CN114632497A - Magnetic covalent nano material and preparation method and application thereof - Google Patents

Magnetic covalent nano material and preparation method and application thereof Download PDF

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CN114632497A
CN114632497A CN202210240830.6A CN202210240830A CN114632497A CN 114632497 A CN114632497 A CN 114632497A CN 202210240830 A CN202210240830 A CN 202210240830A CN 114632497 A CN114632497 A CN 114632497A
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magnetic
covalent
nano material
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cofs
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贺泽英
王汭
孔德明
李薇
姜红新
贾昊
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Agro Environmental Protection Institute Ministry of Agriculture
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    • C02F1/285—Treatment of water, waste water, or sewage by sorption using synthetic organic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract

The invention provides a magnetic covalent nano material and a preparation method and application thereof, wherein the magnetic covalent nano material is synthesized by sequentially coating magnetic nanoparticles, a silanization reagent and a covalent organic framework from inside to outside, the magnetic covalent organic framework nano material with controllable pore size and controllable functional group type quantity and uniform appearance is synthesized by reasonable design, the magnetic covalent organic framework nano material has the pore size similar to that of a pigment molecule and uniformly distributed carboxyl functional groups, the removal rate of the magnetic covalent organic framework nano material on chlorophyll and lutein can reach more than 90 percent, simultaneously, the full recovery of 140 pesticides can be realized, and the magnetic covalent organic framework nano material has the capability of efficiently and selectively purifying pigment interferents in a complex matrix sample.

Description

Magnetic covalent nano material and preparation method and application thereof
Technical Field
The invention relates to the field of synthesis of nano materials, in particular to a preparation method of a magnetic covalent organic framework nano material and application of the magnetic covalent organic framework nano material in pigment purification in pesticide residue analysis of plant-derived food.
Background
Agriculture is the foundation of national economic development and social stability, and for years, pesticide is used as a necessary agricultural input product, makes immeasurable contribution in the aspects of effectively controlling plant diseases and insect pests and eliminating weeds, and is an important guarantee for realizing agricultural modernization and high and stable agricultural yield. However, the phenomenon of pesticide residue caused by excessive and unreasonable application of pesticide is ubiquitous, and the residual pesticide can finally enter human bodies through environmental food chains, destroy the immune systems of the human bodies and seriously threaten human health. Therefore, the accurate detection of the pesticide residue has very important significance in various fields such as environment, food, medicine and the like.
However, because the content of the residual pesticide in the sample is low, and the matrix of the food sample such as fruits and vegetables is complex, and the interference impurities are many, the sample pretreatment steps such as effective separation, purification and the like are required before the instrumental analysis. In the pretreatment process of the sample, impurities are removed as much as possible, and the extraction efficiency of the pesticide is ensured, which are the key points of the whole pretreatment process. The QuEChERS method has the characteristics of quickness (Quick), simplicity (Easy), cheapness (Cheap), effectiveness (Effective), reliability (Rugged) and safety (Safe), and is the most favored pretreatment technology for pesticide residues in food at present. However, the main limiting factor affecting the development of the technology is that the matrix effect is obvious during on-machine detection due to incomplete matrix purification, so that accurate qualitative and quantitative analysis cannot be realized. Fruit and vegetable samples generally contain a large amount of pigment molecules (chlorophyll, lutein, carotene and the like), and the pigment purificant (adsorbent) ethylenediamine N-propyl silica gel (PSA) commonly used in the QuEChERS technology can only remove about 50% of pigments; although more than 90% of the pigment can be removed by the Graphitized Carbon Black (GCB), the GCB has strong adsorbability, so that part of the analyte can be adsorbed while the pigment is removed, and a false negative result is generated.
Therefore, the method finds the sample pretreatment material with excellent performance, effectively removes the interference of pigment impurities in food, reduces the matrix effect, reduces the loss of target substances in the sample pretreatment, and has important significance for realizing accurate quantitative analysis of pesticide residues in complex matrix samples. Currently, with the continuous development of nanoscience, a plurality of novel nanomaterials emerge in succession, and a Covalent Organic Framework (COFs) is a novel porous crystalline material formed by connecting Organic monomers consisting of light elements (H, B, C, N, O) through chemical Covalent bonds. The material has ultrahigh specific surface area, finely adjustable pore diameter/morphology/functional groups and strong adsorption capacity, and has great potential of becoming a high-efficiency purification matrix material.
Disclosure of Invention
The invention provides a magnetic covalent nano material and a preparation method and application thereof, which aim to effectively remove the interference of pigment impurities in food, reduce matrix effect and reduce the loss of target substances in the pretreatment of samples.
Firstly, the magnetic covalent nano-material is synthesized by sequentially coating magnetic nano-particles, silanization reagents and Covalent Organic Frameworks (COFs) from inside to outside, wherein the covalent organic frameworks contain carboxyl functional groups, and the number of the carboxyl functional groups on each layer of COFs structure is 6.
Further, the magnetic nanoparticles are selected from Fe3O4、FeNi(Mo)、FeSi、FeAl、BaO·6Fe2O3One or more of the above silane reagents are selected from tetraethoxysilane and 3-aminopropyl triethoxysilane; the covalent organic framework is synthesized by three monomers of trialdehyde phloroglucinol, benzidine and 4, 4-diaminobiphenyl-2, 2-dicarboxyl.
Furthermore, the magnetic nano covalent material is of a spherical core-shell structure, and the morphology of COFs bonded on the outer layer of the core-shell structure is a hexagonal structure.
And secondly, the preparation method of the magnetic covalent nano material comprises the steps of carrying out hydrolytic polymerization on the surface of the magnetic nano particles through a silanization reagent to synthesize a silicon-coated magnetic composite material, and then growing a covalent organic framework on the surface of the magnetic composite material through amino bonding to obtain the magnetic covalent nano material.
Optionally, the thickness of the magnetic COFs nano material is 600-750nm, the particle size range of the magnetic composite material is 180-350nm, the particle size range of the magnetic nanoparticle is 100-250nm, the pore size of the covalent organic framework is 1.41-2.32nm, and the ratio of the pore size to the pigment molecule size is 1: 0.9-0.6.
Further, the magnetic COFs nano material is prepared by the following method:
s1, 0.5-3.0g of ferric trichloride hexahydrate and 1.3-7.9g of anhydrous sodium acetate are dissolved in 10-60mL of glycol and uniformly stirred to form a solution a; dissolving 0.5-3.5g of silylation agent in glycol, and heating at 60-90 ℃ for 1-10min to form a solution b; slowly pouring the solution b into the solution a, magnetically stirring for 10-60min, transferring to a 25-100mL high-pressure reaction kettle, and reacting at 200 ℃ for 8-20 h; and after the reaction kettle is cooled to room temperature, repeatedly washing the product with ethanol and deionized water, and carrying out vacuum drying at the temperature of 30-80 ℃ for 2-10 h.
S2, and the magnetic nanoparticles (Fe) prepared in the step S13O4) Dissolving 50-400mg in 20-120mL of anhydrous ethanol and 5-60mL of deionized water, ultrasonically dispersing uniformly, then adding 0.5-5.0mL of ammonia water and 0.2-2.0mL of silanization reagent, stirring for 4-12h, adding 0.2-2.0mL of 3-aminopropyltriethoxysilane, stirring for 4-12h, alternately washing with ethanol and deionized water for 3-7 times, and vacuum drying at 30-80 ℃ for 2-10h to obtain the magnetic composite material (Fe)3O4@SiO2-NH2)。
S3, obtaining the magnetic composite material (Fe) through the step S23O4@SiO2-NH2) Dissolving 50-400mg and 10-40mg of trialdehyde phloroglucinol (Tp) in 10-40mL of 1, 4-dioxane, adding 0.1-0.4mL of acetic acid after uniform ultrasonic dispersion, then placing the mixture in a reaction kettle, and reacting at the temperature of 120 ℃ for 1h to obtain Fe3O4@SiO2-NH2-Tp。
S4, obtaining the magnetic composite material (Fe) through the step S33O4@SiO2-NH2Tp)50mg, 63mg of trialdehyde phloroglucinol (Tp), 41mg of Benzidine (BD), 67mg of 4, 4-diaminobiphenyl-2, 2-dicarboxylic acid (DAA) were dissolved in a miscible solvent (1, 4-dioxane: mesitylene is 1:1) adding 1.0mL of 7mol/L acetic acid after ultrasonic dispersion, then placing the mixture into a reaction kettle, and reacting for 3 days at the temperature of 120 ℃ to obtain the magnetic COFs nano material (Fe)3O4@SiO2-NH2@COFs)。
Optionally, the solvent in step S2 is one of ethanol, water or isopropanol, and the mass ratio of the magnetic nanoparticles to the solvent is 1-5: 1000.
Optionally, the solvent in step S4 is one of 1, 4-dioxane or mesitylene, and the mass ratio of the magnetic composite material to the solvent is 1-3: 100.
Optionally, the reaction temperature for preparing the magnetic COFs nano material is 25-150 ℃, and the preparation time is 3-7 days.
The preparation principle of the magnetic COFs nano material is that most COFs are synthesized by a solvothermal method, and generally, the method needs to control synthesis reaction monomers, a solvent system, reaction time, reaction temperature, reaction pressure and catalyst dosage. The reaction is carried out in a liquid phase environment, usually in a high-pressure reaction kettle, the reaction temperature can reach 200 ℃, the solvent and the reactant react under the critical condition, an intermediate state or a metastable state phase appears, the reaction activity is improved, and the reaction is promoted. The invention takes glycol as solvent and reducer, sodium acetate as precipitator and electrostatic stabilizer, ferric trichloride hexahydrate as iron source, and polyethylene glycol as surfactant, and magnetic nano particles are prepared by reaction at 200 deg.C, and magnetic covalent nano material can be synthesized by post-modification step.
And finally, the magnetic covalent nano material is applied to food detection, the magnetic COFs nano material can be used for adsorbing pigments in the pretreatment of detecting the plant-derived food pesticide residue, and the magnetic COFs nano material is used as a pigment purifying agent and is combined with liquid chromatography tandem mass spectrometry to detect and analyze the pesticide residue in the vegetable food.
Further, the detection plant-derived food is one or more of spinach, Chinese chive, rape, cucumber, leaf lettuce, grapes and green tea, and the specific method comprises the steps of carrying out pretreatment on the detection plant-derived food to obtain a pigment extracting solution, adding 1-3mg of the magnetic covalent nano material, carrying out vortex oscillation for 10min, carrying out adsorption removal on the pigment extracting solution, separating the magnetic material by using an external magnetic field, analyzing the chlorophyll concentration by using ultraviolet absorption spectrum, and calculating the removal rate; and simultaneously, 140 kinds of pesticide residues are added into a sample, and the recovery rate of the 140 kinds of pesticide residues is inspected based on a liquid chromatography method after pretreatment by using a magnetic covalent material.
The magnetic COFs material synthesized by the invention has a plane large ring conjugated structure, has strong pi-pi action and hydrophobic action with pigment molecules, and simultaneously, carboxyl functional groups uniformly distributed in the COFs material can have chemical action with hydroxyl groups on the pigment molecules, so that the removal efficiency is improved.
Advantageous effects
1. According to the invention, through reasonable design, the magnetic COFs nano material with controllable pore size and functional group number and uniform appearance is synthesized, and the magnetic COFs material has the pore size similar to that of pigment molecules and uniformly distributed carboxyl functional groups.
2. Under the optimized condition, the COFs nano material provided by the invention only needs to vibrate for 30s, the removal rate of chlorophyll and lutein by the magnetic COFs nano material can reach more than 90%, and meanwhile, the total recovery of 140 pesticides can be realized, so that the COFs nano material has the capability of efficiently and selectively purifying pigment interferents in a complex matrix sample.
3. The magnetic COFs can be rapidly separated through an external magnetic field, the processes of centrifugation, filtration and the like are avoided, repeated use can be realized, the adsorption efficiency is effectively improved, the operation process is simplified, and important materials and tools are provided for researching and developing a novel high-efficiency rapid pretreatment technology and realizing accurate quantitative analysis of trace target objects in complex matrix samples.
Drawings
FIG. 1 is a structural diagram of the synthesis process of magnetic covalent nano-materials
FIG. 2 is a schematic diagram of the synthesis of magnetic covalent nano-materials
FIG. 3 is a schematic view of a transmission electron microscope (A is Fe)3O4B is Fe3O4@SiO2-NH2C is Fe3O4@SiO2-NH2@COFs)
FIG. 4 shows Fe3O4、Fe3O4@SiO2-NH2、Fe3O4@SiO2-NH2Infrared spectrum schematic diagram of @ COFs and COFs
FIG. 5 shows Fe3O4、Fe3O4@SiO2-NH2、Fe3O4@SiO2-NH2X-ray powder diffraction pattern of @ COFs and COFs
FIG. 6 shows Fe3O4@SiO2-NH2@ COFs Nitrogen adsorption-desorption isotherm (A) and pore size distribution plot (B)
FIG. 7 shows Fe3O4@SiO2-NH2Hysteresis loop diagram of @ COFs
FIG. 8 is a graph showing an ultraviolet absorption spectrum (A) of a dye and a histogram showing a removal rate of the dye after adsorption (B)
FIG. 9 is a liquid chromatography tandem mass spectrometry MRM chromatogram
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Examples 1-2 below describe the synthesis of magnetic covalent nanomaterials of the present invention and the adsorption of pigments in detail with reference to the schematic diagrams of the synthesis of magnetic covalent nanomaterials in fig. 1 and 2.
Example 1
Synthesis method of magnetic covalent nano material
(1) Preparation of ferroferric oxide nanoparticles (Fe) by solvothermal method3O4 NPs)
a. 1.36g of FeCl3·6H2O was dissolved in 40ml of ethylene glycol, dissolved by sonication, and 3.6g of a precipitant (CH) was added3COONa) and stirring for 4 hours by magnetic force;
b. dissolving 1.5g polyethylene glycol (PEG 6000) as surfactant in 40ml ethylene glycol, heating and stirring at 70 deg.C for 10 min; slowly adding the solution obtained in the step b into the solution obtained in the step a, uniformly stirring, transferring the solution into a high-pressure reaction kettle, and putting the high-pressure reaction kettle into a high-temperature oven to react for 10 hours at 200 ℃; cooling to room temperature to prepare Fe3O4Collecting the nanoparticles with a magnet, alternately washing with deionized water and ethanol, and drying in a vacuum drying oven at 65-75 deg.C for 10 hr to obtain Fe3O4The particles are ready for use.
(2) Magnetic composite material (Fe)3O4@SiO2-NH2) Preparation of (2)
c. Fe to be prepared3O4300mg of particles are weighed and dispersed into a mixed solution of 75ml of ethanol and 20ml of deionized water, the mixture is subjected to ultrasonic treatment until the mixture is uniform, 2ml of ammonia water is dropwise added, then 0.5ml of TEOS and 0.5ml of APTES are respectively diluted to 3ml, TEOS is dropwise added for three times under mechanical stirring, and 1ml of TEOS is dropwise added every hour; after 6 hours, dropwise adding APTES for three times under mechanical stirring, wherein the amount of APTES is 1ml each time, mechanically stirring for 10 hours, washing with deionized water and ethanol, and drying in a vacuum drying oven at 55-65 ℃ for 8 hours to obtain Fe3O4@SiO2-NH2And (5) standby.
(3) Preparation of Fe3O4@SiO2-NH2-Tp
300mg of Fe3O4@SiO2-NH2Dissolving 20mg trialdehyde phloroglucinol (Tp) in 20ml 1, 4-dioxane, ultrasonic treating for 3min, adding 300 μ L catalyst (acetic acid), ultrasonic treating for 5min, and transferring the solutionPutting the mixture into a high-pressure reaction kettle, putting the mixture into a high-temperature oven at 120 ℃ for 1h, washing the mixture by using 1, 4-dioxane, and putting the mixture into a vacuum drying oven to dry the mixture for 2h at 55-65 ℃ until Fe is obtained3O4@SiO2-NH2Tp for use.
(4) Preparation of a magnetic covalent organic framework (Fe) with carboxyl groups3O4@SiO2-NH2@COFs)
Preparing mixed solvent (1, 4-dioxane and mesitylene as 1:1)
② weighing prepared Fe3O4@SiO2-NH2-Tp 50mg；
③ weighing 63mg of trialdehyde phloroglucinol (Tp)
Weighing the proportion of 4, 4-diaminobiphenyl-2, 2-Dicarboxyl (DAA) and benzidine carboxyl (1:5 ═ 20.42mg +69.1 mg;), adding 2.5ml of mixed solvent into the ②, adding 3ml of mixed solvent into the (XII), ultrasonically dissolving, finally adding catalyst (7mol/L HAC) to shake uniformly, ultrasonically dissolving, pouring into a reaction kettle, washing for three days at 120 ℃, using 1, 4-dioxane to wash, putting into a vacuum drying oven, and drying overnight at 55-65 ℃ to obtain Fe3O4@SiO2-NH2@ COFs is ready for use.
Secondly, the magnetic covalent nano material is applied to the processing process before the food sample is detected
Weighing 1-5mg/mL of magnetic covalent nano material, adding 1-5mg/mL of pretreated chlorophyll extracting solution, carrying out ultrasonic treatment for 3-5 minutes, shaking for 2-3 minutes, separating the magnetic covalent nano material in a sample by adopting an external magnetic field mode, and analyzing the pesticide residue content of the sample by using the separated sample solution in liquid chromatography or mass spectrometry.
Example 2
Synthesis of magnetic COFs nano material
(1) Ferroferric oxide nanoparticles (Fe)3O4NPs) preparation
FeCl is added3·6H2O in ethylene glycol, FeCl3·6H2Stirring for 4 hours, wherein the mass-volume ratio of O to glycol is 1 g: 60 mL; then, FeCl was added to the resulting solution3·6H2NaAc and FeCl with 2-3 times of O mass3·6H2PEG 6000 with the mass of 0.8 time of that of O is stirred until reactants are completely dissolved, the solution is transferred to a high-pressure reaction kettle and put into a high-temperature oven to react for 10 hours at 200 ℃; cooling to room temperature, Fe3O4Collecting the nanoparticles by using a magnet, alternately washing the nanoparticles by using deionized water and ethanol, and drying the nanoparticles in a vacuum drying oven at 65-75 ℃ for 10 hours for later use.
(2) Composite magnetic nanoparticles (Fe)3O4@SiO2-NH2) Preparation of
Prepared Fe3O4Dispersing the solid in ethanol water solution, Fe3O4The mass-volume ratio of the aqueous solution of the iron oxide and the ethanol is 1 g: 150mL, the aqueous solution of the ethanol is formed by mixing absolute ethanol and water according to the volume ratio of 4-6: 1, ammonia water with the mass concentration of 23-27% is dripped after ultrasonic treatment is carried out for 15-25 min, and the dripping amount of the ammonia water is 1g of Fe3O4Dropwise adding 5-6 mL of ammonia water meter; then 0.5ml of tetraethoxysilane and 0.5ml of 3-aminopropyltriethoxysilane are respectively diluted to 3ml, and tetraethoxysilane is added dropwise three times under mechanical stirring, and 1ml of tetraethoxysilane is added per hour; and after 6 hours, dropwise adding 3-aminopropyltriethoxysilane for three times under mechanical stirring, washing with deionized water and ethanol after mechanical stirring for 10 hours, and drying in a vacuum drying oven at 55-65 ℃ for 8 hours for later use.
(3) Preparation of Fe3O4@SiO2-NH2-Tp
Mixing Fe3O4@SiO2-NH2Dissolving the Fe-Al-containing compound and trialdehyde phloroglucinol (Tp) in 20ml of 1, 4-dioxane according to the ratio of 15:1, performing ultrasonic treatment uniformly, adding 300 mu L of catalyst (acetic acid), performing ultrasonic treatment for 3-5min, transferring the solution to a high-pressure reaction kettle, putting the high-temperature reaction kettle into a high-temperature oven at 120 ℃, performing reaction for 1h, washing the reaction product with the 1, 4-dioxane, putting the reaction product into a vacuum drying oven, and drying the reaction product for 1-5h at 55-65 ℃ to obtain Fe3O4@SiO2-NH2Tp for use.
(4)(Fe3O4@SiO2-NH2@ COFs) preparation
50mg of Fe are weighed3O4@SiO2-NH263mg of trialdehyde phloroglucinol (Tp), 41mg of Benzidine (BD) and 67mg of 4, 4-diaminobiphenyl-2, 2-Dicarboxyl (DAA) are dissolved in 10.0mL of mixed solvent (1, 4-dioxane: mesitylene 1:1), 1.0mL of 7mol/L acetic acid is added after uniform ultrasonic dispersion, then the mixture is placed in a reaction kettle and reacted for 3 days at the temperature of 120 ℃ to prepare the magnetic COFs nano material (Fe)3O4@SiO2-NH2@COFs)。
Second, the magnetic COFs nano material is used for removing pigments in plant-derived food samples
Representative plant-derived foods with high pigment content (spinach, leek, rape, cucumber, leaf lettuce, grape and green tea) used in the experiments were purchased from local supermarkets. The required extracting solution is obtained by pretreating the sample according to the method provided by the national food safety standard GB 23200.121-2021. Weighing 10g of crushed vegetable and fruit samples with high water content, adding 10mL of acetonitrile and 1 ceramic proton, violently shaking for 1min, adding 4g of anhydrous magnesium sulfate, 1g of sodium chloride, 1g of sodium citrate dihydrate and 0.5g of disodium citrate sesquihydrate, violently shaking for 1min, and centrifuging at 4200r/min for 5min to obtain an extracting solution containing the pigment. For dry samples such as tea leaves, 2g of the pulverized sample is weighed, added with 10mL of water, mixed evenly in a vortex mode, and kept stand for 30 min. Adding 15mL acetonitrile-acetic acid solution (99/1, V/V) and 1 ceramic proton, shaking vigorously for 1min, adding 6g anhydrous magnesium sulfate and 1.5g sodium acetate, shaking vigorously for 1min, and centrifuging at 4200r/min for 5min to obtain pigment-containing extractive solution. Since the sample has the highest chlorophyll content, the purification efficiency is calculated mainly from the total chlorophyll concentration. The absorbances at 645nm and 663nm were measured, respectively, and the chlorophyll concentration in the sample was calculated according to the Arnon formula.
In the adsorption process, 1-5mg of magnetic covalent nano material is weighed, 5-20mL of pretreated pigment extracting solution (added with water in equal proportion) is added, the mixture is shaken for 2-3 minutes, then the magnetic COFs nano material in the sample is separated in an external magnetic field mode, and the concentration of the pigment in the supernatant is measured through UV-vis spectroscopy. During desorption, the pigment adsorbed by the MCOFs was eluted with 1mL of acetone. After adsorptionAdding eluent into MCOFs, performing ultrasonic treatment for 5min, and separating with external magnetic field. The concentration of pigment in the supernatant was then determined by UV-vis spectroscopic analysis. Adsorption capacity (q) of dye, removal rate (R%), and elution efficiency (E)e%) can be calculated by the following formula:
Figure BDA0003541329210000091
Figure BDA0003541329210000092
Figure BDA0003541329210000093
in the above formula, q represents the adsorption capacity (mg/g), R% represents the removal of adsorbate, and Ee% represents the elution efficiency. C0And Ce is the initial concentration and equilibrium concentration (mg/g) of the pigment and Cd is the eluent concentration (mg/g). W represents the mass (g) of the magnetic COFs, and V represents the volume (mL) of the adsorption solution.
The structure and performance of the magnetic covalent nano-material prepared by the invention are described in detail below with reference to the attached figures 2-9.
Experimental example 1: transmission electron microscopy analysis
The magnetic COFs nanomaterial prepared in example 1 of the present invention was analyzed by a Transmission Electron Microscope (TEM) with model number TF20, Jeol 2100F, and the result is shown in FIG. 3, where Fe3O4And Fe3O4@SiO2-NH2In the form of monodisperse spheres, Fe3O4@SiO2-NH2The morphology of @ COFs is a typical core-shell structure, the coating layer is relatively uniform, the particle size is obviously increased, and the successful synthesis of the magnetic COFs is further confirmed. In FIG. 3A, magnetic nanoparticles (Fe) in the field of view with a 100nm scale are shown3O4) The particle size of the magnetic composite material (Fe) is 240nm, and the magnetic composite material (Fe) in the visual field when the scale is 100nm is shown in FIG. 3B3O4@SiO2-NH2) The structure diagram of the topographyThe particle size is 320nm, and FIG. 3C shows the magnetic COFs nano material (Fe) in the visual field when the scale is 200nm3O4@SiO2-NH2@ COFs), the particle size of which is about 650 nm.
Experimental example 2: infrared spectroscopic analysis
Fourier transform Infrared Spectroscopy (FT-IR) also demonstrated the successful synthesis of magnetic COFs. Fe3O4，Fe3O4@SiO2-NH2，Fe3O4@SiO2-NH2FT-IR spectra of @ COFs and COFs are shown in FIG. 4. In Fe3O4，Fe3O4@SiO2-NH2And Fe3O4@SiO2-NH2541cm can be clearly observed in FT-IR spectrum of @ COFs-1The peak Fe-O stretching vibration peak. With Fe3O4In contrast, Fe3O4@SiO2-NH2In the FT-IR spectrum of (5)-1The Si-O peak at (A) indicates successful coating of the silicon layer, at the same time 795cm-1The occurrence of a new N-H bending vibration peak also demonstrates successful bonding of the amino group. These two newly appearing peaks may also be at Fe3O4@SiO2-NH2@ COFs. Fe3O4@SiO2-NH2FT-IR spectra of @ COFs of 1574cm-1and 1224cm-1The newly appeared strong peak belongs to a C ═ C bond C-N bond, the formation of a ketone structure is predicted, and the successful package of the carboxyl COFs on the magnetic sphere is further proved.
Experimental example 3: x-ray powder diffraction analysis
The magnetic covalent nanomaterials were analysed using an X-ray powder diffractometer model Rigaku SmartLab and a powder X-ray diffraction (PXRD) experiment was performed in order to determine the crystal structure of the synthetic magnetic COFs. In the PXRD curve of the magnetic COFs (fig. 5), two strong peaks were observed at 2.21 °, 16.89 °, representing the diffraction of the (100) and (001) crystal planes, respectively. In the range of 2-30 DEG, Fe3O4@SiO2-NH2，Fe3O4@SiO2-NH2X-ray derivatives of @ COFsFe can be observed by shooting a map3O4Characteristic peaks of face centered cubic crystal form.
Experimental example 4: analysis of Nitrogen adsorption experiment
The porosity and pore size distribution of the material was evaluated by nitrogen adsorption experiments. As shown in fig. 6, the adsorption curve shows a combination of type IV nitrogen adsorption isotherms, theoretically indicating the presence of mesopores in the COFs. The specific surface area of the COFs, Brunauer Emmett-Teller (BET), was found to be 122.10m2In terms of/g, total pore volume of 0.33cm3(ii) in terms of/g. The pore size is 13.5, which is smaller than the theoretical calculation value, through the non-local density functional theory calculation. The results prove that the COFs nano material successfully grows on the magnetic ball, and also prove that the magnetic COFs nano material is successfully prepared.
Experimental example 5: fe3O4@SiO2-NH2@ COFs magnetic assay
The ferromagnetic properties of magnetic COFs were demonstrated by hysteresis curve measurements. As shown in FIG. 7, Fe3O4The magnetic strength of the magnetic material is 68.34emu/g, and the magnetic COFs are reduced to 28.06 emu/g. Although an increase in the thickness of the modified layer reduces the magnetic saturation strength, the magnetic properties of magnetic COFs materials are still satisfactory for subsequent magnetic separation applications.
Experimental example 6: analysis of pigment removal Rate
As shown in FIG. 8(A), water was added to the sample extract in equal proportion, and the UV absorbance of the solution after shaking adsorption for 30s by 3mg/mL magnetic COFs nanomaterial, and FIG. 8(B) is a histogram of the pigment removal rate after adsorption. It can be seen that the removal rate of the magnetic COFs nano material prepared by the method can reach 99.37% and 93.61% for chlorophyll and lutein molecules.
Experimental example 7: recovery rate analysis of 140 kinds of pesticide residues
The influence of magnetic COFs on the analytical recovery rate of pesticide residues was evaluated by an additive recovery test. Pesticide standards are added into the selected representative plant-derived matrixes respectively, so that the content of each pesticide is 0.05mg/kg respectively. The recovery rate was calculated by extracting according to the method of example 1 or example 2 (two), purifying according to the method of experimental example 6, and analyzing the content of the pesticide residue in the sample using liquid chromatography-tandem mass spectrometry (see fig. 9). As shown in Table 1, the recovery rates of 140 pesticides in different plant-derived food samples are all 70-120%, and the relative standard deviation is less than 20%, which indicates that the recovery rate of the target pesticide can be ensured while the pigments are removed by the magnetic COFs, and the requirement of pesticide residue detection is met.
TABLE 1 pesticide recovery and relative standard deviation of different plant-derived food samples
Figure BDA0003541329210000121
Figure BDA0003541329210000131
Figure BDA0003541329210000141
Figure BDA0003541329210000151
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, so that any modifications, equivalents and the like included in the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. The magnetic covalent nano material is synthesized by sequentially coating magnetic nano particles, a silanization reagent and a covalent organic framework from inside to outside, and is characterized in that the covalent organic framework contains carboxyl functional groups, and the number of the carboxyl functional groups on each layer of covalent organic framework structure is 6.
2. The magnetic covalent nanomaterial of claim 1, wherein the magnetic nanoparticles are selected from Fe3O4、FeNi(Mo)、FeSi、FeAl、BaO·6Fe2O3One or more of the above silane reagents are selected from tetraethoxysilane and 3-aminopropyl triethoxysilane; the covalent organic framework is synthesized by three monomers of trialdehyde phloroglucinol, benzidine and 4, 4-diaminobiphenyl-2, 2-dicarboxyl.
3. A preparation method of a magnetic covalent nano material is characterized in that a silicon-coated magnetic composite material is synthesized by carrying out hydrolytic polymerization on the surface of magnetic nano particles through a silanization reagent, and then a covalent organic framework is grown on the surface of the magnetic composite material through amino bonding to obtain the magnetic covalent nano material.
4. The method as claimed in claim 3, wherein the thickness of the magnetic covalent nanomaterial is 600-750nm, the particle size of the magnetic composite material is 180-350nm, and the particle size of the magnetic nanoparticle is 100-250 nm; the aperture of the covalent organic framework is 1.41-2.32nm, and the ratio of the aperture to the size of the pigment molecule is 1: 0.9-0.6.
5. The method for preparing a magnetic covalent nanomaterial according to claim 3, wherein the method for preparing a magnetic covalent nanomaterial comprises:
s1, dissolving ferric trichloride hexahydrate and anhydrous sodium acetate in ethylene glycol to form a, dissolving a silanization reagent in the ethylene glycol, heating to form b, and drying after the b and the a react to obtain magnetic nanoparticles;
s2, dissolving the magnetic nanoparticles prepared in the step S1 in absolute ethyl alcohol and deionized water, adding ammonia water and a silanization reagent after ultrasonic dispersion, adding 3-aminopropyl triethoxysilane, alternately washing with ethyl alcohol and deionized water, and drying to obtain the magnetic composite material Fe3O4@SiO2-NH2；
S3, dissolving the magnetic composite material obtained in the step S2 and trialdehyde phloroglucinol into 1, 4-dioxane, and performing ultrasonic dispersionThen adding acetic acid, reacting to obtain Fe3O4@SiO2-NH2-Tp；
S4, and Fe prepared in the step S33O4@SiO2-NH2Dissolving Tp, trialdehyde phloroglucinol, benzidine and 4, 4-diaminobiphenyl-2, 2-dicarboxyl in a solvent, adding acetic acid after ultrasonic dispersion, and reacting to obtain the magnetic covalent nano material.
6. The method as claimed in claim 5, wherein the solvent in step S2 is one of ethanol, water or isopropanol, and the mass ratio of the magnetic nanoparticles to the solvent is 1-5: 1000.
7. The method according to claim 5, wherein the solvent in step S4 is one of 1, 4-dioxane or mesitylene, and the mass ratio of the magnetic composite material to the solvent is 1-3: 100.
8. The method as claimed in claim 5, wherein the reaction temperature of the process of steps S1-S4 is 25 ℃ to 150 ℃ and the preparation time is 3-7 days.
9. The application of the magnetic covalent nano material in food detection is characterized in that the magnetic covalent nano material prepared according to any one of claims 1 to 8 is used for pretreatment of plant-derived food pesticide residue detection.
10. The use of the magnetic covalent nanomaterial in food detection according to claim 9, wherein the food of plant origin is one or more of spinach, leek, rape, cucumber, lettuce, grape and green tea, and the specific method comprises pretreating the food of plant origin to obtain a pigment extract, adding 1-3mg of the magnetic covalent nanomaterial, performing vortex oscillation for 10min, removing the pigment extract by adsorption, separating the magnetic material with an applied magnetic field, analyzing chlorophyll concentration with ultraviolet absorption spectroscopy, and calculating removal rate; and simultaneously, 140 kinds of pesticide residues are added into a sample, and the recovery rate of the 140 kinds of pesticide residues is inspected based on a liquid chromatography method after the pretreatment of the magnetic covalent material.
CN202210240830.6A 2022-03-10 2022-03-10 Magnetic covalent nano material and preparation method and application thereof Pending CN114632497A (en)

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CN110215904A (en) * 2019-06-14 2019-09-10 河南中医药大学 Magnetic carboxylated covalent organic framework nanocomposite and its preparation method and application
CN110575817A (en) * 2019-07-29 2019-12-17 南开大学 Magnetic different-pore covalent nano material and preparation method and application thereof
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CN113801336A (en) * 2021-09-26 2021-12-17 中山大学 Functionalization of metal organic framework material UiO-67-4Me, functionalized product and application thereof
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CN109261128A (en) * 2018-10-15 2019-01-25 西北大学 A kind of borate type magnetism COFs material, preparation method and applications
CN110215904A (en) * 2019-06-14 2019-09-10 河南中医药大学 Magnetic carboxylated covalent organic framework nanocomposite and its preparation method and application
CN110575817A (en) * 2019-07-29 2019-12-17 南开大学 Magnetic different-pore covalent nano material and preparation method and application thereof
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