CN116041745A - A kind of surface epoxy functionalized magnetic polystyrene microsphere and its preparation method - Google Patents

Abstract

The invention relates to the technical field of magnetic polymer microspheres, in particular to a surface epoxy functional magnetic polystyrene microsphere and a preparation method thereof, wherein the microsphere is of a three-layer core-shell structure, the inner core is a polystyrene microsphere with carboxyl, the middle layer is a magnetic nano ferroferric oxide particle or ferric oxide particle, and the outermost layer is a polymer shell layer containing epoxy groups; the preparation method of the invention comprises the steps of firstly synthesizing polystyrene microsphere with carboxyl on the surface, mixing the polystyrene microsphere with magnetic nano particles to obtain magnetic polymer microsphere, finally coating the magnetic polymer microsphere with oleic acid, reacting the magnetic polymer microsphere with functional monomer and cross-linking agent, and forming an epoxy functional polymer shell layer on the surface of the magnetic polymer microsphere. Compared with the prior art, the invention effectively solves the problem of low detection sensitivity caused by uneven magnetic content of the magnetic microsphere and insufficient number of groups on the surface of the microsphere.

Description

A kind of surface epoxy functionalized magnetic polystyrene microsphere and its preparation method

【Technical field】

The invention relates to the technical field of magnetic polymer microspheres, in particular to surface epoxy-functionalized magnetic polystyrene microspheres and a preparation method thereof.

【Background technique】

In recent years, magnetic polymer composite materials have attracted more and more attention. Because it is not only magnetic, easy to guide movement and quickly separated from the system, but also contains reactive functional groups on the surface, which can bind bioactive molecules, it has broad application prospects in in vitro diagnosis, cell separation, targeted drugs, etc. At present, the common preparation methods of magnetic microspheres include embedding method, in-situ polymerization method, core-shell method and so on.

Chinese patent CN110396148A discloses a preparation method of magnetic polystyrene microspheres. According to the description, the magnetic microsphere structure is a three-layer spherical structure. The magnetic particles and the inner core polystyrene microspheres are combined by the electrostatic interaction between the positive charges on the surface of the microspheres and the negative charges of the magnetic particles. The outermost layer is functionalized polystyrene microspheres. Vinyl shell. In this method, the positive charge on the surface of polystyrene microspheres in the inner core is provided by a cationic initiator, so the number of magnetic particles that can be adsorbed on the surface of the microspheres is limited, resulting in weak magnetic properties of the final magnetic microspheres; and the number of functional groups contained in the outermost layer is limited. , which may result in lower detection sensitivity.

【Content of invention】

In order to overcome the above-mentioned problems, the present invention proposes a surface epoxy-functionalized magnetic polystyrene microsphere and a preparation method thereof which can effectively solve the above-mentioned problems.

A technical solution provided by the present invention to solve the above technical problems is to provide a surface epoxy-functionalized magnetic polystyrene microsphere and a preparation method thereof, comprising the following steps:

Step S1, synthesizing polystyrene microspheres with carboxyl groups on the surface;

In step S2, the polystyrene microspheres with carboxyl groups on the surface synthesized in step S1 are mixed with magnetic nano ferric oxide particles or ferric oxide particles in an aqueous solution to obtain magnetic polystyrene microspheres;

Step S3, coating the magnetic polystyrene microspheres obtained in step S2 with oleic acid, adding a functional monomer and a crosslinking agent, emulsifying in an aqueous solution with an emulsifier, adding an initiator, and reacting at a temperature of 6-8 hours to obtain Surface epoxy functionalized magnetic polystyrene microspheres.

Preferably, in the step S1, dispersion polymerization can be used to prepare monodisperse polystyrene microspheres containing carboxyl groups on the surface.

Preferably, in the step S1, synthesizing polystyrene microspheres containing carboxyl groups on the surface comprises the following steps:

Step S11, under the protection of nitrogen, add an oil-soluble initiator to the styrene-ethanol solution, and react for 6-8 hours;

Step S12, adding a carboxyl-containing functional monomer, continuing to react for 2-4 hours, centrifuging, and drying to obtain the polystyrene microspheres with carboxyl groups on the surface.

Preferably, in the step S11, the oil-soluble initiator is azobisisobutyronitrile or benzoyl peroxide, and the dosage is 0.5-3% of the mass of styrene;

In the step S12, the carboxyl group-containing functional monomer is one or more of acrylic acid, methacrylic acid or undecylenic acid, the dosage is 5-20% of the mass of styrene, and the reaction temperature is 60-80°C.

Preferably, in the step S2, the magnetic nano ferric oxide particles or ferric oxide particles are hydrophilic magnetic particles with a particle diameter of 1-20 nm.

Preferably, the preparation method of the magnetic nano ferric oxide particles or ferric oxide particles comprises the following steps:

Step A1, dissolving 1.057g of ferric chloride and 1.148g of ferrous chloride tetrahydrate in 30ml of deionized water, heating the solution to 60°C, and stirring evenly;

Step A2, after reacting for 30 minutes, slowly add 1M sodium hydroxide solution dropwise to the solution until the pH value of the solution is about 11, and the solution is completely black at this time;

Step A3, heat up to 80°C, continue the reaction for 2-3h, and cool to room temperature after the reaction;

In step A4, wash repeatedly with deionized water for 5 times to remove unreacted impurity ions on the surface of the magnetic particles, and then disperse the obtained final product in deionized water for subsequent use.

Preferably, in the step S3, coating the magnetic polystyrene microspheres obtained in the step S2 with oleic acid includes the following steps:

Step S31, uniformly dispersing the magnetic polystyrene microspheres in the ethanol solution, adding oleic acid, shaking and ultrasonication, so that the oleic acid is uniformly coated on the surface of the magnetic polystyrene microspheres;

Step S32, washing with ethanol several times to remove excess oleic acid on the surface;

Step S33, centrifuging to obtain oleic acid-coated magnetic polystyrene microspheres.

Preferably, in the step S3, the functional monomer is glycidyl methacrylate;

In the step S3, the crosslinking agent is divinylbenzene or ethylene glycol dimethacrylate, and the dosage is 0-50% of the mass of the functional monomer;

In the step S3, the emulsifier is one or more of sodium lauryl sulfate, Tween, lauryl ammonium chloride or cetyltrimethylammonium bromide, and the consumption is 1/2 of the volume of the solution. 1-10%;

In the step S3, the initiator is one of potassium persulfate, ammonium persulfate or azobisisobutylamidine hydrochloride, and the dosage is 0.5-4% of the mass of the functional monomer; the reaction temperature is 60-80 ℃.

A surface epoxy-functionalized magnetic polystyrene microsphere obtained by the preparation method described in any one of claims 1-8.

Preferably, the surface epoxy-functionalized magnetic polystyrene microspheres have a three-layer core-shell structure, the inner core is polystyrene microspheres with carboxyl groups, and the middle layer is magnetic nanometer ferric oxide particles or ferric oxide Particles, the outermost layer is a polymer shell containing epoxy groups.

Compared with the prior art, the surface epoxy-functionalized magnetic polystyrene microspheres of the present invention and the preparation method thereof have the following beneficial effects:

1. The magnetic content of magnetic microspheres is determined by the amount of carboxyl groups contained in the polystyrene core, which effectively solves the problems of low magnetic content of magnetic microspheres and uneven magnetic content among microspheres;

2. The outermost shell layer of the coated magnetic microspheres is composed of functional monomers and cross-linking agents. Except for cross-linking agents, it does not contain non-functional monomers, thus greatly increasing the content of functional groups on the surface of the microspheres and solving the problem of The problem of low detection sensitivity caused by the insufficient number of surface groups of the functionalized magnetic microspheres prepared by the existing method is solved.

【Description of drawings】

Fig. 1 is the flow chart of the steps of the method for preparing surface epoxy-functionalized magnetic polystyrene microspheres of the present invention;

Fig. 2 is the scanning electron micrograph of epoxy-functionalized magnetic polystyrene microspheres obtained in the second embodiment of the method for preparing surface epoxy-functionalized magnetic polystyrene microspheres of the present invention;

Fig. 3 is a scanning electron micrograph of epoxy-functionalized magnetic polystyrene microspheres obtained in the third embodiment of the method for preparing surface epoxy-functionalized magnetic polystyrene microspheres of the present invention.

【Detailed ways】

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and implementation examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back, ...) in the embodiments of the present invention are limited to relative positions on the specified view, rather than absolute positions.

In addition, in the present invention, descriptions such as "first", "second" and so on are used for description purposes only, and should not be understood as indicating or implying their relative importance or implicitly indicating the quantity of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

Please refer to Fig. 1 to Fig. 3, the preparation method of surface epoxy functionalized magnetic polystyrene microspheres of the present invention, comprises the following steps:

Step S1, synthesizing polystyrene microspheres with carboxyl groups on the surface.

In the step S1, dispersion polymerization can be used to prepare monodisperse polystyrene microspheres containing carboxyl groups on the surface.

In the step S1, synthesizing polystyrene microspheres containing carboxyl groups on the surface comprises the following steps:

Step S11, under the protection of nitrogen, add an oil-soluble initiator to the styrene-ethanol solution, and react for 6-8 hours;

Step S12, adding a carboxyl-containing functional monomer, continuing to react for 2-4 hours, centrifuging, and drying to obtain the polystyrene microspheres with carboxyl groups on the surface.

In the step S11, the oil-soluble initiator is azobisisobutyronitrile or benzoyl peroxide, and the dosage is 0.5-3% of the mass of styrene.

In the step S12, the carboxyl group-containing functional monomer is one or more of acrylic acid, methacrylic acid or undecylenic acid, the dosage is 5-20% of the mass of styrene, and the reaction temperature is 60-80°C.

Step S2, mixing the polystyrene microspheres with carboxyl groups on the surface synthesized in step S1 with magnetic nano Fe ₃ O ₄ particles or Fe ₂ O ₃ particles in an aqueous solution to obtain magnetic polystyrene microspheres. _Fe3 O ₄ is ferric oxide, and _Fe2 O ₃ is ferric oxide.

In the step S2, the magnetic nano ferric oxide particles or ferric oxide particles are hydrophilic magnetic particles with a particle diameter of 1-20 nm.

The preparation method of the magnetic nano ferric oxide particles or ferric oxide particles comprises the following steps:

Step A1, dissolving 1.057g of ferric chloride and 1.148g of ferrous chloride tetrahydrate in 30ml of deionized water, heating the solution to 60°C, and stirring evenly;

Step A2, after reacting for 30 minutes, slowly add 1M sodium hydroxide solution dropwise to the solution until the pH value of the solution is about 11, and the solution is completely black at this time;

Step A3, heat up to 80°C, continue the reaction for 2-3h, and cool to room temperature after the reaction;

In step A4, wash repeatedly with deionized water for 5 times to remove unreacted impurity ions on the surface of the magnetic particles, and then disperse the obtained final product in deionized water for subsequent use.

Step S3, coating the magnetic polystyrene microspheres obtained in step S2 with oleic acid, adding a functional monomer and a crosslinking agent, emulsifying in an aqueous solution with an emulsifier, adding an initiator, and reacting at a temperature of 6-8 hours to obtain Surface epoxy functionalized magnetic polystyrene microspheres.

In the step S3, coating the magnetic polystyrene microspheres obtained in the step S2 with oleic acid includes the following steps:

Step S31, uniformly dispersing the magnetic polystyrene microspheres in the ethanol solution, adding oleic acid, shaking and ultrasonication, so that the oleic acid is uniformly coated on the surface of the magnetic polystyrene microspheres;

Step S32, washing with ethanol several times to remove excess oleic acid on the surface;

Step S33, centrifuging to obtain oleic acid-coated magnetic polystyrene microspheres.

In the step S3, the functional monomer is glycidyl methacrylate.

In the step S3, the crosslinking agent is divinylbenzene or ethylene glycol dimethacrylate, and the dosage is 0-50% of the mass of the functional monomer.

In the step S3, the emulsifier is one or more of sodium lauryl sulfate, Tween, lauryl ammonium chloride or cetyltrimethylammonium bromide, and the consumption is 1/2 of the volume of the solution. 1-10%.

In the step S3, the initiator is one of potassium persulfate, ammonium persulfate or azobisisobutylamidine hydrochloride, and the dosage is 0.5-4% of the mass of the functional monomer; the reaction temperature is 60-80 ℃.

The method for preparing surface epoxy-functionalized magnetic polystyrene microspheres of the present invention first utilizes the characteristics that monodisperse microspheres can be prepared by dispersion polymerization, and prepares polystyrene microspheres with carboxyl groups on the surface with narrow particle size distribution; Using the ion adsorption effect of surface carboxyl groups on magnetic particles, the magnetic particles are adsorbed to the surface of polystyrene microspheres, and the adsorption amount depends on the carboxyl content in polystyrene microspheres, so as to ensure that the magnetic load of each microsphere is basically the same; The surface of magnetic polystyrene microspheres is coated with oleic acid, so that the surface changes from hydrophilic to lipophilic. It is emulsified in aqueous solution to form an o/w system. Using the principle of interfacial polymerization, the surface is coated with a layer of epoxy Polymer shell.

The method for preparing surface epoxy-functionalized magnetic polystyrene microspheres of the present invention, the first embodiment is:

a1. Preparation of polystyrene microspheres with carboxyl groups on the surface: Add ethanol into a three-necked flask, pass nitrogen gas, add 10ml styrene and 200mg azobisisobutyronitrile under nitrogen protection, heat up to 65°C, and react for 8h; Add 2ml of methacrylic acid under protection, continue to react for 2h; wash with deionized water several times, centrifuge, and dry the product at a constant temperature of 35°C for 12h to obtain polystyrene microspheres with carboxyl groups on the surface.

b1. Take 1 g of the polystyrene microspheres with carboxyl groups on the surface prepared in the above a1, dissolve them in 100 ml of deionized water, add the magnetic particle aqueous solution, and stir mechanically at room temperature for 3 hours; after the reaction, wash repeatedly with deionized water, and magnetically separate until the supernatant was clear and transparent.

c1. Dissolve the magnetic polystyrene microspheres prepared in b1 above in ethanol, add 5ml of oleic acid, oscillate and ultrasonicate for 30 minutes, wash with ethanol 3 times to remove excess oleic acid on the surface; coat the obtained oleic acid with magnetic Microspheres, 1ml of glycidyl methacrylate and 0.5ml of divinylbenzene were dispersed in 10% sodium lauryl sulfate aqueous solution, emulsified for 3min, added to a three-necked flask under nitrogen protection, heated to 70°C, and 30mg of supernatant was added Potassium sulfate, reacted for 3 hours; after the reaction, washed three times with ethanol and deionized water respectively, magnetically separated, and the final product was dried at a constant temperature of 35°C for 12 hours to obtain surface epoxy-functionalized magnetic polystyrene microspheres.

The second embodiment is:

a2. Preparation of polystyrene microspheres with carboxyl groups on the surface: Add ethanol into a three-necked flask, pass nitrogen gas, add 10ml styrene and 200mg azobisisobutyronitrile under nitrogen protection, heat up to 65°C, and react for 6h; Add 0.5ml of methacrylic acid under protection and continue to react for 4h; wash with deionized water several times, centrifuge and dry the product at a constant temperature of 35°C for 12h to obtain polystyrene microspheres with carboxyl groups on the surface.

b2. Take 1 g of the polystyrene microspheres with carboxyl groups on the surface prepared in a2 above, dissolve them in 100 ml of deionized water, add an aqueous solution of magnetic particles, and stir mechanically at room temperature for 3 hours; after the reaction, wash repeatedly with deionized water, and magnetically separate until the supernatant was clear and transparent.

c2. Dissolve the magnetic polystyrene microspheres prepared in b2 above in ethanol, add 5ml of oleic acid, shake and sonicate for 30 minutes, wash with ethanol 3 times to remove excess oleic acid on the surface; coat the obtained oleic acid with magnetic Disperse microspheres and 3ml glycidyl methacrylate into 10% sodium lauryl sulfate aqueous solution, emulsify for 3 minutes, add to a three-necked flask under nitrogen protection, heat up to 70°C, add 30mg of potassium persulfate, and react for 3 hours; After the reaction, wash three times with ethanol and deionized water respectively, magnetically separate, and dry the final product at a constant temperature of 35° C. for 12 hours to obtain surface epoxy-functionalized magnetic polystyrene microspheres.

In the second embodiment, the carboxyl group content of the innermost microsphere is low, so there are few magnetic particles on the surface corresponding to Fig. 2 .

The third embodiment is:

a3. Preparation of polystyrene microspheres with carboxyl groups on the surface: add ethanol into a three-necked flask, pass nitrogen gas, add 10ml styrene and 400mg azobisisobutyronitrile under nitrogen protection, heat up to 70°C, and react for 6h; Add 2ml of methacrylic acid under protection, continue to react for 2h; wash with deionized water several times, centrifuge, and dry the product at a constant temperature of 35°C for 12h to obtain polystyrene microspheres with carboxyl groups on the surface.

b3. Take 1 g of the polystyrene microspheres with carboxyl groups on the surface prepared in a3 above, dissolve them in 100 ml of deionized water, add the magnetic particle aqueous solution, and stir mechanically at room temperature for 3 hours; after the reaction, wash repeatedly with deionized water, and magnetically separate until the supernatant was clear and transparent.

c3. Dissolve the magnetic polystyrene microspheres prepared in b3 above in ethanol, add 5ml of oleic acid, shake and sonicate for 30 minutes, wash with ethanol 3 times to remove excess oleic acid on the surface; coat the obtained oleic acid with magnetic Microspheres, 1ml of glycidyl methacrylate and 0.3ml of ethylene glycol dimethacrylate were dispersed in 10% 1:1 mixture of cetyltrimethylammonium bromide and Tween aqueous solution, emulsified for 3min, in Add it into a three-necked flask under nitrogen protection, raise the temperature to 70°C, add 30 mg of potassium persulfate, and react for 3 hours; after the reaction, wash with ethanol and deionized water three times, magnetically separate, and dry the final product at 35°C for 12 hours to obtain Surface epoxy functionalized magnetic polystyrene microspheres.

The third embodiment has a high content of carboxyl groups, and Fig. 3 corresponds to a large number of magnetic particles.

The surface epoxy-functionalized magnetic polystyrene microspheres of the present invention are prepared by the preparation method of the surface epoxy-functionalized magnetic polystyrene microspheres of the present invention, and have a three-layer core-shell structure, and the inner core is Polystyrene microspheres, the middle layer is magnetic nano ferric oxide/ferric oxide particles, and the outermost layer is a polymer shell layer containing epoxy groups. The surface epoxy-functionalized magnetic polystyrene microspheres of the present invention are monodisperse microspheres, the particle diameter is in the range of 3-10 μm, the inner magnetic content of the microspheres is relatively high and uniform, and the surface epoxy group content is high.

Compared with the prior art, the surface epoxy-functionalized magnetic polystyrene microspheres of the present invention and the preparation method thereof have the following beneficial effects:

1. The magnetic content of magnetic microspheres is determined by the amount of carboxyl groups contained in the polystyrene core, which effectively solves the problems of low magnetic content of magnetic microspheres and uneven magnetic content among microspheres;

2. The outermost shell layer of the coated magnetic microspheres is composed of functional monomers and cross-linking agents. Except for cross-linking agents, it does not contain non-functional monomers, thus greatly increasing the content of functional groups on the surface of the microspheres and solving the problem of The problem of low detection sensitivity caused by the insufficient number of surface groups of the functionalized magnetic microspheres prepared by the existing method is solved.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any modifications made within the concept of the present invention, equivalent replacements and improvements, etc. should be included in the scope of patent protection of the present invention. Inside.

Claims (10)

1. The preparation method of the surface epoxy functional magnetic polystyrene microsphere is characterized by comprising the following steps:

step S1, synthesizing polystyrene microspheres with carboxyl groups on the surfaces;

step S2, mixing the polystyrene microsphere with carboxyl on the surface synthesized in the step S1 with magnetic nano ferroferric oxide particles or ferric oxide particles in an aqueous solution to obtain the magnetic polystyrene microsphere;

and S3, coating the magnetic polystyrene microsphere obtained in the step S2 with oleic acid, adding a functional monomer and a cross-linking agent, emulsifying in an aqueous solution through an emulsifying agent, adding an initiator, and heating to react for 6-8 hours to obtain the surface epoxy functional magnetic polystyrene microsphere.

2. The method for preparing surface epoxy functionalized magnetic polystyrene microsphere according to claim 1, wherein in the step S1, a dispersion polymerization is used to prepare a monodisperse polystyrene microsphere having carboxyl groups on the surface.

3. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 1, wherein in the step S1, the step of synthesizing the polystyrene microsphere with carboxyl groups on the surface comprises the following steps:

step S11, adding an oil-soluble initiator into a styrene ethanol solution under the protection of nitrogen, and reacting for 6-8 hours;

and S12, adding a functional monomer containing carboxyl, continuing to react for 2-4 hours, centrifugally separating, and drying to obtain the polystyrene microsphere with the carboxyl on the surface.

4. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 3, wherein in the step S11, the oil-soluble initiator is azobisisobutyronitrile or benzoyl peroxide, and the amount is 0.5-3% of the mass of styrene;

in the step S12, the functional monomer containing carboxyl is one or more of acrylic acid, methacrylic acid or undecylenic acid, the dosage is 5-20% of the mass of styrene, and the reaction temperature is 60-80 ℃.

5. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 1, wherein in the step S2, the magnetic nano ferroferric oxide particles or ferric oxide particles are hydrophilic magnetic particles, and the particle size is 1-20nm.

6. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 5, wherein the method for preparing the magnetic nano ferroferric oxide particles or ferric oxide particles comprises the following steps:

step A1, 1.057g of ferric chloride and 1.148g of ferrous chloride tetrahydrate are dissolved in 30ml of deionized water, the temperature of the solution is raised to 60 ℃, and the solution is mechanically stirred uniformly;

step A2, after reacting for 30min, slowly dropwise adding 1M sodium hydroxide solution into the solution until the pH value of the solution is about 11, wherein the solution is completely black;

step A3, heating to 80 ℃, continuing to react for 2-3 hours, and cooling to room temperature after the reaction is finished;

and A4, repeatedly washing with deionized water for 5 times, and washing out unreacted impurity ions on the surfaces of the magnetic particles, wherein the obtained final product is dispersed in the deionized water for later use.

7. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 1, wherein in the step S3, the step of coating the magnetic polystyrene microsphere obtained in the step S2 with oleic acid comprises the following steps:

step S31, uniformly dispersing the magnetic polystyrene microspheres in an ethanol solution, adding oleic acid, vibrating and performing ultrasonic treatment to uniformly coat the oleic acid on the surfaces of the magnetic polystyrene microspheres;

step S32, washing with ethanol for several times, and washing off superfluous oleic acid on the surface;

and step S33, centrifugally separating to obtain the magnetic polystyrene microsphere coated with the oleic acid.

8. The method for preparing the surface epoxy functional magnetic polystyrene microsphere according to claim 7, wherein in the step S3, the functional monomer is glycidyl methacrylate;

in the step S3, the cross-linking agent is divinylbenzene or ethylene glycol dimethacrylate, and the dosage is 0-50% of the mass of the functional monomer;

in the step S3, the emulsifier is one or more of sodium dodecyl sulfate, tween, dodecyl ammonium chloride or hexadecyl trimethyl ammonium bromide, and the dosage is 1-10% of the volume of the solution;

in the step S3, the initiator is one of potassium persulfate, ammonium persulfate or azo diisobutyl amidine hydrochloride, and the dosage is 0.5-4% of the mass of the functional monomer; the reaction temperature is 60-80 ℃.

9. A surface epoxy functionalized magnetic polystyrene microsphere obtained by the preparation method of any one of claims 1-8.

10. The surface epoxy functionalized magnetic polystyrene microsphere according to claim 9, wherein the surface epoxy functionalized magnetic polystyrene microsphere has a three-layer core-shell structure, the inner core is a polystyrene microsphere with carboxyl, the middle layer is magnetic nano ferroferric oxide particles or ferric oxide particles, and the outermost layer is a polymer shell layer containing epoxy groups.

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