CN114836045B

CN114836045B - Mg/Zn-MOF-74@Fe 3 O 4 Magnetic composite material and application thereof in aflatoxin enrichment

Info

Publication number: CN114836045B
Application number: CN202210543026.5A
Authority: CN
Inventors: 陈翊平; 黄伟; 杨宏; 李晓晗
Original assignee: Huazhong Agricultural University
Current assignee: Huazhong Agricultural University
Priority date: 2022-05-18
Filing date: 2022-05-18
Publication date: 2023-05-02
Anticipated expiration: 2042-05-18
Also published as: CN114836045A

Abstract

The invention discloses a Mg/Zn-MOF-74@Fe ₃ O ₄ Magnetic composite material and application thereof in enriching aflatoxin. The invention adopts the hydrothermal method to successfully prepare Fe with uniform particle size and stronger magnetic response ₃ O ₄ Magnetic nanoparticles. Then synthesizing a hollow-structure organic framework material Mg/Zn-MOF-74 mixed with two metals of Mg/Zn by an ion exchange method, and combining Fe by a layer-by-layer combination method ₃ O ₄ The amino on the surface is compounded with Mg/Zn metal of the metal framework material, and the Mg/Zn-MOF-74@Fe is rapidly synthesized under the action of microwave assistance ₃ O ₄ . Due to Zn in the material ²⁺ Can be combined with aflatoxin B ₁ The beta-dicarbonyl in the structure generates stable chemical bonding effect, so that the application of the material in magnetic solid phase extraction can realize aflatoxin B in food ₁ The maximum adsorption capacity can reach 8.921mg/g. The Mg/Zn-MOF-74@Fe prepared by the method ₃ O ₄ Compared with the traditional pretreatment method, the method has the advantages of high separation speed, high extraction efficiency, environment friendliness, low price and the like.

Description

Mg/Zn-MOF-74@Fe 3 O 4 Magnetic composite material and application thereof in aflatoxin enrichment

Technical Field

The invention belongs to the field of food safety and magnetic nano materials, and in particular relates to Mg/Zn-MOF-74@Fe ₃ O ₄ Magnetic composite material and application thereof in enriching aflatoxin.

Background

The food is the basis for human survival, and the food safety has important significance for the health of people and national economy. However, food products are extremely susceptible to fungal contamination during storage, transportation and sale, producing mycotoxins with strong teratogenicity, carcinogenicity and mutagenicity. Currently, mycotoxins of varying morphological structures have been found to be more than hundreds of which aflatoxin B ₁ (AFB ₁ ) Is Aspergillus flavusThe small molecule metabolites produced by aspergillus parasiticus are considered to be the strongest carcinogens found to date. However, AFB ₁ Are usually present in trace or ultra trace amounts in food samples, and there is a large amount of starch, protein and fat in the food, which greatly increases the difficulty of detection, thus AFB ₁ The full enrichment extraction of (1) is the premise of accurate detection, and the efficient sample pretreatment method is as important as the sensitive analysis detection technology.

The pretreatment of the sample is a basic link for treating a complex matrix sample, and aims to enrich and extract an object to be detected through chemical or physical action, so that the interference of the complex matrix is reduced, and the detection accuracy is improved. Currently, AFB ₁ The sample pretreatment method mainly comprises liquid-liquid extraction, solid phase extraction and immunoaffinity method. In the liquid-liquid extraction operation process, rotary evaporation or nitrogen blow-drying and other operations are often needed to reduce matrix interference generated by an organic phase, so that the operation complexity is increased, and meanwhile, serious harm is caused to the health of experimenters; solid phase extraction, although efficient, requires centrifugation in separating the analyte, which may cause some unwanted interference or induce co-precipitation; the immunoaffinity method adopts antigen-antibody specific binding to separate the object to be detected, and has high selectivity, but the method is expensive and can only be used once, and meanwhile, the use of the method is greatly limited due to the defects of poor stability and the like of immune reaction.

Aiming at a plurality of defects of the traditional pretreatment method, the invention develops the AFB in enriched food based on the magnetic solid phase extraction method ₁ Magnetic nanomaterial (Mg/Zn-MOF-74@Fe) ₃ O ₄ ) The material has the advantages of high separation speed, high extraction efficiency, environment friendliness, low cost and the like, and is AFB in food ₁ The sample pretreatment work of (3) brings a new method.

Disclosure of Invention

The invention aims to solve the problems of low adsorption efficiency, low extraction speed, high use cost and the like of the existing food sample pretreatment method, and provides a method for preparing Mg/Zn-MOF-74@Fe ₃ O ₄ Magnetic composite material and application thereof in enrichment of aflatoxinThe material prepared by the method can efficiently and rapidly enrich AFB in food ₁ 。

The technical scheme of the invention is as follows:

Mg/Zn-MOF-74@Fe ₃ O ₄ A method of preparing a magnetic composite material, the method comprising the steps of:

S1：Fe ₃ O ₄ preparation of magnetic nanoparticles:

anhydrous sodium acetate (NaAc), ferric chloride hexahydrate (FeCl) ₃ ·6H ₂ O) and Sodium Dodecyl Sulfate (SDS) are uniformly mixed and added into glycol solution for reaction to obtain a mixture; separating the precipitate after the reaction is completed, washing and drying to obtain Fe ₃ O ₄ Magnetic nanoparticles;

s2: preparation of Mg/Zn-MOF-74:

titanium sheets were immersed in a solution containing magnesium nitrate hexahydrate (Mg (NO) ₃ ) ₂ ·6H ₂ O) and hydrochloric acid; immersing the reacted titanium sheet in N, N-Dimethylformamide (DMF), 2, 5-dihydroxyterephthalic acid (DHTA) and zinc nitrate hexahydrate (Zn (NO) ₃ ) ₂ ·6H ₂ Ion exchange in the mixed solution of O); separating the obtained surface particles from the titanium plate after ion exchange is completed, washing and drying to obtain a Mg/Zn-MOF-74 material;

S3：Mg/Zn-MOF-74@Fe ₃ O ₄ is prepared from the following steps:

fe prepared in the step S1 ₃ O ₄ Uniformly mixing the magnetic nano particles and the Mg/Zn-MOF-74 prepared in the step S2, adding a DMF solution, reacting, separating the obtained precipitate, washing and drying to obtain the Mg/Zn-MOF-74@Fe ₃ O ₄ A magnetic composite material.

Preferably, in the step S1, anhydrous sodium acetate (NaAc), ferric chloride hexahydrate (FeCl) ₃ ·6H ₂ The molar ratio of O) to Sodium Dodecyl Sulfate (SDS) is (1-2): (2-4): 1.

preferably, in the step S1, ethylene glycol and FeCl ₃ ·6H ₂ The ratio of O is (2-4) in mL/mmol: 1.

preferably, in the step S1, the reaction condition is that the reaction is carried out at a temperature of 180-240 ℃ for 8-12h.

Preferably, in the step S1, the separation is performed by using an externally applied magnetic field to separate the precipitate from the liquid.

Preferably, in the step S1, deionized water and ethanol are used for washing.

Preferably, in the step S1, the drying condition is: drying at 60-100deg.C for 2-4 hr.

Further preferably, in the step S1, anhydrous sodium acetate (NaAc), ferric chloride hexahydrate (FeCl) ₃ ·6H ₂ The molar ratio of O) to Sodium Dodecyl Sulfate (SDS) was 1.3:3.3:1.

further preferably, in the step S1, ethylene glycol and FeCl ₃ ·6H ₂ The ratio of O in mL/mmol was 2.5:1.

further preferably, in the step S1, the reaction is performed at a temperature of 220 ℃ for 10 hours.

Further preferably, in the step S1, the ultrapure water and the absolute ethanol are washed five times.

Further preferably, in the step S1, the drying is performed at a temperature of 80 ℃ for 2.5 hours.

Preferably, in the step S2, mg (NO ₃ ) ₂ ·6H ₂ The mol ratio of O to hydrochloric acid is (1-3): 1.

preferably, in said step S2, DMF, DHTA and Zn (NO ₃ ) ₂ ·6H ₂ The ratio of O is in mL/mmol/mmol (120-200): (2-5): 1.

preferably, in the step S2, the reaction condition is that the reaction is carried out for 12-48 hours at the temperature of 100-150 ℃.

Preferably, in the step S2, deionized water is used for washing.

Preferably, in the step S2, the drying condition is that the drying is performed at a temperature of 60-100 ℃ for 2-4 hours.

Further preferably, in the step S2, mg (NO ₃ ) ₂ ·6H ₂ The molar ratio of O to hydrochloric acid is 2:1.

further preferably, in said step S2, DMF, DHTA and Zn (NO ₃ ) ₂ ·6H ₂ The ratio of O in mL/mmol/mmol was 150:3:1.

further preferably, in the step S2, the reaction condition is a temperature of 130 ℃ for 24 hours.

Further preferably, in the step S2, the washing is performed five times with ultrapure water.

Further preferably, in the step S2, the drying condition is a temperature of 80 ℃ for 2.5 hours.

Preferably, in the step S3, fe ₃ O ₄ The mass ratio of the catalyst to Mg/Zn-MOF-74 is (3-6): 1.

preferably, in the step S3, fe ₃ O ₄ Ratio to DMF in mg/mL (3-5): 1.

preferably, in the step S3, the reaction condition is that the reaction is carried out at a temperature of 120-140 ℃ for 1-3h.

The separation adopts an external magnetic field to separate sediment and liquid.

The drying conditions are as follows: drying at 80-120deg.C for 2-5 hr.

Further preferably, in the step S3, fe ₃ O ₄ The mass ratio of the catalyst to Mg/Zn-MOF-74 is 4.8:1.

further preferably, in the step S3, fe ₃ O ₄ The ratio to DMF in mg/mL is 4:1.

further preferably, in the step S3, the reaction condition is a temperature of 130 ℃ for 2 hours.

Further preferably, in the step S3, the washing is performed five times with DMF and methanol.

Further preferably, in the step S3, the drying condition is: drying at 100deg.C for 3 hr.

Mg/Zn-MOF-74@Fe prepared by using method ₃ O ₄ Magnetic composite material for enriching and extracting aflatoxin B in food ₁ 。

Preferably, the application comprises the steps of:

(1) Crushing and grinding the solid food sample by using a wall breaking machine, sieving the crushed and ground solid food sample, and storing the crushed solid food sample in a dry room temperature environment; transferring the crushed food sample into a centrifuge tube, adding the mixed extraction solution to extract the sample, centrifuging, discarding the precipitate, and collecting supernatant to obtain a pretreated food sample; the mixed extraction solution is a mixed solution of water and methanol, wherein the volume ratio of the water to the methanol is 7-10:1, a step of;

transferring the liquid food sample into a centrifuge tube, adding the mixed extraction solution to extract the sample, centrifuging, discarding the precipitate, and collecting the supernatant to obtain a pretreated liquid food sample; the mixed extraction solution is a mixed solution of water and methanol, wherein the volume ratio of the water to the methanol is 7-10:1, a step of;

(2) Mg/Zn-MOF-74@Fe ₃ O ₄ Adding the mixture into the pretreated food sample obtained in the step (1), performing vortex mixing at room temperature to complete adsorption, and performing adsorption on Mg/Zn-MOF-74@Fe ₃ O ₄ Separating from the solution; the adsorbed Mg/Zn-MOF-74@Fe is then subjected to ₃ O ₄ Mixing with the eluting solution, and ultrasonically eluting the supported aflatoxin B ₁ Magnetic separation to obtain Mg/Zn-MOF-74@Fe ₃ O ₄ The obtained aflatoxin B-containing composition contains ₁ Is not in the presence of the elution solution N ₂ Blow-drying, and using the residue for subsequent detection.

Preferably, in the step (1), the mixed extraction solution is a mixed solution of water and methanol, wherein the volume ratio of water to methanol is (7-10): 1.

further preferably, in the step (1), the volume ratio of water to methanol is 9:1.

preferably, in step (1), the screen is an 80 mesh to 120 mesh screen.

Further preferably, in the step (1), the screen is a 100 mesh screen.

Preferably, in the step (1), the extraction is ultrasonic extraction, wherein the ultrasonic time is 2-5min.

Further preferably, in the step (1), the ultrasonic time is 3min.

Preferably, in the step (1), the ratio of the food (solid or liquid) sample and the mixed extraction solution is 1 in g/mL or volume ratio: (2-5).

Further preferably, in the step (1), the ratio of the food (solid or liquid) sample and the mixed extraction solution is 1 in g/mL or volume ratio: 3.

preferably, in the step (1), the centrifugation is performed for 5 to 15 minutes under the condition of 6000 to 8000 r/min.

Further preferably, in the step (1), the centrifugation is performed for 10 minutes under 7000 r/min.

Preferably, in the step (2), mg/Zn-MOF-74@Fe ₃ O ₄ The ratio to the pretreated food sample was 1 in mg/mL: (2-5).

Further preferably, in the step (2), mg/Zn-MOF-74@Fe ₃ O ₄ The ratio to the pretreated food sample was 1 in mg/mL: 3.

preferably, in the step (2), the adsorption time is 1-5min.

Further preferably, in the step (2), the adsorption time is 3min;

preferably, in the step (2), the turbine mixing is uniformly mixed in a turbine rotator at the speed of 450-550 r/min.

Preferably, in the step (2), the separation is to separate the magnetic adsorbent from the liquid under the action of an externally applied magnetic field.

Preferably, in the step (2), the eluting solution is formic acid, acetone, methanol or acetonitrile solution or a combination thereof.

Further preferably, in the step (2), an acetonitrile solution is used.

Preferably, in the step (2), the ratio of Mg/Zn-MOF-74 to elution solution is in the range of Mg/mL (3-10): 1.

further preferably, in the step (2), the ratio of Mg/Zn-MOF-74 to elution solution is 5 in Mg/mL: 1.

preferably, in the step (2), the pH of the eluting solution is 5-10.

Further preferably, in the step (2), the pH of the eluting solution is 6.

Preferably, in the step (2), the elution condition is: eluting under ultrasonic condition for 2-5min.

Further preferably, in the step (2), the elution is performed for 3min under ultrasonic conditions.

PreferablyIn the step (2), the drying is carried out at 75-85 ℃ and N ₂ The flow rate is 0.3-0.6mL/min.

Further preferably, in the step (2), the drying is 80 ℃, N ₂ The flow rate was 0.5mL/min.

Optimally Fe ₃ O ₄ The specific preparation method of the magnetic nano-particles comprises the following steps:

FeCl ₃ ·6H ₂ o (10.0 mmol) and NaAc (4.0 mmol) were added to 25mL of ethylene glycol followed by 3.0mmol of SDS and stirred at 400r/min for 15-30 min. The solution was then transferred to a 50mL synthesis vessel and heated at 220 ℃ for 10h. After cooling to room temperature, magnetic separation separates Fe ₃ O ₄ Separating black precipitate from the rest solution, and repeatedly washing with deionized water (ultrapure water) and absolute ethanol for five times to obtain Fe ₃ O ₄ Magnetic nanoparticles until the supernatant is neutral. Finally, vacuum drying is carried out for 2.5 hours at 80 ℃ by a vacuum drying oven, and the Fe with superparamagnetism is obtained ₃ O ₄ The magnetic nanoparticles were stored at 4 ℃ for use.

The specific preparation method of the Mg/Zn-MOF-74 is as follows:

a titanium plate having a diameter of about 10mm and a thickness of about 3mm was prepared, and washed with methanol and ultrapure water a plurality of times. The clean titanium sheet was immersed in 10mol/L NaOH for 8 hours, and then the treated titanium sheet was immersed in 1mL of 0.1mol/L hydrochloric acid for 1 hour and then 1mL of 0.2mol/L Mg (NO) ₃ ) ₂ ·6H ₂ O1h. After the completion of the reaction, the titanium plate, 0.3mmol DHTA, 0.1mmol Zn (NO ₃ ) ₂ ·6H ₂ Adding O and 15mLDMF into a polytetrafluoroethylene reactor, heating at 130 ℃ for 24 hours, cooling to room temperature, cleaning with ultrapure water for five times, scraping a sample on the surface of a titanium sheet, putting into a vacuum drying oven at 80 ℃ for drying for 2.5 hours, and preserving at 4 ℃ for standby.

Mg/Zn-MOF-74@Fe ₃ O ₄ The specific preparation method of (2) is as follows:

100mg of Fe prepared according to the first object ₃ O ₄ The magnetic nano-particles and 20.83Mg of Mg/Zn-MOF-74 prepared in the second purpose are added into 25ml of LDMF solution, after being stirred uniformly, the mixture is transferred into a microwave reactor for reaction for 2 hours at the temperature of 130 ℃,cooling to room temperature, magnetically separating to obtain brown-black compound, washing with DMF and methanol for five times, and drying in oven at 100deg.C for 3 hr to obtain Mg/Zn-MOF-74@Fe ₃ O ₄ A magnetic composite material. Mg/Zn-MOF-74@Fe ₃ O ₄ Enriching aflatoxin B in food ₁ The specific method of (2) is as follows:

(1) 10g of the solid food sample was crushed and ground by a wall breaking machine, sieved by a 100-mesh sieve, and stored in a dry room temperature environment. The crushed food sample is transferred into a 50mL centrifuge tube, added with 30mL of methanol aqueous solution (1:9/v: v), fully shaken, ultrasonically extracted for 3min and centrifuged at 7000r/min for 10min. This procedure was repeated three times and the supernatants were combined in a new 50mL centrifuge tube. Collecting the obtained food extract, and storing at 4deg.C.

10mL of the liquid food sample was transferred to a 50mL centrifuge tube, and after adding 30mL of an aqueous methanol solution (1:9/v: v), the mixture was sufficiently shaken, sonicated for 3min, and centrifuged at 7000r/min for 10min. This procedure was repeated three times and the supernatants were combined in a new 50mL centrifuge tube. Collecting the obtained food extract, and storing at 4deg.C.

(2) 5.0mg of Mg/Zn-MOF-74@Fe ₃ O ₄ Adding 15mL of the food extract, mixing the mixed solution at room temperature with 500r/min vortex for 3min, and adding Mg/Zn-MOF-74@Fe under the action of external magnetic field ₃ O ₄ From the solution, 1mL of acetonitrile solution at pH 6 was separated from the Mg/Zn-MOF-74@Fe ₃ O ₄ Mixing, ultrasonic treating at room temperature for 3min, and loading AFB ₁ Desorption is performed. After magnetic separation, the resulting eluted solution was purified using N ₂ (80 ℃ C., 0.5 mL/min) and drying, and the residue is used for subsequent detection.

Reaction principle: the invention is based on an ion exchange method and a hydrothermal method, firstly, a protecting film on the surface of a titanium plate is destroyed by chemical corrosion so as to introduce Mg on the surface of the titanium plate ²⁺ Since the active form of Mg is stronger than Zn, zn ²⁺ More easily accept lone pair electrons and Mg is carried out based on the lone pair electrons ²⁺ With Zn ²⁺ Form mixed metal Ti-Mg// Zn. Then mixing the titanium plate with DHTA, performing solvothermal reaction under the action of water and utilizing 2, 5-dihydroxyterephthalic acid and Mg/Zn goldThe coordination of the metal forms Mg/Zn-MOF-74 with a hollow structure. Finally through Fe ₃ O ₄ The amino group of (2) is compounded with Mg/Zn metal of the metal framework material, and the Mg/Zn-MOF-74@Fe is rapidly synthesized under the action of microwave assistance ₃ O ₄ . During the adsorption process, mg/Zn-MOF-74@Fe dispersed in the solution ₃ O ₄ Zn of (2) ²⁺ Can be combined with AFB ₁ The dicarbonyl structure is tightly combined, and in addition, mg/Zn-MOF-74@Fe ₃ O ₄ Surface charge and AFB ₁ The electrostatic adsorption force between the two can further improve the adsorption effect. After the adsorption is finished, under the action of an external magnetic field and the action of a desorption solvent, AFB in food can be easily realized ₁ Is separated and purified.

Compared with the traditional pretreatment method, the method is based on Mg/Zn-MOF-74@Fe ₃ O ₄ Enriching AFB in food ₁ The method of (2) has the following advantages:

(1) The pretreatment material is novel. The Mg/Zn-MOF-74@Fe prepared by the method ₃ O ₄ Mg/Zn-MOF-74 with Fe ₃ O ₄ The combination of magnetic nanoparticles to form magnetic MOFs materials in combination with MSPE is used in sample pretreatment. The material has the characteristics of structural adaptability, flexibility, high porosity and the like of MOFs materials and the advantage of superparamagnetism of magnetic nano particles, and can realize effective separation of target objects under the action of an externally applied magnetic field, and the physical and chemical properties of the composite material are incomparable with those of a single material.

(2) The pretreatment cost is low. The Mg/Zn-MOF-74@Fe prepared by the method ₃ O ₄ The raw materials are simple and easily obtained common materials, and the price is low; and the material consumes less reagent in the pretreatment process, can be recycled, and greatly reduces the pretreatment cost.

(3) The pretreatment efficiency is high. The Mg/Zn-MOF-74@Fe prepared by the method ₃ O ₄ Has good dispersibility and high specific surface area, and can provide enough adsorption sites and AFB ₁ And combining to realize a rapid mass transfer process. Analysis of AFB under optimal conditions ₁ Is Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Maximum adsorption of (2)The capacity is 8.921mg/g, which is superior to other pretreatment methods.

Drawings

FIG. 1 is a graph of four different MOFs-74@Fe in example 2 ₃ O ₄ Is a supernatant ion release profile of (2);

FIG. 2 shows different n [ Mg ] values in example 2 ²⁺ ]：n[Zn ²⁺ ]Ratio of Mg/Zn-MOF-74@Fe ₃ O ₄ Particle size distribution map of (2);

fig. 3 is a scanning electron microscope image of example 3: FIG. 3a shows Fe in example 3 ₃ O ₄ Is a scanning electron microscope image of (2);

FIG. 3b is a schematic diagram of Mg/Zn-MOF-74@Fe in example 3 ₃ O ₄ Is a scanning electron microscope image of (2);

FIG. 4 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 3 ₃ O ₄ Is of (2)

FIG. 5 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 3 ₃ O ₄ X-ray diffraction pattern of (2);

FIG. 6 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 3 ₃ O ₄ Hysteresis loop diagram of (2);

FIG. 7 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 4 ₃ O ₄ Enriching AFB in food ₁ Is a schematic diagram of (a);

FIG. 8 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 6 ₃ O ₄ Adsorption of AFB ₁ Front and rear infrared spectrograms;

FIG. 9 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 6 ₃ O ₄ Adsorption of AFB ₁ Is a fitting graph of the adsorption model;

FIG. 10 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 6 ₃ O ₄ Is a reusability map of (2);

FIG. 11 is a schematic diagram of Mg/Zn-MOF-74@Fe in example 7 ₃ O ₄ Enrichment of AFB with immunoaffinity column ₁ Is a chromatographic comparison chart of (3).

Detailed Description

The present invention is described in further detail below with reference to the drawings and examples, which should be understood by those skilled in the art as merely aiding in the understanding of the present invention and should not be construed as a specific limitation of the present invention.

Test materials

Aflatoxin B ₁ (1 mg/mL): purchased from Shanghai Source leaf Biotechnology Co. N, N-dimethylformamide (DMF, analytical grade), 2, 5-dihydroxyterephthalic acid (DHTA, analytical grade): purchased from Shanghai Ara Ding Shenghua technologies Inc. Acetonitrile (chromatographic purity), formic acid (chromatographic purity): purchased from sammer femto-tech company, usa. Ferric chloride hexahydrate (FeCl) ₃ ·6H ₂ O), sodium acetate (NaAc), sodium Dodecyl Sulfate (SDS), magnesium nitrate hexahydrate (Mg (NO) ₃ ) ₂ ·6H ₂ O), zinc nitrate hexahydrate (Zn (NO) ₃ ) ₂ ·6H ₂ O): purchased from chinese national drug group.

Example 1 preparation of Mg/Zn-MOF-74@Fe ₃ O ₄ Is a method of (2)

(1)Fe ₃ O ₄ Preparation of magnetic nanoparticles

FeCl is added ₃ ·6H ₂ O (10.0 mmol) and NaAc (4.0 mmol) were added to 25mL of ethylene glycol (50 mL beaker, convenient for stirring), followed by 3.0mmol of SDS and magnetic stirring at 400r/min for 15-30 min. The yellow transparent mixed solution was then transferred to a 50mL synthesis vessel and heated at 220 ℃ for 10h. After cooling to room temperature, fe was separated by magnetic separation ₃ O ₄ Separating black precipitate from the rest solution, and repeatedly washing with deionized water and absolute ethanol to obtain Fe ₃ O ₄ Magnetic nanoparticles until the supernatant is neutral. Finally, the prepared magnetic nano particles are placed in a vacuum drying oven to be dried for 2.5 hours at 80 ℃ to obtain Fe with superparamagnetism ₃ O ₄ The magnetic nanoparticles were stored at 4 ℃ for later use.

(2) Preparation of Mg/Zn-MOF-74

A titanium plate having a diameter of about 10mm and a thickness of about 3mm was prepared, and washed with methanol and ultrapure water a plurality of times. The clean titanium sheet was immersed in 10mol/L NaOH for 8 hours, and then the treated titanium sheet was immersed in 1mL of 0.1mol/L hydrochloric acid for 1 hour and then 1mL of 0.1mol/L Mg (NO) ₃ ) ₂ ·6H ₂ O1h. After the completion of the reaction, the titanium plate, 0.3mmol DHTA, 0.1mmol Zn (NO ₃ ) ₂ ·6H ₂ O and 15mAdding LDMF into polytetrafluoroethylene reactor (microwave assisted heating), heating at 130deg.C for 24 hr, cooling to room temperature, cleaning with ultrapure water for five times, scraping sample on the surface of titanium sheet, drying in vacuum oven at 80deg.C for 2.5 hr, and preserving at 4deg.C.

(3)Mg/Zn-MOF-74@Fe ₃ O ₄ Is prepared from

100mg of Fe prepared in step (1) was added ₃ O ₄ Adding 25 mM MF solution into magnetic nano-particles and 20.83Mg of Mg/Zn-MOF-74 prepared in the step (2), stirring uniformly, transferring to a microwave reactor, reacting at 130 ℃ for 2 hours, cooling to room temperature, magnetically separating (externally adding a magnet) to obtain a brown-black compound, washing with DMF and methanol for five times respectively, and finally drying in a 100 ℃ oven (or 80 ℃ vacuum drying oven, -0.6 Mpa) for 3 hours to obtain Mg/Zn-MOF-74@Fe ₃ O ₄ A magnetic composite material.

Example 2 selection and optimization of synthetic raw materials

(1) Fe was prepared according to the procedure (1) of example 1 ₃ O ₄ Magnetic nanoparticles;

(2) Mg/Zn-MOF-74 was prepared as in step (2) of example 1;

preparation of Mg-MOF-74: immersing the pretreated titanium sheet in 1mL of 0.1mol/L Mg (NO) ₃ ) ₂ ·6H ₂ O1h. After the reaction was completed, the titanium plate, 0.3mmol DHTA and 5ml dmf were charged into a polytetrafluoroethylene reactor (microwave-assisted heating), and heated at 130 ℃ for 24 hours. The pretreatment method of the titanium sheet and the cleaning and drying method of Mg-MOF-74 were the same as in the step (2) of example 1.

Preparation of Zn-MOF-74: pretreated titanium sheet, 0.3mmol DHTA, 1mmol Zn (NO ₃ ) ₂ ·6H ₂ O and 15mLDMF were added to a polytetrafluoroethylene reactor (microwave assisted heating) and heated at 130℃for 24h. The pretreatment method of the titanium sheet and the cleaning and drying method of Zn-MOF-74 were the same as in step (2) of example 1.

Preparation of Mg/Ca-MOF-74: immersing the pretreated titanium sheet in 1mL of 0.1mol/L Mg (NO) ₃ ) ₂ ·6H ₂ O1h. After completion of the reaction, the titanium plate, 0.3mmol DHTA, 0.1mmol Ca (NO ₃ ) ₂ And 5mLDMF added polytetrafluoroIn the ethylene reactor, the ethylene was heated at 130℃for 24 hours using a microwave-assisted heating method. The pretreatment method of the titanium sheet and the cleaning and drying method of Mg/Ca-MOF-74 were the same as in the step (2) of example 1.

(3) Fe is added in step (3) of example 1 ₃ O ₄ The magnetic nano particles are assembled with four different MOFs-74 layer by layer respectively, the weight of the added MOFs-74 is controlled to be Mg/Zn-MOFs-74 (20.83 Mg), the weight of the added MOFs-74 is controlled to be Mg-MOFs-74 (16.57 Mg), the weight of the added MOFs-74 is controlled to be Zn-MOFs-74 (15.77 Mg), the weight of the added Mg/Ca-MOFs-74 (25.47 Mg), other conditions are kept unchanged, and the ion release amount, the mass density, the specific surface area, the adsorption time and the maximum adsorption amount ratio of the supernatant liquid are compared with those of four different MOFs-74@Fe ₃ O ₄ Stability, physical structure and adsorption properties of (c).

FIG. 1 shows the MOF-74@Fe of different metal elements ₃ O ₄ Ion release amount of (2). The results show that before ion exchange modification, mg-MOF-74@Fe ₃ O ₄ And Zn-MOF-74@Fe ₃ O ₄ The total ion release amount within 20 days was 0.61. Mu. Mol/L and 1.2. Mu. Mol/L. After modification, mg/Ca-MOF-74@Fe ₃ O ₄ The ion release amount of (C) is obviously improved, and Mn/Zn-MOF-74@Fe ₃ O ₄ Then compared with single metal element MOF-74@Fe ₃ O ₄ The ion release amount of (C) is reduced by 51% and 103%, which means that Mn/Zn-MOF-74@Fe ₃ O ₄ Stable structure, showing that the MOF-74@Fe modified by Mn/Zn ion exchange method ₃ O ₄ Has good stability.

TABLE 1 different synthetic Metal pairs MOF-74@Fe ₃ O ₄ Mass density, specific surface area, adsorption time and AFB ₁ Effect of maximum adsorption.

Table 1 shows the MOF-74@Fe of different metal elements ₃ O ₄ Mass density, specific surface area, adsorption time and maximum adsorption capacity. The results show that the bimetallic MOF-74@Fe ₃ O ₄ Is significantly higher than MOF-74@Fe of single metal (Mg and Zn) ₃ O ₄ Description of the bimetal MOF-74@Fe ₃ O ₄ The porous structure is more obvious, more adsorption sites can be provided, so that the adsorption equilibrium time is obviously reduced and the adsorption capacity is larger. Although the Ca/Mn and Zn/Mn are selectively exchanged with the organic ligand solution by ion exchange to obtain Mg/Zn-MOF-74@Fe ₃ O ₄ And Mg/Ca-MOF-74@Fe ₃ O ₄ The crystal nucleus can be subjected to fine structure adjustment modification, but Mn/Zn is used as a metal binding site for MOF-74@Fe ₃ O ₄ The modification effect of the specific surface area and the mass density is better.

Synthesis of different n [ Mg ] as in step (2) of example 1 ²⁺ ]：n[Zn ²⁺ ]Mg/Zn-MOF-74 of (C) controlling n [ Mg ] in the raw material ² ⁺ ]：n[Zn ²⁺ ]The ratio of the synthetic raw materials is examined by the particle size distribution of the synthesized Mg/Zn-MOF-74, and other conditions are kept unchanged (6:4), (7:3), (8:2) and (9:1).

FIG. 2 shows the synthesis of different n [ Mg ] by ion exchange ²⁺ ]：n[Zn ²⁺ ]Particle size distribution of (3). It can be seen from FIG. 2 that as n [ Mg ] ²⁺ ]：n[Zn ²⁺ ]Is added with synthesized Mg/Zn-MOF-74@Fe ₃ O ₄ The particle diameter of (B) gradually increases, when n [ Mg ] ²⁺ ]：n[Zn ²⁺ ]Is 9:1, the particle size distribution is uniform and the peak width is the narrowest, which means that Mg is the main part of the material, with n [ Mg ] ²⁺ ]Is mature, and the shape, structure and uniformity of the material are further improved. Thus, n (Mg ²⁺ )：n(Zn ²⁺ ) =9: 1 as synthesis conditions, a novel magnetic material having good properties and shape can be obtained.

Example 3 Mg/Zn-MOF-74@Fe ₃ O ₄ Structural characterization of (2)

Preparation of Mg/Zn-MOF-74@Fe as in example 1 ₃ O ₄ 。

(1) Scanning Electron Microscope (SEM) characterization

FIG. 3 is Fe ₃ O ₄ And Mg/Zn-MOF-74@Fe ₃ O ₄ Is a scanning electron microscope image of (c). As shown in FIG. 3, fe ₃ O ₄ Nanoparticles and Mg/Zn-MOF-74 metal frameworksThe cross-linking and the combination of the two components form a clear regular hexagonal cluster structure, and the size of the regular hexagonal cluster structure is about 380-480nm. Wherein the regular hexagonal cluster structure of each region has different sizes, presumably obvious crystal growth occurs in the high-temperature synthesis process, and the electron microscope intuitively proves that the Mg/Zn-MOF-74@Fe ₃ O ₄ Is a synthesis of (a). This indicates Fe ₃ O ₄ The nanoparticles were successfully incorporated into the Mg/Zn-MOF-74 metal framework.

(2) Energy Dispersive (EDS) characterization

Table 2 shows Mg/Zn-MOF-74@Fe ₃ O ₄ The element distribution table of (2) shows that the material consists of five elements of C, H, O, mg and Zn, and the Fe is verified ₃ O ₄ Combination of nanoparticles and Mg/Zn-MOF-74 Metal skeleton, and ratio of carbon element to Metal element [ C (Mg+Zn)]About 3.78, indicating that a 2, 5-dihydroxyterephthalic acid molecule containing eight carbon atoms in Mg/Zn-MOF-74 can be efficiently reacted with two metal ions (Mg ²⁺ Or Zn ²⁺ ) Coordination.

TABLE 2 Mg/Zn-MOF-74@Fe ₃ O ₄ Content distribution table of each element (Fe, C, O, mg, zn)

Element(s)	Proportion (%)
		Fe	44.67
C	15.12
		O	36.21
Mg	1.74
		Zn	2.26
Totals to	100

(3) Infrared Spectroscopy (FT-IR) characterization

FIG. 4 is a schematic diagram of Mg/Zn-MOF-74@Fe ₃ O ₄ Is a spectrum of infrared light of (a) is obtained. As shown in the figure, mg/Zn-MOF-74@Fe ₃ O ₄ At 600cm ^-1 And 3400cm ^-1 Near to appear to be with Fe ₃ O ₄ The same absorption peaks for Fe-O and O-H; and at 1680cm ^-1 And 1585cm ^-1 There are stronger absorption peaks corresponding to characteristic absorption peaks of c=o and c=c, respectively, which illustrate the formation of metal framework skeleton of Mg/Zn-MOF-74 and with Fe ₃ O ₄ Effectively combine to form a novel magnetic material Mg/Zn-MOF-74@Fe with special functional groups ₃ O ₄ 。

(4) X-ray diffraction (XRD) characterization

FIG. 5 is a diagram of Mg/Zn-MOF-74@Fe ₃ O ₄ Is a crystal structure diagram of (a). As shown in the figure, fe ₃ O ₄ The six typical 2 theta angles of (a) are 30.1 degrees (220), 35.5 degrees (311), 43.2 degrees (400), 53.4 degrees (422)), 57.1 degrees (511) and 62.5 degrees (440) diffraction peaks (JCPCDS No.75e 0449), and the element peaks of Mg/Zn-MOF-74 are positioned at the 2 theta angles of 6.79 degrees and 11.75 degrees, which correspond to the Mg and Zn elements in the material respectively, so that the feasibility of synthesizing the bimetallic structure MOF-74 by an ion exchange method is illustrated. Mg/Zn-MOF-74@Fe ₃ O ₄ The XRD patterns of (2) and the diffraction peaks of the two are completely confirmed, and the element peak of the Mg/Zn-MOF-74 is in the range of Mg/Zn-MOF-74@Fe ₃ O ₄ Is reduced in XRD pattern, which indicates that Mg/Zn-MOF-74@Fe ₃ O ₄ Is Fe ₃ O ₄ Shell crystals covering the Mg/Zn-MOF-74 surface.

(5) Saturation Magnetization (VSM) characterization

FIG. 6 is Fe ₃ O ₄ And Mg/Zn-MOF-74@Fe ₃ O ₄ From the hysteresis loop diagram of (C), it can be seen that Mg/Zn-MOF-74@Fe ₃ O ₄ From Fe ₃ O ₄ The 65.13emu/g of (C) was reduced to 48.78emu/g, indicating that Mg/Zn-MOF-74 and Fe are not magnetic ₃ O ₄ Grafting was successful. Although Mg/Zn-MOF-74@Fe ₃ O ₄ Fe with relatively pure saturation magnetization ₃ O ₄ Slightly reduced, but still meets the requirement of rapid separation under a magnetic field.

Example 4 Mg/Zn-MOF-74@Fe-based ₃ O ₄ Enriching aflatoxin B in food ₁ Is a method of (2)

(1) 10g of the solid food sample was crushed and ground (wall breaking machine), sieved through a 100 mesh sieve and stored in a dry room temperature environment. The crushed solid food sample was transferred to a 50mL centrifuge tube, and after adding 30mL of aqueous methanol (1:9/v: v), the solid food sample was sufficiently shaken, sonicated for 3min, and centrifuged at 7000r/min for 10min. This procedure was repeated three times and the supernatants were combined in a new 50mL centrifuge tube. Collecting the obtained food extract, and storing at 4deg.C.

(2) As shown in FIG. 7, 5.0Mg of Mg/Zn-MOF-74@Fe prepared in example 1 ₃ O ₄ Adding into 15mL of the food extract, mixing at room temperature with 500r/min vortex for 3min, and adding Mg/Zn-MOF-74@Fe under the action of external magnetic field (small magnet) ₃ O ₄ From the solution, 1mL of acetonitrile solution at pH 6 was separated from the Mg/Zn-MOF-74@Fe ₃ O ₄ Mixing, ultrasonic treating at room temperature for 3min, and loading AFB ₁ Desorption is performed. After magnetic separation, the eluate obtained is treated with N ₂ (60 ℃ C., 0.5 mL/min) and drying, and the residue is used for subsequent detection.

Example 5 Mg/Zn-MOF-74@Fe ₃ O ₄ Enriching aflatoxin B in food ₁ Condition optimization of (c)

(1) Preparing a marked sample: accurately weighing 10g solid food sample or 10mL liquid food sample, and adding 1mL AFB with concentration of 0.05, 0.5 and 5 (ng/mL) ₁ Standard solution the rest of the procedure was as in step (1) of example 4 to prepare a labelled sample.

(2) Optimization of adsorption time

Enrichment of AFB in the labeled sample by the procedure of step (2) of example 4 ₁ The rotation time of the turbine is controlled to be 1min, 2min, 3min and 4min respectively, other conditions are kept unchanged, and the recovery rate is measured by HPLC to examine Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is a natural gas, and is an adsorption effect of the catalyst.

As can be seen from Table 3, the recovery rate increased significantly after increasing the turbine rotation adsorption from 1min to 3min, and the recovery rate did not change significantly with the increase of the adsorption time, indicating AFB ₁ And Mg/Zn-MOF-74@Fe ₃ O ₄ A complete contact and adsorption equilibrium is reached. Therefore, 3min was chosen as the adsorption time for this experiment to ensure optimal extraction efficiency.

TABLE 3 different adsorption times of Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is to be adsorbed by the adsorption layer

(3) Optimization of elution solution type

Enrichment of AFB in the labeled sample by the procedure of step (2) of example 4 ₁ After adsorption balance, four eluent pairs of methanol, acetonitrile, acetone and methanol are selected for Mg/Zn-MOF-74@Fe ₃ O ₄ Eluting under other conditions, and examining Mg/Zn-MOF-74@Fe by HPLC measurement of recovery rate ₃ O ₄ For AFB ₁ Is a natural gas, and is an adsorption effect of the catalyst.

As shown in Table 4, the desorption capacity of acetonitrile is significantly higher than that of the other three eluents, and the recovery rate is as high as 92.1%, which indicates that acetonitrile can be destroyed more effectivelyThe binding force between the adsorbent and the target object is improved, thereby improving the AFB ₁ From Mg/Zn-MOF-74@Fe ₃ O ₄ Thus acetonitrile is selected as the eluting solution

TABLE 4 different elution solutions Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is to be adsorbed by the adsorption layer

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(4) Optimization of elution time

Enrichment of AFB in the labeled sample by the procedure of step (2) of example 4 ₁ After adsorption balance, other conditions of elution time of 1min, 2min, 3min and 4min are controlled to be unchanged, and the recovery rate is measured by HPLC to examine Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is a natural gas, and is an adsorption effect of the catalyst.

The results of the examination are shown in Table 5, and the recovery rate gradually increases with the increase of the elution time and becomes stable after 3min, indicating that Mg/Zn-MOF-74@Fe ₃ O ₄ And AFB (alpha-fetoprotein) ₁ The hydrogen bond and electrostatic adsorption force between the two completely disappear in 3min under the organic environment. Therefore, 3min was considered to be the optimal elution time.

TABLE 5 different elution times Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is to be adsorbed by the adsorption layer

(5) Optimization of the pH of the elution solution

Procedure of step (2) according to example 4Enrichment of AFB in a labeled sample ₁ After adsorption equilibrium, the pH value of the eluent is respectively adjusted to 4.0, 5.0, 6.0 and 7.0, other conditions are kept unchanged, and the recovery rate is measured by HPLC to examine Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Is a natural gas, and is an adsorption effect of the catalyst.

The results are shown in Table 6, and the recovery rate is highest at pH=6.0, at which time AFB ₁ The adsorption amount of (2) is the largest.

TABLE 6 Mg/Zn-MOF-74@Fe at different pH values ₃ O ₄ For AFB ₁ Is to be adsorbed by the adsorption layer

Example 6 Mg/Zn-MOF-74@Fe ₃ O ₄ Enrichment of aflatoxin B ₁ Performance testing of (C)

Mg/Zn-MOF-74@Fe ₃ O ₄ Enrichment of aflatoxin B ₁ Performance test experimental procedure the procedure was performed according to example 4, with conditions according to the optimal conditions of example 5.

(1)Mg/Zn-MOF-74@Fe ₃ O ₄ Adsorption capacity test of (2)

FIG. 8 is a diagram of Mg/Zn-MOF-74@Fe ₃ O ₄ Adsorption of AFB ₁ From the FT-IR image of the front and rear, FIG. 8 shows that Mg/Zn-MOF-74@Fe ₃ O ₄ After the material is adsorbed, 1730cm ^-1 AFB appears from side to side ₁ Is described for AFB by the material ₁ Has effective adsorption effect.

FIG. 9 is a diagram of Mg/Zn-MOF-74@Fe ₃ O ₄ Adsorption of AFB ₁ The Langmuir model and the Freundlich model have higher correlations with the actual adsorption curve at different concentrations, respectively. When balancing AFB ₁ At concentrations below 60mg/L, adsorption isotherms can be embedded in the Langmuir model. But balance AFB ₁ The concentration exceeds 60mg/L, and it is evident that AFB ₁ The model is more suitable. This illustrates the initial Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB ₁ Adsorption as a single layer, and C _e The multi-layer heterogeneous adsorption is carried out(C _e The AFB remaining for adsorption to reach equilibrium ₁ Concentration). The adsorption capacity of the adsorbent is usually the maximum adsorption capacity of the Langmuir model, so that the Mg/Zn-MOF-74@Fe is calculated by an adsorption equilibrium equation ₃ O ₄ For AFB ₁ The maximum adsorption amount of (C) was 8.921mg/g.

Langmuir model:

freundlich model:

adsorption equilibrium equation:

q in _e Is Mg/Zn-MOF-74@Fe ₃ O ₄ Adsorption capacity (mg/g) of the material at equilibrium; c (C) _e The AFB remaining for adsorption to reach equilibrium ₁ Concentration; q (Q) _L 、max、b、K _f N is a fitting parameter; c (C) ₀ Initial AFB for solution ₁ Concentration (. Mu.g/L); m is additive Mg/Zn-MOF-74@Fe ₃ O ₄ Mass (mg); v is AFB ₁ Volume of solution (mL).

(2)Mg/Zn-MOF-74@Fe ₃ O ₄ Re-usability test of (c)

1.0g of Mg/Zn-MOF-74@Fe is accurately weighed ₃ O ₄ Placed in a 1.5mL centrifuge tube, and 1mL of AFB at a concentration of 1ng/mL, 5ng/mL, 10ng/mL was added ₁ After shaking the standard solution at room temperature for 3min, the procedure of step (2) according to example 4 was repeated five times of adsorption and desorption under an externally applied magnetic field.

As shown in FIG. 10, after 5 times of continuous adsorption and desorption under the optimal conditions, the Mg/Zn-MOF-74@Fe ₃ O ₄ Adsorption of three different concentrationsAFB of degree ₁ The recovery rate of (C) is still above 85%, and the RSD is less than 5%, which indicates that the Mg/Zn-MOF-74@Fe ₃ O ₄ Can be repeatedly used for more than 5 times.

EXAMPLE 7 Mg/Zn-MOF74@Fe ₃ O ₄ Enrichment of AFB with immunoaffinity column ₁ Is a comparison of (2)

Enrichment method of immunoaffinity column: 10.0g of solid food sample (after sufficiently grinding through a 80 mesh sieve) or 10mL of liquid food sample was weighed into a conical flask, to which 100mL of acetonitrile/water (10/90, v/v) mixed solution was added, and mixed uniformly on a shaker at room temperature for 20min. The mixture was filtered and 10mL of the filtrate was diluted to 50mL with PBS. The immunoaffinity column preserved at 4 ℃ in advance is restored to room temperature, 25mL of the sample liquid is taken and moved into a glass syringe barrel, an air pump is connected with the other end of the syringe to regulate the dripping speed, and the liquid is controlled to flow out at the speed of 1-2 drops/second until air enters the column. After discarding the remaining liquid, 2mL of methanol eluent was added to the immunoaffinity column, the eluent was collected in a centrifuge tube, filtered through a 0.22 μm filter and used for HPLC test analysis.

Mg/Zn-MOF-74@Fe ₃ O ₄ Enrichment of AFB ₁ Reference is made to example 4.

FIG. 11 shows AFB enrichment in two ways ₁ The chromatogram of the labeled sample is shown in FIG. 11, mg/Zn-MOF-74@Fe ₃ O ₄ AFB similar to immunoaffinity column ₁ Peak area, which is based on Mg/Zn-MOF-74@Fe ₃ O ₄ Is characterized in that AFB is adsorbed in a real sample by a magnetic solid phase extraction technology ₁ Reliability of (3).

TABLE 7 Mg/Zn-MOF-74@Fe ₃ O ₄ Comparison with the method of immunoaffinity column in labeled food sample

Table 7 shows that Mg/Zn-MOF-74@Fe ₃ O ₄ For AFB in actual samples ₁ Can maintain excellent adsorption capacity, recovery rate of 88.47-101.44%, and immunoaffinity columnThe effects are not quite different. The lower Relative Standard Deviation (RSD) also indicates that this method has good stability and can be used as a commercial process. In addition, mg/Zn-MOF-74@Fe ₃ O ₄ The method has the characteristics of simple synthesis, high adsorption efficiency, high separation speed and the like, and has the advantages of processing speed and cost which are incomparable with other pretreatment materials.

The above embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the embodiments and features in the embodiments in the present application may be arbitrarily combined with each other without collision. The protection scope of the present invention is defined by the claims, and the protection scope includes equivalent alternatives to the technical features of the claims. I.e., equivalent replacement modifications within the scope of this invention are also within the scope of the invention.

Claims

1. Mg/Zn-MOF-74@Fe ₃ O ₄ A method of preparing a magnetic composite material, the method comprising the steps of:

S1：Fe ₃ O ₄ preparation of magnetic nanoparticles:

s2: preparation of Mg/Zn-MOF-74:

in the step S2 of the above-mentioned process,

Mg(NO ₃ ) ₂ ·6H ₂ the mol ratio of O to hydrochloric acid is (1-3): 1, a step of;

DMF, DHTA and Zn (NO ₃ ) ₂ ·6H ₂ The ratio of O is in mL/mmol/mmol (120-200): (2-5): 1, a step of;

the reaction condition is that the reaction is carried out for 12 to 48 hours at the temperature of 100 to 150 ℃;

washing with deionized water;

drying at 60-100deg.C for 2-4 h;

S3：Mg/Zn-MOF-74 @ Fe ₃ O ₄ is prepared from the following steps:

2. The Mg/Zn-MOF-74@ Fe composition according to claim 1 ₃ O ₄ The preparation method of the magnetic composite material is characterized in that in the step S1, anhydrous sodium acetate (NaAc) and ferric chloride hexahydrate (FeCl) ₃ ·6H ₂ The molar ratio of O) to Sodium Dodecyl Sulfate (SDS) is (1-2): (2-4): 1, a step of;

ethylene glycol and FeCl ₃ ·6H ₂ The ratio of O is (2-4) in mL/mmol: 1, a step of;

the reaction condition is that the reaction is carried out for 8 to 12 hours at the temperature of 180 to 240 ℃;

separating sediment and liquid by adopting an external magnetic field;

the washing adopts deionized water and ethanol for washing respectively;

the drying conditions are as follows: drying at 60-100deg.C for 2-4h.

3. The Mg/Zn-MOF-74@ Fe composition according to claim 1 ₃ O ₄ A method for producing a magnetic composite material, characterized in that in the step S3, fe ₃ O ₄ The mass ratio of the catalyst to Mg/Zn-MOF-74 is (3-6): 1, a step of;

Fe ₃ O ₄ ratio to DMF in mg/mL (3-5): 1, a step of;

the reaction condition is that 1-3h is reacted at the temperature of 120-140 ℃;

separating sediment and liquid by adopting an external magnetic field;

washing with DMF and methanol;

the drying conditions are as follows: drying at 80-120deg.C for 2-5h.

4. The Mg/Zn-MOF-74@Fe prepared by the method of any one of claims 1 to 3 ₃ O ₄ The application of the magnetic composite material in enriching and extracting aflatoxin in food.

5. The use according to claim 4, characterized in that: the application is to extract aflatoxin B ₁ Comprising the following steps:

(1) Crushing and grinding the solid food sample by using a wall breaking machine, sieving the crushed and ground solid food sample, and storing the crushed solid food sample in a dry room temperature environment; transferring the solid food sample into a centrifuge tube, adding the mixed extraction solution to extract the sample, centrifuging, discarding the precipitate, and collecting the supernatant to obtain a pretreated solid food sample;

transferring the liquid food sample into a centrifuge tube, adding the mixed extraction solution to extract the sample, centrifuging, discarding the precipitate, and collecting the supernatant to obtain a pretreated liquid food sample;

(2) Mg/Zn-MOF-74@ Fe ₃ O ₄ Adding the mixture into the pretreated food sample obtained in the step (1), performing vortex mixing at room temperature to complete adsorption, and performing adsorption on Mg/Zn-MOF-74@ Fe ₃ O ₄ Separating from the solution; the adsorbed Mg/Zn-MOF-74@ Fe is then subjected to ₃ O ₄ Mixing with the eluting solution, and ultrasonically eluting the supported aflatoxin B ₁ Magnetic separation to obtain Mg/Zn-MOF-74@Fe ₃ O ₄ The obtained aflatoxin B-containing composition contains ₁ Is not in the presence of the elution solution N ₂ Blow-drying, and using the residue for subsequent detection.

6. The use according to claim 5, wherein in step (1), the mixed extraction solution is a mixed solution of water and methanol, wherein the volume ratio of water and methanol is (7-10): 1, a step of;

in the step (1), the sieve is an 80-120 mesh sieve;

the extraction is ultrasonic extraction, wherein the ultrasonic time is 2-5 min;

the ratio of the solid or liquid food sample to the mixed extraction solution is 1 in g/mL or volume ratio: (2-5);

the centrifugation is carried out at 6000-8000r/min for 5-15min.

7. The use according to claim 5, wherein in step (2), mg/Zn-MOF-74@ Fe ₃ O ₄ The ratio to the pretreated food sample was 1 in mg/mL: (2-5);

the adsorption time is 1-5 min;

the turbine mixing is carried out in a turbine rotator at the speed of 450-550 r/min;

the separation is to separate the magnetic adsorbent from the liquid under the action of an externally applied magnetic field;

the eluting solution is formic acid, acetone, methanol or acetonitrile solution or their combination;

the ratio of Mg/Zn-MOF-74 to elution solution was (3-10) in Mg/mL: 1, a step of;

the pH of the eluting solution is 5-10;

the elution conditions were: eluting for 2-5min under ultrasonic condition;

blow-drying to 75-85 deg.C, N ₂ The flow rate is 0.3-0.6mL/min.