows: DB-WAX capillary column (30 m × 0.25 mm, 0.25 μm); temperature programming: initial temperature 40°C, rising to 100°C at 15.0°C / min and holding for 3.0 min; rising to 240°C at 20.0°C / min and holding for 1.0 min; inlet temperature: 250°C; carrier gas: He (99.999%); constant flow: column flow rate 1.0 mL / min; split ratio: 20:1; injection volume: 1.0 μL; the mass spectrometry conditions for the GC-MS analysis were as follows: ionization mode was electron impact ionization (EI); electron energy 70 eV; mass spectrometry detector temperature 250°C; qualitative analysis was performed in full scan mode (Full Scan); mass scan range 50 - 500 m / z, dwell time 0.2 s; solvent delay 8 min, and quantitative determination was performed in selected ion (SIM) mode.

[0080] In the following experiments, the GC-MS conditions were as follows: chromatographic column: DB-WAX capillary column (30 m × 0.25 mm, 0.25 μm); temperature programming: initial temperature 40°C, rising to 100°C at 15.0°C / min and holding for 3.0 min; rising to 240°C at 20.0°C / min and holding for 1.0 min; inlet temperature: 250°C; carrier gas: He (99.999%); constant flow: column flow rate 1.0 mL / min; split ratio: 20:1; injection volume: 1.0 μL; mass spectrometry conditions: ionization mode was electron impact ionization (EI); electron energy 70 eV; mass spectrometry detector temperature 250°C; qualitative analysis was performed in full scan mode (Full Scan); mass scan range 50 m / z - 500 m / z, dwell time 0.2 s; solvent delay 8 min.

[0081] In the following experiments, the steps of the adsorption kinetics experiment were as follows: In different 50 mL centrifuge tubes, add 5 mL of simulated wine samples, add a certain volume of the ester standard solution to be measured (including ethyl benzoate, ethyl phenylacetate, phenethyl acetate, and ethyl phenylpropionate), so that the initial concentrations of each target substance in the reaction system are 20 mg / L, adjust the solution pH = 4.0, vortex for 30 s at 2800 rpm, and add 25 mg of magnetic solid phase extraction adsorbent (Fe 3 O 4@TPB-Dha), oscillate at a constant temperature (25°C) at 200 rpm for 0 min, 0.5 min, 1.0 min, 2.0 min, 5.0 min, 10.0 min, 20.0 min, 30.0 min, 40.0 min, 50.0 min, 60.0 min and 90.0 min, respectively, and then use an external magnetic field to perform magnetic separation on the adsorbent (separation time is 2 min), take the supernatant and place it in a 10 mL centrifuge tube, add 10 μL of internal standard solution (ethyl laurate, concentration is 1000 mg / L), vortex at 2800 rpm for 30 s, add 0.5 mL of cyclohexane, continue to vortex at 2800 rpm for 2 min, and then centrifuge at 8000 r / min for 5 min to separate the layers, and draw the upper organic phase into a sampling vial for GC-MS analysis; the adsorption amount at time t (Q t , mg / g) can be obtained by the following formula:

[0082]

[0083] Among them, C 0 is the initial concentration of the target compound in the simulated wine sample (mg·L -1 ), C t is the concentration of the target compound in the simulated wine sample at time t (mg·L -1 ), m is the mass of the adsorbent (g); V is the volume of the simulated wine sample (L).

[0084] The data of adsorption content change with time obtained from the experiment were kinetically fitted to analyze the magnetic solid phase adsorbent Fe 3 O 4 @TPB-Dha adsorption mechanism of aromatic esters; Among them, two classic adsorption kinetic models, pseudo-first-order and pseudo-second-order adsorption kinetic models, were selected for fitting, and the specific formula is as follows:

[0085] (1) Pseudo-first-order model: The first-order model proposed by Lagergren is the earliest adsorption kinetic model to describe the adsorption rate. Its equation is shown in the formula:

[0086]

[0087] Among them, Q e Indicates the adsorption amount at equilibrium concentration, mg·g -1 ;Q t Represents the adsorption amount at different time points, mg·g -1 ;k 1 represents the pseudo-first-order kinetic rate constant, g·mg -1 ·min-1 ; t is time, in min. However, the pseudo-first-order kinetic model has its limitations and is generally only suitable for describing the kinetic process in the initial stage of adsorption, and cannot accurately describe the entire adsorption process.

[0088] (2) Pseudo-second-order kinetic adsorption rate model:

[0089]

[0090] where k 2 represents the pseudo-second-order kinetic rate constant, g·mg -1 ·min -1 ; the pseudo-second-order kinetic parameter k 2 and Q e are measured through the intercept and slope of the curve of t / Q t versus t. The pseudo-second-order kinetic model includes processes such as external liquid film diffusion and surface adsorption, and can more truly and comprehensively reflect the adsorption process of adsorbate on the adsorbent than the pseudo-first-order kinetic model.

[0091] To further clarify the adsorption mechanism of Fe 3 O 4 @TPB-Dha for the target ester, this experiment uses the pseudo-first-order kinetic model and the pseudo-second-order kinetic model to fit the adsorption process of 4 aromatic esters on Fe 3 O 4 @TPB-Dha; that is, the adsorption kinetic experiment of Fe 3 O 4 @TPB-Dha prepared in Example 1 for aromatic esters (ethyl benzoate, ethyl phenylacetate, phenethyl acetate, and ethyl phenylpropionate); among them, the pseudo-first-order kinetic model assumes that the adsorption rate is proportional to the adsorbate concentration, while the pseudo-second-order kinetic model assumes that the adsorption rate is proportional to the square of the adsorbate concentration; these models can be used to fit the experimental data to obtain key parameters such as the rate constant and equilibrium adsorption capacity of the adsorption process.

[0092] The experimental results are as Figure 9a and 9b shown. The magnetic adsorbent Fe 3 O 4The adsorption rate of @TPB-Dha for the target is rapid. The vast majority of the target is rapidly adsorbed within 20 min, and then enters a relatively slow adsorption process until adsorption equilibrium is reached. Finally, when the target analyte reaches adsorption equilibrium, its adsorption capacity ranges from 1.2897 mg / g to 1.5896 mg / g (as shown in Table 2); in addition, the linear correlation coefficient (R 2 = 0.9995 - 0.9999) obtained by fitting the experimental data of the target ester with the pseudo-second-order kinetic model is significantly higher than the linear correlation coefficient (R 2 = 0.5971 - 0.9409) in the pseudo-first-order kinetic model, and the Q e value (1.2857 mg / g - 1.5845 mg / g) of the target ester calculated by the pseudo-second-order kinetic model is very close to the experimental value (1.2897 mg / g - 1.5896 mg / g).

[0093] Table 2 Adsorption capacity of Fe 3 O 4 @TPB-Dha for different esters

[0094]

[0095] In summary, the pseudo-second-order kinetic model can better describe the adsorption of the target ester in the test sample by Fe 3 O 4 @TPB-Dha, and further indicates that Fe 3 O 4 @TPB-Dha mainly realizes the extraction of the target ester in the test sample through surface adsorption.

[0096] III. Adsorption isotherm experiment of the functionalized magnetic covalent organic framework material (Fe 3 O 4 @TPB-Dha)

[0097] In the following experiment, the GC-MS conditions were as follows: Chromatographic column: DB-WAX capillary column (30 m × 0.25 mm, 0.25 μm); Temperature programming: Initial temperature 40°C, rising to 100°C at 15.0°C / min and holding for 3.0 min; Rising to 240°C at 20.0°C / min and holding for 1.0 min; Injector temperature: 250°C; Carrier gas: He (99.999%); Constant flow: Column flow rate 1.0 mL / min; Split ratio: 20:1; Injection volume: 1.0 μL; Mass spectrometry conditions: Ionization mode was electron impact ionization (EI); Electron energy 70 eV; Mass spectrometry detector temperature 250°C; Qualitative analysis was performed in full scan mode (FullScan); Mass scan range 50 m / z to 500 m / z, dwell time 0.2 s; Solvent delay 8 min.

[0098] In the following experiment, the steps of the adsorption isotherm (when the temperature is constant, the relationship curve between the adsorption amount and the equilibrium concentration of the adsorbate is called the adsorption isotherm; the adsorption isotherm can clarify the action mode of the adsorption system and reflect the interaction mode between the adsorbent and the analyte under certain temperature conditions) experiment were as follows: In different 50 mL centrifuge tubes, a certain volume of the standard solution of the ester to be measured was added respectively to prepare 5 mL of simulated wine samples with different initial concentrations. The concentrations were set as: 1000.0 mg / L, 500.0 mg / L, 200.0 mg / L, 100.0 mg / L, 50.0 mg / L, 20.0 mg / L, 15.0 mg / L, 10.0 mg / L, 5.0 mg / L, and 1.0 mg / L. The solution pH was adjusted to 4.0, and it was vortexed for 30 s at 2800 rpm to mix well. 25 mg of the magnetic solid-phase extraction adsorbent Fe3O4@TPB-Dha was added respectively, and it was shaken at a constant temperature (25°C) at 200 rpm for sufficient time. The adsorbent was separated by applying an external magnetic field. The supernatant was placed in a 10 mL centrifuge tube, 10 μL of the internal standard solution (ethyl laurate, concentration 1000 mg / L) was added, and it was vortexed for 30 s at 2800 rpm and then 0.5 mL of cyclohexane was added. It was vortexed for another 2 min at 2800 rpm for extraction, centrifuged at 8000 r / min for 5 min and allowed to stand for stratification. The upper organic phase was aspirated into an injection vial for GC-MS analysis. The equilibrium adsorption amount (Q e , mg·g -1 ) can be obtained by the formula:

[0099]

[0100] where C0 and Ce are the initial concentration and adsorption equilibrium concentration of the target compound in the simulated wine sample (mg·L -1 ), respectively; m is the mass of the adsorbent (g); V is the volume of the simulated wine sample (L).

[0101] In the embodiments of the present invention, two classic adsorption isotherm models, Langmuir and Freundlich, are used to fit the obtained experimental data with the isotherm model. The specific formulas are as follows:

[0102] (1) Langmuir adsorption isotherm equation:

[0103]

[0104] Among them, Q e represents the adsorption amount at equilibrium concentration, mg·g -1 ; Q max represents the saturated adsorption amount, mg·g -1 ; C e represents the concentration of the solution at adsorption equilibrium, mg·L -1 ; K L is a constant related to the adsorption heat of the solute and the solvent, L·g -1 ; R L The value can be used to measure the feasibility of the adsorption process.

[0105] (2) Freundlich adsorption isotherm equation:

[0106]

[0107] Among them, K F is the Freundlich adsorption constant, and 1 / n represents the parameter of the non-linear degree.

[0108] Taking the logarithm of Equation (A) gives the following equation:

[0109] ln Q e = ln K F + (1 / n)ln C e ,

[0110] Plotting lnQ e against lnC e results in a straight line. From the slope and intercept of the straight line, n and K F can be obtained; when 0.1 < 1 / n ≤ 0.5, the adsorption is very easy to proceed; when 0.5 < 1 / n ≤ 1, the adsorption has a certain degree of difficulty; when 1 / n > 1, the adsorption hardly proceeds. K F is related to the adsorption capacity, and the larger its value, the stronger the adsorption ability.

[0111] The embodiments of the present invention use the Fe 3 O 4Adsorption isotherm experiment of @TPB-Dha on aromatic esters (ethyl benzoate, ethyl phenylacetate, phenethyl acetate, ethyl phenylpropionate). At 25 °C, the Fe prepared in Example 1 was investigated in the range of initial concentration from 1 mg / L to 1000 mg / L 3 O 4 Adsorption isotherm of @TPB-Dha on the target ester to be measured; In this example of the present invention, two classic isothermal adsorption models, Langmuir and Freundlich, were selected to fit the above experimental data.

[0112] The detection results are as Figure 9c and Figure 9d and Table 3 show that the linear correlation coefficients (R 3 O 4 obtained by fitting the data of the adsorption of the target ester by Fe 2 @TPB-Dha prepared in Example 1 using the Langmuir adsorption isotherm model are 0.994, 0.9974, 0.9968 and 0.9929, which are higher than the linear correlation coefficients (R 2 obtained by fitting the data using the Freundlich adsorption isotherm model, which are 0.9744, 0.9677, 0.9165 and 0.9574). Therefore, the above results indicate that the adsorption isotherm of Fe 3 O 4 @TPB-Dha prepared in Example 1 for the target ester conforms better to the Langmuir isothermal adsorption model.

[0113] Table 3 Adsorption of two isothermal adsorption models, Langmuir and Freundlich

[0114]

[0115] In addition, the R L constant of the Langmuir adsorption isotherm model can help analyze the process. Therefore, in order to further investigate whether the Fe 3 O 4 @TPB-Dha magnetic nano-adsorbent prepared in this Example 1 is beneficial to the adsorption of the target ester in the sample solution to be measured, the separation coefficient R L is calculated; among them, when R L > 1, it indicates that the adsorption system is not conducive to the occurrence of adsorption; when R L = 1, the adsorption process is a linear adsorption; when 0 < R L < 1, it indicates that the adsorption system is conducive to the occurrence of adsorption; when R L = 0, the adsorption process is irreversible. The detection results are shown in Table 4.

[0116] Table 4 Fe 3O 4 R of @TPB-Dha for different adsorption objects L Constant

[0117]

[0118] As can be seen from Table 4 above, the novel magnetic nano-adsorbent Fe 3 O 4 @TPB-Dha prepared in Example 1 of the present invention is beneficial to the adsorption of the target ester, and the adsorption process is likely to occur.

[0119] In summary, the adsorption isotherm of Fe 3 O 4 @TPB-Dha prepared in Example 1 for the target ester conforms to the Langmuir isothermal adsorption model; meanwhile, the above adsorption process is a monolayer adsorption occurring on a homogeneous surface, and all the adsorption sites provided by Fe 3 O 4 @TPB-Dha have the same adsorption energy and the same affinity for the target ester. Finally, under the condition of 25 °C, the maximum adsorption amounts of Fe 3 O 4 @TPB-Dha prepared in Example 1 for the target ester are 55.56 mg / g (ethyl benzoate), 52.63 mg / g (ethyl phenylacetate), 56.18 mg / g (phenethyl acetate), and 58.82 mg / g (ethyl phenylpropionate), respectively.

[0120] In addition, according to the Langmuir isothermal adsorption model, the maximum adsorption amounts of Fe 3 O 4 @TPB-Dha prepared in Example 2 for the target ester were tested according to the above test method, and the test results were: the maximum adsorption amounts of the target ester were 53.22 mg / g (ethyl benzoate), 51.19 mg / g (ethyl phenylacetate), 57.31 mg / g (phenethyl acetate), and 60.12 mg / g (ethyl phenylpropionate), respectively.

[0121] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A magnetic covalent organic framework material, characterized in that: The magnetic covalent organic framework material is a spherical particle, which includes Fe3O4 and COF. COF is wrapped on the Fe3O4 nanoparticles to form a shell layer. The shell layer formed by COF is obtained by connecting the first building monomer and the second building monomer through a covalent bond, wherein the first building monomer is selected from 1,3,5-tri(4-aminophenyl)benzene or tri(4-aminophenyl)amine, and the second building monomer is selected from 2,3-dihydroxyterephthalaldehyde or 2,5-dihydroxyterephthalaldehyde.

2. The magnetic covalent organic framework material according to claim 1, characterized in that: The structure of COF is shown below:

3. The magnetic covalent organic framework material according to claim 1, characterized in that: The diameter of the spherical particles is 100nm-200nm.

4. The magnetic covalent organic framework material according to claim 3, characterized in that: The diameter of the spherical particles is 140nm-150nm.

5. The magnetic covalent organic framework material according to any one of claims 1 to 4, characterized in that: The thickness of the shell layer formed by COF is 20nm-30nm.

6. The magnetic covalent organic framework material according to claim 5, characterized in that: The thickness of the shell layer formed by COF is 24nm-26nm.

7. The method for preparing the magnetic covalent organic framework material according to any one of claims 1 to 6, characterized in that: include: The first building monomer, the second building monomer and Fe3O4(Na3Cit) are mixed, dispersed and reacted to obtain a magnetic covalent organic framework material.

8. The preparation method according to claim 7, characterized in that: The preparation method meets one or more of the following conditions: (i) A method for preparing Fe3O4(Na3Cit) comprises: mixing FeCl3·6H2O, sodium citrate and sodium acetate in an ethanol environment; and then performing a hydrothermal reaction to obtain Fe3O4(Na3Cit); (ii) the mass ratio of the first building block, the second building block and Fe3O4(Na3Cit) is (2-4):(1-3):(3-5); (iii) mixing and dispersing the first building block, the second building block and Fe3O4(Na3Cit) in a weak alkaline solution environment; Then, an acid is added to react to obtain a magnetic covalent organic framework material; (iv) using ultrasonic waves for dispersion treatment, the power of the ultrasonic waves being 500W-1000W; (v) adding the acid in a manner including: dropping at a rate of 0.1 mL / min to 0.2 mL / min; (vi) the volume ratio of the added acid to the weak base solution is 0.05-0.2; (vii) The reaction time is ≥ 10 min.

9. The preparation method according to claim 8, characterized in that: The preparation method meets one or more of the following conditions: (a) The mass ratio of FeCl3·6H2O, sodium citrate and sodium acetate is 5:1:10; (b) The temperature of the hydrothermal reaction is 180°C-250°C; (c) the acid is acetic acid; (d) the weak base solution is a dimethyl sulfoxide (DMSO) solution, and the molar concentration of the weak base solution is 0.2 mol / L-0.7 mol / L; (e) The concentration of the acid is 15 mol / L-20 mol / L.

10. Use of the magnetic covalent organic framework material according to any one of claims 1 to 6 in the adsorption of aromatic ester compounds; the aromatic ester compounds comprise one or more of ethyl benzoate, ethyl phenylacetate, phenylethyl acetate and ethyl phenylpropionate.

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