Amphiphilic hybrid shell magnetic particle, preparation method thereof and application thereof in efficient purification of oil-containing sewage

Abstract

The present application relates to a kind of amphiphilic mixed shell magnetic particle and its preparation method and application in oil-containing sewage high-efficiency purification.The present application is from two block copolymer, using chemical crosslinking induction micellization method to prepare amphiphilic mixed shell particle.Coorperation in core with iron ion is used, and magnetic nanoparticle is grown in situ in core, and amphiphilic mixed shell magnetic particle is obtained.The particle is strongly magnetic response, can be stably dispersed in water and oil, can realize the high-efficiency preparation of conversion rate close to 100%.At the same time, since the particle has high interfacial activity, it can effectively reduce oil-water interfacial tension, firmly occupy the interface of oil droplet and water (dispersed phase is oil phase in oil-containing sewage).External magnetic field is applied to the above oil-containing sewage, and oil droplet moves along the direction of magnetic field and is enriched on one side, so as to realize the high-efficiency purification of oil-containing sewage, and the oil-water separation efficiency is as high as 99.5%.After the cyclic use of the amphiphilic mixed shell magnetic particle for 4 times, the oil-water separation efficiency of more than 99% can still be obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil-water separation, and in particular relates to amphiphilic mixed-shell magnetic particles, a preparation method thereof, and application thereof in the efficient purification of oily wastewater. Background Art

[0002] Oily wastewater from crude oil spills and substandard discharges of oily wastewater from water injection production processes pose serious threats to the sustainable development of the ecological environment and human health. In leaked and substandard oily wastewater, crude oil exists in various forms, primarily as suspended oil, dispersed oil, and emulsified oil. Dispersed oil has poor interfacial stability. After a period of stagnant water, dispersed oil droplets coalesce into larger droplets and float to the surface, forming suspended oil, which can be removed using methods such as absorbent pads. Therefore, the core issue in oily wastewater purification is the purification of emulsified oil from this wastewater.

[0003] Among traditional oily wastewater purification methods (including reverse osmosis filtration, flotation, adsorption, flocculation, and chemical demulsification), reverse osmosis filtration has been widely used for treating oily wastewater in various oilfields. While this method can achieve a certain degree of effective oil-water separation, it is very energy-intensive. High levels of dissolved solids and oil content in oily wastewater, as well as hydrocarbon compounds in crude oil, can contaminate reverse osmosis membranes, causing them to fail. Frequent replacement of reverse osmosis membranes in filtration systems results in additional economic losses.

[0004] Therefore, a series of methods have been developed, including reverse osmosis filtration, flotation, adsorption, flocculation, and chemical demulsification. The basic principle is to destroy the stable oil droplets in the water phase as much as possible, thereby achieving separation of the oil and water phases, and then separating them by physical means. For example, the adsorption method achieves the purpose of oil-water separation by adding an adsorbent to adsorb the emulsified oil in the water. Its disadvantage is that the separation efficiency is not high and it cannot be recycled. The flotation method is to inject air into the wastewater, and the oil droplets adhere to the microbubbles in the water phase to increase the buoyancy, and then float to the water surface. Its disadvantage is that the separation time is long and the energy consumption is high. Therefore, it is necessary to develop a method with high separation efficiency, recyclability and low energy consumption.

[0005] Particulate surfactants have attracted considerable attention due to their low toxicity, excellent biocompatibility, interfacial activity, and interfacial stability. For example, Pickering emulsions prepared from these particles often remain stable for months or even longer. This high stability facilitates their application in complex environments. Among particulate surfactants, amphiphilic Janus particles, in which hydrophilic and hydrophobic polymer chains are grafted onto both sides of the particle, exhibit exceptional interfacial stability. These Janus particles are equivalent to multiple amphiphilic diblock polymers arranged with the hydrophilic block on one side and the hydrophobic block on the other, converging at the block junction; this convergence point is replaced by the particle. At the oil-water interface, the hydrophilic polymer chains on one side of the particle extend into the aqueous phase, while the hydrophobic polymer chains on the other side extend into the oil phase, forming a three-dimensional structure in which multiple hydrophilic and hydrophobic polymer chains are simultaneously inserted into both the aqueous and oil phases. This three-dimensional structure exhibits greater interfacial stability than a single amphiphilic diblock polymer (i.e., one hydrophilic polymer chain inserted into the aqueous phase and one hydrophobic polymer chain inserted into the oil phase), allowing for more robust anchoring at the oil-water interface. Therefore, forming this three-dimensional structure is the core key to the excellent interfacial stability of these Janus particles. However, the preparation process of these Janus particles is complex and costly, which greatly limits their industrialization. Summary of the Invention

[0006] In view of the current situation that the preparation process of amphiphilic Janus particles in the prior art is complicated and costly, the present invention provides an amphiphilic mixed-shell magnetic particle and a preparation method thereof and application in the efficient purification of oily wastewater.

[0007] The amphiphilic mixed-shell magnetic particles provided by the present invention have magnetic responsiveness and excellent oily wastewater purification capabilities. They can be widely used to effectively separate oil-water mixtures containing emulsions and achieve efficient purification of oily wastewater. At the same time, the amphiphilic mixed-shell magnetic particles provided by the present invention can still have excellent oily wastewater purification capabilities after multiple cycles of use.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The present invention provides a method for preparing amphiphilic mixed-shell magnetic particles, comprising the following steps:

[0010] (1) Using various block copolymers, amphiphilic mixed-shell particles with a cross-linked core were prepared by cross-linking-induced micellization in the presence of a cross-linking agent;

[0011] (2) By utilizing the coordination between the cross-linked core and the iron ions, magnetic particles are grown in situ in the cross-linked core of the amphiphilic mixed shell particles to obtain amphiphilic mixed shell magnetic particles.

[0012] In one embodiment of the present invention, the partial block copolymer in step (1) is for preparing a nucleating block copolymer of amphiphilic mixed shell particles, and the nucleating block copolymer is selected from one of polyacrylic acid, polymethacrylic acid, poly-4-vinylpyridine or poly-2-vinylpyridine.

[0013] Part of the block copolymer in step (1) is to prepare the hydrophilic shell block copolymer of the amphiphilic mixed shell particles, and the hydrophilic shell block copolymer is selected from the group consisting of N,N -Dimethylacrylamide, polyethylene glycol, polyvinyl pyrrolidone, polyhydroxyethyl acrylate, poly(ethylene glycol) methyl ether (meth)acrylate, polymethacrylic acid N,N - one of dimethylaminoethyl ester, polyhydroxyethyl methyl acrylate or poly N-isopropylacrylamide;

[0014] The partial block copolymer in step (1) is for preparing a hydrophobic shell-forming block copolymer of amphiphilic mixed shell particles, wherein the hydrophobic shell-forming block copolymer is selected from one of polyethyl acrylate, poly-n-butyl acrylate, poly-n-pentyl acrylate, polystyrene, polyhexafluorobutyl acrylate, polyhexafluorobutyl methacrylate, polyethyl methacrylate, poly-n-butyl methacrylate or poly-n-pentyl acrylate.

[0015] In one embodiment of the present invention, in step (1), the degree of polymerization of the core-forming block copolymer is 100-500, and the degree of polymerization of the hydrophilic shell-forming block copolymer or the hydrophobic shell-forming block copolymer is 50-1500;

[0016] The number average molecular weight of the core-forming block copolymer, the hydrophilic shell-forming block copolymer or the hydrophobic shell-forming block copolymer is in the range of 12,000-80,000 g / mol.

[0017] In one embodiment of the present invention, the cross-linking agent in step (1) is selected from one of hexamethylene diisocyanate, m-xylylenediisocyanate, 1,8-diisocyanate, 1,4-dibromobutane, 1,4-diiodobutane, 1,4-dibromopentane, 1,7-dibromoheptane or 1,11-dibromodoundecane.

[0018] In one embodiment of the present invention, the preparation concentration of the amphiphilic mixed-shell magnetic particles obtained in step (1) is 20-150 mg / mL, and a conversion rate close to 100% can be achieved.

[0019] In one embodiment of the present invention, the magnetic particles grown in situ in the cross-linked core in step (2) are selected from ferrosoferric oxide particles or γ-iron oxide particles.

[0020] In one embodiment of the present invention, the preparation concentration of the amphiphilic mixed-shell magnetic particles obtained in step (2) is 20-50 mg / mL, and a conversion rate close to 100% can be achieved.

[0021] The present invention also provides amphiphilic mixed-shell magnetic particles prepared based on the above preparation method.

[0022] The amphiphilic mixed-shell magnetic particles provided by the present invention have strong magnetic responsiveness, stable dispersion in water, high interfacial activity, and can be efficiently prepared with a conversion rate close to 100%.

[0023] The present invention further provides the application of amphiphilic mixed-shell magnetic particles in purifying oily wastewater and recycling it.

[0024] Furthermore, the method for purifying and recycling oily wastewater using amphiphilic mixed-shell magnetic particles comprises the following steps:

[0025] Step S1, dispersing amphiphilic mixed-shell magnetic particles in an aqueous phase, and adding the aqueous phase to the oily wastewater;

[0026] Step S2: applying an external magnetic field to the oily wastewater, causing the oil droplets to move along the direction of the magnetic field and accumulate on one side;

[0027] Step S3: recover the enriched oil droplets, and use a solvent washing-magnetic separation method to recover the amphiphilic mixed shell magnetic particles, and redisperse them in an aqueous solution for the next oily wastewater purification.

[0028] In one embodiment of the present invention, the oil-containing wastewater in step S1 has a total volume ratio of oil to 1:10-100, preferably 1:15-35, more preferably about 1:20, for example, 1:21.

[0029] In one embodiment of the present invention, the amount of amphiphilic mixed-shell magnetic particles added in step S1 is 0.1-1 mg / mL.

[0030] In one embodiment of the present invention, the waiting time from adding the amphiphilic mixed-shell magnetic particle aqueous dispersion to the oily wastewater in step S2 to applying the external magnetic field is 60 seconds.

[0031] In one embodiment of the present invention, in step S2, the magnetic field strength of the external magnetic field is 0.2-1.0 T, and the magnetic field application time is 10 seconds to 30 minutes.

[0032] In one embodiment of the present invention, in step S3, the solvent used for recovery and cleaning is selected from one of ethanol, isobutanol, chloroform, propanol or methanol.

[0033] The present invention uses amphiphilic mixed-shell magnetic particles to purify and recycle oily wastewater, with a high oil-water separation efficiency (about 99.5%), and can still obtain an oil-water separation efficiency of more than 99% after four cycles.

[0034] Amphiphilic mixed-shell particles, whose shells contain both hydrophilic and lipophilic polymer segments, can stably disperse in both water and oil. This stable dispersion is achieved by adjusting the conformation of the shell molecular chains: in water, the hydrophilic chains expand and the lipophilic chains collapse; in oil, the lipophilic chains expand and the hydrophilic chains collapse. Therefore, when these amphiphilic mixed-shell particles are at the oil-water interface, they can achieve a Janus conformation through asymmetric conformational changes in the shell molecular chains on both sides, firmly anchoring them to the oil-water interface and exhibiting high interfacial activity and stability. In the present invention, magnetically responsive amphiphilic mixed-shell magnetic particles are prepared using these mixed-shell polymer particles as templates. These amphiphilic mixed-shell magnetic particles still possess high interfacial activity and can effectively occupy the oil-water interface of emulsified oil. Driven by a magnetic field, the emulsified oil containing the magnetic particles at the interface moves to one side for collection, thereby achieving efficient purification of oily wastewater. Due to their particle properties, solvent washing methods can achieve nearly 100% efficient recovery of the magnetic particles. The recovered magnetic particles can be used for oil-water separation, which can still maintain high efficiency in purifying oily wastewater, reduce costs and minimize pollution to the environment.

[0035] The present invention provides amphiphilic mixed-shell magnetic particles that are magnetically responsive and have excellent oily wastewater purification capabilities. These particles maintain excellent, efficient oily wastewater purification capabilities after multiple cycles of use. Starting from a diblock copolymer, the present invention employs a chemical crosslinking-induced micellization method to prepare amphiphilic mixed-shell particles. Utilizing the coordination of the crosslinked core with iron ions, magnetic nanoparticles are grown in situ within the core to obtain amphiphilic mixed-shell magnetic particles. These particles exhibit strong magnetic responsiveness, can be stably dispersed in both water and oil, and can be efficiently prepared with a conversion rate approaching 100%. Furthermore, due to their high interfacial activity, the particles can effectively reduce oil-water interfacial tension and firmly occupy the interface between oil droplets and water (the dispersed phase in oily wastewater is the oil phase). When an external magnetic field is applied to the oily wastewater, the oil droplets move along the magnetic field and accumulate on one side, thereby achieving efficient purification of the oily wastewater with an oil-water separation efficiency of up to 99.5%. After recycling the amphiphilic mixed-shell magnetic particles four times, an oil-water separation efficiency exceeding 99% can still be achieved.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] (1) The amphiphilic mixed-shell magnetic particles act as a solid emulsifier. Therefore, the oil-water separation method of the present invention is applicable to various oil-water mixture environments.

[0038] (2) Amphiphilic mixed-shell magnetic particles can form water-in-oil emulsions under various emulsification methods and have excellent emulsification effects.

[0039] (3) The water-in-oil emulsion stabilized by amphiphilic mixed-shell magnetic particles can be quickly separated in a magnetic field environment and the operation is simple, which has the advantages of reducing costs and simplifying equipment for oil-water separation in industry.

[0040] (4) The amphiphilic mixed shell magnetic particles can be recovered and reused by cleaning to avoid secondary pollution of water quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the interfacial tension test curve of amphiphilic mixed-shell magnetic particles (test temperature is 25 ℃).

[0042] Figure 2 The amphiphilic mixed-shell magnetic particles 1 are used in the magnetic separation process of oily wastewater.

[0043] Figure 3 This is a test of the separation efficiency of the amphiphilic mixed-shell magnetic particles 1 after multiple cycles of use.

[0044] Figure 4 The separation efficiency test of amphiphilic mixed-shell magnetic particles 2 after multiple cycles of use. DETAILED DESCRIPTION

[0045] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0046] In this specification, the numerical range expressed using "a value to a value b" means a range including the endpoints a and b.

[0047] Example 1:

[0048] Two block polymers polyacrylic acid -b- Gather N,N -Dimethylacrylamide) / polyacrylic acid -b- Polybutyl acrylate (PAA- b -PDMA / PAA- b -P n BA) dissolved in N,N-dimethylformamide solution (polymer concentration is 20 mg / mL, chain number ratio is 6:4). Subsequently, hexamethylene diisocyanate (crosslinker, the molar ratio of crosslinker to crosslinkable nucleating segment repeating unit is 0.2) was added to the system and reacted at 25 °C for 24 h to obtain a mixed shell particle dispersion. The mixed shell particle dispersion was diluted to 2 mg / mL, and an appropriate amount of FeCl2 and FeCl3 mixed solution was added to the above dispersion (so that the FeCl2 in the system is 0.03). 2+ 、Fe 3+ The molar ratio of the carboxyl group is 4:4:5), and the mixture is stirred mechanically for 30 minutes under the protection of inert gas (the reaction temperature is 50 ℃). After that, ammonia water is quickly added to the system (ammonia water and N,N The reaction mixture was stirred under inert gas for 30 minutes (maintaining the reaction temperature at 50°C). The temperature was then raised to 80°C and aged for 1 hour. The reaction solution was centrifuged and washed to obtain amphiphilic mixed-shell magnetic particles 1.

[0049] The above process and the obtained particles have the following characteristics: (1) High-efficiency preparation with a conversion rate close to 100% can be achieved. (2) The amphiphilic mixed-shell magnetic particles 1 can be dispersed in water and can be stably dispersed for a long time. (3) The amphiphilic mixed-shell magnetic particles 1 can reduce the interfacial tension between n-decane and water from 46.3 mN / m to 21.8 mN / m, and their interfacial activity is comparable to that of Janus particles.

[0050] Example 2:

[0051] The process of preparing the amphiphilic mixed-shell magnetic particles 2 by covalent cross-linking is similar to that in Example 1.

[0052] Two block polymers polyacrylic acid- b- Gather N,N -Dimethylacrylamide) / polyacrylic acid -b- Polybutyl acrylate (PAA- b -PDMA / PAA- b -P n BA) dissolved in N,N -dimethylformamide solution (polymer concentration is 20 mg / mL, chain number ratio is 7:3). Subsequently, hexamethylene diisocyanate (crosslinker, the molar ratio of crosslinker to crosslinkable nucleating segment repeating unit is 0.2) was added to the system and reacted at 25 °C for 24 h to obtain a mixed shell particle dispersion. The mixed shell particle dispersion was diluted to 2 mg / mL, and an appropriate amount of FeCl2 and FeCl3 mixed solution was added to the above dispersion (so that the FeCl2 in the system is 0.03). 2+ 、Fe 3+The molar ratio of the carboxyl group is 4:4:5), and the mixture is stirred mechanically for 30 minutes under the protection of inert gas (the reaction temperature is 50 ℃). After that, ammonia water is quickly added to the system (ammonia water and N,N The reaction mixture was stirred under inert gas for 30 minutes (maintaining the reaction temperature at 50°C). The temperature was then raised to 80°C and aged for 1 hour. The reaction solution was centrifuged and washed to obtain amphiphilic mixed-shell magnetic particles 2.

[0053] The above process and the obtained particles have the following characteristics: (1) High-efficiency preparation with a conversion rate close to 100% can be achieved. (2) The amphiphilic mixed-shell magnetic particles 2 can be dispersed in water and can be stably dispersed for a long time. (3) The amphiphilic mixed-shell magnetic particles 2 can reduce the interfacial tension between n-decane and water from 46.3 mN / m to 22.3 mN / m, and their interfacial activity is comparable to that of Janus particles.

[0054] Example 3:

[0055] Two block polymers polyacrylic acid -b- Gather N,N -Dimethylacrylamide) / polyacrylic acid -b- Polybutyl acrylate (PAA -b- PDMA / PAA -b- P n BA) dissolved in N,N -dimethylformamide solution (polymer concentration is 20 mg / mL, chain number ratio is 8:2). Subsequently, hexamethylene diisocyanate (crosslinker, the molar ratio of crosslinker to crosslinkable nucleating segment repeating unit is 0.2) was added to the system and reacted at 25 °C for 24 h to obtain a mixed shell particle dispersion. The mixed shell particle dispersion was diluted to 2 mg / mL, and an appropriate amount of FeCl2 and FeCl3 mixed solution was added to the above dispersion (so that the FeCl2 in the system is 0.03). 2+ 、Fe 3+ The molar ratio of the carboxyl group is 4:4:5), and the mixture is stirred mechanically for 30 minutes under the protection of inert gas (the reaction temperature is 50 ℃). After that, ammonia water is quickly added to the system (ammonia water and N,N The reaction mixture was stirred under inert gas for 30 minutes (maintaining the reaction temperature at 50°C). The temperature was then raised to 80°C and aged for 1 hour. The reaction solution was centrifuged and washed to obtain amphiphilic mixed-shell magnetic particles 3.

[0056] The above process and the obtained particles have the following characteristics: (1) High-efficiency preparation with a conversion rate close to 100% can be achieved. (2) The amphiphilic mixed-shell magnetic particles 3 can be dispersed in water and can be stably dispersed for a long time. (3) The amphiphilic mixed-shell magnetic particles 3 can reduce the interfacial tension between n-decane and water from 46.3 mN / m to 24.1 mN / m, and their interfacial activity is comparable to that of Janus particles.

[0057] The interfacial tension test curves of the amphiphilic mixed shell magnetic particles 1, amphiphilic mixed shell magnetic particles 2 and amphiphilic mixed shell magnetic particles 3 obtained in Examples 1, 2 and 3 are shown in FIG. Figure 1 The interfacial tension values ​​of the amphiphilic mixed-shell magnetic particles 1, amphiphilic mixed-shell magnetic particles 2, and amphiphilic mixed-shell magnetic particles 3 obtained in Examples 1, 2, and 3, respectively, are shown in Table 1.

[0058] Table 1 Interfacial tension of amphiphilic mixed shell particles (test temperature 25 ℃)

[0059]

[0060] Example 4:

[0061] Using n-decane-water as a simulation system for oily wastewater (the volume ratio of oil phase to water phase is 1:20), the aqueous dispersion of amphiphilic mixed-shell magnetic particles 1 was added dropwise to the system. The final concentration of amphiphilic mixed-shell magnetic particles 1 in the aqueous phase was 1 mg / mL.

[0062] A 0.5 T neodymium magnet was then placed on one side of the oily wastewater to apply an external magnetic field, causing the oil droplets to concentrate on that side. After 30 minutes, a sample of the oily wastewater was extracted and its carbon content was measured using a Sievers M9 Total Organic Carbon Analyzer. This carbon content includes both residual n-decane and the amphiphilic mixed-shell magnetic particles in the aqueous phase.

[0063] Amphiphilic mixed shell magnetic particles 1 are used in the magnetic separation process of oily wastewater, such as Figure 2 shown.

[0064] The oil-water separation efficiency of the amphiphilic mixed-shell magnetic particles 1 (the ratio of the mass of n-decane in the water after separation to the total weight of the oil phase in the mixture before separation) was 99.5%, indicating that there was essentially no n-decane oil phase in the water phase and no particles remained in the water.

[0065] Example 5:

[0066] The process of achieving oil-water separation by magnetic separation using the amphiphilic mixed-shell magnetic particles 3 is similar to that of Example 4.

[0067] Using n-decane-water as a simulation system for oily wastewater (the volume ratio of oil phase to water phase is 1:20), the aqueous dispersion of amphiphilic mixed-shell magnetic particles 3 was added dropwise to the system. The final concentration of amphiphilic mixed-shell magnetic particles 3 in the aqueous phase was 1 mg / mL.

[0068] Subsequently, a 0.5 T neodymium magnet was placed on one side of the oily wastewater to apply an external magnetic field, causing the oil droplets to concentrate on that side. After 30 minutes, a sample of the oily wastewater was extracted and the carbon content (including residual n-decane in the aqueous phase and residual amphiphilic mixed-shell magnetic particles in the aqueous phase) was measured using a Sievers M9 Total Organic Carbon Analyzer. The oil-water separation efficiency of amphiphilic mixed-shell magnetic particles 3 (the ratio of the mass of n-decane in the water after separation to the total weight of the oil phase in the mixture before separation) was 99.5%, indicating that the n-decane oil phase was essentially absent from the aqueous phase and that no particles remained in the water.

[0069] Example 6:

[0070] The n-decane oil phase enriched in Example 4 was recovered. It was washed with isobutanol and deionized water in turn to obtain an aqueous dispersion of amphiphilic mixed-shell magnetic particles 1, which was then put into the magnetic field driven oil-water separation experiment in Example 4 again. This cycle was repeated 4 times. The separation efficiency of each time was as follows: Figure 3 As shown, the separation efficiencies are 99.0%, 98.9%, 99.0% and 98.8% respectively.

[0071] Example 7:

[0072] The n-decane oil phase enriched in Example 5 was recovered. It was washed with isobutanol and deionized water in turn to obtain an aqueous dispersion of amphiphilic mixed-shell magnetic particles 3, which was then put into the magnetic field driven oil-water separation experiment in Example 5 again. This cycle was repeated 4 times. The separation efficiency of each time was as follows: Figure 4 As shown, the separation efficiencies are 99.5%, 99.5%, 99.2% and 99.1% respectively.

[0073] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A method for preparing amphiphilic mixed-shell magnetic particles, characterized in that: The following steps are involved: (1) Using various block copolymers, amphiphilic mixed-shell particles with a cross-linked core were prepared by cross-linking-induced micellization in the presence of a cross-linking agent; (2) Utilizing the coordination between the cross-linked core and the iron ions, magnetic particles are grown in situ in the cross-linked core of the amphiphilic mixed shell particles to obtain amphiphilic mixed shell magnetic particles; The partial block copolymer in step (1) is for preparing a nucleating block copolymer of amphiphilic mixed shell particles, wherein the nucleating block copolymer is selected from one of polyacrylic acid and polymethacrylic acid; Part of the block copolymer in step (1) is to prepare the hydrophilic shell block copolymer of the amphiphilic mixed shell particles, and the hydrophilic shell block copolymer is selected from the group consisting of N,N -Dimethylacrylamide, polyethylene glycol, polyvinyl pyrrolidone, polyhydroxyethyl acrylate, poly(ethylene glycol) methyl ether (meth)acrylate, polymethacrylic acid N,N - one of dimethylaminoethyl ester, polyhydroxyethyl methyl acrylate or poly N-isopropylacrylamide; The partial block copolymer in step (1) is for preparing a hydrophobic shell-forming block copolymer of amphiphilic mixed shell particles, wherein the hydrophobic shell-forming block copolymer is selected from one of polyethyl acrylate, poly-n-butyl acrylate, poly-n-pentyl acrylate, polystyrene, polyhexafluorobutyl acrylate, polyhexafluorobutyl methacrylate, polyethyl methacrylate, poly-n-butyl methacrylate or poly-n-pentyl acrylate; The cross-linking agent in step (1) is selected from hexamethylene diisocyanate; the molar ratio of the cross-linking agent to the number of repeating units of the cross-linkable nucleating segment is 0.2; When the amphiphilic mixed shell magnetic particles are at the oil-water interface, they can obtain a Janus conformation through asymmetric conformational changes of the shell molecular chain on both sides, can be firmly fixed at the oil-water interface, and have high interfacial activity and stability.

2. The method for preparing amphiphilic mixed-shell magnetic particles according to claim 1, characterized in that: In step (1), the degree of polymerization of the core-forming block copolymer is 100-500, and the degree of polymerization of the hydrophilic shell-forming block copolymer or the hydrophobic shell-forming block copolymer is 50-1500; The number average molecular weight of the core-forming block copolymer, the hydrophilic shell-forming block copolymer or the hydrophobic shell-forming block copolymer is in the range of 12,000-80,000 g / mol.

3. The method for preparing amphiphilic mixed-shell magnetic particles according to claim 1, characterized in that: The magnetic particles grown in situ in the cross-linked core in step (2) are selected from ferrosoferric oxide particles or γ-iron oxide particles.

4. Amphiphilic mixed-shell magnetic particles prepared by the preparation method according to any one of claims 1 to 3.

5. The use of the amphiphilic mixed-shell magnetic particles according to claim 4 for purification and recycling of oily wastewater, characterized in that: The following steps are involved: Step S1, dispersing amphiphilic mixed-shell magnetic particles in an aqueous phase, and adding the aqueous phase to the oily wastewater; Step S2: applying an external magnetic field to the oily wastewater, causing the oil droplets to move along the direction of the magnetic field and accumulate on one side; Step S3: recover the enriched oil droplets, and use a solvent washing-magnetic separation method to recover the amphiphilic mixed shell magnetic particles, and redisperse them in an aqueous solution for the next oily wastewater purification.

6. The use of the amphiphilic mixed-shell magnetic particles according to claim 5 for purification and recycling of oily wastewater, characterized in that: The oil-containing wastewater in step S1 has a total volume ratio of oil to 10:100; The amount of amphiphilic mixed-shell magnetic particles added in step S1 is 0.1-1 mg / mL.

7. The use of the amphiphilic mixed-shell magnetic particles according to claim 5 for purification and recycling of oily wastewater, characterized in that: In step S2, the waiting time from adding the aqueous dispersion of amphiphilic mixed-shell magnetic particles to the oily wastewater to applying the external magnetic field is 60 seconds; In step S2, the magnetic field strength of the external magnetic field is 0.2-1.0 T, and the magnetic field application time is 10 seconds to 30 minutes.

8. The use of the amphiphilic mixed-shell magnetic particles according to claim 5 for purification and recycling of oily wastewater, characterized in that: In step S3, the solvent used for recovery and cleaning is selected from one of ethanol, isobutanol, chloroform, propanol or methanol.

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